a preliminary investigation of the influence of basal and surface topography on supraglacial lake distribution near jakobshavn isbrae western greenland the spatial distribution of supraglacial lakes has been hypothesized to be dominantly controlled by the component of surface roughness influenced by basal topography basal topography and surface roughness profiles within the jakobshavn isbrae drainage basin in western greenland acquired from an ice penetrating radar echo sounder were analysed through fourier and wavelet decompositions spectral analyses of basal to surface transfer under a range of ice thickness were compared with spatial distribution of lakes mapped from high resolution landsat imagery fourier analysis identifies dominant signals in both the basal and surface profiles to be ranging between wavelengths of 1 25 12 5 km the strongest peaks of transfer of basal signals to the surface were identified at wavelengths 11 5 km wavelet analysis identifies these peaks with thicker 1200 1400 m and thinner 500 700 m ice respectively and also identifies surface frequencies not present in the basal signal indicating some influence from other factors spatial autocorrelation analysis of supraglacial lake distribution indentifies high correlations at 1 9 5 6 11 24 and 30 km lags lags at 5 6 and 11 km correspond to dominant frequencies present in the basal and surface profiles over thinner and thicker ice respectively these 5 and 11 km frequency components present in the basal topography surface roughness and lake distribution are within the theoretical transfer window of basal to surface transfer as a function of ice thickness the transect analysed in this study does not contain wavelengths in the surface structure that are less than the ice thickness even though there are relatively higher frequencies present in the surface profile between 0 and 15 km that have less power in the basal profile copyright 2011 john wiley sons ltd

deformation rates across the placerita northridge mw 6 7 aftershock zone and hopper canyon segments of the western transverse ranges deformation belt abstract aftershocks of the 1994 northridge m w 6 7 earthquake provide insights into the geometry of the seismic source faults in the san fernando valley and the east ventura basin and allow the calculation of deformation rates for the region the northridge thrust and santa susana faults dip in opposite directions with the northridge thrust entirely beneath the santa susana fault these opposing reverse faults interact resulting in a folded active santa susana fault and uplift in the footwall block of that reverse fault two balanced cross sections suggest thick skinned deformation of the western transverse ranges the western section across the modelo lobe segment of the north dipping san cayetano fault and the easternmost surface trace of the south dipping oak ridge fault is west of any aftershocks of the northridge earthquake and has been termed the hopper canyon segment of the deformation belt structural modeling predicts a dip of 46 s on the oak ridge fault at seismogenic depths horizontal shortening rates are calculated by adding the products of the dip slip displacements and the cosines of the dips of both faults the eastern cross section shows the northridge mainshock with a 45 south dipping nodal plane at a depth of 18 km aftershocks reach a depth of 20 km in a thin skinned paradigm a hinge should occur at the surface near the santa monica mountains due to rocks moving from a decollement at the brittle plastic transition and changing dip as they move up the ramp no hinge of that magnitude occurs there calculation of horizontal short ening rates across this part of the western transverse ranges must take into account the displacement on both the northridge thrust eastern extension of the oak ridge fault and the santa susana fault placerita segment horizontal shortening rates are 8 2 2 4 mm yr across the modelo lobe segment of the san cayetano fault and the oak ridge fault and 5 7 2 5 mm yr across the northridge thrust and the santa susana fault these rates are consistent with those based on tectonic geodesy using gps dip slip displacement rates on the faults are 1 7 mm yr for the northridge thrust since 2 3 ma 4 1 0 4 mm yr for the oak ridge fault since 500 ka 5 9 3 9 3 8 mm yr for the santa susana fault since 600 to 2300 ka and 7 4 3 0 mm yr for the modelo lobe segment of the san cayetano fault since 500 ka this indicates that the slip rates on the north dipping the eastern san cayetano and the santa susana faults are comparable but the slip rate on the south dipping faults decreases eastward the slip rate on the oak ridge fault in the ventura basin is more than double that of the northridge thrust

postseismic relaxation following the 1994 mw6 7 northridge earthquake southern california 1 we have reexamined the postearthquake deformation of a 65 km long linear array of 11 geodetic monuments extending north south across the rupture reverse slip on a blind thrust dipping 40 s 20 w associated with the 1994 mw6 7 northridge earthquake that array was surveyed frequently in the interval from 4 to 2650 days after the earthquake the velocity of each of the monuments over the interval 100 2650 days postearthquake appears to be constant moreover the profile of those velocities along the length of the array is very similar to a preearthquake velocity profile for a nearby similarly oriented array we take this to indicate that significant postseismic relaxation is evident only in the first 100 days postseismic and that the subsequent linear trend is typical of the interseismic interval the postseismic relaxation postseismic displacement less displacement that would have occurred at the preseismic velocity is found to be almost wholly parallel n70 w to the nearby 40 km san andreas fault with only negligible relaxation in the direction of coseismic slip n20 e on the northridge rupture we suggest that the n70 w relaxation is caused by aseismic right lateral slip at depth on the san andreas fault excess slip presumably triggered by the northridge rupture finally using the dieterich 1994 stress seismicity relation we show that return to the preseismic deformation rate within 100 days following the earthquake could be consistent with the cumulative number of m 2 5 earthquakes observed following the main shock

