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Sample records for jochen zschau andreas

  1. [Andrea's story].

    PubMed

    Nobili, A; Tognoni, G; Staszewsky, L

    2001-01-01

    First-hand accounts of illness experiences provide important insights for other patients and their carers and can be a powerful tool for patient information and professional education. Andrea was ran over by a motor-bike while he was carried by bike and reported a complicated femur fracture. Three different representations of the story are reported and confronted: the bold chronicle of events, that sets the scenery and time sequence; Andrea's mother point of view on what happened after the accident, and during the course of the illness; and Andrea's story, told with his words and drawings. The methodological comments offered as discussion, stress how the collection of relevant patients stories can be a valuable research resource because it can offer a broad perspective which cannot be obtained by other means. PMID:11910835

  2. [Andreas Vesalius in Pisa].

    PubMed

    Ciranni, Rosalba

    2010-01-01

    Andreas Vesalius is the most commanding figure in European medicine, after Galen and before Harvey. His dissections and lectures were in considerable demand. Having just published the De humani corporis fabrica, and before operating as a private physician of Emperor Charles V, the anatomist spent some months conducting demonstrations of anatomy at the universities of Bologna, Pisa and Florence. The present study aim to reconstruct the journey he made to Pisa, where he was invited by Duke Cosimo I De' Medici. The work of Andrea Corsini and O'Malley, the study of Vesalius' Epistola... rationem modumque propinandi radicis Chynae dedocti... , and other documents make possible a more detailed reconstruction of the period Vesalius spent in the Nuovo Studio Pisano, carrying out public human dissections, discussing and refuting most of the Galenic doctrine. PMID:21563472

  3. 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.

  4. 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.

  5. 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).

  6. [Andreas Vesalius--the life].

    PubMed

    De Caro, Raffaele; Goddeeris, Theodoor; Plessas, Pavlos; Biebrouck, Maurits; Steeno, Omer

    2014-01-01

    The details of Vesalius' life can be found in Charles O'Malley, Andreas Vesalius of Brussels, 1514-1564, (University of California Press, 1964) and in Stephen N Joffe, Andreas Vesalius: The Making, The Madman, and the Myth, (Persona Publishing, 2009). This session reviews the circumstances of his last voyage and his death and other aspects of his life. PMID:25181776

  7. Andreas Vesalius' corpses.

    PubMed

    Biesbrouck, Maurits; Steeno, Omer

    2014-01-01

    Judging from his writings, Andreas Vesalius must have had dozens of bodies at his disposal, thirteen of which were definitely from before 1543. They came from cemeteries, places of execution or hospitals. Not only did his students help him obtain the bodies, but also public and judicial authorities. At first, he used the corpses for his own learning purposes, and later to teach his students and to write De humani corporis fabrica, his principal work. Clearly he had an eye for comparative anatomy. He observed anatomical variants and studied foetal anatomy. Occasionally, he would dissect a body to study physiological processes, while the post-mortems on the bodies brought in by the families of the deceased gave him an insight into human pathology. Some of his dissection reports have been preserved. PMID:25310608

  8. [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. PMID:8209577

  9. GOES video of Tropical Storm Andrea

    NASA Video Gallery

    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...

  10. Update: San Andreas Fault experiment

    NASA Technical Reports Server (NTRS)

    Christodoulidis, D. C.; Smith, D. E.

    1984-01-01

    Satellite laser ranging techniques are used to monitor the broad motion of the tectonic plates comprising the San Andreas Fault System. The San Andreas Fault Experiment, (SAFE), has progressed through the upgrades made to laser system hardware and an improvement in the modeling capabilities of the spaceborne laser targets. Of special note is the launch of the Laser Geodynamic Satellite, LAGEOS spacecraft, NASA's only completely dedicated laser satellite in 1976. The results of plate motion projected into this 896 km measured line over the past eleven years are summarized and intercompared.

  11. GOES-14 Sees Remnants of Andrea

    NASA Video Gallery

    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 ...

  12. Radon emanation on San Andreas Fault

    USGS Publications Warehouse

    King, C.-Y.

    1978-01-01

    Subsurface radon emanation monitored in shallow dry holes along an active segment of the San Andreas fault in central California shows spatially coherent large temporal variations that seem to be correlated with local seismicity. ??1978 Nature Publishing Group.

  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 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

  14. 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. PMID:8725935

  15. Satellite Shows Landfall and Movement of Tropical Storm Andrea

    NASA Video Gallery

    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...

  16. 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

  17. 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

  18. Andreas Vesalius--the reformer of anatomy.

    PubMed

    Holomanova, A; Ivanova, A; Brucknerova, I; Benuska, J

    2001-01-01

    This paper deals with two main topics. The first part provides data on the life of Andreas Vesalius, a scholar and anatomist of the 16th century, and describes the environment in which he lived and worked. It highlights his personality of a great doctor and teacher and points out the importance of his scientific methods and techniques as opposed to speculative methods that were prevalent in the scientific research in those days. The second part of the paper is devoted to the characteristics and description of his famous and, given the times he lived in, grand work called "De Humani Corporis Fabrica", which opened a new epoch in the history of anatomy. Andreas Vesalius is considered to be the founder of the science of anatomy which is based on observation and experience gained by using scalpel on dead bodies of humans. This is how he proved the then valid statements wrong. This complex view of life and work of Andreas Vesalius is aimed at highlighting the milestone which he represents in this traditional science of anatomy that has been conscientiously developed since the Classical times. (Fig. 4, Ref. 6.) PMID:11723674

  19. 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. PMID:21560612

  20. Homage to genial anatomist - Andreas Vesalius.

    PubMed

    Brucknerova, Ingrid; Holomanova, Anna

    2013-01-01

    The paper highlights the personality of the founder of modern anatomy, who was able to use his knowledge and skills to change the view on the construction of the human body extending over centuries. He introduced a new scientific approach and highlighted the importance of autopsies for understanding of human body which carefully demonstrated and documented. De humani corporis fabrica - the spectacular work, in which he summarized results of his theoretical and practical findings, has opened a new path for the study of anatomy. Andreas Vesalius became a pioneer in the history of medical education. In 2014 will pass 500 years since his birth. PMID:24378449

  1. 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. 

  2. [Andreas Vesalius in the Spanish Court].

    PubMed

    Izumi, Hyonosuke

    2004-12-01

    After the publication of "Fabrica," Andreas Vesalius entered the Spanish court and became a court physician to Charles the Fifth, Holy Roman Emperor, and then to Philip the Second, Spanish king. The author studied this process and its historical background. The ancestors of Vesalius had close relations with the Hapsburgs and the dukes of BUrgundy, and served them as court physician or a court pharmacist. Vesalius was born in Brussels, obtained his degree at the University of Padua, Italy, became professor of anatomy and surgery there, and published "Tabulae Anatomicae Sex" and "Fabrica."In the ear of the Spanish court, the treatments of Henry the Second, French king, and of Don Carlos, Spanish crown prince, are famous among Vesalius' medical contributions. In the year of his resignation, Charles the Fifth conferred the title of count palatine on Vesalius. PMID:15818875

  3. Taking the pulse of the San Andreas Fault

    USGS Publications Warehouse

    Kerr, R. A.

    1989-01-01

    But the same research suggests that the fault's average behavior could be misleading. A newly refined dating of the past 10 San Andreas ruptures adjacent to Los Angeles reveals a previously unrecognized clustering of large earthquakes in bunches of two or three. If this pattern were to hold, Los Angeles would wait at least another 80 years for another jolt from there. But the San Andreas is not that easy to get around. 

  4. San Andreas Fault in the Carrizo Plain

    NASA Technical Reports Server (NTRS)

    2000-01-01

    The 1,200-kilometer (800-mile)San Andreas is the longest fault in California and one of the longest in North America. This perspective view of a portion of the fault was generated using data from the Shuttle Radar Topography Mission (SRTM), which flew on NASA's Space Shuttle last February, and an enhanced, true-color Landsat satellite image. The view shown looks southeast along the San Andreas where it cuts along the base of the mountains in the Temblor Range near Bakersfield. The fault is the distinctively linear feature to the right of the mountains. To the left of the range is a portion of the agriculturally rich San Joaquin Valley. In the background is the snow-capped peak of Mt. Pinos at an elevation of 2,692 meters (8,831 feet). The complex topography in the area is some of the most spectacular along the course of the fault. To the right of the fault is the famous Carrizo Plain. Dry conditions on the plain have helped preserve the surface trace of the fault, which is scrutinized by both amateur and professional geologists. In 1857, one of the largest earthquakes ever recorded in the United States occurred just north of the Carrizo Plain. With an estimated magnitude of 8.0, the quake severely shook buildings in Los Angeles, caused significant surface rupture along a 350-kilometer (220-mile) segment of the fault, and was felt as far away as Las Vegas, Nev. This portion of the San Andreas is an important area of study for seismologists. For visualization purposes, topographic heights displayed in this image are exaggerated two times.

    The elevation data used in this image was acquired by 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 Endeavour in 1994. SRTM was designed to collect three-dimensional measurements of Earth's land surface. To collect the 3-D SRTM data, engineers added a mast 60

  5. 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. PMID:23752981

  6. The martyrdom of Doctor Andreas Vesalius.

    PubMed

    Lasky, I I

    1990-10-01

    The development of modern medicine began in the 16th century when Dr. Andreas Vesalius overthrew the previously uncontested medical dogma of the Greek physician Galen. Medical progress had been hindered for more than a millennium by strict adherence to Galen's authority. Flemish-born Vesalius challenged the political and societal forces of the time. At the University of Padua, he studied and later taught human anatomy by performing dissections. His discoveries were published in 1543 in his monumental De Humani Corporis Fabrica. Controversy led to his resignation from the University of Padua. His magnum opus was interpreted as a challenge to both academia and the church. He went to Spain, where he served as personal physician to Emperor Charles V. After almost 20 years in Spain, he became involved in an unfortunate incident that incurred the condemnation of the Inquisition. The royal court's intervention saved Vesalius from being burned at the stake, however, and he was ordered to make a pilgrimage to Jerusalem to atone for his error. On the return voyage, he became ill and died on the Greek island of Zante. PMID:2208869

  7. Andreas Vesalius' understanding of pulmonary ventilation.

    PubMed

    Hage, J Joris; Brinkman, Romy J

    2016-09-01

    The historical evolution of understanding of the mechanical aspects of respiration is not well recorded. That the anatomist Andreas Vesalius (1515-1564) first recorded many of these mechanics in De Humani Corporis Fabrica Libri Septem has received little attention. We searched a digital copy of De Fabrica (1543) and its English translation as provided by Richardson and Carman (1998-2009) for references to aspects of pulmonary ventilation. We found that Vesalius grasped the essentials of tidal and forced respiration. He recognized that atmospheric pressure carried air into the lungs, approximately 100 years before Borelli did. He described an in vivo experiment of breathing, some 120 years before John Mayow produced his artificial model. He reported on positive pressure ventilation through a tracheotomy and on its life-saving effect, some 100 years before Robert Hook did. In publicly recording his insights over 450 years ago, Vesalius laid a firm basis for our understanding of the physiology of respiration and the management of its disorders. PMID:27238371

  8. [Epitome, an ignored work of Andreas Vesalius].

    PubMed

    Vons, Jacqueline

    2006-01-01

    A few days before De humani corporis fabrica libri septem publication, in 1543, from Oporinus' office at Basel, a very large but not too bulky in-folio was published, which Andreas Vesalius, the author; offered as the Epitome or Summary of the seven Fabricae books. This work, written in latin, is divided into two parts: the first of them includes six chapters describing the human body, the second is composed of eleven anatomical plates with indices; the reader is invited to cut up the last two and stick them onto the preceding, so as to make a human three-dimensional figure. This method inserts the work in a modern conception of anatomical learning. Vesalius involves himself patiently gives many explanations for learning the body in dissection order through plates and text as well. But these plates--and most of them are different from those in the Fabrica-, are not simple illustrations, but play an active part in anatomical knowledge acquisition, just as the text does, but through a different access. We will attract your attention on this originality, often ignored, of the Epitome. PMID:17152529

  9. 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

  10. Crustal deformation along the San Andreas, California

    NASA Astrophysics Data System (ADS)

    Li, Victor C.

    1992-03-01

    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.

  11. 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.

  12. Andrea del Sarto rehabilitated: a psychoanalytic emendation.

    PubMed

    Trosman, Harry

    2002-01-01

    Ernest Jones's "The Influence of Andrea del Sarto's Wife on His Art" (1913) is an early example of psychoanalysis applied to the study of a prominent painter. Greatly influenced by Freud's Leonardo da Vinci and a Memory of His Childhood, Jones gave excessive credence to Vasari's highly prejudicial account of the life of del Sarto, on which the study relied heavily. Jones attempted to account psychologically for the circumstance that del Sarto, though highly skilled and "faultless," was not the equal of the three preeminent masters of the Italian High Renaissance: Leonardo, Michelangelo, and Raphael. Jones's uncritical acceptance of the Vasari biography encouraged him to view Sarto's assumed deficiency as the result of excessive attachment to his wife, a pathological uxoriousness. A contemporary psychoanalytic perspective, with its emphasis on the emotive response of the analyst, requires us to pay attention to the evocative nature of the work of the artist, an approach Jones neglected. In an examination of several paintings, the artist's sensitivity to the position of the spectator is explored, as is the interest in involving the viewer spatially and emotionally. An appreciation for the viewer's position is consistent with a capacity for using projected internal objects for creative purposes. The presence of this capacity suggests a revised view of del Sarto's contribution to art and of his relationship with his wife. PMID:12580329

  13. Observing the San Andreas Fault at Depth

    NASA Astrophysics Data System (ADS)

    Ellsworth, W.; Hickman, S.; Zoback, M.; Davis, E.; Gee, L.; Huggins, R.; Krug, R.; Lippus, C.; Malin, P.; Neuhauser, D.; Paulsson, B.; Shalev, E.; Vajapeyam, B.; Weiland, C.; Zumberge, M.

    2005-12-01

    Extending 4 km into the Earth along a diagonal path that crosses the divide between Salinian basement accreted to the Pacific Plate and Cretaceous sediments of North America, the main hole at the San Andreas Fault Observatory at Depth (SAFOD) was designed to provide a portal into the inner workings of a major plate boundary fault. The successful drilling and casing of the main hole in the summer of 2005 to a total vertical depth of 3.1 km make it possible to conduct spatially extensive and long-duration observations of active tectonic processes within the actively deforming core of the San Andreas Fault. In brief, the observatory consists of retrievable seismic, deformation and environmental sensors deployed inside the casing in both the main hole (maximum temperature 135 C) and the collocated pilot hole (1.1 km depth), and a fiber optic strainmeter installed behind casing in the main hole. By using retrievable systems deployed on either wire line or rigid tubing, each hole can be used for a wide range of scientific purposes, with instrumentation that takes maximum advantage of advances in sensor technology. To meet the scientific and technical challenges of building the observatory, borehole instrumentation systems developed for use in the petroleum industry and by the academic community in other deep research boreholes have been deployed in the SAFOD pilot hole and main hole over the past year. These systems included 15Hz omni-directional and 4.5 Hz gimbaled seismometers, micro-electro-mechanical accelerometers, tiltmeters, sigma-delta digitizers, and a fiber optic interferometeric strainmeter. A 1200-m-long, 3-component 80-level clamped seismic array was also operated in the main hole for 2 weeks of recording in May of 2005, collecting continuous seismic data at 4000 sps. Some of the observational highlights include capturing one of the M 2 SAFOD target repeating earthquakes in the near-field at a distance of 420 m, with accelerations of up to 200 cm/s and a

  14. Taking the pulse of the San Andreas Fault

    SciTech Connect

    Kerr, R.A.

    1989-01-01

    The ninth of January, 1989, was the 132nd anniversary of the great southern California earthquake of 1857. The latest research shows that, on average, at least part of the section of the San Andreas fault that broke then should break again this year. But the same research suggests that the fault's average behavior could be misleading. A newly refined dating of the past 10 San Andreas ruptures adjacent to Los Angeles reveals a previously unrecognized clustering of large earthquakes in bunches of two or three. If this pattern were to hold, Los Angeles would wait at least another 80 years for another jolt from there. But the San Andreas is not that easy to get around. The paper discusses these findings.

  15. Stress diffusion along the san andreas fault at parkfield, california.

    PubMed

    Malin, P E; Alvarez, M G

    1992-05-15

    Beginning in January 1990, the epicenters of microearthquakes associated with a 12-month increase in seismicity near Parkfield, California, moved northwest to southeast along the San Andreas fault. During this sequence of events, the locally variable rate of cumulative seismic moment increased. This increase implies a local increase in fault slip. These data suggest that a southeastwardly diffusing stress front propagated along the San Andreas fault at a speed of 30 to 50 kilometers per year. Evidently, this front did not load the Parkfield asperities fast enough to produce a moderate earthquake; however, a future front might do so. PMID:17795004

  16. Von Tondern nach Gotha. Der Astronom Peter Andreas Hansen, 1795 - 1874.

    NASA Astrophysics Data System (ADS)

    Strumpf, M.; Pehlemann, E.; Wolfschmidt, G.

    This companion booklet to an exposition in honor of Peter Andreas Hansen's 200th birthday contains three papers. Contents: 1. Peter Andreas Hansen - Leben und Wirken in Gotha (M. Strumpf). 2. Peter Andreas Hansens wissenschaftliches Werk (E. Pehlemann). 3. Beobachtungsinstrumente der Sternwarte Gotha zur Zeit Hansens (G. Wolfschmidt).

  17. 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…

  18. Andreas Vesalius and his De humani corporis Fabrica libri septem.

    PubMed

    Steele, Lloyd

    2014-01-01

    Andreas Vesalius of Brussels (1514-1564) was a Renaissance physician and surgeon whose most famous work was the De humani corporis fabrica libri septem a monograph describing human anatomy, first published in 1543. The Fabrica precipitated advances both anatomical and pedagogical, and its influence was such that Vesalius has since been described as the 'founder of modern anatomy'. PMID:25181775

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

    NASA Video Gallery

    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...

  20. 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

  1. The Influence of the Geometry of the San Andreas Fault System on Earthquakes in California

    NASA Astrophysics Data System (ADS)

    Li, Q.; Liu, M.

    2004-12-01

    The San Andreas Fault is believed to be the main surface trace of the plate boundary between the North American and the Pacific plates. From 1800 to present, three large historical earthquakes (1857 M7.9, 1906 M8.25, and 1989 M7.1) ruptured the San Andreas Fault. At the same time, more than a dozen M>7.0 earthquakes occurred outside the main trace of the San Andreas Fault. Most of the off-main-trace large earthquakes were scattered in Southern California, whereas in northern and central California, earthquakes were clustered along the main trace of the San Andreas Fault. Such a seismic distribution may be related to the geometry of the San Andreas Fault, which is curved with a major bending in southern California. In this study, we constructed a finite element model to explore the influence of the geometry of the San Andreas Fault system on stress distribution and seismicity in California. In the model, the San Andreas Fault is simulated with a weak zone that obeys the Coulomb Friction Law. The model results show that along relative straight segments of the San Andreas Fault in northern and central California, fault slip on the main fault trace causes low level stresses in nearby regions. Along the bended San Andreas Fault in southern California, however, the relative plate motion causes significant off-main-trace stress buildup, consistent with the distribution of large historical earthquakes outside the San Andreas Fault.

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

    NASA Technical Reports Server (NTRS)

    Li, Victor C.

    1989-01-01

    The goal of this project remains to be the achievement of a better understanding of the regional and local deformation and crustal straining processes in western North America, particularly the effect 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 deformations. In the present period, special focus is placed on the 3-D effect of irregular fault locked patches on the ground measured deformation fields. Specifically, use is made of a newly developed 3-D boundary element program to analyze the fault slip and vertical ground motion in the Parkfield area on the San Andreas.

  3. The North Sea Andrea storm and numerical simulations

    NASA Astrophysics Data System (ADS)

    Bitner-Gregersen, E. M.; Fernandez, L.; Lefèvre, J. M.; Monbaliu, J.; Toffoli, A.

    2014-06-01

    A coupling of a spectral wave model with a nonlinear phase-resolving model is used to reconstruct the evolution of wave statistics during a storm crossing the North Sea on 8-9 November 2007. During this storm a rogue wave (named the Andrea wave) was recorded at the Ekofisk field. The wave has characteristics comparable to the well-known New Year wave measured by Statoil at the Draupner platform 1 January 1995. Hindcast data of the storm at the nearest grid point to the Ekofisk field are here applied as input to calculate the evolution of random realizations of the sea surface and its statistical properties. Numerical simulations are carried out using the Euler equations with a higher-order spectral method (HOSM). Results are compared with some characteristics of the Andrea wave record measured by the down-looking lasers at Ekofisk.

  4. Expression of San Andreas fault on Seasat radar image

    NASA Technical Reports Server (NTRS)

    Sabins, F. F., Jr.; Blom, R.; Elachi, C.

    1980-01-01

    A Seasat image (23.5 cm wavelength) of the Durmid Hills in southern California, the San Andreas Fault was analyzed. It is shown that a prominent southeast trending tonal lineament exists that is bright on the southwest side and dark on the northeast side. The cause of the contrasting signatures on opposite sides of the lineament was determined and the geologic signficance of the lineament was evaluated.

  5. 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.

  6. San Andreas fault zone head waves near Parkfield, California

    SciTech Connect

    Ben-Zion, Y.; Malin, P. Univ. of California, Santa Barbara, CA )

    1991-03-29

    Microearthquakes 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.

  7. Coulomb Stress Accumulation along the San Andreas Fault System

    NASA Technical Reports Server (NTRS)

    Smith, Bridget; Sandwell, David

    2003-01-01

    Stress accumulation rates along the primary segments of the San Andreas Fault system are computed using a three-dimensional (3-D) elastic half-space model with realistic fault geometry. The model is developed in the Fourier domain by solving for the response of an elastic half-space due to a point vector body force and analytically integrating the force from a locking depth to infinite depth. This approach is then applied to the San Andreas Fault system using published slip rates along 18 major fault strands of the fault zone. GPS-derived horizontal velocity measurements spanning the entire 1700 x 200 km region are then used to solve for apparent locking depth along each primary fault segment. This simple model fits remarkably well (2.43 mm/yr RMS misfit), although some discrepancies occur in the Eastern California Shear Zone. The model also predicts vertical uplift and subsidence rates that are in agreement with independent geologic and geodetic estimates. In addition, shear and normal stresses along the major fault strands are used to compute Coulomb stress accumulation rate. As a result, we find earthquake recurrence intervals along the San Andreas Fault system to be inversely proportional to Coulomb stress accumulation rate, in agreement with typical coseismic stress drops of 1 - 10 MPa. This 3-D deformation model can ultimately be extended to include both time-dependent forcing and viscoelastic response.

  8. 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. PMID:17793143

  9. Conductivity Structure of the San Andreas Fault, Parkfield, Revisited

    NASA Astrophysics Data System (ADS)

    Park, S. K.; Roberts, J. J.

    2003-12-01

    Laboratory measurements of samples of sedimentary rocks from the Parkfield syncline reveal resistivities as low as 1 ohm m when saturated with fluids comparable to those found in nearby wells. The syncline lies on the North American side of the San Andreas fault at Parkfield and plunges northwestward into the fault zone. A previous interpretation of a high resolution magnetotelluric profile across the San Andreas fault at Parkfield identified an anomalously conductive (1-3 ohm m) region just west of the fault and extending to depths of 3 km. These low resistivity rocks were inferred to be crushed rock in the fault zone that was saturated with brines. As an alternative to this interpretation, we suggest that this anomalous region is actually the Parkfield syncline and that the current trace of the San Andreas fault at Middle Mountain does not form the boundary between the Salinian block and the North American plate. Instead, that boundary is approximately 1 km west and collocated with current seismicity. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by the Office of Basic Energy Science. Additional support was provided by the U.S. Geological Survey (USGS), Department of the Interior, under USGS Award number 03HQGR0041. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

  10. Thermal regime of the San Andreas Fault near Parkfield, California

    NASA Astrophysics Data System (ADS)

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

    1997-12-01

    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 1500m, 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 seismicaseismic transition for the Parkfield segment corresponds to temperatures in the range of

  11. Mantle fluids in the San Andreas fault system, California

    USGS Publications Warehouse

    Kennedy, B.M.; Kharaka, Y.K.; Evans, William C.; Ellwood, A.; DePaolo, D.J.; Thordsen, J.; Ambats, G.; Mariner, R.H.

    1997-01-01

    Fluids associated with the San Andreas and companion faults n central and south-central California have high 3He/4He ratios. The lack of correlation between helium isotopes and fluid chemistry or local geology requires that fluids enter the fault system from the mantle. Mantle fluids passing through the ductile lower crust must enter the brittle fault zone at or near lithostatic pressures; estimates of fluid flux based on helium isotopes suggest that they may thus contribute directly to fault-weakening high-fluid pressures at seismogenic depths.

  12. Periodic pulsing of characteristic microearthquakes on the San Andreas fault.

    PubMed

    Nadeau, Robert M; McEvilly, Thomas V

    2004-01-01

    Deep fault slip information from characteristically repeating microearthquakes reveals previously unrecognized patterns of extensive, large-amplitude, long-duration, quasiperiodic repetition of aseismic events along much of a 175-kilometer segment of the central San Andreas fault. Pulsing occurs both in conjunction with and independent of transient slip from larger earthquakes. It extends to depths of approximately 10 to 11 kilometers but may be deeper, and it may be related to similar phenomena occurring in subduction zones. Over much of the study area, pulse onset periods also show a higher probability of larger earthquakes, which may provide useful information for earthquake forecasting. PMID:14716011

  13. 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. PMID:15591163

  14. Mantle fluids in the San Andreas fault system, California

    SciTech Connect

    Kennedy, B.M.; Kharaka, Y.K.; Evans, W.C.

    1997-11-14

    Fluids associated with the San Andreas and companion faults in central and south-central California have high {sup 3}He/{sup 4}He ratios. The lack of correlation between helium isotopes and fluid chemistry or local geology requires that fluids enter the fault system from the mantle. Mantle fluids passing through the ductile lower crust must enter the brittle fault zone at or near lithostatic pressures; estimates of fluid flux based on helium isotopes suggest that they may thus contribute directly to fault-weakening high-fluid pressures at seismogenic depths. 31 refs., 4 figs.

  15. Internal structure of the San Andreas fault at Parkfield, California

    SciTech Connect

    Unsworth, M.J.; Booker, J.R.; Malin, P.E.; Egbert, G.D.

    1997-04-01

    Magnetotelluric and seismic reflection surveys at Parkfield, California, show that the San Andreas fault zone is characterized by a vertical zone of low electrical resistivity. This zone is {approx} 500 m wide and extends to a depth of {approx} 4000 m. The low electrical resistivity is attributed to high porosity of saline fluids present in the highly fractured fault zone. The occurrence of microearthquakes and creep in the low resistivity zone is consistent with suggestions that seismicity at Parkfield is fluid driven. 33 refs., 3 figs.

  16. New evidence on the state of stress of the san andreas fault system.

    PubMed

    Zoback, M D; Zoback, M L; Mount, V S; Suppe, J; Eaton, J P; Healy, J H; Oppenheimer, D; Reasenberg, P; Jones, L; Raleigh, C B; Wong, I G; Scotti, O; Wentworth, C

    1987-11-20

    Contemporary in situ tectonic stress indicators along the San Andreas fault system in central California show northeast-directed horizontal compression that is nearly perpendicular to the strike of the fault. Such compression explains recent uplift of the Coast Ranges and the numerous active reverse faults and folds that trend nearly parallel to the San Andreas and that are otherwise unexplainable in terms of strike-slip deformation. Fault-normal crustal compression in central California is proposed to result from the extremely low shear strength of the San Andreas and the slightly convergent relative motion between the Pacific and North American plates. Preliminary in situ stress data from the Cajon Pass scientific drill hole (located 3.6 kilometers northeast of the San Andreas in southern California near San Bernardino, California) are also consistent with a weak fault, as they show no right-lateral shear stress at approximately 2-kilometer depth on planes parallel to the San Andreas fault. PMID:17839366

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  19. 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.

  20. 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

  1. 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

  2. Pemeability and frictional properties of San Andreas fault gouges

    SciTech Connect

    Chu, C.L.; Wang, C.Y.; Lin, W.

    1981-06-01

    The permeability of a San Andreas fault gouge is determined under confining pressures up to 220 bars; it decreases with pressure from 10 nanodarcy at 15 bars to 0.3 nanodarcy at 220 bars. These values are lower than the values determined by Morrow et al. (1981). Five different samples of fault gouge with significantly different grain-size distributions were sheared between rock joints under confining pressures to determine the effects of grain size and constitution on the strength of the fault gouge. The strength of fault gorge clearly depends on its constitution and grain size distribution, with the coarser sandy fault gouge being stronger than the finer clayey gouge. Furthermore, the coarser gouge tends to strain harden after yielding, leading to greater strength. Thus, on the San Andreas fault, inhomogeneties in gouge materials may cause spatial variations in strength. Using the permeability determined above, we estimate that the excess pore pressure generated in the fault gauge samples during the experimental shear loading may be negligible.

  3. 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.

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

    PubMed

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

    2003-12-01

    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 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. PMID:14657494

  5. 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.

  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. Andreas Vesalius (1514-1564) - an unfinished life.

    PubMed

    Ambrose, Charles T

    2014-01-01

    The fame of Andreas Vesalius (1514-1564) rests on his anatomy text, De humani corporis fabrica, regarded as a seminal book in modern medicine. It was compiled while he taught anatomy at Padua, 1537-1543. Some of his findings challenged Galen's writings of the 2c AD, and caused De fabrica to be rejected immediately by classically trained anatomists. At age 29, Vesalius abandoned his studies and over the next two decades served as physician to Emperor Charles V of the Holy Roman Empire (HRE) and later to King Philip II of Spain in Madrid. In 1564, he sought to resume teaching anatomy in Padua, but release from royal service obliged him first to make a pilgrimage to Palestine. During the return voyage to Venice, he became ill and was put ashore alone on an Ionian island Zakynthos, where he died days later at age 50. PMID:25811684

  8. 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. PMID:26255386

  9. Tilt Precursors before Earthquakes on the San Andreas Fault, California.

    PubMed

    Johnston, M J; Mortensen, C E

    1974-12-13

    An array of 14 biaxial shallow-borehole tiltmeters (at 1O(-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. PMID:17843056

  10. Electromagnetic Imaging of Fluids in the San Andreas Fault

    SciTech Connect

    Martyn Unsworth

    2002-05-01

    OAK 270 - Magnetotelluric data were collected on six profiles across the san Andreas Fault at Cholame,Parkfield, and Hollister in Central California. On each profile, high electrical resistivities were imaged west of the fault, and are due to granitic rocks of the Salinian block. East of the fault, lower electrical resistivities are associated with rocks of the Fanciscan formation. On the seismically active Parkfield and Hollister segments, a region of low resistivity was found in the fault zone that extends to a depth of several kilometers. This is due to a zone of fracturing (the damaged zone) that has been infiltrated by saline ground water. The shallowest micro-earthquakers occur at a depth that is coincident with the base of the low resistivity wedge. This strongly suggests that above this depth, the fault rocks are too weak to accumulate sufficient stress for earthquake rupture to occur and fault motion is accommodated through aseismic creep.

  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. 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. PMID:17738534

  13. 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.

  14. Lithosphere-Asthenosphere interactions near the San Andreas fault.

    NASA Astrophysics Data System (ADS)

    Houlie, N.

    2015-12-01

    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 degrees of rotation across a 50 km distance from 50 degrees 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.

  15. Fracture surface energy of the Punchbowl fault, San Andreas system.

    PubMed

    Chester, Judith S; Chester, Frederick M; Kronenberg, Andreas K

    2005-09-01

    Fracture energy is a form of latent heat required to create an earthquake rupture surface and is related to parameters governing rupture propagation and processes of slip weakening. Fracture energy has been estimated from seismological and experimental rock deformation data, yet its magnitude, mechanisms of rupture surface formation and processes leading to slip weakening are not well defined. Here we quantify structural observations of the Punchbowl fault, a large-displacement exhumed fault in the San Andreas fault system, and show that the energy required to create the fracture surface area in the fault is about 300 times greater than seismological estimates would predict for a single large earthquake. If fracture energy is attributed entirely to the production of fracture surfaces, then all of the fracture surface area in the Punchbowl fault could have been produced by earthquake displacements totalling <1 km. But this would only account for a small fraction of the total energy budget, and therefore additional processes probably contributed to slip weakening during earthquake rupture. PMID:16136142

  16. 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.

  17. A slow earthquake sequence on the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Linde, Alan T.; Gladwin, Michael T.; Johnston, Malcolm J. S.; Gwyther, Ross L.; Bilham, Roger G.

    1996-09-01

    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, observations1-13 and laboratory experiments14 have indicated that rupture can also occur more slowly, with durations up to hours. Such events may be important in earthquake nucleation15 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. A simulation of the San Andreas fault experiment

    NASA Technical Reports Server (NTRS)

    Agreen, R. W.; Smith, D. E.

    1974-01-01

    The San Andreas fault experiment (Safe), which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, has been simulated for an 8-yr observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 km apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C spacecraft has been simulated for these two stations during August and September for 8 consecutive years. An error analysis of the recovery of the relative location of Quincy from the data has been made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and biases and noise in the laser systems. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 cm. Projected improvements in these model parameters and in the laser systems over the next few years will bring the precision to about 1-2 cm by 1980.

  19. A simulation of the San Andreas fault experiment

    NASA Technical Reports Server (NTRS)

    Agreen, R. W.; Smith, D. E.

    1973-01-01

    The San Andreas Fault Experiment, which employs two laser tracking systems for measuring the relative motion of two points on opposite sides of the fault, was simulated for an eight year observation period. The two tracking stations are located near San Diego on the western side of the fault and near Quincy on the eastern side; they are roughly 900 kilometers apart. Both will simultaneously track laser reflector equipped satellites as they pass near the stations. Tracking of the Beacon Explorer C Spacecraft was simulated for these two stations during August and September for eight consecutive years. An error analysis of the recovery of the relative location of Quincy from the data was made, allowing for model errors in the mass of the earth, the gravity field, solar radiation pressure, atmospheric drag, errors in the position of the San Diego site, and laser systems range biases and noise. The results of this simulation indicate that the distance of Quincy from San Diego will be determined each year with a precision of about 10 centimeters. This figure is based on the accuracy of earth models and other parameters available in 1972.

  20. Northern San Andreas fault near Shelter Cove, California

    USGS Publications Warehouse

    Prentice, C.S.; Merritts, D.J.; Beutner, E.C.; Bodin, P.; Schill, A.; Muller, J.R.

    1999-01-01

    The location of the San Andreas fault in the Shelter Cove area of northern California has been the subject of long-standing debate within the geological community. Although surface ruptures were reported near Shelter Cove in 1906, several subsequent workers questioned whether these ruptures represented true fault slip or shaking-related, gravity-driven deformation. This study, involving geologic and geomorphic mapping, historical research, and excavation across the 1906 rupture zone, concludes that the surface ruptures reported in 1906 were the result of strike-slip faulting, and that a significant Quaternary fault is located onshore near Shelter Cove. Geomorphic arguments suggest that the Holocene slip rate of this fault is greater than about 14 mm/yr, indicating that it plays an important role within the modern plate-boundary system. The onshore trace of the fault zone is well expressed as far north as Telegraph Hill; north of Telegraph Hill, its location is less well-constrained, but we propose that a splay of the fault may continue onshore northward for at least 9 km to the vicinity of Saddle Mountain.

  1. 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

  2. Aspects of the earthquake geology and seismotectonics of the southern San Andreas and related faults

    NASA Astrophysics Data System (ADS)

    Williams, Patrick Lee

    Aspects of the mechanics and movement history of the southernmost San Andreas or related faults are addressed. The seismotectonic context of the southernmost San Andreas fault is investigated. Microstratigraphic and geomorphological investigations of the fault's segmentation, slip potential and latest seismogenic slip history are presented. Measurements of geological deposits, man-made structures, alignment arrays and creepmeters offset across the southernmost San Andreas fault are presented. These measure the fault's aseismic slip rate during the past three hundred years. Observations of triggered aseismic slippage along the southernmost 100 km of the San Andreas fault soon after the North Palm Springs earthquake are described. Dextral surficial slip ranging from less than or equal to 9 mm and occurred on three sections of the San Andreas fault that lie between 44 and 86 km from the epicenter near North Palm Springs. Data complied and interpretations gleaned from repeated measurements of surface slip at dozens of site along the Superstition Hills fault during the period of two hours to one year after the Superstition Hills earthquake are presented. The common result of these five investigations is increased understanding of phenomena associated with fault motion along the highly active border between the Pacific and North American plates.

  3. 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.

