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Sample records for jochen zschau andreas

  1. The Andrea Levialdi Fellowship

    NASA Astrophysics Data System (ADS)

    Fieschi, Roberto

    My first encounter with Cuba dates back to winter 1967-1968 at the Cultural Congress of La Havana, a very large international event to promote greater understanding of the reality of the Cuban Revolution. In fact the person invited was my friend and colleague Andrea Levialdi (Andrea already knew Cuba and loved it) who, unable to participate, allowed me to go in her place. So I landed at the airport of the "first free country in Latin America" with the delegation of the Italian Communist Party. In Havana I met other Italian physicists whom I already knew, among them Bruno Vitale and Daniele Amati. They, like me, were embarrassed by the generous hospitality of `Havana Libre,' especially in a country which was going through such difficulties. Despite our best efforts we did not succeed in receiving a more modest welcome.

  2. Subtropical Storm Andrea

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The circling clouds of an intense low-pressure system sat off the southeast coast of the United States on May 8, 2007, when the Moderate Resolution Imaging Spectroradiometer (MODIS) on NASA's Terra satellite captured this image. By the following morning, the storm developed enough to be classified as a subtropical storm, a storm that forms outside of the tropics, but has many of the characteristics--hurricane-force winds, driving rains, low pressure, and sometimes an eye--of a tropical storm. Although it arrived several weeks shy of the official start of the hurricane season (June 1), Subtropical Storm Andrea became the first named storm of the 2007 Atlantic hurricane season. The storm has the circular shape of a tropical cyclone in this image, but lacks the tight organization seen in more powerful storms. By May 9, the storm's winds reached 75 kilometers per hour (45 miles per hour), and the storm was not predicted to get any stronger, said the National Hurricane Center. Though Subtropical Storm Andrea was expected to remain offshore, its strong winds and high waves pummeled coastal states, prompting a tropical storm watch. The winds fueled wild fires (marked with red boxes) in Georgia and Florida. The wind-driven flames generated thick plumes of smoke that concentrated in a gray-brown mass over Tampa Bay, Florida. Unfortunately for Georgia and Florida, which are experiencing moderate to severe drought, Subtropical Storm Andrea was not predicted to bring significant rain to the region right away, according to reports on the Washington Post Website.

  3. Andrea Levialdi in Memoriam

    NASA Astrophysics Data System (ADS)

    Waisman, Dina

    Professor Andrea Levialdi was born in Bologna Italy in 1911, son of a very modest scientist who at the time was active in the socialist ranks. From an early age Levialdi felt the contradictions between the bourgeois environment surrounding him and his family's deep antifascism. He earned a doctorate in mathematics and physics at the University of Rome in 1937 with a dissertation on photoelasticity, methods and applications. Soon after, he was awarded a scholarship for specializing in optics at the Arcetri National Optics Institute (Florence).

  4. Andrea: The Casting of Her Spell.

    ERIC Educational Resources Information Center

    Frechette, Phyllis

    A case study examined the classroom behavior of a third grader named Andrea. Andrea's lips moved but no response could be heard. Because Andrea was an appealing child, her lack of oral communication became a challenge for her teacher. Members of the Educators Forum supported feelings that Andrea needed to be helped to use oral language. An…

  5. [Andreas Vesalius and surgery].

    PubMed

    Van Hee, R

    1993-01-01

    By publishing De Humani Corporis Fabrica Libri Septem in 1543, Andries van Wesel (1514-1564) gave surgical science an immense impulse. The revolutionary renovation in the knowledge of man's anatomical structure changed slowly and progressively into topographical and physiological understanding of surgical diseases. At the same time, this made better aimed and more secure operations possible. Apart from the importance of this anatomical publication, Andreas Vesalius also won his spurs as a surgeon. He taught surgery in Padua for many years. He was appointed court physician and surgeon at the Habsburg Court of Charles V and Philip II. He personally performed lots of operations known at the time as major ones. He not only quickly adopted the surgical innovations of his fellow-surgeon Ambroise Paré, but he even performed operations that had been forgotten during several centuries, among which thoracocentesis for pleural empyema. His clinical perspicacity in discovering the indication for some operations was staggering and was appreciated by all great monarchs of Europe in the 16th century. In his several consilia, numerous pieces of advice were given for the treatment of surgical patients. The surgical practice which Vesalius had in Brussels for many years, consequently became most successful. Many publications by Vesalius about surgery and blood-letting are well-known. His Chirurgia magna in septem Libros digesta still remains controversial; these books were published by Prospero Borgarruccio (1560) in 1568 by the Venetian editor Valgrisi. This book gives an excellent survey of surgical pathology as it was taught and treated in the 16th century. The scientific method that Vesalius used, not only in his anatomical studies but also in his surgical practice, deserves not only our full appraisal but should still be studied in our own time.

  6. GOES video of Tropical Storm Andrea

    NASA Image and Video Library

    This NOAA GOES-East satellite animation shows the development of System 91L into Tropical Storm Andrea over the course of 3 days from June 4 to June 6, just after Andrea was officially designated a...

  7. GOES-14 Sees Remnants of Andrea

    NASA Image and Video Library

    This animation of GOES-14 satellite data from Saturday, June 8, through Monday, June 10 at 7:31 a.m. EDT shows Post-Tropical Storm Andrea’s movement. On June 8, Andrea was centered off the coast ...

  8. Perspective View, San Andreas Fault

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The prominent linear feature straight down the center of this perspective view is California's famous San Andreas Fault. The image, created with data from NASA's Shuttle Radar Topography Mission (SRTM), will be used by geologists studying fault dynamics and landforms resulting from active tectonics. This segment of the fault lies west of the city of Palmdale, Calif., about 100 kilometers (about 60 miles) northwest of Los Angeles. The fault is the active tectonic boundary between the North American plate on the right, and the Pacific plate on the left. Relative to each other, the Pacific plate is moving away from the viewer and the North American plate is moving toward the viewer along what geologists call a right lateral strike-slip fault. Two large mountain ranges are visible, the San Gabriel Mountains on the left and the Tehachapi Mountains in the upper right. Another fault, the Garlock Fault lies at the base of the Tehachapis; the San Andreas and the Garlock Faults meet in the center distance near the town of Gorman. In the distance, over the Tehachapi Mountains is California's Central Valley. Along the foothills in the right hand part of the image is the Antelope Valley, including the Antelope Valley California Poppy Reserve. The data used to create this image were acquired by SRTM aboard the Space Shuttle Endeavour, launched on February 11, 2000.

    This type of display adds the important dimension of elevation to the study of land use and environmental processes as observed in satellite images. The perspective view was created by draping a Landsat satellite image over an SRTM elevation model. Topography is exaggerated 1.5 times vertically. The Landsat image was provided by the United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota.

    SRTM uses the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space

  9. Andreas Vesalius 1514-1564.

    PubMed

    Benini, A; Bonar, S K

    1996-06-01

    Andreas Vesalius was born in Brussels on December 31, 1514. After having spent some disappointing years at the Universities of Louvain and Paris, he graduated as Doctor of Medicine in Padua on December 5, 1537. The next day he was appointed as a teacher of both human anatomy and surgery. During the 6 years he held this chair, Vesalius engaged in impressive academic activities and published three masterly anatomic books: Tabulae Anatomicae Sex, De Humani Corporis Fabrica Libri Septem, and Epitome. The last two works contain anatomic woodcuts of incomparable artistic quality by Titian's pupils (by Stefan v. Calcar in particular). In 1544, at the age of 28, Vesalius gave up his chair and took up service as a court physician, first with Emperor Charles V and later with his son, Philip II of Spain. He died in 1564 on the small Greek island of Zante on return from a pilgrimage to the Holy Land. The gist of Vesalius' teaching was his conviction that valid anatomic knowledge could be gained only through dissection of the human corpse and not through the study of the traditional texts. Vesalius rid the study of human anatomy of mythic speculations, which had encrusted it for two millennia. Through Vesalius' work, human anatomy became an empirical science. Like Copernicus, Kepler, Bruno, and Galileo, Vesalius was one of the initiators of the new science. The tables of osteology and of the spine in Fabrica and Epitome are most impressive. Much of the nomenclature used for the spine today can be credited to him.

  10. Satellite Shows Landfall and Movement of Tropical Storm Andrea

    NASA Image and Video Library

    This NOAA GOES-East satellite animation shows the landfall and movement of Tropical Storm Andrea from June 5 to June 7. The video ends as Andrea's center was moving over South Carolina on its way u...

  11. CloudSat Profiles Tropical Storm Andrea

    NASA Image and Video Library

    2007-05-10

    CloudSat's Cloud Profiling Radar captured a profile across Tropical Storm Andrea on Wednesday, May 9, 2007, near the South Carolina/Georgia/Florida Atlantic coast. The upper image shows an infrared view of Tropical Storm Andrea from the Moderate Resolution Imaging Spectroradiometer instrument on NASA's Aqua satellite, with CloudSat's ground track shown as a red line. The lower image is the vertical cross section of radar reflectivity along this path, where the colors indicate the intensity of the reflected radar energy. CloudSat orbits approximately one minute behind Aqua in a satellite formation known as the A-Train. http://photojournal.jpl.nasa.gov/catalog/PIA09379

  12. Andrea Dworkin on Pornography: Exposing "Male Truth."

    ERIC Educational Resources Information Center

    VerLinden, Jay G.

    Radical feminist Andrea Dworkin has been instrumental in efforts to curtail pornography by defining it as a violation of women's civil rights and allowing individual women to sue the distributors for damages. Dworkin's position derives from the tension between "what should be" and "what is." Her conception of the difference…

  13. Perspective View, San Andreas Fault

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The prominent linear feature straight down the center of this perspective view is the San Andreas Fault in an image created with data from NASA's shuttle Radar Topography Mission (SRTM), which will be used by geologists studying fault dynamics and landforms resulting from active tectonics. This segment of the fault lies west of the city of Palmdale, California, about 100 kilometers (about 60 miles) northwest of Los Angeles. The fault is the active tectonic boundary between the North American plate on the right, and the Pacific plate on the left. Relative to each other, the Pacific plate is moving away from the viewer and the North American plate is moving toward the viewer along what geologists call a right lateral strike-slip fault. This area is at the junction of two large mountain ranges, the San Gabriel Mountains on the left and the Tehachapi Mountains on the right. Quail Lake Reservoir sits in the topographic depression created by past movement along the fault. Interstate 5 is the prominent linear feature starting at the left edge of the image and continuing into the fault zone, passing eventually over Tejon Pass into the Central Valley, visible at the upper left.

    This type of display adds the important dimension of elevation to the study of land use and environmental processes as observed in satellite images. The perspective view was created by draping a Landsat satellite image over an SRTM elevation model. Topography is exaggerated 1.5 times vertically. The Landsat image was provided by the United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota.

    Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994

  14. The San Andreas Fault 'Supersite' (Invited)

    NASA Astrophysics Data System (ADS)

    Hudnut, K. W.

    2013-12-01

    An expanded and permanent Supersite has been proposed to the Committee on Earth Observation Satellites (CEOS) for the San Andreas Fault system, based upon the successful initial Group on Earth Observations (GEO) Geohazard Supersite for the Los Angeles region from 2009-2013. As justification for the comprehensive San Andreas Supersite, consider the earthquake history of California, in particular the devastating M 7.8 San Francisco earthquake of 1906, which occurred along the San Andreas Fault, as did an earthquake of similar magnitude in 1857 in southern California. Los Angeles was only a small town then, but now the risk exposure has increased for both of California's megacities. Between the San Francisco and Los Angeles urban areas lies a section of the San Andreas Fault known to creep continually, so it has relatively less earthquake hazard. It used to be thought of as capable of stopping earthquakes entering it from either direction. Transitional behavior at either end of the creeping section is known to display a full range of seismic to aseismic slip events and accompanying seismicity and strain transient events. Because the occurrence of creep events is well documented by instrumental networks such as CISN and PBO, the San Andreas Supersite can be expected to be especially effective. A good baseline level of geodetic data regarding past events and strain accumulation and release exists. Many prior publications regarding the occurrence of geophysical phenomena along the San Andreas Fault system mean that in order to make novel contributions, state-of-the-art science will be required within this Supersite region. In more recent years, the 1989 Loma Prieta earthquake struck adjacent to the San Andreas Fault and caused the most damage along the western side of the San Francisco Bay Area. More recently, the concern has focused on the potential for future events along the Hayward Fault along the eastern side of San Francisco Bay. In Southern California, earthquakes

  15. The San Andreas Fault System, California, USA

    USGS Publications Warehouse

    Brown, R.D.; Wallace, R.E.; Hill, D.P.

    1992-01-01

    Geologists, seismologists, and geophysicists have intensively studied the San Andreas fault system for the past 20 to 30 years. Their goals were to learn more about damaging earthquakes, the behavior of major stirke-slip faults, and methods of reducing earthquake hazards in populated areas. Field geologic investigations, seismic networks, post-earthquake studies, precision geodetic surveys, and reflection and refraction seismic surveys are among the methods used to decipher the history, geometry, and mechanics of the system. -from Authors

  16. San Andreas Fault tremor and retrograde metamorphism

    NASA Astrophysics Data System (ADS)

    Fagereng, Åke; Diener, Johann F. A.

    2011-12-01

    Tectonic tremor is an enigmatic low-frequency seismic phenomenon mainly observed in subduction zones, but also documented along the deep extension of the central San Andreas Fault. The physical mechanisms behind this unusual seismic event are not yet determined for any tectonic setting; however, low effective stress conditions arising from metamorphic fluid production are commonly inferred for subduction-related tremor. We investigate the petrologic conditions at which the San Andreas tectonic tremor is inferred to occur through calculations of the pressure - temperature - time evolution of stable mineral assemblages and their water content in the dominant lithologies of the Franciscan Complex. We find that tremor locations around Parkfield and Cholame are currently experiencing retrograde metamorphic conditions. Within the temperature-depth conditions of observed tremor activity, at approximately 500°C and 20 km depth, several mineralogical transitions may occur in cooling greywacke and mafic rocks, leading to localised, significant removal of free water and an associated volume decrease. This indicates that, contrary to subduction-related tremor, tremor on the San Andreas Fault is not linked to prograde, crustal metamorphic fluid production within the fault zone; rather it might be related to mantle-derived fluids from below the tremor zone, and/or fault zone weakening that occurs as phyllosilicates replace more competent and granular mineral phases.

  17. Aerial views of the San Andreas Fault

    USGS Publications Warehouse

    Moore, M.

    1988-01-01

    These aerial photographs of the San Andreas fault were taken in 1965 by Robert E. Wallace of the U.S Geological Survey. The pictures were taken with a Rolliflex camera on 20 format black and white flim; Wallace was aboard a light, fixed-wing aircraft, flying mostly at low altitudes. He photographed the fault from San Francisco near its north end where it enters by the Salton Sea. These images represent only a sampling of the more than 300 images prodcued during this project. All the photographs reside in the U.S Geological Survey Library in Menlo Park, California. 

  18. The last months of Andreas Vesalius.

    PubMed

    Biesbrouck, Maurits; Steeno, Omer

    2010-12-01

    A good deal has already been written about the last months of Andreas Vesalius' life. Most of it has been fairly speculative, because the necessary primary sources have been lacking. Much of what was supposedly known for sure seemed bizarre, and various writers even frankly characterised their own accounts as 'legend'. It is only since the discovery of several letters in the archives of Simancas by Josh Baron in 1962 that various points have become somewhat clearer. Baron presented these letters at the 19th International Congress on the History of Medicine in Basel in September 1964.

  19. Crustal deformation along the San Andreas, California

    NASA Technical Reports Server (NTRS)

    Li, Victor C.

    1992-01-01

    The goal is to achieve a better understanding of the regional and local deformation and crustal straining processes in western North America, particularly the effects of the San Andreas and nearby faults on the spatial and temporal crustal deformation behavior. Construction of theoretical models based on the mechanics of coupled elastic plate, viscoelastic foundation and large scale crack mechanics provide a rational basis for the interpretation of seismic and aseismic anomalies and expedite efforts in forecasting the stability of plate boundary deformation. Special focus is placed on the three dimensional time dependent surface deformation due to localized slippage in a elastic layer coupled to a visco-elastic substrate. The numerical analysis is based on a 3-D boundary element technique. Extension to visco-elastic coupling demands the derivation of 3-D time dependent Green's function. This method was applied to analyze the viscoelastic surface displacements due to a dislocated embedded patch. Surface uplift as a function of time and position are obtained. Comparisons between surface uplift for long and short dislocated patches are made.

  20. Rhazes in the renaissance of Andreas Vesalius.

    PubMed

    Compier, Abdul Haq

    2012-01-01

    Andreas Vesalius' (1514-64) first publication was a Paraphrasis of the ninth book of the Liber ad Almansorem, written by the Arab-Persian physician and alchemist Rhazes (854-925). The role of Rhazes in Vesalius' oeuvre has thus far been much disregarded. The different ways Rhazes recurs reveal an intellectual evolution in Vesalius' work. In the Paraphrasis, Vesalius subjects Rhazes to the authority of Galen in the context of the early sixteenth-century humanist campaign for the substitution of Arab influences by Greek 'originals'. Over the years Vesalius continues his work on Rhazes, but his approach becomes more internationalistic. Ultimately, Vesalius criticises Galen while expressing sympathy for the Arab author. This may be the more significant as Rhazes could have influenced Vesalius in the act of criticising Galen - critical discussions of Galen were available to Vesalius in Latin translations of Rhazes's Liber Continens. Although Vesalius never refers to the work, it is hardly possible he was unaware of it: similarities in structure, rhetoric and form between the Continens and the De humani corporis fabrica could support this hypothesis.

  1. Rhazes in the Renaissance of Andreas Vesalius

    PubMed Central

    Compier, Abdul Haq

    2012-01-01

    Andreas Vesalius' (1514–64) first publication was a Paraphrasis of the ninth book of the Liber ad Almansorem, written by the Arab–Persian physician and alchemist Rhazes (854–925). The role of Rhazes in Vesalius' oeuvre has thus far been much disregarded. The different ways Rhazes recurs reveal an intellectual evolution in Vesalius' work. In the Paraphrasis, Vesalius subjects Rhazes to the authority of Galen in the context of the early sixteenth-century humanist campaign for the substitution of Arab influences by Greek ‘originals’. Over the years Vesalius continues his work on Rhazes, but his approach becomes more internationalistic. Ultimately, Vesalius criticises Galen while expressing sympathy for the Arab author. This may be the more significant as Rhazes could have influenced Vesalius in the act of criticising Galen – critical discussions of Galen were available to Vesalius in Latin translations of Rhazes's Liber Continens. Although Vesalius never refers to the work, it is hardly possible he was unaware of it: similarities in structure, rhetoric and form between the Continens and the De humani corporis fabrica could support this hypothesis. PMID:23752981

  2. San Andreas tremor cascades define deep fault zone complexity

    USGS Publications Warehouse

    Shelly, David R.

    2015-01-01

    Weak seismic vibrations - tectonic tremor - can be used to delineate some plate boundary faults. Tremor on the deep San Andreas Fault, located at the boundary between the Pacific and North American plates, is thought to be a passive indicator of slow fault slip. San Andreas Fault tremor migrates at up to 30 m s-1, but the processes regulating tremor migration are unclear. Here I use a 12-year catalogue of more than 850,000 low-frequency earthquakes to systematically analyse the high-speed migration of tremor along the San Andreas Fault. I find that tremor migrates most effectively through regions of greatest tremor production and does not propagate through regions with gaps in tremor production. I interpret the rapid tremor migration as a self-regulating cascade of seismic ruptures along the fault, which implies that tremor may be an active, rather than passive participant in the slip propagation. I also identify an isolated group of tremor sources that are offset eastwards beneath the San Andreas Fault, possibly indicative of the interface between the Monterey Microplate, a hypothesized remnant of the subducted Farallon Plate, and the North American Plate. These observations illustrate a possible link between the central San Andreas Fault and tremor-producing subduction zones.

  3. Perspective view, Landsat overlay San Andreas Fault, Palmdale, California

    NASA Image and Video Library

    2000-02-21

    The prominent linear feature straight down the center of this perspective view is the San Andreas Fault. This segment of the fault lies near the city of Palmdale, CA the flat area in the right half of the image about 60 kilometers north of Los Angeles.

  4. NASA's 3-D TRMM Satellite Animation of Tropical Storm Andrea

    NASA Image and Video Library

    This 3-D view from the west was derived from TRMM Precipitation Radar (PR) data captured when Andrea was examined by the TRMM satellite with the June 5, 2234 UTC (6:34 p.m. EDT) orbit. It clearly s...

  5. Empowering Andrea to Help Year 5 Students Construct Fraction Understanding

    ERIC Educational Resources Information Center

    Baturo, Annette R

    2004-01-01

    This paper provides a glimpse into the positive effect on student learning as a result of empowering a classroom teacher of 20 years (Andrea) with subject matter knowledge relevant to developing fraction understanding. Having a facility with fractions is essential for life skills in any society, whether metricated or non-metricated, and yet…

  6. How often will earthquakes recur on the San Andreas Fault?

    USGS Publications Warehouse

    Wallace, R.E.

    1978-01-01

    My own approach to estimating average recurrence intervals has been somewhat different. I have used the history of slip rates along the San Andreas fault that are preserved in the geologic record. The main advantage in this method is that is samples a very long period of time, which gives a better estimate of the recurrence of small earthquakes.  

  7. Fractal geometry in the San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Okubo, Paul G.; Aki, Keiiti

    1987-01-01

    It has been noted that the spatial distribution of earthquakes and the mode of strain release in the San Andreas fault system is related to the complexity of fault geometry. Because of their rough appearance over many length scales, faults can be regarded as fractal surfaces. Direct estimates of fractal dimension D of portions of the San Andreas fault system between the northern Gabilan Range and the Salton Sea, including the postulated extent of the great 1857 Fort Tejon earthquake, are obtained from measured fault lengths, analogous to the lengths of coastlines as discussed by Mandelbrot. Regions characterized by complicated fault geometry are associated with larger values of D. Based on fault traces mapped at a scale of 1:750,000, D is 1.3 for this reach of the fault defined as a 30-km-wide band about a main fault trace. For that part near Parkfield which could be associated with the nucleation of the 1857 earthquake, D is 1.1; at this same scale, D is 1.4 for the San Andreas and related faults near San Bernardino where the 1857 rupture stopped, compared to 1.2 for the San Andreas-San Juan fault segments near the point of arrest of the 1966 Parkfield earthquake. At finer map scales (1:24,000 and 1:62,500) critical lengths of ˜ 500 m and 1 km are identified which might relate to the extent of off-San Andreas fault offsets. The critical lengths also suggest that fault geometry is not self-similar. If this fractal geometry persists through the seismic cycle, it may be possible to use a quantitative measure of complexity to explain the occurrence of great and characteristic earthquakes along a given reach of fault.

  8. Continuity of the San Andreas Fault at San Gorgonio Pass

    NASA Astrophysics Data System (ADS)

    Carena, S.; Suppe, J.

    2002-12-01

    The San Andreas fault at San Gorgonio Pass does not have a clear surface trace and is considered aseismic. Our findings suggest in fact that the existence of a through-going vertical or near-vertical San Andreas fault between Yucaipa and North Palm Springs is highly unlikely. We mapped over 70 faults in the San Gorgonio Pass-San Bernardino Mountains region using the catalog of 43,500 relocated 1975-1998 earthquakes of Richards-Dinger and Shearer (2000). A clustering algorithm was applied to the relocated earthquakes in order to obtain tighter earthquake clouds and thus better-defined fault surfaces. The earthquakes were then imported into Gocad, a 3D modeling software that allowed us to separate earthquakes into coplanar clusters associated with different faults and fault strands and to fit optimized surfaces to them. We also used the catalog of 13,000 focal mechanisms of Hauksson (2000) to confirm the nature of the mapped faults. We were able to constrain the 3D geometry of the San Andreas fault near San Gorgonio Pass from the 3D geometry of the fault network surrounding it. None of these faults show any displacement due to an hypothetical sub-vertical San Andreas. The San Andreas fault must therefore rotate to much shallower dips, or lose its continuity at depths between 3 and 15 km The most likely configuration is the one where the San Andreas fault merges into the shallow-dipping San Gorgonio Pass thrust W of North Palm Springs. Strike-slip motion is taken up by both the thrust (the slip vector on the N. Palm Springs segment is reverse/right-lateral strike-slip) and by a series of NW striking faults in the footwall of the thrust. The W termination of the most active part of the San Gorgonio Pass thrust coincides with one of these footwall faults at depth, and with the south bend in the San Andreas fault strand N of Banning. This boundary also marks a change in the stress field, with a dominant strike-slip regime to the E (and localized thrusting between San

  9. Andreas Rett and benign familial neonatal convulsions revisited.

    PubMed

    Zimprich, F; Ronen, G M; Stögmann, W; Baumgartner, C; Stögmann, E; Rett, B; Pappas, C; Leppert, M; Singh, N; Anderson, V E

    2006-09-12

    In 1964 Andreas Rett published the first account of a family with benign familial neonatal convulsions (BFNC). The authors retraced Rett's family and report that the clinical and genetic features of this original family fit the currently accepted definitions of BFNC. They also consider the career of Dr. Rett, a researcher and social reformer as well as an advocate for the rights of children with developmental disabilities.

  10. San andreas fault zone head waves near parkfield, california.

    PubMed

    Ben-Zion, Y; Malin, P

    1991-03-29

    Microearthquake seismograms from the borehole seismic network on the San Andreas fault near Parkfield, California, provide three lines of evidence that first P arrivals are "head" waves refracted along the cross-fault material contrast. First, the travel time difference between these arrivals and secondary phases identified as direct P waves scales linearly with the source-receiver distance. Second, these arrivals have the emergent wave character associated in theory and practice with refracted head waves instead of the sharp first breaks associated with direct P arrivals. Third, the first motion polarities of the emergent arrivals are reversed from those of the direct P waves as predicted by the theory of fault zone head waves for slip on the San Andreas fault. The presence of fault zone head waves in local seismic network data may help account for scatter in earthquake locations and source mechanisms. The fault zone head waves indicate that the velocity contrast across the San Andreas fault near Parkfield is approximately 4 percent. Further studies of these waves may provide a way of assessing changes in the physical state of the fault system.

  11. The Making of the Andrea Wave and other Rogues

    NASA Astrophysics Data System (ADS)

    Donelan, Mark A.; Magnusson, Anne-Karin

    2017-03-01

    Unexpectedly large ocean waves or ‘rogues’ are sometimes claimed to be the cause of damage to ships at sea and to offshore structures. While wind-driven wave models are capable of predicting the average characteristics of waves, the maximum height of rogues that may occur is yet unknown. Rogues form in the open ocean through the addition of elemental wave trains or groups and, infrequently, with many elements coming together in phase, producing rogues. Here we perform directional analyses on one of the steepest rogues ever recorded: the Andrea wave. We find that the Andrea wave was close to the breaking-limited height. Analysis of the 72 twenty minute records on the day of the Andrea wave yields encounter return periods of about 21 days for maximally steep waves, while less steep rogues occur about twice daily. An explicit formula is given for the encounter probability, based on the target area. This work answers the critical questions regarding rogues in the design and operation of ships and offshore structures: how high can rogues be and how frequently they occur.

  12. The Making of the Andrea Wave and other Rogues

    PubMed Central

    Donelan, Mark A.; Magnusson, Anne-Karin

    2017-01-01

    Unexpectedly large ocean waves or ‘rogues’ are sometimes claimed to be the cause of damage to ships at sea and to offshore structures. While wind-driven wave models are capable of predicting the average characteristics of waves, the maximum height of rogues that may occur is yet unknown. Rogues form in the open ocean through the addition of elemental wave trains or groups and, infrequently, with many elements coming together in phase, producing rogues. Here we perform directional analyses on one of the steepest rogues ever recorded: the Andrea wave. We find that the Andrea wave was close to the breaking-limited height. Analysis of the 72 twenty minute records on the day of the Andrea wave yields encounter return periods of about 21 days for maximally steep waves, while less steep rogues occur about twice daily. An explicit formula is given for the encounter probability, based on the target area. This work answers the critical questions regarding rogues in the design and operation of ships and offshore structures: how high can rogues be and how frequently they occur. PMID:28272520

  13. The Making of the Andrea Wave and other Rogues.

    PubMed

    Donelan, Mark A; Magnusson, Anne-Karin

    2017-03-08

    Unexpectedly large ocean waves or 'rogues' are sometimes claimed to be the cause of damage to ships at sea and to offshore structures. While wind-driven wave models are capable of predicting the average characteristics of waves, the maximum height of rogues that may occur is yet unknown. Rogues form in the open ocean through the addition of elemental wave trains or groups and, infrequently, with many elements coming together in phase, producing rogues. Here we perform directional analyses on one of the steepest rogues ever recorded: the Andrea wave. We find that the Andrea wave was close to the breaking-limited height. Analysis of the 72 twenty minute records on the day of the Andrea wave yields encounter return periods of about 21 days for maximally steep waves, while less steep rogues occur about twice daily. An explicit formula is given for the encounter probability, based on the target area. This work answers the critical questions regarding rogues in the design and operation of ships and offshore structures: how high can rogues be and how frequently they occur.

  14. Earthquakes and fault creep on the northern San Andreas fault

    USGS Publications Warehouse

    Nason, R.

    1979-01-01

    At present there is an absence of both fault creep and small earthquakes on the northern San Andreas fault, which had a magnitude 8 earthquake with 5 m of slip in 1906. The fault has apparently been dormant after the 1906 earthquake. One possibility is that the fault is 'locked' in some way and only produces great earthquakes. An alternative possibility, presented here, is that the lack of current activity on the northern San Andreas fault is because of a lack of sufficient elastic strain after the 1906 earthquake. This is indicated by geodetic measurements at Fort Ross in 1874, 1906 (post-earthquake), and 1969, which show that the strain accumulation in 1969 (69 ?? 10-6 engineering strain) was only about one-third of the strain release (rebound) in the 1906 earthquake (200 ?? 10-6 engineering strain). The large difference in seismicity before and after 1906, with many strong local earthquakes from 1836 to 1906, but only a few strong earthquakes from 1906 to 1976, also indicates a difference of elastic strain. The geologic characteristics (serpentine, fault straightness) of most of the northern San Andreas fault are very similar to the characteristics of the fault south of Hollister, where fault creep is occurring. Thus, the current absence of fault creep on the northern fault segment is probably due to a lack of sufficient elastic strain at the present time. ?? 1979.

  15. Overview of the Southern San Andreas Fault Model

    USGS Publications Warehouse

    Weldon, Ray J.; Biasi, Glenn P.; Wills, Chris J.; Dawson, Timothy E.

    2008-01-01

    This appendix summarizes the data and methodology used to generate the source model for the southern San Andreas fault. It is organized into three sections, 1) a section by section review of the geological data in the format of past Working Groups, 2) an overview of the rupture model, and 3) a manuscript by Biasi and Weldon (in review Bulletin of the Seismological Society of America) that describes the correlation methodology that was used to help develop the ?geologic insight? model. The goal of the Biasi and Weldon methodology is to quantify the insight that went into developing all A faults; as such it is in concept consistent with all other A faults but applied in a more quantitative way. The most rapidly slipping fault and the only known source of M~8 earthquakes in southern California is the San Andreas fault. As such it plays a special role in the seismic hazard of California, and has received special attention in the current Working Group. The underlying philosophy of the current Working Group is to model the recurrence behavior of large, rapidly slipping faults like the San Andreas from observed data on the size, distribution and timing of past earthquakes with as few assumptions about underlying recurrence behavior as possible. In addition, we wish to carry the uncertainties in the data and the range of reasonable extrapolations from the data to the final model. To accomplish this for the Southern San Andreas fault we have developed an objective method to combine all of the observations of size, timing, and distribution of past earthquakes into a comprehensive set of earthquake scenarios that each represent a possible history of earthquakes for the past ~1400 years. The scenarios are then ranked according to their overall consistency with the data and then the frequencies of all of the ruptures permitted by the current Working Group?s segmentation model are calculated. We also present 30-yr conditional probabilities by segment and compare to previous

  16. San Andreas fault geometry in the Parkfield, California, region

    USGS Publications Warehouse

    Simpson, R.W.; Barall, M.; Langbein, J.; Murray, J.R.; Rymer, M.J.

    2006-01-01

    In map view, aftershocks of the 2004 Parkfield earthquake lie along a line that forms a straighter connection between San Andreas fault segments north and south of the Parkfield reach than does the mapped trace of the fault itself. A straightedge laid on a geologic map of Central California reveals a ???50-km-long asymmetric northeastward warp in the Parkfield reach of the fault. The warp tapers gradually as it joins the straight, creeping segment of the San Andreas to the north-west, but bends abruptly across Cholame Valley at its southeast end to join the straight, locked segment that last ruptured in 1857. We speculate that the San Andreas fault surface near Parkfield has been deflected in its upper ???6 km by nonelastic behavior of upper crustal rock units. These units and the fault surface itself are warped during periods between large 1857-type earthquakes by the presence of the 1857-locked segment to the south, which buttresses intermittent coseismic and continuous aseismic slip on the Parkfield reach. Because of nonelastic behavior, the warping is not completely undone when an 1857-type event occurs, and the upper portion of the three-dimensional fault surface is slowly ratcheted into an increasingly prominent bulge. Ultimately, the fault surface probably becomes too deformed for strike-slip motion, and a new, more vertical connection to the Earth's surface takes over, perhaps along the Southwest Fracture Zone. When this happens a wedge of material currently west of the main trace will be stranded on the east side of the new main trace.

  17. Thermal regime of the San Andreas fault near Parkfield, California

    USGS Publications Warehouse

    Sass, J.H.; Williams, C.F.; Lachenbruch, A.H.; Galanis, S.P.; Grubb, F.V.

    1997-01-01

    Knowledge of the temperature variation with depth near the San Andreas fault is vital to understanding the physical processes that occur within the fault zone during earthquakes and creep events. Parkfield is near the southern end of the Coast Ranges segment of the San Andreas fault. This segment has higher mean heat flow than the Cape Mendocino segment to the northwest or the Mojave segment to the southeast. Boreholes were drilled specifically for the U.S. Geological Survey's Parkfield earthquake prediction experiment or converted from other uses at 25 sites within a few kilometers of the fault near Parkfield. These holes, which range in depth from 150 to over 1500 m, were intended mainly for the deployment of volumetric strain meters, water-level recorders, and other downhole instruments. Temperature profiles were obtained from all the holes, and heat flow values were estimated from 17 of them. For a number of reasons, including a paucity of thermal conductivity data and rugged local topography, the accuracy of individual determinations was not sufficiently high to document local variations in heat flow. Values range from 54 to 92 mW m-2, with mean and 95% confidence limits of 74 ?? 4 mW m-2. This mean is slightly lower than the mean (83 ?? 3) of 39 previously published values from the central Coast Ranges, but it is consistent with the overall pattern of elevated heat flow in the Coast Ranges, and it is transitional to the mean of 68 ?? 2 mW m-2 that characterizes the Mojave segment of the San Andreas fault immediately to the south. The lack of a heat flow peak near the fault underscores the absence of a frictional thermal anomaly and provides additional support for a very small resolved shear stress parallel to the San Andreas fault and the nearly fault-normal maximum compressive stress observed in this region. Estimates of subsurface thermal conditions indicate that the seismic-aseismic transition for the Parkfield segment corresponds to temperatures in the

  18. Nonvolcanic tremors deep beneath the San Andreas Fault.

    PubMed

    Nadeau, Robert M; Dolenc, David

    2005-01-21

    We have discovered nonvolcanic tremor activity (i.e., long-duration seismic signals with no clear P or S waves) within a transform plate boundary zone along the San Andreas Fault near Cholame, California, the inferred epicentral region of the 1857 Fort Tejon earthquake (moment magnitude approximately 7.8). The tremors occur between 20 to 40 kilometers' depth, below the seismogenic zone (the upper approximately 15 kilometers of Earth's crust where earthquakes occur), and their activity rates may correlate with variations in local earthquake activity.

  19. Deep permeability of the San Andreas Fault from San Andreas Fault Observatory at Depth (SAFOD) core samples

    USGS Publications Warehouse

    Morrow, Carolyn A.; Lockner, David A.; Moore, Diane E.; Hickman, Stephen H.

    2014-01-01

    The San Andreas Fault Observatory at Depth (SAFOD) scientific borehole near Parkfield, California crosses two actively creeping shear zones at a depth of 2.7 km. Core samples retrieved from these active strands consist of a foliated, Mg-clay-rich gouge containing porphyroclasts of serpentinite and sedimentary rock. The adjacent damage zone and country rocks are comprised of variably deformed, fine-grained sandstones, siltstones, and mudstones. We conducted laboratory tests to measure the permeability of representative samples from each structural unit at effective confining pressures, Pe up to the maximum estimated in situ Pe of 120 MPa. Permeability values of intact samples adjacent to the creeping strands ranged from 10−18 to 10−21 m2 at Pe = 10 MPa and decreased with applied confining pressure to 10−20–10−22 m2 at 120 MPa. Values for intact foliated gouge samples (10−21–6 × 10−23 m2 over the same pressure range) were distinctly lower than those for the surrounding rocks due to their fine-grained, clay-rich character. Permeability of both intact and crushed-and-sieved foliated gouge measured during shearing at Pe ≥ 70 MPa ranged from 2 to 4 × 10−22 m2 in the direction perpendicular to shearing and was largely insensitive to shear displacement out to a maximum displacement of 10 mm. The weak, actively-deforming foliated gouge zones have ultra-low permeability, making the active strands of the San Andreas Fault effective barriers to cross-fault fluid flow. The low matrix permeability of the San Andreas Fault creeping zones and adjacent rock combined with observations of abundant fractures in the core over a range of scales suggests that fluid flow outside of the actively-deforming gouge zones is probably fracture dominated.

  20. Monitoring microearthquakes with the San Andreas fault observatory at depth

    USGS Publications Warehouse

    Oye, V.; Ellsworth, W.L.

    2007-01-01

    In 2005, the San Andreas Fault Observatory at Depth (SAFOD) was drilled through the San Andreas Fault zone at a depth of about 3.1 km. The borehole has subsequently been instrumented with high-frequency geophones in order to better constrain locations and source processes of nearby microearthquakes that will be targeted in the upcoming phase of SAFOD. The microseismic monitoring software MIMO, developed by NORSAR, has been installed at SAFOD to provide near-real time locations and magnitude estimates using the high sampling rate (4000 Hz) waveform data. To improve the detection and location accuracy, we incorporate data from the nearby, shallow borehole (???250 m) seismometers of the High Resolution Seismic Network (HRSN). The event association algorithm of the MIMO software incorporates HRSN detections provided by the USGS real time earthworm software. The concept of the new event association is based on the generalized beam forming, primarily used in array seismology. The method requires the pre-computation of theoretical travel times in a 3D grid of potential microearthquake locations to the seismometers of the current station network. By minimizing the differences between theoretical and observed detection times an event is associated and the location accuracy is significantly improved.

  1. Andreas Vesalius 500 years - A Renaissance that revolutionized cardiovascular knowledge

    PubMed Central

    Mesquita, Evandro Tinoco; de Souza Júnior, Celso Vale; Ferreira, Thiago Reigado

    2015-01-01

    The history of medicine and cardiology is marked by some geniuses who dared in thinking, research, teaching and transmitting scientific knowledge, and the Italian Andreas Vesalius one of these brilliant masters. His main scientific work "De Humani Corporis Fabrica" is not only a landmark study of human anatomy but also an artistic work of high aesthetic quality published in 1543. In the year 2014 we celebrated 500 years since the birth of the brilliant professor of Padua University, who with his courage and sense of observation changed the understanding of cardiovascular anatomy and founded a school to date in innovative education and research of anatomy. By identifying "the anatomical errors" present in Galen's book and speech, he challenged the dogmas of the Catholic Church, the academic world and the doctors of his time. However, the accuracy of his findings and his innovative way to disseminate them among his students and colleagues was essential so that his contributions are considered by many the landmark of modern medicine. His death is still surrounded by mysteries having different hypotheses, but a certainty, suffered sanctions of the Catholic Church for the spread of their ideas. The cardiologists, cardiovascular surgeons, interventional cardiologists, electrophysiologists and cardiovascular imaginologists must know the legacy of genius Andreas Vesalius that changed the paradigm of human anatomy. PMID:26107459

  2. Strain accumulation and surface deformation along the San Andreas, California

    NASA Technical Reports Server (NTRS)

    Li, Victor C.

    1986-01-01

    Stressing and rupture of a locked zone adjacent to a creeping fault segment was studied with special reference to strength heterogeneity depthwise and along-strike. The resulting precursory temporal and spatial variations of surface strain rate profiles were compared to geodetic measurements on the San Andreas fault in central California. Crustal deformation in great California earthquake cycles was also studied with special reference to the temporal decay of strain rate observed since the 1957 and 1906 great earthquakes, and comtemporary surface strain rate and velocity profiles at several locations along the San Andreas. The effect of viscoelastic response in the deep aseismic shear zone on the surface deformation behavior was examined. Work was begun on a fundamental reformulation of the crustal deformation problem focusing on the crustal deformation process affected by deep aseismic slip as the slip zone progresses toward an instability and as deep seismic slip continues postseismically, the 3-D nature of the problem due to geometry and material heterogeneity, and the time-dependent source coming from the lithosphere/astenospheric coupling process.

  3. Heat flow and energetics of the San Andreas fault zone.

    USGS Publications Warehouse

    Lachenbruch, A.H.; Sass, J.H.

    1980-01-01

    Approximately 100 heat flow measurements in the San Andreas fault zone indicate 1) there is no evidence for local frictional heating of the main fault trace at any latitude over a 1000-km length from Cape Mendocino to San Bernardino, 2) average heat flow is high (ca.2 HFU, ca.80 mW m-2) throughout the 550-km segment of the Coast Ranges that encloses the San Andreas fault zone in central California; this broad anomaly falls off rapidly toward the Great Valley to the east, and over a 200-km distance toward the Mendocino Triple Junction to the northwest. As others have pointed out, a local conductive heat flow anomaly would be detectable unless the frictional resistance allocated to heat production on the main trace were less than 100 bars. Frictional work allocated to surface energy of new fractures is probably unimportant, and hydrologic convection is not likely to invalidate the conduction assumption, since the heat discharge by thermal springs near the fault is negligible. -Authors

  4. Heat flow and energetics of the San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Lachenbruch, Arthur H.; Sass, J. H.

    1980-11-01

    Approximately 100 heat flow measurements in the San Andreas fault zone indicate (1) there is no evidence for local factional heating of the main fault trace at any latitude over a 1000-km length from Cape Mendocino to San Bernardino, (2) average heat flow is high (˜2 HFU, ˜80 mW m-2) throughout the 550-km segment of the Coast Ranges that encloses the San Andreas fault zone in central California; this broad anomaly falls off rapidly toward the Great Valley to the east, and over a 200-km distance toward the Mendocino Triple Junction to the northwest. As others have pointed out, a local conductive heat flow anomaly would be detectable unless the frictional resistance allocated to heat production on the main trace were ≲100 bars. Frictional work allocated to surface energy of new fractures is probably unimportant, and hydrologic convection is not likely to invalidate the conduction assumption, since the heat discharge by thermal springs near the fault is negligible. Explanations for the low dynamic friction fall into two intergradational classes: those in which the fault is weak all of the time and those in which it is weak only during earthquakes (possibly just large ones). The first class includes faults containing anomalously weak gouge materials and faults containing materials with normal frictional properties under near-lithostatic steady state fluid pressures. In the second class, weakening is caused by the event (for example, a thermally induced increase in fluid pressure, dehydration of clay minerals, or acoustic fluidization). In this class, unlike the first, the average strength and ambient tectonic shear stress may be large, ˜1 kbar, but the stress allocated to elastic radiation (the apparent stress) must be of similar magnitude, an apparent contradiction with seismic estimates. Unless seismic radiation is underestimated for large earthquakes, it is difficult to justify average tectonic stresses on the main trace of the San Andreas fault in excess of

  5. The San Andreas fault experiment. [gross tectonic plates relative velocity

    NASA Technical Reports Server (NTRS)

    Smith, D. E.; Vonbun, F. O.

    1973-01-01

    A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

  6. The San Andreas fault experiment. [gross tectonic plates relative velocity

    NASA Technical Reports Server (NTRS)

    Smith, D. E.; Vonbun, F. O.

    1973-01-01

    A plan was developed during 1971 to determine gross tectonic plate motions along the San Andreas Fault System in California. Knowledge of the gross motion along the total fault system is an essential component in the construction of realistic deformation models of fault regions. Such mathematical models will be used in the future for studies which will eventually lead to prediction of major earthquakes. The main purpose of the experiment described is the determination of the relative velocity of the North American and the Pacific Plates. This motion being so extremely small, cannot be measured directly but can be deduced from distance measurements between points on opposite sites of the plate boundary taken over a number of years.

  7. The Last Months of Andreas Vesalius: a Coda.

    PubMed

    Biesbrouck, Maurits; Goddeeris, Theodoor; Steeno, Omer

    2012-12-01

    Since the publication in this journal of our two articles on the end of Andreas Vesalius' life, some very old sources have recently become available that we were unable to consult at the time of writing and that now prompt us to add a coda. These sources give an even better picture of both the circumstances of the disaster that led to Vesalius' death and the correct site of his burial. Firstly, there is a text by Reinerus Solenander that casts a completely different light on the circumstances in which his ship was at sea and the way in which it reached land; in addition, there is a new early eye-witness report of his burial-place by Christoph Fürer von Haimendorf, dating from 6 August 1565.

  8. Tilt precursors before earthquakes on the San Andreas fault, California

    USGS Publications Warehouse

    Johnston, M.J.S.; Mortensen, C.E.

    1974-01-01

    An array of 14 biaxial shallow-borehole tiltmeters (at 10-7 radian sensitivity) has been installed along 85 kilometers of the San Andreas fault during the past year. Earthquake-related changes in tilt have been simultaneously observed on up to four independent instruments. At earthquake distances greater than 10 earthquake source dimensions, there are few clear indications of tilt change. For the four instruments with the longest records (>10 months), 26 earthquakes have occurred since July 1973 with at least one instrument closer than 10 source dimensions and 8 earthquakes with more than one instrument within that distance. Precursors in tilt direction have been observed before more than 10 earthquakes or groups of earthquakes, and no similar effect has yet been seen without the occurrence of an earthquake.

  9. A Look Inside the San Andreas fault at Parkfield Through Vertical Seismic Profiling

    USGS Publications Warehouse

    Chavarria, J.A.; Malin, P.; Catchings, R.D.; Shalev, E.

    2003-01-01

    The San Andreas Fault Observatory at Depth pilot hole is located on the southwestern side of the Parkfield San Andreas fault. This observatory includes a vertical seismic profiling (VSP) array. VSP seismograms from nearby micro-earthquakes contain signals between the P and S waves. These signals may be P and S waves scattered by the local geologic structure. The collected scattering points form planar surfaces that we interpret as the San Andreas fault and four other secondary faults. The scattering process includes conversions between P and S waves, the strengths of which suggest large contrasts in material properties, possibly indicating the presence of cracks or fluids.

  10. A look inside the San Andreas Fault at Parkfield through vertical seismic profiling.

    PubMed

    Chavarria, J Andres; Malin, Peter; Catchings, Rufus D; Shalev, Eylon

    2003-12-05

    The San Andreas Fault Observatory at Depth pilot hole is located on the southwestern side of the Parkfield San Andreas fault. This observatory includes a vertical seismic profiling (VSP) array. VSP seismograms from nearby microearthquakes contain signals between the P and S waves. These signals may be P and S waves scattered by the local geologic structure. The collected scattering points form planar surfaces that we interpret as the San Andreas fault and four other secondary faults. The scattering process includes conversions between P and S waves, the strengths of which suggest large contrasts in material properties, possibly indicating the presence of cracks or fluids.

  11. Resurvey of site stability quadrilaterals, Otay Mountain and Quincy, California. [San Andreas fault experiment

    NASA Technical Reports Server (NTRS)

    Scholz, C. H.

    1977-01-01

    Trilateration quadrilaterals established across two faults near the San Andreas Fault Experiment laser/satellite ranging sites were resurveyed after four years. No evidence of significant tectonic motion was found.

  12. San Andreas Fault, Southern California, Shaded Relief, Wrapped Color as Height

    NASA Image and Video Library

    2000-02-17

    This topographic map acquired by NASA Shuttle Radar Topography Mission SRTM from data collected on February 16, 2000 vividly displays California famous San Andreas Fault along the southwestern edge of the Mojave Desert, Calif.

  13. San Andreas Fault, Southern California , Radar Image, Wrapped Color as Height

    NASA Image and Video Library

    2000-02-17

    This topographic map acquired by NASA Shuttle Radar Topography Mission SRTM from data collected on February 16, 2000 vividly displays California famous San Andreas Fault along the southwestern edge of the Mojave Desert, Calif.

  14. Earthquake swarm along the San Andreas fault near Palmdale, Southern California, 1976 to 1977

    USGS Publications Warehouse

    Mcnally, K.C.; Kanamori, H.; Pechmann, J.C.; Fuis, G.

    1978-01-01

    Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude ??? 3) occurred on or near the San Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 81/4+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown. Copyright ?? 1978 AAAS.

  15. Earthquake Swarm Along the San Andreas Fault near Palmdale, Southern California, 1976 to 1977.

    PubMed

    McNally, K C; Kanamori, H; Pechmann, J C; Fuis, G

    1978-09-01

    Between November 1976 and November 1977 a swarm of small earthquakes (local magnitude Andreas fault near Palmdale, California. This swarm was the first observed along this section of the San Andreas since cataloging of instrumental data began in 1932. The activity followed partial subsidence of the 35-centimeter vertical crustal uplift known as the Palmdale bulge along this "locked" section of the San Andreas, which last broke in the great (surface-wave magnitude = 8(1/4)+) 1857 Fort Tejon earthquake. The swarm events exhibit characteristics previously observed for some foreshock sequences, such as tight clustering of hypocenters and time-dependent rotations of stress axes inferred from focal mechanisms. However, because of our present lack of understanding of the processes that precede earthquake faulting, the implications of the swarm for future large earthquakes on the San Andreas fault are unknown.

  16. Lithosphere-asthenosphere interactions near the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Chamberlain, C. J.; Houlié, N.; Bentham, H. L. M.; Stern, T. A.

    2014-08-01

    We decipher the strain history of the upper mantle in California through the comparison of the long-term finite strain field in the mantle and the surface strain-rate field, respectively inferred from fast polarization directions of seismic phases (SKS and SKKS), and Global Positioning System (GPS) surface velocity fields. We show that mantle strain and surface strain-rate fields are consistent in the vicinity of San Andreas Fault (SAF) in California. Such an agreement suggests that the lithosphere and strong asthenosphere have been deformed coherently and steadily since >1 Ma. We find that the crustal stress field rotates (up to 40° of rotation across a 50 km distance from 50° relative to the strike of the SAF, in the near-field of SAF) from San Francisco to the Central Valley. Both observations suggest that the SAF extends to depth, likely through the entire lithosphere. From Central Valley towards the Basin and Range, the orientations of GPS strain-rates, shear wave splitting measurements and seismic stress fields diverge indicating reduced coupling or/and shallow crustal extension and/or presence of frozen anisotropy.

  17. A slow earthquake sequence on the San Andreas fault

    USGS Publications Warehouse

    Linde, A.T.; Gladwin, M.T.; Johnston, M.J.S.; Gwyther, R.L.; Bilham, R.G.

    1996-01-01

    EARTHQUAKES typically release stored strain energy on timescales of the order of seconds, limited by the velocity of sound in rock. Over the past 20 years, observations and laboratory experiments have indicated that capture can also occur more slowly, with durations up to hours. Such events may be important in earthquake nucleation and in accounting for the excess of plate convergence over seismic slip in subduction zones. The detection of events with larger timescales requires near-field deformation measurements. In December 1992, two borehole strainmeters close to the San Andreas fault in California recorded a slow strain event of about a week in duration, and we show here that the strain changes were produced by a slow earthquake sequence (equivalent magnitude 4.8) with complexity similar to that of regular earthquakes. The largest earthquakes associated with these slow events were small (local magnitude 3.7) and contributed negligible strain release. The importance of slow earthquakes in the seismogenic process remains an open question, but these observations extend the observed timescale for slow events by two orders of magnitude.

  18. Vertical tectonic deformation associated with the San Andreas fault zone offshore of San Francisco, California

    USGS Publications Warehouse

    Ryan, H.F.; Parsons, T.; Sliter, R.W.

    2008-01-01

    A new fault map of the shelf offshore of San Francisco, California shows that faulting occurs as a distributed shear zone that involves many fault strands with the principal displacement taken up by the San Andreas fault and the eastern strand of the San Gregorio fault zone. Structures associated with the offshore faulting show compressive deformation near where the San Andreas fault goes offshore, but deformation becomes extensional several km to the north off of the Golden Gate. Our new fault map serves as the basis for a 3-D finite element model that shows that the block between the San Andreas and San Gregorio fault zone is subsiding at a long-term rate of about 0.2-0.3??mm/yr, with the maximum subsidence occurring northwest of the Golden Gate in the area of a mapped transtensional basin. Although the long-term rates of vertical displacement primarily show subsidence, the model of coseismic deformation associated with the 1906 San Francisco earthquake indicates that uplift on the order of 10-15??cm occurred in the block northeast of the San Andreas fault. Since 1906, 5-6??cm of regional subsidence has occurred in that block. One implication of our model is that the transfer of slip from the San Andreas fault to a fault 5??km to the east, the Golden Gate fault, is not required for the area offshore of San Francisco to be in extension. This has implications for both the deposition of thick Pliocene-Pleistocene sediments (the Merced Formation) observed east of the San Andreas fault, and the age of the Peninsula segment of the San Andreas fault.

  19. Vertical tectonic deformation associated with the San Andreas fault zone offshore of San Francisco, California

    NASA Astrophysics Data System (ADS)

    Ryan, H. F.; Parsons, T.; Sliter, R. W.

    2008-10-01

    A new fault map of the shelf offshore of San Francisco, California shows that faulting occurs as a distributed shear zone that involves many fault strands with the principal displacement taken up by the San Andreas fault and the eastern strand of the San Gregorio fault zone. Structures associated with the offshore faulting show compressive deformation near where the San Andreas fault goes offshore, but deformation becomes extensional several km to the north off of the Golden Gate. Our new fault map serves as the basis for a 3-D finite element model that shows that the block between the San Andreas and San Gregorio fault zone is subsiding at a long-term rate of about 0.2-0.3 mm/yr, with the maximum subsidence occurring northwest of the Golden Gate in the area of a mapped transtensional basin. Although the long-term rates of vertical displacement primarily show subsidence, the model of coseismic deformation associated with the 1906 San Francisco earthquake indicates that uplift on the order of 10-15 cm occurred in the block northeast of the San Andreas fault. Since 1906, 5-6 cm of regional subsidence has occurred in that block. One implication of our model is that the transfer of slip from the San Andreas fault to a fault 5 km to the east, the Golden Gate fault, is not required for the area offshore of San Francisco to be in extension. This has implications for both the deposition of thick Pliocene-Pleistocene sediments (the Merced Formation) observed east of the San Andreas fault, and the age of the Peninsula segment of the San Andreas fault.

  20. Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula

    USGS Publications Warehouse

    Zoback, M.L.; Jachens, R.C.; Olson, J.A.

    1999-01-01

    Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ???470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate "fault-normal" compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (???10??) through the southernmost peninsula. A zone of seismic quiescence ???15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a ML = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudo-gravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ???3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San

  1. Vibroseis Monitoring of San Andreas Fault in California

    SciTech Connect

    Korneev, Valeri; Nadeau, Robert

    2004-06-11

    A unique data set of seismograms for 720 source-receiver paths has been collected as part of a controlled source Vibroseis experiment San Andreas Fault (SAF) at Parkfield. In the experiment, seismic waves repeatedly illuminated the epicentral region of the expected M6 event at Parkfield from June 1987 until November 1996. For this effort, a large shear-wave vibrator was interfaced with the 3-component (3-C) borehole High-Resolution Seismic Network (HRSN), providing precisely timed collection of data for detailed studies of changes in wave propagation associated with stress and strain accumulation in the fault zone (FZ). Data collected by the borehole network were examined for evidence of changes associated with the nucleation process of the anticipated M6 earthquake at Parkfield. These investigations reported significant traveltime changes in the S coda for paths crossing the fault zone southeast of the epicenter and above the rupture zone of the 1966 M6 earthquake. Analysis and modeling of these data and comparison with observed changes in creep, water level, microseismicity, slip-at-depth and propagation from characteristic repeating microearthquakes showed temporal variations in a variety of wave propagation attributes that were synchronous with changes in deformation and local seismicity patterns. Numerical modeling suggests 200 meters as an effective thickness of SAF. The observed variations can be explained by velocity 6 percent velocity variation within SAF core. Numerical modeling studies and a growing number of observations have argued for the propagation of fault-zone guided waves (FZGW) within a SAF zone that is 100 to 200 m wide at seismogenic depths and with 20 to 40 percent lower shear-wave velocity than the adjacent unfaulted rock. Guided wave amplitude tomographic inversion for SAF using microearthquakes, shows clearly that FZGW are significantly less attenuated in a well-defined region of the FZ. This region plunges to the northwest along the

  2. San Andreas-sized Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This mosaic of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, about the size of the California portion of the San Andreas fault, which runs from the California-Mexico border north to the San Francisco Bay.

    In a strike-slip fault, two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. Overall motion along the fault seems to have followed a continuous narrow crack along the feature's entire length, with a path resembling steps on a staircase crossing zones that have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. The fault's opposite sides can be reconstructed like a puzzle, matching the shape of the sides and older, individual cracks and ridges broken by its movements.

    [figure removed for brevity, see original site]

    The red line marks the once active central crack of the fault. The black line outlines the fault zone, including material accumulated in the regions which have been pulled apart.

    Bends in the fault have allowed the surface to be pulled apart. This process created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling-apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, in Death Valley and the Dead Sea. In those cases, the pulled-apart regions can include upwelled materials, but may be filled mostly by sedimentary and eroded material from above.

    One theory is that fault motion on Europa is induced by the pull of variable daily tides generated by Jupiter's gravitational tug on Europa. Tidal tension

  3. San Andreas-sized Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This mosaic of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, about the size of the California portion of the San Andreas fault, which runs from the California-Mexico border north to the San Francisco Bay.

    In a strike-slip fault, two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. Overall motion along the fault seems to have followed a continuous narrow crack along the feature's entire length, with a path resembling steps on a staircase crossing zones that have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. The fault's opposite sides can be reconstructed like a puzzle, matching the shape of the sides and older, individual cracks and ridges broken by its movements.

    [figure removed for brevity, see original site]

    The red line marks the once active central crack of the fault. The black line outlines the fault zone, including material accumulated in the regions which have been pulled apart.

    Bends in the fault have allowed the surface to be pulled apart. This process created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling-apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, in Death Valley and the Dead Sea. In those cases, the pulled-apart regions can include upwelled materials, but may be filled mostly by sedimentary and eroded material from above.

    One theory is that fault motion on Europa is induced by the pull of variable daily tides generated by Jupiter's gravitational tug on Europa. Tidal tension

  4. Complexity of the deep San Andreas Fault zone defined by cascading tremor

    NASA Astrophysics Data System (ADS)

    Shelly, David R.

    2015-02-01

    Weak seismic vibrations--tectonic tremor--can be used to delineate some plate boundary faults. Tremor on the deep San Andreas Fault, located at the boundary between the Pacific and North American plates, is thought to be a passive indicator of slow fault slip. San Andreas Fault tremor migrates at up to 30 m s-1, but the processes regulating tremor migration are unclear. Here I use a 12-year catalogue of more than 850,000 low-frequency earthquakes to systematically analyse the high-speed migration of tremor along the San Andreas Fault. I find that tremor migrates most effectively through regions of greatest tremor production and does not propagate through regions with gaps in tremor production. I interpret the rapid tremor migration as a self-regulating cascade of seismic ruptures along the fault, which implies that tremor may be an active, rather than passive participant in the slip propagation. I also identify an isolated group of tremor sources that are offset eastwards beneath the San Andreas Fault, possibly indicative of the interface between the Monterey Microplate, a hypothesized remnant of the subducted Farallon Plate, and the North American Plate. These observations illustrate a possible link between the central San Andreas Fault and tremor-producing subduction zones.

  5. Viscoelastic coupling model of the San Andreas fault along the big bend, southern California

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.

    1997-01-01

    The big bend segment of the San Andreas fault is the 300-km-long segment in southern California that strikes about N65??W, roughly 25?? counterclockwise from the local tangent to the small circle about the Pacific-North America pole of rotation. The broad distribution of deformation of trilateration networks along this segment implies a locking depth of at least 25 km as interpreted by the conventional model of strain accumulation (continuous slip on the fault below the locking depth at the rate of relative plate motion), whereas the observed seismicity and laboratory data on fault strength suggest that the locking depth should be no greater than 10 to 15 km. The discrepancy is explained by the viscoelastic coupling model which accounts for the viscoelastic response of the lower crust. Thus the broad distribution of deformation observed across the big bend segment can be largely associated with the San Andreas fault itself, not subsidiary faults distributed throughout the region. The Working Group on California Earthquake Probabilities [1995] in using geodetic data to estimate the seismic risk in southern California has assumed that strain accumulated off the San Andreas fault is released by earthquakes located off the San Andreas fault. Thus they count the San Andreas contribution to total seismic moment accumulation more than once, leading to an overestimate of the seismicity for magnitude 6 and greater earthquakes in their Type C zones.

  6. Correction to “Constraints on the stress state of the San Andreas Fault with analysis based on core and cuttings from San Andreas Fault Observatory at Depth (SAFOD) drilling phases 1 and 2”

    USGS Publications Warehouse

    Tembe, Sheryl; Lockner, David; Wong, Teng-Fong

    2010-01-01

    This article corrects: Constraints on the stress state of the San Andreas Fault with analysis based on core and cuttings from San Andreas Fault Observatory at Depth (SAFOD) drilling phases 1 and 2. Vol. 114, Issue B11, Article first published online: 5 NOV 2009.

  7. Irregular Recurrence of Large Earthquakes along the San Andreas Fault: Evidence from Trees

    NASA Astrophysics Data System (ADS)

    Jacoby, Gordon C.; Sheppard, Paul R.; Sieh, Kerry E.

    1988-07-01

    Old trees growing along the San Andreas fault near Wrightwood, California, record in their annual ring-width patterns the effects of a major earthquake in the fall or winter of 1812 to 1813. Paleoseismic data and historical information indicate that this event was the ``San Juan Capistrano'' earthquake of 8 December 1812, with a magnitude of 7.5. The discovery that at least 12 kilometers of the Mojave segment of the San Andreas fault ruptured in 1812, only 44 years before the great January 1857 rupture, demonstrates that intervals between large earthquakes on this part of the fault are highly variable. This variability increases the uncertainty of forecasting destructive earthquakes on the basis of past behavior and accentuates the need for a more fundamental knowledge of San Andreas fault dynamics.

  8. A Case for Historic Joint Rupture of the San Andreas and San Jacinto Faults

    NASA Astrophysics Data System (ADS)

    Lozos, J.

    2015-12-01

    The ~M7.5 southern California earthquake of 8 December 1812 ruptured the San Andreas Fault from Cajon Pass to at least as far north as Pallet Creek (Biasi et al., 2002). The 1812 rupture has also been identified in trenches at Burro Flats to the south (Yule and Howland, 2001). However, the lack of a record of 1812 at Plunge Creek, between Cajon Pass and Burro Flats (McGill et al., 2002), complicates the interpretation of this event as a straightforward San Andreas rupture. Paleoseismic records of a large early 19th century rupture on the northern San Jacinto Fault (Onderdonk et al., 2013; Kendrick and Fumal, 2005) allow for alternate interpretations of the 1812 earthquake. I use dynamic rupture modeling on the San Andreas-San Jacinto junction to determine which rupture behaviors produce slip patterns consistent with observations of the 1812 event. My models implement realistic fault geometry, a realistic velocity structure, and stress orientations based on seismicity literature. Under these simple assumptions, joint rupture of the two faults is the most common behavior. My modeling rules out a San Andreas-only rupture that is consistent with the data from the 1812 earthquake, and also shows that single fault events are unable to match the average slip per event for either fault. The choice of nucleation point affects the details of rupture directivity and slip distribution, but not the first order result that multi-fault rupture is the preferred behavior. While it cannot be definitively said that joint San Andreas-San Jacinto rupture occurred in 1812, these results are consistent with paleoseismic and historic data. This has implications for the possibility of future multi-fault rupture within the San Andreas system, as well as for interpretation of other paleoseismic events in regions of complex fault interactions.

  9. Low strength of deep San Andreas fault gouge from SAFOD core

    USGS Publications Warehouse

    Lockner, David A.; Morrow, Carolyn A.; Moore, Diane E.; Hickman, Stephen H.

    2011-01-01

    The San Andreas fault accommodates 28–34 mm yr−1 of right lateral motion of the Pacific crustal plate northwestward past the North American plate. In California, the fault is composed of two distinct locked segments that have produced great earthquakes in historical times, separated by a 150-km-long creeping zone. The San Andreas Fault Observatory at Depth (SAFOD) is a scientific borehole located northwest of Parkfield, California, near the southern end of the creeping zone. Core was recovered from across the actively deforming San Andreas fault at a vertical depth of 2.7 km (ref. 1). Here we report laboratory strength measurements of these fault core materials at in situ conditions, demonstrating that at this locality and this depth the San Andreas fault is profoundly weak (coefficient of friction, 0.15) owing to the presence of the smectite clay mineral saponite, which is one of the weakest phyllosilicates known. This Mg-rich clay is the low-temperature product of metasomatic reactions between the quartzofeldspathic wall rocks and serpentinite blocks in the fault2, 3. These findings provide strong evidence that deformation of the mechanically unusual creeping portions of the San Andreas fault system is controlled by the presence of weak minerals rather than by high fluid pressure or other proposed mechanisms1. The combination of these measurements of fault core strength with borehole observations1, 4, 5 yields a self-consistent picture of the stress state of the San Andreas fault at the SAFOD site, in which the fault is intrinsically weak in an otherwise strong crust.

  10. Low strength of deep San Andreas fault gouge from SAFOD core

    USGS Publications Warehouse

    Lockner, D.A.; Morrow, C.; Moore, D.; Hickman, S.

    2011-01-01

    The San Andreas fault accommodates 28-"34-???mm-???yr ????'1 of right lateral motion of the Pacific crustal plate northwestward past the North American plate. In California, the fault is composed of two distinct locked segments that have produced great earthquakes in historical times, separated by a 150-km-long creeping zone. The San Andreas Fault Observatory at Depth (SAFOD) is a scientific borehole located northwest of Parkfield, California, near the southern end of the creeping zone. Core was recovered from across the actively deforming San Andreas fault at a vertical depth of 2.7-???km (ref. 1). Here we report laboratory strength measurements of these fault core materials at in situ conditions, demonstrating that at this locality and this depth the San Andreas fault is profoundly weak (coefficient of friction, 0.15) owing to the presence of the smectite clay mineral saponite, which is one of the weakest phyllosilicates known. This Mg-rich clay is the low-temperature product of metasomatic reactions between the quartzofeldspathic wall rocks and serpentinite blocks in the fault. These findings provide strong evidence that deformation of the mechanically unusual creeping portions of the San Andreas fault system is controlled by the presence of weak minerals rather than by high fluid pressure or other proposed mechanisms. The combination of these measurements of fault core strength with borehole observations yields a self-consistent picture of the stress state of the San Andreas fault at the SAFOD site, in which the fault is intrinsically weak in an otherwise strong crust. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  11. First epoch measurements by Mark III VLBI of the San Andreas Fault experiment baseline

    SciTech Connect

    Ryan, J.W.

    1985-08-01

    The 883-km-long San Andreas Fault Experiment (SAFE) baseline between Quincy in northern California and Monument Peak in southern California spans the San Andreas Fault in a way designed to measure motion between the North American and the Pacific Plates. This baseline and a closely related baseline have been measured with the satellite laser ranging techniques (SLR) for over 10 years. The baseline was measured with the very-long-baseline interferometry (VLBI) technique to confirm or reject the results already obtained from SLR.

  12. Paleoseismic displacement history, Coachella Valley segment, San Andreas fault

    NASA Astrophysics Data System (ADS)

    Williams, P. L.

    2009-12-01

    This paper examines individual earthquake displacements and slip curves for the southern segment of the San Andreas fault. In prior work, detailed geomorphic slip evidence (features offset up to ~20 meters right-laterally) were inventoried along the southern 50 km (Bombay Beach to Thermal) of the Coachella Valley Segment (CVS). Compilation of that survey, and current work indicate that the latest 5 events produced moderate offsets, averaging 3-4 meters from Durmid Hill (adjacent to the Salton Sea) through the central Indio Hills (adjacent to Palm Desert). Streams exhibiting cumulative offset of 15 to 18 meters are interpreted to record five events, with locally higher values obtained in the southern Mecca Hills and central Indio Hills. Stream displacements of 21 to 24 and 25 to 28 meters have been documented at a small number of sites. The presence of larger values, and absence of intervening values, indicates these events likely were characterized by offsets larger than 3-4 meters. Addressing the contribution to total offset from fault creep is especially important to characterize slip-per-event on the CVS, since creep contributes up to 20 to 30% of the long-term slip rate there (Sieh and Williams 1990). While creep probably can't be discriminated from seismic offset in geomorphic study of multi-event fault offsets, the consistency of field evidence indicates that creep may be a neutral or minor factor in interpreting the offset record: i.e., the surface slip in a given earthquake cycle, while a sum of seismic + postseismic surface slip, approximates total seismogenic slip at depth. In the present open interval, for example, the strongest signal for prior event slip is ~3.5m. 1-1.5m of this is presumed to be postseismic creep (ibid). Thus the latest seismic surface slip was probably about 2-2.5m, and the latest seismogenic rupture (at depth) was probably in the range of 3-3.5 m, and 1-1.5m of this occurred as postseismic slip plus creep at the surface. Prior event

  13. Slip characteristics of San Andreas Fault transition zone segments

    NASA Astrophysics Data System (ADS)

    Johanson, Ingrid Anne

    Transition zones are areas of mixed behavior that divide areas of velocity strengthening and velocity weakening frictional parameters. Their slip characteristics have implications for the underlying mechanism for interseismic creep, the relationship between aseismic slip and earthquakes, and the seismic potential of the transition zones. Two transition zones on the San Andreas fault in California, USA are included in this work; the San Juan Bautista and the Parkfield segments. They are analyzed in three phases of the earthquake cycle; the interseismic, coseismic and postseismic. The San Juan Bautista segment currently undergoes only moderate seismicity. However, six M≥6 earthquakes occurred near the SJB segment between 1840 and 1899. A joint inversion of Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) measurements was performed to determine its current rate and distribution of interseismic creep. The model resolves two low-slip asperities surrounded by creep, indicating that its behavior arises from the heterogeneous distribution of fault frictional properties. InSAR and GPS data were also used to constrain models of coseismic and post-seismic slip in the 2004 Parkfield earthquake. The models indicate that coseismic and postseismic slip occurred in separate regions of the fault, suggesting that the distribution of frictional parameters on the fault exerted some control over the size of the earthquake. The postseismic model included nearly equal amounts of slip as the coseismic, suggesting that this is an important method of relieving stress along areas of the fault that slip aseismically and that these areas may not participate in earthquakes. The sensitivity of the Parkfield segment to outside stresses was also explored. Static stress changes from the 2003 San Simeon earthquake encouraged right-lateral strike slip on the Parkfield segment. While there is no clear correlation between the distribution of slip in the 2004

  14. Chicks in Charge: Andrea Baker & Amy Daniels--Airport High School Media Center, Columbia, SC

    ERIC Educational Resources Information Center

    Library Journal, 2004

    2004-01-01

    This article briefly discusses two librarians exploration of Linux. Andrea Baker and Amy Daniels were tired of telling their students that new technology items were not in the budget. They explored Linux, which is a program that recycles older computers, installs free operating systems and free software.

  15. Andreas Vesalius on the anatomy and function of the lower thoracic vertebrae.

    PubMed

    Biesbrouck, Maurits; Vanden Berghe, Alex

    2016-04-01

    Some remarkable statements made by Andreas Vesalius (1514-1564) in his principal work De Humani Corporis Fabrica (1543) about the anatomy and function of the lower thoracic vertebrae are discussed in the light of information from the literature. Their accuracy is evaluated on the basis of several pieces of anatomical evidence and clinical cases.

  16. Neotectonics of the San Andreas Fault system, basin and range province juncture

    NASA Technical Reports Server (NTRS)

    Estes, J. E.; Crowell, J. C.

    1982-01-01

    The development, active processes, and tectonic interplay of the southern San Andreas fault system and the basin and range province were studied. The study consist of data acquisition and evaluation, technique development, and image interpretation and mapping. Potentially significant geologic findings are discussed.

  17. Chicks in Charge: Andrea Baker & Amy Daniels--Airport High School Media Center, Columbia, SC

    ERIC Educational Resources Information Center

    Library Journal, 2004

    2004-01-01

    This article briefly discusses two librarians exploration of Linux. Andrea Baker and Amy Daniels were tired of telling their students that new technology items were not in the budget. They explored Linux, which is a program that recycles older computers, installs free operating systems and free software.

  18. Andrea Dworkin's "Mercy": Pain, Ad Personam, and Silence in the "War Zone."

    ERIC Educational Resources Information Center

    Eberly, Rosa A.

    1993-01-01

    Studies the public responses to Andrea Dworkin's novel "Mercy" (about rape specifically and the sexual abuse of women in general). Suggests that Dworkin's "Mercy"--like other controversial cultural texts--fostered a type of literary public sphere and that defining these spheres as "war zones" does not foster open debate or a common space for…

  19. 1855 and 1991 Surveys of the San Andreas Fault: Implications for Fault Machanics

    NASA Technical Reports Server (NTRS)

    Grant, Lisa B.; Donnellan, Andrea

    1993-01-01

    Two monuments from an 1855 survey that spans the San Andreas fault in the Carrizo Plain have been displaced 11.0+/-2.5m right-laterally by the 1857 Fort Tejon earthquake and associated seismicity and afterslip by the 1857 Fort Tejon earthquake and associated seismicity and afterslip.

  20. Fine-scale delineation of the location of and relative ground shaking within the San Andreas Fault zone at San Andreas Lake, San Mateo County, California

    USGS Publications Warehouse

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Prentice, C.S.; Sickler, R.R.

    2013-01-01

    The San Francisco Public Utilities Commission is seismically retrofitting the water delivery system at San Andreas Lake, San Mateo County, California, where the reservoir intake system crosses the San Andreas Fault (SAF). The near-surface fault location and geometry are important considerations in the retrofit effort. Because the SAF trends through highly distorted Franciscan mélange and beneath much of the reservoir, the exact trace of the 1906 surface rupture is difficult to determine from surface mapping at San Andreas Lake. Based on surface mapping, it also is unclear if there are additional fault splays that extend northeast or southwest of the main surface rupture. To better understand the fault structure at San Andreas Lake, the U.S. Geological Survey acquired a series of seismic imaging profiles across the SAF at San Andreas Lake in 2008, 2009, and 2011, when the lake level was near historical lows and the surface traces of the SAF were exposed for the first time in decades. We used multiple seismic methods to locate the main 1906 rupture zone and fault splays within about 100 meters northeast of the main rupture zone. Our seismic observations are internally consistent, and our seismic indicators of faulting generally correlate with fault locations inferred from surface mapping. We also tested the accuracy of our seismic methods by comparing our seismically located faults with surface ruptures mapped by Schussler (1906) immediately after the April 18, 1906 San Francisco earthquake of approximate magnitude 7.9; our seismically determined fault locations were highly accurate. Near the reservoir intake facility at San Andreas Lake, our seismic data indicate the main 1906 surface rupture zone consists of at least three near-surface fault traces. Movement on multiple fault traces can have appreciable engineering significance because, unlike movement on a single strike-slip fault trace, differential movement on multiple fault traces may exert compressive and

  1. Variable selection in large margin classifier-based probability estimation with high-dimensional predictors.

    PubMed

    Shin, Seung Jun; Wu, Yichao

    2014-07-01

    This is a discussion of the papers: "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Theory" by Jochen Kruppa, Yufeng Liu, Gérard Biau, Michael Kohler, Inke R. König, James D. Malley, and Andreas Ziegler; and "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Applications" by Jochen Kruppa, Yufeng Liu, Hans-Christian Diener, Theresa Holste, Christian Weimar, Inke R. König, and Andreas Ziegler.

  2. Risk prediction with machine learning and regression methods.

    PubMed

    Steyerberg, Ewout W; van der Ploeg, Tjeerd; Van Calster, Ben

    2014-07-01

    This is a discussion of issues in risk prediction based on the following papers: "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Theory" by Jochen Kruppa, Yufeng Liu, Gérard Biau, Michael Kohler, Inke R. König, James D. Malley, and Andreas Ziegler; and "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Applications" by Jochen Kruppa, Yufeng Liu, Hans-Christian Diener, Theresa Holste, Christian Weimar, Inke R. König, and Andreas Ziegler.

  3. What subject matter questions motivate the use of machine learning approaches compared to statistical models for probability prediction?

    PubMed

    Binder, Harald

    2014-07-01

    This is a discussion of the following papers: "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Theory" by Jochen Kruppa, Yufeng Liu, Gérard Biau, Michael Kohler, Inke R. König, James D. Malley, and Andreas Ziegler; and "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Applications" by Jochen Kruppa, Yufeng Liu, Hans-Christian Diener, Theresa Holste, Christian Weimar, Inke R. König, and Andreas Ziegler.

  4. Perspective view, Landsat overlay San Andreas Fault, Palmdale, California

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The prominent linear feature straight down the center of this perspective view is the San Andreas Fault. This segment of the fault lies near the city of Palmdale, California (the flat area in the right half of the image) about 60 kilometers (37 miles) north of Los Angeles. The fault is the active tectonic boundary between the North American plate on the right, and the Pacific plate on the left. Relative to each other, the Pacific plate is moving away from the viewer and the North American plate is moving toward the viewer along what geologists call a right lateral strike-slip fault. Two large mountain ranges are visible, the San Gabriel Mountains on the left and the Tehachapi Mountains in the upper right. The Lake Palmdale Reservoir, approximately 1.5 kilometers (0.9 miles) across, sits in the topographic depression created by past movement along the fault. Highway 14 is the prominent linear feature starting at the lower left edge of the image and continuing along the far side of the reservoir. The patterns of residential and agricultural development around Palmdale are seen in the Landsat imagery in the right half of the image. SRTM topographic data will be used by geologists studying fault dynamics and landforms resulting from active tectonics.

