activity of the offshore newport inglewood rose canyon fault zone coastal southern california from relocated microseismicity an offshore zone of faulting approximately 10 km from the southern california coast connects the seismically active strike slip newport inglewood fault zone in the los angeles metropolitan region with the active rose canyon fault zone in the san diego area relatively little seismicity has been recorded along the offshore newport inglewood rose canyon fault zone although it has long been suspected of being seismogenic active low angle thrust faults and quaternary folds have been imaged by seismic reflection profiling along the offshore fault zone raising the question of whether a through going active strike slip fault zone exists we applied a waveform cross correlation algorithm to identify clusters of microseismicity consisting of similar events analysis of two clusters along the offshore fault zone shows that they are associated with nearly vertical north northwest striking faults consistent with an offshore extension of the newport inglewood and rose canyon strike slip fault zones p wave polarities from a 1981 event cluster are consistent with a right lateral strike slip focal mechanism solution manuscript received 23 july 2003

analysis techniques for coherent airborne radar sounding application to west antarctic ice streams 1 analysis of coherent radar sounding echoes from polar ice sheets can provide information suitable for classifying the subglacial environment echoes from a general interface consist of both specularly reflected and diffusely scattered contributions specular reflection results from smooth uniform interfaces whereas diffuse scattering results from rough nonuniform interfaces and inhomogeneous media this article discusses how these phenomena are important to the acquisition and analysis of coherent radar sounding data reflection results are presented from airborne surveys conducted in 1987 over the downstream portions of whillans ice stream and ice stream c west antarctica additionally reflection and scattering analyses along with new results are presented for repeat profiles flown in 2001 over ice stream c analysis methods include using echo amplitudes to compute reflection coefficients which are used for inferring the dielectric properties of the subglacial material echo phase analysis provides the locations of dominant scattering centers which relate to reflection or scattering from the interface as well as provide interface roughness estimates comparison of low and high resolution imaging obtained from synthetic aperture radar techniques indicates a reflecting and or scattering interface combining the results from these independent analyses provides classification of the subglacial environment classified regions include smooth seawater smooth saturated sediments accreted marine ice rough bottom crevasses mixed conditions with partial subglacial water and dry frozen conditions

late quaternary uplift and earthquake potential of the san joaquin hills southern los angeles basin california analysis of emergent marine terraces in the san joaquin hills california and 230 th dating of solitary corals from the lowest terraces reveal that the san joaquin hills have risen at a rate of 0 21 0 27 m k y during the past 122 k y movement on a blind thrust fault in the southern los angeles basin has uplifted the san joaquin hills and has the potential to generate an m w 7 3 earthquake within this densely populated area our structural modeling suggests that the fault dips to the southwest and slips at 0 42 0 79 m k y yielding an estimated minimum average recurrence interval of 1650 3100 yr for moderate sized earthquakes recognition of this blind thrust extends the known area of active blind thrusts and fault related folding southward from los angeles into coastal orange county

how fault evolution changes strain partitioning and fault slip rates in southern california results from geodynamic modeling in southern california the pacific north america relative plate motion is accommodated by the complex southern san andreas fault system that includes many young faults 2 ma the initiation of these young faults and their impact on strain partitioning and fault slip rates are important for understanding the evolution of this plate boundary zone and assessing earthquake hazard in southern california using a three dimensional viscoelasto plastic finite element model we have investigated how this plate boundary fault system has evolved to accommodate the relative plate motion in southern california our results show that when the plate boundary faults are not optimally configured to accommodate the relative plate motion strain is localized in places where new faults would initiate to improve the mechanical efficiency of the fault system in particular the eastern california shear zone the san jacinto fault the elsinore fault and the offshore dextral faults all developed in places of highly localized strain these younger faults compensate for the reduced fault slip on the san andreas fault proper because of the big bend a major restraining bend the evolution of the fault system changes the apportionment of fault slip rates over time which may explain some of the slip rate discrepancy between geological and geodetic measurements in southern california for the present fault configuration our model predicts localized strain in western transverse ranges and along the dextral faults across the mojave desert where numerous damaging earthquakes occurred in recent years

distributed subglacial discharge drives significant submarine melt at a greenland tidewater glacier this is the publisher s final pdf the article is copyrighted by american geophysical union and published by john wiley sons inc it can be found at http agupubs onlinelibrary wiley com agu journal 10 1002 28issn 291944 8007