  4. Interseismic strain accumulation and the earthquake potential on the southern San Andreas fault system.

    PubMed

    Fialko, Yuri

    2006-06-22

    The San Andreas fault in California is a mature continental transform fault that accommodates a significant fraction of motion between the North American and Pacific plates. The two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857, respectively. The southern section of the fault, however, has not produced a great earthquake in historic times (for at least 250 years). Assuming the average slip rate of a few centimetres per year, typical of the rest of the San Andreas fault, the minimum amount of slip deficit accrued on the southern section is of the order of 7-10 metres, comparable to the maximum co-seismic offset ever documented on the fault. Here I present high-resolution measurements of interseismic deformation across the southern San Andreas fault system using a well-populated catalogue of space-borne synthetic aperture radar data. The data reveal a nearly equal partitioning of deformation between the southern San Andreas and San Jacinto faults, with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces. The observed strain rates confirm that the southern section of the San Andreas fault may be approaching the end of the interseismic phase of the earthquake cycle. PMID:16791192

  5. Crustal Dehydration and Overpressure Development on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    Previous authors have hypothesized that the apparent weakness of the San Andreas Fault may be explained by fluid overpressures resulting from the combination of crustal dehydration of the Franciscan mélange and the presence of a low-permeability serpentinite cap at its geologic contact with the Great Valley Sequence. We previously evaluated this hypothesis by calculating the spatial and temporal distribution of fluid sources and then incorporating these sources in 2-D models of fluid flow and heat transport perpendicular to the fault. We have refined our fluid source calculations using theoretical values of whole-rock H2O content and PT histories for the Franciscan crust in the wake of northward migration of the Mendocino Triple Junction (MTJ). The sources obtained reach peak values of 10-16 s-1. The coupled fluid flow and heat transport model now accommodates large-scale crustal deformation in a more rigorous manner by constructing new model grids after each change in crustal thickness. In the models, we assign permeability of the crust as a function of depth. A 500-m-thick, low-permeability serpentinite body (k=10-20 m-2) extends across the eastern half of the 50 km-wide model domain at a depth of 2 km. In addition, various model simulations include fault structures centered in the model domain such as: a 500 m wide low permeability fault barrier (kfault = kcrust/100), a fault conduit (kfault = kcrust x 100), a barrier within a 1.5 km wide conduit damage zone, and a conduit plugged by a 3 km-thick and 2 km-wide barrier simulating a broad, clay-rich, low-permeability zone, at shallow depth within the fault system, which is one possible interpretation of seismic and electromagnetic data. We also test additional scenarios to evaluate sensitivity to changes in model permeability. Model results show overpressures, as large as 162% of hydrostatic (62% of lithostatic) for the model with a serpentinite cap and fault barrier, develop within 4 Ma of Mendocino Triple

  6. 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

  7. 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

  8. Scattered Wavefield Within the San Andreas Fault System, California

    NASA Astrophysics Data System (ADS)

    Taira, T.; Silver, P. G.; Niu, F.; Nadeau, R. M.

    2004-12-01

    Since transient aseismic deformation at seismogenic depth is one of the key phenomena related to earthquake occurrence, it is important to estimate the physical characteristics of such stress/strain transients within the deeper structure of the fault zone. Analysis of coda (scattered) waves has the potential for identifying such transients because the scattered wavefield is attributed mainly to small-scale heterogeneity that is likely formed by these transient events. In addition, the sampling area of scattered waves is concentrated within the fault zone, compared to the area sampled by direct waves. We have begun a program to map the spatial distribution of fault-zone scatterers and their time dependence within two regions of San Andreas Fault system: the Hayward Fault and the Parkfield segment of the San Andreas Fault. In order to most reliably evaluate the scattered wavefields, we limited our analysis to records from borehole seismographs recorded by the Hayward Fault Network (HFN) and the High-Resolution Seismic Network (HRSN) in each area. For the Hayward fault, we mapped the spatial distribution of scatterers by analysis of the S-wave coda amplification factor (CAF) in a manner similar to Taira and Yomogida (2003). CAF is defined as the amplitude ratio of coda waves among different stations after corrections for source, station, and overall propagation effects (e.g., coda Q). This parameter allows for a statistical characterization of the distribution of scatterers. The station effect for each station and the coda Q averaged over all the seismograms in this area were estimated by the coda-normalization and maximum likelihood methods, respectively, using five regional earthquakes (epicentral distance > 50 km). We evaluated the CAF value of each source-station pair for the transverse-component, using 294 seismograms for 39 local earthquakes (epicentral distance < 50 km) recorded by 14 stations of the HFN. A map of CAF values for stations near the Hayward Fault

  9. Nanoscale porosity in SAFOD core samples (San Andreas Fault)

    NASA Astrophysics Data System (ADS)

    Janssen, Christoph; Wirth, Richard; Reinicke, Andreas; Rybacki, Erik; Naumann, Rudolf; Wenk, Hans-Rudolf; Dresen, Georg

    2011-01-01

    With transmission electron microscopy (TEM) we observed nanometer-sized pores in four ultracataclastic and fractured core samples recovered from different depths of the main bore hole of the San Andreas Fault Observatory at Depth (SAFOD). Cutting of foils with a focused ion beam technique (FIB) allowed identifying porosity down to the nm scale. Between 40 and 50% of all pores could be identified as in-situ pores without any damage related to sample preparation. The total porosity estimated from TEM micrographs (1-5%) is comparable to the connected fault rock porosity (2.8-6.7%) estimated by pressure-induced injection of mercury. Permeability estimates for cataclastic fault rocks are 10- 21-10- 19 m2 and 10- 17 m2 for the fractured fault rock. Porosity and permeability are independent of sample depth. TEM images reveal that the porosity is intimately linked to fault rock composition and associated with deformation. The TEM-estimated porosity of the samples increases with increasing clay content. The highest porosity was estimated in the vicinity of an active fault trace. The largest pores with an equivalent radius > 200 nm occur around large quartz and feldspar grains or grain-fragments while the smallest pores (equivalent radius < 50 nm) are typically observed in the extremely fine-grained matrix (grain size < 1 μm). Based on pore morphology we distinguish different pore types varying with fault rock fabric and alteration. The pores were probably filled with formation water and/or hydrothermal fluids at elevated pore fluid pressure, preventing pore collapse. The pore geometry derived from TEM observations and BET (Brunauer, Emmett and Teller) gas adsorption/desorption hysteresis curves indicates pore blocking effects in the fine-grained matrix. Observations of isolated pores in TEM micrographs and high pore body to pore throat ratios inferred from mercury injection suggest elevated pore fluid pressure in the low permeability cataclasites, reducing shear strength

  10. 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.

  11. The Flemish anatomist Andreas Vesalius (1514-1564) and the kidney.

    PubMed

    DeBroe, M E; Sacré, D; Snelders, E D; De Weerdt, D L

    1997-01-01

    Andreas Vesalius was born in Brussels on December 31, 1514 from a long line of physicians. He died in Zante in 1564. He was a typical son of the Renaissance. In 1543, his two most important books were published: De Humani Corporis Fabrica, Libri Septum and the Epitome. The former was a book of over 700 pages with several illustrations, highly systematically composed and fully indexed. Andreas Vesalius was the first modern anatomist who based his anatomical descriptions on personal observation. The kidney was a fascinating organ to Vesalius, whose function, particularly regarding the production of urine, he did not fully grasp. He makes short work of the 'perforated membrane theory' which was the current conception of the origin of urine in the kidney. Andreas Vesalius broke with the established rigid and fabricated way of teaching anatomy, and introduced the modern concept of learning based on personal observations, using illustration combined with a critical spirit and sense of experiment. PMID:9189243

  12. A comparison of the measured North Sea Andrea rogue wave with numerical simulations

    NASA Astrophysics Data System (ADS)

    Bitner-Gregersen, E. M.; Fernandez, L.; Lefèvre, J. M.; Monbaliu, J.; Toffoli, A.

    2013-09-01

    A coupling of a spectral wave model with a nonlinear phase resolving model is used to reconstruct the evolution of wave statistics during a storm crossing the North Sea on 8-9 November 2007. During this storm a rogue wave (named the Andrea wave) was recorded at the Ekofisk field. The wave has characteristics comparable to the well-known New Year wave measured by Statoil at the Draupner platform the 1 January 1995. Hindcast data of the storm are here applied as input to calculate random realizations of sea surface and evolution of its statistical properties associated with this specific wave event by solving the Euler equations with a Higher Order Spectral Method (HOSM). The numerical results are compared with the Andrea wave profile as well as characteristics of the Andrea wave record measured by the down-looking lasers at the Ekofisk field.

  13. Postseismic relaxation along the San Andreas fault at Parkfield from continuous seismological observations.

    PubMed

    Brenguier, F; Campillo, M; Hadziioannou, C; Shapiro, N M; Nadeau, R M; Larose, E

    2008-09-12

    Seismic velocity changes and nonvolcanic tremor activity in the Parkfield area in California reveal that large earthquakes induce long-term perturbations of crustal properties in the San Andreas fault zone. The 2003 San Simeon and 2004 Parkfield earthquakes both reduced seismic velocities that were measured from correlations of the ambient seismic noise and induced an increased nonvolcanic tremor activity along the San Andreas fault. After the Parkfield earthquake, velocity reduction and nonvolcanic tremor activity remained elevated for more than 3 years and decayed over time, similarly to afterslip derived from GPS (Global Positioning System) measurements. These observations suggest that the seismic velocity changes are related to co-seismic damage in the shallow layers and to deep co-seismic stress change and postseismic stress relaxation within the San Andreas fault zone. PMID:18787165

  14. Irregular recurrence of large earthquakes along the san andreas fault: evidence from trees.

    PubMed

    Jacoby, G C; Sheppard, P R; Sieh, K 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. PMID:17841050

  15. 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.

  16. 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.

  17. 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.

  18. Late Cenozoic geology of Cajon Pass: implications for tectonics and sedimentation along the San Andreas fault

    SciTech Connect

    Weldon, R.J. II

    1986-01-01

    The geology in Cajon Pass, southern California, provides a detailed history of strike-slip activity on the San Andreas fault, compressional deformation associated with the uplift of the central Transverse Ranges and an excellent Cenozoic record of syntectonic sedimentation. Age control was established in all of the sediments deposited since the Early Miocene, using biostratigraphy, magnetostratigraphy, fission-track dating of volcanic ashes, radiocarbon dating, soil development, and the relative stratigraphic and geomorphic position of the units. Detailed mapping revealed that tectonic deformation and sedimentation styles varied through time, reflecting the evolution of the San Andreas fault zone within the Pacific-North American plate boundary and climatic changes. Three distinct phases of the uplift of the San Bernardino Mountains have been recognized, suggesting a long-term interaction between the strike-slip activity on the San Andreas system and the compressional tectonics of the Transverse Ranges. Uplift began in the late Miocene, paused during the Pliocene, recommenced in the earliest Pleistocene and culminated in the late Pleistocene. The average slip rate across the combined San Andreas and San Jacinto faults was 37.5 +/- 2 mm/yr during the Quaternary Period. The Holocene slip rate on the San Andreas fault in Cajon Pass was determined to be 24.5 +/- 3.5 mm/yr. This investigation indicates that the last earthquake associated wit rupture on the San Andreas fault in Cajon Pass occurred around 1700 AD and that the average recurrence interval between earthquakes is between 150 and 200 years. A kinematic model was constructed from the structural and slip rate data developed here that produces internally consistent motions for all of the fault-bounded blocks in southern California.

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

    PubMed

    Lockner, David A; Morrow, Carolyn; Moore, Diane; Hickman, Stephen

    2011-04-01

    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. PMID:21441903

  20. Crustal Deformation Along the Northern San Andreas Fault System From Geodetic and Geologic Data

    NASA Astrophysics Data System (ADS)

    Murray, M. H.

    2004-12-01

    The San Andreas fault system north of the San Francisco Bay area is composed of three sub-parallel right-lateral faults: the San Andreas, Rodgers Creek-Ma'acama, and Green Valley-Bartlett Springs. The San Andreas has been essentially aseismic since it last ruptured in 1906, and no major historical earthquakes have occurred on the more seismically active Ma'acama and Bartlett Springs faults, although the slip deficit on the Ma'acama fault may now be large enough to generate a magnitude 7 earthquake. Since 2002, we have been collecting GPS measurements at about 80 monuments that form roughly 10-station profiles across the northern San Andreas fault system from Pt. Reyes to Cape Mendocino. Most of the monuments were last observed in 1993 or 1995, so the new observations significantly improve estimates of their relative motion and models of average interseismic strain accumulation, including possible spatial variations along the fault system. We use angular velocity-backslip block modeling to determine a self-consistent northern California deformation field and rates of strain accumulation along the northern San Andreas fault system. Preliminary results from our modeling, which includes 2 blocks within the San Andreas fault system, as well as a Sierran-Great Valley block, and the Pacific and North America plates, show agreement between observed and predicted velocities at less than 2 mm/yr. Fault-parallel deformation across the entire San Andreas fault system is 38 mm/yr, but deep slip rates on the sub-parallel faults are poorly constrained due to significant correlations between the deep slip rates and locking depths, which we fully characterize using Monte Carlo techniques. We use Bayesian techniques to combine the GPS observations with constraints derived from other seismic, geodetic, and paleoseismic observations, such as locking depths, surface creep rates, and inferred geologic slip rates. These additional constraints significantly improve the estimates of the

  1. 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.

  2. Local geomagnetic events associated with displacements on the san andreas fault.

    PubMed

    Breiner, S; Kovach, R L

    1967-10-01

    The piezomagnetic properties of rock suggest that a change in subsurface stress will manifest itself as a change in the magnetic susceptibility and remanent magnetization and hence the local geomagnetic field. A differential array of magnetometers has been operating since late 1965 on the San Andreas fault in the search for piezomagnetic signals under conditions involving active fault stress. Local changes in the geomagnetic field have been observed near Hollister, California, some tens of hours preceding the onset of abrupt creep displacement on the San Andreas fault. PMID:17798647

  3. 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

  4. 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.

  5. Andreas Vesalius and the Occo medals of Augsburg. Evidence of a professional friendship.

    PubMed

    Houtzager, H L

    2000-06-01

    The friendly connection that existed between Andreas Vesalius (1514-1564) and his learned friends in Augsburg comprised three periods in the life of the emperor's court physician. The close ties that must have connected Adolphus Occo II and III and Vesalius are expressed in a number of medals carrying their images. PMID:11624585

  6. 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. PMID:27385301

  7. 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.

  8. 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…

  9. 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.

  10. Behavior of the southernmost San Andreas fault during the past 300 years

    SciTech Connect

    Sieh, K.E.; Williams, P.L. )

    1990-05-10

    Surficial creep occurs at low rates along the Coachella Valley segment of the San Andreas fault, which has not produced a large earthquake during the period of historical record. Geodetic data indicate, however, that the crust adjacent to this segment of the San Andreas fault is accumulating strain at a high rate. Furthermore, neotectonic and paleoseismic data indicate that the fault does produce very large earthquakes every two to three centuries. In view of its long-term behavior, the occurrence of creep along the surficial trace of the fault in the Coachella Valley is of particular interest. Along two short reaches of the San Andreas fault in the Coachella Valley, measurements of offset geological deposits and man-made structures and from alignment arrays and creep meters show that slip rates of 2-4 mm/yr near Indio and near the Salton Sea have persisted for the past three centuries. This slow aseismic surficial creep is not a transient precursor to seismic failure of this segment of the fault. The authors suggest that the Coachella Valley segment of the San Andreas fault creeps in its upper few kilometers. This behavior may be due to tectonically induced high pore pressures in the coarse sediments that abut the fault.

  11. State of stress near the San Andreas fault: implications for wrench tectonics

    SciTech Connect

    Mount, V.S.; Suppe, J.

    1987-12-01

    Borehole elongations or breakouts in central California show that the direction of regional maximum horizontal stress is nearly perpendicular to the San Andreas fault and to the axes of young thrust-related anticlines. This observation resolves much of the controversy over shear-stress magnitude in the crust and around the San Andreas fault specifically. A low shear stress of 10-20 MPa (100-200 bar) or less on the San Andreas fault, suggested by heat-flow and seismic observations, is compatible with a high regional deviatoric stress (100 MPa, 1 kbar) when the observed principal stress directions are considered. Therefore, the San Andreas fault is a nearly frictionless interface, which causes the transpressive plate motion to be decoupled into a low-stress strike-slip component and a high-stress compressive component. These observations suggest that standard concepts of transpressive wrench tectonics - which envisage drag on a high-friction fault - are wrong. The thrust structures are largely decoupled from the strike-slip fault.

  12. 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

  13. 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

  14. Permeability of the San Andreas Fault Zone at Depth

    NASA Astrophysics Data System (ADS)

    Rathbun, A. P.; Song, I.; Saffer, D.

    2010-12-01

    Quantifying fault rock permeability is important toward understanding both the regional hydrologic behavior of fault zones, and poro-elastic processes that affect fault mechanics by mediating effective stress. These include long-term fault strength as well as dynamic processes that may occur during earthquake slip, including thermal pressurization and dilatancy hardening. Despite its importance, measurements of fault zone permeability for relevant natural materials are scarce, owing to the difficulty of coring through active fault zones seismogenic depths. Most existing measurements of fault zone permeability are from altered surface samples or from thinner, lower displacement faults than the SAF. Here, we report on permeability measurements conducted on gouge from the actively creeping Central Deformation Zone (CDZ) of the San Andreas Fault, sampled in the SAFOD borehole at a depth of ~2.7 km (Hole G, Run 4, sections 4,5). The matrix of the gouge in this interval is predominantly composed of particles <10 µm, with ~5 vol% clasts of serpentinite, very fine-grained sandstone, and siltstone. The 2.6 m-thick CDZ represents the main fault trace and hosts ~90% of the active slip on the SAF at this location, as documented by repeated casing deformation surveys. We measured permeability in two different configurations: (1) in a uniaxial pressure cell, in which a sample is placed into a rigid steel ring which imposes a zero lateral strain condition and subjected to axial load, and (2) in a standard triaxial system under isostatic stress conditions. In the uniaxial configuration, we obtained permeabilities at axial effective stresses up to 90 MPa, and in the triaxial system up to 10 MPa. All experiments were conducted on cylindrical subsamples of the SAFOD core 25 mm in diameter, with lengths ranging from 18mm to 40mm, oriented for flow approximately perpendicular to the fault. In uniaxial tests, permeability is determined by running constant rate of strain (CRS) tests up

  15. 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

  16. 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.

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

    PubMed

    Moore, Diane E; Rymer, Michael J

    2007-08-16

    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. PMID:17700697

  18. 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

  19. Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure

    NASA Astrophysics Data System (ADS)

    Jeppson, Tamara N.; Bradbury, Kelly K.; Evans, James P.

    2010-12-01

    We examine the relationships between borehole geophysical data and physical properties of fault-related rocks within the San Andreas Fault as determined from data from the San Andreas Fault Observatory at Depth borehole. Geophysical logs, cuttings data, and drilling data from the region 3- to 4-km measured depth of the borehole encompass the active part of the San Andreas Fault. The fault zone lies in a sequence of deformed sandstones, siltstone, shale, serpentinite-bearing block-in-matrix rocks, and sheared phyllitic siltstone. The borehole geophysical logs reveal the presence of a low-velocity zone from 3190 to 3410 m measured depth with Vp and Vs values 10-30% lower than the surrounding rocks and a 1-2 m thick zone of active shearing at 3301-3303 m measured depth. Seven low-velocity excursions with increased porosity, decreased density, and mud-gas kick signatures are present in the fault zone. Geologic data on grain-scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data. In places, Vp and Vs increase with grain-scale deformation and alteration and decrease with porosity in the fault zone. The low-velocity zone is associated with a significant lithologic and structural transition to low-velocity rocks, dominated by phyllosilicates and penetratively foliated, sheared rocks. The zone of active shearing and the regions of low sonic velocity appear to be associated with clay-rich rocks that exhibit fine-scale foliation and higher porosities that may be a consequence of the fault-related shearing of foliated and fine-grained sedimentary rocks.

  20. 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

  1. 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

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

    SciTech Connect

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

    1990-04-10

    The mapped active traces of the San Andreas fault are separated by a 1-km-wide right-stepping offset in Cholame Valley. The authors 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. 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 ({le} 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 San Andreas fault. The offset in Cholame Valley is characterized by a gentle downwarping of sediments into the offset, the presence of many small faults and discontinuous reflections between the traces of the main fault, localized subsidence abutting the main strike-slip fault, the formation of a basin, near the offset, that is about as deep as the jog is wide, and the southward propagation of the deformation associated with the offset. Strain field modeling based on simple geometries of the San Andreas and associated faults successfully predicts the general features of the observed topography and subsurface structure of southern Cholame Valley, including subsidence and basin formation near the offset, a discontinuous San Andreas fault plane, and at least one fault in southeastern Cholame Valley.

  3. 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.

  4. On simultaneous tilt and creep observations on the San Andreas Fault

    USGS Publications Warehouse

    Johnston, M.J.S.; McHugh, S.; Burford, S.

    1976-01-01

    THE installation of an array of tiltmeters along the San Andreas Fault 1 has provided an excellent opportunity to study the amplitude and spatial scale of the tilt fields associated with fault creep. We report here preliminary results from, and some implications of, a search for interrelated surface tilts and creep event observations at four pairs of tiltmeters and creepmeters along an active 20-km stretch of the San Andreas Fault. We have observed clear creep-related tilts above the instrument resolution (10 -8 rad) only on a tiltmeter less than 0.5 km from the fault. The tilt events always preceded surface creep observations by 2-12 min, and were not purely transient in character. ?? 1975 Nature Publishing Group.

  5. [Legitimation of Andries Van Wesele, Andreas Vesalius's father, by the Holy Roman Emperor Charles the Fifth].

    PubMed

    Izumi, Hyonosuke

    2006-06-01

    Andries van Wesele, Andreas Vesalius's father and a court pharmacist of the Holy Roman Emperor Charles the fifth, was an illegitimate son of Everard van Wesele, a court physician of the Hapsburgs. In the year of 1531, Andries was legitimated by the Emperor. The legitimation letter was written in French. The author tried to translate and analyze the letter. By this legitimation, not only Andries himself was legitimated but also his successors were approved to succeed Andries. By this letter, Andreas Vesalius obtained his position as a hereditary member of a family serving the court of the Hapsburgs, and as a result, he started his career as a physician of the court. PMID:17152536

  6. 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.

  7. 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

  8. 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. PMID:20093436

  9. Cumulative offset of the San Andreas fault in Central California: A seismic approach

    SciTech Connect

    Revenaugh, J.; Reasoner, C.

    1997-02-01

    Scattered-wave imaging of upper crustal heterogeneity along nearly 500 km of the San Andreas fault in central California is used to estimate cumulative offset of basement rocks in the fault zone. Optimal cross-fault realignment of scattering patterns in achieved through removal of nearly 315 km of right-lateral slip. This value agrees with most previous estimates of early Miocene displacement, placing the initiation of movement on the San Andreas no earlier than ca, 23.1 Ma. Scattering along the fault correlates with segment boundaries established on the basis of historic and paleo seismicity, corroborating evidence from southern California that the upper crustal structures responsible for scattering are important in seismogenesis. 23 refs., 3 figs.

  10. Strain on the san andreas fault near palmdale, california: rapid, aseismic change.

    PubMed

    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. PMID:17731244

  11. Aseismic slip and seismogenic coupling along the central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Jolivet, R.; Simons, M.; Agram, P. S.; Duputel, Z.; Shen, Z.-K.

    2015-01-01

    We use high-resolution Synthetic Aperture Radar- and GPS-derived observations of surface displacements to derive the first probabilistic estimates of fault coupling along the creeping section of the San Andreas Fault, in between the terminations of the 1857 and 1906 magnitude 7.9 earthquakes. Using a fully Bayesian approach enables unequaled resolution and allows us to infer a high probability of significant fault locking along the creeping section. The inferred discreet locked asperities are consistent with evidence for magnitude 6+ earthquakes over the past century in this area and may be associated with the initiation phase of the 1857 earthquake. As creeping segments may be related to the initiation and termination of seismic ruptures, such distribution of locked and creeping asperities highlights the central role of the creeping section on the occurrence of major earthquakes along the San Andreas Fault.

  12. 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.

  13. 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.

  14. Andreas Vesalius on the teeth: an annotated translation from De humani corporis fabrica. 1543.

    PubMed

    Hast, M H; Garrison, D H

    1995-01-01

    An annotated translation into English of Chapter 11, Book One, "On the Teeth, Which Are Also Counted as Bones," from Andreas Vesalius' De humani corporis fabrica. The translation incorporates the text of both the 1543 and 1555 editions, and verified citations of ancient sources. In this chapter, Vesalius corrects errors of Galen and demonstrates and describes for the first time the anatomy and function of the dental pulp cavity. PMID:7712325

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

    PubMed

    Shelly, David R

    2010-02-01

    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. PMID:20130648

  16. 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.

  17. 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.

  18. 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.

  19. Lake level observations to detect crustal tilt: San Andreas Lake, California, 1979-1989

    SciTech Connect

    Mueller, R.J.; Johnston, M.J.S.; Myren, G.D. ); Murray, T. )

    1989-07-01

    A pair precision lake level gauging stations, installed in 1978, have been monitoring differential crustal uplift (crustal tilt) at San Andreas lake, California, near the suspected epicenter on the San Andreas fault of the M = 8.3, 1906 San Francisco earthquake. The stations are installed in the lake with a 4.2 km station separation parallel to the San Andreas fault. The gauging stations use quartz pressure transducers that are capable of detecting intermediate to long-term vertical displacements greater than 0.4 mm relative to a fluid surface. Differencing data from the two sites reduces the noise contributed by atmospheric pressure, temperature, and density changes, and isolates the relative elevation changes between the ends of the lake. At periods less than 20 minutes, the differenced data are dominated by lake seiches which have a fundamental mode at a period of 13 {plus minus} 0.3 minutes. These seiche harmonics can be filtered or predicted and removed from the data. Wind shear, typically lasting several days, can generate apparent short term tilt of the lake and large seiche amplitudes. The tilt noise power spectrum obtained from these data decreases by about 15 dB/decade of frequency. Monthly averages of the data between 1979-1989 indicate a tilt rate of 0.02 {plus minus} 0.08 microradians/yr (down S34{degree}E). No measurable horizontal tilt has apparently occurred in this region of the San Andreas fault during the last decade, however, measurements of trilateration networks show this region to be undergoing a horizontal strain of 0.6 {plus minus} 0.2 {mu}strain/yr.

  20. The morphology of strike-slip faults - Examples from the San Andreas Fault, California

    NASA Technical Reports Server (NTRS)

    Bilham, Roger; King, Geoffrey

    1989-01-01

    The dilatational strains associated with vertical faults embedded in a horizontal plate are examined in the framework of fault kinematics and simple displacement boundary conditions. Using boundary element methods, a sequence of examples of dilatational strain fields associated with commonly occurring strike-slip fault zone features (bends, offsets, finite rupture lengths, and nonuniform slip distributions) is derived. The combinations of these strain fields are then used to examine the Parkfield region of the San Andreas fault system in central California.

  1. Electrical resistivity variations associated with earthquakes on the san andreas fault.

    PubMed

    Mazzella, A; Morrison, H F

    1974-09-01

    A 24 percent precursory change in apparent electrical resistivity was observed before a magnitude 3.9 earthquake of strike-slip nature on the San Andreas fault in central California. The experimental configuration and numerical calculations suggest that the change is associated with a volume at depth rather than some near-surface phenomenon. The character and duration of the precursor period agree well with those of other earthquake studies and support a dilatant earthquake mechanism model. PMID:17833697

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

    PubMed

    Lozos, Julian C

    2016-03-01

    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

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

    Thatcher, W.; Savage, J. C.; Simpson, R. W.

    2016-04-01

    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.

  6. Major Quaternary uplift along the northernmost San Andreas fault, King Range, northwestern California

    SciTech Connect

    Dumitru, T.A. )

    1991-05-01

    The King Range is a rugged coastal mountain range that parallels the San Andreas transform fault system just south of the Mendocino triple junction. Point Delgada is a small coastal headland that projects into the Pacific Ocean just southwest of the King Range. Apatite fission-track ages from parts of the King Range are remarkably young, averaging 1.2 Ma, indicating that a minimum of 2-5 km of uplift and unroofing have occured in the past 1.2 m.y. In contrast, ages from Point Delgada are about 12 Ma, and fission-track length data indicate that rocks there have resided at low temperatures ({le}50{degree}C) and thus at shallow depths since soon after 12 Ma. Therefore Point Delgada has experienced relative vertical stability. The contrast in uplift histories indicates that the two areas are separated by a major fault with a minimum of {approximately}1 km of Quaternary vertical offset. The fault is probably part of the San Andreas system and so may also have undergone major Quaternary strike-slip offset. The uplift in the King Range seems too great and too localized to have resulted from isostatic effects accompanying passage of the Mendocino triple junction and development of a slab-free window; rather, it is probably a local response to space problems among the various moving crustal blocks around the triple junction and San Andreas fault.

  7. 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

  8. 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

  9. 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

  10. Impact of a Large San Andreas Fault Earthquake on Tall Buildings in Southern California

    NASA Astrophysics Data System (ADS)

    Krishnan, S.; Ji, C.; Komatitsch, D.; Tromp, J.

    2004-12-01

    In 1857, an earthquake of magnitude 7.9 occurred on the San Andreas fault, starting at Parkfield and rupturing in a southeasterly direction for more than 300~km. Such a unilateral rupture produces significant directivity toward the San Fernando and Los Angeles basins. The strong shaking in the basins due to this earthquake would have had a significant long-period content (2--8~s). If such motions were to happen today, they could have a serious impact on tall buildings in Southern California. In order to study the effects of large San Andreas fault earthquakes on tall buildings in Southern California, we use the finite source of the magnitude 7.9 2001 Denali fault earthquake in Alaska and map it onto the San Andreas fault with the rupture originating at Parkfield and proceeding southward over a distance of 290~km. Using the SPECFEM3D spectral element seismic wave propagation code, we simulate a Denali-like earthquake on the San Andreas fault and compute ground motions at sites located on a grid with a 2.5--5.0~km spacing in the greater Southern California region. We subsequently analyze 3D structural models of an existing tall steel building designed in 1984 as well as one designed according to the current building code (Uniform Building Code, 1997) subjected to the computed ground motion. We use a sophisticated nonlinear building analysis program, FRAME3D, that has the ability to simulate damage in buildings due to three-component ground motion. We summarize the performance of these structural models on contour maps of carefully selected structural performance indices. This study could benefit the city in laying out emergency response strategies in the event of an earthquake on the San Andreas fault, in undertaking appropriate retrofit measures for tall buildings, and in formulating zoning regulations for new construction. In addition, the study would provide risk data associated with existing and new construction to insurance companies, real estate developers, and

  11. 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. PMID:17778356

  12. 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.

  13. Evidence for Late Oligocene-Early Miocene episode of transtension along San Andreas Fault system in central California

    SciTech Connect

    Stanley, R.G.

    1986-04-01

    The San Andreas is one of the most intensely studied fault systems in the world, but many aspects of its kinematic history remain controversial. For example, the period from the late Eocene to early Miocene is widely believed to have been a time of negligible strike-slip movement along the San Andreas fault proper, based on the rough similarity of offset of the Eocene Butano-Point of rocks Submarine Fan, the early Miocene Pinnacles-Neenach volcanic center, and an early Miocene shoreline in the northern Gabilan Range and San Emigdio Mountains. Nonetheless, evidence indicates that a late Oligocene-early Miocene episode of transtension, or strike-slip motion with a component of extension, occurred within the San Andreas fault system. The evidence includes: (1) about 22-24 Ma, widespread, synchronous volcanic activity occurred at about 12 volcanic centers along a 400-km long segment of the central California coast; (2) most of these volcanic centers are located along faults of the San Andreas system, including the San Andreas fault proper, the San Gregorio-Hosgri fault, and the Zayante-Vergeles fault, suggesting that these and other faults were active and served as conduits for magmas rising from below; (3) during the late Oligocene and early Miocene, a pull-apart basin developed adjacent to the San Andreas fault proper in the La Honda basin near Santa Cruz; and (4) during the late Oligocene and early Miocene, active faulting, rapid subsidence, and marine transgression occurred in the La Honda and other sedimentary basins in central California. The amount of right-lateral displacement along the San Andreas fault proper during this transtentional episode is unknown but was probably about 7.5-35 km, based on model studies of pull-apart basin formation. This small amount of movement is well within the range of error in published estimates of the offset of the Eocene to early Miocene geologic features noted.

  14. 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.

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

    PubMed

    Becken, Michael; Ritter, Oliver; Bedrosian, Paul A; Weckmann, Ute

    2011-12-01

    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. PMID:22129729

  16. The Earthquake Cycle on the San Andreas Fault System in northern California

    NASA Astrophysics Data System (ADS)

    Yikilmaz, M. B.; Turcotte, D. L.; Beketova, O.; Kellogg, L. H.; Rundle, J. B.

    2012-12-01

    An important aspect of the tectonics in northern California is the northward migration of the triple junction across the region which gave birth to the San Andreas transform fault about 28 Myrs ago. The triple junction has formed by the subduction of a spreading ridge that once bounded the Farallon and the Pacific plates. A "slab window" has also been formed during this subduction event. Due to the high heat flow caused by this slab window, a soft zone of deformation with a width of ~100 km has been generated. This deformation zone is bounded on the west by the near rigid Pacific Plate and on the east by the near rigid Sierra-Nevada Central Valley Plate. Continuous and campaign GPS measurements indicate a near-uniform shear strain in this zone of deformation. We propose a hypothesis for the deformation pattern associated with great earthquakes and the linear strain field discussed above. We separate the earthquake cycle into three parts, beginning with the great 1906 earthquake on the San Andreas Fault, these are: 1) The coseismic behavior associated with the great earthquake. We take the slip to be 4 m and the associated stress drop extends some 15 km on either side of the fault. 2) Stress relaxation following the earthquake. This relaxation results in a near uniform state of stress across the zone of deformation and a reloading of the San Andreas Fault. 3)Uniform shear stress loading until the next great earthquake occurs in agreement with the GPS observations. We attribute this near uniform shear to fluid-like behavior beneath the brittle upper lithosphere in which earthquakes occur.

  17. Time-Dependent Coulomb Stres along the San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Smith, B. R.; Sandwell, D. T.

    2003-12-01

    Many questions remain regarding the evolution of stress along the San Andreas Fault System: Which segments of the San Andreas System are approaching failure? What is the stress interaction along different fault segments for likely slip scenarios? To what extent does locking depth influence the regional stress field? To better address these questions, we have developed and tested a semi-analytic, time-dependent model for 3-D displacement and stress caused by a dislocation in an elastic layer over a viscoelastic half-space. Our model is remarkably efficient: a single time-step computation of 2048 by 2048 horizontal grid cells, containing over 400 fault elements within a 900 x 1700 km fault zone, requires approximately 1 minute of CPU time on an ordinary workstation. This speed enables us to rapidly explore various full 3-D viscoelastic models with realistic 1000-year faulting scenarios. Our approach for investigating time-dependent deformation and stress evolution of the San Andreas Fault System is as follows: We represent far-field plate motion by continuous slip in the lower portion of a 50 km thick elastic layer. Earthquakes are modeled by episodic slip along individual faults using spatially-variable locking depth and geologically-estimated recurrence intervals. Each co-seismic event results in an instantaneous change of stress within the viscoelastic half-space that slowly relaxes with time and is coupled with the evolution of stresses within the elastic plate. We investigate such evolving stresses by computing time-dependent Coulomb stress within the seismogenic zone. We find that the evolving stress field is sensitive to plate thickness, half-space viscosity, and faulting scenario. We are currently establishing a suite of models, consistent with both geodetic and geological observations, that will increase our understanding of how temporal plate-boundary deformation and stress variations within the seismogenic crust can result from different tectonic settings

  18. 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

  19. 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.

  20. 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.

  1. 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

  2. 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

  3. 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.

  4. [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. PMID:25962217

  5. 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. PMID:25733589

  6. 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.

  7. 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. PMID:24173678

  8. SEISMIC-REFRACTION PROFILE ACROSS THE SAN ANDREAS, SARGENT, AND CALAVERAS FAULTS, WEST-CENTRAL CALIFORNIA.

    USGS Publications Warehouse

    Mooney, Walter D.; Colburn, Robert H.

    1985-01-01

    Geophysical studies of the upper crustal structure of west-central California are important for the further understanding of the geologic structure and tectonics in this seismically active region. In 1981, the United States Geological Survey recorded a seismic-refraction profile across the southern Santa Cruz Mountains in west-central California to examine the shallow velocity structure of this seismogenic region. This 40-km-long profile, which consisted of three shotpoints, extended northeastward from near Watsonville, California, to Coyote Lake, crossing the San Andreas, Sargent, and Calaveras faults. Refs.