the 1994 northridge earthquake sequence in california seismological and tectonic aspects the m w 6 7 northridge earthquake occurred on january 17 1994 beneath the san fernando valley two seismicity clusters located 25 km to the south and 35 km to the north northwest preceded the mainshock by 7 days and 16 hours respectively the mainshock hypocenter was relatively deep at 19 km depth in the lower crust it had a thrust faulting focal mechanism with a rake of 100 on a fault plane dipping 35 to the south southwest and striking n75 w because the mainshock did not rupture the surface its association with surficial geological features remains difficult to resolve nonetheless its occurrence reemphasized the seismic hazard of concealed faults associated with the contractional deformation of the transverse ranges the northridge earthquake is part of the temporal increase in earthquake activity in the los angeles area since 1970 the mainshock was followed by an energetic aftershock sequence eight aftershocks of m 5 0 and 48 aftershocks of 4 m 5 occurred between january 17 and september 30 1994 the aftershocks extend over most of the western san fernando valley and santa susana mountains they form a diffuse spatial distribution around the mainshock rupture plane illuminating a previously unmapped thrust ramp extending from 7 10 km depth into the lower crust to a depth of 23 km no flattening of the aftershock distribution is observed near its bottom at shallow depths above 7 10 km the thrust ramp is topped by a dense distribution of aftershock hypocenters bounded by some of the surficial faults the dip of the ramp increases from east to west the west side of the aftershock zoae is characterized by a dense steeply dipping and north northeast striking planar cluster of aftershocks that exhibited mostly thrust faulting these events coincided with the gillibrand canyon lateral ramp along the east side of the aftershock zone the aftershocks also exhibited primarily thrust faulting focal mechanisms the focal mechanisms of the aftershocks were dominated by thrust faulting in the large aftershocks with some strike slip and normal faulting in the smaller aftershocks the 1971 san fernando and the 1994 northridge earthquakes ruptured partially abutting fault surfaces on opposite sides of a ridge both earthquakes accommodated north south contractional deformation of the transverse ranges the two earthquakes differ primarily in the dip direction of the faults and the depth of faulting the 1971 north northeast trend of left lateral faulting chatsworth trend was not activated in 1994

high resolution 3d p wave velocity model for the east ventura san fernando basin california and relocation of events in the northridge and san fernando aftershock sequences we determined a high resolution 3d p wave velocity model for an 80 km 80 km area around the san fernando valley extending 22 km below sea level we used events recorded from 1981 to 2000 as well as 799 aftershocks of the 1971 san fernando earthquake recorded by a portable network the total number of events and stations used were 13 455 and 101 respectively most of the events are aftershocks of the 1994 northridge earthquake the inversion software includes a raytracing subroutine that can handle the sharp lateral velocity variations that exist in the area the resulting model shows an overall good agreement with the southern california earthquake center scec 3d velocity model but images the deeper structure of the san fernando valley in more detail in addition our results are supported by the inversion of synthetic data and by the remarkable agreement with a density model derived from gravity data along a 55 km long profile an approximately 10 km wide and sharply defined zone of northridge aftershocks occurred in basement rocks between about 8 and 20 km depth and identifies the fault that slipped during the mainshock horizontal slices at deep 8 18 km levels show that the northridge earthquake occurred within a high velocity basement block that may have controlled the size of the earthquake the fault plane inferred from the seismicity is in good agreement with the geodetic fault plane determined by hudnut et al 1996 assuming uniform slip most of the aftershocks of the northridge earthquake occurred within the sedimentary rocks of the san fernando basin with a large concentration of events located to the east of the eastern boundary of the mainshock fault plane the latter events form a zone that dips about 45 to the southwest at depths less than about 14 km these may represent a lateral ramp this zone terminates at the steeply inclined eastern edge of the san fernando basin these events do not lie on the mainshock fault plane and because the san fernando aftershocks also lie east of the northridge fault plane the san fernando and the northridge mainshocks must have occurred on conjugate en echelon faults i e they do not abut each other in addition an 8 km wide cross section along the density model referred to previously suggests the northridge aftershocks east of the mainshock and most of the aftershocks of the san fernando earthquake illuminate two thrust faults that have a common high velocity basement block in their footwalls the velocity model produced by our analysis suggests that thrust faults formed by modern contraction in this region are strongly influenced by prior basin and basement block geometry online material 3d p wave velocity models without seismicity

