hypocentre determination offshore of eastern taiwan using the maximum intersection method summary the maximum intersection maxi method which derives from the master station method msm determines within a 3 d velocity model the absolute hypocentral location based on observed arrival times first the spatial node that better satisfies the arrival time differences computed at all station pairs plus or minus an error tolerance value in seconds is defined as the preliminary hypocentral solution pred second because pred depends neither on the estimate of origin time nor on the residual root mean square rms residual outliers are objectively detected and cleaned out from the original data set without any iterative process or weighting third a statistical minimization residual rms is conducted in a small domain around the pred node which results in a unique final solution the maxi method is applied to the determination of earthquake hypocentres with the proper station correction terms in the southernmost extremity of the ryukyu subduction zone where several dense seismic clusters occur near the seismogenic plate interface the location of earthquakes recorded at both the taiwanese and japanese networks is obtained for about a thousand events between 1992 and 1997 the process uses a detailed 3 d velocity model based on multiple geophysical data sources obtained in the junction area between subduction and collision east of taiwan the earthquake clustering and the significant drop in residual statistics 1 20 0 80 and 0 35 s for taiwanese catalogue msm and maxim solutions respectively indicate the accuracy of the method which can be used to routinely determine absolute hypocentre location based on observed arrival times

geochronology of the pre kbs tuff sequence omo group turkana basin the omo turkana basin of northern kenya and southern ethiopia developed in the northern kenya rift about 4 3 ma ago in the early pliocene nearly 800 m of sediments included within the omo group crop out in the basin numerous rhyolitic tuffs in the sequence not only have facilitated secure correlations between the formations of the omo group but also have provided material for precise 40 ar 39 ar age measurements here we report ages on alkali feldspar crystals from pumice clasts within tuffs in the lower part of the omo group up to the level of the kbs tuff which has previously been dated at 1 87 0 02 ma the results from 17 stratigraphic levels encompassing the 2 4 ma time interval from the base of the group to the kbs tuff provide a numerical time framework for the geological history of the lower part of the pliocene sequence the new ages which have a precision of the order of 1 are all consistent with the stratigraphic order providing confidence that they accurately record the ages of the volcanic eruptions with deposition of the tuffs and pumices occurring shortly thereafter

diagnosis of time of increased probability of strong earthquakes in different regions of the world algorithm cn abstract an algorithm for intermediate term earthquake prediction is suggested which allows diagnosis of the times of increased probability of strong earthquakes tips tips are declared for the time period of one year and an area with linear dimensions of a few hundred kilometers and can be extended in time the algorithm is based on the following traits of an earthquake flow level of seismic activity its temporal variation clustering of earthquakes in space and time their concentration in space and their long range interaction the algorithm is normalized so that it can be applied in various regions without readaptation tips diagnosed by the algorithm precede 80 of strong earthquakes and take on average 24 of the total time

near field deformation seen on distant broadband seismograms although far field body waves and surface waves are widely recognized the improvements in broadband networks now allow the measurement of near field deformation of large earthquakes at great distances near field motions have been recognized previously only in theory and in close in recordings of earthquakes we show examples from two recent events for the large deep event on june 9 1994 in bolivia there is a clear offset after the arrival of the p wave that has the amplitude expected for the near field term in the shallow september 2 1992 nicaragua earthquake the very long period motion observed between the p and s waves has roughly the amplitude expected from near field terms such near field terms are insensitive to earth structure but supply information on long period source processes and their observation begins to close the gap between long period seismology and geodesy

elastic finite difference modeling of the 1971 san fernando california earthquake finite difference seismograms calculated for the 1971 san fernando earthquake show strong effects due to lateral variation in sediment thickness in the san fernando valley and the los angeles basin using basin structure derived mostly from well logs and teleseismically determined source parameters two dimensional sh and p sv finite difference calculations reproduce the amplitude and duration of the strong motion velocities recorded across the los angeles and san fernando basins for the period range of 2 to 10 sec the edges of basins nearest the seismic source show ground motion amplification up to a factor of 3 over the case without the basin and tend to convert direct shear waves into love and rayleigh waves that travel within the basins

