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Sample records for jochen zschau andreas

  1. [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

  2. 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.

  3. [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.

  4. 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).

  5. [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

  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.

  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' 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.

  9. [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.

  10. [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

  11. 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...

  12. 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.

  13. 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 ...

  14. 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

  15. 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

  16. 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.

  17. 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...

  18. [The botanist and doctor Pietro Andrea Matthioli].

    PubMed

    Daxecker, F

    2005-06-01

    The physician Pietro Andrea Mattioli (1500 - 1577) is known for his Italian translation and commentary of the work of the Greek botanist Pedanios Dioscurides: "Di Pedacio Dioscoride Anazerbeo libri cinque ..." (first published in 1544). The physician broadened Dioscurides' studies by including new medicinal plants and numerous detailed woodcuts. In 1554 the fifth edition had already been published: "I Discorsi di M. Pietro Andrea Matthioli Sanese, Medico Cesareo ... Di Pedacio Dioscuride Anacarbeo della materia Medicinale ...". The book was also translated into Latin, French, Spanish, German and Bohemian. Matthioli describes plants, that can be used to treat eye-diseases.

  19. 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

  20. 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

  1. 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

  2. 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.)

  3. 78 FR 37659 - Requested Administrative Waiver of the Coastwise Trade Laws: Vessel MISS ANDREA; Invitation for...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2013-06-21

    ... ANDREA; Invitation for Public Comments AGENCY: Maritime Administration, Department of Transportation... the applicant the intended service of the vessel MISS ANDREA is: Intended Commercial Use Of...

  4. 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. 

  5. 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

  6. 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

  7. 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.

  8. 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.

  9. [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

  10. [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.

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. [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

  17. 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.

  18. 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.

  19. [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.

  20. Rhazes in the renaissance of Andreas Vesalius.

    PubMed

    Compier, Abdul Haq

    2012-01-01

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

  1. 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.

  2. 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.

  3. 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).

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

    USGS Publications Warehouse

    Wallace, R.E.

    1978-01-01

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

  5. 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

  6. 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...

  7. 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…

  8. 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'.

  9. 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.

  10. 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.

  11. Overview of the Southern San Andreas Fault Model

    USGS Publications Warehouse

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

    2008-01-01

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

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

    USGS Publications Warehouse

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

    2006-01-01

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

  13. 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.

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

    USGS Publications Warehouse

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

    1997-01-01

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

  15. 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.

  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. 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

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

    USGS Publications Warehouse

    Oye, V.; Ellsworth, W.L.

    2007-01-01

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

  19. 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

  20. 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.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

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

    USGS Publications Warehouse

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Zoback, Mary Lou; Jachens, Robert C.; Olson, Jean A.

    1999-05-01

    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 pseudogravity 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 Andreas

  15. 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

  16. Structure and mechanics of the San Andreas-San Gregorio fault junction, San Francisco, California

    NASA Astrophysics Data System (ADS)

    Parsons, Tom; Bruns, Terry R.; Sliter, Ray

    2005-01-01

    The right-lateral San Gregorio and San Andreas faults meet west of the Golden Gate near San Francisco. Coincident seismic reflection and refraction profiling across the San Gregorio and San Andreas faults south of their junction shows the crust between them to have formed shallow extensional basins that are dissected by parallel strike-slip faults. We employ a regional finite element model to investigate the long-term consequences of the fault geometry. Over the course of 2-3 m.y. of slip on the San Andreas-San Gregorio fault system, elongated extensional basins are predicted to form between the two faults. An additional consequence of the fault geometry is that the San Andreas fault is expected to have migrated eastward relative to the San Gregorio fault. We thus propose a model of eastward stepping right-lateral fault formation to explain the observed multiple fault strands and depositional basins. The current manifestation of this process might be the observed transfer of slip from the San Andreas fault east to the Golden Gate fault.

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

    USGS Publications Warehouse

    Savage, J.C.; Lisowski, M.

    1997-01-01

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

  18. 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

  19. Structure of the San Andreas Fault at SAFOD (Invited)

    NASA Astrophysics Data System (ADS)

    Chester, J. S.; Chester, F. M.; Sills, D. W.; Heron, B.; Almeida, R. V.; Guillemette, R. N.

    2010-12-01

    The San Andreas Fault Observatory at Depth (SAFOD) provides a unique opportunity to characterize the deformation of sedimentary and crystalline rocks subjected to variable loading rates and chemically reactive fluids at seismogenic depths along an active continental transform fault. The spot core captured relatively undeformed host rock, highly fractured and sheared rock from within the fault zone, and gouge from two prominent zones of aseismic creep, the Southwestern Deforming Zone (SDZ), and the Central Deforming Zone (CDZ). Distinct structural units sampled from west to east, include: (i) deformed crystalline rock west of the active zone, (ii) a fault-bordering damage zone composed of two distinct, highly fractured and cemented arkosic sandstones, (iii) a fault core associated with the SDZ composed of foliated cataclasites, gouge, and variably sheared siltstones and shales, (iv) deformed siltstones and shales within the central portion of the low velocity zone, and (v) the gouge associated with the CDZ. We have characterized the structure and syndeformation-alteration reactions of these units through detailed mapping at the mesoscopic and microscopic scales, XCT imaging, scanning electron microscopy, and elemental mapping. The San Andreas Fault zone at SAFOD is a broad zone of damage containing multiple fault-cores that juxtapose distinct structural-petrologc units. Multiple episodes of fracture, chemically-assisted comminution, neomineralization, and fault healing through cementation are evident. The SDZ and CDZ are composed of distinct 1-3 m-thick layers of incohesive, foliated fault gouge containing survior clasts up to 4 cm in diameter. Deformation of the gouge is relatively homogeneous at mesoscopic scale, occurring by slip along penetrative anastomosing polished shears that often occur at the boundaries of the survivor clasts. We suggest that 1) the extremely low frictional strength of the gouge reflects slip in shears containing a significant fraction of

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Lozos, J.

    2015-12-01

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

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

    USGS Publications Warehouse

    Lockner, 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.

  10. 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.

  11. [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.

  12. Vertical deformation along the Indio Hills, San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Scharer, K. M.; Blisniuk, K.; Sharp, W. D.; Williams, P. L.; Johnson, K.

    2014-12-01

    Halfway between the Salton Sea and San Gorgonio Pass, the southernmost San Andreas Fault (SAF) bifurcates into the Mission Creek and Banning strands. These strands bound the Indio Hills (IH), and mark the first of a series of left-stepping branches that define the transpressional, southern Big Bend of the SAF. Between the fault strands, the Quaternary Ocotillo Formation is deformed with fold axis orientations consistent with dextral shear; structurally the IH are synclinal in the east, transitioning to a complex antiform with increased uplift suggested by exhumation of Tertiary units in the west. We report new long- and short-term erosion rates across the IH and uplift rates on the Banning strand, and we evaluate these measurements in terms of slip rates across the fault system and structural deformation within the IH. Two methods of catchment-averaged erosion rates provide minimum rates yield similar results, (0.08 to 0.34 mm/yr) across 6 catchments. The long-term rates are calculated from eroded volumes estimated from a 10-m DEM surface enveloping the Indio Hills and assume that all folding and uplift initiated ca. 500ka (the 750 ka Bishop ash is uplifted and warped within the IH). The short-term rates, determined from 10Be dating of alluvial sediments, increase gradually to the northwest. Similarity of the rates suggests steady state uplift over the history of the fold; ongoing structural analysis and dating needed to constrain the maximum rates will test this possibility. The new uplift rate for the Banning strand at the east end of the IH is determined from a 60 pts/m^2 DEM produced by structure from motion photogrammetry and U-series ages and cosmogenic dates that provide an age range of 20-76ka for a fan vertically offset by ~2.5 m. The resulting uplift rate on the fault (0.03-0.125 mm/yr) overlaps with the short-term catchment-averaged erosion rate for this location (0.08 mm/yr). Consequently, we interpret that vertical strain is partitioned onto both the

  13. 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

  14. 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

  15. 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…

  16. 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.

  17. 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.

  18. 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.

  19. Electrical Structure of the Creeping San Andreas Fault at Hollister, California

    NASA Astrophysics Data System (ADS)

    Bedrosian, P. A.; Unsworth, M. J.; Egbert, G.; Thurber, C.

    2001-12-01

    Individual segments of the San Andreas Fault (SAF) exhibit markedly different patterns of seismicity ranging from locked to creeping. The factors controlling such variation are not well understood, but could include fault geometry, geology, and the presence or absence of fault-zone fluids. Magnetotelluric data have been used to image the geoelectric structure of the San Andreas Fault zone and surrounding areas in an attempt to understand the distribution and role of fault-zone fluids. Previous surveys have studied the locked Carrizo segment and the transitional Parkfield segment. This study has been extended to consider creeping segments of the San Andreas and Calaveras Faults. Magnetotelluric data were collected in 1999 along two profiles near Paicines and Bear Valley, with continuous coverage within 1-2 km of the faults. Robust time-series processing and a non-linear conjugate gradient algorithm were employed to produce models of the electrical structure of the fault-zone. The features of the model required by the data include: 1) A highly resistive body southwest of the SAF, adjacent to the SAF with a near-vertical contact. This unit is coincident with the Gabilan granites. 2) A broad zone of enhanced electrical conductivity is imaged between the San Andreas and Calaveras Faults. Discrete shallow regions of high conductivity are coincident with the San Andreas and Calaveras Faults. 3) A prominent fault-zone conductor (FZC) is imaged down to at least 8 km depth. This zone has a (horizontally-integrated) conductance of 600 Siemens, similar in magnitude to that observed at Parkfield. The upper to mid-crustal depths of these conductive zones suggest that they are due to the presence of saline fluids, since nearby wells have encountered brines at depths of several hundred meters. Additionally, seismic tomographic studies image a zone of decreased Vp and enhanced Poisson's ratio which is essentially coincident with the imaged zone of high conductivity beneath the

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

    USGS Publications Warehouse

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

    2013-01-01

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

  1. 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

  2. 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

  3. 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.

  4. 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

  5. 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

  6. 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

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

    USGS Publications Warehouse

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

    1990-01-01

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

  8. 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.

  9. 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

  10. 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.

  11. [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

  12. 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.

  13. 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.

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

    USGS Publications Warehouse

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

    2008-01-01

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

  15. 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.

  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. 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.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    USGS Publications Warehouse

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

    2016-01-01

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

  6. 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.

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

    USGS Publications Warehouse

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

    2006-01-01

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

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

    PubMed Central

    Lozos, Julian C.

    2016-01-01

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

  9. 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

  10. 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

  11. 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

  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. 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

  17. 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.

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

    PubMed

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

    2011-11-30

    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.

  19. Distributed Plate Boundary Deformation Across the San Andreas Fault System, Central California

    NASA Astrophysics Data System (ADS)

    Dyson, M.; Titus, S. J.; Demets, C.; Tikoff, B.

    2007-12-01

    Plate boundaries are now recognized as broad zones of complex deformation as opposed to narrow zones with discrete offsets. When assessing how plate boundary deformation is accommodated, both spatially and temporally, it is therefore crucial to understand the relative contribution of the discrete and distributed components of deformation. The creeping segment of the San Andreas fault is an ideal location to study the distribution of plate boundary deformation for several reasons. First, the geometry of the fault system in central California is relatively simple. Plate motion is dominated by slip along the relatively linear strike-slip San Andreas fault, but also includes lesser slip along the adjacent and parallel Hosgri-San Gregorio and Rinconada faults, as well as within the borderlands between the three fault strands. Second, the aseismic character of the San Andreas fault in this region allows for the application of modern geodetic techniques to assess creep rates along the fault and across the region. Third, geologic structures within the borderlands are relatively well-preserved allowing comparison between modern and ancient rates and styles of deformation. Continuous GPS stations, alignment arrays surveys, and other geodetic methods demonstrate that approximately 5 mm/yr of distributed slip is accumulated (on top of the fault slip rate) across a 70-100 km wide region centered on the San Andreas fault. New campaign GPS data also suggest 2-5 mm/yr of deformation in the borderlands. These rates depend on the magnitude of the coseismic and postseismic corrections that must be made to our GPS time series to compensate for the 2003 San Simeon and 2004 Parkfield earthquakes, which rupture faults outside, but near the edges of our GPS network. The off-fault deformation pattern can be compared to the style of permanent deformation recorded in the geologic record. Fold and thrust belts in the borderlands are better developed in the Tertiary sedimentary rocks west of

  20. 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.

  1. 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.

  2. [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

  3. 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

  4. 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.

  5. 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

  6. 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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Cherneva, Z.; Guedes Soares, C.

    2014-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Cherneva, Z.; Guedes Soares, C.

    2014-02-01

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

  10. 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.

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

    PubMed

    Ségal, Alain

    2014-01-01

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

  13. 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.

  14. Deep crustal heterogeneity along and around the San Andreas fault system in central California and its relation to the segmentation

    NASA Astrophysics Data System (ADS)

    Nishigami, Kin'ya

    2000-04-01

    The three-dimensional distribution of scatterers in the crust along and around the San Andreas fault system in central California is estimated using an inversion analysis of coda envelopes from local earthquakes. I analyzed 3801 wave traces from 157 events recorded at 140 stations of the Northern California Seismic Network. The resulting scatterer distribution shows a correlation with the San Gregorio, San Andreas, Hayward, and Calaveras faults. These faults seem to be almost vertical from the surface to ˜15 km depth. Some of the other scatterers are estimated to be at shallow depths, 0-5 km, below the Diablo Range, and these may be interpreted as being generated by topographic roughness. The depth distribution of scatterers shows relatively stronger scattering in the lower crust, at ˜15-25 km depth, especially between the San Andreas fault and the Hayward-Calaveras faults. This suggests a subhorizontal detachment structure connecting these two faults in the lower crust. Several clusters of scatterers are located along the San Andreas fault at intervals of ˜20-30 km from south of San Francisco to the intersection with the Calaveras fault. This part of the San Andreas fault appears to consist of partially locked segments, also ˜20-30 km long, which rupture during M6-7 events, and segment boundaries characterized by stronger scattering and stationary microseismicity. The segment boundaries delineated by the present analysis correspond with those estimated from the slip distribution of the great 1906 San Francisco earthquake, and from the fault geometry as reported by the Working Group on California Earthquake Probabilities [1990], although the segment boundaries along the San Andreas fault in and around the San Francisco Bay area are still uncertain.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

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

    PubMed

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

    2015-01-01

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

  20. 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

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

    USGS Publications Warehouse

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

    2010-01-01

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

  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. 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.

  4. [Kidney disease in Sant' Andrea Hospital: a biopsy based epidemiologic study].

    PubMed

    Mei, Mariachiara; Menè, Paolo; Stoppacciaro, Antonella

    2016-01-01

    The aim of this retrospective study is to investigate the prevalence and pathological features of kidney inflammatory nephropathies diagnosed in Sant'Andrea Hospital, from January 2003 to April 2015. In this period, 246 kidney biopsies have been diagnosed in our Hospital. Excluding cases of kidney neoplasms and non-diagnostic samples, 195 cases were reviewed. Primary glomerulonephritis (GN) is the most common diagnosis. Among these, Membranous GN represents the majority of cases (20.4%), followed by IgA Nephropathy (12.7%). The higher prevalence of Membranous GN than IgA Nephropathy represents a difference between our study and national and international kidney biopsies registries. It can be considered a consequence of the average age of patients undergoing renal biopsy in our center (54,1 years). Patients with Diabetic Nephropathy are 1.5%. 10 out of 195 cases (5.1%) show end stage renal disease. This epidemiological study evaluates the prevalence of various kidney diseases in our database, the biopsy policy of SantAndrea Hospital and compares our results with national and international renal biopsies registries.

  5. 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.

  6. 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.

  7. Geodetic measurement of deformation east of the San Andreas fault in central California

    NASA Astrophysics Data System (ADS)

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

    Triangulation and trilateration data from two geodetic networks located between the San Andreas fault and the Great Valley 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. The shear strain rates, γ1 and γ2, were estimated independently from angle changes using Prescott's method and from the simultaneous reduction for station position and strain parameters using the DYNAP method with corrections to reduce the triangulation and trilateration data to a common reference surface. On the basis of Prescott's method, the average shear strain rate across the Diablo Range for the time period between 1962 and 1982 is 0.15±0.08 μrad/yr, with the orientation of the most compressive strain (β) at N16°E±14°. Utilizing corrections for the deflection of the vertical and the geoid reference ellipsoid separation computed on the basis of local gravity observations, γ = 0.19±0.09 μrad/yr and β = N16°E±13°. Although γ is not significantly greater than zero, at the 95% confidence level the orientation of β is similar to the direction of maximum compressive strain indicated by the orientation of major fold structures in the region (N25°E). We infer 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 5.7±2.7 mm/yr. In contrast to the situation throughout most of the Coast Ranges where fold axes have orientations approximately parallel to the San Andreas fault, within the Diablo Range between Hollister and Coalinga the trends of the fold axes are different and are thought to be controlled by reactivation of older structures. From trilateration measurements made between 1972 and 1987 on lines that are within 10 km of the San Andreas fault, a slip rate of 10-12 mm/yr was calculated for the Calaveras-Paicines fault south of Hollister. The slip rate on the Paicines

  8. 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.

  9. 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.

  10. 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.

  11. 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

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    USGS Publications Warehouse

    Shelly, David R.; Hardebeck, Jeanne L.

    2010-01-01

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

  3. Nonlinear strain buildup and the earthquake cycle on the San Andreas fault.

    USGS Publications Warehouse

    Thatcher, W.

    1983-01-01

    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. -Author

  4. 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.

  5. 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.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  7. 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. 

  8. 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

  9. Stress fields of the San Andreas and Queen Charlotte transform faults

    NASA Astrophysics Data System (ADS)

    Kilty, Kevin T.

    1981-08-01

    Analytic solutions to the stress fields resulting from the San Andreas and Queen Charlotte transform faults may be found by applying conformal mappings to the generalized plane stress solution of stresses in a half-plane. The mean stress fields (one-half the trace of the stress tensor) found in this manner show a similarity to the deformation found in western Canada and the western United States. The results refute the hypothesis that Alaska acts as a continental buttress against deformation of the Canadian Cordillera. Moreover, these results imply that the differences in the tectonics of major transform boundaries are caused primarily by differences in lithospheric structure and differences in stress distribution along the plate boundaries.

  10. 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.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

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

  19. 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.

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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).

  8. 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

  9. 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

  10. 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.

  11. 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.

  12. 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.

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

    PubMed

    Steeno, Omer P; Deruyttere, Michel

    2008-06-01

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

  14. 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

  15. Geophysical evidence for Quaternary deformation within the offshore San Andreas Fault System, Point Reyes Peninsula, California

    NASA Astrophysics Data System (ADS)

    Stozek, B.

    2010-12-01

    Our previous work studying the rate and style of uplift of marine terraces on the Point Reyes Peninsula indicates the peninsula has been undergoing differential uplift due to interacting fault geometries in the offshore zone. To better understand offshore fault interactions, recently collected mini-sparker seismic reflection data acquired by the USGS and multi-beam bathymetric data acquired by California State University at Monterey Bay within the 3-mile (5 km) limit offshore of the Point Reyes Peninsula, are being used to reinterpret the tectono-stratigraphic framework of the San Andreas fault (SAF) system. Eight offshore Shell exploratory well logs that provide seismic velocity and paleontologic data are being used in conjunction with industry multichannel (deep-penetration) seismic reflection profiles to provide age control and extend the analyses beyond 3 mile limit of the high-resolution data. Isopach and structure maps of key stratigraphic intervals were generated to show how the stratigraphic units are influenced by fault interactions. These datasets allow for new interpretations of the offshore Neogene stratigraphy and the evolution of the Point Reyes fault, an offshore component of the SAF system. Observations of Quaternary sedimentary sequences in the high-resolution mini-sparker dataset provide evidence of localized areas of subsidence and uplift within the offshore SAF system. For example, the most recent angular unconformity above the Point Reyes fault deepens to the north where the fault bends from an east-west to a more northerly orientation. Stratigraphic horizons in the offshore zone are correlated with the same geologic units exposed on the Point Reyes Peninsula. Both unconformity-bounded sedimentary sequences mapped on reflection profiles in the offshore and marine terraces that have been uplifted on the peninsula are tied to sea-level fluctuations. Our new interpretation of the Point Reyes fault zone will be incorporated into a kinematic fault

  16. 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

  17. 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

  18. 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

  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. 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

  1. 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

  2. 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

  3. 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

  4. 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

  5. Geodetic Investigation of Compliant Fault Zones on the San Francisco Peninsula segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Materna, K.; Burgmann, R.

    2015-12-01

    At many places along the San Andreas Fault, geodetic and seismic studies have suggested the presence of near-field compliant fault zones (CFZs). These zones of damaged rock display reduced elastic moduli compared to intact rock, resulting in both higher geodetic strain rates and lower seismic velocities within the fault zones. In this study, we investigate the CFZ surrounding the San Andreas Fault in the San Francisco Peninsula by examining interseismic deformation over the past several decades. We use new and existing survey GPS measurements, as well as older electronic distance measurements, to characterize the deformation of the CFZ. The data come from networks at Black Mountain and Lake San Andreas, both small-aperture geodetic networks on the San Francisco Peninsula with survey GPS occupations spanning at least 15 years. We compare the inferred fault zone properties between the two networks, which are separated by less than 40 kilometers but which represent different geologic boundaries and show different fault ages. We also compare patterns in seismicity between the two regions. The differences in inferred fault parameters between these two regions may be related to differences in fault age and development, giving clues into how CFZs develop over time.