tectonic setting of the 1971 sylmar and 1994 northridge earthquakes in the san fernando valley california the san fernando valley lies above the north dipping 1971 sylmar and south dipping 1994 northridge earthquake faults to understand the tectonic setting of these two earthquakes we mapped subsurface geology of the san fernando valley down to a depth of 3 km using industry oil well and seismic data the 1994 northridge earthquake did not rupture the surface and the south dipping aftershock zone terminated against the north dipping 1971 aftershock zone at a depth of 5 8 km however the blind northridge fault has a near surface geologic expression fault propagation folding related to the northridge fault has preserved a thick forelimb sequence of plio pleistocene saugus formation in the sylmar basin and merrick syncline which are located on the hanging wall side of north dipping reverse faults the north dipping mission hills verdugo and northridge hills reverse faults are interpreted to be potential seismic sources because fault propagation folds above these faults have tectonic geomorphic expression these north dipping reverse faults were initiated during the deposition of the saugus formation between 2 3 and 0 5 ma and have minimum dip slip rates of 0 35 to 1 1 mm yr based on the oldest possible age of the initiation of faulting the northridge hills and mission hills faults are interpreted to merge at depth and are located at the updip extension of the 1971 aftershock zone even though these faults did not rupture during the 1971 earthquake surface breaks appeared north of these faults mostly along north dipping bedding planes and are interpreted as secondary features related to flexural slip folding rather than a direct extension of the 1971 seismogenic fault surface and subsurface geology together with seismological data of the 1971 and 1994 earthquakes suggests that the north and south dipping deformation zones in the san fernando valley are divided into multiple segments separated by northeast trending structural discontinuities

three dimensional seismo tectonic imaging an example from the southern california transverse ranges abstract we present a new technique to image deformation 3d seismo tectonic imaging which juxtaposes instantaneous and accumulated deformation by combining earthquake and structural geology data we test the technique using three independent data sets we find concordance between the predicted finite deformation field and related instantaneous deformation surfaces inferred from aftershock and background seismicity data as well as structure imaged by seismic reflection data these results indicate that 1 the 1994 northridge event ruptured a transverse high angle reverse fault linking two ew striking listric thrust systems the pico and oak ridge the rupture terminated on the thrusts and was capped by a north dipping forward breaking imbricate of the santa susana fault 2 the los angeles seismic zone is a region of thrusting associated with the development of a new mountain front forming south of the present one represented by the santa monica anticline the thrust is rooted on a mid crustal ramp forming beneath the los angeles basin we conclude that seismo tectonic imaging by linking earthquake data to an empirically based quantitative description of the finite deformation field provides a new and fruitful method for integrating geological and seismological data

discrepancy between geological and geodetic deformation rates in the ventura basin space geodesy provides a new tool for measuring neotectonic deformation which when combined with geological and geophysical observations and models can be used to infer rates and styles of deformation in the ventnra basin region of southern california the geodetically measured convergence rates of 7 10 mm yr 1 ref 1 are significantly lower than the 20 25 mm yr 1 estimated from geological data2 3 here we investigate the possible implications of this discrepancy it might be for example that temporal variations cause the short and long term convergence rates to differ but if this were the case we would expect to observe the long term rate by extending the geodetic measurements over a broader region yet only 11 3 mm yr 1 of regional convergence is observed4 our preferred explanation of the discrepancy is that the geological models require revision and to this end we present two deformation models that satisfy both the geological and geodetic constraints our modelling suggests that the faults bounding the basin are locked at the surface but are slipping at depths below 2 5 km

mechanical modeling of compressional basins origin and interaction of faults erosion and subsidence in the ventura basin california using geophysical observations and some basic geological ideas on the present structure of the ventura basin we model its possible mechanical evolution during the last 4 million years we use a two dimensional finite element model with frictional and elastoviscoplastic rheologies that allow strain localization this allows us to study the mechanical origin of the san cayetano thrust fault scf and its interaction with the oak ridge fault orf the results of our modeling indicate that the geometry and activity of a shear zone which mimics the san cayetano fault are conditioned both by the preexistence of the oak ridge fault and by the shape of the brittle ductile transition furthermore the presence of a decollement level is shown to favor the development of the san cayetano fault shear zone as a low angle structure the value of the effective friction on the oak ridge fault is evaluated from this model possible values of the viscosity of the sediments are also estimated it is shown that low sediment viscosity may completely hinder the activity of such a fault at the surface while slip at depth continues the stratigraphic profile of the basin is also shown to depend on the relative strengths of the orf and scf which also provide an explanation for the shortening and rapid subsidence of the basin

using vertical rock uplift patterns to constrain the three dimensional fault configuration in the los angeles basin comparison of geologic uplift patterns with results of three dimensional mechanical models provides constraints on the fault geometry compiled by the south ern california earthquake center community fault model in the northern los angeles basin california the modeled uplift matches well the geologic pattern of uplift as sociated with the santa fe springs and coyote hills segments of the puente hills thrust fault but does not match structures to the west of the san gabriel river to better match the geologic patterns in this area alternative fault configurations were tested the best match to geologic uplift is attained with a model incorporating 1 a steep blind thrust fault at the location of the los angeles segment of the puente hills thrust system following interpretations of the las cienegas fault geometry at this location 2 removal of an inferred linking fault between the raymond and holly wood faults and 3 lateral continuation of the lower elysian park fault a blind low angle detachment at 10 km depth along strike to the northwest these geometric revisions alter the connectivity of northern los angeles basin faults and significantly improve the match of model uplift pattern to geologic data model results suggest that fault connectivity may be more important in governing fault slip rate than are fault dip and fault area the preferred model alters slip rates by 0 2 mm yr for the upper elysian park hollywood lower elysian park raymond sierra madre west and verdugo faults additionally the preferred model alters the surface area of several faults in the northern los angeles basin such as the puente hills thrust and the lower elysian park fault which may have important implications for seismic hazard assess ment in the northern los angeles basin

