The study of the electrical structure and fluid content of the southern San Andreas Fault(SSAF)plays a significant role in understanding the geological processes and earthquake genesis.The paper analyzes the Bahr skew...The study of the electrical structure and fluid content of the southern San Andreas Fault(SSAF)plays a significant role in understanding the geological processes and earthquake genesis.The paper analyzes the Bahr skew and G-B decomposition from magnetotelluric sounding data in the SSAF to determine the strike direction is north-eastward 135°.Using the Nonlinear Conjugate Gradient algorithm,a reliable 2D electrical structure model was obtained.The Mission Creek and Banning faults,components of the SSAF,exhibit high conductivity within the crust,whereas the Eastern Transverse Ranges to the northeast of the fault show high resistivity characteristics.By integrating the modified Archie's law,the relations between conductivity,temperature,salinity,and fluid content were established,leading to conductivity-temperature and conductivity-fluid content relationships.Combining the results from the electrical structure model and fluid model of the SSAF,it is inferred that the fluid content in the high-conductivity crust reach up to 20%.When the fluid salinity is 10 wt%,the fluid content required to achieve the same high bulk conductivity reduces to 2%.A comparison of the electrical structure and focal depth of the Tan-Lu Fault Zone reveals that the collision between the low-viscosity fluids of the Mission Creek and Banning faults and the rigid Eastern Transverse Ranges contributes to the earthquake in the SSAF.展开更多
In this article,we review our previous research for spatial and temporal characterizations of the San Andreas Fault(SAF)at Parkfield,using the fault-zone trapped wave(FZTW)since the middle 1980s.Parkfield,California h...In this article,we review our previous research for spatial and temporal characterizations of the San Andreas Fault(SAF)at Parkfield,using the fault-zone trapped wave(FZTW)since the middle 1980s.Parkfield,California has been taken as a scientific seismic experimental site in the USA since the 1970s,and the SAF is the target fault to investigate earthquake physics and forecasting.More than ten types of field experiments(including seismic,geophysical,geochemical,geodetic and so on)have been carried out at this experimental site since then.In the fall of 2003,a pair of scientific wells were drilled at the San Andreas Fault Observatory at Depth(SAFOD)site;the main-hole(MH)passed a~200-m-wide low-velocity zone(LVZ)with highly fractured rocks of the SAF at a depth of~3.2 km below the wellhead on the ground level(Hickman et al.,2005;Zoback,2007;Lockner et al.,2011).Borehole seismographs were installed in the SAFOD MH in 2004,which were located within the LVZ of the fault at~3-km depth to probe the internal structure and physical properties of the SAF.On September 282004,a M6 earthquake occurred~15 km southeast of the town of Parkfield.The data recorded in the field experiments before and after the 2004 M6 earthquake provided a unique opportunity to monitor the co-mainshock damage and post-seismic heal of the SAF associated with this strong earthquake.This retrospective review of the results from a sequence of our previous experiments at the Parkfield SAF,California,will be valuable for other researchers who are carrying out seismic experiments at the active faults to develop the community seismic wave velocity models,the fault models and the earthquake forecasting models in global seismogenic regions.展开更多
Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was ...Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee's law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.展开更多
The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise loc...The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.展开更多
In 1555,the Florentine Mannerist painter Giorgio Vasari(1511-1574)created two significant oil panels,the Chariot of the Sun and the Chariot of the Moon,on the ceiling of the Hall of the Elements in the Palazzo Vecchio...In 1555,the Florentine Mannerist painter Giorgio Vasari(1511-1574)created two significant oil panels,the Chariot of the Sun and the Chariot of the Moon,on the ceiling of the Hall of the Elements in the Palazzo Vecchio,Florence.1 Cosimo I de’Medici,Duke of Tuscany(1519-1574),commissioned Vasari to renovate his apartments in the Palazzo Vecchio.Vasari restructured and painted the ceiling and walls of the Hall of the Elements on the second floor,named for its depicted subjects.The walls were painted using the fresco technique,while the ceiling was executed in oil on panels.The walls depicted the elements of Fire,Earth,and Water,whereas the ceiling illustrated the element of Air,containing the panels of the Chariots.Vasari began his education in classical culture in