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

parallel fault strands at 9 km depth resolved on the imperial fault southern california 1 precision relocation of hundreds of small earthquakes occurring along the imperial fault in southern california during the last two decades reveals parallel steaks of seismicity at 9 km depth these strands are spaced about 0 5 km apart within a 2 km wide zone of earthquakes near the brittle ductile transition between the shallow locked part of the fault and a creeping zone at depth these results suggest that the lower crustal shear zone below the imperial fault site of major earthquakes in 1940 and 1979 must be at least two kilometers wide

late cenozoic tectonic evolution of the los angeles basin and inner california borderland a model for core complex like crustal extension we propose that the los angeles basin inner california borderland lab ib and the southern borderland off baja california formed by large magnitude crustal extension beginning in latest oligocene earliest miocene time and that these regions represent major late cenozoic rifts the southern borderland is analogous to the gulf of california rift but the onset of rifting in this region may have preceded the opening of the gulf by as much as 15 to 20 m y the lab ib rift is more complex than the southern borderland because it formed in the wake of the rotating western transverse ranges wtr a large crustal block that has undergone more than 90 of neogene clockwise rotation total extension in both rifted regions is estimated to be in excess of 200 km or comparable to the magnitude of late cenozoic crustal extension now estimated for the basin and range province also like the basin and range the crustal floors of the basins in these highly extended domains are characterized by metamorphic core complexes and detachment faults voluminous miocene volcanic rocks and hanging wall fragments of pre rift strata and basement rocks stranded atop detachments during extension in support of this model we synthesize a wide variety of existing geologic data and present interpretations of new geophysical data seismic reflection profiles these profiles image features that we infer are detachment faults and overlying remnants of fragmented and rifted hanging wall rocks we also suggest that a similar but slightly earlier onset of crustal extension affected the santa maria basin and adjacent regions in central california and that the southern margin of this santa maria basin rift was overridden during neogene clockwise rotation of the wtr

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

source related variations of ground motions in 3 d media application to the newport inglewood fault los angeles basin summary deterministic earthquake scenario simulations are playing an increasingly important role in seismic hazard and risk estimation our aim is to calculate a substantial number of different finite source scenarios embedded in a 3 d structure for a particular fault or fault system by pre calculating numerical green s functions ngfs a large seismic fault is divided into subfaults of appropriate size for which synthetic green s functions at the surface are calculated and stored consequently ground motions from arbitrary kinematic sources can be simulated for the whole fault or parts of it by superposition to illustrate this approach and its functionalities we simulate m 7 up to 0 5 hz scenario earthquakes for a simplified model of the newport inglewood ni fault in the los angeles la basin we quantify the variations of surface ground motion e g peak ground velocity pgv and synthetic seismograms due to source parameters e g hypocentre location and corresponding slip history the results show a complex behaviour with dependence of absolute pgv and its variation on asperity location source directionality and local structure and demonstrate the necessity to combine 3 d structural and finite source effects to quantify ground motion characteristics and their variations

the palos verdes fault offshore southern california late pleistocene to present tectonic geomorphology seascape evolution and slip rate estimate based on auv and rov surveys the palos verdes fault pvf is one of few active faults in southern california that crosses the shoreline and can be studied using both terrestrial and subaqueous methodologies to characterize the near seafloor fault morphology tectonic influences on continental slope sedimentary processes and late pleistocene to present slip rate a grid of high resolution multibeam bathymetric data and chirp subbottom profiles were acquired with an autonomous underwater vehicle auv along the main trace of pvf in water depths between 250 and 600 m radiocarbon dates were obtained from vibracores collected using a remotely operated vehicle rov and ship based gravity cores the pvf is expressed as a well defined seafloor lineation marked by subtle along strike bends right stepping transtensional bends exert first order control on sediment flow dynamics and the spatial distribution of holocene depocenters deformed strata within a small pull apart basin record punctuated growth faulting associated with at least three holocene surface ruptures an upper shallower landslide scarp a buried sedimentary mound and a deeper scarp have been right laterally offset across the pvf by 55 5 52 4 and 39 8 m respectively the ages of the upper scarp and buried mound are approximately 31 ka the age of the deeper scarp is bracketed to 17 24 ka these three piercing points bracket the late pleistocene to present slip rate to 1 3 2 8 mm yr and provide a best estimate of 1 6 1 9 mm yr the deformation observed along the pvf is characteristic of strike slip faulting and accounts for 20 30 of the total right lateral slip budget accommodated offshore southern california

bedmachine v3 complete bed topography and ocean bathymetry mapping of greenland from multibeam echo sounding combined with mass conservation greenland s bed topography is a primary control on ice flow grounding line migration calving dynamics and subglacial drainage moreover fjord bathymetry regulates the penetration of warm atlantic water aw that rapidly melts and undercuts greenland s marine terminating glaciers here we present a new compilation of greenland bed topography that assimilates seafloor bathymetry and ice thickness data through a mass conservation approach a new 150 m horizontal resolution bed topography bathymetric map of greenland is constructed with seamless transitions at the ice ocean interface yielding major improvements over previous data sets particularly in the marine terminating sectors of northwest and southeast greenland our map reveals that the total sea level potential of the greenland ice sheet is 7 42 0 05 m which is 7 cm greater than previous estimates furthermore it explains recent calving front response of numerous outlet glaciers and reveals new pathways by which aw can access glaciers with marine based basins thereby highlighting sectors of greenland that are most vulnerable to future oceanic forcing