a balanced cross section of the 1994 northridge earthquake southern california the northridge earthquake of 17 january 19941 was the latest in a series of very damaging thrust fault generated earthquakes to strike california following the san fernando2 1971 coalinga3 1983 and whittier narrows4 5 1987 events like the last two of these the northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic hazard methods6 7 balanced cross sections8 9 which flatten and remove the crustal deformation can be used to identify and quantify the seismic hazard posed by thrust faults here we present a balanced cross section through the northridge portion of the transverse ranges fold and thrust belt10 which shows that the earthquake occurred on what we call the pico thrust a cross section of this sort constructed before the earthquake would have revealed the fault although it would not have predicted the earthquake cross sectional modelling of the pico thrust yields an average slip rate of 1 4 1 7 mm yr 1 and a recurrence interval of northridge sized mw 6 7 earthquakes every 1 500 1 800 years we show that the pico thrust is the back thrust to the 170 km elysian park thrust3 4 which underlies some of the most densely urbanized portions of the los angeles basin

geology and tsunamigenic potential of submarine landslides in santa barbara channel southern california abstract a large submarine landslide complex and four small landslides developed under the santa barbara channel suggesting a potential hazard from landslide generated tsunamis we integrate offshore stratigraphy and geologic structure multibeam bathymetric information and several kinds of seismic reflection data to understand how and when the submarine landslides formed seismic reflection data show that mass failure along the slope began at least 200 ka ago landslides appear as zones of poor reflectivity having an irregular upper surface and these zones alternate vertically with strong parallel reflections the emplacement ages of two of the three main landslide lobes are well established at 8 and 10 ka the source material for the youngest part of the landslide complex was sediment of probable late pleistocene and holocene age that accumulated in a shelf edge delta directly under this delta growth of faults and anticlines was particularly intense and tended to oversteepen the deltaic deposits these active structures also formed migration pathways and reservoirs for aqueous and hydrocarbon fluids from the deep basin tsunami deposits have been described from a low lying area near santa barbara and numerical modeling of tsunamis generated by hypothetical landslides in santa barbara channel indicates a moderate to severe threat borrero j c dolan j f and synolakis c e 2001 tsunamis within the eastern santa barbara channel geophys res lett 28 4 643 646 involving wave runups of 2 20 m for a range of assumed landslide volumes inundation from these waves however is expected to be highly focused so that only narrow 10 km sections of the shoreline would be affected

three dimensional vp and vp vs velocity models of the los angeles basin and central transverse ranges california we use p and s arrival times from 5225 earthquakes and 53 explosions recorded by the southern california seismographic network to invert for the three dimensional p velocity v p and the p and s velocity ratio v p v s in the central transverse ranges and the los angeles basin to model long wavelength features of the velocity structure we invert for the models by interpolating models determined successively from a sparse medium to a dense grid with 40 20 and 10 km spacing of horizontal grid nodes layers of grid nodes are placed at depths of 1 4 6 8 12 16 and 20 km the data variance decreased about 80 in the gradational inversion ample data from the 1994 northridge and other earthquake sequences the rich background seismicity and the dense station distribution along with controlled sources made the model well resolved except along the edges to the southwest in the offshore region and at depths greater than 20 km the v p model images the shape of the los angeles and east ventura basins down to depths of 8 and 12 km three low velocity areas at 1 km depth in the los angeles basin that coincide with recent sediment depositional areas are also imaged the north edge of the peninsular ranges the santa monica and the san gabriel mountains form discontinuous high velocity ridges extending to depths of 20 km the high v p v s ratios in the near surface are consistent with high pore fluid pressures in the basin sediments at depth beneath the east ventura basin the high v p v s and high v p suggest the presence of ophiolitic assemblages or mid miocene volcanics in contrast a body with normal v p and low v p v s that is identified in the upper crust beneath santa monica bay may be a fragment of quartz rich continental crust the v p model of both the ventura and the los angeles basins shows features that suggest deformation of the hanging wall or basin closure at seismogenic depths of 16 km the hypocenters of moderate sized and large earthquakes are located within or adjacent to high v p velocity bodies in most cases these high velocity bodies form the upper block consistent with shortening of the lower crust as described in thick skinned tectonic interpretations

