postseismic relaxation following the 1989 ms7 1 loma prieta earthquake central california 1 the postseismic relaxation postseismic displacement less displacement that would have occurred at the preseismic rate measured by gps and leveling following the 1989 ms7 1 loma prieta earthquake is reexamined the temporal dependence of the relaxation over the first 1200 days postseismic is well described by 1 e t where 414 92 days quoted uncertainties are standard deviations that temporal dependence appears to be a linear function of the cumulative number of m 2 5 aftershocks that have occurred the relaxation is attributed to afterslip 1 56 0 20 m dextral strike slip and 0 60 0 04 m reverse slip on the downdip extension depth 16 21 km of the coseismic rupture plus a collapse 0 11 0 02 m fault normal displacement of the rupture zone depth 5 16 km because the postseismic uplift was determined by leveling over a route with relief in excess of 1000 m an allowance 18 2 ppm of height above the base elevation for excess beyond corrections already applied height dependent error in the measured uplift was estimated simultaneously with the afterslip and collapse parameters this new solution for afterslip and collapse on the plane of the rupture provides an alternative explanation to the suggestion by burgmann et al 1997 that the postseismic deformation was due to afterslip on the coseismic rupture and on a nearby shallow 30 dipping thrust

a general geomorphological recession flow model for river basins 1 recession flows in a basin are controlled by the temporal evolution of its active drainage network adn the geomorphological recession flow model grfm assumes that both the rate of flow generation per unit adn length q and the speed at which adn heads move downstream c remain constant during a recession event thereby it connects the power law exponent of dq dt versus q discharge at the outlet at time t curve with the structure of the drainage network a fixed entity in this study we first reformulate the grfm for horton strahler networks and show that the geomorphic g is equal to d d 1 where d is the fractal dimension of the drainage network we then propose a more general recession flow model by expressing both q and c as functions of horton strahler stream order we show that it is possible to have g for a recession event even when q and c do not remain constant the modified grfm suggests that is controlled by the spatial distribution of subsurface storage within the basin by analyzing streamflow data from 39 u s geological survey basins we show that is having a power law relationship with recession curve peak which indicates that the spatial distribution of subsurface storage varies across recession events

the 1930 santa monica and the 1979 malibu california earthquakes the malibu earthquake m l 5 0 that occurred 1 january 1979 in santa monica bay was located at 33 56 9 n and 118 41 3 w and at a depth of 10 km the focal mechanism of the main shock as determined from first motions recorded by short period high gain seismic stations in southern california shows reverse faulting with one plane dipping 55 to 60 to the north striking 275 to 290 and the second plane dipping 30 to 38 to the south and striking 100 to 120 more than 400 aftershocks were recorded during 1979 focal mechanisms for 20 aftershocks of m 3 0 show similar reverse mechanisms as the main shock the main shock and aftershocks m 2 5 were relocated using a local velocity model and a set of corresponding station delays the aftershocks define a volumetric hypocentral zone 4 km 6 km west trending with depths ranging from 6 to 11 km this 1979 malibu main shock aftershock sequence probably occurred on the eastern end of the anacapa dume fault the santa monica earthquake m l 5 2 that occurred 31 august 1930 was relocated using station delays calculated from the 1979 date set the relocated 1930 epicenter is located near the western end of the santa monica fault the 1979 and 1930 main shocks can be interpreted to define a 8 to 10 km north south sidestep between the anacapa dume and santa monica faults possible segmentation of these two fault systems suggests that they are unlikely to rupture simultaneously in one large earthquake

spatial variations in stress within the 1987 whittier narrows california aftershock sequence new techniques and results the ml 5 9 whittier narrows california earthquake of october 1 1987 triggered a complex aftershock sequence the aftershocks had many different focal mechanisms including thrusting on e w striking north dipping planes similar to the main shock right lateral motion on nw se striking planes similar to the ml 5 3 aftershock on october 4 1987 thrusting on n s striking planes and left lateral motion on n s striking planes i attempt to interpret these mechanisms in terms of a stress field that may have caused them previously stress inversion methods based on focal mechanisms assumed that the stress field was spatially uniform in order to test for the spatially varying effect of the main shock s dislocation on the aftershocks focal mechanisms a new inversion technique was developed that solves for a uniform stress field that is superimposed on a given spatially varying stress field a series of simulations were performed to test both the new method and an older method that uses only the uniform component of the stress field these simulations show that both techniques work but will be limited by the amount of noise in the data and the accuracy to which the given spatially varying stress field resembles the actual spatially varying stresses most importantly the simulations show that the older methods do work when the stress field has a uniform component that is at least as large as the spatially varying component the simulations also show that when applying the older stress inversion techniques one can determine if the results are valid and the amount of spatially varying stresses present by examining the misfit between the data and the model application of these techniques to the whittier narrows aftershocks suggests that the uniform component of the stress field and the complex faulting corresponds to the response of an elastic halfspace to a simple regional n s compression the misfit between the data and the uniform model demonstrate the presence of spatially varying stresses at whittier narrows however their form as shown by the simulations can not be determined with this data set and these techniques

reply to comment on source complexity of the october 1 1987 whittier narrows earthquake by allison l bent and donald v helmberger

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

dating low grade metamorphic events by shrimp u pb analysis of monazite in shales although the u pb isotopic system is widely used to date magmatism and medium to high grade metamorphism dating low grade metamorphic events has been hampered by a scarcity of suitable minerals we show that monazite forms in shales during low grade metamorphism and can be dated by in situ u pb analysis providing precise ages for low temperature thermal events in proterozoic shales from the pine creek inlier of northern australia monazite and xenotime crystals that formed in a contact aureole yield ages synchronous with granite intrusion ca 1830 ma in the pilbara craton of northwestern australia monazite growth 2192 5 m y ago coincided with basaltic volcanism and rifting an event apparently responsible for hydrothermal iron oxide mineralization in a nearby giant iron ore deposit the mineralizing environment was highly oxic and bathed by meteoric fluids thus our results imply the existence of an oxygen rich atmosphere by 2200 ma given the abundance of shales in the stratigraphic record and the likely widespread distribution of monazite in such rocks in situ u pb dating of monazite may become an important chronometer for low grade metamorphic events

seismicity and geometry of a 110 km long blind thrust fault 1 the 1985 kettleman hills california earthquake the august 4 1985 kettleman hills earthquake was the third in a sequence of moderate shocks to occur beneath the northern half of a 110 km long fold chain bounding the eastern california coast ranges the 1982 mw 5 4 new idria 1983 mw 6 5 coalinga and 1985 mw 6 1 kettleman hills events define a southward progression of seismic activity beneath the fold we use teleseismic waveforms geodetic modeling hypocenters relocated in a three dimensional velocity model and subsurface structural data to investigate the kettleman hills earthquake the main shock results from motion on a shallowly dipping thrust fault buried at 10 km depth aftershocks and coseismic fault slip extend 20 km along the fold axis nearly the full extent of the kettleman hills north dome anticline aftershocks occur primarily several kilometers in front of the fault tip and in the core of the anticline the main shock and several foreshocks occurred at a 2 km right step in the quaternary fold axis which also corresponds to the southern end of the 1983 coalinga and northern end of the 1985 kettleman hills aftershock zones from this we infer that the step in the fold is caused by an offset or tear in the underlying fault the scalar seismic moment is 1 6 1018 n m consistent with the geodetic deformation and the duration of rupture is 16 s 3 4 times greater than for the average earthquake with this scalar moment the slow rate of moment release provides an explanation for the low level of ground shaking and low local magnitude reported for the event the peak of the geodetic uplift is located 5 km perpendicular to the quaternary fold axis we argue that the fault is propagating northeast into the undeformed san joaquin valley sediments and that the overlying fold is growing at about 0 5 mm yr

the mission link between the hayward and calaveras faults the left stepover between the calaveras and hayward faults gives rise to compressive strain that is accommodated by vertical deformation producing the highest hills bordering the east side of san francisco bay monument peak to mission peak the projection of the active trace of the hayward fault is separated 3 5 km from the junction of the northern and southern segments of the calaveras fault at calaveras reservoir for pure strike slip on the hayward and calaveras faults the stepover region is compressed in area at a rate given by the separation times the long term slip rate of 9 mm yr on the hayward fault assuming a seismogenic depth of 10 km the horizontal compression accumulated over 150 years is equivalent to a dip slip seismic moment of 2 8 1018 n m this moment if released in a single event would generate an earthquake of magnitude 6 3 due to dip slip alone dip slip may occur on buried faults throughout the stepover region the base of the southwest face of monument peak suggests a buried thrust or reverse fault dipping northeast the prominent scarp on mission peak has the same strike and sense of slip current microearthquakes between the calaveras and hayward faults align parallel to the mission fault but show only horizontal slip on a vertical fault plane a dipping fault is needed to satisfy the geometric constraint of the convergence therefore the mission fault zone must consist of two or more fault surfaces inclined at different dip angles as is observed in the san andreas fault zone in the loma prieta area horizontal slip is building up stress on the inclined fault which is currently locked growing compressive stress will increasingly impede horizontal slip until a thrust or reverse slip event occurs allowing then more horizontal slip to be transferred from the calaveras to the hayward fault the dip slip fault might be the unstable element governing slip in the larger system

redistribution of rare earth elements during diagenesis of turbidite hemipelagite mudrock sequences of llandovery age from central wales

a simple algorithm for tracing synthetic isoseismals probabilistic calculation of regional seismic hazard maps also requires the use of the so called attenuation relations which give the reference shake ability at certain distances from the earthquake sources this article achieves progress in this area in fact the present tests on a series of earthquakes in california san fernando 1971 whittier narrows 1987 northridge 1994 suggest that in some regions the areal shapes of the territories damaged by past earthquakes may be synthetically traced sometimes amazingly well with a simple algorithm that considers some gross features of the sources and this is compatible with theory it seems that this algorithm gives rather stable results moreover when the detailed modeling techniques available nowadays are inapplicable due to lack of data or for purpose of saving time and money it might be useable for improving seismic hazard calculations and conversely for retrieving information about sources of earthquakes from the preinstrumental era

pb diffusion in monazite a combined rbs sims study abstract we report measurements of pb diffusion in both synthetic cepo4 and natural monazites run under dry 1 atm conditions powdered mixtures of prereacted cepo4 and pbzro3 were used as the source of pb diffusant for in diffusion experiments conducted in sealed pt capsules for durations ranging from a few hours to several weeks following the diffusion anneals pb concentration profiles were measured with rutherford backscattering spectroscopy rbs and supplemented by measurements with secondary ion mass spectrometry sims in order to evaluate potential compositional effects upon pb diffusivity and simulate diffusional pb loss that might occur in natural systems we also conducted out diffusion experiments on pb bearing natural monazites in these experiments monazite grains were surrounded by a synthetic zircon powder to act as a sink monazites from these experiments were analyzed with sims over the temperature range 1100 to 1350 c the arrhenius relation determined for in diffusion experiments on synthetic monazite is given by d 0 94 exp 592 39 kj mol 1 rt m 2 s 1 diffusivities for synthetic and natural monazites are similar as are results of measurements made on the same samples using both rbs and sims the activation energy for pb diffusion we determined is more than three times that for natural monazite reported previously with pb diffusivities at

groundwater flow and capture zone analysis of the central passaic river basin new jersey delineating capture zones of pumping wells is an important part of safe drinking water and well protection programs capture zones or contributing areas of a groundwater extraction well are the parts of the aquifer recharge areas from which the wells draw their water their extent and location depend on the hydrogeologic conditions such as groundwater recharge pumping scenario and the aquifer properties such as hydraulic conductivity porosity heterogeneity of the medium and hydraulic gradient different methods of delineation can be used depending on the complexity of the hydrogeologic conditions in this study a 3 dimensional transient numerical modflow model was developed for the central passaic river basin cprb and used with a modpath particle tracking code to determine 3 dimensional transient capture zones analytically calculated capture zones from previous studies at the site were compared with the new numerically simulated capture zones the study results revealed that the analytical solution was more conservative estimating larger capture zones than the numerical models of all the parameters that can impact the size shape and location of a capture zone the hydraulic conductivity is one of the most critical capture zones tend to be smaller in lower hydraulic conductivity areas