upper crustal structure and neogene tectonic development of the california continental borderland multichannel seismic reflection data sonobuoy seismic refraction data and regional geology are used to define the upper crustal structure of the southern california continental borderland and to delineate the characteristics of the main lithotectonic belts of the region the catalina schist belt is separated on its west side from the gently deformed nicolas forearc belt by faults that have steep west dips and pronounced normal separations on its east side the schist belt is bounded by a large detachment fault that dips gently to the east beneath the west edge of the peninsular ranges belt at the coastline near oceanside the catalina schist was uplifted from middle crustal depths and exposed during a major event of extensional tectonism that started in early miocene time in conjunction with about 10 of clockwise rotation of the western transverse ranges belt part of the uplift of the catalina schist could have occurred on the detachment fault but it is thought to have mostly occurred on the steep faults that bound the west edge of the schist belt a large amount of uplift is required and it probably involved strong footwall flexural deformation in the wake of the translating and rotating western transverse ranges and nicolas forearc belts extension accompanied by probable large amounts of right slip continued in the borderland region during and after middle miocene time the later stage of extension was accompanied by rapid clockwise rotation of the western transverse ranges of at least 90 most of the borderland including the belt of schist that was uplifted in early miocene time was further deformed into numerous basins and ridges during this stage of oblique extension the primary driving force for the deformation is thought to have been derived from the rapid northwest motion of the pacific plate after it had become coupled to the farallon plate system which had previously been subducted beneath the borderland

north atlantic warming and the retreat of greenland s outlet glaciers mass loss from the greenland ice sheet quadrupled over the past two decades contributing a quarter of the observed global sea level rise increased submarine melting is thought to have triggered the retreat of greenland s outlet glaciers which is partly responsible for the ice loss however the chain of events and physical processes remain elusive recent evidence suggests that an anomalous inflow of subtropical waters driven by atmospheric changes multidecadal natural ocean variability and a long term increase in the north atlantic s upper ocean heat content since the 1950s all contributed to a warming of the subpolar north atlantic this led in conjunction with increased runoff to enhanced submarine glacier melting future climate projections raise the potential for continued increases in warming and ice mass loss with implications for sea level and climate

source and basin effects on rotational ground motions comparison with translations the recent availability of accurate observations of rotational ground mo tions has reopened interest in understanding near fault characteristics of such motions in the context of strong ground motion and earthquake engineering in order to in vestigate source and structure dependent variations of rotational motions we simulate several m 7 earthquakes with varying source scenarios on the newport inglewood ni fault embedded in the 3d los angeles basin using a finite difference method in the frequency range up to 0 5 hz we use a precalculated database with several hundred numerical green s functions for a discretized model of the ni fault that al lows arbitrary finite fault scenarios to be synthesized by superposition we investigate source and basin effects on the rotational part of ground motion namely maximum peak ground rotation rates and their variations and compare them with the corre sponding values of translational motion our main conclusions are 1 the pure strike slip source mechanism leads to larger rotation rates around the vertical axis than around the horizontal ones 2 variation of hypocenter introduces more scatter on ground rotation rate than variations of slip history 3 the coprocessing of translation and rotation recordings might reveal information on local velocity structure as indi cated by plane wave theory and 4 the attenuation of accelerations horizontal com ponents and rotation rate vertical component with distance from the fault are very similar suggesting that similar expressions as a function of distance as for the peak accelerations can be adopted for the peak rotation rates when determining their at tenuation relations

coastal uplift of the san joaquin hills southern los angeles basin california by a large earthquake since a d 1635 late holocene marsh deposits and a shoreline along the coast of the san joaquin hills southern los angeles basin range from 1 to 3 6 m above the active shoreline radiocarbon dating of ancient marsh shows that emergence occurred after a d 1635 the age distribution and geomorphic expression of elevated marsh and shoreline are best explained by tectonic uplift due to a m 7 earthquake radio carbon dates and the historic record of seismicity suggest the earthquake occurred between a d 1635 and 1855 possibly in 1769 the historic record of earthquakes in the los angeles basin begins in a d 1769 and contains no other earthquakes greater than m 6 7 therefore the san joaquin hills earthquake may be the largest historic earthquake in the los angeles basin

ice flow in greenland for the international polar year 2008 2009 a digital representation of ice surface velocity is essential for a variety of glaciological geologic and geophysical analyses and modeling here we present a new reference comprehensive high resolution digital mosaic of ice motion in greenland assembled from satellite radar interferometry data acquired during the international polar year 2008 to 2009 by the envisat advanced synthetic aperture radar asar the advanced land observation system alos s phase array l band sar palsar and the radarsat 1 sar that covers 99 of the ice sheet in area the best mapping performance is obtained using alos palsar data due to higher levels of temporal coherence at the l band frequency but c band frequency sar data are less affected by the ionosphere the ice motion map reveals various flow regimes ranging from patterned enhanced flow into a few large glaciers in the cold low precipitation areas of north greenland to diffuse enhanced flow into numerous narrow fast moving glaciers in the warmer high precipitation sectors of northwest and southeast greenland we find that the 100 fastest glaciers v 800m yr drain 66 of the ice sheet in area marine terminating glaciers drain 88 of greenland and basal sliding motion dominates internal deformation over more than 50 of the ice sheet this view of ice sheet motion provides significant new constraints on ice flow modeling copyright 2012 by the american geophysical union