patterns of historical earthquake rupture in the iranian plateau the iranian plateau accommodates the 35 mrn yr convergence rate be tween the eurasian and arabian plates by strike slip and reverse faults with relatively low slip rates in a zone 1000 km across although these faults have only locally been the subject of paleoseismological studies a rich historical and archeological record spans several thousand years long enough to establish recurrence intervals of 1000 to 5000 yr on individual fault segments several clusters of earthquakes provide evidence of interaction among reverse and strike slip faults probably due to adjacent faults being loaded by individual earthquakes the dasht e bayaz sequence of 1936 to 1997 includes earthquakes on left lateral right lateral and reverse faults the neyshabur sequence of four earthquakes between 1209 and 1405 respected the seg ment boundary between the neyshabur and binalud reverse fault systems the two pairs of earthquakes may have ruptured different faults in each segment similar to the 1971 and 1994 san fernando california earthquakes the 1978 tabas reverse fault earthquake was preceded by the 1968 ferdows earthquake part of the dasht e bayaz sequence the north tabriz fault system ruptured from southeast to north west in three earthquakes from 1721 to 1786 a previous cluster may have struck this region in 855 to 958 the mosha fault north of tehran ruptured in three earthquakes in 958 1665 and 1830 five large earthquakes struck the tehran region from 743 to 1177 but only two that large have struck the area since 1177 other earthquakes occurred in pairs in the talesh mountains near the caspian sea 1863 1896 the iran turkey border 1840 1843 and the nayband gowk fault system both 1981 other historical events did not occur as parts of sequences the historic seismic moment release in iran accounts for only a small part of the plate convergence rate which may be due to aseismic slip or to the iranian historical record long as it is being too short to sample long term deformation across the plateau no historic earthquakes of m 8 have struck iran however several long straight strike slip faults doruneh west neh east neh and nayband have not sustained large historical earthquakes raising the possibility that these long faults could produce earthquakes of m 8 thereby removing at least part of the apparent slip deficit an increased understanding of iran s seismic hazard could be obtained by an extensive paleoseismology program and space geodetic arrays supplementing the abundant historical and archaeological record

fault systems of the 1971 san fernando and 1994 northridge earthquakes southern california relocated aftershocks and seismic images from larse ii we have constructed a composite image of the fault systems of the m 6 7 san fernando 1971 and northridge 1994 california earthquakes using industry reflection and oil test well data in the upper few kilometers of the crust relocated aftershocks in the seismogenic crust and larse ii los angeles region seismic experiment phase ii reflection data in the middle and lower crust in this image the san fernando fault system appears to consist of a decollement that extends 50 km northward at a dip of 25 from near the surface at the northridge hills fault in the northern san fernando valley to the san andreas fault in the middle to lower crust it follows a prominent aseismic reflective zone below and northward of the main shock hypocenter interpreted upward splays off this decollement include the mission hills and san gabriel faults and the two main rupture planes of the san fernando earthquake which appear to divide the hanging wall into shingle or wedge like blocks in contrast the fault system for the northridge earthquake appears simple at least east of the larse ii transect consisting of a fault that extends 20 km southward at a dip of 33 from 7 km depth beneath the santa susana mountains where it abuts the interpreted san fernando decollement to 20 km depth beneath the santa monica mountains it follows a weak aseismic reflective zone below and southward of the main shock hypocenter the middle crustal reflective zone along the interpreted san fernando decollement appears similar to a reflective zone imaged beneath the san gabriel mountains along the larse i transect to the east in that it appears to connect major reverse or thrust faults in the los angeles region to the san andreas fault however it differs in having a moderate versus a gentle dip and in containing no mid crustal bright reflections

the oak ridge fault system and the 1994 northridge earthquake the 17 january 1994 northridge earthquake moment magnitude m w 6 7 in the san fernando valley in southern california illuminated a hitherto unrecognized blind reverse fault with a moderate southward dip 1 this fault lies beneath the active north dipping santa susana fault system and uplifted both the footwall and the hanging wall of the santa susana fault during the earthquake1 here we argue that footwall uplift on the santa susana fault before the earthquake could have been used to identify the northridge blind thrust as an active fault moreover we propose that the northridge earthquake occurred on a continuation of the oak ridge fault system which reaches the surface in the ventura basin to the west slip rates on the western part of this fault system 2 3 are nearly three times larger than on the northridge blind thrust 4 increasing the probability of a n or t bridge sized earthquake in the heavily populated ventura basin

estimating total resisting force in flexible barrier impacted by a granular avalanche using physical and numerical modeling flexible barriers are a promising tool for protection against extremely rapid landslides such as debris flow and debris avalanches with landslide impacts of any size the total force induced withi

geodetic measurement of deformation in the ventura basin region southern california we have measured the deformation in the ventura basin region southern california with global positioning system gps measurements carried out over 4 6 years between 1987 and 1992 the deformation within our network is spatically variable on scales of tens of kilometers with strain rates reaching 0 6 1 micro rad yr in the east central basin blocklike rotations are observed south and northwest of the basin where the maximum shear strain rates are an order of magnitude lower 0 06 1 micro rad yr to the south we also observed clockwise rotations of 1 deg 7 deg m y shear strain rates determined by comparing angle changes from historical triangulation spanning several decades and gps measurements give consistent though less precise results the geodetic rates of shortening across the basin and western transverse ranges are lower than those estimated from geological observations but the patterns of deformation from the two methods agree qualitatively

