san andreas fault earthquake chronology and lake cahuilla history at coachella california 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

past and future earthquakes on the san andreas fault the san andreas fault in calfornia is one of the best studied earthquake generating faults in the world in their perspective weldon et al discuss recent efforts to construct rupture scenarios that is possible histories of the date location and length of fault rupture of past earthquakes on the fault existing knowledge of the locations and dates of past earthquakes can be explained by different scenarios but the authors argue that the evidence favors the hypothesis that the fault breaks in relatively infrequent large earthquakes they caution that the current 148 year hiatus since the last big earthquake is likely to end within the next 50 years with a large rupture or sequence of ruptures spanning a substantial part of the fault

san andreas fault geometry through the san gorgonio pass california three dimensional numerical models are needed to investigate the role of nonvertical strike slip fault segments on the deformation within restraining bends numerical models simulate geologic deformation of two alternative three dimensional present day configurations for the san andreas fault through the restraining bend within the san gorgonio pass region sgpr in southern california both models produce decreasing strike slip rates southward along the san bernardino strand of the san andreas fault similar to geologic data the north dipping san andreas fault model better matches the available strike slip data as well as the geologic uplift data for the southern san bernardino mountains than the vertical san andreas fault model we conclude that a north dipping fault configuration is preferred for models of the san andreas fault in the sgpr the complexity of the active fault geometry at the sgpr promotes the transfer of strike slip from the san andreas fault to the nearby but unconnected san jacinto fault slip rates and uplift patterns are sensitive to fault geometry within strike slip restraining bends

rupture of a seismic gap in southeastern alaska the 1972 sitka earthquake ms 7 6 abstract the sitka alaska earthquake of july 30 1972 m s 7 6 is one of the largest strike slip events since 1963 this earthquake is thought to have ruptured the pacific north america plate boundary segment between the large strike slip events in 1949 and 1958 and the sitka earthquake was heralded as one of the first successful forecasts of an earthquake based on the seismic gap hypothesis another motivation to study this event is the availability of a strong ground motion recording 50 km from the epicenter which is near the middle of the 180 km long plate boundary segment the teleseismically located aftershocks occur only in the southern half of this segment we have analyzed rayleigh waves and p waves recorded by wwssn long period vertical instruments a total of 25 very long period rayleigh phases r2 r5 define a symmetric four lobed radiation pattern from which we can infer a nearly pure right lateral strike slip fault striking 340 n20 w and a bilateral rupture comparison of synthetic and observed rayleigh waves yields a seismic moment of 3 10 27 dyn cm m w 7 6 the p waves are characterized by a dominant complex pulse in the first 40 s and a succession of smaller pulses after that the source time functions are deconvolved from 32 p waves with good azimuthal distribution to obtain the moment depth extent and rupture history the mean moment of the source time functions is 5 0 2 4 10 27 dyn cm and the depth extent is 0 10 km tomographic inversion of the source time functions produces an image of the earthquake rupture process this procedure maps the moment release of the complex pulse into two high displacement regions i e asperities 1 the epicentral area to 40 km north and 2 between 60 and 90 km south of the epicenter the main asperity just north of the epicenter coincides with a quiescent zone of microaftershocks while the overall average seismic displacement is 6 m the displacement at the main asperity is 7 m the same value as the tectonic displacement accumulated since the previous earthquake in 1848 the fault averaged stress drop is 100 bars while the asperity stress drop is 130 bars tomographic imaging of the source time functions thus resolves several features of the rupture process notably the bilateral propagation and rupture initiation at the largest asperity this is in contrast to the large 1976 guatemala strike slip earthquake where the largest displacements occurred away from rupture initiation

the foreshock sequence of the february 4 1975 haicheng earthquake m 7 3 we have examined the locations and radiation patterns of the foreshocks of the february 4 1975 haicheng earthquake m 7 3 using arrival times from six local seismic stations the foreshocks and mainshock were located relative to a master event the foreshocks occurred in a tight cluster that elongated with time before the largest foreshock the activity was located within a small approximately equidimensional volume with a diameter of about 2 km after the largest foreshock the activity spread northwest and southeast forming a 6 km long northwest trending zone first motions and ratios of p to s amplitudes indicate that two different faulting mechanisms occurred during the foreshock sequence the two radiation patterns can tentatively be correlated with different parts of the zone the hypocenter of the mainshock was not located on the same fault as that defined by the foreshocks hypocenters but rather was located 6 km south of and several kilometers shallower than the foreshock cluster we think this large separation between foreshocks and mainshock in a direction perpendicular both to the plane of rupture of the mainshock and to the trend of the foreshocks might be the result of an en echelon step in the fault that slipped during the mainshock an analysis of the change in stress due to slip during the foreshocks shows that the increase in shear stress on the mainshock fault caused by the foreshocks is very small and that direct triggering of the mainshock by the foreshocks is unlikely

could organic matter have been preserved on mars for 3 5 billion years abstract 3 5 billion years byr ago when it is thought that mars and earth had similar climates biological evolution on earth had made considerable progress such that life was abundant it is therefore surmised that prior to this time period the advent of chemical evolution and subsequent origin of life occurred on earth and may have occurred on mrs analysis for organic compounds in the soil buried beneath the martian surface may yield useful information regarding the occurrence of chemical evolution and possibly biological evolution calculations based on the stability of amino acids lead to the conclusion that remnants of these compounds if they existed on mars 3 5 byr ago might have been preserved buried beneath the surface oxidizing layer for example if phenylalanine an amino acid of average stability existed on mars 3 5 byr ago then 1 6 would remain buried today or 25 pg 2 5 ng of c g 1 martian soil may exist from remnants of meteoritic and cometary bombardment assuming that 1 of the organics survived impact

latest quaternary paleoseismology and slip rates of the longriba fault zone eastern tibet implications for fault behavior and strain partitioning 1 although much work has been done on active tectonics of eastern tibet little is known about the longriba fault zone and its role in strain partitioning whether its two sub parallel strands longriqu and maoergai faults can rupture simultaneously in a large earthquake remains unknown we conducted trenching combined with the interpretation of satellite imagery field investigations topographic surveys and radiocarbon and optically stimulated luminescence osl dating to reconstruct paleoseismic history and we used displaced terrace risers to estimate geological slip rates our results demonstrate that the longriba fault zone is predominantly right lateral with a small southeast verging thrust component four surface rupturing events occurred on the longriqu fault at 5080 90 11 100 380 13 000 260 and 17 830 530 cal yr b p together with our previous trenches on the maoergai fault we found that the last event probably ruptured both the longriqu and maoergai faults prior to the last event the two strands of the longriba fault zone experienced alternating earthquakes the fault zone has a high potential for an earthquake larger than mw 7 the slip rate of the longriba fault zone decreases from 7 5 mm yr in latest pleistocene to 2 1 mm yr in the holocene probably related to a slowing down of the eastern motion of the tibetan plateau the comparison with slip rates at the longmen shan fault zone suggests that the longriba fault zone has an equally important role in strain partitioning in eastern tibet this study is helpful to seismic hazard assessment and an understanding of deformation mechanism in eastern tibet

synthetic earthquake catalogs simulating seismic activity in the corinth gulf greece fault system the characteristic earthquake hypothesis is the basis of time dependent modeling of earthquake recurrence on major faults however the characteristic earthquake hypothesis is not strongly supported by observational data few fault segments have long historical or paleoseismic records of individually dated ruptures and when data and parameter uncertainties are allowed for the form of the recurrence distribution is difficult to establish this is the case for instance of the corinth gulf fault system cgfs for which documents about strong earthquakes exist for at least 2000 years although they can be considered complete for m 6 0 only for the latest 300 years during which only few characteristic earthquakes are reported for individual fault segments the use of a physics based earthquake simulator has allowed the production of catalogs lasting 100 000 years and containing more than 500 000 events of magnitudes 4 0 the main features of our simulation algorithm are 1 an average slip rate released by earthquakes for every single segment in the investigated fault system 2 heuristic procedures for rupture growth and stop leading to a self organized earthquake magnitude distribution 3 the interaction between earthquake sources and 4 the effect of minor earthquakes in redistributing stress the application of our simulation algorithm to the cgfs has shown realistic features in time space and magnitude behavior of the seismicity these features include long term periodicity of strong earthquakes short term clustering of both strong and smaller events and a realistic earthquake magnitude distribution departing from the gutenberg richter distribution in the higher magnitude range

evidence for large earthquakes on the san andreas fault at the wrightwood california paleoseismic site a d 500 to present 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 in filled 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 the southeast suggest that at least the southermost 200 km of the san andreas fault is near failure

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

adjoint analysis of the source and path sensitivities of basin guided waves summary simulations of earthquake rupture on the southern san andreas fault saf reveal large amplifications in the san gabriel and los angeles basins sgb and lab apparently associated with long range path effects geometrically similar excitation patterns can be recognized repeatedly in different saf simulations e g love wave like energy with predominant period around 4 s channelled southwestwardly from the sgb into lab yet the amplitudes with which these distinctive wavefield patterns are excited change depending upon source details slip distribution direction and velocity of rupture we describe a method for rapid calculation of the sensitivity of such predicted wavefield features to perturbations of the source kinematics using a time reversed adjoint wavefield simulation the calculations are analogous to those done in adjoint tomography and the same time reversed calculation also yields path sensitivity kernels that give further insight into the excitation mechanism for rupture on the southernmost 300 km of saf lab excitation is greatest for slip concentrated between the northern coachella valley and the transverse ranges propagating to the ne and with rupture velocities between 3250 and 3500 m s 1 along that fault segment that is within or slightly above the velocity range between rayleigh and s velocities that is energetically precluded in the limit of a sharp rupture front highlighting the potential value of imposing physical constraints such as from spontaneous rupture models on source parametrizations lab excitation is weak for rupture to the sw and for ruptures in either direction located north of the transverse transverse ranges whereas ventura basin vtb is preferentially excited by ne ruptures situated north of the transverse ranges path kernels show that lab excitation is mediated by surface waves deflected by the velocity contrast along the southern margin of the transverse ranges having most of their energy in basement rock until they impinge on the eastern edge of sgb through which they are then funnelled into lab vtb amplification is enhanced by a similar waveguide effect