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

    NASA Technical Reports Server (NTRS)

    Prescott, W. H.; Nur, A.

    1981-01-01

    Plate motion below the seismogenic layer along the San Andreas fault system in California is assumed to form by aseismic slip along a deeper extension of the fault or may result from lateral distribution of deformation below the seismogenic layer. The shallow depth of California earthquakes, the depth of the coseismic slip during the 1906 San Francisco earthquake, and the presence of widely separated parallel faults indicate that relative motion is distributed below the seismogenic zone, occurring by inelastic flow rather than by aseismic slip on discrete fault planes.

  10. Structural analysis and risk assessment of the All American pipeline at the San Andreas fault crossing

    SciTech Connect

    Hart, J.D.; Row, D.G.; Drugovich, D.

    1995-12-31

    The All American oil transmission pipeline crosses the San Andreas fault and a series of smaller, associated faults in a fault zone southwest (SW) of Bakersfield, California. The possibility of fault rupture on any of these faults during a major earthquake is a source of concern since such an event could result in pipeline damage or failure. This paper describes the development of a fault displacement risk model, the evaluation of the risk at the All American Pipeline (AAPL) site provided by an initial crossing design, and the evaluation of various alternative designs. A practical alternative design scheme, which significantly reduces the risk of pipeline damage or failure is then recommended.

  11. 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

  12. Sawtooth segmentation and deformation processes on the southern San Andreas fault, California

    NASA Technical Reports Server (NTRS)

    Bilham, R.; Williams, P.

    1985-01-01

    Five contiguous 12-13 km fault segments form a sawtooth geometry on the southernmost San Andreas fault. The kinematic and morphologic properties of each segment depend on fault strike, despite differences of strike between segments of as little as 3 degrees. Oblique slip (transpression) of fault segments within the Indio Hills, Mecca Hills and Durmid Hill results from an inferred 8:1 ratio of dextral slip to convergence across the fault zone. Triggered slip and creep are confined almost entirely to transpressive segments of the fault. Durmid Hill has been formed in the last 28 + or - 6 ka by uplift at an average rate of 3 + or - 1 mm/a.

  13. 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.

  14. Stress near geometrically complex strike-slip faults - Application to the San Andreas fault at Cajon Pass, southern California

    NASA Technical Reports Server (NTRS)

    Saucier, Francois; Humphreys, Eugene; Weldon, Ray, II

    1992-01-01

    A model is presented to rationalize the state of stress near a geometrically complex major strike-slip fault. Slip on such a fault creates residual stresses that, with the occurrence of several slip events, can dominate the stress field near the fault. The model is applied to the San Andreas fault near Cajon Pass. The results are consistent with the geological features, seismicity, the existence of left-lateral stress on the Cleghorn fault, and the in situ stress orientation in the scientific well, found to be sinistral when resolved on a plane parallel to the San Andreas fault. It is suggested that the creation of residual stresses caused by slip on a wiggle San Andreas fault is the dominating process there.

  15. Complex fault interactions in a restraining bend on the San Andreas fault, southern Santa Cruz Mountains, California

    SciTech Connect

    Schwartz, S.Y.; Orange, D.L.; Anderson, R.S. )

    1990-07-01

    The unusual oblique thrust mechanism of the October 18, 1989 Loma Prieta earthquake focused attention on the complex tectonic setting of this segment of the San Andreas Fault. Near the mainshock epicenter, the San Andreas Fault curves to the left defining a restraining bend. The large thrust component of the mainshock focal mechanism is consistent with the horizontal compression expected across restraining bends. However, repeated Loma Prieta type earthquakes cannot exclusively produce the observed topography of the southern Santa Cruz Mountains, the highest point of which experienced subsidence during the 1989 earthquake. In this paper, the authors integrate seismic, geomorphic and tectonic data to investigate the possibility that motions on faults adjacent to the San Andreas Fault play an important role in producing the observed topography. The three-dimensional geometry of active faults in this region is imaged using the Loma Prieta preshock and aftershock sequences. The most conspicuous features of the fault geometries at depth are: (1) the presence of two distinct zones of seismicity corresponding to the San Andreas and the Sargent-Berrocal Fault Zones, (2) the concave upward shape of the Loma Prieta rupture surface, (3) the reduction in dip of the deepest portions of the rupture plane as the mainshock hypocenter is approached, (4) the apparent transfer of shallow slip in some areas from faults in the San Andreas Fault Zone to those in the Sargent-Berrocal Fault Zone, and (5) the presence of a deep northeasterly dipping plane associated with the Sargent-Berrocal Fault Zone. The authors find that a model of fault interactions which involves displacement on faults in both the San Andreas and the Sargent-Berrocal Fault Zones is consistent with Loma Prieta coseismic displacements, preshock and aftershock seismicity and observed topography.

  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. 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.

  18. Structure and Composition of the San Andreas Fault at Seismogenic Depths: Recent Results from the SAFOD Experiment

    NASA Astrophysics Data System (ADS)

    Hickman, S.; Zoback, M.; Ellsworth, W.; Kirschner, D.; Solum, J.

    2004-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) was drilled into the San Andreas Fault Zone to study the physics of earthquake nucleation and rupture and determine the composition, physical properties, and mechanical behavior of an active, plate-bounding fault at seismogenic depths. SAFOD is located 10 km NW of Parkfield, CA, and penetrates a section of the fault that is moving through a combination of repeating microearthquakes and fault creep. During Phases 1 and 2 in the summers of 2004 and 2005, SAFOD was drilled vertically to a depth of 1.5 km and then deviated to penetrate the active San Andreas Fault Zone at a vertical depth of about 2.7 km. During Phase 3 in the summer of 2007, cores were acquired from holes branching off the main SAFOD borehole to directly sample fault and country rocks at depth. Geophysical logs and cuttings analyses conducted during Phases 1 and 2 define the San Andreas Fault Zone to be relatively broad (~250 m), containing several discrete, highly localized 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 3194 m and 3301 m, indicating that they are actively creeping shear zones. These active shear zones were targeted for coring during Phase 3. The 3194 m casing deformation zone lies ~100 m above a cluster of repeating M2 earthquakes that form the southwestern boundary of the creeping and microseismically active San Andreas Fault Zone. Casing deformation is most pronounced across the 3301 m zone; hence this zone is believed to accommodate most of the current creep deformation across the San Andreas Fault at this location. During Phase 3 we have obtained core from just outside the geologically defined San Andreas Fault Zone, at the boundary between the Salinian and Great Valley/Franciscan terranes, and from the active deformation zones at 3194 and 3301 m. The cores obtained from these deformation zones

  19. Structure and Composition of the San Andreas Fault at Seismogenic Depths: Recent Results from the SAFOD Experiment

    NASA Astrophysics Data System (ADS)

    Hickman, S.; Zoback, M.; Ellsworth, W.; Kirschner, D.; Solum, J.

    2007-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) was drilled into the San Andreas Fault Zone to study the physics of earthquake nucleation and rupture and determine the composition, physical properties, and mechanical behavior of an active, plate-bounding fault at seismogenic depths. SAFOD is located 10 km NW of Parkfield, CA, and penetrates a section of the fault that is moving through a combination of repeating microearthquakes and fault creep. During Phases 1 and 2 in the summers of 2004 and 2005, SAFOD was drilled vertically to a depth of 1.5 km and then deviated to penetrate the active San Andreas Fault Zone at a vertical depth of about 2.7 km. During Phase 3 in the summer of 2007, cores were acquired from holes branching off the main SAFOD borehole to directly sample fault and country rocks at depth. Geophysical logs and cuttings analyses conducted during Phases 1 and 2 define the San Andreas Fault Zone to be relatively broad (~250 m), containing several discrete, highly localized 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 3194 m and 3301 m, indicating that they are actively creeping shear zones. These active shear zones were targeted for coring during Phase 3. The 3194 m casing deformation zone lies ~100 m above a cluster of repeating M2 earthquakes that form the southwestern boundary of the creeping and microseismically active San Andreas Fault Zone. Casing deformation is most pronounced across the 3301 m zone; hence this zone is believed to accommodate most of the current creep deformation across the San Andreas Fault at this location. During Phase 3 we have obtained core from just outside the geologically defined San Andreas Fault Zone, at the boundary between the Salinian and Great Valley/Franciscan terranes, and from the active deformation zones at 3194 and 3301 m. The cores obtained from these deformation zones

  20. Seismic images of the deep structure of the San Andreas fault system, central coast ranges, California

    SciTech Connect

    Zandt, G.

    1981-06-10

    Three-dimensional inversion of teleseimic P wave travel time residuals recorded at the U.S. Geological Survey central California array has resolved small-scale (approx.tens of kilometers) crustal and upper mantle heterogeneity down to depths of 90 km beneath the California coast ranges. Upper crustal lateral velocity variations of +- 8% correlate closely with surface geology. Lower-than-average velocities are associated with thick Tertiary sedimentary fill and higher-than-average velocities with basement exposures. Lower crustal velocity heterogeneity of +- 4% appear to reflect crustal thickness variations. A thinner crust is indicated southwest of the San Andreas fault and northwest of San Pablo Bay. A linear zone of low-velocities (0 to -40%) subparallel to the San Andreas fault was resolved in the upper mantle. The preferred interpretation is that the low-velocities indicate a narrow upwarp of asthenosphere to unusually shallow depths (approx.45 km) beneath the coast ranges. Such an unusual upper mantle structure may have been produced by the northwestward migration along the California coast of a transiently unstable Mendocino triple junction. The inversion results also indicate the possibility of partial decoupling of the crust from the upper mantle.

  1. Isotope constraints on the involvement of fluids in the San Andreas Fault System, California

    SciTech Connect

    Pili, E.; Kennedy, B.M.; Conrad, S.M.; Gratier, J.-P.; Poitrasson, F.

    1998-07-01

    Fluids are suspected to play a major role in earthquake mechanics, especially in the case of the weak San Andreas Fault (SAF). Models developed to explain the weakness of the fault are similar but rely on different fluid sources. A recent study of groundwaters associated with the SAF has provided evidence for a geopressured mantle fluid source (Kennedy et al., 1997). We present here an isotope study comparing deformation zones (gouges, breccias, fault veins, slickensides, cataclasites), and vein fillings with their hosts and the fluids associated with these materials, as sampled by fluid inclusions. We are investigating ca. 250 samples from over 20 localities along the San Andreas and adjacent faults from South San Francisco to East Los Angeles. Samples from the exhumed San Gabriel Fault, a deeper equivalent of the SAF, are included as well as samples from the Santa Ynez Fault, another former strand of the SAF embedded in Miocene limestones. All the major lithologies (granites, gneisses, sandstones, limestones, marbles and serpentinites) have been sampled for isotope analyses of C, O, H, He, Ne, Ar, Sr, Nd, and Pb.

  2. Fault coupling and potential for earthquakes on the creeping section of the central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Maurer, Jeremy; Johnson, Kaj

    2014-05-01

    The 150 km long central section of the San Andreas Fault (CSAF) in central California creeps at the surface and has not produced a large earthquake historically. However, sections of the San Andreas Fault to the north and south are known to have ruptured repeatedly in M~7-8 earthquakes. It is currently unclear whether the creeping CSAF could rupture in large earthquakes, either individually or along with earthquakes on the locked sections to the north and south. We invert Global Positioning System and interferometric synthetic aperture radar data with elastic block models to estimate the degree of locking on the CSAF and place bounds on the moment accumulation rate on the fault. We find that the inferred moment accumulation rate is highly dependent on the long-term fault slip rate, which is poorly constrained along the CSAF. The inferred moment accumulation rate, normalized by shear modulus, ranges from 3.28 × 104 to 5.85 × 107 m3/yr, which is equivalent to a Mw = 5.5-7.2 earthquake every 150 years 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. The comparisons of slip distributions with microseismicity and repeating earthquakes indicate a possible locked patch between 10 and 20 km depth on the CSAF that could potentially rupture with Mw = 6.5.

  3. Geodimeter measurements of slip and strain accumulation along the san andreas fault

    USGS Publications Warehouse

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

    1974-01-01

    The U.S. Geological Survey conducts repeated geodimeter surveys of trilateration networks in central California in order to study the processes of slip and strain accumulation along the San Andreas fault. The precision of distance measurement is described by a standard deviation ?? = (a2 + b2L2) 1 2 where a = 3mm, b = 2 ?? 10-7, and L is the line length. Within the precision of measurement, no anomalous strain episodes preceding earthquakes or even strain discontinuities at the time of earthquakes were detected from repeated measurements of lines near the epicenters of small (magnitude 4.5-5.1) earthquakes. Annual measurements of small (5-km aperture) strain polygons near the San Andreas fault have not proved strain accumulation in a 3-year period. Repeated measurements of longer lines over periods of 8 to 14 years indicate changes that cannot be attributed to fault slip and must represent strain accumulation at the level of a few parts in 107 per year. ?? 1974.

  4. 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. PMID:26107459

  5. 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. PMID:20033046

  6. Layered crustal anisotropy around the San Andreas Fault near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Audet, Pascal

    2015-05-01

    The rheology of the Earth's crust controls the long-term and short-term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials. In this paper we examine the seismic structure and anisotropy of the crust around the San Andreas Fault (SAF) near Parkfield, California, using teleseismic receiver functions. These data indicate that the crust is characterized by spatially variable and strongly anisotropic upper and middle crustal layers, with a Moho at ˜35 km depth. The upper layer is ˜5-10 km thick and is characterized by strong (≥30%) anisotropy with a slow axis of hexagonal symmetry, where the plane of fast velocity has a strike parallel to that of the SAF and a dip of ˜40∘. We interpret this layer as pervasive fluid-filled microcracks within the brittle deformation regime. The ˜10-15 km thick midcrustal layer is also characterized by a weak axis of hexagonal symmetry with ≥20% anisotropy, but the dip direction of the plane of fast velocity is reversed. The midcrustal anisotropic layer is more prominent to the northeast of the San Andreas Fault. We interpret the mid crustal anisotropic layer as fossilized fabric within fluid-rich foliated mica schists. When combined with various other geophysical observations, our results suggest that fault creep behavior around Parkfield is favored by intrinsically weak and overpressured crustal fabric.

  7. 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.

  8. 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.

  9. 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.

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

    USGS Publications Warehouse

    Hickman, Stephen; Younker, Leland; Zobeck, Mark; Cooper, George

    1994-01-01

    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 an integrated program of coring, fluid sampling, in-situ and laboratory experimentation and long-term monitoring, we hope to provide fundamental constraints 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 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 seismicity and a broad range of physical and chemical properties over 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 regions of greatest scientific interest.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  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. Reinterpretation of the Northern Terminus of the San Andreas Transform System: Implications for basin development and hydrocarbon exploration

    SciTech Connect

    Foland, S.S. ); Enzor, K.J. )

    1994-07-01

    The northern San Andreas transform system was studied to evaluate the tectonic history of offshore Point Arena basin, northern California. The Point Arena basin lies 250 km north of San Francisco and encompasses 8500 km[sup 2] on the outer continental shelf. It is a tertiary basin formed during Eocene subduction and overprinted by Pliocene-Pleistocene strike-slip motion of the San Andreas fault system. Interpretation of the data yields a new tectonic model for the northern San Andreas fault system and Point Arena basin. Previous models curved the fault system east parallel to the coast, intersecting faults exposed on Point Delgada, and then bending the fault sharply west to join the Mendocino triple junction. The new model projects the San Andreas fault system due northwest, straight into the offshore basin, as a series of parallel faults aligned with the onshore fault trace to directly intersect the triple junction. The new interpretation is supported by aeromagnetic data, which indicates the basin is divided by a major northwest-trending structural boundary and floored by two distinct basement types (Mesozoic Salinian granies and Jurassic Franciscan metasediments). The latest seismic data contain enough information to determine the genesis and orientation of the offshore fault system and associated folds. Basin modeling indicates hydrocarbon generation has occurred in the Miocene source beds. The model estimates the Point Arena basin contains multibillion barrel potential trapped in large antiforms associated with the through-going San Andreas system. Integration of all geotechnical data allowed reinterpretation of the tectonic history, and produced an enhanced understanding of Point Arena basin.

  19. Break of slope in earthquake size distribution and creep rate along the San Andreas Fault system

    NASA Astrophysics Data System (ADS)

    Vorobieva, Inessa; Shebalin, Peter; Narteau, Clément

    2016-07-01

    Crustal faults accommodate slip either by a succession of earthquakes or continuous slip, and in most instances, both these seismic and aseismic processes coexist. Recorded seismicity and geodetic measurements are therefore two complementary data sets that together document ongoing deformation along active tectonic structures. Here we study the influence of stable sliding on earthquake statistics. We show that creep along the San Andreas Fault is responsible for a break of slope in the earthquake size distribution. This slope increases with an increasing creep rate for larger magnitude ranges, whereas it shows no systematic dependence on creep rate for smaller magnitude ranges. This is interpreted as a deficit of large events under conditions of faster creep where seismic ruptures are less likely to propagate. These results suggest that the earthquake size distribution does not only depend on the level of stress but also on the type of deformation.

  20. A 100-year average recurrence interval for the San Andreas fault at Wrightwood, California

    USGS Publications Warehouse

    Fumal, T.E.; Pezzopane, S.K.; Weldon, R.J., II; Schwartz, D.P.

    1993-01-01

    Evidence for five large earthquakes during the past five centuries along the San Andreas fault zone 70 kilometers northeast of Los Angeles, California, indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought. Rapid sedimentation during the past 5000 years in a 150-meter-wide structural depression has produced a greater than 21-meter-thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers. Fault scarps, colluvial wedges, fissure infills, upward termination of ruptures, and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in A.D. 1857, 1812, and about 1700, 1610, and 1470.

  1. 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.

  2. 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. PMID:25742586

  3. 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. PMID:26761152

  4. Andreas Vesalius' 500th Anniversary: First Description of the Mammary Suspensory Ligaments.

    PubMed

    Brinkman, Romy J; Hage, J Joris

    2016-09-01

    Sir Astley Paston Cooper has, to date, been acknowledged to be the first to describe the suspensory ligaments of the breast, or Cooper's ligaments, in 1840. We found these ligaments to be recorded in the first edition of 'De Humani Corporis Fabrica Libri Septem' by Andreas Vesalius, published in 1543. To commemorate Vesalius' 500th birthday, we quote and discuss this earlier record. Vesalius' record of the nature and function of the fleshy membrane between mammary gland and pectoral muscle, the hard fat intervening the mammary glands, and the fibers running from the fleshy membrane to the skin are a clear representation of posterior layer of the superficial fascial system, the fibro-adipose stroma surrounding and linking the mammary glandular elements, and the suspensory ligaments as we know them. Vesalius recorded the anatomy and function of the latter structures nearly 300 years before Sir Astley Paston Cooper did. PMID:26943658

  5. 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. 

  6. A 100-year average recurrence interval for the san andreas fault at wrightwood, california.

    PubMed

    Fumal, T E; Schwartz, D P; Pezzopane, S K; Weldon, R J

    1993-01-01

    Evidence for five large earthquakes during the past five centuries along the San Andreas fault zone 70 kilometers northeast of Los Angeles, California, indicates that the average recurrence interval and the temporal variability are significantly smaller than previously thought. Rapid sedimentation during the past 5000 years in a 150-meter-wide structural depression has produced a greater than 21-meter-thick sequence of debris flow and stream deposits interbedded with more than 50 datable peat layers. Fault scarps, colluvial wedges, fissure infills, upward termination of ruptures, and tilted and folded deposits above listric faults provide evidence for large earthquakes that occurred in A.D. 1857, 1812, and about 1700, 1610, and 1470. PMID:17790984

  7. Evidence for chaotic fault interactions in the seismicity of the San Andreas fault and Nankai trough

    NASA Technical Reports Server (NTRS)

    Huang, Jie; Turcotte, D. L.

    1990-01-01

    The dynamical behavior introduced by fault interactions is examined here using a simple spring-loaded, slider-block model with velocity-weakening friction. The model consists of two slider blocks coupled to each other and to a constant-velocity driver by elastic springs. For an asymmetric system in which the frictional forces on the two blocks are not equal, the solutions exhibit chaotic behavior. The system's behavior over a range of parameter values seems to be generally analogous to that of weakly coupled segments of an active fault. Similarities between the model simulations and observed patterns of seismicity on the south central San Andreas fault in California and in the Nankai trough along the coast of southwestern Japan.

  8. Geodetic measurement of deformation east of the San Andreas Fault in Central California

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    The shear strain rates in the Diablo Range of California have been calculated, and the slip rate along the Calaveras and Paicines faults in Central California have been estimated, on the basis of triangulation and trilateration data from two geodetic networks located between the western edge of the Great Valley and the San Andreas Fault. The orientation of the principal compressive strain predicted from the azimuth of the major structures in the region is N 25 deg E, leading to an average shear strain value that corresponds to a relative shortening rate of 4.5 + or - 2.4 mm/yr. It is inferred that the measured strain is due to compression across the fold of this area. The hypothesized uniform, fault-normal compression within the Coast Ranges is not supported by these results.

  9. Clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield, california.

    PubMed

    Nadeau, R M; Foxall, W; McEvilly, T V

    1995-01-27

    The San Andreas fault at Parkfield, California, apparently late in an interval between repeating magnitude 6 earthquakes, is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters (<20-meter radius) of microearthquakes. Within these clusters, which account for 63% of the earthquakes in a 1987-92 study interval, virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes. Sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second. The rate of earthquake occurrence, particularly at depth, increased significantly during the study period, but the fraction of earthquakes that were cluster members decreased. PMID:17788785

  10. Periodic, chaotic, and doubled earthquake recurrence intervals on the deep San Andreas fault.

    PubMed

    Shelly, David R

    2010-06-11

    Earthquake recurrence histories may provide clues to the timing of future events, but long intervals between large events obscure full recurrence variability. In contrast, small earthquakes occur frequently, and recurrence intervals are quantifiable on a much shorter time scale. In this work, I examine an 8.5-year sequence of more than 900 recurring low-frequency earthquake bursts composing tremor beneath the San Andreas fault near Parkfield, California. These events exhibit tightly clustered recurrence intervals that, at times, oscillate between approximately 3 and approximately 6 days, but the patterns sometimes change abruptly. Although the environments of large and low-frequency earthquakes are different, these observations suggest that similar complexity might underlie sequences of large earthquakes. PMID:20538948

  11. Steep-dip seismic imaging of the shallow San Andreas fault near Parkfield.

    PubMed

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

    2001-11-16

    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 degrees 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. PMID:11711672

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

    PubMed

    Jones, C H; Wesnousky, S G

    1992-04-01

    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. PMID:17802597

  13. Comparative geometry of the San Andreas Fault, California, and laboratory fault zones

    USGS Publications Warehouse

    Moore, Diane E.; Byerlee, J.D.

    1991-01-01

    Textural examination of fault gouge deformed in triaxial friction experiments has revealed differences in the orientations of secondary shear sets between the stably sliding and stick-slip samples. In order to determine whether such differences can be identified in natural faults, maps of recently active breaks along the San Andreas fault were examined to compare the types and orientations of secondary structures mapped in the creeping and locked sections. The fault zone was divided into 52 geometrically defined segments of uniform strike, which were then grouped into 7 sections: 4 straight and two curved sections, and Cholame Valley. Many of the gross geometric characteristics of the individual segments, such as length, width, and stepover size, reflect their position in either a straight or a curved section. In contrast, with respect to the orientations of the recent breaks within the segments, the single creeping section differs from all of the locked sections, both straight and curved. -from Authors

  14. 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

  15. 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.

  16. 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. PMID:24376313

  17. Potential role of mantle-derived fluids in weakening the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Fulton, Patrick M.; Saffer, Demian M.

    2009-07-01

    On the basis of both geomechanical and thermal data, the San Andreas Fault (SAF) has been interpreted to act as a weak plane within much stronger crust, allowing it to slip at very low shear stresses. One explanation for this weakness is that large fluid overpressures exist locally within the fault zone. However, mechanisms for generating, maintaining, and localizing pressures within the fault are poorly quantified. Here we evaluate whether realistic sources of mantle-derived fluids, proposed on the basis of high mantle helium signatures near the SAF, can generate localized fluid pressures within the fault zone in a manner consistent with a wide range of observations along the fault and in the San Andreas Fault Observatory at Depth borehole. We first calculate a reasonable estimate of the magnitude and location of a mantle-derived flux of water into the crust. This fluid flux results from dehydration of a serpentinized mantle wedge following the northward migration of the Mendocino Triple Junction and the transition from subduction to strike-slip tectonics. We then evaluate the potential effect of this water on fluid pressures within the crust using 2-D cross-sectional models of coupled fluid flow and heat transport. We show that in models with realistic permeability anisotropy, controlled by NE dipping faults and fractures within the country rock, large localized fluid pressures can be focused within a SAF acting as a hydrologic barrier. Our results illustrate a simple and potentially plausible means of weakening the SAF in a manner generally consistent with available hydrologic, thermal, and mechanical constraints.

  18. 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.

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) scientific drill hole 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 Ω-m) and permeability (10-21 to 10-22 m2) in the actively deforming zones were 1 to 2 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.

  3. San Andreas fault zone velocity structure at SAFOD at core, log, and seismic scales

    NASA Astrophysics Data System (ADS)

    Jeppson, Tamara N.; Tobin, Harold J.

    2015-07-01

    The San Andreas Fault (SAF), like other mature brittle faults, exhibits a zone of low seismic velocity hypothesized to result from fluid pressure effects and/or development of a damage zone. To address the relative contributions of these mechanisms in developing low-velocity zones, we measured P and S wave velocities ultrasonically at elevated confining and pore pressures on core samples from the San Andreas Fault Observatory at Depth (SAFOD). We compared those data to wireline and seismic-scale velocities to examine the scale dependence of acoustic properties of the fault core and damage zone. Average laboratory P and S wave velocities of the fault gouge at estimated in situ conditions are 3.1 and 1.5 km/s, respectively, consistent with the sonic log from the same intervals. These data show that fault core has intrinsically low velocity, even if no anomalous pore pressure is assumed, due to alteration and mechanical damage. In contrast, laboratory average P and S wave velocities for the damage zone are 4.7 and 2.5 km/s, up to 41% greater than the sonic log in the damage zone. This scale dependence indicates that stress conditions or macroscale features dominate the damage zone's acoustic properties, although velocity dispersion could play a role. Because no pressure anomaly was detected while drilling the SAFOD borehole, we infer that damage at a scale larger than core samples controls the elastic properties of the broader damage zone. This result bolsters other independent lines of evidence that the SAF does not contain major pore fluid overpressure at SAFOD.

  4. The San Andreas fault zone drilling project: Scientific objectives and technological challenges

    SciTech Connect

    Hickman, S.; Younker, L.; Zobeck, M.; Cooper, G.

    1994-12-31

    The authors 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 an integrated program of coring, fluid sampling, in-situ and laboratory experimentation and long-term monitoring, the authors hope to provide fundamental constraints 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 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 seismicity and a broad range of physical and chemical properties over 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, the authors expect to encounter difficult drilling, coring and hole-completion conditions in the regions of greatest scientific interest.

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

    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.

  6. Response of creepmeters on the San Andreas fault near Parkfield to the earthquake

    SciTech Connect

    Schulz, S.S.; Mavko, G.M.; Brown, B.D.

    1990-01-01

    A total of 14 US Geological Survey creepmeters on the San Andreas fault in central California recorded coseismic steps coincident with the M = 6.7 May 2 earthquake. Creepmeters near Parkfield recorded the largest effects. Postearthquake creep rates slowed significantly, and creep at one station reversed to left lateral. About 4 months after the earthquake, decreased rates caused cumulative creep at four Parkfield stations to fall below long-term linear trends observed before May 2. At several stations, creep continued to be either left lateral or slower than normal for the rest of 1983. By January 31, 1984, all but two stations recorded resumption of right-lateral creep at reduced rates. As late as April 1, 1984, however, one station north of Parkfield continued to record left-lateral drift, and another station at the south end of the creeping section south of Parkfield recorded little or no movement. One interpretation of the creep slowdown after May 2 is that the Coalinga main shock released accumulated stress in the upper kilometer or so of the San Andreas fault near Parkfield, and several months elapsed before stress built up sufficiently to allow creep to resume. A multiple-linear-regression analysis of coseismic-step size as a function of distance from the creepmeter to an earthquake focus and (or) earthquake magnitude showed a linear correlation between step size and magnitude for the data from two stations. No correlation was found between step size and distance to focus for the data from any of the stations. Reduction in step sizes after May 2, despite numerous large aftershocks, suggests that stored local stress is the dominant factor in coseismic-step size.

  7. The San Andreas fault zone drilling project: Scientific objectives and technological challenges

    SciTech Connect

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

    1995-12-01

    The authors 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, the authors 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, the authors expect to encounter difficult drilling, coring and hole-completion conditions in the region of greatest scientific interest.

  8. A more precise chronology of earthquakes produced by the San Andreas fault in southern California

    SciTech Connect

    Sieh, K. ); Stuiver, M. ); Brillinger, D. )

    1989-01-10

    Improved methods of radiocarbon analysis have enabled the authors to date more precisely the earthquake ruptures of the San Andreas fault that are recorded in the sediments at Pallett Creek. New error limits are less than 23 calendar years for all but two of the dated event. The new date ranges, with one exception, fall within the broader ranges estimated previously, but the estimate of the average interval between the latest 10 episodes of faulting is now about 132 years. Five of the nine intervals are shorter than a century: Three of the remaining four intervals are about two to three centuries long. Despite the wide range of these intervals, a pattern in the occurrence of large earthquakes at Pallett Creek is apparent in the new data. The past 10 earthquakes occur in four clusters, each of which consists of two or three events. Earthquakes within the clusters are separated by periods of several decades, but the clusters are separated by dormant periods of two to three centuries. This pattern may reflect important mechanical aspects of the fault's behavior. If this pattern continues into the future, the current period of dormancy will probably be greater than two centuries. This would mean that the section of the fault represented by the Pallett Creek site is currently in the middle of one of its longer periods of repose between clusters, and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in California. The greater precision of dates now available for large earthquakes recorded at the Pallett Creek site enables speculative correlation of events between paleoseismic sites along the southern half of the San Andreas fault. A history of great earthquakes with overlapping rupture zones along the Mojave section of the fault remains one of the more attractive possibilities.

  9. 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.

  10. Samples and Data Products from the San Andreas Fault Observatory at Depth (SAFOD)

    NASA Astrophysics Data System (ADS)

    Weiland, C.; Zoback, M.; Hickman, S.; Ellsworth, W.

    2007-12-01

    The San Andreas Fault Observatory at Depth (SAFOD), a part of the National Science Foundation's EarthScope program, has recently completed the third phase of drilling and coring. With additional support from the USGS and the International Continental Drilling Program (ICDP), we have obtained over 30m of core from active deforming sections of the San Andreas Fault. In addition to the core, cuttings, and fluid samples collected at the drill site, there have been several successful instrument deployments in both the Pilot Hole and Main Hole, during the past year. This paper will discuss the acquisition, storage and distribution plan for the diverse types of data and samples that have been collected at SAFOD to date. The website at http://safod.icdp-online.org provides the detailed descriptions of all the physical samples (cuttings, core and fluid samples) available from SAFOD, together with sample request form and other general information on the SAFOD project. The samples are being archived at the , Integrated Ocean Drilling Program's Gulf Coast Repository in College Station, Texas. The geophysical monitoring program at SAFOD continues to expand. There is a real-time seismic data stream of 250 sample/sec data (downsampled from the 4000 sample/sec onsite data). Helicorder previews can be viewed at http://quake.wr.usgs.gov/cgi-bin/helipark.pl. The high sample rate data are available in SEED format from the Northern California Earthquake Data Center (http://quake.geo.berkeley.edu/safod/) and from the IRIS data center (http://www.iris.edu/data/data.htm). And, new this year, there are now both tiltmeter and strainmeter data flowing to the data centers on a daily basis, available at http://www.ncedc.org. As with all elements of EarthScope, these data and samples are openly available to members of the scientific and educational communities.

  11. Northern California LIDAR Data: A Tool for Mapping the San Andreas Fault and Pleistocene Marine Terraces in Heavily Vegetated Terrain

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Crosby, C. J.; Harding, D. J.; Haugerud, R. A.; Merritts, D. J.; Gardner, T. W.; Koehler, R. D.; Baldwin, J. N.

    2003-12-01

    Recent acquisition of airborne LIDAR (also known as ALSM) data covering approximately 418 square kilometers of coastal northern California provides a powerful new tool for mapping geomorphic features related to the San Andreas Fault and coastal uplift. LIDAR data has been previously used in the Puget Lowland region of Washington to identify and map Holocene faults and uplifted shorelines concealed under dense vegetation (Haugerud et al., 2003; see http://pugetsoundlidar.org). Our effort represents the first use of LIDAR data for this purpose along the San Andreas Fault. This data set is the result of a collaborative effort between NASA Solid Earth and Natural Hazards Program, Goddard Space Flight Center, Stennis Space Center, USGS, and TerraPoint, LLC. The coverage extends from near Fort Ross, California, in Sonoma County, along the coast northward to the town of Mendocino, in Mendocino County, and as far inland as about 1-3 km east of the San Andreas Fault. The survey area includes about 70 km of the northern San Andreas Fault under dense redwood forest, and Pleistocene coastal marine terraces both north and south of the fault. The average data density is two laser pulses per square meter, with up to four LIDAR returns per pulse. Returns are classified as ground or vegetation, allowing construction of both canopy-top and bare-earth DEMs with 1.8m grid spacing. Vertical accuracy is better than 20 cm RMSE, confirmed by a network of ground-control points established using high-precision GPS surveying. We are using hillshade images generated from the bare-earth DEMs to begin detailed mapping of geomorphic features associated with San Andreas Fault traces, such as scarps, offset streams, linear valleys, shutter ridges, and sag ponds. In addition, we are using these data in conjunction with field mapping and interpretation of conventional 1:12,000 and 1:6000 scale aerial photographs to map and correlate marine terraces to better understand rates of coastal uplift, and

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. Crustal structure across the San Andreas Fault at the SAFOD site from potential field and geologic studies

    USGS Publications Warehouse

    McPhee, D.K.; Jachens, R.C.; Wentworth, C.M.

    2004-01-01

    We present newly compiled magnetic, gravity, and geologic datasets from the Parkfield region around the San Andreas Fault Observatory at Depth (SAFOD) pilot hole in order to help define the structure and geophysical setting of the San Andreas Fault (SAF). A 2-D cross section of the SAF zone at SAFOD, based on new, tightly spaced magnetic and gravity observations and surface geology, shows that as drilling proceeds NE toward the SAF, it is likely that at least 2 fault bounded magnetic slivers, possibly consisting of magnetic granitic rock, serpentinite, or unusually magnetic sandstone, will be encountered. The upper 2 km of the model is constrained by an order of magnitude increase in magnetic susceptibility at 1400 m depth observed in pilot hole measurements. NE of the SAF, a flat lying, tabular body of serpentinite at 2 km depth separates two masses of Franciscan rock and truncates against the SAF.

  17. 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. PMID:20093439

  18. A nonlinear least-squares inverse analysis of strike-slip faulting with application to the San Andreas fault

    NASA Technical Reports Server (NTRS)

    Williams, Charles A.; Richardson, Randall M.

    1988-01-01

    A nonlinear weighted least-squares analysis was performed for a synthetic elastic layer over a viscoelastic half-space model of strike-slip faulting. Also, an inversion of strain rate data was attempted for the locked portions of the San Andreas fault in California. Based on an eigenvector analysis of synthetic data, it is found that the only parameter which can be resolved is the average shear modulus of the elastic layer and viscoelastic half-space. The other parameters were obtained by performing a suite of inversions for the fault. The inversions on data from the northern San Andreas resulted in predicted parameter ranges similar to those produced by inversions on data from the whole fault.

  19. Evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend.

    PubMed

    Anderson, R S

    1990-07-27

    The late Quaternary marine terraces near Santa Cruz, California, reflect uplift associated with the nearby restraining bend on the San Andreas fault. Excellent correspondence of the coseismic vertical displacement field caused by the 17 October 1989 magnitude 7.1 Loma Prieta earthquake and the present elevations of these terraces allows calculation of maximum long-term uplift rates 1 to 2 kilometers west of the San Andreas fault of 0.8 millimeters per year. Over several million years, this uplift, in concert with the right lateral translation of the resulting topography, and with continual attack by geomorphic processes, can account for the general topography of the northern Santa Cruz Mountains. PMID:17755944

  20. 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

  1. 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

  2. Shallow structure and geomorphology, northern San Andreas fault, Bodega Bay to Fort Ross, California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Hartwell, S. R.; Manson, M. W.