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

a comparison of historical and paleoseismicity in a newly formed fault zone and a mature fault zone north canterbury new zealand the timing of large holocene prehistoric earthquakes is determined by dated surface ruptures and landslides at the edge of the australia pacific plate boundary zone in north canterbury new zealand collectively these data indicate two large m 7 earthquakes during the last circa 2500 years within a newly formed zone of hybrid strike slip and thrust faulting herein described as the porter s pass to amberley fault zone ppafz two earlier events during the holocene are also recognized but the data prior to 2500 years are presumed to be incomplete a return period of 1300 2000 years between large earthquakes in the ppafz is consistent with a late holocene slip rate of 3 4 mm yr if each displacement is in the range 4 8 m historical seismicity in the ppafz is characterized by frequent small and moderate magnitude earthquakes and a seismicity rate that is identical to a region surrounding the structurally mature hope fault of the marlborough fault system farther north this is despite an order of magnitude difference in slip rate between the respective fault zones and considerable differences in the recurrence rate of large earthquakes the magnitude frequency distribution in the hope fault region is in accord with the characteristic earthquake model whereas the rate of large earthquakes in the ppafz is approximated but over predicted by the gutenberg richter model the comparison of these two fault zones demonstrates the importance of the structural maturity of the fault zone in relation to seismicity rates inferred from recent historical and paleoseismic data

relationships in regional groundwater discharge to streams an analysis by numerical simulation baseflow components of streamflow were determined for 32 selected basins in the plains regions of alberta plots of baseflow per unit area vs total basin surface q a curves show a rapid increase in baseflow rate with initial increase in basin area followed by a reduced rate of increase at larger basin areas thereby suggesting a functional dependence of baseflow rate on basin size the empirically determined baseflow relationships were studied by numerical simulations of groundwater flow in two dimensional vertical sections of type environments of the alberta plains these models show that the baseflow relationships develop according to the theory of regional gravity flow of groundwater the types of discharge relationships indicate greater baseflow in regional discharge areas areas of low topography and including local recharge regions than in regional recharge areas areas of high topography and including local discharge regions an asymptotic discharge drainage area relationship was obtained in this analysis which showed a high rate of increase of specific discharge with initial increase in basin area from the headwaters downgradient in the regional setting at and above a basin area of 10 000 km2 the rate of increase of specific discharge approaches a maximum value asymptotically with further increase in basin area the asymptotic relationship signifies the loss of water from high to low elevation in a flow pattern that consists of all local intermediate and regional systems several hydrogeological environmental parameters act to modify the shape and nature of the asymptotic relationship namely depth to width ratio regional slope and geology of the basin low depth to width ratio and low regional slope convert the asymptotic relationship to a stationary discharge drainage area relationship which gives a constant specific discharge for the entire range of basin area and identifies a flow pattern of wholly local systems contrarily high depth to width ratio high regional slope and the presence of aquifers in a basin transform the asymptotic relationship into a linear discharge drainage area relationship which describes a linear increase in specific discharge with basin area inverse discharge drainage area relationships or mirror images of all three above relationships are formed when specific discharge is plotted against basin area which increases from low elevation upgradient towards the headwaters the discharge drainage area relationships uncovered in this study demonstrate quantitatively that sub basins at low topographic elevations possess more water than those of equivalent sizes at high topography for example a basin with an area of 5000 m2 at a low topographic elevation discharges naturally at 1 4 10 2m3s 1m 2 whereas a similar basin at a high elevation would discharge at 7 8 10 3m3s 1m 2

timing of diagenesis and very low grade metamorphism in the eastern sector of the sierra de cameros iberian range spain a u pb shrimp study on monazite the sierra de cameros is an intracontinental orogen and represents the north western part of the iberian range in northern spain it comprises a thick sequence of syn rift continental sediments mainly sandstones and carbonates deposited during lower cretaceous times a unique characteristic of the sierra de cameros in relation to the rest of the iberian range is the presence of low grade metamorphism in certain parts of the basin an event that predates basin inversion this paper describes the presence textural relationships and geochemical aspects of authigenic and or metamorphic monazite within different lithologies from the deepest parts of the basin sensitive high resolution ion microprobe shrimp u pb dating of monazite records the presence of two age populations the first with 206 pb 238 u ages ranging from 122 to 116 ma which is considered as diagenetic in origin whilst the second is dated at 99 2 ma and postdates the metamorphic climax

seismicity and active compressional tectonics in santa monica bay southern california during 1973 1986 the seismicity in santa monica bay consisted of an average of four events per year of m l 2 5 in addition to the 1979 malibu m l 5 0 mainshock aftershock sequence the 1979 sequence ruptured a north dipping thrust fault at 10 15 km depth beneath the bay a diffuse distribution of seismicity extends across the bay from the terminus of the palos verdes fault to point dume two thirds of the single event focal mechanisms of 36 events that are located within the bay show mostly thrust or reverse faulting on west to west northwest striking planes a third of the focal mechanisms exhibit strike slip faulting on north to north northwest striking planes a stress inversion of the focal mechanism data shows that the maximum principal stress is oriented n13 e in a horizontal plane and the minimum principal stress is oriented n102 e and plunging 47 hence the tectonics in santa monica bay are dominated by compression with thrust reverse and strike slip faulting the coexistence of thrust and strike slip faults suggests that the bay is not a part of the peninsular ranges terrane but forms a transition zone that accommodates the change from strike slip in the peninsular ranges to the south to reverse faulting in the transverse ranges to the north mapped anticlines and the previously unrecognized thrust faults beneath the bay form two fold and thrust belts that present additional seismic hazards to los angeles and the southern california coastal zone through seismic shaking and possible generation of small tsunamis

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

dislocation modeling of blind thrusts in the eastern los angeles basin california 1 the east and west coyote hills in the eastern los angeles basin are the surface expression of uplift accompanying blind reverse faulting folded quaternary strata indicate that the hills are growing and that the faults underlying them are active detailed subsurface mapping in the east coyote oil field shows that a previously mapped reverse separation fault is predominantly an inactive left lateral strike slip fault that is not responsible for the uplift of the east coyote hills the fault responsible for folding and uplift of the coyote hills does not cut wells in either the east or west coyote oil fields to characterize the geometry of the blind fault responsible for folding we employ dislocation modeling the dip and upper fault tip depths obtained from modeling suggest that the thrust fault beneath the coyote hills may be an extension of the puente hills blind thrust fault that continues westward beneath the santa fe springs oil field modeling results suggest that the segment of the thrust fault responsible for folding the coyote hills would have accumulated 1500 m of reverse displacement over the last 1 2 myr yielding an average slip rate of 1 3 0 5 mm yr the santa fe springs segment of the fault has a slip rate of 1 5 0 4 mm yr for the last 1 2 myr the estimated moment magnitude for a reverse displacement earthquake on the puente hills blind thrust ranges from 6 6 to 7 2 depending on the length of the rupture the estimated average recurrence interval for these earthquakes is 1700 3200 years

pre seismic slip on the 26 september 1997 umbria marche earthquake fault unexpected clues from the analysis of 1951 1992 elevation changes we studied 1951 1992 elevation changes recorded by a first order leveling line that intercepts the surface projection of the 26 sep 1997 mw 6 0 umbria marche earthquake causative fault the line documents 1951 1992 localized subsidence along a 12 km section above the fault we calculated the expected 1997 coseismic elevation changes along the line using standard dislocation modeling and found that their trend has an amplitude three times larger than the trend of the observed pre 1997 signal but with a similar shape we suggest that this signal is the result of 10 cm of pre 1992 slip along the northernmost 5 km of the 1997 earthquake fault where coseismic slip was found to be less than the average estimated for the entire fault this result implies unusually fast slip along this section of the fault and may suggest slip acceleration in preparation for the impending failure

tectonics of the san gabriel basin and surroundings southern california the sangabriel basin is a pliocene pleistocene transverse ranges structure bounded by the san gabriel mountains on the north the san jose and puente hills on the east and the repetto and montebello hills on the west a basement boundary between gneissoid rocks of san gabriel mountains aspect and peninsular ranges rocks strikes east across the basin and connects with the san jose fault this boundary may represent the eastward continuation of the canton fault a middle miocene precursor of the san gabriel fault system with up to 30 km of right slip canton fault displacement is largely canceled by 22 5 km of left slip on a precursor to the raymond fault such that an oligocene dacite in the san jose hills and clasts derived from it show little evidence of large horizontal displacement between the san gabriel mountains and puente hills clockwise rotation in the middle miocene probably influenced the distribution of lateral slip the fill in the northeast trending pliocene pleistocene san gabriel basin is a basal shallow marine sequence overlain by the nonmarine duarte conglomerate in contrast to the deep water fernando formation of the los angeles basin the paleoslope trends south in the direction of the repetto and puente hills evidence that uplift of these hills postdated deposition the triangular san gabriel basin is currently a stable block bounded by the right slip northwest striking east montebello fault on the west and the left slip northeast striking walnut creek fault on the east farther east the san jose and puente hills are underlain by an east trending active fold belt including the san jose reverse fault and anticline the walnut anticline and the puente hills anticline adjacent to the right lateral whittier fault the east montebello fault is bounded on the west by the elysian park anticlinorium a fold belt in downtown los angeles the left slip holocene raymond fault joins the sierra madre reverse fault at its segment boundary marked by the clamshell sawpit fault the triangular stable block between east trending fold belts is bounded on the south by the puente hills blind thrust and on the north by the sierra madre fault documenting north south quaternary convergence east west extension is also indicated although not confirmed by geodetic measurements