field study of a highly active fault zone the xianshuihe fault of southwestern china the xianshuihe fault of western sichuan province china is one of the world s most active faults having produced 4 earthquakes during this century of magnitude 7 along a 350 km length of the fault at least 8 such events have occurred since 1725 in the more limited 150 km long segment including luhuo and daofu major earthquakes in 1904 1923 1973 and 1981 m 7 7 7 6 6 9 were associated with overlapping surficial fault ruptures and with individual left lateral displacements as large as 3 6 m field studies indicate that this high degree of activity is typical of the fault s longer term history the holocene left lateral slip rate on the north western segment of the fault has been 15 5 mm yr decreasing to about 5 mm yr on its southeastern segment based on radiometrically dated offset stream channel and terrace deposits and on offset glacial moraines physiographic features of active faulting are fully as diagrammatic as those of california s san andreas fault mainly because of high altitude preservation and the absence of cultural modification on this eastern margin of the tibetan plateau detailed en echelon tensional and pushup features resulting from surface ruptures in 1973 1955 1923 and 1893 can still be recognized today and new data have been collected bearing on the offsets and fault rupture lengths during these and other events the locations and magnitudes of historic earthquakes suggest that the characteristic earthquake model may apply to the xianshuihe fault obvious geometric segmentation of the fault has controlled the initiation and termination of ruptures in some events whereas segmentation control for others remains obscure based on the historic record repeat times estimated from slip rates and current seismic gaps two segments are particularly likely sites for m 7 earthquakes in the near future the 65 km long segment between daofu and qianning and the 135 km long segment bracketing kangding continuing creep has been documented along some segments of the fault and this together with the high degree of activity and other unique attributes makes the xianshuihe fault one of the most promising sites in the world for earthquake prediction and hazard evaluation studies

rupture complexity of a moderate sized mb 6 0 earthquake broadband body wave analysis of the north yemen earthquake of 13 december 1982 abstract the occurrence of the north yemen earthquake of 13 december 1982 provides an important opportunity to study source properties of earthquakes in the southern arabian peninsula although moderate in size m b 6 0 this earthquake is the largest to have occurred in the region since the deployment of the global digital seismograph network p waves recorded at teleseismic distances can be obtained from stations of this network and of the graefenberg array that are flat to displacement and velocity in the frequency range from 0 01 to 5 0 hz the broad bandwidth of the data is necessary for deriving a dynamic description of the earthquake as well as the static properties of the source in contrast inversions using only long period data provide much less insight into the complexity of rupture by fitting the displacement pulse shapes with synthetics we find that the yemen earthquake was a complex rupture consisting of two events that occurred about 3 0 sec apart the depth of both hypocenters is estimated to be 7 km the focal mechanisms of the events each have a nodal plane that strikes 340 and dips 60 to the east however the slip directions of the focal mechanisms are in slightly different directions 230 and 300 respectively the total moment of the earthquake is 3 0 10 25 dyne cm with the second event having three times the moment of the initial event by inverting p wave arrival time differences at each station we find the second hypocenter is located 7 5 km from the initial hypocenter in a direction that is nearly colinear with the nnw striking nodal plane of the focal mechanisms of each event the trend of extensional ground cracks in the epicentral region and the predominant strike of composite focal mechanisms of locally recorded aftershocks are also in a nnw direction from the consistency of these observations we infer that the east dipping nnw striking nodal planes are the fault planes the static stress drop of the first and second events are 44 and 31 bars respectively inverting the energy flux in the velocity waveforms we find the energy radiated by the earthquake is 4 8 10 20 dyne cm this implies an average apparent stress of 4 bars at different times during the aftershock sequence seismicity tended to cluster about one or another of two different planes which although having roughly the same strike had conjugate dips one of these planes delineated late in the aftershock sequence coincides with the inferred fault plane for the main shock the complexity of the main shock and of the aftershock sequence suggests that strain accumulated on a system of strongly interdependent faults as the region became critically loaded the effect of a major rupture was to critically stress faults adjacent to the initial nucleation the second event of the main shock represents the rapid release of stress from the fault system while the ensuing aftershock sequence represents the gradual release of stress

the 1988 and 1990 upland earthquakes left lateral faulting adjacent to the central transverse ranges two earthquakes m l 4 6 and m l 5 2 occurred at almost the same location in upland southern california in june 1988 and february 1990 and had similar strike slip focal mechanisms with left lateral motion on a northeast striking plane the focal mechanisms and aftershock locations showed that the causative fault was the san jose fault an 18 km long concealed fault that splays west southwest from the frontal fault of the central transverse ranges left lateral strike slip faults adjacent to the frontal faults may play an important role in the deformation of the transverse ranges and the los angeles basin as suggested by these upland earthquakes the left lateral strike slip 1988 m l 4 9 pasadena earthquake on the raymond fault 30 km to the west of upland and scattered background seismicity along other active left lateral faults these faults may transfer slip away from part of the frontal fault toward the south alternatively these faults could represent secondary faulting related to the termination of the northwest striking right lateral strike slip faults to the south of the range front the 1988 and 1990 upland earthquakes ruptured abutting or possibly overlapping segments of the san jose fault the edges of the overlapping aftershock zones which are sharply defined together with background seismicity outline a 14 km long aseismic segment of the san jose fault the 1988 mainshock originated at 9 5 km depth and caused aftershocks between 5 and 12 km in contrast the 1990 mainshock focus occurred at the top of its aftershock zone at 5 km and caused aftershocks down to 13 km depth these deep aftershocks tapered off within 2 weeks the rate of occurrence of aftershocks in magnitude time space was the same for both sequences the state of stress reflected in the focal mechanisms of the aftershocks is identical to that determined from background activity and did not change with time during the aftershock sequence the constant stress state suggests that the 1988 and 1990 events did not completely release all the stored slip on that segment of the fault the presence of 14 km of unbroken fault the abrupt temporal termination of deep aftershocks and the constant stress state all suggest that a future moderate sized earthquake m l 6 0 6 5 on the san jose fault is possible with a rupture length of at least 14 km and possibly 18 km

earthquake hazards rivers rifts and ruptures the southern san andreas fault is due for a large earthquake seismic images of sediments deposited in an ancient lake overlying the southern end of the fault indicate that episodic flooding may have triggered earthquakes in the past

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

a quantitative assessment of dinsar measurements of interseismic deformation the southern san andreas fault case study we investigate the capabilities and limitations of the differential interferometric synthetic aperture radar dinsar techniques in particular of the small baseline subset sbas approach to measure surface deformation in active seismogenetic areas the dinsar analysis of low amplitude long wavelength deformation such as that due to interseismic strain accumulation is limited by intrinsic trade offs between deformation signals and orbital uncertainties of sar platforms in their contributions to the interferometric phases the latter being typically well approximated by phase ramps such trade offs can be substantially reduced by employing auxiliary measurements of the long wavelength velocity field we use continuous global positioning system gps measurements from a properly distributed set of stations to perform a pre filtering operation of the available dinsar interferograms in particular the gps measurements are used to estimate the secular velocity signal approximated by a spatial ramp within the azimuth range radar imaging plane the phase ramps derived from the gps data are then subtracted from the available set of dinsar interferograms this pre filtering step allows us to compensate for the major component of the long wavelength range change that within the sbas procedure might be wrongly interpreted and filtered out as orbital phase ramps with this correction the final results are obtained by simply adding the pre filtered long wavelength deformation signal to the sbas retrieved time series the proposed approach has been applied to a set of ers 1 2 sar data acquired during the 1992 2006 time interval over a 200 200 km area around the coachella valley section of the san andreas fault in southern california usa we present results of the comparison between the sbas and the line of sight los projected gps time series of the usgc pbo network as well as the mean los velocity fields derived using sbas gps and stacking techniques our analysis demonstrates the effectiveness of the presented approach and provides a quantitative assessment of the accuracy of dinsar measurements of interseismic deformation in a tectonically active area

source complexity of the october 1 1987 whittier narrows earthquake long and short period body waveform data recorded at regional and teleseismic distances are modeled to obtain the source parameters of the whittier narrows earthquake of october 1 1987 although the long period data can be satisfied by a simple thrust earthquake on a plane striking 280 at a depth of 14 km we require a double source solution to satisfy both the long and short period teleseismic data the first subevent has a focal mechanism of strike 250 dip 30 n and a slip vector 90 the second is 280 40 n and 98 the second event occurred 1 0 s after the first was 5 times larger 1 2 1025 dyn cm for the second 0 23 1025 for the first in terms of seismic moment and was also shallower 12 km whereas the first subevent was at 15 km the two subevents probably occurred on a north dipping listric fault but may have occurred on two subparallel faults these features were determined by studying a variety of phases including teleseismic p and sh and regional pnl the whittier narrows earthquake was a high stress drop event but a single value for stress drop cannot be obtained because of the complex nature of the source if we define the fault area as the aftershock area we obtain a stress drop of about 750 bars

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

an assessment of source parameters of earthquakes in the cordillera of the western united states abstract source parameters for 50 earthquakes occurring between 1915 and 1988 have been used to examine the faulting characteristics of magnitude 5 5 to 7 8 earthquakes within the western u s cordillera an area extending from the eastern sierra nevada to the great plains and from northwestern montana to trans pecos texas source parameters used in this study include seismic information from first motion analyses body and surface waveform modeling geodetic studies and geological studies of surface faulting the principal results of this analysis include 1 all earthquakes occurred on faults dipping 38 or more and no evidence for listric of low angle planar faulting was found 2 all m 7 0 earthquakes occurred at depths 12 km and were composed of multiple subevents 3 most earthquakes 70 per cent had unilateral ruptures and 4 no individual subevent had a rupture length 21 km

broadband study of the 1989 loma prieta earthquake we determined the source characteristics of the oct 18 1989 loma prieta california earthquake using teleseismic data the solution from body waves gives a mechanism with dip 70 rake 138 and strike 128 and a seismic moment of 3 10 26 dyne cm m w 6 9 this solution is similar to those obtained from long period rayleigh and love waves p nl waves and first motion data the body wave form suggests a depth of about 15 km the effective duration of the source is 6 sec which suggests a fault length of 30 km and 15 km for bilateral and unilateral faulting respectively considering the extent of the aftershock area we used 35 km as an estimate of the total rupture length the strike slip and the thrust components of the coseismic slip are 177 and 159 cm respectively the large thrust component raises an important question regarding the recurrence pattern if the loma prieta earthquake is a characteristic earthquake with a recurrence interval of about 100 years the 159 cm displacement implies a long term uplift rate of about 1 cm year which appears too large for this region three hypotheses for reconciling this apparent conflict are 1 the geometry of plate motion along the santa cruz mountain segment changes over a time scale of several thousand years so that the coseismic displacement has not accumulated enough to produce high topographic relief 2 the coseismic shp direction varies from event to event 3 the slip plane of the 1989 loma prieta earthquake is different from the major boundary between the pacific and the north american plates if this is the case the loma prieta earthquake is a rather rare non characteristic event the surface slip of about l m for the 1906 san francisco earthquake is one of the key data in long term forecasting no surface slip was observed for the 1989 loma prieta earthquake even if the horizontal slip at depth is as large as 1 8 m this points to a risk of relying too heavily on surface observations for long term seismic risk analysis