broadband modelling along a regional shield path harvard recording of the saguenay earthquake summary the saguenay earthquake 1988 november 25 is one of the first large shield type events recorded by a broadband high dynamic range instrument the streckeisen system installed at harvard station hrv the event is sufficiently large to be well recorded teleseismically and thus the source characteristics can be determined by independent means and considered known this allows a detailed study of the propagational effects along this path at an epicentral distance of 625 km where the strengths of the surface waves can be compared with the crustal body phases broadband modelling using standard analytical techniques and flat layered models works amazingly well over the period range of 0 5 20 s a detailed strategy for modelling broadband regional phases is given in terms of a decomposition of the vertical and radial seismograms into three segments pnl containing pn ppn spn pmp p coupled pl waves snl containing sn ssn sms etc and the fundamental rayleigh waves information about the upper crust is obtained from the fundamental rayleigh waves while crustal thickness and velocity gradients in the mantle are obtained from pnl and snl this particular crustal model has a thickness of 35 km with a sharp moho and a substantial gradient in the top 20 km of the mantle 0 01 km s 1 per km for both p and s velocities the mantle velocities 8 2 and 4 55 km s 1 are slower than expected for a shield environment attenuation is not required for waveform modelling or for absolute amplitude estimation

modeling of energy amplification recorded within greater los angeles using irregular structure we have investigated energy amplification observed within greater los angeles basin by analyzing regional waveforms recorded from several nevada test site nts nuclear explosions although the stations are located nearly at the same azimuth distances ranging from 350 to 400 km the seismograms recorded in compton the central part of the basin long beach the southern edge of the basin and downtown los angeles are remarkably different even for a common explosion following the onset of l g waves the long beach sites have recorded surface waves for more than 100 sec from one explosion the sites within downtown los angeles have recorded seismograms with strong 3 sec surface waves these waves are not observed on the seismograms recorded in the neighboring hard rock site california institute of technology cit station thus they must have been generated by local wave guides numerically we modeled these 3 sec waves by convolving the cit seismogram with the response of a sedimentary strata dipping gently about 6 from cit toward downtown we also examined the irregular basin effect by analyzing the variation of cumulative temporal energy across the basin relative to the energy recorded at cit from the same explosion variation up to a factor of 30 was observed to model the energy variation that is caused by extended surface waves in the long beach area we used numerically simulated site transfer functions stf from a nne ssw oriented two dimensional basin structure extending from montebello to palos verdes that included low velocity sedimentary material in the uppermost layers these stfs were convolved with the cit seismogram recorded from the mast explosion to simulate elongated duration of surface waves we introduced in the upper sedimentary structure some discontinuous microbasin structures of varying size each microbasin delaying the seismic waves propagating through them consequently the surface reflected phases through these structures are delayed and reflected into the upper medium by the underlying interfaces this mechanism helps delayed energy to appear at a later time and result in a longer time duration at sites located at southern edge of the basin

crustal velocity structure in italy from analysis of regional seismic waveforms abstract in this article we use regional seismic waveforms recorded by the recently installed istituto nazionale di geofisica e vulcanologia ingv national network and the mediterranean very broadband seismographic network mednet stations to develop 1d crustal velocity models for the italian peninsula about 55 000 p wave and 35 000 s wave arrival times from 4727 events are used to derive average seismic parameters in the crust and uppermost mantle we define four regions according to geological constraints and recent travel time tomography results based on the average seismic parameters we combine broadband seismic waveforms and travel times of regional phases to model crustal structures for the four regions by applying the genetic algorithm our results indicate smooth velocity gradients with a depth beneath the apennines and a deep moho beneath the central alps green s functions from the regionalized 1d velocity models are used to determine source depths and focal mechanisms for 37 events with a magnitude larger than 3 5 by a grid search technique our results show that normal and strike slip faulting source mechanisms dominate the apenninic belt and that most thrust faulting events occur in the adriatic sea and the outer margin of the northern apennines