coseismic deformation field of the m 6 7 northridge california earthquake of january 17 1994 recorded by two radar satellites using interferometry interferometric combination of pairs of synthetic aperture radar sar images acquired by the ers 1 and jers 1 satellites before and after the northridge california earthquake of january 17 1994 provide two maps of the coseismic deformation field the fringes corresponding to contours of equal change in satellite to ground distance show the coseismic displacement of the mainshock the fringe patterns remain clear for over a year even in urban areas with structural damage elastic dislocation fault models fitting the two radar interferograms are substantially equivalent despite the different radar wavelengths 56 and 235 mm for ers 1 and jers 1 respectively a single fault model based on surveying measurements using the global positioning system gps fails to account for parts of the fringe patterns observed by radar satellite particularly the effects of several aftershocks and localized ground motion

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

collapse sinkholes and radar interferometry reveal neotectonics concealed within the dead sea basin 1 the dead sea ds pull apart basin is one of the more seismically active segments of the ds transform plate boundary in the last decade hundreds of collapse sinkholes have been formed along the ds coastlines in israel and jordan causing severe damage to the regional infrastructure the formation of these sinkholes is attributed to the dissolution of a buried salt layer by fresh groundwater due to the drop of the ds and the associated groundwater levels here we show that the sinkhole distribution combined with gradual land subsidence measured by radar interferometry insar track young fault systems suspected as active concealed within the fill of the ds rift this notion is supported by 1 sinkholes clustering along discrete lineaments with a striking trend similarity to that of the exposed rift margin faults 2 prominent discontinuities in seismic reflection profiles offsetting young sediments several kyrs old below sinkhole lines and 3 straight boundaries of gradual subsidence features that coincide with or parallel sinkhole lines combined the sinkhole lineaments and the insar measurements reveal a zigzag pattern of buried faults within the ds rift fill

kinematics of postseismic relaxation from aftershock focal mechanisms of the 1994 northridge california earthquake geodetic observations of surface deformation associated with the 1994 northridge southern california earthquake generally are reproduced by simple models of a large scale elastic dislocation on a blind or buried thrust fault the smaller scale aftershocks of the northridge earthquake are distributed throughout much of the volume of crust that appears to have deformed elastically during the mainshock these aftershocks averaged over volumes that are large relative to their rupture radii reflect a distributed permanent deformation that is accommodated by local brittle fracture we use a micropolar continuum model to invert the aftershocks in such volumes for the average incremental strain and we compare that deformation both with the elastic strain from the dislocation model of the mainshock and with geodetically measured strain aftershock deformation that occurred at depths below about 6 km and which is associated with the primary rupture zone is consistent with slow continuation of the southwest side up reverse slip on the blind northridge thrust fault in contrast aftershock deformation from the upper 5 7 km of the hanging wall block directly above the thrust fault can be characterized by horizontal ne sw shortening and horizontal nw se i e fault parallel extension this pattern of deformation is similar to that associated with the mainshock as observed geodetically and as calculated from the elastic dislocation model we interpret that the aftershock activity in the hanging wall represents the quasi ductile accommodation by brittle deformation mechanisms of a permanent strain distributed through the hanging wall block the aftershocks along the mainshock rupture zone are interpreted as resulting from either 1 the time dependent release along a weakened fault zone of part of the remaining accumulated elastic strain in the upper crust or 2 the continued slip in the weakened fault zone driven by the deformation of a ductile elastic lower crustal layer that relaxes under the stress transferred by the coseismic loss of cohesion in the upper crust in either case the aftershock activity suggests that the crust undergoes quasi ductile flow as a brittle elastic material and is not a strictly elastic material

evidence from a cluster of small earthquakes for a fault at 18 km depth beneath oak ridge southern california abstract a swarm of about 50 small earthquakes m 1 5 occurred for a month during 1989 beneath oak ridge southern california location accuracy using conventional analysis of arrival time picks is limited for these events by the weak emergent nature of arrivals on the available seismograms however waveform cross correlation techniques are found to provide precise relative event locations due to the similarity of the waveforms recorded at individual stations the relocated events form a small cluster about 1 km across at a depth of 18 km and are aligned along a plane that dips 35 to the northwest estimated standard errors for the locations are generally less than 50 m the time evolution of the sequence shows a gradual migration of activity away from its initiation point three additional events occurred several months later these align along the same plane but are displaced about 500 m to the southeast from the main swarm reliable fault plane solutions are difficult to obtain for these events due to the small number of station records available the limited range of takeoff angles and the weak initial arrivals on many of the seismograms stacking the records at each station over the different events greatly reduces prearrival noise levels and assists in resolving the average p first motions analysis of these first motion data indicates that the slip planes of probable focal mechanisms are not in agreement with the plane defined by the seismicity the seismicity alignment may represent the extension of the simi fault in which case some shallowing of the fault dip would be required to match the observed 35 dip at 18 km