a plate boundary earthquake record from a wetland adjacent to the alpine fault in new zealand refines hazard estimates abstract discovery and investigation of millennial scale geological records of past large earthquakes improve understanding of earthquake frequency recurrence behaviour and likelihood of future rupture of major active faults here we present a 2000 year long seven event earthquake record from john o groats wetland adjacent to the alpine fault in new zealand one of the most active strike slip faults in the world we linked this record with the 7000 year long 22 event earthquake record from hokuri creek 20 km along strike to the north to refine estimates of earthquake frequency and recurrence behaviour for the south westland section of the plate boundary fault eight cores from john o groats wetland revealed a sequence that alternated between organic dominated and clastic dominated sediment packages transitions from a thick organic unit to a thick clastic unit that were sharp involved a significant change in depositional environment and were basin wide were interpreted as evidence of past surface rupturing earthquakes radiocarbon dates of short lived organic fractions either side of these transitions were modelled to provide estimates for earthquake ages of the seven events recognised at the john o groats site three post date the most recent event at hokuri creek two match events at hokuri creek and two events at john o groats occurred in a long interval during which the hokuri creek site may not have been recording earthquakes clearly the preferred john o groats hokuri creek earthquake record consists of 27 events since 6000 bc for which we calculate a mean recurrence interval of 291 23 years shorter than previously estimated for the south westland section of the fault and shorter than the current interseismic period the revised 50 year conditional probability of a surface rupturing earthquake on this fault section is 29 the coefficient of variation is estimated at 0 41 we suggest the low recurrence variability is likely to be a feature of other strike slip plate boundary faults similar to the alpine fault

uniform california earthquake rupture forecast version 2 ucerf 2 the 2007 working group on california earthquake probabilities wgcep 2007 presents the uniform california earthquake rupture forecast version 2 ucerf 2 this model comprises a time independent poisson process earthquake rate model developed jointly with the national seismic hazard mapping program and a time dependent earthquake probability model based on recent earthquake rates and stress renewal statistics conditioned on the date of last event the models were developed from updated statewide earthquake catalogs and fault deformation databases using a uniform methodology across all regions and implemented in the modular extensible open seismic hazard analysis framework the rate model satisfies integrating measures of deformation across the plate boundary zone and is consistent with historical seismicity data an overprediction of earthquake rates found at intermediate magnitudes 6 5 m 7 0 in previous models has been reduced to within the 95 confidence bounds of the historical earthquake catalog a logic tree with 480 branches represents the epistemic uncertainties of the full time dependent model the mean ucerf 2 time dependent probability of one or more m 6 7 earthquakes in the california region during the next 30 yr is 99 7 this probability decreases to 46 for m 7 5 and to 4 5 for m 8 0 these probabilities do not include the cascadia subduction zone largely north of california for which the estimated 30 yr m 8 0 time dependent probability is 10 the m 6 7 probabilities on major strike slip faults are consistent with the wgcep 2003 study in the san francisco bay area and the wgcep 1995 study in southern california except for significantly lower estimates along the san jacinto and elsinore faults owing to provisions for larger multisegment ruptures important model limitations are discussed

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

centroid moment tensor solutions for 35 earthquakes in western north america 1977 1983 abstract seismic records from the gdsn sro asro dwwssn rstn and ida networks were used to obtain long period t 45 sec focal mechanisms for 35 earthquakes in western north america longitude 140 to 110 latitude 30 to 60 employing the centroid moment tensor method of dziewonski et al 1981 and dziewonski and woodhouse 1983 the same algorithm was applied to all events the smallest m 0 6 4 10 23 dyne cm being an aftershock to the 1979 imperial valley california earthquake and the largest m 0 8 5 10 26 dyne cm the 1980 eureka california earthquake all events were analyzed with and without the constraint m r m r 0 on the moment tensor an ad hoc criterion on the relative variance reduction was employed to determine a favored solution our solutions show general agreement with other published results as well as with tectonic structures agreement with results obtained using the abundant local and regional data confirms the adequacy of the method in determining long period source parameters and verifies its applicability in regions where local and regional data are scarce or nonexistent in some cases disagreement between our solution and results from first motion studies appears to be related to source complexities our moment tensor represents the total stress release of the composite event a consistent westward movement of the centroid locations reflects lateral heterogeneities in the crust and mantle

sea surface pco2 sst relationships across a cold core cyclonic eddy implications for understanding regional variability and air sea gas exchange 1 this study is designed to improve the understanding of how biologically productive cold core cyclonic eddies affect sea surface pco2 in the lee of the main hawaiian islands in the subtropical north pacific gyre we identified three unique relationships between pco2 and sea surface temperature sst a positive correlation between pco2 and sst was observed in the waters surrounding the eddy suggesting surface co2 is controlled primarily by thermodynamics in contrast a negative relationship was observed within the eddy core as a result of the upwelling of co2 enriched subsurface waters a third relationship existed throughout the rest of the eddy with reduced pco2 suggesting a combination of biological uptake physical upwelling and thermodynamic controls in the absence of an eddy this region is a co2 sink with the passage of the cold core mesoscale eddy decreasing the magnitude of the sink by 17 however if the general temperature correlation is used to predict pco2 inside the cold eddy it would overestimate the co2 sink inside the eddy by 100

paleoearthquakes on the southern san andreas fault wrightwood california 3000 to 1500 b c a new method for evaluating paleoseismic evidence and earthquake horizons 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 radiocarbon 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 to suggest significant variations in the average recurrence rate at wrightwood during the past 5000 years

aftershocks of the western argentina caucete earthquake of 23 november 1977 some tectonic implications an aftershock survey using a network of eight portable and two permanent seismographs was conducted for the western argentina caucete earthquake ms 7 3 of november 23 1977 monitoring began december 6 almost 2 weeks after the main shock and continued for 11 days the data set includes 185 aftershock hypocenters that range in the depth from near surface to more than 30 km the spatial distribution of those events occupied a volume of about 100 km long 50 km wide 30 km thick the volumnar nature of the aftershock distribution is interpreted to be a result of a bimodal distribution of foci that define east and west dipping planar zones efforts to select which of those zones was associated with the causal faulting include special attention to the determination of the mainshock focal depth and dislocation theory modeling of the coseismic surface deformation in the epicentral region our focal depth 25 35 km and modeling studies lead us to prefer an east dipping plane as causal a previous interpretation by other investigators used a shallower focal depth 17 km and similar modeling calculations in choosing a west dipping plane our selection of the east dipping plane is physically more appealing because it places fault initiation at the base of the crustal seismogenic layer rather than in the middle of that layer which requires fault propagation to be updip rather than downdip

seismicity and associated strain of central greece between 1890 and 1988 summary we examined the seismicity of central greece between 1890 and 1988 using macroseismic and instrumental data to ask two questions 1 does the seismicity of this period reveal all the major tectonic structures that are known to be active and 2 what are the likely strains associated with the seismicity over this period many known active structures have been effectively aseismic for the last hundred years and even the inclusion of all known large events earlier than 1890 reveals no activity associated with the ne coast of evia gulf of argos or graben ne of mt parnassos it is clear that even 100 years data are inadequate for either a reasonable assessment of seismic risk or for a confident estimation of maximum magnitude however we are aware of no earthquakes in central greece during the last 200 yr that were larger than ms 7 0 it is probable that the maximum magnitude is restricted by the maximum length of fault segments which appears to be around 15 20 km the earthquakes of ms 5 8 during 1890 1988 can account for a n s displacement of around 45 70 cm with maximum and minimum estimates a factor of two greater and smaller than this across part of a 1890 1900 triangulation network in central greece that was resurveyed in 1988 the contribution of smaller events may increase this displacement by about 50 per cent this cumulative seismic displacement is similar to that estimated from the geodetic work about 100 cm but a detailed comparison of the two sets of observations will be reported elsewhere a re evaluation of all the important earthquakes of 1890 1988 in central greece is presented in the appendix which summarizes information of use to both earth scientists and engineers

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

structure of earthquake occurrence in space time and magnitude distributions of time between consecutive earthquakes verify an approximately universal scaling law for stationary seismicity the shape of these distributions is shown to arise as a mixture of one distribution for short distance events and an exponential distribution for far off events the distinction from short and long distances being relative to the size of the region studied the distributions of consecutive distances show a double power law decay and verify an approximate scaling law which guarantees the simultaneous fulfillment of the scaling laws for time the interplay between space and time can be seen as well by looking at the distribution of distances for a fixed time separation these results suggest that seismicity can be understood as a series of intertwined independent continuous time random walks with power law distributed waiting times and levy flight jumps however a simple model based on these ideas does not capture the invariance of seismicity under renormalization

thermally altered palagonitic tephra a spectral and process analog to the soil and dust of mars we studied six palagonitic soil samples ph 1 through ph 6 which were collected at 30 cm intervals from a lava slab on mauna kea hawaii the samples represent an alteration sequence caused by heating during emplacement of molten lava over a preexisting tephra cone they are both spectral and weathering alteration process analogs to the martian surface techniques employed included visible and near ir spectroscopy mossbauer spectroscopy and magnetic analysis the two samples collected from beyond 90 cm from the slab ph 5 and ph 6 did not see the transient heating event and are composed of coarse grained glassy basaltic hawaiitic particles some of which have been moderately palagonitized since formation of the cone in the late pleistocene the four samples closest to the slab ph 1 through ph 4 have been strongly altered in response to heating during its emplacement their iron oxide mineralogy is dominated by nanophase ferric oxide the sample adjacent to the slab ph 1 which would have seen the highest temperatures has a factor of 3 less h2o and contains crystalline hematite and magnetite in addition to nanophase ferric oxide lesser amounts of magnetite but not hematite are present in samples 30 cm ph 2 and 60 cm ph 3 from the slab the reflectivity spectra of samples ph 2 through ph 4 are similar to spectra of palagonites reported by other workers to be good mars visible to near ir spectral analogs the reflectivity spectrum of ph 1 is an even better spectral analog to mars in that it exhibits absorption features indicative of both nanophase and crystalline ferric oxides similar to several new martian telescopic data sets our sampling site may also be a process analog for mars in that heating episodes by volcanism and or impact cratering could produce crystalline ferric oxides from poorly crystalline palagonitic material thus localized thermal alteration events may provide a volumetrically important mechanism for the palagonitization of basaltic glass and the production of crystalline ferric oxides on mars

quasi periodic recurrence of large earthquakes on the southern san andreas fault 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