earthquake locations in the inner continental borderland offshore southern california the inner continental borderland region offshore southern california is tectonically active and contains several faults that are potential seismic hazards to nearby cities however fault geometries in this complex region are often poorly constrained due to a lack of surface observations and uncertainties in earthquake locations and focal mechanisms to improve the accuracy of event locations in this area we apply new location methods to 4312 offshore seismic events that occurred between 1981 and 1997 in seven different regions within the borderland the regions are defined by either temporal or spatial clustering of seismic activity in the southern california seismic network scsn catalog obtaining accurate locations for these events is difficult due to the lack of nearby stations the limited azimuthal coverage and uncertainties in the velocity structure for this area our location procedure is based on the l 1 norm grid search waveform cross correlation method of shearer 1997 except that we use a nearest neighbor approach astiz et al 2000 to identify suitable event pairs for waveform cross correlation and we explore the effect of different velocity models on the locations and associated station terms in general our relocated events have small estimated relative location errors and the events are more clustered than the scsn catalog locations a quarry on the south tip of catalina island provides a test of our location accuracy and suggests that under ideal conditions offshore events can be located to within 1 to 2 km of their true locations our final locations for most clusters are well correlated with known local tectonic features we relate the 1981 santa barbara island m l 5 3 earthquake with the santa cruz fault the 13 july 1986 oceanside m l 5 3 sequence with the san diego trough fault zone and events near san clemente island with the known trace of the san clemente fault zone over 3000 of the offshore events during this time period are associated with the 1986 oceanside earthquake and its extended aftershock sequence our locations define a northeast dipping fault plane for the oceanside sequence but in cross section the events are scattered over a broad zone about 4 km thick this could either be an expression of fault complexity or location errors due to unaccounted for variations in the velocity structure events that occur near coronado bank in the scsn catalog are relocated closer to the san diego coast and suggest a shallow angle northeast dipping fault plane at 10 to 15 km depth manuscript received 12 february 1999

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

source parameters of the 1933 long beach earthquake regional seismographic network and teleseismic data for the 1933 m l 6 3 long beach earthquake sequence have been analyzed both the teleseismic focal mechanism of the main shock and the distribution of the aftershocks are consistent with the event having occurred on the newport inglewood fault the focal mechanism had a strike of 315 dip of 80 to the northeast and rake of 170 relocation of the foreshock main shock aftershock sequence using modern events as fixed reference events shows that the rupture initiated near the huntington beach newport beach city boundary and extended unilaterally to the northwest to a distance of 13 to 16 km the centroidal depth was 10 2 km the total source duration was 5 sec and the seismic moment was 5 10 25 dyne cm which corresponds to an energy magnitude of m w 6 4 the source radius is estimated to have been 6 6 to 7 9 km which corresponds to a brune stress drop of 44 to 76 bars both the spatial distribution of aftershocks and inversion for the source time function suggest that the earthquake may have consisted of at least two subevents when the slip estimate from the seismic moment of 85 to 120 cm is compared with the long term geological slip rate of 0 1 to 1 0 mm yr along the newport inglewood fault the 1933 earthquake has a repeat time on the order of a few thousand years

tomographic investigation of the wear along the san jacinto fault southern california the seismic properties of the wear along the san jacinto fault are investigated using local seismic records for clustered fault zone earthquakes spatial reciprocity allows us to use the seismicity along fault plane to mimic the situation where receiver arrays are placed at depth on the fault plane a seismic record at the event location is constructed by stacking the original station records waveform cross correlations is then used to calculate the traveltimes of shear waves traveling between the pair of events we analyze 157 small earthquakes occurring between 1998 and 2004 on the san jacinto and elsinore fault zones low shear velocities in the san jacinto fault zone related to wear and gouge are persistently observed up to the depth of brittle ductile transition zone 16 km on the other hand low velocities in the elsinore fault zone are only visible in the northwestern portion at shallow depth the wear structures in the san jacinto fault zone display lower shear velocities by 6 8 than those of the wall rock 2005 elsevier b v all rights reserved

earthquake locations in southern california obtained using source specific station terms we relocate 297 400 events recorded by the southern california seismic network scsn between 1975 and 1998 using spatially varying station terms to improve relative location accuracy our method uses existing scsn p and s picks a smooth one dimensional velocity model and an iterative grid search approach based on the l1 norm we apply empirical corrections for three dimensional structure by computing station timing corrections that continuously vary as a function of source position station terms for each event are obtained by smoothing the residuals from nearby events using a natural neighbor delaunay tessellation of the seismicity and then iterating until a stable set of locations and station terms is achieved our approach achieves relative location accuracy comparable locally to master event methods but can be applied uniformly over large regions median estimated standard errors for our final locations are 328 m in horizontal position and 741 m in depth our locations exhibit much less scatter particularly in depth than those of the scsn catalog and a greater tendency to align into linear and planar features suggestive of fault structures our results appear comparable to and in some cases better than previous scsn relocation studies using joint hypocenter velocity inversion techniques plots of daytime versus nighttime events permit discrimination between clusters of natural and artificial seismicity we observe no simple relationship between the maximum depth of seismicity and surface geology