broadband waveform modeling of moderate earthquakes in the san francisco bay area and preliminary assessment of the usgs 3d seismic velocity model abstract recently the united states geologic survey earthquake hazards program developed a 3d seismic velocity model of northern california based on geology including a detailed model of the urbanized san francisco bay area in this study we report comparisons of observed three component broadband 0 03 0 25 hz waveforms with synthetic seismograms computed with the new 3d model using an elastic finite difference method we selected a set of 12 moderate earthquakes m w 4 0 5 1 that occurred within the greater san francisco bay area having well constrained source parameters and broadband recordings with high signal to noise ratios the objective of this study was to investigate how well the 3d velocity model predicts observed waveforms and to identify features of the model that may require revision to improve the waveform fits and predictions of ground motions for future events we show for the 3 september 2000 yountville earthquake that reported source parameters accurately predict waveforms at two close strong motion stations approximately 10 km from the epicenter by comparing synthetics for the average 1d model gil7 stidham et al 1999 and the 3d structures we show that the effects of seismic wave propagation in the 3d model become important for frequencies at and above 0 1 hz periods less than 10 sec comparison of observed and synthetic seismograms for the 3d model consistently shows that the model predicts energy arriving earlier than is observed particularly for the surface waves indicating that the shear velocities in the upper crust must be reduced we cross correlated the observed and synthetic waveforms and recorded the delay time and linear correlation for best alignment of the data and delayed synthetic the results indicate that generally the 3d model predicts the observed waveforms well mean linear correlations 0 41 and includes features that arise from the interaction of the wave field with 3d structure especially the major sedimentary basins in san pablo bay san francisco bay santa clara valley and livermore valley simple conversion of the observed delay times for optimal alignment suggests shear velocities should be reduced by 4 5 on average based on these findings we conclude that the model is an excellent first step suggesting that the overall structure of the model is accurate i e the basin and discontinuity geometry however the velocities must be reduced to improve the observed timing of surface wave arrivals

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

moment tensor solutions of the 1994 to 1996 double spring flat nevada earthquake sequence and implications for local tectonic models abstract the 12 september 1994 m w 5 8 double spring flat nevada earthquake initiated at the intersection of a northeast and northwest striking set of conjugate faults within an overlapping zone between the genoa and antelope valley fault zones of the eastern sierra nevadan range frontal fault system the mainshock ruptured on the northeast striking fault plane eight days after the mainshock the aftershock activity migrated from the mainshock fault plane to the northwest striking conjugate fault over the next 2 years aftershocks migrated southward onto another set of conjugate faults and then onto the antelope valley fault zone the focal mechanisms of 17 m 4 aftershocks were estimated from a time domain moment tensor inversion using regional broadband data the t axis minimum stress direction is oriented east west n80 e to n100 e for the m 4 events as is commonly observed along the eastern sierra nevadan range front in northwestern nevada from these results we make some general points that can be considered in seismic hazard assessment the maximum magnitude in overlapping normal fault zone is limited to the size of the overlapping zone this makes small to moderate size m m 7 earthquakes the seismicity within this overlapping zone may indicate interseismic strain accumulation from east west extension mainly through strike slip deformation the apparent scarcity of modern normal faulting earthquakes along the sierran range front faults suggests a characteristic model while a gutenberg and richter model for the recurrence behavior of earthquakes applies to the overlap zones between the normal faults the pattern of seismicity and principle stress directions from the aftershock fault plane solutions suggest a tectonic model of changing fault geometry for the overlapping zone between the genoa and antelope valley fault zones two plausible long term tectonic outcomes may develop with this model a normal fault growth model where the overlapping segments of the genoa and antelope valley faults eventually become hard linked form a throughgoing fault or a normal fault growth model where the overlapping segment of the genoa fault system grows southward while the antelope valley fault is isolated in the formation of new basins and ranges

crustal complexity from regional waveform tomography aftershocks of the 1992 landers earthquake california we construct a two dimensional velocity section sampling the mojave crustal block in southern california by modeling shear wave sh seismograms our approach uses individual generalized rays computed from a layered model the model is divided into blocks with variable velocity perturbations such that ray responses are allowed to shift relative to each other to maximize synthetic waveform fits to data an efficient simulated annealing algorithm is employed in this search the technique is applied to a collection of 25 aftershocks landers earthquake as recorded at two stations gsc and pfo separated by 200 km which bracket the event population along the landers fault system the events are assumed to have known mechanisms and epicenters but both their depths and origin times are allowed to vary the results indicate considerable variation especially in the top layer up to 13 which mirrors surface geology best fitting models contain a low velocity zone in the lower crust if we constrain the crustal thickness 29 km from receiver function analysis reduced lower crustal velocities imply crustal weakening which appears compatible with the shallow seismogenic zone found in the northern end of this section there is also evidence for a lateral jump in velocity of several percent across the san andreas with the faster velocities on the west