    This type of display adds the important dimension of elevation to the study of land use and environmental processes as observed in satellite images. The perspective view was created by draping a Landsat satellite image over an SRTM elevation model. Topography is exaggerated 1.5 times vertically. The Landsat image was provided by the United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota.

    Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture

  5. Frictional strength and heat flow of southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Zhu, P. P.

    2016-01-01

    Frictional strength and heat flow of faults are two related subjects in geophysics and seismology. To date, the investigation on regional frictional strength and heat flow still stays at the stage of qualitative estimation. This paper is concentrated on the regional frictional strength and heat flow of the southern San Andreas Fault (SAF). Based on the in situ borehole measured stress data, using the method of 3D dynamic faulting analysis, we quantitatively determine the regional normal stress, shear stress, and friction coefficient at various seismogenic depths. These new data indicate that the southern SAF is a weak fault within the depth of 15 km. As depth increases, all the regional normal and shear stresses and friction coefficient increase. The former two increase faster than the latter. Regional shear stress increment per kilometer equals 5.75 ± 0.05 MPa/km for depth ≤15 km; regional normal stress increment per kilometer is equal to 25.3 ± 0.1 MPa/km for depth ≤15 km. As depth increases, regional friction coefficient increment per kilometer decreases rapidly from 0.08 to 0.01/km at depths less than ~3 km. As depth increases from ~3 to ~5 km, it is 0.01/km and then from ~5 to 15 km, and it is 0.002/km. Previously, frictional strength could be qualitatively determined by heat flow measurements. It is difficult to obtain the quantitative heat flow data for the SAF because the measured heat flow data exhibit large scatter. However, our quantitative results of frictional strength can be employed to investigate the heat flow in the southern SAF. We use a physical quantity P f to describe heat flow. It represents the dissipative friction heat power per unit area generated by the relative motion of two tectonic plates accommodated by off-fault deformation. P f is called "fault friction heat." On the basis of our determined frictional strength data, utilizing the method of 3D dynamic faulting analysis, we quantitatively determine the regional long-term fault

  6. Perspective view, Landsat overlay San Andreas Fault, Palmdale, California

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The prominent linear feature straight down the center of this perspective view is the San Andreas Fault. This segment of the fault lies near the city of Palmdale, California (the flat area in the right half of the image) about 60 kilometers (37 miles) north of Los Angeles. The fault is the active tectonic boundary between the North American plate on the right, and the Pacific plate on the left. Relative to each other, the Pacific plate is moving away from the viewer and the North American plate is moving toward the viewer along what geologists call a right lateral strike-slip fault. Two large mountain ranges are visible, the San Gabriel Mountains on the left and the Tehachapi Mountains in the upper right. The Lake Palmdale Reservoir, approximately 1.5 kilometers (0.9 miles) across, sits in the topographic depression created by past movement along the fault. Highway 14 is the prominent linear feature starting at the lower left edge of the image and continuing along the far side of the reservoir. The patterns of residential and agricultural development around Palmdale are seen in the Landsat imagery in the right half of the image. SRTM topographic data will be used by geologists studying fault dynamics and landforms resulting from active tectonics.

    This type of display adds the important dimension of elevation to the study of land use and environmental processes as observed in satellite images. The perspective view was created by draping a Landsat satellite image over an SRTM elevation model. Topography is exaggerated 1.5 times vertically. The Landsat image was provided by the United States Geological Survey's Earth Resources Observations Systems (EROS) Data Center, Sioux Falls, South Dakota.

    Elevation data used in this image was acquired by the Shuttle Radar Topography Mission (SRTM) aboard the Space Shuttle Endeavour, launched on February 11,2000. SRTM used the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture

  7. Talc-bearing serpentinite and the creeping section of the San Andreas fault

    USGS Publications Warehouse

    Moore, Diane E.; Rymer, M.J.

    2007-01-01

    The section of the San Andreas fault located between Cholame Valley and San Juan Bautista in central California creeps at a rate as high as 28 mm yr -1 (ref. 1), and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust. Serpentinized ultramafic rocks have been associated with creeping faults in central and northern California, and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the San Andreas fault. However, the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength, and these minerals also have the potential for unstable slip under some conditions. Here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the San Andreas fault that was intersected during drilling of the San Andreas Fault Observatory at Depth (SAFOD) main hole in 2005. We infer that the talc is forming as a result of the reaction of serpentine minerals with silica-saturated hydrothermal fluids that migrate up the fault zone, and the talc commonly occurs in sheared serpentinite. This discovery is significant, as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault, and its inherently stable sliding behaviour is consistent with fault creep. Talc may therefore provide the connection between serpentinite and creep in the San Andreas fault, if shear at depth can become localized along a talc-rich principal-slip surface within serpentinite entrained in the fault zone. ??2007 Nature Publishing Group.

  8. Subsurface geometry of the San Andreas-Calaveras fault junction: influence of the Coast Range Ophiolite

    NASA Astrophysics Data System (ADS)

    Watt, J. T.; Ponce, D. A.; Graymer, R. W.; Jachens, R. C.; Simpson, R. W.

    2013-12-01

    Potential-field modeling, surface geologic mapping, and relocated seismicity are used to investigate the three-dimensional structure of the San Andreas-Calaveras fault junction to gain insight into regional tectonics, fault kinematics, and seismic hazard. South of the San Francisco Bay area, the San Andreas and Hayward-Calaveras fault zones join to become a single San Andreas Fault. The fault junction, as defined in this study, represents a three-dimensional volume of crust extending from San Juan Bautista in the north to Bitterwater Valley in the south, bounded by the San Andreas Fault on the southwest and the Calaveras fault zone on the northeast. South of Hollister, the Calaveras fault zone includes the Paicines, San Benito, and Pine Rock faults. Within the junction, the San Andreas and Calaveras faults are both creeping at the surface, and strike parallel to each other for about 50 km, separated by only 2 to 6 km, but never actually merge at the surface. Geophysical evidence suggests that the San Andreas and Calaveras faults dip away from each other within the northern portion of the fault junction, bounding a triangular wedge of crust. This wedge changes shape to the south as the dips of both the San Andreas and Calaveras faults vary along strike. The main trace of the San Andreas Fault is clearly visible in cross-sections of relocated seismicity as a vertical to steeply southwest-dipping structure between 5 and 10 km depth throughout the junction. The Calaveras fault dips steeply to the northeast in the northern part of the junction. Near the intersection with the Vallecitos syncline, the dip of the Calaveras fault, as identified in relocated seismicity, shallows to 60 degrees. Northeast of the Calaveras fault, we identify a laterally extensive magnetic body 1 to 8 km below the surface that we interpret as a folded 1 to 3 km-thick tabular body of Coast Range Ophiolite at the base of the Vallecitos syncline. Potential-field modeling and relocated seismicity

  9. Earthquake geology and paleoseismology of major strands of the San Andreas fault system: Chapter 38

    USGS Publications Warehouse

    Rockwell, Thomas; Scharer, Katherine M.; Dawson, Timothy E.

    2016-01-01

    The San Andreas fault system in California is one of the best-studied faults in the world, both in terms of the long-term geologic history and paleoseismic study of past surface ruptures. In this paper, we focus on the Quaternary to historic data that have been collected from the major strands of the San Andreas fault system, both on the San Andreas Fault itself, and the major subparallel strands that comprise the plate boundary, including the Calaveras-Hayward- Rogers Creek-Maacama fault zone and the Concord-Green Valley-Bartlett Springs fault zone in northern California, and the San Jacinto and Elsinore faults in southern California. The majority of the relative motion between the Pacific and North American lithospheric plates is accommodated by these faults, with the San Andreas slipping at about 34 mm/yr in central California, decreasing to about 20 mm/yr in northern California north of its juncture with the Calaveras and Concord faults. The Calaveras-Hayward-Rogers Creek-Maacama fault zone exhibits a slip rate of 10-15 mm/yr, whereas the rate along the Concord-Green Valley-Bartlett Springs fault zone is lower at about 5 mm/yr. In southern California, the San Andreas exhibits a slip rate of about 35 mm/yr along the Mojave section, decreasing to as low as 10-15 mm/yr along its juncture with the San Jacinto fault, and about 20 mm/yr in the Coachella Valley. The San Jacinto and Elsinore fault zones exhibit rates of about 15 and 5 mm/yr, respectively. The average recurrence interval for surface-rupturing earthquakes along individual elements of the San Andreas fault system range from 100-500 years and is consistent with slip rate at those sites: higher slip rates produce more frequent or larger earthquakes. There is also evidence of short-term variations in strain release (slip rate) along various fault sections, as expressed as “flurries” or clusters of earthquakes as well as periods of relatively fewer surface ruptures in these relatively short records. This

  10. Seismic tomography and deformation modeling of the junction of the San Andreas and Calaveras faults

    USGS Publications Warehouse

    Dorbath, C.; Oppenheimer, D.; Amelung, F.; King, G.

    1996-01-01

    Local earthquake P traveltime data is inverted to obtain a three-dimensional tomographic image of the region centered on the junction of the San Andreas and Calaveras faults. The resulting velocity model is then used to relocate more than 17,000 earthquakes and to produce a model of fault structure in the region. These faults serve as the basis for modeling the topography using elastic dislocation methods. The region is of interest because active faults join, it marks the transition zone from creeping to locked fault behavior on the San Andreas fault, it exhibits young topography, and it has a good spatial distribution of seismicity. The tomographic data set is extensive, consisting of 1445 events, 96 stations, and nearly 95,000 travel time readings. Tomographic images are resolvable to depths of 12 km and show significant velocity contrasts across the San Andreas and Calaveras faults, a low-velocity zone associated with the creeping section of the San Andreas fault, and shallow low-velocity sediments in the southern Santa Clara valley and northern Salinas valley. Relocated earthquakes only occur where vp>5 km/s and indicate that portions of the San Andreas and Calaveras faults are non vertical, although we cannot completely exclude the possibility that all or part of this results from ray tracing problems. The new dips are more consistent with geological observations that dipping faults intersect the surface where surface traces have been mapped. The topographic modeling predicts extensive subsidence in regions characterized by shallow low-velocity material, presumably the result of recent sedimentation. Some details of the topography at the junction of the San Andreas and Calaveras faults are not consistent with the modeling results, suggesting that the current position of this "triple junction" has changed with time. The model also predicts those parts of the fault subject to contraction or extension perpendicular to the fault strike and hence the sense of any

  11. Shallow structure and deformation along the San Andreas Fault in Cholame Valley, California, based on high-resolution reflection profiling

    USGS Publications Warehouse

    Shedlock, K.M.; Brocher, T.M.; Harding, S.T.

    1990-01-01

    The mapped active traces of the San Andreas fault are separated by a 1-km-wide right-stepping offset in Cholame Valley. The geometry of this offset, defined in other strike-slip systems as a releasing bend or a dilational jog, has resulted in the formation of a pull-apart basin. Various researchers have inferred that this offset served as a rupture terminus for earthquakes on both strands of the San Andreas fault (1966 Parkfield and 1857 Fort Tejon); thus, this en echelon offset may represent a barrier to the propagation of rupture between two segments of the San Andreas fault. We collected 18 km of high-resolution seismic reflection data specifically designed to image the San Andreas fault zone in the shallow crust surrounding this offset. -from Authors

  12. Tectonic history of the north portion of the San Andreas fault system, California, inferred from gravity and magnetic anomalies

    USGS Publications Warehouse

    Griscom, A.; Jachens, R.C.

    1989-01-01

    Geologic and geophysical data for the San Andreas fault system north of San Francisco suggest that the eastern boundary of the Pacific plate migrated eastward from its presumed original position at the base of the continental slope to its present position along the San Andreas transform fault by means of a series of eastward jumps of the Mendocino triple junction. These eastward jumps total a distance of about 150 km since 29 Ma. Correlation of right-laterally displaced gravity and magnetic anomalies that now have components at San Francisco and on the shelf north of Point Arena indicates that the presently active strand of the San Andreas fault north of the San Francisco peninsula formed recently at about 5 Ma when the triple junction jumped eastward a minimum of 100 km to its present location at the north end of the San Andreas fault. -from Authors

  13. Loading of the San Andreas fault by flood-induced rupture of faults beneath the Salton Sea

    USGS Publications Warehouse

    Brothers, Daniel; Kilb, Debi; Luttrell, Karen; Driscoll, Neal W.; Kent, Graham

    2011-01-01

    The southern San Andreas fault has not experienced a large earthquake for approximately 300 years, yet the previous five earthquakes occurred at ~180-year intervals. Large strike-slip faults are often segmented by lateral stepover zones. Movement on smaller faults within a stepover zone could perturb the main fault segments and potentially trigger a large earthquake. The southern San Andreas fault terminates in an extensional stepover zone beneath the Salton Sea—a lake that has experienced periodic flooding and desiccation since the late Holocene. Here we reconstruct the magnitude and timing of fault activity beneath the Salton Sea over several earthquake cycles. We observe coincident timing between flooding events, stepover fault displacement and ruptures on the San Andreas fault. Using Coulomb stress models, we show that the combined effect of lake loading, stepover fault movement and increased pore pressure could increase stress on the southern San Andreas fault to levels sufficient to induce failure. We conclude that rupture of the stepover faults, caused by periodic flooding of the palaeo-Salton Sea and by tectonic forcing, had the potential to trigger earthquake rupture on the southern San Andreas fault. Extensional stepover zones are highly susceptible to rapid stress loading and thus the Salton Sea may be a nucleation point for large ruptures on the southern San Andreas fault.

  14. Strain on the San Andreas fault near Palmdale, California: Rapid, aseismic change

    USGS Publications Warehouse

    Savage, J.C.; Prescott, W.H.; Lisowski, M.; King, N.E.

    1981-01-01

    Frequently repeated strain measurements near Palmdale, California, during the period from 1971 through 1980 indicate that, in addition to a uniform accumulation of right-lateral shear strain (engineering shear, 0.35 microradian per year) across the San Andreas fault, a 1-microstrain contraction perpendicular to the fault that accumulated gradually during the interval 1974 through 1978 was aseismically released between February and November 1979. Subsequently (November 1979 to March 1980), about half of the contraction was recovered. This sequence of strain changes can be explained in terms of south-southwestward migration of a slip event consisting of the south-southwestward movement of the upper crust on a horizontal detachment surface at a depth of 10 to 30 kilometers. The large strain change in 1979 corresponds to the passage of the slip event beneath the San Andreas fault. Copyright ?? 1980 AAAS.

  15. Probabilistic fault displacement hazards for the southern san andreas fault using scenarios and empirical slips

    USGS Publications Warehouse

    Chen, R.; Petersen, M.D.

    2011-01-01

    We apply a probabilistic method to develop fault displacement hazard maps and profiles for the southern San Andreas Fault. Two slip models are applied: (1) scenario slip, defined by the ShakeOut rupture model, and (2) empirical slip, calculated using regression equations relating global slip to earthquake magnitude and distance along the fault. The hazard is assessed using a range of magnitudes defined by the Uniform California Earthquake Rupture Forecast and the ShakeOut. For hazard mapping we develop a methodology to partition displacement among multiple fault branches basedon geological observations. Estimated displacement hazard extends a few kilometers wide in areas of multiple mapped fault branches and poor mapping accuracy. Scenario and empirical displacement hazard differs by a factor of two or three, particularly along the southernmost section of the San Andreas Fault. We recommend the empirical slip model with site-specific geological data to constrain uncertainties for engineering applications. ?? 2011, Earthquake Engineering Research Institute.

  16. ["... here I am entirely among patients now..": the psychoanalytical practice of Lou Andreas-Salomé].

    PubMed

    Klemann, Manfred

    2005-01-01

    The aim of this article is to disprove the widespread prejudice depicting Andreas-Salomé merely as a femme fatale, or companion of a few famous contemporaries (Nietzsche, Rilke, and Freud), while suppressing her original intellectual and clinical-practical achievement as a psychoanalyst. An evaluation of both published and hitherto unpublished sources clearly confirms the broad and thorough foundations of her psychoanalytical training in theory as well as in practice. Between 1913 and 1933 Andreas-Salomé conducted a relatively large number of analyses, discussed some of them with Freud in a kind of "supervision" by correspondence and published several articles on central psychoanalytical issues. So far, however, many psychoanalysts seem to have been unaware of her status as a former accomplished colleague.

  17. Predictive Upper Cretaceous to Early Miocene Paleogeography of the San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Burnham, K.

    2006-12-01

    Paleogeographic reconstruction of the region of the San Andreas fault was hampered for more than twenty years by the apparent incompatibility of authoritative lithologic correlations. These led to disparate estimates of dextral strike-slip offsets, notably 315 km between Pinnacles and Neenach Volcanics (Matthews, 1976), versus 563 km between Anchor Bay and Eagle Rest Peak (Ross et al., 1973). In addition, estimates of total dextral slip on the San Gregorio fault have ranged from 5 km to 185 km. Sixteen upper Cretaceous and Paleogene conglomerates of the California Coast Ranges, from Anchor Bay to Simi Valley, have been included in a multidisciplinary study. Detailed analysis, including microscopic petrography and microprobe geochemistry, verified Seiders and Cox's (1992) and Wentworth's (1996) correlation of the upper Cretaceous Strata of Anchor Bay with an unnamed conglomerate east of Half Moon Bay. Similar detailed study, with the addition of SHRIMP U/Pb zircon dating, verified that the Paleocene or Eocene Point Reyes Conglomerate at Point Reyes is a tectonically displaced segment of the Carmelo Formation of Point Lobos. These studies centered on identification of matching unique clast varieties, rather than on simply counting general clast types, and included analyses of matrices, fossils, paleocurrents, diagenesis, adjacent rocks, and stratigraphy. The work also led to three new correlations: the Point Reyes Conglomerate with granitic source rock at Point Lobos; a magnetic anomaly at Black Point with a magnetic anomaly near San Gregorio; and the Strata of Anchor Bay with previously established source rock, the potassium-poor Logan Gabbro (Ross et al., 1973) at a more recently recognized location (Brabb and Hanna, 1981; McLaughlin et al., 1996) just east of the San Gregorio fault, south of San Gregorio. From these correlations, an upper Cretaceous early Oligocene paleogeography of the San Andreas fault system was constructed that honors both the Anchor Bay

  18. Slip in the 1857 and Earlier Large Earthquakes Along the Carrizo Plain, San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Zielke, Olaf; Arrowsmith, J. Ramón; Ludwig, Lisa Grant; Akçiz, Sinan O.

    2010-02-01

    The moment magnitude (Mw) 7.9 Fort Tejon earthquake of 1857, with a ~350-kilometer-long surface rupture, was the most recent major earthquake along the south-central San Andreas Fault, California. Based on previous measurements of its surface slip distribution, rupture along the ~60-kilometer-long Carrizo segment was thought to control the recurrence of 1857-like earthquakes. New high-resolution topographic data show that the average slip along the Carrizo segment during the 1857 event was 5.3 ± 1.4 meters, eliminating the core assumption for a linkage between Carrizo segment rupture and recurrence of major earthquakes along the south-central San Andreas Fault. Earthquake slip along the Carrizo segment may recur in earthquake clusters with cumulative slip of ~5 meters.

  19. Slip in the 1857 and earlier large earthquakes along the Carrizo Plain, San Andreas Fault.

    PubMed

    Zielke, Olaf; Arrowsmith, J Ramón; Grant Ludwig, Lisa; Akçiz, Sinan O

    2010-02-26

    The moment magnitude (Mw) 7.9 Fort Tejon earthquake of 1857, with a approximately 350-kilometer-long surface rupture, was the most recent major earthquake along the south-central San Andreas Fault, California. Based on previous measurements of its surface slip distribution, rupture along the approximately 60-kilometer-long Carrizo segment was thought to control the recurrence of 1857-like earthquakes. New high-resolution topographic data show that the average slip along the Carrizo segment during the 1857 event was 5.3 +/- 1.4 meters, eliminating the core assumption for a linkage between Carrizo segment rupture and recurrence of major earthquakes along the south-central San Andreas Fault. Earthquake slip along the Carrizo segment may recur in earthquake clusters with cumulative slip of approximately 5 meters.

  20. Paleomagnetic reorientation of San Andreas Fault Observatory at Depth (SAFOD) core

    USGS Publications Warehouse

    Pares, J.M.; Schleicher, A.M.; van der Pluijm, B.A.; Hickman, S.

    2008-01-01

    We present a protocol for using paleomagnetic analysis to determine the absolute orientation of core recovered from the SAFOD borehole. Our approach is based on determining the direction of the primary remanent magnetization of a spot core recovered from the Great Valley Sequence during SAFOD Phase 2 and comparing its direction to the expected reference field direction for the Late Cretaceous in North America. Both thermal and alternating field demagnetization provide equally resolved magnetization, possibly residing in magnetite, that allow reorientation. Because compositionally similar siltstones and fine-grained sandstones were encountered in the San Andreas Fault Zone during Stage 2 rotary drilling, we expect that paleomagnetic reorientation will yield reliable core orientations for continuous core acquired from directly within and adjacent to the San Andreas Fault during SAFOD Phase 3, which will be key to interpretation of spatial properties of these rocks. Copyright 2008 by the American Geophysical Union.

  1. The wister mud pot lineament: Southeastward extension or abandoned strand of the San Andreas fault?

    USGS Publications Warehouse

    Lynch, D.K.; Hudnut, K.W.

    2008-01-01

    We present the results of a survey of mud pots in the Wister Unit of the Imperial Wildlife Area. Thirty-three mud pots, pot clusters, or related geothermal vents (hundreds of pots in all) were identified, and most were found to cluster along a northwest-trending line that is more or less coincident with the postulated Sand Hills fault. An extrapolation of the trace of the San Andreas fault southeastward from its accepted terminus north of Bombay Beach very nearly coincides with the mud pot lineament and may represent a surface manifestation of the San Andreas fault southeast of the Salton Sea. Additionally, a recent survey of vents near Mullet Island in the Salton Sea revealed eight areas along a northwest-striking line where gas was bubbling up through the water and in two cases hot mud and water were being violently ejected.

  2. Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

    USGS Publications Warehouse

    Saffer, D.M.; Bekins, B.A.; Hickman, S.

    2003-01-01

    Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

  3. Scientific drilling into the San Andreas Fault Zone - an overview of SAFOD's first five years

    USGS Publications Warehouse

    Zoback, Mark; Hickman, Stephen; Ellsworth, William; ,

    2011-01-01

    The San Andreas Fault Observatory at Depth (SAFOD) was drilled to study the physical and chemical processes controlling faulting and earthquake generation along an active, plate-bounding fault at depth. SAFOD is located near Parkfield, California and penetrates a section of the fault that is moving due to a combination of repeating microearthquakes and fault creep. Geophysical logs define the San Andreas Fault Zone to be relatively broad (~200 m), containing several discrete zones only 2–3 m wide that exhibit very low P- and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented casing at measured depths of 3192 m and 3302 m. Cores from both deforming zones contain a pervasively sheared, cohesionless, foliated fault gouge that coincides with casing deformation and explains the observed extremely low seismic velocities and resistivity. These cores are being now extensively tested in laboratories around the world, and their composition, deformation mechanisms, physical properties, and rheological behavior are studied. Downhole measurements show that within 200 m (maximum) of the active fault trace, the direction of maximum horizontal stress remains at a high angle to the San Andreas Fault, consistent with other measurements. The results from the SAFOD Main Hole, together with the stress state determined in the Pilot Hole, are consistent with a strong crust/weak fault model of the San Andreas. Seismic instrumentation has been deployed to study physics of faulting—earthquake nucleation, propagation, and arrest—in order to test how laboratory-derived concepts scale up to earthquakes occurring in nature.

  4. Elevated time-dependent strengthening rates observed in San Andreas Fault drilling samples

    NASA Astrophysics Data System (ADS)

    Ikari, Matt J.; Carpenter, Brett M.; Vogt, Christoph; Kopf, Achim J.

    2016-09-01

    The central San Andreas Fault in California is known as a creeping fault, however recent studies have shown that it may be accumulating a slip deficit and thus its seismogenic potential should be seriously considered. We conducted laboratory friction experiments measuring time-dependent frictional strengthening (healing) on fault zone and wall rock samples recovered during drilling at the San Andreas Fault Observatory at Depth (SAFOD), located near the southern edge of the creeping section and in the direct vicinity of three repeating microearthquake clusters. We find that for hold times of up to 3000 s, frictional healing follows a log-linear dependence on hold time and that the healing rate is very low for a sample of the actively shearing fault core, consistent with previous results. However, considering longer hold times up to ∼350,000 s, the healing rate accelerates such that the data for all samples are better described by a power law relation. In general, samples having a higher content of phyllosilicate minerals exhibit low log-linear healing rates, and the notably clay-rich fault zone sample also exhibits strong power-law healing when longer hold times are included. Our data suggest that weak faults, such as the creeping section of the San Andreas Fault, can accumulate interseismic shear stress more rapidly than expected from previous friction data. Using the power-law dependence of frictional healing on hold time, calculations of recurrence interval and stress drop based on our data accurately match observations of discrete creep events and repeating Mw = 2 earthquakes on the San Andreas Fault.

  5. Correlation of data on strain accumulation adjacent to the San Andreas Fault with available models

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1986-01-01

    Theoretical and numerical studies of deformation on strike slip faults were performed and the results applied to geodetic observations performed in the vicinity of the San Andreas Fault in California. The initial efforts were devoted to an extensive series of finite element calculations of the deformation associated with cyclic displacements on a strike-slip fault. Measurements of strain accumulation adjacent to the San Andreas Fault indicate that the zone of strain accumulation extends only a few tens of kilometers away from the fault. There is a concern about the tendency to make geodetic observations along the line to the source. This technique has serious problems for strike slip faults since the vector velocity is also along the fault. Use of a series of stations lying perpendicular to the fault whose positions are measured relative to a reference station are suggested to correct the problem. The complexity of faulting adjacent to the San Andreas Fault indicated that the homogeneous elastic and viscoelastic approach to deformation had serious limitations. These limitation led to the proposal of an approach that assumes a fault is composed of a distribution of asperities and barriers on all scales. Thus, an earthquake on a fault is treated as a failure of a fractal tree. Work continued on the development of a fractal based model for deformation in the western United States. In order to better understand the distribution of seismicity on the San Andreas Fault system a fractal analog was developed. The fractal concept also provides a means of testing whether clustering in time or space is a scale-invariant process.

  6. Migrating tremors illuminate complex deformation beneath the seismogenic San Andreas fault

    USGS Publications Warehouse

    Shelly, D.R.

    2010-01-01

    The San Andreas fault is one of the most extensively studied faults in the world, yet its physical character and deformation mode beneath the relatively shallow earthquake-generating portion remain largely unconstrained. Tectonic non-volcanic tremor, a recently discovered seismic signal probably generated by shear slip on the deep extension of some major faults, can provide new insight into the deep fate of such faults, including that of the San Andreas fault near Parkfield, California. Here I examine continuous seismic data from mid-2001 to 2008, identifying tremor and decomposing the signal into different families of activity based on the shape and timing of the waveforms at multiple stations. This approach allows differentiation between activities from nearby patches of the deep fault and begins to unveil rich and complex patterns of tremor occurrence. I find that tremor exhibits nearly continuous migration, with the most extensive episodes propagating more than 20 kilometres along fault strike at rates of 15-80 kilometres per hour. This suggests that the San Andreas fault remains a localized through-going structure, at least to the base of the crust, in this area. Tremor rates and recurrence behaviour changed markedly in the wake of the 2004 magnitude-6.0 Parkfield earthquake, but these changes were far from uniform within the tremor zone, probably reflecting heterogeneous fault properties and static and dynamic stresses decaying away from the rupture. The systematic recurrence of tremor demonstrated here suggests the potential to monitor detailed time-varying deformation on this portion of the deep San Andreas fault, deformation which unsteadily loads the shallower zone that last ruptured in the 1857 magnitude-7.9 Fort Tejon earthquake. ?? 2010 Macmillan Publishers Limited. All rights reserved.

  7. Migrating tremors illuminate complex deformation beneath the seismogenic San Andreas fault.

    PubMed

    Shelly, David R

    2010-02-04

    The San Andreas fault is one of the most extensively studied faults in the world, yet its physical character and deformation mode beneath the relatively shallow earthquake-generating portion remain largely unconstrained. Tectonic 'non-volcanic' tremor, a recently discovered seismic signal probably generated by shear slip on the deep extension of some major faults, can provide new insight into the deep fate of such faults, including that of the San Andreas fault near Parkfield, California. Here I examine continuous seismic data from mid-2001 to 2008, identifying tremor and decomposing the signal into different families of activity based on the shape and timing of the waveforms at multiple stations. This approach allows differentiation between activities from nearby patches of the deep fault and begins to unveil rich and complex patterns of tremor occurrence. I find that tremor exhibits nearly continuous migration, with the most extensive episodes propagating more than 20 kilometres along fault strike at rates of 15-80 kilometres per hour. This suggests that the San Andreas fault remains a localized through-going structure, at least to the base of the crust, in this area. Tremor rates and recurrence behaviour changed markedly in the wake of the 2004 magnitude-6.0 Parkfield earthquake, but these changes were far from uniform within the tremor zone, probably reflecting heterogeneous fault properties and static and dynamic stresses decaying away from the rupture. The systematic recurrence of tremor demonstrated here suggests the potential to monitor detailed time-varying deformation on this portion of the deep San Andreas fault, deformation which unsteadily loads the shallower zone that last ruptured in the 1857 magnitude-7.9 Fort Tejon earthquake.

  8. A case for historic joint rupture of the San Andreas and San Jacinto faults

    PubMed Central

    Lozos, Julian C.

    2016-01-01

    The San Andreas fault is considered to be the primary plate boundary fault in southern California and the most likely fault to produce a major earthquake. I use dynamic rupture modeling to show that the San Jacinto fault is capable of rupturing along with the San Andreas in a single earthquake, and interpret these results along with existing paleoseismic data and historic damage reports to suggest that this has likely occurred in the historic past. In particular, I find that paleoseismic data and historic observations for the ~M7.5 earthquake of 8 December 1812 are best explained by a rupture that begins on the San Jacinto fault and propagates onto the San Andreas fault. This precedent carries the implications that similar joint ruptures are possible in the future and that the San Jacinto fault plays a more significant role in seismic hazard in southern California than previously considered. My work also shows how physics-based modeling can be used for interpreting paleoseismic data sets and understanding prehistoric fault behavior. PMID:27034977

  9. The Eastern California Shear Zone as the northward extension of the southern San Andreas Fault

    USGS Publications Warehouse

    Thatcher, Wayne R.; Savage, James C.; Simpson, Robert W.

    2016-01-01

    Cluster analysis offers an agnostic way to organize and explore features of the current GPS velocity field without reference to geologic information or physical models using information only contained in the velocity field itself. We have used cluster analysis of the Southern California Global Positioning System (GPS) velocity field to determine the partitioning of Pacific-North America relative motion onto major regional faults. Our results indicate the large-scale kinematics of the region is best described with two boundaries of high velocity gradient, one centered on the Coachella section of the San Andreas Fault and the Eastern California Shear Zone and the other defined by the San Jacinto Fault south of Cajon Pass and the San Andreas Fault farther north. The ~120 km long strand of the San Andreas between Cajon Pass and Coachella Valley (often termed the San Bernardino and San Gorgonio sections) is thus currently of secondary importance and carries lesser amounts of slip over most or all of its length. We show these first order results are present in maps of the smoothed GPS velocity field itself. They are also generally consistent with currently available, loosely bounded geologic and geodetic fault slip rate estimates that alone do not provide useful constraints on the large-scale partitioning we show here. Our analysis does not preclude the existence of smaller blocks and more block boundaries in Southern California. However, attempts to identify smaller blocks along and adjacent to the San Gorgonio section were not successful.

  10. Shared life narratives in the work of Lou Andreas-Salomé.

    PubMed

    Bos, J

    2000-06-01

    The author presents a re-reading of the works of Lou Andreas-Salomé (1861-1937), one of the key figures in the early history of psychoanalysis. He focusses in particular on her biographical and autobiographical works, as well as her correspondences with Freud, Rilke and other influential people of her time, arguing that Andreas-Salomé disappears from her own works as an autonomous speaking subject, while reappearing in the works of others as a silent, tacit influence. On closer examination, a specific genre emerges from her works that has so far gone unnoticed: the shared life narrative. The author claims that Andreas-Salomé developed this genre of shared life narratives in an attempt to match her theoretical notions of narcissism to a practical communicative position that is neither subjectivistic nor objectivistic. Relating the notion of shared life narratives to the psychoanalytic discourse, new possibilities may be opened up for expanding and enlarging our knowledge of human interaction.

  11. Structure of the San Andreas fault zone at SAFOD from a seismic refraction survey

    USGS Publications Warehouse

    Hole, J.A.; Ryberg, T.; Fuis, G.S.; Bleibinhaus, F.; Sharma, A.K.

    2006-01-01

    Refraction traveltimes from a 46-km long seismic survey across the San Andreas Fault were inverted to obtain two-dimensional velocity structure of the upper crust near the SAFOD drilling project. The model contains strong vertical and lateral velocity variations from <2 km/s to ???6 km/s. The Salinian terrane west of the San Andreas Fault has much higher velocity than the Franciscan terrane east of the fault. Salinian basement deepens from 0.8 km subsurface at SAFOD to ???2.5 km subsurface 20 km to the southwest. A strong reflection and subtle velocity contrast suggest a steeply dipping fault separating the Franciscan terrane from the Great Valley Sequence. A low-velocity wedge of Cenozoic sedimentary rocks lies immediately southwest of the San Andreas Fault. This body is bounded by a steep fault just northeast of SAFOD and approaches the depth of the shallowest earthquakes. Multiple active and inactive fault strands complicate structure near SAFOD. Copyright 2006 by the American Geophysical Union.

  12. Base and precious metal occurrences along the San Andreas Fault, Point Delgada, California

    USGS Publications Warehouse

    McLaughlin, Robert J.; Sorg, D.H.; Ohlin, H.N.; Heropoulos, Chris

    1979-01-01

    Previously unrecognized veins containing lead, zinc, and copper sulfide minerals at Point Delgada, Calif., are associated with late Mesozoic(?) and Tertiary volcanic and sedimentary rocks of the Franciscan assemblage. Sulfide minerals include pyrite, sphalerite, galena, and minor chalcopyrite, and galena-rich samples contain substantial amounts of silver. These minerals occur in a quartz-carbonate gangue along northeast-trending faults and fractures that exhibit (left?) lateral and vertical slip. The sense of fault movement and the northeasterly strike are consistent with predicted conjugate fault sets of the present San Andreas fault system. The sulfide mineralization is younger than the Franciscan rocks of Point Delgada and King Range, and it may have accompanied or postdated the inception of San Andreas faulting. Mineralization largely preceded uplift, the formation of a marine terrace, and the emplacement of landslide-related debris-flow breccias that overlie the mineralized rocks and truncate the sulfide veins. These field relations indicate that the sulfide mineralization and inception of San Andreas faulting were clearly more recent than the early Miocene and that the mineralization could be younger than about 1.2 m.y. The sulfide veins at Point Delgada may be of economic significance. However, prior to any exploitation of the occurrence, economic and environmental conflicts of interest involving private land ownership, the Shelter Cove home development, and proximity of the coast must be resolved.

  13. Dipping San Andreas and Hayward faults revealed beneath San Francisco Bay, California

    USGS Publications Warehouse

    Parsons, T.; Hart, P.E.

    1999-01-01

    The San Francisco Bay area is crossed by several right-lateral strike-slip faults of the San Andreas fault zone. Fault-plane reflections reveal that two of these faults, the San Andreas and Hayward, dip toward each other below seismogenic depths at 60?? and 70??, respectively, and persist to the base of the crust. Previously, a horizontal detachment linking the two faults in the lower crust beneath San Francisco Bay was proposed. The only near-vertical-incidence reflection data available prior to the most recent experiment in 1997 were recorded parallel to the major fault structures. When the new reflection data recorded orthogonal to the faults are compared with the older data, the highest, amplitude reflections show clear variations in moveout with recording azimuth. In addition, reflection times consistently increase with distance from the faults. If the reflectors were horizontal, reflection moveout would be independent of azimuth, and reflection times would be independent of distance from the faults. The best-fit solution from three-dimensional traveltime modeling is a pair of high-angle dipping surfaces. The close correspondence of these dipping structures with the San Andreas and Hayward faults leads us to conclude that they are the faults beneath seismogenic depths. If the faults retain their observed dips, they would converge into a single zone in the upper mantle -45 km beneath the surface, although we can only observe them in the crust.

  14. Integrated Static and Dynamic Stress Modeling for Investigating Tremor Source Regions in the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Hardy, S.; Gonzalez-Huizar, H.; Smith-Konter, B. R.

    2015-12-01

    The frictional and stress conditions at aseismic depths in tectonic boundaries are difficult to estimate, these are important parameters in computing stress transfer from plate motion to the seismogenetic zones of the plate boundaries, and thus, in creating seismic hazard models. Ambient and triggered tectonic tremor can be useful in the estimation of friction and stress parameters at large crustal depths. Seismic waves can trigger tremor in tectonic environments, specifically in the San Andreas Fault. A large number of ambient and triggered tremors have been reported near the creeping to locking transition zone along the Parkfield-Cholame section of the San Andreas Fault as well as in the San Jacinto and Calaveras Faults, both triggered by the 2002 Denali Fault earthquake. Ambient and triggered tremor along California is well located and documents well due to the large number of seismic stations in the region. We use recorded seismic signal from magnitude > 7.5 earthquakes to calculate the dynamic stresses capable to trigger tremor in these regions; this is integrated with local tectonic stress models with the objective to estimate the spatial variability of frictional and stress parameters along the areas where tremor are triggered. Integrating static and dynamic stress for San Andreas Fault will allow us to better understand the stress and frictional conditions necessary for tremor occurrence.

  15. Earthquakes, Segments, Bends, and Fault-Face Geology: Correlations Within the San Andreas System, California

    NASA Astrophysics Data System (ADS)

    Jachens, R. C.; Simpson, R. W.; Thurber, C. H.; Murray, J. R.

    2006-12-01

    Three-dimensional geologic maps of regions surrounding parts of the San Andreas Fault system reveal correlations between fault face geology and both short- and long-term behavior of the faults. The Loma Prieta fault segment that ruptured during the 1989 M6.9 earthquake, as defined by its aftershocks, closely corresponds to the subsurface reach (80 km long) where a large body of Logan gabbro is truncated at the fault, as defined by its magnetic anomaly. This Jurassic ophiolitic gabbro and its related rocks occupy an unusual fault-bounded basement block within Salinaa, a largely Cretaceous granitic terrane SW of the San Andreas Fault. The along-fault reach of the Logan gabbro also coincides with essentially the entire Santa Cruz Mountains left-bend in the San Andreas Fault. Rejecting a chance coincidence, the position of the Logan gabbro with respect to the left bend implies that the bend is fixed relative to Salinia and that the block NE of the San Andreas Fault has been forced to negotiate around the bend as the blocks moved past each other. Thus the basement rocks of the Logan block appear to define (control?) the Loma Prieta segment in terms both of short-term behavior (earthquakes) and long-term behavior (restraining bend fault geometry). The Parkfield segment of the San Andreas Fault also closely corresponds to a characteristic geologic unit in the NE face of the fault, the greenstone-rich Permanente terrane of the Franciscan Complex. The along-fault subsurface extent of the Permanente terrane at the fault face, as inferred from a recent 3D tomographic wavespeed model, corresponds to the reach filled by the aftershocks of the 2004 Parkfield earthquake. Furthermore, the 2004 co-seismic slip inferred from geodetic observations also coincides with the Permanente terrane at the fault face. To test whether these observations are directly related to the presence of the Permanente terrane along the fault face, we looked at fault behavior at the location of its offset

  16. Focal mechanisms and the state of stress on the San Andreas Fault in southern California

    NASA Astrophysics Data System (ADS)

    Jones, Lucile M.

    1988-08-01

    Focal mechanisms have been determined from P wave first motion polarities for 138 small to moderate (2.6 ≤ M ≤ 4.3) earthquakes that occurred within 10 km of the surface trace of the San Andreas fault in southern California between 1978 and 1985. On the basis of these mechanisms the southern San Andreas fault has been divided into five segments with different stress regimes. Earthquakes in the Fort Tejon segment show oblique reverse sup on east-west and northwest striking faults. The Mojave segment has earthquakes with oblique reverse and right-lateral strikesup motion on northwest strikes. The San Bernardino segment has normal faulting earthquakes on north-south striking planes, while the Banning segment has reverse, strike-sup, and normal faulting events all occurring in the same area. The earthquakes in the Indio segment show strike-slip and oblique normal faulting on northwest to north-south striking planes. These focal mechanism data have been inverted to determine how the stresses acting on the San Andreas fault in southern California vary with position along strike of the fault. One of the principal stresses is vertical in all of the regions. The vertical stress is the minimum principal stress in Fort Tejon and Mojave, the intermediate principal stress in Banning and Indio, and the maximum principal stress in San Bernardino. The orientations of the horizontal principal stresses also vary between the regions. The trend of the maximum horizontal stress rotates over 35°, from N15°W at Fort Tejon to N20° at Indio. Except for the San Bernardino segment, the trend of the maximum horizontal stress is at a constant angle of about 65° to the local strike of the San Andreas fault, implying a weak fault. The largest change in the present stress state occurs at the end of the rupture zone of the 1857 Fort Tejon earthquake. It appears that the 1857 rupture ended when it propagated into an area of low stress amplitude, possibly caused by the 15° angle between the

  17. Change in failure stress on the southern san andreas fault system caused by the 1992 magnitude = 7.4 landers earthquake.

    PubMed

    Stein, R S; King, G C; Lin, J

    1992-11-20

    The 28 June Landers earthquake brought the San Andreas fault significantly closer to failure near San Bernardino, a site that has not sustained a large shock since 1812. Stress also increased on the San Jacinto fault near San Bernardino and on the San Andreas fault southeast of Palm Springs. Unless creep or moderate earthquakes relieve these stress changes, the next great earthquake on the southern San Andreas fault is likely to be advanced by one to two decades. In contrast, stress on the San Andreas north of Los Angeles dropped, potentially delaying the next great earthquake there by 2 to 10 years.

  18. Change in failure stress on the southern San Andreas fault system caused by the 1992 magnitude = 7.4 Landers earthquake

    USGS Publications Warehouse

    Stein, R.S.; King, G.C.P.; Lin, J.

    1992-01-01

    The 28 June Landers earthquake brought the San Andreas fault significantly closer to failure near San Bernardino, a site that has not sustained a large shock since 1812. Stress also increased on the San Jacinto fault near San Bernardino and on the San Andreas fault southeast of Palm Springs. Unless creep or moderate earthquakes relieve these stress changes, the next great earthquake on the southern San Andreas fault is likely to be advanced by one to two decades. In contrast, stress on the San Andreas north of Los Angeles dropped, potentially delaying the next great earthquake there by 2 to 10 years.

  19. Shallow structure and deformation along the San Andreas Fault in Cholame Valley, California, based on high-resolution reflection profiling

    NASA Astrophysics Data System (ADS)

    Shedlock, Kaye M.; Brocher, Thomas M.; Harding, Samuel T.

    1990-04-01

    The mapped active traces of the San Andreas fault are separated by a 1-km-wide right-stepping offset in Cholame Valley. The geometry of this offset, defined in other strike-slip systems as a releasing bend or a dilational jog, has resulted in the formation of a pullapart basin. Various researchers have inferred that this offset served as a rupture terminus for earthquakes on both strands of the San Andreas fault (1966 Parkfield and 1857 Fort Tejon); thus, this en echelon offset may represent a barrier to the propagation of rupture between two segments of the San Andreas fault. We collected 18 km of high-resolution seismic reflection data specifically designed to image the San Andreas fault zone in the shallow crust surrounding this offset. Four short profiles (≤ 3.3 km long) of Mini-Sosie reflection data (1 s of two-way travel time ≈ 1.5 km deep) were collected perpendicular to the San Andreas fault; three of these profiles were tied by a 7-km-long profile that trended northwest through Cholame Valley, subparallel to the San Andreas fault. A zone of incoherent energy, narrow at the surface but widening with depth, underlies the mapped active traces of the San Andreas fault and abruptly terminates shallow reflections on both sides. The reflection profiles and available well data indicate that west of the mapped active traces of the San Andreas fault the shallow subsurface structure of the crust consists of thin (≤400 m thick), offset packages of reflections, laterally coherent on the scale of tens of meters, overlying deformed clastic sedimentary rocks. East of the San Andreas fault, the structure of the shallow crust in southern Cholame Valley is characterized by thick packages of reflections, laterally coherent on the scale of kilometers, overlying the Franciscan complex. All of the strata east of the fault (within Cholame Valley) dip toward the San Andreas fault and the offset, into an approximately 1-km-deep sedimentary basin abutting the south strand of

  20. Recurrence of seismic migrations along the central California segment of the San Andreas fault system

    USGS Publications Warehouse

    Wood, M.D.; Allen, S.S.

    1973-01-01

    VERIFICATIONS of tectonic concepts1 concerning seafloor spreading are emerging in a manner that has direct bearing on earthquake prediction. Although the gross pattern of worldwide seismicity contributed to the formulation of the plate tectonic hypothesis, it is the space-time characteristics of this seismicity that may contribute more toward understanding the kinematics and dynamics of the driving mechanism long speculated to originate in the mantle. If the lithosphere is composed of plates that move essentially as rigid bodies, then there should be seismic edge effects associated with this movement. It is these interplate effects, especially seismic migration patterns, that we discuss here. The unidirectional propagation at constant velocity (80 km yr-1 east to west) for earthquakes (M???7.2) on the Antblian fault for the period 1939 to 1956 (ref. 2) is one of the earliest observations of such a phenomenon. Similar studies3,4 of the Alaska Aleutian seismic zone and certain regions of the west coast of South America suggest unidirectional and recurring migrations of earthquakes (M???7.7) occur in these areas. Between these two regions along the great transform faults of the west coast of North America, there is some evidence 5 for unidirectional, constant velocity and recurrent migration of great earthquakes. The small population of earthquakes (M>7.2) in Savage's investigation5 indicates a large spatial gap along the San Andreas system in central California from 1830 to 1970. Previous work on the seismicity of this gap in central California indicates that the recurrence curves remain relatively constant, independent of large earthquakes, for periods up to a century6. Recurrence intervals for earthquakes along the San Andreas Fault have been calculated empirically by Wallace7 on the basis of geological evidence, surface measurements and assumptions restricted to the surficial seismic layer. Here we examine the evidence for recurrence of seismic migrations along

  1. Correlation between deep fluids, tremor and creep along the central San Andreas fault

    USGS Publications Warehouse

    Becken, M.; Ritter, O.; Bedrosian, P.A.; Weckmann, U.

    2011-01-01

    The seismicity pattern along the San Andreas fault near Parkfield and Cholame, California, varies distinctly over a length of only fifty kilometres. Within the brittle crust, the presence of frictionally weak minerals, fault-weakening high fluid pressures and chemical weakening are considered possible causes of an anomalously weak fault northwest of Parkfield. Non-volcanic tremor from lower-crustal and upper-mantle depths is most pronounced about thirty kilometres southeast of Parkfield and is thought to be associated with high pore-fluid pressures at depth. Here we present geophysical evidence of fluids migrating into the creeping section of the San Andreas fault that seem to originate in the region of the uppermost mantle that also stimulates tremor, and evidence that along-strike variations in tremor activity and amplitude are related to strength variations in the lower crust and upper mantle. Interconnected fluids can explain a deep zone of anomalously low electrical resistivity that has been imaged by magnetotelluric data southwest of the Parkfield-Cholame segment. Near Cholame, where fluids seem to be trapped below a high-resistivity cap, tremor concentrates adjacent to the inferred fluids within a mechanically strong zone of high resistivity. By contrast, subvertical zones of low resistivity breach the entire crust near the drill hole of the San Andreas Fault Observatory at Depth, northwest of Parkfield, and imply pathways for deep fluids into the eastern fault block, coincident with a mechanically weak crust and the lower tremor amplitudes in the lower crust. Fluid influx to the fault system is consistent with hypotheses of fault-weakening high fluid pressures in the brittle crust. ?? 2011 Macmillan Publishers Limited. All rights reserved.

  2. Earthquake geology of the northern San Andreas Fault near Point Arena, California

    SciTech Connect

    Prentice, C.S.

    1989-01-01

    Excavations into a Holocene alluvial fan provided exposures of a record of prehistoric earthquakes near Point Arena, California. At least five earthquakes were recognized in the section. All of these occurred since the deposition of a unit that is approximately 2000 years old. Radiocarbon dating allows constraints to be placed on the dates of these earthquakes. A buried Holocene (2356-2709 years old) channel has been offset a maximum of 64 {plus minus} 2 meters. This implies a maximum slip rate of 25.5 {plus minus} 2.5 mm/yr. These data suggest that the average recurrence interval for great earthquakes on this segment of the San Andreas fault is long - between about 200 and 400 years. Offset marine terrace risers near Point Arena and an offset landslide near Fort Ross provide estimates of the average slip rate since Late Pleistocene time. Near Fort Ross, an offset landslide implies a slip rate of less than 39 mm/yr. Correlation and age estimates of two marine terrace risers across the San Andreas fault near Point Arena suggest slip rates of about 18-19 mm/yr since Late Pleistocene time. Tentative correlation of the Pliocene Ohlson Ranch Formation in northwestern Sonoma County with deposits 50 km to the northwest near Point Arean, provides piercing points to use in calculation of a Pliocene slip rate for the northern San Andreas fault. A fission-track age 3.3 {plus minus} 0.8 Ma was determined for zicrons separated from a tuff collected from the Ohlson Ranch Formation. The geomorphology of the region, especially of the two major river drainages, supports the proposed 50 km Pliocene offset. This implies a Pliocene slip rate of at least 12-20 mm/yr. These rates for different time periods imply that much of the Pacific-North American plate motion must be accommodated on other structures at this latitude.

  3. Photomosaics and logs of trenches on the San Andreas Fault at Mill Canyon near Watsonville, California

    USGS Publications Warehouse

    Fumal, Thomas E.; Dawson, Timothy E.; Flowers, Rebecca; Hamilton, John C.; Heingartner, Gordon F.; Kessler, James; Samrad, Laura

    2004-01-01

    We present photomosaics and logs of the walls of trenches excavated for a paleoseismic study at Mill Canyon, one of two sites along the San Andreas fault in the Santa Cruz Mtns. on the Kelley-Thompson Ranch. This site was a part of Rancho Salsipuedes begining in 1834. It was purchased by the present owner’s family in 1851. Remnants of a cabin/mill operations still exist up the canyon dating from 1908 when the area was logged. At this location, faulting has moved a shutter ridge across the mouth of Mill Canyon ponding Holocene sediment. Recent faulting is confined to a narrow zone near the break in slope.

  4. Photomosaics and logs of trenches on the San Andreas Fault, Thousand Palms Oasis, California

    USGS Publications Warehouse

    Fumal, Thomas E.; Frost, William T.; Garvin, Christopher; Hamilton, John C.; Jaasma, Monique; Rymer, Michael J.

    2004-01-01

    We present photomosaics and logs of the walls of trenches excavated for a paleoseismic study at Thousand Palms Oasis (Fig. 1). The site is located on the Mission Creek strand of the San Andreas fault zone, one of two major active strands of the fault in the Indio Hills along the northeast margin of the Coachella Valley (Fig. 2). The Coachella Valley section is the most poorly understood major part of the San Andreas fault with regard to slip rate and timing of past large-magnitude earthquakes, and therefore earthquake hazard. No large earthquakes have occurred for more than three centuries, the longest elapsed time for any part of the southern San Andreas fault. In spite of this, the Working Group on California Earthquake Probabilities (1995) assigned the lowest 30-year conditional probability on the southern San Andreas fault to the Coachella Valley. Models of the behavior of this part of the fault, however, have been based on very limited geologic data. The Thousand Palms Oasis is an attractive location for paleoseismic study primarily because of the well-bedded late Holocene sedimentary deposits with abundant layers of organic matter for radiocarbon dating necessary to constrain the timing of large prehistoric earthquakes. Previous attempts to develop a chronology of paleoearthquakes for the region have been hindered by the scarcity of in-situ 14C-dateable material for age control in this desert environment. Also, the fault in the vicinity of Thousand Palms Oasis consists of a single trace that is well expressed, both geomorphically and as a vegetation lineament (Figs. 2, 3). Results of our investigations are discussed in Fumal et al. (2002) and indicate that four and probably five surface-rupturing earthquakes occurred along this part of the fault during the past 1200 years. The average recurrence time for these earthquakes is 215 ± 25 years, although interevent times may have been as short as a few decades or as long as 400 years. Thus, although the elapsed

  5. Peter Andreas Hansen und die astronomische Gemeinschaft - eine erste Auswertung des Hansen-Nachlasses.

    NASA Astrophysics Data System (ADS)

    Schwarz, O.; Strumpf, M.

    The literary assets of Peter Andreas Hansen are deposited in the Staatsarchiv Hamburg, the Forschungs- und Landesbibliothek Gotha and the Thüringer Staatsarchiv Gotha. They were never systematically investigated. The authors present here some results of a first evaluation. It was possible to reconstruct the historical events with regard to the maintenance of the Astronomische Nachrichten and the Altona observatory in 1854. Hansen was a successful teacher for many young astronomers. His way of stimulating the evolution of astronomy followed Zach's tradition.

  6. Impulsive radon emanation on a creeping segment of the San Andreas fault, California

    USGS Publications Warehouse

    King, C.-Y.

    1985-01-01

    Radon emanation was continuously monitored for several months at two locations along a creeping segment of the San Andreas fault in central California. The recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations. Some of the radon increases were accompanied or followed by earthquakes or fault-creep events. They were possibly the result of some sudden outbursts of relatively radon-rich ground gas, sometimes triggered by crustal deformation or vibration. ?? 1985 Birkha??user Verlag.

  7. Time-frequency analysis of the sea state with the Andrea freak wave

    NASA Astrophysics Data System (ADS)

    Cherneva, Z.; Guedes Soares, C.

    2014-12-01

    The nonlinear and nonstationary properties of a special field wave record are analysed with the Wigner spectrum with the Choi-Williams kernel. The wave time series, which was recorded at the Ekofisk complex in the central North Sea at 00:40 UTC (universal time coordinated) on 9 November 2007, contains an abnormally high wave known as the "Andrea" wave. The ability of the Wigner spectrum to reveal the wave energy distribution in frequency and time is demonstrated. The results are compared with previous investigations for different sea states and also the state with Draupner's abnormal "New Year" wave.

  8. Time-frequency analysis of the sea state with the "Andrea" freak wave

    NASA Astrophysics Data System (ADS)

    Cherneva, Z.; Guedes Soares, C.

    2014-02-01

    The non-linear and non-stationary properties of a special field wave record are analyzed with the Wigner spectrum with the Choi-Williams kernel. The wave time series, which was recorded at the Ekofisk complex in the Central North Sea at 00:40 UTC on 9 November 2007, contains an abnormally high wave known as "Andrea" wave. The ability of the Wigner spectrum to reveal the wave energy distribution in frequency and time is demonstrated. The results are compared with previous investigations for different sea states and also the state with the abnormal Draupner's New Year wave.

  9. Aseismic Slip Events along the Southern San Andreas Fault System Captured by Radar Interferometry

    SciTech Connect

    Vincent, P

    2001-10-01

    A seismic slip is observed along several faults in the Salton Sea and southernmost Landers rupture zone regions using interferometric synthetic aperture radar (InSAR) data spanning different time periods between 1992 and 1997. In the southernmost Landers rupture zone, projecting south from the Pinto Mountain Fault, sharp discontinuities in the interferometric phase are observed along the sub-parallel Burnt Mountain and Eureka Peak Faults beginning three months after the Landers earthquake and is interpreted to be post-Landers after-slip. Abrupt phase offsets are also seen along the two southernmost contiguous 11 km Durmid Hill and North Shore segments of the San Andreas Fault with an abrupt termination of slip near the northern end of the North Shore Segment. A sharp phase offset is seen across 20 km of the 30 km-long Superstition Hills Fault before phase decorrelation in the Imperial Valley along the southern 10 km of the fault prevents coherent imaging by InSAR. A time series of deformation interferograms suggest most of this slip occurred between 1993 and 1995 and none of it occurred between 1992 and 1993. A phase offset is also seen along a 5 km central segment of the Coyote Creek fault that forms a wedge with an adjoining northeast-southwest trending conjugate fault. Most of the slip observed on the southern San Andreas and Superstition Hills Faults occurred between 1993 and 1995--no slip is observed in the 92-93 interferograms. These slip events, especially the Burnt Mountain and Eureka Peak events, are inferred to be related to stress redistribution from the June, 1992 M{sub w} = 7.3 Landers earthquake. Best-fit elastic models of the San Andreas and Superstition Hills slip events suggest source mechanisms with seismic moments over three orders of magnitude larger than a maximum possible summation of seismic moments from all seismicity along each fault segment during the entire 4.8-year time interval spanned by the InSAR data. Aseismic moment releases of this

  10. Deformation rates across the San Andreas Fault system, central California determined by geology and geodesy

    NASA Astrophysics Data System (ADS)

    Titus, Sarah J.

    The San Andreas fault system is a transpressional plate boundary characterized by sub-parallel dextral strike-slip faults separating internally deformed crustal blocks in central California. Both geodetic and geologic tools were used to understand the short- and long-term partitioning of deformation in both the crust and the lithospheric mantle across the plate boundary system. GPS data indicate that the short-term discrete deformation rate is ˜28 mm/yr for the central creeping segment of the San Andreas fault and increases to 33 mm/yr at +/-35 km from the fault. This gradient in deformation rates is interpreted to reflect elastic locking of the creeping segment at depth, distributed off-fault deformation, or some combination of these two mechanisms. These short-term fault-parallel deformation rates are slower than the expected geologic slip rate and the relative plate motion rate. Structural analysis of folds and transpressional kinematic modeling were used to quantify long-term distributed deformation adjacent to the Rinconada fault. Folding accommodates approximately 5 km of wrench deformation, which translates to a deformation rate of ˜1 mm/yr since the start of the Pliocene. Integration with discrete offset on the Rinconada fault indicates that this portion of the San Andreas fault system is approximately 80% strike-slip partitioned. This kinematic fold model can be applied to the entire San Andreas fault system and may explain some of the across-fault gradient in deformation rates recorded by the geodetic data. Petrologic examination of mantle xenoliths from the Coyote Lake basalt near the Calaveras fault was used to link crustal plate boundary deformation at the surface with models for the accommodation of deformation in the lithospheric mantle. Seismic anisotropy calculations based on xenolith petrofabrics suggest that an anisotropic mantle layer thickness of 35-85 km is required to explain the observed shear wave splitting delay times in central

  11. Animals, Pictures, and Skeletons: Andreas Vesalius's Reinvention of the Public Anatomy Lesson.

    PubMed

    Shotwell, R Allen

    2016-01-01

    In this paper, I examine the procedures used by Andreas Vesalius for conducting public dissections in the early sixteenth century. I point out that in order to overcome the limitations of public anatomical demonstration noted by his predecessors, Vesalius employed several innovative strategies, including the use of animals as dissection subjects, the preparation and display of articulated skeletons, and the use of printed and hand-drawn illustrations. I suggest that the examination of these three strategies for resolving the challenges of public anatomical demonstration helps us to reinterpret Vesalius's contributions to sixteenth-century anatomy.

  12. [The copy of De humani corporis fabrica of Andreas Vesalius of the municipal library of Reims].

    PubMed

    Ségal, Alain

    2014-01-01

    The author presents a copy of the De humani corporis fabrica by Andreas Vesalius; this book is preserved in the department of rare books of the municipal Library in Reims. This copy is a first edition as the author gives positive proofs. This book results of a donation to the Minimes's congregation of Reims by Seigneur Guillaume Le Vergeur, Count of Saint Souplet and Baillif of Vermandois in the 17th century. Guillaume Le Vergeur has also given other precious books to the monastery's library and his name is inscribed on the register of obituaries and on the pediment of the Minimes' Church.

  13. The Renaissance and the universal surgeon: Giovanni Andrea Della Croce, a master of traumatology.

    PubMed

    Di Matteo, Berardo; Tarabella, Vittorio; Filardo, Giuseppe; Viganò, Anna; Tomba, Patrizia; Marcacci, Maurilio

    2013-12-01

    All the medical knowledge of all time in one book, the universal and perfect manual for the Renaissance surgeon, and the man who wrote it. This paper depicts the life and works of Giovanni Andrea della Croce, a 16th Century physician and surgeon, who, endowed with true spirit of Renaissance humanism, wanted to teach and share all his medical knowledge through his opus magnum, titled "Universal Surgery Complete with All the Relevant Parts for the Optimum Surgeon". An extraordinary book which truly represents a defining moment and a founding stone for traumatology, written by a lesser known historical personality, but nonetheless the Renaissance Master of Traumatology.

  14. Photomosaics and logs of trenches on the San Andreas Fault at Arano Flat near Watsonville, California

    USGS Publications Warehouse

    Fumal, Thomas E.; Heingartner, Gordon F.; Samrad, Laura; Dawson, Timothy E.; Hamilton, John C.; Baldwin, John N.

    2004-01-01

    We present photomosaics and logs of the walls of trenches excavated for a paleoseismic study at Arano Flat, one of two sites along the San Andreas fault in the Santa Cruz Mountains on the Kelley-Thompson Ranch. At this location, the fault consists of a narrow zone along the northeast side of a low ridge adjacent to a possible sag pond and extends about 60-70 meters across a broad alluvial flat. This site was a part of Rancho Salsipuedes beginning in 1834 and was purchased by the present owner’s family in 1851.

  15. Near-field stress and pore pressure observations along the Carrizo Plain segment of the San Andreas fault in California

    SciTech Connect

    Castillo, D.A. ); Hickman, S.H. )

    1996-01-01

    Preliminary observations of wellbore breakouts from 9 wells drilled to depths approaching 5 km and located within 3-10 km of the San Andreas fault in the Carrizo Plain area indicate maximum principal stress orientations (SHmax) 30-40[degrees] from the fault trend, consistent with high shear stress resolved unto the fault. Analysis of stress orientation data from additional wells located >10 km from the fault confirm previous observations that SHmax stresses are at high angles to the fault trend, consistent with low shear stress on the San Andreas. We suggest that the overall variation in shear stresses resolved onto the fault may be depth dependent, with greater shear stress at shallower depths. Alternatively, these stress rotations observed in the vicinity of the San Andreas might also reflect the influence of local secondary faulting and folding, variations in lithology and/or slip heterogeneties associated with the 1857 M8+ Fort Tejon earthquake. Estimates of crustal pore pressure inferred from drilling mud-weights and drill-stem tests from wells in the vicinity (<10 km) of the San Andreas fault indicate near-hydrostatic conditions to depths of about 5 km. However, 20-30 km from the San Andreas fault and within the central portions of the southern San Joaquin Valley, crustal pore pressures approach 60% of the lithostatic load starting at about 3.5 km depth. Thus, our data close to the fault suggests that elevated fluid pressures within the fault zone, as proposed to explain the long-term low-strength of the San Andreas, either do not penetrate far into the adjacent crust and/or are confined largely to deeper portions of the fault zone.

  16. Near-field stress and pore pressure observations along the Carrizo Plain segment of the San Andreas fault in California

    SciTech Connect

    Castillo, D.A.; Hickman, S.H.

    1996-12-31

    Preliminary observations of wellbore breakouts from 9 wells drilled to depths approaching 5 km and located within 3-10 km of the San Andreas fault in the Carrizo Plain area indicate maximum principal stress orientations (SHmax) 30-40{degrees} from the fault trend, consistent with high shear stress resolved unto the fault. Analysis of stress orientation data from additional wells located >10 km from the fault confirm previous observations that SHmax stresses are at high angles to the fault trend, consistent with low shear stress on the San Andreas. We suggest that the overall variation in shear stresses resolved onto the fault may be depth dependent, with greater shear stress at shallower depths. Alternatively, these stress rotations observed in the vicinity of the San Andreas might also reflect the influence of local secondary faulting and folding, variations in lithology and/or slip heterogeneties associated with the 1857 M8+ Fort Tejon earthquake. Estimates of crustal pore pressure inferred from drilling mud-weights and drill-stem tests from wells in the vicinity (<10 km) of the San Andreas fault indicate near-hydrostatic conditions to depths of about 5 km. However, 20-30 km from the San Andreas fault and within the central portions of the southern San Joaquin Valley, crustal pore pressures approach 60% of the lithostatic load starting at about 3.5 km depth. Thus, our data close to the fault suggests that elevated fluid pressures within the fault zone, as proposed to explain the long-term low-strength of the San Andreas, either do not penetrate far into the adjacent crust and/or are confined largely to deeper portions of the fault zone.

  17. Tremor-tide correlations and near-lithostatic pore pressure on the deep San Andreas fault.

    PubMed

    Thomas, Amanda M; Nadeau, Robert M; Bürgmann, Roland

    2009-12-24

    Since its initial discovery nearly a decade ago, non-volcanic tremor has provided information about a region of the Earth that was previously thought incapable of generating seismic radiation. A thorough explanation of the geologic process responsible for tremor generation has, however, yet to be determined. Owing to their location at the plate interface, temporal correlation with geodetically measured slow-slip events and dominant shear wave energy, tremor observations in southwest Japan have been interpreted as a superposition of many low-frequency earthquakes that represent slip on a fault surface. Fluids may also be fundamental to the failure process in subduction zone environments, as teleseismic and tidal modulation of tremor in Cascadia and Japan and high Poisson ratios in both source regions are indicative of pressurized pore fluids. Here we identify a robust correlation between extremely small, tidally induced shear stress parallel to the San Andreas fault and non-volcanic tremor activity near Parkfield, California. We suggest that this tremor represents shear failure on a critically stressed fault in the presence of near-lithostatic pore pressure. There are a number of similarities between tremor in subduction zone environments, such as Cascadia and Japan, and tremor on the deep San Andreas transform, suggesting that the results presented here may also be applicable in other tectonic settings.

  18. Slow and Go: Pulsing slip rates on the creeping section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Turner, Ryan C.; Shirzaei, Manoochehr; Nadeau, Robert M.; Bürgmann, Roland

    2015-08-01

    Rising and falling slip rates on the creeping section of the San Andreas Fault have been inferred from variations of recurrence intervals of characteristically repeating microearthquakes, but this observation has not previously been confirmed using modern geodetic data. Here we report on observations of this "pulsing" slip obtained from advanced multitemporal interferometric synthetic aperture radar (InSAR) data, confirmed using continuous GPS sites of the Plate Boundary Observatory. The surface deformation time series show a strong correlation to the previously documented slip rate variations derived from repeating earthquakes on the fault interface, at various spatial and temporal scales. Time series and spectral analyses of repeating earthquake and InSAR data reveal a quasiperiodic pulsing with a roughly 2 year period along some sections of the fault, with the earthquakes on the fault interface lagging behind the far-field deformation by about 6 months. This suggests a temporal delay between the pulsing crustal strain generated by deep-seated shear and the time-variable slip on the shallow fault interface, and that at least in some places this process may be cyclical. There exist potential impacts for time-dependent seismic hazard forecasting in California and, as it becomes better validated in the richly instrumented natural laboratory of the central San Andreas Fault, the process used here will be even more helpful in characterizing hazard and fault zone rheology in areas without California's geodetic infrastructure.

  19. Andreas Vesalius 500 years--A Renaissance that revolutionized cardiovascular knowledge.

    PubMed

    Mesquita, Evandro Tinoco; Souza Júnior, Celso Vale de; Ferreira, Thiago Reigado

    2015-01-01

    The history of medicine and cardiology is marked by some geniuses who dared in thinking, research, teaching and transmitting scientific knowledge, and the Italian Andreas Vesalius one of these brilliant masters. His main scientific work "De Humani Corporis Fabrica" is not only a landmark study of human anatomy but also an artistic work of high aesthetic quality published in 1543. In the year 2014 we celebrated 500 years since the birth of the brilliant professor of Padua University, who with his courage and sense of observation changed the understanding of cardiovascular anatomy and founded a school to date in innovative education and research of anatomy. By identifying "the anatomical errors" present in Galen's book and speech, he challenged the dogmas of the Catholic Church, the academic world and the doctors of his time. However, the accuracy of his findings and his innovative way to disseminate them among his students and colleagues was essential so that his contributions are considered by many the landmark of modern medicine. His death is still surrounded by mysteries having different hypotheses, but a certainty, suffered sanctions of the Catholic Church for the spread of their ideas. The cardiologists, cardiovascular surgeons, interventional cardiologists, electrophysiologists and cardiovascular imaginologists must know the legacy of genius Andreas Vesalius that changed the paradigm of human anatomy.

  20. Ground-squirrel mounds and related patterned ground along the San Andreas Fault in Central California

    USGS Publications Warehouse

    Wallace, Robert E.

    1991-01-01

    Extensive areas of mound topography and related patterned ground, apparently derived from the mounds of the California Ground Squirrel (Spermophilus beecheyi beecheyi), are in central California.  The relation of patterned ground to the San Andreas fault west of Bakersfield may provide insight into the timing of deformation along the fault as well as the history of ground squirrels.  Mound topography appears to have evolved through several stages from scattered mounds currently being constructed on newly deposited alluvial surfaces, to saturation of areas by mounds, followed by coalescence, elongation and lineation of the mounds.  Elongation, coalescence and modification of the mounds has been primarily by wind, but to a lesser extent by drainage and solifluction.  A time frame including ages of 4,000, 10,500, 29,000, and 73,000 years BP is derived by relating the patterns to slip on the San Andreas fault.  Further relating of the patterns to faulting, tilting, and warping may illuminate details of the rates and history of deformation.  Similarly, relating the patterns to the history of ground squirrel activity may help answer such problems as rates of dispersal and limits on population density.

  1. The accommodation of relative motion at depth on the San Andreas fault system in California.

    USGS Publications Warehouse

    Prescott, W.H.; Nur, A.

    1981-01-01

    Plate motion below the seismogenic layer along the San Andreas fault system in California is generally assumed to occur by aseismic slip along a deeper extension of the fault. It is also possible that below the seismogenic layer, deformation is distributed laterally over a zone. Several observed features of the San Andreas fault in California have implications about the mode of accommodation of relative motion along the plate boundary beneath the seismogenic zone: the shallow depth of all earthquakes in California, the depth to which coseismic slip occurred during the 1906 San Francisco earthquake, the broad zone of strain accumulation, the broad heat flow anomaly, and the existence of widely separated parallel faults. The observations strongly imply that below the seismogenic zone, relative motion is distributed over a zone and occurs by inelastic flow rather than by aseismic slip on discrete fault planes. The existence of multiple faults further suggests that tractions at the base of the brittle layer are significant over time periods of years to hundreds of years.-Authors

  2. Simulations of tremor-related creep reveal a weak crustal root of the San Andreas Fault

    USGS Publications Warehouse

    Shelly, David R.; Bradley, Andrew M.; Johnson, Kaj M.

    2013-01-01

    Deep aseismic roots of faults play a critical role in transferring tectonic loads to shallower, brittle crustal faults that rupture in large earthquakes. Yet, until the recent discovery of deep tremor and creep, direct inference of the physical properties of lower-crustal fault roots has remained elusive. Observations of tremor near Parkfield, CA provide the first evidence for present-day localized slip on the deep extension of the San Andreas Fault and triggered transient creep events. We develop numerical simulations of fault slip to show that the spatiotemporal evolution of triggered tremor near Parkfield is consistent with triggered fault creep governed by laboratory-derived friction laws between depths of 20–35 km on the fault. Simulated creep and observed tremor northwest of Parkfield nearly ceased for 20–30 days in response to small coseismic stress changes of order 104 Pa from the 2003 M6.5 San Simeon Earthquake. Simulated afterslip and observed tremor following the 2004 M6.0 Parkfield earthquake show a coseismically induced pulse of rapid creep and tremor lasting for 1 day followed by a longer 30 day period of sustained accelerated rates due to propagation of shallow afterslip into the lower crust. These creep responses require very low effective normal stress of ~1 MPa on the deep San Andreas Fault and near-neutral-stability frictional properties expected for gabbroic lower-crustal rock.

  3. San Andreas fault zone drilling project: scientific objectives and technological challenges

    USGS Publications Warehouse

    Hickman, S.H.; Younker, L.W.; Zoback, M.D.

    1995-01-01

    We are leading a new international initiative to conduct scientific drilling within the San Andreas fault zone at depths of up to 10 km. This project is motivated by the need to understand the physical and chemical processes operating within the fault zone and to answer fundamental questions about earthquake generation along major plate-boundary faults. Through a comprehensive program of coring, fluid sampling, downhole measurements, laboratory experimentation, and long-term monitoring, we hope to obtain critical information on the structure, composition, mechanical behavior and physical state of the San Andreas fault system at depths comparable to the nucleation zones of great earthquakes. The drilling, sampling and observational requirements needed to ensure the success of this project are stringent. These include: 1) drilling stable vertical holes to depths of about 9 km in fractured rock at temperatures of up to 300°C; 2) continuous coring and completion of inclined holes branched off these vertical boreholes to intersect the fault at depths of 3, 6, and 9 km; 3) conducting sophisticated borehole geophysical measurements and fluid/rock sampling at high temperatures and pressures; and 4) instrumenting some or all of these inclined core holes for continuous monitoring of earthquake activity, fluid pressure, deformation and other parameters for periods of up to several decades. For all of these tasks, because of the overpressured clay-rich formations anticipated within the fault zone at depth, we expect to encounter difficult drilling, coring and hole-completion conditions in the region of greatest scientific interest.

  4. Quasi-periodic recurrence of large earthquakes on the southern San Andreas fault

    USGS Publications Warehouse

    Scharer, Katherine M.; Biasi, Glenn P.; Weldon, Ray J.; Fumal, Tom E.

    2010-01-01

    It has been 153 yr since the last large earthquake on the southern San Andreas fault (California, United States), but the average interseismic interval is only ~100 yr. If the recurrence of large earthquakes is periodic, rather than random or clustered, the length of this period is notable and would generally increase the risk estimated in probabilistic seismic hazard analyses. Unfortunately, robust characterization of a distribution describing earthquake recurrence on a single fault is limited by the brevity of most earthquake records. Here we use statistical tests on a 3000 yr combined record of 29 ground-rupturing earthquakes from Wrightwood, California. We show that earthquake recurrence there is more regular than expected from a Poisson distribution and is not clustered, leading us to conclude that recurrence is quasi-periodic. The observation of unimodal time dependence is persistent across an observationally based sensitivity analysis that critically examines alternative interpretations of the geologic record. The results support formal forecast efforts that use renewal models to estimate probabilities of future earthquakes on the southern San Andreas fault. Only four intervals (15%) from the record are longer than the present open interval, highlighting the current hazard posed by this fault.

  5. Expected seismic shaking in Los Angeles reduced by San Andreas fault zone plasticity

    NASA Astrophysics Data System (ADS)

    Roten, D.; Olsen, K. B.; Day, S. M.; Cui, Y.; Fäh, D.

    2014-04-01

    Computer simulations of large (M≥7.8) earthquakes rupturing the southern San Andreas Fault from SE to NW (e.g., ShakeOut, widely used for earthquake drills) have predicted strong long-period ground motions in the densely populated Los Angeles Basin due to channeling of waves through a series of interconnected sedimentary basins. Recently, the importance of this waveguide amplification effect for seismic shaking in the Los Angeles Basin has also been confirmed from observations of the ambient seismic field. By simulating the ShakeOut earthquake scenario (based on a kinematic source description) for a medium governed by Drucker-Prager plasticity, we show that nonlinear material behavior could reduce the earlier predictions of large long-period ground motions in the Los Angeles Basin by up to 70% as compared to viscoelastic solutions. These reductions are primarily due to yielding near the fault, although yielding may also occur in the shallow low-velocity deposits of the Los Angeles Basin if cohesions are close to zero. Fault zone plasticity remains important even for conservative values of cohesions, suggesting that current simulations assuming a linear response of rocks are overpredicting ground motions during future large earthquakes on the southern San Andreas Fault.

  6. Hydrologic and geochemical properties of the San Andreas fault at the Stone Canyon well

    NASA Astrophysics Data System (ADS)

    Stierman, Donald J.; Williams, Alan E.

    1984-03-01

    The Stone Canyon well penetrates 600 m of highly fractured and severely altered quartz diorite intimately associated with the creeping segment of the San Andreas fault of central California. Geophysical logs reveal a complex hydrology dominated by major fractures. Fluid pressure in some fractures is sufficient to prevent invasion of the formation by heavy drilling mud, implying pore pressures at least 10% higher than hydrostatic ones. At least three chemically distinct waters are encountered, including a chloride brine clearly segregated from the shallow, potable groundwater. Chemical alteration of the quartz diorite persists throughout the well, far below the depth where the water-rock reactions responsible for the ubiquitous chlorite and mixed-layer clays can be considered weathering. Whole-rock δ18O analyses indicate significant interaction of the rocks with a low δ18O fluid within some of the fractured and altered zones, whereas a deeper sample shows18O enrichment. High pore pressures encountered in Stone Canyon may be due to tectonic compression. Measurements of temporal variations in the pore pressure at the well may provide a means of predicting earthquakes along this segment of the San Andreas fault.

  7. Nonlinear strain buildup and the earthquake cycle on the San Andreas Fault

    SciTech Connect

    Thatcher, W.

    1983-07-10

    Two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault, accompanied by a progressive broadening of the zone of deformation adjacent to it. In the thin lithosphere model, transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere. For an earth model with a thick elastic lithosphere (plate thickness >> depth of seismic slip), transient motions are due to postearthquake aseismic slip below the coseismic fault plane. Data from the San Andreas fault indicate a long-term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle. Observations support a cycle-long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar. If so, the usually lower strain rates and broader deformation zone currently observed on the sourthern San Andreas represent a later evolutionary stage of the northern locked section, where a great earthquake is a more recent occurrence. Although the data allow some extreme models to be discarded, no sufficiently strong constraints exist to decide between the thin and thick lithosphere models. Regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause signficant departures fromm recurrence estimates based on linear strain accumulation and the time-predictable model.

  8. San Andreas Fault damage at SAFOD viewed with fault-guided waves

    NASA Astrophysics Data System (ADS)

    Li, Yong-Gang; Malin, Peter E.