    2013-12-01

    We mapped a 35-km-long section of the northwest-trending San Andreas fault zone (SAFZ), extending through Bodega Bay, crossing the onshore Bodega Head isthmus, and continuing in the offshore to Fort Ross, California. Mapping is based on integrated analysis of high-resolution seismic-reflection profiles (38 fault crossings), multibeam bathymetry and backscatter data, onshore geology, seafloor-sediment samples, and digital camera and video imagery. In Bodega Bay, the SAFZ comprises multiple parallel to subparallel strands that extend through a 2-km-wide basin flanked by massive basement terranes, Cretaceous granitic rock on the southwest and Jurassic and Cretaceous Franciscan Complex on the northeast. Seismic profiles reveal the smooth basin seafloor is underlain by a thin (1 to 12 m) layer of latest Pleistocene and Holocene sediments and an underlying inferred Pleistocene unit characterized by faulted and folded reflections revealing numerous angular unconformities and channels. This geology suggests that Bodega Bay originated as a pull-apart basin formed by an eastern transfer of slip within the SAFZ. If so, the pervasive internal folding and faulting of the young basin fill suggests basin subsidence has largely ended and the basin fill is now being deformed. North of the Bodega Head isthmus, the SAFZ is relatively narrow (200 to 500 m wide) and cuts across relatively flat seafloor covered by sediments derived from the Russian River and Salmon Creek. Gentle fault bends and transfers of slip between subparallel strands have resulted in small fault-zone uplifts and four distinct, elongate (~ 500- to 2300-m long), narrow (~ 200- to 300-m wide) sag basins containing as much as 56 m of inferred latest Pleistocene to Holocene sediment. The offshore mapping suggests the presence of an important, previously unrecognized onshore SAFZ strand cutting across the Bodega Head isthmus about 800 m southwest of the only reported 1906 surface rupture in the map area. Onshore, this

  3. 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.

  4. 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.

  5. Magnitude of shear stress on the san andreas fault: implications of a stress measurement profile at shallow depth.

    PubMed

    Zoback, M D; Roller, J C

    1979-10-26

    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 shortterm prediction of large earthquakes. PMID:17809367

  6. 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.

  7. Body-Wave Scattering from Seismic Interferometry: Preliminary Results from the San Andreas Fault near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Mosher, S. G.; Audet, P.

    2015-12-01

    High-resolution direct tomographic imaging of subsurface Earth structures is generally limited by the distribution of seismic sources necessary for such studies. However, seismic interferometry has the potential to significantly overcome this issue through the use of ambient seismic noise recordings. Whereas the recovery of virtual surface waves via seismic interferometry techniques are the most abundant results produced by such studies, it has recently been shown that virtual body waves can also be recovered under appropriate conditions. Of particular interest to us is the scattering of body waves produced by velocity discontinuities in the subsurface, which dramatically improves our ability to characterize seismic velocity structures. In this work, using ambient seismic noise recordings across a network of stations near Parkfield, California, we observe both virtual P waves traversing the San Andreas Fault as well as non-fault-traversing P waves on either side. From observed fault-traversing P waves we propose a P wave velocity model of the San Andreas Fault. We further investigate the possibility of recovering body-wave scattering from interactions with velocity discontinuities associated with the fault. From such body-wave scattering interactions we test whether mode-conversions (P to S waves) can be observed using these virtual Green's functions. Additionally, using non-fault-traversing P waves we explore differences in velocity structure on either side of the San Andreas Fault in the Parkfield region. Finally, we examine the potential of seismic interferometry to produce time-lapse body-wave characterizations of the San Andreas Fault, in which properties of the fault can be seen to change in time

  8. 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

  9. The B4 Project: Scanning the San Andreas and San Jacinto Fault Zones

    NASA Astrophysics Data System (ADS)

    Bevis, M.; Hudnut, K.; Sanchez, R.; Toth, C.; Grejner-Brzezinska, D.; Kendrick, E.; Caccamise, D.; Raleigh, D.; Zhou, H.; Shan, S.; Shindle, W.; Yong, A.; Harvey, J.; Borsa, A.; Ayoub, F.; Shrestha, R.; Carter, B.; Sartori, M.; Phillips, D.; Coloma, F.

    2005-12-01

    We performed a high-resolution topographic survey of the San Andreas and San Jacinto fault zones in southern California, in order to obtain pre-earthquake imagery necessary to determine near-field ground deformation after a future large event (hence the name B4), and to support tectonic and paleoseismic research. We imaged the faults in unprecedented detail using Airborne Laser Swath Mapping (ALSM) and all-digital navigational photogrammetry. The scientific purpose of such spatially detailed imaging is to establish actual slip and afterslip heterogeneity so as to help resolve classic `great debates' in earthquake source physics. We also expect to be able to characterize near-field deformation associated with the along-strike transition from continuously creeping to fully locked sections of the San Andreas fault with these data. In order to ensure that the data are extraordinarily well georeferenced, an abnormally intensive array of GPS ground control was employed throughout the project. For calibration and validation purposes, numerous areas along the fault zones were blanketed with kinematic GPS profiles. For redundant determination of the airborne platform trajectory, the OSU independent inertial measurement unit and GPS system were included in the flight payload along with the NCALM equipment. Studies using the ground control are being conducted to estimate true accuracy of the airborne data, and the redundant flight trajectory data are being used to study and correct for errors in the airborne data as well. All of this work is directed at overall improvement in airborne imaging capabilities, with the intent of refining procedures that may then be used in the large-scale GeoEarthScope project over the next few years, led by UNAVCO. More generally, we also intend to improve airborne imaging to the point of geodetic quality. The present NSF-funded project, led by Ohio State University and the U. S. Geological Survey, was supported in all aspects of the airborne

  10. 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

  11. Investigating the Creeping Segment of the San Andreas Fault using InSAR time series analysis

    NASA Astrophysics Data System (ADS)

    Rolandone, Frederique; Ryder, Isabelle; Agram, Piyush S.; Burgmann, Roland; Nadeau, Robert M.

    2010-05-01

    We exploit the advanced Interferometric Synthetic Aperture Radar (InSAR) technique referred to as the Small BAseline Subset (SBAS) algorithm to analyze the creeping section of the San Andreas Fault in Central California. Various geodetic creep rate measurements along the Central San Andreas Fault (CSAF) have been made since 1969 including creepmeters, alignment arrays, geodolite, and GPS. They show that horizontal surface displacements increase from a few mm/yr at either end to a maximum of up to ~34 mm/yr in the central portion. They also indicate some discrepancies in rate estimates, with the range being as high as 10 mm/yr at some places along the fault. This variation is thought to be a result of the different geodetic techniques used and of measurements being made at variable distances from the fault. An interferometric stack of 12 interferograms for the period 1992-2001 shows the spatial variation of creep that occurs within a narrow (<2 km) zone close to the fault trace. The creep rate varies spatially along the fault but also in time. Aseismic slip on the CSAF shows several kinds of time dependence. Shallow slip, as measured by surface measurements across the narrow creeping zone, occurs partly as ongoing steady creep, along with brief episodes with slip from mm to cm. Creep rates along the San Juan Bautista segment increased after the 1989 Loma Prieta earthquake and slow slip transients of varying duration and magnitude occurred in both transition segments The main focus of this work is to use the SBAS technique to identify spatial and temporal variations of creep on the CSAF. We will present time series of line-of-sight (LOS) displacements derived from SAR data acquired by the ASAR instrument, on board the ENVISAT satellite, between 2003 and 2009. For each coherent pixel of the radar images we compute time-dependent surface displacements as well as the average LOS deformation rate. We compare our results with characteristic repeating microearthquakes that

  12. San Andreas Structural Interpretation: Merging Geophysical and Geological Data at SAFOD and Vicinity

    NASA Astrophysics Data System (ADS)

    Wood, R. E.; Evans, J. P.; Malin, P.

    2010-12-01

    Cross sections across the San Andreas Fault (SAF) have gradually evolved from depicting the fault as a simple vertical strike-slip fault into an elaborate network of faults. We present new data bearing on this issue from the San Andreas Fault Observatory at Depth (SAFOD) project. We have integrated borehole geology and geophysics with earlier surface mapping to reveal an imbricate fault zone with complex lithologic and structural interactions. Our data include vertical seismic profiles (VSP) from the drill bit seismic (DBS) method and sample analyses along the SAFOD borehole. The DBS method yields a seismic profile which complements surface seismic data as the drill bit penetrated the rock. The SAFOD Pilot Hole (PH) array of seismometers was used to record waves from steeply dipping reflectors in and around the fault zone. The DBS images resolve the subvertical structure below 2 km depth - previously hidden in surface seismic data. These data can be combined with P-wave velocity tomography and fault-guided wave data to reveal features not seen on surface data, but that are important elements of the fault zone structure. We find that the fault consists of an 83° SW-dipping active plane to a depth of 5 km. At this depth it approaches the steeply NE-dipping Buzzard Canyon fault. Together these faults bound a highly fractured and steeply dipping sequence of the deformed arkosic rocks retrieved from the SAFOD borehole. The bounding faults may merge at ~ 6 km depth, each consisting of several subparallel strands. The seismic reflectors and borehole well logs document the presence of steep-dipping arkosic beds and steeply SW-dipping faults. The main trace of the SAF resides within a low-velocity zone (LVZ) ~ 200 m wide. A well-defined reflector ~ 400 m northeast of this zone may be the fault contact between the Cretaceous Great Valley and Jurassic Franciscan formations, consistent with the down-dip projection of the Gold Hill Fault. These data indicate the faults bound a

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. A Study of the San Andreas Slip Rate on the San Francisco Peninsula, California

    NASA Astrophysics Data System (ADS)

    Feigelson, L. M.; Prentice, C.; Grove, K.; Caskey, J.; Ritz, J. F.; Leslie, S.

    2008-12-01

    The most recent large earthquake on the San Andreas Fault (SAF) along the San Francisco Peninsula was the great San Francisco earthquake of April 18, 1906, when a Mw= 7.8 event ruptured 435-470 km of the northern SAF. The slip rate for this segment of the SAF is incompletely known but is important for clarifying seismic hazard in this highly urbanized region. A previous study south of our site has found an average slip rate of 17±4 mm/yr for the late Holocene on the San Francisco Peninsula segment of the SAF. North of the Golden Gate, the SAF joins the San Gregorio Fault with an estimated slip rate of 6 mm/yr. A trench study north of where the two faults join has produced an average late Holocene slip rate of 24±3 mm/yr. To refine slip-rate estimates for the peninsula segment of the SAF, we excavated a trench across the fault where we located an abandoned channel between the San Andreas and Lower Crystal Springs reservoirs. This abandoned channel marks the time when a new channel cut across the SAF; the new channel has since been offset in a right-lateral sense about 20 m. The measured amount of offset and the age of the youngest fluvial sediments in the abandoned channel will yield a slip rate for the San Francisco Peninsula segment of the SAF. We excavated a trench across the abandoned channel and logged the exposed sediments. Our investigation revealed channel-fill alluvium incised and filled by probable debris flow sediments, and a wide fault zone in bedrock, west of the channel deposits. The most prominent fault is probably the strand that moved in 1906. We completed a total-station survey to more precisely measure the offset stream, and to confirm that the fault exposed in the trench aligns with a fence that is known to have been offset 2.8m during the 1906 earthquake. We interpret the debris flow sediments to represent the last phase of deposition prior to abandonment of the old channel. We collected samples for radiocarbon dating, optically stimulated

  19. Balloon Angioplasty - The Legacy of Andreas Grüntzig, M.D. (1939-1985).

    PubMed

    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 40(th) 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 his 75(th

  20. 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.

  1. Frictional properties of the active San Andreas Fault at SAFOD: Implications for fault strength and slip behavior

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Saffer, D. M.; Marone, C.

    2015-07-01

    We present results from a comprehensive laboratory study of the frictional strength and constitutive properties for all three active strands of the San Andreas Fault penetrated in the San Andreas Observatory at Depth (SAFOD). The SAFOD borehole penetrated the Southwest Deforming Zone (SDZ), the Central Deforming Zone (CDZ), both of which are actively creeping, and the Northeast Boundary Fault (NBF). Our results include measurements of the frictional properties of cuttings and core samples recovered at depths of ~2.7 km. We find that materials from the two actively creeping faults exhibit low frictional strengths (μ = ~0.1), velocity-strengthening friction behavior, and near-zero or negative rates of frictional healing. Our experimental data set shows that the center of the CDZ is the weakest section of the San Andreas Fault, with μ = ~0.10. Fault weakness is highly localized and likely caused by abundant magnesium-rich clays. In contrast, serpentine from within the SDZ, and wall rock of both the SDZ and CDZ, exhibits velocity-weakening friction behavior and positive healing rates, consistent with nearby repeating microearthquakes. Finally, we document higher friction coefficients (μ > 0.4) and complex rate-dependent behavior for samples recovered across the NBF. In total, our data provide an integrated view of fault behavior for the three active fault strands encountered at SAFOD and offer a consistent explanation for observations of creep and microearthquakes along weak fault zones within a strong crust.

  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. PMID:24615859

  3. Investigation of Quaternary slip rates along the Banning strand of the southern San Andreas Fault near San Gorgonio Pass

    NASA Astrophysics Data System (ADS)

    Gold, P. O.; Behr, W. M.; Rood, D.; Kendrick, K. J.; Rockwell, T. K.; Sharp, W. D.

    2013-12-01

    Present-day Pacific-North American relative plate motion in southern California is shared primarily between the San Jacinto and San Andreas faults. At the north end of the Coachella Valley, the San Andreas fault splits into the Banning and Mission Creek strands, which are sub-parallel to each other within the Indio Hills. Northwest of the Indio Hills, the Mission Creek fault diverges from the Banning and continues northwest toward the southeastern San Bernardino Mountains, but loses surface expression beneath Quaternary alluvial deposits in Morongo Wash. The Banning fault, upon exiting the Indio Hills, is deflected toward the west and transitions into a structurally complex fault zone at San Gorgonio Pass, where it is delineated by thrust scarps in Holocene alluvium. The slip rates of the Banning and Mission Creek fault strands northwest of the Indio Hills and southeast of San Gorgonio Pass are presently unconstrained, but understanding how slip is partitioned between these two strands is critical to southern California earthquake forecasting efforts. Here we present preliminary slip rate data for the Banning fault ~2 km southeast of San Gorgonio Pass at Devers Hill. Using the B4 LiDAR as a base, we have mapped the extents of three truncated and offset alluvial fan deposits, which we have differentiated based on both field and remote (LiDAR- and air photo-based) observations of texture: in particular, the distribution of different clast sizes, pavement and soil development, and color and appearance. To confirm across-fault correlation of the displaced deposits, we have measured 26 cosmogenic Be-10 ages from boulders and cobble samples taken from each of the three fan surfaces on both sides of the fault. One debris flow deposit (Q2a) has been dated to ~80 ka, and appears to be offset 1.6-2.2 km, though confirming this reconstruction will depend on future excavations and uranium-series dating of soil carbonate. A second debris flow deposit (Q2b), for which ages are

  4. 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

  5. Examining the Evolution of the Peninsula Segment of the San Andreas Fault, Northern California, Using a 4-D Geologic Model

    NASA Astrophysics Data System (ADS)

    Horsman, E.; Graymer, R. W.; McLaughlin, R. J.; Jachens, R. C.; Scheirer, D. S.

    2008-12-01

    Retrodeformation of a three-dimensional geologic model allows us to explore the tectonic evolution of the Peninsula segment of the San Andreas Fault and adjacent rock bodies in the San Francisco Bay area. By using geological constraints to quantitatively retrodeform specific surfaces (e.g. unfolding paleohorizontal horizons, removing fault slip), we evaluate the geometric evolution of rock bodies and faults in the study volume and effectively create a four-dimensional model of the geology. The three-dimensional map is divided into fault-bounded blocks and subdivided into lithologic units. Surface geologic mapping provides the foundation for the model. Structural analysis and well data allow extrapolation to a few kilometers depth. Geometries of active faults are inferred from double-difference relocated earthquake hypocenters. Gravity and magnetic data provide constraints on the geometries of low density Cenozoic deposits on denser basement, highly magnetic marker units, and adjacent faults. Existing seismic refraction profiles constrain the geometries of rock bodies with different seismic velocities. Together these datasets and others allow us to construct a model of first-order geologic features in the upper ~15 km of the crust. Major features in the model include the active San Andreas Fault surface; the Pilarcitos Fault, an abandoned strand of the San Andreas; an active NE-vergent fold and thrust belt located E of the San Andreas Fault; regional relief on the basement surface; and several Cenozoic syntectonic basins. Retrodeformation of these features requires constraints from all available datasets (structure, geochronology, paleontology, etc.). Construction of the three-dimensional model and retrodeformation scenarios are non-unique, but significant insights follow from restricting the range of possible geologic histories. For example, we use the model to investigate how the crust responded to migration of the principal slip surface from the Pilarcitos Fault

  6. 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.

  7. Seismic trapped modes in the oroville and san andreas fault zones.

    PubMed

    Li, Y G; Leary, P; Aki, K; Malin, P

    1990-08-17

    Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake event recording with a near-fault three-component borehole seismometer on the San Andreas fault at Parkfield, California, have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals. These wave trains are interpreted as fault zone-trapped seismic modes. Parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers, as shallow as 4 kilometers, and extend 12 kilometers along the fault on either side of the recording station. Selected Oroville and Parkfield wave forms are modeled as the fundamental and first higher trapped SH modes of a narrow low-velocity layer at the fault. Modeling results suggest that the Oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second, whereas at Parkfield, the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1.1 to 1.8 kilometers per second. These low-velocity layers are probably the rupture planes on which earthquakes occur. PMID:17756789

  8. 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.

  9. Constraints on the source parameters of low-frequency earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Thomas, Amanda M.; Beroza, Gregory C.; Shelly, David R.

    2016-02-01

    Low-frequency earthquakes (LFEs) are small repeating earthquakes that occur in conjunction with deep slow slip. Like typical earthquakes, LFEs are thought to represent shear slip on crustal faults, but when compared to earthquakes of the same magnitude, LFEs are depleted in high-frequency content and have lower corner frequencies, implying longer duration. Here we exploit this difference to estimate the duration of LFEs on the deep San Andreas Fault (SAF). We find that the M ~ 1 LFEs have typical durations of ~0.2 s. Using the annual slip rate of the deep SAF and the average number of LFEs per year, we estimate average LFE slip rates of ~0.24 mm/s. When combined with the LFE magnitude, this number implies a stress drop of ~104 Pa, 2 to 3 orders of magnitude lower than ordinary earthquakes, and a rupture velocity of 0.7 km/s, 20% of the shear wave speed. Typical earthquakes are thought to have rupture velocities of ~80-90% of the shear wave speed. Together, the slow rupture velocity, low stress drops, and slow slip velocity explain why LFEs are depleted in high-frequency content relative to ordinary earthquakes and suggest that LFE sources represent areas capable of relatively higher slip speed in deep fault zones. Additionally, changes in rheology may not be required to explain both LFEs and slow slip; the same process that governs the slip speed during slow earthquakes may also limit the rupture velocity of LFEs.

  10. Is stress accumulating on the creeping section of the San Andreas fault?

    NASA Astrophysics Data System (ADS)

    Johnson, K. M.

    2013-12-01

    The creeping section of the San Andreas fault (CSAF) in central California is a proposed barrier to propagation of large earthquakes. Yet, recent studies show that the creeping section is not entirely uncoupled but is accumulating slip deficit at a rate equivalent to a Mw=7.2-7.4 earthquake every 150years. A critical piece to understanding earthquake potential on the CSAF is determining whether slip deficit is occurring with stress accumulation on stick‒slip regions or without stress accumulation on stable‒sliding regions shadowed by surrounding locked areas. We use a physical model to estimate the spatial distribution of locked, stress‒accumulating areas of the fault constrained by surface creep rate measurements and GPS‒derived velocities. We find that the area of the fault accumulating stress, if ruptured every 150years, would release slip equivalent to at most a Mw=6.75 earthquake, significantly less than the Mw=7.2-7.4, 150year equivalent total slip deficit rate.

  11. 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.

  12. 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.

  13. 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. PMID:18807610

  14. 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

  15. 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.

  16. Mineral carbonation of serpentinite in the San Andreas Fault: Implications for aseismic creep

    NASA Astrophysics Data System (ADS)

    Klein, F.; Goldsby, D. L.; Lin, J.

    2013-12-01

    Here we present a new model that highlights the impact of peridotite-water-CO2 interactions on aseismic creep in the San Andreas Fault (SAF) zone. Serpentinization of peridotite is commonly invoked as the cause of aseismic slip (creep) observed in the SAF of central and northern California, as the creeping section coincides with the mapped extent of the Coast Range ophiolite (Irwin and Barnes, 1975). However, more recently it has been demonstrated that serpentinization alone cannot account for the high rates of aseismic slip (Moore et al., 1996). Moore and Rymer (2007) hypothesized that the reaction of silica-rich fluids with serpentinite causes the formation of mechanically weak talc, which is presently held responsible for fault-zone weakening in this area. While silica-metasomatism can transform serpentinite into steatite (talc rock), the common and widespread occurrence of CO2-rich springs in the fault zone, and silica-carbonate altered serpentinite, points to carbonation (i.e., CO2-metasomatism) of serpentinite as the major cause of fault-zone weakening in central and northern California. Initial results of our field program, mineralogical analyses and friction experiments will be presented, which highlight the evolution in shear strength from serpentine, to soapstone (talc-magnesite rock), to listvenite (quartz-magnesite rock), the final product of CO2-metasomatism.

  17. 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.

  18. The paleoseismology of the San Andreas fault at Pitman Canyon, San Bernadino, California

    SciTech Connect

    Seitz, G.; Weldon, R.J. . Dept. of Geological Sciences)

    1993-04-01

    The San Andreas fault at Pitman Canyon creates a well-defined downhill-facing scarp in young alluvium deposited mainly as debris flows. Groundwater rising on the uphill side of the scarp produces marshes that accumulate peat deposits. Trench exposures and C-14 dates confirm that this depositional environment, resulting in a datable section of inter-layered debris flows and peats, has existed for at least 1,400 years. The scarp extends across the entire canyon floor with the exception of a central shutterridge, offset along the fault, and the active channel. At the shutterridge this datable section overlies the fault and is involved in the faulting. A debris flow levee is offset approximately 4 meters and is inferred to be caused by the 1812 earthquake. To the northwest similar 4 meter offsets exist in Purdue and Lone Pine Canyons (Weldon and Sieh, 1985). An older debris flow lobe which postdates 1659 AD, the earliest possible age of a directly underlying C-14 dated peat is offset 7--8 meter indicating a similar size event post 1659 AD. Up to three additional events prior to 1280 AD were recognized in trench exposures based upon the upward termination of fault breaks, facies mismatches, and folding. Further study of offset buried debris flows and channels should allow determination of displacement per event. This preliminary record suggests extending the 1812 rupture into the San Bernadino region and is compatible with extending an approximately 1700 AD event from Indio to Wrightwood.

  19. 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.

  20. Seismic trapped modes in the Oroville and San Andreas Fault zones

    SciTech Connect

    Li, Yong-Gang; Leary, P.; Aki, K. ); Malin, P. )

    1990-08-17

    Three-component borehole seismic profiling of the recently active Oroville, California, normal fault and microearthquake event recording with a near-fault three-component borehole seismometer on the San Andreas fault at Parkfield, California, have shown numerous instances of pronounced dispersive wave trains following the shear wave arrivals. These wave trains are interpreted as fault zone-trapped seismic modes. Parkfield earthquakes exciting trapped modes have been located as deep as 10 kilometers, as shallow as 4 kilometers, and extend 12 kilometers along the fault on either side of the recording station. Selected Oroville and Parkfield wave forms are modeled as the fundamental and first higher trapped SH modes of a narrow low-velocity layer at the fault. Modeling results suggest that the Oroville fault zone is 18 meters wide at depth and has a shear wave velocity of 1 kilometer per second, whereas at Parkfield, the fault gouge is 100 to 150 meters wide and has a shear wave velocity of 1.1 to 1.8 kilometers per second. These low-velocity layers are probably the rupture planes on which earthquakes occur. 15 refs., 5 figs., 1 tab.

  1. Synchronous low frequency earthquakes and implications for deep San Andreas Fault slip

    NASA Astrophysics Data System (ADS)

    Trugman, Daniel T.; Wu, Chunquan; Guyer, Robert A.; Johnson, Paul A.

    2015-08-01

    Low Frequency Earthquakes (LFEs) are slip events that occur repeatedly at source locations within the lower crust. LFEs, and the associated seismic broadcast known as tremor, have been observed in a diverse array of tectonic environments. Here we develop a suite of statistical tools to conduct a systematic study of the spatial and temporal correlations of the event occurrence patterns of the 88 LFE sources beneath the greater Parkfield section of the San Andreas Fault. We first examine correlations in the occurrence patterns on long time scales to show that the regions to the north and south of Parkfield behave independently. We next use the cumulative event signatures of each source to characterize the individual occurrence patterns on shorter time scales. Through application of a statistical clustering algorithm, we demonstrate that individual LFE sources form spatially coherent clusters that may represent localized elastic structures or asperities on the deep fault interface. We conclude by examining the fine-scale features of the event rates within the LFE occurrence patterns. Through quantitative comparison to analogous laboratory shear experiments on granular, fault gouge-like materials, we infer that the distinctive features of LFE occurrence patterns reflect variations in the in-situ stress and frictional conditions at the individual LFE source locations. These observations provide a framework to understand the spatial and temporal diversity of fault slip that occurs within the lower crust beneath Parkfield and that may influence seismic hazard in the region.

  2. Seismicity and fault geometry of the San Andreas fault around Parkfield, California and their implications

    NASA Astrophysics Data System (ADS)

    Kim, Woohan; Hong, Tae-Kyung; Lee, Junhyung; Taira, Taka'aki

    2016-05-01

    Fault geometry is a consequence of tectonic evolution, and it provides important information on potential seismic hazards. We investigated fault geometry and its properties in Parkfield, California on the basis of local seismicity and seismic velocity residuals refined by an adaptive-velocity hypocentral-parameter inversion method. The station correction terms from the hypocentral-parameter inversion present characteristic seismic velocity changes around the fault, suggesting low seismic velocities in the region east of the fault and high seismic velocities in the region to the west. Large seismic velocity anomalies are observed at shallow depths along the whole fault zone. At depths of 3-8 km, seismic velocity anomalies are small in the central fault zone, but are large in the northern and southern fault zones. At depths > 8 km, low seismic velocities are observed in the northern fault zone. High seismicity is observed in the Southwest Fracture Zone, which has developed beside the creeping segment of the San Andreas fault. The vertical distribution of seismicity suggests that the fault has spiral geometry, dipping NE in the northern region, nearly vertical in the central region, and SW in the southern region. The rapid twisting of the fault plane occurs in a short distance of approximately 50 km. The seismic velocity anomalies and fault geometry suggest location-dependent piecewise faulting, which may cause the periodic M6 events in the Parkfield region.

  3. 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.

  4. 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.

  5. 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

  6. Predictive model of San Andreas fault system paleogeography, Late Cretaceous to early Miocene, derived from detailed multidisciplinary conglomerate correlations

    NASA Astrophysics Data System (ADS)

    Burnham, Kathleen

    2009-01-01

    Paleogeographic reconstruction of the region of the San Andreas fault system in western California, USA, was hampered for more than two decades by the apparent incompatibility of authoritative lithologic correlations. These led to disparate estimates of dextral strike-slip offsets across the San Andreas fault, notably 315 km between Pinnacles and Neenach Volcanics, versus 563 km offset between Anchor Bay and Eagle Rest peak. Furthermore, one section of the San Andreas fault between Pinnacles and Point Reyes had been reported to have six pairs of features showing only ~ 30 km offset, while several younger features in that same area were reported consistent with ~ 315 km offset. Estimates of total dextral slip on the adjoining 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, were included in a multidisciplinary study centered on identification of matching unique clast varieties, rather than on simply counting general clast types. Detailed analysis verified the prior correlation of the Upper Cretaceous strata of Anchor Bay at Anchor Bay with a then-unnamed conglomerate at Highway 92 and Skyline Road (south of San Francisco); and verified that the Paleocene or Eocene Point Reyes Conglomerate at Point Reyes is a tectonically displaced segment of the Carmelo Formation of Point Lobos (near Monterey). The work also led to three new correlations: Point Reyes Conglomerate with granitic source rock at Point Lobos; a magnetic anomaly at Black Point (near Sea Ranch) with a magnetic anomaly near San Gregorio; and strata of Anchor Bay with previously established source rock, the potassium-poor Logan Gabbro of Eagle Rest peak, at a more recently recognized subsurface location just east of the San Gregorio fault, south of San Gregorio. From these correlations, a Late Cretaceous to early Oligocene paleogeography was constructed which was unique in utilizing modern

  7. Insights from low-temperature thermochronometry into transpressional deformation and crustal exhumation along the San Andreas fault in the western Transverse Ranges, California

    NASA Astrophysics Data System (ADS)

    Niemi, Nathan A.; Buscher, Jamie T.; Spotila, James A.; House, Martha A.; Kelley, Shari A.

    2013-12-01

    San Emigdio Mountains are an example of an archetypical, transpressional structural system, bounded to the south by the San Andreas strike-slip fault, and to the north by the active Wheeler Ridge thrust. Apatite (U-Th)/He and apatite and zircon fission track ages were obtained along transects across the range and from wells in and to the north of the range. Apatite (U-Th)/He ages are 4-6 Ma adjacent to the San Andreas fault, and both (U-Th)/He and fission track ages grow older with distance to the north from the San Andreas. The young ages north of the San Andreas fault contrast with early Miocene (U-Th)/He ages from Mount Pinos on the south side of the fault. Restoration of sample paleodepths in the San Emigdio Mountains using a regional unconformity at the base of the Eocene Tejon Formation indicates that the San Emigdio Mountains represent a crustal fragment that has been exhumed more than 5 km along the San Andreas fault since late Miocene time. Marked differences in the timing and rate of exhumation between the northern and southern sides of the San Andreas fault are difficult to reconcile with existing structural models of the western Transverse Ranges as a thin-skinned thrust system. Instead, these results suggest that rheologic heterogeneities may play a role in localizing deformation along the Big Bend of the San Andreas fault as the San Emigdio Mountains are compressed between the crystalline basement of Mount Pinos and oceanic crust that underlies the southern San Joaquin Valley.

  8. 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.

  9. 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

  10. 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

  11. 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

  12. Creep avalanches on the Central San Andreas Fault: Clues and Causes

    NASA Astrophysics Data System (ADS)

    Khoshmanesh, M.; Shirzaei, M.; Nadeau, R. M.

    2015-12-01

    The Central segment of San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. However, observations of the creep rate obtained using Characteristically Repeating Earthquakes (CREs) show a quasi-periodic temporal variation, which is recently confirmed using both InSAR surface deformation time series and geodetic-based time-dependent kinematic model of creep along the CSAF. Here, we show that the statistical analysis of creep fronts along the CSAF indicates a sporadic behavior, signature of a burst-like creep dynamics. Moreover, the probability of creep velocities follows a Gumbel distribution characterized by longer tail toward the extreme positive rates. Fourier analysis of the time series of surface creep rate indicates a self-affine regime with Hurst exponent altering between 0.6 and 0.9 during the observation period of 2003-2011. The variable Hurst component is an indicator for temporal variation in the roughness of the fault zone. To explain the causes of creep avalanches, two possible mechanisms are considered, including temporal variation in: 1) fault geometry, and 2) Ambient normal stress. We find that the overall statistical dependence between the pattern of surface creep rate and the fault geometry is insignificant. To investigate the effect of ambient normal stress, primarily due to variation in pore pressure, we implement a rate and state friction law to link the time-dependent kinematic creep model to the spatiotemporal variations of the normal stress on the velocity-strengthening fault zones. These observations and models help to understand the driving mechanisms that govern the creep rate variations at short spatial length and low velocities. Under these circumstances, the other mechanisms such as thermal pressurization are not feasible.

  13. 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.

  14. 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.

  15. Near-field Observations of Very-low-frequency Earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Fault rupture at varying time scales has been detected in multiple subduction zones, e.g., in slow-slip events (SSEs), very-low-frequency earthquakes (VLFEs), and low-frequency earthquakes (LFEs) or tectonic tremor. However, only LFEs or tremor have been identified and studied in detail along strike-slip faults, like the San Andreas Fault (SAF). Here, we present evidence for VLFEs on the SAF near Parkfield, California. Using data from permanent broadband stations and a temporary deployment of 13 broadband stations installed in 2010-2011 near Cholame, California, we detect 5 VLFEs, with 1 VLFE occurring unambiguosly when there is visible tremor activity. We check that the signals we detect are local by confirming that they appear only on stations within a 70 km radius, and removing time periods when teleseismic events occur, as identified in the global Centroid Moment Tensor (CMT) and the Northern California Seismic Network (NCSN) catalogs. VLFEs have to-date been observed to only occur simultaneously in time and space with tremor activity, but our detections suggests that VLFEs can occur independent of tremor along strike-slip faults. This may indicate that the slipping patches that produce slow earthquakes in transform faults have different mechanical properties than the patches in subducting plates, althought it does not rule out that VLFEs are only observed with tremor in subduction zones simply due to detection methods. An approximate estimation of the apparent velocity, based on a grid-search location using variance reduction, suggests that the observed phase velocity of the VLFEs is ~ 3km/s, corresponding to surface waves. We perform a focal mechanism inversion with a grid search to find a more precise location, depth and orientation of the VLFEs. These results provide new insight into the behavior of the SAF and more generally contribute to an improved understanding of transform fault systems.

  16. 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.

  17. Tomographic imaging of the tectonic tremor zone beneath the San Andreas fault in the Parkfield region

    NASA Astrophysics Data System (ADS)

    Peterson, D. E.; Thurber, C. H.; Shelly, D. R.; Bennington, N. L.; Zhang, H.; Brown, J. R.

    2012-12-01

    The fine-scale seismic velocity structure around zones of tectonic (nonvolcanic) tremor and low-frequency earthquakes (LFE's) has been imaged successfully in subduction zones. This success is due in part to the occurrence of earthquakes in the subducting slab beneath the zone of tremor and LFE's. Such studies have found the tremor and LFE's to lie within zones of reduced seismic velocity and high Vp/Vs, which have been interpreted to reflect high pore fluid pressure (e.g., Shelly et al., 2006). For the San Andreas fault, the observed tremor and LFE's in the Parkfield region occur at depths greater than 15 km, which is below the deepest conventional earthquakes in the region. This makes tomographic imaging of the tremor zone more challenging. We use a combination of P and S arrival times and corresponding differential times from stacked seismograms of LFE's (Shelly and Hardebeck, 2010) along with absolute and differential times from shallower microearthquakes to image the three-dimensional P- and S- wave velocity structure to ~20 km depth. Our initial results indicate the LFE's near SAFOD lie within or adjacent to zones with slightly reduced P-wave velocity and more sharply reduced S- wave velocity. The estimated Vp/Vs values are approximately 1.85 to 1.95 in these zones. The elevated Vp/Vs values are interpreted to reflect high pore fluid pressure and low effective stress. This is consistent with results from subduction zones and with observations of triggering and tidal modulation of LFE's and tremor on this deep extension of the SAF. We will present refined tomography results that expand the area imaged and include additional LFE arrival time picks from temporary array data. Cross-section from SW to NE through SAFOD at Y=0. Vs is shown by black contours (labeled with km/sec) and colors from red (slow) to blue (fast). Black diamonds are hypocenters of LFE's and earthquakes used in the inversion.

  18. Paleoseismic Studies of the Peninsula San Andreas Fault at the Filoli Estate, Woodside, California

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Clahan, K.; Sickler, R. R.; Salin, A.; DeLong, S. B.; McDermott, R.; Pickering, A.; Baldwin, J. N.

    2014-12-01

    The Peninsula section of the San Andreas Fault (SAFP) is within 10 km of downtown San Francisco, making it among the most significant sources of seismic hazard in the San Francisco Bay area. However, the history of earthquakes along this fault segment is poorly known. The most recent ground-rupturing earthquake occurred in 1906, but the dates of earlier surface-rupturing earthquakes on this segment remain uncertain. Earlier work at the Crystal Springs South trench site showed that a ground-rupturing paleo-earthquake occurred 830-930 Cal. yr BP, but poor stratigraphic resolution hampered our ability to determine whether or not earthquakes occurred between then and 1906. We combined existing airborne LiDAR data with newly-collected terrestrial laser scanner data to create a high-resolution digital elevation model that we used to guide the locations of two trenches at a new site near Scarp Creek on the Filoli Estate, about 0.5km to the southeast along the fault. The new trenches exposed a stratigraphic section of faulted fluvial, overbank, and lacustrine deposits overlying a massive colluvial deposit. Our preliminary results show evidence for at least three surface ruptures, including the 1906 earthquake, since deposition of the colluvial material. Preliminary radiocarbon analyses show that these three earthquakes occurred during the last 900 years. We expect that radiocarbon analyses of samples of the abundant organic material exposed in the trenches will constrain more closely the ages of the prehistoric events. In addition, we anticipate that additional work at this site will provide an opportunity to test our earlier results and will provide additional data to better constrain the timing of pre-1906 surface ruptures on the SAFP.