episodic folding inferred from syntectonic carbonate sedimentation the santaren anticline bahamas foreland abstract sedimentation coeval with growth of the santaren anticline provides an excellent opportunity to study the relationships between sedimentation and anticline uplift through time the santaren anticline is a kilometre scale nw se trending fold offshore of cuba in the bahamas foreland of the cuban fold and thrust belt the growth strata associated with this anticline consist of a thick package of carbonate sediments that were deposited without major interruptions from neogene and perhaps before to present day the excellent seismic resolution and age control of a number of seismic horizons within the growth strata allowed us to define 25 growth beds each of them representing between 0 1 and 3 2 ma an analysis of the thickness of these beds allowed us to determine accurate quantitative values of cumulative decompacted thickness and crestal structural relief at the time of their deposition in addition for the same periods sedimentation and fold uplift rates were calculated moreover some information on relationships between sedimentation and fold uplift rates was inferred from the growth stratal geometry growth beds that overlap the fold crest and thin over it indicate that sedimentation rates outpaced fold growth rates during their deposition some overlapping beds have constant thickness indicating that no fold uplift occurred during their sedimentation the rest of the growth beds exhibit onlap offlap geometries that do not indicate a unique sedimentation fold uplift rate relationship only in those cases in which the geometry of the underlying bed at the end of its deposition is known is it possible to infer a specific sedimentation fold uplift rate relationship as a result of this analysis we have been able to 1 illustrate that the geometry of the growth strata associated with the santaren anticline results from competition between sedimentation and tectonic fold uplift 2 document the episodic and non steady nature of fold growth and 3 show that short term rates at the scale of hundreds of thousands years provide much insight into the interplay between sedimentation and tectonic fold uplift that control the growth stratal patterns

seismotectonics of the newport inglewood fault zone in the los angeles basin southern california the newport inglewood fault zone nif strikes northwest along the western margin of the los angeles basin in southern california the seismicity 1973 to 1985 of m l 2 5 that occurred within a 20 km wide rectangle centered on the nif extending from the santa monica fault in the north to newport beach in the south is analyzed a simultaneous full inversion scheme velest is used to invert for hypocentral parameters two velocity models and a set of station delays arrival time data from three quarry blasts are included to stabilize the inversion the first velocity model applies to stations located along the rim and outside the los angeles basin and is well resolved it is almost identical to the starting model which is the model routinely used by the cit usgs southern california seismic network for locating local earthquakes the second velocity model applies to stations located within the los angeles basin it shows significantly lower velocities down to depths of 12 to 16 km which is consistent with basement of catalina schist below the sediments in the western los angeles basin the distribution of relocated hypocenters shows an improved correspondence to mapped surface traces of late quaternary fault segments of the nif a diffuse trend of seismicity is observed along the inglewood fault from the dominguez hills across the baldwin hills to the santa monica fault in the north the seismicity adjacent to long beach however is offset 4 to 5 km to the east near the trace of the subsurface los alamitos fault the depth distribution of earthquakes along the nif shows clustering from 6 to 11 km depth which is similar to average seismogenic depths in southern california thirty nine single event focal mechanisms of small earthquakes 1977 to 1985 show mostly strike slip faulting with some reverse faulting along the north segment north of dominguez hills and some normal faulting along the south segment south of dominguez hills to newport beach the results of an inversion of the focal mechanism data for orientations of the principal stress axes and their relative magnitudes indicate that the minimum principal stress is vertical along the north segment while the intermediate stress is vertical along the south segment the maximum principal stress axis is oriented 10 to 25 east of north reverse faulting along the north segment indicates that a transition zone of mostly compressive deformation exists between the los angeles block and the central transverse ranges

validation of the automatic nonlinear source inversion of the u s geological survey intensities of the whittier narrows 1987 earthquake in this work we validated the automatic inversion of the u s geological survey usgs intensity data set of the whittier narrows m l 5 9 1987 earthquake this validation of our new technique was obtained by comparing the source inversion results with the principal source parameters coming from instrumental measurements independent of our study to perform the inversion first we used a genetic algorithm ga with a population of 20 000 individuals i e sources second because the problem is bimodal we also used a niching genetic algorithm nga with four demes of 2 000 individuals this gave us almost the same results the site intensities were calculated by our kinematic kf function twelve source parameters were involved in the inversions the most sensitive of which are the epicentral coordinates and the fault plane solution two minimum variance models were determined by both the ga and the nga inversions 1 one east west trending dip slip source which is in agreement with that already known from instrumental measurements and 2 one almost coinciding with its auxiliary plane in the fault plane solution these findings almost coincide with those produced by the grid search inversion method but the ga nga inversion is much faster and does not need strong constraints this confirms that it is possible to get an approximate idea of the source of the studied earthquake also by automatically inverting the regional pattern of the usgs intensities this result encourages us to validate our inversion technique with more well documented earthquakes and to treat intensities of preinstrumental earthquakes which are the principal target of our work manuscript received 30 july 2003

reassessment of the source of the 1976 friuli ne italy earthquake sequence from the joint inversion of high precision levelling and triangulation data summary in this study we revisit the mechanism of the 1976 friuli ne italy earthquake sequence main shocks mw 6 4 5 9 and 6 0 we present a new source model that simultaneously fits all the available geodetic measurements of the observed deformation we integrate triangulation measurements which have never been previously used in the source modelling of this sequence with high precision levelling that covers the epicentral area we adopt a mixed linear non linear optimization scheme in which we iteratively search for the best fitting solution by performing several linear slip inversions while varying fault location using a grid search method our preferred solution consists of a shallow north dipping fault plane with assumed azimuth of 282 and accommodating a reverse dextral slip of about 1 m the estimated geodetic moment is 6 6 1018 nm mw 6 5 in agreement with seismological estimates yet our preferred model shows that the geodetic solution is consistent with the activation of a single fault system during the entire sequence the surface expression of which could be associated with the buia blind thrust supporting the hypothesis that the main activity of the eastern alps occurs close to the relief margin as observed in other mountain belts the retrieved slip pattern consists of a main coseismic patch located 3 5 km depth in good agreement with the distribution of the main shocks additional slip is required in the shallower portions of the fault to reproduce the local uplift observed in the region characterized by quaternary active folding we tentatively interpret this patch as postseismic deformation afterslip occurring at the edge of the main coseismic patch finally our rupture plane spatially correlates with the area of the locked fault determined from interseismic measurements supporting the hypothesis that interseismic slip on the creeping dislocation causes strain to accumulate on the shallow above 10 km depth locked section assuming that all the long term accommodation between adria and eurasia is seismically released a time span of 500 700 years of strain accumulating plate motion would result in a 1976 like earthquake

the 1987 whittier narrows earthquake in the los angeles metropolitan area california the whittier narrows earthquake sequence local magnitude m l 5 9 which caused over 358 million damage indicates that assessments of earthquake hazards in the los angeles metropolitan area may be underestimated the sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east west length of the northern margin of the los angeles basin peak horizontal accelerations from the main shock which were measured at ground level and in structures were as high as 0 6g where g is the acceleration of gravity at sea level within 50 kilometers of the epicenter the distribution of the modified mercalli intensity vii reflects a broad north south elongated zone of damage that is approximately centered on the main shock epicenter

estimated ground motions in los angeles due to mw 7 earthquake on the elysian thrust fault abstract the elysian thrust fault has been identified as a blind thrust fault davis et al 1989 hauksson and jones 1989 representing a potentially serious seismic hazard to the metropolitan los angeles and its neighboring areas we have simulated time histories peak ground accelerations and their uncertainties using a semi empirical method for a m w 7 0 earthquake on the elysian thrust fault using a flat layered crustal structure the accelerograms from the 4 october 1987 whittier narrows aftershock 10h 50m m l 5 3 are used to represent the source functions of each subfault on the fault surface to account for the velocity variation in the surface sediments we compared simulated ground motions using two separate shearwave velocities 0 6 km sec and 0 9 km sec respectively in the top layer of the crustal model the use of such a simple crustal model is validated by modeling the accelerograms recorded during the 1 october 1987 whittier narrows mainshock m l 6 0 the duration and the relative frequency content observed on these accelerograms are successfully modeled at some stations the simulated peak accelerations agree well with the observed values however at some sites the simulated and observed values differ by a factor of 2 to 3 the variation is attributed to a laterally varying crustal structure that is significant for small earthquakes additional site specific study is needed for an improved prediction of the observed peak accelerations for large magnitude earthquakes the near source peak ground acceleration appears to be controlled by the source receiver geometry relative to the fault as well as the location of asperities on the fault surface this is validated by simulating the peak acceleration data of the 1989 loma prieta earthquake recorded within 30 km of the source for our simulations on the elysian thrust fault an additional component is added to the uncertainty by analyzing several asperity models finally an analytical representation is given to the simulated average peak horizontal ground accelerations y r which is expressed by ln y r 5 38 0 085 2 09 0 0268 ln r 8 0 0 343 in the range of 7 5 r 35 km r is the closest distance to the seismogenic rupture zone this functional form predicts a rapid fall off rate for the simulated ground motions compared with the fall off rate predicted by the other published empirical attenuation relations we use the finite difference method to investigate the effects of irregular structure on ground motions resulting from point sources on the elysian park fault the response computed at several depths beneath the basin suggests that the response is dominated by the initial direct arrivals for sources located interior to the basin when the receivers are located at one end of the basin and the seismic sources are located at the opposite edge the characteristic features on the seismograms are the long durations caused by the trapped energy within the basin the level of trapped energy decreases as the depth of the source increases thus the fault model becomes important in determining the level of peak ground motions and shaking duration

rupture models for the a d 900 930 seattle fault earthquake from uplifted shorelines a major earthquake on the seattle fault washington ca a d 900 930 was first inferred from uplifted shorelines and tsunami deposits despite follow up geophysical and geological investigations the rupture parameters of the earthquake and the geometry of the fault are uncertain here we estimate the fault geometry slip direction and magnitude of the earthquake by modeling shoreline elevation change the best fitting model geometry is a reverse fault with a shallow roof ramp consisting of at least two back thrusts the best fitting rupture is a sw ne oblique reverse slip with horizontal shortening of 15 m rupture depth of 12 5 km and magnitude mw 7 5

the growth of geological structures by repeated earthquakes 1 conceptual framework in many places earthquakes with similar characteristics have been shown to recur if this is common then relatively small deformations associated with individual earthquake cycles should accumulate over time to create geological structures following this paradigm we show that existing models developed to describe leveling line changes associated with the seismic cycle can be adapted to explain geological features associated with a fault in these models an elastic layer containing the fault overlies a viscous half space with a different density fault motion associated with an earthquake results in immediate deformation followed by a long period of readjustment as stresses relax in the viscous layer and isostatic equilibrium is restored deformation is also caused as a result of the loading and unloading due to sediment deposition and erosion in this paper the parameters that control the growth of dip slip structures are identified we find that the flexural rigidity of the crust or the apparent elastic thickness provides the main control of the width of a structure the loading due to erosion and deposition of sediment determines the ratio of uplift to subsidence between the two sides of the fault the flexure due to sediment load is much more important in this respect than whether the fault is normal or reverse in character we find that in general real structures are associated with apparent elastic thicknesses of 4 km or less and thus with very low flexural rigidities

high precision levelling dinsar and geomorphological effects in the emilia 2012 epicentral area abstract in may 2012 two moderate earthquakes mw 6 1 and 5 9 associated with a noticeable aftershock sequence affected the eastern sector of the po plain northern italy the co seismic areal uplift events are crucial for a better understanding of the seismotectonics of the broader area and thus for a better assessment of the seismic hazard in the region in the present study we compared the results of analyses based on high precision levelling the dinsar technique the distribution of liquefaction occurrences the geomorphological map of the area and the structural model of the region the dinsar technique revealed a marked uplift of the ground up to 17 cm which was confirmed by high precision levelling the results of both techniques substantially agreed although there were some considerable local discrepancies due to well documented and diffuse liquefaction phenomena some strategic precautions when planning high precision levelling networks are suggested