a mass conservation approach for mapping glacier ice thickness the traditional method for interpolating ice thickness data from airborne radar sounding surveys onto regular grids is to employ geostatistical techniques such as kriging while this approach provides continuous maps of ice thickness it generates products that are not consistent with ice flow dynamics and are impractical for high resolution ice flow simulations here we present a novel approach that combines sparse ice thickness data collected by airborne radar sounding profilers with high resolution swath mapping of ice velocity derived from satellite synthetic aperture interferometry to obtain a high resolution map of ice thickness that conserves mass and minimizes the departure from observations we apply this approach to the case of nioghalvfjerdsfjorden 79north glacier a major outlet glacier in northeast greenland that has been relatively stable in recent decades the results show that our mass conserving method removes the anomalies in mass flux divergence yields interpolated data that are within about 5 of the original data and produces thickness maps that are directly usable in high spatial resolution high order ice flow models we discuss the application of this method to the broad and detailed radar surveys of ice sheet and glacier thickness copyright 2011 by the american geophysical union

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

increase in radon emission due to rock failure an experimental study 1 radon anomalies are commonly observed prior to dynamic failure in the crust and are interpreted as cracking of the medium thus attracting considerable attention in understanding the precursory phenomena of earthquakes and volcanic activity in this study we have compared the starting radon emissions from low porosity crystalline lava phonolite samples with those from damaged and failed samples the damaged sample was loaded up to just beyond the end of the linear elastic phase as evidenced by the output of ae energy the increase in total porosity and a decrease in p wave and s wave velocity relative to the intact sample whereas the failed sample showed deformation behaviour characteristically brittle with increasing values of ae output and porosity as the sample approached macroscopic failure radon measurements have evidenced that dilatational microcracking of deformed sample produced no significant variation in radon emanation with respect to the intact sample in contrast after macroscopic failure radon emanation drastically increased therefore major finding from this study is that in the case of low porosity and relatively high strength crystalline lavas the development of a macroscopic fracture provides new large exhaling surface resulting in a substantial increase in radon emission rate

precise relocations and stress change calculations for the upland earthquake sequence in southern california we relocate earthquakes that occurred near the 1988 ml 4 7 and the 1990 ml 5 5 upland california earthquakes to map the fault geometry of the poorly defined san jose fault and to test the static stress triggering hypothesis for this sequence we adopt the l1 norm waveform cross correlation method of shearer 1997 to obtain precise relocations for 1573 events between 1981 and 1997 in the upland area to limit computation time we only perform waveform cross correlation on 60 of the nearest neighbors of each relocated event our final relocations show two linear features the first is imaged by the locations of the initial month of aftershocks of the 1988 upland earthquake which delineate a fault with a dip angle of 45 between 7 and 9 km depth consistent with the mainshock focal mechanism the second linear feature is a plane dipping at about 74 from 2 to 9 km depth which is illuminated by both the 1988 and 1990 upland sequences in agreement with the inferred location of the san jose fault at depth however below 9 km the event locations become more diffuse giving rise to two different interpretations of the fate of the san jose fault at depth one possibility is that the fault shallows at depth consistent with our relocations but not with the focal mechanism of a ml 4 7 deep aftershock alternatively the fault may be offset at depth by the more shallow dipping fault strand broken during the 1988 earthquake using these inferred fault geometries we compute stress changes resulting from slip during the mainshocks to test whether the relocated aftershocks are consistent with the hypothesis that more aftershocks occur where the change in static coulomb failure stress is positive on faults optimally oriented for failure this requires an extension of previous models of changes in the failure stress to three dimensions and arbitrary fault orientation we find that patterns of change in coulomb failure stress differ little between the different fault geometries all are nearly symmetric about the fault and so do not match the aftershock distribution in which most of the off fault events occur to one side of the fault plane

coarse grained volcanic detritus in deep sea sediments of the northeastern equatorial pacific abstract coarse grained volcanic detritus in near surface sediments of the northeastern equatorial pacific consists mainly of feldspar plagioclase with an35 70or0 4 and magnetite with minor parts of pyroxene augite wo25 32en53 32 and volcanic quartz except for plagioclase 0 005 0 5 of total sediment all concentrations range between 0 and 30 grains m 1 of piston core where differences exist within the stratigraphic sequence and also from mineral to mineral the following relationships have been found plagioclase magnetite volcanic quartz pyroxene contents are low in plio quaternary sediments and in lower miocene pure radiolarian ooze they increase within the late eocene to early oligocene sediments and near the early oligocene hiatus the morphology distribution and alteration of the minerals are described and singlegrain analyses for plagioclase and pyroxene are given the origin of plagioclase pyroxene and magnetite is related to the formation of new oceanic crust at the east pacific ridge transport and distribution by slumping high density currents and reworking of older sediments are assumed the origin of volcanic quartz from potential source areas in northern central america and western mexico and transport and accumulation in deepsea sediments are discussed