  19. Remote triggering of fault-strength changes on the San Andreas fault at Parkfield.

    PubMed

    Taira, Taka'aki; Silver, Paul G; Niu, Fenglin; Nadeau, Robert M

    2009-10-01

    Fault strength is a fundamental property of seismogenic zones, and its temporal changes can increase or decrease the likelihood of failure and the ultimate triggering of seismic events. Although changes in fault strength have been suggested to explain various phenomena, such as the remote triggering of seismicity, there has been no means of actually monitoring this important property in situ. Here we argue that approximately 20 years of observation (1987-2008) of the Parkfield area at the San Andreas fault have revealed a means of monitoring fault strength. We have identified two occasions where long-term changes in fault strength have been most probably induced remotely by large seismic events, namely the 2004 magnitude (M) 9.1 Sumatra-Andaman earthquake and the earlier 1992 M = 7.3 Landers earthquake. In both cases, the change possessed two manifestations: temporal variations in the properties of seismic scatterers-probably reflecting the stress-induced migration of fluids-and systematic temporal variations in the characteristics of repeating-earthquake sequences that are most consistent with changes in fault strength. In the case of the 1992 Landers earthquake, a period of reduced strength probably triggered the 1993 Parkfield aseismic transient as well as the accompanying cluster of four M > 4 earthquakes at Parkfield. The fault-strength changes produced by the distant 2004 Sumatra-Andaman earthquake are especially important, as they suggest that the very largest earthquakes may have a global influence on the strength of the Earth's fault systems. As such a perturbation would bring many fault zones closer to failure, it should lead to temporal clustering of global seismicity. This hypothesis seems to be supported by the unusually high number of M >or= 8 earthquakes occurring in the few years following the 2004 Sumatra-Andaman earthquake. PMID:19794490

  20. 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.`

  1. 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.

  2. Structure and composition of the San Andreas Fault in central California: Recent results from SAFOD sample analyses

    NASA Astrophysics Data System (ADS)

    Hickman, S.; Zoback, M.; Ellsworth, W.; Chester, J.; Chester, F.; Evans, J.; Moore, D.; Kirschner, D.; Schleicher, A.; van der Pluijm, B.; Solum, J.

    2008-12-01

    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 through a combination of repeating microearthquakes and fault creep. In 2004 and 2005, SAFOD was drilled vertically to a depth of 1.5 km and then deviated across the entire San Andreas Fault Zone to a vertical depth of 3.1 km. In 2007, cores were acquired from holes branching off the main hole to sample directly the country rock and actively deforming traces of the fault. Geophysical logs define the San Andreas Fault Zone to be about 200 m wide, containing several discrete zones only 2-3 m wide with very low P- and S-wave velocities and low resistivity. Two of these zones have progressively deformed the cemented well casing at measured depths of 3194 m and 3301 m (corresponding to vertical depths of 2.6 - 2.7 km), indicating that they are actively creeping shear zones. The 3194 m casing deformation zone lies about 100 m above a cluster of repeating M2 earthquakes along the southwestern boundary of the active fault zone. Talc and serpentine discovered in drill cuttings associated with the deepest casing deformation zone may be responsible for the predominantly creeping behavior and anomalously low shear strength of the San Andreas Fault at this location. Hydrous clay minerals found as thin-film coatings on polished slip surfaces in cuttings may also be important in controlling fault strength and stability of sliding. Core was obtained in 2007 across the active deformation zones at 3194 and 3301 m and from just outside the geologically defined San Andreas Fault Zone. Cores crossing the two deformation zones are composed of shales, siltstones and mudstones and contain 1-2 m of a highly foliated, relatively incohesive fault gouge. In both cases, this fault gouge exactly

  3. 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.

  4. 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.

  5. 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. PMID:19579335

  6. Observations of strain accumulation across the san andreas fault near palmdale, california, with a two-color geodimeter.

    PubMed

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

    1982-12-17

    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. PMID:17802470

  7. A rheologically layered three-dimensional model of the San Andreas fault in central and southern California

    NASA Technical Reports Server (NTRS)

    Williams, Charles A.; Richardson, Randall M.

    1991-01-01

    The effects of rheological parameters and the fault slip distribution on the horizontal and vertical deformation in the vicinity of the fault are investigated using 3D kinematic finite element models of the San Andreas fault in central and southern California. It is shown that fault models with different rheological stratification schemes and slip distributions predict characteristic deformation patterns. Models that do not include aseismic slip below the fault locking depth predict deformation patterns that are strongly dependent on time since the last earthquake, while models that incorporate the aseismic slip below the locking depth depend on time to a significantly lesser degree.

  8. 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

  9. The Frictional Behavior of San Andreas Fault Materials Formed by Carbonation of Serpentinite

    NASA Astrophysics Data System (ADS)

    Klein, F.; Goldsby, D. L.; Lin, J.; Andreani, M.

    2014-12-01

    The exposure of serpentinite to CO2-rich fluids leads to a sequence of carbonation reactions involving the formation of soapstone and listvenite. Since CO2-rich springs, serpentinite, and listvenite outcrops co-occur along the San Andreas Fault between Cholame Valley and San Juan Bautista, we hypothesize that this sequence explains both the high creeping rates and frequent micro-earthquakes along this section. To test this hypothesis we studied the frictional behaviors of powdered magnesite and mineral assemblages representative of soapstone (magnesite:talc = 1:1, 1:9, and 9:1 by weight) and listvenite (magnesite:quartz = 1:1), and their implications for fault stability, in a suite of experiments using a rotary-shear apparatus. Dry powders were sheared between sandstone forcing blocks at a normal stress of 60 MPa, and subjected to order-of-magnitude step changes in slip rate in the range of 0.1 to 10 μm/s, over sliding displacements of 0.15-0.5 m. Experiments on magnesite reveal velocity-strengthening friction at all sliding displacements up to ~200 mm. Intriguingly, mixtures of magnesite and talc reveal an evolution of frictional behavior, from velocity-strengthening friction at the onset of sliding, to velocity-weakening friction and subsequently to velocity-neutral behavior with increasing slip. The transition to velocity-weakening friction is unexpected, given the velocity-strengthening behavior of end-member powders (talc, V. Scruggs, unpubl.). We also observe that magnesite:talc mixtures yield peak values of the friction coefficient µ ≥0.8, well in excess of values of µ for magnesite, ~0.6, and talc, <<0.4 (Moore and Lockner, 2007). Tests on the quartz-magnesite mixture reveal a transition from velocity-strengthening to velocity-weakening friction over a displacement of ~100 mm, followed by a transition to velocity-strengthening behavior at larger displacements. This behavior contrasts with that of pure quartz gouge, which exhibits velocity

  10. Fluid overpressures on the San Andreas Fault following the passage of the Mendocino Triple Junction

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    Fluid pressures significantly greater than hydrostatic have been hypothesized to account for the weak nature of many large plate-boundary faults. However, on the San Andreas Fault, the hypothesized subsurface processes which could create, sustain, and potentially localize such pressures over millions of years are not well understood. In this study, we use two-dimensional finite element models of coupled fluid flow and heat transport perpendicular to the fault to evaluate hypothesized mechanisms for generating elevated pore pressure. The models account for transient changes in crustal geotherm and thickness of the seismogenic crust in response to the passage of the Mendocino Triple Junction. Theoretical curves of whole-rock fluid content as functions of pressure and temperature allow us to calculate fluid sources due to metamorphic dehydration within the Franciscan mélange as a function of depth and thermal history. Average fluid sources in the seismogenic crust range from 10-18 to 10-16 s-1 over the 15 Myr spanned by our models. We consider a variety of permeability distributions within the models, including a range of homogenous permeability and depth-dependent permeability. We also consider heterogeneous permeability distributions reflecting fault properties and geologic features such as serpentine sills. Our results show that over 15 Myr, thermal expansion of pore fluids due to initial burial, followed by additional heating during exhumation, can create significant overpressures. In addition, models which include fluid sources from metamorphic dehydration of the Franciscan mélange result in pore pressures approaching a significant fraction of lithostatic. Generally, all model results show overpressures extending several kilometers to each side of the fault. Due to the continual nature of many of these processes, overpressures are sustained for millions of years without the need for complex and/or extremely low-permeability seals. Models which include geologic

  11. High-resolution electromagnetic imaging of the San Andreas fault in Central California

    SciTech Connect

    Unsworth, M.; Egbert, G.; Booker, J.

    1999-01-01

    Although there is increasing evidence that fluids may play a significant role in the earthquake rupture process, direct observation of fluids in active fault zones remains difficult. Since the presence of an electrically conducting fluid, such as saline pore water, strongly influences the overall conductivity of crustal rocks, electrical and electromagnetic methods offer great potential for overcoming this difficulty. Here we present and compare results from high-resolution magnetotelluric (MT) profiles across two segments of the San Andreas Fault (SAF) which exhibit very different patterns of seismicity: Parkfield, which has regular small earthquakes and creep events, and in the Carrizo Plain, where the fault is seismically quiescent and apparently locked. In both surveys, electric fields were sampled continuously, with 100 m long dipoles laid end-to-end across the fault. From 100 to 0.1 Hz the data from both profiles are consistent with a two-dimensional (2-D) fault-parallel resistivity model. When both transverse electric and magnetic (TE and TM) mode data are included in the interpretation, narrow ({approximately}300{endash}600 m wide) zones of low resistivity extending to depths of 2{endash}4 km in the core of the fault are required at both locations. However, at Parkfield the conductance (conductivity thickness product) of the anomalous region is an order of magnitude larger than at Carrizo Plain, suggesting much higher concentrations of fluids for the more seismically active Parkfield segment. We also image structural differences between the two segments. At Carrizo Plain, resistive, presumably crystalline, rocks are present on both sides of the fault at depths below 3{endash}4 km. In particular, we clearly image resistive basement extending {approximately}10 km or more east of the SAF, beneath the Elkhorn Hills and Temblor Range. At Parkfield the situation is quite different with a resistive block of Salinian granite west of the fault and an electrically

  12. 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

  13. Spatial variations in slip deficit on the central San Andreas Fault from InSAR

    NASA Astrophysics Data System (ADS)

    Ryder, Isabelle; Bürgmann, Roland

    2008-12-01

    We use ERS InSAR measurements to record spatial variations in creep rate along the creeping segment of the San Andreas Fault (SAF), California, between 1992 and 2001. Inversion of geodetic data yields a slip rate distribution along the creeping segment, which is used for first-order moment release and deficit calculations. We present a time-averaged spatial picture of surface deformation and associated subsurface creep. An interferometric stack is constructed from 12 interferograms that show good coherence. For the decade of observation, the total right-lateral offset spanned by the data is ~34 mmyr-1. Along most of the length of the creeping segment, this offset occurs within a narrow (<2 km) zone close to the fault trace. In the northern part, a minor part of the offset is taken up by the nearby Calaveras-Paicines Fault. In general, the observed rates of surface creep are consistent with those obtained by several other studies for a longer and/or earlier period of time, using different geodetic methods. This suggests that the average creep rate has been constant over a period of almost four decades. A joint GPS-InSAR inversion implies that the shallow creep rate is variable along strike, reaching up to 31.5 +/- 1 mmyr-1 in the central section of the creeping segment, tapering off along-strike to the south and becoming partitioned across two subparallel faults in the north. The deep slip rate beneath the seismogenic layer is 33 +/- 3 mmyr-1. The difference between shallow and deep slip rates suggests that there is a shallow slip deficit on the creeping segment of the SAF (CSAF). Moment release rate due to aseismic slip is approximately three orders of magnitude greater than seismic moment release. The annual creep on the CSAF is equivalent to the moment released in a M 6 earthquake. The equivalent moment of the slip deficit relative to the deep slip rate is between 4.1 × 1017 and 8.4 × 1017 N myr-1, which is equivalent to a magnitude 5.7-5.9 earthquake. Over a

  14. Absolute Strength of the San Andreas Fault Inferred from Tectonic Loading Simulation and CMT Data Inversion

    NASA Astrophysics Data System (ADS)

    Terakawa, T.; Matsu'Ura, M.

    2006-12-01

    In order to estimate the absolute strength of the big-bend segment (BBS) of the San Andreas Fault (SAF) we combined two different approaches, one of which is the numerical simulation of tectonic stress accumulation at and around plate boundaries and the other is the inversion analysis of seismic events to estimate tectonic stress release. With the 3-D tectonic loading model based on elastic dislocation theory, we numerically computed the absolute tectonic stress fields at and around BBS for six representative cases with different friction coefficients (0.6, 0.3 and 0.1) of SAF and surrounding thrust faults. In order to compare the theoretical results with seismological observations, we extracted only the stress field related to shear faulting (seismogenic stress field) from the computed absolute stress field. The patterns of the stress field for the representative cases are significantly different from each other within the distance range of 50 km from BBS. In this range, the rotation angle of the maximum horizontal compressive principal stress axis measured from the strike of BBS changes from 45o to 90o with distance from BBS. The range of the stress rotation becomes broader as the absolute strength of BBS becomes higher. The expected type of faulting in this range also depends on the absolute strength of BBS. On the other hand, we obtained the pattern of seismogenic stress field around BBS through an inversion analysis with CMT data. The type of faulting expected from the inverted stress field changes with distance from BBS as follows: thrust faulting with a strike oblique to BBS in the vicinity of BBS, thrust faulting with the dip-angle of 45o and a strike parallel to BBS in the range of 50-100 km from BBS, and vertical strike-slip faulting with a strike oblique to BBS in the region farther than 100 km. From the inverted stress field we can find a fault-parallel zone with high moment release rates at about 40 km southwest of BBS, which can be considered to play

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

    NASA Astrophysics Data System (ADS)

    Beeler, N. M.; Thomas, Amanda; Bürgmann, Roland; Shelly, David

    2013-11-01

    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 source is on the

  16. 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

  17. New slip rate estimates for the Mission Creek strand of the San Andreas fault zone

    NASA Astrophysics Data System (ADS)

    Blisniuk, K.; Scharer, K. M.; Sharp, W. D.; Burgmann, R.; Rymer, M. J.; Williams, P. L.

    2013-12-01

    The potential for a large-magnitude earthquake (Mw ≥ 6.7) on the southern San Andreas fault zone (SAFZ) is generally considered high (Working Group on California Earthquake Probabilities, 2007). However, the proportion of slip accommodated by each of its three major fault strands (Mission Creek, Banning, and Garnet Hill, from north to south) in the Indio Hills is poorly constrained. Each of these strands cut through San Gorgonio Pass west to the Los Angeles metropolitan region. To better assess the relative importance of these faults and their potential for a major earthquake, we dated offsets at two sites on the Mission Creek fault in the central Indio Hills, an offset channel at Pushawalla Canyon and an offset debris cone at a small unnamed canyon located ~1.5 km farther southeast. Previous work on this strand at Biskra Palms, in the southern Indio Hills, demonstrated a slip rate between 12 and 22 mm/yr, with a preferred rate of 14-17 mm/yr (Behr et al., GSAB, 2010). It is generally assumed that the slip rate on the Mission Creek fault decreases northwestwards from Biskra Palms (e.g. Fumal et al., BSSA, 2002) towards these two sites in the central Indio Hills. However, our initial results from uranium-series dating of pedogenic carbonate and 10Be cosmogenic exposure dating of surface clasts from deposits offset 1.3-1.6 km since ~70 ka and 44-50 m since ~2.5 ka indicate that during the late Pleistocene and Holocene slip on the Mission Creek fault in the central Indio Hills has occurred at a relatively constant and unexpectedly high rate of ~20 mm/yr. Combined with published paleoseismic studies for the Mission Creek fault, which show an average earthquake recurrence interval of 225 years for the past 5 events since 900 AD (Fumal et al., 2002), these data imply an average slip-per-event of ~4.5 m. The last earthquake to rupture this section of the Mission Creek fault occurred over 300 years ago (ca. 1690), which indicates that ca. 5.0 to 7.5 m of strain may have

  18. Seismic Noise Analysis to Constrain Shallow Velocity Structure in the southern San Andreas Fault Region

    NASA Astrophysics Data System (ADS)

    Tsang, Stephanie D.

    The seismic velocity structure in the southern San Andreas Fault region is characterized by a known, distinct seismic velocity contrast on opposite sides of the fault, with a thick sedimentary region on the west side (Salton Sea area). Reverberations would affect the duration of shaking for El Centro, Mexicali, and other communities in the Coachella Valley and Imperial Valley. Furthermore, there are other areas where deep basins are bounded by faults that could have similar effects. Therefore, being able to determine the 3D structure is a critical facet of assessing the overall seismic hazard for structures on such basins. By utilizing the particle motion of surface waves, we are able extract useful information about the S-wave velocity structure. To accomplish this, we measured Rayleigh-wave ellipticity of continuous broadband data from 2010 to 2014 for 67 stations within the Southern California Seismic Network (SCSN). Measurements of Rayleigh-wave ellipticity were computed as the ratio between the vertical and horizontal amplitudes. Regional variations in the Rayleigh-wave ellipticity measurements at frequencies of 0.10 Hz up to and including 0.30 Hz illuminate small ellipticity values (i.e. horizontal elongation in Rayleigh-wave particle motion) across the entire frequency band in the regions specific to the thick sedimentary region. In this region, minimum ellipticity values (<0.20) observed at 0.10 Hz, 0.15 Hz, and at 0.20 Hz show a gradual increase up to 0.60 between 0.25 Hz to 0.40 Hz. In most areas exterior to the thick sedimentary region, ellipticity values are generally constant across the frequency band and are significantly higher (>0.90). The observed, small ellipticity values, which are characteristic of a slow velocity layer at shallow depths (upper 5-10 km), could have significant implications on the S-wave velocity structure. As the ZH-Ratio method is highly sensitive to the near-surface structure, combination of the ellipticity data with phase

  19. 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.

  20. 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.

  1. Layered anisotropy around the San Andreas Fault near Parkfield, California: Structural control on seismic and aseismic behaviour

    NASA Astrophysics Data System (ADS)

    Audet, P.

    2015-12-01

    The rheology of the Earth's crust controls the long-term and short-term strength and stability of plate boundary faults and depends on the architecture and physical properties of crustal materials. Here we examine the seismic structure and anisotropy of the crust around the San Andreas Fault (SAF) near Parkfield, California, using teleseismic receiver functions. These data indicate that the crust is characterized by spatially variable and strongly anisotropic upper and middle crustal layers, with a Moho at ˜35 km depth. The upper layer is ˜5-10 km thick and is characterized by strong (≥30%) anisotropy with a slow axis of hexagonal symmetry, where the plane of fast velocity has a strike parallel to that of the SAF and a dip of ˜40 degrees. We interpret this layer as pervasive fluid-filled microcracks within the brittle deformation regime. The ˜10-15 km thick midcrustal layer is also characterized by a weak axis of hexagonal symmetry with ≥20% anisotropy, but the dip direction of the plane of fast velocity is reversed. The midcrustal anisotropic layer is more prominent to the northeast of the San Andreas Fault. We interpret the mid crustal anisotropic layer as fossilized fabric within fluid-rich foliated mica schists. When combined with various other geophysical observations, our results suggest that fault creep behavior around Parkfield is favored by intrinsically weak and overpressured crustal fabric.

  2. The personages of Jan Stephan van Calcar's frontispiece to Andreas Vesalius' book "On the Structure of the Human Body".

    PubMed

    Speransky, L S; Bocharov, V J; Goncharov, N I

    1983-01-01

    More than 400 years have passed since the edition of the prominent anatomical treatise "On the Structure of the Human Body" in 7 books of Andreas Vesalius, the founder of the modern anatomical science, the outstanding scientist of the Renaissance. The role of Andreas Vesalius in the history of medicine and anatomy, his life and creative work are described in detail by many following generations (Choulant 1852; Jackschath 1903; Anson 1945; Deshin 1915; Leibson 1940, 1951; Kasatkin 1956; Kuprijanov 1964; Ternovsky 1965; Goncharov 1976, 1978). However the interest both in that man and the epoch he lived and created does not grow weak nowadays. At the USSR Order of Lenin State Library in the section of rare books there is one of a few left copies of A. Vesalius' book (published in 1543 in Basel of Johann Oporin's publication) published by Johann Oporin in 1543 in Basel. This book is exhibited unfold and its frontispiece is great interest to readers (Fig. 1). PMID:6349420

  3. [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. PMID:26137670

  4. 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.

  5. Accelerating and spatially-varying crustal uplift and its geomorphic expression, San Andreas Fault zone north of San Francisco, California

    NASA Astrophysics Data System (ADS)

    Grove, Karen; Sklar, Leonard S.; Scherer, Anne Marie; Lee, Gina; Davis, Jerry

    2010-12-01

    Marine terraces that bevel the western flank of the Point Reyes Peninsula were used to measure crustal uplift rates west of the San Andreas Fault segment north of San Francisco. Field measurements of platform inner edges, and luminescence ages from overlying marine sediments, suggest the youngest platform was cut by waves during the ~ 80-ka sea-level high stand (MIS 5a). Since 80 ka, the platform has been uplifted slowly throughout most of the peninsula, but more rapidly in the southern part, where uplift reaches a rate of ~ 1 m/ka. Analyses of the spatial distributions of hillslope gradient and elevation are consistent with the terrace data. Correlations of older terrace levels to high-stand ages suggest that crustal uplift has accelerated in the southern part of the peninsula during the past ~ 300 ky, probably as a result of a contractional zone that has been migrating northward. This study is the first to quantify the rate and style of crustal uplift west of this San Andreas Fault segment. Although the transform motions in this region are well documented, the complex nature of interacting fault strands are only beginning to be understood. These results imply that other faults, with reverse-motions, are also active and potentially contributing to earthquake hazards.

  6. 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.

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. 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. PMID:25340483

  12. Leuven: birthplace of modern skeletology, thanks to Andreas Vesalius, with the help of Gemma Frisius, his friend and fellow-physician.

    PubMed

    Biesbrouck, M; Steeno, O

    2012-01-01

    The skeleton-making technique of Andreas Vesalius is described and is compared with that of others. An overview is added of the skeletons he constructed himself. The significance of his friend Gemma Frisius is discussed as well as the translations of the chapter of this technique in the De humani corporis fabrica. PMID:22442919

  13. 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.

  14. Development of the New Zealand and San Andreas Continental Transforms: From Plate Kinematics to Lithospheric Geodynamics (Invited)

    NASA Astrophysics Data System (ADS)

    Furlong, K. P.

    2009-12-01

    Although oftentimes compared as being two similar continental transforms, the development of the San Andreas and Alpine Fault plate boundary systems reflect two distinctly different geodynamic paths to formation, localization, and evolution. Characteristics that lead to fundamental differences in their present-day tectonic behavior. The San Andreas system has formed in response to the migration of two triple junctions, and it lengthens over time at these transitions from subduction to translation. The San Andreas system forms within the region of thin lithosphere left in the wake of slab removal or subduction cessation, and therefore thermal processes dominate in the development of a localized plate boundary. There are associated short-lived deformational events including significant crustal thickening and subsequent crustal thinning that serve to substantially modify the overlying North American crust during this 3-5 million year transition time. In contrast the development of the Alpine Fault plate boundary system through New Zealand follows a different geodynamic path, and this transform boundary reflects an intermediate point in the overall transition of that Australia-Pacific plate boundary through New Zealand from an extensional to convergent boundary. Since approximately 25 Ma, with rapid changes in Australia-Pacific plate interactions, the plate boundary structure through continental New Zealand rapidly changed from extensional to translation/transpression. This transpression was accommodated by the initiation of two subduction regimes, whose positions were controlled by continent-ocean transitions linked by the translational/transpressional (proto) Alpine Fault system. This trench-transform-trench plate boundary system has migrated southward, maintaining essentially a constant length, but not constant localization, and along the way, ephemerally incorporating segments of the Australia and Pacific plates into the boundary - modifying, exhuming, and removing

  15. Shape Preferred Orientation of Porphyroclasts in the Active Gouge Zones of the San Andreas Fault at SAFOD

    NASA Astrophysics Data System (ADS)

    Sills, D. W.; Chester, J. S.; Chester, F. M.

    2009-12-01

    Recovered core samples from the San Andreas Fault Observatory at Depth (SAFOD) offer a unique opportunity to study the products of faulting and to learn about the mechanisms of slip at 3 km depth. Active creep is occurring at two locations in the borehole that correspond to meters-thick intervals of gouge recovered by coring. Both gouge layers consist of a clay-bearing, ultrafine grain matrix containing porphyroclasts of sandstone and serpentinite; these layers correspond to the southwest creeping zone at 3194 m measured depth (MD) and the main creeping zone at 3301 m MD. We have used X-ray Computed Tomography (XCT) imaging to investigate the mesoscale structure of the core samples, specifically to characterize the shape, preferred orientation, and size distribution of the porphyroclasts. Using various image processing techniques, porphyroclast shape and size are characterized in 3D by best-fit ellipsoids. The resolution of the XCT imaging to date permits characterization of porphyroclasts with equivalent spherical diameters greater than 8 mm; current work involves higher resolution imaging of representative samples to investigate the 3D shape of porphyroclasts to the sub-millimeter size. The porphyroclast population in each gouge layer can be approximated with a scalene-oblate ellipsoid; size and aspect ratio (major to minor axis ratios) distributions also are similar throughout. Aspect ratios generally range between 1.5 and 4, with the majority occurring between 2-2.5. A strong shape preferred orientation (SPO) exists in both creeping zones, where the minor axes form a SPO normal to the plane of the San Andreas Fault, and the major axes define a lineation in the plane of the fault. The SPO in the main creeping zone is particularly well defined, and the orientation distribution, assuming the major-axis lineation is horizontal (strike-slip kinematics), indicates a slight synthetic asymmetry relative to the macroscopic orientation of the San Andreas Fault. The

  16. Thermal-rheologic evolution of the upper mantle and the development of the San Andreas fault system

    NASA Astrophysics Data System (ADS)

    Furlong, Kevin P.

    1993-07-01

    Furlong, K.P., 1993. Thermal-rheologic evolution of the upper mantle and the development of the San Andreas fault system. In: M.J.R. Wortel, U. Hansen and R. Sabadini (Editors), Relationships between Mantle Processes and Geological Processes at or near The Earth's Surface. Tectonophysics, 223: 149-164. The evolution of the San Andreas fault system differs from that of many other major fault zones in that it can be directly linked to processes in and properties of the underlying mantle. This fault system serves as the plate boundary between the North American and Pacific plates. It has progressively formed since ~ 30 Ma in response to a fundamental change in plate boundary structure: subduction replaced by transform motion with the northward migration of a triple junction. As a result of triple junction migration, major adjustments to lithospheric structure occur and cause the growth and maturation of the fault system. The geodynamic processes which have driven the development of the San Andreas system are primarily associated with the thermal and rheologic evolution of the uppermost mantle in the vicinity of the plate boundary. The emplacement of asthenospheric mantle at shallow levels beneath the North America crust after triple junction passage has led to crustal partial melting and volcanism, development of a well-defined plate-bounding mantle shear zone, and a sequence of events which produced the observed pattern of crustal faults and terranes. As a result of a complex three-dimensional thermal structure, plate boundary deformation (within the lithospheric mantle) is localized to a narrow zone. High strain rates and cooling-induced strengthening of the plate boundary zone lead to changes in grain size and ultimately to changes in deformation processes. The overall result of this is the development of a well-defined and relatively narrow plate boundary within the mantle lithosphere which is initially offset from the crustal fault zone. The mismatch between

  17. Vegetation Lineaments Near Pearblossom: Indicators of San Andreas Foreberg-Style Faulting?

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    An isolated cluster of 24 vegetation lineaments (VLs) on and around Holcomb Ridge near Pearblossom, CA, were identified using Google Earth imagery. Field inspection verified that they are natural structures. They ranged in length from 0.21 to 2.29 km (mean 0.8 km) and were ~15-20 m wide. The cluster is roughly 13 km long by 2 km wide, and is located ~ 3 km north of the San Andreas Fault (SAF). The cluster and the VLs trend subparallel to the SAF. The cluster's long axis trends ~297° (N63W), the same as the SAF's strike of N63W here. The VLs mean headings strike 304° ± 11° (1 sigma), or N56W, consistent with the local strike of the SAF. Most VLs strike ~perpendicular to the general direction of streams flowing northward from the San Gabriel Mountains. None of the VLs coincide with faults in USGS OF 2003-293 or in the CGS-USGS Quaternary Faults database, although one (VL15) clearly corresponds to a suspected fault identified by Dibblee (2002). The lineaments were visible on many earlier studies of the area (e.g. Barrows et. al 1975, 1976, 1979, 1080, 1985) but were not marked or identified as being significant. Several lineaments cross or intersect the California aqueduct and were identified as faults in California Department of Water Resources reports. Field reconnaissance revealed a number of low, subtle scarps (0.5 - 2 m high) and offset channels (5-15 m) on several of the VLs. A few VLs coincide with metamorphic lineations mapped by Dibblee (2002) as Precambrian pendants of marble, dolomite, and mica schist. Considerable float derived from granitic pegmatites was found near some of the metamorphic lithologies. These VLs presumably indicate relatively shallow or seasonally persistent moisture sources, though where they correspond to metamorphic bodies, soil chemistry or interface fracturing may also play a role. If these VLs mark the surface traces of faults, they may indicate the presence of a heretofore unrecognized region of localized lithospheric fractures

  18. 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

  19. Extending Seismic Tomography along the San Andreas Fault to the Lower Crust with Low Frequency Earthquakes

    NASA Astrophysics Data System (ADS)

    McClement, K.; Thurber, C. H.; Shelly, D. R.; Sumy, D. F.; Bennington, N. L.; Peterson, D. E.; Cochran, E.; Harrington, R. M.

    2013-12-01

    Similarities within families of low frequency earthquakes (LFE's) occurring within non-volcanic tremor (NVT) beneath the San Andreas fault (SAF) in central California facilitates applying high-precision location techniques to the LFE's and tomographic imaging of the tremor zone. In turn, this will allow us to examine the geometry and character of the SAF deep in the crust and evaluate the lithologies and physical conditions (e.g., fluid content) surrounding the tremor zone. We build on the work of Shelly and coworkers (Shelly et al., 2009; Shelly and Hardebeck, 2010) to stack and pick LFE "tremorgrams" for temporary array stations and other stations not previously analyzed. Our initial work focused on the 2001-2002 Parkfield Area Seismic Observatory (PASO) array and 15 LFE families directly beneath it. Augmenting our existing PASO earthquake and explosion dataset with the LFE picks allows us to extend our PASO tomographic model deeper to include the tremor zone, where we find slightly reduced Vp and more sharply reduced Vs near the LFE locations. We are now expanding our work to include PASO records of more distant LFE families and other seismic stations. We find that the high amplitudes and more frequent recurrence of LFE's to the southeast of PASO results in high quality stacks for most PASO stations. We can also produce good stacks for weaker, less frequent LFE's northwest of PASO. We will present examples of our new tremorgrams along with preliminary LFE relocations. There are three main underlying goals for this project. The first is to extend the existing Vp model and develop the new Vs model to cover the depth range of the NVT present beneath the SAF in the Parkfield region. The presence of ambient and triggered NVT in this area has mainly been attributed to the presence of fluids (Ghosh et al., 2008; Peng et al., 2008, 2009; Nadeau and Guilhem, 2009; Thomas et al., 2011; Hill et al., 2013). The velocity models we will develop will also help constrain the

  20. 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

  1. 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.

  2. Continuation of a deep borehole stress measurement profile near the San Andreas Fault: 2. Hydraulic fracturing stress measurements at Black Butte, Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Stock, J. M.; Healy, J. H.

    1988-12-01

    Hydraulic fracturing stress measurements were obtained in the Black Butte drill hole, 18 km northeast of the San Andreas fault in the Mojave Desert, at depths from 251 to 635 m. In all tests the least and greatest horizontal principal stresses (Sh and SH, respectively) exceeded the vertical stress (Sν), indicating a thrust faulting stress regime. A single good-quality hydraulic fracture impression from 309 m depth indicates an SH direction of N41°E ± 10°. This SH direction should be interpreted with caution because it is based on only one observation. This orientation is fairly compatible with nearby surface stress measurements but is incompatible with most of the hydraulic fracturing stress orientations reported from comparable depths in the Mojave Desert and is not favorable for right-lateral slip on either the San Andreas fault or NW striking faults present farther to the east. The stress regime measured in the Black Butte hole is comparable to that measured at nearby shallow depths but differs from the strike-slip or transitional (strike-slip to thrust faulting) stress regime present at similar depths in two nearby holes: Crystallaire, 4 km northeast of fhe San Andreas fault, and Hi Vista, 32 km northeast of the San Andreas fault. The SH direction measured in these holes is approximately 60° counterclockwise of that observed in the Black Butte hole. The differences in stress magnitudes and orientation among these holes substantiate previous indications of local variations in stress in the upper kilometer of the crust in this area and cast doubt on the validity of linear elastic models in which the effects of the San Andreas fault dominate the stress field in the western Mojave Desert.

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

    USGS Publications Warehouse

    Brown, Robert D., Jr.; 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.

  4. 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.

  5. Slip deficit on the San Andreas fault at Parkfield, California, as revealed by inversion of geodetic data

    USGS Publications Warehouse

    Segall, P.; Harris, R.

    1986-01-01

    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 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.

  6. 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.

  7. 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

  8. 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

  9. 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

  10. Tremor Source Interactions and Implications for the Structure of the Lower-Crustal San Andreas Fault Near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Shelly, D. R.

    2013-12-01

    Propagation of the tremor source has been documented along the strike-slip San Andreas fault as well as in the Cascadia and Nankai subduction zones. In these locations, tremor migrates with observed velocities ranging from a few km/day (a few cm/s) to more than 100 km/hr (~30 m/s), but in most cases this behavior has not been studied systematically. Variations in tremor migration characteristics along the fault have the potential to reflect corresponding variations in the structure of the lower crustal fault zone and the manner in which the fault is loaded. With this goal in mind, I use an updated catalog of more than 800,000 low-frequency earthquakes (LFEs) located at depths of 16-29 km along the San Andreas fault in central California [Shelly and Hardebeck, 2010] to systematically analyze tremor source interactions as a function space and time. Preliminary results show several interesting features. Some tremor sources are often preceded or followed in time by activity in neighboring sources, while others are mostly or completely isolated. Pairs of strongly interacting tremor sources exhibit characteristic delay times, reflecting the distance and typical propagation velocity between the sources. In some cases, we observe a preferred migration direction, which gives clues to the loading process of the fault. In general, we observe two distinct modes of tremor propagation: a 'slow' propagation of ~10 km/day and a 'fast' propagation of 20-60 km/hr. Typically, shallower, more episodic sources exhibit 'slow' migration, while deeper sources exhibit 'fast' migration. Fast migration dominantly occurs along the strike (and slip) direction, with little or no communication between nearby sources at different depths. Interactions tend to be strongest and farthest reaching (up to 35 km) south of Parkfield beneath Cholame, which is also the zone of highest amplitude tremor. A second zone of extensive interaction exists well north of Parkfield, beneath the creeping section of

  11. Clay-Rich Gouge Identified in Serpentinite from the San Andreas Fault Zone at Nelson Creek, Monterey County, California

    NASA Astrophysics Data System (ADS)

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

    2009-12-01

    A clay-rich gouge has been found in an outcrop of serpentinite along the San Andreas fault at Nelson Creek, about 2.4 km NNE of the San Andreas Fault Observatory at Depth (SAFOD). A small section of the clayey gouge, about 0.15 m wide and 0.5 m long, is exposed along a fault trace that slipped during the 2004 Parkfield earthquake and that juxtaposes the serpentinite against sandstone. The serpentinite body is 3-50 m wide and extends along the fault as a tectonic smear for at least 4 to 5 km. The clay-rich, foliated gouge contains clasts of serpentinite, shale, siltstone, quartz, albite, and K-feldspar. Based on electron microprobe analyses, clay minerals in the matrix of the gouge are saponitic smectite clays containing on average 24-25 wt% MgO and ~7 wt% Al2O3. The Mg-rich clay compositions combined with textural evidence suggest that the gouge is the product of metasomatic reaction between the Mg-rich serpentinite and adjoining quartzofeldspathic sedimentary rocks. Serpentinite-bearing clayey gouge has also been identified in Phase 3 SAFOD core recovered from the two actively creeping traces of the San Andreas fault at ~3190 m and ~3300 m measured depth (MD). Phase 2 SAFOD cuttings associated with the 3190 m active trace were examined for comparison with the Nelson Creek samples. Cuttings of foliated clays containing serpentinite grains were identified in cuttings samples beginning at 3197 m MD, and these are inferred to represent the foliated fault gouge of the 3190 m active trace. Many of the clays in the grains of gouge also have saponitic compositions. Other clays with higher Al/Si and Fe/Mg ratios are more consistent with corrensite, a regularly interlayered chlorite-smectite clay. In the few grains in which both clays were identified, the saponite appears to be younger than the corrensitic clay. We conclude that the clayey gouge in the Nelson Creek outcrop is equivalent to that found at ~2700 m (true depth) in the actively creeping strands of the San

  12. 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. PMID:17830739

  13. 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. PMID:17818388

  14. "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. PMID:18548903

  15. Mechanical and Microphysical Constraints on Co-seismic Rupture into the Creeping Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    French, M. E.; Chester, F. M.; Chester, J. S.