    2008-04-01

    Highly damaged rocks within the San Andreas fault zone at Parkfield form a low-velocity waveguide for seismic waves, giving rise to fault-guided waves. Prominent fault-guided waves have been observed at the San Andreas Fault Observatory at Depth (SAFOD) site, including a surface array across the fault zone and a borehole seismograph placed in the SAFOD well at a depth of ~2.7 km below ground. The resulting observations are modeled here using 3-D finite-difference methods. To fit the amplitude, frequency, and travel-time characteristics of the data, the models require a downward tapering, 30-40-m wide fault-core embedded in a 100-200-m wide jacket. Compared with the intact wall rocks, the core velocities are reduced by ~40% and jacket velocities by ~25%. Based on the depths of earthquakes generating guided waves, we estimate that the low-velocity waveguide along the fault at SAFOD extends at least to depths of ~7 km, more than twice the depth reported in pervious studies.

  9. Paragenesis and tectonic significance of base and precious metal occurrences along the San Andreas fault at Point Delgada, California.

    USGS Publications Warehouse

    McLaughlin, R.J.; Sorg, D.H.; Morton, J.L.; Theodore, T.G.; Meyer, C.E.; Delevaux, M.H.

    1985-01-01

    The mineralogy, geochemistry and origin of sulphide veins along cross faults in the San Andreas fault system are described and cited for a natural history of local plate tectonics and for 'a detailed understanding of the role of major strike-slip faults in the formation and tectonic translation of hydrothermal ore deposits'. -G.J.N.

  10. A critical evaluation of crustal dehydration as the cause of an overpressured and weak San Andreas Fault

    USGS Publications Warehouse

    Fulton, P.M.; Saffer, D.M.; Bekins, B.A.

    2009-01-01

    Many plate boundary faults, including the San Andreas Fault, appear to slip at unexpectedly low shear stress. One long-standing explanation for a "weak" San Andreas Fault is that fluid release by dehydration reactions during regional metamorphism generates elevated fluid pressures that are localized within the fault, reducing the effective normal stress. We evaluate this hypothesis by calculating realistic fluid production rates for the San Andreas Fault system, and incorporating them into 2-D fluid flow models. Our results show that for a wide range of permeability distributions, fluid sources from crustal dehydration are too small and short-lived to generate, sustain, or localize fluid pressures in the fault sufficient to explain its apparent mechanical weakness. This suggests that alternative mechanisms, possibly acting locally within the fault zone, such as shear compaction or thermal pressurization, may be necessary to explain a weak San Andreas Fault. More generally, our results demonstrate the difficulty of localizing large fluid pressures generated by regional processes within near-vertical fault zones. ?? 2009 Elsevier B.V.

  11. M ≥ 7.0 earthquake recurrence on the San Andreas fault from a stress renewal model

    USGS Publications Warehouse

    Parsons, Thomas E.

    2006-01-01

     Forecasting M ≥ 7.0 San Andreas fault earthquakes requires an assessment of their expected frequency. I used a three-dimensional finite element model of California to calculate volumetric static stress drops from scenario M ≥ 7.0 earthquakes on three San Andreas fault sections. The ratio of stress drop to tectonic stressing rate derived from geodetic displacements yielded recovery times at points throughout the model volume. Under a renewal model, stress recovery times on ruptured fault planes can be a proxy for earthquake recurrence. I show curves of magnitude versus stress recovery time for three San Andreas fault sections. When stress recovery times were converted to expected M ≥ 7.0 earthquake frequencies, they fit Gutenberg-Richter relationships well matched to observed regional rates of M ≤ 6.0 earthquakes. Thus a stress-balanced model permits large earthquake Gutenberg-Richter behavior on an individual fault segment, though it does not require it. Modeled slip magnitudes and their expected frequencies were consistent with those observed at the Wrightwood paleoseismic site if strict time predictability does not apply to the San Andreas fault.

  12. The San Andreas fault in the San Francisco Bay region, California: Structure and kinematics of a Young plate boundary

    USGS Publications Warehouse

    Jachens, R.C.; Zoback, M.L.

    1999-01-01

    Recently acquired high-resolution aeromagnetic data delineate offset and/or truncated magnetic rock bodies of the Franciscan Complex that define the location and structure of, and total offset across, the San Andreas fault in the San Francisco Bay region. Two distinctive magnetic anomalies caused by ultramafic rocks and metabasalts east of, and truncated at, the San Andreas fault have clear counterparts west of the fault that indicate a total right-lateral offset of only 22 km on the Peninsula segment, the active strand that ruptured in 1906. The location of the Peninsula segment is well defined magnetically on the northern peninsula where it goes offshore, and can be traced along strike an additional ~6 km to the northwest. Just offshore from Lake Merced, the inferred fault trace steps right (northeast) 3 km onto a nearly parallel strand that can be traced magnetically northwest more than 20 km as the linear northeast edge of a magnetic block bounded by the San Andreas fault, the Pilarcitos fault, and the San Gregorio-Hosgri fault zone. This right-stepping strand, the Golden Gate segment, joins the eastern mapped trace of the San Andreas fault at Bolinas Lagoon and projects back onshore to the southeast near Lake Merced. Inversion of detailed gravity data on the San Francisco Peninsula reveals a 3 km wide basin situated between the two strands of the San Andreas fault, floored by Franciscan basement and filled with Plio-Quaternary sedimentary deposits of the Merced and Colma formations. The basin, ~1 km deep at the coast, narrows and becomes thinner to the southeast along the fault over a distance of ~12 km. The length, width, and location of the basin between the two strands are consistent with a pull-apart basin formed behind the right step in the right-lateral strike-slip San Andreas fault system and currently moving southeast with the North American plate. Slight nonparallelism of the two strands bounding the basin (implying a small component of convergence

  13. High Resolution Seismic Imaging of Fault Zones: Methods and Examples From The San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Catchings, R. D.; Rymer, M. J.; Goldman, M.; Prentice, C. S.; Sickler, R. R.; Criley, C.

    2011-12-01

    Seismic imaging of fault zones at shallow depths is challenging. Conventional seismic reflection methods do not work well in fault zones that consist of non-planar strata or that have large variations in velocity structure, two properties that occur in most fault zones. Understanding the structure and geometry of fault zones is important to elucidate the earthquake hazard associated with fault zones and the barrier effect that faults impose on subsurface fluid flow. In collaboration with the San Francisco Public Utilities Commission (SFPUC) at San Andreas Lake on the San Francisco peninsula, we acquired combined seismic P-wave and S-wave reflection, refraction, and guided-wave data to image the principal strand of the San Andreas Fault (SAF) that ruptured the surface during the 1906 San Francisco earthquake and additional fault strands east of the rupture. The locations and geometries of these fault strands are important because the SFPUC is seismically retrofitting the Hetch Hetchy water delivery system, which provides much of the water for the San Francisco Bay area, and the delivery system is close to the SAF at San Andreas Lake. Seismic reflection images did not image the SAF zone well due to the brecciated bedrock, a lack of layered stratigraphy, and widely varying velocities. Tomographic P-wave velocity images clearly delineate the fault zone as a low-velocity zone at about 10 m depth in more competent rock, but due to soil saturation above the rock, the P-waves do not clearly image the fault strands at shallower depths. S-wave velocity images, however, clearly show a diagnostic low-velocity zone at the mapped 1906 surface break. To image the fault zone at greater depths, we utilized guided waves, which exhibit high amplitude seismic energy within fault zones. The guided waves appear to image the fault zone at varying depths depending on the frequency of the seismic waves. At higher frequencies (~30 to 40 Hz), the guided waves show strong amplification at the

  14. Mineralogy of Faults in the San Andreas System That are Characterized by Creep

    NASA Astrophysics Data System (ADS)

    Moore, D. E.; Rymer, M. J.; McLaughlin, R. J.; Lienkaemper, J. J.

    2011-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) is a deep-drilling program sited in the central creeping section of the San Andreas Fault (SAF) near Parkfield, California. Core was recovered from two locations at ~2.7 km vertical depth that correspond to the places where the well casing is being deformed in response to fault creep. The two creeping strands are narrow zones of fault gouge, 1.6 and 2.6 m in width, respectively, that are the products of shear-enhanced metasomatic reactions between serpentinite tectonically entrained in the fault and adjoining sedimentary wall rocks. Both gouge zones consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-rich, saponitic ± corrensitic clays, and porphyroclasts of all types are variably altered to the same Mg-rich clays as the gouge matrix. Some serpentinite porphyroclasts also contain the assemblage talc + actinolite + chlorite + andradite garnet, which is characteristic of reaction zones developed between ultramafic and crustal rocks at greenschist- to subgreenschist-facies conditions. The presence of this higher-temperature assemblage raises the possibility that the serpentinite and its alteration products may extend to significantly greater depths in the fault. Similar fault gouge has also been identified in a serpentinite outcrop near the drill site that forms part of a sheared serpentinite body mapped for several kilometers within the creeping section of the SAF. The SAFOD core thus supports the long-held view that serpentinite is implicated in the origin of creep, as does at least one other creeping fault of the San Andreas System. The Bartlett Springs Fault (BSF) is a right-lateral strike-slip fault located north of San Francisco, California. Its slip rate currently is estimated to be 6 +/- 2 mm/yr, and along a segment that crosses Lake Pillsbury half the surface slip rate is taken up by creep. An exposure of this fault segment near Lake Pillsbury consists of

  15. The San Andreas Fault: A state of stress analysis in central and northern California

    NASA Astrophysics Data System (ADS)

    Provost, Ann-Sophie

    The San Andreas Fault system is a network of faults extending from the Gulf of California to the Mendocino Triple Junction that accommodates the motion between the North American and Pacific tectonic plates. The faults' types, slip rates and distributions of seismicity varies from south to north; the question addressed by this dissertation is whether or not the mechanical behavior of this plate boundary varies as well. We used suites of fault plane solutions of earthquakes occurring in central and northern California, and inverted them for the best stress tensors. We obtained a map of stress orientations close to and far away from the major strands of the San Andreas Fault system in these areas. In the creeping zone on the central San Andreas the maximum horizontal compression, S H, is oriented almost perpendicular to the fault trend far away from it and as close as 2 km from it, whereas in the fault zone itself SH lies at a smaller angle to the fault (˜50°). In northern California there is no clear difference between on-fault and off-fault orientations and SH orientations are on average at 55° from the trend of major faults. The Bay Area shows an intermediate behavior between the two just mentioned. This difference in the orientation of SH from central to northern California suggest a change in the mechanical behavior of the plate boundary between these two regions. This situation could be related to the "young and multiple stranded" SAF system in northern California compared to the "old" SAF in central California where much more slip has accumulated on this one fault strand. Using the same data we investigated possible temporal variations in the orientation of SH before and after the occurrence of a major earthquake. Such variations could be related to the stress release produced by the mainshock. For the four events studied, 1986 Mt. Lewis, 1984 Morgan Hill, 1979 Coyote Lake, and 1989 Loma Prieta earthquakes, a rotation of SH to an orientation more normal to

  16. Styles of deformation in zones of oblique convergence: An example from the Mecca Hills, southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Damte, Alula Bereded

    The Mecca Hills area, located along the Coachella Valley segment of the San Andreas fault was characterized by a period of basin formation and sediment accumulation between ˜2.3 Ma and 0.8 Ma. Transpression and basin inversion in the last 700 ka, which resulted from an 8sp° angular difference between the orientation of the Mecca Hills segment of the San Andreas fault and the Pacific-North American plate motion vector, is accommodated by two end member and contrasting styles of deformation. The Mecca anticline, Mecca syncline, and numerous small scale folds along the Painted Canyon and San Andreas faults, in the Painted Canyon domain, are on average oriented 30sp° counter-clockwise from the San Andreas fault, typical of distributed style of deformation. On the other hand, the Skeleton Canyon syncline, Chuckawalla syncline and Skeleton Canyon reverse/thrust fault, in Skeleton Canyon domain, have formed parallel to the San Andreas fault, in partitioned style of deformation. Gravity modeling in the Mecca Hills area shows that the morphology of the basement surface follows large scale structures in the overlying sedimentary units, indicating that part of the basement and the overlying sedimentary unit deformed as one. However, it is postulated that no more than the upper 3-4 km of the basement has been shortened during transpression based on a volume balance calculation in laterally confined deformation. In the absence of shallow level detachment, basement involved deformation in the Painted Canyon domain is accommodated by distributed style of deformation. The intensely deformed, silt-dominated Box Canyon sub-member of the upper Palm Spring Formation provides the mechanically weak layer that is required to partition oblique strain into its respective components in the Skeleton Canyon domain. Therefore, local anisotropy, expressed as mechanical layering between competent and incompetent units, has been found to be sufficient to produce contrasting styles of

  17. Neogene contraction between the San Andreas fault and the Santa Clara Valley, San Francisco Bay region, California

    USGS Publications Warehouse

    McLaughlin, R.J.; Langenheim, V.E.; Schmidt, K.M.; Jachens, R.C.; Stanley, R.G.; Jayko, A.S.; McDougall, K.A.; Tinsley, J.C.; Valin, Z.C.

    1999-01-01

    In the southern San Francisco Bay region of California, oblique dextral reverse faults that verge northeastward from the San Andreas fault experienced triggered slip during the 1989 M7.1 Loma Prieta earthquake. The role of these range-front thrusts in the evolution of the San Andreas fault system and the future seismic hazard that they may pose to the urban Santa Clara Valley are poorly understood. Based on recent geologic mapping and geophysical investigations, we propose that the range-front thrust system evolved in conjunction with development of the San Andreas fault system. In the early Miocene, the region was dominated by a system of northwestwardly propagating, basin-bounding, transtensional faults. Beginning as early as middle Miocene time, however, the transtensional faulting was superseded by transpressional NE-stepping thrust and reverse faults of the range-front thrust system. Age constraints on the thrust faults indicate that the locus of contraction has focused on the Monte Vista, Shannon, and Berrocal faults since about 4.8 Ma. Fault slip and fold reconstructions suggest that crustal shortening between the San Andreas fault and the Santa Clara Valley within this time frame is ~21%, amounting to as much as 3.2 km at a rate of 0.6 mm/yr. Rates probably have not remained constant; average rates appear to have been much lower in the past few 100 ka. The distribution of coseismic surface contraction during the Loma Prieta earthquake, active seismicity, late Pleistocene to Holocene fluvial terrace warping, and geodetic data further suggest that the active range-front thrust system includes blind thrusts. Critical unresolved issues include information on the near-surface locations of buried thrusts, the timing of recent thrust earthquake events, and their recurrence in relation to earthquakes on the San Andreas fault.

  18. Tidal triggering of earthquakes suggests poroelastic behavior on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Delorey, Andrew A.; van der Elst, Nicholas J.; Johnson, Paul A.

    2017-02-01

    Tidal triggering of earthquakes is hypothesized to provide quantitative information regarding the fault's stress state, poroelastic properties, and may be significant for our understanding of seismic hazard. To date, studies of regional or global earthquake catalogs have had only modest successes in identifying tidal triggering. We posit that the smallest events that may provide additional evidence of triggering go unidentified and thus we developed a technique to improve the identification of very small magnitude events. We identify events applying a method known as inter-station seismic coherence where we prioritize detection and discrimination over characterization. Here we show tidal triggering of earthquakes on the San Andreas Fault. We find the complex interaction of semi-diurnal and fortnightly tidal periods exposes both stress threshold and critical state behavior. Our findings reveal earthquake nucleation processes and pore pressure conditions - properties of faults that are difficult to measure, yet extremely important for characterizing earthquake physics and seismic hazards.

  19. Tidal triggering of earthquakes suggests poroelastic behavior on the San Andreas Fault

    SciTech Connect

    Delorey, Andrew A.; van der Elst, Nicholas J.; Johnson, Paul Allan

    2016-12-28

    Tidal triggering of earthquakes is hypothesized to provide quantitative information regarding the fault's stress state, poroelastic properties, and may be significant for our understanding of seismic hazard. To date, studies of regional or global earthquake catalogs have had only modest successes in identifying tidal triggering. We posit that the smallest events that may provide additional evidence of triggering go unidentified and thus we developed a technique to improve the identification of very small magnitude events. We identify events applying a method known as inter-station seismic coherence where we prioritize detection and discrimination over characterization. Here we show tidal triggering of earthquakes on the San Andreas Fault. We find the complex interaction of semi-diurnal and fortnightly tidal periods exposes both stress threshold and critical state behavior. Lastly, our findings reveal earthquake nucleation processes and pore pressure conditions – properties of faults that are difficult to measure, yet extremely important for characterizing earthquake physics and seismic hazards.

  20. Christian Andreas Doppler: A legendary man inspired by the dazzling light of the stars

    PubMed Central

    Katsi, V; Felekos, I; Kallikazaros, I

    2013-01-01

    Christian Andreas Doppler is renowned primarily for his revolutionary theory of the Doppler effect, which has deeply influenced many areas of modern science and technology, including medicine. His work has laid the foundations for modern ultrasonography and his ideas are still inspiring discoveries more than a hundred years after his death. Doppler may well earn the title of Homo Universalis for his broad knowledge of physics, mathematics and astronomy and most of all for his indefatigable investigations for new ideas and his ingenious mind. According to Bolzano: “It is hard to believe how fruitful a genius Austria has in this man”. His legacy of scientific achievement have seen Doppler honoured in the later years on coinage and money, names of streets, educational institutions, rock groups, even of a lunar crater; while the ultimate tribute to his work is the countless references to the homonymous medical eponym. PMID:24376313

  1. Constraining deformation at the lithosphere-asthenosphere boundary beneath the San Andreas fault with Sp phases

    NASA Astrophysics Data System (ADS)

    Fischer, K. M.; Ford, H. A.; Lekic, V.

    2013-12-01

    The geometry of deformation in the deep mantle lithosphere beneath strike-slip plate boundaries has been enigmatic, with models ranging from localized shear zones that are deep extensions of individual crustal faults to broad zones of diffuse, distributed shear with widths of hundreds of kilometers. Using seismic phases that convert from shear to compressional motion (Sp) at the base of the lithosphere beneath California, we find evidence for strike-slip deformation in the deepest mantle lithosphere beneath the central San Andreas fault that occurs over a horizontal width of 50 km or less. This study is based on over 135,000 Sp receiver functions from 730 seismic stations, including the Northern and Southern California Seismic Networks and the NSF EarthScope Transportable and Flexible Arrays. Individual Sp receiver functions were calculated using an extended-time multi-taper method and were migrated and stacked according to their three-dimensional conversion point locations using a model for crust (Lowry and Pérez-Gussinyé, 2011) and mantle (Obrebski et al., 2010 and 2011) velocity structure beneath each station and a spline-function representation of the Sp Fresnel zone. Sp conversion points at lithosphere-asthenosphere boundary depths are very dense on both sides of the San Andreas fault, and we interpreted the Sp common conversion point stack only at those nodes with information from more than 300 receiver functions. To the east of the plate boundary, a strong coherent Sp phase, indicative of a decrease in shear-wave velocity with depth, is present in the depth range where tomographic studies image the transition from high velocity lithosphere to low velocity asthenosphere. This phase, interpreted as the seismological lithosphere-asthenosphere boundary, has systematically lower amplitudes on the western side of the plate boundary, indicating that the drop in shear velocity from lithosphere to asthenosphere is either smaller or is distributed over a larger

  2. Annual modulation of seismicity along the San Andreas Fault near Parkfield, CA

    USGS Publications Warehouse

    Christiansen, L.B.; Hurwitz, S.; Ingebritsen, S.E.

    2007-01-01

    We analyze seismic data from the San Andreas Fault (SAF) near Parkfield, California, to test for annual modulation in seismicity rates. We use statistical analyses to show that seismicity is modulated with an annual period in the creeping section of the fault and a semiannual period in the locked section of the fault. Although the exact mechanism for seasonal triggering is undetermined, it appears that stresses associated with the hydrologic cycle are sufficient to fracture critically stressed rocks either through pore-pressure diffusion or crustal loading/ unloading. These results shed additional light on the state of stress along the SAF, indicating that hydrologically induced stress perturbations of ???2 kPa may be sufficient to trigger earthquakes.

  3. The California geodimeter network; measuring movement along the San Andreas Fault

    USGS Publications Warehouse

    Savage, J.C.

    1974-01-01

    Following the great California earthquake of 1906 H. F. Reid, a contemporary seismologist, proposed the elastic rebound theory which in effect says that earthquake potential arises from the accumulation of elastic strain within the Earth's crust, just as the stretching of a rubberband creates the potential for violent rebound upon rupture. A direct manifestation of this crustal strain accumulation is the change in distance between adjacent points along opposite sides of a fault. In order to measure the rate at which strain is accumulating along California's San Andreas fault, a netwrok of precise survey lines which criss-cross the fault along its entire lenght in the State is periodically resurveyed with very accurate electro-opitcal distance measuring devices called geodimeters. 

  4. Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Shelly, David R.; Hardebeck, Jeanne L.

    2010-07-01

    We precisely locate 88 tremor families along the central San Andreas Fault using a 3D velocity model and numerous P and S wave arrival times estimated from seismogram stacks of up to 400 events per tremor family. Maximum tremor amplitudes vary along the fault by at least a factor of 7, with by far the strongest sources along a 25 km section of the fault southeast of Parkfield. We also identify many weaker tremor families, which have largely escaped prior detection. Together, these sources extend 150 km along the fault, beneath creeping, transitional, and locked sections of the upper crustal fault. Depths are mostly between 18 and 28 km, in the lower crust. Epicenters are concentrated within 3 km of the surface trace, implying a nearly vertical fault. A prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6.0 Parkfield earthquake.

  5. Variations in strength and slip rate along the san andreas fault system.

    PubMed

    Jones, C H; Wesnousky, S G

    1992-04-03

    Convergence across the San Andreas fault (SAF) system is partitioned between strike-slip motion on the vertical SAF and oblique-slip motion on parallel dip-slip faults, as illustrated by the recent magnitude M(s) = 6.0 Palm Springs, M(s) = 6.7 Coalinga, and M(s) = 7.1 Loma Prieta earthquakes. If the partitioning of slip minimizes the work done against friction, the direction of slip during these recent earthquakes depends primarily on fault dip and indicates that the normal stress coefficient and frictional coefficient (micro) vary among the faults. Additionally, accounting for the active dip-slip faults reduces estimates of fault slip rates along the vertical trace of the SAF by about 50 percent in the Loma Prieta and 100 percent in the North Palm Springs segments.

  6. San Andreas fault earthquake chronology and Lake Cahuilla history at Coachella, California

    USGS Publications Warehouse

    Philibosian, B.; Fumal, T.; Weldon, R.

    2011-01-01

    The southernmost ~100 km of the San Andreas fault has not ruptured historically. It is imperative to determine its rupture history to better predict its future behavior. This paleoseismic investigation in Coachella, California, establishes a chronology of at least five and up to seven major earthquakes during the past ~1100 yr. This chronology yields a range of average recurrence intervals between 116 and 221 yr, depending on assumptions, with a best-estimate average recurrence interval of 180 yr. The most recent earthquake occurred c.1690, more than 300 yr ago, suggesting that this stretch of the fault has accumulated a large amount of tectonic stress and is likely to rupture in the near future, assuming the fault follows a stress renewal model. This study also establishes the timing of the past 5-6 highstands of ancient Lake Cahuilla since A.D. 800.We found that earthquakes do not tend to occur at any particular stage in the lake cycle.

  7. Andreas Vesalius as a renaissance innovative neuroanatomist: his 5th centenary of birth.

    PubMed

    Gomes, Marleide da Mota; Moscovici, Mauricio; Engelhardt, Eliasz

    2015-02-01

    Andreas Vesalius (1514-1564) is considered the Father of Modern Anatomy, and an authentic representative of the Renaissance. His studies, founded on dissection of human bodies, differed from Galeno, who based his work on dissection of animals, constituted a notable scientific advance. Putting together science and art, Vesalius associated himself to artists of the Renaissance, and valued the images of the human body in his superb work De Humani Corporis Fabrica.This paper aims to honor this extraordinary European Renaissance physician and anatomist, who used aesthetic appeal to bind text and illustration, science and art. His achievements are highlighted, with an especial attention on neuroanatomy. Aspects about his personal life and career are also focused.

  8. Steep-dip seismic imaging of the shallow San Andreas Fault near Parkfield

    USGS Publications Warehouse

    Hole, J.A.; Catchings, R.D.; St. Clair, K.C.; Rymer, M.J.; Okaya, D.A.; Carney, B.J.

    2001-01-01

    Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70° to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.

  9. Johann Andreas Cramer and Chemical Mineral Assay in the Eighteenth Century.

    PubMed

    Bortolotto, Andréa

    2015-01-01

    Although little studied now, the work of Johann Andreas Cramer (1710-1777) on mineralogy and metallurgy was much appreciated by his peers and influenced the development those fields throughout the eighteenth century. Well versed in the theoretical and practical problems of analysing and grouping minerals, Cramer sought to solve them by formulating a new, accurate system for identifying and classifying metals. He also developed faster and less expensive metal extraction methods than those previously available. This paper traces the chemical ideas that underpinned Cramer's novel methods, including the theories of Hermann Boerhaave and Georg Ernst Stahl, and shows where Cramer both followed and departed from these authorities in his own influential Elementa Artis Docimasticae (1739). In the process, I seek to map Cramer's scholarly network in order to contribute to a more thorough understanding of the communication of chemical ideas and procedures in eighteenth-century Europe.

  10. Andreas Vesalius' 500th Anniversary: Initiation of the Superficial Facial System and Superficial Musculoaponeurotic System Concepts.

    PubMed

    Brinkman, Romy J; Hage, J Joris

    2016-02-01

    Because of their relevance for liposuction and rhytidectomies, respectively, the superficial fascial system (SFS) and superficial musculoaponeurotic system (SMAS) have been thoroughly studied over the past decennia. Although it is well known that the SMAS concept was introduced by Tessier in 1974, it remains unknown who first properly described the stratum membranosum of the SFS. In light of the 500th birthday of Andreas Vesalius (1515-1564), we searched his 1543 masterwork De Humani Corporis Fabrica Libri Septem and related work for references to these structures. We found ample reference to both structures as the membrana carnosa (or fleshy membrane) in his works and concluded that Vesalius recognized the extension, nature, and functions of the stratum membranosum of the SFS, as well as its more musculous differentiation as the SMAS in the head and neck area, and the dartos in the perineogenital area. In doing so, Vesalius recorded most details of the SFS and SMAS concepts avant la lettre.

  11. Ruptures of the San Andreas fault system in San Gorgonio Pass

    NASA Astrophysics Data System (ADS)

    Yule, D.; Sieh, K. E.

    2010-12-01

    Fault behavior models for the San Andreas fault system in San Gorgonio Pass hinge upon contrasting interpretations of the structural complexity and diffuse seismicity in the Pass region. One model maintains that the fault system can rupture through the Pass in ~ M 7.8 earthquakes that extend from the Salton Sea to the Mojave Desert. Another model argues that the structural complexity here arrests San Andreas ruptures as they approach from either side of the Pass and limits their size to ~ M 7.5. One way to test these models is to examine the paleoseismic record of active faults in the Pass. Work at the Burro Flats site, located where the San Bernardino strand feeds into San Gorgonio Pass from the north, reveals evidence for at least nine earthquakes in the last 2000 yrs. The average earthquake recurrence is about 200 yrs with the maximum and minimum intervals between earthquakes equal to about 550 and 80 yrs, respectively. The average recurrence is considered to be a maximum value because a hiatus in sedimentation during the Early Middle Ages may ‘hide’ one or more event during this time period. The maximum recurrence interval of 550 yrs is likely an overestimate owing to the large errors in the timing of one event ~1300 yrs ago. In general, the Burro Flats event record and average recurrence is very similar to those at sites in the San Bernardino and Coachella Valley regions. The most recent rupture at Burro Flats cuts strata that contain European-introduced pollen and is interpreted to record the southeastern extent of the 1812 Wrightwood earthquake, a possible example of a ‘Pass-as-a-barrier’, moderate-sized event. The timing of pre-1812 events at Burro Flats correlate with the timing of San Andreas events in the San Bernardino and Coachella Valley regions, possible examples of through going, larger-sized earthquakes. Work at the Cabezon site, located on a thrust segment of the San Gorgonio Pass fault zone, shows evidence for two ruptures since ~ AD 1300

  12. Testing geomorphology-derived rupture histories against the paleoseismic record of the southern San Andreas fault

    USGS Publications Warehouse

    Scharer, Katherine M.; Weldon, Ray; Bemis, Sean

    2016-01-01

    Evidence for the 340-km-long Fort Tejon earthquake of 1857 is found at each of the high-resolution paleoseismic sites on the southern San Andreas Fault. Using trenching data from these sites, we find that the assemblage of dated paleoearthquakes recurs quasi-periodically (coefficient of variation, COV, of 0.6, Biasi, 2013) and requires ~80% of ruptures were shorter than the 1857 rupture with an average of Mw7.5. In contrast, paleorupture lengths reconstructed from preserved geomorphic offsets extracted from lidar are longer and have repeating displacements that are quite regular (COV=0.2; Zielke et al., 2015). Direct comparison shows that paleoruptures determined from geomorphic offset populations cannot be reconciled with dated paleoearthquakes. Our study concludes that the 1857 rupture was larger than average, average displacements must be < 5 m, and suggests that fault geometry may play a role in fault behavior.

  13. Christian Andreas Doppler: A legendary man inspired by the dazzling light of the stars.

    PubMed

    Katsi, V; Felekos, I; Kallikazaros, I

    2013-04-01

    Christian Andreas Doppler is renowned primarily for his revolutionary theory of the Doppler effect, which has deeply influenced many areas of modern science and technology, including medicine. His work has laid the foundations for modern ultrasonography and his ideas are still inspiring discoveries more than a hundred years after his death. Doppler may well earn the title of Homo Universalis for his broad knowledge of physics, mathematics and astronomy and most of all for his indefatigable investigations for new ideas and his ingenious mind. According to Bolzano: "It is hard to believe how fruitful a genius Austria has in this man". His legacy of scientific achievement have seen Doppler honoured in the later years on coinage and money, names of streets, educational institutions, rock groups, even of a lunar crater; while the ultimate tribute to his work is the countless references to the homonymous medical eponym.

  14. Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault

    USGS Publications Warehouse

    Shelly, David R.; Hardebeck, Jeanne L.

    2010-01-01

    We precisely locate 88 tremor families along the central San Andreas Fault using a 3D velocity model and numerous P and S wave arrival times estimated from seismogram stacks of up to 400 events per tremor family. Maximum tremor amplitudes vary along the fault by at least a factor of 7, with by far the strongest sources along a 25 km section of the fault southeast of Parkfield. We also identify many weaker tremor families, which have largely escaped prior detection. Together, these sources extend 150 km along the fault, beneath creeping, transitional, and locked sections of the upper crustal fault. Depths are mostly between 18 and 28 km, in the lower crust. Epicenters are concentrated within 3 km of the surface trace, implying a nearly vertical fault. A prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6.0 Parkfield earthquake.

  15. Fault coupling and potential for earthquakes on the creeping section of the Central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Maurer, J.; Johnson, K. M.; Segall, P.

    2013-12-01

    The San Andreas Fault (SAF) has been known historically to produce large earthquakes in northern California along the northern coast section and in southern California along the Carrizo and Mojave sections. However, it is currently unclear whether the 150-km long central creeping section between these two sections could also rupture in large earthquakes. This section of the fault is known to be creeping at the surface, and in some areas may creep at nearly the long-term slip rate. We invert Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data to estimate the degree of locking on the central San Andreas Fault (CSAF) that place bounds on potential moment release. We use an elastic block model to compute present-day creep rates on the CSAF and compare these rates to seismicity patterns and observed surface creep rates. We find the inferred moment accumulation rate on the fault is highly dependent on the long-term fault slip rate, which is poorly constrained along the CSAF. The inferred potency accumulation rates on the creeping section, defined to be the seismic moment rate divided by shear modulus, range from 3.28x10^4 to 5.85x10^7 m^3/yr. The equivalent 150-year recurring earthquake magnitude is Mw = 5.5 - 7.2 for a long-term slip rate of 26 mm/yr and Mw = 7.3-7.65 for a long-term slip rate of 34 mm/yr. Although it is unclear how much of the accumulating moment would be released in future earthquakes, comparisons of slip distributions with seismicity indicate a possible locked patch between 10 and 20 km depth on the CSAF that could potentially rupture with Mw=6.5.

  16. Fault coupling and potential for earthquakes on the creeping section of the Central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Maurer, Jeremy Lee

    The San Andreas Fault (SAF) has been known historically to produce large earthquakes in northern California along the northern coast section and in southern California along the Carrizo and Mojave sections. However, it is currently unclear whether the 150-km long central creeping section between these two sections could also rupture in large earthquakes. This section of the fault is known to be creeping at the surface, and in some areas may creep at nearly the long-term slip rate. We invert Global Positioning System (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data to estimate the degree of locking on the central San Andreas Fault (CSAF) that place bounds on potential moment release. We use an elastic block model to compute present-day creep rates on the CSAF and compare these rates to seismicity patterns and observed surface creep rates. We find the inferred moment accumulation rate on the fault is highly dependent on the long-term fault slip rate, which is poorly constrained along the CSAF. The inferred potency accumulation rates on the creeping section, defined to be the seismic moment rate divided by shear modulus, range from 3.28x104 to 5.85x107m 3/yr. The equivalent 150-year recurring earthquake magnitude is M w = 5.5 - 7.2 for a long-term slip rate of 26 mm/yr and Mw = 7.3-7.65 for a long-term slip rate of 34 mm/yr. Although it is unclear how much of the accumulating moment would be released in future earthquakes, comparisons of slip distributions with seismicity indicate a possible locked patch between 10 and 20 km depth on the CSAF that could potentially rupture with M w=6.5.

  17. Fault Creep along the Southern San Andreas from Interferometric Synthetic Aperture Radar, Permanent Scatterers, and Stacking

    NASA Technical Reports Server (NTRS)

    Lyons, Suzanne; Sandwell, David

    2003-01-01

    Interferometric synthetic aperture radar (InSAR) provides a practical means of mapping creep along major strike-slip faults. The small amplitude of the creep signal (less than 10 mm/yr), combined with its short wavelength, makes it difficult to extract from long time span interferograms, especially in agricultural or heavily vegetated areas. We utilize two approaches to extract the fault creep signal from 37 ERS SAR images along the southem San Andreas Fault. First, amplitude stacking is utilized to identify permanent scatterers, which are then used to weight the interferogram prior to spatial filtering. This weighting improves correlation and also provides a mask for poorly correlated areas. Second, the unwrapped phase is stacked to reduce tropospheric and other short-wavelength noise. This combined processing enables us to recover the near-field (approximately 200 m) slip signal across the fault due to shallow creep. Displacement maps fiom 60 interferograms reveal a diffuse secular strain buildup, punctuated by localized interseismic creep of 4-6 mm/yr line of sight (LOS, 12-18 mm/yr horizontal). With the exception of Durmid Hill, this entire segment of the southern San Andreas experienced right-lateral triggered slip of up to 10 cm during the 3.5-year period spanning the 1992 Landers earthquake. The deformation change following the 1999 Hector Mine earthquake was much smaller (4 cm) and broader than for the Landers event. Profiles across the fault during the interseismic phase show peak-to-trough amplitude ranging from 15 to 25 mm/yr (horizontal component) and the minimum misfit models show a range of creeping/locking depth values that fit the data.

  18. Geodetic Measurement of Deformation East of the San Andreas Fault in Central California

    NASA Technical Reports Server (NTRS)

    Sauber, Jeanne M.; Lisowski, Michael; Solomon, Sean C.

    1988-01-01

    Triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas fault have been used to calculate shear strain rates in the Diablo Range and to estimate the slip rate along the Calaveras and Paicines faults in Central California. Within the Diablo Range the average shear strain rate was determined for the time period between 1962 and 1982 to be 0.15 + or - 0.08 microrad/yr, with the orientation of the most compressive strain at N 16 deg E + or - 14 deg. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E. It is inferred that the measured strain is due to compression across the folds of this area: the average shear straining corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. From an examination of wellbore breakout orientations and the azimuths of P-axes from earthquake focal mechanisms the inferred orientation of maximum compressive stress was found to be similar to the direction of maximum compressive strain implied by the trend of local fold structures. Results do not support the hypothesis of uniform fault-normal compression within the Coast Ranges. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10 to 12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate of the Paicines fault decreases to 4 mm/yr near Bitter.

  19. Low resistivity and permeability in actively deforming shear zones on the San Andreas Fault at SAFOD

    USGS Publications Warehouse

    Morrow, Carolyn A.; Lockner, David A.; Hickman, Stephen H.

    2015-01-01

    The San Andreas Fault Observatory at Depth (SAFOD) scientific drillhole near Parkfield, California crosses the San Andreas Fault at a depth of 2.7 km. Downhole measurements and analysis of core retrieved from Phase 3 drilling reveal two narrow, actively deforming zones of smectite-clay gouge within a roughly 200 m-wide fault damage zone of sandstones, siltstones and mudstones. Here we report electrical resistivity and permeability measurements on core samples from all of these structural units at effective confining pressures up to 120 MPa. Electrical resistivity (~10 ohm-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were one to two orders of magnitude lower than the surrounding damage zone material, consistent with broader-scale observations from the downhole resistivity and seismic velocity logs. The higher porosity of the clay gouge, 2 to 8 times greater than that in the damage zone rocks, along with surface conduction were the principal factors contributing to the observed low resistivities. The high percentage of fine-grained clay in the deforming zones also greatly reduced permeability to values low enough to create a barrier to fluid flow across the fault. Together, resistivity and permeability data can be used to assess the hydrogeologic characteristics of the fault, key to understanding fault structure and strength. The low resistivities and strength measurements of the SAFOD core are consistent with observations of low resistivity clays that are often found in the principal slip zones of other active faults making resistivity logs a valuable tool for identifying these zones.

  20. Holocene geologic slip rate for the Banning strand of the southern San Andreas Fault, southern California

    USGS Publications Warehouse

    Gold, Peter O.; Behr, Whitney M.; Rood, Dylan; Sharp, Warren D.; Rockwell, Thomas; Kendrick, Katherine J.; Salin, Aaron

    2015-01-01

    Northwest directed slip from the southern San Andreas Fault is transferred to the Mission Creek, Banning, and Garnet Hill fault strands in the northwestern Coachella Valley. How slip is partitioned between these three faults is critical to southern California seismic hazard estimates but is poorly understood. In this paper, we report the first slip rate measured for the Banning fault strand. We constrain the depositional age of an alluvial fan offset 25 ± 5 m from its source by the Banning strand to between 5.1 ± 0.4 ka (95% confidence interval (CI)) and 6.4 + 3.7/−2.1 ka (95% CI) using U-series dating of pedogenic carbonate clast coatings and 10Be cosmogenic nuclide exposure dating of surface clasts. We calculate a Holocene geologic slip rate for the Banning strand of 3.9 + 2.3/−1.6 mm/yr (median, 95% CI) to 4.9 + 1.0/−0.9 mm/yr (median, 95% CI). This rate represents only 25–35% of the total slip accommodated by this section of the southern San Andreas Fault, suggesting a model in which slip is less concentrated on the Banning strand than previously thought. In rejecting the possibility that the Banning strand is the dominant structure, our results highlight an even greater need for slip rate and paleoseismic measurements along faults in the northwestern Coachella Valley in order to test the validity of current earthquake hazard models. In addition, our comparison of ages measured with U-series and 10Be exposure dating demonstrates the importance of using multiple geochronometers when estimating the depositional age of alluvial landforms.

  1. Fault Creep along the Southern San Andreas from Interferometric Synthetic Aperture Radar, Permanent Scatterers, and Stacking

    NASA Technical Reports Server (NTRS)

    Lyons, Suzanne; Sandwell, David

    2003-01-01

    Interferometric synthetic aperture radar (InSAR) provides a practical means of mapping creep along major strike-slip faults. The small amplitude of the creep signal (less than 10 mm/yr), combined with its short wavelength, makes it difficult to extract from long time span interferograms, especially in agricultural or heavily vegetated areas. We utilize two approaches to extract the fault creep signal from 37 ERS SAR images along the southem San Andreas Fault. First, amplitude stacking is utilized to identify permanent scatterers, which are then used to weight the interferogram prior to spatial filtering. This weighting improves correlation and also provides a mask for poorly correlated areas. Second, the unwrapped phase is stacked to reduce tropospheric and other short-wavelength noise. This combined processing enables us to recover the near-field (approximately 200 m) slip signal across the fault due to shallow creep. Displacement maps fiom 60 interferograms reveal a diffuse secular strain buildup, punctuated by localized interseismic creep of 4-6 mm/yr line of sight (LOS, 12-18 mm/yr horizontal). With the exception of Durmid Hill, this entire segment of the southern San Andreas experienced right-lateral triggered slip of up to 10 cm during the 3.5-year period spanning the 1992 Landers earthquake. The deformation change following the 1999 Hector Mine earthquake was much smaller (4 cm) and broader than for the Landers event. Profiles across the fault during the interseismic phase show peak-to-trough amplitude ranging from 15 to 25 mm/yr (horizontal component) and the minimum misfit models show a range of creeping/locking depth values that fit the data.

  2. Multi-scale InSAR analysis of aseismic creep across the San Andreas, Calevaras,and Hayward Fault systems

    NASA Astrophysics Data System (ADS)

    Agram, P. S.; Simons, M.

    2011-12-01

    We apply the Multi-scale Interferometric Time-series (MInTS) technique, developed at Caltech,to study spatial variations in aseismic creep across the San Andreas, Calaveras and Hayward Faultsystems in Central California.Interferometric Synthetic Aperture Radar (InSAR) Time-series methods estimate the spatio-temporal evolution of surface deformation using multiple SAR interferograms. Traditional time-series analysis techniques like persistent scatterers and short baseline methods assume the statistical independence of InSAR phase measurements over space and time when estimating deformation. However, existing atmospheric phase screen models clearly show that noise in InSAR phase observations is correlated over the spatial domain. MInTS is an approach designed to exploit the correlation of phase observations over space to significantly improve the signal-to-noise ratio in the estimated deformation time-series compared to the traditional time-series InSAR techniques. The MInTS technique reduces the set of InSAR observations to a set of almost uncorrelated observations at various spatial scales using wavelets. Traditional inversion techniques can then be applied to the wavelet coefficients more effectively. Creep across the Central San Andreas Fault and the Hayward Fault has been studied previously using C-band (6 cm wavelength) ERS data, but detailed analysis of the transition zone between the San Andreas and Hayward Faults was not possible due to severe decorrelation. Improved coherence at L-band (24 cm wavelength) significantly improves the spatial coverage of the estimated deformation signal in our ALOS PALSAR data set. We analyze 450 ALOS PALSAR interferograms processed using 175 SAR images acquired between Dec 2006 and Dec 2010 that cover the area along the San Andreas Fault System from Richmond in the San Francisco Bay Area to Maricopa in the San Joaquin Valley.We invert the InSAR phase observations to estimate the constant Line-of-Sight (LOS) deformation

  3. Constraints on the stress state of the San Andreas Fault with analysis based on core and cuttings from San Andreas Fault Observatory at Depth (SAFOD) drilling phases 1 and 2

    USGS Publications Warehouse

    Tembe, S.; Lockner, D.; Wong, T.-F.

    2009-01-01

    Analysis of field data has led different investigators to conclude that the San Andreas Fault (SAF) has either anomalously low frictional sliding strength (?? 0.6). Arguments for the apparent weakness of the SAF generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone. Some models assert that weak gouge and/or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip. The present paper is composed of three parts. First, we develop generalized equations, based on and consistent with the Rice (1992) fault zone model to relate stress orientation and magnitude to depth-dependent coefficient of friction and pore pressure. Second, we present temperature-and pressure-dependent friction measurements from wet illite-rich fault gouge extracted from San Andreas Fault Observatory at Depth (SAFOD) phase 1 core samples and from weak minerals associated with the San Andreas Fault. Third, we reevaluate the state of stress on the San Andreas Fault in light of new constraints imposed by SAFOD borehole data. Pure talc (?????0.1) had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure. Other fault gouges showed a systematic increase in strength with increasing temperature and pressure. In this case, heat flow and stress orientation constraints would require elevated pore pressure and, in some cases, fault zone pore pressure in excess of vertical stress. Copyright 2009 by the American Geophysical Union.

  4. Peter Andreas Hansen and the astronomical community - a first investigation of the Hansen papers. (German Title: Peter Andreas Hansen und die astronomische Gemeinschaft - eine erste Auswertung des Hansen-Nachlasses. )

    NASA Astrophysics Data System (ADS)

    Schwarz, Oliver; Strumpf, Manfred

    The literary assets of Peter Andreas Hansen are deposited in the Staatsarchiv Hamburg, the Forschungs- und Landesbibliothek Gotha and the Thüringer Staatsarchiv Gotha. They were never systematically investigated. We present here some results of a first evaluation. It was possible to reconstruct the historical events with regard to the maintenance of the Astronomische Nachrichten and the Altona observatory in 1854. Hansen was a successful teacher for many young astronomers. His way of stimulating the evolution of astronomy followed Zach's tradition.

  5. Late Holocene slip rate of the San Andreas fault and its accommodation by creep and moderate-magnitude earthquakes at Parkfield, California

    USGS Publications Warehouse

    Toke, N.A.; Arrowsmith, J.R.; Rymer, M.J.; Landgraf, A.; Haddad, D.E.; Busch, M.; Coyan, J.; Hannah, A.

    2011-01-01

    Investigation of a right-laterally offset channel at the Miller's Field paleoseismic site yields a late Holocene slip rate of 26.2 +6.4/-4.3 mm/yr (1??) for the main trace of the San Andreas fault at Park-field, California. This is the first well-documented geologic slip rate between the Carrizo and creeping sections of the San Andreas fault. This rate is lower than Holocene measurements along the Carrizo Plain and rates implied by far-field geodetic measurements (~35 mm/yr). However, the rate is consistent with historical slip rates, measured to the northwest, along the creeping section of the San Andreas fault (<30 mm/yr). The paleoseismic exposures at the Miller's Field site reveal a pervasive fabric of clay shear bands, oriented clockwise oblique to the San Andreas fault strike and extending into the upper-most stratigraphy. This fabric is consistent with dextral aseismic creep and observations of surface slip from the 28 September 2004 M6 Parkfield earthquake. Together, this slip rate and deformation fabric suggest that the historically observed San Andreas fault slip behavior along the Parkfield section has persisted for at least a millennium, and that significant slip is accommodated by structures in a zone beyond the main San Andreas fault trace. ?? 2011 Geological Society of America.

  6. Detection of a locked zone at depth on the Parkfield, California, segment of the San Andreas fault ( USA).

    USGS Publications Warehouse

    Harris, R.A.; Segall, P.

    1987-01-01

    The Parkfield, California, segment of the San Andreas fault is transitional in character between the creeping segment of the fault to the NW and the locked Carrizo Plain segment to the SE. The rate of shallow fault slip decreases from 25-30 mm/yr NW of the epicenter of the 1966 Parkfield earthquake to zero at the SE end of the 1966 rupture zone. Data from a network of trilateration lines spanning the San Andreas fault near Parkfield and extending to the Pacific coast near San Luis Obispo shed light on the rate of fault slip at depth since the 1966 earthquake. In this study, average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the Parkfield fault segment. -from Authors

  7. Climate-modulated channel incision and rupture history of the San Andreas Fault in the Carrizo Plain.

    PubMed

    Grant Ludwig, Lisa; Akçiz, Sinan O; Noriega, Gabriela R; Zielke, Olaf; Arrowsmith, J Ramón

    2010-02-26

    The spatial and temporal distribution of fault slip is a critical parameter in earthquake source models. Previous geomorphic and geologic studies of channel offset along the Carrizo section of the south central San Andreas Fault assumed that channels form more frequently than earthquakes occur and suggested that repeated large-slip earthquakes similar to the 1857 Fort Tejon earthquake illustrate typical fault behavior. We found that offset channels in the Carrizo Plain incised less frequently than they were offset by earthquakes. Channels have been offset by successive earthquakes with variable slip since ~1400. This nonuniform slip history reveals a more complex rupture history than previously assumed for the structurally simplest section of the San Andreas Fault.

  8. Investigating the creeping section of the San Andreas Fault using ALOS PALSAR interferometry

    NASA Astrophysics Data System (ADS)

    Agram, P. S.; Wortham, C.; Zebker, H. A.

    2010-12-01

    In recent years, time-series InSAR techniques have been used to study the temporal characteristics of various geophysical phenomena that produce surface deformation including earthquakes and magma migration in volcanoes. Conventional InSAR and time-series InSAR techniques have also been successfully used to study aseismic creep across faults in urban areas like the Northern Hayward Fault in California [1-3]. However, application of these methods to studying the time-dependent creep across the Central San Andreas Fault using C-band ERS and Envisat radar satellites has resulted in limited success. While these techniques estimate the average long-term far-field deformation rates reliably, creep measurement close to the fault (< 3-4 Km) is virtually impossible due to heavy decorrelation at C-band (6cm wavelength). Shanker and Zebker (2009) [4] used the Persistent Scatterer (PS) time-series InSAR technique to estimate a time-dependent non-uniform creep signal across a section of the creeping segment of the San Andreas Fault. However, the identified PS network was spatially very sparse (1 per sq. km) to study temporal characteristics of deformation of areas close to the fault. In this work, we use L-band (24cm wavelength) SAR data from the PALSAR instrument on-board the ALOS satellite, launched by Japanese Aerospace Exploration Agency (JAXA) in 2006, to study the temporal characteristics of creep across the Central San Andreas Fault. The longer wavelength at L-band improves observed correlation over the entire scene which significantly increased the ground area coverage of estimated deformation in each interferogram but at the cost of decreased sensitivity of interferometric phase to surface deformation. However, noise levels in our deformation estimates can be decreased by combining information from multiple SAR acquisitions using time-series InSAR techniques. We analyze 13 SAR acquisitions spanning the time-period from March 2007 to Dec 2009 using the Short Baseline

  9. San Andreas Fault, California, M 5.5 or greater Earthquakes 1800-2000

    NASA Astrophysics Data System (ADS)

    Toppozada, T.; Branum, D.; Reichle, M.; Hallstrom, C.

    2001-12-01

    The San Andreas fault has been the most significant source of major California earthquakes since 1800. From 1812 to 1906 it generated four major earthquakes of M 7.2 or greater in two pairs on two major regions of the fault. A pair of major earthquakes occurred on the Central to Southern region, where the 1857 faulting overlapped the 1812 earthquake faulting. And a pair of major earthquakes occurred on the Northern region, where the 1906 faulting overlapped the 1838 earthquake faulting. The 1812 earthquake resulted from a rupture of up to about 200 km, from the region of Cajon Pass to as far as about 50 km west of Fort Tejon (Sieh and others, 1989). This rupture is the probable source of both the destructive 1812.12.8 "San Juan Capistrano" and the 1812.12.21 "Santa Barbara Channel" earthquakes. The 1838 earthquake's damage effects throughout the Bay area, from San Francisco to Santa Clara Valley and Monterey, were unequalled by any Bay area earthquake other than the 1906 event. The mainshock's effects, and numerous strong probable aftershocks in the San Juan Bautista vicinity in the following three years, suggest 1838 faulting from San Francisco to San Juan Bautista, and M about 7.4. The 630 km length of the San Andreas fault between San Francisco and Cajon Pass ruptured in the 1838 and 1857 earthquakes, except for about 75 km between Bitterwater and San Juan Bautista. The 1840-1841 probable aftershocks of the 1838 event occurred near San Juan Bautista, and the foreshocks and aftershocks of the 1857 event occurred near Bitterwater. In the Bitterwater area, strong earthquakes continued to occur until the 1885 earthquake of M 6.5. Near Parkfield, 40 to 70 km southeast of Bitterwater, M 5.5 or greater earthquakes have occurred from the 1870s to the 1960s. In the total Bitterwater to Parkfield zone bracketing the northern end of the 1857 rupture, the seismicity and moment release has decreased steadily since 1857, and has tended to migrate southeastward with time. The

  10. Speculation on Mendocino Triple Junction Evolution: Instability and Interactions of Multiple San Andreas Fault System Strands

    NASA Astrophysics Data System (ADS)

    Wakabayashi, J.

    2006-12-01

    Instability of the Mendocino triple junction (MTJ) results from non-colinearity of the San Andreas fault system (SAFS) and the Cascadia subduction zone. How this instability drives the evolution of the triple junction depends in part on how one depicts the MTJ. The "textbook" way represents the SAFS as a single fault with N40W strike, the average strike of the northern part SAFS. This geometry predicts the opening of a gap in the MTJ region, but this conflicts with observations of focused shortening and uplift in MTJ area instead of extension. An alternative uses current local MTJ geometry. This departs from the "textbook" because the San Andreas fault (SAF) bends right from about N40W to N5W in the offshore reach between Pt. Arena and Pt. Delgada. Because this strike is more northerly than that of Cascadia, this geometry predicts shortening in the MTJ area. The N40W-N5W bend in the SAF is a releasing bend, predicting transtension in the area south of the active shortening. The multiple strands of the SAFS, including the SAF and several strands to the east of it (I will call the latter the eastern faults) may also generate complexity in the MTJ area. San Andreas-age dextral faults are not present north of the MTJ. In the northern SAFS, 230-250 km of slip associated with the eastern faults, must transfer or have transferred westward to the MTJ, otherwise there would be slip incompatibilities along the eastern faults with zero displacement at their northern tips and a large displacements to the south. Transfer of slip from the eastern faults to the MTJ is a restraining (left) slip transfer or step-over, but the observed amount of exhumation and shortening MTJ area falls short of that predicted by any model that would transfer the slip of the eastern faults in one area. The eastern faults die out northward as well-defined faults. This may be because the northern tips of the eastern faults are propagating northward, while slip transfers to the MTJ that migrates at

  11. Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San Andreas fault

    USGS Publications Warehouse

    d'Alessio, M. A.; Williams, C.F.; Burgmann, R.

    2006-01-01

    Heat flow measurements along much of the San Andreas fault (SAF) constrain the apparent coefficient of friction (??app) of the fault to 0.2 should be detectable even with the sparse existing observations, implying that ??app for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures. Copyright 2006 by the American Geophysical Union.

  12. Multi-Scale Crustal Seismic Anisotropy in the Region Surrounding the San Andreas Fault Near Parkfield, CA.

    NASA Astrophysics Data System (ADS)

    Boness, N. L.; Zoback, M. D.

    2004-12-01

    The region surrounding the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, CA is an ideal location to study the effect of crustal structure and the state of stress on seismic velocity anisotropy because the direction of maximum horizontal compression is at a high angle to the predominantly northwest-southeast structural trend. Data from the 2.2-km-deep pilot hole and upper section of the main SAFOD borehole provides a unique opportunity for studying the in-situ physical properties of the crust adjacent to the San Andreas Fault Zone. To study seismic anisotropy in the crust at multiple scales, we utilize a suite of geophysical logs from the SAFOD boreholes, in addition to earthquake data recorded on the Pilot Hole array and on the regional High Resolution Seismic Network (HRSN) operated by U.C. Berkeley. At the smallest scale, dipole sonic logs in the SAFOD boreholes indicate that the shear-wave velocity anisotropy of the rocks within a few feet of the wellbore is on the order of 3 to 10% and controlled by the tectonic stress field. An analysis of earthquake seismograms shows that ray paths through the crust adjacent to the fault exhibit fast shear wave polarizations aligned with the direction of maximum horizontal compression, in agreement with the SAFOD measurements, whereas ray paths along the San Andreas fault yield fault-parallel fast directions. The delay times of the lagging shear wave are also much larger when the waves have traveled along the fault zone indicating that structural fabric has a stronger influence on velocity anisotropy than the regional stress field. We conclude that within the San Andreas Fault Zone, the structural fabric is the dominant mechanism responsible for velocity anisotropy whereas in the surrounding crust, the direction of maximum horizontal compression is the most important controlling factor.

  13. An unknown treasure in Brugge (Bruges): the oldest portrait of Andreas Vesallius on a stained glass window.

    PubMed

    Steeno, Omer P; Deruyttere, Michel

    2008-06-01

    Four iconographic pictures of Andreas Vesalius on glass painted windows, in Rochester, Minnesota, USA; Leuven (Louvain, Belgium); Saint Paul, Minnesota, USA; and Innsbruck (Austria), were made in the period between 1943 and 1956. Recently, we have found in Brugge (Bruges) a much older portrait of Vesalius, in the form of a medallion on glass. It was painted between 1860 and 1870 by Samuel Coucke who had been commissioned by Dr. François Vanden Abeele for the decoration of his medical office.

  14. Magnitude of shear stress on the San Andreas fault: Implications of a stress measurement profile at shallow depth

    USGS Publications Warehouse

    Zoback, M.D.; Roller, J.C.

    1979-01-01

    A profile of measurements of shear stress perpendicular to the San Andreas fault near Palmdale, California, shows a marked increase in stress with distance from the fault. The pattern suggests that shear stress on the fault increases slowly with depth and reaches a value on the order of the average stress released during earthquakes. This result has important implications for both long- and short-term prediction of large earthquakes. Copyright ?? 1979 AAAS.

  15. Response of deformation patterns to reorganizations of the southern San Andreas fault system since ca. 1.5 Ma

    NASA Astrophysics Data System (ADS)

    Cooke, M. L.; Fattaruso, L.; Dorsey, R. J.; Housen, B. A.

    2015-12-01

    Between ~1.5 and 1.1 Ma, the southern San Andreas fault system underwent a major reorganization that included initiation of the San Jacinto fault and termination of slip on the extensional West Salton detachment fault. The southern San Andreas fault itself has also evolved since this time, with several shifts in activity among fault strands within San Gorgonio Pass. We use three-dimensional mechanical Boundary Element Method models to investigate the impact of these changes to the fault network on deformation patterns. A series of snapshot models of the succession of active fault geometries explore the role of fault interaction and tectonic loading in abandonment of the West Salton detachment fault, initiation of the San Jacinto fault, and shifts in activity of the San Andreas fault. Interpreted changes to uplift patterns are well matched by model results. These results support the idea that growth of the San Jacinto fault led to increased uplift rates in the San Gabriel Mountains and decreased uplift rates in the San Bernardino Mountains. Comparison of model results for vertical axis rotation to data from paleomagnetic studies reveals a good match to local rotation patterns in the Mecca Hills and Borrego Badlands. We explore the mechanical efficiency at each step in the evolution, and find an overall trend toward increased efficiency through time. Strain energy density patterns are used to identify regions of off-fault deformation and potential incipient faulting. These patterns support the notion of north-to-south propagation of the San Jacinto fault during its initiation. The results of the present-day model are compared with microseismicity focal mechanisms to provide additional insight into the patterns of off-fault deformation within the southern San Andreas fault system.

  16. Deformation Bands in the Etchegoin Formation of Central California: Implications for Stress Orientations NE of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Lindquist, P.; Newman, A. C.; Livesay, L.; Titus, S.

    2016-12-01

    The late Miocene-early Pliocene Etchegoin Formation is exposed in several large-scale structures northeast of the San Andreas fault in central California. Because these rocks were deposited while the San Andreas system was active at this latitude, any evidence of deformation within them provides a record of off-fault, plate boundary deformation. We observe well-developed deformation bands at many outcrops of the Etchegoin Formation of central California. Regionally, these structures most commonly occur in conspicuous beds of poorly cemented blue sandstone, though occasionally appear in other lithologies. In outcrop, deformation bands are expressed as individual tabular structures as well as multiple, closely-spaced bands in zones several centimeters to decimeters in width. These deformation band zones can be traceable for up to ten meters. Where markers are present, deformation bands show mm- to cm- displacements. While there are no piercing points, displacements are most commonly observed on vertical faces indicating normal motion; more rarely, strike-slip displacements are observed on the tops of outcrops in a few locales. We have measured the orientation of deformation bands at 100 sites northeast of the San Andreas fault. These sites lie in four major off-faults structures at various distances from the fault: the Parkfield syncline (1-3 km), the Sunflower Valley syncline (17 km), the Kreyenhagen Hills homocline (23 km), and the Kettleman Hills anticlines (32 km). Each site or group of sites often exhibit at least two sets of steeply dipping deformation bands. Typically, we observe a NE-striking set and a NW-striking set, with varying angles between the two. Restoration of beds to horizontal tends to increase the scatter in deformation band orientations, suggesting many are syn-structural features. Thus, their orientations can be used to infer relatively recent stress orientations in the plate boundary region adjacent to the San Andreas fault in central

  17. Detection of aseismic creep along the San Andreas fault near Parkfield, California with ERS-1 radar interferometry

    NASA Technical Reports Server (NTRS)

    Werner, Charles L.; Rosen, Paul; Hensley, Scott; Fielding, Eric; Buckley, Sean

    1997-01-01

    The differential interferometric analysis of ERS data from Parkfield (CA) observations revealed the wide area distribution of creep along the moving fault segment of the San Andreas fault over a 15 month interval. The removal of the interferometric phase related to the surface topography was carried out. The fault was clearly visible in the differential interferogram. The magnitude of the tropospheric water vapor phase distortions is greater than the signal and hinders quantitative analysis beyond order of magnitude calculations.

  18. Modeling of periodic great earthquakes on the San Andreas fault: Effects of nonlinear crustal rheology

    NASA Technical Reports Server (NTRS)

    Reches, Ze'ev; Schubert, Gerald; Anderson, Charles

    1994-01-01

    We analyze the cycle of great earthquakes along the San Andreas fault with a finite element numerical model of deformation in a crust with a nonlinear viscoelastic rheology. The viscous component of deformation has an effective viscosity that depends exponentially on the inverse absolute temperature and nonlinearity on the shear stress; the elastic deformation is linear. Crustal thickness and temperature are constrained by seismic and heat flow data for California. The models are for anti plane strain in a 25-km-thick crustal layer having a very long, vertical strike-slip fault; the crustal block extends 250 km to either side of the fault. During the earthquake cycle that lasts 160 years, a constant plate velocity v(sub p)/2 = 17.5 mm yr is applied to the base of the crust and to the vertical end of the crustal block 250 km away from the fault. The upper half of the fault is locked during the interseismic period, while its lower half slips at the constant plate velocity. The locked part of the fault is moved abruptly 2.8 m every 160 years to simulate great earthquakes. The results are sensitive to crustal rheology. Models with quartzite-like rheology display profound transient stages in the velocity, displacement, and stress fields. The predicted transient zone extends about 3-4 times the crustal thickness on each side of the fault, significantly wider than the zone of deformation in elastic models. Models with diabase-like rheology behave similarly to elastic models and exhibit no transient stages. The model predictions are compared with geodetic observations of fault-parallel velocities in northern and central California and local rates of shear strain along the San Andreas fault. The observations are best fit by models which are 10-100 times less viscous than a quartzite-like rheology. Since the lower crust in California is composed of intermediate to mafic rocks, the present result suggests that the in situ viscosity of the crustal rock is orders of magnitude

  19. A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California

    USGS Publications Warehouse

    Becken, M.; Ritter, O.; Park, S.K.; Bedrosian, P.A.; Weckmann, U.; Weber, M.

    2008-01-01

    Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block

  20. San Andreas Fault, Southern California , Radar Image, Wrapped Color as Height

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This topographic radar image vividly displays California's famous San Andreas Fault along the southwestern edge of the Mojave Desert, 75 kilometers (46 miles) north of downtown Los Angeles. The entire segment of the fault shown in this image last ruptured during the Fort Tejon earthquake of 1857. This was one of the greatest earthquakes ever recorded in the U.S., and it left an amazing surface rupture scar over 350 kilometers in length along the San Andreas. Were the Fort Tejon shock to happen today, the damage would run into billions of dollars, and the loss of life would likely be substantial, as the communities of Wrightwood, Palmdale, and Lancaster (among others) all lie upon or near the 1857 rupture area. The Lancaster/Palmdale area appears as bright patches just below the center of the image and the San Gabriel Mountains fill the lower left half of the image. At the extreme lower left is Pasadena. High resolution topographic data such as these are used by geologists to study the role of active tectonics in shaping the landscape, and to produce earthquake hazard maps.

    This image combines two types of data from the Shuttle Radar Topography Mission. The image brightness corresponds to the strength of the radar signal reflected from the ground, while colors show the elevation as measured by SRTM. Each cycle of colors (from pink through blue back to pink) represents an equal amount of elevation difference (400 meters, or 1300 feet) similar to contour lines on a standard topographic map. This image contains about 2400 meters (8000 feet) of total relief.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11,2000, uses the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission is designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200

  1. Is there a discrepancy between geological and geodetic slip rates along the San Andreas Fault System?

    NASA Astrophysics Data System (ADS)

    Tong, X.; Smith-Konter, B. R.; Sandwell, D. T.

    2013-12-01

    NO. Several previous inversions for slip rate along the San Andreas Fault System (SAFS), based on elastic half-space models, show a significant discrepancy between the geological and geodetic slip rates along a few major fault segments. In this study we use a more realistic model representing an elastic plate (schizosphere) over a viscoelastic half-space (plastosphere) to demonstrate that there is no significant discrepancy between long-term geologic and geodetic slip rates. The model includes ~ 50 major fault segments having steady slip from the base of the locked zone to the base of the elastic plate and episodic shallow slip based on known ruptures and geologic recurrence intervals. The slip rates are constrained by 1989 present-day velocity measurements from EarthScope GPS and high-resolution interseismic velocity data from L-band InSAR onboard ALOS. Five models with different rheological properties, including an elastic half-space, are tested in a slip-rate inversion. A model with a thick elastic plate (60 km) and half-space viscosity of 1019 Pa s is preferred because it produces the smallest misfit to both the geodetic data and the geological slip rates. We find that the geodetic slip rates from the 60 km thick plate model agree to within the bounds of the geological slip rates, while the rates from the half-space model disagree on certain important fault segments such as the Mojave and the North Coast segment of the San Andreas fault. In particular, along the Mojave segment the recovered geodetic slip rate is 24.7 mm/yr for the half-space model but our result comes closer to the preferred geological rates of 34 mm/yr using a 60 km thick plate model (27.5 mm/yr) and a 30 km thin plate model (34.4 mm/yr). The plate models have generally higher slip rates than the half-space model because most of the faults along the SAFS are late in the earthquake cycle so today they are moving slower than the long-term cycle-averaged velocity as governed by the viscoelastic

  2. Noncharacteristic Slip on the Northern San Andreas Fault at the Vedanta Marsh, Marin County, CA

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Niemi, T. M.; Allison, A.; Fumal, T. E.

    2004-12-01

    Three-dimensional excavations along the 1906 trace of the northern San Andreas fault at the Vedanta marsh paleoseismic site near Olema, CA have yielded new data on the timing and amount of slip during the penultimate earthquake on this fault section. The excavations exposed a 3-m-wide paleochannel that has been offset right-laterally 7.8-8.3 m by coseismic slip during the past two large earthquakes: 1906 and the penultimate earthquake. The paleochannel was eroded into a silty clay marsh deposit and was filled after AD 1400. Both the silty clay layer and the paleochannel deposit are directly overlain by an in situ burn/peat sequence. The penultimate earthquake occurred while the peat was at the ground surface whereas faulting from the 1906 earthquake terminates within an overlying gravel/fill sequence. Preliminary OxCal analyses of radiocarbon dates indicate that the penultimate earthquake occurred in the late 17th to early 18th century. In plan view, two main fault traces were mapped in the excavation. The northwestern portion of the paleochannel is offset across a single fault trace. Just southeast of this portion of the channel the fault splits into two traces. We believe that one of these traces likely slipped only during 1906 and the other trace slipped on during the penultimate earthquake. Unfortunately, the overlying stratigraphic section that could resolve the exact reconstruction of movement on these faults is missing due to the excavation of an artificial drainage ditch at this location in the 1940's. Matching the north margin of the paleochannel to the first exposure of gravel in the zone between the two fault traces gives an offset of 5 m. We have historic records that show the 1906 coseismic slip near the study site was about 5m from field notes of David Starr Jordan (Stanford University Archives) who describes two 16 ft (5m) offsets: one of a tree located about 150m SE of the offset channel and the other of a path to the Shafter barn located about 300m

  3. Complexities of the San Andreas fault near San Gorgonio Pass: Implications for large earthquakes

    NASA Astrophysics Data System (ADS)

    Yule, Doug; Sieh, Kerry

    2003-11-01

    Geologic relationships and patterns of crustal seismicity constrain the three-dimensional geometry of the active portions of San Andreas fault zone near San Gorgonio Pass, southern California. Within a 20-km-wide contractional stepover between two segments of the fault zone, the San Bernardino and Coachella Valley segments, folds, and dextral-reverse and dextral-normal faults form an east-west belt of active structures. The dominant active structure within the stepover is the San Gorgonio Pass-Garnet Hill faults, a dextral-reverse fault system that dips moderately northward. Within the hanging wall block of the San Gorgonio Pass-Garnet Hill fault system are subsidiary active dextral and dextral-normal faults. These faults relate in complex but understandable ways to the strike-slip faults that bound the stepover. The pattern of crustal seismicity beneath these structures includes a 5-8 km high east-west striking step in the base of crustal seismicity, which corresponds to the downdip limit of rupture of the 1986 North Palm Springs earthquake. We infer that this step has been produced by slip on the linked San Gorgonio Pass-Garnet Hill-Coachella Valley Banning (SGP-GH-CVB) fault. This association enables us to construct a structure contour map of the fault plane. The large step in the base of seismicity downdip from the SGP-GH-CVB fault system probably reflects a several kilometers offset of the midcrustal brittle-plastic transition. (U/Th)/He thermochronometry supports our interpretation that this south-under-north thickening of the crust has created the region's 3 km of topographic relief. We conclude that future large earthquakes generated along the San Andreas fault in this region will have a multiplicity of mostly specifiable sources having dimensions of 1-20 km. Two tasks in seismic hazard evaluation may now be attempted with greater confidence: first, the construction of synthetic seismograms that make useful predictions of ground shaking, and second

  4. San Andreas Fault, Southern California , Radar Image, Wrapped Color as Height

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This topographic radar image vividly displays California's famous San Andreas Fault along the southwestern edge of the Mojave Desert, 75 kilometers (46 miles) north of downtown Los Angeles. The entire segment of the fault shown in this image last ruptured during the Fort Tejon earthquake of 1857. This was one of the greatest earthquakes ever recorded in the U.S., and it left an amazing surface rupture scar over 350 kilometers in length along the San Andreas. Were the Fort Tejon shock to happen today, the damage would run into billions of dollars, and the loss of life would likely be substantial, as the communities of Wrightwood, Palmdale, and Lancaster (among others) all lie upon or near the 1857 rupture area. The Lancaster/Palmdale area appears as bright patches just below the center of the image and the San Gabriel Mountains fill the lower left half of the image. At the extreme lower left is Pasadena. High resolution topographic data such as these are used by geologists to study the role of active tectonics in shaping the landscape, and to produce earthquake hazard maps.

    This image combines two types of data from the Shuttle Radar Topography Mission. The image brightness corresponds to the strength of the radar signal reflected from the ground, while colors show the elevation as measured by SRTM. Each cycle of colors (from pink through blue back to pink) represents an equal amount of elevation difference (400 meters, or 1300 feet) similar to contour lines on a standard topographic map. This image contains about 2400 meters (8000 feet) of total relief.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11,2000, uses the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission is designed to collect three-dimensional measurements of the Earth's surface. To collect the 3-D data, engineers added a 60-meter-long (200

  5. Low-altitude aerial color digital photographic survey of the San Andreas Fault

    USGS Publications Warehouse

    Lynch, David K.; Hudnut, Kenneth W.; Dearborn, David S.P.

    2010-01-01

    Ever since 1858, when Gaspard-Félix Tournachon (pen name Félix Nadar) took the first aerial photograph (Professional Aerial Photographers Association 2009), the scientific value and popular appeal of such pictures have been widely recognized. Indeed, Nadar patented the idea of using aerial photographs in mapmaking and surveying. Since then, aerial imagery has flourished, eventually making the leap to space and to wavelengths outside the visible range. Yet until recently, the availability of such surveys has been limited to technical organizations with significant resources. Geolocation required extensive time and equipment, and distribution was costly and slow. While these situations still plague older surveys, modern digital photography and lidar systems acquire well-calibrated and easily shared imagery, although expensive, platform-specific software is sometimes still needed to manage and analyze the data. With current consumer-level electronics (cameras and computers) and broadband internet access, acquisition and distribution of large imaging data sets are now possible for virtually anyone. In this paper we demonstrate a simple, low-cost means of obtaining useful aerial imagery by reporting two new, high-resolution, low-cost, color digital photographic surveys of selected portions of the San Andreas fault in California. All pictures are in standard jpeg format. The first set of imagery covers a 92-km-long section of the fault in Kern and San Luis Obispo counties and includes the entire Carrizo Plain. The second covers the region from Lake of the Woods to Cajon Pass in Kern, Los Angeles, and San Bernardino counties (151 km) and includes Lone Pine Canyon soon after the ground was largely denuded by the Sheep Fire of October 2009. The first survey produced a total of 1,454 oblique digital photographs (4,288 x 2,848 pixels, average 6 Mb each) and the second produced 3,762 nadir images from an elevation of approximately 150 m above ground level (AGL) on the

  6. Paleoseismic Studies of the Peninsula San Andreas Fault near Crystal Springs Reservoir, Woodside, California

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Zachariasen, J. A.; Kozaci, O.; Clahan, K.; Sickler, R. R.; Rosa, C. M.; Hassett, W.; Feigelson, L.; Haproff, P. J.; DeLong, S.; Perkins, A.; Brooks, B. A.; Delano, J.; Baldwin, J. N.

    2013-12-01

    The Peninsula section of the San Andreas Fault (SAFP) is within 10 km of downtown San Francisco, making it among the most significant contributors to seismic hazard in the San Francisco Bay area. However, the history of earthquakes along this fault is poorly known. The most recent ground-rupturing earthquake occurred in 1906, but the ages of earlier earthquakes associated with surface rupture on this fault segment remain uncertain. Most researchers assume that the historically documented earthquake in 1838 occurred on the SAFP, but no definitive evidence of surface rupture at that time has been found. South of Crystal Springs Reservoir, the San Andreas Fault zone is expressed as a prominent fault scarp that is cut back in several locations by recent fluvial processes. At our Crystal Springs South (CSS) trench site, the fault is expressed as a low scarp with no other surface expression to suggest additional young fault traces. Excavations at this site revealed two distinct sets of faults, a younger set of faults that extend nearly to the modern ground surface that we assume represent the 1906 surface rupture, and an older set of faults that terminate lower in the stratigraphic section and are overlain by a scarp-derived colluvial deposit. Radiocarbon dating constrains the age of this older earthquake to 830-930 Cal. years BP. We determined that a buried channel deposit that dates to 790-960 Cal. years BP is displaced approximately 6-7m across both sets of faults. The closest 1906 offset measurement was made about 11 km northwest of this site, and is about 2.9m. Therefore our measurement of 6-7m of offset on the buried channel deposit at the CSS site could represent slip from 1906 and only one previous event comparable in size to the 1906 earthquake. The surprisingly old age of the earlier earthquake raises concerns that one or both of the event horizons exposed at the CSS site could represent multiple earthquakes. We therefore excavated an exploratory trench about 0

  7. High Resolution Interseismic Velocity Model of the San Andreas Fault From GPS and InSAR

    NASA Astrophysics Data System (ADS)

    Tong, X.; Sandwell, D. T.; Smith-Konter, B. R.

    2011-12-01

    We recover the interseismic deformation along the entire San Andreas Fault System (SAFS) at a spatial resolution of 200 meters by combining InSAR and GPS observations using a dislocation model. Previous efforts to compare 17 different GPS-derived strain rate models of the SAFS shows that GPS data alone cannot uniquely resolve the rapid velocity gradients near faults, which are critical for understanding the along-strike variations in stress accumulation rate and associated earthquake hazard. To improve the near-fault velocity resolution, we integrate new GPS observations with InSAR observations, initially from ALOS (Advanced Land Observation Satellite launched by Japan Aerospace Exploration Agency) ascending data (spanning 2006.5-2010), using a remove/restore approach. More than 1100 interferograms were processed with the newly developed InSAR processing software GMTSAR. The integration uses a dislocation-based velocity model to interpolate the Line-Of-Sight (LOS) velocity at the full resolution of the InSAR data in radar coordinates. The residual between the model and InSAR LOS velocity are stacked and high-pass filtered, then added back to the model. This LOS velocity map covers almost entire San Andreas Fault System (see Figure 1) from Maacama Fault to the north to the Superstition Hills Fault to the south. The average standard deviation of the LOS velocity model ranges from 2 to 4 mm/yr. Our initial results show previously unknown details in along-strike variations in surface fault creep. Moreover, the high resolution velocity field can resolve asperities in these "creeping" sections that are important for understanding moment accumulation rates and seismic hazards. We find that much of the high resolution velocity signal is related to non-tectonic processes (e.g., ground subsidence and uplift) sometimes very close to the fault zone. The near-fault deformation signal extracted from this velocity map can provide tighter constraints on fault slip rates and

  8. San Andreas fault geometry at Desert Hot Springs, California, and its effects on earthquake hazards and groundwater

    USGS Publications Warehouse

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Gandhok, G.

    2009-01-01

    The Mission Creek and Banning faults are two of the principal strands of the San Andreas fault zone in the northern Coachella Valley of southern California. Structural characteristics of the faults affect both regional earthquake hazards and local groundwater resources. We use seismic, gravity, and geological data to characterize the San Andreas fault zone in the vicinity of Desert Hot Springs. Seismic images of the upper 500 m of the Mission Creek fault at Desert Hot Springs show multiple fault strands distributed over a 500 m wide zone, with concentrated faulting within a central 200 m wide area of the fault zone. High-velocity (up to 5000 m=sec) rocks on the northeast side of the fault are juxtaposed against a low-velocity (6.0) earthquakes in the area (in 1948 and 1986) occurred at or near the depths (~10 to 12 km) of the merged (San Andreas) fault. Large-magnitude earthquakes that nucleate at or below the merged fault will likely generate strong shaking from guided waves along both fault zones and from amplified seismic waves in the low-velocity basin between the two fault zones. The Mission Creek fault zone is a groundwater barrier with the top of the water table varying by 60 m in depth and the aquifer varying by about 50 m in thickness across a 200 m wide zone of concentrated faulting.