seismicity based earthquake forecasting techniques ten years of progress abstract earthquake fault systems interact over a broad spectrum of spatial and temporal scales and in recent years studies of the regional seismicity in a variety of regions have produced a number of new techniques for seismicity based earthquake forecasting while a wide variety of physical assumptions and statistical approaches are incorporated into the various methodologies they all endeavor to accurately replicate the statistics and properties of both the historic and instrumental seismic records as a result the last ten years have seen significant progress in the field of intermediate and short term seismicity based earthquake forecasting these include general agreement on the need for prospective testing and successful attempts to standardize both evaluation methods and the appropriate null hypotheses here we differentiate the predominant approaches into models based upon techniques for identifying particular physical processes and those that filter or smooth the seismicity comparison of the methods suggests that while smoothed seismicity models provide improved forecast capability over longer time periods higher probability gain over shorter time periods is achieved with methods that integrate statistical techniques with our knowledge of the physical process such as the epidemic type aftershock sequence etas model or those related to changes in the b value for example in general while both classes of seismicity based forecasts are limited by the relatively short time period available for the instrumental catalog significant advances have been made in our understanding of both the limitations and potential of seismicity based earthquake forecasting there is general agreement that both short term forecasting on the order of days to weeks and longer term forecasting over five to ten year periods is within reach this recent progress serves to illuminate both the critical nature of the different temporal scales intrinsic to the earthquake process and the importance of high quality seismic data for the accurate quantification of time dependent earthquake hazard

late quaternary ice flow in a west greenland fjord and cross shelf trough system submarine landforms from rink isbrae to uummannaq shelf and slope sea floor landforms and acoustic stratigraphic records allow interpretation of the past form and flow of a westward draining ice stream of the greenland ice sheet rink isbrae the late pliocene pleistocene glacial package is several hundred metres thick and down laps onto an upper miocene horizon several acoustic facies are mapped from sub bottom profiler records of the 400 km long uummannaq fjord shelf slope system an acoustically stratified facies covers much of the fjord and trough floor interpreted as glacimarine sediment from rain out of fine grained debris in turbid meltwater beneath this facies is a semi transparent deformation till unit which includes buried streamlined landforms landform distribution in the uummannaq system is used to reconstruct past ice extent and flow directions the presence of streamlined landforms mega scale glacial lineations drumlins crag and tails shows that an ice stream advanced through the fjord system to fill uummannaq trough reaching the shelf edge at the last glacial maximum beyond the trough there is a major fan built mainly of glacigenic debris flows turbidity current channels were not observed on uummannaq fan contrasting with well developed channels on disko fan 300 km to the south ice retreat had begun by 14 8 cal ka ago grounding zone wedges gzw in uummannaq trough imply that retreat was episodic punctuated by several still stands ice retreat between gzws may have been relatively rapid there is little sedimentary evidence for still stands in the inner fjords except for a major moraine ridge marking a little ice age maximum position on the shallow banks either side of uummannaq trough iceberg ploughing has reworked any morphological evidence of earlier ice sheet activity

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

an unusual occurrence of probable pleistocene corestone within a cretaceous dioritic enclave peninsular ranges california abstract we here document an unusual occurrence of probable pleistocene corestone within an 5 m by 5 m dioritic enclave contained within a cretaceous tonalitic pluton santa margarita ecological reserve sw california the enclave lies within 3 5 km of the seismically active 1 5 2 ma elsinore fault zone and may have been subjected to 70 90 ground shaking events since 22 000 18 000 years ago the studied corestone is elliptical with major axis measuring 55 cm and minor axis 26 cm in length it is surrounded by a discontinuous 7 cm thick rind that breaks apart under slightly greater finger pressure than does the surrounding saprolite in order to assess changes in the physical and chemical properties of the corestone rind and saprolite we collected along an 66 5 cm long traverse 4 samples from the corestone 1 from the rind and 5 from the saprolite for bulk and grain density porosity and major and trace element analyses textural and clay mineral data along with the redistribution of elemental mass indicate that the weathering of biotite and to much lesser degrees apatite and the an rich cores of plagioclase played critical roles in the production of saprolite especially in a narrow 20 cm wide zone adjacent to the rind of the corestone within this zone bulk densities reach their minimum values while porosities and positive volume strains reach their maximums in addition the maximum loss of k fe mn and ca mass occurred just inside this region and is paralleled by the highest cia values and highest additions of si and rb mass in contrast the masses of na and sr are progressively increased and decreased respectively along the entire sampling traverse while the loss of mg ti and p mass is episodic with the greatest losses occurring within the narrow zone adjacent to the rind and at the end of the traverse the above observations indicate that the conversion of biotite to expandable mixed layered clay minerals aided by the alteration of the an rich cores of plagioclase produced sufficient stress on grain boundaries that a weakening or loss of intercrystalline cohesion occurred however unlike the well documented isovolumetric development of saprolite in other areas at the study site saprolitization was accompanied by a volume expansion we speculate that repeated ground shaking in response to earthquakes generated in the nearby elsinore fault zone may be responsible for this difference important byproducts of ground shaking would include additional weakening or loss of intercrystalline cohesion and the production and enhancement of new and older fluid pathways respectively the fact that the most intensely altered material at the study site lies adjacent to the boundary between the rind and saprolite suggests that this interface acted to guide fluid flow around the corestone and rind and into the adjacent saprolite where elemental mass was redistributed down various paths leading to the underlying water table most of the leached elemental mass was removed from the area of the sampling traverse but small increases in si rb and na mass suggest redistribution of these elements from elevated areas outside the area sampled during this study the result of the above complex set of processes is a variably porous and chemically altered saprolitic enclave that is still undergoing modification as it adjusts to the vicissitudes of the paralithic environment and continuing ground shaking during earthquakes generated along the elsinore fault