    2014-12-01

    Experimentally-determined mechanical properties of clay-rich fault rock, and the associated micromechanical processes, are used to constrain the conditions of slip instability along the San Andreas Fault (SAF). Using smectite-rich fault gouge collected from the Central Deforming Zone (CDZ) of the SAF in the San Andreas Fault Observatory at Depth (SAFOD), rotary and triaxial shear deformation experiments were conducted at rates that correspond to co-seismic slip (1 m/s) and in-situ creep (~10-10 s-1). Frictional strength depends on rate, temperature, availability of pore water, and fabric development, all of which reflect operation of different microscopic mechanisms at high and low shear rates. On the basis of the results, we use an energy balance for a propagating rupture to evaluate the potential for seismic slip along the CDZ. Appropriate scaling of the gouge strength from experimental to in-situ conditions, particularly for seismic slip rates, is critical to evaluating seismic hazards. Accordingly, the micromechanical processes identified from results of the deformation experiments are used to constrain and evaluate several different scaling relations between strength, critical displacement, and normal stress for the CDZ gouge. Experiments show that, at in situ creep rates, dislocation glide in clay is the rate-controlling mechanism and is responsible for the low strength (μ = 0.11), which limits the potential energy available for sustaining co-seismic frictional slip. As a consequence, microseismic patches within the CDZ are predicted to arrest for all scaling relationships under in-situ deformation conditions. Dynamic weakening at co-seismic rates involves thermal fluid pressurization, and for some scaling relations may be sufficient to sustain propagation of a rupture that nucleates within the adjacent locked segment into the CDZ

  16. 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%.

  17. Synthesis of Creep Measurements from Strainmeters and Creepmeters along the San Andreas Fault: Implications for Seismic vs. Aseismic Partitioning

    NASA Astrophysics Data System (ADS)

    Mencin, D.; Gottlieb, M. H.; Hodgkinson, K. M.; Bilham, R. G.; Mattioli, G. S.; Johnson, W.; Van Boskirk, E.; Meertens, C. M.

    2015-12-01

    Strainmeters and creepmeters have been operated along the San Andreas Fault, observing creep events for decades. In particular, the EarthScope Plate Boundary Observatory (PBO) has added a significant number of borehole strainmeters along the San Andreas Fault (SAF) over the last decade. The geodetic data cover a significant temporal portion of the inferred earthquake cycle along this portion of the SAF. Creepmeters measure the surface displacement over time (creep) with short apertures and have the ability to capture slow slip, coseismic rupture, and afterslip. Modern creepmeters deployed by the authors have a resolution of 5 µm over a range of 10 mm and a dynamic sensor with a resolution 25 µm over a range 2.2 m. Borehole strainmeters measure local deformation some distance from the fault with a broader aperture. Borehole tensor strainmeters principally deployed as part of the PBO, measure the horizontal strain tensor at a depth of 100-200 m with a resolution of 10-11 strain and are located 4 - 10 km from the fault with the ability to image a 1 mm creep event acting on an area of ~500 m2 from over 4 km away (fault perpendicular). A single borehole tensor strainmeter is capable of providing broad constraints on the creep event asperity size, location, direction and depth of a single creep event. The synthesis of these data from all the available geodetic instruments proximal to the SAF presents a unique opportunity to constrain the partitioning between aseismic and seismic slip on the central SAF. We show that simple elastic half-space models allow us to loosely constrain the location and depth of any individual creep event on the fault, even with a single instrument, and to image the accumulation of creep with time.

  18. 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.

  19. 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.

  20. A large mantle water source for the northern San Andreas fault system: a ghost of subduction past

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Recent research indicates that the shallow mantle of the Cascadia subduction margin under near-coastal Pacific Northwest, USA 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.

  1. 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.

    2016-01-01

    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

  2. Core Across the San Andreas Fault at SAFOD - Photographs, Physical Properties Data, and Core-Handling Procedures

    NASA Astrophysics Data System (ADS)

    Kirschner, D. L.; Carpenter, B.; Keenan, T.; Sandusky, E.; Sone, H.; Ellsworth, B.; Hickman, S.; Weiland, C.; Zoback, M.

    2007-12-01

    Core samples were obtained that cross three faults of the San Andreas Fault Zone north of Parkfield, California, during the summer of 2007. The cored intervals were obtained by sidetracking off the SAFOD Main Hole that was rotary drilled across the San Andreas in 2005. The first cored interval targeted the pronounced lithologic boundary between the Salinian terrane and the Great Valley and Franciscan formations. Eleven meters of pebbly conglomerate (with minor amounts of fine sands and shale) were obtained from 3141 to 3152 m (measured depth, MD). The two conglomerate units are heavily fractured with many fractures having accommodated displacement. Within this cored interval, there is a ~1m zone with highly sheared, fine-grained material, possibly ultracataclasite in part. The second cored interval crosses a creeping segment of a fault that has been deforming the cemented casing of the adjacent Main Hole. This cored interval sampled the fault 100 m above a seismogenic patch of M2 repeating earthquakes. Thirteen meters of core were obtained across this fault from 3186 to 3199 m (MD). This fault, which is hosted primarily in siltstones and shales, contains a serpentinite body embedded in a highly sheared shale and serpentinite-bearing fault gouge unit. The third cored interval crosses a second creeping fault that has also been deforming the cemented casing of the Main Hole. This fault, which is the most rapidly shearing fault in the San Andreas fault zone based on casing deformation, contains multiple fine- grained clay-rich fault strands embedded in highly sheared shales and lesser deformed sandstones. Initial processing of the cores was carried out at the drill site. Each core came to the surface in 9 meter-long aluminum core barrels. These were cut into more manageable three-foot sections. The quarter-inch-thick aluminum liner of each section was cut and then split apart to reveal the 10 cm diameter cores. Depending on the fragility and porosity of the rock, the

  3. Deformation of Sedimentary Rock Across the San Andreas Fault Zone: Mesoscale and Microscale Structures Displayed in Core From SAFOD

    NASA Astrophysics Data System (ADS)

    Chester, J. S.; Chester, F. M.; Kirschner, D. L.; Almeida, R.; Evans, J. P.; Guillemette, R. N.; Hickman, S.; Zoback, M.; Ellsworth, W.

    2007-12-01

    Sedimentary rocks captured in cores taken at the San Andreas Fault Observatory at Depth (SAFOD) provide an unparalleled sampling of deformation in the transition zone between creeping and locked segments of a major transform fault at 2.5-3.1 km vertical depth. These samples provide the unique opportunity to study deformation processes and the development of brittle structures within porous and granular rocks that have been subjected to variable loading rates and chemically reactive fluids while residing at the top of the seismogenic zone. The samples provide a transect from relatively undeformed host rock through highly fractured and sheared rock, and capture the two prominent zones of active, aseismic slip. Core recovery was almost complete. Wrap-around 1:1 map tracings of the outer surfaces of all cores characterize the lithology and mesoscale deformation. Cores from 3056-3067 m and 3141-3153 m measured depth (MD) sample moderately deformed rock at the western boundary of the fault zone. The cores display massive to finely laminated, pebbly arkosic sandstones with lesser amounts of fine-grained sandstone and siltstone. Numerous shear fractures and cm-thick cataclastic shear zones form a conjugate geometry indicating contraction at high angles to the San Andreas fault. Both intervals display minor faults that juxtapose different lithologies consistent with meters or greater of slip. Fracture density is variable but tends to increase with proximity to the minor faults. Cross-cutting relationships between shear fractures and cataclastic zones indicate a general progression from early faulting along thicker shear zones to later, more localized slip within shear zones and along fractures. Microstructures provide ample evidence for densification of the sandstones through grain-scale fracture and crushing, as well as fluid assisted processes of crack-sealing, dissolution-precipitation, and alteration-neocrystallization. Grain-scale features are consistent with these

  4. 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

  5. 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

  6. [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. PMID:2198714

  7. Numerical analysis of the creeping behavior of the S. Andrea di Perarolo secondary landslide (Italian Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Cioli, C.; Genevois, R.; Iafelice, M.; Zorzi, L.

    2012-04-01

    The S. Andrea landslide is a complex secondary phenomenon characterized by continuous movements causing a very high hazard condition for the near Perarolo di Cadore village (Italian Eastern Alps). A significant amount of geological and geotechnical investigations has been carried out in the past allowing the detection of the basal sliding surface. In specific, the sliding surface coincides with the contact between the bedrock and the overlying mass of an old landslides, involving a volume of about 180.000 cubic meters. A numerical approach has been adopted to analyze the stability of slope. This method is able to simulate the formation and development of shear zones as areas of strain localization in the model. Indeed, the S. Andrea landslide has been, then, investigated using FLAC, a two-dimensional explicit finite difference program, particularly useful in case of slopes with complex geometry. In order to build up a suitable model, variation of geological, hydrogeological and geotechnical parameters have been identified from the interpretation of all available data. In a preliminary stage, a Mohr-Coulomb plasticity model has been adopted except for the bedrock, which was characterized by an isotropic elastic model. Groundwater flow condition has been performed evaluating the change in pore pressure coupled to the mechanical deformation calculation. Numerical results show that this model cannot simulate real displacement behavior of the slope mainly due to both the complex material behavior and lithological heterogeneity, and due to geotechnical spatial complexity of different soils and mechanical parameters. It has been assumed that it was necessary to improve the model in the light of a time dependent behavior of existing soils. An elastic-viscoplastic model has been then used to reproduce the observed creeping behavior, and only in viscoplastic region time effects have been considered. Discussion of results points out on: i) the evolution of the ``mechanical

  8. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Thatcher, Wayne; England, Philip 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

  9. 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

  10. Upper-Crustal Reflectivity of the Central California Coast Range Near the San Andreas Fault Observatory at Depth (SAFOD), USA

    NASA Astrophysics Data System (ADS)

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

    2005-12-01

    We describe a new method of extracting seismic reflections that are visually evident in shot gathers but which may or may not come into focus in an image processed using conventional CDP reflection processing. This method has proven extremely useful in the central California Coast Range, near the San Andreas Fault Observatory at Depth (SAFOD), where conventional CDP processing has thus far produced an image that has few to no clear reflections, although special processing has imaged a couple of steeply dipping reflectors. The image described here includes both gently and steeply dipping reflections that combine to produce an interpretable image of the subsurface. Our data was recorded along a 46-km profile centered on SAFOD and perpendicular to the San Andreas Fault (SAF), with 62 shots and 912 recorders (shot spacing 0.5 to 1 km; receiver spacing 25 to 50 m). Although conventional CDP processing produced an image with few to no clear reflections, reflections are definitely visible in shot gathers. Using our new method, coherent energy (reflections and other phases) are picked on shot gathers and converted automatically to line drawings, and then the line drawings are migrated in a tomographic velocity model. The final image has clear reflectivity, including both gently and steeply dipping events. We see subhorizontal to gently west-dipping reflective bands within the granitic Salinian block at depths of 6 to 14 km, beginning at approximately the SAF. Within the Franciscan melange east of the fault, we see diffuse gently west-dipping reflectivity at depths of 4 to 10 km. Near the Coast Range (or here Waltham Canyon) fault (CRF), we see a sharp, steeply east-dipping reflector that begins approximately 2 km below the surface and 2 km west of the surface trace of the CRF. At approximately 4 km depth this reflector bends to become gently east dipping. A short but clear zone of west-dipping reflectors connects the top of this curved reflector to the surface trace of the

  11. Emplacement, offset history, and recent uplift of basement within the San Andreas Fault System, northeast San Gabriel Mountains, California

    NASA Astrophysics Data System (ADS)

    Kenney, Miles Douglas

    1999-11-01

    Mapping, petrography, cross-sections, structure contours, earthquake locations, and focal mechanism analogues of summed moment tensors have provided insights into the reconstruction and deformation associated with the San Andreas Fault System in the San Gabriel and Western San Bernardino Mountains (WSBM) of the Central Transverse Ranges. The San Gabriel Mountains (SGM) represent a Quaternary 'arch' that extends across the northwest trending San Andreas Fault (SAF). Mechanisms to explain the relatively large magnitudes of uplift on both sides of this relatively straight strike slip fault have been problematical. The uplift results from the interactions between the right lateral San Jacinto Fault (SJF) and SAF, and the thrust Cucamonga-Sierra Madre Faults (CF-SMF). Uplift south of the SAF occurs as the SGM Block propagates through the restraining bend at the intersection of the SJF and SAF at the surface, which has produced an antiform in the topography of the range and in the Vincent Thrust. Uplift is also due to motion on the CF-SMF. Uplift north of the SAF is attributed to an upper-crustal north-dipping subsurface restraining bend in the SAF due to the projected intersection of the CF-SMF and SJF, with the SAF. Northwest migration of the restraining bend in the Quaternary has produced a ˜1.5 km high, northeast dipping monocline in crystalline basement which is adjacent and parallel to the SAF. Reverse faults and deformation of alluvial terraces document a northwest migrating locus of compression and uplift. Toward the southeast, the subsurface restraining bend becomes a subsurface lateral ramp where the SJF intersects the SAF at depth. Crystalline basement of the Holcomb Ridge-Table Mountain 'slice' consists of a syntectonically emplaced, intercalated, north-dipping, igneous and metamorphic suite. Cretaceous igneous rocks were emplaced as tabular bodies, which now strike eastwest, and are concordant with a relatively older metasedimentary screen and para

  12. Characterization of deformation perpendicular to relative plate motion and major faults of the northern San Andreas system using geodetic data

    NASA Astrophysics Data System (ADS)

    Murray, J. R.; Pollitz, F. F.

    2014-12-01

    The northern San Andreas fault system NW of Clear Lake, CA is comprised of the subparallel San Andreas, Maacama, and Bartlett Springs faults. The dominant geodetic signal across the region is right lateral shear strain largely accommodated by infrequent earthquakes on these three faults and creep on the upper 5 km of the latter two. Here we use a newly densified Global Positioning System (GPS) velocity field (Murray et al., 2014) to assess the existence of regional contraction/extension. If present, the degree to which this deformation contributes to oblique slip in future earthquakes or, conversely, is partitioned into off-fault strain has implications for anticipated ground motions and inferred on-fault and off-fault moment deficit rates used in seismic hazard assessment. We inspect the observed horizontal GPS velocity field in a Sierra Nevada-Great Valley (SNGV) fixed frame. To first order the maximum contractile strain rate axis is well-aligned with the maximum compressive stress orientation (Provost and Houston, 2003). Although observed velocities at coastal sites compared to those on the SNGV block show little net strain perpendicular to the direction of Pacific-SNGV relative motion, velocity profiles transecting the three faults show both contraction and extension perpendicular to relative plate motion within the zone between the Great Valley and the coast. To evaluate this signal in the context of fault slip, we consider the residual fault-perpendicular velocity after removing predicted velocities due to the strike-slip component of estimated creep and interseismic locking (Murray et al., 2014). The slip rate model accounts for the fact that the orientations of the three major faults vary along their lengths, the faults are neither uniformly parallel to each other nor to the relative plate motion direction, and strike-slip creep rates vary along strike. In many locations near-fault residual strain rates are small, suggesting geometry and non-uniform creep

  13. 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

  14. 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

  15. 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

  16. Continuation of a deep borehole stress measurement profile near the San Andreas Fault: 1. Hydraulic fracturing stress measurements at Hi Vista, Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Hickman, Stephen H.; Zoback, Mark D.; Healy, John H.

    1988-12-01

    Hydraulic fracturing stress measurements were made in a 592-m-deep well at Hi Vista, California, 32 km from the San Andreas fault in the western Mojave Desert. The relative magnitudes of the horizontal principal stresses and the calculated overburden stress indicate that the stress regime at this site is transitional between thrust faulting and strike-slip faulting. The azimuths of the induced hydraulic fractures at Hi Vista exhibit considerable scatter, and the indicated direction of the maximum horizontal principal stress ranges from north-northeast to northwest. The measured magnitudes of the horizontal principal stresses and the horizontal deviatoric stress in this well are less than or equal to those measured in a nearby well of comparable depth 4 km from the San Andreas fault. This result contrasts with the increase in these stress components with distance from the San Andreas fault that was observed in a shallower borehole profile in the same area. Marked fluctuations in both stress magnitudes and orientations with depth in the Hi Vista well, however, may result from a localized perturbation to the regional stress regime. No correlation was found to exist in this well between stress magnitudes and either P wave velocities or natural fracture densities, although the low stresses measured at a depth of about 540 m may reflect proximity to an intensely fractured and permeable zone at the bottom of the well.

  17. 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.

  18. 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.

  19. Evaluation of LiDAR Imagery as a Tool for Mapping the Northern San Andreas Fault in Heavily Forested Areas of Mendocino and Sonoma Counties, California

    NASA Astrophysics Data System (ADS)

    Prentice, C. S.; Koehler, R. D.; Baldwin, J. N.; Harding, D. J.

    2004-12-01

    We are mapping in detail active traces of the San Andreas Fault in Mendocino and Sonoma Counties in northern California, using recently acquired airborne LiDAR (also known as ALSM) data. The LiDAR data set provides a powerful new tool for mapping geomorphic features related to the San Andreas Fault because it can be used to produce high-resolution images of the ground surfaces beneath the forest canopy along the 70-km-long section of the fault zone encompassed by the data. Our effort represents the first use of LiDAR data to map active fault traces in a densely vegetated region along the San Andreas Fault. We are using shaded relief images generated from bare-earth DEMs to conduct detailed mapping of fault-related geomorphic features (e.g. scarps, offset streams, linear valleys, shutter ridges, and sag ponds) between Fort Ross and Point Arena. Initially, we map fault traces digitally, on-screen, based only on the geomorphology interpreted from LiDAR images. We then conduct field reconnaissance using the initial computer-based maps in order to verify and further refine our mapping. We found that field reconnaissance is of utmost importance in producing an accurate and detailed map of fault traces. Many lineaments identified as faults from the on-screen images were determined in the field to be old logging roads or other features unrelated to faulting. Also, in areas where the resolution of LiDAR data is poor, field reconnaissance, coupled with topographic maps and aerial photographs, permits a more accurate location of fault-related geomorphic features. LiDAR images are extremely valuable as a base for field mapping in this heavily forested area, and the use of LiDAR is far superior to traditional mapping techniques relying only on aerial photography and 7.5 minute USGS quadrangle topographic maps. Comparison with earlier mapping of the northern San Andreas fault (Brown and Wolfe, 1972) shows that in some areas the LiDAR data allow a correction of the fault trace

  20. 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

  1. Preliminary Results from SAFOD Phase 3: Implications for the state of stress and shear localization in and near the San Andreas Fault at depth in central California

    NASA Astrophysics Data System (ADS)

    Zoback, M. D.; Hickman, S. H.; Ellsworth, W.; Kirschner, D.; Pennell, N. B.; Chery, J.; Sobolev, S.

    2007-12-01

    Strain localization along the San Andreas fault system in central California appears to result from both a thermally-weak lower crust and upper mantle (reflecting northward migration of the Mendocino triple junction and its associated slab window) and a fault zone in the upper brittle crust that is distinctly weaker than the surrounding crust. Geophysical logs and cuttings analyses from SAFOD Phase 2 (completed in 2005) revealed the San Andreas Fault Zone at approximately 2.7 km depth to be relatively broad (about 250 m), with several discrete, localized zones only 2-3 m wide with very low P- and S-wave velocities and low resistivity. Since 2005, fault creep at two of these localized zones has deformed the casing and thus demonstrates that these zones are actively creeping faults. During SAFOD Phase 3, continuous cores were obtained across these two actively creeping faults. Another core was obtained near the geologic boundary between the Salinian terrane (Pacific plate) and Great Valley/Franciscan terrane (North American plate). Each set of cores reveal zones of profound strain localization and probable weakening. These include ultracataclasites, highly-foliated shear zones (some containing veined serpentine) and intervals that appear to be cohesionless, compacted fault gouges which are likely composed of minerals with low frictional strength. No evidence of significantly elevated fluid pressure is observed within the fault zone. Information about the state of stress in the fault zone and adjacent crust comes from observations and modeling of wellbore failures, direct measurements of the magnitude of the least principal stress and the direction of stress-induced shear wave velocity anisotropy. Observations made after rotary drilling through the fault in 2005 indicate that the San Andreas is a weak fault imbedded in a strong crust. These observations made within about 100 m of the active fault zone at 2.7 km include i) stress orientations that are nearly

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. Aseismic slip and fault-normal strain along the central creeping section of the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Rolandone, F.; Bürgmann, R.; Agnew, D. C.; Johanson, I. A.; Templeton, D. C.; d'Alessio, M. A.; Titus, S. J.; DeMets, C.; Tikoff, B.

    2008-07-01

    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 μstrain/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.

  7. [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. PMID:8928938

  8. 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.

  9. 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.

  10. Heterogeneous slip and rupture models of the San Andreas fault zone based upon three-dimensional earthquake tomography

    SciTech Connect

    Foxall, W.

    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.

  11. Geomorphotectonic studies of the Wilshire blind thrust fault and the San Andreas fault, Los Angeles area, California

    SciTech Connect

    Thiessen, R.L.

    1996-08-01

    WSUs Nodes program finds geomorphologic features formed by active faults and folds using a DEM. Two active faults in the Los Angeles basin, California were studied. The Wilshire fault was recently designated a fault based on the presence of the Wilshire Arch cored by a blind thrust. A new Nodes detector was designed to look for the observed parabolic ridge over it. The detector was 2.5 km in diameter with ridges 1 to 6 m high. The axis of the Wilshire arch, freeways, other oil fields probably controlled by arches, and interfluve dissection drainage ridges in older alluvium were all detected. Complex strike slip and thrust faults exist near Cajon Pass. The major strike slip faults (San Andreas, San Jacinto) have a {open_quotes}rift{close_quotes} valley 1 km wide that was found with a 41 pixel (1200 m) diameter Nodes detector, as were east-west oriented thrusts. The SAF and SJF were also found with a slope break detector.

  12. Fault-zone guided waves from explosions in the San Andreas fault at Parkfield and Cienega Valley, California

    USGS Publications Warehouse

    Li, Y.-G.; Ellsworth, W.L.; Thurber, C.H.; Malin, P.E.; Aki, K.

    1997-01-01

    Fault-zone guided waves were successfully excited by near-surface explosions in the San Andreas fault zone both at Parkfield and Cienega Valley, central California. The guided waves were observed on linear, three-component seismic arrays deployed across the fault trace. These waves were not excited by explosions located outside the fault zone. The amplitude spectra of guided waves show a maximum peak at 2 Hz at Parkfield and 3 Hz at Cienega Valley. The guided wave amplitude decays sharply with observation distance from the fault trace. The explosion-excited fault-zone guided waves are similar to those generated by earthquakes at Parkfield but have lower frequencies and travel more slowly. These observations suggest that the fault-zone wave guide has lower seismic velocities as it approaches the surface at Parkfield. We have modeled the waveforms as S waves trapped in a low-velocity wave guide sandwiched between high-velocity wall rocks, resulting in Love-type fault-zone guided waves. While the results are nonunique, the Parkfield data are adequately fit by a shallow wave guide 170 m wide with an S velocity 0.85 km/sec and an apparent Q ??? 30 to 40. At Cienega Valley, the fault-zone wave guide appears to be about 120 m wide with an S velocity 0.7 km/sec and a Q ??? 30.

  13. 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.

  14. 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).

  15. 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, II; 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.

  16. 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.

  17. 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.

  18. Lithology and internal structure of the San Andreas fault at depth based on characterization of Phase 3 whole-rock core in the San Andreas Fault Observatory at Depth (SAFOD) borehole

    NASA Astrophysics Data System (ADS)

    Bradbury, Kelly K.; Evans, James P.; Chester, Judith S.; Chester, Frederick M.; Kirschner, David L.

    2011-10-01

    We characterize the lithology and structure of the spot core obtained in 2007 during Phase 3 drilling of the San Andreas 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.

  19. Fragmented Landscapes in the San Gorgonio Pass Region: Insights into Quaternary Strain History of the Southern San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Kendrick, K. J.; Matti, J. C.; Landis, G. P.; Alvarez, R. M.

    2006-12-01

    The San Gorgonio Pass (SGP) region is a zone of structural complexity within the southern San Andreas Fault system that is characterized by (1) multiple strands of the San Andreas 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

  20. Deformation in the lower crust and downward extent of the San Andreas Fault as revealed by teleseismic waveforms

    NASA Astrophysics Data System (ADS)

    Zhu, Lupei

    2002-11-01

    High resolution images of crustal structure across the San Andreas Fault (SAF) were obtained by using the common conversion point stacking of teleseismic P-to- S converted waves recorded during the Los Angeles Region Seismic Experiments (LARSE-I and II). In the upper crust, several sedimentary basins were delineated in the images, including the San Fernando and the Santa Clarita Basins. The San Fernando Basin reaches a depth of 8 km under the northern edge of the San Fernando Valley. On the LARSE-I profile, the downward projection of the SAF truncates several lower crustal interfaces including the Moho on both sides. The Moho is vertically offset by as much as 8 km. Along the LARSE-II profile, the impedance contrast and slope of the Moho are seen to change across the fault. These results indicate that the fault penetrates into the lower crust and probably uppermost mantle as a narrow (<10 km) feature. The Moho beneath the San Gabriel Mountains is shallower (˜26 km) than under the San Gabriel Valley to the south and the Mojave Desert to the north, suggesting that the mountain ranges were lifted en masse by horizontal compression. On the northeast side of the SAF, the Mojave Desert has a sharp and essentially flat Moho at a depth of ˜32 km. The lower crustal structure beneath the San Fernando and Santa Clarita Valleys along the LARSE-II profile south of the SAF is complicated as indicated by the large undulation and low impedance contrast of the Moho. These observations suggest that the deformation in the lower crust is localized and often concentrates near boundaries of crustal blocks or beneath those places which have experienced intensive faulting and deformation in the upper crust.

  1. Orientation of three-component geophones in the San Andreas Fault observatory at depth Pilot Hole, Parkfield, California

    USGS Publications Warehouse

    Oye, V.; Ellsworth, W.L.

    2005-01-01

    To identify and constrain the target zone for the planned SAFOD Main Hole through the San Andreas 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.

  2. Visco-elastic full waveform inversion of controlled seismic data from the San Andreas Fault Observatory at Depth

    NASA Astrophysics Data System (ADS)

    Zeiß, Jens; Paschke, Marco; Bleibinhaus, Florian

    2016-04-01

    We apply visco-elastic full waveform inversion (FWI) to a 50-km-long controlled-source refraction/reflection seismic survey at the San Andreas 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).

  3. Forward and Reverse Modeling Compressive Deformation in a 3D Geologic Model along the Central San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Roberts, M. A.; Graymer, R. W.; McPhee, D.

    2015-12-01

    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 Andreas 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.

  4. Progressive deformation and degradation along the northern portion of the Big Bend of the San Andreas Fault

    SciTech Connect

    Arrowsmith, R. . Dept. of Geology)

    1992-01-01

    The 1-to-5-km-wide Elkhorn Hills in the southeastern Carrizo Plain, California (bounded by the San Andreas Fault (SAF) on the southwest and a series of reverse faults on the northeast), are progressively deformed as they are displaced along the SAF into the northern portion of the Big Bend. The structural development follows this sequence: (1) an alluvial fan surface is cut by reverse faults about 500 m northeast of the SAF, and grabens form in the foot-wall block of the faults; (2) a reverse fault striking 25 degrees counterclockwise from the SAF cuts the fan surface 2 to 3 km northeast of the SAF, left-stepping grabens form in the reverse fault hanging wall; their orientation is controlled by distributed SAF parallel shear and by dip variations in the reverse fault surface; (3) reverse faults accumulate displacement, increasing relief in the Elkhorn Hills, while hanging wall extension decreases; (4) slip on deeper thrusts accommodates contraction within the Big Bend, and Elkhorn Hills deformation decreases. Within the Northern Elkhorn Hills, the evidence for the development of deformation in time and space includes a southeastward increase in total displacement on the normal and reverse faults, a southeastward increase in the degradation of the normal fault scarps, and the beheading of a southwest flowing drainage by slip on the reverse fault, as well as cutting of that drainage by normal faults, implying contemporaneous propagation of normal and reverse faults. Based on a ground pattern age of 4 to 10 ka for the beheaded drainage and the present location of the reverse fault, a propagation rate of 3.5 to 10 cm/yr is calculated: consistent with the 3.5 cm/yr at which the Elkhorn Hills are displaced into the Big Bend by strike-slip motion along the SAF.

  5. Geomorphological expression of a complex structural region: San Andreas Fault through the San Gorgonio Pass, southern California

    NASA Astrophysics Data System (ADS)

    Kendrick, K. J.; Matti, J. C.

    2015-12-01

    The San Gorgonio Pass (SGP) region of southern California is a locus of extensive Quaternary deformation surrounding a complex section of the San Andreas Fault (SAF) zone. The geomorphology of the SGP region reflects the complicated history of geologic events in the formation of this structural 'knot'. Critical questions remain in assessing earthquake hazard for this region: What is the likelihood that rupture will propagate through the SGP? If rupture is able to propagate, what pathway will connect the various fault strands? To address these questions, we focus on the geology and geomorphology of the SGP region. We have identified fault-bounded blocks, and focus on three that are developed within crystalline bedrock: the Yucaipa Ridge block (YRB) block, the Kitching Peak block (KPB), and the Pisgah Peak block (PPB). The latter two blocks are positioned south of the YRB, and partially separated from each other by the San Bernardino strand; this strand cannot be mapped at the surface as an active connection between fault strands. Both KPB and PPB are bounded to the south by the San Gorgonio Pass Fault Zone. Morphometric analyses consistently demonstrate distinctions between KPB and PPB, though the bedrock lithologies are the same. Geologic mapping of the region highlights the differences in Quaternary units within the blocks. These geomorphic and geologic distinctions lead to our interpretation that KPB and PPB have experienced markedly different uplift histories that constrain the history of dextral slip on the SAF through SGP. Specifically, although the latest Quaternary geologic setting of SGP raises questions about modern slip transfer through the Pass, the contrasting uplift histories of KPB and PPB strongly suggest that earlier in Quaternary time SGP was not a barrier to slip transfer between the Coachella Valley to the SE and the San Bernardino Basin to the NW.

  6. Variations Of Velocity Contrast Along The Rupture Zone Of The 2004 M6 Parkfield Earthquake On The San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Zhao, P.; Peng, Z.; Ben-Zion, Y.; Lewis, M.; Shi, Z.

    2007-12-01

    We systematically investigate the velocity contrast along the Parkfield section of the San Andreas Fault (SAF) that ruptured during the 2004 M6 Parkfield earthquake, using fault zone head waves (FZHW) that refract along the bimaterial interface. The analysis employs a total of 322 repeating earthquakes clusters identified from 8993 earthquakes in the relocated catalog of Thurber et al. (2006). The seismic data are recorded by 13 borehole stations in the High Resolution Seismic Network (HRSN) since 1987 and 23 surface stations in the Northern California Seismic Network (NCSN) since 1984, with normal distances to the fault less than 6 km. The study is part of a larger project on imaging bimaterial interfaces in the Parkfield region with multiple seismic networks. We stack waveforms of each repeating earthquake cluster, and align the peaks or troughs of the direct P waves assuming right-lateral strike-slip focal mechanisms. Clear FZHW are observed at surface and borehole stations that are within a few kms on the NE (slow) side of the SAF. The obtained velocity contrast is about 8% north of Middle Mountain, and decreases rapidly toward Gold Hill near the epicenter of the 2004 event. This implies an abrupt change of velocity contrast along the Parkfield section of SAF near Gold Hill. The observed variation of velocity contrast is consistent with 3-D tomography models of the Parkfield section, which include a high velocity body near Gold Hill on the NE side that produces a local reversal of the velocity contrast, and geological observations of a sliver of high-velocity rock immediately to the NE of the SAF associated with the Gold Hill fault.

  7. Frictional and hydrologic behavior of the San Andreas Fault: Insights from laboratory experiments on SAFOD cuttings and core

    NASA Astrophysics Data System (ADS)

    Carpenter, B. M.; Marone, C.; Saffer, D. M.

    2010-12-01

    The debate concerning the apparent low strength of tectonic faults, including the San Andreas Fault (SAF), continues to focus on: 1) low intrinsic friction resulting from mineralogy and/or fabric, and 2) decreased effective normal stress due to elevated pore pressure. Here we inform this debate with laboratory measurements of the frictional behavior and permeability of cuttings and core returned from the SAF at a vertical depth of 2.7 km. We conducted experiments on cuttings and core recovered during SAFOD Phase III drilling. All samples in this study are adjacent to and within the active fault zone penetrated at 10814.5 ft (3296m) measured depth in the SAFOD borehole. We sheared gouge samples composed of drilling cuttings in a double-direct shear configuration subject to true-triaxial loading under constant effective normal stress, confining pressure, and pore pressure. Intact wafers of material were sheared in a single-direct shear configuration under similar conditions of effective stress, confining pressure, and pore pressure. We also report on permeability measurements on intact wafers of wall rock and fault gouge prior to shearing. Initial results from experiments on cuttings show: 1) a weak fault (µ=~0.21) compared to the surrounding wall rock (µ=~0.35), 2) velocity strengthening behavior, (a-b > 0), consistent with aseismic slip, and 3) near zero healing rates in material from the active fault. XRD analysis on cuttings indicates the main mineralogical difference between fault rock and wall rock, is the presence of significant amounts of smectite within the fault rock. Taken together, the measured frictional behavior and clay mineral content suggest that the clay composition exhibits a basic control on fault behavior. Our results document the first direct evidence of weak material from an active fault at seismogenic depths. In addition, our results could explain why the SAF in central California fails aseismically and hosts only small earthquakes.

  8. Elemental Geochemistry of Samples From Fault Segments of the San Andreas Fault Observatory at Depth (SAFOD) Drill Hole

    NASA Astrophysics Data System (ADS)

    Tourscher, S. N.; Schleicher, A. M.; van der Pluijm, B. A.; Warr, L. N.

    2006-12-01

    Elemental geochemistry of mudrock samples from phase 2 drilling of the San Andreas Fault Observatory at Depth (SAFOD) is presented from bore hole depths of 3066 m to 3169 m and from 3292 m to 3368 m, which contain a creeping section and main trace of the fault, respectively. In addition to preparation and analysis of whole rock sample, fault grains with neomineralized, polished surfaces were hand picked from well-washed whole rock samples, minimizing the potential contamination from drilling mud and steel shavings. The separated fractions were washed in deionized water, powdered using a mortar and pestle, and analyzed using an Inductively Coupled Plasma- Optical Emission Spectrometer for major and minor elements. Based on oxide data results, systematic differences in element concentrations are observed between the whole rock and fault rock. Two groupings of data points are distinguishable in the regions containing the main trace of the fault, a shallow part (3292- 3316 m) and a deeper section (3320-3368 m). Applying the isocon method, assuming Zr and Ti to be immobile elements in these samples, indicates a volume loss of more than 30 percent in the shallow part and about 23 percent in the deep part of the main trace. These changes are minimum estimates of fault-related volume loss, because the whole rock from drilling samples contains variable amount of fault rock as well. Minimum estimates for volume loss in the creeping section of the fault are more than 50 percent when using the isocon method, comparing whole rock to plucked fault rock. The majority of the volume loss in the fault rocks is due to the dissolution and loss of silica, potassium, aluminum, sodium and calcium, whereas (based on oxide data) the mineralized surfaces of fractures appear to be enriched in Fe and Mg. The large amount of element mobility within these fault traces suggests extensive circulation of hydrous fluids along fractures that was responsible for progressive dissolution and leaching

  9. Heat flow, strong near-fault seismic waves, and near-fault tectonics on the central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Sleep, Norman H.

    2016-05-01

    The main San Andreas Fault strikes subparallel to compressional folds and thrust faults. Its fault-normal traction is on average a factor of γ=1+2μthr>(√(1+μthr2)+μthr>), where μthr is the coefficient of friction for thrust faults, times the effective lithostatic pressure. A useful upper limit for μthr of 0.6 (where γ is 3.12) is obtained from the lack of heat flow anomalies by considering off-fault convergence at a rate of 1 mm/yr for 10 km across strike. If the fault-normal traction is in fact this high, the well-known heat flow constraint of average stresses of 10-20 MPa during strike slip on the main fault becomes more severe. Only a few percent of the total slip during earthquakes can occur at the peak stress before dynamic mechanisms weaken the fault. The spatial dimension of the high-stress rupture-tip zone is ˜10 m for γ = 3.12 and, for comparison, ˜100 m for γ = 1. High dynamic stresses during shaking occur within these distances of the fault plane. In terms of scalars, fine-scale tectonic stresses cannot exceed the difference between failure stress and dynamic stress. Plate-scale slip causes stresses to build up near geometrical irregularities of the fault plane. Strong dynamic stresses near the rupture tip facilitate anelastic deformation with the net effects of relaxing the local deviatoric tectonic stress and accommodating deformation around the irregularities. There also is a mild tendency for near-fault material to extrude upward. Slip on minor thrust faults causes the normal traction on the main fault to be spatially variable.