  9. Tidal triggering of earthquakes suggests poroelastic behavior on the San Andreas Fault

    DOE PAGES

    Delorey, Andrew A.; van der Elst, Nicholas J.; Johnson, Paul Allan

    2016-12-28

    Tidal triggering of earthquakes is hypothesized to provide quantitative information regarding the fault's stress state, poroelastic properties, and may be significant for our understanding of seismic hazard. To date, studies of regional or global earthquake catalogs have had only modest successes in identifying tidal triggering. We posit that the smallest events that may provide additional evidence of triggering go unidentified and thus we developed a technique to improve the identification of very small magnitude events. We identify events applying a method known as inter-station seismic coherence where we prioritize detection and discrimination over characterization. Here we show tidal triggering ofmore » earthquakes on the San Andreas Fault. We find the complex interaction of semi-diurnal and fortnightly tidal periods exposes both stress threshold and critical state behavior. Lastly, our findings reveal earthquake nucleation processes and pore pressure conditions – properties of faults that are difficult to measure, yet extremely important for characterizing earthquake physics and seismic hazards.« less

  10. Seismicity, crustal structure, and tectonics near the northern termination of the San Andreas fault

    SciTech Connect

    Knapp, J.S.

    1982-01-01

    Further evidence supporting the supposition that a triple junction has existed near Cape Mendocino in Late Cenezoic time was provided by the discovery of a layer of seismic activity dipping 12/sup 0/ beneath the continent north of the Mendocino fracture. A seismic refraction profile shot along the continental slope and onshore velocity modeling confirms that this layer of earthquakes is confined within subducted oceanic layers 2 and 3. In this region, layer 2 appears to be slightly thickened and layer 3 anomalously thin. Travel time delays from offshore explosions and from teleseismically-recorded earthquakes indicate the presence of a large velocity discontinuity as great as 10% across the Mendocino escarpment represents the juxtaposition of two distinct lithospheric plates. The tectonic development of the region seems, however, to be shifting away from a stable triple junction configuration. Because the spreading direction at the Gorda ridge is no longer parallel to the Mendocino fracture, the Gorda plate is breaking up along a complex series of left-lateral, northeast-trending faults, as suggested by the high level of intraplate seismicity and by some aftershock distributions. By asymmetric spreading, the Gorda and Juan de Fuca ridges are undergoing clockwise rotation to bring them into alignment with the San Andreas-East Pacific rise system, eventually leading to the cessation of subduction beneath the northern California, Oregon, and Washington coasts.

  11. Earthquake recurrence on the southern San Andreas modulated by fault-normal stress

    NASA Technical Reports Server (NTRS)

    Palmer, Randy; Weldon, Ray; Humphreys, Eugene; Saucier, Francois

    1995-01-01

    Earthquake recurrence data from the Pallett Creek and Wrightwood paleoseismic sites on the San Andreas fault appear to show temporal variations in repeat interval. We investigate the interaction between strike-slip faults and auxiliary reverse and normal faults as a physical mechanism capable of producing such variations. Under the assumption that fault strength is a function of fault-normal stress (e.g. Byerlee's Law), failure of an auxiliary fault modifies the strength of the strike-slip fault, thereby modulating the recurrence interval for earthquakes. In our finite element model, auxiliary faults are driven by stress accumulation near restraining and releasing bends of a strike-slip fault. Earthquakes occur when fault strength is exceeded and are incorporated as a stress drop which is dependent on fault-normal stress. The model is driven by a velocity boundary condition over many earthquake cycles. Resulting synthetic strike-slip earthquake recurrence data display temporal variations similar to observed paleoseismic data within time windows surrounding auxiliary fault failures. Our simple model supports the idea that interaction between a strike-slip fault and auxiliary reverse or normal faults can modulate the recurrence interval of events on the strike-slip fault, possibly producing short term variations in earthquake recurrence interval.

  12. Leonardo da Vinci and Andreas Vesalius; the shoulder girdle and the spine, a comparison.

    PubMed

    Ganseman, Y; Broos, P

    2008-01-01

    Leonardo Da Vinci and Andreas Vesalius were two important renaissance persons; Vesalius was a surgeon-anatomist who delivered innovative work on the study of the human body, Leonardo da Vinci was an artist who delivered strikingly accurate and beautiful drawings on the human body. Below we compare both masters with regard to their knowledge of the working of the muscles, their method and system of dissection and their system and presentation of the drawings. The investigation consisted of a comparison between both anatomists, in particular concerning their study on the shoulder girdle and spine, by reviewing their original work as well as already existing literature on this subject. The investigation led to the conclusion that the drawings mentioned meant a change in history, and were of high quality, centuries ahead of their time. Both were anatomists, both were revolutionary, only one changed history at the moment itself, while the other changed history centuries later. Leonardo has made beautiful drawings that are at a match with the drawings of today or are even better. Vesalius set the start for medicine as a science as it is until this day. Their lives differed as strongly as their impact. In the light of their time, the achievement they made was extraordinary.

  13. Relating seismicity to the velocity structure of the San Andreas Fault near Parkfield, CA

    NASA Astrophysics Data System (ADS)

    Lippoldt, Rachel; Porritt, Robert W.; Sammis, Charles G.

    2017-06-01

    The central section of the San Andreas Fault (SAF) displays a range of seismic phenomena including normal earthquakes, low-frequency earthquakes (LFE), repeating microearthquakes (REQ) and aseismic creep. Although many lines of evidence suggest that LFEs are tied to the presence of fluids, their geological setting is still poorly understood. Here, we map the seismic velocity structures associated with LFEs beneath the central SAF using surface wave tomography from ambient seismic noise to provide constraints on the physical conditions that control LFE occurrence. Fault perpendicular sections show that the SAF, as revealed by lateral contrasts in relative velocities, is contiguous to depths of 50 km and appears to be relatively localized at depths between about 15 and 30 km. This is consistent with the hypothesis that LFEs are shear-slip events on a deep extension of the SAF. We find that along strike variations in seismic behaviour correspond to changes in the seismic structure, which support proposed connections between fluids and seismicity. LFEs and REQs occur within low-velocity structures, suggesting that the presence of fluids, weaker minerals, or hydrous phase minerals may play an important role in the generation of slow-slip phenomena.

  14. Airborne Hyperspectral Infrared Imaging Survey of the Southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Lynch, D. K.; Tratt, D. M.; Buckland, K. N.; Johnson, P. D.

    2014-12-01

    The San Andreas Fault (SAF) between Desert Hot Springs and Bombay Beach has been surveyed with Mako, an airborne hyperspectral imager operating across the wavelength range 7.6-13.2 μm in the thermal-infrared (TIR) spectral region. The data were acquired with a 4-km swath width centered on the SAF, and many tectonic features are recorded in the imagery. Spectral analysis using diagnostic features of minerals can identify rocks, soils and vegetation. Mako imagery can also locate rupture zones and measure slip distances. Designed and built by The Aerospace Corporation, the innovative and highly capable airborne imaging spectrometer used for this work enables low-noise performance (NEΔT ≲ 0.1 K @ 10 μm) at small pixel IFOV (0.55 mrad) and high frame rates, making possible an area-coverage rate of 20 km2 per minute with 2-m ground resolution from 12,500 ft (3.8 km) above-ground altitude. Since its commissioning in 2010, Mako has been used in numerous studies involving other earthquake fault systems (Hector Mine, S. Bristol Mts.), mapping of surface geology, geothermal sources (fumaroles near the Salton Sea), urban surveys, and the detection, quantification, and tracking of natural and anthropogenic gaseous emission plumes. Mako is available for airborne field studies and new applications are of particular interest. It can be flown at any altitude below 20,000 ft to achieve the desired GSD.

  15. Andreas Vesalius' 500th anniversary: the initiation of hand and forearm myology.

    PubMed

    Brinkman, R J; Hage, J J

    2015-11-01

    Andreas Vesalius (1515-1564) was the first to market an illustrated text on the freshly dissected muscular anatomy of the human hand and forearm when he published his De Fabrica Corporis Humani Libri Septem, in 1543. To commemorate his 500th birthday, we searched the second of seven books composing De Fabrica, the annotated woodcut illustrations of De Fabrica, the Tabulae Sex, and Epitome, and an eyewitness report of a public dissection by Vesalius for references to the morphology and functions of these muscles. We found Vesalius to have recognized all currently distinguished muscles except the palmaris brevis and he noted occasional absence of some muscles. Generally, he limited the origin and insertion to bones, largely disregarding attachments to membranes and fascia. Functionally, he recorded the muscles as having a single vector and operating on only one joint. We conclude that Vesalius was nearly completely correct about the anatomy of the muscles of the forearm, but much less accurate about their function. 5. © The Author(s) 2015.

  16. Stress drops of repeating earthquakes on the San Andreas Fault at Parkfield

    NASA Astrophysics Data System (ADS)

    Abercrombie, Rachel E.

    2014-12-01

    I calculate well-resolved corner frequencies and stress drops for 25 earthquakes (1989-2006) in the three repeating sequences targeted by the San Andreas Fault Observatory at Depth, using borehole data and multiple, highly correlated empirical Green's functions (EGFs). The earthquakes in the largest magnitude (M ~ 2.1) cluster exhibit source spectra well-fit by a circular source model. The corner frequencies correlate with those from the regional study by Allmann and Shearer, suggesting that the interevent variability is resolvable. The earthquakes have stress drops between 25 and 65 MPa, with a gradual increase before the 2004 M6 earthquake, followed by an immediate decrease, then a rapid return to previous levels. The spectra of the cluster of M ~ 1.9 earthquakes include high-frequency energy not fit by simple source models and so stress drops are unreliable, and probably underestimated (1-20 MPa). There is no correlation with previous studies, and interevent variation is not resolvable. The earthquakes in the smallest magnitude cluster (M ~ 1.8) have the highest corner frequencies, but similar stress drops (4-120 MPa). The stress drops exhibit the same temporal variation as the first cluster, but there is poor correlation with Allmann and Shearer, probably because their frequency bandwidth is too limited.

  17. Southern San Andreas Fault seismicity is consistent with the Gutenberg-Richter magnitude-frequency distribution

    USGS Publications Warehouse

    Page, Morgan T.; Felzer, Karen

    2015-01-01

    The magnitudes of any collection of earthquakes nucleating in a region are generally observed to follow the Gutenberg-Richter (G-R) distribution. On some major faults, however, paleoseismic rates are higher than a G-R extrapolation from the modern rate of small earthquakes would predict. This, along with other observations, led to formulation of the characteristic earthquake hypothesis, which holds that the rate of small to moderate earthquakes is permanently low on large faults relative to the large-earthquake rate (Wesnousky et al., 1983; Schwartz and Coppersmith, 1984). We examine the rate difference between recent small to moderate earthquakes on the southern San Andreas fault (SSAF) and the paleoseismic record, hypothesizing that the discrepancy can be explained as a rate change in time rather than a deviation from G-R statistics. We find that with reasonable assumptions, the rate changes necessary to bring the small and large earthquake rates into alignment agree with the size of rate changes seen in epidemic-type aftershock sequence (ETAS) modeling, where aftershock triggering of large earthquakes drives strong fluctuations in the seismicity rates for earthquakes of all magnitudes. The necessary rate changes are also comparable to rate changes observed for other faults worldwide. These results are consistent with paleoseismic observations of temporally clustered bursts of large earthquakes on the SSAF and the absence of M greater than or equal to 7 earthquakes on the SSAF since 1857.

  18. [Lou Andreas-Salome (1861-1937)--psychoanalytical and feministic contribution to understanding her biography].

    PubMed

    Bramness, J G

    2001-06-30

    Lou (Louise) Andreas-Salomé's life and work has preoccupied many biographers. The interest may have be sparked by her liaisons with many of the greatest men of her time. She had an intimate relationship with Friedrich Nietzsche in a period of great change for him. She was Rainer Marie Rilke's mistress for several years. And she pursued a close friendship and working relationship with Sigmund Freud in the latter part of her life. But her significance goes beyond these associations. She was a celebrated novelist and essayist in her own right, with ten novels and more than 50 essays, also on psychoanalytical subjects. She has been viewed as femme fatale, opportunist, feminist, radical, liberal, but also as a significant contributor to psychoanalytical thought. There have been two biographical approaches: a psychoanalytical approach focusing on her loss of father-figures and later difficult relationships with famous men, and a feministic approach accusing psychoanalysts of not contributing to insight, but belittling Salomé's legitimate position. A fuller understanding may be obtained by integrating these two views.

  19. Anomalous hydrogen emissions from the San Andreas fault observed at the Cienega Winery, central California

    USGS Publications Warehouse

    Sato, M.; Sutton, A.J.; McGee, K.A.

    1985-01-01

    We began continuous monitoring of H2 concentration in soil along the San Andreas and Calaveras faults in central California in December 1980, using small H2/O2 fuel-cell sensors. Ten monitoring stations deployed to date have shown that anomalous H2 emissions take place occasionally in addition to diurnal changes. Among the ten sites, the Cienega Winery site has produced data that are characterized by very small diurnal changes, a stable baseline, and remarkably distinct spike-like H2 anomalies since its installation in July 1982. A major peak appeared on 1-10 November 1982, and another on 3 April 1983, and a medium peak on 1 November 1983. The occurrences of these peaks coincided with periods of very low seismicity within a radius of 50 km from the site. In order to methodically assess how these peaks are related to earthquakes, three H2 degassing models were examined. A plausible correlational pattern was obtained by using a model that (1) adopts a hemicircular spreading pattern of H2 along an incipient fracture plane from the hypocenter of an earthquake, (2) relies on the FeO-H2O reaction for H2 generation, and (3) relates the accumulated amount of H2 to the mass of serpentinization of underlying ophiolitic rocks; the mass was tentatively assumed to be proportional to the seismic energy of the earthquake. ?? 1985 Birkha??user Verlag.

  20. Analysis of regional deformation and strain accumulation data adjacent to the San Andreas fault

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1991-01-01

    A new approach to the understanding of crustal deformation was developed under this grant. This approach combined aspects of fractals, chaos, and self-organized criticality to provide a comprehensive theory for deformation on distributed faults. It is hypothesized that crustal deformation is an example of comminution: Deformation takes place on a fractal distribution of faults resulting in a fractal distribution of seismicity. Our primary effort under this grant was devoted to developing an understanding of distributed deformation in the continental crust. An initial effort was carried out on the fractal clustering of earthquakes in time. It was shown that earthquakes do not obey random Poisson statistics, but can be approximated in many cases by coupled, scale-invariant fractal statistics. We applied our approach to the statistics of earthquakes in the New Hebrides region of the southwest Pacific because of the very high level of seismicity there. This work was written up and published in the Bulletin of the Seismological Society of America. This approach was also applied to the statistics of the seismicity on the San Andreas fault system.

  1. Correlated radon and CO2 variations near the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Shapiro, M. H.; Melvin, J. D.; Tombrello, T. A.; Fong-liang, Jiang; Gui-ru, Li; Mendenhall, M. H.; Rice, A.; Epstein, S.; Jones, V. T.; Masdea, D.; Kurtz, M.

    1982-05-01

    Correlations have been observed between groundwater radon and thoron concentrations and carbon dioxide discharges at the Lake Hughes station of the Caltech radon monitoring network. The Lake Hughes site is one of three radon monitoring stations located near the "big bend" segment of the San Andreas fault which began to record anomalous radon levels in August 1981. Two stations, Lake Hughes and Lytle Creek, recorded anomalous increases in radon while the third, Sky Forest, recorded an anomalous decrease. Several weeks after the onset of the anomaly, strongly correlated radon fluctuations began at Lake Hughes and Lytle Creek. These radon spikes also were found to be phase anti-correlated with barometric pressure fluctuations. Analyses of gas grab samples showed relatively high levels of CO2 and ethylene in borehole air at Lake Hughes and Lytle Creek, while analyses of water samples showed relatively large increases in HCO3- at both sites. Isotopic analysis of one gas sample from Lake Hughes yielded a 13C δ value of -22 ‰, which suggests that the CO2 originates from the oxidation of organic material. The correlation in radon fluctuations at Lake Hughes and Lytle Creek and their common dependence on barometric pressure changes began shortly after the onset of the radon anomaly in August, and probably resulted from the simultaneous saturation of the water in these boreholes with carbon dioxide.

  2. The San Andreas Fault and a Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The mosaic on the right of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, the size of the California portion of the San Andreas fault on Earth which runs from the California-Mexico border north to the San Francisco Bay.

    The left mosaic shows the portion of the San Andreas fault near California's san Francisco Bay that has been scaled to the same size and resolution as the Europa image. Each covers an area approximately 170 by 193 kilometers(105 by 120 miles). The red line marks the once active central crack of the Europan fault (right) and the line of the San Andreas fault (left).

    A strike-slip fault is one in which two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. The overall motion along the Europan fault seems to have followed a continuous narrow crack along the entire length of the feature, with a path resembling stepson a staircase crossing zones which have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. Opposite sides of the fault can be reconstructed like a puzzle, matching the shape of the sides as well as older individual cracks and ridges that had been broken by its movements.

    Bends in the Europan fault have allowed the surface to be pulled apart. This pulling-apart along the fault's bends created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, and in Death Valley and the Dead Sea. In those cases, the pulled apart regions can include upwelled

  3. Local magnetic field measurements and fault creep observations on the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Johnston, M. J. S.; Smith, B. E.; Burford, R. O.

    1980-04-01

    Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored.

  4. Local magnetic field measurements and fault creep observations on the San Andreas fault

    USGS Publications Warehouse

    Johnston, M.J.S.; Smith, B.E.; Burford, R.O.

    1980-01-01

    Simultaneous creep and magnetic field records have been obtained for more than 60 episodic creep events since early 1974, no clear magnetic transients or offsets, as suggested by Breiner and Kovach (1968), are observed at or up to several days before the occurrence times of these events. Although some patterns of creep onset times at adjacent stations over periods of weeks to months appear to correspond to some periods of longer term change in local magnetic field, these changes do not always occur and other groups of creep events have no corresponding changes in local magnetic field. Changes in stress related to the surface expression of episodic fault creep on the San Andreas fault can be estimated from dislocation models fit to observations of simultaneous strains and tilts at points near the fault. These stress values are generally less than 1 bar. For these stress levels and with the apparent limited extent of surface failure, tectonomagnetic models of creep events indicate that simultaneous observations of related magnetic field variations at detectable levels of a gamma or so are unlikely. Slip at greater depth may occur more smoothly and would load the near-surface material to failure. These data also argue against large-scale dilatant cracking occurring along the region of the fault presently monitored. ?? 1980.

  5. The San Andreas Fault and a Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The mosaic on the right of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, the size of the California portion of the San Andreas fault on Earth which runs from the California-Mexico border north to the San Francisco Bay.

    The left mosaic shows the portion of the San Andreas fault near California's san Francisco Bay that has been scaled to the same size and resolution as the Europa image. Each covers an area approximately 170 by 193 kilometers(105 by 120 miles). The red line marks the once active central crack of the Europan fault (right) and the line of the San Andreas fault (left).

    A strike-slip fault is one in which two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. The overall motion along the Europan fault seems to have followed a continuous narrow crack along the entire length of the feature, with a path resembling stepson a staircase crossing zones which have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. Opposite sides of the fault can be reconstructed like a puzzle, matching the shape of the sides as well as older individual cracks and ridges that had been broken by its movements.

    Bends in the Europan fault have allowed the surface to be pulled apart. This pulling-apart along the fault's bends created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, and in Death Valley and the Dead Sea. In those cases, the pulled apart regions can include upwelled

  6. Bimodal distribution of creep event amplitudes on the San Andreas fault, California

    USGS Publications Warehouse

    Burford, R.O.

    1977-01-01

    EPISODIC fault creep, at several instrument sites along the San Andreas and associated faults in central California consists of a few small and large slip events per year generally superimposed on a background of gradual yielding at low rates1-3. Most of the events are aseismic, but a few minor displacement steps have occured in association with local earthquakes 12. After removal of earthquake steps, event lists for several sites include significant numbers of small events about an order or magnitude below the typical 1-4-mm amplitude range for large events1, 3. Recent experimental rock-deformation results demonstrate that under biaxial loading some rocks show episodic slip on pre-cut surfaces9,10. It is not yet clear how the laboratory and field observations are related, but the data presented here indicate that episodic fault creep in nature may be more complex than previously realised. In light of the laboratory results, it is more important than ever to consider all the details of the field data concerning fault creep. ?? 1977 Nature Publishing Group.

  7. Hydrogeologic Architecture of the San Andreas Fault near the Logan Quarry

    NASA Astrophysics Data System (ADS)

    Xue, L.; Brodsky, E. E.; Erskine, J.; Fulton, P. M.; Carter, R.

    2015-12-01

    Hydrogeologic properties of fault zones are critical to the faulting processes; however, they are not well understood and difficult to measure in situ. Recording the tidal response of water level is a useful method to measure the in-situ properties. We utilize an array of wells near the San Andreas Fault zone in the Logan Quarry to study the fault zone hydrogeologic architecture by measuring the water tidal response. The measured specific storage and permeability show that there is a localized zone near the fault with higher specific storage and larger permeability than the surrounding region. This change of properties might be related to the fault zone fracture distribution. Surprisingly, the change of the specific storage is the clearest signal. The inferred compliance contrast is consistent with prior estimates of elastic moduli change in the near-fault environment, but the hydrogeologic effects of the compliance change have never before been measured on a major active fault. The observed specific storage structure implies that the fault zone plays an important role in permeability enhancement by seismic shaking. In addition, the measured diffusivity is about 10-2 m2/s, which is comparable to the post-earthquake hydraulic diffusivity measured on the Wenchuan Earthquake Fault. This observed high diffusivity with little variability inside the fault zone might suggest the accumulated pore pressure during interseismic period distributes over a broad region.

  8. A permeability and compliance contrast measured hydrogeologically on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Xue, Lian; Brodsky, Emily E.; Erskine, Jon; Fulton, Patrick M.; Carter, Reed

    2016-03-01

    Hydrogeologic properties of fault zones are critical to faulting processes; however, they are not well understood and difficult to measure in situ, particularly in low-permeability fractured bedrock formations. Analysis of continuous water level response to Earth tides in monitoring wells provides a method to measure the in situ hydrogeologic properties. We utilize four monitoring wells within the San Andreas Fault zone near Logan Quarry to study the fault zone hydrogeologic architecture by measuring the water level tidal response. The specific storage and permeability inferred from the tidal response suggest that there is a difference in properties at different distances from the fault. The sites closer to the fault have higher specific storage and higher permeability than farther from the fault. This difference of properties might be related to the fault zone fracture distribution decreasing away from the fault. Although permeability channels near faults have been documented before, the difference in specific storage near the fault is a new observation. The inferred compliance contrast is consistent with prior estimates of elastic moduli in the near-fault environment, but the direct measurements are new. The combination of measured permeability and storage yields a diffusivity of about 10-2 m2/s at all the sites both near and far from the fault as a result of the competing effects of permeability and specific storage. This uniform diffusivity structure suggests that the permeability contrast might not efficiently trap fluids during the interseismic period.

  9. Juan Valverde de Hamusco's unauthorized reproduction of a brain dissection by Andreas Vesalius.

    PubMed

    Lanska, Douglas J; Lanska, John R

    2013-02-26

    The objective of the present work is to examine images of the brain dissection by Flemish-born anatomist Andreas Vesalius (1514-1564) as originally represented in the Fabrica (1543), and later copied without Vesalius' permission by Spanish anatomist Juan Valverde de Hamusco (c1525-c1587) in Historia de la composicion del cuerpo humano (1556). Illustrations of the brain dissection in the Fabrica were obtained in digital form, resized, and arranged in a comparable montage to that presented by Valverde. Computer manipulations were used to assess image correspondence. The Valverde illustrations are approximately half the size and are mirror images of those in the Fabrica, but otherwise show the same dissection stages, and identical transverse brain levels and structures. The Valverde illustrations lack shadowing and show minor variations in perspective and fine details (e.g., branching pattern of the middle meningeal artery) from those in the Fabrica. Craftsmen under the direction of Valverde copied the woodcut prints in the Fabrica in close but approximate form by freehand engraving onto copper plates. Differences in the sizes of the images, and in perspective and fine detail, preclude direct tracing of images as the means of copying. Because engravings are in effect "flipped over" to make further prints, subsequent prints made from Valverde's copperplate engravings are mirror images of the prints in Vesalius' Fabrica.

  10. Tremor evidence for dynamically triggered creep events on the deep San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Peng, Z.; Shelly, D. R.; Hill, D. P.; Aiken, C.

    2010-12-01

    Deep tectonic tremor has been observed along major subduction zones and the San Andreas fault (SAF) in central and southern California. It appears to reflect deep fault slip, and it is often seen to be triggered by small stresses, including passing seismic waves from large regional and teleseismic earthquakes. Here we examine tremor activity along the Parkfield-Cholame section of the SAF from mid-2001 to early 2010, scrutinizing its relationship with regional and teleseismic earthquakes. Based on similarities in the shape and timing of seismic waveforms, we conclude that triggered and ambient tremor share common sources and a common physical mechanism. Utilizing this similarity in waveforms, we detect tremor triggered by numerous large events, including previously unreported triggering from the recent 2009 Mw7.3 Honduras, 2009 Mw8.1 Samoa, and 2010 Mw8.8 Chile earthquakes at teleseismic distances, and the relatively small 2007 Mw5.4 Alum Rock and 2008 Mw5.4 Chino Hills earthquakes at regional distances. We also find multiple examples of systematic migration in triggered tremor, similar to ambient tremor migration episodes observed at other times. Because these episodes propagate much more slowly than the triggering waves, the migration likely reflects a small, triggered creep event. As with ambient tremor bursts, triggered tremor at times persists for multiple days, probably indicating a somewhat larger creep event. This activity provides a clear example of delayed dynamic triggering, with a mechanism perhaps also relevant for triggering of regular earthquakes.

  11. Nonvolcanic Deep Tremors in the Transform Plate Bounding San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Nadeau, R. M.; Dolenc, D.

    2004-12-01

    Recently, deep ( ˜ 20 to 40 km) nonvolcanic tremor activity has been observed on convergent plate boundaries in Japan and in the Cascadia region of North America (Obara, 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). Because of the abundance of available fluids from subduction processes in these convergent zones, fluids are believed to play an important role in the generation of the tremor activity. The transient rates of tremor activity in these regions are also observed to correlate either with the occurrence of larger earthquakes (Obara, 2002) or with geodetically determined transient creep events that release large amounts of strain energy deep beneath the locked Cascadia megathrust (M.M. Miller et al., 2002; Rodgers and Dragert, 2003; Szeliga et al., 2004). These associations suggest that nonvolcanic tremor activity may participate in a fundamental mode of deep moment release and in the triggering of large subduction zone events (Rodgers and Dragert, 2003). We report the discovery of deep ( ˜ 20 to 45 km) nonvolcanic tremor activity on the transform plate bounding San Andreas Fault (SAF) in central California where, in contrast to subduction zones, long-term deformation directions are horizontal and fluid availability from subduction zone processes is absent. The source region of the SAF tremors lies beneath the epicentral region of the great 1857 magnitude (M) ˜ 8, Fort Tejon earthquake whose rupture zone is currently locked (Sieh, 1978). Activity rate transients of the tremors occurring since early 2001 also correlate with seismicity rate variations above the tremor source region.

  12. Historic surface slip along the San Andreas Fault near Parkfield, California

    USGS Publications Warehouse

    Lienkaemper, J.J.; Prescott, W.H.

    1989-01-01

    The Parkfield Earthquake Prediction Experiment is focusing close attention on the 44-km-long section of the San Andreas fault that last ruptured seismically in 1966 (Ms 6.0). The 20-km-long central segment of the 1966 Parkfield rupture, extending from the mainshock epicenter at Middle Mountain southeastward to Gold Hill, forms a 1- to 2-km salient northeastward away from the dominant N40??W strike. Following the 1966 earthquake afterslip, aseismic slip has been nearly constant. Moderate Parkfield earthquakes have recurred on average every 21 years since 1857, when a great earthquake (M ~ 8) ruptured at least as far north as the southern Parkfield segment. Many measurements of slip have been made near Parkfield since 1966. Nevertheless, much of the history of surface slip remained uncertain, especially the total amount associated with the 1966 event. In 1985 we measured accumulated slip on the four oldest cultural features offset by the fault along the 1966 Parkfield rupture segment. -from Authors

  13. Dating offset fans along the Mojave section of the San Andreas fault using cosmogenic 26Al and 10Be

    USGS Publications Warehouse

    Matmon, A.; Schwartz, D.P.; Finkel, R.; Clemmens, S.; Hanks, T.

    2005-01-01

    Analysis of cosmogenic 10Be and 26Al in samples collected from exposed boulders (n = 20) and from buried sediment (n = 3) from offset fans along the San Andreas fault near Little Rock, California, yielded ages, ranging from 16 to 413 ka, which increase with distance from their source at the mouth of Little Rock Creek. In order to determine the age of the relatively younger fans, the erosion rate of the boulders and the cosmogenic nuclide inheritance from exposure prior to deposition in the fan were established. Cosmogenic nuclide inheritance values that range between 8.5 ?? 103 and 196 ?? 103 atoms 10Be g-1 quartz were determined by measuring the concentrations and ratios of 10Be and 26Al in boulders (n = 10) and fine sediment (n = 7) at the outlet of the present active stream. Boulder erosion rate, ranging between 17 and 160 mm k.y.-1, was estimated by measuring 10Be and 26Al concentrations in nearby bedrock outcrops (n = 8). Since the boulders on the fans represent the most resistant rocks in this environment, we used the lowest rate for the age calculations. Monte Carlo simulations were used to determine ages of 16 ?? 5 and 29 ?? 7 ka for the two younger fan surfaces. Older fans (older than 100 ka) were dated by analyzing 10Be and 26Al concentrations in buried sand samples. The ages of the three oldest fans range between 227 ?? 242 and 413 ?? 185 ka. Although fan age determinations are accompanied by large uncertainties, the results of this study show a clear trend of increasing fan ages with increasing distance from the source near Little Rock Creek and provide a long-term slip rate along this section of the San Andreas fault. Slip rate along the Mojave section of the San Andreas fault for the past 413 k.y. can be determined in several ways. The average slip rate calculated from the individual fan ages is 4.2 ?? 0.9 cm yr-1. A linear regression through the data points implies a slip rate of 3.7 ?? 1.0 cm yr-1. A most probable slip rate of 3.0 ?? 1.0 cm yr-1 is

  14. The response of creeping parts of the San Andreas fault to earthquakes on nearby faults: Two examples

    USGS Publications Warehouse

    Simpson, R.W.; Schulz, S.S.; Dietz, L.D.; Burford, R.O.

    1988-01-01

    Rates of shallow slip on creeping sections of the San Andreas fault have been perturbed on a number of occasions by earthquakes occurring on nearby faults. One example of such perturbations occurred during the 26 January 1986 magnitude 5.3 Tres Pinos earthquake located about 10 km southeast of Hollister, California. Seven creepmeters on the San Andreas fault showed creep steps either during or soon after the shock. Both left-lateral (LL) and right-lateral (RL) steps were observed. A rectangular dislocation in an elastic half-space was used to model the coseismic fault offset at the hypocenter. For a model based on the preliminary focal mechanism, the predicted changes in static shear stress on the plane of the San Andreas fault agreed in sense (LL or RL) with the observed slip directions at all seven meters; for a model based on a refined focal mechanism, six of the seven meters showed the correct sense of motion. Two possible explanations for such coseismic and postseismic steps are (1) that slip was triggered by the earthquake shaking or (2) that slip occurred in response to the changes in static stress fields accompanying the earthquake. In the Tres Pinos example, the observed steps may have been of both the triggered and responsive kinds. A second example is provided by the 2 May 1983 magnitude 6.7 Coalinga earthquake, which profoundly altered slip rates at five creepmeters on the San Andreas fault for a period of months to years. The XMM1 meter 9 km northwest of Parkfield, California recorded LL creep for more than a year after the event. To simulate the temporal behavior of the XMM1 meter and to view the stress perturbation provided by the Coalinga earthquake in the context of steady-state deformation on the San Andreas fault, a simple time-evolving dislocation model was constructed. The model was driven by a single long vertical dislocation below 15 km in depth, that was forced to slip at 35 mm/yr in a RL sense. A dislocation element placed in the

  15. Class probability estimation for medical studies.

    PubMed

    Simon, Richard

    2014-07-01

    I provide a commentary on two papers "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Theory" by Jochen Kruppa, Yufeng Liu, Gérard Biau, Michael Kohler, Inke R. König, James D. Malley, and Andreas Ziegler; and "Probability estimation with machine learning methods for dichotomous and multicategory outcome: Applications" by Jochen Kruppa, Yufeng Liu, Hans-Christian Diener, Theresa Holste, Christian Weimar, Inke R. König, and Andreas Ziegler. Those papers provide an up-to-date review of some popular machine learning methods for class probability estimation and compare those methods to logistic regression modeling in real and simulated datasets.

  16. San Andreas Fault, Southern California, Shaded relief, wrapped color as height

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This topographic image vividly displays California's famous San Andreas Fault along the southwestern edge of the Mojave Desert, 75 kilometers (46 miles) north of downtown Los Angeles. The entire segment of the fault shown in this image last ruptured during the Fort Tejon earthquake of 1857. This was one of the greatest earthquakes ever recorded in the U.S., and it left an amazing surface rupture scar over 350 kilometers in length along the San Andreas. Were the Fort Tejon shock to happen today, the damage would run into billions of dollars, and the loss of life would likely be substantial, as the communities of Wrightwood, Palmdale, and Lancaster (among others) all lie upon or near the 1857 rupture area. The San Gabriel Mountains fill the lower left half of the image. At the extreme lower left is Pasadena. High resolution topographic data such as these are used by geologists to study the role of active tectonics in shaping the landscape, and to produce earthquake hazard maps.

    This image was generated using topographic data from the Shuttle Radar Topography Mission. Colors show the elevation as measured by SRTM. Each cycle of colors (from pink through blue back to pink) represents an equal amount of elevation difference (400 meters, or 1300 feet) similar to contour lines on a standard topographic map. This image contains about 2400 meters (8000 feet) of total relief. For the shading, a computer-generated artificial light source illuminates the elevation data to produce a pattern of light and shadows. Slopes facing the light appear bright, while those facing away are shaded. Shaded relief maps are commonly used in applications such as geologic mapping and land use planning.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11,2000, uses the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission is designed to

  17. Investigating Fault Slip and Rheology Along the San Andreas Fault in the San Juan Bautista Region

    NASA Astrophysics Data System (ADS)

    Taira, T.; Burgmann, R.; Nadeau, R. M.; Dreger, D. S.

    2012-12-01

    An improved understanding of the connection between seismic behavior and fault-zone rheology at depth is an essential step toward understanding the underlying mechanics of the faulting process. We investigate the seismicity along the northernmost creeping section of the San Andreas fault near San Juan Bautista (SJB), California, by systematically examining spatiotemporal behaviors of the aftershock sequences following the 12 August 1998 Mw 5.1 SJB earthquake. This 1998 SJB earthquake was the largest historic earthquake in the SJB area and was associated with a large slow slip event. Using a waveform cross-correlation approach (Peng and Zhao, 2009, NatureGeo), we have detected previously uncataloged earthquakes (about 500 events), resolving details of the aftershock activity in a zone at a depth of 9 km about 7 km northwest of the 1998 SJB mainshock. This aftershock zone is marked by one of the highest changes in the seismicity rate, exhibiting a delayed peak (about 20 hours after the mainshock) in the rate of aftershocks preceded by a period of very low rate of aftershocks since the mainshock. Subsequently, the rate of aftershocks shows power-law decay with time for about 1 month, and then the aftershock activity approached the pre-earthquake background level. This temporal behavior of the aftershock activity is different from the predicted aftershock decay based on the model of Dieterich (1994, JGR). Instead, our observation is more consistent with the decay rate of aftershocks occurring in the transition zone between locked and stable slip, as simulated numerically by Kaneko and Lapusta (2008, JGR). Our waveform analysis also identifies over 20 repeating microearthquake sequences (or groups of earthquakes with similar waveforms) associated with the 1998 SJB mainshock. The majority of the sequences have events occurring in the first month of the postseismic period. In other words, they reflect short-lived, accelerated repeater recurrences activated by the 1998 SJB

  18. Extensive Deep Rock Damage in the San Andreas Fault at SAFOD

    NASA Astrophysics Data System (ADS)

    Ellsworth, W. L.; Malin, P. E.

    2011-12-01

    When earthquakes rupture faults they release elastic strain energy stored in the surrounding rocks and reduce the strength of the fault through inelastic deformation. Over time, mechanical damage accumulates resulting in the formation of a low-velocity channel in the fault zone that dramatically affects the propagation of seismic waves. These effects include scattering and attenuation of body waves, and the generation of fault zone head waves and fault zone guided waves (FZGW). Core samples, well logs, and seismograms recorded at multiple locations in the San Andreas Fault Observatory at Depth (SAFOD) borehole near Parkfield, CA define a laterally-extensive low-velocity channel that extends from the surface more than half way through the seismogenic crust. At the SAFOD crossing of the San Andreas Fault (SAF), a complex 200-m-wide zone of anomalously low P and S velocities defines the damage zone. FZGW observations show that it continues to the northeast for 10 km. Southeast of SAFOD, FZGW are observed for some but not all earthquakes, consistent with the multi-stranded nature of the fault shown by microearthquake locations. The SAFOD damage zone is heterogeneous and contains three 2-m-wide ultra-low-velocity active fault "cores," the bounding Southwest Deforming Zones (SDZ) and Northeastern Boundary Fault (NBF), and the main fault trace at the Central Deforming Zone (CDZ). The CDZ also forms the southwestern border of a 30-m-wide zone of reduced seismic velocities that are intermediate to those of the broader damage zone and the CDZ, SDZ and NBF. FZGW observations show that the 30 to 60-m-wide-channel extends to a depth of 7 km below SAFOD. The channel's extent, low seismic velocities and location are difficult to explain by processes associated with a creeping fault and sparsely distributed microearthquakes. While some fracturing in the rocks adjacent to the creeping fault trace would be expected, the asymmetry with respect to the creeping fault and the channel

  19. San Andreas Fault, Southern California, Shaded relief, wrapped color as height

    NASA Technical Reports Server (NTRS)

    2000-01-01

    This topographic image vividly displays California's famous San Andreas Fault along the southwestern edge of the Mojave Desert, 75 kilometers (46 miles) north of downtown Los Angeles. The entire segment of the fault shown in this image last ruptured during the Fort Tejon earthquake of 1857. This was one of the greatest earthquakes ever recorded in the U.S., and it left an amazing surface rupture scar over 350 kilometers in length along the San Andreas. Were the Fort Tejon shock to happen today, the damage would run into billions of dollars, and the loss of life would likely be substantial, as the communities of Wrightwood, Palmdale, and Lancaster (among others) all lie upon or near the 1857 rupture area. The San Gabriel Mountains fill the lower left half of the image. At the extreme lower left is Pasadena. High resolution topographic data such as these are used by geologists to study the role of active tectonics in shaping the landscape, and to produce earthquake hazard maps.

    This image was generated using topographic data from the Shuttle Radar Topography Mission. Colors show the elevation as measured by SRTM. Each cycle of colors (from pink through blue back to pink) represents an equal amount of elevation difference (400 meters, or 1300 feet) similar to contour lines on a standard topographic map. This image contains about 2400 meters (8000 feet) of total relief. For the shading, a computer-generated artificial light source illuminates the elevation data to produce a pattern of light and shadows. Slopes facing the light appear bright, while those facing away are shaded. Shaded relief maps are commonly used in applications such as geologic mapping and land use planning.

    The Shuttle Radar Topography Mission (SRTM), launched on February 11,2000, uses the same radar instrument that comprised the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) that flew twice on the Space Shuttle Endeavour in 1994. The mission is designed to

  20. Talc-Bearing Fault at Coseismic Velocities: an Attempt to explain the San Andreas Fault Behavior

    NASA Astrophysics Data System (ADS)

    Boutareaud, S.; Hirose, T.; Doan, M.; Andreani, M.; Calugaru, D.

    2009-12-01

    Talc is one of the few minerals not following the Byerlee law: friction coefficient of ~0.25 at low velocities and poorly known frictional properties, especially at seismic velocities. Talc has recently been identified in the San Andreas Fault (Moore and Rymer, 2007), and is expected to occur along fault zones within subduction zone. Talc can then affect their seismic behaviour significantly. The properties of the talc were studied by high-velocity rotary-shear experiments carried out at 1.31 m/s, at normal stresses of 0.6 to 1.9 MPa, using the frictional testing apparatus at Kochi/JAMSTEC. The experimental gouge is a pure natural talc schist powder (99.9 wt.%). The samples were sheared under dry (room moisture conditions) or wet (saturated) conditions. During experiments, we measured the evolution of shear stress, simulated fault thickness, moisture release and temperature through the whole simulated fault. Main results are as follows: 1) At the onset of slip, a slip weakening is observed for all experiments with a higher slope value in wet conditions, and a larger Dc value for dry conditions: a value comprised between 0.05 and 6.06 m for wet tests, and 5.72 and 30.87 m for dry tests. 2) The weakening behaviour is strongly dependent on normal stress. 3) The dynamic friction is lower in wet conditions: a peak value of 0.98-0.65 to a steady state value of 0.17-0.26 for dry tests, and a peak value of 0.25-0.52 to a steady state value of 0.08-0.22 for wet tests. 4) Dry samples only experienced large fault dilation comprised between 0.14 and 1.86 mm, as applied normal stress increases. 5) Wet samples only exhibited a large release of water steam. 6) A higher maximum temperature for dry conditions at 1 MPa normal stress: 570 °C for dry tests and 350 °C for wet tests. Microstructural observation with an optical microscope and SEM showed evidence that shear localization processes are different between wet and dry experiments, but a Principal Slip Zone formed by with

  1. The San Andreas Fault in the San Francisco Bay area, California: a geology fieldtrip guidebook to selected stops on public lands

    USGS Publications Warehouse

    Stoffer, Philip W.

    2005-01-01

    This guidebook contains a series of geology fieldtrips with selected destinations along the San Andreas Fault in part of the region that experienced surface rupture during the Great San Francisco Earthquake of 1906. Introductory materials present general information about the San Andreas Fault System, landscape features, and ecological factors associated with faults in the South Bay, Santa Cruz Mountains, the San Francisco Peninsula, and the Point Reyes National Seashore regions. Trip stops include roadside areas and recommended hikes along regional faults and to nearby geologic and landscape features that provide opportunities to make casual observations about the geologic history and landscape evolution. Destinations include the sites along the San Andreas and Calaveras faults in the San Juan Bautista and Hollister region. Stops on public land along the San Andreas Fault in the Santa Cruz Mountains in Santa Clara and Santa Cruz counties include in the Loma Prieta summit area, Forest of Nicene Marks State Park, Lexington County Park, Sanborn County Park, Castle Rock State Park, and the Mid Peninsula Open Space Preserve. Destinations on the San Francisco Peninsula and along the coast in San Mateo County include the Crystal Springs Reservoir area, Mussel Rock Park, and parts of Golden Gate National Recreation Area, with additional stops associated with the San Gregorio Fault system at Montara State Beach, the James F. Fitzgerald Preserve, and at Half Moon Bay. Field trip destinations in the Point Reyes National Seashore and vicinity provide information about geology and character of the San Andreas Fault system north of San Francisco.

  2. Crustal velocity field near the big bend of California's San Andreas fault

    USGS Publications Warehouse

    Snay, R.A.; Cline, M.W.; Philipp, C.R.; Jackson, D.D.; Feng, Y.; Shen, Z.-K.; Lisowski, M.

    1996-01-01

    We use geodetic data spanning the 1920-1992 interval to estimate the horizontal velocity field near the big bend segment of California's San Andreas fault (SAF). More specifically, we estimate a horizontal velocity vector for each node of a two-dimensional grid that has a 15-min-by-15-min mesh and that extends between latitudes 34.0??N and 36.0??N and longitudes 117.5??W and 120.5??W. For this estimation process, we apply bilinear interpolation to transfer crustal deformation information from geodetic sites to the grid nodes. The data include over a half century of triangulation measurements, over two decades of repeated electronic distance measurements, a decade of repeated very long baseline interferometry measurements, and several years of Global Positioning System measurements. Magnitudes for our estimated velocity vectors have formal standard errors ranging from 0.7 to 6.8 mm/yr. Our derived velocity field shows that (1) relative motion associated with the SAF exceeds 30 mm/yr and is distributed on the Earth's surface across a band (> 100 km wide) that is roughly centered on this fault; (2) when velocities are expressed relative to a fixed North America plate, the motion within our primary study region has a mean orientation of N44??W ?? 2?? and the surface trace of the SAF is congruent in shape to nearby contours of constant speed yet this trace is oriented between 5?? and 10?? counterclockwise relative to these contours; and (3) large strain rates (shear rates > 150 nrad/yr and/or areal dilatation rates < -150 nstr/yr) exist near the Garlock fault, near the White Wolf fault, and in the Ventura basin.

  3. Shallow soil CO2 flow along the San Andreas and Calaveras Faults, California

    USGS Publications Warehouse

    Lewicki, J.L.; Evans, William C.; Hilley, G.E.; Sorey, M.L.; Rogie, J.D.; Brantley, S.L.

    2003-01-01

    We evaluate a comprehensive soil CO2 survey along the San Andreas fault (SAF) in Parkfield, and the Calaveras fault (CF) in Hollister, California, in the context of spatial and temporal variability, origin, and transport of CO2 in fractured terrain. CO2 efflux was measured within grids with portable instrumentation and continously with meteorological parameters at a fixed station, in both faulted and unfaulted areas. Spatial and temporal variability of surface CO2 effluxes was observed to be higher at faulted SAF and CF sites, relative to comparable background areas. However, ??13C (-23.3 to - 16.4???) and ??14C (75.5 to 94.4???) values of soil CO2 in both faulted and unfaulted areas are indicative of biogenic CO2, even though CO2 effluxes in faulted areas reached values as high as 428 g m-2 d-1. Profiles of soil CO2 concentration as a function of depth were measured at multiple sites within SAF and CF grids and repeatedly at two locations at the SAF grid. Many of these profiles suggest a surprisingly high component of advective CO2 flow. Spectral and correlation analysis of SAF CO2 efflux and meteorological parameter time series indicates that effects of wind speed variations on atmospheric air flow though fractures modulate surface efflux of biogenic CO2. The resulting areal patterns in CO2 effluxes could be erroneously attributed to a deep gas source in the absence of isotopic data, a problem that must be addressed in fault zone soil gas studies.

  4. Constraints on the mechanics of the Southern San Andreas fault system from GPS velocity and stress

    NASA Astrophysics Data System (ADS)

    Becker, T. W.; Hardebeck, J. L.; Anderson, G.

    2003-12-01

    We use Global Positioning System (GPS) derived velocities and stress-orientations to study the distribution of long-term slip on the system of faults comprising the southern California plate boundary region. Of particular interest is how slip is partitioned over multiple earthquake cycles between the San Andreas Fault (SAF), the San Jacinto Fault (SJF) and the Eastern California Shear Zone. Some prior paleoseismologic and geodetic work places the majority of slip on the SAF. Other studies, however, find that the SJF accommodates about half of the slip in the south, implying half as much slip on the San Bernardino segment of the SAF. Two new data sets are used to further constrain the mechanics of the SAF. The first is the Southern California Earthquake Center's geodetic velocity field version 3 (Shen et al., 2003), which includes much improved coverage over prior models. The second is a regional map of stress field orientations at seismogenic depths, as determined from an inversion of earthquake focal mechanisms. While GPS data has been used in similar studies, this is the first application of stress field observations to this problem. We construct a simplified version of the southern California fault system, and model the surface velocities using a block model with elastic strain accumulation, following Meade et al. (2002). Additionally, we model the stress orientations at seismogenic depths, assuming that the stress field results from the loading of active faults. An inversion for fault slip rates is performed to simultaneously fit the GPS and stress observations. The model fit to the data is good in general, indicating that a simple mechanical model can capture both observed interseismic strain and stress accumulation. We evaluate the sensitivity of the slip rate solutions to the different datasets and identify "anomalous" fault segments with stresses that deviate from our simple loading model.

  5. Strain accumulation along the San Andreas fault system East of San Francisco Bay, California

    USGS Publications Warehouse

    Prescott, W.H.; Lisowski, M.

    1983-01-01

    The occurrence of several large earthquakes to the east of San Francisco Bay during historical times, and present high levels of microseismicity, indicate that a significant part of the relative plate motion may be occurring east of San Francisco Bay. Furthermore, the Hayward fault is known to be slipping aseismically at the surface, and the Calaveras fault may be slipping aseismically also. These facts raise an important question: Is the observed creep rate accommodating all of the east bay deformation or is there a significant amount of strain accumulating along these faults? Several small survey networks (< 2 km diameter) located along the Hayward and Calaveras faults, have been measured occasionally since 1965. Recent observations of these and other networks have been made by the U.S. Geological Survey. These observations imply a surface slip rate on the Hayward fault at Fremont, Hayward, Berkeley, and Richmond of about 6 mm/yr. On the Calaveras fault, north of the Hayward-Calaveras fault junction, surface slip rates have been determined from only four data sets. Three of which give a rate of 3 mm/yr. The U.S. Geological Survey annually measures 32 longer lines (10-30 km) in the east bay. Observations of these lines extend back to 1977 for most and to 1970 for some of the lines. The observed creep rates and the data for the longer east-bay lines provide constraints on the amount and position of deeper slip on the Hayward and Calaveras faults. After correcting for line-length changes due to fault slip, we calculated the strain accumulation rate. The shear strain rate parallel to east bay faults is 0.07 ?? 0.02 ??strain/yr, a rate well below that of other areas along the San Andreas fault system, suggesting that creep is relieving a large part of the strain in this area. ?? 1983.

  6. Properties of shallow creep on the Southern San Andreas Fault from InSAR and GPS

    NASA Astrophysics Data System (ADS)

    Lindsey, E. O.; Fialko, Y.; Bock, Y.

    2012-12-01

    We present a detailed characterization of surface creep and off-fault deformation along the Coachella Valley segment of the San Andreas Fault from 33.3-33.7 deg. North using a combination of campaign GPS and multiple InSAR viewing geometries. An array of 30 survey monuments spanning 3km across the fault at Painted Canyon was occupied with campaign-mode GPS between 2007 and 2012, providing a direct measurement of creep at that location; the rate of 3+/-1mm/yr is in good agreement with long-term geologic estimates of 2-4 mm/yr (Sieh and Williams, 1990). A combination of over 400 radar interferograms from ascending and descending Envisat (Tracks 356 and 77), ALOS (Tracks 213-214) (Tong et. al, 2012), and ERS (Track 356) were used to isolate the creep signal from other non-tectonic sources of deformation, providing a high-resolution image of the near-fault horizontal deformation pattern. The results indicate a creep rate consistent with the GPS at Painted Canyon, and reveal along-strike variations in both the creep rate and effective shear zone width. This width varies from less than a few meters at Painted Canyon to as wide as 4km along the North Shore section of the fault. In this area, previous geologic and geodetic observations have not identified localized surface creep. Instead, the satellite data indicates 3-4 mm/yr of fault-parallel surface deformation is distributed over a wide shear zone. We compare the geodetic data to numerical simulations of earthquake cycles incorporating laboratory-derived rate and state friction, allowing us to constrain the depth extent of the velocity-strengthening and velocity-weakening layers and the process of stress evolution in the seismogenic zone.

  7. Locating Very-Low-Frequency Earthquakes in the San Andreas Fault.

    NASA Astrophysics Data System (ADS)

    Peña-Castro, A. F.; Harrington, R. M.; Cochran, E. S.

    2016-12-01

    The portion of tectonic fault where rheological properties transtition from brittle to ductile hosts a variety of seismic signals suggesting a range of slip velocities. In subduction zones, the two dominantly observed seismic signals include very-low frequency earthquakes ( VLFEs), and low-frequency earthquakes (LFEs) or tectonic tremor. Tremor and LFE are also commonly observed in transform faults, however, VLFEs have been reported dominantly in subduction zone environments. Here we show some of the first known observations of VLFEs occurring on a plate boundary transform fault, the San Andreas Fault (SAF) between the Cholame-Parkfield segment in California. We detect VLFEs using both permanent and temporary stations in 2010-2011 within approximately 70 km of Cholame, California. We search continous waveforms filtered from 0.02-0.05 Hz, and remove time windows containing teleseismic events and local earthquakes, as identified in the global Centroid Moment Tensor (CMT) and the Northern California Seismic Network (NCSN) catalog. We estimate the VLFE locations by converting the signal into envelopes, and cross-correlating them for phase-picking, similar to procedures used for locating tectonic tremor. We first perform epicentral location using a grid search method and estimate a hypocenter location using Hypoinverse and a shear-wave velocity model when the epicenter is located close to the SAF trace. We account for the velocity contrast across the fault using separate 1D velocity models for stations on each side. Estimated hypocentral VLFE depths are similar to tremor catalog depths ( 15-30 km). Only a few VLFEs produced robust hypocentral locations, presumably due to the difficulty in picking accurate phase arrivals with such a low-frequency signal. However, for events for which no location could be obtained, the moveout of phase arrivals across the stations were similar in character, suggesting that other observed VLFEs occurred in close proximity.

  8. Effects of Hayward fault interactions with the Rodgers Creek and San Andreas faults

    NASA Astrophysics Data System (ADS)

    Parsons, T.; Geist, E.; Jachens, R.; Sliter, R.; Jaffe, B.

    2003-12-01

    Finite-element and crustal-structure models of the Hayward fault emphasize its position within a network of interacting faults, and indicate a number of expected influences from other faults. For example, a new structural cross section across San Pablo Bay in association with potential field maps allows us to map and model detailed interactions between the Hayward and Rodgers Creek faults. The two faults do not appear to connect at depth, and finite-element models indicate growing extensional stress in the stepover between the two faults. A model consequence of extensional stress in the stepover, combined with long-term interaction with the San Andreas fault, is normal-stress reduction (unclamping) of the north Hayward fault. If this occurs in the real Earth, then substantial reduction in frictional resistance on the north Hayward fault is expected, which might in turn be expected to influence the distribution of creep. Interaction effects on a shorter time scale are also evident. The 1906 San Francisco, and 1989 Loma Prieta earthquakes are calculated to have reduced stress on the Hayward fault at seismogenic depths. Models of the 1906 earthquake show complex interactions; coseismic static stress changes drop stress on the north Hayward fault while upper mantle viscoelastic relaxation slightly raises the stressing rate. Stress recovery is calculated to have occurred by ~1980, though earthquake probability is still affected by the delay induced by stress reduction. We conclude that the model Hayward fault is strongly influenced by its neighbors, and it is worth considering these effects when studying and attempting to understand the real fault.

  9. Variability of fault slip behavior along the San Andreas Fault in the San Juan Bautista Region

    NASA Astrophysics Data System (ADS)

    Taira, Taka'aki; Bürgmann, Roland; Nadeau, Robert M.; Dreger, Douglas S.

    2014-12-01

    An improved understanding of the time history of fault slip at depth is an essential step toward understanding the underlying mechanics of the faulting process. Using a waveform cross-correlation approach, we document spatially and temporally varying fault slip along the northernmost creeping section of the San Andreas Fault near San Juan Bautista (SJB), California, by systematically examining spatiotemporal behaviors of characteristically repeating earthquakes (CREs). The spatial distribution of pre-1998 SJB earthquake (1984-1998) fault slip rate inferred from the CREs reveals a ~15 km long low creep or partially locked section located near the 1998 Mw 5.1 SJB earthquake rupture. A finite-fault slip inversion reveals that the rupture of the 1998 SJB earthquake is characterized by the failure of a compact ~4 km2 asperity with a maximum slip of about 90 cm and corresponding peak stress drop of up to 50 MPa, whereas the mean stress drop is about 15 MPa. Following the 1998 earthquake, the CRE activity was significantly increased in a 5-10 km deep zone extending 2-7 km northwest of the main shock, which indicates triggering of substantial aseismic slip. The postseismic slip inferred from the CRE activity primarily propagated to the northwest and released a maximum slip of 9 cm. In this 5-10 km depth range, the estimated postseismic moment release is 8.6 × 1016 N m, which is equivalent to Mw 5.22. The aseismic slip distribution following the 1998 earthquake is not consistent with coseismic stress-driven afterslip but represents a triggered, long-lasting slow earthquake.

  10. Paleoseismic evidence of clustered earthquakes on the San Andreas fault in the Carrizo Plain, California

    SciTech Connect

    Grant, L.B.; Sieh, K.

    1994-04-01

    Exposures we have excavated across the San Andreas fault contradict the hypothesis that part of the fault in the Carrizo Plain is unusually strong and experiences relatively infrequent rupture. The exposures record evidence of at least seven surface-rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in-situ plants. Five large earthquakes have occurred since 1218 A.D. The most recent earthquake, event A, was the 1857 Fort Tejon earthquake, which we have associated with 6.6-10 m of dextral slip along the main fault trace. The penultimate earthquake, event B, most likely occurred within the period A.D. 1405-1510. Slip from either events B and C combined or from event B alone, totals 7-11 m. Three earthquakes, events C, D, and E, occurred in a temporal cluster prior to event B and after approximately A.D. 1218. The average recurrence interval within this cluster is 73-116 years, depending on assumptions. Events F and G occurred after 200 years B.C. A depositional hiatus between events E and F may hide evidence of additional earthquakes. Events B and D within the Carrizo cluster of A.D. 1218-1510 may correlate with events T (A.D. 1329-1363) and V (A.D. 1465-1495) at Pallett Creek on the Mojave `segment` of the fault. This suggests two fault ruptures similar in length to that of 1857. Events C and E apparently did not rupture the Mojave section, which suggests that the Carrizo segment has ruptured independently or in combination with segments to the north. Irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic `supercycles.`

  11. Paleoseismic evidence of clustered earthquakes on the San Andreas fault in the Carrizo Plain, California

    NASA Astrophysics Data System (ADS)

    Grant, Lisa B.; Sieh, Kerry

    1994-04-01

    Exposures we have excavated across the San Andreas fault contradict the hypothesis that part of the fault in the Carrizo Plain is unusually strong and experiences relatively infrequent rupture. The exposures record evidence of at least seven surface-rupturing earthquakes which have been approximately dated by accelerated mass spectrometry radiocarbon analysis of detrital charcoal and buried in-situ plants. Five large earthquakes have occurred since 1218 A.D. The most recent earthquake, event A, was the 1857 Fort Tejon earthquake, which we have associated with 6.6-10 m of dextral slip along the main fault trace. The penultimate earthquake, event B, most likely occurred within the period A.D. 1405-1510. Slip from either events B and C combined or from event B alone, totals 7-11 m. Three earthquakes, events C, D, and E, occurred in a temporal cluster prior to event B and after approximately A.D. 1218. The average recurrence interval within this cluster is 73-116 years, depending on assumptions. Events F and G occurred after 200 years B.C. A depositional hiatus between events E and F may hide evidence of additional earthquakes. Events B and D within the Carrizo cluster of A.D. 1218-1510 may correlate with events T (A.D. 1329-1363) and V (A.D. 1465-1495) at Pallett Creek on the Mojave 'segment' of the fault. This suggests two fault ruptures similar in length to that of 1857. Events C and E apparently did not rupture the Mojave section, which suggests that the Carrizo segment has ruptured independently or in combination with segments to the north. Irregular repeat times of large earthquakes suggest a pattern of clustered events at the end of seismic 'supercycles.'

  12. A Composite Chronology of Earthquakes From the Bidart fan Paleoseismic Site, San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Grant, L. B.; Arrowsmith, J. R.; Akciz, S.

    2005-12-01

    Chronologies of earthquakes spanning at least ten ruptures at multiple sites are required for developing robust models of fault behavior and forecasts of future earthquakes. Such a long chronology can be obtained by placing multiple trenches across the San Andreas fault at the Bidart alluvial fan paleoseismic site in the Carrizo Plain to capture the spatio-temporal record of earthquakes created by the interplay of surface rupture and spatially varying deposition. Exposures from one trench reveal evidence of at least 6 and probably 7 earthquakes since 3000 BP. Evidence of 7 earthquakes since 2200 BP has been interpreted from exposures in 3 other trenches. Analysis of exposures from two new trenches is in progress. Excavations reveal alternating sequences of depositional preservation and gaps in the record of earthquakes. The "gaps" are massive featureless zones caused by bioturbation of the fan surface while that portion of the fan was depositionally inactive. When the depositional record of 4 trenches is combined, it yields a composite chronology of at least10 surface ruptures over the last 3000 years, for a minimum average recurrence interval of 300 years if the most recent event exposed in all trenches is assumed to be the 1857 Fort Tejon earthquake. So far, the uncertainty in dates of pre-1857 ruptures ranges from decades to millennia, and at least 5 of the 10 recognized earthquakes are obscured by depositional gaps at one of the trench sites. Therefore, synchroneity of ruptures at different trench sites is difficult to establish, and there is the possibility that the existing record contains more than 10 earthquakes and/or additional ruptures may have occurred that are not preserved by deposition.

  13. A San Andreas-sized Strike-slip Fault on Europa

    NASA Astrophysics Data System (ADS)

    Tufts, R.; Greenberg, R.; Geissler, P.

    1996-09-01

    Astypalaea Linea, a lineament in the extreme southern hemisphere of Europa, has been found to be a global-scale strike-slip fault, based on a palinspastic reconstruction of landscape on reprojected Voyager 2 images. The fault accommodates 35 km of right-lateral offset and extends at least 810 km - a length comparable to the San Andreas Fault in California. It exhibits familiar strike-slip features including braids and pull-aparts. Straight segments of the fault are concentric about an Euler pole provisionally located at (-48deg , 247.25deg W). Spanning over 29deg from (-60deg ,191deg W) to (-78.5deg , 268.5deg W) Astypalaea Linea is the longest strike-slip fault yet identified on Europa. The fault is consistent with differential stress magnitudes and stress directions predicted for high Europan latitudes due to possible non- synchronous rotation (tidal bulge in its present location) (Greenberg and Weidenschilling, 1984; Helfenstein and Parmentier, 1985). Extension on neighboring gray band Thynia Linea matches the same stress field (Pappalardo and Sullivan, 1996); thus, Astypalaea Linea and Thynia Linea may be part of a south polar deformation zone which acts as a "structural set" (Lucchitta and Soderblom, 1982). Analogous structures may exist at the Europan north pole, although factors such as a possible global structural dichotomy (Lucchitta and Soderblom, 1981) may affect their occurrence. Lateral crustal motion, as implied by the fault, is consistent with a subsurface viscous horizon structurally decoupling the outer layer of the icy Jovian satellite from its interior (e.g. Schenk and McKinnon, 1989).

  14. Tectonic framework of the Parkfield-Cholame area, central San Andreas fault zone, California

    SciTech Connect

    Sims, J.D.; Ross, D.C.; Irwin, W.P.

    1985-01-01

    Recent geologic mapping of the NW-trending San Andreas fault zone (SAFZ) in the southern Diablo Range reveals details of this structurally complex region. Movement on the fault juxtaposes dissimilar tectonic terranes. The region on the NE side is characterized by complexly folded and faulted rocks of the Franciscan assemblage, the Coast Range ophiolite, and sedimentary rocks of the Great Valley sequence and younger formations. The region on the SW side is characterized by crystalline basement rocks of the Salinia terrane overlain by slightly deformed Pliocene and Pleistocene gravel and Miocene and Pliocene sedimentary rocks. The active trace of the SAFZ is along the SW side of a belt of melange that separates the Salinia terrane from the terranes to the NE. The active main trace is notable for a right step over of about 1 km in the southern part of the area and a 5/sup 0/ left bend in the northern part of the area. The melange consists of highly sheared and deformed rocks of late Cenozoic units, and exotic blocks of granite, gabbro, and marble. Deformation of Late Cretaceous and younger rocks east of the SAFZ varies with their age as follows: 1) Late Cretaceous rocks are strongly deformed and overlain by late Cenozoic rocks with angular unconformity, 2) early(.) and middle Miocene rocks are the most complexly folded, 3) late Miocene and early Pliocene strata are less complexly deformed, and 4) Pliocene and Pleistocene rocks the least deformed. Folding resulted from north-south compression across the SAFZ since early (.) Miocene time.

  15. Detection of a locked zone at depth on the Parkfield, California, segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Harris, Ruth A.; Segall, Paul

    1987-07-01

    The Parkfield, California, segment of the San Andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked Carrizo Plain segment to the southeast. The rate of shallow fault slip decreases from 25-30 mm/yr northwest of the epicenter of the 1966 Parkfield earthquake to zero at the southeastern end of the 1966 rupture zone. Data from a network of trilateration lines spanning the San Andreas fault near Parkfield and extending to the Pacific coast near San Luis Obispo shed light on the rate of fault slip at depth since the 1966 earthquake. In this study, average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the Parkfield fault segment. The fault is taken to be a vertical surface with unknown distribution of strike-slip displacement in an elastic half-space. A striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 Parkfield earthquake. The data require that the locked zone extend nearly as far north as the 1966 epicenter; however, the vertical extent of the locked zone is not well resolved. Over much of the Parkfield segment the fault is slipping faster at the earth's surface than it is at seismogenic depths. In order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the San Andreas. The inversion results suggest a spatially uniform normal strain of -0.06 μstrain/yr. The orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region. The magnitude of the contraction is consistent with convergence rates inferred from global plate motion models.

  16. High-resolution seismic velocities and shallow structure of the San Andreas fault zone at Middle Mountain, Parkfield, California

    USGS Publications Warehouse

    Catchings, R.D.; Rymer, M.J.; Goldman, M.R.; Hole, J.A.; Huggins, R.; Lippus, C.

    2002-01-01

    A 5-km-long, high-resolution seismic imaging survey across the San Andreas fault (SAF) zone and the proposed San Andreas Fault Observatory at Depth (SAFOD) drill site near Parkfield, California, shows that velocities vary both laterally and vertically. Velocities range from 4.0 km/sec) probably correspond to granitic rock of the Salinian block, which is exposed a few kilometers southwest of the SAF. The depth to the top of probable granitic rock varies laterally along the seismic profile but is about 600 m below the surface at the proposed SAFOD site. We observe a prominent, lateral low-velocity zone (LVZ) beneath and southwest of the surface trace of the SAF. The LVZ is about 1.5 km wide at 300-m depth but tapers to about 600 m wide at 750-m depth. At the maximum depth of the velocity model (750 m), the LVZ is centered approximately 400 m southwest of the surface trace of the SAF. Similar velocities and velocity gradients are observed at comparable depths on both sides of the LVZ, suggesting that the LVZ is anomalous relative to rocks on either side of it. Velocities within the LVZ are lower than those of San Andreas fault gouge, and the LVZ is also anomalous with respect to gravity, magnetic, and resistivity measurements. Because of its proximity to the surface trace of the SAF, it is tempting to suggest that the LVZ represents a zone of fractured crystalline rocks at depth. However, the LVZ instead probably represents a tectonic sliver of sedimentary rock that now rests adjacent to or encompasses the SAF. Such a sliver of sedimentary rock implies fault strands on both sides and possibly within the sliver, suggesting a zone of fault strands at least 1.5 km wide at a depth of 300 m, tapering to about 600 m wide at 750-m depth. Fluids within the sedimentary sliver are probably responsible for observed low-resistivity values.

  17. Evaluating the San Andreas Fault Zone Permeability Structure by Using On-Line mud gas Monitoring Data

    NASA Astrophysics Data System (ADS)

    Wiersberg, T.; Erzinger, J.

    2006-12-01

    To archieve a better understanding of the permeability structure at seismogenic depths of the San Andreas Fault, we have evaluated data from drill mud gas from the SAFOD Main Hole (San Andreas Fault Observatory at Depth). Two gas-rich zones at the margins of the fault core differ significantly in the composition of CH4, H2 and CO2, which are the most abundant non-atmospheric gases in the entire hole. The gases enter the bore hole through bedding-plane fractures in the upper zone (approx. 2700 2900 m) and probably from below 3550 m. Separation of two individual hydrogeologic systems by a low-permeable fault core is also indicated by the helium isotopic composition, which is 0.4-0.6 Ra in the upper zone and 0.8-0.9 Ra in the lower one. However, the overall contribution of mantle-derived helium is relatively low. The carbon and hydrogen isotopic composition display an organic gas source of hydrocarbons and CO2. High concentration of hydrogen in the fractured zones at the margins of the fault core are consistent with the concept of hydrogen formation by interaction of water with fresh mineral surfaces generated by tectonic activities. The fault core, localized between approx. 3100 - 3450 m depth, is generally low in gas, in particular in hydrogen. Within the fault core, two sections with higher gas content, but distinct gas composition were identified in 3150 3200 m and 3310 - 3340 m depths. We conclude that the SAF consists of permeable strata at the fault zone margins and a generally low- permeable fault core. In the fault core, separate gas-rich lenses are interstratified. The gas inventory of the San Andreas Fault Zone is dominated by in-situ produced gases, the contribution of gases migrated from greater depths is probably low.

  18. Response of deformation patterns to reorganization of the southern San Andreas fault system since ca. 1.5 Ma

    NASA Astrophysics Data System (ADS)

    Fattaruso, Laura A.; Cooke, Michele L.; Dorsey, Rebecca J.; Housen, Bernard A.

    2016-12-01

    Between 1.5 and 1.1 Ma, the southern San Andreas fault system underwent a major reorganization that included initiation of the San Jacinto fault zone and termination of slip on the extensional West Salton detachment fault. The southern San Andreas fault itself has also evolved since this time, with several shifts in activity among fault strands within San Gorgonio Pass. We use three-dimensional mechanical Boundary Element Method models to investigate the impact of these changes to the fault network on deformation patterns. A series of snapshot models of the succession of active fault geometries explore the role of fault interaction and tectonic loading in abandonment of the West Salton detachment fault, initiation of the San Jacinto fault zone, and shifts in activity of the San Andreas fault. Interpreted changes to uplift patterns are well matched by model results. These results support the idea that initiation and growth of the San Jacinto fault zone led to increased uplift rates in the San Gabriel Mountains and decreased uplift rates in the San Bernardino Mountains. Comparison of model results for vertical-axis rotation to data from paleomagnetic studies reveals a good match to local rotation patterns in the Mecca Hills and Borrego Badlands. We explore the mechanical efficiency at each step in the modeled fault evolution, and find an overall trend toward increased efficiency through time. Strain energy density patterns are used to identify regions of incipient faulting, and support the notion of north-to-south propagation of the San Jacinto fault during its initiation.

  19. Observations of strain accumulation across the San Andreas fault near Palmdale, California, with a two-color geodimeter

    USGS Publications Warehouse

    Langbein, J.O.; Linker, M.F.; McGarr, A.; Slater, L.E.

    1982-01-01

    Two-color laser ranging measurements during a 15-month period over a geodetic network spanning the San Andreas fault near Palmdale, California, indicate that the crust expands and contracts aseismically in episodes as short as 2 weeks. Shear strain parallel to the fault has accumulated monotonically since November 1980, but at a variable rate. Improvements in measurement precision and temporal resolution over those of previous geodetic studies near Palmdale have resulted in the definition of a time history of crustal deformation that is much more complex than formerly realized. Copyright ?? 1982 AAAS.

  20. Timing of large earthquakes since A.D. 800 on the Mission Creek strand of the San Andreas fault zone at Thousand Palms Oasis, near Palm Springs, California

    USGS Publications Warehouse

    Fumal, T.E.; Rymer, M.J.; Seitz, G.G.

    2002-01-01

    Paleoseismic investigations across the Mission Creek strand of the San Andreas fault at Thousand Palms Oasis indicate that four and probably five surface-rupturing earthquakes occurred during the past 1200 years. Calendar age estimates for these earthquakes are based on a chronological model that incorporates radio-carbon dates from 18 in situ burn layers and stratigraphic ordering constraints. These five earthquakes occurred in about A.D. 825 (770-890) (mean, 95% range), A.D. 982 (840-1150), A.D. 1231 (1170-1290), A.D. 1502 (1450-1555), and after a date in the range of A.D. 1520-1680. The most recent surface-rupturing earthquake at Thousand Palms is likely the same as the A.D. 1676 ?? 35 event at Indio reported by Sieh and Williams (1990). Each of the past five earthquakes recorded on the San Andreas fault in the Coachella Valley strongly overlaps in time with an event at the Wrightwood paleoseismic site, about 120 km northwest of Thousand Palms Oasis. Correlation of events between these two sites suggests that at least the southernmost 200 km of the San Andreas fault zone may have ruptured in each earthquake. The average repeat time for surface-rupturing earthquakes on the San Andreas fault in the Coachella Valley is 215 ?? 25 years, whereas the elapsed time since the most recent event is 326 ?? 35 years. This suggests the southernmost San Andreas fault zone likely is very near failure. The Thousand Palms Oasis site is underlain by a series of six channels cut and filled since about A.D. 800 that cross the fault at high angles. A channel margin about 900 years old is offset right laterally 2.0 ?? 0.5 m, indicating a slip rate of 4 ?? 2 mm/yr. This slip rate is low relative to geodetic and other geologic slip rate estimates (26 ?? 2 mm/yr and about 23-35 mm/yr, respectively) on the southernmost San Andreas fault zone, possibly because (1) the site is located in a small step-over in the fault trace and so the rate is not be representative of the Mission Creek fault

  1. ["... I shall never forget the gift by which you established yourself as friend in my life!" The letters of Lou Andreas-Salomé to Max Eitingon (1911-1933)].

    PubMed

    Weber, Inge

    2015-01-01

    The correspondence between Andreas-Salomé and the Eitingons draws attention to their long-standing relation. The letters contained among the Eitingon papers in Jerusalem (81 items) were complemented by the much smaller set (5 items) held by the Lou Andreas-Salomé Archives in Göttingen. The material highlights for the first time Eitingon's role in securing Andreas-Salomé's access to the Berlin psychoanalytic association and for her entering psychoanalytic practice. In the 20s the relation between Andreas-Salomé and Mirra Eitingon intensified, based on their common Russian background. Several aspects featured in the letters are discussed in appendixes: the role of Russian language and habits; Max Nachmansohn, an analysand of Andreas-Salomé; her literary gift to Freud's 70th birthday; the dealing with fees in psychoanalysis.

  2. Groundwater withdrawal in the Central Valley, California: implications for San Andreas Fault stressing and lithosphere rheology

    NASA Astrophysics Data System (ADS)

    Lundgren, P.; Liu, Z.; Ali, S. T.; Farr, T.; Faunt, C. C.

    2016-12-01

    Anthropogenic perturbations to crustal loading due to groundwater pumping are increasingly recognized as causing changes in nearby fault stresses. We present preliminary analysis of crustal unloading in the Central Valley (CV), California, for the period 2006-2010 to infer Coulomb stress changes on the central San Andreas Fault (CSAF), lithospheric rheology, and system memory due to more than a century of groundwater withdrawal in the southern CV. We use data-driven unloading estimates to drive three-dimensional (3-D) finite element method models and compare model vertical surface deformation rates with observed GPS uplift rates outside the CV. Groundwater level changes are observed through well water elevation changes and through the resultant surface deformation (subsidence) by interferometric synthetic aperture radar (InSAR) and through broader scale changes in gravity from the GRACE satellite time variable gravity data [Famiglietti et al., 2011] that constrain the overall water volume changes. Combining InSAR with well-water data we are able to estimate the aquifer skeletal elastic and inelastic response and through a linear inversion derive the water volume (load) changes across the Central Valley and compare them with GRACE-inferred groundwater changes. Preliminary 3-D finite element method modeling that considers elastic and viscosity structure in the lithosphere gives three interesting results: 1) elastic models poorly fit the uplift rates near the SAF; 2) viscoelastic models that simulate different unloading histories show the past history of groundwater unloading has significant residual uplift rates and fault stress changes; 3) Coulomb stress change varies from inhibited on the locked (Carrizo) section to promoted on the creeping section of the SAF north of Parkfield. Thus, 3D models that account for lithosphere rheology, loading history viscous relaxation, have significant implications for longer-term time-dependent deformation, stress perturbation, and

  3. Rupture of the Northern San Andreas Fault and Possible Stress Linkages to Cascadia

    NASA Astrophysics Data System (ADS)

    Goldfinger, C.; Grijalva, K.; Burgman, R.; Morey, A.; Johnson, J.; Nelson, H.; Gutierrez-Pastor, J.; Karabanov, E.; Patton, J.; Gracia, E.

    2007-12-01

    We relate the late Holocene Northern San Andreas Fault (NSAF) Offshore/onshore paleoseismic history along the northern California continental margin to a similar dataset from the Cascadia margin. Evidence from stratigraphic correlation and merging of turbidity currents at channel confluences supports synchronous triggering of turbidity currents during the Holocene, when other sources such as storm river flows are less unlikely to reach the abyssal plain. In order to make comparisons between the temporal records from the NSAF and Cascadia, we refine correlations of southern Cascadia great earthquakes using 44 piston/trigger pairs, 7 box cores collected in 1999 and two Kasten cores from 2002, combined with the land paleoseismic record. Stratigraphic correlation is accomplished with P-wave velocity, gamma-ray density, RGB color reflectance, magnetic susceptibility, high-resolution imagery and AMS 14C ages. The late Holocene turbidite record off Cascadia and northern California passes several tests of synchronous triggering. Many turbidites can be correlated stratigraphically between channel sites supported by AMS 14C ages. Paleoseismic work at onshore sites along the Cascadia and NSAF systems shows good correspondence with the offshore record, further circumstantial evidence that the offshore record is primarily earthquake generated. During the last ~2800 years, 15 turbidites including the great 1906 earthquake establish an average repeat time of ~200 years, similar to the onshore value of ~210 years. The combined land and marine paleoseismic record from the southern Cascadia subduction zone, developed using similar methods includes a similar number of events in the past 3000 years. While the recurrence interval for full margin Cascadia events is ~530 years, the southern Cascadia margin has a repeat time of 260-290 years, similar to that of the NSAF. We observe that 11 of the previous 15 NSAF events were preceded by Cascadia events by ~0-80 years, averaging 47 years

  4. Inferring fault rheology from low-frequency earthquakes on the San Andreas

    USGS Publications Warehouse

    Beeler, Nicholas M.; Thomas, Amanda; Bürgmann, Roland; Shelly, David R.