late quaternary slip rate on the oak ridge fault transverse ranges california implications for seismic risk abstract the slip rate on the oak ridge fault at south mountain in the densely populated lower santa clara valley california is estimated as 6 15 to 12 3 mm yr since the end of saugus deposition at 0 4 to 0 2 ma slightly lower slip rate estimates result from a different projection of the top of the saugus in the hanging wall block of the fault an assumed displacement of 3 m per event gives an average recurrence interval of 250 to 500 yr with the major uncertainty being the age of the top of the saugus displacement of 2460 m of the top of the saugus at south mountain includes piercing point displacement and distributed displacement from drag folds near the fault both are the near surface expression of faulting at potential mainshock depths beneath well control slip rates for the nearby san cayetano and red mountain faults are not well constrained because post miocene strata are absent in their hanging wall blocks but available evidence suggests that their slip rates are about the same as that for the oak ridge fault earthquake return times measured in hundreds of years have been shown by others for the 1971 san fernando fault and a small fault near the red mountain fault and comparable return times are suggested for a normal fault in the hanging wall block of the oak ridge fault a trench on the harmon alluvial fan near the ventura county government center revealed evidence of cracks filled with sediments from below suggesting liquefaction during an earthquake the lower santa clara valley has not had a large damaging earthquake in 200 years of record keeping but one is expected there in the near future the december 21 1812 earthquake may have occurred on the offshore continuation of the oak ridge or red mountain fault

strong motion and broadband teleseismic analysis of the 1991 sierra madre california earthquake short period and broadband teleseismic waveform data and three component strong motion records were analyzed to obtain the source parameters of the 1991 sierra madre earthquake close in strong motion velocity records analyzed from 5 s to 5 hz show two distinct pulses about 0 35 s apart requiring some rupture complexity the near field shear wave displacement pulse from this event has a relatively short duration about 1 s for the magnitude of the event requiring a particularly high average stress drop to further constrain the rupture process the data were used in a finite fault source inversion to determine the temporal and spatial distribution of slip we chose a fault plane orientation striking s 62 w and dipping 50 toward the northwest as required by the distribution of aftershocks the first motion mechanism and the teleseismic bodywave point source inversion in addition to the aftershock locations depth constraints are provided by teleseismic short period and broadband recordings which require a centroid depth of 10 11 km our inverse modeling results indicate that both the teleseismic and strong motion data sets can be fit with a compact rupture area about 12 km2 southwest and up dip from the hypocenter the average slip is approximately 50 cm and the maximum slip is 120 cm the seismic moment obtained from either of the separate data sets or both sets combined is about 2 8 0 3 1024 dyn cm and the potency is 0 01 km3 using the area of significant slip estimated from the finite fault inversion the resulting stress drop is on the order of 150 200 bars

the 1987 whittier narrows earthquake sequence in los angeles southern california seismological and tectonic analysis the october 1 1987 whittier narrows earthquake m l 5 9 was located at 34 2 96 n 118 4 86 w at a depth of 14 6 0 5 km in the northeastern los angeles basin the focal mechanism of the mainshock derived from first motion polarities shows pure thrust motion on west striking nodal planes with dips of 25 5 and 65 5 respectively the aftershocks define an approximately circular surface that dips gently to the north centered at the hypocenter of the mainshock with a diameter of 4 6 km hence the spatial distribution of the mainshock and aftershocks as well as the focal mechanisms of the mainshock indicate that the causative fault was a 25 north dipping thrust fault striking west and is confined to depths from 10 to 16 km although most of the 59 aftershock focal mechanisms presented here document a complex sequence of faulting they are consistent with deformation of the hanging wall caused by the thrust faulting observed in the mainshock a cluster of reverse faulting events on north striking planes occurred within hours after the mainshock 2 km to the west of the mainshock the largest aftershock m l 5 3 occurred on october 4 and showed mostly right lateral faulting on the same north northwest striking plane within the hanging wall similarly several left lateral focal mechanisms are observed near the eastern edge of the mainshock rupture the earthquake and calibration blast arrival time data were inverted to obtain two refined crustal velocity models and a set of station delays when relocating the blast using the new models and delays the absolute hypocentral location bias is less than 0 5 km the mainshock was followed by nearly 500 locatable aftershocks which is a small number of aftershocks for this magnitude mainshock the decay rate of aftershock occurrences with time was fast while the b value was low 0 67 0 05 for a los angeles basin sequence

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

hydrogeology of palm valley central australia a pleistocene flora refuge abstract the palm valley oasis finke gorge national park in arid central australia is characterised by large stands of red cabbage palm trees livistona mariae how these unique plants over 1000 km away from nearest relatives in the tropical parts of northern australia persist has long fascinated visitors the hydrogeology of this area helps explain this phenomenon stable isotope 2h 8o analyses shows groundwater to have a uniform composition that plots on or near a local meteoric water line carbon 14 results are observed to vary throughout this aquifer from effectively dead 100 ka along some flow paths indicate groundwater discharge would endure through arid phases associated with quaternary climate oscillations such a flow system can explain the persistence of this population of palms and also highlight the possibility that palm valley has acted as a flora refuge since at least the mid pleistocene

the ms 7 3 1992 suusamyr kyrgyzstan earthquake in the tien shan 2 aftershock focal mechanisms and surface deformation abstract the m s 7 3 suusamyr earthquake of 19 august 1992 was a large thrust type earthquake in the northern tien shan of kyrgyzstan an intracontinental mountain belt in central asia focal mechanisms of both the mainshock and 13 moderate sized aftershocks are consistent with a seismotectonic setting that is dominated by nnw sse horizontal compression which manifests itself in reverse faulting along roughly east west trending steeply dipping fault planes the earthquake produced surface faulting at two widely separated locations along two different fault segments the total length of which was less than 4 km detailed measurements at one of the locations indicate a net slip of at least 4 2 0 4 m a wide variety of secondary surface effects was observed in the macroseismic zone that extended over an area of 2500 km 2 the lack of extensive surface rupture from such a large event can be explained by a combination of 1 redistribution of the net slip at depth among the secondary splays that branches out from the main fault near the surface and 2 variable surface slip over the fault length the active deformation associated with this event documents a structural style that involves steeply dipping reverse faults extending from mid crustal depths to the surface at nearly uniform dip accommodating crustal shortening in the interior of the tien shan

earthquakes faulting and stress in the los angeles basin since 1920 fourteen moderate sized m l 4 9 6 4 earthquakes have been reported in the los angeles basin these events are associated with both mappable surficial faults and concealed faults beneath the basin sediments to determine the style of faulting and state of stress in the basin single event focal mechanisms for 244 earthquakes of m 2 5 that have occurred during 1977 1989 have been calculated fifty nine percent of the events are strike slip and are mostly located near two of the major northwest striking right lateral strike slip faults in the basin the newport inglewood fault and the palos verdes fault the 1988 pasadena and the 1988 upland earthquakes showed left lateral strike slip on northeast striking faults numerous small earthquakes in the eastern part of the basin show left lateral strike slip faulting and form a northeast trend near yorba linda thirty two percent of the events have reverse mechanisms and are distributed along two broad zones the first the elysian park fold and thrust belt coincides with anticlines along the eastern and northern flank of the los angeles basin extending into santa monica bay the second the torrance wilmington fold and thrust belt coincides with anticlines mapped on the southwest flank of the basin and extends from offshore newport beach to the northwest into santa monica bay oblique faulting that could be inferred by the merging of strike slip and compressional tectonics does not occur in the basin instead the coexistence of zones of thrusting and large strike slip faults in the basin suggests that the thrust and strike slip movements are mostly decoupled a few normal faulting mechanisms appear to be related to faulting orthogonal to the axes of plunging anticlines the trend of the maximum horizontal stress varies from n1 w to n31 e across the basin and consistently forms high angles with the fold axes the stress field that exists along the flanks of the basin has a vertical minimum stress axis this stress field and ongoing folding and thrusting suggest that tectonic deformation is concentrated along the flanks of the deep central basin today the deformation of the basin consists of uplift and crustal thickening and lateral block movement to accommodate the north south compression across the basin

empirical observations regarding reverse earthquakes blind thrust faults and quaternary deformation are blind thrust faults truly blind active thrust faults pose a significant seismic hazard worldwide many of these faults include blind thrusts where the propagating fault tip does not reach the earth s surface and buried faults where the geomorphic expression of the fault is obscured by subsequent sedimentation and or erosion this raises the issue of whether conventional geologic geomorphic and paleoseismic methods can be used to identify and characterize thrust faults for the assessment of seismic hazards or whether these faults sometimes are truly blind we compiled a data base of 148 worldwide moderate to large magnitude thrust reverse earthquakes to evaluate whether or not the event occurred on a fault that could have been identified prior to the earthquake on the basis of recognizable quaternary surface deformation i e a pre existing fault or fold analysis of the data shows that interplate reverse earthquakes almost always are associated with pre existing quaternary deformation that was or could have been recognized prior to the earthquake in particular most interplate reverse earthquakes are associated with an active reverse fault at the surface and or an active anticline in contrast intraplate reverse earthquakes seldom occur on faults associated with pre existing recognizable surface deformation we conclude that thrust faults can be detected in interplate regions with careful quaternary geologic and geomorphic mapping furthermore the absence of quaternary surface deformation can be used to infer the absence of an underlying active blind thrust fault in interplate tectonic settings however the data show that quaternary geologic mapping techniques alone likely are insufficient to characterize blind thrusts in intraplate regions in these areas inclusion of a floating or random earthquake may be necessary to assess earthquake hazards

seismic potential revealed by surface folding 1983 coalinga california earthquake the 2 may 1983 coalinga california earthquake magnitude 6 5 failed to rupture through surface deposits and instead elastically folded the top few kilometers of the crust the subsurface rate of fault slip and the earthquake repeat time are estimated from seismic geodetic and geologic data three larger earthquakes up to magnitude 7 5 during the past 20 years are also shown to have struck on reverse faults concealed beneath active folds

nature of the recent vertical ground movements inferred from high precision leveling data in an intraplate setting ne ardenne belgium yearly high precision leveling surveys have been performed from 1993 to 1998 along a 48 km long local network centered on gileppe lake at the foot of the ardenne massif belgium institut geographique militaire and institut geographique national igm ign levelings of 1948 and 1974 yielded additional information the data were corrected for collimation and thermal errors other sources of error earth tides atmospheric refraction rod miscalibration were estimated and corrections were made when necessary random errors of individual surveys range from 0 15 to 0 74 mm km the recorded elevation changes indicate the existence of tilted segments some 5 to 10 km in length with yearly tilt values amounting up to 2 rads fault movements of a few mm yr are also demonstrated the segment limits are spatially stable from one year to the next but very frequent sense reversals of the vertical motions are observed this explains why the total movement over a 20 to 30 year period is barely higher than the yearly displacements various nontectonic causes of vertical ground movement e g monument instability varying water loading of the lake sediment compaction etc have been considered yielding little satisfactory explanation of the patterns of observed elevation changes we propose that the recorded motions which we call reversible fault creep and reversible tilt respectively are a true tectonic signal reflecting the tectonic noise which accompanies the long term deformation of uplifting areas in intraplate settings such movements are characteristic of fault segments which may occasionally generate earthquakes