late holocene rupture behavior and earthquake chronology on the hope fault new zealand the hope fault is the most active and southernmost splay of the marlborough fault system in the northern south island of new zealand the fault consists of five geometrically defined segments we used trenching to acquire paleoseismic data and radiocarbon dating of faulted late holocene sediments on the hurunui segment of the hope fault to derive an earthquake chronology that extends from the historic 1888 mw 7 1 amuri earthquake to ca 300 c e thereby providing the longest chronologic record of earthquakes on the hope fault to date earthquake event horizons were identified by upward fault terminations colluvial wedges unconformities and or progressive folding of shutter basin deposits six earthquakes identified at c e 1888 1740 1840 1479 1623 819 1092 439 551 and 373 419 indicate a mean recurrence interval of 298 88 yr with successive median interevent times ranging from 98 to 595 yr the large variance in interevent times with respect to mean recurrence interval is explained by 1 possible coalescence of rupture overlap from the adjacent hope river segment onto the hurunui segment at our study site including the 1888 mw 7 1 amuri earthquake sourced primarily from the hope river segment which results in apparently shorter interevent times at the study site compared to mean recurrence intervals from adjacent fault segments 2 possible earthquake temporal clustering on the hurunui segment which could result in interevent times that are significantly shorter or longer than interevent times and mean recurrence intervals predicted by a periodic earthquake rupture model and or 3 missing events which could result in interevent times and mean recurrence intervals at the study site that are longer than the actual mean recurrence interval while we cannot exclude option 3 as a possibility we prefer options 1 and 2 to explain earthquake chronologies and rupture behavior on the hurunui segment of the hope fault given the detailed nature of our geologic and chronologic investigations by demonstrating that the 1888 amuri earthquake propagated through a proposed segment boundary we provide the first evidence for coseismic multisegment ruptures on the hope fault in contrast the penultimate earthquake ruptured the hurunui segment at 1740 1840 c e with no known rupture of the hope river segment paleoearthquake records near geometrically complex segment structural boundaries on major strike slip faults may show temporal recurrence distributions resulting from earthquake ruptures that variably arrest or propagate through proposed segment boundaries we note that earthquake recurrence along major strike slip plate boundary faults may vary between more periodic and more episodic end members even on adjacent geometrically defined segments

rupture patterns and preshocks of large earthquakes in the southern san jacinto fault zone we relocated the large 1937 1942 and 1954 earthquakes in the san jacinto fault zone the epicenters of the main shocks aftershocks and some preshocks were determined using empirical station corrections from recent small events in the study areas the 1937 ml 5 9 earthquake has an epicenter between the surface traces of the san jacinto and buck ridge faults and aftershocks suggest about 7 km of rupture predominantly to the northwest a significant increase in small earthquake activity occurred about formula yr before this event the 1954 m l 6 2 earthquake is located at the southeast end of the mapped trace of the san jacinto fault and aftershocks suggest about 15 km of rupture further southeast into an area of folded young sediments with no surface fault trace this event was preceded by a cluster of small earthquakes which occurred within an 8 hr period 10 weeks before the main event and in the eventual rupture zone the 1942 m l 6 3 earthquake is located southwest of the southeast end of the coyote creek fault large aftershocks of this event are spread over a 15 by 18 km area southwest of the coyote creek fault and are not associated with any one fault the relation of the 1942 event to the san jacinto fault zone is not simple

structural analysis of recent and active faults and regional state of stress in the epicentral area of the 1978 thessaloniki earthquakes northern greece during spring and summer 1978 macedonia greece suffered damaging seismic activity during the two main shocks which occurred on may 23 mb 5 7 and june 20 mb 6 1 seismic open cracks and faults were formed in the epicentral area 25 km nne from thessaloniki they have been mapped and their kinematics analyzed these studies have shown that they result from the reactivation of existing faults of pleistocene recent and historical age and that the crust is stretching along a n s to nne ssw direction in that part of the north aegean principal stress directions have been computed from the slip vectors measured on recent neotectonic faults and seismic cracks and faults this computation utilizing a simple mechanical model homogeneous deformation through the addition of small and independent displacements of rigid blocks in a highly fractured body a striking feature of this analysis is that the tensional directions 3 deduced from seismic faulting and from recent neotectonic faulting are nearly the same they are compatible with the regional tension axis deduced from focal mechanisms of north aegean and with the focal mechanisms of the 1978 thessaloniki main shocks they are also compatible with in situ stress measurements in this region studies of superficial seismic faulting strongly support previous assumptions proposed from aftershock distribution the 1978 thessaloniki earthquakes resulted from reactivation of several different faults situated within the same ne dipping fault zone of upper eocene lower oligocene age and older separating the serbo macedonian massif from the peonias east vardar zone

structure and earthquake offsets on the san andreas fault at the wrightwood california paleoseismic site thirty eight trenches and natural exposures across the san andreas fault zone four km northwest of wrightwood california reveal the structure and stratigraphy of this paleoseismic site a 25 m thick stratigraphic section of late holocene peat debris flows and fluvial sediments have accumulated syntectonically and are deformed in a complicated flower or flake structure within the fault zone whereas slip is everywhere parallel to the trend of the san andreas fault layering within the fan shaped section guides the surface faulting and transtensive portions of the structure are connected to transpressive portions by bedding parallel detachment faults the structure has grown through time widely distributing the evidence for individual earthquakes the broad zone of deformation and rapid sedimentation permit the characterization of an unusually large number of prehistoric earthquakes the presence of at least four geomorphically similar sites within 10 km along the fault zone suggests that this kind of site is common and other sites should be exploited to date the upper 12 m of section deposited during the past 1600 yr has been completely characterized and dated to show evidence of 14 prehistoric earthquakes the a d 1857 earthquake produced only 1 2 m of slip here commensurate with the site9s proximity to the southern end of the rupture six to 10 m of slip accumulated during the past three earthquakes and 30 60 m of cumulative slip occurred during the past 14 events suggesting a mean displacement of 2 4 m per event at the site coupled with the mean recurrence interval of slightly more than 100 yr this implies a slip rate of 2 4 cm yr for the san andreas fault north of its junction with the san jacinto fault

interseismic strain accumulation and the earthquake potential on the southern san andreas fault system the southern section of the san andreas fault is the only part of the fault that hasn t ruptured in historic times for this reason it is believed to pose the largest seismic risk in california although whether tectonic stress is actually accumulating there is a topic of heated debate using data from radar interferometry satellites yuri fialko has produced a detailed map of surface deformation in the area that shows that elastic stress is accumulating at a fairly high rate during the past 300 years a displacement of 6 to 9 metres has built up this suggests that the southern san andreas fault is nearing the end of the interseismic phase of the earthquake cycle and that increased seismic activity of some kind can be expected the san andreas fault in california is a mature continental transform fault that accommodates a significant fraction of motion between the north american and pacific plates the two most recent great earthquakes on this fault ruptured its northern and central sections in 1906 and 1857 respectively the southern section of the fault however has not produced a great earthquake in historic times for at least 250 years assuming the average slip rate of a few centimetres per year typical of the rest of the san andreas fault the minimum amount of slip deficit accrued on the southern section is of the order of 7 10 metres comparable to the maximum co seismic offset ever documented on the fault1 2 here i present high resolution measurements of interseismic deformation across the southern san andreas fault system using a well populated catalogue of space borne synthetic aperture radar data the data reveal a nearly equal partitioning of deformation between the southern san andreas and san jacinto faults with a pronounced asymmetry in strain accumulation with respect to the geologically mapped fault traces the observed strain rates confirm that the southern section of the san andreas fault may be approaching the end of the interseismic phase of the earthquake cycle

dependence of earthquake recurrence times and independence of magnitudes on seismicity history the fulfillment of a scaling law for earthquake recurrence time distributions is a clear indication of the importance of correlations in the structure of seismicity in order to characterize these correlations we measure conditional recurrence time and magnitude distributions for worldwide seismicity as well as for southern california during stationary periods disregarding the spatial structure we conclude that the relevant correlations in seismicity are those of the recurrence time with previous recurrence times and magnitudes in the latter case the conditional distribution verifies a scaling relation depending on the difference between the magnitudes of the two events defining the recurrence time in contrast with our present resolution magnitude seems to be independent on the history contained in the seismic catalogs except perhaps for southern california for very short time scales less than about 30 min for the magnitude ranges analyzed

broadband simulations for mw 7 8 southern san andreas earthquakes ground motion sensitivity to rupture speed using the high performance computing resources of the southern california earthquake center we simulate broadband 0 10 hz ground motions for three m w 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

lake sediments record high intensity shaking that provides insight into the location and rupture length of large earthquakes on the alpine fault new zealand abstract understanding the seismic hazard posed by large earthquakes requires paleoseismic investigation because most faults have not ruptured repeatedly during the period of historic records however determining the location and length of fault ruptures using paleoseismic data remains challenging our study demonstrates that lake sediments record the high intensity shaking that occurs proximal to fault rupture allowing the location and length of ruptures to be reconstructed in two lakes adjacent to the alpine fault new zealand seismic shaking is recorded as subaqueous mass wasting derived turbidites formed by coseismic subaqueous slope failures which are overlain by sets of hyperpycnites representing elevated fluvial sediment fluxes from earthquake induced landslides precise radiocarbon age models show that shaking events are synchronous between the two lake sites and correlate with the timing of known alpine fault earthquakes modelled shaking intensities for the last two alpine fault earthquakes show that subaqueous mass wasting occurs when shaking intensities exceed modified mercalli scale mm vi vii and that fluvial sediment fluxes from earthquake induced landslides occur when shaking intensities exceed mm ix the data demonstrate that lake records distinguish between strong mm vi and violent mm ix shaking at a lake site the ability to map the spatial extent of mm ix shaking provides new insights into the timing and extent of rupture for the last five earthquakes on the alpine fault the study demonstrates that lake deposits constrain the spatial extent of rupture during large earthquakes and may yield long records of the spatial and temporal patterns of fault rupture

fault slip and earthquake recurrence along strike slip faults contributions of high resolution geomorphic data article i nfo understanding earthquake eq recurrence relies on information about the timing and size of past eq ruptures along a given fault knowledge of a fault s rupture history provides valuable information on its potential future behavior enabling seismic hazard estimates and loss mitigation stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing eqs analysis of the latter data sets culminated during the mid 1980s in the formulation of now classical eq recurrence models now routinely used to assess seismic hazard within the last decade light detection and ranging lidar surveying technology and other high resolution data sets became increasingly available to tectono geomorphic studies promising to contribute to better informed models of eq recurrence and slip accumulation patterns after reviewing motivation and background we outline requirements to successfully reconstruct a fault s offset accumulation pattern from geomorphic evidence we address sources of uncertainty affecting offset measure ment and advocate approaches to minimize them a number of recent studies focus on single eq slip distribu tions and along fault slip accumulation patterns we put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation cv for eq inter event time and slip per event and find that a single event offsets vary over a wide range of length scales and the sources for offset variability differ with length scale b at fault segment length scales single event offsets are essentially constant c along fault offset accumulation as resolved in the geomorphic record is dominated by essentially same size large offset in crements and d there is generally no one to one correlation between the offset accumulation pattern constrained in the geomorphic record and eq occurrence as identified in the stratigraphic record revealing the higher resolution and preservation potential of the latter while slip accumulation along a fault segment may be dominated by repetition of large nearly constant offset increments timing of surface rupture is less regular