    2013-01-01

    Families of recurring low-frequency earthquakes (LFEs) within nonvolcanic tremor (NVT) on the San Andreas fault in central California show strong sensitivity to shear stress induced by the daily tidal cycle. LFEs occur at all levels of the tidal shear stress and are in phase with the very small, ~400 Pa, stress amplitude. To quantitatively explain the correlation, we use a model from the existing literature that assumes the LFE sources are small, persistent regions that repeatedly fail during shear of a much larger scale, otherwise aseismically creeping fault zone. The LFE source patches see tectonic loading, creep of the surrounding fault which may be modulated by the tidal stress, and direct tidal loading. If the patches are small relative to the surrounding creeping fault then the stressing is dominated by fault creep, and if patch failure occurs at a threshold stress, then the resulting seismicity rate is proportional to the fault creep rate or fault zone strain rate. Using the seismicity rate as a proxy for strain rate and the tidal shear stress, we fit the data with possible fault rheologies that produce creep in laboratory experiments at temperatures of 400 to 600°C appropriate for the LFE source depth. The rheological properties of rock-forming minerals for dislocation creep and dislocation glide are not consistent with the observed fault creep because strong correlation between small stress perturbations and strain rate requires perturbation on the order of the ambient stress. The observed tidal modulation restricts ambient stress to be at most a few kilopascal, much lower than rock strength. A purely rate dependent friction is consistent with the observations only if the product of the friction rate dependence and effective normal stress is ~ 0.5 kPa. Extrapolating the friction rate strengthening dependence of phyllosilicates (talc) to depth would require the effective normal stress to be ~50 kPa, implying pore pressure is lithostatic. If the LFE

  5. Paleoseismic and Holocene slip rate investigations along the San Andreas Fault, at Parkfield, California

    NASA Astrophysics Data System (ADS)

    Toke, N. A.; Arrowsmith, J. R.

    2007-12-01

    Prior to the 2004 Parkfield M6 earthquake, we excavated two paleoseismic trenches across the main San Andreas Fault (SAF) ~1 km south of Parkfield, CA. These excavations showed evidence of deformation from both aseismic creep and ground rupturing earthquakes such as the 2004 event. Despite this effort, it remains unclear if the Parkfield segment of the SAF experiences ground rupture from earthquakes >M6. This is an important question for understanding earthquake hazard in central and southern California, especially considering the central California foreshocks that were felt just prior to the 1857 Fort Tejón M 7.9 earthquake. Additionally, numerous slip budget calculations predict a slip deficit of ~5 m extending into the Parkfield segment and suggest that coseismic slip along the Parkfield segment could propagate further southeast. However, these slip budgets do not include a locally-determined geologic slip rate for the Parkfield segment. It is plausible that the slip rate at Parkfield is lower than along the Carrizo segment to the southeast. A lower slip rate would imply a lower seismic hazard from the SAF and indicate that slip is distributed along adjacent structures at Parkfield. To more thoroughly understand the Parkfield segment of the SAF, the Southwest Fracture Zone (SWFZ; which also ruptured in 2004) must be considered in both paleoseismic and slip rate investigations. One site along the SWFZ, Miller's Vineyard site, is located ~1 km west of Carr Hill along the Ranchita Canyon Rd. Here the SWFZ strikes ~315 degrees (parallel to the SAF) and ruptured in the 2004 earthquake. The Miller's Vineyard site is located along an ephemeral tributary of the Little Cholame Creek that appears to be offset right-laterally. Aerial photography suggests that the SWFZ is delineated by a 30 m wide zone of enhanced vegetation that extends more than 100 m. We expect that excavating this site will reveal deformed Holocene layers of fluvial sand, silt, and channel gravels that

  6. Holocene geologic slip rate for Mission Creek strand of the southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Fryer, R.; Behr, W. M.; Sharp, W. D.; Gold, P. O.

    2015-12-01

    The San Andreas Fault (SAF) is the primary structure accommodating motion between the Pacific and North American plates. The Coachella Valley segment of the southern SAF has not ruptured historically, and is considered overdue for an earthquake because it has exceeded its average recurrence interval. In the northwestern Coachella Valley, this fault splits into three additional fault strands: the Mission Creek strand, which strikes northwest in the San Bernardino Mountains, and the Banning and Garnet Hill strands, which continue west, transferring slip into San Gorgonio Pass. Determining how slip is partitioned between these faults is critical for southern California seismic hazard models. Recent work near the southern end of the Mission Creek strand at Biskra Palms yielded a slip rate of ~14-17 mm/yr since 50 ka, and new measurements from Pushawalla Canyon suggest a possible rate of ~20 mm/yr since 2.5 ka and 70 ka. Slip appears to transfer away from the Mission Creek strand and to the Banning and Garnet Hill strands within the Indio Hills, but the slip rate for the Garnet Hill strand is unknown and the 4-5 mm/yr slip rate for the Banning strand is applicable only since the mid Holocene. Additional constraints on the Holocene slip rate for the Mission Creek strand are critical for resolving the total slip rate for the southern SAF, and also for comparing slip rates on all three fault strands in the northern Coachella Valley over similar time scales. We have identified a new slip rate site at the southern end of the Mission Creek strand between Pushawalla and Biskra Palms. At this site, (the Three Palms Site), three alluvial fans sourced from three distinct catchments have been displaced approximately 80 meters by the Mission Creek Strand. Initial observations from an exploratory pit excavated into the central fan show soil development consistent with Holocene fan deposition and no evidence of soil profile disruption. To more precisely constrain the minimum

  7. Structural features of the San Andreas fault at Tejon Pass, California

    NASA Astrophysics Data System (ADS)

    Dewers, T. A.; Reches, Z.; Brune, J. N.

    2002-12-01

    We mapped a 2 km belt along the San Andreas fault (SAF) in the Tejon Pass area where road cuts provide fresh exposures of the fault zone and surrounding rocks. Our 1:2,000 structural mapping is focused on analysis of faulting processes and is complementary to regional mapping at 1:12,000 scale by Ramirez (M.Sc., UC Santa Barbara, 1984). The dominant rock units are the Hungry Valley Formation of Pliocene age (clastic sediments) exposed south of the SAF, and the Tejon Lookout granite (Cretaceous) and Neenach Volcanic Formation exposed north of it. Ramirez (1983) deduced ~220 km of post-Miocene lateral slip. The local trend of the SAF is about N60W and it includes at least three main, subparallel segments that form a 200 m wide zone. The traces of the segments are quasi-linear, discontinuous, and they are stepped with respect to each other, forming at least five small pull-aparts and sag ponds in the mapping area. The three segments were not active semi-contemporaneously and the southern segment is apparently the oldest. The largest pull-apart, 60-70 m wide, displays young (Quaternary?) silt and shale layers. We found two rock bodies that are suspected as fault-rocks. One is a 1-2 m thick sheet-like body that separates the Tejon Lookout granite from young (Recent?) clastic rocks. In the field, it appears as a gouge zone composed of poorly cemented, dark clay size grains; however, the microstructure of this rock does not reveal clear shear features. The second body is the 80-120 m wide zone of Tejon Lookout granite that extends for less than 1 km along the SAF in the mapped area. It is characterized by three structural features: (1) pulverization into friable, granular material by multitude of grain-crossing fractures; (2) abundance of dip-slip small faults that are gently dipping toward and away from the SAF; and (3) striking lack of evidence for shear parallel to the SAF. The relationships between these features and the large right-lateral shear along the SAF are

  8. Characterization of fault behavior along the central San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Young, Jeri Joanne

    Rupture characterization of the central San Andreas fault system (SAF) provides the basis for seismic hazard evaluations and the interpretation of fault segmentation. Although the central SAF is capable of producing large earthquakes, such as the Fort Tejon 1857 earthquake; its paleoseismic history is largely incomplete. We tested fault behavior models with paleoseismic data collected from the Cholame segment of the SAF, and with synthetically paleoseismic data. We simulated paleoseismic site conditions to determine the resolution of various paleoseismic data. We conducted paleoseismic investigations at the Las Yeguas 4 site to determine earthquake frequency and amount of offset from the last ground-rupturing event. We interpreted 3 ground-rupturing events, and one ground-shaking event. Two ground-rupturing earthquakes occurred between 1030 to 1300 and 1390 to 1460 cal A.D. The most recent event (MRE) occurred between cal. A.D. 1390 to 1460 age and 1865. Based on historic records and detailed analysis of pollen concentrated from sediments in my excavations, the MRE is interpreted as the 1857 Fort Tejon earthquake. Three-dimensional excavation of an alluvial fan edge indicates that 3.0 +/- 0.70 meters of near-fault slip occurred during the 1857 event. The Cholame segment did not have a, higher frequency of earthquakes as expected when compared to neighboring segments. Synthetic radiocarbon and earthquake ages were generated by random selection from normal distributions that define the frequency of deposition within a trench and the time between earthquakes, respectively. For earthquake recurrence intervals less than 200 years, R.I.s calculated based on hounding radiocarbon ages and associated earthquake events have uncertainties of approximately 40% (1sigma). Recurrence intervals need to he two times greater than the frequency of carbon deposition to adequately record earthquake occurrence. Uncertainties in recurrence intervals indicate that resolution of temporal

  9. Geometry of the San Andreas Fault and Sedimentary Basin in the Northern Salton Trough

    NASA Astrophysics Data System (ADS)

    Fuis, G. S.; Bauer, K.; Catchings, R.; Goldman, M.; Ryberg, T.; Scheirer, D. S.; Langenheim, V. E.; Rymer, M. J.; Persaud, P.; Stock, J. M.; Hole, J. A.

    2014-12-01

    The Salton Seismic Imaging Project (SSIP) was undertaken, in part, to provide more accurate information on the plate-boundary faults and basin geometry in the Salton Trough region. One of these faults, the southernmost San Andreas Fault (SAF) zone in the northern Salton Trough (Coachella Valley), is considered by many to be likely to produce a large-magnitude earthquake in the near future. We report here on the geometry of the SAF and the adjacent sedimentary basin beneath the Coachella Valley. We interpret two seismic profiles in the northern Salton Trough that are orthogonal to the axis of the Coachella Valley. Seismic imaging, potential-field studies, and (or) earthquake hypocentral relocations along these profiles indicate that the active strand of the SAF dips NE. On a southern profile, through the Mecca Hills, we obtain a reflection image of the SAF zone in the depth range of 6-12 km that coincides with the microearthquake pattern reported by Hauksson et al. (2012), dipping ~ 60° NE. Steeply dipping reflectors above 6 km emerge at the surface at mapped secondary fault traces in the Mecca Hills, clearly defining a "flower structure" for the upper SAF. On the second profile, from Palm Springs to Landers, two alternative interpretations of SAF structure are possible. By one interpretation, which is based on earthquakes alone, the Banning and Garnet Hill Faults are two closely spaced faults, dipping ~ 60° NNE that pass through two aftershock clusters of the 1986 M 5.9 North Palm Springs earthquake. By the second interpretation, which is based on our reflection imaging on this line, the Banning and Garnet Hills faults converge at 10-km depth; below that depth, a single SAF dips ~ 60° NNE. In the second interpretation, the faults above 10 km resemble the flower structure interpreted beneath the Mecca Hills on our southern profile. The deeper fault in the second interpretation is subparallel to the closely spaced faults of the first interpretation but a few km

  10. First Results from a Forward, 3-Dimensional Regional Model of a Transpressional San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Fitzenz, D. D.; Miller, S. A.

    2001-12-01

    We present preliminary results from a 3-dimensional fault interaction model, with the fault system specified by the geometry and tectonics of the San Andreas Fault (SAF) system. We use the forward model for earthquake generation on interacting faults of Fitzenz and Miller [2001] that incorporates the analytical solutions of Okada [85,92], GPS-constrained tectonic loading, creep compaction and frictional dilatancy [Sleep and Blanpied, 1994, Sleep, 1995], and undrained poro-elasticity. The model fault system is centered at the Big Bend, and includes three large strike-slip faults (each discretized into multiple subfaults); 1) a 300km, right-lateral segment of the SAF to the North, 2) a 200km-long left-lateral segment of the Garlock fault to the East, and 3) a 100km-long right-lateral segment of the SAF to the South. In the initial configuration, three shallow-dipping faults are also included that correspond to the thrust belt sub-parallel to the SAF. Tectonic loading is decomposed into basal shear drag parallel to the plate boundary with a 35mm yr-1 plate velocity, and East-West compression approximated by a vertical dislocation surface applied at the far-field boundary resulting in fault-normal compression rates in the model space about 4mm yr-1. Our aim is to study the long-term seismicity characteristics, tectonic evolution, and fault interaction of this system. We find that overpressured faults through creep compaction are a necessary consequence of the tectonic loading, specifically where high normal stress acts on long straight fault segments. The optimal orientation of thrust faults is a function of the strike-slip behavior, and therefore results in a complex stress state in the elastic body. This stress state is then used to generate new fault surfaces, and preliminary results of dynamically generated faults will also be presented. Our long-term aim is to target measurable properties in or around fault zones, (e.g. pore pressures, hydrofractures, seismicity

  11. Structure of the California Coast Ranges and San Andreas Fault at SAFOD from seismic waveform inversion and reflection imaging

    USGS Publications Warehouse

    Bleibinhaus, F.; Hole, J.A.; Ryberg, T.; Fuis, G.S.

    2007-01-01

    A seismic reflection and refraction survey across the San Andreas Fault (SAF) near Parkfield provides a detailed characterization of crustal structure across the location of the San Andreas Fault Observatory at Depth (SAFOD). Steep-dip prestack migration and frequency domain acoustic waveform tomography were applied to obtain highly resolved images of the upper 5 km of the crust for 15 km on either side of the SAF. The resulting velocity model constrains the top of the Salinian granite with great detail. Steep-dip reflection seismic images show several strong-amplitude vertical reflectors in the uppermost crust near SAFOD that define an ???2-km-wide zone comprising the main SAF and two or more local faults. Another prominent subvertical reflector at 2-4 km depth ???9 km to the northeast of the SAF marks the boundary between the Franciscan terrane and the Great Valley Sequence. A deep seismic section of low resolution shows several reflectors in the Salinian crust west of the SAF. Two horizontal reflectors around 10 km depth correlate with strains of seismicity observed along-strike of the SAF. They represent midcrustal shear zones partially decoupling the ductile lower crust from the brittle upper crust. The deepest reflections from ???25 km depth are interpreted as crust-mantle boundary. Copyright 2007 by the American Geophysical Union.

  12. Fault depth and seismic moment rate estimates of the San Andreas Fault System: Observations from seismology and geodesy

    NASA Astrophysics Data System (ADS)

    Smith-Konter, B. R.; Sandwell, D. T.; Shearer, P. M.

    2010-12-01

    The depth of the seismogenic zone is a critical parameter for earthquake hazard models of the San Andreas Fault System. Independent observations from both seismology and geodesy can provide insight into the depths of faulting, however these depths do not always agree. Here we inspect variations in fault depths of 12 segments of the southern San Andreas Fault System derived from over 1000 GPS velocities and 66,000 relocated earthquake hypocenters. Geodetically-determined locking depths range from 6-22 km, while seismogenic thicknesses are largely limited to depths of 11-20 km. Seismogenic depths best match the geodetic locking depths when estimated at the 95% cutoff depth in seismicity and most fault segment depths agree to within 2 km. However, we identify 3 outliers (Imperial, Coyote Creek, and Borrego segments) with significant discrepancies. In these cases the geodetically-inferred locking depths are much shallower than the seismogenic depths. We also inspect seismic moment accumulation rates per unit fault length, with the highest rates estimated for the Mojave and Carrizo segments (~1.8 x 1013 Nm/yr/km) and the lowest rates (~0.2 x 1013 Nm/yr/km) found along several San Jacinto segments. The largest variation in seismic moment is calculated for the Imperial segment, where the moment rate from seismic depths is nearly a factor of 2.5 larger than that from geodetic depths. Such variability has important implications for the accuracy to which the magnitude of future major earthquakes can be estimated.

  13. Strength of chrysotile-serpentinite gouge under hydrothermal conditions: Can it explain a weak San Andreas fault?

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, D.A.; Summers, R.; Shengli, M.; Byerlee, J.D.

    1996-01-01

    Chrysotile-bearing serpentinite is a constituent of the San Andreas fault zone in central and northern California. At room temperature, chrysotile gouge has a very low coefficient of friction (?? ??? 0.2), raising the possibility that under hydrothermal conditions ?? might be reduced sufficiently (to ???0.1) to explain the apparent weakness of the fault. To test this hypothesis, we measured the frictional strength of a pure chrysotile gouge at temperatures to 290??C and axial-shortening velocities as low as 0.001 ??m/s. As temperature increases to ???100??C, the strength of the chrysotile gouge decreases slightly at low velocities, but at temperatures ???200??C, it is substantially stronger and essentially independent of velocity at the lowest velocities tested. We estimate that pure chrysotile gouge at hydrostatic fluid pressure and appropriate temperatures would have shear strength averaged over a depth of 14 km of 50 MPa. Thus, on the sole basis of its strength, chrysotile cannot be the cause of a weak San Andreas fault. However, chrysotile may also contribute to low fault strength by forming mineral seals that promote the development of high fluid pressures.

  14. Evidence for two surface ruptures in the past 500 years on the San Andreas fault at Frazier Mountain, California

    USGS Publications Warehouse

    Lindvall, S.C.; Rockwell, T.K.; Dawson, T.E.; Helms, J.G.; Bowman, K.W.

    2002-01-01

    We conducted paleoseismic studies in a closed depression along the San Andreas fault on the north flank of Frazier Mountain near Frazier Park, California. We recognized two earthquake ruptures in our trench exposure and interpreted the most recent rupture, event 1, to represent the historical 1857 earthquake. We also exposed evidence of an earlier surface rupture, event 2, along an older group of faults that did not rerupture during event 1. Radiocarbon dating of the stratigraphy above and below the earlier event constrains its probable age to between A.D. 1460 and 1600. Because we documented continuous, unfaulted stratigraphy between the earlier event horizon and the youngest event horizon in the portion of the fault zone exposed, we infer event 2 to be the penultimate event. We observed no direct evidence of an 1812 earthquake in our exposures. However, we cannot preclude the presence of this event at our site due to limited age control in the upper part of the section and the possibility of other fault strands beyond the limits of our exposures. Based on overlapping age ranges, event 2 at Frazier Mountain may correlate with event B at the Bidart fan site in the Carrizo Plain to the northwest and events V and W4 at Pallett Creek and Wrightwood, respectively, to the southeast. If the events recognized at these multiple sites resulted from the same surface rupture, then it appears that the San Andreas fault has repeatedly failed in large ruptures similar in extent to 1857.

  15. Late Holocene slip rate and recurrence of great earthquakes on the San Andreas fault in northern California

    SciTech Connect

    Niemi, T.M. Earth Sciences Associates, Palo Alto, CA ); Hall, N.T. )

    1992-03-01

    The slip rate of the San Andreas fault 45 km north of San Francisco at Olema, California, is determined by matching offset segments of a buried late Holocene stream channel. Stream deposits from 1,800 {plus minus} 78 yr B.P. are offset 42.5 {plus minus} 3.5 m across the active (1906) fault trace for a minimum late Holocene slip rate of 24 {plus minus} 3 mm/yr. When local maximum coseismic displacements of 4.9 to 5.5 m from the 1906 earthquake are considered with this slip rate, the recurrence of 1906-type earthquakes on the North Coast segment of the San Andreas fault falls within the interval of 221 {plus minus} 40 yr. Both comparable coseismic slip in 1906 and similar late Holocene geologic slip rates at the Olema site and a site 145 km northwest at Point Arena (Prentice, 1989) suggest that the North Coast segment behaves as a coherent rupture unit.

  16. Distinctive Triassic megaporphyritic monzogranite: Evidence for only 160 km offset along the San Andreas Fault, southern California

    NASA Astrophysics Data System (ADS)

    Frizzell, Virgil A., Jr.; Mattinson, James M.; Matti, Jonathan C.

    1986-12-01

    Distinctive megaporphyritic bodies of monzogranite to quartz monzonite that occur in the Mill Creek region of the San Bernardino Mountains and across the San Andreas fault on Liebre Mountain share identical modal and chemical compositions, intrusive ages, and petrogenesis and similar thermal histories. Both bodies are strontium-rich and contain large potassium feldspar phenocrysts and hornblende. U-Pb determinations on zircon from both bodies indicate Triassic intrusive ages (215 Ma) and derivation, in part, from homogeneous Precambrian continental crust. U-Pb analyses on apatite and sphene and K-Ar analyses on hornblende and biotite show that the bodies suffered a Late Cretaceous thermal event (70-75 Ma). The strong similarities between the two bodies suggest that they constitute segments of a formerly continuous pluton that has been offset about 160 km by movement on the San Andreas fault, about 80 km less than the generally accepted distance. Plutons having monzonitic compositions, reassembled with the megaporphyritic bodies are used as a piercing point, form a relatively coherent province within the varied suite of Mesozoic batholithic and prebatholithic rocks in southern California.

  17. [Andreas Vesalius: his rich imagination and colorful detail account in his book: 'Research of the anatomical observations of Gabriel Falloppius'].

    PubMed

    Gilias, Guy

    2015-03-01

    In a long letter, Andreas Vesalius reacts to the comments made by Gabriel Falloppius to his work 'De Humani Corporis Fabrica'. In this letter, he proves Falloppius wrong in a number of assertions and corrects him on more than one occasion. In doing so, Vesalius as a renaissance humanist uses a classic Latin language with long elegant sentences in the style of the old Roman orator Cicero. Remarkably interesting is the fact that this whole argumentation is spiced with comparisons and examples from daily life. To make it clear to the reader what a certain part of the skeleton looks like, he compares this part with an object everybody knows. All parts of the human body are depicted in such an almost graphic way that even an interested reader without any medical or anatomic education can picture them. And Vesalius is very creative in doing so, an artist as it were with a very rich imagination. Moreover, it's remarkable how the famous anatomist manages to put himself on the level of any ordinary person, using comparative images on that level. This last work of Vesalius, which he himself considers to be a supplement to his De Humani Corporis Fabrica, deserves special attention, not only because it illustrates the scientific evolution of the anatomist Vesalius, but also because it offers an insight in the psychology of that fascinating scientist Andreas Vesalius.

  18. GPS-aided inertial technology and navigation-based photogrammetry for aerial mapping the San Andreas fault system

    USGS Publications Warehouse

    Sanchez, Richard D.; Hudnut, Kenneth W.

    2004-01-01

    Aerial mapping of the San Andreas Fault System can be realized more efficiently and rapidly without ground control and conventional aerotriangulation. This is achieved by the direct geopositioning of the exterior orientation of a digital imaging sensor by use of an integrated Global Positioning System (GPS) receiver and an Inertial Navigation System (INS). A crucial issue to this particular type of aerial mapping is the accuracy, scale, consistency, and speed achievable by such a system. To address these questions, an Applanix Digital Sensor System (DSS) was used to examine its potential for near real-time mapping. Large segments of vegetation along the San Andreas and Cucamonga faults near the foothills of the San Bernardino and San Gabriel Mountains were burned to the ground in the California wildfires of October-November 2003. A 175 km corridor through what once was a thickly vegetated and hidden fault surface was chosen for this study. Both faults pose a major hazard to the greater Los Angeles metropolitan area and a near real-time mapping system could provide information vital to a post-disaster response.

  19. The Ash of Ohlson Ranch: A well-dated Stratigraphic Marker for Constraining Deformation Across the Northern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Vazquez, J. A.; Fleck, R. J.; DeLong, S.; Sarna-Wojcicki, A.; Wan, E.; Powell, C., II; Prentice, C. S.

    2012-12-01

    The marine to non-marine transgressional - regressional Ohlson Ranch Formation of northern California was deposited mainly east of the San Andreas Fault and the Gualala structural block during Pliocene sea level high stands. The formation transitions eastward from marine to fluvial deposits and the marine strata are deposited on a mildly warped, pholad-bored erosional surface cut near Pliocene sea level (probably above storm wave-base), on rocks of the Coastal and Central belts of the Franciscan Complex. West of the San Andreas fault near Point Arena, a right-laterally displaced remnant of the wave-cut surface occurs at ca. 100m above modern sea level. East of the fault this surface varies in elevation from ca. 200-350m and a 12-15 cm thick light gray silicic tephra, the ash of Ohlson Ranch (AOR) locally occurs ~10m above the base of the marine section. The AOR consists of very fine-grained glass shards with conspicuous brown biotite in the upper 2 cm and rare co-magmatic clinopyroxene, hornblende and euhedral, weakly zoned zircons. The zircons are relatively uniform in size and little abraded, suggesting they are primary and not re-worked. The fine-grained nature of the AOR deposit suggests it is water lain and chemical analysis of the volcanic glass indicates that the eruptive source was in the southern Cascade Range. We analyzed both polished section mounts of zircon crystals and unpolished rims by ion microprobe (SHRIMP-RG) and LA-ICPMS in order to establish a precise U-Pb age for the AOR. Ages were adjusted for initial 230Th deficiency in the U-Pb chain using Th/U measured in zircon and host glass shards. Thirty-two zircon grains measured by LA-ICPMS at the University of Arizona LaserChron Center yield a mean U-Pb age of 4.58 ± 0.30 Ma (2σ , MSWD=0.53, n=23). SHRIMP analyses of zircon interiors exposed in polished epoxy-mounts yield a mean U-Pb age of 4.36 ± 0.11 Ma (2σ, MSWD 0.72, n=19). To further refine the likely eruption age of the AOR, the SHRIMP was

  20. Quaternary crustal deformation along a major branch of the San Andreas fault in central California

    USGS Publications Warehouse

    Weber, G.E.; Lajoie, K.R.; Wehmiller, J. F.

    1979-01-01

    Deformed marine terraces and alluvial deposits record Quaternary crustal deformation along segments of a major, seismically active branch of the San Andreas fault which extends 190 km SSE roughly parallel to the California coastline from Bolinas Lagoon to the Point Sur area. Most of this complex fault zone lies offshore (mapped by others using acoustical techniques), but a 4-km segment (Seal Cove fault) near Half Moon Bay and a 26-km segment (San Gregorio fault) between San Gregorio and Point Ano Nuevo lie onshore. At Half Moon Bay, right-lateral slip and N-S horizontal compression are expressed by a broad, synclinal warp in the first (lowest: 125 ka?) and second marine terraces on the NE side of the Seal Cove fault. This structure plunges to the west at an oblique angle into the fault plane. Linear, joint0controlled stream courses draining the coastal uplands are deflected toward the topographic depression along the synclinal axis where they emerge from the hills to cross the lowest terrace. Streams crossing the downwarped part of this terrace adjacent to Half Moon Bay are depositing alluvial fans, whereas streams crossing the uplifted southern limb of the syncline southwest of the bay are deeply incised. Minimum crustal shortening across this syncline parallel to the fault is 0.7% over the past 125 ka, based on deformation of the shoreline angle of the first terrace. Between San Gregorio and Point Ano Nuevo the entire fault zone is 2.5-3.0 km wide and has three primary traces or zones of faulting consisting of numerous en-echelon and anastomozing secondary fault traces. Lateral discontinuities and variable deformation of well-preserved marine terrace sequences help define major structural blocks and document differential motions in this area and south to Santa Cruz. Vertical displacement occurs on all of the fault traces, but is small compared to horizontal displacement. Some blocks within the fault zone are intensely faulted and steeply tilted. One major block 0

  1. Geophysical Surveys of the San Andreas and Crystal Springs Reservoir System Including Seismic-Reflection Profiles and Swath Bathymetry, San Mateo County, California

    USGS Publications Warehouse

    Finlayson, David P.; Triezenberg, Peter J.; Hart, Patrick E.

    2010-01-01

    This report describes geophysical data acquired by the U.S. Geological Survey (USGS) in San Andreas Reservoir and Upper and Lower Crystal Springs Reservoirs, San Mateo County, California, as part of an effort to refine knowledge of the location of traces of the San Andreas Fault within the reservoir system and to provide improved reservoir bathymetry for estimates of reservoir water volume. The surveys were conducted by the Western Coastal and Marine Geology (WCMG) Team of the USGS for the San Francisco Public Utilities Commission (SFPUC). The data were acquired in three separate surveys: (1) in June 2007, personnel from WCMG completed a three-day survey of San Andreas Reservoir, collecting approximately 50 km of high-resolution Chirp subbottom seismic-reflection data; (2) in November 2007, WCMG conducted a swath-bathymetry survey of San Andreas reservoir; and finally (3) in April 2008, WCMG conducted a swath-bathymetry survey of both the upper and lower Crystal Springs Reservoir system. Top of PageFor more information, contact David Finlayson.

  2. 500th birthday of Andreas Vesalius, the founder of modern anatomy: "vivitur ingenio, caetera mortis erunt" ("genius lives on, all else is mortal").

    PubMed

    Hadzic, Admir; Sadeghi, Neda; Vandepitte, Catherine; Vandepitte, Walter; Van de Velde, Marc; Hadzic, Alen; Van Robays, Johan; Heylen, Rene; Herijgers, Paul; Vloka, Caroline; Van Zundert, Jan

    2014-01-01

    It is often said that regional anesthesia is the practice of applied anatomy. Therefore, it is fitting that on the occasion of his 500th birthday, we celebrate the life and work of the brilliant Flemish anatomist, Andreas Vesalius (1514-1564), the founder of modern anatomy.

  3. Is magnitude variability on North-Anatolian and San-Andreas fault segments a consequence of geometry and resultant irregular tectonic loading?

    NASA Astrophysics Data System (ADS)

    Parsons, T.

    2006-12-01

    Large earthquakes of varying magnitude are observed rupturing the same fault segments on the North Anatolian fault in Turkey, and on the San Andreas fault in California. In Turkey there enough reports of historical earthquake damage [Ambraseys, 2002] to assemble a ~500-yr catalog of M greater than 7 events along the Marmara-Sea portion of the right-lateral obliquely divergent North Anatolian fault. In California, analysis by Weldon et al. [2004, 2005] from paleoseismology on the right-lateral obliquely convergent southern San Andreas fault enabled a long slip-history at the Wrightwood site. In both cases there is resolvable magnitude variation on fault segments where at least two large earthquakes ruptured the same point(s). Characteristic earthquake models posit that repeated versions of the same earthquake rupture fault segments over time, and form the basis for time-dependent probability calculations. Finite element models of the North Anatolian and San Andreas fault systems driven by geodetically-determined displacements show variable long- term stress-loading on these faults. Stressing-rate variability comes from changes in fault geometry along strike, non-uniform motions of crustal blocks, and fault interactions. The North Anatolian and San Andreas finite element models show parts of faults achieving failure stresses sooner than others. Modeled heterogeneous fault loading suggests complex rupture sequences that are consistent with observations.

  4. Paleoseismology and Tectonic Geomorphology: Results From the Parkfield, CA Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Toké, N. A.; Arrowsmith, J. R.; Crosby, C. J.; Young, J. J.

    2004-12-01

    The Parkfield segment of the San Andreas Fault (SAF) is the transition zone between the creep-dominated segment of the SAF to the northwest and the locked segment to the southeast. Geodetic studies indicate ~10 mm/year of the SAF 35 mm/year slip-rate is accommodated by creep at shallow depths of the SAF near Carr Hill, suggesting the remaining slip may occur in moderate to large earthquakes. Foreshock intensities of the 1857 M7.8 Fort Tejon earthquake were similar to 20th century Parkfield events, suggesting that the 1857 event may have nucleated in the Parkfield area. Paleoseismic investigations near Parkfield have achieved limited success in exposing useful fault zone stratigraphy. Our goals were to investigate the style and timing of late Pleistocene and Holocene faulting along this segment of the SAF. Specifically, did the 1857 or similar large prehistoric earthquakes rupture through the Parkfield segment? In addition, is it possible to distinguish deformation caused by these large magnitude earthquakes from deformation associated with the moderate 1966-style earthquakes and aseismic creep? Geomorphic mapping from Middle Mountain to Carr Hill revealed numerous tectonic landforms that define the fault trace and indicated possible excavation sites, including the sites used for this study. Two fault-perpendicular excavations were cut in a late Pleistocene fluvial terrace of Little Cholame Creek just north-northeast of Carr Hill. A thirty-meter excavation across an elongate sag pond, containing an apparently right-laterally offset fluvial channel and several small springs, revealed four fault zones. The outer fault zones were parallel with the regional trend of the SAF (313°), while the inner fault zones trended obliquely at ~350°. The three easternmost fault zones show apparent dip-slip deformation including truncation and down warping of sag and terrace deposits. The westernmost fault zone was characterized by upward splaying sub-vertical clay shear bands

  5. Preliminary Holocene History of Fault Slip for the Mojave Section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Compton, T.; Cowgill, E.; Scharer, K. M.; Gold, R. D.; Westerteiger, R.; Bernardin, T. S.; Kellogg, L. H.

    2012-12-01

    The Mojave section of the San Andreas fault (MSAF) shows an apparent discrepancy between slip rates where geodetic rates are systematically slower relative to geologic rates. Resolving this discrepancy is important for determining whether or not the MSAF exhibits temporal changes in slip, advancing the understanding of the mechanical behavior of fault systems, and improving seismic-hazard assessment for the MSAF. Paleoseismic data along the MSAF suggest temporal variations in strain release over the last 2 kyr, but more studies are needed to extend the slip history back in time. Here we address the problem of the apparent slip rate discrepancy and possible temporal variations in strain release by employing Monte Carlo analysis of previously reported displacement-time data to investigate the extent to which these data constrain the Holocene slip history. We evaluated 42 previously reported piercing lines for possible inclusion in our analysis, 15 of which were unused because they are either duplicate reports or poorly documented. The remaining 27 data points reveal that slip rates are nonexistent for 5 offset distances (19-27m, 33-42m, 45-63m, 65-129m, and 131-300m) and for 3 time periods from 10-3.9 kyr, 3.9-2.8 kyr, and 2.8-1.4 kyr BP. Results of this analysis suggest slip rate along the MSAF varied between 0 and 4.5 kyr BP, with 5 possible phases of strain release, 3 of which are faster than the average of ~30 mm/yr. The oldest fast phase was from 4.5-2.9 kyr with an average slip rate of 61 mm/yr. The next fast phase, with an average rate of 81 mm/yr, was from 1.5-1.1 kyr. The youngest fast phase resulted in a rate of 36 mm/yr between 0.4 kyr and the 1857 event. Slower phases of slip occurred from 2.9-1.5 kyr, with an average rate of 12 mm/yr, and from 1.1-0.4 kyr, with a slip rate of 20 mm/yr. These slip history findings are considered preliminary because they are based on a limited dataset that contain data gaps. To aide in our search for additional potentially

  6. Permeability and of the San Andreas Fault core and damage zone from SAFOD drill core

    NASA Astrophysics Data System (ADS)

    Rathbun, A. P.; Fry, M.; Kitajima, H.; Song, I.; Carpenter, B. M.; Marone, C.; Saffer, D. M.

    2012-12-01

    Quantifying fault-rock permeability is important toward understanding both the regional hydrologic behavior of fault zones, and poro-elastic processes that may affect faulting and earthquake mechanics by mediating effective stress. These include persistent fluid overpressures hypothesized to reduce fault strength, as well as dynamic processes that may occur during earthquake slip, including thermal pressurization and dilatancy hardening. To date, studies of permeability on fault rocks and gouge from plate-boundary strike-slip faults have mainly focused on samples from surface outcrops. We report on permeability tests conducted on the host rock, damage zone, and a major actively creeping fault strand (Central Deformation Zone, CDZ) of the San Andreas Fault (SAF), obtained from coring across the active SAF at ~2.7 km depth as part of SAFOD Phase III. We quantify permeability on subsamples oriented both perpendicular and parallel to the coring axis, which is nearly perpendicular to the SAF plane, to evaluate permeability anisotropy. The fault strand samples were obtained from the CDZ, which accommodates significant creep, and hosts ~90% of the observed casing deformation measured between drilling phases. The CDZ is 2.6 m thick with a matrix grain size < 10 μm and ~5% vol. clasts, and contains ~80% clay, of which ~90% is smectite. We also tested damage zone samples taken from adjacent core sections within a few m on either side of the CDZ. Permeability experiments were conducted in a triaxial vessel, on samples 25.4 mm in diameter and ~20-35 mm in length. We conducted measurements under isotropic stress conditions, at effective stress (Pc') of ~5-70 MPa. We measure permeability using a constant head flow-through technique. At the highest Pc', low permeability of the CDZ and damage zone necessitates using a step loading transient method and is in good agreement with permeabilities obtained from flow-through experiments. We quantify compression behavior by monitoring

  7. Strength of the San Andreas Fault Zone: Insight From SAFOD Cuttings and Core

    NASA Astrophysics Data System (ADS)

    Tembe, S.; Lockner, D. A.; Solum, J. G.; Morrow, C. A.; Wong, T.; Moore, D. E.

    2005-12-01

    Cuttings acquired during drilling of the SAFOD scientific hole near Parkfield, California offer a continuous physical record of the lithology across the San Andreas fault (SAF) zone and provide the only complete set of samples available for laboratory testing. Guided by XRD clay mineral analysis and velocity and gamma logs, we selected washed cuttings from depths spanning the main hole from 1.85 to 3.0 km true vertical depth. Cuttings were chosen to represent primary lithologic units as well as significant shear zones, including candidates for the currently active SAF. To determine frictional properties triaxial sliding tests were conducted on cylindrical granite blocks containing sawcuts inclined at 30° and filled with 1 mm-thick sample gouge layers. Tests were run at constant effective normal stresses of 10 and 40 MPa and constant pore pressure of 1 MPa. Samples were sheared up to 10.4 mm at room temperature and velocities of 1, 0.1 and 0.01 μm/s. Stable sliding behavior and overall strain hardening were observed in all tests. The coefficient of friction typically showed a modest decrease with increasing effective normal stress and mostly velocity strengthening was observed. Preliminary results yield coefficients of friction, μ, which generally fell into two clusters spanning the range of 0.45 to 0.8. The higher values of friction (~0.7 - 0.8) corresponded to quartzofeldspathic samples derived from granodiorites and arkoses encountered in the drill hole. Lower values of friction (0.45 - 0.55) were observed at depth intervals interpreted as shear zones based on enriched clay content, reduced seismic velocities and increased gamma radiation. Arguments for a weak SAF suggest coseismic frictional strength of μ = 0.1 to 0.2 yet the actual fault zone materials studied here appear consistently stronger. At least two important limitations exist for inferring in-situ fault strength from cuttings. (1) Clays and weak minerals are preferentially lost during drilling and

  8. Strength of the Creeping Segment of the San Andreas Fault Inferred from Intact SAFOD Core Material

    NASA Astrophysics Data System (ADS)

    Lockner, D. A.; Morrow, C. A.; Moore, D. E.; Hickman, S.

    2012-12-01

    A primary goal of the SAFOD fault zone drilling project was to determine the strength and frictional properties of the San Andreas Fault (SAF) at seismogenic depth. Laboratory testing of SAFOD core material has now provided measurements under near-in-situ conditions of the shear strength of the creeping portion of the SAF at a vertical depth of 2.7 km. Early measurements made on SAFOD spot core and drilling cuttings before core from within the SAF zone was available [Tembe et al. (2006), Morrow et al. (2007), Carpenter et al. (2011)] associated low strength material with currently inactive faults southwest of the SAF and actively deforming zones associated with the SAF that were identified from casing deformation data. In Phase 3 drilling in 2007, core was retrieved from two actively deforming shear zones within the approximately 200-m-wide SAF damage zone. The two zones contained clay-rich foliated gouge and have been designated as the Southwest Deforming Zone (SDZ - width ~1.6 m) and Central Deforming Zone (CDZ - width ~2.6 m). Casing deformation [Zoback et al. (2010)] suggests that deformation is localized within these weak foliated gouge zones. Deformation tests on crushed and sieved samples of the foliated gouge [Lockner et al. (2011) and Carpenter et al. (2012)] showed low strength (coefficient of friction μ in the range 0.1 to 0.2) due to the high concentration of saponite, an Mg-rich smectite clay. We now present results from deformation tests on intact CDZ foliated gouge that, combined with similar deformation tests by Carpenter et al. (2012), allow comparison with crushed/sieved samples. We find: (1) no significant difference in strength of intact and crushed/sieved foliated gouge samples. Apparently, the high concentration of the weak mineral phase (>60%) makes strength variations due to fabric irrelevant in this case. Therefore, crushed/sieved samples that are significantly easier to prepare and test can be used to infer strength and other rheological

  9. Cretaceous mafic conglomerate near Gualala offset 350 miles by San Andreas fault from oceanic crustal source near Eagle Rest Peak, California

    USGS Publications Warehouse

    Ross, Donald C.; Wentworth, Carl M.; McKee, Edwin D.

    1973-01-01

    Upper Cretaceous mafic conglomerate and quartz-plagioclase arkose that crop out on the southwest side of the San Andreas fault near Gualala, Calif., may have been eroded from a gabbroic terrane that now lies about 350 miles to the southeast, on the opposite side of the San Andreas fault. The plagioclase arkose near Gualala contains little or no K-feldspar, and the conglomerate is characterized by quartz-bearing mafic rocks that lack K-feldspar volcanic rocks, diabase, and diorite to gabbro. Hornblendes from these clasts yield K/Ar ages of 141±4,175±7, and 186±7 m.y. The arkose and conglomerate appear to have been eroded from a chert-poor ophiolite (oceanic crust) sequence that, according to paleocurrent evidence, lay east of the present San Andreas fault. Near Eagle Rest Peak, 350 milessoutheast of Gualala, similar mafic quartz-bearing volcanic rocks, diabase, and gabbro are exposed in a small structurally isolated areathat abuts the San Andreas fault on the southwest. These rocks yield hornblende K/Ar ages of 134±4, 165±4, and 207±10 m.y. They mayalso be the source of two small fault slivers of similar mafic rocks, which yield hornblende K/Ar ages between 144 and 172 m.y. Theseslivers now lie 100 and 200 miles to the northwest along the San Andreas fault at Gold Hill and Logan.

  10. Long-distance dispersal, low connectivity and molecular evidence of a new cryptic species in the obligate rafter Caprella andreae Mayer, 1890 (Crustacea: Amphipoda: Caprellidae)

    NASA Astrophysics Data System (ADS)

    Cabezas, M. Pilar; Navarro-Barranco, Carlos; Ros, Macarena; Guerra-García, José Manuel

    2013-09-01

    The amphipod Caprella andreae Mayer, 1890 was recorded for the first time in Southern Iberian Peninsula (36°44'15″N, 3°59'38″W). This species is the only obligate rafter of the suborder Caprellidea and has been reported to attach not only to floating objects such as ropes or driftwoods but also to turtle carapaces. Mitochondrial and nuclear markers were used to examine dispersal capabilities and population genetic structure of C. andreae across seven localities in the Mediterranean and Atlantic Ocean collected from floating substrata with different dispersal patterns. The strong population differentiation with no haplotypes shared between populations suggests that C. andreae is quite faithful to the substratum on which it settles. In addition, the proportionally higher genetic diversity displayed in populations living on turtles as well as the presence of highly differentiated haplotypes in the same turtle population may be indicative that these populations survive longer, which could lead C. andreae to prefer turtles instead of floating objects to settle and disperse. Therefore, rafting on floating objects may be sporadic, and ocean currents would not be the most important factor shaping patterns of connectivity and population structure in this species. Furthermore, molecular phylogenetic analyses revealed the existence of a cryptic species whose estimates of genetic divergence are higher than those estimated between C. andreae and other congeneric species (e.g. Caprella dilatata and Caprella penantis). Discovery of cryptic species among widely distributed small marine invertebrates is quite common and, in this case, prompts for a more detailed phylogenetic analysis and taxonomic revision of genus Caprella. On the other hand, this study also means the first record of the gammarids Jassa cadetta and Elasmopus brasiliensis and the caprellid Caprella hirsuta on drifting objects.

  11. Fine-scale structure of the San Andreas fault zone and location of the SAFOD target earthquakes

    USGS Publications Warehouse

    Thurber, C.; Roecker, S.; Zhang, H.; Baher, S.; Ellsworth, W.

    2004-01-01

    We present results from the tomographic analysis of seismic data from the Parkfield area using three different inversion codes. The models provide a consistent view of the complex velocity structure in the vicinity of the San Andreas, including a sharp velocity contrast across the fault. We use the inversion results to assess our confidence in the absolute location accuracy of a potential target earthquake. We derive two types of accuracy estimates, one based on a consideration of the location differences from the three inversion methods, and the other based on the absolute location accuracy of "virtual earthquakes." Location differences are on the order of 100-200 m horizontally and up to 500 m vertically. Bounds on the absolute location errors based on the "virtual earthquake" relocations are ??? 50 m horizontally and vertically. The average of our locations places the target event epicenter within about 100 m of the SAF surface trace. Copyright 2004 by the American Geophysical Union.

  12. "Paradoxes, absurdities, and madness": conflict over alchemy, magic and medicine in the works of Andreas Libavius and Heinrich Khunrath.

    PubMed

    Forshaw, Peter J

    2008-01-01

    Both Andreas Libavius and Heinrich Khunrath graduated from Basel Medical Academy in 1588, though the theses they defended reveal antithetical approaches to medicine, despite their shared interests in iatrochemistry and transmutational alchemy. Libavius argued in favour of Galenic allopathy while Khunrath promoted the contrasting homeopathic approach of Paracelsus and the utility of the occult doctrine of Signatures for medical purposes. This article considers these differences in the two graduates' theses, both as intimations of their subsequent divergent notions of the boundaries of alchemy and its relations with medicine and magic, and also as evidence of the surprisingly unstable academic status of Paracelsian philosophy in Basel, its main publishing centre, at the end of the sixteenth century.

  13. Map showing recently active breaks along the San Andreas Fault between Pt. Delgada and Bolinas Bay, California

    USGS Publications Warehouse

    Brown, Robert D.; Wolfe, Edward W.

    1970-01-01

    This strip map is one of a series of maps showing recently active fault breaks along the San Andreas and other active faults in California. It is designed to inform persons who are concerned with land use near the fault of the location of those fault breaks that have moved recently. The lines on the map are lines of rupture and creep that can be identified by field evidence and that clearly affect the present surface of the land. Map users should keep in mind that these lines are intended primarily as guides to help locate the fault; the mapped lines are not necessarily shown with the precision demanded by some engineering or land utilization needs.

  14. Slip deficit on the san andreas fault at parkfield, california, as revealed by inversion of geodetic data.

    PubMed

    Segall, P; Harris, R

    1986-09-26

    A network of geodetic lines spanning the San Andreas fault near the rupture zone of the 1966 Parkfield, California, earthquake (magnitude M = 6) has been repeatedly surveyed since 1959. In the study reported here the average rates of line-length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault. These results indicate that the Parkfield rupture surface has not slipped significantly since 1966. Comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip-deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989, although this may not occur until 1995. These results lend independent support to the earlier forecast of an M = 6 earthquake near Parkfield within 5 years of 1988.

  15. Interaction of the san jacinto and san andreas fault zones, southern california: triggered earthquake migration and coupled recurrence intervals.

    PubMed

    Sanders, C O

    1993-05-14

    Two lines of evidence suggest that large earthquakes that occur on either the San Jacinto fault zone (SJFZ) or the San Andreas fault zone (SAFZ) may be triggered by large earthquakes that occur on the other. First, the great 1857 Fort Tejon earthquake in the SAFZ seems to have triggered a progressive sequence of earthquakes in the SJFZ. These earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1.7 kilometers per year along the SJFZ after the 1857 earthquake. Second, the similarity in average recurrence intervals in the SJFZ (about 150 years) and in the Mojave segment of the SAFZ (132 years) suggests that large earthquakes in the northern SJFZ may stimulate the relatively frequent major earthquakes on the Mojave segment. Analysis of historic earthquake occurrence in the SJFZ suggests little likelihood of extended quiescence between earthquake sequences.

  16. Human-induced uplift of the Sierra Nevada Mountains and seismicity modulation on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Amos, Colin; Audet, Pascal; Hammond, William C.; Burgmann, Roland; Johanson, Ingrid A.; Blewitt, Geoffrey

    2014-05-01

    We investigate the cause of geodetically observed mountain uplift in the Sierra Nevada, western US. In the process, we reveal a possible human-induced mechanism that may be driving Sierra Nevada uplift, and may also be pushing the San Andreas Fault closer to failure. An initial study of the Sierra Nevada [Hammond et al., Geology, 40, 2012] exploited the complementary strengths of point positions from GPS and blanket coverage measurements from InSAR, to show that contemporary vertical motion of the Sierra Nevada is between 1 - 2 mm/yr relative to the comparatively stable Great Basin to the east. One possible interpretation of this is that the most modern episode of tectonic uplift is still active in the Sierra Nevada. However, we now discover that GPS stations surrounding the southern San Joaquin Valley in California show a pattern of uplift concentrated not only in the Sierra Nevada to the east, but more broadly along the basin margins, including the adjacent central Coast Range to the west. Peak vertical velocities reach values up to 1 - 3 mm/yr. This suggests the San Joaquin Valley plays a key role in the uplift of the Sierra Nevada to the east, with possible implications for the San Andreas Fault to the west. Anthropogenic groundwater depletion in the southern San Joaquin Valley has been massive and sustained, therefore hydrological loading variation might explain contemporary uplift. To test this, we apply a simple elastic model that uses a line load centered along the valley axis, a range of elastic parameters, and published estimates of the integrated rate of mass loss due to groundwater removal over the last decade. Predicted uplift centered along the valley axis matches well with patterns of GPS motion, with the upward vertical rates decaying away from the valley margins. Observed seasonal variability in the vertical GPS positions lends support for this model, showing peak uplift for stations surrounding the valley during the dry summer and fall months. On

  17. Re-evaluation of heat flow data near Parkfield, CA: Evidence for a weak San Andreas Fault

    USGS Publications Warehouse

    Fulton, P.M.; Saffer, D.M.; Harris, Reid N.; Bekins, B.A.

    2004-01-01

    Improved interpretations of the strength of the San Andreas Fault near Parkfield, CA based on thermal data require quantification of processes causing significant scatter and uncertainty in existing heat flow data. These effects include topographic refraction, heat advection by topographically-driven groundwater flow, and uncertainty in thermal conductivity. Here, we re-evaluate the heat flow data in this area by correcting for full 3-D terrain effects. We then investigate the potential role of groundwater flow in redistributing fault-generated heat, using numerical models of coupled heat and fluid flow for a wide range of hydrologic scenarios. We find that a large degree of the scatter in the data can be accounted for by 3-D terrain effects, and that for plausible groundwater flow scenarios frictional heat generated along a strong fault is unlikely to be redistributed by topographically-driven groundwater flow in a manner consistent with the 3-D corrected data. Copyright 2004 by the American Geophysical Union.

  18. A Bayesian exploration of the distribution of aseismic slip along the creeping section of the San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Jolivet, R.; Agram, P. S.; Simons, M.; Shen, Z.; Zhang, H.

    2013-12-01

    The 175-km-long creeping section of the San Andreas fault extends from the Bay Area region in the north to the Carizo plain in the south, and separates two fault sections that ruptured during the 1906 Mw 7.9, San Francisco earthquake and the 1857 Mw 7.9, Fort Tejon earthquake. In between San Juan Bautista and Parkfield, the San Andreas Fault slips continuously at rates close to the plate rate without accumulating a significant slip deficit - at least near the surface. However, previous studies indicate that surface creep rate vary along strike, suggesting variable slip deficit build-up. Here we map the distribution of slip at depth to illuminate where strain is localized along the fault and to investigate the relationship between this strain and local seismicity. We use Synthetic Aperture Radar (SAR) images from the ALOS satellite on the 4 ascending tracks 218, 219, 221 and 222, covering the whole creeping section from 2006 to 2010, to generate 4 Line-Of-Sight velocity maps. We use the Stanford Mocomp processor to generate the interferograms. We unwrap the interferograms using Snaphu and remove residual orbital errors using the GPS time series from SOPAC. For each track, we generate 4 maps of the ground velocity using the Multiscale Interferometric Time Series (MInTS) method. Interferograms are first decomposed into the wavelet domain. Then, we invert for a linear trend and an annual seasonal oscillation using a damped least-square scheme, on which the damping parameter has been determined by cross-validation. Finally, the linear trend determined on wavelets is transformed back into the space domain. We apply a Bayesian method to infer the creep rate distribution along the San Andreas Fault (SAF) and the southern section of the Calaveras-Paicines fault (CPF). In addition to the 4 InSAR rate maps, we use the Unified Western US Crustal motion GPS velocity field, including 200+ velocity measurements from both campaign and continuous GPS sites around the creeping

  19. Interaction of the San Jacinto and San Andreas Fault Zones, Southern California: Triggered Earthquake Migration and Coupled Recurrence Intervals

    NASA Astrophysics Data System (ADS)

    Sanders, Christopher O.

    1993-05-01

    Two lines of evidence suggest that large earthquakes that occur on either the San Jacinto fault zone (SJFZ) or the San Andreas fault zone (SAFZ) may be triggered by large earthquakes that occur on the other. First, the great 1857 Fort Tejon earthquake in the SAFZ seems to have triggered a progressive sequence of earthquakes in the SJFZ. These earthquakes occurred at times and locations that are consistent with triggering by a strain pulse that propagated southeastward at a rate of 1.7 kilometers per year along the SJFZ after the 1857 earthquake. Second, the similarity in average recurrence intervals in the SJFZ (about 150 years) and in the Mojave segment of the SAFZ (132 years) suggests that large earthquakes in the northern SJFZ may stimulate the relatively frequent major earthquakes on the Mojave segment. Analysis of historic earthquake occurrence in the SJFZ suggests little likelihood of extended quiescence between earthquake sequences.

  20. Paleoearthquakes at Frazier Mountain, California delimit extent and frequency of past San Andreas Fault ruptures along 1857 trace

    NASA Astrophysics Data System (ADS)

    Scharer, Katherine; Weldon, Ray; Streig, Ashley; Fumal, Thomas

    2014-07-01

    Large earthquakes are infrequent along a single fault, and therefore historic, well-characterized earthquakes exert a strong influence on fault behavior models. This is true of the 1857 Fort Tejon earthquake (estimated M7.7-7.9) on the southern San Andreas Fault (SSAF), but an outstanding question is whether the 330 km long rupture was typical. New paleoseismic data for six to seven ground-rupturing earthquakes on the Big Bend of the SSAF restrict the pattern of possible ruptures on the 1857 stretch of the fault. In conjunction with existing sites, we show that over the last ~650 years, at least 75% of the surface ruptures are shorter than the 1857 earthquake, with estimated rupture lengths of 100 to <300 km. These results suggest that the 1857 rupture was unusual, perhaps leading to the long open interval, and that a return to pre-1857 behavior would increase the rate of M7.3-M7.7 earthquakes.

  1. Seismic and Aseismic Moment Budget and Implication for the Seismic Potential of the Parkield Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Michel, S. G. R. M.

    2015-12-01

    This study explores methods to assess the seismic potential of a fault based on geodetic measurements, geological information of fault slip rate and seismicity data. The methods are applied to the Parkfield's section along the San Andreas Fault at the transition zone between the SAF creeping segment in the North and the locked section to the south, where a Mw~6 earthquake has occurred every 24.5 years on average since the M7.7 Fort Tejon event in 1857. We compare the moment released by all the known earthquakes and associated postseismic deformation with the moment deficit accumulated during the interseismic period. We find that the recurrence of Mw6 earthquakes is insufficient to close the slip budget and that larger events are probably needed. We will discuss and evaluate various possible scenarios which might account for the residual moment deficit and implications of the possible magnitude and return period of Mw6 earthquakes on that fault segment.

  2. Andrea Pasta (1706-1782), eclectic scholar of anatomy and clinical medicine, communication and the history of art.

    PubMed

    Clerici, Carlo Alfredo; Veneroni, Laura; Patriarca, Carlo

    2014-11-01

    Andrea Pasta was an eclectic visionary light years ahead of his time. He made numerous contributions to the field of medicine, some recognized by his contemporaries and others so visionary that they are being applied only in modern times. His contributions spanned the disciplines of psychology, gynaecology, haematology, infectious diseases and the doctor-patient relationship. Well known among his contemporaries, he combined a passion for clinical medicine and a keen interest in history and art with a strict research methodology and an approach to caring for patients as human beings. By studying his life and works, we can better understand the magnitude and significance of his innovative method and its applicability in modern times and also the significance of his many contributions.

  3. The Development of the San Andreas Plate Boundary through Northern California: Insights from GPS, Crustal Structure, and Lithospheric Modeling

    NASA Astrophysics Data System (ADS)

    Furlong, K. P.; Williams, T.; Hayes, G. P.

    2007-12-01

    The San Andreas plate boundary lengthens in the wake of the Mendocino triple junction (MTJ), and over the last ca. 7-10 Ma it has developed into a localized plate boundary shear zone between the North America and Pacific plates. The pathway from a diffuse deformation swath to a few major fault related plate boundary structures reflects the interplay of thermal and deformational processes acting on the inherited structures of the Cascadia forearc. Furlong and Govers (1998) proposed the Mendocino Crustal Conveyor (MCC) model (supported by numerical modeling) that argued for temporal and spatial variations in lithospheric deformation in association with MTJ passage, which have led to the formation of the main plate boundary structures. The general concept of faults developing and eventually coalescing into a primary plate boundary structure after MTJ passage serves as the framework for most tectonic and geodetic analyses of the fault system. What has been less well understood or quantified is specifically how the fault systems form, what drives fault localization, and how does the concomitant crustal evolution play a role in the plate boundary development. The substantial augmentation of the geodetic data for northern California through a combination of campaign and most recently (through the PBO component of EarthScope) continuous GPS observations in concert with seismological analyses of crustal structure now allows us to test, calibrate, and refine the MCC model. Specifically, the (1) crustal thickening at and north of the MTJ, predicted by MCC processes, is clearly seen in the crustal velocity and GPS derived strain fields, (2) the approx, E-W extent of MCC deformation is delineated by the GPS data to occur primarily through the core of the northern Coast Ranges - consistent with the topographic and fluvial evolution of the region, (3) compatible with seismic observations, the GPS data imply that the upper crust is only a minor participant in the MCC crustal

  4. What Did Stiglitz, Sen and Fitoussi Get Right and What Did They Get Wrong?

    ERIC Educational Resources Information Center

    Michalos, Alex C.

    2011-01-01

    The aim of this critical assessment of the Stiglitz, Sen and Fitoussi Report was to provoke discussion and improvements in future developments of quality of life research undertaken by official statistical agencies. I would like to thank Jochen Jesinghaus and Andrea Saltelli for their helpful comments on earlier drafts of the paper.

  5. What Did Stiglitz, Sen and Fitoussi Get Right and What Did They Get Wrong?

    ERIC Educational Resources Information Center

    Michalos, Alex C.

    2011-01-01

    The aim of this critical assessment of the Stiglitz, Sen and Fitoussi Report was to provoke discussion and improvements in future developments of quality of life research undertaken by official statistical agencies. I would like to thank Jochen Jesinghaus and Andrea Saltelli for their helpful comments on earlier drafts of the paper.

  6. Subsurface geometry of the San Andreas-Calaveras fault junction: influence of serpentinite and the Coast Range Ophiolite

    USGS Publications Warehouse

    Watt, Janet Tilden; Ponce, David A.; Graymer, Russell W.; Jachens, Robert C.; Simpson, Robert W.

    2014-01-01

    While an enormous amount of research has been focused on trying to understand the geologic history and neotectonics of the San Andreas-Calaveras fault (SAF-CF) junction, fundamental questions concerning fault geometry and mechanisms for slip transfer through the junction remain. We use potential-field, geologic, geodetic, and seismicity data to investigate the 3-D geologic framework of the SAF-CF junction and identify potential slip-transferring structures within the junction. Geophysical evidence suggests that the San Andreas and Calaveras fault zones dip away from each other within the northern portion of the junction, bounding a triangular-shaped wedge of crust in cross section. This wedge changes shape to the south as fault geometries change and fault activity shifts between fault strands, particularly along the Calaveras fault zone (CFZ). Potential-field modeling and relocated seismicity suggest that the Paicines and San Benito strands of the CFZ dip 65° to 70° NE and form the southwest boundary of a folded 1 to 3 km thick tabular body of Coast Range Ophiolite (CRO) within the Vallecitos syncline. We identify and characterize two steeply dipping, seismically active cross structures within the junction that are associated with serpentinite in the subsurface. The architecture of the SAF-CF junction presented in this study may help explain fault-normal motions currently observed in geodetic data and help constrain the seismic hazard. The abundance of serpentinite and related CRO in the subsurface is a significant discovery that not only helps constrain the geometry of structures but may also help explain fault behavior and the tectonic evolution of the SAF-CF junction.

  7. Activity of the Mill Creek and Mission Creek fault strands of the San Andreas fault through the San Gorgonio Pass

    NASA Astrophysics Data System (ADS)

    Morelan, A. E., III; Oskin, M. E.; Valentine, M.

    2016-12-01

    We present new observations that constrain the recent slip history of the Mill Creek and Mission Creek strands of the San Andreas fault. These faults are the northern strands of a complex series of strike-slip and thrust faults through the San Gorgonio Pass stepover, an important structural barrier that affects seismic hazard in southern California. Understanding the activity on each of the faults in this complex region will reveal the potential for large, throughgoing San Andreas fault ruptures. The Mill Creek fault strand cuts the base of the upper Raywood Flat fill, a 50 m thick package of debris-flow deposits. However, the upper section of these deposits overlap, and are not cut by the fault. On the surface of this deposit, a 15 m-wide channel, flanked by bouldery debris-flow levees, crosses the projection of the Mill Creek fault without evidence of offset. We collected boulder-top samples for cosmogenic exposure age-dating of these levees and present preliminary results. Additionally, we mapped inset terraces along the incised channel of the East Fork Whitewater River drainage that also do not show evidence of fault offset, and we collected a depth profile through the uppermost Raywood Flat fill in order to further assess its age. Along the Mission Creek strand, newly devegetated B4 airborne lidar data reveals fault scarps cutting across hillslopes and alluvial fans between the San Bernardino strand and lower Raywood Flat for a distance of 4 km. We identify a lateral offset of 4-6 m in an alluvial fan deposit within a tributary of Banning canyon, and sampled a suite of boulders to estimate the age of this deposit. This site shows that the Mission Creek fault is active and could rupture through the San Gorgonio Pass, bypassing the structural complexity of the San Gorgonio Pass thrust to the south. Conversely, the Mill Creek fault appears to be inactive through the pass since the latest Pleistocene.

  8. Geophysical evidence for wedging in the San Gorgonio Pass structural knot, southern San Andreas fault zone, southern California

    USGS Publications Warehouse

    Langenheim, V.E.; Jachens, R.C.; Matti, J.C.; Hauksson, E.; Morton, D.M.; Christensen, A.

    2005-01-01

    Geophysical data and surface geology define intertonguing thrust wedges that form the upper crust in the San Gorgonio Pass region. This picture serves as the basis for inferring past fault movements within the San Andreas system, which are fundamental to understanding the tectonic evolution of the San Gorgonio Pass region. Interpretation of gravity data indicates that sedimentary rocks have been thrust at least 5 km in the central part of San Gorgonio Pass beneath basement rocks of the southeast San Bernardino Mountains. Subtle, long-wavelength magnetic anomalies indicate that a magnetic body extends in the subsurface north of San Gorgonio Pass and south under Peninsular Ranges basement, and has a southern edge that is roughly parallel to, but 5-6 km south of, the surface trace of the Banning fault. This deep magnetic body is composed either of upper-plate rocks of San Gabriel Mountains basement or rocks of San Bernardino Mountains basement or both. We suggest that transpression across the San Gorgonio Pass region drove a wedge of Peninsular Ranges basement and its overlying sedimentary cover northward into the San Bernardino Mountains during the Neogene, offsetting the Banning fault at shallow depth. Average rates of convergence implied by this offset are broadly consistent with estimates of convergence from other geologic and geodetic data. Seismicity suggests a deeper detachment surface beneath the deep magnetic body. This interpretation suggests that the fault mapped at the surface evolved not only in map but also in cross-sectional view. Given the multilayered nature of deformation, it is unlikely that the San Andreas fault will rupture cleanly through the complex structures in San Gorgonio Pass. ?? 2005 Geological Society of America.

  9. Post-1906 stress recovery of the San Andreas fault system calculated from three-dimensional finite element analysis

    USGS Publications Warehouse

    Parsons, T.

    2002-01-01

    The M = 7.8 1906 San Francisco earthquake cast a stress shadow across the San Andreas fault system, inhibiting other large earthquakes for at least 75 years. The duration of the stress shadow is a key question in San Francisco Bay area seismic hazard assessment. This study presents a three-dimensional (3-D) finite element simulation of post-1906 stress recovery. The model reproduces observed geologic slip rates on major strike-slip faults and produces surface velocity vectors comparable to geodetic measurements. Fault stressing rates calculated with the finite element model are evaluated against numbers calculated using deep dislocation slip. In the finite element model, tectonic stressing is distributed throughout the crust and upper mantle, whereas tectonic stressing calculated with dislocations is focused mostly on faults. In addition, the finite element model incorporates postseismic effects such as deep afterslip and viscoelastic relaxation in the upper mantle. More distributed stressing and postseismic effects in the finite element model lead to lower calculated tectonic stressing rates and longer stress shadow durations (17-74 years compared with 7-54 years). All models considered indicate that the 1906 stress shadow was completely erased by tectonic loading no later than 1980. However, the stress shadow still affects present-day earthquake probability. Use of stressing rate parameters calculated with the finite element model yields a 7-12% reduction in 30-year probability caused by the 1906 stress shadow as compared with calculations not incorporating interactions. The aggregate interaction-based probability on selected segments (not including the ruptured San Andreas fault) is 53-70% versus the noninteraction range of 65-77%.

  10. Andreas Grüntzig's balloon catheter for angioplasty of peripheral arteries (PTA) is 25 years old.

    PubMed

    Bollinger, A; Schlumpf, M

    1999-02-01

    History of Andreas Grüntzig's time spent in Angiology and Radiology of the Zürich University Hospital (1969-1975). First, the pioneer of catheter therapy discovered that the Achilles tendon reflex is significantly prolonged during claudication pain. Furthermore, he participated actively in the clinical evaluation of Doppler ultrasound. After a stay in the Aggertalklinik (Engelskirchen near Köln, Germany), where he learnt Charles Dotter's original procedure with Eberhard Zeitler, he introduced catheter therapy of peripheral arteries in Zürich. In the same period he developed a new, rigid, sausage-shaped balloon catheter (polyvinylchloride), manufactured the device on his kitchen table together with his wife Michaela, Maria and Walter Schlumpf, and used it first on February 12, 1974 in a patient with intermittent claudication due to subtotal stenosis of the superficial femoral artery. The first successful dilatation of an iliac artery stenosis by his double-lumen catheter, which was modified later on into the famous coronary catheter, followed on January 23, 1975. Soon, the innovative catheter became commercially available (Cook and Schneider Companies). Andreas Grüntzig not only excelled in pioneering novel techniques, but also in patient care, in a prospective follow-up study of his own 242 patients lasting 15 years (results summarized in this article), in the teaching of Swiss scholars like Felix Mahler, Ernst Schneider and Bernhard Meier and many more in the world, and in organizing life demonstrations for large numbers of participants. His career in Cardiology, his work in Atlanta Georgia, USA, and his early tragic death in an airplane accident are briefly mentioned.

  11. A large mantle water source for the northern San Andreas Fault System: A ghost of subduction past

    USGS Publications Warehouse

    Kirby, Stephen H.; Wang, Kelin; Brocher, Thomas M.

    2014-01-01

    Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest U.S. is cold and partially serpentinized, storing large quantities of water in this wedge-shaped region. Such a wedge probably formed to the south in California during an earlier period of subduction. We show by numerical modeling that after subduction ceased with the creation of the San Andreas Fault System (SAFS), the mantle wedge warmed, slowly releasing its water over a period of more than 25 Ma by serpentine dehydration into the crust above. This deep, long-term water source could facilitate fault slip in San Andreas System at low shear stresses by raising pore pressures in a broad region above the wedge. Moreover, the location and breadth of the water release from this model gives insights into the position and breadth of the SAFS. Such a mantle source of water also likely plays a role in the occurrence of Non-Volcanic Tremor (NVT) that has been reported along the SAFS in central California. This process of water release from mantle depths could also mobilize mantle serpentinite from the wedge above the dehydration front, permitting upward emplacement of serpentinite bodies by faulting or by diapiric ascent. Specimens of serpentinite collected from tectonically emplaced serpentinite blocks along the SAFS show mineralogical and structural evidence of high fluid pressures during ascent from depth. Serpentinite dehydration may also lead to tectonic mobility along other plate boundaries that succeed subduction, such as other continental transforms, collision zones, or along present-day subduction zones where spreading centers are subducting.

  12. Geodetic measurement of crustal deformation on the San Andreas, Hayward, and Calaveras faults near San Francisco, California

    SciTech Connect

    Prescott, W.H.; Lisowski, M.; Savage, J.C.

    1981-11-10

    Analysis of a geodetic network of 115 lines crossing the San Andreas, Hayward, and Calaveras faults in the vicinity of San Francisco Bay and measured repeatedly between 1970 and 1980 has revealed details about the accommodation of relative plate motion in this area. The most striking result is that the deformation is not uniformly distributed across the area. In the east bay, along the Hayward and Calaveras faults, all motion appears to take place as slip directly on the fault, with no accumulation of strain in the adjacent crust. On both the Calaveras and the Hayward faults the rate obtained for the 1970 to 1980 period agrees with geologic rates spanning a few million years and with creep rates spanning a few decades. The Hayward fault slip rate is 7 +- 1 mm/yr. The Calaveras fault slip rate is 7 +- 1 mm/yr, with perhaps half of this slip distributed across a zone a few kilometers wide, probably as inelatic deformation of weak near-surface material. The absence of strain accumulation in the east bay is surprising since the Hayward and Calaveras faults have been the site of large earthquakes in the past. A block located east of the Calaveras fault and south of the Las Positas fault has been rotating clockwise at the rate of 0.3 +- 0.1 ..mu..rad/yr with very little internal deformation. Along the San Francisco peninsula no detectable slip occurs (less than 1.5 mm/yr) at the surface, but appreciable strain is accumulating. Near fault shear strain rates are 0.6 +- 0.1 ..mu..strain/yr (engineering) with direction N47/sup 0/W +- 9. The slip rate near the San Andreas fault is 12.2 +- 3.9 mm/yr distributed across a broad zone. The relative motion across the whole region during the period 1970--1980 is 32.1 +- 7.4 mm/yr.

  13. On Offset Stream Measurements and Recent Coseismic Surface Rupture in the Carrizo Section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Brooks, B. A.; Hudnut, K. W.; Akciz, S. O.; Delano, J.; Glennie, C. L.; Prentice, C. S.; DeLong, S.

    2013-12-01

    Recent studies using airborne laser swath mapping (ALSM) topographic data have provoked debate about whether the Mw 7.9 Fort Tejon 1857 earthquake produced ~5m or ~10m of surface strike-slip displacement in the Carrizo section of the south-central San Andreas fault. Resolution of this discrepancy is important not only for understanding the proposed role of the Carrizo section in controlling repeated south-central San Andreas rupture but also for understanding the general utility of stream offset measurements for earthquake process studies. To explore if higher-resolution topographic data of the offset features would help reconcile the different interpretations, we used a mobile laser scanning (MLS) backpack-mounted system to survey 11 ~5m offset streams given 'high' quality rankings by previous studies. In our surveys, point density was on the order of 1000s pts/m^2 in comparison to 1-4 pts/m^2 for the ALSM data, enabling us to faithfully make digital elevation models with grid spacing smaller than 10cm. We adapt a geometric method that relies on a small number of user-dependent decisions to produce an offset estimate from a set of geomorphic markers (thalweg, channel margins, channel shoulders) from upstream and downstream locations. We typically derive an ensemble of at least 10 offset measurements per stream channel and from these calculate a mean and standard deviation. We also explore using gradient changes in long profiles of the offset stream reaches to diagnose the possibility of a ~10m channel experiencing 2 ~5m slip events. Preliminary results suggest a tendency towards the higher value offset estimates, although this does not necessarily preclude the possibility of two or more events causing the cumulative offset.

  14. Structure of the 1906 near-surface rupture zone of the San Andreas Fault, San Francisco Peninsula segment, near Woodside, California

    USGS Publications Warehouse

    Rosa, C.M.; Catchings, R.D.; Rymer, M.J.; Grove, Karen; Goldman, M.R.

    2016-07-08

    High-resolution seismic-reflection and refraction images of the 1906 surface rupture zone of the San Andreas Fault near Woodside, California reveal evidence for one or more additional near-surface (within about 3 meters [m] depth) fault strands within about 25 m of the 1906 surface rupture. The 1906 surface rupture above the groundwater table (vadose zone) has been observed in paleoseismic trenches that coincide with our seismic profile and is seismically characterized by a discrete zone of low P-wave velocities (Vp), low S-wave velocities (Vs), high Vp/Vs ratios, and high Poisson’s ratios. A second near-surface fault strand, located about 17 m to the southwest of the 1906 surface rupture, is inferred by similar seismic anomalies. Between these two near-surface fault strands and below 5 m depth, we observed a near-vertical fault strand characterized by a zone of high Vp, low Vs, high Vp/Vs ratios, and high Poisson’s ratios on refraction tomography images and near-vertical diffractions on seismic-reflection images. This prominent subsurface zone of seismic anomalies is laterally offset from the 1906 surface rupture by about 8 m and likely represents the active main (long-term) strand of the San Andreas Fault at 5 to 10 m depth. Geometries of the near-surface and subsurface (about 5 to 10 m depth) fault zone suggest that the 1906 surface rupture dips southwestward to join the main strand of the San Andreas Fault at about 5 to 10 m below the surface. The 1906 surface rupture forms a prominent groundwater barrier in the upper 3 to 5 m, but our interpreted secondary near-surface fault strand to the southwest forms a weaker barrier, suggesting that there has been less or less-recent near-surface slip on that strand. At about 6 m depth, the main strand of the San Andreas Fault consists of water-saturated blue clay (collected from a hand-augered borehole), which is similar to deeply weathered serpentinite observed within the main strand of the San Andreas Fault at

  15. Geomorphology, denudation rates, and stream channel profiles reveal patterns of mountain building adjacent to the San Andreas fault in northern California, USA

    USGS Publications Warehouse

    DeLong, Stephen B.; Hilley, George E.; Prentice, Carol S.; Crosby, Christopher J.; Yokelson, Intan N.

    2017-01-01

    Relative horizontal motion along strike-slip faults can build mountains when motion is oblique to the trend of the strike-slip boundary. The resulting contraction and uplift pose off-fault seismic hazards, which are often difficult to detect because of the poor vertical resolution of satellite geodesy and difficulty of locating offset datable landforms in active mountain ranges. Sparse geomorphic markers, topographic analyses, and measurement of denudation allow us to map spatiotemporal patterns of uplift along the northern San Andreas fault. Between Jenner and Mendocino, California, emergent marine terraces found southwest of the San Andreas fault record late Pleistocene uplift rates between 0.20 and 0.45 mm yr–1 along much of the coast. However, on the northeast side of the San Andreas fault, a zone of rapid uplift (0.6–1.0 mm yr–1) exists adjacent to the San Andreas fault, but rates decay northeastward as the coast becomes more distant from the San Andreas fault. A newly dated 4.5 Ma shallow-marine deposit located at ∼500 m above sea level (masl) adjacent to the San Andreas fault is warped down to just 150 masl 15 km northeast of the San Andreas fault, and it is exposed at just 60–110 masl to the west of the fault. Landscape denudation rates calculated from abundance of cosmogenic radionuclides in fluvial sediment northeast of, and adjacent to, the San Andreas fault are 0.16–0.29 mm yr–1, but they are only 0.03–0.07 mm yr–1 west of the fault. Basin-average channel steepness and the denudation rates can be used to infer the erosive properties of the underlying bedrock. Calibrated erosion rates can then be estimated across the entire landscape using the spatial distribution of channel steepness with these erosive properties. The lower-elevation areas of this landscape that show high channel steepness (and hence calibrated erosion rate) are distinct from higher-elevation areas with systematically lower channel steepness and denudation rates

  16. Retardations in fault creep rates before local moderate earthquakes along the San Andreas fault system, central California

    USGS Publications Warehouse

    Burford, R.O.

    1988-01-01

    Records of shallow aseismic slip (fault creep) obtained along parts of the San Andreas and Calaveras faults in central California demonstrate that significant changes in creep rates often have been associated with local moderate earthquakes. An immediate postearthquake increase followed by gradual, long-term decay back to a previous background rate is generally the most obvious earthquake effect on fault creep. This phenomenon, identified as aseismic afterslip, usually is characterized by above-average creep rates for several months to a few years. In several cases, minor step-like movements, called coseismic slip events, have occurred at or near the times of mainshocks. One extreme case of coseismic slip, recorded at Cienega Winery on the San Andreas fault 17.5 km southeast of San Juan Bautista, consisted of 11 mm of sudden displacement coincident with earthquakes of ML=5.3 and ML=5.2 that occurred 2.5 minutes apart on 9 April 1961. At least one of these shocks originated on the main fault beneath the winery. Creep activity subsequently stopped at the winery for 19 months, then gradually returned to a nearly steady rate slightly below the previous long-term average. The phenomena mentioned above can be explained in terms of simple models consisting of relatively weak material along shallow reaches of the fault responding to changes in load imposed by sudden slip within the underlying seismogenic zone. In addition to coseismic slip and afterslip phenomena, however, pre-earthquake retardations in creep rates also have been observed. Onsets of significant, persistent decreases in creep rates have occurred at several sites 12 months or more before the times of moderate earthquakes. A 44-month retardation before the 1979 ML=5.9 Coyote Lake earthquake on the Calaveras fault was recorded at the Shore Road creepmeter site 10 km northwest of Hollister. Creep retardation on the San Andreas fault near San Juan Bautista has been evident in records from one creepmeter site for

  17. The Nature of Fault Creep and Weakening in the San Andreas System Deduced from Studies of SAFOD Core (Invited)

    NASA Astrophysics Data System (ADS)

    Moore, D. E.; Rymer, M. J.; Lockner, D. A.