Arezzo under the Latin grammarian Antonio da Saccone and the ancient historian and literary scholar Giovanni Pollio Lappoli,known as Pollastra(1465-1540).He continued his studies within the Medici household under the humanist and hieroglyphologist Pierio Valeriano(1477-1558).In 1539,he met the Milanese law professor and emblematist Andrea Alciato(1492-1550)in Bologna,from whom he learned about the moral aspects of emblems.Through their historical,philosophical,mythographic,and emblematic symbolism,Vasari skillfully synthesize d knowledge to construct intellectual programs that encompass the concepts of ekphrasis and history paintings in his decorative cycles,as revealed in the Chariots.In depicting the cosmic movement of stars and time in the Chariots,Vasari integrated the idea of the chariot illustrated in Baccio Baldini’s astrological engravings and the mythographic account of Apollo and Diana’s chariots in Vincenzo Cartari’s Le Imagini degli dei degli antichi(1547 and 1571).In the discourse regarding the physical and metaphysical movements of the cosmos,Vasari underscores the influence of Italian Neoplatonism,with particular emphasis on insights derived from Marsilio Ficino’s exploration of alchemical colors in nature,as articulated in Liber de Arte Chemica(Books 14 and 15),while also elucidating the importance of Plato’s Chariot of the Soul or Allegory of the Chariot(Jones,Litt,&Ormerod,1918,p.246).展开更多
基金supported by the National Natural Science Foundation of China(42167023)the China Postdoctoral Science Foundation(2024MD753947)+1 种基金the National Natural Science Foundation of Inner Mongolia(2023QN04007,2022MS04009)the Basic Scientific Research Project of Institutions of Higher Learning in Inner Mongolia(JY20230090).
文摘The study of the electrical structure and fluid content of the southern San Andreas Fault(SSAF)plays a significant role in understanding the geological processes and earthquake genesis.The paper analyzes the Bahr skew and G-B decomposition from magnetotelluric sounding data in the SSAF to determine the strike direction is north-eastward 135°.Using the Nonlinear Conjugate Gradient algorithm,a reliable 2D electrical structure model was obtained.The Mission Creek and Banning faults,components of the SSAF,exhibit high conductivity within the crust,whereas the Eastern Transverse Ranges to the northeast of the fault show high resistivity characteristics.By integrating the modified Archie's law,the relations between conductivity,temperature,salinity,and fluid content were established,leading to conductivity-temperature and conductivity-fluid content relationships.Combining the results from the electrical structure model and fluid model of the SSAF,it is inferred that the fluid content in the high-conductivity crust reach up to 20%.When the fluid salinity is 10 wt%,the fluid content required to achieve the same high bulk conductivity reduces to 2%.A comparison of the electrical structure and focal depth of the Tan-Lu Fault Zone reveals that the collision between the low-viscosity fluids of the Mission Creek and Banning faults and the rigid Eastern Transverse Ranges contributes to the earthquake in the SSAF.
文摘In this article,we review our previous research for spatial and temporal characterizations of the San Andreas Fault(SAF)at Parkfield,using the fault-zone trapped wave(FZTW)since the middle 1980s.Parkfield,California has been taken as a scientific seismic experimental site in the USA since the 1970s,and the SAF is the target fault to investigate earthquake physics and forecasting.More than ten types of field experiments(including seismic,geophysical,geochemical,geodetic and so on)have been carried out at this experimental site since then.In the fall of 2003,a pair of scientific wells were drilled at the San Andreas Fault Observatory at Depth(SAFOD)site;the main-hole(MH)passed a~200-m-wide low-velocity zone(LVZ)with highly fractured rocks of the SAF at a depth of~3.2 km below the wellhead on the ground level(Hickman et al.,2005;Zoback,2007;Lockner et al.,2011).Borehole seismographs were installed in the SAFOD MH in 2004,which were located within the LVZ of the fault at~3-km depth to probe the internal structure and physical properties of the SAF.On September 282004,a M6 earthquake occurred~15 km southeast of the town of Parkfield.The data recorded in the field experiments before and after the 2004 M6 earthquake provided a unique opportunity to monitor the co-mainshock damage and post-seismic heal of the SAF associated with this strong earthquake.This retrospective review of the results from a sequence of our previous experiments at the Parkfield SAF,California,will be valuable for other researchers who are carrying out seismic experiments at the active faults to develop the community seismic wave velocity models,the fault models and the earthquake forecasting models in global seismogenic regions.