a structural vp model of the salton trough california and its implications for seismic hazard we present a high resolution three dimensional p wave seismic veloc ity model of the sedimentary basin in the salton trough southern california and use the model for spectral element method sem wave propagation and ground motion simulations to quantitatively assess seismic hazard in the region the basin geometry is defined by a surface representing the top of crystalline basement which was constrained by seismic refraction profiles and free air gravity data sonic logs from petroleum wells in the imperial valley and isovelocity surfaces defined by seismic refraction studies were used to define p wave velocity within the sedimentary basin as a function of two variables 1 absolute depth and 2 depth of the underlying crystalline basement surface cbs this velocity function was used to populate cells of a three dimensional spatial array voxet defining the p wave velocity structure in the basin the new model was then resampled in a computational mesh used for earthquake wave propagation and strong ground motion simulations based upon the sem komatitsch et al 2004 simulation of the 3 november 2002 mw 4 2 yorba linda earthquake demonstrates that the new model provides accurate simulation of strong ground motion amplification effects in the salton trough sedimentary basin offering substantial improvements over previous models a hypothetical mw 7 9 earthquake on the southern san andreas fault was then simulated in an effort to better understand the seismic hazard associated with the basin structure these sim ulations indicate that great amplification will occur during large earthquakes in the region due to the low seismic velocity of the sediments and the basin shape and depth

source characteristics of the loma prieta california earthquake of october 18 1989 from global digital seismic data displacement velocity and acceleration records of p and sh body waves recorded at teleseismic distances are analyzed to determine the static and dynamic source parameters of the loma prieta california earthquake of october 18 1989 m sub b 6 6 m sub s 7 1 three distinct bursts of energy corresponding to three subevents can be recognized in most records the displacement waveforms indicate that the first subevent contributes negligible moment while the largest releases of moment and energy are controlled by the second and third subevents the second and third subevents are located north and south of the initial nucleation a fourth small subevent needed to model later features of the p waveforms suggests that slow slip continued after the major releases of energy occurred the waveforms are fit with a fault plane solution having strike 130 degree dip 65 degree and slip 140 degree for all the subevents the focal depths of the two major subevents are 16 and 12 km and their asperity radii are 4 0 and 6 0 km respectively the seismic moment m sub o is 2 2 times 10 sup 26 dyne cm from spectral analysis of teleseismic velocity the radiated energy e sub s is estimated to be 1 1 times 10 sup 22 dyne cm implying an apparent stress of 15 bars more from the high frequency level of the teleseismic acceleration spectrum and a rupture area of 440 km sup 2 the authors derive a dynamic stress drop of 51 bars less

stress evolution of the san andreas fault system recurrence interval versus locking depth 1 major ruptures along the san andreas fault system safs are driven by stress that has accumulated in the upper locked portion of the crust the present day stress accumulation rate on any given fault segment is fairly well resolved by current geodetic measurements model stress accumulation rates vary between 0 5 and 7 mpa per century and are inversely proportional to earthquake recurrence intervals in contrast the total accumulated stress on a given fault segment is poorly resolved since it depends on the uncertain rupture history of each fault over the past few thousand years we simulate accumulated stress at crustal depths for both past and present day conditions by assuming complete release of accumulated slip deficit during major ruptures these speculative results indicate that the southern san andreas which has not ruptured in a major earthquake in over 300 years is currently approaching a threshold stress level

a more precise chronology of earthquakes produced by the san andreas fault in southern california improved methods of radiocarbon analysis have enabled us to date more precisely the earthquake ruptures of the san andreas fault that are recorded in the sediments at pallett creek previous dates of these events had 95 confidence errors of 50 100 calendar years new error limits are less than 23 calendar years for all but two of the dated events this greater precision is due to larger sample size longer counting time lower background noise levels more precise conversion of radiocarbon ages to calendric dates and better stratigraphic constraints and statistical techniques the new date ranges with one exception fall within the broader ranges estimated previously but our estimate of the average interval between the latest 10 episodes of faulting is now about 132 years variability about the mean interval is much greater than was suspected previously five of the nine intervals are shorter than a century three of the remaining four intervals are about two to three centuries long despite the wide range of these intervals a pattern in the occurrence of large earthquakes at pallett creek is apparent in the new data the past 10 earthquakes occur in four clusters each of which consists of two or three events earthquakes within the clusters are separated by periods of several decades but the clusters are separated by dormant periods of two to three centuries this pattern may reflect important mechanical aspects of the fault s behavior if this pattern continues into the future the current period of dormancy will probably be greater than two centuries this would mean that the section of the fault represented by the pallett creek site is currently in the middle of one of its longer periods of repose between clusters and sections of the fault farther to the southeast are much more likely to produce the next great earthquake in california the greater precision of dates now available for large earthquakes recorded at the pallett creek site enables speculative correlation of events between paleoseismic sites along the southern half of the san andreas fault a history of great earthquakes with overlapping rupture zones along the mojave section of the fault remains one of the more attractive possibilities

earthquake supercycles and long term fault memory abstract long records often show large earthquakes occurring in supercycles sequences of temporal clusters of seismicity cumulative displacement and cumulative strain release separated by less active intervals supercycles and associated earthquake clusters are only partly characterized via the traditionally used aperiodicity which measures the extent that a sequence differs from perfectly periodic supercycles are not well described by commonly used models of earthquake recurrence in the poisson model the probability of a large earthquake is constant with time so the fault has no memory in a seismic cycle renewal model the probability is quasi periodic dropping to zero after a large earthquake then increasing with time so the probability of a large earthquake depends only on the time since the past one and the fault has only short term memory we describe supercycles with a long term fault memory ltfm model where the probability of a large earthquake reflects the accumulated strain rather than elapsed time the probability increases with accumulated strain and time until an earthquake happens after which it decreases but not necessarily to zero hence the probability of an earthquake can depend on the earthquake history over multiple prior cycles we use ltfm to simulate paleoseismic records from plate boundaries and intraplate areas simulations suggest that over timescales corresponding to the duration of paleoseismic records the distribution of earthquake recurrence times can appear strongly periodic weakly periodic poissonian or bursty thus a given paleoseismic window may not capture long term trends in seismicity this effect is significant for earthquake hazard assessment because whether an earthquake history is assumed to contain clusters can be more important than the probability density function chosen to describe the recurrence times in such cases probability estimates of the next earthquake will depend crucially on whether the cluster is treated as ongoing or over

repeat times of large earthquakes implications for earthquake mechanics and long term prediction information on the time intervals between large earthquakes is now available for several fault segments along plate boundaries in japan alaska california cascadia and turkey when dates in a sequence are known historically as along much of the nankai trough they provide information on the natural intrinsic variability of the rupture process most sets of repeat times however are dominated by paleoseismic determinations of dates of older large earthquakes which contain measurement uncertainties in addition to intrinsic variability a bayesian technique along with prior information on measurement uncertainties is used to make maximum likelihood estimates of intrinsic repeat time and its normalized standard deviation the coefficient of variation cv it is these intrinsic parameters and their uncertainties that are most useful for understanding the mechanics of earthquakes and for prediction for timescales of a few decades our estimates of intrinsic cv are small 0 to 0 25 for several very active fault segments where deformation is relatively simple large events do not appear to be missing in historic and paleoseismic records and data are available at or near major asperities and away from the ends of rupture zones cv is larger for regions of multibranched faulting overlapping slip near the ends of rupture zones and for data from uplifted terraces at subduction zones a poisson process is an inferior characterization of all of the 11 segments we examined scenarios used by recent working groups that assume either poissonian behavior or renewal processes with cv of 0 5 0 2 for the most active fault segments in the san francisco bay area likely lead to incorrect 30 year probability estimates the hayward fault and perhaps the peninsular segment of the san andreas fault in the san francisco bay area appear to be advanced in their buildup of stress that will be released in future large earthquakes multibranched faulting may account for why the predicted tokai earthquake in japan has not occurred as of 2006 parkfield earthquakes from 1857 to 2004 were characterized by the largest uncertainty of the sequences we studied cv 0 37 which may account for the failure of past predictions the large cv for parkfield fits our hypothesis that relatively weak fault segments are characterized by more irregular earthquake recurrence paleoseismic data from coastal sites along the cascadia subduction zone are characterized by cvs of about 0 3

slip along the san andreas fault associated with the great 1857 earthquake historical records indicate that several meters of lateral slip along the san andreas fault accompanied the great 1857 earthquake in central and southern california these records together with dendrochronological evidence suggest that the rupture occurred along 360 to 400 km of the fault including several tens of kilometers of the currently creeping reach in central california geomorphic expressions of late holocene right lateral offsets are abundant along the 1857 rupture along 300 kilometers of the 1857 rupture between cholame and wrightwood the youngest discernible offset ranges from 3 to 9 1 2 meters dormancy of the fault since 1857 almost certainly indicates that this latest offset was created in 1857 fault slip apparently associated with the 1857 earthquake varies in a broadly systematic way along the trace of the fault it is relatively uniform along each of several long segments but changes rather abruptly in value between these segments this nonuniform displacement pattern may imply that some segments of the fault rupture more frequently or experience a slower long term slip rate than others the 1857 offsets indicate a seismic moment m o between 5 3 and 8 7 10 27 dyne cm assuming a 10 to 15 km depth of rupture and relatively uniform slip as a function of depth a comparison with the rupture length average slip value and tectonic setting of the california earthquake of 1906 m s 8 1 4 indicates a value of m 8 1 4 for the 1857 event

the pyrenean earthquake of february 29 1980 an example of complex faulting abstract an m b 5 1 earthquake occurred on february 29 1980 in the western pyrenees near arudy france the telemetred network of the i p g p operating in this area since 1978 allowed a good localization of this earthquake 43 4 21 n 0 24 59 w depth 4km during the two years preceding this earthquake the seismic activity exhibited a gradual decrease a foreshock of magnitude 1 6 was recorded three hours before the main shock a temporary network set up in the epicentral area a few days after the main shock permitted a precise study of the aftershock sequence fifty fault plane solutions for earthquakes ranging from magnitude 1 5 4 were obtained a complex pattern of faulting was revealed with both strike slip and normal faulting however a regional tectonic stress tensor can be proposed from a detailed investigation of the aftershock sequence this stress tensor is in agreement with previous results in this area