new oligocene early miocene microflora from the southwestern turkana basin palaeoenvironmental implications in the northern kenya rift we report five oligocene early miocene pollen assemblages from the loperot 1 exploration well drilled in the semi desert lokichar basin latitude 02 21 46 15 n longitude 35 52 23 47 e ground elevation 615 m above msl near lake turkana in northern kenya they represent the second oldest plant microfossils so far recovered from east africa and add significantly to the paleogene neogene tropical african fossil plant record the loperot pollen indicate a mosaic environment of semi deciduous forest and humid woodland whose floristic composition presents strong affinities with the vegetation occurring today in the guinea congolia zambezia phytogeographical transition zone with a rainfall more than 1000 mm year and a well defined dry season the weak representation of poaceae and herbaceous taxa characteristic of grassland dry bushland or savanna and the abundance of shade tolerant plants such as ferns all point to a vegetation composed to a variety of communities with closed forest formations predominant the lack of typical temperate mountains elements mainly podocarpus and juniperus today widespread on the east african highlands indicates that the geography of the region was different from that of today the plateaux or uplands adjacent to the lokichar basin were probably still not high enough during this period of early rifting in east africa to support the temperate coniferous forests characteristic of the plio pleistocene

regional wave propagation in new england and new york we validate and improve 1d velocity models of the two main crustal provinces in the northeastern united states neus using seismograms from the 20 april 2002 m 5 au sable forks earthquake which is the largest earthquake in the region to be recorded by multiple recently deployed good quality regional broad band stations to predict and mitigate the effects of future earthquakes in the north eastern united states more information is needed regarding both the local earthquake sources and how seismic waves travel through the region we investigate the source and regional wave propagation for the au sable forks earthquake the earthquake epicenter is located near the boundary of two distinct geological provinces the appalachian new england and grenville new york we use a forward modeling approach to study the waveforms recorded at 16 stations located within 400 km of the epicenter we generate synthetic seismograms using the frequency wavenumber method testing several published models for the two provinces several models per form well at low frequencies 0 1 hz we refine these models and generate two alternative 1d crustal models for intermediate frequencies 1 hz of engineering interest our new grenville model performs better than previously published models for all six source station paths modeled in that province according to goodness of fit statistics variance reduction and correlation coefficient our alternative appalachian model improves the fit of synthetics to data for five of the ten paths modeled in that province from the results we identify two specific sources of wave field complex ities that should be investigated in future studies of earthquake ground motions in neus 3 azimuthal anisotropy in the appalachian province and complex wave paths along the boundary between the two provinces

lake level changes and hominin occupations in the arid turkana basin during volcanic closure of the omo river outflows to the indian ocean in the east african rift the western margin of lake turkana northern kenya exposes mio plio pleistocene lake sediments with dated volcanic horizons constraining basin dynamics at the astronomical time scale since the late pliocene coastal archaeological sites have formed within the lacustrine dynamics here lake levels are reconstructed from 2 4 to 1 7 ma using sedimentary facies and water depth controlled sediment association the lacustrine stratigraphy is measured with a total station and cyclostratigraphy is derived from tephrochronology the water depths are evaluated from paleochemical properties of lake sediments analyzed by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry our reconstruction highlights that lake turkana rose during 100 ka insolation eccentricity maxima periods in response to higher monsoonal inputs of the omo river however lake turkana also expanded through an insolation minimum at 2 17 1 95 ma this asynchronous lake phase coincides with volcanic closure of the omo river and lake turkana outflow sill to the east and the indian ocean an archaeological hiatus occurs during this endorheic lake phase and alkalinity increases at the beginning of the hiatus the lake rose again during insolation eccentricity maxima at 1 9 1 7 ma and a new outflow sill opened to the west and the nile basin hominin coastal occupations return during this exorheic freshwater lake phase