  6. Monitoring of hydrogen along the San Andreas and Calaveras faults in central California in 1980-1984

    NASA Astrophysics Data System (ADS)

    Sato, Motoaki; Sutton, A. J.; McGee, K. A.; Russell-Robinson, Susan

    1986-11-01

    Hydrogen (H2) has been monitored continuously at 1.5-m depth at nine sites along the San Andreas and Calaveras faults in central California since December 1980. Site characteristic small noninstrumental diurnal variations were recorded during quiescent periods at most sites. Abrupt H2 changes were observed concurrently at two sites on the Calaveras fault; some of these were correlated with oscillatory fault slips. Large (1000-4000 ppm) H2 increases were recorded at some sites on the San Andreas fault between July 1982 and November 1983, which may be correlated with eleven M ≥ 5 earthquakes that occurred near Coalinga during this period. We attribute both the H2 increases and the triggering of the earthquakes to a large-scale compressive stress field within the ductile mafic crust near the plate boundary. The stress perhaps caused bulging of the base of the brittle upper crust and thus caused dilation of the San Andreas fault zone, allowing the escape of pent-up H2 generated by hydration reaction of the mafic crust. At the same time, mobile serpentinites may have squeezed into the seismogenic fault beneath the Coalinga area triggering the earthquakes.

  7. 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.

  8. Crustal structure of the Salton Trough and southern San Andreas Fault based on gravity and magnetic investigations

    NASA Astrophysics Data System (ADS)

    Athens, N. D.; Scheirer, D. S.; Langenheim, V. E.

    2011-12-01

    Gravity and magnetic investigations reveal regional and local features of the subsurface structure of the Salton Trough and southern San Andreas Fault. Regional gravity features include a prominent, narrow gravity low in Coachella Valley that decreases in amplitude to the southeast near the north shore of the Salton Sea. At the south end of the Salton Sea, the gravity low has become a large gravity high that has been attributed to crustal thinning and mafic lower crust. The northeast margin of the gravity low is linear and coincides with both the San Andreas Fault and a distinctive magnetic high that is probably related to crystalline basement rocks of the Little San Bernardino Mountains. The southwest margin of the gravity low is also marked by a gravity gradient, but is not linear in map-view and is generally less steep. The gradient mimics the irregular contact between pre-Cenozoic basement rocks and Cenozoic basin fill. Gravity data were collected to augment existing data along transects of the Salton Seismic Imaging Project. Measurement spacing averaged about 800-m, except along the high-resolution seismic line near Salt Creek, where a detailed grid of gravity measurements spaced about 400-m is supplemented by ground magnetic transects. The detailed data reveal a bench in the gravity gradient that is coincident with a narrow (500-m) 100-nT magnetic high that may reflect multiple strands of the San Andreas Fault or interactions with the Hidden Springs fault. These anomalies, however, only extend along strike for about 2-km before diminishing. Along the stretch of the San Andreas Fault between Indio and Salt Creek, the San Andreas Fault is located near the base of the southwest-facing steep gravity gradient, indicating a steep northeast dip of the basement contact, with higher-density rocks northeast of the fault. North of Indio, the gradient becomes more diffuse, suggestive of a gentler northeast dip. About 5-km south of Salt Creek, the fault changes its

  9. Paleoseismic Study on the Peninsula Section of the San Andreas Fault South of Crystal Springs Reservoir, San Mateo County, California

    NASA Astrophysics Data System (ADS)

    Zachariasen, J. A.; Prentice, C. S.; Kozaci, O.; Sickler, R. R.; Baldwin, J. N.; Sanquini, A.; Knudsen, K. L.

    2010-12-01

    The Peninsula section of the San Andreas Fault is a significant hazard for the San Francisco Bay area, but little is known about the timing of earthquakes on this section of the fault prior to the great earthquake of April 18, 1906. An earthquake in 1838 resulted in strong shaking on the San Francisco Peninsula. Estimates of the magnitude of the 1838 earthquake vary from 6.8 to 7.4, based on historical accounts, and most workers have assumed that this event occurred on the San Andreas Fault. However, paleoseismic excavations across the fault near San Andreas Lake failed to provide evidence that the 1838 earthquake was associated with surface rupture on the Peninsula section of the San Andreas Fault (Prentice et al., 2008, 2009). Earlier work at the Filoli Estate, south of Crystal Springs Reservoirs, by Hall et al. (1999) suggested that both the 1838 and 1906 earthquakes ruptured the Peninsula section, based on the projected offsets of buried stream channels that crossed the fault. While this interpretation is permissible, the data also allow alternative interpretations that do not require surface rupture in 1838. We used LiDAR images produced from data collected by the GeoEarthScope project to search for promising paleoseismic sites along the Peninsula section of the San Andreas Fault. At a site about 1.2 km southeast of Crystal Springs Reservoir, we excavated two trenches across the fault and exposed fluvial gravel and overbank deposits cut by two distinct generations of faults. The younger set of faults break nearly to the ground surface, and we interpret these to represent 1906 surface faulting that has been buried post-1906 sediments. The older faults terminate below a colluvial wedge derived from one of the fluvial gravel deposits. The scarp-derived colluvium overlies a faulted fine-grained overbank deposit that in turn rests on the channel gravel, and represents the ground surface at the time of the older earthquake. The scarp-derived colluvium is overlain by

  10. 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

  11. Earthquake processes and geologic structure of the San Andreas Fault at Parkfield through the SAFOD seismic array

    NASA Astrophysics Data System (ADS)

    Chavarria, Juan Andres

    The San Andreas Fault Observatory at Depth (SAFOD) has the goal of understanding earthquake processes at hypocentral depths. In July 2002 Duke University installed a vertical array of seismometers in the SAFOD Pilot Hole (PH). Seismograms recorded by the array give insights into the structure of the SAFOD site. The ratios of P- and S-wave velocities (Vp/Vs) along the array suggest the presence of two faults intersecting the PH. The Vp/Vs ratios also depend on source location, with high values for sources to the northwest along the San Andreas, and lower ones to the southeast. This distribution correlates with high and low creep rates along the SAF. Since higher Vp/Vs ratios can be produced by increasing fluid saturation, this effect could be the one guiding the frequent seismicity and creep along this segment of the fault. The SAFOD PH Vertical Seismic Profiling-seismograms from nearby microearthquake and explosion sources also contain secondary signals between the P- and S-waves. These signals are shown to be P and S waves scattered by the local structure. Kirchhoff migration was applied to define the origin points of these scattered signals. Both 2D and 3D analysis of microearthquake and explosion seismograms showed that the collected scattering points form planar surfaces, interpreted as a vertical San Andreas Fault and four other secondary faults forming a flower structure. These structures along with seismicity located in secondary fault strands suggest that stresses along the San Andreas at Parkfield could be distributed in more complex ways, modifying the local earthquake cycle. Modeling of scattered phases indicates strong geologic contrasts that have recently been drilled by SAFOD. A granite-sediment interface may constitute the boundary of a hanging block with sedimentary materials with low electrical resistivities. Shallow earthquakes at Parkfield take place at the interface of the northeastern boundary of this block, adjacent to the San Andreas Fault

  12. 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.

  13. 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.

  14. Slow and Go: Pulsing Slip Rates on the Creeping Section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Turner, R. C.; Shirzaei, M.; Nadeau, R. M.; Burgmann, R.

    2014-12-01

    Rising and falling slip rates on the creeping section of the San Andreas Fault have been inferred from variations of recurrence intervals of repeating micro-earthquakes, but this observation has not previously been confirmed using modern geodetic data. Here, we report on observations of this 'pulsing' slip obtained from advanced multi-temporal Interferometric Synthetic Aperture Radar (InSAR) data. 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 analysis reveals a quasi-periodic pulsing with approximately 2-year-long intervals along some sections of the fault in both InSAR and repeating earthquake datasets, with the earthquakes on the fault interface lagging behind the far-field deformation by about six 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.

  15. 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.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

    Abercrombie, Rachel E.

    2014-12-01

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

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

  20. 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.

  1. 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.

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

    NASA Technical Reports Server (NTRS)

    1998-01-01

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

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

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

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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. 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

  10. 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.

  11. 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

  12. Seismic Attenuation in the Parkfield area of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Kelly, C. M.; Rietbrock, A.; Faulkner, D. R.

    2010-12-01

    Fault zone structure and rock properties at depth within the Parkfield area of San Andreas Fault are investigated through a seismic attenuation study. Attenuation is sensitive to the degree of fracturing, water saturation and other rock properties. The Parkfield area is of interest as it marks the boundary between the creeping area of the San Andreas Fault and an area which ruptured seismically in 1966 and again in 2004. It is also the area of the SAFOD drilling project. Previous studies of this area have suggested a complex picture of fault strands linking at depth and small bodies of high-velocity material (e.g. Li et al. 1997, Michael & Eberhart-Philips 1991). Various temporary and local seismic networks have been installed in the region and data from the PASO, PASO TRES and HRSN networks are used in this study. PASO data runs from 2001-2002 at sampling rate of 100sps. The PASO TRES data spans the time period 2004-2006 at 200sps. The HRSN network has been running since March 2001 to present with sampling at 250sps. Attenuation parameters (e.g. Q-values) are established using the spectral ratios technique. A window of 1.28 seconds around each event arrival is extracted together with a window of the same length within the noise directly preceding. Instrument corrected frequency spectra from both the event and the noise are smoothed in a logarithmically-scaled smoothing function. Only frequencies with a signal/noise ratio of 3 or above are used. The ratio between frequency spectra from event arrivals and synthetic frequency spectra of known seismic parameters is determined. A gridsearch method is used to fit the event corner frequency, searching within a range of corner frequencies implied from the reported event magnitude and assuming a stress drop of between 0.1 and 10MPa. A Brune source model is assumed (gamma=2, n=1) for the source spectra (Brune 1970). When the correct corner frequency is fitted, there should be a linear relationship between frequency and the

  13. 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

  14. Geologic structure of Middle Mountain within the San Andreas Fault zone near Parkfield, California

    NASA Astrophysics Data System (ADS)

    Thayer, M. R.; Arrowsmith, R.; Young, J.; Fayon, A.; Rymer, M.

    2004-12-01

    Knowledge of the geometry and history of motion of rock bodies within fault zones such as the San Andreas fault (SAF) is essential input into mechanical models of earthquake rupture dynamics and fault evolution. The Parkfield segment of the SAF is the focus of significant geophysical characterization and borehole studies. In order to enhance the geologic information about the SAF structure in this area, we undertook an intensive high-resolution geologic mapping effort (1:6000 scale) of the Middle Mountain area (about 40 km^2). The geologic structure differs dramatically across the San Andreas fault zone. The northeast side contains numerous sub-parallel faults that likely accommodated significant strike slip motion. These high-angle faults bound granite, marble, and sedimentary rock slivers. The density and complexity of these faults increases toward the center of the fault zone. The Gold Hill reverse fault on the northeast side of the SAF is a low-angle southwest-dipping fault that locally displaces the older Tertiary Monterey Formation over the younger Tertiary Etchegoin Formation. Folds with axes trending parallel to the strike of the Gold Hill reverse fault are present within the hanging wall. The Plio-Pleistocene Paso Robles Formation dominates the southwest side of the SAF and is a formidable cover. Fault-bounded granitoid slivers are also present within the southwest terrain. One fault striking nearly normal to the SAF cuts rock units near the mid-section of Middle Mountain. To the northwest of this fault, older Tertiary formations are present. The folds within the hanging wall of the Gold Hill reverse fault and the reverse fault itself indicate SAF-normal shortening near the SAF zone. The Gold Hill fault most likely cuts the numerous high-angle sub-parallel faults at depth. With the northeastward-verging nature of this fault, the cross-section on the northeast side is a roughly hewn half-flower structure. The sedimentary basin into which the Paso Robles

  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. 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.

  17. 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.

  18. Geometry of the southern San Andreas fault and its implications for seismic hazard

    NASA Astrophysics Data System (ADS)

    Langenheim, V. E.; Dorsey, R. J.; Fuis, G. S.; Cooke, M. L.; Fattaruso, L.; Barak, S.

    2015-12-01

    The southern San Andreas fault (SSAF) provides rich opportunities for studying the geometry and connectivity of fault stepovers and intersections, including recently recognized NE tilting of the Salton block between the SSAF and San Jacinto fault (SJF) that likely results from slight obliquity of relative plate motion to the strike of the SSAF. Fault geometry and predictions of whether the SSAF will rupture through the restraining bend in San Gorgonio Pass (SGP) are controversial, with significant implications for seismic hazard. The evolution of faulting in SGP has led to various models of strain accommodation, including clockwise rotation of fault-bounded blocks east of the restraining bend, and generation of faults that siphon strike slip away from the restraining bend onto the SJF (also parallel to the SSAF). Complex deformation is not restricted to the upper crust but extends to mid- and lower-crustal depths according to magnetic data and ambient-noise surface-wave tomography. Initiation of the SJF ~1.2 Ma led to formation of the relatively intact Salton block, and end of extension on the West Salton detachment fault on the west side of Coachella Valley. Geologic and geomorphic data show asymmetry of the southern Santa Rosa Mountains, with a steep fault-bounded SW flank produced by active uplift, and gentler topographic gradients on the NE flank with tilted, inactive late Pleistocene fans that are incised by modern upper fan channels. Gravity data indicate the basin floor beneath Coachella Valley is also asymmetric, with a gently NE-dipping basin floor bound by a steep SSAF; seismic-reflection data suggest that NE tilting took place during Quaternary time. 3D numerical modeling predicts gentle NE dips in the Salton block that result from the slight clockwise orientation of relative motion across a NE-dipping SSAF. A NE dip of the SSAF, supported by various geophysical datasets, would reduce shaking in Coachella Valley compared to a vertical fault.

  19. Aftershock asymmetry/rupture directivity among central San Andreas fault microearthquakes

    NASA Astrophysics Data System (ADS)

    Rubin, Allan M.; Gillard, Dominique

    2000-08-01

    Using a waveform cross-correlation technique, we have obtained precise relative locations for nearly 75% of the Northern California Seismic Network catalog (4300 earthquakes) occurring between 1984 and 1997 along 50 km of the San Andreas fault. Errors in relative location are meters to tens of meters for events separated by tens to hundreds of meters. We find that consecutive earthquakes in the relocated catalog occur no closer than a distance approximately equal to the radius of the first rupture, as estimated from the moment-magnitude relationship of Abercrombie [1996] assuming a 10-MPa stress drop. When the relative position vectors between consecutive events are normalized by this distance and projected onto the fault surface, they define a hole whose shape suggests that typical microearthquakes are elongate in the mode II (slip-parallel) direction by several tens of percent. Moreover, of the 100 immediate aftershocks occurring closest to the mode II edges of the prior rupture, more than twice as many occur to the northwest than to the southeast. We interpret this asymmetry as resulting from the large contrast in material properties across the fault. Models of dynamic rupture between dissimilar media predict that ruptures in this region may run preferentially to the southeast, in the direction of motion of the lower-velocity material. If so, then the barriers that stop rupture fronts moving to the southeast should initially be farther from failure, on average, than the barriers that stop rupture fronts moving to the northwest. Once the rupture stops, the induced stress change is more symmetric but the fault remains farther from failure (on average) to the southeast. This interpretation receives some support from pulse width measurements on a localized set of 72 magnitude 0.6 to 3.6 earthquakes.

  20. 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.

  1. 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.

  2. 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.

  3. Three-dimensional deformation and stress models of the Death Valley and San Andreas Fault Zones

    NASA Astrophysics Data System (ADS)

    Del Pardo, Cecilia

    Crustal deformation studies of tectonic motions have been the topic of many scientific investigations, as they can provide critical information about how tectonic structures shape and deform the Earth. While crustal deformation studies using observational data alone can provide a great deal of information about how the Earth is presently deforming, it is standard practice to implement mathematical and physics-based models to investigate the underlying causes of deformation in the crust. These models, constrained by geological, geodetic and seismic data, have successfully contributed key constraints of ongoing deformation processes and have provided predictions of past and future tectonic behavior of the Earth. One of the most popular regions of study on Earth is the San Andreas Fault System (SAFS), as it provides an ideal environment for investigating the deformation caused by a major continental transform boundary. Furthermore, the Death Valley Fault Zone (DVFZ) is an ideal area to study large-scale crustal deformation due to its well-exposed features related to progressive extensional deformation. This dissertation presents new information about the deformation, stress accumulation rates, and strain rates taking place in the DVFZ and SAFS using three-dimensional (3-D) crustal deformation models. Chapter 1 provides the background and motivation of the modeling work applied to both fault systems. Chapter 2 provides the results obtained from applying a 3-D semi-analytic viscoelastic model constrained by GPS measurements to explore the kinematics and stress accumulation in the DVFZ. Chapter 3 analyzes the influence of intrusions on the motion and deformation of the DVFZ through a finite difference modeling approach. Chapter 4 explores the strain rate distribution within the SAFS, assuming a dipping fault geometry for its southern segments, utilizing a modified 3-D semi-analytic viscoelastic model. Lastly, Chapter 5 gives a description of the future work that may be

  4. 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.

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

    USGS Publications Warehouse

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

    2003-01-01

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

  6. Tidal Triggering of Earthquakes near Parkfield, California Indicates a High Coefficient of Friction on the Shallow San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Delorey, A. A.; Johnson, P. A.

    2015-12-01

    Investigators have searched for evidence of tidal triggering of earthquakes for decades because triggering behavior provides potentially valuable information about the stress conditions on faults and how earthquake nucleate. Earth tides are caused by the gravitational pull of the sun and moon which induce periodic stresses with two important components related to the rotation of the Earth relative to the sun and moon (semi-diurnal 12 and ~12.4 hours) and the orbit of the moon around the Earth (fortnightly, ~14.7 days). Semi-diurnal tidal stresses have previously been shown to trigger low frequency earthquakes (LFEs) and non-volcanic tremors (NVTs) on the San Andreas Fault. LFEs and NVTs occur within the brittle-ductile transition of the Earth's crust, deeper than where regular earthquakes occur. Here we show that tidal stresses trigger earthquakes in the brittle upper crust, which is caused by and detectable due to interactions between the semi-diurnal and fortnightly stress cycles. The triggering of LFEs and NVTs are correlated with tidal shear stresses indicating a low coefficient of friction on the deep San Andreas Fault. In contrast, we find that regular earthquakes are correlated with tidal normal stresses indicating a high coefficient of friction in the shallow San Andreas Fault. That earthquakes are triggered during peak normal (extensional) tidal stresses suggests that pore pressures are below lithostatic pressure in the upper crust. These findings suggests tidal triggering can be applied to infer crustal stress state and pore pressure conditions, two properties of faults that are difficult to measure but are important for understanding earthquake physics and seismic hazards.

  7. 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.

  8. 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.

  9. 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

  10. 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

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

    PubMed

    Weber, Inge

    2015-01-01

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

  12. 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

  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. 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

  15. 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

  16. EarthScope imaging of 4D stress evolution of the San Andreas Fault System

    NASA Astrophysics Data System (ADS)

    Smith-Konter, B. R.; Del Pardo, C.

    2011-12-01

    EarthScope seismic and geodetic observations, combined with sophisticated computational models and powerful visualization tools, are now providing a critical ensemble of information about interseismic stressing rates along the San Andreas Fault System (SAFS). When combined with paleoseismic chronologies of earthquake ruptures spanning the last several hundreds of years, four-dimensional (4D) simulations of stress evolution spanning multiple earthquake cycles are now possible. To investigate stress variations at depth along the SAFS over multiple earthquake cycles, we use a 4D semi-analytic model that simulates interseismic strain accumulation, coseismic displacement, and post-seismic viscoelastic relaxation of the mantle. The model utilizes geologic estimates of fault locations and slip rates, as well as paleoseismic earthquake rupture histories, and is computed at a 500 m grid resolution to better resolve the sharp deformation gradients at creeping faults. Using EarthScope PBO and ALOS InSAR data, we tune the model locking depths and slip rates to compute the 4D stress accumulation within the seismogenic crust. 4D models show that stress accumulation and stress drop are a complex function of space and time. We use ParaView 3.10, an open-source multi-platform visualization package, for manipulation and visualization of 4D stress variations of fault segments at depth. We use ParaView to create a 3D meshed volume spanning a ~1000 x 1500 x 50 km region of the SAFS and present both volume and sliced views of stress from several viewpoints along the plate boundary. These models reveal pockets of stress concentrated at depth due to the interaction of neighboring fault segments and at fault segment branching junctions. We present several sensitivity tests that reveal the variation of stress at depth as a function of locking depth, slip rate, coefficient of friction, elastic plate thickness, and viscosity. These visualizations lay the groundwork for 4D time

  17. Rupture directivity of micro-earthquakes along the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Wang, E.; Rubin, A. M.

    2009-12-01

    Theoretically, it is expected that earthquakes occurring on an interface separating materials with different elastic properties might have a preferential rupture propagation direction. To test for this, we searched for indications of directivity by examining spectral ratios of multiple pairs of nearby earthquakes at azimuthally distributed seismic stations. By taking the spectral ratios, this technique is capable of canceling path and station terms in seismic spectra. It differs from a typical empirical Green's Function approach in that it compares events with similar sizes as well as events with significant size differences. The spectral ratios are fitted with a simple forward model, in which a bidirectional earthquake source is composed of two point sources moving at constant velocities in opposite directions (assumed to be horizontal). Each bidirectional earthquake has four model parameters: the lengths of the two rupture halves running in opposite directions, and their propagation velocities. A priori information concerning the total rupture length of bidirectional events are computed from catalog magnitude using a moment-magnitude relation and a 3MPa stress drop on an equidimensional rupture. The a priori rupture velocity is peaked at 0.8Vs and constrained to be smaller than Vs. Since identical earthquakes would produce frequency-independent spectral ratios at all azimuths, determining the initiation points of earthquakes requires variability in event size and/or relative directivity. The relocated catalog of Rubin [2002] was used to define 78 clusters of repeating earthquakes along the central San Andreas fault. The spectral ratios of all combinations of earthquake pairs in each cluster were fitted with synthetic spectral ratios at stations with sufficient signal-to-noise ratio and coherence. The inversion results show that, as might have been expected, differences in rupture processes (duration and relative directivity) of the earthquakes within most

  18. San Andreas Fault Branching at SAFOD From Fault Guided Wave Mapping and P-wave Tomography

    NASA Astrophysics Data System (ADS)

    Malin, P. E.; Shalev, E.