文摘Finite Element (FE) modeling under plane stress condition is used to analyze the fault type variation with depth along and around the San Andreas Fault (SAF) zone. In this simulation elastic rheology was used and was thought justifiable as the variation in depth from 0.5 km to 20 km was considered. Series of calculations were performed with the variation in domain properties. Three types of models were created based on simple geological map of California, namely, 1) single domain model considering whole California as one homogeneous domain, 2) three domains model including the North American plate, Pacific plate, and SAF zone as separate domains, and 3) Four domains model including the three above plus the Garlock Fault zone. Mohr-Coulomb failure criterion and Byerlee's law were used for the calculation of failure state. All the models were driven by displacement boundary condition imposing the fixed North American plate and Pacific plate motion along N34°W vector up to the northern terminus of SAF and N50°E vector motion for the subducting the Gorda and Juan de Fuca plates. Our simulated results revealed that as the depth increased, the fault types were generally normal, and at shallow depth greater strike slip and some thrust faults were formed. It is concluded that SAF may be terminated as normal fault at depth although the surface expression is clearly strike slip.
文摘The three largest earthquakes in northern California since 1849 were preceded by increased decadal activity for moderate-size shocks along surrounding nearby faults. Increased seismicity, double-difference precise locations of earthquakes since 1968, geodetic data and fault offsets for the 1906 great shock are used to re-examine the timing and locations of possible future large earthquakes. The physical mechanisms of regional faults like the Calaveras, Hayward and Sargent, which exhibit creep, differ from those of the northern San Andreas, which is currently locked and is not creeping. Much decadal forerunning activity occurred on creeping faults. Moderate-size earthquakes along those faults became more frequent as stresses in the region increased in the latter part of the cycle of stress restoration for major and great earthquakes along the San Andreas. They may be useful for decadal forecasts. Yearly to decadal forecasts, however, are based on only a few major to great events. Activity along closer faults like that in the two years prior to the 1989 Loma Prieta shock needs to be examined for possible yearly forerunning changes to large plate boundary earthquakes. Geodetic observations are needed to focus on identifying creeping faults close to the San Andreas. The distribution of moderate-size earthquakes increased significantly since 1990 along the Hayward fault but not adjacent to the San Andreas fault to the south of San Francisco compared to what took place in the decades prior to the three major historic earthquakes in the region. It is now clear from a re-examination of the 1989 mainshock that the increased level of moderate-size shocks in the one to two preceding decades occurred on nearby East Bay faults. Double-difference locations of small earthquakes provide structural information about faults in the region, especially their depths. The northern San Andreas fault is divided into several strongly coupled segments based on differences in seismicity.
文摘In 1555,the Florentine Mannerist painter Giorgio Vasari(1511-1574)created two significant oil panels,the Chariot of the Sun and the Chariot of the Moon,on the ceiling of the Hall of the Elements in the Palazzo Vecchio,Florence.1 Cosimo I de’Medici,Duke of Tuscany(1519-1574),commissioned Vasari to renovate his apartments in the Palazzo Vecchio.Vasari restructured and painted the ceiling and walls of the Hall of the Elements on the second floor,named for its depicted subjects.The walls were painted using the fresco technique,while the ceiling was executed in oil on panels.The walls depicted the elements of Fire,Earth,and Water,whereas the ceiling illustrated the element of Air,containing the panels of the Chariots.Vasari began his education in classical culture in Arezzo under the Latin grammarian Antonio da Saccone and the ancient historian and literary scholar Giovanni Pollio Lappoli,known as Pollastra(1465-1540).He continued his studies within the Medici household under the humanist and hieroglyphologist Pierio Valeriano(1477-1558).In 1539,he met the Milanese law professor and emblematist Andrea Alciato(1492-1550)in Bologna,from whom he learned about the moral aspects of emblems.Through their historical,philosophical,mythographic,and emblematic symbolism,Vasari skillfully synthesize d knowledge to construct intellectual programs that encompass the concepts of ekphrasis and history paintings in his decorative cycles,as revealed in the Chariots.In depicting the cosmic movement of stars and time in the Chariots,Vasari integrated the idea of the chariot illustrated in Baccio Baldini’s astrological engravings and the mythographic account of Apollo and Diana’s chariots in Vincenzo Cartari’s Le Imagini degli dei degli antichi(1547 and 1571).In the discourse regarding the physical and metaphysical movements of the cosmos,Vasari underscores the influence of Italian Neoplatonism,with particular emphasis on insights derived from Marsilio Ficino’s exploration of alchemical colors in nature,as articulated in Liber de Arte Chemica(Books 14 and 15),while also elucidating the importance of Plato’s Chariot of the Soul or Allegory of the Chariot(Jones,Litt,&Ormerod,1918,p.246).