active thrusting and folding along the northern tien shan and late cenozoic rotation of the tarim relative to dzungaria and kazakhstan we have studied geometries and rates of late cenozoic thrust faulting and folding along the northern piedmont of the tien shan mountain belt west of urumqi where the m 8 3 manas earthquake occurred on december 23 1906 the northern range of the tien shan rising above 5000 m overthrusts a flexural foredeep filled with up to 11 000 m of sediment of the dzungarian basement our fieldwork reveals that the active thrust reaches the surface 30 km north of the range front within a 200 km long zone of neogene quaternary anticlines fault scarps are clearest across inset terraces within narrow valleys incised through the anticlines by large rivers flowing down from the range in all the valleys the scarps offset vertically the highest terrace surface by the same amount 10 2 0 7 m inferring an early holocene age 10 2 kyr for this terrace which is continuous with the largest recent fans of the piedmont yields a rate of vertical throw of 1 0 0 3mm yr on the main active thrust at the surface a quantitative morphological analysis of the degradation of terrace edges that are offset by the thrust corroborates such a rate and yields a mass diffusivity of 5 5 2 5 m 2 kyr a rather fresh surface scarp 0 8 0 15 m high that is unlikely to result from shallow earthquakes with 6 m 7 in the last 230 years is visible at the extremities of the main fold zone we associate this scarp with the 1906 manas earthquake and infer that a structure comprising a deep basement ramp under the range gently dipping flats in the foreland and shallow ramps responsible for the formation of the active fault propagation anticlines could have been activated by that earthquake if so the return period of a 1906 type event would be 850 380 years the small size of the scarp for an earthquake of this magnitude suggests that a large fraction of the slip at depth 2 3 is taken up by incremental folding near the surface comparable earthquakes might activate flat detachments and ramp anticlines at a distance from the front of other rising quaternary ranges such as the san gabriel mountains in california or the mont blanc aar massifs in the alps we estimate the finite cenozoic shortening of the folded dzungarian sediments to be of the order of 30 km and the cenozoic shortening rate to have been 3 1 5 mm yr assuming comparable shortening along the tarim piedmont and minor additional active thrusting within the mountain belt we infer the rate of shortening across the tien shan to be at least 6 3 mm yr at the longitude of manas 85 5 e a total shortening of 125 30 km is estimated from crustal thickening assuming local airy isostatic equilibrium under the same assumption serial n s sections imply that cenozoic shortening across the belt increases westwards to 203 50 km at the longitude of kashgar 76 e as reflected by the westward increase of the width of the belt this strain gradient implies a clockwise rotation of tarim relative to dzungaria and kazakhstan of 7 2 5 around a pole located near the eastern extremity of the tien shan west of hami 96 e 43 5 n comparable to that revealed by paleomagnetism between tarim and dzungaria 8 6 8 7 a 6 mm yr rate of shortening at the longitude of manas would imply a rate of rotation of 0 45 m y and would be consistent with a shortening rate of 12 mm yr north of kashgar taking such values to be representative of late cenozoic rates would place the onset of reactivation of the tien shan by the india asia collision in the early to middle miocene 16 22 9 m y in accord with the existence of particularly thick late neogene and quaternary deposits such reactivation would thus have started much later than the collision roughly at the time of the great mid miocene changes in tectonic regimes denudation and sedimentation rates observed in southeast asia the himalayas and the bay of bengal and of the correlative rapid change in seawater sr isotopic ratio 20 to 15 ma like these other changes the rise of the tien shan might be a distant consequence of the end of indochina s escape

strontium isotope systematics of base flow in piedmont province watersheds georgia usa abstract 87 sr 86 sr ratio variations were analyzed in rainfall shallow ground water and base flow collected from 4 piedmont streams within the middle oconee river basin in northeastern georgia during the period between march 2003 and march 2004 they sr isotope ratio analyses were accompanied by measurements of stream discharge rainfall stable o isotope ratios and major ion and 3 h concentrations the average sr ion concentration and 87 sr 86 sr ratio for the terminal stream basin the middle oconee river were 23 6 g l and 0 7172 respectively the average 87 sr 86 sr ratios of the rainwater and shallow ground water were below 0 7125 indicating that most of the sr in this stream water is input by weathering reactions in deeper ground water rather than by ion exchange in shallow soil horizons this is consistent with the higher alkalinity concentrations 23 47 mg l and specific conductance values 60 113 s cm that characterize stream base flow piedmont streams are characterized by lower concentrations of sr and higher 87 sr 86 sr ratios than average global stream flow base flow rates decreased by a factor of 2 3 during the summer months and this is accompanied by increased alkalinity concentrations 87 sr 86 sr ratios however were temporally invariant for a given stream basin and were independent of season antecedent rainfall and discharge 87 sr 86 sr ratios were unique for each of the 4 basins and a general trend toward higher ratios with increasing basin area was apparent the inferred contribution from minerals with high rb contents such as k feldspar and muscovite may have resulted from the greater integration of flow from mineralogically diverse pathways afforded by a larger basin area the basin specificity and temporal or seasonal invariability make 87 sr 86 sr ratios an invaluable hydrological tracer that can be readily employed in mass balance studies of stream flow within the piedmont province

seismicity and geometry of a 110 km long blind thrust fault 2 synthesis of the 1982 1985 california earthquake sequence during 1982 1985 three 5 4 mw 6 5 earthquakes migrated 65 km along the north half of a string of quaternary folds at the east front of the california coast ranges there is no surface fault associated with these earthquakes but the fold chain oriented parallel to the san andreas fault 30 km to the west takes up contraction normal to the san andreas fault identification of active blind thrust faults is hindered by the absence of a fault trace but may be revealed by the presence of growing folds at the surface and by earthquakes at depth because of excellent seismic geodetic and geologic data this earthquake sequence illuminates the geometry of the blind faults and enables us to probe their mechanics we relocate seismicity and compute focal mechanisms in a three dimensional velocity space and model the vertical deformation associated with the 1983 m 6 5 coalinga earthquake the aftershock zones abut at echelon offsets in the fold axes and the mainshocks display reverse slip perpendicular to the axes suggesting that the folds conceal a contiguous segmented thrust fault background seismicity concentrates at bends and breaks in the fold chain sites that may correspond to tears and ramps in the thrust fault at depth seismic reflection profiles reveal thrust and reverse faults dipping toward the san andreas fault at depths of 5 10 km with several kilometers of cumulative slip and high angle reverse faults in the anticlines with several hundred meters cumulative slip coseismic fold uplift accompanied the coalinga and kettleman hills north dome earthquakes suggesting that fold growth is episodic and coupled closely to repeated earthquakes on the underlying thrusts the north half of the fold chain has been the site of several 6 m 6 5 earthquakes since 1885 thus kettleman hills middle dome the next fold segment to the south has an elevated seismic potential the aftershock zones of the three main shocks are diffuse and occupy a region much larger than the site of seismic slip aftershocks occur 5 7 km from the fault regions where on the basis of a boundary element model the shear strain increase caused by the fault slip exceeds 20 ppm equivalent to about 0 7 mpa we argue that the broad aftershock zone is a product of high sustained off fault stress caused by repeated displacement on faults that do not cut the earth s surface the fault tip stresses lead to the formation of secondary faults which can become sites of aftershocks and postseismic creep

saugus palmdale california field test for refraction error in historical leveling surveys a field test designed to measure atmospheric refraction error in historical and modern leveling was conducted in may june 1981 on a 50 km long grade from saugus to palmdale california during 1955 1971 the length of sights made between the level instrument and rods systematically decreased from 60 m to 26 m the difference in height near palmdale measured by single run long sight 42 m and short sight 22 m leveling during the test was 6 times larger than expected random error correction for refraction by using either the observed or modeled vertical temperature gradient in kukkamaki s balanced sight equation reduced the height difference to the level of random error uncertainty the observed temperature gradient obeyed a power law relation t a bzc where z is the height and a b and c are constants that depended on atmospheric conditions and the ground surface beneath the line of sight the refraction corrected leveling satisfies the specifications and meets all standards of first order control surveys the six historical surveys of the saugus palmdale grade were corrected for refraction error using the results of the experiment and for rod scale errors and nontectonic subsidence considered in previous investigations the corrected uplift near palmdale reached 56 16 mm with respect to saugus during the period 1955 1965 this amount of uplift is about one third that obtained before removal of refraction error the corrected displacement profiles also reveal previously unrecognized deformation in the epicentral region of the 1971 san fernando ml 6 4 earthquake during the decade before the main shock

tests of source parameter inversion of the u s geological survey intensities of the whittier narrows 1987 earthquake we validated the source inversions of the intensity data set of the whittier narrows m l 5 9 1987 earthquake by comparing the source characteristics retrieved by our inversion technique with those already known from instrumental measurements in our grid search technique the squared residuals calculated minus observed intensity at the sparse sites are weighted by the voronoi polygons tessellation and then the sum of the weighted squared residuals is minimized for comparison we also minimize the sum of the unweighted squared residuals the intensities are calculated by our kinematic kf function twelve source parameters are involved in the inversions the most sensitive of which are the epicentral coordinates and the fault plane solution to find the minimum variance model we explore the whole space of the angular values that control the fault plane solution and place some reasonable constraints on the other parameters two minimum variance models were determined by the inversions one source that is in agreement with that already known from instrumental measurements and one almost coinciding with its auxiliary plane in the fault plane solution this finding confirms that notwithstanding the introduction of more source parameters the nature of the problem of the inversion of an almost pure dip slip earthquake is still close to bimodality it is demonstrated that it is possible to get an approximate idea of the source of the studied earthquake by inverting the u s geological survey intensities this result encourages us to validate our inversion technique with more well documented earthquakes and to treat intensities of preinstrumental earthquakes which are the principal target of our work manuscript received 10 february 2001

comparison of the 1959 hebgen lake montana and the 1983 borah peak idaho earthquakes from geodetic observations abstract we deduce the fault geometry coseismic slip and moment for two of the largest historic earthquakes that have occurred in the basin and range of the western united states the m 7 3 1959 hebgen lake montana earthquake and the m 6 9 1983 borah peak idaho event newly augmented data sets of vertical deformation from geodetic leveling and from lake shoreline changes were modeled by simple dislocations in an elastic half space the rms signal to noise ratio is 12 for the hebgen lake data and 38 for the borah peak set the residuals for both models are about twice as large as the noise the hebgen lake earthquake struck on the 15 to 25 km long en echelon hebgen and red canyon faults dipping 45 to 50 and extending to a depth of 10 to 15 km the 7 0 and 7 8 m of dip slip on these faults produced a combined moment of 1 2 10 20 n m the dip of the red canyon fault may decrease slightly with depth in a listric manner abutting the planar hebgen fault at a depth of 8 km in addition up to 1 m of deep slip occurred on the holocene segment of the adjacent madison range fault 10 km west of the hebgen fault the borah peak segment of the lost river fault was found to dip 49 slip of 2 1 m occurred at the south fault end extending to a depth of 14 km 1 4 m of slip occurred at the north end where the fault reached only to 6 km depth a listric fault shape is not permitted by the geodetic data at borah peak both the hebgen red canyon and the lost river faults are high angle and nearly planar despite the much greater age and length of the lost river fault in comparison to the en echelon hebgen faults the chief difference between the earthquakes is the 3 to 4 fold higher slip at hebgen relative to borah peak and all other well studied basin and range shocks thrust faults located close to these active normal faults must either dip steeply at depth or were not reactivated