    2005-12-01

    In 2004, drilling in the San Andreas Fault Observatory at Depth Main Hole (MH) stopped at ~2.5 km underground and ~0.7 m short of the SAF surface trace. A seismograph temporarily placed there recorded fault zone guided waves from SAF earthquakes, but only from events more than ~2 km northwest and ~3 km southeast of the seismograph. P-wave tomography of seismograms recorded in the SAFOD Pilot Hole (PH) show the seismograph was near the bottom of a synclinal low velocity zone, which also extends across the surface trace. Evidently, the seismograph was in a branch of the SAF that bounds a sliver of sedimentary rock. Our observations were take with a 3-component, 4.5 Hz seismograph temporarily locked in near the bottom of the MH. The seismograph's position was on the southwestern edge of a structure previously imaged using scattered microearthquake waves as recorded on the PH array. It is also near a highly fractured lithological contact seen in the drill core recovered from the end of the 2004 drilling. Seismograms from SAF microearthquakes originating several km to the northwest and southeast of the seismograph appear to contain large fault zone guided waves ("Fg" waves). These data imply that the structure seen in the migration image and drill core is a significant fault zone with a low velocity core that can trap seismic waves. They further suggest that the fault at the end of the 2004 drilling maybe connected to the active trace of the SAF to the north and south of the SAFOD site. Since the SAFOD site is situated on the flower structure of the Middle Mountain segment of the SAF, this branch may still connect to the surface trace fault but at a depth greater than the target events. Previous geological mapping show that the SAFOD site sits above the Middle Mountain syncline. Our P-wave velocity tomography also suggests that its structure extends deeper than indicated by the surface geology. Further, both the 2004 branch and surface-trace-fault cut through this

  19. 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.

  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. 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

  2. High-resolution interseismic velocity data along the San Andreas Fault from GPS and InSAR

    NASA Astrophysics Data System (ADS)

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

    2013-01-01

    We compared four interseismic velocity models of the San Andreas Fault based on GPS observations. The standard deviations of the predicted secular velocity from the four models are larger north of the San Francisco Bay area, near the creeping segment in Central California, and along the San Jacinto Fault and the East California Shear Zone in Southern California. A coherence spectrum analysis of the secular velocity fields indicates relatively high correlation among the four models at longer wavelengths (>15-40 km), with lower correlation at shorter wavelengths. To improve the short-wavelength accuracy of the interseismic velocity model, we integrated interferometric synthetic aperture radar (InSAR) observations, initially from Advanced Land Observing Satellite (ALOS) ascending data (spanning from the middle of 2006 to the end of 2010, totaling more than 1100 interferograms), with GPS observations using a Sum/Remove/Filter/Restore approach. The final InSAR line of sight data match the point GPS observations with a mean absolute deviation of 1.5 mm/yr. We systematically evaluated the fault creep rates along major faults of the San Andreas Fault and compared them with creepmeters and alignment array data compiled in Uniform California Earthquake Rupture Forecast, Version 2 (UCERF2). Moreover, this InSAR line of sight dataset can constrain rapid velocity gradients near the faults, which are critical for understanding the along-strike variations in stress accumulation rate and associated earthquake hazard.

  3. 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.

  4. 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.

  5. [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

  6. 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.

  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. [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.

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

    USGS Publications Warehouse

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

    1979-01-01

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

  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. 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.

  14. 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.

  15. 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.

  16. 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

  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. 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.

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

    USGS Publications Warehouse

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

    1973-01-01

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

  20. 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

  1. 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.

  2. Paleocurrent evidence for lateral displacement of the Pliocene Colorado River delta by the San Andreas fault system, southeastern California

    NASA Astrophysics Data System (ADS)

    Winker, Charles D.; Kidwell, Susan M.

    1986-09-01

    More than 600 paleocurrent measurements from fluvial paleochannels of the early Colorado River delta plain, preserved in the Palm Spring Formation in the Fish Creek Vallecito (FCV) section of southern California, indicate that the FCV section was on the Gulf of California (southeastern) flank of the delta plain as recently as 2.8 Ma. These measurements imply ˜130 km of tectonic translation to the northwest since 2.8 Ma, which can be accounted for by the displacement histories of Baja California and component faults of the San Andreas system. Stratigraphic data from the FCV section and other Neogene localities, when plotted on a palinspastic base, indicate (1) marine transgression of a narrow Gulf of California rift basin and Bouse embayment (site of modern lower Colorado River) by 5.5 Ma, and (2) uplift of the Bouse embayment, initiation of the: lower Colorado River, and southward progradation of the delta to essentially its present position by 4 Ma.

  3. 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

  4. Preliminary Observations of Stress and Fluid Pressure in and Near the San Andreas Fault at Depth in the SAFOD Boreholes

    NASA Astrophysics Data System (ADS)

    Zoback, M. D.; Hickman, S. H.

    2005-12-01

    A variety of observations in the SAFOD pilot hole, drilled in 2002, and the first two Phases of the main SAFOD borehole allow us to place preliminary constraints on the orientations and magnitudes of principal stresses as well as pore pressure at depth. It will be possible to improve these preliminary results once detailed data on the shape of the main hole acquired during Phase 2 (i.e., through the San Andreas fault zone) are fully processed. In addition, the core holes to be drilled during Phase 3 in 2007 will be used to make measurements of the least principal stress via hydraulic fracturing. Stress orientation has been determined from the orientation of wellbore breakouts in both the vertical pilot hole to a depth of 2.2 km and in the deviated portion of the Phase 1 SAFOD hole down to a vertical depth of 2.5 km. These indicate that the maximum horizontal principal stress rotates with depth, attaining a high angle to the San Andreas Fault at depth and consistent with the hypothesis that there are low shear stresses acting on the fault. A similar conclusion was reached based on the direction of shear velocity anisotropy determined from cross-dipole sonic logs conducted in SAFOD during Phase 1 (see abstract by N. Boness and M.D. Zoback). Three hydraulic fracturing tests were carried out to constrain the magnitude of the least principal stress along the trajectory of the SAFOD borehole, at vertical depths of 1.5 km, 2.5 km, and 3.2 km. The 1.5- and 3.2-km-deep tests, which were conducted at distances of about 1.1 km SW and 0.5 km NE, respectively, from the two seismically active traces of the San Andreas identified at this location, indicate that the least principal stress is the vertical stress. In conjunction with modeling of wellbore failure and estimates of rock strength, these tests further indicate a transitional strike-slip/reverse faulting stress state, which is consistent with our earlier stress analyses from the pilot hole. The test at 2.5 km, carried out

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

    USGS Publications Warehouse

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

    2004-01-01

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

  6. "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.

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

    PubMed

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

    2014-11-01

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

  8. 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.

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

    USGS Publications Warehouse

    Brown, Robert D.; Wolfe, Edward W.

    1970-01-01

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

  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. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  14. 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.

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

    USGS Publications Warehouse

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

    2005-01-01

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

  16. 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.

  17. 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%.

  18. 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

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

    USGS Publications Warehouse

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

    2016-07-08

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

  20. 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

  1. 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

  2. [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.

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. A 100-Year Average Recurrence Interval for the San Andreas Fault, Southern San Francisco Bay Area, California

    NASA Astrophysics Data System (ADS)

    Fumal, T. E.; Heingartner, G. F.; Dawson, T. E.; Flowers, R.; Hamilton, J. C.; Kessler, J.; Reidy, L. M.; Samrad, L.; Seitz, G. G.; Southon, J.

    2003-12-01

    Paleoseismic excavations at Mill Canyon and Arano Flat, two sites 0.6 km apart on the San Andreas fault near Watsonville, California, provide the first high-resolution chronology of large earthquakes on the Santa Cruz Mountains segment of the fault. At Mill Canyon, a 2-m-wide zone of faulting has deformed latest Holocene deposits consisting of well-sorted sand and gravel interbedded with poorly sorted, commonly organic-rich debris flows ponded behind a small shutter ridge. We found evidence for the 1906 San Francisco earthquake and three additional ground-rupturing earthquakes since about 1500 A.D.. Radiocarbon ages and pollen analyses indicate that the penultimate earthquake at this site occurred about 1700-1790 A.D.. This indicates that the 1838 San Francisco peninsula earthquake did not rupture this portion of the fault. At Arano Flat, faulting is expressed as a 1 to 2-m-wide zone that deforms alluvial fan deposits overlying well-bedded overbank deposits. We found evidence at this location for at least nine earthquakes since about 1000 A.D. We constrain earthquake ages using a chronological model incorporating AMS radiocarbon ages of 113 samples of detrital charcoal from 19 layers and stratigraphic ordering. The mean recurrence interval is about 105 years, while individual intervals range from about 10-310 years. Two offset features at Arano Flat provide slip-per-event and slip rate data. A partially buried channel containing bottles from 1887-1890 is offset 3.5 m. Given that we found no evidence at either site for the 1890 M 6.3 earthquake, which produced surface rupture on the San Andreas fault southeast of Parajo Gap, this entire slip may have occurred during the 1906 earthquake. This value is unexpectedly high compared to the geodetic estimate of 2.3-3.1 m for the slip at depth (Thatcher et al., 1997) or the geologic estimate of 1.7-1.8 m of surface slip at Wright's tunnel (Prentice and Ponti, 1997), about 33 km northwest of Arano Flat. A fold that formed

  9. 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

  10. Pore fluid ‘ages’ suggest fluid replacement events across the San Andreas Fault at Depth, Parkfield, CA (Invited)

    NASA Astrophysics Data System (ADS)

    Ali, S.; Stute, M.; Torgersen, T.; Hemming, S. R.; Fleisher, M. Q.; Winckler, G.

    2009-12-01

    The presence of aqueous reaction produced low strength mineral surfaces is linked to low friction slip along the San Andreas Fault Zone (SAFZ) as shown in core samples recovered from the San Andreas Fault Observatory at Depth (SAFOD) in Parkfield, CA. These mineral phases are a product of fluid-rock interaction in the fault zone. SAFOD drill cores show multiple zones of alteration and deformation due to fluid-rock interaction (Schleicher et. al, 2008), which requires transport of fluids into the fault zone. We present pore fluid ages, age gradients, as well as 3He and 4He isotope profiles of matrix fluids obtained from drill core samples during SAFOD phases 1, 2, and 3 to constrain fluid flow across the SAFZ. Helium and argon concentration profiles in the pore fluids suggest the fault represents a sink for 3He, 4He and 40Ar. The 3He/4He profile across the SAFZ confirms the mantle helium signature is introduced from the North American Plate side of the SAFOD drillhole and the lack of mantle-derived fluid component through the fault zone. Noble gas measurements on the solid phase indicate that more than 90% of in situ produced He has entered the fluid phase. The presence of mantle-derived He in both plates and the fault zone suggests that the fluids are accumulating both locally produced and externally produced He. Apparent maximum pore fluid ages range from ˜300,000-700,000 years (3050m-measured depth (MD)) in the Pacific Plate and ˜300,000 -500,000 years (3989m-MD) in the North American Plate, compared to relatively younger ages of <200,000 years in the actively creeping trace of the SAFZ at 3300m-MD. The pore fluid ages suggest fluid flow events on these or shorter timescales in the respective zones. Each fluid event results into further dissolution and precipitation in the SAFZ creating a new layer of minerals, which in turn can enhance further slip along the fault.

  11. 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.

  12. 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.

  13. Paleoseismic investigations in the Santa Cruz mountains, California: Implications for recurrence of large-magnitude earthquakes on the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Schwartz, D. P.; Pantosti, D.; Okumura, K.; Powers, T. J.; Hamilton, J. C.

    1998-08-01

    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-1600 s, 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-1600 s. 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-1600 s 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

  14. 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

  15. 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

  16. 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

  17. Late Holocene movement along the San Andreas Fault at Melendy Ranch: Implications for the distribution of fault slip in central California

    NASA Astrophysics Data System (ADS)

    Perkins, James A.; Sims, John D.; Sturgess, Steven S.

    1989-08-01

    An alluvial deposit of the San Benito River at Melendy Ranch, which is located along the creeping segment of the San Andreas fault in central California, records an 800-year-long average slip rate of 22-4+6 mm/yr. The rate is calculated from one radiocarbon age and two measures of displacement and is based on various sedimentologic and stratigraphic data. Numerous other radiocarbon ages were determined for detrital charcoal from the alluvium at Melendy Ranch. These radiocarbon ages appear to be at variance with the age of the alluvium on the basis of sedimentologic and stratigraphic data. The 22 mm/yr long-term rate is similar to the 20-23 mm/yr range of slip rates that are recorded by geodetic instruments at Melendy Ranch and a 22 mm/yr slip rate recorded by an offset corral fence built in 1945. This suggests that the historic rate of movement along the San Andreas fault at Melendy Ranch is near its 800-year average. The long-term slip rate of about 22 mm/yr at Melendy Ranch is 12-5+7 mm/yr less than the long-term rate found along the San Andreas fault south of the creeping segment, and it is greater than the minimum long-term rate of about 12 mm/yr found along the fault north of the creeping segment on the San Francisco Peninsula. Thus the long-term slip-rate data suggest a ˜20 mm/yr northwestward decrease in slip rate along the San Andreas fault. The northwestward decrease in long-term slip rate is attributed to a two-part transfer of slip, south of Hollister, from the San Andreas fault to the Paicines and Calaveras faults. If the Paicines and Calaveras faults south of Hollister have a combined long-term slip rate of about ˜20 mm/yr, then a similar rate may also represent slip across the Calaveras and Hayward faults north of Hollister.

  18. 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

  19. 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.

  20. Ambient Noise Tomography of Southern California Images Dipping San Andreas-Parallel Structure and Low-Velocity Salton Trough Mantle

    NASA Astrophysics Data System (ADS)

    Barak, S.; Klemperer, S. L.; Lawrence, J. F.

    2014-12-01

    Ambient noise tomography (ANT) images the entire crust but does not depend on the spatial and temporal distribution of events. Our ANT high-resolution 3D velocity model of southern California uses 849 broadband stations, vastly more than previous studies, and four years of data, 1997-1998, 2007, and 2011, chosen to include our own broadband Salton Seismic Imaging Project, a 40-station transect across the Salton Trough, as well as other campaign stations in both Mexico and the U.S.A., and permanent stations. Our shear-wave model has 0.05° x 0.05° lateral and 1 km vertical blocks. We used the Harvard Community Velocity Model (CVM-H) as the initial model for the inversion. We show significant differences relative to the CVM-H model, especially in the lower crust and upper mantle. We observe prominent low-velocity anomalies in the upper mantle under the Salton Buttes and Cerro Prieto geothermal fields, indicating high-temperatures and possibly partial-melt. Similar low-velocity zones have been previously observed along the Gulf of California. We also observe vertical to gradually dipping lateral velocity contrasts in the lower crust under the southern part of the San Andreas Fault. The east to northeast dip may represent crustal fabric sheared by movement of the Pacific plate under the North American plate prior to the initiation of transform motion.

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

    USGS Publications Warehouse

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

    2014-01-01

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

  2. 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.

  3. 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.

  4. The ShakeOut scenario: A hypothetical Mw7.8 earthquake on the Southern San Andreas Fault

    USGS Publications Warehouse

    Porter, K.; Jones, L.; Cox, D.; Goltz, J.; Hudnut, K.; Mileti, D.; Perry, S.; Ponti, D.; Reichle, M.; Rose, A.Z.; Scawthorn, C.R.; Seligson, H.A.; Shoaf, K.I.; Treiman, J.; Wein, A.

    2011-01-01

    In 2008, an earthquake-planning scenario document was released by the U.S. Geological Survey (USGS) and California Geological Survey that hypothesizes the occurrence and effects of a Mw7.8 earthquake on the southern San Andreas Fault. It was created by more than 300 scientists and engineers. Fault offsets reach 13 m and up to 8 m at lifeline crossings. Physics-based modeling was used to generate maps of shaking intensity, with peak ground velocities of 3 m/sec near the fault and exceeding 0.5 m/sec over 10,000 km2. A custom HAZUS??MH analysis and 18 special studies were performed to characterize the effects of the earthquake on the built environment. The scenario posits 1,800 deaths and 53,000 injuries requiring emergency room care. Approximately 1,600 fires are ignited, resulting in the destruction of 200 million square feet of the building stock, the equivalent of 133,000 single-family homes. Fire contributes $87 billion in property and business interruption loss, out of the total $191 billion in economic loss, with most of the rest coming from shakerelated building and content damage ($46 billion) and business interruption loss from water outages ($24 billion). Emergency response activities are depicted in detail, in an innovative grid showing activities versus time, a new format introduced in this study. ?? 2011, Earthquake Engineering Research Institute.

  5. 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.

  6. [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

  7. 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.

  8. Assessment of Creep Events as Potential Earthquake Precursors: Application to the Creeping Section of the San Andreas Fault, California

    NASA Astrophysics Data System (ADS)

    Thurber, C.; Sessions, R.

    We report the analysis of over 16 years of fault creep and seismicity data from part of the creeping section of the San Andreas fault to examine and assess the temporal association between creep events and subsequent earthquakes. The goal is to make a long-term evaluation of creep events as a potential earthquake precursor. We constructed a catalog of creep events from available digital creepmeter data and compared it to a declustered seismicity catalog for the area between San Juan Bautista and San Benito, California, for 1980 to 1996. For magnitude thresholds of 3.8 and above and time windows of 5 to 10 days, we find relatively high success rates (40% to 55% 'hits') but also very high false alarm rates (generally above 90%). These success rates are statistically significant (0.0007 < P < 0.04). We also tested the actual creep event catalog against two different types of synthetic seismicity catalogs, and found that creep events are followed closely in time by earthquakes from the real catalog far more frequently than the average for the synthetic catalogs, generally by more than two standard deviations. We find no identifiable spatial pattern between the creep events and earthquakes that are hit or missed. We conclude that there is a significant temporal correlation between creep events and subsequent small to moderate earthquakes, however that additional information (such as from other potential precursory phenomena) is required to reduce the false alarm rate to an acceptable level.

  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. 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.

  11. 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).

  12. Hydrothermal frictional strengths of rock and mineral samples relevant to the creeping section of the San Andreas Fault

    USGS Publications Warehouse

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

    2016-01-01

    We compare frictional strengths in the temperature range 25–250 °C of fault gouge from SAFOD (CDZ and SDZ) with quartzofeldspathic wall rocks typical of the central creeping section of the San Andreas Fault (Great Valley sequence and Franciscan Complex). The Great Valley and Franciscan samples have coefficients of friction, μ > 0.35 at all experimental conditions. Strength is unchanged between 25° and 150 °C, but μ increases at higher temperatures, exceeding 0.50 at 250 °C. Both samples are velocity strengthening at room temperature but show velocity-weakening behavior beginning at 150 °C and stick-slip motion at 250 °C. These rocks, therefore, have the potential for unstable seismic slip at depth. The CDZ gouge, with a high saponite content, is weak (μ = 0.09–0.17) and velocity strengthening in all experiments, and μ decreases at temperatures above 150 °C. Behavior of the SDZ is intermediate between the CDZ and wall rocks: μ < 0.2 and does not vary with temperature. Although saponite is probably not stable at depths greater than ∼3 km, substitution of the frictionally similar minerals talc and Mg-rich chlorite for saponite at higher temperatures could potentially extend the range of low strength and stable slip down to the base of the seismogenic zone.

  13. 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.

  14. [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.

  15. 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.

  16. 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.

  17. 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.

  18. Seismic Documentation for Rock Damage and Heal on the San Andreas Fault Involved in the 2004 M6 Parkfield Earthquake

    NASA Astrophysics Data System (ADS)

    Malin, P. M.; Li, Y.; Chen, P.; Cochran, E. M.; Vidale, J. E.

    2007-12-01

    After the M6 Parkfield earthquake that occurred on 28 September 2004, we deployed a dense seismic array at the same sites as used in our experiment in the fall of 2002. The measurements using moving-window cross- correlation of waveforms for the repeated explosions and microearthquakes recorded in 2002 and 2004 show a decrease in shear velocity of at least ~2.5% within a ~200-m-wide zone across the San Andreas main fault trace most likely owing to co-seismic damage of fault rocks caused by dynamic rupture in this M6 earthquake. The width of the damage zone characterized by larger velocity changes is consistent with the low-velocity waveguide model on the SAF near Parkfield derived from fault-zone trapped waves [Li et al., 2004]. The estimated ratio between the P and S wave traveltime changes is 0.57 within the rupture zone and ~0.65 in the surrounding rocks, indicating wetter cracks within the damaged fault zone, probably due to the ground water percolating into the cracks opened in the mainshock. The measurements of traveltime changes for repeated aftershocks in 21 clusters, with a total of ~130 events, located at different depths along the rupture in 2004 show that the maximum shear velocity increased by ~1.2% within the damage zone in 3.5 months starting a week after the mainshock, indicating that the fault heals in the post-seismic stage due to the closure of cracks in the damaged rock. The data recorded at a seismograph installed in the SAFOD mainhole passing the San Andreas fault zone at ~3-km depths for repeated aftershocks in December of 2004 and later show that seismic velocities within the damage zone were changed by ~0.3% in a month, but no changes were registered at seismographs installed in the vertical pilot borehole drilled ~1.8 km away from the main fault trace for the same repeated events. We find that the healing rate is logarithmically decreasing through time with greater healing rate in the earlier stage after the mainshock. The magnitude of

  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. New constraints on the geometry and evolution of the Southern San Andreas Fault and Salton Pull-apart basin

    NASA Astrophysics Data System (ADS)

    Sahakian, V. J.; Holmes, J. J.; Kell, A. M.; Harding, A. J.; Driscoll, N. W.; Kent, G.