paleoseismic event dating and the conditional probability of large earthquakes on the southern san andreas fault california 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 sedimentolog ical and historical data can be used quantitatively in the process of estimating earth quake 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 dis tributions 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 pre viously 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 were not favorable for recording earthquake evidence previously pro posed correlations of pallett creek x with wrightwood w3 in the 1690s and pallett creek event v with w5 around 1480 fumal et al 1993 appear unlikely after our dating reevaluation apparent internal inconsistencies among event layer and dating relationships around events r and v identify them as candidates for further inves tigation at the site conditional probabilities of earthquake recurrence were estimated using poisson lognormal and empirical models the presence of 12 or 13 events at wrightwood during the same interval that 10 events are reported at pallett creek is reflected in mean recurrence intervals of 105 and 135 years respectively average poisson model 30 year conditional probabilities are about 20 at pallett creek and 25 at wrightwood the lognormal model conditional probabilities are somewhat higher about 25 for pallett creek and 34 for wrightwood lognormal variance rln estimates of 0 76 and 0 70 respectively imply only weak time predictability conditional probabilities of 29 and 46 respectively were estimated for an em pirical distribution derived from the data alone conditional probability uncertainties are dominated by the brevity of the event series dating uncertainty contributes only secondarily wrightwood and pallett creek event chronologies both suggest varia tions in recurrence interval with time hinting that some form of recurrence rate modulation may be at work but formal testing shows that neither series is more ordered than might be produced by a poisson process

space and time dependent probabilities for earthquake fault systems from numerical simulations feasibility study and first results in weather forecasting current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed model steering here we describe a similar approach that is motivated by analyses of previous forecasts of the working group on california earthquake probabilities wgcep our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike slip fault system in california by systematically comparing simulation data to observed paleoseismic data a series of spatial probability density functions pdfs can be computed that describe the probable locations of future large earthquakes we develop this approach and show examples of pdfs associated with magnitude m 6 5 and m 7 0 earthquakes in california

determination of magnitudes of ancient earthquakes from dimensions of observed seismodislocations abstract equations to estimate the magnitude of ancient earthquakes where seismotectonic crustal deformations normal faults strike slip faults etc have been preserved in the epicentral region are presented the equations are based on the results of over one hundred earthquakes including 96 recent continental earthquakes in the magnitude range 5 2 8 7

the evolution of the gulf of corinth greece an aftershock study of the 1981 earthquakes summary a preliminary study of the aftershocks of three earthquakes that occurred near to corinth greece in 1981 is combined with observations of the morphology and faulting to understand the evolution of the eastern gulf of corinth the well located aftershocks form a zone 60km long and 20km wide they do not lie on the main fault planes and are mostly located between the north dipping faulting on which the first two earthquakes occurred and the south dipping faulting associated with the third event a cluster of aftershocks also lies in the footwall of the eastern end of the south dipping fault of the third event morphologically it is observed that in the evolution of the eastern gulf of corinth antithetic faulting apparently predates the appearance of the main faulting at the surface this evolution can be explained by motion on a deep seated shallow angle aseismic normal fault a model based on such a fault also accounts for the aftershock distribution of the 1981 earthquakes

historical pattern and behavior of earthquake ruptures along the eastern boundary of the sichuan yunnan faulted block southwestern china abstract the eastern boundary of the sichuan yunnan faulted block in southwestern china which contains four major fault zones named xianshuihe anninghe zemuhe and xiaojiang behaves as a huge left lateral strike slip active fault system where the most frequent seismicity in continental china occurs to uncover the history of earthquake ruptures of this fault system we developed an empirical relation between rupture extent and seismic intensity distribution based on data of those earthquakes whose rupture extents and intensity distributions are well known through analyzing various types of data including distributions of damage or intensity of historical earthquakes as well as surface ruptures and aftershock zones of modern earthquakes we determined systematically the locations and spatial extents of ruptures for 36 main earthquakes and built up a spatial temporal pattern of the rupture history of the fault system for the last several hundred years the spatial temporal rupture pattern contains information of multi cycle and broad scale ruptures from which we find that for most fault segments scales of segment ruptures are time or cycle variable and only in two or three cases do scales of segment ruptures in successive cycles seem to be characteristic in infrequent cases several adjacent and connecting fault units may rupture simultaneously resulting in cascading ruptures triggering of ruptures is common along the fault system but differs in various periods even on a single fault zone triggered ruptures may not occur on fault segments adjacent to a preceding rupture of major earthquake but on other segments at some distance away from the preceding rupture implying that the rupture history determines whether a segment can be triggered or not recurrence intervals of major segment ruptures are longer on the anninghe and zemuhe fault zones and on the southernmost segment of the xiaojiang fault zone than that on the xianshuihe fault zone and the northern and middle segments of the xiaojiang fault zone probably due to the partitioning of slip along major and secondary faults and their complicated fault geometry four seismic gaps along the fault system are recognized where major earthquakes have been absent for a long time

quantitative relations of seismic source parameters and a classification of earthquakes abstract relations between earthquake parameters moment m0 fault area s fault length l and width w stress drop time characteristics and magnitudes and faulting type dip slip ds and strike slip ss are quantitatively analyzed using a dataset of 240 events m 5 the analysis is carried further toward an earthquake systematization by introducing earthquake classes the results are 1 1 l w 2 1 for ds l w 2 30 for ss and l w 3 7 for giant m0 1029 dyne cm earthquakes respectively 2 2 log m0 1 5 log s 22 2 s in km2 and tentatively log m0 2 45 log s 17 49 for ds and ss and giant earthquakes respectively 3 3 the large scatter of data in m0 s dependences is the result of the combined effect of the variation in and l w 4 4 the concept of constant is replaced by variable to explain the large variations in relations between m0 s l and w for both ds and ss earthquakes and partly between body and surface wave magnitudes low intermediate and high stress drop gd 30 30 60 and 60 bar respectively earthquakes are defined 5 5 a relation of reciprocity exists between seismic slip fault length and width and stress drop 6 6 a saturation of s for some very large earthquakes is suggested from the interpretation of actual data on m0 s l w etc 7 7 the total source duration tsd increases with m0 in relation with earthquake type and tentatively log m0 2 16 log tsd 24 50 holds for ds earthquakes 8 8 log m0 1 5 mm 16 1 holds for mm brune engen mantle wave magnitude 8 5 8 75 9 9 more magnitudes of shorter or longer period on both body and surface wave basis are useful in constraining significant earthquake features 10 10 low and high frequency earthquakes can be distinguished using the gutenberg richter relation ms mb as a reference relation or a relation between ms and mmaxb 11 11 aki s similarity conditions are extended by adding two more conditions as to express more specifically four basic features geometry deformation frequency and time of the earthquake source 12 12 a reference earthquake is defined by criteria consistent with the similarity conditions 13 13 on this basis and in view of nonsimilarity of earthquakes in their totality a scheme for earthquake classification is proposed

source complexity of the 1988 armenian earthquake evidence for a slow after slip event we analyzed teleseismic p and s waves using a multiple event deconvolution method to investigate the source process of the spitak armenia earthquake of december 7 1988 teleseismic long period body waves exhibit complex waveforms significantly more complex than those normally seen for an event of this size we identified two groups of subevents one is a group of strike slip events during the first 20 s the other is a dip slip event initiating at about 30 s after the initial rupture the tensor sum of all the subevents is essentially strike slip strike 302 dip 59 rake 143 with a scalar moment of 1 47 10 19 n m the seismic moment of the dip slip event strike 89 dip 60 rake 88 is 5 6 10 18 n m nearly 40 of the total and the moment release rate is slower than the other subevents with a strike slip mechanism we call this event a slow after slip event the mechanism of the after sup event is consistent with the present day deformation pattern in the caucasus where north south compression is predominant due to the continental collision between the arabian plate and the russian platform this result suggests that in a region where both strike slip motion and crustal shortening are taking place like southern california a large strike slip event may accompany large thrust events and vice versa in order to determine the total coseismic deformation pattern it is essential to resolve these multiple events in time space and mechanism

source mechanisms of three moderate california earthquakes of july 1986 abstract we studied the source processes of three moderate size earthquakes in california the m s 6 0 event of july 8 1986 near palm springs the m s 5 8 shock of july 13 1986 offshore of oceanside and the m s 6 2 event of july 21 1986 in the chalfant valley on the east side of the sierra nevada the centroidal source parameters are estimated by inversion of long period p and sh waves recorded at teleseismic distances by seismographs of worldwide networks a more detailed description of the source is then obtained by analyzing broadband seismograms the north palm springs earthquake had a simple rupture process most of the seismic moment was released in the first 3 sec in a single step the strike of the source fault plane follows the average trend of the banning fault and its dip agrees with the dip of the fault plane delineated by the aftershocks the faulting mechanism of the main shock is right lateral strike slip with a sizable reverse component that is consistent with uplift north of the banning fault the earthquake offshore of oceanside had a slightly more complex rupture process the far field source time function consists of two pulses that represent the release of most of the moment in the first 3 sec the source mechanism indicates reverse faulting with the compressional axis trending northeast almost perpendicular to the trend of mapped faults offshore the event does not appear to be associated with major mapped faults in the area but the strike of one of the nodal planes agrees with the trend of the major mapped faults offshore and its mechanism is consistent with the missing component of plate convergence not taken up by the onshore strike slip fault systems and the idea of a weak san andreas fault system the rupture process of the chalfant valley earthquake was yet more complicated the source time function indicates that in a 4 sec time window three asperities were broken the source mechanism indicates right lateral strike slip faulting with a small normal faulting component on a fault that dips approximately 50 southwest earthquake activity suggests that presently the deformation in the northern part of the owens valley which includes the chalfant valley is dominated by conjugate strike slip faults which strike obliquely to the main range bounding normal faults the waveforms indicate the presence of a low velocity zone at a depth of about 20 km in the crust in the chalfant valley a synthesis of information from waveform modeling first motion fault plane solutions and aftershock distributions indicates that the nucleation and or termination of rupture for the north palm springs and the chalfant valley events were controlled by preexisting fault geometry