inverting for slip on three dimensional fault surfaces using angular dislocations the increasing quality of geodetic data synthetic aperture radar interferometry insar dense global positioning system gps arrays now available to geophysicists and geologists are not fully exploited in slip inversion procedures most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries these geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults and they preclude a more complete understanding of the role of fault geometry in the earthquake process we have developed a new three dimensional slip inversion method based on the analytical solution for an angular dislocation in a linear elastic homogeneous isotropic half space the approach uses the boundary element code poly3d that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces the use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three dimensional surfaces bounded by curved tiplines shapes that commonly are imaged by three dimensional reflection seismic data and inferred from relocated aftershock data we demonstrate the method s ability to model three dimensional rupture geometries by inverting for slip associated with the 1999 hector mine earthquake the resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models improving the fit to the geodetic data by 32 and honors the observed surface ruptures thereby allowing more direct comparisons between geologic and geodetic data on slip distributions online material hector mine input files and file format description

shallow afterslip following the 2003 may 21 mw 6 9 boumerdes earthquake algeria summary we investigated post seismic deformation following the 2003 may 21 mw 6 9 boumerdes algeria earthquake using surface displacements from six continuous global positioning system sites that operated in the epicentral area for 2 5 yr following the event we find up to 4 cm of cumulative horizontal displacement during that time period with a time dependence well fit by a logarithmic decay post seismic deformation appears to continue at all sites after the 2 5 yr observation period with rates on the order of 1 cm yr 1 or less the data is consistent with shallow afterslip 0 5 km and shows no evidence for afterslip downdip of the coseismic rupture the data is poorly explained by viscoelastic relaxation in the lower crust or upper mantle or by poroelastic rebound the concentration of afterslip adjacent to and updip of the coseismic rupture at least in the western half of the fault suggests that afterslip is driven by coseismic stresses the correlation between the depth of afterslip and that of the sedimentary wedge along the algerian margin while coseismic slip occurs in deeper basement rocks suggests 1 that post seismic deformation may also involve folding and 2 that spatial variations in frictional properties along the fault correlate with the type of rocks involved

mechanisms and depths of atlantic transform earthquakes we have studied 40 earthquakes on seven major transforms along the mid atlantic ridge the majority show the expected transform parallel strike slip motion on steeply dipping fault planes some anomalous mechanisms suggesting either unusually shallow dip or a component of dip slip motion occur near ridge transform intersections the vertical tectonism suggested by transform morphology may thus be restricted to intersections where thermal contrast across the transform is greatest and stress orientations can be oblique to both ridge and transform centroid depths determined by waveform inversion are limited to a shallow zone corresponding approximately to the area above the 400 c isotherm of the thermal structure expected from lithospheric cooling the depth extent of faulting predicted by estimating fault area from seismic moments extends approximately to the predicted 600 c isotherm assuming that the areas above the 400 c or 600 c isotherms fail seismically moment release for six of the transforms accounts for varying fractions of the slip predicted by plate motion suggesting that some aseismic slip occurs if the time period sampled is representative in contrast on the vema transform the inferred seismic slip is greater than predicted unless faulting extends to the 650 c isotherm alternatively the vema may have an unusually long recurrence time or be mechanically anomalous due to its complex history in contrast to transform events centroids for oceanic intraplate earthquakes extend to approximately the 750 c isotherm this result is intriguing if depths reflect lithospheric strength as a function of depth transforms have much higher strain rates than intraplate areas so if both had the same rheology the limiting isotherm for transforms should be higher alternatively if a weaker rheology were appropriate the higher strain rate should cancel the weakening and yield a limiting isotherm similar to that for intra plate regions transforms may thus be either weaker and or have higher temperatures than expected in the latter model the required high temperatures perhaps due to intrusion at depth predict measurable heat flow anomalies the second possibility unusual rheological weakness is reminiscent of the unexplained weakness of the san andreas fault where heat flow data exclude anomalously high temperatures

seismic and aseismic deformation associated with the 1952 kern county california earthquake and relationship to the quaternary history of the white wolf fault synthesis of geodetic geologic and seismic data from the white wolf fault california indicates that the fault separates an area of late quaternary and continuing rapid uplift in the tehachapi mountains and transverse ranges from even more rapid subsidence in the southern san joaquin valley on july 21 1952 rupture of the white wolf fault produced the ml 7 2 kern county earthquake we used the aftershock zone to delimit the size of the faulted slip surface and applied constraints imposed by the known 1952 1953 horizontal shear strains to model the measured coseismic vertical displacements with an elastic dislocation model a curved fault trace with decreasing fault depth 27 to 10 km from the surface vertically to the base slip 3 to 1 m and dip 75 to 20 from the 1952 epicenter at the southwest end of the fault toward the northeast provides the fit most consistent with the geodetic record the measured seismic moment the fault plane solution and the pattern of surface rupture two short releveled lines near the 1952 epicenter tilted 4 and 17 rad down to the north from 5 10 years before the earthquake the preseismic tilts differ significantly from ten other surveys of these lines left lateral fault crossing shear strain from 0 2 20 years before the quake was two times greater than both preseismic off fault strains and the post seismic fault crossing strains during the first seven years after the earthquake aseismic deformation was negligible from 1959 to 1972 uplift reached 160 mm over an area larger than the aftershock zone rising first in the epicentral region and then at the northeast end of the fault this was unaccompanied by any surface fault slip reconstruction of the vertical separation on the white wolf fault from late quaternary and late miocene stratigraphic marker beds shows that the rate of reverse fault slip increased forty fold from 0 1 0 2 mm yr to 3 9 mm yr between the past 10 15 m y and the most recent 0 6 1 2 m y we estimate a 170 to 450 yr average recurrence interval for earthquakes on the white wolf fault with slip equivalent to that in 1952 the 1952 earthquake appears to be characteristic of the quaternary record of fault displacement in the increase in white wolf slip toward the san andreas fault the ratio of reverse to lateral slip 1 3 1 and the ratio of vertical fault slip to emergence of the hanging wall block 3 1 the 8500 m deep sedimentary basin on the down thrown block cannot be explained by repeated slip of the white wolf fault in an elastic medium

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

evidence for large holocene earthquakes on the compton thrust fault los angeles california 1 we demonstrate that the compton blind thrust fault is active and has generated at least six large magnitude earthquakes mw 7 0 7 4 during the past 14 000 years this large concealed fault underlies the los angeles metropolitan area and thus poses one of the largest deterministic seismic risk in the united states we employ a methodology that uses a combination of high resolution seismic reflection profiles and borehole excavations to link blind faulting at seismogenic depths directly to near surface fault related folding deformed holocene strata record recent activity on the compton thrust and are marked by discrete sequences that thicken repeatedly across a series of buried fold scarps we interpret the intervals of growth as occurring after the formation of now buried paleofold scarps that formed during uplift events on the underlying compton thrust ramp minimum uplift in each of the scarp forming events which occurred at 0 7 1 75 ka event 1 0 7 3 4 ka or 1 9 3 4 event 2 5 6 7 2 ka event 3 5 4 8 4 ka event 4 10 3 12 5 ka event 5 and 10 3 13 7 ka event 6 ranged from 0 6 to 1 9 m indicating minimum thrust displacements of 1 3 to 4 2 m such large displacements are consistent with the occurrence of large magnitude earthquakes mw 7 this multidisciplinary methodology provides a means of defining the recent seismic behavior and therefore the hazard for blind thrust faults that underlie other major metropolitan regions around the world

holocene shortening rates and seismic hazard assessment for the frontal potwar plateau nw himalaya of pakistan insights from 10 be concentrations on fluvial terraces of the mahesian anticline abstract we present the results of a structural neotectonic survey undertaken on the mahesian anticline in the frontal himalaya of pakistan this anticline resulted from the folding of precambrian to tertiary layers that was controlled by a thrust and a backthrust interacting in a complex way four generations of fluvial terraces formed by the jhelum river and two tributaries have been distinguished on the se flank of the anticline two of these terraces t2 and t3 have been left hanging by fold development and have been dated by cosmogenic 10 be to 6 5 0 2 ka and 3 3 0 7 ka respectively from such ages an uplift rate of 10 mm y was determined for the holocene that uplift is induced by a shortening rate of 10 mm y we highlight that the mahesian anticline and frontal salt range thrust together with the kalabagh western lateral ramp and the jhelum eastern lateral ramp delineate the active tectonic boundary of the potwar plateau this thrust sheet moves above the salt level without out of sequence deformation moreover the small but significant difference between the long term deformation rates 8 4 mm y and the geodetic velocities 2 5 mm y detected for the central potwar plateau seems to be linked to episodic spurts of accelerated creeping of the thick salt level triggered by earthquakes located to the north on the deep 15 km part of the mht in addition the large difference between the long term deformation rates and the geodetic velocities less than 2 mm y reported for the eastern potwar plateau seems to be linked to the accumulation of a slip deficit around asperities formed where the salt is missing this deficit may be recovered during earthquakes potentially as great as mw 7

bushveld aged fluid flow peak metamorphism and gold mobilization in the witwatersrand basin south africa constraints from in situ shrimp u pb dating of monazite and xenotime in situ u pb dating of monazite and xenotime in gold reefs and unmineralized greenschist facies sedimentary rocks from the witwatersrand basin south africa reveals two episodes of tectonothermal activity a major event between 2 06 and 2 03 ga is recorded in the wit watersrand and transvaal supergroups in the northwestern and central basin and broadly coincides with the ca 2 06 ga bushveld event in the central and southern basin a previously unrecognized event has been dated between 2 14 and 2 12 ga the widespread geographic and stratigraphic occurrence of bushveld aged monazite and xenotime including both auriferous reefs and unmineralized strata indicates that metamorphism and fluid flow associated with magmatism was pervasive affecting most of the succession 10 km thick in the central and northern parts of the basin the metamorphic phosphate dates which are younger away from the complex indicate a lag of 20 30 m y between emplacement and phosphate growth in the central basin 100 km south suggesting that heat related to magmatism was transferred southward at an average rate of 3 5 mm yr 1 the absence of 2 06 2 03 ga phosphates in the welkom goldfield at the southern end of the basin implies that bushveld related heating and fluid flow did not affect this part of the basin the intergrowth of ca 2 045 ga monazite with gold in quartz pebble conglomerate from the west rand goldfield indicates that fluid flow related to the bushveld event caused mobilization of gold in the witwatersrand basin