    2013-12-01

    In the recent geologic past, the Salton pull-apart basin, northern Imperial Fault (IF) and Southern San Andreas Fault (SSAF) have been part of an evolving tectonic regime, subject to strain partitioning. This part of the North American/Pacific plate boundary has the potential for generating a large earthquake. Several lines of active-source seismic reflection and refraction data in the Salton Sea were analyzed to better understand the fault interactions and evolution in this region by investigating the SSAF geometry, stratigraphy, and velocity structure. These data, collected in conjunction with the Salton Seismic Imaging Project (SSIP) include two fault-perpendicular lines: one adjacent to the southern terminus of the SSAF (Line 7), and one just south of the terminus (Line 8). We present results from Multi Channel Seismic (MCS) data along Line 7, and refraction data along Lines 7 and 8. Velocity models along these lines were constructed from the refraction data. Included in the Line 7 model is an interface representing a strong reflector observed in the MCS data, which helps to constrain the raypaths and velocities in the model. Line 7 MCS data image stratigraphic layers thickening to and dipping down to the east towards the SSAF, indicative of a westward-dipping, oblique strike-slip fault. The refraction data along this line are consistent with a westward dipping SSAF and a down the west normal component. We present velocity models for Line 7 and 8, as well as resolution tests supporting the fault's geometry. The results from these two lines and a fault parallel line suggest that the SSAF is dipping to the west and is in transtension. We propose that the SSAF has migrated northward through time, partitioning its strain onto the IF. As the IF migrates northwards it forms the Salton pull-apart basin.

  1. 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.

  2. 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.

  3. 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).

  4. 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.

  5. Identifying and locating tectonic tremor beneath the San Andreas Fault near Parkfield, CA, with the PASO array

    NASA Astrophysics Data System (ADS)

    Peterson, D. E.; Thurber, C. H.; Montgomery-Brown, E. D.; Brown, J. R.; Shelly, D. R.

    2011-12-01

    Tectonic tremor is a weak but persistent shaking of the Earth that was first discovered in subduction zones and later found beneath the San Andreas Fault (SAF). Tremor events represent spasmodic slip on the deep extension of the SAF, occurring at a depth of about 20-25 kilometers. Tremor occurs deeper than the nearby regular earthquakes, which can be found at maximum depths of 12-15 kilometers. Tremor is characterized by bursts of low frequency and/or very low frequency earthquakes (LFE/VLF) with dominant energy in the 1-10 Hz range. Tremor tells us about fault slip at depth in both space and time by illuminating the fault down to about the base of the crust. In the pursuit of deriving information about deep fault behavior and crustal structure, we are analyzing continuous data from the previously untapped Parkfield Area Seismic Observatory (PASO) temporary array, operated in 2000-2002 and 2004-2006. We started the identification process by correlating templates of known events from a nearby station array based on an existing catalog of tremor events. Using the dense PASO array and various correlation methods, including autocorrelation (Brown et. al. 2008), a scanning algorithm (Rowe, 2005), and cross correlation of template events (Shelly et al., 2007), we will refine the locations of these known events and seek to identify undiscovered clusters of LFEs and tremor. After generating an updated catalog initially for the month of September 2002, we will use S-wave arrivals from the 59 stations comprising the PASO array to provide strong constraints on the locations of identified events.

  6. 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.

  7. 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.

    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.

  8. Three-dimensional magnetotelluric inversion in practice—the electrical conductivity structure of the San Andreas Fault in Central California

    NASA Astrophysics Data System (ADS)

    Tietze, Kristina; Ritter, Oliver

    2013-10-01

    3-D inversion techniques have become a widely used tool in magnetotelluric (MT) data interpretation. However, with real data sets, many of the controlling factors for the outcome of 3-D inversion are little explored, such as alignment of the coordinate system, handling and influence of data errors and model regularization. Here we present 3-D inversion results of 169 MT sites from the central San Andreas Fault in California. Previous extensive 2-D inversion and 3-D forward modelling of the data set revealed significant along-strike variation of the electrical conductivity structure. 3-D inversion can recover these features but only if the inversion parameters are tuned in accordance with the particularities of the data set. Based on synthetic 3-D data we explore the model space and test the impacts of a wide range of inversion settings. The tests showed that the recovery of a pronounced regional 2-D structure in inversion of the complete impedance tensor depends on the coordinate system. As interdependencies between data components are not considered in standard 3-D MT inversion codes, 2-D subsurface structures can vanish if data are not aligned with the regional strike direction. A priori models and data weighting, that is, how strongly individual components of the impedance tensor and/or vertical magnetic field transfer functions dominate the solution, are crucial controls for the outcome of 3-D inversion. If deviations from a prior model are heavily penalized, regularization is prone to result in erroneous and misleading 3-D inversion models, particularly in the presence of strong conductivity contrasts. A `good' overall rms misfit is often meaningless or misleading as a huge range of 3-D inversion results exist, all with similarly `acceptable' misfits but producing significantly differing images of the conductivity structures. Reliable and meaningful 3-D inversion models can only be recovered if data misfit is assessed systematically in the frequency

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. [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

  18. 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).

  19. [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.

  20. 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

  1. 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).

  2. 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

  3. Coulomb Stress Interactions Among Earthquakes in the Gorda Deformation Zone, the San Andreas, Mendocino Fracture Zone, and Cascadia Megathrust

    NASA Astrophysics Data System (ADS)

    Rollins, C.; Stein, R. S.

    2008-12-01

    During the last 30 years the most prolific source of large earthquakes in the western U.S. has been the Gorda deformation zone, a region of diffuse shear off the coast of northernmost California and southern Oregon. Fifteen M≥6 earthquakes have occurred there since 1980, including M≥7 shocks. The abundance of large earthquakes on different fault systems provides fertile ground for the study of earthquake interaction. We find five strong examples of triggering attributable to static stress transfer. A left- lateral Mw=7.3 earthquake in 1980 promoted slip on the right-lateral Mendocino Fracture Zone (MFZ) in an area where aftershocks were abundant, and inhibited slip on a section of the MFZ where aftershocks were absent. The 1980 earthquake appears to have inhibited slip on the Gorda zone faults except within an off- fault stress trigger lobe where three M≥6 shocks subsequently struck. The Mw=6.9 earthquake at Cape Mendocino in 1992 promoted failure on the rupture planes of Mw=6.5 and Mw=6.6 aftershocks. M≥7 earthquakes in 1994 and 2005 are found to have promoted the rupture of subsequent Mw=6.6 earthquakes. We also calculate that the 1906 San Andreas earthquake promoted slip on the MFZ and left-lateral slip on Gorda deformation zone faults, consistent with the M~5.8 shock offshore Cape Mendocino in 1909 and earthquakes in 1922, 1941 and 1954. However, the 1991 Mw=7.0 earthquake should have inhibited the rupture of the 2005 Mw=7.2 earthquake. There are also examples of earthquakes closely spaced in time that occurred more than two source dimensions apart, the approximate limit of static stress transfer for earthquakes with 30-bar stress-drops. A 16 Aug 1991 Mw=6.3 shock was followed 21 hr later by the 17 Aug event 200 km away; the 17 Aug 1991 Mw=6.1 shock was followed 3 hr later by a Mw=7.0 shock 200 km away; and a 25 Nov 1954 M=6.1 shock was followed 26 days later by a M=6.5 shock 120 km away. Together these counter-examples suggest that dynamic triggering

  4. 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

  5. Salton Seismic Imaging Project Line 5—the San Andreas Fault and Northern Coachella Valley Structure, Riverside County, California

    NASA Astrophysics Data System (ADS)

    Rymer, M. J.; Fuis, G.; Catchings, R. D.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.

    2012-12-01

    The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San Andreas Fault (SAF) and the adjacent basins (Imperial and Coachella Valleys) in southern California. Here, we focus on SSIP Line 5, one of four 2-D NE-SW-oriented seismic profiles that were acquired across the Coachella Valley. The 38-km-long SSIP-Line-5 seismic profile extends from the Santa Rosa Ranges to the Little San Bernardino Mountains and crosses both strands of the SAF, the Mission Creek (MCF) and Banning (BF) strands, near Palm Desert. Data for Line 5 were generated from nine buried explosive sources (most spaced about 2 to 8 km apart) and were recorded on approximately 281 Texan seismographs (average spacing 138 m). First-arrival refractions were used to develop a refraction tomographic velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 8 km depth, P-wave velocities range from about 2 km/s to more than 7.5 km/s, with the lowest velocities within a well-defined (~2-km-deep, 15-km-wide) basin (< 4 km/s), and the highest velocities below the transition from the Coachella Valley to the Santa Rosa Ranges on the southwest and within the Little San Bernardino Mountains on the northeast. The MCF and BF strands of the SAF bound an approximately 2.5-km-wide horst-type structure on the northeastern side of the Coachella Valley, beneath which the upper crust is characterized by a pronounced low-velocity zone that extends to the bottom of the velocity image. Rocks within the low-velocity zone have significantly lower velocities than those to the northeast and the southwest at the same depths. Conversely, the velocities of rocks on both sides of the Coachella Valley are greater than 7 km/s at depths exceeding about 4 km. The relatively narrow zone of shallow high-velocity rocks between the surface traces of

  6. 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

  7. High-Resolution Imaging of San Andreas Fault at Parkfield, California, Using Seismic Velocity and Anisotropy Tomography and Seismic Interferometry

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Thurber, C.; Liu, Y.; Roecker, S.; Lu, R.; Toksoz, N.

    2004-12-01

    We characterized the detailed structure of the San Andreas fault zone at multiple scales using an extensive dataset collected around the SAFOD site from our long-term deployments of PASSCAL and USArray seismic instruments, and the USGS Northern California and UC Berkeley HRSN networks, SAFOD borehole logs, borehole seismometers, and several active-source projects. A suite of techniques are employed to better constrain the internal structure of the fault zone, including seismic travel-time tomography, shear-wave splitting tomography and seismic interferometry. Adaptive-mesh double-difference tomography is used to derive high-resolution Vp and Vs models around the fault zone with the waveform cross-correlation derived differential times. Knowing three-dimensional (3-D) Vp/Vs variations is helpful to have a more complete characterization of the mechanical properties and geological identity of fault zone materials. Vp/Vs variations are reliably determined by the inversion of S-P time differences constructed only from similar P and S ray paths. Our velocity models show the high-velocity granitic rocks on the southwest side of the fault, a complex low-velocity zone beneath and southwest of the surface fault trace, and an extensive low-velocity zone overlying deeper bedrock on the northeast side. We systematically analyzed shear wave splitting for seismic data observed at PASO and UC Berkeley HRSN networks. Although polarization direction of the fast shear wave and the delay time show substantial scatter for different events observed at a common station, there are spatially consistent patterns when projecting them to various depths along corresponding ray paths, derived from a 3-D shear velocity model. We developed a 3-D shear-wave splitting tomography method to image the spatial anisotropy distribution by back projecting shear wave splitting delay times along ray paths. The anisotropy percentage model shows strong heterogeneities, consistent with the strong spatial

  8. High-Resolution Imaging of San Andreas Fault at Parkfield, California, Using Seismic Velocity and Anisotropy Tomography and Seismic Interferometry

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Thurber, C.; Liu, Y.; Roecker, S.; Lu, R.; Toksoz, N.

    2007-12-01

    We characterized the detailed structure of the San Andreas fault zone at multiple scales using an extensive dataset collected around the SAFOD site from our long-term deployments of PASSCAL and USArray seismic instruments, and the USGS Northern California and UC Berkeley HRSN networks, SAFOD borehole logs, borehole seismometers, and several active-source projects. A suite of techniques are employed to better constrain the internal structure of the fault zone, including seismic travel-time tomography, shear-wave splitting tomography and seismic interferometry. Adaptive-mesh double-difference tomography is used to derive high-resolution Vp and Vs models around the fault zone with the waveform cross-correlation derived differential times. Knowing three-dimensional (3-D) Vp/Vs variations is helpful to have a more complete characterization of the mechanical properties and geological identity of fault zone materials. Vp/Vs variations are reliably determined by the inversion of S-P time differences constructed only from similar P and S ray paths. Our velocity models show the high-velocity granitic rocks on the southwest side of the fault, a complex low-velocity zone beneath and southwest of the surface fault trace, and an extensive low-velocity zone overlying deeper bedrock on the northeast side. We systematically analyzed shear wave splitting for seismic data observed at PASO and UC Berkeley HRSN networks. Although polarization direction of the fast shear wave and the delay time show substantial scatter for different events observed at a common station, there are spatially consistent patterns when projecting them to various depths along corresponding ray paths, derived from a 3-D shear velocity model. We developed a 3-D shear-wave splitting tomography method to image the spatial anisotropy distribution by back projecting shear wave splitting delay times along ray paths. The anisotropy percentage model shows strong heterogeneities, consistent with the strong spatial

  9. 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

  10. The microstructural character and evolution of fault rocks from SAFOD and potential weakening mechanisms along the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    van Diggelen, E.; Holdsworth, R. E.; de Bresser, J. H.; Spiers, C.; Smith, S. A.; Walker, R. J.; Bowen, L.

    2010-12-01

    The San Andreas Fault (SAF) forms the boundary between two geological terranes; the Salinian block (SB, Pacific plate) and the Great Valley block (GVB, North American plate). The SB contains arkosic sandstones, the GVB consists mostly of claystones and siltstones. The SAFOD borehole provides an extensive set of samples across the SAF and permits direct study of fault zone processes at 2-3 km depth. In order to determine the fault rock properties and deformation mechanisms in the SAF, in particular in two actively creeping fault segments, we have visually assessed the SAFOD phase 3 core material and we have performed detailed optical and electron microscopy, including chemical analyses using EDX. We compared the natural microstructures with microstructures developed in simulated fault gouges deformed in laboratory experiments. The rocks in Core interval 1 (SB) are mildly deformed and show evidence of cataclasis, pressure solution and reaction of feldspar to form phyllosilicates. Most of Core interval 3 (GVB) is also only mildly deformed, similar to Core interval 1. Sedimentary features are still visible, together with limited evidence for cataclasis, pressure solution and reaction of feldspar to phyllosilicates. The rocks in Core interval 2 (GVB) show ample evidence for micro-folding, foliation development, development of anastomosing shear bands, gouge formation, veining, and reworking of earlier microstructures. In addition, evidence is widespread for cataclasis, pressure solution and reaction of feldspar to form phyllosilicates. The SB and GVB host rocks are cut by numerous minor faults and small calcite-filled veins. Thin foliated gouges contain fine-grained, Fe-rich smectitic phyllosilicates. The development of interconnected networks of these phyllosilicates following cataclasis is prevalent in the inactive gouges. The actively creeping zones in Core intervals 2 and 3 consist mostly of Mg-rich smectitic phyllosilicates and show a strong, wavy foliation, lens

  11. Results of 3-D georadar surveying and trenching: the San Andreas fault near its northern landward limit

    NASA Astrophysics Data System (ADS)

    Green, A.; Gross, R.; Holliger, K.; Horstmeyer, H.; Baldwin, J.

    2003-04-01

    As part of a program to determine the location and geometry of the San Andreas Fault (SAF) buried beneath shallow sediments near its northern landward limit, three >20 m long parallel trenches were constructed at positions distributed over a distance of ˜55 m. The majority of excavated material comprised unconsolidated fluvial sediments deposited in a number of paleochannels. Single zones of active faulting identified in each of the trenches were initially interpreted in terms of a solitary strand of the SAF. To map the SAF between and beyond the trenches and to detect other active fault zones hidden by the young sedimentary cover, we collected a dense ground-penetrating radar (georadar) data set across a 23.2 x 72 m area. The data were recorded using a semi-automated acquisition system that included a conventional georadar unit coupled to a self-tracking laser theodolite with automatic target recognition capabilities. Since these data were plagued by system ringing as a result of the moderate- to high-electrical conductivities of the surficial sediments, an extensive data processing scheme was required to extract meaningful subsurface information. The final processed georadar volume (cuboid) contained numerous subhorizontal and trough-shaped reflections that originated from the fluvial paleochannels. Using the geological interpretation of the trench walls as a guide to pick semi-automatically the times of the most important reflecting horizons, we discovered that alignments of the nearly linear boundaries of these horizons defined two NW-SE trending strands of the SAF within the survey area. The georadar expression of the eastern SAF strand could only be traced over a distance of ˜38 m. It had been intersected in the northern trench. In contrast, the western SAF strand extended over the entire length of the georadar volume and had been intersected in the central and southern trenches. Prominent reflections on georadar cross-sections were found to be vertically

  12. Results of 3-D georadar surveying and trenching the San Andreas fault near its northern landward limit

    NASA Astrophysics Data System (ADS)

    Green, Alan; Gross, Ralf; Holliger, Klaus; Horstmeyer, Heinrich; Baldwin, John

    2003-06-01

    As part of a program to determine the location and geometry of the San Andreas Fault (SAF) buried beneath shallow sediments near its northern landward limit, three >20-m-long parallel trenches were constructed at positions distributed over a distance of ˜55 m. The majority of excavated material comprised unconsolidated fluvial sediments deposited in a number of paleochannels. Single zones of active faulting identified in each of the trenches were initially interpreted in terms of a solitary strand of the SAF. To map the SAF between and beyond the trenches and to detect other active fault zones hidden by the young sedimentary cover, we collected a dense ground-penetrating radar (georadar) data set across a 23.2×72 m area. The data were recorded using a semi-automated acquisition system that included a conventional georadar unit coupled to a self-tracking laser theodolite with automatic target recognition capabilities. Since these data were plagued by system ringing as a result of the moderate-to-high electrical conductivities of the surficial sediments, an extensive data processing scheme was required to extract meaningful subsurface information. The final processed georadar volume (cuboid) contained numerous subhorizontal and trough-shaped reflections that originated from the fluvial paleochannels. Using the geological interpretation of the trench walls as a guide to pick semi-automatically the times of the most important reflecting horizons, we discovered that alignments of the nearly linear boundaries of these horizons defined two NW-SE trending strands of the SAF within the survey area. The georadar expression of the eastern SAF strand could only be traced over a distance of ˜38 m. It had been intersected in the northern trench. In contrast, the western SAF strand extended over the entire length of the georadar volume and had been intersected in the central and southern trenches. Prominent reflections on georadar cross sections were found to be vertically

  13. Photomosaics and event evidence from the Frazier Mountain paleoseismic site, trench 1, cuts 5–24, San Andreas Fault Zone, southern California (2010–2012)

    USGS Publications Warehouse

    Scharer, Katherine M.; Fumal, Tom E.; Weldon, Ray J.; Streig, Ashley R.

    2015-08-24

    The Frazier Mountain paleoseismic site is located within the northern Big Bend of the southern San Andreas Fault (lat 34.8122° N., lon 118.9034° W.), in a small structural basin formed by the fault (fig. 1). The site has been the focus of over a decade of paleoseismic study due to high stratigraphic resolution and abundant dateable material. Trench 1 (T1) was initially excavated as a 50-m long, fault-perpendicular trench crossing the northern half of the basin (Lindvall and others, 2002; Scharer and others, 2014a). Owing to the importance of a high-resolution trench site at this location on a 200-km length of the fault with no other long paleoseismic records, later work progressively lengthened and deepened T1 in a series of excavations, or cuts, that enlarged the original excavation. Scharer and others (2014a) provide the photomosaics and event evidence for the first four cuts, which largely show the upper section of the site, represented by alluvial deposits that date from about A.D. 1500 to present. Scharer and others (2014b) discuss the earthquake evidence and dating at the site within the context of prehistoric rupture lengths and magnitudes on the southern San Andreas Fault. Here we present the photomosaics and event evidence for a series of cuts from the lower section, covering sediments that were deposited from about A.D. 500 to 1500 (fig. 2).

  14. 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.

  15. Photomosaics and event evidence from the Frazier Mountain paleoseismic site, trench 1, cuts 1–4, San Andreas Fault Zone, southern California (2007–2009)

    USGS Publications Warehouse

    Scharer, Katherine M.; Fumal, Tom E.; Weldon, Ray J.; Streig, Ashley R.

    2014-01-01

    The Frazier Mountain paleoseismic site is located at the northwest end of the Mojave section of the San Andreas Fault, in a small, closed depression at the base of Frazier Mountain near Tejon Pass, California (lat 34.8122° N., long 118.9034° W.). The site was known to contain a good record of earthquakes due to previous excavations by Lindvall and others (2002). This report provides data resulting from four nested excavations, or cuts, along trench 1 (T1) in 2007 and 2009 at the Frazier Mountain site. The four cuts were excavated progressively deeper and wider in an orientation perpendicular to the San Andreas Fault, exposing distal fan and marsh sediments deposited since ca. A.D. 1200. The results of the trenching show that earthquakes that ruptured the site have repeatedly produced a small depression or sag on the surface, which is subsequently infilled with sand and silt deposits. This report provides high-resolution photomosaics and logs for the T1 cuts, a detailed stratigraphic column for the deposits, and a table summarizing all of the evidence for ground rupturing paleoearthquakes logged in the trenches.

  16. 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

  17. Spectral Analysis of Localized Stress Variations, the Spatial Distribution of Faults, and the Scaling of Physical Properties near the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Day-Lewis, A.; Zoback, M. D.; Hickman, S. H.

    2005-12-01

    Statistical characterization of stress-induced wellbore failures and rock property heterogeneity from well logs offers potential insight into the scaling properties and mechanisms of stress heterogeneity. Wellbore breakouts identified in acoustic wellbore image data obtained adjacent to the San Andreas Fault, from both the San Andreas Fault Observatory at Depth (SAFOD) and the Cajon Pass Scientific Borehole, reveal multi-scale rotations in the direction of maximum horizontal compressive stress (SHmax) as a function of depth. Similar breakout rotations are frequently observed in other deep wellbores and, in most cases, reflect small variations in the directions and/or magnitudes of the in situ principal stresses superimposed on a relatively uniform regional stress state. To determine possible physical causes for these rotations, we employ spectral and statistical methods to investigate the relationships between the breakout rotations observed in our study wells and stress drops associated with slip on faults in highly fractured crust adjacent to a major fault zone. We also address the possible role of rock property variability as a controlling mechanism, taking into account drilling and data acquisition artifacts. We find that physical property heterogeneity in the SAFOD Pilot Hole behaves as self-similar, flicker noise (i.e., 1/f) over wavelengths from one meter to one kilometer, a result that agrees with similar investigations at Cajon Pass and a variety of other locations throughout the world. The stress orientations in both wells, however, exhibit behavior between that of flicker noise and Brownian motion over wavelengths from one decimeter to several kilometers, which is similar to how earthquake frequency has been shown to scale with fault size. The fractal scaling of observed stress heterogeneity appears to be more closely related to the distribution of faults in the crust adjacent to the study wells than to heterogeneity of elastic or other in-situ physical

  18. 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

  19. 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

  20. Paleoseismic event dating and the conditional probability of large earthquakes on the southern San Andreas fault, California

    USGS Publications Warehouse

    Biasi, G.P.; Weldon, R.J.; Fumal, T.E.; Seitz, G.G.