    2013-12-01

    Our understanding of the processes operative at depth in fault zones is severely hampered by the general inability to study the actively deforming fault rocks in situ. One of the main goals of the San Andreas Fault Observatory at Depth (SAFOD), a key component of Earthscope, was the recovery of core to allow petrographic, chemical, and physical examination of an active, plate-boundary fault at seismogenic depths, something that had never before been attempted. The SAFOD drill site is located 14 km northwest of Parkfield in central California, along a portion of the San Andreas Fault (SAF) that is characterized by a combination of aseismic slip and microseismicity. Innovations in the design and implementation of SAFOD (summarized in Zoback, Hickman and Ellsworth, Scientific Drilling, No. 11, March 2011) led to the identification of two actively creeping fault traces at 2.65 and 2.70 km vertical depth (~112°C). Subsequent multilateral coring operations successfully sampled the two zones of foliated gouge where creep is localized: the 2.6-m-wide central deforming zone (CDZ) and the 1.6-m-wide southwest deforming zone (SDZ). The two gouge zones are closely similar in character, consisting of porphyroclasts of serpentinite and sedimentary rock dispersed in a fine-grained, foliated matrix of Mg-rich smectitic clays (saponite × corrensite). The boundaries of the CDZ and SDZ with adjoining sedimentary rocks of the Great Valley Group are mineralogically, chemically, and texturally sharp. The Mg-rich clay minerals in the gouge zones are interpreted to be the product of fluid-assisted, shear-enhanced metasomatic reactions between the quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the SAF from a source in the Coast Range ophiolite. Laboratory friction tests indicate that gouge from the CDZ and SDZ deforms stably (i.e., creeps) at anomalously low levels of shear stress (coefficient of friction, μ ~ 0.15), which is sufficient to explain the

  18. Constraints on the stress state of the San Andreas fault with analysis based on core and cuttings from SAFOD drilling phases I and II

    USGS Publications Warehouse

    Lockner, David A.; Tembe, Cheryl; Wong, Teng-fong

    2009-01-01

    Analysis of field data has led different investigators to conclude that the San Andreas Fault (SAF) has either anomalously low frictional sliding strength (m < 0.2) or strength consistent with standard laboratory tests (m > 0.6). Arguments for the apparent weakness of the SAF generally hinge on conceptual models involving intrinsically weak gouge or elevated pore pressure within the fault zone. Some models assert that weak gouge and/or high pore pressure exist under static conditions while others consider strength loss or fluid pressure increase due to rapid coseismic fault slip. The present paper is composed of three parts. First, we develop generalized equations, based on and consistent with the Rice (1992) fault zone model to relate stress orientation and magnitude to depth-dependent coefficient of friction and pore pressure. Second, we present temperature- and pressure-dependent friction measurements from wet illite-rich fault gouge extracted from San Andreas Fault Observatory at Depth (SAFOD) phase 1 core samples and from weak minerals associated with the San Andreas Fault. Third, we reevaluate the state of stress on the San Andreas Fault in light of new constraints imposed by SAFOD borehole data. Pure talc (m0.1) had the lowest strength considered and was sufficiently weak to satisfy weak fault heat flow and stress orientation constraints with hydrostatic pore pressure. Other fault gouges showed a systematic increase in strength with increasing temperature and pressure. In this case, heat flow and stress orientation constraints would require elevated pore pressure and, in some cases, fault zone pore pressure in excess of vertical stress.

  19. Continuous borehole strain in the San Andreas fault zone before, during, and after the 28 June 1992, MW 7.3 Landers, California, earthquake

    USGS Publications Warehouse

    Johnston, M.J.S.; Linde, A.T.; Agnew, D.C.

    1994-01-01

    High-precision strain was observed with a borehole dilational strainmeter in the Devil's Punchbowl during the 11:58 UT 28 June 1992 MW 7.3 Landers earthquake and the large Big Bear aftershock (MW 6.3). The strainmeter is installed at a depth of 176 m in the fault zone approximately midway between the surface traces of the San Andreas and Punchbowl faults and is about 100 km from the 85-km-long Landers rupture. We have questioned whether unusual amplified strains indicating precursive slip or high fault compliance occurred on the faults ruptured by the Landers earthquake, or in the San Andreas fault zone before and during the earthquake, whether static offsets for both the Landers and Big Bear earthquakes agree with expectation from geodetic and seismologic models of the ruptures and with observations from a nearby two-color geodimeter network, and whether postseismic behavior indicated continued slip on the Landers rupture or local triggered slip on the San Andreas. We show that the strain observed during the earthquake at this instrument shows no apparent amplification effects. There are no indications of precursive strain in these strain data due to either local slip on the San Andreas or precursive slip on the eventual Landers rupture. The observations are generally consistent with models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake. Finally, there are some indications of minor postseismic behavior, particularly during the month following the earthquake.

  20. (U-Th)/He thermochronometry reveals Pleistocene punctuated deformation and synkinematic hematite mineralization in the Mecca Hills, southernmost San Andreas Fault zone

    NASA Astrophysics Data System (ADS)

    Moser, Amy C.; Evans, James P.; Ault, Alexis K.; Janecke, Susanne U.; Bradbury, Kelly K.

    2017-10-01

    The timing, tempo, and processes of punctuated deformation in strike-slip fault systems are challenging to resolve in the rock record. Faults in the Mecca Hills, adjacent to the southernmost San Andreas Fault, California, accommodate active deformation and exhumation in the Plio-Pleistocene sedimentary rocks and underlying crystalline basement. We document the spatiotemporal patterns of San Andreas Fault-related deformation as recorded in crystalline basement rocks of the Mecca Hills using fault microstructural observations, geochemical data, and hematite (n = 24) and apatite (n = 44) (U-Th)/He (hematite He, apatite He) thermochronometry data. Reproducible mean hematite He dates from minor hematite-coated fault surfaces in the Painted Canyon Fault damage zone range from ∼0.7-0.4 Ma and are younger than ∼1.2 Ma apatite He dates from adjacent crystalline basement host rock. These data reveal concomitant Pleistocene pulses of fault slip, fluid flow, and synkinematic hematite mineralization. Hematite textures, crystal morphology, and hematite He data patterns imply some damage zone deformation occurred via cyclic crack-seal and creep processes. Apatite He data from crystalline basement define distinct date-eU patterns and indicate cooling across discrete fault blocks in the Mecca Hills. Uniform ∼1.2 Ma apatite He dates regardless of eU are located exclusively between the Painted Canyon and Platform faults. Outside of this fault block, samples yield individual apatite He dates from ∼30-1 Ma that define a positive apatite He date-eU correlation. These patterns reveal focused exhumation away from the main trace of the San Andreas Fault at ∼1.2 Ma. Low-temperature thermochronometry of fault-related rocks provides an unprecedented window into the 105-106-yr record of San Andreas Fault-related deformation in the Mecca Hills and documents hematite deformation mechanisms that may be operative in other strike-slip faults world-wide.

  1. [Christian Andreas Cothenius (1708-1789). A pro-memoria on the occasion of the 200th anniversary of his death].

    PubMed

    Völker, A

    1990-04-01

    The 200th anniversary of the death of Christian Andreas Cothenius gave occasion to appreciate life and work of this personage of a physician. Cothenius maintained manifold connections to Halle, of which the golden doctorate and the heritage of the pharmaceutic enterprises of his teacher Friedrich Hoffmann were treated in this place. The picture of the local relations was supplemented by the history of the Cothenius medal which is today awarded by the Leopoldina of Halle.

  2. The 2004 Earthquake in Light of M>5.5 San Andreas Fault Seismicity Within ~70 km NW of Parkfield Since 1857.

    NASA Astrophysics Data System (ADS)

    Toppozada, T.; Branum, D.; Reichle, M.; Wills, C.

    2004-12-01

    The 2004 Parkfield earthquake occurred at least 12 years later than predicted by the model of quasi-regularly recurring characteristic earthquakes. That model was based on the occurrence of two "Parkfield" events in the 1800s, including the 1857 foreshock ~50 km NW of Parkfield, and four events in the 1900s. The 2004 earthquake better fits the larger and historically more complete picture, which includes at least four additional M~6 or stronger earthquakes on the San Andreas fault within ~70 km NW of Parkfield from 1860 to 1885. These large 1800s earthquakes occurred on the segment of the San Andreas fault that since 1930 has been creeping with no M>5 earthquakes. The great 1857 Fort Tejon earthquake had immediate foreshocks in the zone ~50 km NW of Parkfield near Lonoak. In this northern end of the 1857 rupture, including Parkfield, the rate of seismic moment release has decreased steadily with time since 1857. More strong earthquakes occurred in the ~50 years after 1857 than in the following ~100 years when seismicity was nearer to Parkfield. The high pre-1900 seismicity in the currently creeping segment of the San Andreas fault may have resulted from the stress loading at the 1857 rupture end from the ~9 m displacements in the Carrizo Plain ~80 km SE of Parkfield. This would also explain the decay of the seismicity with time after 1857. The strong earthquakes in the Parkfield-Lonaok end of the 1857 rupture have generally migrated ~70 km with time from NW to SE along the San Andreas fault. In 1857 they were around Lonoak in the presently creeping zone, and in 1966-2004 they bordered the locked zone near Parkfield. If this southeasterly migration continues, the next earthquake might be further SE from Parkfield toward the locked zone that is capable of M~7 or larger earthquakes.

  3. Variations in Creep Rate along the Central San Andreas Fault from InSAR and GPS Observations

    NASA Astrophysics Data System (ADS)

    Ryder, I. M.; Burgmann, R.

    2007-12-01

    The San Andreas Fault is locked along most of its length, but the 170 km-long section between San Juan Bautista and Parkfield undergoes creep. Measurements from creepmeters, alignment arrays and GPS over the last 25 years have shown that surface creep rates reach about 30 mm/year in the central portion, tapering off towards the locked segments at either end. Though useful, these measurements have been spatially isolated and intermittent in time. We present InSAR observations of creep across the fault, which have superior spatial coverage than previous data, and analyse them to investigate spatial variations in creep rate along the fault segment. From multiple ERS-1 and ERS-2 descending interferograms covering 1992 to 2001, we produce a stack which gives the spatial distribution of creep rate up to about 50 km either side of the fault. We find a maximum creep rate of about 32 mm/year. Deformation is step-like most of the way along the segment, but more distributed at the northern end, where the Calaveras Fault comes very close to the San Andreas Fault. We perform a linear inversion for shallow and deep sliding velocity on these faults using both the InSAR stack and GPS velocities from continuous (PBO) and campaign networks. Creep in the top few kilometers is variable along strike, with patches of faster creep interspersed with more slowly-moving patches. Creep at intermediate depths is greatest in the centre of the segment, reaching a few mm/yr less than the relative plate rate. The deep (> 12 km) sliding velocity is constrained to be less than or equal to the estimated long term relative plate velocity, and we estimate it to be a few mm/yr less than this. We compare the depth-averaged creep rate profile along the fault segment with that estimated by Nadeau and McEvilly (2004) from characteristic repeating microearthquakes. Between them, the three datasets utilised in this study suggest that creep is a spatially heterogeneous process.

  4. Balloon Angioplasty – The Legacy of Andreas Grüntzig, M.D. (1939–1985)

    PubMed Central

    Barton, Matthias; Grüntzig, Johannes; Husmann, Marc; Rösch, Josef

    2014-01-01

    In 1974, at the Medical Policlinic of the University of Zürich, German-born physician-scientist Andreas Grüntzig (1939–1985) for the first time applied a balloon-tipped catheter to re-open a severely stenosed femoral artery, a procedure, which he initially called “percutaneous transluminal dilatation”. Balloon angioplasty as a therapy of atherosclerotic vascular disease, for which Grüntzig and Charles T. Dotter (1920–1985) received a nomination for the Nobel Prize in Physiology or Medicine in 1978, became one of the most successful examples of translational medicine in the twentieth century. Known today as percutaneous transluminal angioplasty (PTA) in peripheral arteries or percutaneous transluminal coronary angioplasty (PTCA) or percutaneous coronary intervention (PCI) in coronary arteries, balloon angioplasty has become the method of choice to treat patients with acute myocardial infarction or occluded leg arteries. On the occasion of the 40th anniversary of balloon angioplasty, we summarize Grüntzig’s life and career in Germany, Switzerland, and the United States and also review the developments in vascular medicine from the 1890s to the 1980s, including Dotter’s first accidental angioplasty in 1963. The work of pioneers of catheterization, including Pedro L. Fariñas in Cuba, André F. Cournand in France, Werner Forssmann, Werner Porstmann and Eberhard Zeitler in Germany, António Egas Moniz and Reynaldo dos Santos in Portugal, Sven-Ivar Seldinger in Sweden, and Barney Brooks, Thomas J. Fogarty, Melvin P. Judkins, Richard K. Myler, Dickinson W. Richards, and F. Mason Sones in the United States, is discussed. We also present quotes by Grüntzig and excerpts from his unfinished autobiography, statements of Grüntzig’s former colleagues and contemporary witnesses, and have included hitherto unpublished historic photographs and links to archive recordings and historic materials. This year, on June 25, 2014, Andreas Grüntzig would have celebrated

  5. Understanding strain transfer and basin evolution complexities in the Salton pull-apart basin near the Southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Kell, A. M.; Sahakian, V. J.; Kent, G. M.; Driscoll, N. W.; Harding, A. J.; Baskin, R. L.; Barth, M.; Hole, J. A.; Stock, J. M.; Fuis, G. S.

    2015-12-01

    Active source seismic data in the Salton Sea provide insight into the complexity of the pull-apart system development. Seismic reflection data combined with tomographic cross sections give constraints on the timing of basin development and strain partitioning between the two dominant dextral faults in the region; the Imperial fault to the southwest and the Southern San Andreas fault (SSAF) to the northeast. Deformation associated with this step-over appears young, having formed in the last 20-40 k.a. The complexity seen in the Salton Sea is similar to that seen in pull-apart basins worldwide. In the southern basin of the Salton Sea, a zone of transpression is noted near the southern termination of the San Andreas fault, though this stress regime quickly transitions to a region of transtension in the northern reaches of the sea. The evolution seen in the basin architecture is likely related to a transition of the SSAF dying to the north, and giving way to youthful segments of the Brawley seismic zone and Imperial fault. Stratigraphic signatures seen in seismic cross-sections also reveal a long-term component of slip to the southwest on a fault 1-2 km west of the northeastern Salton Sea shoreline. Numerous lines of evidence, including seismic reflection data, high-resolution bathymetry within the Salton Sea, and folding patterns in the Borrego Formation to the east of the sea support an assertion of a previously unmapped fault, the Salton Trough fault (STF), parallel to the SAF and just offshore within the Salton Sea. Seismic observations are seen consistently within two datasets of varying vertical resolutions, up to depths of 4-5 km, suggesting that this fault strand is much longer-lived than the evolution seen in the southern sub-basin. The existence of the STF unifies discrepancies between the onshore seismic studies and data collected within the sea. The STF likely serves as the current bounding fault to the active pull-apart system, as it aligns with the "rung

  6. Pore fluid ‘ages’ suggest fluid replacement events across the San Andreas Fault at Depth, Parkfield, CA (Invited)

    NASA Astrophysics Data System (ADS)

    Ali, S.; Stute, M.; Torgersen, T.; Hemming, S. R.; Fleisher, M. Q.; Winckler, G.

    2009-12-01

    The presence of aqueous reaction produced low strength mineral surfaces is linked to low friction slip along the San Andreas Fault Zone (SAFZ) as shown in core samples recovered from the San Andreas Fault Observatory at Depth (SAFOD) in Parkfield, CA. These mineral phases are a product of fluid-rock interaction in the fault zone. SAFOD drill cores show multiple zones of alteration and deformation due to fluid-rock interaction (Schleicher et. al, 2008), which requires transport of fluids into the fault zone. We present pore fluid ages, age gradients, as well as 3He and 4He isotope profiles of matrix fluids obtained from drill core samples during SAFOD phases 1, 2, and 3 to constrain fluid flow across the SAFZ. Helium and argon concentration profiles in the pore fluids suggest the fault represents a sink for 3He, 4He and 40Ar. The 3He/4He profile across the SAFZ confirms the mantle helium signature is introduced from the North American Plate side of the SAFOD drillhole and the lack of mantle-derived fluid component through the fault zone. Noble gas measurements on the solid phase indicate that more than 90% of in situ produced He has entered the fluid phase. The presence of mantle-derived He in both plates and the fault zone suggests that the fluids are accumulating both locally produced and externally produced He. Apparent maximum pore fluid ages range from ˜300,000-700,000 years (3050m-measured depth (MD)) in the Pacific Plate and ˜300,000 -500,000 years (3989m-MD) in the North American Plate, compared to relatively younger ages of <200,000 years in the actively creeping trace of the SAFZ at 3300m-MD. The pore fluid ages suggest fluid flow events on these or shorter timescales in the respective zones. Each fluid event results into further dissolution and precipitation in the SAFZ creating a new layer of minerals, which in turn can enhance further slip along the fault.

  7. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas fault zone

    USGS Publications Warehouse

    Thatcher, W.; England, P.C.

    1998-01-01

    We have carried out two-dimensional (2-D) numerical experiments on the bulk flow of a layer of fluid that is driven in a strike-slip sense by constant velocities applied at its boundaries. The fluid has the (linearized) conventional rheology assumed to apply to lower crust/upper mantle rocks. The temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations, as has thermal conduction in an overlying crustal layer. Two end-member boundary conditions have been considered, corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive, weak crust. In many cases of practical interest, shear heating is concentrated close to the axial plane of the shear zone for either boundary condition. For these cases, the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half-space at a depth corresponding to the top of the fluid layer. This approximation, along with the application of a theoretical result for one-dimensional shear zones, permits us to obtain simple analytical approximations to the thermal effects of 2-D ductile shear zones for a range of assumed rheologies and crustal geotherms, making complex numerical calculations unnecessary. Results are compared with observable effects on heat flux near the San Andreas fault using constraints on the slip distribution across the entire fault system. Ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the Mendocino triple junction and match the amplitude of the regional heat flux anomaly in the California Coast Ranges. Because ductile dissipation depends only weakly on slip rate, faults moving only a few millimeters per year can be important heat sources, and the superposition of effects of localized ductile shearing on both currently active and now

  8. Long Period Ground Motions in the San Bernardino Region for Hypothetical San Andreas and San Jacinto Earthquakes

    NASA Astrophysics Data System (ADS)

    Graves, R. W.

    2001-12-01

    The San Bernardino region of southern California is situated on a wedge shaped sedimentary basin bounded to the north by the San Andreas fault and to the south by the San Jacinto fault. Not only is this region fairly heavily populated, but both of these active faults are capable of generating Mw 7+ earthquakes, stressing the need for timely assessment of the ground shaking hazard for future scenario earthquakes. Ground motion estimation in this region is further complicated by the highly variable nature of the subsurface geology. Sediment accumulations are relatively thin in the northern portion of the basin, and then steadily increase in thickness toward the south. The maximum sediment thickness is about 1.5 km just north of the San Jacinto fault, with an abrupt step-up and shallowing of the basement surface along (and to the south of) the San Jacinto fault. Existing observations of long period (T > 1 sec) ground motions for both large (1999 Mw 7.2 Hector Mine) and small (2001 Mw 4.7 Big Bear Lake) earthquakes show significant amplification and extended durations of shaking at recording sites within the basin. Recent studies using 3D numerical simulation methods have modeled these recorded ground motions in order to develop and constrain the 3D velocity structure of the basin region. The current 3D velocity models do reasonably well at matching the recorded waveforms at periods of about 2 seconds and longer. To estimate the expected levels of ground shaking for future events in this region, I have performed 3D finite difference ground motion simulations for hypothetical Mw 7 earthquakes on the San Andreas and San Jacinto faults. The simulations use the existing 3D structural models of the region and incorporate a suite of variable slip finite-fault rupture models. To address uncertainty in the source characterizion, I consider several hypocenter locations and slip distributions on each of the faults. Preliminary results indicate that the largest long period

  9. TremorScope: A Tool to Image the Deep Workings of the San Andreas Fault near Cholame, CA

    NASA Astrophysics Data System (ADS)

    Hellweg, M.; Burgmann, R.; Taira, T.; Nadeau, R. M.; Dreger, D. S.; Allen, R. M.

    2015-12-01

    Until recently, active fault zones were thought to deform via seismic slip during earthquakes in the upper, brittle portion of the crust, and by steady, aseismic shear below. However, since 2000, this view has been shaken by seismological observations of seismic tremor deep in the roots of active fault zones, including on the section of the San Andreas to the southeast of Parkfield, CA, deep (~20-30 km) beneath the nucleation zone of the great 1857 Fort Tejon earthquake. With funding from the Gordon and Betty Moore Foundation, we have improved the seismic network in the area above the tremor source by installing four new broadband/strong motion surface stations and four borehole sites with uphole accelerometers and downhole geophones, broadband and strong motion sensors. Data from all stations are telemetered in real-time. They are analysed as part of normal earthquake monitoring, and archived and distributed through the Northern California Earthquake Data Center (NCEDC). Data from the TremorScope project is improving earthquake monitoring in the region south of Parkfield, including allowing empirical Greens function finite fault analysis of moderate events in the area. Locations and characterization of tremor episodes are improved by the data recorded by TremorScope stations. For example, the rate of ambient tremor activity in the TremorScope area increased by a factor of ~8 within ~12 hours of the 2014 Napa M6.0 earthquake and remained elevated for ~ 100 days, exceeding the tremor rate increase following the 2004 Parkfield M6.0 quake despite the differences in epicentral distance (~300 km vs. ~15 km). No comparable increases in tremor rates have been observed between the Parkfield and Napa events. This suggests that the sensitivity to external stressing in the in the deep tremor zone of the TremorScope region may have increased since 2004. We also show how this network's strong motion instrumentation will provide unprecedented and exciting insights into the

  10. Correlation of clayey gouge in a surface exposure of the San Andreas fault with gouge at depth from SAFOD: Implications for the role of serpentinite in fault mechanics

    USGS Publications Warehouse

    Moore, Diane E.; Rymer, Michael J.

    2012-01-01

    Magnesium-rich clayey gouge similar to that comprising the two actively creeping strands of the San Andreas Fault in drill core from the San Andreas Fault Observatory at Depth (SAFOD) has been identified in a nearby outcrop of serpentinite within the fault zone at Nelson Creek. Each occurrence of the gouge consists of porphyroclasts of serpentinite and sedimentary rocks dispersed in a fine-grained, foliated matrix of Mg-rich smectitic clays. The clay minerals in all three gouges are interpreted to be the product of fluid-assisted, shear-enhanced reactions between quartzofeldspathic wall rocks and serpentinite that was tectonically entrained in the fault from a source in the Coast Range Ophiolite. We infer that the gouge at Nelson Creek connects to one or both of the gouge zones in the SAFOD core, and that similar gouge may occur at depths in between. The special significance of the outcrop is that it preserves the early stages of mineral reactions that are greatly advanced at depth, and it confirms the involvement of serpentinite and the Mg-rich phyllosilicate minerals that replace it in promoting creep along the central San Andreas Fault.

  11. Long-term slip rate of the southern San Andreas Fault, from 10Be-26Al surface exposure dating of an offset alluvial fan

    SciTech Connect

    der Woerd, J v; Klinger, Y; Sieh, K; Tapponnier, P; Ryerson, F; M?riaux, A

    2006-01-13

    We determine the long-term slip rate of the southern San Andreas Fault in the southeastern Indio Hills using {sup 10}Be and {sup 26}Al isotopes to date an offset alluvial fan surface. Field mapping complemented with topographic data, air photos and satellite images allow to precisely determine piercing points across the fault zone that are used to measure an offset of 565 {+-} 80 m. A total of twenty-six quartz-rich cobbles from three different fan surfaces were collected and dated. The tight cluster of nuclide concentrations from 19 samples out of 20 from the offset fan surface implies a simple exposure history, negligible prior exposure and erosion, and yield an age of 35.5 {+-} 2.5 ka. The long-term slip rate of the San Andreas Fault south of Biskra Palms is thus 15.9 {+-} 3.4 mm/yr. This rate is about 10 mm/yr slower than geological (0-14 ka) and short-term geodetic estimates for this part of the San Andreas Fault implying changes in slip rate or in faulting behavior. This result puts new constraints on the slip rate of the San Jacinto and on the Eastern California Shear Zone for the last 35 ka. Our study shows that more sites along the major faults of southern California need to be targeted to better constrain the slip-rates over different time scales.

  12. Ambient Noise Tomography of Southern California Images Dipping San Andreas-Parallel Structure and Low-Velocity Salton Trough Mantle

    NASA Astrophysics Data System (ADS)

    Barak, S.; Klemperer, S. L.; Lawrence, J. F.

    2014-12-01

    Ambient noise tomography (ANT) images the entire crust but does not depend on the spatial and temporal distribution of events. Our ANT high-resolution 3D velocity model of southern California uses 849 broadband stations, vastly more than previous studies, and four years of data, 1997-1998, 2007, and 2011, chosen to include our own broadband Salton Seismic Imaging Project, a 40-station transect across the Salton Trough, as well as other campaign stations in both Mexico and the U.S.A., and permanent stations. Our shear-wave model has 0.05° x 0.05° lateral and 1 km vertical blocks. We used the Harvard Community Velocity Model (CVM-H) as the initial model for the inversion. We show significant differences relative to the CVM-H model, especially in the lower crust and upper mantle. We observe prominent low-velocity anomalies in the upper mantle under the Salton Buttes and Cerro Prieto geothermal fields, indicating high-temperatures and possibly partial-melt. Similar low-velocity zones have been previously observed along the Gulf of California. We also observe vertical to gradually dipping lateral velocity contrasts in the lower crust under the southern part of the San Andreas Fault. The east to northeast dip may represent crustal fabric sheared by movement of the Pacific plate under the North American plate prior to the initiation of transform motion.

  13. Heterogeneous slip and rupture models of the San Andreas fault zone based upon three-dimensional earthquake tomography

    SciTech Connect

    Foxall, William

    1992-11-01

    Crystal fault zones exhibit spatially heterogeneous slip behavior at all scales, slip being partitioned between stable frictional sliding, or fault creep, and unstable earthquake rupture. An understanding the mechanisms underlying slip segmentation is fundamental to research into fault dynamics and the physics of earthquake generation. This thesis investigates the influence that large-scale along-strike heterogeneity in fault zone lithology has on slip segmentation. Large-scale transitions from the stable block sliding of the Central 4D Creeping Section of the San Andreas, fault to the locked 1906 and 1857 earthquake segments takes place along the Loma Prieta and Parkfield sections of the fault, respectively, the transitions being accomplished in part by the generation of earthquakes in the magnitude range 6 (Parkfield) to 7 (Loma Prieta). Information on sub-surface lithology interpreted from the Loma Prieta and Parkfield three-dimensional crustal velocity models computed by Michelini (1991) is integrated with information on slip behavior provided by the distributions of earthquakes located using, the three-dimensional models and by surface creep data to study the relationships between large-scale lithological heterogeneity and slip segmentation along these two sections of the fault zone.

  14. Hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Moore, Diane E.; Lockner, David A.; Hickman, Stephen

    2016-08-01

    We compare frictional strengths in the temperature range 25-250 °C of fault gouge from SAFOD (CDZ and SDZ) with quartzofeldspathic wall rocks typical of the central creeping section of the San Andreas Fault (Great Valley sequence and Franciscan Complex). The Great Valley and Franciscan samples have coefficients of friction, μ > 0.35 at all experimental conditions. Strength is unchanged between 25° and 150 °C, but μ increases at higher temperatures, exceeding 0.50 at 250 °C. Both samples are velocity strengthening at room temperature but show velocity-weakening behavior beginning at 150 °C and stick-slip motion at 250 °C. These rocks, therefore, have the potential for unstable seismic slip at depth. The CDZ gouge, with a high saponite content, is weak (μ = 0.09-0.17) and velocity strengthening in all experiments, and μ decreases at temperatures above 150 °C. Behavior of the SDZ is intermediate between the CDZ and wall rocks: μ < 0.2 and does not vary with temperature. Although saponite is probably not stable at depths greater than ∼3 km, substitution of the frictionally similar minerals talc and Mg-rich chlorite for saponite at higher temperatures could potentially extend the range of low strength and stable slip down to the base of the seismogenic zone.

  15. Paleobathymetric maps of tertiary La Honda Basin and implications for offset along San Andreas fault in central California

    SciTech Connect

    Stanley, R.G.

    1987-05-01

    Paleobathymetric maps of the La Honda basin of central California were constructed for ten intervals of geologic time from late Paleocene (Nezian) to middle Miocene (Luisian). The maps are based on analyses of benthic foraminiferal biofacies in more than 800 faunal lists compiled from the literature and from subsurface data provided by oil companies. The sequence of paleobathymetric maps shows the paleogeographic evolution of the La Honda basin. From the late Paleocene (Ynezian) to the early Oligocene (early Zemorrian), deep-sea sands and muds accumulated at water depths of 2000 m and more on a surface that sloped gently to the north and northeast. Striking changes in the configuration of the La Honda basin occurred during the late Oligocene and early Miocene (late Zemorrian). Much of the basin floor remained at water depths of 2000 m and greater, but submarine volcanic rocks locally built up to form seamounts, and movement along the Zayante-Vergeles fault led to shoaling and development of a narrow shelf and very steep slope along the southwestern margin of the basin. During the early and middle Miocene (Relizian and Luisian), the entire basin shoaled to depths of less than 1500 m. Comparison of paleobathymetric maps of the La Honda and San Joaquin basins lends support to the notion that the two basins were once contiguous but have been separated by about 320 to 330 km of right-lateral displacement along the San Andreas fault since the earliest Miocene (late Zemorrian and Saucesian).

  16. Broadband simulations for Mw 7.8 southern san andreas earthquakes: Ground motion sensitivity to rupture speed

    USGS Publications Warehouse

    Graves, R.W.; Aagaard, B.T.; Hudnut, K.W.; Star, L.M.; Stewart, J.P.; Jordan, T.H.

    2008-01-01

    Using the high-performance computing resources of the Southern California Earthquake Center, we simulate broadband (0-10 Hz) ground motions for three Mw 7.8 rupture scenarios of the southern San Andreas fault. The scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0.96, 0.89, and 0.84 times the local shear wave velocity. Consistent with previous simulations, a southern hypocenter efficiently channels energy into the Los Angeles region along the string of basins south of the San Gabriel Mountains. However, we find the basin ground motion levels are quite sensitive to the prescribed rupture speed, with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15%. These results have important implications for estimating seismic hazards in Southern California and emphasize the need for improved understanding of earthquake rupture processes. Copyright 2008 by the American Geophysical Union.

  17. Scientific drilling into the San Andreas fault and site characterization research: Planning and coordination efforts. Final technical report

    SciTech Connect

    Zoback, M.D.

    1998-08-30

    The fundamental scientific issue addressed in this proposal, obtaining an improved understanding of the physical and chemical processes responsible for earthquakes along major fault zones, is clearly of global scientific interest. By sampling the San Andreas fault zone and making direct measurements of fault zone properties to 4.0 km at Parkfield they will be studying an active plate-boundary fault at a depth where aseismic creep and small earthquakes occur and where a number of the scientific questions associated with deeper fault zone drilling can begin to be addressed. Also, the technological challenges associated with drilling, coring, downhole measurements and borehole instrumentation that may eventually have to be faced in deeper drilling can first be addressed at moderate depth and temperature in the Parkfield hole. Throughout the planning process leading to the development of this proposal they have invited participation by scientists from around the world. As a result, the workshops and meetings they have held for this project have involved about 350 scientists and engineers from about a dozen countries.

  18. Aseismic slip and fault-normal strain along the central creeping section of the San Andreas fault

    USGS Publications Warehouse

    Rolandone, F.; Burgmann, R.; Agnew, D.C.; Johanson, I.A.; Templeton, D.C.; d'Alessio, M. A.; Titus, S.J.; DeMets, C.; Tikoff, B.

    2008-01-01

    We use GPS data to measure the aseismic slip along the central San Andreas fault (CSAF) and the deformation across adjacent faults. Comparison of EDM and GPS data sets implies that, except for small-scale transients, the fault motion has been steady over the last 40 years. We add 42 new GPS, velocities along the CSAF to constrain the regional strain distribution. Shear strain rates are less than 0.083 ?? 0.010 ??strain/yr adjacent to the creeping SAF, with 1-4.5 mm/yr of contraction across the Coast Ranges. Dislocation modeling of the data gives a deep, long-term slip rate of 31-35 mm/yr and a shallow (0-12 km) creep rate of 28 mm/yr along the central portion of the CSAF, consistent with surface creep measurements. The lower shallow slip rate may be due to the effect of partial locking along the CSAF or reflect reduced creep rates late in the earthquake cycle of the adjoining SAF rupture zones. Copyright 2008 by the American Geophysical Union.

  19. The ShakeOut scenario: A hypothetical Mw7.8 earthquake on the Southern San Andreas Fault

    USGS Publications Warehouse

    Porter, K.; Jones, L.; Cox, D.; Goltz, J.; Hudnut, K.; Mileti, D.; Perry, S.; Ponti, D.; Reichle, M.; Rose, A.Z.; Scawthorn, C.R.; Seligson, H.A.; Shoaf, K.I.; Treiman, J.; Wein, A.

    2011-01-01

    In 2008, an earthquake-planning scenario document was released by the U.S. Geological Survey (USGS) and California Geological Survey that hypothesizes the occurrence and effects of a Mw7.8 earthquake on the southern San Andreas Fault. It was created by more than 300 scientists and engineers. Fault offsets reach 13 m and up to 8 m at lifeline crossings. Physics-based modeling was used to generate maps of shaking intensity, with peak ground velocities of 3 m/sec near the fault and exceeding 0.5 m/sec over 10,000 km2. A custom HAZUS??MH analysis and 18 special studies were performed to characterize the effects of the earthquake on the built environment. The scenario posits 1,800 deaths and 53,000 injuries requiring emergency room care. Approximately 1,600 fires are ignited, resulting in the destruction of 200 million square feet of the building stock, the equivalent of 133,000 single-family homes. Fire contributes $87 billion in property and business interruption loss, out of the total $191 billion in economic loss, with most of the rest coming from shakerelated building and content damage ($46 billion) and business interruption loss from water outages ($24 billion). Emergency response activities are depicted in detail, in an innovative grid showing activities versus time, a new format introduced in this study. ?? 2011, Earthquake Engineering Research Institute.

  20. Deep rock damage in the San Andreas Fault revealed by P- and S-type fault-zone-guided waves

    USGS Publications Warehouse

    Ellsworth, William L.; Malin, Peter E.

    2011-01-01

    Damage to fault-zone rocks during fault slip results in the formation of a channel of low seismic-wave velocities. Within such channels guided seismic waves, denoted by Fg, can propagate. Here we show with core samples, well logs and Fg-waves that such a channel is crossed by the SAFOD (San Andreas Fault Observatory at Depth) borehole at a depth of 2.7 km near Parkfield, California, USA. This laterally extensive channel extends downwards to at least half way through the seismogenic crust, more than about 7 km. The channel supports not only the previously recognized Love-type- (FL) and Rayleigh-type- (FR) guided waves, but also a new fault-guided wave, which we name FF. As recorded 2.7 km underground, FF is normally dispersed, ends in an Airy phase, and arrives between the P- and S-waves. Modelling shows that FF travels as a leaky mode within the core of the fault zone. Combined with the drill core samples, well logs and the two other types of guided waves, FF at SAFOD reveals a zone of profound, deep, rock damage. Originating from damage accumulated over the recent history of fault movement, we suggest it is maintained either by fracturing near the slip surface of earthquakes, such as the 1857 Fort Tejon M 7.9, or is an unexplained part of the fault-creep process known to be active at this site.

  1. Locking depths estimated from geodesy and seismology along the San Andreas Fault System: Implications for seismic moment release

    NASA Astrophysics Data System (ADS)

    Smith-Konter, Bridget R.; Sandwell, David T.; Shearer, Peter

    2011-06-01

    The depth of the seismogenic zone is a critical parameter for earthquake hazard models. Independent observations from seismology and geodesy can provide insight into the depths of faulting, but these depths do not always agree. Here we inspect variations in fault depths of 12 segments of the southern San Andreas Fault System derived from over 1000 GPS velocities and 66,000 relocated earthquake hypocenters. Geodetically determined locking depths range from 6 to 22 km, while seismogenic thicknesses are largely limited to depths of 11-20 km. These seismogenic depths best match the geodetic locking depths when estimated at the 95% cutoff depth in seismicity, and most fault segment depths agree to within 2 km. However, the Imperial, Coyote Creek, and Borrego segments have significant discrepancies. In these cases the geodetically inferred locking depths are much shallower than the seismogenic depths. We also examine variations in seismic moment accumulation rate per unit fault length as suggested by seismicity and geodesy and find that both approaches yield high rates (1.5-1.8 × 1013 Nm/yr/km) along the Mojave and Carrizo segments and low rates (˜0.2 × 1013 Nm/yr/km) along several San Jacinto segments. The largest difference in seismic moment between models is calculated for the Imperial segment, where the moment rate from seismic depths is a factor of ˜2.5 larger than that from geodetic depths. Such variability has important implications for the accuracy to which future major earthquake magnitudes can be estimated.

  2. Locating non-volcanic tremor along the San Andreas Fault using a multiple array source imaging technique

    USGS Publications Warehouse

    Ryberg, T.; Haberland, C.H.; Fuis, G.S.; Ellsworth, W.L.; Shelly, D.R.

    2010-01-01

    Non-volcanic tremor (NVT) has been observed at several subduction zones and at the San Andreas Fault (SAF). Tremor locations are commonly derived by cross-correlating envelope-transformed seismic traces in combination with source-scanning techniques. Recently, they have also been located by using relative relocations with master events, that is low-frequency earthquakes that are part of the tremor; locations are derived by conventional traveltime-based methods. Here we present a method to locate the sources of NVT using an imaging approach for multiple array data. The performance of the method is checked with synthetic tests and the relocation of earthquakes. We also applied the method to tremor occurring near Cholame, California. A set of small-aperture arrays (i.e. an array consisting of arrays) installed around Cholame provided the data set for this study. We observed several tremor episodes and located tremor sources in the vicinity of SAF. During individual tremor episodes, we observed a systematic change of source location, indicating rapid migration of the tremor source along SAF. ?? 2010 The Authors Geophysical Journal International ?? 2010 RAS.

  3. Paleoearthquakes at Frazier Mountain, California delimit extent and frequency of past San Andreas Fault ruptures along 1857 trace

    USGS Publications Warehouse

    Scharer, Katherine M.; Weldon, Ray; Streig, Ashley; Fumal, Thomas

    2014-01-01

    Large earthquakes are infrequent along a single fault, and therefore historic, well-characterized earthquakes exert a strong influence on fault behavior models. This is true of the 1857 Fort Tejon earthquake (estimated M7.7–7.9) on the southern San Andreas Fault (SSAF), but an outstanding question is whether the 330 km long rupture was typical. New paleoseismic data for six to seven ground-rupturing earthquakes on the Big Bend of the SSAF restrict the pattern of possible ruptures on the 1857 stretch of the fault. In conjunction with existing sites, we show that over the last ~650 years, at least 75% of the surface ruptures are shorter than the 1857 earthquake, with estimated rupture lengths of 100 to <300 km. These results suggest that the 1857 rupture was unusual, perhaps leading to the long open interval, and that a return to pre-1857 behavior would increase the rate of M7.3–M7.7 earthquakes.

  4. A reevaluation of the Pallett Creek earthquake chronology based on new AMS radiocarbon dates, San Andreas fault, California

    NASA Astrophysics Data System (ADS)

    Scharer, Katherine M.; Biasi, Glenn P.; Weldon, Ray J., II

    2011-12-01

    The Pallett Creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern San Andreas fault. Previous estimates of earthquake ages at Pallett Creek were determined by decay counting radiocarbon methods. That method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers. In contrast, accelerator mass spectrometry (AMS) radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section. We present 65 new AMS radiocarbon dates that span nine ground-rupturing earthquakes at Pallett Creek. Overall, the AMS dates are similar to and reveal no dramatic bias in the conventional dates. For many layers, however, individual charcoal samples were younger than the conventional dates, leading to earthquake ages that are overall slightly younger than previously reported. New earthquake ages are determined by Bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints. The new chronology is more regular than previously published records in large part due to new samples constraining the age of event R. The closed interval from event C to 1857 has a mean recurrence of 135 years (σ = 83.2 years) and a quasiperiodic coefficient of variation (COV) of 0.61. We show that the new dates and resultant earthquake chronology have a stronger effect on COV than the specific membership of this long series and dating precision improvements from sedimentation rates.

  5. [Illustration of humans in the anatomy of the Renaissance: Andrea Vesalius' De humani corporis fabrica libri septem, Basel 1543].

    PubMed

    Hildebrand, R

    1996-08-01

    The position of Andreas Vesalius and his most influential book De humani corporis fabrica in the history of medicine are reevaluated in the context of renaissance-humanism. Vesalius's conception of the reconstruction of the living body is discussed in the light of the macrocosm-microcosm-correspondance considering equally directed considerations of the humanist and reformator Philipp Melanchthon. In both their no longer ontological but epistemological approach when changing from the deductive to the inductive method, microcosm man is becoming an anthropological concept and thus assumes a new quality: a psychophysical unit with a transcendental dimension. Against this background the great tables of the skeletons and musclemen in the De humani corporis fabrica are studied considering the unity of art and anatomy in the visual media. At that point, however, where the limits of Vesalius's anatomical conception in representing structure and function become manifest, the disruption of this unity eventually occurring in the end of the 18th century is already visible. Where anatomy is taken up in the expression of art, in the cosciousness of his finality the tragic horizon of man expands.

  6. Hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the San Andreas Fault

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, David A.; Hickman, Stephen H.

    2016-01-01

    We compare frictional strengths in the temperature range 25–250 °C of fault gouge from SAFOD (CDZ and SDZ) with quartzofeldspathic wall rocks typical of the central creeping section of the San Andreas Fault (Great Valley sequence and Franciscan Complex). The Great Valley and Franciscan samples have coefficients of friction, μ > 0.35 at all experimental conditions. Strength is unchanged between 25° and 150 °C, but μ increases at higher temperatures, exceeding 0.50 at 250 °C. Both samples are velocity strengthening at room temperature but show velocity-weakening behavior beginning at 150 °C and stick-slip motion at 250 °C. These rocks, therefore, have the potential for unstable seismic slip at depth. The CDZ gouge, with a high saponite content, is weak (μ = 0.09–0.17) and velocity strengthening in all experiments, and μ decreases at temperatures above 150 °C. Behavior of the SDZ is intermediate between the CDZ and wall rocks: μ < 0.2 and does not vary with temperature. Although saponite is probably not stable at depths greater than ∼3 km, substitution of the frictionally similar minerals talc and Mg-rich chlorite for saponite at higher temperatures could potentially extend the range of low strength and stable slip down to the base of the seismogenic zone.

  7. Paleoseismic investigations in the Santa Cruz mountains, California: Implications for recurrence of large-magnitude earthquakes on the San Andreas fault

    USGS Publications Warehouse

    Schwartz, D.P.; Pantosti, D.; Okumura, K.; Powers, T.J.; Hamilton, J.C.

    1998-01-01

    Trenching, microgeomorphic mapping, and tree ring analysis provide information on timing of paleoearthquakes and behavior of the San Andreas fault in the Santa Cruz mountains. At the Grizzly Flat site alluvial units dated at 1640-1659 A.D., 1679-1894 A.D., 1668-1893 A.D., and the present ground surface are displaced by a single event. This was the 1906 surface rupture. Combined trench dates and tree ring analysis suggest that the penultimate event occurred in the mid-1600s, possibly in an interval as narrow as 1632-1659 A.D. There is no direct evidence in the trenches for the 1838 or 1865 earthquakes, which have been proposed as occurring on this part of the fault zone. In a minimum time of about 340 years only one large surface faulting event (1906) occurred at Grizzly Flat, in contrast to previous recurrence estimates of 95-110 years for the Santa Cruz mountains segment. Comparison with dates of the penultimate San Andreas earthquake at sites north of San Francisco suggests that the San Andreas fault between Point Arena and the Santa Cruz mountains may have failed either as a sequence of closely timed earthquakes on adjacent segments or as a single long rupture similar in length to the 1906 rupture around the mid-1600s. The 1906 coseismic geodetic slip and the late Holocene geologic slip rate on the San Francisco peninsula and southward are about 50-70% and 70% of their values north of San Francisco, respectively. The slip gradient along the 1906 rupture section of the San Andreas reflects partitioning of plate boundary slip onto the San Gregorio, Sargent, and other faults south of the Golden Gate. If a mid-1600s event ruptured the same section of the fault that failed in 1906, it supports the concept that long strike-slip faults can contain master rupture segments that repeat in both length and slip distribution. Recognition of a persistent slip rate gradient along the northern San Andreas fault and the concept of a master segment remove the requirement that

  8. The stress shadow effect: a mechanical analysis of the evenly-spaced parallel strike-slip faults in the San Andreas fault system

    NASA Astrophysics Data System (ADS)

    Zuza, A. V.; Yin, A.; Lin, J. C.

    2015-12-01

    Parallel evenly-spaced strike-slip faults are prominent in the southern San Andreas fault system, as well as other settings along plate boundaries (e.g., the Alpine fault) and within continental interiors (e.g., the North Anatolian, central Asian, and northern Tibetan faults). In southern California, the parallel San Jacinto, Elsinore, Rose Canyon, and San Clemente faults to the west of the San Andreas are regularly spaced at ~40 km. In the Eastern California Shear Zone, east of the San Andreas, faults are spaced at ~15 km. These characteristic spacings provide unique mechanical constraints on how the faults interact. Despite the common occurrence of parallel strike-slip faults, the fundamental questions of how and why these fault systems form remain unanswered. We address this issue by using the stress shadow concept of Lachenbruch (1961)—developed to explain extensional joints by using the stress-free condition on the crack surface—to present a mechanical analysis of the formation of parallel strike-slip faults that relates fault spacing and brittle-crust thickness to fault strength, crustal strength, and the crustal stress state. We discuss three independent models: (1) a fracture mechanics model, (2) an empirical stress-rise function model embedded in a plastic medium, and (3) an elastic-plate model. The assumptions and predictions of these models are quantitatively tested using scaled analogue sandbox experiments that show that strike-slip fault spacing is linearly related to the brittle-crust thickness. We derive constraints on the mechanical properties of the southern San Andreas strike-slip faults and fault-bounded crust (e.g., local fault strength and crustal/regional stress) given the observed fault spacing and brittle-crust thickness, which is obtained by defining the base of the seismogenic zone with high-resolution earthquake data. Our models allow direct comparison of the parallel faults in the southern San Andreas system with other similar strike

  9. Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California

    NASA Astrophysics Data System (ADS)