source parameters of earthquakes in the nevada seismic zone 1915 1943 the nevada seismic zone has historically been one of the most active seismic regions of the intermountain west although all large m 7 0 earthquakes located within this zone occurred prior to the establishment of a worldwide seismograph network most have been well recorded instrumentally this study uses available instrumental data to determine the source parameters for some of the earliest earthquakes occurring within the region namely the 1915 m 7 6 pleasant valley and 1932 m 7 2 cedar mountain earthquakes and several smaller events of 5 5 m 6 5 occurring within the cedar mountain region between 1934 and 1943 results of body waveform inversions suggest that the pleasant valley earthquake at the northern end of the nevada seismic zone is a complex event best fit by a multiple source time function waveform and first motion information for the cedar mountain earthquake located within the walker lane suggest the earthquake was composed of two events each having significant components of right lateral strike slip motion rakes of 176 to 179 waveforms of the m 6 5 excelsior mountain earthquake located only 40 km southwest of cedar mountain suggest the earthquake was a simple rupture along a normal fault rake of 90 20 although surface faulting indicates that the event had a component of left lateral strike slip motion

holocene geologic slip rate for the banning strand of the southern san andreas fault southern california 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

coseismic slip on the southern cascadia megathrust implied by tsunami deposits in an oregon lake and earthquake triggered marine turbidites 1 we test hypothetical tsunami scenarios against a 4 600 year record of sandy deposits in a southern oregon coastal lake that offer minimum inundation limits for prehistoric cascadia tsunamis tsunami simulations constrain coseismic slip estimates for the southern cascadia megathrust and contrast with slip deficits implied by earthquake recurrence intervals from turbidite paleoseismology we model the tsunamigenic seafloor deformation using a three dimensional elastic dislocation model and test three cascadia earthquake rupture scenarios slip partitioned to a splay fault slip distributed symmetrically on the megathrust and slip skewed seaward numerical tsunami simulations use the hydrodynamic finite element model selfe that solves nonlinear shallow water wave equations on unstructured grids our simulations of the 1700 cascadia tsunami require 12 13 m of peak slip on the southern cascadia megathrust offshore southern oregon the simulations account for tidal and shoreline variability and must crest the 6 m high lake outlet to satisfy geological evidence of inundation accumulating this slip deficit requires 360 400 years at the plate convergence rate exceeding the 330 year span of two earthquake cycles preceding 1700 predecessors of the 1700 earthquake likely involved 8 9 m of coseismic slip accrued over 260 years simple slip budgets constrained by tsunami simulations allow an average of 5 2 m of slip per event for 11 additional earthquakes inferred from the southern cascadia turbidite record by comparison slip deficits inferred from time intervals separating earthquake triggered turbidites are poor predictors of coseismic slip because they meet geological constraints for only 4 out of 12 33 cascadia tsunamis

source parameters of earthquakes along the coastal margin of west africa and comparisons with earthquakes in other coastal margin settings abstract the coastal margins of western africa and most of the eastern americas are considered to be stable continental interiors where large earthquakes occur infrequently since these regions have similar geologic and tectonic histories it might seem reasonable to expect similarities between their large earthquakes on the other hand current plate forces acting on these regions differ and may lead to regional differences in earthquakes to examine the similarities of coastal margin earthquakes we first determined the source parameters for six earthquakes of m 5 5 occurring along the coastal margin of west africa a region that has not previously been studied in detail results of this analysis indicate that the earthquakes are shallow 8 15 km strike slip events along high angle faults dips generally 80 with nodal planes having orientations similar to those of faults mapped in the exposed precambrian basement five out of seven events show complexities in their source time functions east of the cameroon line most p axes trend northeast southwest to east west earthquakes west of the cameroon line show less coherency of stress field with p axes for onshore events trending northwest southeast and for offshore events north south to northeast southwest in contrast m 5 5 earthquakes of the eastern coastal margin of north and south america have reverse mechanisms with more moderate dips on nodal planes 45 70 and over 50 have east west oriented p axes which reflect stresses caused by the motion of north and south america relative to europe and africa in north america earthquakes appear to occur on faults that cannot be associated with surficial geology occur shallower or deeper than west african events and have shorter rupture lengths for the equivalent moment these differences suggest that west african events may not serve as useful analogs for events expected along the american coastal margin

the spitak armenia earthquake of 7 december 1988 field observations seismology and tectonics the epicentre of the destructive earthquake that devastated northern armenia the strongest in the region since historical times is located within the lesser caucasus a mountain country subjected to north south compression by the push of the arabian plate a french soviet field expedition studied surface breaks and aftershock activity the fault scarp could be followed for 13 kilometres and showed a reverse dislocation of 1 6 metres aftershocks are shallower than 13 kilometres and delimit a ruptured surface of about 300km2

eddy induced carbon transport across the antarctic circumpolar current the implications of a mesoscale eddy for relevant properties of the southern ocean carbon cycle are examined with in situ observations we explored carbon properties inside a large 190 km diameter cyclonic eddy that detached from the subantarctic front saf south of tasmania in march 2016 based on remote sensing the eddy was present for 2 months in the subantarctic zone saz an important region of oceanic carbon dioxide co2 uptake throughout the annual cycle and carbon subduction i e where mode and intermediate waters form before it was reabsorbed into the saf the eddy was sampled during the middle of its life 1 month after it spawned comparatively the eddy was 3 c colder 0 5 practical salinity unit fresher and less biologically productive than surrounding saz waters the eddy was also richer in dissolved inorganic carbon dic and had lower saturation states of aragonite and calcite than the surrounding saz waters as a consequence it was a strong source of co2 to the atmosphere with fluxes up to 25 mmol c m 2 d 1 compared to the saf waters from which it originated dic concentration in the eddy was 20 mol kg 1 lower indicating lateral mixing small scale recirculation or eddy stirring with lower dic saz waters by the time the eddy was observed as they are commonly spawned from the antarctic circumpolar current and as 50 of them decay in the saz the rest being reabsorbed by the saf n these types of eddies may represent a significant south north transport pathway for carbon across the acc and may alter the carbon properties of saz waters

active tectonics in 4d high resolution abstract with a little more than 100 years since the publication of seminal and field defining investigations active tectonics is still a relatively young sub discipline of structural geology this research field addresses the accumulation of strain due to plate tectonic motion and more importantly release thereof through the occurrence of earthquakes or other strain releasing events in that regard active tectonics aims to characterize the incremental steps of plate tectonics determining earthquake chronologies fault slip rates and other common objectives importantly feed into our understanding of for example fault mechanics and crustal rheology characterizing the recurrence of large and potentially devastating earthquakes is further motivated by seismic hazard assessment and risk mitigation the primary data source in active tectonics is surface and shallow subsurface evidence of faulting presenting itself in topographic and stratigraphic data sets respectively field observations and air photo interpretation of displaced stratigraphic and geomorphic markers were used almost 40 years ago to formulate end member models of earthquake recurrence technological developments since then especially within the last two decades have dramatically increased the abundance and resolution of topographic data sets and the ability to date stratigraphic units and geomorphic surfaces enabling the formulation of better informed conceptual models of earthquake recurrence here we provide an overview of the high resolution topographic data sets and dating methods that enabled the recent advances of active tectonics

the carbon dioxide system and net community production within a cyclonic eddy in the lee of hawaii abstract the dynamics of dissolved inorganic carbon dic and processes controlling net community production ncp were investigated within a mature cyclonic eddy cyclone opal which formed in the lee of the main hawaiian islands in the subtropical north pacific gyre within the eddy core physical and biogeochemical properties suggested that nutrient and dic rich deep waters were uplifted by 80 m relative to surrounding waters enhancing biological production a salt budget indicates that the eddy core was a mixture of deep water 68 and surface water 32 ncp was estimated from mass balances of dic nitrate nitrite total organic carbon and dissolved organic nitrogen making rational inferences about the unobserved initial conditions at the time of eddy formation results consistently suggest that ncp in the center of the eddy was substantially enhanced relative to the surrounding waters ranging from 14 1 10 6 0 110 m within the euphotic zone to 14 2 9 2 0 50 m within the mixed layer to 18 5 10 7 0 75 m within the deep chlorophyll maximum layer mmol c m 2 d 1 depending on the depth of integration ncp in the ambient waters outside the eddy averaged about 2 37 4 24 mmol c m 2 d 1 in the mixed layer 0 95 m most of the enhanced ncp inside the eddy appears to have accumulated as dissolved organic carbon doc rather than exported as particulate organic carbon poc to the mesopelagic our results also suggest that the upper euphotic zone 0 75 m above the deep chlorophyll maximum is characterized by positive ncp while ncp in the lower layer 75 m is close to zero or negative

application of an iterative least squares waveform inversion of strong motion and teleseismic records to the 1978 tabas iran earthquake an iterative least squares technique is used to simultaneously invert the strong motion records and teleseismic p waveforms for the 1978 tabas iran earthquake to deduce the rupture history the method solves for both slip amplitudes and rupture times on a finite fault several inversions of the data are done to determine the best fitting hypocenter average rupture velocity and source time function within the range of our parameter search the effects of using different data sets and different parametrizations of the problem linear versus nonlinear are also considered teleseismic body waves are shown to be essential to obtain a reliable solution due to the sparse coverage of the fault plane by strong motion stations a simple triangular source time function is compared with a modified kostrov source time function for a circular rupture and a constant propagating stress drop although the waveforms used in the inversions can not resolve between these two time functions the kostrov source time function gives a moment estimate and maximum fault displacement more consistent with long period surface waves and field observations the results of the iterative inversion for slip amplitudes and rupture times are compared with the results of a linear inversion for slip amplitudes in which the rupture velocity is fixed flexibility in the sequence of faulting for the linear inversion is obtained by allowing multiple rupture intervals a consensus of all the inversion runs indicates a complex multiple source for the tabas earthquake with four main source regions over a fault length of 90 km and an average rupture velocity of 2 5 km sec