holocene activity of the rose canyon fault zone in san diego california the rose canyon fault zone in san diego california has many well expressed geomorphic characteristics of an active strike slip fault including scarps offset and deflected drainages and channel walls pressure ridges a closed depression and vegetation lineaments geomorphic expression of the fault zone from mount soledad south to mission bay indicates that the mount soledad strand is the most active a network of trenches excavated across the mount soledad strand in rose creek demonstrate a minimum of 8 7 m of dextral slip in a distinctive early to middle holocene gravel filled channel that crosses the fault zone the gravel filled channel was preserved within and east of the fault but was removed west of the fault zone by erosion or possibly grading during development consequently the actual displacement of the channel could be greater than 8 7 m radiocarbon dates on detrital charcoal recovered from the sediments beneath the channel yield a maximum calibrated age of about 8 1 0 2 kyr the minimum amount of slip along with the maximum age yield a minimum slip rate of 1 07 0 03 mm yr on this strand of the rose canyon fault zone for much of holocene time other strands of the rose canyon fault zone which are east and west of our site may also have holocene activity based on an analysis of the geomorphology of fault traces within the rose canyon fault zone along with the results of our trenching study we estimate the maximum likely slip rate at about 2 mm yr and a best estimate of about 1 5 mm yr stratigraphie evidence of at least three events is present during the past 8 1 kyr the most recent surface rupture displaces the modern a horizon topsoil suggesting that this event probably occurred within the past 500 years stratigraphie and structural relationships also indicate the occurrence of a scarp forming event at about 8 1 kyr prior to deposition of the gravel filled channel that was used as a piercing line a third event is indicated by the presence of several fault strands that displace the channel but did not move during the most recent event other events may also have occurred but these data suggest that the return time for surface rupturing earthquakes is no more than about 4 kyr

high resolution mapping of offshore and onshore glaciogenic features in metamorphic bedrock terrain melville bay northwestern greenland abstract geomorphological studies of previously glaciated landscapes are important to understand how ice sheets and glaciers respond to rapidly changing climate melville bay in northwestern greenland contains some of the most sensitive but least studied ice sheet sectors in the northern hemisphere where the bathymetric knowledge previously was restricted to a few sparsely distributed single beam echo soundings we present here the results of high resolution geomorphological mapping of the offshore and onshore landscapes in melville bay using multibeam sonar and satellite data at 5 and 10 m resolutions respectively the results show a similar areally scoured bedrock dominated landscape with a glacially modified cnoc and lochan morphology on the inner shelf 150 500 m depth and on the nearby exposed coast this is manifested by the presence of u shaped troughs moutonee type elongated landforms stoss and lee forms and streamlined features the submarine landscape shows features that are characteristic of bedrock in folded faulted and weathered metamorphic terrain and to a lesser extent glacially molded bedforms while coastal landforms exhibit higher relief irregular shaped basins and more subdued fracture valleys although generally similar the onshore and offshore landscapes contain examples of distinctly different landform patterns which are interpreted to reflect a longer exposure to long term deep weathering as well as to more recent periglacial weathering processes on land the spatial variability in the distribution of landforms across the landscape in both study areas is mostly attributed to differences in lithological properties of the bedrock the lack of sediment cover on the inner shelf is likely a result of a capacity for sediment erosion and removal by the west greenland current flowing northward over the area in combination with limited sediment supply from long sea ice cover seasons the distribution and orientation of the landforms in the offshore part indicate ice movement toward the nw and suggests that this area acted as a tributary or onset region for the major paleo ice stream that formed the present day melville bay trough

radar mapping of isunnguata sermia greenland ice thickness estimates using advanced nadir sounding and tomographic radar processing techniques are compared and combined in a study of isunnguata sermia glacier greenland using an ensemble of operation icebridge flight lines spaced at 500m intervals and running approximately along the flow direction we find there is a statistically excellent comparison between subglacial terrains derived from two dimensional tomography and gridded nadir sounding analysis shows that tomographic data better capture short wavelength 1 2 km patterns in basal terrain but interpolated nadir sounding data yield more spatially extensive and continuous coverage across the glacier especially in deep subglacial troughs using derived surface and basal topography maps we find that driving stress and measured and modeled surface velocity comparisons indicate that basal sliding is an important component of the glacier motion but is also only weakly coupled to the detailed bed topography save for the deepest troughs as might be expected for this land terminating relatively slow moving glacier the subglacial and proglacial topography is similar suggesting the erosional processes acting on the modern glacier bed once helped sculpt the now exposed land