structural transect of the western transverse ranges california implications for lithospheric kinematics and seismic risk evaluation a retrodeformable cross section that integrates surface and subsurface data across the western transverse ranges california illustrates an actively developing fold and thrust belt that began forming at 2 3 ma high level thrusts are interpreted to root in a mid crustal detachment at 12 15 km depth which coincides with the maximum depth of earthquakes the cross section documents 53 km of convergence above the mid crustal detachment dividing this by the time since onset of deformation yields convergence rates of 17 6 26 5 mm yr the high density lithospheric anomaly beneath the transverse ranges is related to subduction of lower crust and lithosphere below the mid crustal detachment to balance the shallow crustal shortening thrust ramps coincide with zones of high seismicity in the transverse ranges this suggests that ramp regions have the highest potential for compressive earthquake events e g the recent whittier narrows earthquake of october 1 1987 m sub l 5 9 occurred along the eastern part of a ramp zone

recent plate motions and crustal deformation reports by u s workers on geodetic measurements of recent plate motions or crustal deformation published in 1987 1990 are reviewed the review begins with global plate motions proceeds through plate boundaries in california alaska and the pacific northwest and finishes with volcanic phenomena monument stability and longevity and gps relative position measurements 184 refs

source inversion of the 1987 whittier narrows earthquake california using the isochron method abstract we determine the earthquake source process from an isochron synthetic method and the recursive stochastic inverse algorithm using the strong motion records from 16 stations within 15 km of the epicenter we determined the earthquake slip and rupture time distribution on the fault with different fault geometries for the whittier narrows earthquake in our study we have chosen two best fit fault geometries with strike direction and dip angle of 270 and 35 and 280 and 30 respectively the inversion results indicated dominantly two regions of slip on the fault plane for the whittier narrows mainshock one located immediately below the hypocenter and the other near the lower east corner of the fault in addition there are three or four other smaller localized source areas near the hypocenter together they indicate a highly heterogeneous fault slip distribution for the whittier narrows mainshock the great majority of seismic moment release occurs in a 10 by 4 km region which is consistent with the geodetic modeling results the inversion result for the model allowing variable slip and rupture time model gave the best fit in terms of both the euclidean norm and the weighted euclidean norm suggesting that the rupture velocity may be not constant but we find no simple causal relation between these rupture velocity variations and the slip amplitude distributions on the other hand by comparing the mainshock slip pattern of our inversion results with the early aftershock we found that the aftershocks tend to occur over patches on the rupture surface deficient in mainshock slip this observation can be well explained by the barrier model of fault heterogeneity

coseismic folding earthquake recurrence and the 1987 source mechanism at whittier narrows los angeles basin california static deformation associated with the october 1 1987 whittier narrows california m 6 0 earthquake was detected by geodetic elevation changes the earthquake uplifted a 1 5 km high quaternary fold the santa monica mountains anticlinorium by 50 mm but caused no fault rupture at the ground surface this suggests that folding and faulting of the los angeles basin sediments are coincident and continuing after correction for surveying errors and nontectonic subsidence we model the 214 geodetic observations with a simple dislocation in an elastic half space a thrust fault with reverse slip of 1 1 0 3 m and dipping 30 4 n with an upper edge at a depth of 12 1 km and a lower edge at 17 1 km fits the geodetic data best and is consistent with the main shock hypocenter fault plane solution and initial aftershock distribution the upper limit on the static stress drop is 17 5 5 0 mpa 175 50 bar the lower limit on the geodetic moment is 1 0 0 2 1025 dyne cm in accord with seismic estimates indicating that most of the slip took place during seismic rupture if earthquakes of m 6 characterize the blind thrust fault on which the earthquake occurred we estimate a 200 year repeat time at whittier narrows and a 5 18 year rate of earthquake occurrence within a 150 km long band in the northern los angeles basin and santa monica bay to the west the 25 year rate of historical occurrence since 1860 is less than this prediction the deficit in moment release implies that either vigorous aseismic slip or infrequent larger earthquakes occur here

earthquake by earthquake fold growth above the puente hills blind thrust fault los angeles california implications for fold kinematics and seismic hazard 1 boreholes and high resolution seismic reflection data collected across the forelimb growth triangle above the central segment of the puente hills thrust fault pht beneath los angeles california provide a detailed record of incremental fold growth during large earthquakes on this major blind thrust fault these data document fold growth within a discrete kink band that narrows upward from 460 m at the base of the quaternary section 200 250 m depth to 82 at 250 m depth folding and uplift occur within discrete kink bands thereby enabling us to develop a paleoseismic history of the underlying blind thrust fault the borehole data reveal that the youngest part of the growth triangle in the uppermost 20 m comprises three stratigraphically discrete growth intervals marked by southward thickening sedimentary strata that are separated by intervals in which sediments do not change thickness across the site we interpret the intervals of growth as occurring after the formation of now buried paleofold scarps during three large pht earthquakes in the past 8 kyr the intervening intervals of no growth record periods of structural quiescence and deposition at the regional near horizontal stream gradient at the study site minimum uplift in each of the scarp forming events which occurred at 0 2 2 2 ka event y 3 0 6 3 ka event x and 6 6 8 1 ka event w ranged from 1 1 to 1 6 m indicating minimum thrust displacements of 2 5 to 4 5 m such large displacements are consistent with the occurrence of large magnitude earthquakes mw 7 cumulative minimum uplift in the past three events was 3 3 to 4 7 m suggesting cumulative thrust displacement of 7 to 10 5 m these values yield a minimum holocene slip rate for the pht of 0 9 to 1 6 mm yr the borehole and seismic reflection data demonstrate that dip within the kink band is acquired incrementally such that older strata that have been deformed by more earthquakes dip more steeply than younger strata specifically strata dip 0 4 at 4 m depth 0 7 at 20 m depth 8 at 90 m 16 at 110 m and 17 at 200 m moreover structural restorations of the borehole data show that the locus of active folding the anticlinal active axial surface does not extend to the surface in exactly the same location from earthquake to earthquake rather that the axial surfaces migrate from earthquake to earthquake reflecting a component of fold growth by kink band migration the incremental acquisition of bed dip in the growth triangle may reflect some combination of fold growth by limb rotation in addition to kink band migration possibly through a component of trishear or shear fault bend folding alternatively the component of limb rotation may result from curved hinge fault bend folding and or the mechanical response of loosely consolidated granular sediments in the shallow subsurface to folding at depth

a geodesy and seismicity based local earthquake likelihood model for central los angeles we estimate time independent earthquake likelihoods in central los angeles using a model of interseismic strain accumulation and the 1932 2017 seismic catalog we assume that on the long term average earthquakes and aseismic deformation collectively release seismic moment at a rate balancing interseismic loading mainshocks obey the gutenberg richter law a log linear magnitude frequency distribution mfd up to a maximum magnitude and a poisson process and aftershock sequences obey the gutenberg richter and bath laws we model a comprehensive suite of these long term systems assess how likely each system would be to have produced the mfd of the instrumental catalog and use these likelihoods to probabilistically estimate the long term mfd we estimate m max 6 8 1 05 0 4 every 300 years or m max 7 05 0 95 0 4 assuming a truncated or tapered gutenberg richter mfd respectively our results imply that for example the median likelihood of one or more m w 6 5 mainshocks is 0 2 in 1 year 2 in 10 years and 18 21 in 100 years

denudation vertical crustal movements and sedimentary basin infill denudation and vertical crustal movements are linked through the isostatic equation for conservation of lithospheric mass recent empirical results from a wide range of sources are presented on the rates of these processes denudation alone can cause non tectonic isostatic surface uplift of the right magnitude predicted by theory a case is made following ahnert for a single linear relationship although with much scatter between denudation rate and mean drainage basin relief for large basins some recent determinations of denudational time constants have neglected to include tectonic and isostatic terms which oppose the reduction of relief by denudation application of diffusional transport models to determine the rate of sediment deposition are severely limited by inherent one dimensionality and neglect of suspended and washload contributions basin infill sequences may be used to determine past sediment transfer coefficients from a hinterland but problems arise in the apportionment of the various hinterland fluxes that occur in real world three dimensional basins sediment yields in smaller half graben and growth fold basins must reflect the magnitude of drainage basins and the complex local controls upon sediment yields examples are given from extensional basins in the western usa and greece the length of tectonic relief produced in tilt blocks and growth folds will control the area of drainage basin developed through the fractal form of hack s law and hence the magnitude of deposition in sedimentary basins adjoining tectonic uplands

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

source parameters of the october 1 1987 whittier narrows earthquake from crustal deformation data offsets in the regional strain field generated by the october 1 1987 whittier narrows earthquake were recorded with large amplitudes on two deep borehole dilational strainmeters at distances of 46 7 and 65 5 km from the hypocenter and marginally on instruments at greater distances in the parkfield area and at pinon flat where laser extensometers also recorded small offsets these data are insufficient to solve for the location and physical parameters of the earthquake but by also using the measured elevation changes in the epicentral area we are able to invert for source models consistent with all available observations of crustal deformation the source models obtained indicate that slip extends to a depth of about 30 km well below the recorded aftershock zone the requirement for deeper and presumably aseismic slip derives from the large negative dilatation experienced by the nearest strainmeter pubs but high frequency data from the same site exclude any significant slow component of moment release by ignoring pubs we obtain a moment of about 0 7 1018 n m on a fault that has a strike and dip of about n60 w and 40 down to the north respectively and extends to a depth of about 16 km the most likely reason for the anomalous offset at pubs appears to be sympathetic slip triggered on a nearby fault by the main shock precursive strain during the month prior to the earthquake is not apparent at the nanostrain level in the data from the closest instrument but the event was accompanied by a change in strain rate at the two nearer sites

why blind thrust faults do not propagate to the earth s surface numerical modeling of coseismic deformation associated with thrust related anticlines high fault tip stress concentrations are associated with coseismic slip on blind thrust faults and suggest that these structures should readily propagate to the earth s surface seismic profiles of blind thrust related earthquakes reveal diffuse zones of aftershocks surrounding the fault tip which are attributed to inelastic deformation such as flexural slip or extensional fracturing the complex interaction between blind thrust faults and secondary structures may control the evolution of blind thrust systems the influence of bedding plane slip on fault propagation is simulated with numerical models using the boundary element method we use two parameters to estimate the tendency for thrust fault propagation 1 the mode ii stress intensity factor and 2 the maximum coulomb stress near the fault tip calculations from both analyses suggest that shallow thrust faults may exhibit an increased tendency to propagate as a result of interaction with the earth s surface and slip along bedding planes above the fault tip and a decreased tendency to propagate due to slip along bedding planes at or below the fault tip our results demonstrate that the magnitude and style of inelastic deformation in active fault systems control fault propagation