  10. Micromechanisms of creep in clay-rich gouge from the Central Deforming Zone of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    French, M. E.; Chester, F. M.; Chester, J. S.

    2015-02-01

    We report the strength and constitutive behavior of gouge sampled from the Central Deforming Zone (CDZ) of the San Andreas Fault. Layers of flaked CDZ gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 × 10-10s-1 and within an order of magnitude of in situ rates. Deformation conditions correspond to the in situ effective normal stress (100 MPa) and temperature (65 to 120°C) at the sampling depth of 2.7 km. Gouge was sheared dry and with brine pore fluid at 25 MPa pore pressure. Dry gouge is stronger and more rate strengthening than brine-saturated gouge. Brine-saturated CDZ gouge strengthens with increasing strain rate and decreasing temperature, and the dependencies of strength on strain rate and temperature increase at rates below ˜5 × 10-9s-1. At strain rates greater than ˜5 × 10-9s-1, the rate dependence is consistent with previous studies on the CDZ gouge conducted at even higher rates. The increase in rate dependence below ˜5 × 10-9s-1 indicates a change in the rate-controlling deformation mechanism. The magnitude of the friction rate dependence parameter, a, and the temperature sensitivity of a are consistent with crystal plasticity of the phyllosilicates. We hypothesize a micromechanical model for the CDZ gouge whereby a transition from fracture and delamination-accommodated frictional flow to crystal plasticity-accommodated frictional flow occurs with decreasing strain rate.

  11. Erosion in the Mecca Hills: using GIS to investigate potential erosion factors along the southern San Andreas Fault.

    NASA Astrophysics Data System (ADS)

    Maneerat, P.; Reinen, L. A.; Fukutaki, K. G.; Rittiron, S.; Mejias, R.

    2015-12-01

    The Mecca Hills (MH) occur in a region of transpression along the southern San Andreas 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.

  12. A reevaluation of the Pallett Creek earthquake chronology based on new AMS radiocarbon dates, San Andreas fault, California

    USGS Publications Warehouse

    Scharer, K.M.; Biasi, G.P.; Weldon, R.J., II

    2011-01-01

    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 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.

  13. An integral method to estimate the moment accumulation rate on the Creeping Section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Tong, Xiaopeng; Sandwell, David T.; Smith-Konter, Bridget

    2015-10-01

    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 Andreas 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.

  14. Physical and chemical characterization of pulverized granite from a shallow drill along the San Andreas Fault, Little Rock, CA

    NASA Astrophysics Data System (ADS)

    Wechsler, N.; Allen, E. E.; Rockwell, T. K.; Chester, J. S.; Girty, G. H.; Ben-Zion, Y.

    2008-12-01

    We present results from a continuous 42 meter deep core through damaged granitoids adjacent to the San Andreas fault near Little Rock Creek. We employed several methods to measure particle size distribution (pipette, elutriator, laser particle analyzer), as well as x-ray diffraction and fluorescence (XRD, XRF) methods to investigate the relation between depth, pulverization and chemical processes that may affect the degree of damage. The drill site is characterized by extensive outcrops of granitic rocks with varying degrees of damage at distances of up to a few hundreds of meters from the fault's primary active strand. The drill core is composed mainly of pulverized granite and granodiorite, and crosses several high clay content secondary shears. Results of particle size distributions measured using standard sieving and pipette methods indicate that medium to coarse silt and fine sand are the dominant particle size range in the cored section, similar to pulverized granitic rocks analyzed by Rockwell et al. (2008). Very few clay-size particles were observed, but minor amounts of clay weathering products are present. We observe a minor shift in the particle size distribution towards finer sizes with depth, in agreement with the results of Anderson et al. (1980), and find somewhat different distributions for different lithologies. Several zones displaying significant chemical alteration were captured over the cored interval, but XRF data indicate that there is no systematic change in chemical alteration with depth. Where substantial chemical alterations do occur, different lithologies show different weathering trends. Those chemical alterations occur in proximity to secondary shears, suggesting fluid induced mass transfer.

  15. Long Return Periods for Earthquakes in San Gorgonio Pass and Implications for Large Ruptures of the San Andreas Fault in Southern California

    NASA Astrophysics Data System (ADS)

    Yule, J.; McBurnett, P.; Ramzan, S.

    2011-12-01

    The largest discontinuity in the surface trace of the San Andreas fault occurs in southern California at San Gorgonio Pass. Here, San Andreas motion moves through a 20 km-wide compressive stepover on the dextral-oblique-slip thrust system known as the San Gorgonio Pass fault zone. This thrust-dominated system is thought to rupture during very large San Andreas events that also involve strike-slip fault segments north and south of the Pass region. A wealth of paleoseismic data document that the San Andreas fault segments on either side of the Pass, in the San Bernardino/Mojave Desert and Coachella Valley regions, rupture on average every ~100 yrs and ~200 yrs, respectively. In contrast, we report here a notably longer return period for ruptures of the San Gorgonio Pass fault zone. For example, features exposed in trenches at the Cabezon site reveal that the most recent earthquake occurred 600-700 yrs ago (this and other ages reported here are constrained by C-14 calibrated ages from charcoal). The rupture at Cabezon broke a 10 m-wide zone of east-west striking thrusts and produced a >2 m-high scarp. Slip during this event is estimated to be >4.5 m. Evidence for a penultimate event was not uncovered but presumably lies beneath ~1000 yr-old strata at the base of the trenches. In Millard Canyon, 5 km to the west of Cabezon, the San Gorgonio Pass fault zone splits into two splays. The northern splay is expressed by 2.5 ± 0.7 m and 5.0 ± 0.7 m scarps in alluvial terraces constrained to be ~1300 and ~2500 yrs old, respectively. The scarp on the younger, low terrace postdates terrace abandonment ~1300 yrs ago and probably correlates with the 600-700 yr-old event at Cabezon, though we cannot rule out that a different event produced the northern Millard scarp. Trenches excavated in the low terrace reveal growth folding and secondary faulting and clear evidence for a penultimate event ~1350-1450 yrs ago, during alluvial deposition prior to the abandonment of the low terrace

  16. Southern San Andreas-San Jacinto fault system slip rates estimated from earthquake cycle models constrained by GPS and interferometric synthetic aperture radar observations

    NASA Astrophysics Data System (ADS)

    Lundgren, Paul; Hetland, Eric A.; Liu, Zhen; Fielding, Eric J.

    2009-02-01

    We use ground geodetic and interferometric synthetic aperture radar satellite observations across the southern San Andreas (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 Andreas 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 Andreas 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.

  17. SAFOD Core Reveals Low Strength of Deep San Andreas Fault Gouge and Provides Explanation for Low Heat Flow in Creeping Section of Fault

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    Core samples retrieved from the currently creeping the San Andreas Fault (SAF) at a vertical depth of 2.7 km have been tested for shear strength in the laboratory at realistic in-situ stress conditions. Samples were obtained as part of the San Andreas Fault Observatory at Depth (SAFOD) scientific drilling program near Parkfield, California. The core samples come from within a 200 m-wide SAF damage zone and include two actively deforming shear zones, identified on the basis of repeat casing deformation logs, that are 1.6 and 2.6 m wide and are taken to represent the currently active fault core. The shear zones are mineralogically and rheologically distinct from their surroundings. The notably low coefficient of friction in the active shear zones (µ = 0.15 - 0.2) is due to a high percentage of saponite, a Mg-rich smectite clay. In contrast, the host rock friction ranges from 0.54 to 0.65. The fault-core material is sufficiently weak to account for the apparent low strength of the San Andreas Fault that has been inferred from heat flow and stress orientation data. The fault-core material is highly plastic and likely to result in fault creep rather than earthquakes, as expected for this creeping portion of the SAF. The relatively short inter-event times and high stress drops of nearby repeating earthquakes can be understood as a result of bridging between local asperities of the host rock promoted by pinching out of this weak, creeping fault-zone material. Borehole observations, combined with these measurements of fault core strength, provide a self-consistent picture of the stress state of the SAF at the SAFOD site in which the fault is intrinsically weak in an otherwise strong crust.

  18. Northern San Andreas Fault slip rates on the Santa Cruz Mountain section: 10Be dating of an offset alluvial fan complex, Sanborn County Park, Saratoga, CA

    NASA Astrophysics Data System (ADS)

    Guns, K. A.; Prentice, C. S.; DeLong, S. B.; Kiefer, K.; Blisniuk, K.; Burgmann, R.

    2015-12-01

    To better assess seismic hazard and fault behavior along the southern peninsula in the San Francisco Bay Area on the Santa Cruz Mountain section of the San Andreas Fault, we combine field observations and high-resolution lidar topography data with 10Be exposure dating on offset landforms to estimate geologic fault slip rates. Our mapping at Sanborn County Park near Saratoga reveals a progression of alluvial fans and debris flows offset from their upstream sources by dextral slip on the San Andreas Fault. These upstream sources are 3 drainages, Todd Creek, Service Road Creek and Aubry Creek. Coarse alluvial deposits from each of these creeks contain large Tertiary sandstone boulders of varying size and abundance, derived from the Vaqueros Formation, that allow us to constrain the provenance of offset alluvial deposits to their upstream sources. Initial reconstruction, based on clast-count data on lithology and size from Todd Creek (n=68), Service Road Creek (N=32) and the offset deposits (n=68), suggest ≥140 m of dextral fault movement. Initial 10Be cosmogenic dating of sandstone boulders on an offset deposit from Service Road Creek yields a maximum date of 8 ka, a date uncorrected for hillslope residence and fluvial transport of inherited 10Be concentrations. These data suggest a minimum slip rate of at least 17 mm/yr on the Santa Cruz Mountain section of the San Andreas Fault in the peninsula. Ongoing analysis will refine this fault slip rate. Our preliminary data underscore the potential of this site to provide geologic slip rate estimates, and therefore answer a question critical to seismic hazard assessment, in a region where steep terrain, mass wasting, vegetation and urban development have generally made slip rate estimates challenging to obtain.

  19. Uncertainties in slip-rate estimates for the Mission Creek strand of the southern San Andreas fault at Biskra Palms Oasis, southern California

    USGS Publications Warehouse

    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.

    2010-01-01

    This study focuses on uncertainties in estimates of the geologic slip rate along the Mission Creek strand of the southern San Andreas 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 Andreas 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 Andreas fault at Biskra Palms, it cannot be demonstrated with available data. ?? 2010 Geological Society of America.

  20. Basin geometry and cumulative offsets in the Eastern Transverse Ranges, southern California: Implications for transrotational deformation along the San Andreas fault system

    USGS Publications Warehouse

    Langenheim, V.E.; Powell, R.E.

    2009-01-01

    The Eastern Transverse Ranges, adjacent to and southeast of the big left bend of the San Andreas fault, southern California, form a crustal block that has rotated clockwise in response to dextral shear within the San Andreas 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 Andreas 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.

  1. A High shear stress segment along the San Andreas Fault: Inferences based on near-field stress direction and stress magnitude observations in the Carrizo Plain Area

    SciTech Connect

    Castillo, D. A.,; Younker, L.W.

    1997-01-30

    Nearly 200 new in-situ determinations of stress directions and stress magnitudes near the Carrizo plain segment of the San Andreas 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 Andreas 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 Andreas fault-parallel planes becomes negligible. 65 refs., 15 figs.

  2. Early Miocene transpression across the Pacific-North American plate margin, initiation of the San Andreas fault, and tectonic wedge activation

    SciTech Connect

    McLaughlin, R.J. ); Underwood, M.B. )

    1993-04-01

    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 Andreas 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 Andreas 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 Andreas 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.

  3. Earthquake travel time tomography of the southern Santa Cruz Mountains: Control of fault rupture by lithological heterogeneity of the San Andreas fault zone

    SciTech Connect

    Foxall, W.; Michelini, A.; McEvilly, T.V.

    1993-10-10

    The 1989 Loma Prieta earthquake occurred along the stretch of the San Andreas 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 Andreas 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 Andreas 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.

  4. [Knowledge of the human body. At the 450th anniversary of the first edition of Andreas Vesalius' life work. "De Humani Coporis Fabrica Libri Septem"].

    PubMed

    De Schaepdryver, A F

    1993-01-01

    As an introduction to the symposium we pay attention successively: firstly, to the "Magister divinus", to Andreas Vesalius' personality, according to the testimony of his pupil Fallopius; secondly, to his ingenious lifework, the "De Humani Corporis Fabrica", according to the opinion of Sir William Osler, "the greatest medical book ever written", finally, to the historical evolution leading to the Vesalian way of thinking and working. All this proves that Vesalius' work is a fundamental turning point in the development of medicine as well as in the evolution of scientific practice in a general sense. It is also one of the highlights in the construction of mankind's intellectual patrimony. PMID:8209575

  5. Data Files for Ground-Motion Simulations of the 1906 San Francisco Earthquake and Scenario Earthquakes on the Northern San Andreas Fault

    USGS Publications Warehouse

    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

    2009-01-01

    This data set contains results from ground-motion simulations of the 1906 San Francisco earthquake, seven hypothetical earthquakes on the northern San Andreas 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).

  6. Changes in state of stress on the southern san andreas fault resulting from the california earthquake sequence of april to june 1992.

    PubMed

    Jaumé, S C; Sykes, L R

    1992-11-20

    The April to June 1992 Landers earthquake sequence in southern California modified the state of stress along nearby segments of the San Andreas fault, causing a 50-kilometer segment of the fault to move significantly closer to failure where it passes through a compressional bend near San Gorgonio Pass. The decrease in compressive normal stress may also have reduced fluid pressures along that fault segment. As pressures are reequilibrated by diffusion, that fault segment should move closer to failure with time. That fault segment and another to the southeast probably have not ruptured in a great earthquake in about 300 years. PMID:17778355

  7. GPS-derived strain in northwestern California: Termination of the San Andreas fault system and convergence of the Sierra Nevada Great Valley block contribute to southern Cascadia forearc contraction

    NASA Astrophysics Data System (ADS)

    Williams, Todd B.; Kelsey, Harvey M.; Freymueller, Jeffrey T.

    2006-02-01

    GPS-derived velocities (1993-2002) in northwestern California show that processes other than subduction are in part accountable for observed upper-plate contraction north of the Mendocino triple junction (MTJ) region. After removing the component of elastic strain accumulation due to the Cascadia subduction zone from the station velocities, two additional processes account for accumulated strain in northern California. The first is the westward convergence of the Sierra Nevada-Great Valley (SNGV) block toward the coast and the second is the north-northwest impingement of the San Andreas fault system from the south on the northern California coastal region in the vicinity of Humboldt Bay. Sierra Nevada-Great Valley block motion is northwest toward the coast, convergent with the more northerly, north-northwest San Andreas transform fault-parallel motion. In addition to the westward-converging Sierra Nevada-Great Valley block, San Andreas transform-parallel shortening also occurs in the Humboldt Bay region. Approximately 22 mm/yr of distributed Pacific-SNGV motion is observed inland of Cape Mendocino across the northern projections of the Maacama and Bartlett Springs fault zones but station velocities decrease rapidly north of Cape Mendocino. The resultant 6-10 mm/yr of San Andreas fault-parallel shortening occurs above the southern edge of the subducted Gorda plate and at the latitude of Humboldt Bay. Part of the San Andreas fault-parallel shortening may be due to the viscous coupling of the southern edge of the Gorda plate to overlying North American plate. We conclude that significant portions of the upper-plate contraction observed north of the MTJ region are not solely a result of subduction of the Gorda plate but also a consequence of impingement of the western edge of the Sierra Nevada-Great Valley block and growth of the northernmost segments of the San Andreas fault system.

  8. Petrogenesis of cataclastic rocks within the San Andreas fault zone of Southern California U.S.A.

    NASA Astrophysics Data System (ADS)

    Lawford Anderson, J.; Osborne, Robert H.; Palmer, Donald F.

    1980-08-01

    This paper petrologically characterizes cataclastic rocks derived from four sites within the San Andreas fault zone of southern California. In this area, the fault traverses an extensive plutonic and metamorphic terrane and the principal cataclastic rock formed at these upper crustal levels is unindurated gouge derived from a range of crystalline rocks including diorite, tonalite, granite, aplite, and pegmatite. The mineralogical nature of this gouge is decidedly different from the "clay gouge" reported by Wu (1975) for central California and is essentially a rock flour with a quartz, feldspar, biotite, chlorite, amphibole, epidote and oxide mineralogy representing the milled-down equivalent of the original rock. Clay development is minor (less than 4 wt. %) to nonexistent and is exclusively kaolinite. Alterations involve hematitic oxidation, chlorite alteration on biotite and amphibole, and local introduction of calcite. Electron microprobe analysis showed that in general the major minerals were not reequilibrated with the pressure—temperature regime imposed during cataclasis. Petrochemically, the form of cataclasis that we have investigated is largely an isochemical process. Some hydration occurs but the maximum amount is less than 2.2% added H 2O. Study of a 375 m deep core from a tonalite pluton adjacent to the fault showed that for Si, Al, Ti, Fe, Mg, Mn, K, Na, Li, Rb, and Ba, no leaching and/or enrichment occurred. Several samples experienced a depletion in Sr during cataclasis while lesser number had an enrichment of Ca (result of calcite veining). Texturally, the fault gouge is not dominated by clay-size material but consists largely of silt and fine sand-sized particles. An intriguing aspect of our work on the drill core is a general decrease in particulate size with depth (and confining pressure) with the predominate shifting sequentially from fine sand to silt-size material. The original fabric of these rocks is commonly not disrupted during the

  9. Near-surface structure of the 1906 main trace of the San Andreas Fault, San Francisco peninsula segment, California

    NASA Astrophysics Data System (ADS)

    Rosa, C.; Catchings, R. D.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.

    2012-12-01

    The peninsula segment of the San Andreas 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

  10. Seismotectonics of the easternmost transverse ranges, California: Relevance for seismic potential of the southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Williams, Patrick L.; Sykes, Lynn R.; Nicholson, Craig; Seeber, Leonardo

    1990-02-01

    Earthquake locations, depths and focal mechanisms from the Southern California Regional Network (1977-1985) are used to identify the orientation and sense of slip of active subsurface faults in the Easternmost Transverse Ranges (ETR). The ETR are separated from the Salton Trough province by the southernmost strands of the San Andreas fault (SAF). Much of the seismicity in the ETR is concentrated well northeast of the SAF at relatively shallow depths under the Little San Bernardino Mountains. Many of these earthquakes reflect slip on steeply dipping, left-lateral faults striking northeast to east, at relatively high angles to the adjacent SAF. Focal mechanisms in the ETR show predominantly strike-slip, normal, or oblique-normal faulting, and share common near-horizontal T axes striking WNW. P axes range from near vertical to near horizontal and strike mostly NNE. In contrast, reverse and strike-slip focal mechanisms that exhibit persistent north trending, near-horizontal P axes characterize the San Gorgonio Pass area immediately to the west. These different patterns of strain geometries are inferred to represent changes in local stress regime and clearly establish a boundary between contrasting tectonic styles of contemporary secondary deformation along the SAF. This boundary, which in the Coachella Valley may be the Mission Creek fault, is also distinguished by abrupt changes in (1) rate and depth of seismic activity; (2) topography; (3) Quaternary vertical deformation; (4) strikes and dips of major branches of the SAF; and (5) seismic velocities in the crust and upper mantle. The preponderance of secondary normal faulting in the ETR versus secondary reverse faulting in the San Gorgonio Pass region suggests that fault-normal stress is much less across the SAF adjacent to the ETR. If a friction law where strength is proportional to normal stress applies to the SAF, then a smaller tectonic shear stress would be required tor slip in large earthquakes along the Salton

  11. Character and Implications of a Newly Identified Creeping Strand of the San Andreas fault NE of Salton Sea, Southern California

    NASA Astrophysics Data System (ADS)

    Janecke, S. U.; Markowski, D.

    2015-12-01

    The overdue earthquake on the Coachella section, San Andreas 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

  12. Re-measuring the Slip Rate of the San Andreas Fault at Wallace Creek in the Carrizo Plain, CA

    NASA Astrophysics Data System (ADS)

    Grant Ludwig, L.; Akciz, S. O.; Arrowsmith, R.; Sato, T.; Cheiffetz, T.; Haddad, D. E.; Salisbury, J. B.; Marliyani, G. I.; Bohon, W.

    2015-12-01

    Sieh and Jahns (S&J) (1984) reported a slip rate of 33.9 +2.9 mm/yr for the San Andreas 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).

  13. Imaging fault slip variation along the central San Andreas fault from satellite, airborne InSAR and GPS

    NASA Astrophysics Data System (ADS)

    Liu, Z.; Lundgren, P.; Fielding, E. J.; Hensley, S.

    2011-12-01

    The improved spatiotemporal resolution of surface deformation from recent satellite and airborne InSAR measurements provides great potential to improve our understanding of faulting processes and earthquake hazard for a given fault system. A major plate boundary fault in central California, the central San Andreas fault (CSAF) displays a spectrum of complex fault slip behaviors with creeping in its central segment that decreases towards its northwest and southeast ends where the fault transitions to being locked. In the north the CSAF branches into two sub-parallel faults that are both actively accommodating plate motion. To the south, near the Parkfield transition, large earthquakes have occurred with at least six Mw ~6.0 events since 1857, most recently in 2004. To understand the complexity and variety of fault slip behaviors and fault mechanics, we integrate satellite and airborne synthetic aperture radar (SAR) repeat pass interferometry (RPI) observations, with GPS measurements from the Plate Boundary Observatory (PBO) and regional campaign networks to estimate fault slip and shallow slip deficits along the CSAF. Existing C-band ERS-1/2, Envisat and Radarsat SAR data provide long archives of SAR data over the region but are subject to severe decorrelation. The Japan Aerospace Exploration Agency's ALOS satellite has made less frequent acquisitions (5-6/yr per track) since 2006 but its PALSAR L-band sensor provides much improved coherence compared to shorter wavelength radar data. More recently, the NASA UAVSAR airborne SAR has repeated fault perpendicular adjacent swaths imaged from opposing look directions and fault parallel swath flights over the CSAF over the past three years and provides an improved imaging of fault slip related deformation at finer spatial resolution than previous platforms (~6m at 12 azimuth x 3 range looks). Compared to C-band instruments, the UAVSAR provides nearly complete spatial coverage. Compared to the ALOS mission, the UAVSAR

  14. The Magnitude-Frequency Distribution on the Southern San Andreas Fault Follows the Gutenberg-Richter Distribution

    NASA Astrophysics Data System (ADS)

    Page, M.; Felzer, K.; Weldon, R.; Biasi, G.

    2008-12-01

    The magnitudes of any random collection of earthquake hypocenters are generally observed to follow the Gutenberg-Richter (G-R) distribution. One alternative often used in seismic hazard assessments is some form of characteristic magnitude distribution, in which the largest magnitudes on a fault are assigned a higher frequency. The characteristic distribution has been adopted because rates of large paleoseismic earthquakes are found as much as a factor of ~10 higher on selected faults than the G-R prediction (e.g., Wesnousky et al., 1983). However, the short instrumental catalog may not represent the long-term rate. Also, to integrate prehistoric events on a fault with epicenters from a catalog, one must include all regions from which an event could nucleate and then propagate to the fault and leave a paleoseismic signature. We consider the magnitude distribution of the southern San Andreas fault (SAF), a major fault for which a characteristic distribution has been proposed. We include all seismicity nucleating within 20 km of the surface trace, since large earthquakes nucleating up to 20 km from a strike-slip fault may propagate to produce slip on the main fault surface (e.g., Ozacar and Beck, 2004). We look at the historic catalog (1850- 1932), the early instrumental catalog (1932-1984), and the modern instrumental catalog (1984-2008). We find that each catalog, as well as a prehistoric catalog formed by linking paleoseismic event evidence, internally follows a G-R relationship with a b-value of ~1. The most reliable record, the instrumental catalog from 1984-2008, has a rate 3.7 times lower than the paleoseismic rate. We develop an ETAS (Epidemic Type Aftershock Sequence) model (Felzer et al. 2002) that reproduces this observed rate difference. The average seismicity rate of the model matches the observed paleoseismic rate; in addition, due to the clustering of aftershock sequences, selected shorter periods of the synthetic catalog match the instrumental rate

  15. Structural, Geochemical, and Thermal Evolution of the Southen San Andreas and Parallel Subsidiary Faults in the Mecca Hills, Southern California

    NASA Astrophysics Data System (ADS)

    Moser, A. C.; Evans, J. P.; Ault, A. K.; Janecke, S. U.; Keighley Bradbury, K.; Clausnitzer, S. M.

    2015-12-01

    The Mecca Hills, Southern California, is a 30 km-long, 8 km-wide north-plunging anticlinorium related to transpression and dextral/dextral normal faults along the southern San Andreas Fault (SAF). Although an iconic area for studying transpressional deformation and the Late Cenozoic sedimentary record, the long-term history of faulting, significance and kinematics of the subsidiary faults, and relationship between these faults and the main trace of the SAF remain unclear. We examine the petrologic, kinematic, and timing relationships between 4 subsidiary faults and related damage zones that parallel the SAF to evaluate relationships with the SAF and the Eastern California Shear Zone. At least 6 major faults cut the Mesozoic to Late Tertiary crystalline and sedimentary rocks in the Mecca Hills, including the SAF. Hematite- and clay-coated fracture and slip surfaces are common in damage zones of the subsidiary faults. Slip surface orientation data of hematite-coated surfaces in the Painted Canyon Fault damage zone cluster at 110°, 65° SW and at 196°, 90° W. Similar surfaces in the Platform Fault damage zone cluster at 049°, 69 SE° and 003°, 83° E. Clay-coated slip surfaces in the Hidden Springs Fault damage zone cluster at 195°, 53° W and 196°, 11° W. Multiple slip vector orientations are observed on a single fault surface, consistent with oblique and dip-slip motion on faults in the Mecca Hills. Iridescent hematite and smooth clay surfaces suggest frictional heating on these surfaces, possibly from seismic slip. Preliminary scanning electron microscopy data reveal thin (10s-100s of μm), brecciated hematite slip surfaces. The specular hematite appears originally syn-tectonic and subsequently reworked with host rock and comminuted in multiple slip events. We apply hematite and apatite (U-Th)/He dating from the fault surface and host rock, respectively, to constrain fault thermal evolution and evaluate hematite (U-Th)/He dates as recording hematite

  16. Discovery Along the San Andreas Fault: Relocating Photographs From the 1906 Earthquake in San Francisco and San Mateo Counties

    NASA Astrophysics Data System (ADS)

    Grove, K.; Prentice, C.; Polly, J.; Yuen, C.; Wu, K.; Zhong, S.; Lopez, J.

    2005-12-01

    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 Andreas 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

  17. Wide-angle seismic constraints on the evolution of the deep San Andreas plate boundary by Mendocino triple junction migration

    USGS Publications Warehouse

    Hole, J.A.; Beaudoin, B.C.; Henstock, T.J.

    1998-01-01

    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 Andreas 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

  18. Mechanical Modeling of Near-Fault Deformation Within the Dragon's Back Pressure Ridge, San Andreas Fault, Carrizo Plain, California

    NASA Astrophysics Data System (ADS)

    Hilley, G. E.; Arrowsmith, R.

    2011-12-01

    This contribution uses field observations and numerical modeling to understand how slip along the variably oriented fault surfaces in the upper few km of the San Andreas Fault (SAF) zone produces near-fault deformation observed within a 4.5-km-long Dragon's Back Pressure Ridge (DBPR) in the Carrizo Plain, central California. Geologic and geomorphic mapping of this feature indicates that the amplitude of monoclinal warping of Quaternary sediments increases from southeast to northwest along the southwestern third of the DBPR, and remains approximately constant throughout the remaining two thirds of the landform. When viewed with other structural observations and limited near-surface magnetotelluric imaging, these geologic observations are most compatible with a scenario in which shallow offset of the SAF to the northeast creates a structural knuckle that is anchored to the North American plate. Thus, deformation accrues as right-lateral strike-slip motion along the SAF moves this obstruction along the fault plane through the DBPR block. We have used the Gale numerical model to simulate deformation expected for geometries similar to those inferred within the vicinity of the DBPR. This is accomplished by relating stresses and strains in the upper crust according to a Drucker-Prager (plastic yielding) constitutive rule. Deformation in the model is driven by applying 35 mm/yr of right-lateral strike-slip motion to the model boundary; this displacement rate is likewise applied to the base of the model. The model geometry of the SAF at the beginning of the loading was fashioned to produce the discontinuity in the geometry of the fault plane that is inferred from field observations. The friction and cohesion of crust on each side of the fault were changed between models to determine the parameter values that preserve the structural discontinuity along the SAF as finite deformation accrued. The structural discontinuity over the ~4.5 km of model displacement is maintained in

  19. Continuation of the San Andreas fault system into the upper mantle: Evidence from spinel peridotite xenoliths in the Coyote Lake basalt, central California

    NASA Astrophysics Data System (ADS)

    Titus, Sarah J.; Medaris, L. Gordon; Wang, Herbert F.; Tikoff, Basil

    2007-01-01

    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 Andreas 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 Andrea fault system.

  20. Southern San Andreas Fault evaluation field activity: approaches to measuring small geomorphic offsets--challenges and recommendations for active fault studies

    USGS Publications Warehouse

    Scharer, Katherine M.; Salisbury, J. Barrett; Arrowsmith, J. Ramon; Rockwell, Thomas K.

    2014-01-01

    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 Andreas 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 Andreas 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

  1. Using Precariously Balanced Rocks, Historic Records And Paleoseismology To Constrain Rupture Patterns And Rupture Potential Of The San Andreas And San Jacinto Faults In The Los Angeles Region

    NASA Astrophysics Data System (ADS)

    Grant Ludwig, L.; Brune, J. N.

    2010-12-01

    The San Andreas fault (SAF) has been identified as the likely source of a future damaging earthquake that could threaten millions of California residents, and the southern half of the fault has been identified as a likely candidate for rupture because it appears to be loaded with accumulated strain. Forecasts of future large earthquakes on the southern SAF and estimates of co-seismic slip depend critically on the slip rate and date of last rupture. The earliest historically documented rupture of the southern SAF occurred on December 8th and/or 21st, 1812 A.D., as recorded by early California missionaries, and confirmed by tree ring studies at Wrightwood, California. Prior to the tree ring study, the sequence of earthquakes in December 1812 was attributed to the Newport-Inglewood fault and/or another fault offshore of southern California, to explain the collapse of a church at Mission San Juan Capistrano and a tsunami near Mission Santa Barbara. Competing rupture models have been proposed to fit the sparse historic accounts of shaking recorded at the Missions, and sparse paleoseismic data from trenches excavated across the San Andreas and other southern California faults. Confirmation of proposed rupture patterns has been elusive because dates of surface ruptures observed in trenches at several locations along the SAF either cannot be resolved to 1812 due to uncertainty in radiocarbon dating, or preclude rupture. One possibility is that the 1812 earthquake ruptured both the SAF in Wrightwood and the northern San Jacinto fault in the Cajon Pass and San Bernardino Valley. Active traces of the faults are less than 2 km apart in Cajon Pass and it is well documented that ruptures can propagate between fault strands up to several kilometers apart. Here we propose that the distribution of fragile semi-precarious and precariously balanced rocks (PBRs) in the western San Bernardino Mountains is inconsistent with accepted rupture models for the 1812 earthquake. To better fit

  2. Imaging the San Andreas Fault between Parkfield and the Salton Sea Using Wavelet Analysis of Airborne Laser Swath Mapping Data

    NASA Astrophysics Data System (ADS)

    Cheung, K.; Hilley, G. E.; Moon, S.; Saltzman, J.; Sanquini, A.

    2011-12-01

    The distribution of fault related landforms may be used to divulge the spatial and temporal evolution of fault ruptures within a fault zone. In this study, wavelet analysis was performed on high-resolution Airborne Laser Swath Mapping (ALSM) topographic data to image the morphologic structure of the San Andreas Fault Zone (SAFZ) between Parkfield, CA and the US-Mexico border. ASLM data were collected by the National Center for Airborne Laser Mapping as part of the B4 project and were processed these data to produce a 2-m-resolution Digital Elevation Model (DEM). The DEM tiles were imported to ArcMap, which was used to mosaic, rotate, and crop them. Matlab was used to perform a progressive filling of NODATA values within each of the tiles using an iterative nearest-neighbor averaging scheme on these data. Next, scarp-like features roughly paralleling the average trend of the SAFZ were identified using a previously developed wavelet analysis method. This method convolves the second derivative of an elongated template of a scarp-like topography with the directional curvature of the ALSM DEM that is represented by each of the tiles. In this way, the analysis recovers, in a least-squares best-fitting sense, the amplitude of a particular scarp geometry and orientation. The Signal-to-Noise Ratio (SNR) is then computed at each point in the ALSM DEM for a given template scarp geometry and orientation-- this process is repeated for all scarp geometries and orientations to determine those that have the highest SNR. Such scarp forms are automatically identified as the best-fitting scarp geometry, amplitude, and orientation at each point in the DEM. The geometry gives a quantitative measure of the "roundness" of the profile of the scarp form, and supposing that sharper scarps have been created more recently than those whose forms have been rounded by prolonged erosion, a relative chronology of activity of various fault strands within the fault zone can be reconstructed. With

  3. Near-Surface Structure of the Peninsula Segment of the San Andreas Fault, San Francisco Bay Area, California

    NASA Astrophysics Data System (ADS)

    Rosa, C.; Catchings, R.; Rymer, M. J.; Goldman, M.; Grove, K.; Prentice, C. S.

    2013-12-01

    The peninsula segment of the San Andreas 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

  4. Investigation of the Offshore Section of the Northern San Andreas Fault: Slip Partitioning, Shallow Deformation, and Fault Trend Influence

    NASA Astrophysics Data System (ADS)

    Beeson, J. W.; Goldfinger, C.; Johnson, S. Y.

    2012-12-01

    Geodetic studies have shown that the angular velocities between the Pacific Sierra Nevada/Great Valley block are roughly 39 mm/yr and that the Northern San Andreas Fault (NSAF), at Pt. Arena, CA, accommodates roughly 25 mm/yr of that motion. The remaining motion is thought to be accommodated by slip on the Maacamma fault zone and the Bartlett Springs fault zone to the east of the NSAF. Since the NSAF moves offshore north of Point Arena, CA, the use of geodetic techniques to evaluate slip rates on roughly 120 km of the NSAF is challenging. We now have a detailed fault location map from Pt. Arena to Pt. Delgada, CA which allows us to evaluate, qualitatively at present, strain partitioning along this section of the plate boundary. The NSAF is mapped with multibeam bathymetry and ~100 seismic reflection profiles. The fault moves offshore north of Pt. Arena and returns onshore at Pt. Delgada. The entire offshore section of the NSAF can be characterized by a narrow, ~1 km wide deformation zone. Utilizing bathymetric and seismic data we infer that the NSAF loses slip northward based primarily on the presence of numerous northwest-trending splay faults and compressional folds. These splay faults, which are visible for ~10 km away from the NSAF and are steeply dipping, appear to be active and accommodating a proportion of the strike slip motion. These splay faults appear to dive below the penetrating depth of the mini-sparker leaving folded strata above them. They also appear to have recent deformation on the seafloor expressed as uplift and generally trend to the NW with apparent reverse and strike slip motion. Incorporating industry released multi-channel seismic reflection profiles we have also mapped and evaluated other large compressional structures to the west on the Viscano block. A sharp bend of the NSAF, ~9 degrees to the north, is mapped near the submarine Noyo Canyon Head. This right bend in a right lateral strike-slip fault has created a small asymmetric basin

  5. Late Quaternary deformation and slip rates in the northern San Andreas fault zone at Olema Valley, Marin County, California

    NASA Astrophysics Data System (ADS)

    Grove, Karen; Niemi, Tina M.