    2002-01-01

    We introduce a quantitative approach to paleoearthquake dating and apply it to paleoseismic data from the Wrightwood and Pallett Creek sites on the southern San Andreas fault. We illustrate how stratigraphic ordering, sedimentological, and historical data can be used quantitatively in the process of estimating earthquake ages. Calibrated radiocarbon age distributions are used directly from layer dating through recurrence intervals and recurrence probability estimation. The method does not eliminate subjective judgements in event dating, but it does provide a means of systematically and objectively approaching the dating process. Date distributions for the most recent 14 events at Wrightwood are based on sample and contextual evidence in Fumal et al. (2002) and site context and slip history in Weldon et al. (2002). Pallett Creek event and dating descriptions are from published sources. For the five most recent events at Wrightwood, our results are consistent with previously published estimates, with generally comparable or narrower uncertainties. For Pallett Creek, our earthquake date estimates generally overlap with previous results but typically have broader uncertainties. Some event date estimates are very sensitive to details of data interpretation. The historical earthquake in 1857 ruptured the ground at both sites but is not constrained by radiocarbon data. Radiocarbon ages, peat accumulation rates, and historical constraints at Pallett Creek for event X yield a date estimate in the earliest 1800s and preclude a date in the late 1600s. This event is almost certainly the historical 1812 earthquake, as previously concluded by Sieh et al. (1989). This earthquake also produced ground deformation at Wrightwood. All events at Pallett Creek, except for event T, about A.D. 1360, and possibly event I, about A.D. 960, have corresponding events at Wrightwood with some overlap in age ranges. Event T falls during a period of low sedimentation at Wrightwood when conditions

  1. 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

  2. Salton Seismic Imaging Project Line 6: San Andreas Fault and Northern Coachella Valley Structure, Riverside and San Bernardino Counties, California

    NASA Astrophysics Data System (ADS)

    Catchings, R. D.; Fuis, G.; Rymer, M. J.; Goldman, M.; Tarnowski, J. M.; Hole, J. A.; Stock, J. M.; Matti, J. C.

    2012-12-01

    The Salton Seismic Imaging Project (SSIP) is a large-scale, active- and passive-source seismic project designed to image the San Andreas fault (SAF) and adjacent basins (Imperial and Coachella Valleys) in southernmost California. Data and preliminary results from many of the seismic profiles are reported elsewhere (including Fuis et al., Rymer et al., Goldman et al., Langenheim et al., this meeting). Here, we focus on SSIP Line 6, one of four 2-D seismic profiles that were acquired across the Coachella Valley. The 44-km-long, SSIP-Line-6 seismic profile extended from the east flank of Mt. San Jacinto northwest of Palm Springs to the Little San Bernardino Mountains and crossed the SAF (Mission Creek (MCF), Banning (BF), and Garnet Hill (GHF) strands) roughly normal to strike. Data were generated by 10 downhole explosive sources (most spaced about 3 to 5 km apart) and were recorded by approximately 347 Texan seismographs (average spacing 126 m). We used first-arrival refractions to develop a P-wave refraction tomography velocity image of the upper crust along the seismic profile. The seismic data were also stacked and migrated to develop low-fold reflection images of the crust. From the surface to about 7 km depth, P-wave velocities range from about 2.5 km/s to about 7.2 km/s, with the lowest velocities within an ~2-km-deep, ~20-km-wide basin, and the highest velocities below the transition zone from the Coachella Valley to Mt. San Jacinto and within the Little San Bernardino Mountains. The BF and GHF strands bound a shallow sub-basin on the southwestern side of the Coachella Valley, but the underlying shallow-depth (~4 km) basement rocks are P-wave high in velocity (~7.2 km/s). The lack of a low-velocity zone beneath BF and GHF suggests that both faults dip northeastward. In a similar manner, high-velocity basement rocks beneath the Little San Bernardino Mountains suggest that the MCF dips vertically or southwestward. However, there is a pronounced low-velocity zone

  3. 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

  4. Swelling and Thermo-Mechanical Behavior of Smectitic Clay in the San Andreas Fault at Parkfield/California

    NASA Astrophysics Data System (ADS)

    Hofmann, H.; Schleicher, A. M.; van der Pluijm, B. A.

    2011-12-01

    There is growing agreement that smectitic clays play a key role in the behavior of fault rocks from the SAFOD (San Andreas Fault Observatory at Depth) borehole at Parkfield, California. In this study, we focus on the swelling behavior of Mg-rich smectite from the central deformation zone at 3298.4 m, in order to evaluate the occurrence and intake of water in smectite, and its relation to fault zone weakening processes. Understanding swelling behavior is also critical for meaningful laboratory experiments on clay-rich fault rocks. A textured sample of the clay size fraction (< 2 micron) of the sample was measured by X-ray diffraction (XRD) under controlled temperature and humidity conditions, at temperatures of 25°C, 50°C, 75°C, and 95°C, and humidity ranging from 10% Relative Humidity (RH) to 98 %RH. The air-dried sample shows a smectite phase with a characteristic interlayer distance (d-value) of 1.1 nm that increases to 1.4 nm after ethylene glycolization, indicating 1 to 1.5 H2O in the interlayer. With increasing temperatures to 95°C and humidity up to 95 %RH, all samples show similar x-ray patterns, with a stable smectite phase during the entire hydration/heating process. With increasing humidity under isothermal conditions, the hydration of interlayer cations and the particle orientation increases, indicated by increasing d-values and increasing intensities. On the other hand, the intensities under stable humidity and increasing temperature decrease due to lattice distortion and scattering effects. At 25°C and 10 %RH, the sample is a mix of dehydrated smectite (1.1 nm) and 1H2O (1.2 nm) in the interlayer space, which increases to 1.3 nm at 20 % and 30 %RH. Between 30 and 95 %RH, there is a slow transition from 1.3 nm to 1.4 nm (1 H2O to 1.5 H2O). The patterns at 50°C, 75°C and 95°C show similar behavior with slightly lower interlayer spacing. At 95°C, an additional peak appeared with increasing humidity, indicating the formation of an additional

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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.

  10. Pliocene transpressional modification of depositional basins by convergent thrusting adjacent to the "Big Bend" of the San Andreas fault: An example from Lockwood Valley, southern California

    USGS Publications Warehouse

    Kellogg, K.S.; Minor, S.A.

    2005-01-01

    The "Big Bend" of the San Andreas fault in the western Transverse Ranges of southern California is a left stepping flexure in the dextral fault system and has long been recognized as a zone of relatively high transpression compared to adjacent regions. The Lockwood Valley region, just south of the Big Bend, underwent a profound change in early Pliocene time (???5 Ma) from basin deposition to contraction, accompanied by widespread folding and thrusting. This change followed the recently determined initiation of opening of the northern Gulf of California and movement along the southern San Andreas fault at about 6.1 Ma, with the concomitant formation of the Big Bend. Lockwood Valley occupies a 6-km-wide, fault-bounded structural basin in which converging blocks of Paleoproterozoic and Cretaceous crystalline basement and upper Oligocene and lower Miocene sedimentary rocks (Plush Ranch Formation) were thrust over Miocene and Pliocene basin-fill sedimentary rocks (in ascending order, Caliente Formation, Lockwood Clay, and Quatal Formation). All the pre-Quatal sedimentary rocks and most of the Pliocene Quatal Formation were deposited during a mid-Tertiary period of regional transtension in a crustal block that underwent little clockwise vertical-axis rotation as compared to crustal blocks to the south. Ensuing Pliocene and Quaternary transpression in the Big Bend region began during deposition of the poorly dated Quatal Formation and was marked by four converging thrust systems, which decreased the areal extent of the sedimentary basin and formed the present Lockwood Valley structural basin. None of the thrusts appears presently active. Estimated shortening across the center of the basin was about 30 percent. The fortnerly defined eastern Big Pine fault, now interpreted to be two separate, oppositely directed, contractional reverse or thrust faults, marks the northwestern structural boundary of Lockwood Valley. The complex geometry of the Lockwood Valley basin is similar

  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. Coseismic brecciation at fault stepovers and transient fluid pathways in a mid-crustal San Andreas analogue: The Pofadder Shear Zone, Namibia and South Africa

    NASA Astrophysics Data System (ADS)

    Melosh, B. L.; Rowe, C. D.; Gerbi, C. C.

    2015-12-01

    Fluid transport along faults is important throughout the seismic cycle due to the effects on fault strength. Rheological boundaries in the crust such as the quartz brittle-plastic transition coincide with permeability changes, and play an important role in controlling fluid distribution. Here we present a newly recognized mechanism for fluid migration through the brittle-plastic transition in an ancient San Andreas Fault analogue: The Pofadder Shear Zone in Namibia and South Africa. Breccias formed in elongate pods during the passage of an earthquake rupture through a fault stepover. These breccias form subvertical fluid pathways (perpendicular to the slip direction). Over time, many overprinting or adjacent ruptures could have allowed fluid migration over a large (~ kms) scale, facilitating fluid flow through a low porosity region of the crust. These pathways were subsequently closed during breccia compaction by crystal plastic flow, facilitated by the presence of fluids. Thus, fluid migration within and across the brittle-plastic transitional zone is time and rate dependent and can both cause fault weakening and strengthening. We observed breccias formed in slip events with displacements between ~1-15 cm, consistent with small to moderate magnitude earthquakes and/or tectonic tremor, which occurs at similar depths in the San Andreas Fault. In addition to providing a new way of identifying paleo-seismic slip in the rock record, these observations may help explain co- post-seismic fluid advection in mid-crustal faults. This process of local brecciation in stepovers may be the origin of cryptic geophysical signals such as tremor bursts in continental faults.

  14. 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

  15. 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.

  16. Depth-Dependent Low-Velocity Structure of the San Andreas Fault near the SAFOD Drilling Site at Parkfield from Fault-Zone Seismic Waves

    NASA Astrophysics Data System (ADS)

    Alvarez, M.; Li, Y.; Vidale, J.; Cochran, E.

    2004-12-01

    Coordinated by the SAFOD PIs, we used 96 PASSCAL short-period three-component seismometers in linear arrays deployed across and along the San Andreas fault (SAF) near the town of Parkfield and the SAFOD drilling site in 2002 and 2003, respectively. The data recorded for near-surface explosions detonated in the experiments (Li and Vidale), PASO project (Thurber and Roecker) and refraction profiling (Hole), and local earthquakes show fault-zone trapped waves clearly for the source and receivers located close to the fault. The time duration of the dominant trapped energy after S-arrivals increases with the event-to-array distance and focal depth progressively. Using a finite-difference code, we first synthesize fault-zone trapped waves generated by explosions to determine the shallowest 1 or 2 km fault zone structure with the velocity constraints from seismic profiling of the shallow SAF at Parkfield [Catchings et al., 2002]. We then strip shallow effects to resolve deeper structure of the fault zone, and synthesize trapped waves from earthquakes at depths between 2.5 and 11 km to complete a model of the SAF with depth-variable structure in 3-D. We also use the P-first arrivals and polarity as additional information in modeling of velocities and location of the material interface with the structural constraints from seismic tomography at Parkfield [Thurber et al., 2004] to the bed-rock velocities. In grid-search modeling, we tested various values for fault zone depth, width, velocity, Q, and source location. The best-fit model parameters from this study show evidence of a damaged core zone on the main SAF, which likely extends to seismogenic depths. The zone is marked by a low-velocity waveguide ~150 m wide, in which Q is 10-50 and shear velocities are reduced by 30-45% from wall-rock velocities. We also find some seismic energy trapped partitioned in the branching faults that connect to the San Andreas main fault at a shallow depth near Parkfield.

  17. 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

  18. 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

  19. 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

  20. 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

  1. 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.

  2. 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.

  3. 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

  4. 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.

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Flow and Chemistry Pulsations, Monterey: Implications for Stress Transient Modulations of Hydrologic and Geochemical Systems in the Greater San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Brown, K. M.; Fueri, E.; Hilton, D. R.

    2005-12-01

    Submarine fluid venting at continental shelf and slope regions has been recognized over the past ten years as an important, yet under-studied process in marine science. Seeps are now known to be a general feature of the hydrogeology of many tectonically active continental margins. The eastern Pacific margin is characterized by a variety of tectonic settings (i.e. convergent and strike-slip) where active venting of fluids and gases has been documented. Reports include vents off Alaska, Costa Rica, Monterey Bay, Eel River basin, and Heceta Bay, OR. Indications of seismic tremor, linked to hydrologic transience in the offshore regions of subduction zones have recently been published elsewhere (see Brown et al, EPSL 2005). We now address here the varying nature of submarine fluid discharges in a San Andreas strike-slip setting. A key element of the proposed work is the combined multidisciplinary measurement of fluid flow, seep temperatures, and dissolved noble gases and chemistry of the Monterey seep sites at Extrovert Cliff. The seeps are situated close to several active strike-slip faults including the Monterey and San Gregorio fault zones. Initial results of 2 week deployments in 2004 of flow meters at Extravert Cliff indicated high flow rates and elevated seep temperatures that vary by as much as a factor of 2 on diurnal time scales with subtle changes over longer periods (>2 weeks). There are also indicative chemical signals of deeply sourced fluids that vary widely with time that show the following signals: 1) Elevated abundances of both mantle derived Helium (3He) as well as 4He and 40Ar of radiogenic crustal relevant trace element components; 2) Altered fluid chemistry (including, Ca Mg, Li and B); 3) The fluid temperature, flow rates, and gas chemistry, in particular, vary with time. We have both long-term and sub-diurnal variations in flow and temperature as well as the 3He/4He ratios, helium concentration, CO2 concentration and d13C values perhaps influenced

  13. 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 California comprises five branches that exhibit considerable variation in the amount and spatial extent of aseismic release or creep. We estimate the depth extent of creep with a forward elastic model using the algorithms of Okada (1992) and boundary value dislocation solutions for creep rate and depth of creeping patches. For purposes of analysis we label branches, from west to east: A (San Gregorio), B (San Andreas), C (Calaveras-Hayward-Rodgers Creek-Maacama), D (Northern Calaveras-Green Valley-Bartlett Springs) and E (Greenville. Since the 1960s alinement arrays have provided one of the most accurate means to estimate the long-term creep rate and these rates have been reasonably well determined for much of the San Francisco Bay area (SFBA) southward. Over the past decade we have been installing alinement arrays along the more remote faults, especially northward of the SFBA, to monitor the extent of creep on branches C and D. We currently monitor about 80 such arrays throughout the northern SAFS. To analyze the depth extent of creep over the entire system, we model 30 fault sections on these five branches, delineated either by geometric discontinuities between them or by distinctly different creeping behaviors. We have removed any significant transient rate changes imposed by large regional earthquakes. We use crustal velocities determined for global-positioning station pairs of survey mode and continuous (SGPS, CGPS or mixed pairs) that are located near each fault to provide additional constraint on average creep rates. We estimate the mean depth of creep from the mean observed surface creep rate for each section and the rate uncertainty allows estimation of a depth uncertainty. Uncertainties are generally much higher where only five years or less of alinement array data are available, but in some cases the addition of CGPS or multiple SGPS station pairs has been essential for a more complete evaluation of

  14. Fault History and Architecture of the Southernmost San Andreas Fault and Brawley Seismic Zone: New Constraints from CHIRP Data Acquired in the Salton Sea

    NASA Astrophysics Data System (ADS)

    Brothers, D.; Seitz, G.; Williams, P.; Driscoll, N.; Kent, G.

    2006-12-01

    The Salton Trough is the boundary between spreading-center dominated extension in the Gulf of California and dextral strike-slip deformation along the San Andreas Fault (SAF) system. The Salton Trough provides an ideal opportunity to image this transition in modes of deformation. The critical portion of this system, namely the intersection of the SAF and the Brawley Seismic Zone (BSZ) in the southern Salton Sea has not been imaged by geophysical methods. To address this problem, we conducted a pilot, high-resolution seismic CHIRP survey in the Salton Sea offshore Bombay Beach. CHIRP imaging, together with onshore field mapping and paleoseismic investigations, has the potential to define the interaction between the SAF and the BSZ, as well as delineate fault architecture and strain partitioning in the central Salton Trough. Preliminary onshore examination of Lake Cahuilla sediments reveal lake-level changes and earthquake event chronology for the last ~1,000 years, and suggest a relatively long period of seismic quiescence for the southern SAF preceded by several events with shorter recurrence intervals. Fault excavations have revealed several lake episodes separated by terrestrial horizons that include distinct features such as mud-cracks. New CHIRP data show potential correlation of faulted offshore stratigraphy with paleoseismic deformation documented at an excavation site 15 km to the north adjacent to Salt Creek. Profiles image a well-defined fault trending obliquely to the strike of the onshore SAF, and the observed trend is sub-parallel to the BSZ. Offset stratigraphy across the fault imaged in CHIRP profiles increases with depth, with a maximum vertical offset of ~6-8 m. Relief of ~.5 m exists across the post-1905 surface and most likely represents deposition mantling an older scarp. Assuming high amplitude reflectors observed in CHIRP data correlate with lowered lake levels associated with weathering and/or desiccation horizons, then we can correlate the

  15. Compressive and tensile failure at high fluid pressure where preexisting fractures have cohesive strength, with application to the San Andreas fault

    USGS Publications Warehouse

    Fournier, R.O.

    1996-01-01

    In thrusting and strike-slip situations, when the maximum principal horizontal stress S1 acts nearly normal to a fault (a misoriented fault, such as the San Andreas), pore-fluid pressure > the lithostatic load, Pf > Sv, is required to reactivate movement on that fault. Pf > Sv may be achieved without causing hydraulic tensile fracturing if (1) previously existing cracks have regained cohesive strength by chemical processes, (2) subcritical crack growth has been blunted, and (3) the least principal horizontal stress S3 nearly equals Sv. Where Pf > Sv has been attained within a misaligned fault, increasing the stress difference (S1 - S3) at constant Pf > Sv will not lead to shear failure, while a decrease in (S1 - S3) can lead to shear failure of that fault. However, where the cohesive strength of material in a broad misaligned fault zone is less than that of the surrounding intact rock, increasing (S1 - S3) while Pf > Sv can result in shear failure of fractures at near optimum angles to S1, but confined within this weak fault zone. If this faulting results in the local short-lived attainment of Pf > Sv (cataclastic deformation and frictional heating overcoming dilation) and a simultaneous decrease in (S1 - S3), this combination of effects can trigger movement along the main trace of the misaligned fault. When increasing Pf results in hydraulic failure, anisotropy in tensile strength or fracture toughness resulting from foliation within faults allows fractures to propagate along the planes of weakness rather than across the foliation perpendicular to S3.

  16. Thrust-induced collapse of mountains-an example from the "Big Bend" region of the San Andreas Fault, western transverse ranges, California

    USGS Publications Warehouse

    Kellogg, Karl S.

    2005-01-01

    Mount Pinos and Frazier Mountain are two prominent mountains just south of the San Andreas fault in the western Transverse Ranges of southern California, a region that has undergone rapid Quaternary contraction and uplift. Both mountains are underlain, at least in part, by thrusts that place granitic and gneissic rocks over sedimentary rocks as young as Pliocene. Broad profiles and nearly flat summits of each mountain have previously been interpreted as relicts of a raised erosion surface. However, several features bring this interpretation into question. First, lag or stream gravels do not mantle the summit surfaces. Second, extensive landslide deposits, mostly pre?Holocene and deeply incised, mantle the flanks of both mountains. Third, a pervasive fracture and crushed?rock network pervades the crystalline rocks underlying both mountains. The orientation of the fractures, prominent in roadcuts on Mount Pinos, is essentially random. 'Hill?and?saddle' morphology characterizes ridges radiating from the summits, especially on Mount Pinos; outcrops are sparse on the hills and are nonexistent in the saddles, suggesting fractures are concentrated in the saddles. Latest movement on the thrusts underlying the two mountain massifs is probably early Quaternary, during which the mountains were uplifted to considerably higher (although unknown) elevations than at present. A model proposes that during thrusting, ground accelerations in the hanging wall, particularly near thrust tips, were high enough to pervasively fracture the hanging?wall rocks, thereby weakening them and producing essentially an assemblage of loose blocks. Movement over flexures in the fault surface accentuated fracturing. The lowered shear stresses necessary for failure, coupled with deep dissection and ongoing seismic activity, reduced gravitational potential by spreading the mountain massifs, triggering flanking landslides and producing broad, flat?topped mountains. This study developed from mapping in

  17. Imaging the Fine-Scale Structure of the San Andreas Fault in the Northern Gabilan Range with Explosion and Earthquake Sources

    NASA Astrophysics Data System (ADS)

    Xin, H.; Thurber, C. H.; Zhang, H.; Wang, F.

    2014-12-01

    A number of geophysical studies have been carried out along the San Andreas Fault (SAF) in the Northern Gabilan Range (NGR) with the purpose of characterizing in detail the fault zone structure. Previous seismic research has revealed the complex structure of the crustal volume in the NGR region in two-dimensions (Thurber et al., 1996, 1997), and there has been some work on the three-dimensional (3D) structure at a coarser scale (Lin and Roecker, 1997). In our study we use earthquake body-wave arrival times and differential times (P and S) and explosion arrival times (only P) to image the 3D P- and S-wave velocity structure of the upper crust along the SAF in the NGR using double-difference (DD) tomography. The earthquake and explosion data types have complementary strengths - the earthquake data have good resolution at depth and resolve both Vp and Vs structure, although only where there are sufficient seismic rays between hypocenter and stations, whereas the explosions contribute very good near-surface resolution but for P waves only. The original dataset analyzed by Thurber et al. (1996, 1997) included data from 77 local earthquakes and 8 explosions. We enlarge the dataset with 114 more earthquakes that occurred in the study area, obtain improved S-wave picks using an automated picker, and include absolute and cross-correlation differential times. The inversion code we use is the algorithm tomoDD (Zhang and Thurber, 2003). We assess how the P and S velocity models and earthquake locations vary as we alter the inversion parameters and the inversion grid. The new inversion results show clearly the fine-scale structure of the SAF at depth in 3D, sharpening the image of the velocity contrast from the southwest side to the northeast side.