growth and seismic hazard of the montserrat anticline in the north canterbury fold and thrust belt south island new zealand abstract fault related fold growth is a seismic hazard in north canterbury new zealand the north canterbury fold and thrust belt ncftb is located at the southern end of the hikurangi subduction zone south island new zealand where the pacific plate transitions from subduction to transpression along the alpine fault transpression causes shortening beneath the south island resulting in basement thrusts generating folds such as the montserrat anticline we focus on fault geometry and seismic hazard associated with this structure exposed along the coast where pleistocene marine terraces on the backlimb record tectonic uplift to constrain parameters associated with evolution of this fault related fold we model the fold using several trishear kinematic models a listric fault is most compatible with field and regional geophysical studies ages of marine terraces and inner edge elevations constrain uplift rate due to slip on the glendhu fault to 1 1 0 1 m ka 1 an 800 year recurrence interval is calculated for the glendhu fault listric fault geometry lengthens the recurrence interval relative to other fault geometry models an accurate understanding of subsurface fault geometry and kinematics is important for estimating seismic hazard in regions of fault related folding such as the ncftb because it affects recurrence interval estimations

source complexity of the 1987 whittier narrows california earthquake from the inversion of strong motion records strong motion records for the whittier narrows earthquake are inverted to obtain the history of slip both constant rupture velocity models and variable rupture velocity models are considered the results show a complex rupture process within a relatively small source volume with at least four separate concentrations of slip two sources are associated with the hypocenter the larger having a slip of 55 90 cm depending on the rupture model these sources have a radius of approximately 2 3 km and are ringed by a region of reduced slip the aftershocks fall within this low slip annulus other sources with slips from 40 to 70 cm each ring the central source region and the aftershock pattern all the sources are predominantly thrust although some minor right lateral strike slip motion is seen the overall dimensions of the whittier earthquake from the strong notion inversions is 10 km long along the strike and 6 km wide down the dip the preferred dip is 30 degree and the preferred average rupture velocity is 2 5 km s moment estimates range from 7 4 to 10 0 times 10 sup 24 dyn cm depending on the rupture model

southern california earthquake center geologic vertical motion database the southern california earthquake center geologic vertical motion database vmdb integrates disparate sources of geologic uplift and subsidence data at 104 to 106 year time scales into a single resource for investigations of crustal deformation in southern california over 1800 vertical deformation rate data points in southern california and northern baja california populate the database four mature data sets are now represented marine terraces incised river terraces thermochronologic ages and stratigraphic surfaces an innovative architecture and interface of the vmdb exposes distinct data sets and reference frames permitting user exploration of this complex data set and allowing user control over the assumptions applied to convert geologic and geochronologic information into absolute uplift rates online exploration and download tools are available through all common web browsers allowing the distribution of vertical motion results as html tables tab delimited gis compatible text files or via a map interface through the google maps web service the vmdb represents a mature product for research of fault activity and elastic deformation of southern california

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

reply to comments on saugus palmdale california field test for refraction error in historical leveling surveys by ross s stein charles t whalen sanford r holdahl william e strange and wayne thatcher

on a possible connection between three major earthquakes in california and oil production abstract the 1983 coalinga m 6 5 the 1985 kettleman north dome m 6 1 and the 1987 whittier narrows m 5 9 earthquake sequences each occurred beneath major producing oil fields and caused an aftershock sequence whose epicentral extent coincides approximately with that of the overlying oil field despite this coincidence a causal relationship between these sequences and oil production has been discounted because the earthquakes were located at depths of the order of 10 km whereas oil production is confined to the topmost several km moreover because all three oil fields coalinga kettleman north dome and montebello are situated on anticlines that have undergone recent uplift as a consequence of horizontal tectonic compression of the crust natural earthquakes are not unexpected a mechanical connection between oil production and the earthquake sequence is suggested however by the observation that in each case the total seismic deformation was just that required to offset the force imbalance caused by oil production specifically for each of the three sequences m 0 2 m c where m 0 is the sum of the seismic moments is the modulus of rigidity m is the mass of the fluid removed due to oil production is the fraction of the upper crust that is seismogenic and c is the average upper crustal density in essence net extraction of oil and water reduces slightly the average density of the upper crust causing an isostatic imbalance the ductile lower crust deforms in response to this imbalance thus increasing the load on the seismogenic layer which fails seismically to thicken the crust so as to restore static equilibrium locally accordingly earthquakes near the base of the upper crust may be an expected outcome of major oil production from growing anticlines irrespective of the depths of the producing formations

localization of bedding plane slip and backthrust faults above blind thrust faults keys to wrinkle ridge structure a mechanically based model for wrinkle ridge development is developed that combines wrinkle ridge morphologies regional topographic offsets suggestive of subsurface thrust faults and folding of near surface layers this model provides explicit relationships between observed morphologic elements characteristic of wrinkle ridges and plausible mechanisms in the subsurface a key component that is absent in previous qualitative fault based scenarios for these structures as developed in this paper wrinkle ridges are the surface expression of anticlines that grow above a blind thrust fault as a result of both flexural slip folding of near surface strata and the nucleation and growth of echelon arrays of backthrust faults calculations of displacements both horizontal shortening and vertical uplift and coulomb stress change related to slip along blind thrust faults in the model demonstrate physically important spatial inhomogeneities in these quantities with revealing and useful implications 1 the ratio of shortening due to folding at the surface to the shortening due to faulting at depth is characteristically small for coupled wrinkle ridge blind thrust fault systems and decreases with increasing fault depth the depth of the blind thrust fault s upper tip thus profoundly influences the surface strains 2 folding and uplifted topography forming the topographic ridge are produced above the area of the slipping blind thrust fault plane horizontal and vertical deformation at the surface extend over several ridge widths or a total of at least 50 km for a 10 km wide ridge implying that topographic profiles and geologic studies must extend sufficiently far from the wrinkle ridge to fully characterize the surface deformation 3 calculations of coulomb stress changes suggest that fault slip can localize both bedding plane slip in overlying strata and new backthrust faults that propagate upward to become wrinkles on the trailing side of the ridge initiation of bedding plane slip in association with slip along the blind thrust fault likely determines whether the resulting surface structure becomes a wrinkle ridge or a lobate scarp wrinkle ridge spacing may also be related to stress changes associated with slip along the underlying blind thrust fault

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

analysis of regional broadband recordings of the 1987 whittier narrows california earthquake recordings of the whittier narrows earthquake of october 1 1987 brk ml 6 0 and the large aftershock of october 4 brk ml 5 5 from broadband seismographs 10 mhz to 10 hz at six stations in the berkeley seismograph network in northern california at 430 825 km demonstrate the range of information provided on source mechanisms in such circumstances analysis of the waveforms shows that estimation of source mechanisms in this case requires incorporation of the significantly different velocity structures along the coast ranges and the sierra nevada indicated by the broadband signals inversion of the transverse component waveforms after allowance for regional wave dispersion provides the following source estimations for the main shock seismic moment m0 of 1 0 0 06 1025 preferred fault plane strike rake and dip of 259 33 128 16 11 15 the main shock mechanism is interpreted as a shallow north dipping reverse fault with the hanging wall moving southeasterly relative to the footwall sources of error and of differences with the more robust solution from locally recorded first motions include wave mixing and depth bias at the source the broadband recordings indicate clearly that the mechanism of the aftershock m0 of 1 5 0 11 1024 dyn cm although not well resolved by these regional measurements is quite different from the main shock mechanism

apatite monazite and xenotime in metamorphic rocks this chapter focuses on phosphates that are significant in metamorphic rocks a quick survey of phosphate mineral descriptions at a commercial mineral web site revealed over 500 phosphate mineral names remarkably only three are common in metamorphic rocks apatite monazite and xenotime and this chapter is restricted to discussion of these minerals apatite monazite and to a lesser extent xenotime have enjoyed intensive study during the previous half century following world war ii considerable study was made of minerals that contain fissionable materials and the sometimes large concentrations of u and th in monazite culminated in a number of seminal papers on the occurrence of that mineral e g overstreet 1967 during the 1970s and early 1980s the study of apatite and monazite turned towards their role as a sink for rees and other trace elements in rocks e g watson 1980 watson and capobianco 1981 throughout this period monazite and to some extent xenotime enjoyed attention as a geochronometer e g parrish 1990 and through today this attention has continued to grow accessory minerals such as monazite xenotime and apatite have come to the forefront of research in metamorphic petrology in recent years for two reasons first it has recently been recognized that trace elements in metamorphic rocks and especially trace element zoning in garnet and other major phases contain considerable detailed information about the reaction history a rock has experienced coupled with the fact that diffusion of many trace elements in metamorphic minerals is in general considerably slower than diffusion of major elements in those same minerals the possibility has recently emerged of recovering details of metamorphic petrogenesis that were previously unattainable inasmuch as accessory minerals play a dominant role in the mass budget of many trace elements attention has naturally turned to their paragenesis it has also recently been discovered that

the 1987 whittier narrows california earthquake a metropolitan shock just 3 hours after the whittier narrows earthquake struck it became clear that a heretofore unseen geological structure was seismically active beneath metropolitan los angeles contrary to initial expectations of strike slip or oblique slip motion on the whittier fault whose north end abuts the aftershock zone the focal mechanism of the mainshock showed pure thrust faulting on a deep gently inclined surface hauksson et al 1988 this collection of nine research reports spans the spectrum of seismological geodetic and geological investigations carried out as a result of the whittier narrows earthquake although unseen the structure was not unforeseen namson 1987 had published a retrodeformable geologic cross section meaning that the sedimentary strata could be restored to their original depositional position 100 km to the west of the future earthquake epicenter in which blind or subsurface thrust faults were interpreted to be active beneath the folded southern transverse ranges working 25 km to the west hauksson 1987 had also found a surprising number of microearthquakes with thrust focal mechanisms south of the santa monica mountains another clue to a subsurface system of thrust faults finally davis 1987 had presented a preliminary cross section only 18 km to the west of whittier narrows that identified as fault b the thrust that would rupture later that year not only was the earthquake focus and its orientation compatible with the 10 15 km depth and north dipping orientation of davis proposed thrust but fault b appears to continue beneath the northern flank of the los angeles basin skirting within 5 km of downtown los angeles an area of dense commercial high rise building development these results are refined and extended by davis et al this issue

crustal velocity field near the big bend of california s san andreas fault we use geodetic data spanning the 1920 1992 interval to estimate the horizontal velocity field near the big bend segment of california s san andreas fault saf more specifically we estimate a horizontal velocity vector for each node of a two dimensional grid that has a 15 min by 15 min mesh and that extends between latitudes 34 0 n and 36 0 n and longitudes 117 5 w and 120 5 w for this estimation process we apply bilinear interpolation to transfer crustal deformation information from geodetic sites to the grid nodes the data include over a half century of triangulation measurements over two decades of repeated electronic distance measurements a decade of repeated very long baseline interferometry measurements and several years of global positioning system measurements magnitudes for our estimated velocity vectors have formal standard errors ranging from 0 7 to 6 8 mm yr our derived velocity field shows that 1 relative motion associated with the saf exceeds 30 mm yr and is distributed on the earth s surface across a band 100 km wide that is roughly centered on this fault 2 when velocities are expressed relative to a fixed north america plate the motion within our primary study region has a mean orientation of n44 w 2 and the surface trace of the saf is congruent in shape to nearby contours of constant speed yet this trace is oriented between 5 and 10 counterclockwise relative to these contours and 3 large strain rates shear rates 150 nrad yr and or areal dilatation rates 150 nstr yr exist near the garlock fault near the white wolf fault and in the ventura basin