    2005-06-01

    Quaternary sedimentary deposits along the structural depression of the San Andreas fault (SAF) zone north of San Francisco in Marin County provide an excellent record of rates and styles of neotectonic deformation in a location near where the greatest amount of horizontal offset was measured after the great 1906 San Francisco earthquake. A high-resolution gravity survey in the Olema Valley was used to determine the depth to bedrock and the thickness of sediment fill along and across the SAF valley. In the gravity profile across the SAF zone, Quaternary deposits are offset across the 1906 fault trace and truncated by the Western and Eastern Boundary faults, whose youthful activity was previously unknown. The gravity profile parallel to the fault valley shows a basement surface that slopes northward toward an area of present-day subsidence near the head of Tomales Bay. Surface and subsurface investigations of the late Pleistocene Olema Creek Formation (Qoc) indicate that this area of subsidence was located further south during deposition of the Qoc and that it has migrated northward since then. Localized subsidence has been replaced by localized contraction that has produced folding and uplift of the Qoc. This apparent alternation between transtension and transpression may be the result of a northward-diverging fault geometry of fault strands that includes the valley-bounding faults as well as the 1906 SAF trace. The Vedanta marsh is a smaller example of localized subsidence in the fault zone, between the 1906 SAF trace and the Western Boundary fault. Analyses of Holocene marsh sediments in cores and a paleoseismic trench indicate thickening, and probably tilting, toward the 1906 trace, consistent with coseismic deformation observed at the site following the 1906 earthquake. New age data and offset sedimentary and geomorphic features were used to calculate four late Quaternary slip rate estimates for the SAF at this latitude. Luminescence dates of 112-186 ka for the

  6. Northern San Andreas Earthquake Recurrence: Rupture lengths, Correlations and Constrained OxCal Analysis of Event Ages

    NASA Astrophysics Data System (ADS)

    Morey, A. E.; Goldfinger, C.; Erhardt, M.; Nelson, C. H.; Johnson, J. E.; Gutierrez-Pastor, J.

    2005-12-01

    We are using multiple proxies, including XRF analysis, to determine hemipelagic thickness between turbidite events recorded in cores along the offshore northern San Andreas margin. Inter-event times are calculated from these improved estimates of sediment thickness and regression-determined sedimentation rates, and used along with known stratigraphic information to constrain calibrated radiocarbon age ranges using Bayesian statistical methods within the program OxCal. OxCal can also be used to combine multiple ages for the same event. Multiple ages are given "credit" where age ranges overlap, resulting in reduced 1- or 2-sigma age ranges compared to averaging peak ages and propagating errors. These methods reduce calendar age variability of events along strike that are thought to correlate. We tested three methods of estimating calendar ages, using the most recent events in a Noyo Canyon core. These methods are: 1. unconstrained radiocarbon age calibration, 2. age determination using known dates and inter-event time calculated from hemipelagic thickness and the regression-determined sedimentation rate, and 3. (preferred method) use OxCal's sequence option to calibrate and constrain radiocarbon ages given all available stratigraphic information, including date of collection, historical or geological datums, inter-event times and radiocarbon ages. The upper-most event was chosen for these tests because it is known to be the 1906 earthquake and the 20th century reservoir correction is well known in this area. The penultimate event was chosen because it has been dated at multiple land sites. 1906 event: Unconstrained calibration: calibration of the radiocarbon age of the 1906 event yields an age of ~1913, (1σ: 1898-1940). Sedimentation time: subtracting the time represented by the hemipelagic thickness above the 1906 event from the date of collection (1999) yields an age of ~1904. OxCal sequence: constrained calibration yields an age of ~1902 (1σ: 1880

  7. Gravity constraints on the geometry of the Big Bend of the San Andreas Fault in the southern Carrizo Plains and Pine Mountain egion

    NASA Astrophysics Data System (ADS)

    Altintas, Ali Can

    The goal of this project is to combine gravity measurements with geologic observations to better understand the "Big Bend" of the San Andreas 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 Andreas Fault in the Big Bend area. Yet, our models indicate that the San Andreas 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

  8. Sierran affinity (?) metasedimentary rocks beneath the Coast Range Ophiolite of the Sierra Azul block east of the San Andreas fault, Santa Clara County, CA

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Dumitru, T. A.; Ernst, W. G.

    2011-12-01

    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 Andreas 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 Andreas 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 Andreas 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

  9. Monitoring of crustal movements in the San Andreas fault zone by a satellite-borne ranging system. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Kumar, M.

    1976-01-01

    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 Andreas 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.

  10. Post-seismic slip on the San Andreas fault at the northwestern end of the 1989 Loma Prieta earthquake rupture zone

    SciTech Connect

    Langbein, J.O.

    1990-07-01

    A small geodetic network spanning the San Andreas fault was measured 7, 77, 157, and 200 days following the October 17, 1989 Loma Prieta M7.1 earthquake. This network is located at the northwestern end of the rupture plane defined by the locations of numerous aftershocks. In the initial 70-day interval, the measured line-length changes revealed that 5.4 {plus minus} 0.4 mm of right-lateral slip occurred within the network. However, during the later 4 month interval only a marginally significant rate, 3.2 {plus minus} 1.4 mm/yr, of right-lateral slip could be detected. Thus, it appears that the measured slip is a typical response of the fault following a major shock in that the rate of slip decreases rapidly with time. However, the magnitude of the post-seismic slip is less than 0.5% of the inferred co-seismic slip at depth.

  11. Variation in aseismic slip and fault normal strain along the creeping section of the San Andreas fault from GPS, InSAR and trilateration data

    NASA Astrophysics Data System (ADS)

    Rolandone, F.; Johanson, I.; Bürgmann, R.; Agnew, D.

    2004-12-01

    In central California most of the relative motion between the Pacific and North American plates is accommodated by strike slip along the San Andreas fault system. However, a small amount of convergence is accommodated by compressional structures in the California Coast Ranges on both sides of the fault. Recent examples of such activity are the Coalinga and the 2003 San Simeon earthquakes. Along the central San Andreas fault (CSAF), from San Juan Bautista to Parkfield, almost all the slip along the CSAF in the brittle upper crust is accommodated aseismically. We use GPS, InSAR and trilateration data to resolve both the distribution of aseismic slip along the CSAF, and the deformation across adjacent, secondary fault structures. In 2003 and 2004, we conducted several GPS surveys along the CSAF. We resurveyed 15 stations of the San Benito triangulation and trilateration network, which extends 40 km to the northeast of the creeping segment. We combine these measurements with old EDM measurements and data from a GPS campaign in 1998. We also occupied 13 sites along the creeping segment, for which previous data exist in the SCEC archive. These dense GPS measurements, along with data from permanent GPS stations in the area, allow us to constrain the regional strain distribution and contributions from adjacent faults. With the addition of InSAR data, we can also better resolve active strain accumulation and aseismic slip along the CSAF. We use a stack of about 10 interferograms from ERS-1 and ERS-2 satellites spanning 8 years. InSAR is well suited to monitoring details of the shallow slip along the CSAF and, in concert with the broadly spaced GPS velocities, to resolving the distribution of deformation along and across the plate boundary. The results are the basis for determining the kinematics of spatially variable fault slip on the CSAF, and help to better constrain the fault's constitutive properties, and fault interaction processes.

  12. Using surface creep rate to infer fraction locked for sections of the San Andreas fault system in northern California from alignment array and GPS data

    USGS Publications Warehouse

    Lienkaemper, James J.; McFarland, Forrest S.; Simpson, Robert W.; Caskey, S. John

    2014-01-01

    Surface creep rate, observed along five branches of the dextral San Andreas 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 Andreas 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.

  13. Quaternary landscape development, alluvial fan chronology and erosion of the Mecca Hills at the southern end of the San Andreas Fault zone

    USGS Publications Warehouse

    Gray, Harrison J.; Owen, Lewis; Dietsch, Craig; Beck, Richard A.; Caffee, Marc A.; Finkelman, Robert B.; Mahan, Shannon

    2014-01-01

    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 Andreas Fault, in southern California. The similar timing of convergent uplifts along the San Andreas 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.

  14. Quaternary landscape development, alluvial fan chronology and erosion of the Mecca Hills at the southern end of the San Andreas Fault zone

    NASA Astrophysics Data System (ADS)

    Gray, Harrison J.; Owen, Lewis A.; Dietsch, Craig; Beck, Richard A.; Caffee, Marc A.; Finkel, Robert C.; Mahan, Shannon A.

    2014-12-01

    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 Andreas Fault, in southern California. The similar timing of convergent uplifts along the San Andreas 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.

  15. Rock and mineral transformations in a fault zone leading to permanent creep: Interactions between brittle and viscous mechanisms in the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Richard, Julie; Gratier, Jean-Pierre; Doan, Mai-Linh; Boullier, Anne-Marie; Renard, François

    2014-11-01

    Creep processes may relax part of the tectonic stresses in active faults, either by continuous or episodic processes. The aim of this study is to obtain a better understanding of these creep mechanisms and the manner in which they change in time and space. Results are presented from microstructural studies of natural samples collected from San Andreas Fault Observatory at Depth borehole drilled through the San Andreas Fault, which reveal the chronology of the deformation within three domain types. (i) A relatively undeformed zone of the host rock reflects the first step of the deformation process with fracturing and grain indentations showing the coupling between fracturing and pressure solution. (ii) Shear deformation development that associates fracturing and solution cleavage processes leads to profound changes in rock composition and behavior with two types of development depending on the ratio between the amount of dissolution and deposition: abundant mineral precipitation strengthens some zones while pervasive dissolution weakens some others, (iii) zones with mainly dissolution trended toward the present-day creeping zones thanks to both the passive concentration of phyllosilicates and their metamorphic transformation into soft minerals such as saponite. This study shows how interactions between brittle and viscous mechanisms lead to widespread transformation of the rocks and how a shear zone may evolve from a zone prone to earthquakes and postseismic creep to a zone of steady state creep. In parallel, the authors discuss how the creeping mechanism, mainly controlled by the very low friction of the saponite in the first 3-4 km depth, may evolve with depth.

  16. Response of the San Andreas fault to the 1983 Coalinga-Nuñez earthquakes: an application of interaction-based probabilities for Parkfield

    USGS Publications Warehouse

    Toda, Shinji; Stein, Ross S.

    2002-01-01

    The Parkfield-Cholame section of the San Andreas 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 Andreas 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.

  17. Stratigraphic Record of Vertical Crustal Motions in the Past 2-3 Ma Along the Southern San Andreas Fault, Mecca Hills, California

    NASA Astrophysics Data System (ADS)

    McNabb, J. C.; Dorsey, R. J.

    2012-12-01

    Sedimentary rocks exposed on the NE margin of Coachella Valley in the Mecca Hills, southern California, record vertical crustal motions along the San Andreas 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

  18. Cessation of Slip on the Pilarcitos Fault and Initiation of the San Francisco Peninsula Segment of the (Modern) San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Powell, C. L.; McDougall-Reid, K.; Jachens, R. C.

    2007-12-01

    The Pilarcitos Fault (PF) is widely regarded to be the long-term (3-19 Ma) trace of the San Andreas Fault on the San Francisco Peninsula. The active modern San Andreas Fault (MSAF) in this area, however, records less than 3 m.y. of displacement. Middle-Miocene and younger displacement is partitioned to a single San Andreas Fault where the PF and MSAF merge in the Santa Cruz Mountains south of Palo Alto and Monte Bello Ridge. Aside from such general constraints, evidence for the timing of initiation of the MSAF and for cessation of slip on the PF are poorly constrained. As a consequence, there is a lack of consensus on the long term slip rates for the PF as well as the MSAF. Two independent datasets indicate significantly different offsets along the MSAF since 3 Ma. In one dataset distinctive 3.3 Ma (Blancan) fluvial gravels of the Santa Clara Formation are offset 28-31 km from their clast source east of the MSAF near Loma Prieta, yielding a slip rate of 9-10 mm/yr since 3 Ma. In the other dataset, a linear magnetic anomaly associated with Mesozoic serpentinite and gabbro of the Coast Range Ophiolite is offset 22 km across the MSAF, yielding a slip rate since 3.3 Ma of 7 mm/yr. Both datasets assume cessation of slip on the PF by 3 Ma, but imply different amounts of offset for the MSAF. Both offset estimations also yield lower long term slip rates than the present geodetic rate of 13-19 mm/yr. A closer review of these data reveals stratigraphic relations that indicate long term slip rates of 14-21 mm/yr for the PF and MSAF, which are more in line with geodetic rates. These long-term rates result from recognition that the distinctive Santa Clara Formation strata west of the MSAF, that were deposited in a pull-apart wedge between the PF and MSAF, are also underlain by the 5.4-7.0 Ma marine Purisima Formation and by middle Miocene and older marine strata. Along the east side of the MSAF the northwestern most exposures of the Purisima Formation underlain by Miocene

  19. Seismic evidence for rock damage and healing on the San Andreas fault associated with the 2004 M 6.0 Parkfield earthquake

    USGS Publications Warehouse

    Li, Y.-G.; Chen, P.; Cochran, E.S.; Vidale, J.E.; Burdette, T.

    2006-01-01

    We deployed a dense linear array of 45 seismometers across and along the San Andreas fault near Parkfield a week after the M 6.0 Parkfield earthquake on 28 September 2004 to record fault-zone seismic waves generated by aftershocks and explosions. Seismic stations and explosions were co-sited with our previous experiment conducted in 2002. The data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 M 6.0 mainshock show ???1.0%-1.5% decreases in seismic-wave velocity within an ???200-m-wide zone along the fault strike and smaller changes (0.2%-0.5%) beyond this zone, most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 M 6.0 earthquake. The width of the damage zone characterized by larger velocity changes is consistent with the low-velocity waveguide model on the San Andreas fault, near Parkfield, that we derived from fault-zone trapped waves (Li et al., 2004). The damage zone is not symmetric but extends farther on the southwest side of the main fault trace. Waveform cross-correlations for repeated aftershocks in 21 clusters, with a total of ???130 events, located at different depths and distances from the array site show ???0.7%-1.1% increases in S-wave velocity within the fault zone in 3 months starting a week after the earthquake. The velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time, most likely . due to the closure of cracks opened during the mainshock. We estimate that the net decrease in seismic velocities within the fault zone was at least ???2.5%, caused by the 2004 M 6.0 Parkfield earthquake. The healing rate was largest in the earlier stage of the postmainshock healing process. The magnitude of fault healing varies along the rupture zone, being slightly larger for the healing beneath Middle Mountain, correlating well with an area of large mapped slip. The fault healing is most prominent at depths above ???7 km.

  20. Evolution of an Intermontane Basin Along the Northern San Andreas System: Evidence from Basin Structure of Little Lake Valley (Willits), Northern California Inferred from Gravity and Geologic Data

    NASA Astrophysics Data System (ADS)

    Erickson, G.; Kelsey, H.; Langenheim, V.; Furlong, K.

    2007-12-01

    Associated with the northern strands of the San Andreas fault system in California is a series of small intermontane basins. While it is tempting to ascribe their formation to simple pull-apart tectonics along the dominantly strike-slip fault strands, direct evidence for basin genesis is lacking. In this study, a detailed gravity survey throughout the Little Lake Valley region (Willits, California) provides constraints on mechanisms of basin formation along this young segment of the San Andreas fault system. Interpretation of isostatic gravity anomaly data provides insight into fault geometry, basin structure, and thickness of Quaternary fill in Little Lake Valley, California. Although the active strike-slip Maacama fault zone diagonally trends through the southwest part of the valley, gravity and geologic interpretations indicate the valley conceals an earlier basin and faulting history. The isostatic gravity anomaly of the basin is negative (up to 13 mGals) and rhombic in shape. Modeling indicates two splays, less than a km apart, of an up-to-the-east East Valley fault; the basinward fault is buried by fill and the more easterly fault defines the eastern margin of the basin. Cumulative up-to-the-east vertical fault displacement along the East Valley fault increases southward up to 610 m in the southern portion of the valley. Gravity gradients also suggest approximately east-west trending faults bound the northern and southern sides of the valley and offset Quaternary fill. From gravity and geologic data combined, the basin floor dips approximately 7 degrees to the south in the north part of the valley and both the Quaternary sediment and basin floor dip approximately 13 degrees to the north in the south part of the valley, implying an approximately east-west axis of dip reversal of the basin floor at the northern stretch of East Hill Road (latitude 39.39 degrees N). Faults and basin fill structure are not consistent with any one simple structural model of basin

  1. Geomorphic evidence of active tectonics in the San Gorgonio Pass region of the San Andreas Fault system: an example of discovery-based research in undergraduate teaching

    NASA Astrophysics Data System (ADS)

    Reinen, L. A.; Yule, J. D.

    2014-12-01

    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 Andreas 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 Andreas 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

  2. Revealing a strike-slip plate boundary: Drill-bit seismic imaging of the San Andreas Fault at the SAFOD site

    NASA Astrophysics Data System (ADS)

    Taylor, Stewart Thomas

    2006-12-01

    The San Andreas Fault at the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, CA forms the contact between the Pacific and North American tectonic plates. The hypotheses tested in this dissertation are that this boundary (1) is not located beneath the currently recognized surface trace of the SAF, (2) is not composed of a single active strand, but at least two overlapping, positive and negative flower structures, and (3) has juxtaposed, severely folded, and then buried Tertiary to pre-Cretaceous strata not previously known to exist in the Parkfield area. These hypotheses were tested through the construction, analysis, and interpretation of a new type of drill-bit seismic reflection imaging at the SAFOD drill site. Drill-bit seismic (DBS) imaging uses the drill bit as a seismic source. Previous DBS experiments have used geophone receiver arrays laid on the earth's surface. At SAFOD, a vertical receiver array supplemented a surface receiver array, to record the Stage 1 drilling of SAFOD well which was completed in 2004. This dissertation expands the DBS method by utilizing both the vertical and surface arrays to record the drill bit vibrations and produce two types of reverse vertical seismic profiles. A major portion of this dissertation includes research and development of DBS data signal processing techniques for industrial applications and the special case of the SAFOD observations. These observations include downhole geophone recordings which represent a new approach not previously reported in the seismic reflection literature. The application of algorithms produced by these studies has resulted in improved methods for estimating the drill bit seismic source signature. These methods also determine optimal deconvolution operators for DBS signals which produce estimates of the "pilot signal". It is shown that processing of DBS data is possible without drill string pilot accelerometers. This allows more economic deployment of equipment at the drill

  3. Geophysical Investigation of the Offshore Section of the Northern San Andreas Fault: Fault Zone Geometries, Shallow Deformation Patterns, and Holocene Sediment Distribution

    NASA Astrophysics Data System (ADS)

    Beeson, J. W.; Goldfinger, C.; Johnson, S. Y.

    2014-12-01

    We mapped a ~120 km offshore section of the northern San Andreas 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 Andreas likely terminates into a series of "horse tail" splay thrust faults known as the Kings Range Thrust. These

  4. On the origin of mixed-layered clay minerals from the San Andreas Fault at 2.5-3 km vertical depth (SAFOD drillhole at Parkfield, California)

    NASA Astrophysics Data System (ADS)

    Schleicher, A. M.; Warr, L. N.; van der Pluijm, B. A.

    2009-02-01

    A detailed mineralogical study is presented of the matrix of mudrocks sampled from spot coring at three key locations along the San Andreas Fault Observatory at depth (SAFOD) drill hole. The characteristics of authigenic illite-smectite (I-S) and chlorite-smectite (C-S) mixed-layer mineral clays indicate a deep diagenetic origin. A randomly ordered I-S mineral with ca. 20-25% smectite layers is one of the dominant authigenic clay species across the San Andreas Fault zone (sampled at 3,066 and 3,436 m measured depths/MD), whereas an authigenic illite with ca. 2-5% smectite layers is the dominant phase beneath the fault (sampled at 3,992 m MD). The most smectite-rich mixed-layered assemblage with the highest water content occurs in the actively deforming creep zone at ca. 3,300-3,353 m (true vertical depth of ca. 2.7 km), with I-S (70:30) and C-S (50:50). The matrix of all mudrock samples show extensive quartz and feldspar (both plagioclase and K-feldspar) dissolution associated with the crystallization of pore-filling clay minerals. However, the effect of rock deformation in the matrix appears only minor, with weak flattening fabrics defined largely by kinked and fractured mica grains. Adopting available kinetic models for the crystallization of I-S in burial sedimentary environments and the current borehole depths and thermal structure, the conditions and timing of I-S growth can be evaluated. Assuming a typical K+ concentration of 100-200 ppm for sedimentary brines, a present-day geothermal gradient of 35°C/km and a borehole temperature of ca. 112°C for the sampled depths, most of the I-S minerals can be predicted to have formed over the last 4-11 Ma and are probably still in equilibrium with circulating fluids. The exception to this simple burial pattern is the occurrence of the mixed layered phases with higher smectite content than predicted by the burial model. These minerals, which characterize the actively creeping section of the fault and local thin film

  5. Geophysical and hydrogeologic investigations of two primary alluvial aquifers embedded in the southern San Andreas fault system: San Bernardino basin and upper Coachella Valley

    NASA Astrophysics Data System (ADS)

    Wisely, Beth Ann

    This study of alluvial aquifer basins in southern California is centered on observations of differential surface displacement and the search for the mechanisms of deformation. The San Bernardino basin and the Upper Coachella Valley aquifers are bound by range fronts and fault segments of the southern San Andreas fault system. I have worked to quantify long-term compaction in these groundwater dependent population centers with a unique synthesis of data and methodologies using Interferometric Synthetic Aperture Radar (InSAR) and groundwater data. My dissertation contributes to the understanding of alluvial aquifer heterogeneity and partitioning. I model hydrogeologic and tectonic interpretations of deformation where decades of overdraft conditions and ongoing aquifer development contribute to extreme rapid subsidence. I develop the Hydrogeologic InSAR Integration (HII) method for the characterization of surface deformation in aquifer basins. The method allows for the separation of superimposed hydraulic and/or tectonic processes in operation. This formalization of InSAR and groundwater level integration provides opportunities for application in other aquifer basins where overdraft conditions may be causing permanent loss of aquifer storage capacity through compaction. Sixteen years of SAR data for the Upper Coachella Valley exhibit rapid vertical surface displacement (≤ 48mm/a) in sharply bound areas of the western basin margin. Using well driller logs, I categorize a generalized facies analysis of the western basin margin, describing heterogeneity of the aquifer. This allowed for assessment of the relationships between observed surface deformation and sub-surface material properties. Providing the setting and context for the hydrogeologic evolution of California's primary aquifers, the mature San Andreas transform fault is studied extensively by a broad range of geoscientists. I present a compilation of observations of creep, line integrals across the Pacific

  6. 3-D InSAR Phase Unwrapping with Extended Kalman Filter: Applications to interseismic deformation detection across the North Anatolian and San Andreas Fault zones

    NASA Astrophysics Data System (ADS)

    Havazli, E.; Wdowinski, S.; Osmanoglu, B.

    2014-12-01

    Interferometric Synthetic Aperture Radar (InSAR) is a method that allows researchers to map elevations, analyze surface deformation and even detect ground water level changes. The InSAR phase measurements are wrapped between 0 and 2π and therefore have to be unwrapped to reveal the full scale of the observations. Even though there are algorithms for finding discrete irrotational fields among neighboring pixels in two-dimensions, a three dimensional unwrapping approach is important as it can constrain the solution of our data to a more robust and accurate state. We developed a 3-D unwrapping algorithm based on an Extended Kalman Filter (EKF) that is capable of simultaneously filtering, unwrapping and inverting multiple interferograms to obtain a DEM or deformation map. The method is based on a path-following algorithm that unwraps the dataset starting from a reference point and moves to the next-highest quality neighboring point. The EKF algorithm allows us to better resolve unwrapping problems, especially in vegetated areas, which tend to be decorrelated, and hence obtain more accurate results. In this study we apply our 3-D EKF unwrapping algorithm to North Anatolian and San Andreas fault zones in order to detect interseismic crustal movement across these two major fault systems. For the North Anatolian Fault we processed 37 Envisat scenes that covers the Ismetpasa segment of the fault, and generated 237 interferograms. The generated interferograms are used with both EKF and SBAS algorithms to estimate the deformation in the area. Our previous study of this segment based on the SBAS technique revealed that the Ismetpasa segment creeps at a rate of 8 mm/yr. For the San Andreas Fault (SAF) we processed 37 descending Envisat ASAR scenes acquired between November 2005 and October 2010. Our area of interest includes the central SAF near its intersection with the Garlock Fault. Initial results show deformation across the fault but the results have low fit to the data

  7. Evidence of non extensivity in the evolution of seismicity along the San Andreas Fault, California, USA: An approach based on Tsallis statistical physics

    NASA Astrophysics Data System (ADS)

    Efstathiou, A.; Tzanis, A.; Vallianatos, F.

    We examine the nature of the seismogenetic system along the San Andreas Fault (SAF), California, USA, by searching for evidence of complexity and non-extensivity in the earthquake record. We use accurate, complete and homogeneous earthquake catalogues in which aftershocks are included (raw catalogues), or have been removed by a stochastic declustering procedure (declustered catalogues). On the basis of Non-Extensive Statistical Physics (NESP), which generalizes the Boltzmann-Gibbs formalism to non-equilibrating (complex) systems, we investigate whether earthquakes are generated by an extensive self-excited Poisson process or by a non-extensive complex process. We examine bivariate cumulative frequency distributions of earthquake magnitudes and interevent times and determine the size and time dependence of the respective magnitude and temporal entropic indices, which indicate the level on non-equilibrium (correlation). It is shown that the magnitude entropic index is very stable and corresponds to proxy b-values that are remarkably consistent with the b-values computed by conventional means. The temporal entropic index computed from the raw catalogues indicate moderately to highly correlated states during the aftershock sequences of large earthquakes, progressing to quasi-uncorrelated states as these die out and before the next large event. Conversely, the analysis of the declustered catalogues shows that background seismicity exhibits moderate to high correlation that varies significantly albeit smoothly with time. This indicates a persistent sub-extensive seismogenetic system. The degree of correlation is generally higher in the southern SAF segment, which is consistent with the observation of shorter return periods for large earthquakes. A plausible explanation is that because aftershock sequences are localized in space and time, their efficient removal unveils long-range background interactions which are obscured by their presence! Our results indicate

  8. Evidence for large earthquakes on the San Andreas fault at the Wrightwood, California paleoseismic site: A.D. 500 to present

    USGS Publications Warehouse

    Fumal, T.E.; Weldon, R.J.; Biasi, G.P.; Dawson, T.E.; Seitz, G.G.; Frost, W.T.; Schwartz, D.P.

    2002-01-01

    We present structural and stratigraphic evidence from a paleoseismic site near Wrightwood, California, for 14 large earthquakes that occurred on the southern San Andreas 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

  9. Roles of the Mendocino Transform, Vizcaino Block, and Onshore King Range Terrane in Evolution of the Northern San Andreas Fault System and Its Associated Slab Windows

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Barth, G. A.; Scheirer, D. S.; Hoover, S. M.; Trehu, A. M.; Jencks, J.

    2014-12-01

    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 Andreas 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 Andreas 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

  10. Tectonic, Seasonal, and Anthropogenic Deformation Rates in the Western Transverse Ranges, California from the San Andreas to the Santa Barbara Channel

    NASA Astrophysics Data System (ADS)

    Marshall, S. T.; Funning, G. J.; Owen, S. E.

    2011-12-01

    Geodetic data from the Plate Boundary Observatory (PBO) provide a complex and evolving picture of current deformation rates in the western Transverse Ranges of southern California. We combine data from 52 continuous GPS sites in the PBO network with InSAR time series formed from ENVISAT ASAR scenes to determine the rates of seasonal, anthropogenic, and tectonic deformation. To characterize seasonal motions we independently estimate phases and amplitudes of annual and semiannual motions for each GPS time series. Once these seasonal terms are removed from the data, the resultant time series are dominantly linear suggesting that seasonal motions have been successfully removed. To determine if any of the remaining motions are non-tectonic in origin, we use a persistent scatterer InSAR (PSI) data set comprised of 20 ENVISAT scenes. The PSI data show potential anthropogenic subsidence in the Oxnard/Ventura area as well as at a location just south of the Oak Ridge; however, no GPS sites are situated in locations that are likely to be contaminated by these non-tectonic motions. The relative lack of significant anthropogenic motions in the western Transverse Ranges is in stark contrast to the nearby Los Angeles basin where anthropogenic motions can exceed 40 mm/yr. To determine the local deformation rates, we remove strain associated with the nearby San Andreas fault using a rectangular dislocation model. The resultant velocity field shows dominantly north-northwest directed contraction. The central Ventura basin shows the fastest contraction rates with approximately 6 mm/yr of shortening. To the east, approaching the San Andreas fault, contraction rates slow to about 2 mm/yr Contraction rates across the Santa Barbara Channel appear to monotonically decrease westward from approximately 6 mm/yr near at the longitude of Anacapa Island to 2 mm/yr at the longitude of San Miguel Island. To model the interseismic deformation and determine the likely fault slip rates, we use a

  11. The nature of surface tilt along 85 km of the San Andreas fault-preliminary results form a 14-instrument array

    USGS Publications Warehouse

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

    1975-01-01

    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 Andreas 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.

  12. Tectonic Transition Between the Southern Extent of the Cascadia Subduction Zone and the Northernmost San Andreas Fault System near Root Creek, Northern California

    NASA Astrophysics Data System (ADS)

    Nicovich, S.; Leroy, T. H.; Hemphill-Haley, M.; Oswald, J. A.

    2013-12-01

    The primary objective of this project is to characterize the transition between Cascadia subduction zone (CSZ)-related structures and the northern-most extent of faults associated with the San Andreas Fault (SAF) transform margin in northwestern California, specifically the transition between the Maacama Fault zone and the Little Salmon Fault. The Little Salmon Fault, a large, northwest-trending thrust fault, arguably near the base of the fold and thrust belt associated with the Cascadia megathrust, extends southwest near the latitude of the Mendocino Triple Junction. The transition from the southern end of the Cascadia subduction zone and related faults to the northward migrating transform margin is poorly understood. Deformation of Neogene sediments near the confluence of Root Creek and the Van Duzen River, approximately 10 miles west of the town of Bridgeville, may provide clues to the broad evolution from compressional tectonic forces of the southernmost CSZ to translational motion of the northern SAF system. This study includes documentation of a faulted and folded strath terrace near the mouth of Root Creek and mapping of adjacent deformed young deposits. Fracture data gathered at this and other nearby sites provides insight into local tectonic strain. Geological mapping incorporates high resolution topographic data and field information about tectonic geomorphological features and the structural characteristics of this transition zone.

  13. Fault zone structure from topography: signatures of en echelon fault slip at Mustang Ridge on the San Andreas Fault, Monterey County, California

    USGS Publications Warehouse

    DeLong, Stephen B.; Hilley, George E.; Rymer, Michael J.; Prentice, Carol

    2010-01-01

    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 Andreas 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.

  14. Zoogeography of the San Andreas Fault system: Great Pacific Fracture Zones correspond with spatially concordant phylogeographic boundaries in western North America.

    PubMed

    Gottscho, Andrew D

    2016-02-01

    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 Andreas 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. PMID:25521005

  15. Precise location of San Andreas Fault tremors near Cholame, California using seismometer clusters: Slip on the deep extension of the fault?

    USGS Publications Warehouse

    Shelly, D.R.; Ellsworth, W.L.; Ryberg, T.; Haberland, C.; Fuis, G.S.; Murphy, J.; Nadeau, R.M.; Burgmann, R.

    2009-01-01

    We examine a 24-hour period of active San Andreas 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.

  16. Tremor reveals stress shadowing, deep postseismic creep, and depth-dependent slip recurrence on the lower-crustal San Andreas fault near Parkfield

    USGS Publications Warehouse

    Shelly, David R.; Johnson, Kaj M.

    2011-01-01

    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 Andreas 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.

  17. Automatic identification of fault zone head waves and direct P waves and its application in the Parkfield section of the San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Li, Zefeng; Peng, Zhigang

    2016-06-01

    Fault zone head waves (FZHWs) are observed along major strike-slip faults and can provide high-resolution imaging of fault interface properties at seismogenic depth. In this paper, we present a new method to automatically detect FZHWs and pick direct P waves secondary arrivals (DWSAs). The algorithm identifies FZHWs by computing the amplitude ratios between the potential FZHWs and DSWAs. The polarities, polarizations and characteristic periods of FZHWs and DSWAs are then used to refine the picks or evaluate the pick quality. We apply the method to the Parkfield section of the San Andreas Fault where FZHWs have been identified before by manual picks. We compare results from automatically and manually picked arrivals and find general agreement between them. The obtained velocity contrast at Parkfield is generally 5-10 per cent near Middle Mountain while it decreases below 5 per cent near Gold Hill. We also find many FZHWs recorded by the stations within 1 km of the background seismicity (i.e. the Southwest Fracture Zone) that have not been reported before. These FZHWs could be generated within a relatively wide low velocity zone sandwiched between the fast Salinian block on the southwest side and the slow Franciscan Mélange on the northeast side. Station FROB on the southwest (fast) side also recorded a small portion of weak precursory signals before sharp P waves. However, the polarities of weak signals are consistent with the right-lateral strike-slip mechanisms, suggesting that they are unlikely genuine FZHW signals.

  18. Three-dimensional simulations of ground motions in the San Bernardino Valley, California, for hypothetical earthquakes on the San Andreas Fault

    USGS Publications Warehouse

    Frankel, A.

    1993-01-01

    Three-dimensional finite difference simulations of elastic waves in the San Bernardino Valley were performed for two hypothetical earthquakes on the San Andreas 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

  19. Along-strike variations in fault frictional properties along the San Andreas Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations

    USGS Publications Warehouse

    Harrington, R.M; Cochran, Elizabeth S.; Griffiths, E.M.; Zeng, X.; Thurber, C.

    2016-01-01

    Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San Andreas 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.

  20. Delayed dynamic triggering of deep tremor along the Parkfield-Cholame section of the San Andreas Fault following the 2014 M6.0 South Napa earthquake

    NASA Astrophysics Data System (ADS)

    Peng, Zhigang; Shelly, David R.; Ellsworth, William L.

    2015-10-01

    Large, distant earthquakes are known to trigger deep tectonic tremor along the San Andreas Fault and in subduction zones. However, there are relatively few observations of triggering from regional distance earthquakes. Here we show that a small tremor episode about 12-18 km NW of Parkfield was triggered during and immediately following the passage of surface waves from the 2014 Mw 6.0 South Napa main shock. More notably, a major tremor episode followed, beginning about 12 h later, and centered SE of Parkfield near Cholame. This major 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. This episode showed systematic along-strike migration at ~5 km/d, suggesting that it was driven by a slow-slip event. Our results suggest that moderate-size earthquakes are capable of triggering major tremor and deep slow slip at regional distances.

  1. Automatic identification of fault zone head waves and direct P waves and its application in the Parkfield section of the San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Li, Zefeng; Peng, Zhigang

    2016-03-01

    Fault zone head waves (FZHWs) are observed along major strike-slip faults, and can provide high-resolution imaging of fault interface properties at seismogenic depth. In this paper we present a new method to automatically detect FZHWs and pick direct P waves secondary arrivals (DWSAs). The algorithm identifies FZHWs by computing the amplitude ratios between the potential FZHWs and DSWAs. The polarities, polarizations and characteristic periods of FZHWs and DSWAs are then used to refine the picks or evaluate the pick quality. We apply the method to the Parkfield section of the San Andreas Fault where FZHWs have been identified before by manual picks. We compare results from automatically and manually picked arrivals and find general agreement between them. The obtained velocity contrast at Parkfield is generally 5%-10% near Middle Mountain while it decreases below 5% near Gold Hill. We also find many FZHWs recorded by the stations within 1 km of the background seismicity (i.e., the Southwest Fracture Zone) that have not been reported before. These FZHWs could be generated within a relatively wide low velocity zone sandwiched between the fast Salinian block on the southwest side and the slow Franciscan Mélange on the northeast side. Station FROB on the southwest (fast) side also recorded a small portion of weak precursory signals before sharp P waves. However, the polarities of weak signals are consistent with the right-lateral strike-slip mechanisms, suggesting that they are unlikely genuine FZHW signals.

  2. Crustal strain near the Big Bend of the San Andreas Fault: analysis of the Los Padres-Tehachapi Trilateration Networks, California

    USGS Publications Warehouse

    Eberhart-Phillips, D.; Lisowski, M.

    1990-01-01

    In the region of the Los Padres-Tehachapi geodetic network, the San Andreas 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

  3. Two-dimensional seismic image of the San Andreas Fault in the Northern Gabilan Range, central California: Evidence for fluids in the fault zone

    USGS Publications Warehouse

    Thurber, C.; Roecker, S.; Ellsworth, W.; Chen, Y.; Lutter, W.; Sessions, R.

    1997-01-01

    A joint inversion for two-dimensional P-wave velocity (Vp), P-to-S velocity ratio (Vp/Vs), and earthquake locations along the San Andreas 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.

  4. Long-term rates and the depth extent of fault creep along the San Andreas Fault system in northern California from alinement arrays and GPS data

    NASA Astrophysics Data System (ADS)

    Lienkaemper, J. J.; McFarland, F. S.; Simpson, R. W.; Caskey, J.

    2013-12-01

    The dextral San Andreas Fault system (SAFS) in northern Ca