    Heermance, Richard V.; Yule, Doug

    2017-06-01

    The San Gorgonio Pass (SGP) in southern California contains a 40 km long region of structural complexity where the San Andreas Fault (SAF) bifurcates into a series of oblique-slip faults with unknown slip history. We combine new 10Be exposure ages (Qt4: 8600 (+2100, -2200) and Qt3: 5700 (+1400, -1900) years B.P.) and a radiocarbon age (1260 ± 60 years B.P.) from late Holocene terraces with scarp displacement of these surfaces to document a Holocene slip rate of 5.7 (+2.7, -1.5) mm/yr combined across two faults. Our preferred slip rate is 37-49% of the average slip rates along the SAF outside the SGP (i.e., Coachella Valley and San Bernardino sections) and implies that strain is transferred off the SAF in this area. Earthquakes here most likely occur in very large, throughgoing SAF events at a lower recurrence than elsewhere on the SAF, so that only approximately one third of SAF ruptures penetrate or originate in the pass.Plain Language SummaryHow large are earthquakes on the southern San <span class="hlt">Andreas</span> Fault? The answer to this question depends on whether or not the earthquake is contained only along individual fault sections, such as the Coachella Valley section north of Palm Springs, or the rupture crosses multiple sections including the area through the San Gorgonio Pass. We have determined the age and offset of faulted stream deposits within the San Gorgonio Pass to document slip rates of these faults over the last 10,000 years. Our results indicate a long-term slip rate of 6 mm/yr, which is almost 1/2 of the rates east and west of this area. These new rates, combined with faulted geomorphic surfaces, imply that large magnitude earthquakes must occasionally rupture a 300 km length of the San <span class="hlt">Andreas</span> Fault from the Salton Sea to the Mojave Desert. Although many ( 65%) earthquakes along the southern San <span class="hlt">Andreas</span> Fault likely do not rupture through the pass, our new results suggest that large >Mw 7.5 earthquakes are possible</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T21C0435S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T21C0435S"><span>Characterization of fault rock compositions, alteration mineral assemblages, and preliminary implications for fluid-rock interaction in the San <span class="hlt">Andreas</span> Fault system at the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Solum, J. G.; Evans, J. P.; Hickman, S.; Lockner, D.; Moore, D.; Morrow, C.; Kirschner, D.; Chester, J.; Chester, F.; van der Pluijm, B.; Schleicher, A.</p> <p>2006-12-01</p> <p>The San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) drilled in 2004-05 crossed the active San <span class="hlt">Andreas</span> Fault (SAF) at an along hole measured depth (MD) of ~3.3 km (true vertical depth of ~2.7 km). At least five major faults with heterogeneous mineral assemblages, and presumably fluid-rock interaction histories, were penetrated during drilling. In addition fault-bounded, thick (>10s of m) sequences of rock with consistent alteration mineralogy encountered in the hole may reflect modern or paleo fluid reservoirs that were confined by sealing faults. One end member fault type from SAFOD is defined by two clay-poor cataclasite-dominated faults at 1.4 and 1.9 km MD. These faults are laumontite-rich as are the rocks on either side of them for a distance of 100-400 m MD suggesting cross-fault fluid flow perhaps accompanied by broad damage zones. The other end member fault type is defined by a clay-rich (illite, illite-smectite and chlorite) fault at ~2.5 km MD (likely part of a fault zone that extends to ~2.7 km MD). This broad fault zone marks the top of an ~600 m MD thick sequence of laumontite-bearing rocks. The abundance of laumontite suggests significant fluid activity, while the restriction of laumontite to this interval suggests that it was isolated by sealing faults. Plucked fault rocks from this fault are very weak (coefficient of friction /mu of ~0.3 compared to 0.6-0.8 in protolith see poster by Morrow et al.), suggesting that fault-related fluid flow resulted in fault zone weakening. Moreover, while these fault zones may be broad the neoformed smectitic clays within them occur as micron- scale coatings on slip surfaces (see poster by Schleicher et al.). Fluid chemistry dramatically influences the frictional properties of the smectite montmorillonite, affecting its strength by a factor of ~2 (see poster by Lockner et al.), This suggests that changes in fluid chemistry may significantly influence the mechanical properties of this type of fault both through</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011E%26PSL.310..131B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011E%26PSL.310..131B"><span>Lithology and internal structure of the San <span class="hlt">Andreas</span> fault at depth based on characterization of Phase 3 whole-rock core in the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) borehole</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bradbury, Kelly K.; Evans, James P.; Chester, Judith S.; Chester, Frederick M.; Kirschner, David L.</p> <p>2011-10-01</p> <p>We characterize the lithology and structure of the spot core obtained in 2007 during Phase 3 drilling of the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) in order to determine the composition, structure, and deformation processes of the fault zone at 3 km depth where creep and microseismicity occur. A total of approximately 41 m of spot core was taken from three separate sections of the borehole; the core samples consist of fractured arkosic sandstones and shale west of the SAF zone (Pacific Plate) and sheared fine-grained sedimentary rocks, ultrafine black fault-related rocks, and phyllosilicate-rich fault gouge within the fault zone (North American Plate). The fault zone at SAFOD consists of a broad zone of variably damaged rock containing localized zones of highly concentrated shear that often juxtapose distinct protoliths. Two zones of serpentinite-bearing clay gouge, each meters-thick, occur at the two locations of aseismic creep identified in the borehole on the basis of casing deformation. The gouge primarily is comprised of Mg-rich clays, serpentinite (lizardite ± chrysotile) with notable increases in magnetite, and Ni-Cr-oxides/hydroxides relative to the surrounding host rock. The rocks surrounding the two creeping gouge zones display a range of deformation including fractured protolith, block-in-matrix, and foliated cataclasite structure. The blocks and clasts predominately consist of sandstone and siltstone embedded in a clay-rich matrix that displays a penetrative scaly fabric. Mineral alteration, veins and fracture-surface coatings are present throughout the core, and reflect a long history of syn-deformation, fluid-rock reaction that contributes to the low-strength and creep in the meters-thick gouge zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T21B0406K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T21B0406K"><span>Fragmented Landscapes in the San Gorgonio Pass Region: Insights into Quaternary Strain History of the Southern San <span class="hlt">Andreas</span> Fault System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kendrick, K. J.; Matti, J. C.; Landis, G. P.; Alvarez, R. M.</p> <p>2006-12-01</p> <p>The San Gorgonio Pass (SGP) region is a zone of structural complexity within the southern San <span class="hlt">Andreas</span> Fault system that is characterized by (1) multiple strands of the San <span class="hlt">Andreas</span> Fault (SAF), (2) intense and diverse microseismicity, (3) contraction within the SGP fault zone (SGPfz), and (4) complex and diverse landforms - all a consequence of structural complications in the vicinity of the southeastern San Bernardino Mountains (SBM). Multiple strands of the SAF zone in the SGP region partition the landscape into discrete geomorphic/geologic domains, including: San Gorgonio Mountain (SGM), Yucaipa Ridge (YR), Kitching Peak (KP), Pisgah Peak (PP), and Coachella Valley (CV) domains. The morphology of each domain reflects the tectonic history unique to that region. Development of the SGP knot in the Mission Creek strand of the SAF (SAFmi) led to westward deflection of the SAFmi, juxtaposition of the KP, PP, and SGM domains, initiation of uplift of YR domain along thrust faults in headwaters of San Gorgonio River, and development of the San Jacinto Fault. Slip on the SAF diminished as a result, thereby allowing integrated drainage systems to develop in the greater SGP region. San Gorgonio River, Whitewater River, and Mission Creek are discrete drainages that transport sediment across the SGM, YR, PP, KP, and CV domains into alluvial systems peripheral to the SGP region. There, depositional units (San Timoteo Formation, upper member, deformed gravels of Whitewater River) all contain clasts of SBM-type and San Gabriel Mountain-type basement, thus constraining slip on the SAF in the SGP region. Middle and late Pleistocene slip on the Mill Creek strand of the SAF (SAFm) in the SGP region has attempted to bypass the SGP knot, and has disrupted landscapes established during SAFmi quiescence. Restoration of right-slip on the SAFm is key to deciphering landscape history. Matti and others (1985, 1992) proposed that a bi-lobed alluvial deposit in the Raywood Flats area has been</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.S32A..06M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.S32A..06M"><span>Discovery of Talc in SAFOD Serpentinite Cuttings: Possible Implications for the Origin of Creep in the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moore, D. E.; Rymer, M. J.</p> <p>2006-12-01</p> <p>The San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) drillsite is located near the southern end of the creeping section, and a portion of the well casing is actively deforming in response to creep on a fault strand intersected by the drillhole. Moderate amounts of serpentinite are present in SAFOD cuttings collected at 3320-3350 m measured depth, at the eastern margin of the zone of active deformation. Serpentinite also is found locally in surface exposures of the San <span class="hlt">Andreas</span> Fault (SAF) along the creeping section. Aeromagnetic surveys indicate the presence of a flat-lying slab of serpentinite at several kilometers' depth on the northeast side of the SAF; this body truncates against the fault along a 50 kilometer segment northwest of Parkfield. Serpentinite commonly is invoked as the cause of creep along the SAF, but the frictional strengths of the serpentine minerals are too high overall to explain the low strength of the creeping section, as indicated by modelling of heat flow data and earthquake focal mechanisms. In addition, the serpentine minerals have the potential for unstable slip under certain P-T-velocity conditions. However, another mineral sometimes associated with serpentinite -- talc -- potentially could provide the connection between serpentinite and creep. Talc is a magnesium-rich phyllosilicate with a higher Si/Mg ratio than serpentine and it commonly forms as a result of Si-metasomatism of serpentinite and other ultramafic rocks. Recent experimental studies show that talc has a coefficient of friction on the order of 0.10-0.15 in the temperature range 100-400 degrees C (upper crustal temperatures) and it is characterized by inherently stable, velocity-strengthening behavior. Localization of shear in a talc-rich gouge zone could therefore satisfy the conditions for creep without the need to invoke other weakening mechanisms such as fluid overpressures. Talc has been identified in serpentinite grains from the SAFOD cutttings, using scanning electron</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T41B2923M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T41B2923M"><span>Holocene geologic slip rate for the Mission Creek strand of the Southern San <span class="hlt">Andreas</span> Fault, northern Coachella Valley, CA.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Munoz, J. J.; Behr, W. M.; Sharp, W. D.; Fryer, R.; Gold, P. O.</p> <p>2016-12-01</p> <p>Slip on the southern San <span class="hlt">Andreas</span> fault in the northwestern Coachella Valley in Southern California is partitioned between three strands, the Mission Creek, Garnet Hill, and Banning strands. In the vicinity of the Indio Hills, the NW striking Mission Creek strand extends from the Indio Hills into the San Bernardino Mountains, whereas the Banning and Garnet Hill strands strike WNW and transfer slip into the San Gorgonio Pass region. Together, these three faults accommodate 20 mm/yr of right-lateral motion. Determining which strand accommodates the majority of fault slip and how slip rates on these strands have varied during the Quaternary is critical to seismic hazard assessment for the southern California region. Here we present a new Holocene geologic slip rate from an alluvial fan offset along the Mission Creek strand at the Three Palms site in the Indio Hills. Field mapping and remote sensing using the B4 LiDAR data indicates that the Three Palms fan is offset 57 +/- 3 meters. U-series dating on pedogenic carbonate rinds collected at 25-100 cm depth within the fan deposit constrain the minimum depositional age to 3.49 +/- 0.92 ka, yielding a maximum slip rate of 16 +6.1/-3.8 mm/yr. This Holocene maximum slip rate overlaps within errors with a previously published late Pleistocene slip rate of 12-22 mm/yr measured at Biskra Palms, a few kilometers to the south. Cosmogenic 10Be surface exposure samples were also collected from the fan surface to bracket the maximum depositional age. These samples have been processed and are currently awaiting AMS measurement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029192','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029192"><span>Orientation of three-component geophones in the San <span class="hlt">Andreas</span> Fault observatory at depth Pilot Hole, Parkfield, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Oye, V.; Ellsworth, W.L.</p> <p>2005-01-01</p> <p>To identify and constrain the target zone for the planned SAFOD Main Hole through the San <span class="hlt">Andreas</span> Fault (SAF) near Parkfield, California, a 32-level three-component (3C) geophone string was installed in the Pilot Hole (PH) to monitor and improve the locations of nearby earthquakes. The orientation of the 3C geophones is essential for this purpose, because ray directions from sources may be determined directly from the 3D particle motion for both P and S waves. Due to the complex local velocity structure, rays traced from explosions and earthquakes to the PH show strong ray bending. Observed azimuths are obtained from P-wave polarization analysis, and ray tracing provides theoretical estimates of the incoming wave field. The differences between the theoretical and the observed angles define the calibration azimuths. To investigate the process of orientation with respect to the assumed velocity model, we compare calibration azimuths derived from both a homogeneous and 3D velocity model. Uncertainties in the relative orientation between the geophone levels were also estimated for a cluster of 36 earthquakes that was not used in the orientation process. The comparison between the homogeneous and the 3D velocity model shows that there are only minor changes in these relative orientations. In contrast, the absolute orientations, with respect to global North, were significantly improved by application of the 3D model. The average data residual decreased from 13?? to 7??, supporting the importance of an accurate velocity model. We explain the remaining residuals by methodological uncertainties and noise and with errors in the velocity model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70035525','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70035525"><span>A reevaluation of the Pallett Creek earthquake chronology based on new AMS radiocarbon dates, San <span class="hlt">Andreas</span> fault, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scharer, K.M.; Biasi, G.P.; Weldon, R.J.</p> <p>2011-01-01</p> <p>The Pallett Creek paleoseismic record occupies a keystone position in most attempts to develop rupture histories for the southern San <span class="hlt">Andreas</span> fault. Previous estimates of earthquake ages at Pallett Creek were determined by decay counting radiocarbon methods. That method requires large samples which can lead to unaccounted sources of uncertainty in radiocarbon ages because of the heterogeneous composition of organic layers. In contrast, accelerator mass spectrometry (AMS) radiocarbon dates may be obtained from small samples that have known carbon sources and also allow for a more complete sampling of the section. We present 65 new AMS radiocarbon dates that span nine ground-rupturing earthquakes at Pallett Creek. Overall, the AMS dates are similar to and reveal no dramatic bias in the conventional dates. For many layers, however, individual charcoal samples were younger than the conventional dates, leading to earthquake ages that are overall slightly younger than previously reported. New earthquake ages are determined by Bayesian refinement of the layer ages based on stratigraphic ordering and sedimentological constraints. The new chronology is more regular than previously published records in large part due to new samples constraining the age of event R. The closed interval from event C to 1857 has a mean recurrence of 135years (?? = 83.2 years) and a quasiperiodic coefficient of variation (COV) of 0.61. We show that the new dates and resultant earthquake chronology have a stronger effect on COV than the specific membership of this long series and dating precision improvements from sedimentation rates. Copyright 2011 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMED33D0967M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMED33D0967M"><span>Erosion in the Mecca Hills: using GIS to investigate potential erosion factors along the southern San <span class="hlt">Andreas</span> Fault.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Maneerat, P.; Reinen, L. A.; Fukutaki, K. G.; Rittiron, S.; Mejias, R.</p> <p>2015-12-01</p> <p>The Mecca Hills (MH) occur in a region of transpression along the southern San <span class="hlt">Andreas</span> Fault. These geomorphic features are a result of the interplay between uplift and erosion. The MH are mostly covered by uniform sedimentary rocks with > 70% the Pliocene-Pleistocene Palm Spring Formation, > 20% Quaternary sediments and a minor amount of crystalline rock suggesting similar denudation rate over the region. However, Gray et al. (Quat. Sci. Rev. 2014) found a wide range of denudation rates (20 to 150 m/My) by using 10Be concentrations in active-channel alluvial sediment. We investigate potential causes of erosion to understand the variation of the denudation rate and examine the maturity of watersheds in the MH. We use ArcGIS to find the best geomorphic proxy for the published erosion rates by considering elevation, lithology, mean slope and active faults by using the index value method proposed by Gray et al. We apply the best geomorphic proxy to the overall MH to predict the spatial variation of erosion rate over the region. We use hypsometric integral (HI) and basin elongation ratio (BER) to study the maturity of the overall MH watersheds. We found that active faults are the main factor influencing erosion in the MH. Drainage basins located closer to active faults have higher erosion rates than others. Most watersheds are in a mature stage of the erosion cycle. Overall, the watersheds in the central MH are in a more youthful stage of the erosion cycle than the ones to the north and south. BER values suggest that the watersheds in the central MH formed earlier and have more time to develop their stream networks. Although watersheds in the central MH formed earlier than the others, their stage of erosion cycle is more youthful due to the proximity of active faults enhancing local erosion rates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JGRB..111.5410D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JGRB..111.5410D"><span>Frictional strength heterogeneity and surface heat flow: Implications for the strength of the creeping San <span class="hlt">Andreas</span> fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>D'Alessio, M. A.; Williams, C. F.; Bürgmann, R.</p> <p>2006-05-01</p> <p>Heat flow measurements along much of the San <span class="hlt">Andreas</span> fault (SAF) constrain the apparent coefficient of friction (μapp) of the fault to <0.2, much lower than laboratory-derived friction values for most geologic materials. However, heat flow data are sparse near the creeping section of the SAF, a frictional "asperity" where the fault slips almost exclusively by aseismic creep. We test the hypothesis that the creeping section has a substantially higher or lower μapp than adjacent sections of the SAF. We use numerical models to explore the effects of faults with spatially and temporally heterogeneous frictional strength on the spatial distribution of surface heat flow. Heat flow from finite length asperities is uniformly lower than predicted by assuming an infinitely long fault. Over geologic time, lateral offset from strike-slip faulting produces heat flow patterns that are asymmetric across the fault and along strike. We explore a range of asperity sizes, slip rates, and displacement histories for comparing predicted spatial patterns of heat flow with existing measurements. Models with μapp ˜ 0.1 fit the data best. For most scenarios, heat flow anomalies from a frictional asperity with μapp > 0.2 should be detectable even with the sparse existing observations, implying that μapp for the creeping section is as low as the surrounding SAF. Because the creeping section does not slip in large earthquakes, the mechanism controlling its weakness is not related to dynamic processes resulting from high slip rate earthquake ruptures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..18.8339Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..18.8339Z"><span>Visco-elastic full waveform inversion of controlled seismic data from the San <span class="hlt">Andreas</span> Fault Observatory at Depth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zeiß, Jens; Paschke, Marco; Bleibinhaus, Florian</p> <p>2016-04-01</p> <p>We apply visco-elastic full waveform inversion (FWI) to a 50-km-long controlled-source refraction/reflection seismic survey at the San <span class="hlt">Andreas</span> Fault (SAF) to obtain high resolution P-wave and S-wave velocity models for the SAF Observatory at Depth (SAFOD) drill site near Parkfield. The profile consists of 63 explosive sources and a fixed spread of 912 3-component receivers. Traveltime models from Ryberg et al. (2012) and Hole et al. (2006) are used to derive velocity starting models for FWI. Attenuation is estimated from Qp and Qs t*-tomography models after Bennington et al. (2008). Density is estimated from P-wave velocity using Gardner's (1974) relation. Preprocessing includes the muting of noisy traces, the estimation of spatio-temporal weighting factors to exclude Rayleigh waves, which otherwise mask the comparatively low-amplitude body wave signals, and a 3D-to-2D-conversion, which is carried out separately for P- and S-waves and their coda. The separation of P- and S-wave arrivals is based on travel-time and polarization analysis. The forward-modeling is based on a time-domain visco-elastic FD-algorithm of Robertsson et al. (1996). Topography is considered using the image method. The inversion is performed in the frequency-domain using the multi-scale approach. As a first step, we derived individual source wavelets for the different shots at the low frequencies (2-6 Hz). The project is funded by the German Research Foundation (DFG) and is part of the International Continental scientific Drilling Programme (ICDP).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMNH51D1923R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMNH51D1923R"><span>Forward and Reverse Modeling Compressive Deformation in a 3D Geologic Model along the Central San <span class="hlt">Andreas</span> Fault Zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roberts, M. A.; Graymer, R. W.; McPhee, D.</p> <p>2015-12-01</p> <p>During the late Miocene, a small change in the relative motion of the Pacific plate resulted in compressive as well as translational deformation along the central San <span class="hlt">Andreas</span> Fault (SAF), creating thrust faults and folds throughout this region of California. We constructed a 3D model of an upper crustal volume between Pinnacles National Park and Gold Hill by assembling geologic map data and cross sections, geophysical data, and petroleum well logs in MoveTm, software which has the ability to forward and reverse model movement along faults and folds. For this study, we chose a blind thrust fault west of the SAF near Parkfield to compare deformation produced by MoveTm's forward modeling algorithm with that observed. We chose various synclines east of the SAF to explore the software's ability to unfold (reverse model) units. For the initial round of modeling, strike-slip movement has been omitted as the fault algorithm was designed primarily for extensional or compressional environments. Preliminary forward modeling of originally undeformed strata along the blind thrust produced geometries similar to those in the present-day 3D geologic model. The modeled amount of folding produced in hanging wall strata was less severe, suggesting these units were slightly folded before displacement. Based on these results, the algorithm shows potential in predicting deformation related to blind thrusts. Contraction in the region varies with fold axis location and orientation. MoveTm's unfolding algorithm can allow researchers to measure the amount of contraction a fold represents, and compare that amount across the modeled area as a way of observing regional stress patterns. The unfolding algorithm also allows for passive deformation of strata unconformably underlying the fold; one example reveals a steeper orientation of Cretaceous units prior to late Miocene deformation. Such modeling capabilities can allow for a better understanding of the structural history of the region.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T21H..07S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T21H..07S"><span>Earthquake Recurrence and Deformation in the Last Four Events on the Santa Cruz Mountains Section of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Streig, A. R.; Dawson, T. E.; Weldon, R. J.</p> <p>2012-12-01</p> <p>Paleoseismic investigations at the Hazel Dell site on the Santa Cruz Mountains section (SAS) of the San <span class="hlt">Andreas</span> fault has yielded evidence of four earthquakes. We present evidence of the 1906 surface rupture (E1), and 3 earlier events, including new evidence for two 1800's earthquakes. Evidence for the penultimate event, E2, is expressed as upward fault terminations within a massive sand infilling a topographic low. This sand infilled a depression formed by the pre-penultimate earthquake, E3. We identified axe-cut wood stratigraphically below the pre-penultimate earthquake horizon, which suggests that surface rupturing earthquakes E2 and E3 occurred after deposition of the cut wood stratigraphic unit. Lumber harvesting began in the area around 1832, and new radiocarbon dates sampled from redwood growth rings demonstrate that earthquakes E2 and E3 are historical. E4 occurred between A.D. 1651 and 1497. These new event data for the SAS suggest more frequent surface rupturing earthquakes within historical time than previously recognized. The data require at least two modes of behavior in strain release on the SAS through time. One mode of strain release, is through large multi-segment earthquakes; the 1906 event was a large multi-segment earthquake that dominates the moment budget of the fault. During the period prior to 1906, analysis of the historic record suggests that the SAS was characterized by a second mode of moderate seismicity, with six M≥ 6 earthquakes between 1838 and 1890 (Bakun, 1999), all located along the southern half of the segment near the Hazel Dell study area. The two 1800's earthquakes identified in this study support this second mode of moderate seismicity on the SAS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GeoJI.203...48T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GeoJI.203...48T"><span>An integral method to estimate the moment accumulation rate on the Creeping Section of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tong, Xiaopeng; Sandwell, David T.; Smith-Konter, Bridget</p> <p>2015-10-01</p> <p>Moment accumulation rate (also referred to as moment deficit rate) is a fundamental quantity for evaluating seismic hazard. The conventional approach for evaluating moment accumulation rate of creeping faults is to invert for the slip distribution from geodetic measurements, although even with perfect data these slip-rate inversions are non-unique. In this study, we show that the slip-rate versus depth inversion is not needed because moment accumulation rate can be estimated directly from surface geodetic data. We propose an integral approach that uses dense geodetic observations from Interferometric Synthetic Aperture Radar (InSAR) and the Global Positioning System (GPS) to constrain the moment accumulation rate. The moment accumulation rate is related to the integral of the product of the along-strike velocity and the distance from the fault. We demonstrate our methods by studying the Creeping Section of the San <span class="hlt">Andreas</span> fault observed by GPS and radar interferometry onboard the ERS and ALOS satellites. Along-strike variation of the moment accumulation rate is derived in order to investigate the degree of partial locking of the Creeping Section. The central Creeping Segment has a moment accumulation rate of 0.25-3.1 × 1015 Nm yr-1 km-1. The upper and lower bounds of the moment accumulation rates are derived based on the statistics of the noise. Our best-fitting model indicates that the central portion of the Creeping Section is accumulating seismic moment at rates that are about 5 per cent to 23 per cent of the fully locked Carrizo segment that will eventually be released seismically. A cumulative moment budget calculation with the historical earthquake catalogue (M > 5.5) since 1857 shows that the net moment deficit at present is equivalent to a Mw 6.3 earthquake.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.S23B2265P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.S23B2265P"><span>Identifying and locating tectonic tremor beneath the San <span class="hlt">Andreas</span> Fault near Parkfield, CA, with the PASO array</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peterson, D. E.; Thurber, C. H.; Montgomery-Brown, E. D.; Brown, J. R.; Shelly, D. R.</p> <p>2011-12-01</p> <p>Tectonic tremor is a weak but persistent shaking of the Earth that was first discovered in subduction zones and later found beneath the San <span class="hlt">Andreas</span> Fault (SAF). Tremor events represent spasmodic slip on the deep extension of the SAF, occurring at a depth of about 20-25 kilometers. Tremor occurs deeper than the nearby regular earthquakes, which can be found at maximum depths of 12-15 kilometers. Tremor is characterized by bursts of low frequency and/or very low frequency earthquakes (LFE/VLF) with dominant energy in the 1-10 Hz range. Tremor tells us about fault slip at depth in both space and time by illuminating the fault down to about the base of the crust. In the pursuit of deriving information about deep fault behavior and crustal structure, we are analyzing continuous data from the previously untapped Parkfield Area Seismic Observatory (PASO) temporary array, operated in 2000-2002 and 2004-2006. We started the identification process by correlating templates of known events from a nearby station array based on an existing catalog of tremor events. Using the dense PASO array and various correlation methods, including autocorrelation (Brown et. al. 2008), a scanning algorithm (Rowe, 2005), and cross correlation of template events (Shelly et al., 2007), we will refine the locations of these known events and seek to identify undiscovered clusters of LFEs and tremor. After generating an updated catalog initially for the month of September 2002, we will use S-wave arrivals from the 59 stations comprising the PASO array to provide strong constraints on the locations of identified events.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.195..130T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.195..130T"><span>Three-dimensional magnetotelluric inversion in practice—the electrical conductivity structure of the San <span class="hlt">Andreas</span> Fault in Central California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tietze, Kristina; Ritter, Oliver</p> <p>2013-10-01</p> <p>3-D inversion techniques have become a widely used tool in magnetotelluric (MT) data interpretation. However, with real data sets, many of the controlling factors for the outcome of 3-D inversion are little explored, such as alignment of the coordinate system, handling and influence of data errors and model regularization. Here we present 3-D inversion results of 169 MT sites from the central San <span class="hlt">Andreas</span> Fault in California. Previous extensive 2-D inversion and 3-D forward modelling of the data set revealed significant along-strike variation of the electrical conductivity structure. 3-D inversion can recover these features but only if the inversion parameters are tuned in accordance with the particularities of the data set. Based on synthetic 3-D data we explore the model space and test the impacts of a wide range of inversion settings. The tests showed that the recovery of a pronounced regional 2-D structure in inversion of the complete impedance tensor depends on the coordinate system. As interdependencies between data components are not considered in standard 3-D MT inversion codes, 2-D subsurface structures can vanish if data are not aligned with the regional strike direction. A priori models and data weighting, that is, how strongly individual components of the impedance tensor and/or vertical magnetic field transfer functions dominate the solution, are crucial controls for the outcome of 3-D inversion. If deviations from a prior model are heavily penalized, regularization is prone to result in erroneous and misleading 3-D inversion models, particularly in the presence of strong conductivity contrasts. A `good' overall rms misfit is often meaningless or misleading as a huge range of 3-D inversion results exist, all with similarly `acceptable' misfits but producing significantly differing images of the conductivity structures. Reliable and meaningful 3-D inversion models can only be recovered if data misfit is assessed systematically in the frequency</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1998JGR...10310141A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1998JGR...10310141A"><span>Morphologic dating of scarps formed by repeated slip events along the San <span class="hlt">Andreas</span> Fault, Carrizo Plain, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Arrowsmith, J. Ramón; Rhodes, Dallas D.; Pollard, David D.</p> <p>1998-05-01</p> <p>Morphologic dating of fault scarps determines late Cenozoic fault activity by comparing observed topographic profiles with those determined using a calibrated hillslope development model. We postulate that the material transport rate along the profile is a function only of local slope and is transport-limited. Morphologic dating of hillslopes bounded by continuously dropping boundaries or cut by continuously slipping faults is used to determine the material transport rate constant, the time since the downdrop was initiated, or the fault began to slip. We calibrated the hillslope development model on the southwest facing scarp southeast of Wallace Creek along the San <span class="hlt">Andreas</span> Fault (SAF) in the Carrizo Plain, California. The scarp has been exposed by right-lateral offset of a southeast sloping shutter ridge located on the southwest side of the SAF and by vertical offset related to secondary deformation. We assume that all the observed offset occurs after initial exposure of the scarp by passage of the shutter ridge. Forward modeling of profile development yielded a κ (mass diffusivity) of 8.6±0.8 m2 kyr-1. Normal fault slip rates were determined for two graben-bounding faults in the Northern Elkhorn Hills in the southeastern Carrizo Plain by applying the calibrated κ to the degradation of the scarps to determine the scarp age. One fault scarp began to form about 12 kyr ago and the other about 63 kyr ago. Those ages and estimates of the dip slip along the faults result in slip rates of 1-2 mm yr-1.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002AGUFM.S12C..13T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002AGUFM.S12C..13T"><span>M 5.5 to 6.5 Seismicity in the San <span class="hlt">Andreas</span> Fault Creeping Zone NW of Parkfield</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toppozada, T. R.; Branum, D. M.</p> <p>2002-12-01</p> <p>The great 1857 Fort Tejon earthquake apparently initiated about 30 to 60 km NW of Parkfield, based on evidence from faulting and strong foreshocks in the few hours before the main shock. The San <span class="hlt">Andreas</span> fault zone extending ~80 km NW from Parkfield is currently creeping and generating very few M>5 events. This zone has generated many M 5.5 to 6.5 earthquakes before Caltech started to routinely locate earthquakes in 1932. The most recent sequences in 1922, 1934, and 1966 were within 30 km NW of Parkfield. These events and neighboring events in 1857, 1881, and 1901 led to the notion of repeating characteristic Parkfield earthquakes. However, at least 12 other M 5.5 to 6.5 events have occurred from 1853 to 1885 between 10 and 80 km NW of Parkfield near where the 1857 earthquake initiated, even though the record may be incomplete before 1877. These include two M~6.5 events centered 60 and 40 km NW of Parkfield in 1885 and 1901, respectively. The latter event generated a local sea wave in Monterey Bay that was apparently triggered by a submarine landslide, and was followed by several M~5.5 aftershocks. The rate of seismic moment released within 80 km NW of Parkfield, and within 40 km of the 1857 rupture end, has decreased steadily since 1857, and has tended to migrate toward Parkfield with time. This probably reflects the decay with time of the stress loading from the maximum 1857 displacement of ~10 m in the Carrizo Plain ~80 km SE of Parkfield, and explains why the Parkfield earthquake that was predicted to occur before 1993 has not yet occurred.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T41A1950A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T41A1950A"><span>Frequent surface rupturing earthquakes along the Carrizo section of the San <span class="hlt">Andreas</span> Fault since A.D. 1250.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akciz, S. O.; Grant Ludwig, L.; Arrowsmith, J.; Zielke, O.</p> <p>2008-12-01</p> <p>Paleoseismological investigations of the San <span class="hlt">Andreas</span> Fault (SAF) in the Carrizo Plain have greatly influenced general models of fault behavior and our understanding of seismic hazard in southern California. Interpretations from seven new excavations across the SAF at the Bidart Fan site in the Carrizo Plain contradict the widely accepted hypothesis that this section of the fault ruptures relatively infrequently and only during large earthquakes with large (~8 m) offsets. Our new paleoseismic data indicate that the Carrizo section of the southern SAF has ruptured six times since ~A.D. 1250. The most recent earthquake, event A, was the 1857 Fort Tejon earthquake. The penultimate earthquake, event B, occurred sometime after A.D. 1620 and not sometime between A.D. 1405 and A.D. 1510, as previously thought. Four earthquakes, events C, D, E and F, occurred between A.D. 1250 and A.D. 1640. Our findings are similar to the new results from the Frazier Mountain site (worked conducted by Scharer and colleagues about 100 km southeast), which indicate 4-5 earthquakes since A.D. 1400. These new data from the northern section of the southern SAF indicate that since about A.D. 1250, the Carrizo section has failed more regularly and more often than previously thought. Additional paleoseismological investigations are needed to expand the record of the past earthquakes and determine the slip associated with each. This information will better constrain the past SAF rupture pattern-an essential element in the assessment of its future behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoJI.194.1295P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoJI.194.1295P"><span>Kinematics of rotating panels of E-W faults in the San <span class="hlt">Andreas</span> system: what can we tell from geodesy?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Platt, J. P.; Becker, T. W.</p> <p>2013-09-01</p> <p>Sets of E- to NE-trending sinistral and/or reverse faults occur within the San <span class="hlt">Andreas</span> system, and are associated with palaeomagnetic evidence for clockwise vertical-axis rotations. These structures cut across the trend of active dextral faults, posing questions as to how displacement is transferred across them. Geodetic data show that they lie within an overall dextral shear field, but the data are commonly interpreted to indicate little or no slip, nor any significant rate of rotation. We model these structures as rotating by bookshelf slip in a dextral shear field, and show that a combination of sinistral slip and rotation can produce the observed velocity field. This allows prediction of rates of slip, rotation, fault-parallel extension and fault-normal shortening within the panel. We use this method to calculate the kinematics of the central segment of the Garlock Fault, which cuts across the eastern California shear zone at a high angle. We obtain a sinistral slip rate of 6.1 ± 1.1 mm yr-1, comparable to geological evidence, but higher than most previous geodetic estimates, and a rotation rate of 4.0 ± 0.7° Myr-1 clockwise. The western Transverse Ranges transect a similar shear zone in coastal and offshore California, but at an angle of only 40°. As a result, the faults, which were sinistral when they were at a higher angle to the shear zone, have been reactivated in a dextral sense at a low rate, and the rate of rotation of the panel has decreased from its long-term rate of ˜5° to 1.6° ± 0.2° Myr-1 clockwise. These results help to resolve some of the apparent discrepancies between geological and geodetic slip-rate estimates, and provide an enhanced understanding of the mechanics of intracontinental transform systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70028656','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70028656"><span>Slip on the San <span class="hlt">Andreas</span> fault at Parkfield, California, over two earthquake cycles, and the implications for seismic hazard</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Murray, J.; Langbein, J.</p> <p>2006-01-01</p> <p>Parkfield, California, which experienced M 6.0 earthquakes in 1934, 1966, and 2004, is one of the few locales for which geodetic observations span multiple earthquake cycles. We undertake a comprehensive study of deformation over the most recent earthquake cycle and explore the results in the context of geodetic data collected prior to the 1966 event. Through joint inversion of the variety of Parkfield geodetic measurements (trilateration, two-color laser, and Global Positioning System), including previously unpublished two-color data, we estimate the spatial distribution of slip and slip rate along the San <span class="hlt">Andreas</span> using a fault geometry based on precisely relocated seismicity. Although the three most recent Parkfield earthquakes appear complementary in their along-strike distributions of slip, they do not produce uniform strain release along strike over multiple seismic cycles. Since the 1934 earthquake, more than 1 m of slip deficit has accumulated on portions of the fault that slipped in the 1966 and 2004 earthquakes, and an average of 2 m of slip deficit exists on the 33 km of the fault southeast of Gold Hill to be released in a future, perhaps larger, earthquake. It appears that the fault is capable of partially releasing stored strain in moderate earthquakes, maintaining a disequilibrium through multiple earthquake cycles. This complicates the application of simple earthquake recurrence models that assume only the strain accumulated since the most recent event is relevant to the size or timing of an upcoming earthquake. Our findings further emphasize that accumulated slip deficit is not sufficient for earthquake nucleation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JGRB..114.2403L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JGRB..114.2403L"><span>Southern San <span class="hlt">Andreas</span>-San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lundgren, Paul; Hetland, Eric A.; Liu, Zhen; Fielding, Eric J.</p> <p>2009-02-01</p> <p>We use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern San <span class="hlt">Andreas</span> (SAF)-San Jacinto (SJF) fault systems to constrain their slip rates and the viscosity structure of the lower crust and upper mantle on the basis of periodic earthquake cycle, Maxwell viscoelastic, finite element models. Key questions for this system are the SAF and SJF slip rates, the slip partitioning between the two main branches of the SJF, and the dip of the SAF. The best-fitting models generally have a high-viscosity lower crust (η = 1021 Pa s) overlying a lower-viscosity upper mantle (η = 1019 Pa s). We find considerable trade-offs between the relative time into the current earthquake cycle of the San Jacinto fault and the upper mantle viscosity. With reasonable assumptions for the relative time in the earthquake cycle, the partition of slip is fairly robust at around 24-26 mm/a for the San Jacinto fault system and 16-18 mm/a for the San <span class="hlt">Andreas</span> fault. Models for two subprofiles across the SAF-SJF systems suggest that slip may transfer from the western (Coyote Creek) branch to the eastern (Clark-Superstition hills) branch of the SJF from NW to SE. Across the entire system our best-fitting model gives slip rates of 2 ± 3, 12 ± 9, 12 ± 9, and 17 ± 3 mm/a for the Elsinore, Coyote Creek, Clark, and San <span class="hlt">Andreas</span> faults, respectively, where the large uncertainties in the slip rates for the SJF branches reflect the large uncertainty in the slip rate partitioning within the SJF system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/490160','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/490160"><span>A High shear stress segment along the San <span class="hlt">Andreas</span> Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Castillo, D. A.,; Younker, L.W.</p> <p>1997-01-30</p> <p>Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San <span class="hlt">Andreas</span> fault indicate a marked change in stress state occurring within 20 km of this principal transform plate boundary. A natural consequence of this stress transition is that if the observed near-field ``fault-oblique`` stress directions are representative of the fault stress state, the Mohr-Coulomb shear stresses resolved on San <span class="hlt">Andreas</span> sub-parallel planes are substantially greater than previously inferred based on fault-normal compression. Although the directional stress data and near-hydrostatic pore pressures, which exist within 15 km of the fault, support a high shear stress environment near the fault, appealing to elevated pore pressures in the fault zone (Byerlee-Rice Model) merely enhances the likelihood of shear failure. These near-field stress observations raise important questions regarding what previous stress observations have actually been measuring. The ``fault-normal`` stress direction measured out to 70 km from the fault can be interpreted as representing a comparable depth average shear strength of the principal plate boundary. Stress measurements closer to the fault reflect a shallower depth-average representation of the fault zone shear strength. If this is true, only stress observations at fault distances comparable to the seismogenic depth will be representative of the fault zone shear strength. This is consistent with results from dislocation monitoring where there is pronounced shear stress accumulation out to 20 km of the fault as a result of aseismic slip within the lower crust loading the upper locked section. Beyond about 20 km, the shear stress resolved on San <span class="hlt">Andreas</span> fault-parallel planes becomes negligible. 65 refs., 15 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70037328','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70037328"><span>Uncertainties in slip-rate estimates for the Mission Creek strand of the southern San <span class="hlt">Andreas</span> fault at Biskra Palms Oasis, southern California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Behr, W.M.; Rood, D.H.; Fletcher, K.E.; Guzman, N.; Finkel, R.; Hanks, T.C.; Hudnut, K.W.; Kendrick, K.J.; Platt, J.P.; Sharp, W.D.; Weldon, R.J.; Yule, J.D.</p> <p>2010-01-01</p> <p>This study focuses on uncertainties in estimates of the geologic slip rate along the Mission Creek strand of the southern San <span class="hlt">Andreas</span> fault where it offsets an alluvial fan (T2) at Biskra Palms Oasis in southern California. We provide new estimates of the amount of fault offset of the T2 fan based on trench excavations and new cosmogenic 10Be age determinations from the tops of 12 boulders on the fan surface. We present three alternative fan offset models: a minimum, a maximum, and a preferred offset of 660 m, 980 m, and 770 m, respectively. We assign an age of between 45 and 54 ka to the T2 fan from the 10Be data, which is significantly older than previously reported but is consistent with both the degree of soil development associated with this surface, and with ages from U-series geochronology on pedogenic carbonate from T2, described in a companion paper by Fletcher et al. (this volume). These new constraints suggest a range of slip rates between ~12 and 22 mm/yr with a preferred estimate of ~14-17 mm/yr for the Mission Creek strand of the southern San <span class="hlt">Andreas</span> fault. Previous studies suggested that the geologic and geodetic slip-rate estimates at Biskra Palms differed. We find, however, that considerable uncertainty affects both the geologic and geodetic slip-rate estimates, such that if a real discrepancy between these rates exists for the southern San <span class="hlt">Andreas</span> fault at Biskra Palms, it cannot be demonstrated with available data. ?? 2010 Geological Society of America.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/67988','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/67988"><span>Earthquake travel time tomography of the southern Santa Cruz Mountains: Control of fault rupture by lithological heterogeneity of the San <span class="hlt">Andreas</span> fault zone</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Foxall, W.; Michelini, A.; McEvilly, T.V.</p> <p>1993-10-10</p> <p>The 1989 Loma Prieta earthquake occurred along the stretch of the San <span class="hlt">Andreas</span> fault zone within the southern Santa Cruz Mountains that last failed as a major earthquake in 1906. The southeastern end of the 1989 rupture marks the transition from stable, aseismic slip on the central creeping section of the San <span class="hlt">Andreas</span> fault to unstable failure on the locked 1906 segment. The authors investigate this transition and the rupture characteristics of the 1989 earthquake using a 3-D P wave velocity model of the southern Santa Cruz Mountains section of the fault zone. The model images a large anomalous high-velocity body at midcrustal depths within the rupture zone of the 1989 earthquake that the available evidence suggests might have gabbroic or other mafic composition. On the basis of the relationship of the lithological features interpreted from the velocity model to the seismicity and surface creep the authors propose a model in which the high-velocity body is primarily responsible for the transition from stable to unstable fault slip at Pajaro Gap. The active plane of the San <span class="hlt">Andreas</span> fault cuts throughout the body. The fault system attempts to circumvent this barrier by transferring slip to secondary faults, including splay faults that have propagated along the frictionally favorable contact between the high-velocity rock mass and Franciscan country rocks. However, the near arrest of the stable sliding causes stress to concentrate within the body, and the high-strength, unstable contact within it evolves from a barrier to the asperity that failed in the 1989 earthquake. The general features of the 1989 rupture predicted by this asperity model agree with several rupture histories computed for the earthquake. The model implies that as proposed by other workers, the Loma Prieta earthquake did not involve a repeat of the 1906 slip, which has an important bearing on earthquake recurrence estimates for the Santa Cruz Mountains segment of the fault. 114 refs., 11 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/scitech/biblio/5098791','SCIGOV-STC'); return false;" href="https://www.osti.gov/scitech/biblio/5098791"><span>Early Miocene transpression across the Pacific-North American plate margin, initiation of the San <span class="hlt">Andreas</span> fault, and tectonic wedge activation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>McLaughlin, R.J. ); Underwood, M.B. )</p> <p>1993-04-01</p> <p>Magnetic stripes on the Pacific plate (PAC) indicate that subduction along the North American plate (NAM) margin ceased about 26--28 Ma south of the Mendocino fracture zone (MFZ), when the Pacific-Farallon (PAC-FAR) ridge encountered the NAM. In this area the PAC-FAR ridge apparently was segmented and abandoned as it encountered the margin, and was thrust beneath the western lip of the NAM, possibly due to residual FAR slab-pull. Between [approximately] 26 and 23.5 Ma, compressional tectonism in the distal NAM overlying the hot, buoyant ridge, produced ocean floor volcanism and a series of borderland structural basins that filled with continent-derived clastics. Initiation of the San <span class="hlt">Andreas</span> transform, and capture of a large segment of the NAM by the PAC appears to have occurred between [approximately] 24 and [approximately] 14 Ma. Beginning at least as early as 18 Ma, northeast of the San <span class="hlt">Andreas</span> fault, blind thrusts, folding and tilting developed in the roof of a northeastwardly-propagating wedge complex beneath the length of the Coast Ranges. The wedge complex probably was multistage and may have been initiated as early as 70--60 Ma. In the Cape Mendocino and Loma Prieta regions, Miocene or younger northeast-vergent members of the roof thrust system root into the San <span class="hlt">Andreas</span> fault and characteristically displace deep water marine rocks northeastward over the shallower margin. Total shortening across the transform margin based on deep crustal models must exceed 200 km since 70 Ma and is [ge]50 km since 28 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70034898','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70034898"><span>Basin geometry and cumulative offsets in the Eastern Transverse Ranges, southern California: Implications for transrotational deformation along the San <span class="hlt">Andreas</span> fault system</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Langenheim, V.E.; Powell, R.E.</p> <p>2009-01-01</p> <p>The Eastern Transverse Ranges, adjacent to and southeast of the big left bend of the San <span class="hlt">Andreas</span> fault, southern California, form a crustal block that has rotated clockwise in response to dextral shear within the San <span class="hlt">Andreas</span> system. Previous studies have indicated a discrepancy between the measured magnitudes of left slip on through-going east-striking fault zones of the Eastern Transverse Ranges and those predicted by simple geometric models using paleomagnetically determined clockwise rotations of basalts distributed along the faults. To assess the magnitude and source of this discrepancy, we apply new gravity and magnetic data in combination with geologic data to better constrain cumulative fault offsets and to define basin structure for the block between the Pinto Mountain and Chiriaco fault zones. Estimates of offset from using the length of pull-apart basins developed within left-stepping strands of the sinistral faults are consistent with those derived by matching offset magnetic anomalies and bedrock patterns, indicating a cumulative offset of at most ???40 km. The upper limit of displacements constrained by the geophysical and geologic data overlaps with the lower limit of those predicted at the 95% confidence level by models of conservative slip located on margins of rigid rotating blocks and the clockwise rotation of the paleomagnetic vectors. Any discrepancy is likely resolved by internal deformation within the blocks, such as intense deformation adjacent to the San <span class="hlt">Andreas</span> fault (that can account for the absence of basins there as predicted by rigid-block models) and linkage via subsidiary faults between the main faults. ?? 2009 Geological Society of America.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/ds/413/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/ds/413/"><span>Data Files for Ground-Motion Simulations of the 1906 San Francisco Earthquake and Scenario Earthquakes on the Northern San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Aagaard, Brad T.; Barall, Michael; Brocher, Thomas M.; Dolenc, David; Dreger, Douglas; Graves, Robert W.; Harmsen, Stephen; Hartzell, Stephen; Larsen, Shawn; McCandless, Kathleen; Nilsson, Stefan; Petersson, N. Anders; Rodgers, Arthur; Sjogreen, Bjorn; Zoback, Mary Lou</p> <p>2009-01-01</p> <p>This data set contains results from ground-motion simulations of the 1906 San Francisco earthquake, seven hypothetical earthquakes on the northern San <span class="hlt">Andreas</span> Fault, and the 1989 Loma Prieta earthquake. The bulk of the data consists of synthetic velocity time-histories. Peak ground velocity on a 1/60th degree grid and geodetic displacements from the simulations are also included. Details of the ground-motion simulations and analysis of the results are discussed in Aagaard and others (2008a,b).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41A2860L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41A2860L"><span>Crustal Stress Rotation Along the San <span class="hlt">Andreas</span> and San Jacinto Faults: A Modeling Study With Constraints From Seismology, Geodesy, Topography, and Gravity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Luttrell, K. M.; Smith-Konter, B. R.; Sandwell, D. T.</p> <p>2015-12-01</p> <p>The active tectonics of the southern San <span class="hlt">Andreas</span> transform plate boundary system respond to and contribute to the 4 D stress field throughout the region. We investigate the nature of this stress field in Southern California, with particular focus near the major strain-accumulating San <span class="hlt">Andreas</span> and San Jacinto faults, by creating a forward model that incorporates observations from seismology, geodesy, gravity, topography, and earthquake rupture history. The forward model consists of three independent crustal stress field components: (1) a plate driving force of undetermined magnitude and orientation; (2) a heterogeneous fault loading stress accumulation along locked fault segments; and (3) spatial variations in crustal stress due to differences in topography. The forward model is then compared to the in situ stress field orientation inferred from earthquake focal mechanisms. We estimate the magnitude of the in situ stress field as that required to maintain its orientation in the presence of topography, which tends to resist the motion of strike-slip faults. Our results indicate that differential stress at seismogenic depth must exceed 40 MPa. To assess the orientation of the plate driving stress, we consider twelve independent segments of the San <span class="hlt">Andreas</span> Fault System from Imperial Valley through Parkfield. We determine that along much of the central San <span class="hlt">Andreas</span> fault, the maximum horizontal stress (SHmax) is oriented north-south (~0ºEofN), but that from Coachella to Imperial SHmax is rotated clockwise, oriented ~12ºEofN. Furthermore, SHmax along the San Jacinto and Superstition Hills segments gradually rotates clockwise from ~3ºWofN in the south to ~8ºEofN in the north. With these results, we are able to match the in situ stress orientation of most (≥85%) of the near-fault strike-slip areas to within 15º, comparable to the errors associated with focal mechanism determination. Creating a forward model consistent with so many different types of observations</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70019744','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70019744"><span>Wide-angle seismic constraints on the evolution of the deep San <span class="hlt">Andreas</span> plate boundary by Mendocino triple junction migration</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hole, J.A.; Beaudoin, B.C.; Henstock, T.J.</p> <p>1998-01-01</p> <p>Recent wide-angle seismic observations that constrain the existence and structure of a mafic layer in the lower crust place strong constraints on the evolution of the San <span class="hlt">Andreas</span> plate boundary system in northern and central California. Northward migration of the Mendocino Triple Junction and the subducted Juan de Fuca lithospheric slab creates a gap under the continent in the new strike-slip system. This gap must be filled by either asthenospheric upwelling or a northward migrating slab attached to the Pacific plate. Both processes emplace a mafic layer, either magmatic underplating or oceanic crust, beneath the California Coast Ranges. A slab of oceanic lithosphere attached to the Pacific plate is inconsistent with the seismic observation that the strike-slip faults cut through the mafic layer to the mantle, detaching the layer from the Pacific plate. The layer could only be attached to the Pacific plate if large vertical offsets and other complex structures observed beneath several strike-slip faults are original oceanic structures that are not caused by the faults. Otherwise, if oceanic slabs exist beneath California, they do not migrate north to fill the growing slab gap. The extreme heat pulse created by asthenospheric upwelling is inconsistent with several constraints from the seismic data, including a shallower depth to the slab gap than is predicted by heat flow models, seismic velocity and structure that are inconsistent with melting or metamorphism of the overlying silicic crust, and a high seismic velocity in the upper mantle. Yet either the Pacific slab model or the asthenospheric upwelling model must be correct. While the mafic material in the lower crust could have been emplaced prior to triple junction migration, the deeper slab gap must still be filled. A preexisting mafic layer does not reduce the inconsistencies of the Pacific slab model. Such material could, however, compensate for the decrease in mafic magma that would be produced if</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMNS13B1611R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMNS13B1611R"><span>Near-surface structure of the 1906 main trace of the San <span class="hlt">Andreas</span> Fault, San Francisco peninsula segment, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosa, C.; Catchings, R. D.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.</p> <p>2012-12-01</p> <p>The peninsula segment of the San <span class="hlt">Andreas</span> Fault (SAF) is forecasted to have the second highest probability of producing a M6.7 or greater earthquake in the San Francisco Bay Area in the next 30 years; yet, relatively little is known about its slip history. In most places, the surface location of the SAF has been determined primarily on the basis of geomorphic features and from mapping surface ruptures associated with the 1906 M7.9 San Francisco earthquake. To more precisely locate traces of this segment of the SAF along the San Francisco peninsula in the subsurface, we acquired a high-resolution seismic imaging survey, using both seismic refraction and reflection profiling, south of Upper Crystal Springs Reservoir near Woodside, California in June 2012. High-resolution seismic images produced from this study may benefit ongoing paleoseismological investigations along the SAF because the seismic data can be used to precisely locate the main fault trace and auxiliary faults that may contribute to the earthquake hazards associated with the fault zone. Furthermore, the seismic images provide insights into near-surface fault structure and P- and S-wave velocities, which can be important in understanding strong shaking resulting from future earthquakes along this segment of the SAF. We acquired both P- and S-wave data using a 60-channel seismograph system connected via cable to 40-Hz vertical-component and 4-Hz horizontal geophones, which were spaced at 1-m intervals along a 60-m-long transect. Seismic sources (shots) were generated by hammer impacts on a steel plate or aluminum block at each geophone location. All shots were recorded on all channels. This survey design permits simultaneous acquisition of reflection and refraction data so that both refraction tomography and reflection images can be developed. Our initial analysis of the P-wave data shows that seismic velocities across the main trace of the SAF vary from about 700 m/s near the surface to more than 2500 m</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T21B2808K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T21B2808K"><span>Evaluating the Possibility of a joint San <span class="hlt">Andreas</span>-Imperial Fault Rupture in the Salton Trough Region</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kyriakopoulos, C.; Oglesby, D. D.; Meltzner, A. J.; Rockwell, T. K.</p> <p>2016-12-01</p> <p>A geodynamic investigation of possible earthquakes in a given region requires both field data and numerical simulations. In particular, the investigation of past earthquakes is also a fundamental part of understanding the earthquake potential of the Salton Trough region. Geological records from paleoseismic trenches inform us of past ruptures (length, magnitude, timing), while dynamic rupture models allow us to evaluate numerically the mechanics of such earthquakes. The two most recent events (Mw 6.4 1940 and Mw 6.9 1979) on the Imperial fault (IF) both ruptured up to the northern end of the mapped fault, giving the impression that rupture doesn't propagate further north. This result is supported by small displacements, 20 cm, measured at the Dogwood site near the end of the mapped rupture in each event. However, 3D paleoseismic data from the same site corresponding to the most recent pre-1940 event (1710 CE) and 5th (1635 CE) and 6th events back revealed up to 1.5 m of slip in those events. Since we expect the surface displacement to decrease toward the termination of a rupture, we postulate that in these earlier cases the rupture propagated further north than in 1940 or 1979. Furthermore, paleoseismic data from the Coachella site (Philibosian et al., 2011) on the San <span class="hlt">Andreas</span> fault (SAF) indicates slip events ca. 1710 CE and 1588-1662 CE. In other words, the timing of two large paleoseismic displacements on the IF cannot be distinguished from the timing of the two most recent events on the southern SAF, leaving a question: is it possible to have through-going rupture in the Salton Trough? We investigate this question through 3D dynamic finite element rupture modeling. In our work, we considered two scenarios: rupture initiated on the IF propagating northward, and rupture initiated on the SAF propagating southward. Initial results show that, in the first case, rupture propagates north of the mapped northern terminus of the IF only under certain pre</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.S33A0222C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.S33A0222C"><span>Frictional Properties of Sand Collected from the 1906 Rupture Zone of the San <span class="hlt">Andreas</span> Fault at Alder Creek, CA}</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Crawford, R. D.; Cashman, S.; Marone, C.; Carpenter, B.; Baldwin, J.</p> <p>2006-12-01</p> <p>For the purpose of determining fault frictional properties of unconsolidated late Holocene fluvial sediments, samples were collected from trenches excavated across the 1906 rupture trace of the San <span class="hlt">Andreas</span> Fault (SAF) at Alder Creek, CA. Two fault perpendicular ~2.5m deep trenches cut into late Holocene fluvial sand and gravel exposed a narrow (<1m) steeply dipping, branching, and anastomosing fault zone. Fault strands are defined by abrupt contacts and 0.5-2.0cm wide deformation bands. Samples of sand were collected several meters from the fault zone and enclosed in airtight bags to retain their original moisture content. We sheared layers of the sand in a servocontrolled, double direct shear testing machine at room temperature. A leveling jig prepared 5 mm thick layers of sand that were sheared between rough forcing blocks (5cm x 5cm nominal contact). Normal stress was constant during shear and varied over the suite of experiments from 75KPa to 900KPa, to a corresponding burial of ~3-40 meters. Shear loading was accomplished via a displacement rate boundary condition, which was set initially at 20μm/s and then subject to step changes to 200 and 2000μm/s for a cumulative total shear displacement of 25mm. Velocity stepping procedures are used to measure the velocity dependence of friction where the friction rate parameter, a-b, is the change in steady state sliding friction normalized by the log of velocity. In fault gouge it has been demonstrated that stable frictional behavior (a-b>0) is associated with pervasive shearing and velocity strengthening, while unstable velocity weakening frictional behavior (a-b<0) has been correlated with localized shear. The a-b values for the Alder Creek sands decrease steadily from 0.11 at 75KPa normal stress to less than 0.005 at 900KPa normal stress. If this rate can be extrapolated, it would imply a transition to velocity weakening at ~1Mpa normal stress or a burial of ~45m. The average measured and calculated steady</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT.......277S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT.......277S"><span>High resolution timing and style of coseismic deformation: Paleoseismic studies on the northern and southern San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Streig, Ashley Rebecca</p> <p></p> <p>Critical inputs to evaluate fault behavior models include the frequency of large earthquakes on plate boundary faults, amount of displacement, style of deformation in these events, and how these earthquakes are associated with adjacent sites and broader segments. Paleoseismic data provide these inputs and allow the characterization of hazard posed by individual faults. This dissertation presents results from paleoseismic studies at Hazel Dell and Frazier Mountain that provide new earthquake chronologies and slip estimates for the San <span class="hlt">Andreas</span> Fault (SAF). These data provide new insights into the recurrence and style of coseismic deformation for surface rupturing earthquakes on the SAF. The Hazel Dell site provides the first definitive paleoseismic evidence of two pre-1906, 19th century earthquakes on the Santa Cruz Mountains section of the SAF. I correlate these paleoseismic findings with the historic record of ground shaking associated with earthquakes in that period and combine the style of deformation in the last 3 events at the site with results from nearby paleoseismic sites to estimate earthquake rupture lengths and magnitudes for these early historic events. These findings increase the frequency of historic surface rupturing earthquakes on the northern SAF three-fold. At the Frazier Mountain site, on the southern SAF, I mapped deformation across a releasing step on the fault for the last five surface rupturing earthquakes to estimate deformation per-event. I compare the geometry and amount of vertical relief generated across the step-over by retrodeforming 3D surfaces interpolated from paleoseismic data step-wise for stratigraphic units deformed by each of those earthquakes. I find that structural relief is similar in four of the last five events, so slip on the fault must be within the same range for these earthquakes to generate approximately equivalent structural relief across the step-over. These results suggest displacement on the fault is comparable at</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T43D3077W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T43D3077W"><span>Testing the shorter and variable recurrence interval hypothesis along the Cholame segment of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Williams, A.; Arrowsmith, R.; Rockwell, T. K.; Akciz, S. O.; Grant Ludwig, L.</p> <p>2016-12-01</p> <p>The Cholame segment of the San <span class="hlt">Andreas</span> Fault interacts with the Parkfield segment to the northwest with its creep and M6 earthquakes and the locked Carrizo segment to the southeast. Although offset reconstructions exist for this 75 km reach, rupture behavior is poorly characterized, limiting seismic hazard evaluation. Here we present new paleoseismic results from 2 fault perpendicular 26 m long trenches connected by a 15 m long fault parallel trench. The site is located south of the Parkfield segment 20 km southeast of Highway 46. Site geomorphology is characterized by several 50 m offset drainages northwest of the trenches, small shutter ridges and sag ponds, and alluvial fans crossing the fault. Fault zone stratigraphy consists of alternating finely bedded sands, silts, and gravels, and bioturbated soil horizons. The strata record 3-4 earthquakes and possible deformation post-1857, similar to the LY4 site 38 km southeast. E4, E3 and the most recent earthquake (MRE) are well supported by evidence of decreasing vertical offset up-sequence, capped fissure fill and colluvial wedges, which create small horst and graben structures. Units display vertical offsets ranging from 60 cm at the base to 12 cm near the MRE horizon, small colluvial wedges, and sag deposits within the 4 m wide fault zone. E2—the penultimate-is less certain, supported only by the decreasing offset in the stratigraphic sequence. The E4 event horizon is a gradational clayey silt sag deposit capped by discontinuous gravel, 18 cm at its thickest point and extending 4.8 m across the fault zone. The E3 and E2 event horizons are capped by thin bedded silty clay, and bounded by discontinuous burn horizons. The MRE horizon extends 6 m across the main fault zone, and consists of a silty clay sag deposit capped by very fine, bedded sand and coarse gravel, 22 cm at its thickest point and overlying a burn horizon. If the MRE is indeed the 1857 event, it has significant potential in correlation with the high</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41A2870J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41A2870J"><span>Character and Implications of a Newly Identified Creeping Strand of the San <span class="hlt">Andreas</span> fault NE of Salton Sea, Southern California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Janecke, S. U.; Markowski, D.</p> <p>2015-12-01</p> <p>The overdue earthquake on the Coachella section, San <span class="hlt">Andreas</span> fault (SAF), the model ShakeOut earthquake, and the conflict between cross-fault models involving the Extra fault array and mapped shortening in the Durmid Hill area motivate new analyses at the southern SAF tip. Geologic mapping, LiDAR, seismic reflection, magnetic and gravity datasets, and aerial photography confirm the existence of the East Shoreline strand (ESS) of the SAF southwest of the main trace of the SAF. We mapped the 15 km long ESS, in a band northeast side of the Salton Sea. Other data suggest that the ESS continues N to the latitude of the Mecca Hills, and is >35 km long. The ESS cuts and folds upper Holocene beds and appears to creep, based on discovery of large NW-striking cracks in modern beach deposits. The two traces of the SAF are parallel and ~0.5 to ~2.5 km apart. Groups of east, SE, and ENE-striking strike-slip cross-faults connect the master dextral faults of the SAF. There are few sinistral-normal faults that could be part of the Extra fault array. The 1-km wide ESS contains short, discontinuous traces of NW-striking dextral-oblique faults. These en-echelon faults bound steeply dipping Pleistocene beds, cut out section, parallel tight NW-trending folds, and produced growth folds. Beds commonly dip toward the ESS on both sides, in accord with persistent NE-SW shortening across the ESS. The dispersed fault-fold structural style of the ESS is due to decollements in faulted mud-rich Pliocene to Holocene sediment and ramps and flats along the strike-slip faults. A sheared ladder-like geometric model of the two master dextral strands of the SAF and their intervening cross-faults, best explains the field relationships and geophysical datasets. Contraction across >40 km2 of the southernmost SAF zone in the Durmid Hills suggest that interaction of active structures in the SAF zone may inhibit the nucleation of large earthquakes in this region. The ESS may cross the northern Coachella</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFMED43A0838G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFMED43A0838G"><span>Discovery Along the San <span class="hlt">Andreas</span> Fault: Relocating Photographs From the 1906 Earthquake in San Francisco and San Mateo Counties</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grove, K.; Prentice, C.; Polly, J.; Yuen, C.; Wu, K.; Zhong, S.; Lopez, J.</p> <p>2005-12-01</p> <p>April of 2006 will mark the 100-year anniversary of the great 1906 San Francisco earthquake. This earthquake was important not only because of its human tragedy (thousands of dead or homeless people), but also because of its scientific significance. The 8.3 magnitude earthquake ruptured 430 km of the northern San <span class="hlt">Andreas</span> fault (SAF) and lasted nearly one minute. Investigations after the earthquake led to discoveries that were the beginning of modern earthquake theories and measuring instruments. This was also one of the first large-scale natural disasters to be photographed. Our research group, which is part of the National Science Foundation funded SF-ROCKS program, acquired photographs that were taken shortly after the earthquake in downtown San Francisco and along the SAF in San Mateo County. The SAF photos are part of a Geographical Information System (GIS) database being published on a U.S. Geological Survey web site. The goal of our project was to improve estimates of photograph locations and to compare the landscape features that were visible after the earthquake with the landscape that we see today. We used the GIS database to find initial photo locations, and we then used a high-precision Global Positioning System (GPS) to measure the geographic coordinates of the locations once we matched our view to what we saw in a photo. Where possible, we used a digital camera to retake photos from the same position, to show the difference in the landscape 100 years later. The 1906 photos show fault zone features such as ground rupture, sag ponds, shutter ridges, and offset fences. Changes to the landscape since 1906 have included erosion and grading of the land, building of houses and other structures, and more tree cover compared to previous grassland vegetation. Our project is part of 1906 Earthquake Centennial activities; it is contributing to the photo archive that helps scientists and engineers who study earthquakes and their effects. It will also help the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007AGUFM.S54A..08D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007AGUFM.S54A..08D"><span>Finite-Source Modeling of Micro-earthquakes on the Parkfield Segment of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dreger, D.; Morrish, A.; Nadeau, R.</p> <p>2007-12-01</p> <p> stress and strength heterogeneity exists along the San <span class="hlt">Andreas</span> fault.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T21B2815D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T21B2815D"><span>Southern San <span class="hlt">Andreas</span> Fault Slip History Refined Using Pliocene Colorado River Deposits in the Western Salton Trough</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dorsey, R. J.; Bennett, S. E. K.; Housen, B. A.</p> <p>2016-12-01</p> <p>Tectonic reconstructions of Pacific-North America plate motion in the Salton Trough region (Bennett et al., 2016) are constrained by: (1) late Miocene volcanic rocks that record 255 +/-10 km of transform offset across the northern Gulf of California since 6 Ma (average 42 mm/yr; Oskin and Stock, 2003); and (2) GPS data that show modern rates of 50-52 mm/yr between Pacific and North America plates, and 46-48 mm/yr between Baja California (BC) and North America (NAM) (Plattner et al., 2007). New data from Pliocene Colorado River deposits in the Salton Trough provide an important additional constraint on the geologic history of slip on the southern San <span class="hlt">Andreas</span> Fault (SAF). The Arroyo Diablo Formation (ADF) in the San Felipe Hills SW of the Salton Sea contains abundant cross-bedded channel sandstones deformed in the dextral Clark fault zone. The ADF ranges in age from 4.3 to 2.8 Ma in the Fish Creek-Vallecito basin, and in the Borrego Badlands its upper contact with the Borrego Formation is 2.9 Ma based on our new magnetostratigraphy. ADF paleocurrent data from a 20-km wide, NW-oriented belt near Salton City record overall transport to the SW (corrected for bedding dip, N=165), with directions ranging from NW to SE. Spatial domain analysis reveals radial divergence of paleoflow to the: W and NW in the NW domain; SW in the central domain; and S in the SE domain. Data near Borrego Sink, which restores to south of Salton City after removing offset on the San Jacinto fault zone, show overall transport to the SE. Pliocene patterns of radial paleoflow divergence strongly resemble downstream bifurcation of fluvial distributary channels on the modern Colorado River delta SW of Yuma, and indicate that Salton City has translated 120-130 km NW along the SAF since 3 Ma. We propose a model in which post-6 Ma BC-NAM relative motion gradually accelerated to 50 mm/yr by 4 Ma, continued at 50 mm/yr from 4-1 Ma, and decreased to 46 mm/yr from 1-0 Ma (split equally between the SAF and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41A2858G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41A2858G"><span>Re-measuring the Slip Rate of the San <span class="hlt">Andreas</span> Fault at Wallace Creek in the Carrizo Plain, CA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Grant Ludwig, L.; Akciz, S. O.; Arrowsmith, R.; Sato, T.; Cheiffetz, T.; Haddad, D. E.; Salisbury, J. B.; Marliyani, G. I.; Bohon, W.</p> <p>2015-12-01</p> <p>Sieh and Jahns (S&J) (1984) reported a slip rate of 33.9 +2.9 mm/yr for the San <span class="hlt">Andreas</span> fault (SAF) at Wallace Creek (WC) in the Carrizo Plain. Referenced hundreds of times, their measurement provides critical constraint for many related studies. Paleoseismologic studies at Bidart Fan (BF), ~5 km southeast of WC, show rupture approximately every 88 yrs between ~A.D. 1350 and 1857 (Akciz et al., 2010). Measurements of slip per event for the last 5 or 6 earthquakes at WC (Liu et al., 2004; Liu-Zeng et al., 2006), when combined with rupture dates from BF, yield slip rates up to 50 mm/yr, well above widely accepted values of ~ 35 mm/yr. The apparent discrepancy between slip rates and slip per event measurements provided motivation to re-measure S&J's (1984) slip rate, which was based on 8 detrital charcoal samples, by collecting samples for radiocarbon dating with new methods that have improved dramatically since the early 1980s. We re-excavated S&J's (1984) original trenches WC-2, 7, 9, 10 and 11, and placed a new trench, WC-12. The new trench exposed a rich history of channel cut and fill prior to abandonment of the beheaded channel and incision of the modern channel. The youngest channel fills, which must be slightly younger than the abandonment, indicate that sedimentation occurred between 3675-3285 BP, after which the channel was fully abandoned. Using S&J's (1984) offset measurement of 130 m since ~3400 BP, we recalculate a late Holocene slip rate of ~38 mm/yr in our preliminary analysis. This rate is slightly higher than the S&J (1984) result of 33.9±2.9 mm/yr and Noriega et al. (2006) result of 32.4±3.1 mm/yr at the Van Matre Ranch in the southern Carrizo. Our results are closer to the higher end of the ~36±2 mm/yr velocity gradient across the SAF from decadal timescale geodetic measurements (Schmalzle, et al., 2006).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.G43A0829N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.G43A0829N"><span>A Study of Current Interseismic Deformation of San <span class="hlt">Andreas</span> Fault, San Bernardino Mountain section, using Interferometric Synthetic Aperture Radar</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nee, P.; Funning, G. J.</p> <p>2010-12-01</p> <p>The San <span class="hlt">Andreas</span> fault (SAF) system accommodates a significant fraction of the relative movement between the Pacific and North American plates. In the past 250 years, no significant earthquake was recorded on the southernmost section of the SAF, and thus there exists a substantial ongoing earthquake hazard. Estimates of its slip deficit rate, made with various geologic and geodetic observations typically fall in the range 15-25 mm/yr, in the vicinity of the San Bernadino Mountains. Assuming the fault system slips at a constant rate of 20mm/yr, a slip deficit of 5 m would have accumulated since the last event, equivalent to a potential Mw 7.5 or larger earthquake. To understand how much strain is accumulating on the southern SAF system during the current interseismic period, we investigate the surface deformation using radar interferometry. We use the entire catalog of ERS and Envisat Synthetic Aperture Radar (SAR) data from a descending track well oriented for the SAF (track 399). 53 images from ERS spanning 1992 to late 2000, and 50 images from Envisat spanning 2003 to 2010 are used. We perform ratemap inversion (Biggs et al. 2007, GJI) to obtain an estimate of interseismic slip deficit rate, and Persistent Scatterer InSAR (PSI) analysis to investigate the tectonic and non-tectonic surface displacements across the region. The ratemap inversion algorithm involves simultaneous estimation of long wavelength orbital errors, construction of a ratemap by finding the best fitting rate of each pixel, and estimation of slip deficit rate using a half-space elastic dislocation model (Okada 1985, BSSA) calculated from a representative fault model. We constructed and tested different conceptual models based on the SCEC rectangular community fault model (CFM-R). We find that our ERS data are strongly affected by the postseismic deformation of the 1992 Mw 7.3 Landers Earthquake. We therefore estimate the slip rate using the Envisat dataset, which is much less affected by the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T52B..06V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T52B..06V"><span>The microstructural character and evolution of fault rocks from SAFOD and potential weakening mechanisms along the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>van Diggelen, E.; Holdsworth, R. E.; de Bresser, J. H.; Spiers, C.; Smith, S. A.; Walker, R. J.; Bowen, L.</p> <p>2010-12-01</p> <p>The San <span class="hlt">Andreas</span> Fault (SAF) forms the boundary between two geological terranes; the Salinian block (SB, Pacific plate) and the Great Valley block (GVB, North American plate). The SB contains arkosic sandstones, the GVB consists mostly of claystones and siltstones. The SAFOD borehole provides an extensive set of samples across the SAF and permits direct study of fault zone processes at 2-3 km depth. In order to determine the fault rock properties and deformation mechanisms in the SAF, in particular in two actively creeping fault segments, we have visually assessed the SAFOD phase 3 core material and we have performed detailed optical and electron microscopy, including chemical analyses using EDX. We compared the natural microstructures with microstructures developed in simulated fault gouges deformed in laboratory experiments. The rocks in Core interval 1 (SB) are mildly deformed and show evidence of cataclasis, pressure solution and reaction of feldspar to form phyllosilicates. Most of Core interval 3 (GVB) is also only mildly deformed, similar to Core interval 1. Sedimentary features are still visible, together with limited evidence for cataclasis, pressure solution and reaction of feldspar to phyllosilicates. The rocks in Core interval 2 (GVB) show ample evidence for micro-folding, foliation development, development of anastomosing shear bands, gouge formation, veining, and reworking of earlier microstructures. In addition, evidence is widespread for cataclasis, pressure solution and reaction of feldspar to form phyllosilicates. The SB and GVB host rocks are cut by numerous minor faults and small calcite-filled veins. Thin foliated gouges contain fine-grained, Fe-rich smectitic phyllosilicates. The development of interconnected networks of these phyllosilicates following cataclasis is prevalent in the inactive gouges. The actively creeping zones in Core intervals 2 and 3 consist mostly of Mg-rich smectitic phyllosilicates and show a strong, wavy foliation, lens</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.G23B..01T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.G23B..01T"><span>Modeling vertical deformation along the San <span class="hlt">Andreas</span> Fault System using geodetic, geologic, groundwater, and tide gauge data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thornton, G. M.; Smith-Konter, B. R.</p> <p>2011-12-01</p> <p>Vertical motions along the San <span class="hlt">Andreas</span> Fault System (SAFS) are recorded by several datasets. Geodetic (EarthScope PBO GPS & InSAR) data offer ideal spatial coverage, but often include anthropogenic effects and span short time periods (~5-20 years). Geologic data (from the SCEC Vertical Motion Database) primarily capture tectonic motions over long time periods (10 Ka to 7 Ma), but offer sparse spatial coverage. Tide gauge data (from the Permanent Service for Mean Sea Level) provide a temporal record of sea level change over intermediate time periods (~30-100+ years) and reflect variations in crustal uplift and subsidence at a few isolated locations along the California coastline. Using a 3-D viscoelastic earthquake cycle deformation model spanning the last 1000 years, this study aims to explore the first-order vertical tectonic motions reflected in each of these data sets. Previous work has shown that vertical GPS and geologic data in southern California do not correlate well, possibly related to groundwater contamination and the different timescales of the datasets. To isolate groundwater deformation recorded by the GPS data, a simple groundwater correction was applied to these data using regional well log data. To isolate a tectonic signal in the tide gauge data, global sea level rise and isostatic adjustment were removed from each station and additional processing was applied to eliminate major ocean-climate signals. A suite of vertical deformation models was then computed, reflecting variations in elastic plate thickness and mantle viscosity, to search the model parameter space for the optimal parameters that minimize residual data-model misfit. Preliminary results suggest that GPS, geologic, and tide gauge datasets are best fit by thick elastic plates ranging from 70 to 90 km and viscosities ranging from 1.5e18 to 1.5e19 Pa s. These values are consistent with previous results, however further work is needed to investigate sources of misfit and unmodeled</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRB..122.3739S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRB..122.3739S"><span>A 15 year catalog of more than 1 million low-frequency earthquakes: Tracking tremor and slip along the deep San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shelly, David R.</p> <p>2017-05-01</p> <p>Low-frequency earthquakes (LFEs) are small, rapidly recurring slip events that occur on the deep extensions of some major faults. Their collective activation is often observed as a semicontinuous signal known as tectonic (or nonvolcanic) tremor. This manuscript presents a catalog of more than 1 million LFEs detected along the central San <span class="hlt">Andreas</span> Fault from 2001 to 2016. These events have been detected via a multichannel matched-filter search, cross-correlating waveform templates representing 88 different LFE families with continuous seismic data. Together, these source locations span nearly 150 km along the central San <span class="hlt">Andreas</span> Fault, ranging in depth from 16 to 30 km. This accumulating catalog has been the source for numerous studies examining the behavior of these LFE sources and the inferred slip behavior of the deep fault. The relatively high temporal and spatial resolutions of the catalog have provided new insights into properties such as tremor migration, recurrence, and triggering by static and dynamic stress perturbations. Collectively, these characteristics are inferred to reflect a very weak fault likely under near-lithostatic fluid pressure, yet the physical processes controlling the stuttering rupture observed as tremor and LFE signals remain poorly understood. This paper aims to document the LFE catalog assembly process and associated caveats, while also updating earlier observations and inferred physical constraints. The catalog itself accompanies this manuscript as part of the electronic supplement, with the goal of providing a useful resource for continued future investigations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2015/1147/ofr20151147_pamphlet.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2015/1147/ofr20151147_pamphlet.pdf"><span>Photomosaics and event evidence from the Frazier Mountain paleoseismic site, trench 1, cuts 5–24, San <span class="hlt">Andreas</span> Fault Zone, southern California (2010–2012)</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scharer, Katherine M.; Fumal, Tom E.; Weldon, Ray J.; Streig, Ashley R.</p> <p>2015-08-24</p> <p>The Frazier Mountain paleoseismic site is located within the northern Big Bend of the southern San <span class="hlt">Andreas</span> Fault (lat 34.8122° N., lon 118.9034° W.), in a small structural basin formed by the fault (fig. 1). The site has been the focus of over a decade of paleoseismic study due to high stratigraphic resolution and abundant dateable material. Trench 1 (T1) was initially excavated as a 50-m long, fault-perpendicular trench crossing the northern half of the basin (Lindvall and others, 2002; Scharer and others, 2014a). Owing to the importance of a high-resolution trench site at this location on a 200-km length of the fault with no other long paleoseismic records, later work progressively lengthened and deepened T1 in a series of excavations, or cuts, that enlarged the original excavation. Scharer and others (2014a) provide the photomosaics and event evidence for the first four cuts, which largely show the upper section of the site, represented by alluvial deposits that date from about A.D. 1500 to present. Scharer and others (2014b) discuss the earthquake evidence and dating at the site within the context of prehistoric rupture lengths and magnitudes on the southern San <span class="hlt">Andreas</span> Fault. Here we present the photomosaics and event evidence for a series of cuts from the lower section, covering sediments that were deposited from about A.D. 500 to 1500 (fig. 2).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/of/2014/1002/pdf/ofr2014-1002_pamphlet.pdf','USGSPUBS'); return false;" href="https://pubs.usgs.gov/of/2014/1002/pdf/ofr2014-1002_pamphlet.pdf"><span>Photomosaics and event evidence from the Frazier Mountain paleoseismic site, trench 1, cuts 1–4, San <span class="hlt">Andreas</span> Fault Zone, southern California (2007–2009)</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scharer, Katherine M.; Fumal, Tom E.; Weldon, Ray J.; Streig, Ashley R.</p> <p>2014-01-01</p> <p>The Frazier Mountain paleoseismic site is located at the northwest end of the Mojave section of the San <span class="hlt">Andreas</span> Fault, in a small, closed depression at the base of Frazier Mountain near Tejon Pass, California (lat 34.8122° N., long 118.9034° W.). The site was known to contain a good record of earthquakes due to previous excavations by Lindvall and others (2002). This report provides data resulting from four nested excavations, or cuts, along trench 1 (T1) in 2007 and 2009 at the Frazier Mountain site. The four cuts were excavated progressively deeper and wider in an orientation perpendicular to the San <span class="hlt">Andreas</span> Fault, exposing distal fan and marsh sediments deposited since ca. A.D. 1200. The results of the trenching show that earthquakes that ruptured the site have repeatedly produced a small depression or sag on the surface, which is subsequently infilled with sand and silt deposits. This report provides high-resolution photomosaics and logs for the T1 cuts, a detailed stratigraphic column for the deposits, and a table summarizing all of the evidence for ground rupturing paleoearthquakes logged in the trenches.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007Tectp.429....1T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007Tectp.429....1T"><span>Continuation of the San <span class="hlt">Andreas</span> fault system into the upper mantle: Evidence from spinel peridotite xenoliths in the Coyote Lake basalt, central California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Titus, Sarah J.; Medaris, L. Gordon; Wang, Herbert F.; Tikoff, Basil</p> <p>2007-01-01</p> <p>The Coyote Lake basalt, located near the intersection of the Hayward and Calaveras faults in central California, contains spinel peridotite xenoliths from the mantle beneath the San <span class="hlt">Andreas</span> fault system. Six upper mantle xenoliths were studied in detail by a combination of petrologic techniques. Temperature estimates, obtained from three two-pyroxene geothermometers and the Al-in-orthopyroxene geothermometer, indicate that the xenoliths equilibrated at 970-1100 °C. A thermal model was used to estimate the corresponding depth of equilibration for these xenoliths, resulting in depths between 38 and 43 km. The lattice preferred orientation of olivine measured in five of the xenolith samples show strong point distributions of olivine crystallographic axes suggesting that fabrics formed under high-temperature conditions. Calculated seismic anisotropy values indicate an average shear wave anisotropy of 6%, higher than the anisotropy calculated from xenoliths from other tectonic environments. Using this value, the anisotropic layer responsible for fault-parallel shear wave splitting in central California is less than 100 km thick. The strong fabric preserved in the xenoliths suggests that a mantle shear zone exists below the Calaveras fault to a depth of at least 40 km, and combining xenolith petrofabrics with shear wave splitting studies helps distinguish between different models for deformation at depth beneath the San <span class="hlt">Andrea</span> fault system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44..162K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44..162K"><span>Nucleation process of magnitude 2 repeating earthquakes on the San <span class="hlt">Andreas</span> Fault predicted by rate-and-state fault models with SAFOD drill core data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaneko, Yoshihiro; Carpenter, Brett M.; Nielsen, Stefan B.</p> <p>2017-01-01</p> <p>Recent laboratory shear-slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two-phase nucleation of stick-slip motion that precedes the dynamic rupture propagation. This behavior was subsequently reproduced by a physics-based model incorporating laboratory-derived rate-and-state friction laws. However, applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths. Here we apply the same physics-based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) experiment and new and existing measurements of friction properties of SAFOD drill core samples. Using this well-constrained model, we predict what the nucleation phase will look like for magnitude ˜2 repeating earthquakes on segments of the San <span class="hlt">Andreas</span> Fault at a 2.8 km depth. We find that despite up to 3 orders of magnitude difference in the physical and friction parameters and stress conditions, the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes, with the nucleation consisting of two distinct phases. Our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude ˜2 earthquakes by strain measurements close (a few hundred meters) to the hypocenter, in a position reached by the existing borehole.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-KSC-20170427-VP-MWC01-INSIDEKSC.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-KSC-20170427-VP-MWC01-INSIDEKSC.html"><span>Inside KSC: <span class="hlt">Andrea</span> Farmer</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-04-28</p> <p>Dozens of little robots descended on the Kennedy Space Center Visitor Complex for the second annual Swarmathon competition. Kennedy also hosted a two days of events that focused on stewardship and sustainability in honor of Earth Day.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.S23A2540R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.S23A2540R"><span>Analysis And Modeling Of Shear Waves Generated By Explosions At The San <span class="hlt">Andreas</span> Fault Observatory At Depth</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rubinstein, J. L.; Pollitz, F. F.; Ellsworth, W. L.</p> <p>2012-12-01</p> <p>Using a deep deployment of an 80-element, 3-component borehole seismic array stretching from 1.5 to 2.3 kilometer (km) depth at the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD), we examine recordings of chemical explosions to better understand the generation of shear waves by explosive sources. The well is near-vertical at 1.5km and gradually transitions to a dip of 38 degrees at the deepest recording location. The chemical shots are high velocity chemical shots buried between 10-30 m and fired electrically, of size ~36 kg. The shotpoints are offset from the wellhead by 1 to 2 km. Previous analysis of zero-offset recordings (Pollitz et al., 2012) gave a velocity structure ranging from 1500 m/s (meters per second) in the upper 50 meters to 5000 m/s at the bottom of the well, as well as attenuation structure. The larger-offset recordings analyzed here have a strong, impulsive P arrival polarized as a longitudinal wave, and S waves composed of dominantly converted P to SV at the internal discontinuities and, to a lesser extent, the upward P to downgoing S converted wave pS. We compute synthetic waveforms using the Direct Radial Integration method of Friederich and Dalkolmo (1995), which handles a layered transversely isotropic medium with anelasticity. We use a hybrid 1D structure consisting of the local Bleibinhaus et al. (2007) structure determined from an active-source experiment combined with the near-well structure determined from the zero-offset shots. Using forward modeling on this velocity structure, both observed P and S wave energy are identified with the traveltimes expected for direct and/or reflected phases as well as the moveout associated with the local velocity structure around the receiver array. For larger-offset shots, S-wave energy is polarized primarily along the radial and propagation direction, consistent with converted P to SV energy. The longer-offset shots analyzed here have more distinct and energetic S arrivals than seen for the zero</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMNS33A1693R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMNS33A1693R"><span>Near-Surface Structure of the Peninsula Segment of the San <span class="hlt">Andreas</span> Fault, San Francisco Bay Area, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rosa, C.; Catchings, R.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.</p> <p>2013-12-01</p> <p>The peninsula segment of the San <span class="hlt">Andreas</span> Fault (SAF) is a section of the fault that has the potential to produce the next large earthquake in the San Francisco Bay Area, yet the slip history of the peninsula segment is relatively unknown. In most places, the surface location of the SAF has been determined primarily on the basis of geomorphic features and from mapping surface ruptures associated with the 1906 M7.9 San Francisco earthquake. To more precisely locate traces of the SAF along the San Francisco peninsula in the subsurface, we acquired a high-resolution seismic imaging survey, using both seismic refraction and reflection profiling, south of Upper Crystal Springs Reservoir near Woodside, California in June 2012. We acquired coincident P- and S-wave data using a 60-channel seismograph system connected via cable to 40-Hz vertical-component and 4-Hz horizontal-component geophones, with spacing at 1-m intervals along a 60-m-long transect across the SAF. Seismic sources (shots) were generated by hammer impacts on a steel plate or aluminum block at each geophone location. All shots were recorded on all channels. This survey design permitted simultaneous acquisition of reflection and refraction data such that both refraction tomography and reflection images were developed. Analysis of the P- and S-wave data, using refraction tomography, shows abrupt variations in the P-wave (Vp) and S-wave (Vs) velocities, including the 1,500 m/s velocity contour that outlines the top to groundwater and images of Vp/Vs and Poisson's ratios. P-wave velocities range from about 700 m/s at the surface to more than 4000 m/s at 20-m depth. S-wave velocities range from about 300 m/s at the surface to about 800 m/s at 20-m depth. The combined data indicate that the near-surface trace of the SAF dips steeply to the southwest in the upper few tens of meters. Variations in the velocity images also suggest the possibility of two additional near-surface fault traces within about 25 m of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T43I..04W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T43I..04W"><span>To what extent does earthquake variability affect slip rate estimates; a test using San <span class="hlt">Andreas</span> fault paleoseismology.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Weldon, R. J.</p> <p>2011-12-01</p> <p>Slip rate is one of the most fundamental properties of a fault, defining its role in local or global tectonics and largely controlling the hazard it poses to society. Unquestionably a fault's slip rate changes through time because faults have a finite lifetime (i.e. they form where they once weren't and they eventually die and become inactive); it is generally accepted that this time scale is related to the rate at which the tectonic driving forces vary, so faults are expected to have relatively constant slip rates over 10s of thousands to millions of years. Because most faults slip in discrete events (earthquakes) it is also clear that one must measure the slip rate over enough time to average the variability due to the seismic cycle. The rapid growth in geologic, geodetic and geochronologic tools to determine slip rate over a broad range of time intervals has generated tremendous interest in and speculation of other processes that vary slip rate between these two accepted extremes. To test hypotheses of processes that vary slip rate between the seismic cycle and a fault's tectonic lifetime one needs to fully understand the uncertainties that are associated with a slip rate estimate, including those introduced by these two accepted variations. This abstract addresses the extent to which variability in the timing and size of earthquakes affects slip rate estimates, and uses the rapidly growing paleoseismic data set for the southern San <span class="hlt">Andreas</span> fault to provide the necessary information to quantitatively address this issue. Good paleoseismic evidence exists for intervals without earthquakes of at least three times the average long term recurrence interval. Often these long hiatuses are balanced by clusters of earthquakes during which at least three earthquakes can occur in a time period less than a single average interval. Thus, slip rates from sample intervals that are similar to the long term average recurrence interval are useless and even slip rates determined</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T13C1901F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T13C1901F"><span>Reconciling patterns of interseismic strain accumulation with thermal observations across the Carrizo segment of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fulton, P. M.; Schmalzle, G. M.; Harris, R. N.; Dixon, T. H.</p> <p>2009-12-01</p> <p>The thermal state of the lithosphere has significant influence on crustal deformation and the depth extent of seismicity. Additional factors such as lithology and stress state are generally thought to impart smaller contributions. Along the Carrizo segment of the San <span class="hlt">Andreas</span> Fault (SAF), however, observed strain accumulation across the fault is counter to that expected based on contrasts in heat flow and microseismicity cutoff depths [Schmalzle et al., JGR, 2006]. We reconcile this discrepancy by suggesting that large overpressures and/or anomalous basement rocks make an important contribution to the crustal rheology in this area. The Carrizo segment of the SAF separates rocks of the Salinian Block to the SW characterized by high heat flow (~75 - 95 mW/m2) and shallow microseismicity (~10 km depth or less) from rocks of the Franciscan Complex and Great Valley Group to the NE associated with low heat flow (50 - 60 mW/m2) and deeper microseismicity (less than ~20 km deep). Intriguingly, GPS data from this region suggest that the NE side of the fault accommodates more strain than the SW side, inconsistent with what is generally expected based on the thermal data and cutoff depth of microseismicity. Viscoelastic models have been able to explain this asymmetric strain accumulation well with a constant elastic thickness coupled with a ~20 km wide soft (i.e., low Young’s modulus) zone NE of the fault. We show that by using this model in combination with the contrast in elastic thickness inferred from heat flow and microseismicity observations, we achieve better agreement with geologically accepted long-term average slip rates. Interestingly, the ~20 km wide soft zone NE of the fault is required to achieve this result. We suggest that this soft zone may be a result of either large overpressures or anomalous basement lithology. The presence of large overpressures is consistent with the subsurface extent of a hydrologic seal that extends ~10 - 20 km NE from the fault</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008AGUFM.T41A1955T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008AGUFM.T41A1955T"><span>Paleoseismic interpretation and a preliminary geologic slip rate for the Parkfield segment of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Toke, N. A.; Arrowsmith, J. R.; Rymer, M.; Landgraf, A.; Coyan, J.; Busch, M.; Haddad, D.</p> <p>2008-12-01</p> <p>The Parkfield segment of the San <span class="hlt">Andreas</span> Fault (SAF) is the northwest terminus of the great 1857 Fort Tejón earthquake. Slip budgets accounting for creep and moderate magnitude earthquakes suggest a slip deficit of 5 m along the extent of the 1857 rupture and a smaller deficit waning into the Parkfield segment. However, a geologic slip-rate for the Parkfield segment has not been established and it is unclear how slip is partitioned between the SAF and nearby sub-parallel faults. In 2007, we excavated three trenches at the Miller's Field paleoseismic site. This effort followed a similar paleoseismic campaign in 2004. Here we present new radiocarbon dating from our previous excavations across a sag pond (MST04) and a pressure ridge (PT04) and interpretations of the new paleoseismic exposures on these same geomorphic features (MST07 and PT07). We also opened two pilot trenches along the Southwest Fracture Zone (SWFZ). The Miller's field paleoseismic site is a Holocene terrace of the Little Cholame Creek. The exposed stratigraphy is overbank deposits of sand and silt. Some units are separated by thin charcoal-rich horizons that we interpret to have settled out during the waning of paleofloods. Along the SAF scarp, several buried soil horizons are deformed by the fault zone and clay-rich layers have accumulated within a sag pond. Deformation within the sag is partitioned among several zones of faulting with multiple splays. Many splays extend to the surface of the trenches and some are oriented obliquely to the trend of the SAF, consistent with formation from en-echelon surface cracking similar to the 2004 M6 Parkfield earthquake rupture. Interpreting ground rupturing paleoearthquakes at Parkfield must be cautionary because the SAF is creeping and numerous moderate magnitude earthquakes have occurred there historically. Upward terminating offsets could be formed on creeping fault splays. Despite this caution, we did observe three upward terminating offsets in the MST04</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51B2583C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51B2583C"><span>Salton Seismic Imaging Project Line 6: San <span class="hlt">Andreas</span> Fault and Northern Coachella Valley Structure, Riverside and San Bernardino Counties, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Catchings, R. D.; Fuis, G.; Rymer, M. J.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.</p> <p>2012-12-01</p> <p>The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San <span class="hlt">Andreas</span> fault (SAF) and adjacent basins (Imperial and Coachella Valleys) in southernmost California. Data and preliminary results from many of the seismic profiles are reported elsewhere (including Fuis et al., Rymer et al., Goldman et al., Langenheim et al., this meeting). Here, we focus on SSIP Line 6, one of four 2-D seismic profiles that were acquired across the Coachella Valley. The 44-km-long, SSIP-Line-6 seismic profile extended from the east flank of Mt. San Jacinto northwest of Palm Springs to the Little San Bernardino Mountains and crossed the SAF (Mission Creek (MCF), Banning (BF), and Garnet Hill (GHF) strands) roughly normal to strike. Data were generated by 10 downhole explosive sources (most spaced about 3 to 5 km apart) and were recorded by approximately 347 Texan seismographs (average spacing 126 m). We used first-arrival refractions to develop a P-wave refraction tomography velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 7 km depth, P-wave velocities range from about 2.5 km/s to about 7.2 km/s, with the lowest velocities within an ~2-km-deep, ~20-km-wide basin, and the highest velocities below the transition zone from the Coachella Valley to Mt. San Jacinto and within the Little San Bernardino Mountains. The BF and GHF strands bound a shallow sub-basin on the southwestern side of the Coachella Valley, but the underlying shallow-depth (~4 km) basement rocks are P-wave high in velocity (~7.2 km/s). The lack of a low-velocity zone beneath BF and GHF suggests that both faults dip northeastward. In a similar manner, high-velocity basement rocks beneath the Little San Bernardino Mountains suggest that the MCF dips vertically or southwestward. However, there is a pronounced low-velocity zone</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024267','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024267"><span>Paleoseismic event dating and the conditional probability of large earthquakes on the southern San <span class="hlt">Andreas</span> fault, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Biasi, G.P.; Weldon, R.J.; Fumal, T.E.; Seitz, G.G.