  18. Evolution of the Gorda Escarpment, San Andreas fault and Mendocino triple junction from multichannel seismic data collected across the northern Vizcaino block, offshore northern California

    USGS Publications Warehouse

    Godfrey, N.J.; Meltzer, A.S.; Klemperer, S.L.; Trehu, A.M.; Leitner, B.; Clarke, S.H.; Ondrus, A.

    1998-01-01

    The Gorda Escarpment is a north facing scarp immediately south of the Mendocino transform fault (the Gorda/Juan de Fuca-Pacific plate boundary) between 126??W and the Mendocino triple junction. It elevates the seafloor at the northern edge of the Vizcaino block, part of the Pacific plate, ??? 1.5 km above the seafloor of the Gorda/Juan de Fuca plate to the north. Stratigraphy interpreted from multichannel seismic data across and close to the Gorda Escarpment suggests that the escarpment is a relatively recent pop-up feature caused by north-south compression across the plate boundary. Close to 126??W. the Vizcaino block acoustic basement shallows and is overlain by sediments that thin north toward the Gorda Escarpment. These sediments are tilted south and truncated at the seafloor. By contrast, in a localized region at the eastern end of the Gorda Escarpment, close to the Mendocino triple junction, the top of acoustic basement dips north and is overlain by a 2-km-thick wedge of pre-11 Ma sedimentary rocks that thickens north, toward the Gorda Escarpment. This wedge of sediments is restricted to the northeast corner of the Vizcaino block. Unless the wedge of sediments was a preexisting feature on the Vizcaino block before it was transferred from the North American to the Pacific plate, the strong spatial correlation between the sedimentary wedge and the triple junction suggests the entire Vizcaino block, with the San Andreas at its eastern boundary, has been part of the Pacific plate since significantly before 11 Ma.

  19. Chemical controls on fault behavior: weakening of serpentinite sheared against quartz-bearing rocks and its significance for fault creep in the San Andreas system

    USGS Publications Warehouse

    Moore, Diane E.; Lockner, David A.

    2013-01-01

    The serpentinized ultramafic rocks found in many plate-tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200-350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, µ, of lizardite and antigorite serpentinite is 0.5-0.6, and µ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to µ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution-transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite-bearing crustal faults at otherwise seismogenic depths. During short-term experiments serpentine minerals reprecipitate in low-stress areas, whereas in longer experiments new Mg-rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite-crustal rock contact. Long-term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.

  20. San Andreas Fault dip, Peninsular Ranges mafic lower crust and partial melt in the Salton Trough, Southern California, from ambient-noise tomography

    NASA Astrophysics Data System (ADS)

    Barak, Shahar; Klemperer, Simon L.; Lawrence, Jesse F.

    2015-11-01

    We use ambient-noise tomography to improve CVM-H11.9, a community velocity model of southern California. Our new 3-D shear-velocity model with 0.05° x 0.05° lateral and 1 km vertical blocks reveals new structure beneath the San Andreas Fault (SAF), Peninsular Ranges batholith (PRB), southern Sierra Nevada batholith (SNB), and the Salton Trough (ST). We use 4 years of data recorded on 849 broadband stations, vastly more than previous studies and including our own broadband Salton Seismic Imaging Project, a 40 station transect across the ST, as well as other campaign stations in both Mexico and the United States. Mean lower crust and upper mantle wave speeds (3.6 km/s at 20 km, 4.2 km/s at 40 km) are low by global standards. Across the SAF, southeast of San Gorgonio Pass, we observe vertical to steeply dipping lateral velocity contrasts that extend beneath the Moho. Beneath the western PRB and westernmost southern SNB, we observe relatively high shear velocities (≥3.8 km/s) in the lower crust that we interpret as the mafic roots of the overlying arc. Relatively high-velocity upper mantle (up to ˜4.5 km/s) may be part of the intact arc, or possibly a remnant of the Farallon plate. Beneath the ST, we observe zones of low shear-velocity in the lower crust and upper mantle which permit up to ˜4.5% melt in the lower crust and up to ˜6% melt in the upper mantle, depending on the assumed composition and pore geometry. Our results preclude the existence of older continental crust beneath the ST and support the creation of new crust beneath the ST.

  1. Paleoearthquakes on the southern San Andreas Fault, Wrightwood, California, 3000 to 1500 B.C.: A new method for evaluating paleoseismic evidence and earthquake horizons

    USGS Publications Warehouse

    Scharer, K.M.; Weldon, R.J.; Fumal, T.E.; Biasi, G.P.

    2007-01-01

    We present evidence of 11-14 earthquakes that occurred between 3000 and 1500 B.C. on the San Andreas fault at the Wrightwood paleoseismic site. Earthquake evidence is presented in a novel form in which we rank (high, moderate, poor, or low) the quality of all evidence of ground deformation, which are called "event indicators." Event indicator quality reflects our confidence that the morphologic and sedimentologic evidence can be attributable to a ground-deforming earthquake and that the earthquake horizon is accurately identified by the morphology of the feature. In four vertical meters of section exposed in ten trenches, we document 316 event indicators attributable to 32 separate stratigraphic horizons. Each stratigraphic horizon is evaluated based on the sum of rank (Rs), maximum rank (Rm), average rank (Ra), number of observations (Obs), and sum of higher-quality event indicators (Rs>1). Of the 32 stratigraphic horizons, 14 contain 83% of the event indicators and are qualified based on the number and quality of event indicators; the remaining 18 do not have satisfactory evidence for further consideration. Eleven of the 14 stratigraphic horizons have sufficient number and quality of event indicators to be qualified as "probable" to "very likely" earthquakes; the remaining three stratigraphic horizons are associated with somewhat ambiguous features and are qualified as "possible" earthquakes. Although no single measurement defines an obvious threshold for designation as an earthquake horizon, Rs, Rm, and Rs>1 correlate best with the interpreted earthquake quality. Earthquake age distributions are determined from radio-carbon ages of peat samples using a Bayesian approach to layer dating. The average recurrence interval for the 10 consecutive and highest-quality earthquakes is 111 (93-131) years and individual intervals are ??50% of the average. With comparison with the previously published 14-15 earthquake record between A.D. 500 and present, we find no evidence

  2. Using a modified time-reverse imaging technique to locate low-frequency earthquakes on the San Andreas Fault near Cholame, California

    USGS Publications Warehouse

    Horstmann, Tobias; Harrington, Rebecca M.; Cochran, Elizabeth S.

    2015-01-01

    We present a new method to locate low-frequency earthquakes (LFEs) within tectonic tremor episodes based on time-reverse imaging techniques. The modified time-reverse imaging technique presented here is the first method that locates individual LFEs within tremor episodes within 5 km uncertainty without relying on high-amplitude P-wave arrivals and that produces similar hypocentral locations to methods that locate events by stacking hundreds of LFEs without having to assume event co-location. In contrast to classic time-reverse imaging algorithms, we implement a modification to the method that searches for phase coherence over a short time period rather than identifying the maximum amplitude of a superpositioned wavefield. The method is independent of amplitude and can help constrain event origin time. The method uses individual LFE origin times, but does not rely on a priori information on LFE templates and families.We apply the method to locate 34 individual LFEs within tremor episodes that occur between 2010 and 2011 on the San Andreas Fault, near Cholame, California. Individual LFE location accuracies range from 2.6 to 5 km horizontally and 4.8 km vertically. Other methods that have been able to locate individual LFEs with accuracy of less than 5 km have mainly used large-amplitude events where a P-phase arrival can be identified. The method described here has the potential to locate a larger number of individual low-amplitude events with only the S-phase arrival. Location accuracy is controlled by the velocity model resolution and the wavelength of the dominant energy of the signal. Location results are also dependent on the number of stations used and are negligibly correlated with other factors such as the maximum gap in azimuthal coverage, source–station distance and signal-to-noise ratio.

  3. Potential and limits of InSAR to characterize interseismic deformation independently of GPS data: Application to the southern San Andreas Fault system

    NASA Astrophysics Data System (ADS)

    Chaussard, E.; Johnson, C. W.; Fattahi, H.; Bürgmann, R.

    2016-03-01

    The evaluation of long-wavelength deformation associated with interseismic strain accumulation traditionally relies on spatially sparse GPS measurements, or on high spatial-resolution InSAR velocity fields aligned to a GPS-based model. In this approach the InSAR contributes only short-wavelength deformation and the two data sets are dependent, thereby challenging the evaluation of the InSAR uncertainties and the justification of atmospheric corrections. Here we present an analysis using 7 years of Envisat InSAR data to characterize interseismic deformation along the southern San Andreas Fault (SAF) and the San Jacinto Fault (SJF) in southern California, where the SAF bifurcates onto the Mission Creek (MCF) and the Banning (BF) fault strands. We outline the processing steps for using InSAR alone to characterize both the short- and long-wavelength deformation, and evaluate the velocity field uncertainties with independent continuous GPS data. InSAR line-of-sight (LOS) and continuous GPS velocities agree within ˜1-2 mm/yr in the study area, suggesting that multiyear InSAR time series can be used to characterize interseismic deformation with a higher spatial resolution than GPS. We investigate with dislocation models the ability of this mean LOS velocity field to constrain fault slip rates and show that a single viewing geometry can help distinguish between different slip-rate scenarios on the SAF and SJF (˜35 km apart) but multiple viewing geometries are needed to differentiate slip on the MCF and BF (<12 km apart). Our results demonstrate that interseismic models of strain accumulation used for seismic hazards assessment would benefit from the consideration of InSAR mean velocity maps.

  4. Time-dependent model of aseismic slip on the central San Andreas Fault from InSAR time series and repeating earthquakes

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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 small characteristically repeating earthquakes (CREs) show pulses of creep along the CSAF, which may indicate spatially and temporally variable seismic hazard along the CSAF. Therefore, the goal of this study is to obtain a high-resolution time-dependent model of creep along the CSAF to examine this hypothesis. To this end, we apply a time-dependent creep modeling approach, which combines interferometric synthetic aperture radar (InSAR) surface deformation time series and observations of fault creep obtained from CREs. The SAR data set includes C band scenes acquired by the ERS-2 and Envisat satellites between 2003 and 2011. The resulting creep rate distribution implies a peak rate up to 32 mm/yr along the central part of the CSAF. Afterslip due to the 2004 Parkfield earthquake on the southeastern segment of the CSAF is also manifest in the model, and there is clear evidence of creep pulsing along strike and depth of the CSAF. Estimated annual rate of slip deficit accumulation is equivalent to a magnitude 5.6-5.7 earthquake. Taking advantage of the time-dependence of our model, we also refine the scaling relationship, which associates the released seismic moment due to a CRE event with the amount of creep on the fault, surrounding the CRE patches. This study provides the first kinematic model of creep pulsing, constrained using geodetic and seismic data, which can enhance time-dependent seismic hazard maps and improve earthquake operational forecast models.

  5. Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: Observations in groundwaters along the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Deeds, Daniel A.; Kulongoski, Justin T.; Mühle, Jens; Weiss, Ray F.

    2015-02-01

    Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (Cre; ∼30 fmol kg-1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1-9 times Cre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10-980 times Cre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20-100 km) suggests that the SAFS potentially emits (0.3- 1) ×10-1 kg CF4 yr-1 to the Earth's surface. For comparison, the chemical weathering of ∼ 7.5 ×104km2 of granitic rock in California is estimated to release (0.019- 3.2) ×10-1 kg CF4 yr-1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial-interglacial transitions.

  6. How can tidally modulated low-frequency earthquakes in the mid crust along the San Andreas Fault be reconciled with its shallow apparent locking depth?

    NASA Astrophysics Data System (ADS)

    Hearn, E. H.

    2014-12-01

    Earthquake-cycle models for major strike-slip faults suggest that stationary, localized interseismic deformation and large-scale, rapidly decaying postseismic transients may be reconciled if a strong lithosphere, a low-viscosity mantle asthenosphere and a largely aseismic shear zone extending from the brittle-ductile transition to the mantle asthenosphere are incorporated. Localized late interseismic deformation around major strike-slip faults seems to call for a "stiff" shear zone (maintaining shear stresses of at least several MPa) in the lower crust and mantle lithosphere, and rapid postseismic deformation requires that part of the shear zone (likely in the mid crust) should have a low effective viscosity per unit width, at least during the postseismic interval (Yamasaki et al., 2014, Hearn and Thatcher, 2014). Recent paleoseismological studies suggest a preponderance of M 7.3 to 7.7 earthquakes during the past 650 years along the 1857 rupture segment of the San Andreas Fault (SAF), with just two events comparable in magnitude to the 1857 earthquake (Scharer et al., 2014). Very low shear stresses (less than 0.001 MPa) and a frictional rheology have also been inferred along the northern part of this segment between depths of 16 and 29 km, based on tidal triggering of low-frequency earthquakes (Beeler et al., 2013). I have refined my 3D viscoelastic finite-element earthquake-cycle models to address whether extremely low SAF-parallel shear stresses in the mid crust can be reconciled with localized and invariant interseismic deformation (and an apparent locking depth of 16-18 km) if earthquakes are smaller and more frequent than assumed by Hearn and Thatcher (2014). Results from models incorporating frictional afterslip and viscous shear zone creep will be presented for a small set of plausible rupture histories that take smaller earthquakes into account.

  7. New insights on stress rotations from a forward regional model of the San Andreas fault system near its Big Bend in southern California

    USGS Publications Warehouse

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

    2004-01-01

    Understanding the stress field surrounding and driving active fault systems is an important component of mechanistic seismic hazard assessment. We develop and present results from a time-forward three-dimensional (3-D) model of the San Andreas fault system near its Big Bend in southern California. The model boundary conditions are assessed by comparing model and observed tectonic regimes. The model of earthquake generation along two fault segments is used to target measurable properties (e.g., stress orientations, heat flow) that may allow inferences on the stress state on the faults. It is a quasi-static model, where GPS-constrained tectonic loading drives faults modeled as mostly sealed viscoelastic bodies embedded in an elastic half-space subjected to compaction and shear creep. A transpressive tectonic regime develops southwest of the model bend as a result of the tectonic loading and migrates toward the bend because of fault slip. The strength of the model faults is assessed on the basis of stress orientations, stress drop, and overpressures, showing a departure in the behavior of 3-D finite faults compared to models of 1-D or homogeneous infinite faults. At a smaller scale, stress transfers from fault slip transiently induce significant perturbations in the local stress tensors (where the slip profile is very heterogeneous). These stress rotations disappear when subsequent model earthquakes smooth the slip profile. Maps of maximum absolute shear stress emphasize both that (1) future models should include a more continuous representation of the faults and (2) that hydrostatically pressured intact rock is very difficult to break when no material weakness is considered. Copyright 2004 by the American Geophysical Union.

  8. Loading Rate-Dependent Elastoviscoplasticity in San Andreas Fault Observatory at Depth (SAFOD) Fault Gouge: Implications for Repeating Earthquakes and Fault Zone-Guided Waves

    NASA Astrophysics Data System (ADS)

    Kohli, A. H.; Lockner, D. A.

    2015-12-01

    Deformation experiments on phyllosilicate-rich fault gouges reveal velocity-strengthening behavior and monotonic strength evolution in response to perturbations in slip velocity below ~10-4 ms-1. Fault gouge from the actively creeping zones at the San Andreas Fault Observatory at Depth (SAFOD) exhibits similar monotonic strength evolution and has been described in terms of rate-state friction-velocity dependence and ageing behavior. While these parameters provide phenomenological descriptions of gouge rheology on relatively short timescales, they are commonly applied in numerical simulations of repeating earthquakes within the SAF creeping section, often being adjusted arbitrarily in order to match seismological observations. With first assuming a deformation constitutive law, we performed comprehensive microstructural and mechanical characterization of fault gouge from the SAFOD Central Deforming Zone (CDZ). An in-situ displacement sensor was developed to provide direct measurements of gouge deformation under various loading conditions, including constant and variable strain rate and constant and variable shear stress. Constant and variable strain-rate tests confirm previous observations of low shear strength and reveal viscoplastic deformation below the frictional yield strength. Variable loading rate tests demonstrate an apparent yield stress for viscoplastic behavior at low loading rates, and a transition to elastic behavior with increasing loading rate up to 0.02 MPas-1. The elastic response of the gouge constrains the static shear modulus ~500 MPa, providing a lower bound of ~450 ms-1 for the shear velocity of the SAFOD fault core. Our microstructural and mechanical characterization of the gouge is consistent with the physical interpretation of an elastically perfect elastoviscoplastic solid. Parameterizing this model with our experimental data demonstrates general agreement with the observed loading rate-dependence of the gouge and provides a physical

  9. Timing of large earthquakes during the past 500 years along the Santa Cruz Mountains segment of the San Andreas fault at Mill Canyon, near Watsonville, California

    USGS Publications Warehouse

    Fumal, Thomas E.

    2012-01-01

    A paleoseismic investigation across the Santa Cruz Mountains section of the San Andreas fault at Mill Canyon indicates that four surface‐rupturing earthquakes have occurred there during the past ~500  years. At this site, right‐lateral fault slip has moved a low shutter ridge across the mouth of the canyon, ponding latest Holocene sediments. These alluvial deposits are deformed along a narrow zone of faulting. There is excellent evidence for a 1906 (M 7.8) and three earlier earthquakes consisting of well‐developed fissures, scarps, and colluvial wedges. Deformation resulting from the earlier earthquakes is comparable to that from 1906, suggesting they also were large‐magnitude events. The earthquake prior to 1906 occurred either about A.D. 1750 (1711–1770) or A.D. 1855 (1789–1904), depending on assumptions incorporated into two alternative OxCal models. If the later age range is correct, then the earthquake may have been a historical early‐to‐mid‐nineteenth‐century earthquake, possibly the A.D. 1838 earthquake. Both models are viable, and there is no way to select one over the other with the available data. Two earlier earthquakes occurred about A.D. 1690 (1660–1720) and A.D. 1522 (1454–1605). Using OxCal, recalculation of the age of the reported penultimate earthquake reported from the Grizzly Flat site, located about 10 km northwest of Mill Canyon, indicates it occurred about A.D. 1105–1545, earlier than any of the past three earthquakes, and possibly correlates to the fourth earthquake at Mill Canyon.

  10. Deformation Band Shear Zones Formed in Unconsolidated Sediment From Repeated Late Holocene Coseismic Deformation Along the 1906 Rupture Trace of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Baldwin, J. N.; Cashman, S. M.; Crawford, R.; Deis, A.; Cashman, K. V.

    2005-12-01

    Two trenches were excavated across the 1906 rupture trace of the San Andreas Fault (SAF) at Alder Creek, near Manchester, CA, in Mendocino County for the purpose of structural and microstructural analysis of deformed late Holocene unconsolidated sediment. The site records coseismic rupture in the form of upward terminations of deformation band faults and written historical accounts of the 1906 rupture directly adjacent to the site. Based on the age of the deposits exposed and paleoseismic record of the northern SAF, as many as three to five surface faulting events have occurred, including ~5 m of dextral displacement during the 1906 earthquake. Deformation band shear zones, 2-20mm thick, form an upward-branching 1-2m. wide array of splay faults developed in unconsolidated silt and very fine- to medium-grained sand. Vertical displacement on individual deformation band faults is generally <5cm. Microstructural characteristics (porosity, grain size, grain orientation) of oriented samples collected at ~ 2 m in depth were measured in thin section using image analysis of SEM backscatter images. Porosity estimated from SEM images is slightly lower in deformation bands (39.0±1.8%) than in sand in the same horizon several m. from the fault (42.9±0.9%) or in 1-5 mm wide sand lenses bracketed by deformation bands (42.9±2.0%). Deformation band samples contain significantly more very fine and fine sand, and less medium and coarse sand, than samples collected from the same horizon several m. from the fault. Grain size distributions record grain size reduction from grain fracturing within deformation bands. Also, fractured grains in sand adjacent to deformation bands and angular to acicular small grains within deformation bands attest to grain breakage accompanying development of deformation bands. All horizontal samples show a strong preferred orientation of elongate grains. Clustering of grain long axis orientations is more pronounced in deformation band faults than in sand

  11. Constraints on Shallow Crustal Structure across the San Andreas Fault Zone, Coachella Valley, Southern California: Results from the Salton Seismic Imaging Project (SSIP)

    NASA Astrophysics Data System (ADS)

    Hernandez, A.; Persaud, P.; Bauer, K.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.

    2015-12-01

    The strong influence of basin structure and crustal heterogeneities on seismic wave propagation suggests that these factors should be included in calculations of strong ground shaking. Knowledge of the shallow subsurface is thus essential for an accurate seismic hazard estimate for the densely populated Coachella Valley, the region north of the potential M7.8 rupture near the Salton Sea. Using SSIP data, we analyzed first arrivals from nine 65-911 kg explosive shots recorded along a profile in the Coachella Valley in order to evaluate the interpretation of our 2D tomographic results and give added details on the structural complexity of the shallow crust. The line extends 37 km from the Peninsular Ranges to the Little San Bernardino Mountains crossing the major strands of the San Andreas Fault Zone. We fit traveltime curves to our picks with forward modeling ray tracing, and determined 1D P-wave velocity models for traveltime arrivals east and west of each shot, and a 2D model for the line. We also inferred the geometry of near-vertical faults from the pre-stack line migration method of Bauer et al. (2013). In general, the 1D models east of individual shots have deeper basement contacts and lower apparent velocities, ~5 km/s at 4 km depth, whereas the models west of individual shots have shallower basement and velocities up to 6 km/s at 2 km depth. Mismatches in basement depths (assuming 5-6 km/s) between individual 1D models indicate a shallowly dipping basement, deepening eastward towards the Banning Fault and shoaling abruptly farther east. An east-dipping structure in the 2D model also gives a better fit than horizontal layers. Based on high velocity zones derived from traveltimes at 9-20 km from the western end of the line, we included an offset from ~2 km to 4 km depth near the middle of the line, which significantly improved the 2D model fit. If fault-related, this offset could represent the Garnet Hill Fault if it continues southward in the subsurface.