the july 1986 oceanside ml 5 3 earthquake sequence in the continental borderland southern california an earthquake of m l 5 3 occurred at 32 58 7 n 117 51 5 w southwest of oceanside in san diego county at 13 47 13 july 1986 ut this main shock was followed by an extensive aftershock sequence with 55 events of m l 3 0 during july 1986 the epicenters of the main shock and aftershocks are located at the northern end of the san diego trough bahia soledad fault zone sdt bs where it changes strike from northwest to a more westerly direction through a left offset or a bend in the fault the northwest striking sdt bs is one of three strike slip fault systems that constitute the offshore agua blanca fault system the spatial distribution of the aftershocks indicates a unilateral 7 to 9 km long rupture to the east southeast away from the epicenter of the main shock the focal mechanism of the main shock also has an east southeast striking and south dipping plane with mostly reverse movement on it focal mechanisms of the m l 3 0 aftershocks show both reverse and strike slip movement the reverse focal mechanisms indicate that this sequence may have occurred on a thrust fault that provides for a left stepping offset or a bend in the san diego trough fault as movement is transferred to the west along the santa cruz catalina island escarpment some of the aftershocks that are located to the southeast of the main shock and have strike slip focal mechanisms suggest activation of the northwest trending san diego trough fault a stress inversion of the focal mechanism data shows that the maximum principal stress determined from the focal mechanisms of the main shock and 22 aftershocks that occurred within 36 hours of the main shock has an azimuth of s30 w plunging 18 the maximum principal stress determined from 30 aftershocks that occurred from 15 july to 2 october 1986 has an azimuth of s20 w plunging 18 the values the measure of the relative sizes of the principal stresses are approximately 0 07 and 0 1 respectively indicating that the intermediate and minimum principal stress are of similar magnitude the results of the stress inversion and the focal mechanisms that showed reverse faulting suggest that the inner continental borderland offshore from oceanside is not currently a pure strike slip tectonic regime but rather a strike slip mixed with reverse faulting regime when the 52 aftershock focal mechanisms are divided into four groups and the stress inversion is repeated the change in stress can be described as a progressive counter clockwise rotation of 14 of the orientation of the maximum principal stress to a more southerly direction with the greatest change in stress orientation observed shortly after the main shock the abundance of aftershocks may be related to the large temporal variation in stress orientation that in turn may have resulted from the small stress drop of the main shock

a 2000 yr rupture history for the alpine fault derived from lake ellery south island new zealand determining the earthquake segmentation of plate boundary transform faults remains a scientific challenge because paleoseismic data sets rarely resolve the end points of past ruptures in this study we test whether lacustrine paleoseismology can be used to assess rupture end points and the earthquake segmentation of the alpine fault one of the longest and fastest slipping plate boundary transform faults on earth sediment cores from lake ellery record eight episodes of high intensity shaking modified mercalli intensity mm ix from alpine fault earthquakes as event sequences of a turbidite produced by coseismic subaqueous mass wasting overlain by deposits representing sediment flux from co and postseismic landsliding in the fluvial catchment age depth modeling constrains the timing of shaking events at a decadal resolution facilitating correlation with two previously published lake records to reconstruct the spatial distribution of mm ix shaking along 150 km of the alpine fault when resolved with existing on and near fault paleoseismic records the lake data set demonstrates that independent ruptures of the south westland and central segments occurred in a d 845 775 and a d 739 646 and a d 646 592 and a d 416 370 respectively lakes adjacent to the alpine fault provide paleoseismic records with sufficient spatial and temporal resolution to define along strike differences in the pattern of rupture capable of distinguishing rupture termination at a geometric segment boundary this multilake study suggests that locating the end points of ruptures using lacustrine paleoseismology will be most applicable in midlatitude convergent plate boundary settings where along strike topography and quaternary glaciation have resulted in the widespread distribution of suitable lakes

changes in the tectonic regime above a subduction zone of andean type the andes of peru and bolivia during the pliocene pleistocene this paper adresses the changes in the tectonic regime in the peruvian and bolivian andes that have occurred since the upper miocene when the present day elevation of the cordillera above sea level has been almost reached the stress patterns are deduced essentially from a field study of fault kinematics and a numerical inversion of the slip vector data measured on the fault planes the cuzco fault system in southern peru is chosen as an example to illustrate the methodology used in this region striations on both active and holocene faults are in agreement with a n s extension but faults affecting early pleistocene deposits exhibit two families of striations the younger results from the previous n s extension the older involving reverse motions results from either an e w or a n s compression faults affecting pliocene formations often show an oldest family of striations resulting from a ne sw or an e w trending extension thus three tectonic regimes are demonstrated which are also supported by regional unconformities and sedimentological data 1 a pliocene extensional regime 2 a lower pleistocene compressional regime and 3 a mid pleistocene present day extensional regime similar analyses conducted in the pacific and sub andean lowlands allow sketching of the successive pliocene pleistocene stress patterns in the central andes the quaternary and present day stress pattern is characterized by a n s extension in the high andes and in the pacific lowlands and by an e w compression in the sub andean lowlands and at the contact between the nazca and south american plates this stress pattern is interpreted at a large wavelength 100 km as an effect of compensated topography this model supposes that the vertical lithospheric stress zz increases with the topography the crustal thickness and the low density mantle beneath and that the lithospheric maximum compressional horizontal stress hmax trending e w roughly parallel to the convergence is fairly constant on both edges of the andes the tectonics being compressional zz is 3 and hmax is 1 in the high andes zz becomes 1 then the e w trending hmax is 2 and hmin trending n s is 3 allowing extension to occur in this direction the pliocene stress pattern was characterized by a ne sw or an e w trending extension in the high andes in the pacific lowlands and possibly in the sub andean lowlands this stress pattern was clearly different from the present day one because the e w trending stress was hmin this required a weak push or eventually tractional boundary forces acting on the south american lithosphere it is suggested that this might result from a strong slab pull due to a long steeply dipping slab which decreased the value of the xx stress transmitted to the overriding plate the early pleistocene state of stress was compressional since the elevation of the andes had not markedly decreased during this period this required an increase of the e w trending stress value this resulted from a strong coupling between the two lithospheric plates possibly due to a rupture of a long slab under its own weight other spatial changes in the stress pattern are related to the particular situation of the forearc to the subduction of the buoyant nazca ridge and to the different dips of the slab extension in the high andes is of small magnitude of the order of 1 during the last 1 2 m y in a few basins it may have attained 40 during the pliocene 5 3 m y

on the oxidation ability of the nasa mars 1 soil simulant during the thermal volatilization step implications for the search of organics on mars 1 the search for organic molecules on mars has been a major goal in planetary science viking performed the first analyses of the martian soil in 1976 but was unable to detect organics at the ppb level using the thermal volatilization tv method three decades later the phoenix lander conducted analyses of martian soil samples by tv and found the release of co2 from 400 to 680 c that was attributed to mg or fe carbonate adsorbed co2 or organic molecules we have previously reported that high levels of iron species present in the soil efficiently oxidize the organics to co and co2 by tv here we explore in detail the oxidation ability of the organic free nasa mars 1 soil simulant during tv in molecular hydrogen or in the presence of stearic and mellitic acids our results imply that there are two sources of strong oxidizers in palagonite soils 1 hydroxyl radicals originating from the dehydroxylation of the silica layer matrix at 320 c to 600 c and 2 oxygen atoms released by the reduction of iron iii to iron ii species at 320 c to 600 c and of iron ii to metallic iron at 850 1150 c these strong oxidizers completely decompose stearic or mellitic acids to carbon dioxide when they are present at low levels 0 05 wt in the nasa mars 1 soil simulant since organics are expected to be present at very low levels on mars future space missions utilizing tv will face the challenge of determining if any co2 released is of inorganic or organic origin

m 7 0 earthquake recurrence on the san andreas fault from a stress renewal model 1 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

the quantitative characteristics of earthquake sources as determined in the seismological practice of the u s s r abstract the source parameter determinations in the u s s r from seismological observations using standard instruments including a station with digital registration stsr and frequency selective equipment tchiss are discussed to determine magnitude from p waves with short period instruments a calibrating function of the homogeneous magnitude system hms is recommended for seismological practice in the u s s r for assessment of source parameters seismic moment displacement and stress drop a special multi factor procedure for focal spectra analysis is developed magnitudes and focal dynamic parameters of 30 strong earthquakes are presented and compared with analogue parameters of the neis and harvard solutions it is proved that magnitudes determined by surface wave m lh essn edinaya systema seismicheskih nabludenii the unified system of seismic observations and m s neis practically coincide magnitude m b neis has been systematically underestimated as compared with m pv essn seismic moments by essn m p o and neis m o cmt are linearly dependent a comparison of fault plane solutions shows almost full agreement in about half the number of the earthquakes considered the orientation of nodal planes and axes of principal stresses coincide despite their belonging to different stages of faulting the time frequency fields by tchiss data for earthquakes with equal magnitudes and seismic moments show a different character of energy release

earthquake supercycles in central italy inferred from 36cl exposure dating we use 36cl surface exposure dating to determine the slip release pattern over the last 15 kyr for the velino magnola fault a major active normal fault in central italy we sampled the fault at five well separated sites along its length and modeled the 36cl concentrations measured in the 376 samples we find that the fault broke in at least 9 large earthquakes that occurred in two 5 6 ka long supercycles each cycle included a 4 5 ka long phase of relative quiescence followed by a cluster of at least 3 large earthquakes or earthquake sequences that released most of the accumulated strain in 1 ka all 9 identified events broke the entire fault and produced maximum surface slips of 2 3 m though the velino magnola fault seems presently in a stage of relative quiescence it may re enter a phase of paroxysmal seismic activity in a few hundred of years

slip history of the 1944 bolu gerede earthquake rupture along the north anatolian fault system implications for recurrence behavior of multisegment earthquakes 1 recent research shows that active fault systems produce multisegment earthquakes however we have yet to understand the faulting behavior of various spatial patterns of segments we conducted a three dimensional trenching survey to reconstruct the detailed slip history of a fault segment that ruptured as one of the multisegment ruptures along the north anatolian fault system the trench site on the gerede segment recorded a maximum right lateral slip of up to 6 m that was associated with the 1944 bolu gerede earthquake m 7 4 fault exposures show evidence of four paleoearthquakes radiocarbon dates a refined probability density distribution and correlation with historical earthquakes place the mean repeat time at 330 years four discrete paleoslips yield a slip per event of 5 0 0 8 m with a coefficient of variation of 0 2 our research suggests that multisegment earthquakes exhibit various spatial patterns regardless of recurrence with quasiperiodicity and characteristic slip coincidentally the fault geometry exhibits extremely linear traces suggesting simple stress accumulation and release through earthquake cycles furthermore the 1944 event did not occur in a single segment and the gerede segment probably ruptured within a slip pulse like rupture during a multisegment earthquake a comparable geological slip rate of 17 mm a 1 based on a gps based strain rate supports the persistence of macroscopic asperity through recent geological time therefore we conclude that a segment with simple fault geometry along a strike slip fault system plays an important role in forecasting the timing of future multisegment earthquakes but the spatial extent of such earthquakes needs to be explored further

six similar sequential ruptures of the san andreas fault carrizo plain california we document the precise sizes but not the dates of the six latest offsets across the san andreas fault at wallace creek california three and perhaps four of these including the latest in 1857 show dextral offset of 7 5 8 m the third and fourth offsets however are just 1 4 and 5 2 m the predominance of similar offsets for the latest six events suggests that the fundamental properties of the fault system that control slip size do not vary greatly from event to event the large offsets imply that ruptures involving this site are typically more than 200 km long