</p> <p>2002-01-01</p> <p>We introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the Wrightwood and Pallett Creek sites on the southern San <span class="hlt">Andreas</span> fault. We illustrate how stratigraphic ordering, sedimentological, and historical data can be used quantitatively in the process of estimating earthquake ages. Calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation. The method does not eliminate subjective judgements in event dating, but it does provide a means of systematically and objectively approaching the dating process. Date distributions for the most recent 14 events at Wrightwood are based on sample and contextual evidence in Fumal et al. (2002) and site context and slip history in Weldon et al. (2002). Pallett Creek event and dating descriptions are from published sources. For the five most recent events at Wrightwood, our results are consistent with previously published estimates, with generally comparable or narrower uncertainties. For Pallett Creek, our earthquake date estimates generally overlap with previous results but typically have broader uncertainties. Some event date estimates are very sensitive to details of data interpretation. The historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data. Radiocarbon ages, peat accumulation rates, and historical constraints at Pallett Creek for event X yield a date estimate in the earliest 1800s and preclude a date in the late 1600s. This event is almost certainly the historical 1812 earthquake, as previously concluded by Sieh et al. (1989). This earthquake also produced ground deformation at Wrightwood. All events at Pallett Creek, except for event T, about A.D. 1360, and possibly event I, about A.D. 960, have corresponding events at Wrightwood with some overlap in age ranges. Event T falls during a period of low sedimentation at Wrightwood when conditions</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70101407','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70101407"><span>Southern San <span class="hlt">Andreas</span> Fault evaluation field activity: approaches to measuring small geomorphic offsets--challenges and recommendations for active fault studies</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scharer, Katherine M.; Salisbury, J. Barrett; Arrowsmith, J. Ramon; Rockwell, Thomas K.</p> <p>2014-01-01</p> <p>In southern California, where fast slip rates and sparse vegetation contribute to crisp expression of faults and microtopography, field and high‐resolution topographic data (<1  m/pixel) increasingly are used to investigate the mark left by large earthquakes on the landscape (e.g., Zielke et al., 2010; Zielke et al., 2012; Salisbury, Rockwell, et al., 2012, Madden et al., 2013). These studies measure offset streams or other geomorphic features along a stretch of a fault, analyze the offset values for concentrations or trends along strike, and infer that the common magnitudes reflect successive surface‐rupturing earthquakes along that fault section. Wallace (1968) introduced the use of such offsets, and the challenges in interpreting their “unique complex history” with offsets on the Carrizo section of the San <span class="hlt">Andreas</span> fault; these were more fully mapped by Sieh (1978) and followed by similar field studies along other faults (e.g., Lindvall et al., 1989; McGill and Sieh, 1991). Results from such compilations spurred the development of classic fault behavior models, notably the characteristic earthquake and slip‐patch models, and thus constitute an important component of the long‐standing contrast between magnitude–frequency models (Schwartz and Coppersmith, 1984; Sieh, 1996; Hecker et al., 2013). The proliferation of offset datasets has led earthquake geologists to examine the methods and approaches for measuring these offsets, uncertainties associated with measurement of such features, and quality ranking schemes (Arrowsmith and Rockwell, 2012; Salisbury, Arrowsmith, et al., 2012; Gold et al., 2013; Madden et al., 2013). In light of this, the Southern San <span class="hlt">Andreas</span> Fault Evaluation (SoSAFE) project at the Southern California Earthquake Center (SCEC) organized a combined field activity and workshop (the “Fieldshop”) to measure offsets, compare techniques, and explore differences in interpretation. A thorough analysis of the measurements from the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.T14B..03E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.T14B..03E"><span>Evaluation of Fault Zone Structure and Properties at Depth, with Insights into Deformation and Alteration of the San <span class="hlt">Andreas</span> Fault at SAFOD</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Evans, J. P.; Jeppson, T. N.; Keighley Bradbury, K.; Lowry, A. R.</p> <p>2009-12-01</p> <p>We examine the physical properties and structure of the San <span class="hlt">Andreas</span> fault with the SAFOD wireline geophysical data combined with data from cuttings and core. We examined geophysical logs from the SAFOD borehole starting at an approximate measured depth of 3 km to the end of the drill hole at 4 km; this area includes the region interpreted to be the main and active part of the San <span class="hlt">Andreas</span> Fault, which lies in a sequence of deformed sandstone, siltstone, shale, and Franciscan rocks. Franciscan lithologies include fine-grained siltstones and block-in-matrix melange. Geophysical logs show the presence of a low velocity zone from 3150 to 3410 m measured depth. Active slip surfaces within the low velocity zone correspond to sharp decreases in velocity and density and increasing porosity. Conventional comparisons of the amount of fracturing, alteration, and cataclasite in the LVZ with wireline data reveal complex relationships. The are few to weak correlations between the velocity data and the measures of the amount of deformation, and in places the velocity increases with deformation features in the low-velocity zone. The LVZ may correlate with low-velocity rock types within the fault zone. We also use inversion methods to examine the data, and found three distinct clusters of data in which velocity, density, and resistivities correlate. This relationship could be due to the presence serpentinite or a decrease in porosity and increase in density due to compaction and/or cementation of the sandstones and siltstones. Estimates of the elastic moduli from the wireline data for the SAF at depth and the Buzzard Canyon fault southwest of the SAF show that both faults exhibit low modulli. The lowest velocity/moduli rocks are sheared mélange/fault gouge diamictites and serpentinites within the narrow zones of the active part of the San <span class="hlt">Andreas</span> fault, and also within the Buzzard Canyon fault, where Salinain grantic rocks are juxtaposed on Salinian-derived arkosic rocks. These</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeoRL..44.1293H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeoRL..44.1293H"><span>Evolution of seismicity near the southernmost terminus of the San <span class="hlt">Andreas</span> Fault: Implications of recent earthquake clusters for earthquake risk in southern California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hauksson, Egill; Meier, Men-Andrin; Ross, Zachary E.; Jones, Lucile M.</p> <p>2017-02-01</p> <p>Three earthquake clusters that occurred in the direct vicinity of the southern terminus of the San <span class="hlt">Andreas</span> Fault (SAF) in 2001, 2009, and 2016 raised significant concern regarding possible triggering of a major earthquake on the southern SAF, which has not ruptured in more than 320 years. These clusters of small and moderate earthquakes with M ≤ 4.8 added to an increase in seismicity rate in the northern Brawley seismic zone that began after the 1979 Mw 6.5 Imperial Valley earthquake, in contrast to the quiet from 1932 to 1979. The clusters so far triggered neither small nor large events on the SAF. The mostly negative Coulomb stress changes they imparted on the SAF may have reduced the likelihood that the events would initiate rupture on the SAF, although large magnitude earthquake triggering is poorly understood. The relatively rapid spatial and temporal migration rates within the clusters imply aseismic creep as a possible driver rather than fluid migration.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19770006642','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19770006642"><span>Monitoring of crustal movements in the San <span class="hlt">Andreas</span> fault zone by a satellite-borne ranging system. Ph.D. Thesis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kumar, M.</p> <p>1976-01-01</p> <p>The Close Grid Geodynamic Measurement System is conceived as an orbiting ranging device with a ground base grid of reflectors or transponders (spacing 1.0 to 30 km), which are projected to be of low cost (maintenance free and unattended), and which will permit the saturation of a local area to obtain data useful to monitor crustal movements in the San <span class="hlt">Andreas</span> fault zone. The system includes a station network of 75 stations covering an area between 36 deg N and 38 deg N latitudes, and 237 deg E and 239 deg E longitudes, with roughly half of the stations on either side of the faults. In addition, the simulation of crustal movements through the introduction of changes in the relative positions between grid stations, weather effect for intervisibility between satellite and station and loss of observations thereof, and comparative evaluation of various observational scheme-patterns have been critically studied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......173A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......173A"><span>Gravity constraints on the geometry of the Big Bend of the San <span class="hlt">Andreas</span> Fault in the southern Carrizo Plains and Pine Mountain egion</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Altintas, Ali Can</p> <p></p> <p>The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San <span class="hlt">Andreas</span> Fault (SAF) and its role in producing hydrocarbon-bearing structures in the southern Central Valley of California. The SAF is the main plate boundary structure between the Pacific and North American plates and accommodates ?35 mm/yr of dextral motion. The SAF can be divided into three main parts: the northern, central and southern segments. The boundary between the central and southern segments is the "Big Bend", which is characterized by an ≈30°, eastward bend. This fault curvature led to the creation of a series of roughly east-west thrust faults and the transverse mountain ranges. Four high-resolution gravity transects were conducted across locations on either side of the bend. A total of 166 new gravity measurements were collected. Previous studies suggest significantly inclined dip angle for the San <span class="hlt">Andreas</span> Fault in the Big Bend area. Yet, our models indicate that the San <span class="hlt">Andreas</span> Fault is near vertical in the Big Bend area. Also gravity cross-section models suggest that flower structures occur on either side of the bend. These structures are dominated by sedimentary rocks in the north and igneous rocks in the south. The two northern transects in the Carrizo plains have an ≈-70 mgal Bouguer anomaly. The SAF has a strike of ≈315° near these transects. The northern transects are characterized by multiple fault strands which cut marine and terrestrial Miocene sedimentary rocks as well as Quaternary alluvial valley deposits. These fault strands are characterized by ?6 mgal short wavelength variations in the Bouguer gravity anomaly, which correspond to low density fault gouge and fault splays that juxtapose rocks of varying densities. The southern transects cross part of the SAF with a strike of 285°, have a Bouguer anomaly of ≈-50 mgal and are characterized by a broad 15 mgal high. At this location the rocks on</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.V11A2501M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.V11A2501M"><span>Sierran affinity (?) metasedimentary rocks beneath the Coast Range Ophiolite of the Sierra Azul block east of the San <span class="hlt">Andreas</span> fault, Santa Clara County, CA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McLaughlin, R. J.; Dumitru, T. A.; Ernst, W. G.</p> <p>2011-12-01</p> <p>The Loma Prieta slate (LPS) is a <100 m thick slice of highly flattened and stretched, pebbly to shaly metasedimentary rocks exposed for a length of 700 m at Loma Prieta Peak, east of the San <span class="hlt">Andreas</span> fault in the southern Santa Cruz Mountains. The LPS occurs along a low-dipping segment of the NW-trending, dextral-reverse Sargent fault, which places the slate and overlying Middle Jurassic Coast Range Ophiolite in the hanging wall, eastward over lower Eocene strata. The LPS and overlying Coast Range Ophiolite, in turn, form the base of a 60-80 km long fault block east of the San <span class="hlt">Andreas</span> fault, overlain by Jurassic-lower Miocene marine strata that together define the Sierra Azul structural block (SAB). These rocks overlie terranes of the Franciscan Complex. The Sargent fault bisects the SAB section and is truncated along-strike and at depth, by the San <span class="hlt">Andreas</span> fault. Reconstituted clastic grains of the LPS have dominant rhyo-dacitic and granitic sources and felsitic to granophyric grains preserve K-feldspar. Newly crystallized phengitic mica, chlorite and speculatively, incipient pumpellyite, are present in the LPS. No new high P/T metamorphic minerals are petrographically discernible, seemingly distinguishing the LPS from known cataclastic Franciscan Complex rocks structurally beneath the SAB. The LPS instead, has been proposed to correlate with the Jurassic arc-derived Mariposa Formation (MFS) in the Sierra Nevada Foothills, metamorphosed during the Nevadan orogeny. The correlation, however, has been problematic due to a lack of age control on the LPS, its limited surface distribution and its wide separation from the MFS. To test the correlation, we dated detrital zircons from the LPS at University of Arizona's LA-ICPMS lab and compared the results with detrital zircon data from the MFS (Snow and Ernst, 2008, GSA Special Paper 438). Weighted mean age calculations indicate a youngest zircon age cluster at about 152.5±2 Ma for the LPS, which indicates its maximum</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Tectp.690..174L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Tectp.690..174L"><span>Constraints on paleofluid sources using the clumped-isotope thermometry of carbonate veins from the SAFOD (San <span class="hlt">Andreas</span> Fault Observatory at Depth) borehole</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Luetkemeyer, P. Benjamin; Kirschner, David L.; Huntington, Katharine W.; Chester, Judith S.; Chester, Frederick M.; Evans, James P.</p> <p>2016-10-01</p> <p>The San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD), near Parkfield, California, is a borehole drilled through two active deforming zones of the San <span class="hlt">Andreas</span> fault, the Southwest Deforming Zone (SDZ) and the Central Deforming Zone (CDZ). These zones accommodate displacement by seismic slip and aseismic creep. Elevated fluid pressures and fluid-rock interactions have been proposed to explain the low apparent strength and aseismic creep observed, but the origin of the fluids and existence of high fluid pressures remains uncertain. We use clumped-isotope thermometry and δ18O-δ13C compositions of calcite in veins to constrain the origin of paleofluids and compare these results to the isotopic composition of modern-day pore fluids from the SAFOD borehole and nearby areas. We observe that: (1) calcite vein temperatures vary from 81 to 134 °C, which overlaps the current ambient borehole temperatures of 110-115 °C at sampled depths; (2) vein calcite is not in carbon isotope equilibrium with modern-day pore fluids; (3) the δ18O values of paleofluids close to the SDZ and CDZ, calculated from vein δ18O and temperature data, are not in equilibrium with local modern-day pore waters but approach equilibrium with modern pore waters far from these zones; and (4) syntectonic vein calcite is only in C- and O-isotopic equilibrium with their host rocks within the SDZ and CDZ. Spatial patterns of δ18O and δ13C show little evidence for across-fault fluid-flow. Clumped isotope temperatures are consistent with locally-derived fluid sources, but not with continuous or episodic replenishment of fluids from shallow sedimentary brines or deep fluid sources. Our findings are compatible with flow of meteoric fluids from the southwestern damage zone into the SDZ and CDZ, which would have favored the formation of weak phyllosilicates and contributed to the present day weakness of the two actively deforming zones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70128987','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70128987"><span>Using surface creep rate to infer fraction locked for sections of the San <span class="hlt">Andreas</span> fault system in northern California from alignment array and GPS data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Lienkaemper, James J.; McFarland, Forrest S.; Simpson, Robert W.; Caskey, S. John</p> <p>2014-01-01</p> <p>Surface creep rate, observed along five branches of the dextral San <span class="hlt">Andreas</span> fault system in northern California, varies considerably from one section to the next, indicating that so too may the depth at which the faults are locked. We model locking on 29 fault sections using each section’s mean long‐term creep rate and the consensus values of fault width and geologic slip rate. Surface creep rate observations from 111 short‐range alignment and trilateration arrays and 48 near‐fault, Global Positioning System station pairs are used to estimate depth of creep, assuming an elastic half‐space model and adjusting depth of creep iteratively by trial and error to match the creep observations along fault sections. Fault sections are delineated either by geometric discontinuities between them or by distinctly different creeping behaviors. We remove transient rate changes associated with five large (M≥5.5) regional earthquakes. Estimates of fraction locked, the ratio of moment accumulation rate to loading rate, on each section of the fault system provide a uniform means to inform source parameters relevant to seismic‐hazard assessment. From its mean creep rates, we infer the main branch (the San <span class="hlt">Andreas</span> fault) ranges from only 20%±10% locked on its central creeping section to 99%–100% on the north coast. From mean accumulation rates, we infer that four urban faults appear to have accumulated enough seismic moment to produce major earthquakes: the northern Calaveras (M 6.8), Hayward (M 6.8), Rodgers Creek (M 7.1), and Green Valley (M 7.1). The latter three faults are nearing or past their mean recurrence interval.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017JGRB..122.2193S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017JGRB..122.2193S"><span>Ground-rupturing earthquakes on the northern Big Bend of the San <span class="hlt">Andreas</span> Fault, California, 800 A.D. to Present</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scharer, Katherine; Weldon, Ray; Biasi, Glenn; Streig, Ashley; Fumal, Thomas</p> <p>2017-03-01</p> <p>Paleoseismic data on the timing of ground-rupturing earthquakes constrain the recurrence behavior of active faults and can provide insight on the rupture history of a fault if earthquakes dated at neighboring sites overlap in age and are considered correlative. This study presents the evidence and ages for 11 earthquakes that occurred along the Big Bend section of the southern San <span class="hlt">Andreas</span> Fault at the Frazier Mountain paleoseismic site. The most recent earthquake to rupture the site was the Mw7.7-7.9 Fort Tejon earthquake of 1857. We use over 30 trench excavations to document the structural and sedimentological evolution of a small pull-apart basin that has been repeatedly faulted and folded by ground-rupturing earthquakes. A sedimentation rate of 0.4 cm/yr and abundant organic material for radiocarbon dating contribute to a record that is considered complete since 800 A.D. and includes 10 paleoearthquakes. Earthquakes have ruptured this location on average every 100 years over the last 1200 years, but individual intervals range from 22 to 186 years. The coefficient of variation of the length of time between earthquakes (0.7) indicates quasiperiodic behavior, similar to other sites along the southern San <span class="hlt">Andreas</span> Fault. Comparison with the earthquake chronology at neighboring sites along the fault indicates that only one other 1857-size earthquake could have occurred since 1350 A.D., and since 800 A.D., the Big Bend and Mojave sections have ruptured together at most 50% of the time in Mw ≥ 7.3 earthquakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70189779','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70189779"><span>Slip rates and spatially variable creep on faults of the northern San <span class="hlt">Andreas</span> system inferred through Bayesian inversion of Global Positioning System data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Murray, Jessica R.; Minson, Sarah E.; Svarc, Jerry L.</p> <p>2014-01-01</p> <p>Fault creep, depending on its rate and spatial extent, is thought to reduce earthquake hazard by releasing tectonic strain aseismically. We use Bayesian inversion and a newly expanded GPS data set to infer the deep slip rates below assigned locking depths on the San <span class="hlt">Andreas</span>, Maacama, and Bartlett Springs Faults of Northern California and, for the latter two, the spatially variable interseismic creep rate above the locking depth. We estimate deep slip rates of 21.5 ± 0.5, 13.1 ± 0.8, and 7.5 ± 0.7 mm/yr below 16 km, 9 km, and 13 km on the San <span class="hlt">Andreas</span>, Maacama, and Bartlett Springs Faults, respectively. We infer that on average the Bartlett Springs fault creeps from the Earth's surface to 13 km depth, and below 5 km the creep rate approaches the deep slip rate. This implies that microseismicity may extend below the locking depth; however, we cannot rule out the presence of locked patches in the seismogenic zone that could generate moderate earthquakes. Our estimated Maacama creep rate, while comparable to the inferred deep slip rate at the Earth's surface, decreases with depth, implying a slip deficit exists. The Maacama deep slip rate estimate, 13.1 mm/yr, exceeds long-term geologic slip rate estimates, perhaps due to distributed off-fault strain or the presence of multiple active fault strands. While our creep rate estimates are relatively insensitive to choice of model locking depth, insufficient independent information regarding locking depths is a source of epistemic uncertainty that impacts deep slip rate estimates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70029429','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70029429"><span>Pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the "Big Bend" of the San <span class="hlt">Andreas</span> fault: An example from Lockwood Valley, southern California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kellogg, K.S.; Minor, S.A.</p> <p>2005-01-01</p> <p>The "Big Bend" of the San <span class="hlt">Andreas</span> fault in the western Transverse Ranges of southern California is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions. The Lockwood Valley region, just south of the Big Bend, underwent a profound change in early Pliocene time (???5 Ma) from basin deposition to contraction, accompanied by widespread folding and thrusting. This change followed the recently determined initiation of opening of the northern Gulf of California and movement along the southern San <span class="hlt">Andreas</span> fault at about 6.1 Ma, with the concomitant formation of the Big Bend. Lockwood Valley occupies a 6-km-wide, fault-bounded structural basin in which converging blocks of Paleoproterozoic and Cretaceous crystalline basement and upper Oligocene and lower Miocene sedimentary rocks (Plush Ranch Formation) were thrust over Miocene and Pliocene basin-fill sedimentary rocks (in ascending order, Caliente Formation, Lockwood Clay, and Quatal Formation). All the pre-Quatal sedimentary rocks and most of the Pliocene Quatal Formation were deposited during a mid-Tertiary period of regional transtension in a crustal block that underwent little clockwise vertical-axis rotation as compared to crustal blocks to the south. Ensuing Pliocene and Quaternary transpression in the Big Bend region began during deposition of the poorly dated Quatal Formation and was marked by four converging thrust systems, which decreased the areal extent of the sedimentary basin and formed the present Lockwood Valley structural basin. None of the thrusts appears presently active. Estimated shortening across the center of the basin was about 30 percent. The fortnerly defined eastern Big Pine fault, now interpreted to be two separate, oppositely directed, contractional reverse or thrust faults, marks the northwestern structural boundary of Lockwood Valley. The complex geometry of the Lockwood Valley basin is similar</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.S51D0083T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.S51D0083T"><span>High-Resolution Seismic Images and 3-D Seismic Velocities of the San <span class="hlt">Andreas</span> Fault Zone at Burro Flats, Southern California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tsai, C.; Catchings, R. D.; Rymer, M. J.; Goldman, M. R.</p> <p>2003-12-01</p> <p>The southern San <span class="hlt">Andreas</span> fault (SAF) has produced large earthquakes in the past 1500 yrs. Burro Flats, a basin within the San Bernardino Mountains, is bounded on the southwest by the southern San <span class="hlt">Andreas</span> fault. Burro Flats has been the site of paleoseismological investigations to determine the slip history of the fault. Additional paleoseismic studies at this location are needed to further resolve the structure and slip history of the SAF. In addition to the main trace of the SAF at Burro Flats, there are splay faults, suggesting a complex geometry for the fault. To better understand the structure of the SAF, we acquired a 3-D, combined seismic reflection/refraction profile centered on the main trace at Burro Flats. The seismic investigation included a 60 m by 70 m rectangular array. Sensors were spaced every 5 m; seismic sources, likewise with a spacing of 5 m, consisted of a combination of down-hole explosives and shallow (approximately 0.3 m) Betsy Seisgun shots. Data were recorded without acquisition filters for 5 s at a 0.5-ms sampling rate. To analyze the data for velocity structure, we used a tomographic inversion procedure to invert first-arrival refractions. Preliminary measurements from shot gathers show that near-surface velocities range between 700 m/s and 1500 m/s. We observe apparent travel-time delays of approximately 7 ms near the main surface trace of the SAF, suggesting that seismic imaging methods may be useful in identifying this and other fault traces. These results will be useful for paleoseismic investigations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.T21E..01L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.T21E..01L"><span>High-resolution geodetic observations of fault zone deformation on the San <span class="hlt">Andreas</span> and San Jacinto faults in southern California (Invited)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lindsey, E. O.; Fialko, Y. A.; Sahakian, V. J.; Bock, Y.; Barbot, S.; Rockwell, T. K.</p> <p>2013-12-01</p> <p>We present high resolution (10-100m) space geodetic observations of interseismic deformation across the major strike-slip faults in southern California. The data reveal several zones of elevated interseismic strain rates extending 1-2 km from the geologically mapped fault traces. In particular, we combined the mean line-of-sight velocities from the ascending and descending swaths of the Envisat satellite (tracks 77 and 356, respectively) to isolate the vertical and horizontal components of ground motion on the Coachella segment of the San <span class="hlt">Andreas</span> fault. The results reveal patterns of localized fault creep and distributed deformation extending up to a kilometer from the fault. These patterns appear to correlate with local variations in fault strike, suggesting a normal-stress control on the degree of strain localization. On the San Jacinto fault at Anza, new survey-mode GPS occupations of a high-density network spanning the fault, in combination with InSAR observations from ERS-1/2, reveal a similar several-kilometer-wide zone of elevated strain accumulation. The zone of enhanced deformation coincides with a tomographically imaged seismic low velocity zone (Allam and Ben-Zion, 2012). However, we find that the inferred reduction in elastic modulus is not sufficient to explain the elevated near-fault strain rate. GPS occupations of an alignment array installed in 1990 allow us to rule out shallow creep as a possible contributor. We show that the observed strain rate may be explained either by a reduced yield stress resulting in inelastic deformation within the shallow fault zone, or by heterogeneous frictional properties at the base of the seismogenic zone, allowing for both robust creep and microseismicity. Fault-parallel creep rate on the southernmost San <span class="hlt">Andreas</span> fault inferred from multi-look direction InSAR (Envisat tracks 356 and 77), showing pattern of localized and distributed deformation along strike, and locations of ground validation (GPS and creepmeters).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T12A..04M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T12A..04M"><span>Coseismic brecciation at fault stepovers and transient fluid pathways in a mid-crustal San <span class="hlt">Andreas</span> analogue: The Pofadder Shear Zone, Namibia and South Africa</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Melosh, B. L.; Rowe, C. D.; Gerbi, C. C.</p> <p>2015-12-01</p> <p>Fluid transport along faults is important throughout the seismic cycle due to the effects on fault strength. Rheological boundaries in the crust such as the quartz brittle-plastic transition coincide with permeability changes, and play an important role in controlling fluid distribution. Here we present a newly recognized mechanism for fluid migration through the brittle-plastic transition in an ancient San <span class="hlt">Andreas</span> Fault analogue: The Pofadder Shear Zone in Namibia and South Africa. Breccias formed in elongate pods during the passage of an earthquake rupture through a fault stepover. These breccias form subvertical fluid pathways (perpendicular to the slip direction). Over time, many overprinting or adjacent ruptures could have allowed fluid migration over a large (~ kms) scale, facilitating fluid flow through a low porosity region of the crust. These pathways were subsequently closed during breccia compaction by crystal plastic flow, facilitated by the presence of fluids. Thus, fluid migration within and across the brittle-plastic transitional zone is time and rate dependent and can both cause fault weakening and strengthening. We observed breccias formed in slip events with displacements between ~1-15 cm, consistent with small to moderate magnitude earthquakes and/or tectonic tremor, which occurs at similar depths in the San <span class="hlt">Andreas</span> Fault. In addition to providing a new way of identifying paleo-seismic slip in the rock record, these observations may help explain co- post-seismic fluid advection in mid-crustal faults. This process of local brecciation in stepovers may be the origin of cryptic geophysical signals such as tremor bursts in continental faults.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70135097','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70135097"><span>Quaternary landscape development, alluvial fan chronology and erosion of the Mecca Hills at the southern end of the San <span class="hlt">Andreas</span> Fault zone</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Gray, Harrison J.; Owen, Lewis; Dietsch, Craig; Beck, Richard A.; Caffee, Marc A.; Finkelman, Robert B.; Mahan, Shannon</p> <p>2014-01-01</p> <p>Quantitative geomorphic analysis combined with cosmogenic nuclide 10Be-based geochronology and denudation rates have been used to further the understanding of the Quaternary landscape development of the Mecca Hills, a zone of transpressional uplift along the southern end of the San <span class="hlt">Andreas</span> Fault, in southern California. The similar timing of convergent uplifts along the San <span class="hlt">Andreas</span> Fault with the initiation of the sub-parallel San Jacinto Fault suggest a possible link between the two tectonic events. The ages of alluvial fans and the rates of catchment-wide denudation have been integrated to assess the relative influence of climate and tectonic uplift on the development of catchments within the Mecca Hills. Ages for major geomorphic surfaces based on 10Be surface exposure dating of boulders and 10Be depth profiles define the timing of surface stabilization to 2.6 +5.6/–1.3 ka (Qyf1 surface), 67.2 ± 5.3 ka (Qvof2 surface), and 280 ± 24 ka (Qvof1 surface). Comparison of 10Be measurements from active channel deposits (Qac) and fluvial terraces (Qt) illustrate a complex history of erosion, sediment storage, and sediment transport in this environment. Beryllium-10 catchment-wide denudation rates range from 19.9 ± 3.2 to 149 ± 22.5 m/Ma and demonstrate strong correlations with mean catchment slope and with total active fault length normalized by catchment area. The lack of strong correlation with other geomorphic variables suggests that tectonic uplift and rock weakening have the greatest control. The currently measured topography and denudation rates across the Mecca Hills may be most consistent with a model of radial topographic growth in contrast to a model based on the rapid uplift and advection of crust.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GGG....17.3865W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GGG....17.3865W"><span>Experimental constraints on the relationship between clay abundance, clay fabric, and frictional behavior for the Central Deforming Zone of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wojatschke, Jasmaria; Scuderi, Marco M.; Warr, Laurence N.; Carpenter, Brett M.; Saffer, Demian; Marone, Chris</p> <p>2016-10-01</p> <p>The presence of smectite (saponite) in fault gouge from the Central Deforming Zone of the San <span class="hlt">Andreas</span> Fault at Parkfield, CA has been linked to low mechanical strength and aseismic slip. However, the precise relationship between clay mineral structure, fabric development, fault strength, and the stability of frictional sliding is not well understood. We address these questions through the integration of laboratory friction tests and FIB-SEM analysis of fault rock recovered from the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) borehole. Intact fault rock was compared with experimentally sheared fault gouge and different proportions of either quartz clasts or SAFOD clasts extracted from the sample. Nano-textural measurements show the development of localized clay particle alignment along shear folia developed within synthetic gouges; such slip planes have multiples of random distribution (MRD) values of 3.0-4.9. The MRD values measured are higher than previous estimates (MRD 1.5) that show lower degrees of shear localization and clay alignment averaged over larger volumes. The intact fault rock exhibits less well-developed nano-clay fabrics than the experimentally sheared materials, and MRD values decrease with smectite content. We show that the abundance, strength, and shape of clasts all influence fabric evolution via strain localization: quartz clasts yield more strongly developed clay fabrics than serpentine-dominated SAFOD clasts. Our results suggest that (1) both clay abundance and the development of nano-scale fabrics play a role in fault zone weakening and (2) aseismic creep is promoted by slip along clay shears with >20 wt % smectite content and MRD values ≥2.7.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024510','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024510"><span>Response of the San <span class="hlt">Andreas</span> fault to the 1983 Coalinga-Nuñez earthquakes: an application of interaction-based probabilities for Parkfield</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Toda, Shinji; Stein, Ross S.</p> <p>2002-01-01</p> <p>The Parkfield-Cholame section of the San <span class="hlt">Andreas</span> fault, site of an unfulfilled earthquake forecast in 1985, is the best monitored section of the world's most closely watched fault. In 1983, the M = 6.5 Coalinga and M = 6.0 Nuñez events struck 25 km northeast of Parkfield. Seismicity rates climbed for 18 months along the creeping section of the San <span class="hlt">Andreas</span> north of Parkfield and dropped for 6 years along the locked section to the south. Right-lateral creep also slowed or reversed from Parkfield south. Here we calculate that the Coalinga sequence increased the shear and Coulomb stress on the creeping section, causing the rate of small shocks to rise until the added stress was shed by additional slip. However, the 1983 events decreased the shear and Coulomb stress on the Parkfield segment, causing surface creep and seismicity rates to drop. We use these observations to cast the likelihood of a Parkfield earthquake into an interaction-based probability, which includes both the renewal of stress following the 1966 Parkfield earthquake and the stress transfer from the 1983 Coalinga events. We calculate that the 1983 shocks dropped the 10-year probability of a M ∼ 6 Parkfield earthquake by 22% (from 54 ± 22% to 42 ± 23%) and that the probability did not recover until about 1991, when seismicity and creep resumed. Our analysis may thus explain why the Parkfield earthquake did not strike in the 1980s, but not why it was absent in the 1990s. We calculate a 58 ± 17% probability of a M ∼ 6 Parkfield earthquake during 2001–2011.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.dtic.mil/docs/citations/ADA428700','DTIC-ST'); return false;" href="http://www.dtic.mil/docs/citations/ADA428700"><span>Beginning of the End: The Leadership of SS Obersturmbannfuehrer <span class="hlt">Jochen</span> Peiper</span></a></p> <p><a target="_blank" href="http://www.dtic.mil/">DTIC Science & Technology</a></p> <p></p> <p>2004-06-17</p> <p>handsome and daring idol. Nice pictures of Peiper were 55 taken to spread over Germany and he was seen in cinema news. He became in the true sense...practically impossible to advance. As a result of the thaw , the subsoil of the secondary roads had become soft and panzers soon plowed it up. It</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T51B2582M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T51B2582M"><span>Stratigraphic Record of Vertical Crustal Motions in the Past 2-3 Ma Along the Southern San <span class="hlt">Andreas</span> Fault, Mecca Hills, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McNabb, J. C.; Dorsey, R. J.</p> <p>2012-12-01</p> <p>Sedimentary rocks exposed on the NE margin of Coachella Valley in the Mecca Hills, southern California, record vertical crustal motions along the San <span class="hlt">Andreas</span> and associated strike-slip faults. A complex history of subsidence, transport, deposition, and uplift can be interpreted from mapping and measuring of sedimentary rocks, analysis of sedimentary lithofacies, and determination of transport directions from clast imbrications and cross-bedding. The 330 m-thick Mecca Fm rests non-conformably on Pre-Cambrian and Cretaceous crystalline rocks SW of the Painted Canyon Fault (PCF), and is not present NE of the PCF. The Mecca Fm is likely late Pliocene or early Pleistocene in age (Boley et al., 1994), and consists of red boulder conglomerate with imbricated clasts showing SSE to WSW paleoflow. It fines up into pebbly sandstone and is gradationally overlain by the lower member of the Palm Spring Formation (PSF). The PSF is likely younger than 2.0-2.6 Ma based on paleomagnetic studies (Boley et al., 1994) and older than the 0.74-Ma Thermal Canyon Ash high in the section (Rymer, 1989). The lower PSF is 340 m thick, with overall SE paleoflow and 3 lithofacies: (1) laterally extensive fluvial sandstone and siltstone; (2) plutonic-clast conglomerate; and (3) a thin lacustrine limestone unit that correlates across the PCF. The contact between the lower and upper members of the PSF changes from a conformable contact in a small area of the central Mecca Hills to an angular unconformity over a much larger area. The upper PSF is ~650 m thick (similar thickness across the PCF), displays overall transport to the SSE (with local exceptions), and has at least 7 lithofacies: (1) alluvial-fan pebbly sandstone and conglomerate; (2) fluvial sandstone and siltstone; (3) fluvial sandstone with conspicuous arkosic composition; (4) marginal-lacustrine bedded siltstone and sandstone; (5) eolian dune sandstone (6) lacustrine laminated siltstone and mudstone; and (7) local red conglomerate. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.G31A..06H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.G31A..06H"><span>Characterization of a Strain Rate Transient Along the San <span class="hlt">Andreas</span> and San Jacinto Faults Following the October 1999 Hector Mine Earthquake.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hernandez, D.; Holt, W. E.; Bennett, R. A.; Dimitrova, L.; Haines, A. J.</p> <p>2006-12-01</p> <p>We are continuing work on developing and refining a tool for recognizing strain rate transients as well as for quantifying the magnitude and style of their temporal and spatial variations. We determined time-averaged velocity values in 0.05 year epochs using time-varying velocity estimates for continuous GPS station data from the Southern California Integrated GPS Network (SCIGN) for the time period between October 1999 and February 2004 [Li et al., 2005]. A self-consistent model velocity gradient tensor field solution is determined for each epoch by fitting bi-cubic Bessel interpolation to the GPS velocity vectors and we determine model dilatation strain rates, shear strain rates, and the rotation rates. Departures of the time dependent model strain rate and velocity fields from a master solution, obtained from a time-averaged solution for the period 1999-2004, with imposed plate motion constraints and Quaternary fault data, are evaluated in order to best characterize the time dependent strain rate field. A particular problem in determining the transient strain rate fields is the level of smoothing or damping that is applied. Our current approach is to choose a damping that both maximizes the departure of the transient strain rate field from the long-term master solution and achieves a reduced chi-squared value between model and observed GPS velocities of around 1.0 for all time epochs. We observe several noteworthy time-dependent changes. First, in the Eastern California Shear Zone (ECSZ) region, immediately following the October 1999 Hector Mine earthquake, there occurs a significant spatial increase of relatively high shear strain rate, which encompasses a significant portion of the ECSZ. Second, also following the Hector Mine event, there is a strain rate corridor that extends through the Pinto Mt. fault connecting the ECSZ to the San <span class="hlt">Andreas</span> fault segment in the Salton Trough region. As this signal slowly decays, shear strain rates on segments of the San</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.T21D2858R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.T21D2858R"><span>Physical Models of a Locked-to-Creeping Transition Along a Strike-Slip Fault: Comparison with the San <span class="hlt">Andreas</span> Fault System in Central California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ross, E. O.; Titus, S.; Reber, J. E.</p> <p>2016-12-01</p> <p>In central California, the plate boundary geometry of the San <span class="hlt">Andreas</span> is relatively simple with several sub-parallel faults; however, slip behavior along the San <span class="hlt">Andreas</span> fault changes from locked to creeping. In the SE, the fault is locked along the Carrizo segment, which last ruptured in the 1857 Fort Tejon earthquake. Towards the NW, the slip rates increase from 0 to 28 mm/yr along the creeping segment, before decreasing towards the locked segment that last ruptured in the 1906 San Francisco earthquake. Near the southern transition from locked behavior to creeping behavior, the GPS velocity field and simple elastic models predict a region of contraction NE of the fault. This region coincides with numerous well-developed folds in the borderlands as well as a series of off-fault earthquakes in the 1980s. Similarly, a region of extension is predicted SW of the transition. This area coincides with a large basin near the town of Paso Robles. In order to understand the development of these regions of contraction and extension and characterize the orientation of vectors in the velocity field, we model the transition from locked to creeping behavior using physical experiments. The model consists of a layer of silicone (PDMS SGM-36) and a layer of wet kaolin, mimicking the ductile lower crust and brittle upper crust. We cut and lubricate the silicone along one section of the basement fault, simulating creeping behavior, while leaving the rest of the silicone intact across the fault to represent the locked portion. With this simple alteration to experimental conditions, we are consistently able to produce a mountain-and-basin pair that forms on either side of the transition at a deformation speed of 0.22mm/sec. To compare the physical model's results to the observed velocity field, we use particle image velocimetry software in conjunction with strain computation software (SSPX). PIV analysis shows highly reproducible vectors, allowing us to examine off-fault deformation</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70024275','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70024275"><span>Evidence for large earthquakes on the San <span class="hlt">Andreas</span> fault at the Wrightwood, California paleoseismic site: A.D. 500 to present</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Fumal, T.E.; Weldon, R.J.; Biasi, G.P.; Dawson, T.E.; Seitz, G.G.; Frost, W.T.; Schwartz, D.P.</p> <p>2002-01-01</p> <p>We present structural and stratigraphic evidence from a paleoseismic site near Wrightwood, California, for 14 large earthquakes that occurred on the southern San <span class="hlt">Andreas</span> fault during the past 1500 years. In a network of 38 trenches and creek-bank exposures, we have exposed a composite section of interbedded debris flow deposits and thin peat layers more than 24 m thick; fluvial deposits occur along the northern margin of the site. The site is a 150-m-wide zone of deformation bounded on the surface by a main fault zone along the northwest margin and a secondary fault zone to the southwest. Evidence for most of the 14 earthquakes occurs along structures within both zones. We identify paleoearthquake horizons using infilled fissures, scarps, multiple rupture terminations, and widespread folding and tilting of beds. Ages of stratigraphic units and earthquakes are constrained by historic data and 72 14C ages, mostly from samples of peat and some from plant fibers, wood, pine cones, and charcoal. Comparison of the long, well-resolved paleoseimic record at Wrightwood with records at other sites along the fault indicates that rupture lengths of past earthquakes were at least 100 km long. Paleoseismic records at sites in the Coachella Valley suggest that each of the past five large earthquakes recorded there ruptured the fault at least as far northwest as Wrightwood. Comparisons with event chronologies at Pallett Creek and sites to the northwest suggests that approximately the same part of the fault that ruptured in 1857 may also have failed in the early to mid-sixteenth century and several other times during the past 1200 years. Records at Pallett Creek and Pitman Canyon suggest that, in addition to the 14 earthquakes we document, one and possibly two other large earthquakes ruptured the part of the fault including Wrightwood since about A.D. 500. These observations and elapsed times that are significantly longer than mean recurrence intervals at Wrightwood and sites to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMED21D3471R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMED21D3471R"><span>Geomorphic evidence of active tectonics in the San Gorgonio Pass region of the San <span class="hlt">Andreas</span> Fault system: an example of discovery-based research in undergraduate teaching</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Reinen, L. A.; Yule, J. D.</p> <p>2014-12-01</p> <p>Student-conducted research in courses during the first two undergraduate years can increase learning and improve student self-confidence in scientific study, and is recommended for engaging and retaining students in STEM fields (PCAST, 2012). At Pomona College, incorporating student research throughout the geology curriculum tripled the number of students conducting research prior to their senior year that culminated in a professional conference presentation (Reinen et al., 2006). Here we present an example of discovery-based research in Neotectonics, a second-tier course predominantly enrolling first-and second-year students; describe the steps involved in the four week project; and discuss early outcomes of student confidence, engagement and retention. In the San Gorgonio Pass region (SGPR) in southern California, the San <span class="hlt">Andreas</span> fault undergoes a transition from predominantly strike-slip to a complex system of faults with significant dip-slip, resulting in diffuse deformation and raising the question of whether a large earthquake on the San <span class="hlt">Andreas</span> could propagate through the region (Yule, 2009). In spring 2014, seven students in the Neotectonics course conducted original research investigating quantifiable geomorphic evidence of tectonic activity in the SGPR. Students addressed questions of [1] unequal uplift in the San Bernardino Mountains, [2] fault activity indicated by stream knick points, [3] the role of fault style on mountain front sinuosity, and [4] characteristic earthquake slip determined via fault scarp degradation models. Students developed and revised individual projects, collaborated with each other on methods, and presented results in a public forum. A final class day was spent reviewing the projects and planning future research directions. Pre- and post-course surveys show increases in students' self-confidence in the design, implementation, and presentation of original scientific inquiries. 5 of 6 eligible students participated in research the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T41B4616M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T41B4616M"><span>Roles of the Mendocino Transform, Vizcaino Block, and Onshore King Range Terrane in Evolution of the Northern San <span class="hlt">Andreas</span> Fault System and Its Associated Slab Windows</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>McLaughlin, R. J.; Barth, G. A.; Scheirer, D. S.; Hoover, S. M.; Trehu, A. M.; Jencks, J.</p> <p>2014-12-01</p> <p>We integrate recent seismic reflection, geochemical and radiometric age data from basalts and sedimentary rocks along the Mendocino Transform (MT) and Gorda Escarpment, with basalt ages and biostratigraphy from the Miocene King Range terrane (KRT) of the Franciscan Complex, to better link the onshore and offshore geology and clarify how the northernmost San <span class="hlt">Andreas</span> Fault (SAF) evolved. The MT extends eastward from the Gorda Ridge spreading center, along the S side of the Gorda Plate, to the edge of the North American plate (NAP) and separates the Cascadia subduction zone to the north, from the modern SAF to the south. Between 127.5º W and the shoreline, the MT and Mendocino Ridge (MR) align with the N side of the S-tilted Vizcaino structural block (VB), a remnant of NAP captured by the Pacific plate ~12 Ma, when the MT was 480 km S of its present location. The modern SAF bounds the NE-side of the VB. The SW side of the VB is bounded at the base of the continental slope by the proto-San <span class="hlt">Andreas</span> fault (PSAF), where extinct remnants of the Pacific-Farallon ridge (PFR) interacted with the paleosubduction margin to form an incipient transform and several microplates, now part of the Pacific plate. Capture of the VB resulted from inboard breaking of the MT with a jump of the PSAF to the modern SAF. Dated ~20-12 Ma basaltic rocks from the MR between ~125º-128º W may be partly exhumed slab window underplating that formed beneath the VB during breakup of the PFR along the PSAF. High Fe and Ti relative to Mg in MR and KRT basalts, suggest eruption near ridge-transform intersections and perhaps, intratransform spreading.Onshore, high KRT relief aligns with the MR offshore. The KRT was assembled ~16-15 Ma (basalt K-Ar age; biostratigraphy); followed by its complex deformation and zeolitic metamorphism, indicating subduction to 5-8 km depth ~15-14 Ma and thermal metamorphism ~13.8 Ma (K-Ar age; vitrinite reflectance). The thermal overprint sets the KRT apart from adjacent</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMOS32A..03B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMOS32A..03B"><span>Geophysical Investigation of the Offshore Section of the Northern San <span class="hlt">Andreas</span> Fault: Fault Zone Geometries, Shallow Deformation Patterns, and Holocene Sediment Distribution</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Beeson, J. W.; Goldfinger, C.; Johnson, S. Y.</p> <p>2014-12-01</p> <p>We mapped a ~120 km offshore section of the northern San <span class="hlt">Andreas</span> Fault (NSAF) between Pt. Arena and Pt. Delgada using closely spaced seismic-reflection profiles, high-resolution multibeam bathymetry and marine magnetics data. This new dataset documents NSAF location and continuity, associated tectonic geomorphology, shallow stratigraphy and deformation. Variable deformation patterns in the generally narrow (~1-km-wide) fault zone are largely associated with fault trend and fault bends. We have described four regions (Pt. Arena, Basin, Shelter Cove, and Mendocino) along and adjacent to the NSAF based on fault trend, deformation styles, seismic stratigraphy, and seafloor bathymetry. The NSAF in the southern region (Pt. Arena) of the survey area is imaged as an arcuate fault trace that changes ~15° (327° to 342°) from south to north over a distance of about 50 km. The NSAF in the middle two regions (Basin and Shelter Cove) passes through two acute fault bends (~9° and ~8°), resulting in both an asymmetric "lazy z" sedimentary basin and an uplifted rocky shoal ("Tolo Bank"). The northwestern region of the survey area (Mendocino) lies west of the NSAF and Shelter Cove, and includes an east-trending fault zone related to the Mendocino transform fault that extends onshore near Punta Gorda. Using the densely spaced seismic-reflection profiles we have created an isopach map of Holocene sediment throughout the survey area. This isopach map has revealed thick sediment piles adjacent to coastal watersheds with high uplift rates. We infer from fault geometries, local bathymetry/topography and aero/marine magnetics that the NSAF zone transitions from a broadly distributed fault zone to a narrow fault zone over a short distance near Shelter Cove, Ca. At Shelter Cove the NSAF is characterized as a narrow, continuous fault. North of Shelter Cove the San <span class="hlt">Andreas</span> likely terminates into a series of "horse tail" splay thrust faults known as the Kings Range Thrust. These</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001AGUFM.S41A0577G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001AGUFM.S41A0577G"><span>High-Resolution Seismic Refraction and Reflection Images and Velocities Across the Mission Creek Strand of the San <span class="hlt">Andreas</span> Fault, Desert Hot Springs, San Bernadino County, CA</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gandhok, G.; Rymer, M.; Goldman, M.</p> <p>2001-12-01</p> <p>In March 1998, the U.S. Geological Survey and Michigan Tech conducted a 700-m-long, high-resolution (5-m shot point and geophone spacing) seismic reflection/refraction survey across the Mission Creek strand of the San <span class="hlt">Andreas</span> fault (SAF) in the town of Desert Hot Springs, California. Desert Hot Springs is located about 150 km east of Los Angeles along the San <span class="hlt">Andreas</span> fault and experiences considerable seismic activity, including a 1948 M 6.5 earthquake. The Mission Creek fault (MCF) poses an obvious earthquake hazard to Desert Hot Springs and other nearby desert communities, including Palm Springs, but it also affects the ground-water resources available to the desert communities because the fault forms a known ground-water barrier. The principal objectives of the seismic imaging survey were: to measure seismic velocities in the upper 100 m, to better locate the principal trace of the MCF in the upper few hundred meters, and to determine lateral variations in the depth of the ground-water table. Because of the acquisition method used, both seismic reflections and refractions were available from the same data. We inverted first-arrival refractions to develop a velocity model and used the resulting velocity model to stack and migrate the reflection images. Velocities range from about 800 m/s at the surface to about 3500 m/s at depths ranging from 50 m to about 200 m, with deeper depths to basement on the southeast side of the MCF. Sediments with a velocity of 1500 m/s, the velocity of the water table in unconsolidated sediments, is about 10 m deep on the northern end of the profile but increases rapidly to 80 m across the MCF. Seismic reflection images show multiple faults along the 700-m-long profile, and several faults appear to form a flower structure similar to the SAF at Parkfield, California. The Mission Creek strand of the SAF, therefore, represents a fault zone that is at least hundreds of meters wide. The proximity of the MCF to Desert Hot Springs and other</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70164444','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70164444"><span>Along-strike variations in fault frictional properties along the San <span class="hlt">Andreas</span> Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Harrington, Rebecca M.; Cochran, Elizabeth S.; Griffiths, Emily M.; Zeng, Xiangfang; Thurber, Clifford H.</p> <p>2016-01-01</p> <p>Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San <span class="hlt">Andreas</span> fault suggest slow‐slip earthquakes occur in a transition zone between the shallow fault, which accommodates slip by a combination of aseismic creep and earthquakes (<15  km depth), and the deep fault, which accommodates slip by stable sliding (>35  km depth). However, the spatial relationship between shallow earthquakes and LFEs remains unclear. Here, we present precise relocations of 34 earthquakes and 34 LFEs recorded during a temporary deployment of 13 broadband seismic stations from May 2010 to July 2011. We use the temporary array waveform data, along with data from permanent seismic stations and a new high‐resolution 3D velocity model, to illuminate the fine‐scale details of the seismicity distribution near Cholame and the relation to the distribution of LFEs. The depth of the boundary between earthquakes and LFE hypocenters changes along strike and roughly follows the 350°C isotherm, suggesting frictional behavior may be, in part, thermally controlled. We observe no overlap in the depth of earthquakes and LFEs, with an ∼5  km separation between the deepest earthquakes and shallowest LFEs. In addition, clustering in the relocated seismicity near the 2004 Mw 6.0 Parkfield earthquake hypocenter and near the northern boundary of the 1857 Mw 7.8 Fort Tejon rupture may highlight areas of frictional heterogeneities on the fault where earthquakes tend to nucleate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70036286','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70036286"><span>Tremor reveals stress shadowing, deep postseismic creep, and depth-dependent slip recurrence on the lower-crustal San <span class="hlt">Andreas</span> fault near Parkfield</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Shelly, David R.; Johnson, Kaj M.</p> <p>2011-01-01</p> <p>The 2003 magnitude 6.5 San Simeon and the 2004 magnitude 6.0 Parkfield earthquakes induced small, but significant, static stress changes in the lower crust on the central San <span class="hlt">Andreas</span> fault, where recently detected tectonic tremor sources provide new constraints on deep fault creep processes. We find that these earthquakes affect tremor rates very differently, consistent with their differing transferred static shear stresses. The San Simeon event appears to have cast a "stress shadow" north of Parkfield, where tremor activity was stifled for 3-6 weeks. In contrast, the 2004 Parkfield earthquake dramatically increased tremor activity rates both north and south of Parkfield, allowing us to track deep postseismic slip. Following this event, rates initially increased by up to two orders of magnitude for the relatively shallow tremor sources closest to the rupture, with activity in some sources persisting above background rates for more than a year. We also observe strong depth dependence in tremor recurrence patterns, with shallower sources generally exhibiting larger, less-frequent bursts, possibly signaling a transition toward steady creep with increasing temperature and depth. Copyright 2011 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/25521005','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/25521005"><span>Zoogeography of the San <span class="hlt">Andreas</span> Fault system: Great Pacific Fracture Zones correspond with spatially concordant phylogeographic boundaries in western North America.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gottscho, Andrew D</p> <p>2016-02-01</p> <p>The purpose of this article is to provide an ultimate tectonic explanation for several well-studied zoogeographic boundaries along the west coast of North America, specifically, along the boundary of the North American and Pacific plates (the San <span class="hlt">Andreas</span> Fault system). By reviewing 177 references from the plate tectonics and zoogeography literature, I demonstrate that four Great Pacific Fracture Zones (GPFZs) in the Pacific plate correspond with distributional limits and spatially concordant phylogeographic breaks for a wide variety of marine and terrestrial animals, including invertebrates, fish, amphibians, reptiles, birds, and mammals. These boundaries are: (1) Cape Mendocino and the North Coast Divide, (2) Point Conception and the Transverse Ranges, (3) Punta Eugenia and the Vizcaíno Desert, and (4) Cabo Corrientes and the Sierra Transvolcanica. However, discussion of the GPFZs is mostly absent from the zoogeography and phylogeography literature likely due to a disconnect between biologists and geologists. I argue that the four zoogeographic boundaries reviewed here ultimately originated via the same geological process (triple junction evolution). Finally, I suggest how a comparative phylogeographic approach can be used to test the hypothesis presented here. © 2014 Cambridge Philosophical Society.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70035969','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70035969"><span>Precise location of San <span class="hlt">Andreas</span> Fault tremors near Cholame, California using seismometer clusters: Slip on the deep extension of the fault?</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Shelly, D.R.; Ellsworth, W.L.; Ryberg, T.; Haberland, C.; Fuis, G.S.; Murphy, J.; Nadeau, R.M.; Burgmann, R.</p> <p>2009-01-01</p> <p>We examine a 24-hour period of active San <span class="hlt">Andreas</span> Fault (SAF) tremor and show that this tremor is largely composed of repeated similar events. Utilizing this similarity, we locate the subset of the tremor with waveforms similar to an identified low frequency earthquake (LFE) "master template," located using P and S wave arrivals to be ???26 km deep. To compensate for low signal-to-noise, we estimate event-pair differential times at "clusters" of nearby stations rather than at single stations. We find that the locations form a near-linear structure in map view, striking parallel to the SAF and near the surface trace. Therefore, we suggest that at least a portion of the tremor occurs on the deep extension of the fault, likely reflecting shear slip, similar to subduction zone tremor. If so, the SAF may extend to the base of the crust, ???10 km below the deepest regular earthquakes on the fault. ?? 2009 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70041916','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70041916"><span>Fault zone structure from topography: signatures of en echelon fault slip at Mustang Ridge on the San <span class="hlt">Andreas</span> Fault, Monterey County, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>DeLong, Stephen B.; Hilley, George E.; Rymer, Michael J.; Prentice, Carol</p> <p>2010-01-01</p> <p>We used high-resolution topography to quantify the spatial distribution of scarps, linear valleys, topographic sinks, and oversteepened stream channels formed along an extensional step over on the San <span class="hlt">Andreas</span> Fault (SAF) at Mustang Ridge, California. This location provides detail of both creeping fault landform development and complex fault zone kinematics. Here, the SAF creeps 10–14 mm/yr slower than at locations ∼20 km along the fault in either direction. This spatial change in creep rate is coincident with a series of en echelon oblique-normal faults that strike obliquely to the SAF and may accommodate the missing deformation. This study presents a suite of analyses that are helpful for proper mapping of faults in locations where high-resolution topographic data are available. Furthermore, our analyses indicate that two large subsidiary faults near the center of the step over zone appear to carry significant distributed deformation based on their large apparent vertical offsets, the presence of associated sag ponds and fluvial knickpoints, and the observation that they are rotating a segment of the main SAF. Several subsidiary faults in the southeastern portion of Mustang Ridge are likely less active; they have few associated sag ponds and have older scarp morphologic ages and subdued channel knickpoints. Several faults in the northwestern part of Mustang Ridge, though relatively small, are likely also actively accommodating active fault slip based on their young morphologic ages and the presence of associated sag ponds.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFMMR33C..04K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFMMR33C..04K"><span>Nucleation process of M 2 earthquakes on the San <span class="hlt">Andreas</span> fault predicted by rate-and-state fault models with SAFOD drill-core data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaneko, Y.; Carpenter, B. M.; Nielsen, S. B.</p> <p>2016-12-01</p> <p>Precursory aseismic slip lasting days to months prior to the initiation of earthquakes has been inferred from seismological observations. Similar precursory slip phenomena have also been observed in laboratory studies of shear rupture nucleation on frictional interfaces. However the mechanisms that govern rupture nucleation, even in idealized laboratory settings, have been widely debated. Here we show that a numerical model incorporating rate-and-state friction laws and elastic continuum can reproduce the behaviors of rupture nucleation seen in laboratory experiments. In particular, we find that both in laboratory experiments and simulations with a wide range of normal stresses, the nucleation consists of two distinct phases: initial slow propagation phase and faster acceleration phase, both of which are likely aseismic processes, followed by dynamic rupture propagation that radiates seismic waves. The distance at which the rupture transitions from the initial slow phase to the acceleration phase can be roughly predicted by a theoretical estimate of critical nucleation length. In addition, our analysis suggests that critical nucleation length and breakdown power derived from the Griffith-crack energy balance control the scaling of nucleating ruptures. Applying this model of rupture onset to data acquired during the San <span class="hlt">Andreas</span> Fault Observatory at Depth (SAFOD) experiment, we predict what the nucleation phase will look like for M 2 repeating earthquakes at a 3-km depth. Our results suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the M 2 earthquakes by instruments located close to the hypocenter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70016318','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70016318"><span>Crustal strain near the Big Bend of the San <span class="hlt">Andreas</span> Fault: analysis of the Los Padres-Tehachapi Trilateration Networks, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Eberhart-Phillips, D.; Lisowski, M.</p> <p>1990-01-01</p> <p>In the region of the Los Padres-Tehachapi geodetic network, the San <span class="hlt">Andreas</span> fault (SAF) changes its orientation by over 30?? from N40??W, close to that predicted by plate motion for a transform boundary, to N73??W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38??0.01??rad/yr at N63??W. In contrast, away from the SAF the strain orientations on both sides of the fault are consistent with the plate motion direction, with maximum shear rate of 0.19??0.01??rad/yr at N44??W. The best fitting Garlock fault model had computed left-lateral slip rate of 11??2mm/yr below 10km. Buried left-lateral slip of 15??6mm/yr on the Big Pine fault, within the Western Transverse Ranges, provides significant reduction in line length residuals; however, deformation there may be more complicated than a single vertical fault. A subhorizontal detachment on the southern side of the SAF cannot be well constrained by these data. -from Authors</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009JGRB..114.1313A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009JGRB..114.1313A"><span>Revised dates of large earthquakes along the Carrizo section of the San <span class="hlt">Andreas</span> Fault, California, since A.D. 1310 ± 30</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Akciz, Sinan O.; Grant Ludwig, Lisa; Arrowsmith, J. Ramon</p> <p>2009-01-01</p> <p>Precise knowledge of the age and magnitude of past earthquakes is essential for characterizing models of earthquake recurrence and key to forecasting future earthquakes. We present 28 new radiocarbon analyses that refine the chronology of the last five earthquakes at the Bidart Fan site along the Carrizo section of the south central San <span class="hlt">Andreas</span> Fault, which last ruptured during the Fort Tejon earthquake in A.D. 1857. The new data show that the penultimate earthquake in the Carrizo Plain occurred not earlier than A.D. 1640 and the modeled 95th percentile ranges of the three earlier earthquakes (and their mean) are A.D. 1540-1630 (1585), A.D. 1360-1425 (1393), and A.D. 1280-1340 (1310), indicating an average time interval of 137 ± 44 years between large earthquakes since A.D. 1310 ± 30. A robust earthquake recurrence model of the Carrizo section will require even more well-dated earthquakes for thorough characterization. However, these new data imply that since A.D. 1310 ± 30, the Carrizo section has failed more regularly and more often than previously thought.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70001224','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70001224"><span>The nature of surface tilt along 85 km of the San <span class="hlt">Andreas</span> fault-preliminary results form a 14-instrument array</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Mortensen, C.E.; Johnston, M.J.S.</p> <p>1975-01-01</p> <p>The continuous monitoring of surface deformation near active faults is clearly necessary for an understanding of elastic strain accumulation and elastic and anelastic strain release associated with earthquakes. Fourteen 2-component tiltmeters have been installed in shallow boreholes along 85 km of the currently most active section of the San <span class="hlt">Andreas</span> fault in the western United States. These instruments operate at a sensitivity of 10-8 radians. Five of these tiltmeters, extending along one 35 km section of the fault, have been in operation since June 1973. The results indicate that regional tectonic tilting has occurred before more than ten individual earthquakes or groups of earthquakes with epicenters within ten earthquake source dimensions of one or more instruments. This tilting has a time scale of up to a month depending on earthquake magnitude. The amplitude of these tilts exceeds by almost an order of magnitude that expected from a dislocation model of the source using seismically determined parameters. No indication of rapid or accelerated tilt just prior to these earthquakes has been seen. ?? 1975 Birkha??user Verlag.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018229','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018229"><span>Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Frankel, A.</p> <p>1993-01-01</p> <p>Three-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San <span class="hlt">Andreas</span> fault: a point source with moment magnitude M5 and an extended rupture with M6.5. A method is presented for incorporating a source with arbitrary focal mechanism in the grid. Synthetics from the 3-D simulations are compared with those derived from 2-D (vertical cross section) and 1-D (flat-layered) models. The synthetic seismograms from the 3-D and 2-D simulations exhibit large surface waves produced by conversion of incident S waves at the edge of the basin. Seismograms from the flat-layered model do not contain these converted surface waves and underestimate the duration of shaking. Maps of maximum ground velocities occur in localized portions of the basin. The location of the largest velocities changes with the rupture propagation direction. Contours of maximum shaking are also dependent on asperity positions and radiation pattern. -from Author</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017E%26PSL.460...76Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017E%26PSL.460...76Z"><span>Imaging the nonvolcanic tremor zone beneath the San <span class="hlt">Andreas</span> fault at Cholame, California using station-pair double-difference tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, Haijiang; Nadeau, Robert M.; Guo, Hao</p> <p>2017-02-01</p> <p>Nonvolcanic tremors have been detected deep beneath the San <span class="hlt">Andreas</span> fault (SAF) near Cholame, California. The tremors are modulated by small stress changes induced by Earth tides and regional and teleseismic earthquakes, implying elevated pore fluid pressure in the tremor zone. In this area, tremors lie beneath the seismogenic zone, limiting the usefulness of local earthquakes for resolving seismic velocity properties in the tremor zone. Station-pair double-difference tomography that uses differential tremor arrival times is used, for the first time, to provide new detailed information about the complexity of the lower-crust and upper-mantle transition and the occurrence of deep tremors in zones of localized low shear wave velocity anomalies. The anomalies may represent zones containing high-pore pressure fluids that migrate into the tremor zone episodically from the southwest and that are ultimately derived from dehydration of deep serpentinized mantle wedge material. These results improve our understanding of the tremor process, why tremors are concentrated in specific zones along the SAF, and possible relationships between tremors and large historic earthquakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70019264','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70019264"><span>Two-dimensional seismic image of the San <span class="hlt">Andreas</span> Fault in the Northern Gabilan Range, central California: Evidence for fluids in the fault zone</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Thurber, C.; Roecker, S.; Ellsworth, W.; Chen, Y.; Lutter, W.; Sessions, R.</p> <p>1997-01-01</p> <p>A joint inversion for two-dimensional P-wave velocity (Vp), P-to-S velocity ratio (Vp/Vs), and earthquake locations along the San <span class="hlt">Andreas</span> fault (SAF) in central California reveals a complex relationship among seismicity, fault zone structure, and the surface fault trace. A zone of low Vp and high Vp/Vs lies beneath the SAF surface trace (SAFST), extending to a depth of about 6 km. Most of the seismic activity along the SAF occurs at depths of 3 to 7 km in a southwest-dipping zone that roughly intersects the SAFST, and lies near the southwest edge of the low Vp and high Vp/Vs zones. Tests indicate that models in which this seismic zone is significantly closer to vertical can be confidently rejected. A second high Vp/Vs zone extends to the northeast, apparently dipping beneath the Diablo Range. Another zone of seismicity underlies the northeast portion of this Vp/Vs high. The high Vp/Vs zones cut across areas of very different Vp values, indicating that the high Vp/Vs values are due to the presence of fluids, not just lithology. The close association between the zones of high Vp/Vs and seismicity suggests a direct involvement of fluids in the faulting process. Copyright 1997 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.earthquakegeology.com/materials/proceedings/2016_Crestone.pdf','USGSPUBS'); return false;" href="http://www.earthquakegeology.com/materials/proceedings/2016_Crestone.pdf"><span>The Elizabeth Lake paleoseismic site: Rupture pattern constraints for the past ~800 years for the Mojave section of the south-central San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Bemis, Sean; Scharer, Katherine M.; Dolan, James F.; Rhodes, Ed</p> <p>2016-01-01</p> <p>The southern San <span class="hlt">Andreas</span> Fault in California has hosted two historic surface-rupturing earthquakes, the ~M7 1812 Wrightwood earthquake and the ~M7.9 1857 Fort Tejon earthquake (e.g., Sieh, 1978; Jacoby et al., 1988). Numerous paleoseismic studies have established chronologies of historic and prehistoric earthquakes at sites along the full length of the 1857 rupture (e.g., Sieh, 1978; Scharer et al., 2014). These studies provide an unparalleled opportunity to examine patterns of recent ruptures; however, at least two significant spatial gaps in high-quality paleoseismic sites remain. At ~100 km long each, these gaps contribute up to 100 km of uncertainty to paleo-rupture lengths and could also permit a surface rupture from an earthquake up to ~M7.2 to go undetected [using scaling relationships of Wells and Coppersmith (1994)]. Given the known occurrence of an ~M7 earthquake on this portion of the SAF (1812), it is critical to fill these gaps in order to better constrain paleo-rupture lengths and to increase the probability of capturing the full spatial record of surface rupturing earthquakes.   In this study, we target a new site within the 100 km long stretch of the San <span class="hlt">Andreas</span> Fault between the Frazier Mountain and Pallett Creek paleoseismic sites (Figure 1), near Elizabeth Lake, California. Prior excavations at the site during 1998-1999 encountered promising stratigraphy but these studies were hindered by shallow groundwater throughout the site. We began our current phase of investigations in 2012, targeting the northwestern end of a 40 x 350 m fault-parallel depression that defines the site (Figure 2). Subsequent investigations in 2013 and 2014 focused on the southeastern end of the depression where the fault trace is constrained between topographic highs and is proximal to an active drainage. In total, our paleoseismic investigations consist of 10 fault-perpendicular trenches that cross the depression (Figure 2) and expose a >2000 year depositional record</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T41D1599B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T41D1599B"><span>Fault History and Architecture of the Southernmost San <span class="hlt">Andreas</span> Fault and Brawley Seismic Zone: New Constraints from CHIRP Data Acquired in the Salton Sea</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brothers, D.; Seitz, G.; Williams, P.; Driscoll, N.; Kent, G.</p> <p>2006-12-01</p> <p>The Salton Trough is the boundary between spreading-center dominated extension in the Gulf of California and dextral strike-slip deformation along the San <span class="hlt">Andreas</span> Fault (SAF) system. The Salton Trough provides an ideal opportunity to image this transition in modes of deformation. The critical portion of this system, namely the intersection of the SAF and the Brawley Seismic Zone (BSZ) in the southern Salton Sea has not been imaged by geophysical methods. To address this problem, we conducted a pilot, high-resolution seismic CHIRP survey in the Salton Sea offshore Bombay Beach. CHIRP imaging, together with onshore field mapping and paleoseismic investigations, has the potential to define the interaction between the SAF and the BSZ, as well as delineate fault architecture and strain partitioning in the central Salton Trough. Preliminary onshore examination of Lake Cahuilla sediments reveal lake-level changes and earthquake event chronology for the last ~1,000 years, and suggest a relatively long period of seismic quiescence for the southern SAF preceded by several events with shorter recurrence intervals. Fault excavations have revealed several lake episodes separated by terrestrial horizons that include distinct features such as mud-cracks. New CHIRP data show potential correlation of faulted offshore stratigraphy with paleoseismic deformation documented at an excavation site 15 km to the north adjacent to Salt Creek. Profiles image a well-defined fault trending obliquely to the strike of the onshore SAF, and the observed trend is sub-parallel to the BSZ. Offset stratigraphy across the fault imaged in CHIRP profiles increases with depth, with a maximum vertical offset of ~6-8 m. Relief of ~.5 m exists across the post-1905 surface and most likely represents deposition mantling an older scarp. Assuming high amplitude reflectors observed in CHIRP data correlate with lowered lake levels associated with weathering and/or desiccation horizons, then we can correlate the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AGUFM.T51B2326S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AGUFM.T51B2326S"><span>Earthquake Recurrence and Slip Over the Past 4 - 5 events on the Southern Santa Cruz Mountains Section of the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Streig, A. R.; Dawson, T. E.; Weldon, R. J.</p> <p>2011-12-01</p> <p>The Santa Cruz Mountains section (SAS) of the San <span class="hlt">Andreas</span> fault last ruptured during the 1906 earthquake, an event that ruptured about 470 km, from Point Arena to San Juan Bautista, California. Paleoseismic studies on the SAS at the Grizzly Flat (GF) and Arano Flat - Mill Creek (AF) paleoseismic sites provide evidence of 1906 surface deformation, but have yielded differing records of prehistoric surface-fault ruptures. GF is located 14 km northwest of the AF site and records one 17th Century earthquake dated between 1632-1659 (Schwartz et al., 1996). The record at AF site records a younger penultimate earthquake between AD 1711 - 1770, with a third event between AD 1660-1670 (Fumal, in review). The AF sites suggest nine earthquakes in the past ~1000 years, and an average recurrence interval of 105 years over the past 1,000 years (Fumal et al., 2003). The Hazel Dell site is located approximately 9.5 km north of AF, between the AF and GF sites. This site has yielded good evidence of the most recent earthquake the 1906 surface rupture (E1), and 3 to 4 earlier events, including new evidence for two mid 1800's earthquakes. Evidence for the penultimate event, E2, is expressed as upward fault terminations within a massive sand infilling a topographic low. This sand infilled a depression formed by the pre-penultimate earthquake, E3. We identified milled wood stratigraphically below the pre-penultimate earthquake horizon, which suggests that surface rupturing earthquakes E2 and E3 occurred after deposition of the milled wood stratigraphic unit. Lumber harvesting began in the area around 1832, which suggests that earthquakes E2 and E3 are historical. Based on the presence of milled wood, the stratigraphic record at Hazel Dell appears more complete during the early historical period than at the AF and GF sites. These new event data for the SAS suggest more frequent surface rupturing earthquakes within historical time than previously recognized. We present a preliminary short</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.T13B0460B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.T13B0460B"><span>Flow and Chemistry Pulsations, Monterey: Implications for Stress Transient Modulations of Hydrologic and Geochemical Systems in the Greater San <span class="hlt">Andreas</span> Fault Zone</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Brown, K. M.; Fueri, E.; Hilton, D. R.</p> <p>2005-12-01</p> <p>Submarine fluid venting at continental shelf and slope regions has been recognized over the past ten years as an important, yet under-studied process in marine science. Seeps are now known to be a general feature of the hydrogeology of many tectonically active continental margins. The eastern Pacific margin is characterized by a variety of tectonic settings (i.e. convergent and strike-slip) where active venting of fluids and gases has been documented. Reports include vents off Alaska, Costa Rica, Monterey Bay, Eel River basin, and Heceta Bay, OR. Indications of seismic tremor, linked to hydrologic transience in the offshore regions of subduction zones have recently been published elsewhere (see Brown et al, EPSL 2005). We now address here the varying nature of submarine fluid discharges in a San <span class="hlt">Andreas</span> strike-slip setting. A key element of the proposed work is the combined multidisciplinary measurement of fluid flow, seep temperatures, and dissolved noble gases and chemistry of the Monterey seep sites at Extrovert Cliff. The seeps are situated close to several active strike-slip faults including the Monterey and San Gregorio fault zones. Initial results of 2 week deployments in 2004 of flow meters at Extravert Cliff indicated high flow rates and elevated seep temperatures that vary by as much as a factor of 2 on diurnal time scales with subtle changes over longer periods (>2 weeks). There are also indicative chemical signals of deeply sourced fluids that vary widely with time that show the following signals: 1) Elevated abundances of both mantle derived Helium (3He) as well as 4He and 40Ar of radiogenic crustal relevant trace element components; 2) Altered fluid chemistry (including, Ca Mg, Li and B); 3) The fluid temperature, flow rates, and gas chemistry, in particular, vary with time. We have both long-term and sub-diurnal variations in flow and temperature as well as the 3He/4He ratios, helium concentration, CO2 concentration and d13C values perhaps influenced</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005AGUFM.T23E..08T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005AGUFM.T23E..08T"><span>Chemical and Isotopic Composition of Water and Gases From the SAFOD Wells: Implications to the Dynamics of the San <span class="hlt">Andreas</span> Fault at Parkfield, California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thordsen, J. J.; Evans, W. C.; Kharaka, Y. K.; Kennedy, B. M.; van Soest, M.</p> <p>2005-12-01</p> <p>To investigate the source of fluids within the San <span class="hlt">Andreas</span> fault zone, we obtained downhole fluid samples from both the SAFOD pilot well (open hole at vertical depth of ~2.2 km) and the adjacent SAFOD main well, from open holes at depths of 1443-1470 m and 2540-2557 m. Each fluid sampling opportunity followed coring runs, which provided open holes at these depths, enabling formation fluid to enter the wells. Prior to coring, the drilling fluids were tagged with fluorescein and Rhodamine WT tracer dyes to allow for calculation of the contamination effects. We used an evacuated Kuster sampler and positive-displacement Westport samplers, that both allow for accurate determination of the dissolved gas concentrations. Chemical data and water-level measurements in the SAFOD pilot well and the shallower zone of SAFOD main well indicated that no significant amount of formation water was produced. Significant amounts of formation water, however, were produced from the deeper open hole of the SAFOD main well. The water level in the well rose ~60 m from completion of coring (October 1, 2004) to the first fluid sampling (April 13, 2005), when three samples were obtained, and rose ~12 m more by June 8, 2005, when an additional 4 samples were collected. Chemical data show that these samples are a mixture of formation water (75-80%) and the dye-tagged `KCl' drilling solution. High pH values (9.5-10.5) and high Ca concentrations indicate contamination from the cement used for casing the well. Mixing proportions and geochemical modeling, utilizing the tracer dyes and conservative solutes, are used to calculate the compositions of formation water. Results show a Na-Ca-Cl type water with a salinity of ~20,000 mg/L TDS, very low Mg (0.1 mg/L) and carbonate alkalinity (<1 mg/L), but moderate SO4 and very high DOC and organic acid anions. This chemical composition is typical of formation water from sedimentary rocks, such as oil field waters from California. The deepest samples from</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993JGR....9817867S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993JGR....9817867S"><span>What do the Cajon Pass stress measurements say about stress on the San <span class="hlt">Andreas</span> Fault? Comment on 'In Situ stress measurements to 3.5 km depth in Cajon Pass scientific research borehole: Implications for the mechanics of crustal faulting' by Mark D. Zoback and John H. Healy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scholz, C. H.; Saucier, J.</p> <p>1993-10-01</p> <p>The results of stress measurements made in the deep borehole at Cajon Pass have long been awaited in the hope that they would resolve the long-lived controversy over the strength of the San <span class="hlt">Andreas</span> fault. Insofar as this central goal is concerned, Zoback and Healy (1992) summarized their result with the statement, 'However, data on the orientation of maximum horizontal compression in the borehole from 1.75-3.5 km (N 57 deg E +/- 19 deg) indicate that the San <span class="hlt">Andreas</span> must be quite weak as a complete absence of right-lateral shear stress resolved on planes parallel to the approximately N 60 deg W striking San <span class="hlt">Andreas</span> fault is observed'. The casual reader, who might think the adjective 'right-lateral' to be redundant in this context, may perhaps be forgiven in omitting it while quoting the result. Nevertheless, this would be incorrect because this adjective is paramount: the measured fault-parallel shear stresses were high, but left lateral. Our point is not to suggest that the quoted statement may be misleading but that it is wrong. Not only cannot the Cajon Pass stress measurements be used to show that the San <span class="hlt">Andreas</span> fault is weak, but it does not appear that they provide any information on the magnitude of shear stresses on the San <span class="hlt">Andreas</span> fault itself.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70159233','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70159233"><span>Using a modified time-reverse imaging technique to locate low-frequency earthquakes on the San <span class="hlt">Andreas</span> Fault near Cholame, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Horstmann, Tobias; Harrington, Rebecca M.; Cochran, Elizabeth S.</p> <p>2015-01-01</p> <p>We present a new method to locate low-frequency earthquakes (LFEs) within tectonic tremor episodes based on time-reverse imaging techniques. The modified time-reverse imaging technique presented here is the first method that locates individual LFEs within tremor episodes within 5 km uncertainty without relying on high-amplitude P-wave arrivals and that produces similar hypocentral locations to methods that locate events by stacking hundreds of LFEs without having to assume event co-location. In contrast to classic time-reverse imaging algorithms, we implement a modification to the method that searches for phase coherence over a short time period rather than identifying the maximum amplitude of a superpositioned wavefield. The method is independent of amplitude and can help constrain event origin time. The method uses individual LFE origin times, but does not rely on a priori information on LFE templates and families.We apply the method to locate 34 individual LFEs within tremor episodes that occur between 2010 and 2011 on the San <span class="hlt">Andreas</span> Fault, near Cholame, California. Individual LFE location accuracies range from 2.6 to 5 km horizontally and 4.8 km vertically. Other methods that have been able to locate individual LFEs with accuracy of less than 5 km have mainly used large-amplitude events where a P-phase arrival can be identified. The method described here has the potential to locate a larger number of individual low-amplitude events with only the S-phase arrival. Location accuracy is controlled by the velocity model resolution and the wavelength of the dominant energy of the signal. Location results are also dependent on the number of stations used and are negligibly correlated with other factors such as the maximum gap in azimuthal coverage, source–station distance and signal-to-noise ratio.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70030759','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70030759"><span>Paleoearthquakes on the southern San <span class="hlt">Andreas</span> Fault, Wrightwood, California, 3000 to 1500 B.C.: A new method for evaluating paleoseismic evidence and earthquake horizons</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scharer, K.M.; Weldon, R.J.; Fumal, T.E.; Biasi, G.P.</p> <p>2007-01-01</p> <p>We present evidence of 11-14 earthquakes that occurred between 3000 and 1500 B.C. on the San <span class="hlt">Andreas</span> fault at the Wrightwood paleoseismic site. Earthquake evidence is presented in a novel form in which we rank (high, moderate, poor, or low) the quality of all evidence of ground deformation, which are called "event indicators." Event indicator quality reflects our confidence that the morphologic and sedimentologic evidence can be attributable to a ground-deforming earthquake and that the earthquake horizon is accurately identified by the morphology of the feature. In four vertical meters of section exposed in ten trenches, we document 316 event indicators attributable to 32 separate stratigraphic horizons. Each stratigraphic horizon is evaluated based on the sum of rank (Rs), maximum rank (Rm), average rank (Ra), number of observations (Obs), and sum of higher-quality event indicators (Rs>1). Of the 32 stratigraphic horizons, 14 contain 83% of the event indicators and are qualified based on the number and quality of event indicators; the remaining 18 do not have satisfactory evidence for further consideration. Eleven of the 14 stratigraphic horizons have sufficient number and quality of event indicators to be qualified as "probable" to "very likely" earthquakes; the remaining three stratigraphic horizons are associated with somewhat ambiguous features and are qualified as "possible" earthquakes. Although no single measurement defines an obvious threshold for designation as an earthquake horizon, Rs, Rm, and Rs>1 correlate best with the interpreted earthquake quality. Earthquake age distributions are determined from radio-carbon ages of peat samples using a Bayesian approach to layer dating. The average recurrence interval for the 10 consecutive and highest-quality earthquakes is 111 (93-131) years and individual intervals are ??50% of the average. With comparison with the previously published 14-15 earthquake record between A.D. 500 and present, we find no evidence</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.usgs.gov/sir/2004/5206/','USGSPUBS'); return false;" href="https://pubs.usgs.gov/sir/2004/5206/"><span>Thrust-induced collapse of mountains-an example from the "Big Bend" region of the San <span class="hlt">Andreas</span> Fault, western transverse ranges, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kellogg, Karl S.</p> <p>2005-01-01</p> <p>Mount Pinos and Frazier Mountain are two prominent mountains just south of the San <span class="hlt">Andreas</span> fault in the western Transverse Ranges of southern California, a region that has undergone rapid Quaternary contraction and uplift. Both mountains are underlain, at least in part, by thrusts that place granitic and gneissic rocks over sedimentary rocks as young as Pliocene. Broad profiles and nearly flat summits of each mountain have previously been interpreted as relicts of a raised erosion surface. However, several features bring this interpretation into question. First, lag or stream gravels do not mantle the summit surfaces. Second, extensive landslide deposits, mostly pre?Holocene and deeply incised, mantle the flanks of both mountains. Third, a pervasive fracture and crushed?rock network pervades the crystalline rocks underlying both mountains. The orientation of the fractures, prominent in roadcuts on Mount Pinos, is essentially random. 'Hill?and?saddle' morphology characterizes ridges radiating from the summits, especially on Mount Pinos; outcrops are sparse on the hills and are nonexistent in the saddles, suggesting fractures are concentrated in the saddles. Latest movement on the thrusts underlying the two mountain massifs is probably early Quaternary, during which the mountains were uplifted to considerably higher (although unknown) elevations than at present. A model proposes that during thrusting, ground accelerations in the hanging wall, particularly near thrust tips, were high enough to pervasively fracture the hanging?wall rocks, thereby weakening them and producing essentially an assemblage of loose blocks. Movement over flexures in the fault surface accentuated fracturing. The lowered shear stresses necessary for failure, coupled with deep dissection and ongoing seismic activity, reduced gravitational potential by spreading the mountain massifs, triggering flanking landslides and producing broad, flat?topped mountains. This study developed from mapping in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70020516','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70020516"><span>Evolution of the Gorda Escarpment, San <span class="hlt">Andreas</span> fault and Mendocino triple junction from multichannel seismic data collected across the northern Vizcaino block, offshore northern California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Godfrey, N.J.; Meltzer, A.S.; Klemperer, S.L.; Trehu, A.M.; Leitner, B.; Clarke, S.H.; Ondrus, A.</p> <p>1998-01-01</p> <p>The Gorda Escarpment is a north facing scarp immediately south of the Mendocino transform fault (the Gorda/Juan de Fuca-Pacific plate boundary) between 126??W and the Mendocino triple junction. It elevates the seafloor at the northern edge of the Vizcaino block, part of the Pacific plate, ??? 1.5 km above the seafloor of the Gorda/Juan de Fuca plate to the north. Stratigraphy interpreted from multichannel seismic data across and close to the Gorda Escarpment suggests that the escarpment is a relatively recent pop-up feature caused by north-south compression across the plate boundary. Close to 126??W. the Vizcaino block acoustic basement shallows and is overlain by sediments that thin north toward the Gorda Escarpment. These sediments are tilted south and truncated at the seafloor. By contrast, in a localized region at the eastern end of the Gorda Escarpment, close to the Mendocino triple junction, the top of acoustic basement dips north and is overlain by a 2-km-thick wedge of pre-11 Ma sedimentary rocks that thickens north, toward the Gorda Escarpment. This wedge of sediments is restricted to the northeast corner of the Vizcaino block. Unless the wedge of sediments was a preexisting feature on the Vizcaino block before it was transferred from the North American to the Pacific plate, the strong spatial correlation between the sedimentary wedge and the triple junction suggests the entire Vizcaino block, with the San <span class="hlt">Andreas</span> at its eastern boundary, has been part of the Pacific plate since significantly before 11 Ma.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S33F4929P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S33F4929P"><span>Tectonic Tremor along the Parkfield-Cholame Section of the San <span class="hlt">Andreas</span> Fault Triggered by the 2014 M6.0 South Napa and Other Regional Earthquakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peng, Z.; Shelly, D. R.; Ellsworth, W. L.; Aiken, C.</p> <p>2014-12-01</p> <p>Large distant earthquakes are known to trigger deep tectonic tremor along the Parkfield-Cholame section of the San <span class="hlt">Andreas</span> Fault. The triggered tremors are mostly modulated by dynamic stresses from large-amplitude surface waves, although sometimes teleseismic body waves are also capable of triggering tremor. However, there are relatively few observations of triggering from regional-distance earthquakes. The 2014 M6.0 South Napa earthquake is the largest earthquake occurring in the Bay Area since the 1989 M6.9 Loma Prieta earthquake. It has triggered an increase of microearthquake activities in the Geysers geothermal field during and immediately following the mainshock waves (Meng et al., this meeting). Although we did not observe any obvious modulated tremors at Parkfield-Cholame during the Napa wavetrain, a small tremor episode occurred just NW of Parkfield coincident with the arrival of seismic waves at the 2.5 km-deep seismometer in the SAFOD main hole. A major tremor episode began about 10 hours later near Cholame (SE of Parkfield). This episode is one of the largest seen over the past several years, containing intense activity for ~3 days and taking more than 3 weeks to return to background levels. While it is impossible to entirely rule out random coincidence at this stage, minor activity beneath Cholame started only 90 minutes after the Napa event in a zone with significant episodes only every few months, suggesting that the major tremor episode may have been triggered. In addition, we plan to systematically examine both tremor catalogs and continuous waveforms following the occurrence of other recent earthquakes in California to better understand the ambient conditions and factors (including amplitude and frequency of the incoming waves) controlling tremor triggering in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015GGG....16.3946B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015GGG....16.3946B"><span>San <span class="hlt">Andreas</span> Fault dip, Peninsular Ranges mafic lower crust and partial melt in the Salton Trough, Southern California, from ambient-noise tomography</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barak, Shahar; Klemperer, Simon L.; Lawrence, Jesse F.</p> <p>2015-11-01</p> <p>We use ambient-noise tomography to improve CVM-H11.9, a community velocity model of southern California. Our new 3-D shear-velocity model with 0.05° x 0.05° lateral and 1 km vertical blocks reveals new structure beneath the San <span class="hlt">Andreas</span> Fault (SAF), Peninsular Ranges batholith (PRB), southern Sierra Nevada batholith (SNB), and the Salton Trough (ST). We use 4 years of data recorded on 849 broadband stations, vastly more than previous studies and including our own broadband Salton Seismic Imaging Project, a 40 station transect across the ST, as well as other campaign stations in both Mexico and the United States. Mean lower crust and upper mantle wave speeds (3.6 km/s at 20 km, 4.2 km/s at 40 km) are low by global standards. Across the SAF, southeast of San Gorgonio Pass, we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the Moho. Beneath the western PRB and westernmost southern SNB, we observe relatively high shear velocities (≥3.8 km/s) in the lower crust that we interpret as the mafic roots of the overlying arc. Relatively high-velocity upper mantle (up to ˜4.5 km/s) may be part of the intact arc, or possibly a remnant of the Farallon plate. Beneath the ST, we observe zones of low shear-velocity in the lower crust and upper mantle which permit up to ˜4.5% melt in the lower crust and up to ˜6% melt in the upper mantle, depending on the assumed composition and pore geometry. Our results preclude the existence of older continental crust beneath the ST and support the creation of new crust beneath the ST.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70047748','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70047748"><span>Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San <span class="hlt">Andreas</span> system</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Moore, Diane E.; Lockner, David A.</p> <p>2013-01-01</p> <p>The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San <span class="hlt">Andreas</span> system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70041940','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70041940"><span>Timing of large earthquakes during the past 500 years along the Santa Cruz Mountains segment of the San <span class="hlt">Andreas</span> fault at Mill Canyon, near Watsonville, California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Fumal, Thomas E.</p> <p>2012-01-01</p> <p>A paleoseismic investigation across the Santa Cruz Mountains section of the San <span class="hlt">Andreas</span> fault at Mill Canyon indicates that four surface‐rupturing earthquakes have occurred there during the past ~500  years. At this site, right‐lateral fault slip has moved a low shutter ridge across the mouth of the canyon, ponding latest Holocene sediments. These alluvial deposits are deformed along a narrow zone of faulting. There is excellent evidence for a 1906 (M 7.8) and three earlier earthquakes consisting of well‐developed fissures, scarps, and colluvial wedges. Deformation resulting from the earlier earthquakes is comparable to that from 1906, suggesting they also were large‐magnitude events. The earthquake prior to 1906 occurred either about A.D. 1750 (1711–1770) or A.D. 1855 (1789–1904), depending on assumptions incorporated into two alternative OxCal models. If the later age range is correct, then the earthquake may have been a historical early‐to‐mid‐nineteenth‐century earthquake, possibly the A.D. 1838 earthquake. Both models are viable, and there is no way to select one over the other with the available data. Two earlier earthquakes occurred about A.D. 1690 (1660–1720) and A.D. 1522 (1454–1605). Using OxCal, recalculation of the age of the reported penultimate earthquake reported from the Grizzly Flat site, located about 10 km northwest of Mill Canyon, indicates it occurred about A.D. 1105–1545, earlier than any of the past three earthquakes, and possibly correlates to the fourth earthquake at Mill Canyon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.S23C4543X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.S23C4543X"><span>Imaging the Fine-Scale Structure of the San <span class="hlt">Andreas</span> Fault in the Northern Gabilan Range with Explosion and Earthquake Sources</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xin, H.; Thurber, C. H.; Zhang, H.; Wang, F.</p> <p>2014-12-01</p> <p>A number of geophysical studies have been carried out along the San <span class="hlt">Andreas</span> Fault (SAF) in the Northern Gabilan Range (NGR) with the purpose of characterizing in detail the fault zone structure. Previous seismic research has revealed the complex structure of the crustal volume in the NGR region in two-dimensions (Thurber et al., 1996, 1997), and there has been some work on the three-dimensional (3D) structure at a coarser scale (Lin and Roecker, 1997). In our study we use earthquake body-wave arrival times and differential times (P and S) and explosion arrival times (only P) to image the 3D P- and S-wave velocity structure of the upper crust along the SAF in the NGR using double-difference (DD) tomography. The earthquake and explosion data types have complementary strengths - the earthquake data have good resolution at depth and resolve both Vp and Vs structure, although only where there are sufficient seismic rays between hypocenter and stations, whereas the explosions contribute very good near-surface resolution but for P waves only. The original dataset analyzed by Thurber et al. (1996, 1997) included data from 77 local earthquakes and 8 explosions. We enlarge the dataset with 114 more earthquakes that occurred in the study area, obtain improved S-wave picks using an automated picker, and include absolute and cross-correlation differential times. The inversion code we use is the algorithm tomoDD (Zhang and Thurber, 2003). We assess how the P and S velocity models and earthquake locations vary as we alter the inversion parameters and the inversion grid. The new inversion results show clearly the fine-scale structure of the SAF at depth in 3D, sharpening the image of the velocity contrast from the southwest side to the northeast side.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015E%26PSL.412..163D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015E%26PSL.412..163D"><span>Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San <span class="hlt">Andreas</span> Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deeds, Daniel A.; Kulongoski, Justin T.; Mühle, Jens; Weiss, Ray F.</p> <p>2015-02-01</p> <p>Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San <span class="hlt">Andreas</span> Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (Cre; ∼30 fmol kg-1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1-9 times Cre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10-980 times Cre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20-100 km) suggests that the SAFS potentially emits (0.3- 1) ×10-1 kg CF4 yr-1 to the Earth's surface. For comparison, the chemical weathering of ∼ 7.5 ×104km2 of granitic rock in California is estimated to release (0.019- 3.2) ×10-1 kg CF4 yr-1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial-interglacial transitions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006AGUFM.T43D1671B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006AGUFM.T43D1671B"><span>The Character of Transpressive Deformation Along the Southern San <span class="hlt">Andreas</span> Fault, Based on Exhumation of the Northern San Gabriel Mountains, Southern California</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Buscher, J. T.; Spotila, J. A.</p> <p>2006-12-01</p> <p>The relationship between transpression and near-field mountain building along major strike-slip faults is yet to be fully characterized. The southern San <span class="hlt">Andreas</span> fault (SAF) has high obliquity (greater than 20 degrees) and rugged topography indicative of major near-field uplift, however vertical deformation has not been fully constrained along this stretch of the fault. The northern San Gabriel Mountains (NSGM) extend along a 50 km segment of the southern SAF, but little is known about the exhumational history of the range. Prominent ridges extend parallel to the SAF in the NSGM, suggesting that pure-shear deformation is generated from the fault zone itself as observed in the San Gabriel and San Bernardino Mountains. However, apatite (U-Th)/He ages and topographic analyses from the NSGM suggest that there is no increase in transpressive deformation towards the SAF. Elongate ridges located within the fault zone (Liebre Mountain and Portal Ridge) have ages older than 10 Ma and crests that have been planed by erosion, suggesting that there has been minimal near- field exhumation generated from the fault zone. The youngest ages (4-5 Ma) are located further away from the SAF in more rugged terrain southeast of Liebre Mountain, implying that there has been asymmetrical exhumation subparallel to the SAF. We interpret this deformation pattern as a short-lived block tilting event that initiated at a transitional restraining bend at approximately 5 Ma as the San Gabriel fault stepped eastward to create the modern SAF. If the NSGM formed by a local fault complexity at this time, then it suggests that near-field transpressive deformation generated from strike-slip fault systems is heterogeneous and that secondary structures play more of a significant role in transpressive mountain uplift.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70026358','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70026358"><span>New insights on stress rotations from a forward regional model of the San <span class="hlt">Andreas</span> fault system near its Big Bend in southern California</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Fitzenz, D.D.; Miller, S.A.</p> <p>2004-01-01</p> <p>Understanding the stress field surrounding and driving active fault systems is an important component of mechanistic seismic hazard assessment. We develop and present results from a time-forward three-dimensional (3-D) model of the San <span class="hlt">Andreas</span> fault system near its Big Bend in southern California. The model boundary conditions are assessed by comparing model and observed tectonic regimes. The model of earthquake generation along two fault segments is used to target measurable properties (e.g., stress orientations, heat flow) that may allow inferences on the stress state on the faults. It is a quasi-static model, where GPS-constrained tectonic loading drives faults modeled as mostly sealed viscoelastic bodies embedded in an elastic half-space subjected to compaction and shear creep. A transpressive tectonic regime develops southwest of the model bend as a result of the tectonic loading and migrates toward the bend because of fault slip. The strength of the model faults is assessed on the basis of stress orientations, stress drop, and overpressures, showing a departure in the behavior of 3-D finite faults compared to models of 1-D or homogeneous infinite faults. At a smaller scale, stress transfers from fault slip transiently induce significant perturbations in the local stress tensors (where the slip profile is very heterogeneous). These stress rotations disappear when subsequent model earthquakes smooth the slip profile. Maps of maximum absolute shear stress emphasize both that (1) future models should include a more continuous representation of the faults and (2) that hydrostatically pressured intact rock is very difficult to break when no material weakness is considered. Copyright 2004 by the American Geophysical Union.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70018604','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70018604"><span>Compressive and tensile failure at high