  12. Variable earthquake recurrence on the Northern San Andreas fault over the past 3,000 years at the Vedanta marsh site, Olema, CA (Invited)

    NASA Astrophysics Data System (ADS)

    Niemi, T. M.

    2010-12-01

    The Vedanta marsh trench site is located along the San Andreas fault (SAF) near the town of Olema approximately 45 km north of San Francisco. Excavations into the Vedanta marsh provided exposures of the sediment across the SAF zone that preserves a nearly continuous earthquake record over the past 3,000 years. Evidence for thirteen earthquakes was identified from the main fault zone based on fault outward splays, fault upward terminations, fissures, colluvial wedges, and soft-sediment deformation. The deposits exposed in the trenches contain abundant organic material including peat, charcoal, and macrofossils such as wood, twigs, and leaves. In order to constrain the age of the deposits and prehistoric earthquakes, we radiocarbon-dated 132 samples. Many of the layers in the marsh contain organic materials with ages that range from hundreds to several thousands of years. Except for the peat that accumulates in-situ, most of the organic materials are detrital, washed in from the surrounding forests with long-lived species such as Douglas fir trees that grow to 400 years old. The age of the pre-1906 seismic events are defined by an age model using the OxCal radiocarbon analysis program. This model incorporated 66 of the original 132 dates, about one-half which is common for studies using dates on detrital materials. The paleoseismic record is most complete for the youngest seven earthquakes where faulting was documented in the upper portion of multiple trench exposures. The penultimate event likely occurred sometime during the interval of AD 1650-1735. The average recurrence interval for the past 1,000 years for the youngest seven earthquakes is ~ 140 years with a range of 79 to 220 years. However, when we consider the stratigraphic section back to approximately 1000 B.C., the longest recurrence time between the mean age of the seismic events is 488 years and the shortest is 40 years. These data yield an average earthquake recurrence time of about 240 years. Either

  13. High Resolution Interseismic Velocity Model of the San Andreas Fault System From a Joint Inversion of GPS and InSAR Data

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Geodetic observations along the plate boundary have been used to constrain moment accumulation rate and stressing rate of active faults during the interseismic period. We compared 4 of these interseismic velocity models of the San Andreas Fault System (SAFS) based on GPS observations [Mccaffrey, 2005; Meade and Hager, 2005; Smith-Konter and Sandwell, 2009; Zeng and Shen, 2010]. The standard deviations of these 4 models are larger north of the Bay Area, near the Creeping segment in Central California, and along the San Jacinto fault and the Eastern California Shear Zone in Southern California. A coherence spectrum analysis indicates relatively high correlation among the 4 models at longer wavelengths (>15-40 km), with lower correlation at shorter wavelengths. To improve the short-wavelength accuracy of our GPS-derived interseismic velocity model, we integrated InSAR observations, initially from ALOS ascending data (spanning from the middle of 2006 to the end of 2010, totaling more than 1100 interferograms), using a Sum/Remove/Filter/Restore (SURF) approach. The final InSAR line-of-site (LOS) data match the point GPS observations with a mean absolute deviation of 1.3 mm/yr. These new LOS data were subsampled according to the magnitude of the strain rate and are available at ftp://topex.ucsd.edu/pub/SAF_models/insar/sample.tar We use this high-resolution InSAR LOS data, combined with geological slip rate constraints and secular GPS vectors to invert for the fault slip rate of 50 active fault segments in California using a 3-D viscoelastic earthquake cycle model. This model simulates interseismic deformation resulting from deep slip on faults extending from a prescribed locking depth to the bottom of an elastic plate which overlies the viscoelastic half-space [Smith-Konter and Sandwell, 2009]. The linear least squares problem is solved by Singular Value Decomposition (SVD) and the uncertainties are estimated using covariance matrix of the solution parameters. In this

  14. S-wave triggering of tremor beneath the Parkfield, California, section of the San Andreas fault by the 2011 Tohoku, Japan earthquake: observations and theory

    USGS Publications Warehouse

    Hill, David P.; Peng, Zhigang; Shelly, David R.; Aiken, Chastity

    2013-01-01

    The dynamic stresses that are associated with the energetic seismic waves generated by the Mw 9.0 Tohoku earthquake off the northeast coast of Japan triggered bursts of tectonic tremor beneath the Parkfield section of the San Andreas fault (SAF) at an epicentral distance of ∼8200  km. The onset of tremor begins midway through the ∼100‐s‐period S‐wave arrival, with a minor burst coinciding with the SHSH arrival, as recorded on the nearby broadband seismic station PKD. A more pronounced burst coincides with the Love arrival, followed by a series of impulsive tremor bursts apparently modulated by the 20‐ to 30‐s‐period Rayleigh wave. The triggered tremor was located at depths between 20 and 30 km beneath the surface trace of the fault, with the burst coincident with the S wave centered beneath the fault 30 km northwest of Parkfield. Most of the subsequent activity, including the tremor coincident with the SHSH arrival, was concentrated beneath a stretch of the fault extending from 10 to 40 km southeast of Parkfield. The seismic waves from the Tohoku epicenter form a horizontal incidence angle of ∼14°, with respect to the local strike of the SAF. Computed peak dynamic Coulomb stresses on the fault at tremor depths are in the 0.7–10 kPa range. The apparent modulation of tremor bursts by the small, strike‐parallel Rayleigh‐wave stresses (∼0.7  kPa) is likely enabled by pore pressure variations driven by the Rayleigh‐wave dilatational stress. These results are consistent with the strike‐parallel dynamic stresses (δτs) associated with the S, SHSH, and surface‐wave phases triggering small increments of dextral slip on the fault with a low friction (μ∼0.2). The vertical dynamic stresses δτd do not trigger tremor with vertical or oblique slip under this simple Coulomb failure model.

  15. Near-Surface San Andreas Fault Location and Dip Near Woodside, California From Tomographic Vp, Vs, and Vp/Vs Ratios

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The slip history of the San Andreas Fault (SAF) on the San Francisco peninsula is not well determined, and paleoseismic investigations to date yield inconsistent results, possibly because previous measurements were made on differing near-surface traces of the SAF. Furthermore, ground-shaking modeling requires accurate shallow-depth S-wave velocities across the fault zone and accurate fault dips; the existing Bay Area 3-D velocity models lack such measurements. To locate all near-surface traces of the SAF within 150 m of the 1906 surface rupture, to determine near-surface shear-wave velocities (VS30 to VS100), and to determine the fault dip, the USGS acquired a set of 300-m-long, high-resolution, P- and S-wave seismic imaging profiles across the SAF near Woodside, California, centered on the 1906 surface rupture zone. Sources (seisgun and hammer) and receivers (40-Hz P-wave and 4.5-Hz S-wave) were spaced at 3-m intervals. We developed independent P- and S-wave tomographic velocity models to depths of ~ 120 m (P-waves) and 80 m (S-waves). P-wave velocities vary widely from near the surface (Vp = 800 m/s, Vs = 250) to 100 m depth (Vp > 3000 m/s, Vs > 500 m/s). The 1906 surface rupture zone forms P- and S-wave low-velocity zones (Vp = 1600 to 1800 m/s; Vs = 250 to 350 m/s) within the fault zone relative to outside the fault zone (Vp = 2000 to 2200 m/s; Vs = 300 to 400 m/s). Vp/Vs ratios range from about 2.8 to about 5.7, with higher ratios on either side of the 1906 surface rupture zone and on the uphill (southwest) side. Southwest-dipping Vp/Vs contours suggest a 60o-southwest dip for one of the fault traces. However, a CDP reflection stack shows a near-vertical dip of the main 1906 rupture zone to 1.2 km depth, and the stack shows evidence for multiple fault traces. Collectively, these new data show a complex fault structure and highly variable velocities across the fault zone, which should aid paleoseismic investigations and improve existing ground-shaking models.

  16. Onset and Mechanisms of Surface Creep on Strike Slip Faults: Clues from the North Anatolian Fault and Comparisons with the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Cakir, Z.; Ergintav, S.; Akoglu, A. M.; Cetin, E.; Meghraoui, M.; Reilinger, R. E.

    2014-12-01

    Aseismic fault slip was first reported over forty years ago along some major strike slip faults including the San Andreas (SAF) and North Anatolian faults (NAF). Yet both their origin and timing on active faults and underlying physical processes remain subjects of debate. The presence of weak minerals and/or trapped fluid overpressures within fault zones have been proposed as mechanics for aseismic fault creep. Our InSAR observations together with GPS measurements and geology along the NAF provide new evidence for the mechanism, characteristics, and initiation of fault surface creep. We have used the persistent scatterer InSAR (PS-InSAR) technique to investigate both the creeping section of the NAF at Ismetpaşa that had ruptured during the 1944 and 1951 earthquakes, and the postseismic era of the 1999 İzmit Earthquake. The results reveal that the central segment of the 1999 Izmit Earthquake rupture has been creeping for over for the past 15 years since the event, becoming the longest lasting afterslip ever recorded. The slip pattern of ongoing surface creep on the İzmit rupture supports the idea that stable fault creep can be initiated as postseismic afterslip, a mechanism we proposed previously but could not have confirmed due to the lack of pre- and post-earthquake observations on creeping faults such as the Ismetpaşa segment of the NAF and the segments of the SAF in the San Francisco Bay area. Geological maps along the Ismetpaşa and Izmit creeping segments show that both fault zones run through ophiolitic and calcareous rocks with phyllosilicates that probably result in fault weakening. Earthquake rupture maps and PS-InSAR velocity fields for these regions also reveal that the creeping faults have simple geometry being fairly rectilinear and continuous along their strike. These common features suggest that following a large earthquake, a stable surface creep can be triggered on a section of a mature fault if it has evolved in to simple geometry and is

  17. Tectonic activity as a significant source of crustal tetrafluoromethane emissions to the atmosphere: observations in groundwaters along the San Andreas Fault

    USGS Publications Warehouse

    Deeds, Daniel A.; Kulongoski, Justin T.; Muhle, Jens; Weiss, Ray F.

    2015-01-01

    Tetrafluoromethane (CF4) concentrations were measured in 14 groundwater samples from the Cuyama Valley, Mil Potrero and Cuddy Valley aquifers along the Big Bend section of the San Andreas Fault System (SAFS) in California to assess whether tectonic activity in this region is a significant source of crustal CF4 to the atmosphere. Dissolved CF4 concentrations in all groundwater samples but one were elevated with respect to estimated recharge concentrations including entrainment of excess air during recharge (CreCre; ∼30 fmol kg−1 H2O), indicating subsurface addition of CF4 to these groundwaters. Groundwaters in the Cuyama Valley contain small CF4 excesses (0.1–9 times CreCre), which may be attributed to an in situ release from weathering and a minor addition of deep crustal CF4 introduced to the shallow groundwater through nearby faults. CF4 excesses in groundwaters within 200 m of the SAFS are larger (10–980 times CreCre) and indicate the presence of a deep crustal flux of CF4 that is likely associated with the physical alteration of silicate minerals in the shear zone of the SAFS. Extrapolating CF4 flux rates observed in this study to the full extent of the SAFS (1300 km × 20–100 km) suggests that the SAFS potentially emits (0.3–1)×10−1 kg(0.3–1)×10−1 kg CF4 yr−1 to the Earth's surface. For comparison, the chemical weathering of ∼7.5×104 km2∼7.5×104 km2 of granitic rock in California is estimated to release (0.019–3.2)×10−1 kg(0.019–3.2)×10−1 kg CF4 yr−1. Tectonic activity is likely an important, and potentially the dominant, driver of natural emissions of CF4 to the atmosphere. Variations in preindustrial atmospheric CF4 as observed in paleo-archives such as ice cores may therefore represent changes in both continental weathering and tectonic activity, including changes driven by variations in continental ice cover during glacial–interglacial transitions.

  18. Time-dependent Model of Aseismic slip on the Central San Andreas Fault from InSAR Time Series and Repeating Earthquakes

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    The Central segment of the San Andreas Fault (CSAF) is characterized by a nearly continuous right-lateral aseismic slip. Geodetic observations of surface deformation along CSAF indicate interseismic strain accumulation with a rate of about 10 mm/yr. The creep rates obtained using Characteristic Repeating Earthquakes (CRE) show pulses of creep affecting most of the CSAF, suggesting spatiotemporal variability of seismic hazard. Therefore, a high resolution time-dependent model of creep on the CSAF can greatly enhance the knowledge of aseismic and seismic faulting processes as well as the seismic hazard estimates. We used InSAR surface deformation time series in conjunction with observations of fault creep obtained from CRE. The SAR data set includes C-band scenes acquired by the ERS-2 and Envisat during period 2003-2011, comprising 46 images, resulted in about 150 interferograms. Within the same observation period, the CRE data set includes more than 630 repeating sequences. Understanding the spatiotemporal distribution of creep, we implement a time-dependent modeling scheme, allowing us to jointly invert the surface deformation time series and CRE estimates of the fault creep.The distribution of obtained creep rate on the CSAF includes features similar to that reported in earlier works. The map of long-term slip rate reveals that fastest creep rate occurs at the central part of CSAF with an average rate of 27 mm/yr, which is less than the long-term shearing rate. Moving northwestward, the slip rate gradually drops to less than half of its long-term rate. The spatiotemporal map of the creep includes unique features such as afterslip due to the 2004 Parkfield earthquake affecting the southeastern part of the CSAF and the clear evidence of creep pulsing along strike and depth of the CSAF with a period of 1.5 to 2 years. Considering 34.5 mm/yr as the long-term shearing rate, the zone of afterslip is characterized by relaxation time of about 16.35 years. The moment

  19. Particle size distributions, microstructures and chemistry of fault rocks in a shallow borehole adjacent to the San Andreas Fault near Little Rock, CA

    NASA Astrophysics Data System (ADS)

    Wechsler, N.; Chester, J. S.; Rockwell, T. K.; Ben-Zion, Y.

    2009-12-01

    In mapping the distribution of fractured crystalline rocks along the Mojave section of the San Andreas Fault (SAF), Dor et al. (2006) found that almost all rocks within 50 to 200 m from the fault are pulverized to some degree. In an effort to characterize the role of surface weathering, and quantify the mesoscale and microscale deformation of these rocks as a function of depth in the shallow subsurface environment, we have collected a nearly continuous, 42 meter-deep core from the pulverized adjacent to the main strand of the SAF near Little Rock, California. The Little Rock site is characterized by extensive outcrops of granitic rock displaying varying degrees of damage up to a few hundreds of meters from the fault’s primary active strand. The cored section primarily is composed of pulverized granites and granodiorites, and is cut by numerous mesoscopic secondary shears. Medium to coarse silt- and fine sand-size particles dominate throughout the cored section; very few micron-scale particles are observed and only minor amounts of clay weathering products are present. Mapping on optical and SEM images of core samples at various depths and magnifications defines the distribution of two main fault rock types, pulverized zones displaying primarily opening-mode fractures, and cataclastic fault zones. The pulverized regions display large host-rock crystals that are fractured to produce angular particles often ranging from 10-100 microns in diameter. The fractured parts display optical continuity and a high density of fluid inclusion trails suggesting episodes of fracture healing. The cataclastic zones are characterized by smaller (0.5-10 microns) and more rounded grains, a greater clay content, and sometimes show repeated stages of calcite cementation and shear. The distribution of pulverized particles and cataclastic zones indicate multiple fracture-healing cycles to produce an outcrop that reduces to powder when dug out with a hammer. Most samples analyzed to date

  20. Volatile fluxes through the Big Bend section of the San Andreas Fault, California: helium and carbon-dioxide systematics

    USGS Publications Warehouse

    Kulongoski, Justin T.; Hilton, David R.; Barry, Peter H.; Esser, Bradley K.; Hillegonds, Darren; Belitz, Kenneth

    2013-01-01

    To investigate the source of volatiles and their relationship to the San Andreas Fault System (SAFS), 18 groundwater samples were collected from wells near the Big Bend section of the SAFS in southern California and analyzed for helium and carbon abundance and isotopes. Concentrations of 4He, corrected for air-bubble entrainment, vary from 4.15 to 62.7 (× 10− 8) cm3 STP g− 1 H2O. 3He/4He ratios vary from 0.09 to 3.52 RA (where RA = air 3He/4He), consistent with up to 44% mantle helium in samples. A subset of 10 samples was analyzed for the major volatile phase (CO2) — the hypothesized carrier phase of the helium in the mantle–crust system: CO2/3He ratios vary from 0.614 to 142 (× 1011), and δ13C (CO2) values vary from − 21.5 to − 11.9‰ (vs. PDB). 3He/4He ratios and CO2 concentrations are highest in the wells located in the Mil Potrero and Cuddy valleys adjacent to the SAFS. The elevated 3He/4He ratios are interpreted to be a consequence of a mantle volatile flux though the SAFS diluted by radiogenic He produced in the crust. Samples with the highest 3He/4He ratios also had the lowest CO2/3He ratios. The combined helium isotope, He–CO2 elemental relationships, and δ13C (CO2) values of the groundwater volatiles reveal a mixture of mantle and deep crustal (metamorphic) fluid origins. The flux of fluids into the seismogenic zone at high hydrostatic pressure may cause fault rupture, and transfer volatiles into the shallow crust. We calculate an upward fluid flow rate of 147 mm a− 1 along the SAFS, up to 37 times higher than previous estimates (Kennedy et al., 1997). However, using newly identified characteristics of the SAFS, we calculate a total flux of 3He along the SAFS of 7.4 × 103 cm3 STP a− 1 (0.33 mol 3He a− 1), and a CO2 flux of 1.5 × 1013 cm3STP a− 1 (6.6 × 108 mol a− 1), ~ 1% of previous estimates. Lower fluxes along the Big Bend section of the SAFS suggest that the flux of mantle volatiles alone is insufficient to cause the

  1. Crustal strain near the big bend of the San Andreas fault: Analysis of the Los Padres-Tehachapi trilateration networks, California

    SciTech Connect

    Eberhart-Phillips, D.; Lisowski, M. ); Zoback, M.D. )

    1990-02-10

    In the region of the Los Padres-Tehachapi geodetic network, the San Andreas fault (SAF) changes its orientation by over 30{degree} from N 40{degree}W, close to that predicted by plate motion for a transform boundary, to N 73{degree}W. The strain orientation near the SAF is consistent with right-lateral shear along the fault, with maximum shear rate of 0.38 {plus minus} 0.01 {mu}rad/yr at N 63{degree}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 {plus minus} 0.01 {mu}rad/yr at N 44{degree}W. The strain rate does not drop off rapidly away from the fault, and thus the area is fit by either a broad shear zone below the SAF or a single fault with a relatively deep locking depth. The fit to the line length data is poor for locking depth d less than 25 km. For d of 25 km a buried slip rate of 30 {plus minus} 6 mm/yr is estimated. The authors also estimated buried slip for models that include the Garlock and Big Pine faults, in addition to the SAF. Slip rates on other faults are poorly constrained by the Los Padres-Tehachapi network. The best fitting Garlock fault model had computed left-lateral slip rate of 11 {plus minus} 2 mm/yr below 10 km. Buried left-lateral slip of 15 {plus minus} 6 mm/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. The authors investigated the location of the SAF and found that a vertical fault below the surface trace fits the data much better than either a dipping fault zone located south of the surface trace.

  2. Structural and Geochemical Characterization of Fault-related Deformation in the Northeastern Block of the Southern San Andreas Fault, Mecca Hills, Southern California

    NASA Astrophysics Data System (ADS)

    Keighley Bradbury, K.; Evans, J. P.; Moser, A. C.; Schulthies, S. A.

    2015-12-01

    We examine the structure and composition of several subsidiary NE-trending faults of the Southern San Andreas Fault (SSAF) within the Mecca Hills, southern California. The Hidden Springs, Platform, Eagle Canyon and related smaller faults are part of a positive flower structure that forms a broad zone of fault-related damage within the northeastern block of the SSAF. Here active creep is localized along the main trace of SSAF during the interseismic period. Exhumed exposures span a wide-range of rock types and fault-related rocks and juxtapose Tertiary to Quaternary sedimentary rocks against variable aged crystalline and meta-sedimentary rocks. Detailed characterization of the textural, compositional, and geochemical aspects of the fault-related rocks, and analyses of variations across the 2 faults and related damage zones use a combination of field, microstructural, XRD, XRF, SEM, and isotope methods. Evidence for multiple episodes of slip and fluid flow with a wide range of orientations and amounts of slip is recorded by the geometry and distribution of slip surfaces, cataclasite, reworked cataclasite, deformed and reworked veins, multiple generations of breccia, iron oxide stained gouge, and hematite coated fracture and slip surfaces. Alteration phases vary between fault surfaces and may include chlorite-serpentine, clays (±illite, ±palygorskite), quartz, calcite, ankerite, zeolites, iron oxides, and/or sulfides, or some combination thereof, suggestive of complex fluid-rock reactions. Millimeter-thin slip surfaces within the crystalline rocks consist of plastically deformed and highly sheared calcite. Major vein systems include a predominately north-northwest striking quartz set, a north-south striking calcite set, and an east-west striking calcite set, where locally these sets are complexly interwoven, finely interlayered with other minerals, and/or brecciated rocks. Slip lineations on fault surfaces 1-5 m2 with calcite±clay coated surfaces exhibit multiple

  3. Insights into Surface Manifestation of Aseismic vs. Coseismic Strike-Slip Faulting from UAV Imagery of Creep-Induced Surface Fracturing Along the Central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Bunds, M. P.; Toke, N. A.; Lawrence, A.; Arrowsmith, R.; Salisbury, J. B.