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

geomorphic indicators of active fold growth south mountain oak ridge anticline ventura basin southern california south mountain oak ridge near ventura california is an asymmetric anticlinal uplift forming at the present time above the active buried oak ridge reverse fault shortening along the oak ridge fault accumulated largely in quaternary time and is responsible for the growth and present topography of the westernmost 15 km of the ridge during the past 0 5 m y tectonic geomorphic analysis using several indices of active tectonics provides information concerning fold growth stream gradient indices are relatively high in the northern eroded fold scarp of the ridge a pattern consistent with the existence of active rapid slip on the oak ridge fault mountain front sinuosity along the northern slope of the anticlinal ridge roughly decreases from 2 to 1 toward the westernmost 10 km of observed surface folding valley floor width to valley height ratios along the northern flank of the ridge generally decrease westward from 1 5 to 0 5 values of the hypsometric integral along the northern flank increase significantly from 0 35 to 0 4 maximum 0 55 from east to west drainage density varies from 4 to 6 km km2 along both flanks of the south mountain oak ridge anticline entrenchment of streams into the southern backlimb of the fold along the westernmost 9 km of the structure decreases from 20 m to 1 m from east to west apparent backlimb rotation as measured by dip of strata along the westernmost 7 km of the fold decreases from east to west from 35 to 20 fold growth of the south mountain oak ridge anticline occurred during the past 0 5 ma following deposition of the saugus formation lateral and vertical fold growth were likely produced by westward decrease in fault slip along the buried oak ridge fault

geomorphic evidence for the geometry and slip rate of a young low angle thrust fault implications for hazard assessment and fault interaction in complex tectonic environments abstract we present surface evidence and displacement rates for a young active low angle 20 reverse thrust fault in close proximity to major population centers in southern california usa the southern san cayetano fault sscf active faulting along the northern flank of the santa clara river valley displaces young landforms such as late quaternary river terraces and alluvial fans geomorphic strain markers are examined using field mapping high resolution lidar topographic data 10be surface exposure dating and subsurface well data to provide evidence for a young active sscf along the northern flank of the santa clara river valley displacement rates for the sscf are calculated over 103 104 yr timescales with maximum slip rates for the central sscf of 1 9 1 0 0 5 mm yr 1 between 19 7 ka and minimum slip rates of 1 3 0 5 0 3 mm yr 1 since 7 ka uplift rates for the central sscf have not varied significantly over the last 58 ka with a maximum value of 1 7 0 9 0 6 mm yr 1 for the interval 58 19 ka and a minimum value of 1 2 0 3 mm yr 1 since 7 ka the sscf is interpreted as a young active structure with onset of activity at some time after 58 ka the geometry for the sscf presented here with a 20 north dip in the subsurface is the first interpretation of the sscf based on geological field data our new interpretation is significantly different from the previously proposed model derived geometry which dips more steeply at 45 60 and intersects the surface in the middle of the santa clara river valley we suggest that the sscf may rupture in tandem with the main san cayetano fault additionally the sscf could potentially act as a rupture pathway between the ventura and san cayetano faults in large magnitude multi fault earthquakes in southern california however given structural complexities including significant changes in dip and varying holocene displacement rates along strike further work is required to examine the possible mechanism likelihood and frequency of potential through going ruptures between the ventura and san cayetano faults confirmation of the sscf in a previously well studied area such as southern california demonstrates that identification of young faults is critical for accurate seismic hazard assessment we suggest that many young active faults remain undetected in other structurally complex and tectonically active regions globally and that significant seismic hazards can be overlooked

mechanical models of fault propagation folds and comparison to the trishear kinematic model abstract faults propagating through the earth generate a wave of deformation ahead of their tip lines we have modeled this process to understand the relationship between fold geometry and fault propagation using finite element modeling fem we investigate the response of incompressible frictionless and frictional materials and a compressible frictional material with associated flow to vertical and dipping faults whose tip lines propagate at rates 3 3 5 times their slip rates the fold geometries finite strain and velocity fields in models with incompressible materials are very similar to those produced by the trishear kinematic model even though the latter uses a purely ad hoc linear velocity field furthermore when the trishear grid search is applied to the final geometry of the mechanical folds the best fit kinematic models have approximately the same propagation to slip ratio as was used in the fem experiments however when the compressible frictional material is used the mechanical models exhibit a main triangular shear band in front of the tip line and a conjugate shear band in the fold backlimb both migrating with the propagating tip line the conjugate shear band antithetic to the fault produces a gentle anticlinal back limb even though there is not a bend in the fault