shallow s wave well logs as an indicator of past strong shaking from earthquakes on the newport inglewood fault numerical calculations assuming linear elasticity by bose et al 2014 indicate that an m w 7 75 earthquake on the newport inglewood fault would cause 5 m s of horizontal peak ground velocity pgv within the los angeles basin however the dynamic strain from this event would take much of the uppermost few hundred meters of basin rock beyond its frictional elastic limit stiff quartz rich beds within the basin are fragile geological features that would fail and crack before the rest of the clay rich rock mass repeated cracking would reduce the shear modulus of the quartz rich beds to the level that cracking barely occurred during strong events when interpreted in this way data from such stiff beds near the los angeles international airport indicate past pgv of 1 6 m s comparable with near field records from the strike slip 2002 denali and 1992 landers earthquakes numerical calculations capable of representing nonlinear failure within shallow bedded rocks are warranted online material digital rosrine s wave borehole logs

seismic constraints on the architecture of the newport inglewood rose canyon fault implications for the length and magnitude of future earthquake ruptures the newport inglewood rose canyon fault zone nirc is an active strike slip fault system within the pacific north american plate boundary in southern california located in close proximity to populated regions of san diego orange and los angeles counties prior to this study the nirc fault zone s continuity and geometry were not well constrained nested marine seismic reflection data with different vertical resolutions are employed to characterize the offshore fault architecture four main fault strands are identified offshore separated by three main stepovers along strike all of which are 2 kilometers or less in width empirical studies of historical ruptures worldwide show that earthquakes have ruptured through stepovers with this offset models of coulomb stress change along the fault zone are presented to examine the potential extent of future earthquake ruptures on the fault zone which appear to be dependent on the location of rupture initiation and fault geometry at the stepover these modeling results show that the southernmost stepover between the la jolla and torrey pines fault strands may act as an inhibitor to through going rupture due to the stepover width and change in fault geometry across the stepover however these results still suggest that rupture along the entire fault zone is possible

undercutting of marine terminating glaciers in west greenland marine terminating glaciers control most of greenland s ice discharge into the ocean but little is known about the geometry of their frontal regions here we use side looking multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough deep glacier grounding enables contact with subsurface warm salty atlantic waters aw which melts ice at rates of meters per day we detect cavities undercutting the base of the calving faces at the sites of subglacial water sgw discharge predicted by a hydrological model the observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of sgw transport warm aw to the ice faces glacier undercutting likely enhances iceberg calving impacting ice front stability and in turn the glacier mass balance

paleoseismicity of the north branch of the newport inglewood fault zone in huntington beach california from cone penetrometer test data abstract application of cone penetrometer testing cpt is a promising method for studying subsurface fault zones in stratified unconsolidated sediment where trenching is not feasible analysis of data from 72 cpts spaced 7 5 to 30 0 m apart and 9 borings indicates that the north branch fault the active strand of the newport inglewood fault zone nifz in huntington beach has generated at least three and most likely five recognizable surface ruptures in the past 11 7 0 7 ka additional smaller earthquakes similar to the m w 6 4 1933 long beach earthquake may also have occurred but would not be recognizable with this method the minimum right lateral holocene slip rate of the nifz in the study area is estimated to be 0 34 to 0 55 mm yr the actual slip rate may be significantly higher

analysis of seismicity and micro seismicity associated with the october november 2010 sampeyre swarm southwestern alps abstract the study presents a detailed analysis of the swarm that occurred in the area surrounding sampeyre piedmont italy during the period october november 2010 the crisis caught the attention of seismologists because of its intense seismic productivity that has never been observed in the past during the swarm 550 earthquakes were recorded and located by the regional seismic network of northwestern italy rsni http www distav unige it geofisica in the study area however including the micro seismicity mainly earthquakes of magnitude lower than 0 detected through an sta lta short term average long term average based algorithm the number of events goes up to approximately 3250 among all these events approximately two hundred exceeded a local magnitude m l of 1 0 but only two earthquakes exceeded m l 3 0 reaching up to m l 3 2 following a general description of the swarm evolution the study presents the results of a waveform similarity analysis and double difference relocation aimed at identifying groups of earthquakes belonging to common genetic sources a statistical analysis of the resulting earthquake families has revealed a variation of the scaling exponent b value of the gutenberg and richter size frequency model with depth in particular our results have evidenced a slightly higher b value at shallower depths where a distinct family of earthquakes was identified through seismogram cross correlation this may reflect variability in the distribution of fractures in the rock volume involved in the swarm

oceanside and thirtymile bank blind thrusts implications for earthquake hazards in coastal southern california we define an active blind thrust system in offshore southern california that extends from los angeles south to the united states mexico international border these blind thrusts formed by tectonic inversion of miocene extensional detachments we attribute the 1986 oceanside ml 5 3 earthquake local uplift of marine terraces seafloor fold scarps and observed geodetic convergence to motion on these faults single and multisegment fault rupture scenarios suggest the potential for large m 7 1 7 6 but infrequent earthquakes that would affect the los angeles and san diego metropolitan areas