    2015-12-01

    Left-stepping en echelon fractures formed at the Dry Lake Valley paleoseismic site (DLV, 36.470N, 121.057W) on the central creeping segment of the San Andreas Fault (SAF) during the 2012-14 drought. The fractures were investigated using high resolution DEMs and orthophotos made by applying Structure from Motion processing to photos taken using a UAV and handheld cameras on 9/20/2014. At DLV the SAF is marked by a distinctive 2-7 m high west-facing scarp that extends northwestward from a dilational step-over. The orthophotos and DEMs were used to measure 110 fractures along a 37 m section of scarp and 15 additional fracture sets along a further 79 m of scarp. The fractures averaged 54 cm long by 1.8 cm wide with 22% overlap, and were mode 1 opening fractures that on average trended 184o, nearly perpendicular to the maximum extension direction for right-lateral slip along the 144o - trending SAF. The fractures occurred in ~5 m long sets that were themselves left-stepping, on average trended 159o, and were confined to a 3-4 m wide zone along the fault scarp. We interpret the fracture sets to be incipient Riedel shears with a component of extension across them based on the orientation of the sets relative to the SAF, the obliquity of the individual fractures to the trend of the sets, and the presence of topographic lows along them. We conservatively estimate 2.5 ± 1 cm of right-lateral creep on the SAF was recorded in the opening of the fractures, which probably began forming at most 21 months before the photographic survey based on precipitation records and prior site inspection. From these results and the 2.5-3.2 cm/yr creep rate for the SAF, we infer that at least ~30%, and probably 50-80% or more of creep occurs along the narrow 5-50 m wide primary geomorphic expression of the fault, and that the same amount of creep can be accommodated by brittle fracturing in a narrow 3-4 m wide zone along the fault scarp during drought periods. In comparison to seismically

  4. Insights into Surface Manifestation of Aseismic vs. Coseismic Strike-Slip Faulting from UAV Imagery of Creep-Induced Surface Fracturing Along the Central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Bunds, M. P.; Toke, N. A.; Lawrence, A.; Arrowsmith, R.; Salisbury, J. B.

    2014-12-01

    Left-stepping en echelon fractures formed at the Dry Lake Valley paleoseismic site (DLV, 36.470N, 121.057W) on the central creeping segment of the San Andreas Fault (SAF) during the 2012-14 drought. The fractures were investigated using high resolution DEMs and orthophotos made by applying Structure from Motion processing to photos taken using a UAV and handheld cameras on 9/20/2014. At DLV the SAF is marked by a distinctive 2-7 m high west-facing scarp that extends northwestward from a dilational step-over. The orthophotos and DEMs were used to measure 110 fractures along a 37 m section of scarp and 15 additional fracture sets along a further 79 m of scarp. The fractures averaged 54 cm long by 1.8 cm wide with 22% overlap, and were mode 1 opening fractures that on average trended 184o, nearly perpendicular to the maximum extension direction for right-lateral slip along the 144o - trending SAF. The fractures occurred in ~5 m long sets that were themselves left-stepping, on average trended 159o, and were confined to a 3-4 m wide zone along the fault scarp. We interpret the fracture sets to be incipient Riedel shears with a component of extension across them based on the orientation of the sets relative to the SAF, the obliquity of the individual fractures to the trend of the sets, and the presence of topographic lows along them. We conservatively estimate 2.5 ± 1 cm of right-lateral creep on the SAF was recorded in the opening of the fractures, which probably began forming at most 21 months before the photographic survey based on precipitation records and prior site inspection. From these results and the 2.5-3.2 cm/yr creep rate for the SAF, we infer that at least ~30%, and probably 50-80% or more of creep occurs along the narrow 5-50 m wide primary geomorphic expression of the fault, and that the same amount of creep can be accommodated by brittle fracturing in a narrow 3-4 m wide zone along the fault scarp during drought periods. In comparison to seismically

  5. Social vulnerability analysis of earthquake risk using HAZUS-MH losses from a M7.8 scenario earthquake on the San Andreas fault

    NASA Astrophysics Data System (ADS)

    Noriega, G. R.; Grant Ludwig, L.

    2010-12-01

    Natural hazards research indicates earthquake risk is not equitably distributed. Demographic differences are significant in determining the risks people encounter, whether and how they prepare for disasters, and how they fare when disasters occur. In this study, we analyze the distribution of economic and social losses in all 88 cities of Los Angeles County from the 2008 ShakeOut scenario earthquake. The ShakeOut scenario earthquake is a scientifically plausible M 7.8 scenario earthquake on the San Andreas fault that was developed and applied for regional earthquake preparedness planning and risk mitigation from a compilation of collaborative studies and findings by the 2007 Working Group on California Earthquake Probabilities (WGCEP). The scenario involved 1) developing a realistic scenario earthquake using the best available and most recent earthquake research findings, 2) estimation of physical damage, 3) estimation of social impact of the earthquake, and 4) identifying changes that will help to prevent a catastrophe due to an earthquake. Estimated losses from this scenario earthquake include 1,800 deaths and $213 billion dollars in economic losses. We use regression analysis to examine the relationship between potential city losses due to the ShakeOut scenario earthquake and the cities' demographic composition. The dependent variables are economic and social losses calculated in HAZUS-MH methodology for the scenario earthquake. The independent variables -median household income, tenure and race/ethnicity- have been identified as indicators of social vulnerability to natural disasters (Mileti, 1999; Cutter, 2006; Cutter & Finch, 2008). Preliminary Ordinary Least Squares (OLS) regression analysis of economic losses on race/ethnicity, income and tenure, indicates that cities with lower Hispanic population are associated with lower economic losses. Cities with higher Hispanic population are associated with higher economic losses, though this relationship is

  6. Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike-slip faults

    USGS Publications Warehouse

    Lin, J.; Stein, R.S.

    2004-01-01

    We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nunez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust-faulting events on the periphery of the seismic rupture and its downdip extension. These features are evident in aftershocks of the 1957 Mw = 9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw = 9.5 and 1995 Mw = 8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2-20 bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We also argue that slip on major strike-slip systems modulates the stress acting on nearby thrust and strike-slip faults. We calculate that the 1857 Mw = 7.9 Fort Tejon earthquake on the San Andreas fault and subsequent interseismic slip brought

  7. Isotopic evidence for the infiltration of mantle and metamorphic CO2-H2O fluids from below in faulted rocks from the San Andreas Fault System

    SciTech Connect

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

    2010-12-15

    To characterize the origin of the fluids involved in the San Andreas Fault (SAF) system, we carried out an isotope study of exhumed faulted rocks from deformation zones, vein fillings and their hosts and the fluid inclusions associated with these materials. Samples were collected from segments along the SAF system selected to provide a depth profile from upper to lower crust. In all, 75 samples from various structures and lithologies from 13 localities were analyzed for noble gas, carbon, and oxygen isotope compositions. Fluid inclusions exhibit helium isotope ratios ({sup 3}He/{sup 4}He) of 0.1-2.5 times the ratio in air, indicating that past fluids percolating through the SAF system contained mantle helium contributions of at least 35%, similar to what has been measured in present-day ground waters associated with the fault (Kennedy et al., 1997). Calcite is the predominant vein mineral and is a common accessory mineral in deformation zones. A systematic variation of C- and O-isotope compositions of carbonates from veins, deformation zones and their hosts suggests percolation by external fluids of similar compositions and origin with the amount of fluid infiltration increasing from host rocks to vein to deformation zones. The isotopic trend observed for carbonates in veins and deformation zones follows that shown by carbonates in host limestones, marbles, and other host rocks, increasing with increasing contribution of deep metamorphic crustal volatiles. At each crustal level, the composition of the infiltrating fluids is thus buffered by deeper metamorphic sources. A negative correlation between calcite {delta}{sup 13}C and fluid inclusion {sup 3}He/{sup 4}He is consistent with a mantle origin for a fraction of the infiltrating CO{sub 2}. Noble gas and stable isotope systematics show consistent evidence for the involvement of mantle-derived fluids combined with infiltration of deep metamorphic H{sub 2}O and CO{sub 2} in faulting, supporting the involvement of

  8. First Long-Term slip-Rate Along the San Andreas Fault Based on 10Be-26Al Surface Exposure Dating : The Biskra Palms Site, 23 mm/yr for the last 30,000 years.

    NASA Astrophysics Data System (ADS)

    van der Woerd, J.; Klinger, Y.; Sieh, K.; Tapponnier, P.; Ryerson, F.

    2001-12-01

    Slip-rate along the San Andreas fault is known precisely at only two locations : at Wallace Creek, 34 +/- 3 mm/yr for the past 13,500 yrs and at Cajon Creek, 24.5+/- 3 mm/yr for the past 14,500 yrs. When compared to the long-term and far-field plate motion, these rates provide important constraint on how and where strain is accommodated across the plate boundary. Here we present a new determination of the slip-rate along the San Andreas Fault at Biskra Palms, based on 10Be-26Al surface exposure dating. The studied area is located southeast of the San Gorgonio restraining bend, a complex section of the fault which has not produced a large earthquake in historical time. At Biskra Palms, the San Andreas Fault offsets an alluvial fan (T2) about 700 m. Keller et al. (1982) recognized the importance of this site and estimated the age of the offset fan surfaces based on degree of soil development between 20 and 70 kyrs, providing a very loosely constraint slip-rate between 10 and 35 mm/yr. We have analyzed 21 quartz rich cobbles from the surface of the fan, upstream, downstream and within the fault zone. 10Be and 26Al measurements yield consistent results implying simple exposure at the surface. 7 samples collected on the T2 fan surface downstream yield an average exposure age of 30.7 +/- 2.1 kyrs. The tight cluster of these ages indicate no or minor pre-exposition during transport in the small catchment upstream. 7 samples from T2 upstream from the fault yield an average exposure age of 29.5 +/- 2.8 kyrs. One additional sample of this surface (38.4+/-3.6 kyrs) is older than the others and may have been pre-exposed before deposition on the fan. 2 samples from a T2 remnant within the fault zone yield an average age of 29.6 +/- 2.6 kyrs. 4 additional samples were collected from two smaller alluvial surfaces (T3 and T4) remnant found only upstream from the fault zone and yield average ages of 33.3 and 27.3 kyrs that are similar to the age of T2. This suggest that these

  9. TRMM Sees Tropical Storm Andrea

    NASA Video Gallery

    The TRMM image showed most of the rain was well ahead of the center of circulation. A broad area of light (shown in blue) to moderate rain (shown in green) covers the eastern half of Georgia and al...

  10. Andreas Vesalius--the work.

    PubMed

    Cobolet, Guy; Garrison, Dan; Vons, Jacqueline; Velut, Stéphane; Nutton, Vivian; Williams, David J

    2014-01-01

    This session focuses on the Fabrica (1543). Karger Publishers of Basel are producing a new English translation, by Daniel Garrison and Malcom Hast, to coincide with the quincentenary while Vivian Nutton's scholarly analysis of a newly discovered second edition indicates that the annotations are of Vesalius himself. PMID:25181777

  11. Andreas Vesalius--the work.

    PubMed

    Cobolet, Guy; Garrison, Dan; Vons, Jacqueline; Velut, Stéphane; Nutton, Vivian; Williams, David J

    2014-01-01

    This session focuses on the Fabrica (1543). Karger Publishers of Basel are producing a new English translation, by Daniel Garrison and Malcom Hast, to coincide with the quincentenary while Vivian Nutton's scholarly analysis of a newly discovered second edition indicates that the annotations are of Vesalius himself.

  12. Holocene slip rates along the San Andreas Fault System in the San Gorgonio Pass and implications for large earthquakes in southern California.

    NASA Astrophysics Data System (ADS)

    Heermance, R. V., III; Yule, D.

    2015-12-01

    Since the late 17th century the San Andreas Fault (SAF) in southern California has produced three large (M7.3-7.8) earthquakes that did not break through San Gorgonio Pass (SGP). This pass-as-a-barrier behavior can be explained by the complexity of the SAF system. Here the fault splays and rotates into a series of en-echelon, oblique-dextral thrusts. In the center of SGP two sub-parallel thrusts are 1.5 km apart (the northern (NF) and southern (SF) splays), and form well-preserved fault scarps (up to 15 m high) in at least 3 alluvial fan terraces formed on the Millard Canyon fan. New, 10Be cosmogenic depth profiles and boulder exposure ages constrain the ages of the two oldest Holocene fan surfaces (Qt4, Qt3) to 8900 (range: 7300-11600) and 8300 (range: 6800-10300) y.b.p.. Radiocarbon ages constrain the younger surface (Qt2) at ~1500 y.b.p.. Qt4 contains a 10.5-15.1 m high scarp along the SF and has an uplift rate of 0.9-2.1 mm/yr. Qt3 is inset 1.5 m within Qt4, and contains a 3.6-6.2 m high scarp on the SF and 2.9-5.3 m high scarp on the NF with 0.4-0.9 mm/yr and 0.3-0.8 mm/yr uplift rates, respectively. Qt2 is inset ~4 m within Qt3, and contains a 1.0-2.9 m high scarp on the NF with a 0.9-2.4 mm/yr uplift rate. Using measured fault dips of 45 (NF) and 20-30 (SF) degrees combined with a slip vector inferred from regional GPS data and 2:1 lateral to thrust offset markers, we calculate the net oblique slip rate on these faults at Millard Canyon at 2.1-4.8 mm/yr for Qt4 and 1.0-2.7 mm/yr for Qt3 (SF), and 0.8-2.2 mm/yr for Qt3 and 1.9-6.8 mm/yr for Qt2 (NF). The cumulative slip rate across Millard Canyon (SF+NF) is therefore 1.8-11.6 mm/yr, or more narrowly constrained at 4.0-5.9 mm/yr by using only the overlapping slip rates along each fault strand. An average slip rate of ~5 mm/yr is ~30-70% of the slip rates outside of SGP. This 'slip deficit' may reflect some combination of slip carried by faults within in the San Bernardino Mountains to the north, transferred

  13. Analysis of nonvolcanic tremor on the San Andreas Fault near Parkfield, CA using U.S. Geological Survey Parkfield Seismic Array

    USGS Publications Warehouse

    Fletcher, Jon B.; Baker, Lawrence M.

    2010-01-01

    Reports by Nadeau and Dolenc (2005) that tremor had been detected near Cholame Valley spawned an effort to use UPSAR (U. S. Geological Survey Parkfield Seismic Array) to study characteristics of tremor. UPSAR was modified to record three channels of velocity at 40–50 sps continuously in January 2005 and ran for about 1 month, during which time we recorded numerous episodes of tremor. One tremor, on 21 January at 0728, was recorded with particularly high signal levels as well as another episode 3 days later. Both events were very emergent, had a frequency content between 2 and 8 Hz, and had numerous high-amplitude, short-duration arrivals within the tremor signal. Here using the first episode as an example, we discuss an analysis procedure, which yields azimuth and apparent velocity of the tremor at UPSAR. We then provide locations for both tremor episodes. The emphasis here is how the tremor episode evolves. Twelve stations were operating at the time of recording. Slowness of arrivals was determined using cross correlation of pairs of stations; the same method used in analyzing the main shock data from 28 September 2004. A feature of this analysis is that 20 s of the time series were used at a time to calculate correlation; the longer windows resulted in more consistent estimates of slowness, but lower peak correlations. These values of correlation (peaks of about 0.25), however, are similar to that obtained for the S wave of a microearthquake. Observed peaks in slowness were traced back to source locations assumed to lie on the San Andreas fault. Our inferred locations for the two tremor events cluster near the locations of previously observed tremor, south of the Cholame Valley. Tremor source depths are in the 14–24 km range, which is below the seismogenic brittle zone, but above the Moho. Estimates of error do not preclude locations below the Moho, however. The tremor signal is very emergent but contains packets that are several times larger than the

  14. Stratigraphic Record of Basin Formation, Deformation, and Destruction in the Past 2 Ma Along the Southern San Andreas Fault, Mecca Hills, California

    NASA Astrophysics Data System (ADS)

    McNabb, J. C.; Dorsey, R. J.; Housen, B. A.; Messe, G. T.

    2013-12-01

    Sedimentary rocks exposed in the Mecca Hills NE of Coachella Valley, southern California, record vertical crustal motions along the San Andreas (SAF) and associated strike-slip faults. A complex history of subsidence, transport, deposition, and uplift can be interpreted from mapping and measuring of sedimentary rocks, lithofacies analysis, and determination of provenance. Recent field studies suggest a poly-phase history of deformation and sedimentation for the stratigraphy in the Mecca Hills that is likely controlled by evolution of fault zone complexities. The Painted Canyon Fault (PCF), a reverse-oblique strike-slip fault sub-parallel to the SAF, has played a major role in basin formation and inversion over the past ca. 2 Myr. Deformation near the PCF coincides with deviations in fault strike relative to modern plate motion, and sedimentation appears to have been largely controlled by vertical motions accommodated by slip on the PCF. Preliminary magnetostratigraphic work provides tentative depositional age brackets. We infer that the Mecca Conglomerate, a locally derived cobble-boulder conglomerate with ~SSW directed paleoflow, was deposited near the PCF scarp during an early phase of SW-side down slip from ~1.8-1.5 Ma. Next, the Lower Palm Spring Formation, a regionally uniform unit of interbedded coarse fluvial sandstone and overbank siltstone with SSE directed paleoflow, appears to have been deposited during limited vertical motion on the PCF from ~1.5-1.2 Ma. We find that the base of the Upper Palm Spring Formation (~1.2 Ma) records the inversion of the PCF to a SW-side up oblique strike-slip fault based on the following: the contact between the Lower and Upper Palm Spring Formation is an angular unconformity throughout the Mecca Hills; large (km's) and small (10's m) scale syntectonic (growth) strata within the Upper Palm Spring; clasts of Lower Palm Spring reworked into the Upper Palm Spring Fm; and pronounced contrast between facies of the Upper Palm

  15. A New Estimate for Total Offset on the Southern San Andreas Fault: Implications for Cumulative Plate Boundary Shear in the Northern Gulf of California

    NASA Astrophysics Data System (ADS)

    Darin, M. H.; Dorsey, R. J.

    2012-12-01

    Development of a consistent and balanced tectonic reconstruction for the late Cenozoic San Andreas fault (SAF) in southern California has been hindered for decades by incompatible estimates of total dextral offset based on different geologic cross-fault markers. The older estimate of 240-270 km is based on offset fluvial conglomerates of the middle Miocene Mint Canyon and Caliente Formations west of the SAF from their presumed source area in the northern Chocolate Mountains NE of the SAF (Ehlig et al., 1975; Ehlert, 2003). The second widely cited offset marker is a distinctive Triassic megaporphyritic monzogranite that has been offset 160 ± 10 km between Liebre Mountain west of the SAF and the San Bernadino Mountains (Matti and Morton, 1993). In this analysis we use existing paleocurrent data and late Miocene clockwise rotation in the eastern Transverse Ranges (ETR) to re-assess the orientation of the piercing line used in the 240 km-correlation, and present a palinspastic reconstruction that satisfies all existing geologic constraints. Our reconstruction of the Mint Canyon piercing line reduces the original estimate of 240-270 km to 195 ± 15 km of cumulative right-lateral slip on the southern SAF (sensu stricto), which is consistent with other published estimates of 185 ± 20 km based on correlative basement terranes in the Salton Trough region. Our estimate of ~195 km is consistent with the lower estimate of ~160 km on the Mojave segment because transform-parallel extension along the southwestern boundary of the ETR during transrotation produces ~25-40 km of displacement that does not affect offset markers of the Liebre/San Bernadino correlation located northwest of the ETR rotating domain. Reconciliation of these disparate estimates places an important new constraint on the total plate boundary shear that is likely accommodated in the adjacent northern Gulf of California. Global plate circuit models require ~650 km of cumulative Pacific-North America (PAC

  16. LiDAR Imagery of the San Andreas Fault Zone at the Vedanta and Olema Ridge Paleoseismic Trench Sites, Pt. Reyes, CA

    NASA Astrophysics Data System (ADS)

    Niemi, T. M.; Kayen, R.; Zhang, H.; Dunn, C. R.; Doolin, D. M.

    2004-12-01

    At the Vedanta and Olema Ridge paleoseismic trench sites along the San Andreas fault (SAF) in Marin County, we experimented with collecting tripod LiDAR (Light Detection And Ranging) data in order to test its utility in stratigraphic and tectonic geomorphic mapping. To characterized the terrain surface surroundings and within the exposed trench walls, we performed ground-based LiDAR surveys using a portable color sensitive tripod-mounted system. To produce a digital terrain model (DTM) for each site, we used a Riegl Z210i laser-scanner to target the ground and saturate it with point targets at three or more locations around the exposed trench. Local geo-referencing and control points were established using temporary auto reflectors. Using the LiDAR-based terrain model software package, ISite3D, we then merged these scans into a single surface model for each site. The same technique was used to image and process the exposed walls of the trench. We found that using a rotating scanning-laser allows us to very rapidly produce ultra-high resolution and quantitative DTMs for geomorphic analysis of a large (>0.1 km2) area surrounding the trench and that that the DTM can be used to resolve fine scale (<2.5 cm) morphologic features associated with the fault. The ability of the LiDAR to resolve color allows us another tool to investigate subtle variations in the soil structure exposed in the trench wall. By artificially modifying the color with false and enhanced colors, we can visually extract information not readily visible to the eye. At the Olema Ridge trench site, the 1906 trace of the SAF lies at the base of an east-facing scarp that formed as a slice of the ridge has been translated northwestward along the fault. As a means to compare technologies, we collected detailed geomorphic data from the site using both Total Station and LiDAR surveys. The superior coverage of the geospatial data recovered from the LiDAR allows for a more accurate rendering of the

  17. Integrating geology and geomorphology; the key to unlocking Quaternary tectonic framework of the San Andreas Fault zone in the San Gorgonio Pass region, southern California

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The San Gorgonio Pass (SGP) region of southern California is a locus of long-continued Quaternary deformation and landscape evolution within a structural complexity, colloquially referred to as a knot in the San Andreas Fault (SAF) zone. The geomorphology of the SGP region reflects the complex history of geologic events involved in the formation and resolution of this structural knot. We recognize five morphologically distinct terrains in and around SGP; the San Gorgonio Block (SGB), Yucaipa Ridge (YRB), Pisgah Peak (PPB), Kitching Peak (KPB), and Devil's Garden blocks (DGB). Morphometric analyses, including drainage density, hypsometry, topographic profiles, and stream-power measurements and discontinuities, consistently demonstrate distinctions between the blocks.