backarc thrust faulting and tectonic uplift along the caribbean sea coast during the april 22 1991 costa rica earthquake surface deformation and a tsunami accompanied the destructive april 22 1991 costa rica panama earthquake ms 7 5 along a 135 km stretch of caribbean coast coseismic uplift was measured between the lower and upper limits of sessile intertidal organisms stranded on coral reefs the preearthquake and postearthquake high tide levels located from driftwood lines on beaches and the preearthquake and postearthquake tide levels as pointed out by local residents the nature and distribution of offshore vertical displacements were further constrained from analysis of measured run up heights and reported arrival times of the tsunami uplift detected along the coast jumped within 4 km from zero to 157 cm near limon and generally decreased over a distance of 70 km southward to the border with panama these data map an axis of uplift that intersects the coastal beach ridge just north of the port of moin and runs offshore to the east and south roughly parallel to the coast no surface faulting was found the earthquake and tsunami were generated by backarc thrusting along faults that bound the north panama deformed belt and dip from the caribbean sea beneath costa rica and northern panama combined geodetic and seismological data indicate that the main rupture dips landward at an angle of about 30 and is approximately 40 km wide and 80 km long dislocation models suggest 2 2 m of slip on a causative thrust fault striking between 105 and 120 we estimate that the repeat time for this type of earthquake is 200 to 1100 years the historical record and new isotopic data favor the middle of the range

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

crustal wedging triggering recent deformation in the andean thrust front between 31 s and 33 s sierras pampeanas precordillera interaction 1 we document a new model of crustal structure of the andean front in argentina where numerous historic earthquakes destroyed the cities of mendoza in 1861 ms 7 and san juan in 1944 mw 7 0 the cerro salinas anticline is formed above the west directed cerro salinas thrust an east facing monocline with an amplitude of about 2 km folds the cerro salinas thrust and overlying neogene succession this monocline is formed above a blind crustal thrust in the basement its dip of 14 west is inferred from fold geometry this thick skinned east directed blind thrust and the thin skinned west directed cerro salinas thrust define a tectonic wedge the wedge tip occurs at a depth of 5 4 km growth of the monocline after 8 5 ma is revealed on multichannel seismic msc profile 31017 repsol ypf rates of cerro salinas thrust displacement are of the order of 1 mm yr whereas vertical uplift of 0 45 mm yr results from the combined displacement on the cerro salinas thrust and growth of east facing monocline the lateral extent of the east directed crustal blind ramp corresponds with the along strike extent of the eastern precordillera when combined with the low displacement rate a long earthquake recurrence interval is implied smaller magnitude earthquakes however indicate that segments of the blind thrust ramps ruptured in historic events if all the segments of the blind thrust ruptured together the fault area is 7000 km 2 and could produce a mw 7 7 earthquake the crustal wedge model provides new constraints on the origin and potential size of earthquakes that threaten the densely populated region

reconciling rapid strain accumulation with deep seismogenic fault planes in the ventura basin california global positioning system measurements across the east central ventura basin transverse ranges southern california before the nearby 1994 northridge earthquake show high strain rates interpreting this rapid strain accumulation using the usual model of deep slip on a dislocation in a uniform elastic half space requires slip to extend to within 5 km of the surface such shallow slip is difficult to reconcile with the substantial coseismic displacement at depths from 7 to 19 km during the northridge earthquake here we model the displacement and velocity fields throughout the earthquake cycle using a two dimensional finite element model with a viscoelastic rheology displacements are driven by far field and basal velocity boundary conditions and by imposed periodic earthquakes on the thrust faults bounding the basin the thrust faults rupture through an elastic upper crust to a depth of 15 km after a transient stage during which stresses and strains build up to quasi equilibrium values the behavior of the model becomes periodic the sum of the coseismic displacement divided by the repeat interval plus the average interseismic velocity is equal to the geologic velocity the temporal variation in surface velocity depends mainly on the elsasser relaxation time proportional to the product of the maxwell time of the lower crust and the ratio of the thicknesses of the entire crust and viscoelastic lower crust we are able to match the observed high strain rate only if we include the observed variations in elastic modulus associated with the deep basin sediments the model reconciles geologic geodetic and seismological observations of deformation there are trade offs among the far field convergence rate the elsasser time the earthquake repeat time and the time into the earthquake cycle acceptable convergence rates range from 8 mm yr for a relaxation time of the lower crust of 300 years to 12 mm yr for a 30 year relaxation time

recent crustal deformation in southern california deduced from the restoration of folded and faulted strata a rigid element method of restoration unfold is used to restore competent folded and faulted layers of the ventura and los angeles basins to their initial horizontal state comparison of initial undeformed state with present deformed state allows one to estimate both the finite crustal deformation and its associated horizontal displacement field relative to an arbitrary fixed line including data from the santa barbara channel basin the total finite displacement field for the western transverse ranges and vicinity within the pacific plate is inferred from this map restoration and is modeled as a double fan closure this model implies a 10 clockwise rotation of the northeen boundary of the western transverse ranges and a 5 counterclockwise rotation of its northeast boundary lateral variation of the deformation reveals the heterogeneity of the subsurface deformation most of the major thrusts appear to initiate as en echelon structures along the left lateral northern margin and the right lateral northeastern margin of the studied area the resulting deformation and displacement values closely match those derived by other geological methods section balancing techniques or fault slip measurements and by geophysical methods geodetic paleomagnetic and focal mechanism data map restoration thus is a method that can independently quantify both local and regional deformation including folds and faults this method also reveals the zones where problems of compatibility appear with the available geological and geophysical data and thus where the next studies might be focused