streaks multiplets and holes high resolution spatio temporal behavior of parkfield seismicity 1 double difference locations of 8000 earthquakes from 1969 2002 on the parkfield section of the san andreas fault reveal detailed fault structures and seismicity that is although complex highly organized in both space and time distinctive features of the seismicity include 1 multiple recurrence of earthquakes of the same size at precisely the same location on the fault multiplets implying frictional or geometric controls on their location and size 2 sub horizontal alignments of hypocenters along the fault plane streaks suggestive of rheological transitions within the fault zone and or stress concentrations between locked and creeping areas 3 regions devoid of microearthquakes with typical dimensions of 1 5 km holes one of which contains the m6 1966 parkfield earthquake hypocenter these features represent long lived structures that persist through many cycles of individual events

three dimensional finite element modeling of stress interaction an application to landers and hector mine fault systems 1 we model the coseismic and postseismic stress changes and the surface deformation caused by earthquake dislocations through a three dimensional 3 d finite element numerical procedure applied to the 1992 landers and the 1999 hector mine earthquakes our goal is to investigate the stress interaction between these complex nonplanar fault systems the modeling strategy proposed in this study allows the calculation of elastic deformation and coulomb stress changes either by imposing the slip distribution as a boundary condition along assigned faults or by retrieving the slip pattern on preexisting faults imposing the regional stress field we study how different initial stress conditions including the depth dependence of isotropic components of the regional stress different values of coulomb friction coefficient and the 1 d rigidity layering can affect the slip pattern on assumed faults and the resulting coulomb stress changes we propose here an original approach to simultaneously model slip distribution surface deformation and stress perturbations consistently with the rheological parameters of the lithosphere and its state of stress

improved seismic velocity reference model from local earthquake data in northwestern italy resolution and reliability estimates of results obtained by seismic tomography strongly depend on the reference model inadequate initial reference models may severely distort tomographic images or introduce artefacts that lead to misinterpretations of the results reference models are usually obtained by means of a priori near surface geological information or by geophysical information derived by controlled source seismology starting from the idea that a reference model must approximate the weighted average of data selected for the three dimensional 3d inversion one dimensional 1d model for northwestern italy is derived that is able to minimize mean of rms of a set of well locatable earthquakes by computing a solution of the coupled hypocentre 1d velocity problem such a model termed the minimum 1d model can be used both as an initial reference model for 3d inversion and as a reference velocity model for high quality routine earthquake location

broadband modeling of local earthquakes three component broadband waveforms of two small earthquakes near upland california recorded on the pasadena broadband high dynamic range instrument were modeled to obtain useful green s functions for this path and to examine the sensitivity of the synthetic seismograms to perturbations of the crustal model we assumed that the source of each event was both simple and known as determined from the caltech usgs array first motions a trapezoidal time function was chosen to fit the width of the direct s wave generalized rays reflectivity and finite difference techniques were used to compute the synthetic seismograms we found that a simple layer over a half space model is an adequate approximation of the upper crust along this profile in particular the waveforms are controlled by a relatively slow 4 km thick surficial layer 4 5km s 1 2 6 km s 1 over a faster layer 5 9 km s 1 3 5 km s 1 the relative amplitudes of direct and multiple s indicate that the main shock occurred at a depth of 6 km while the aftershock occurred at a depth of 8 to 9 km sensitivity analyses indicate that for distances less than 50 km and for periods longer than 1 sec the synthetic seismograms are not very sensitive to perturbations of the deep crustal structure analysis of upper crustal model perturbations revealed that the surficial layer is between 3 to 5 km thick in addition the contact between this layer and the underlying material can be smoothed with a 2 km wide velocity gradient without adversely affecting the fit to the data two dimensional finite difference calculations show that a ridge structure beneath the recorder acts as a lowpass filter the lower frequency phases are largely unaffected other two dimensional models with ridges between the source and receiver clearly did not fit the data synthetic seismograms computed for the best fitting model were used to estimate a long period moment of 6 2 1022 dyne cm ml 4 6 and 1 1022 dyne cm ml 3 7 with identical triangular source time durations of 0 3 sec assuming the same fault dimension of 0 4 km from standard scaling laws stress drop estimates of 410 and 70 bars are obtained for the two events respectively generally we found that it is possible to reproduce local waveforms at frequencies up to 1 hz without a complete knowledge of fine structural detail resulting green s functions can be useful in studying historic events and in simulations of large events from a given source region

relative importance of near intermediate and far field displacement terms in layered earth synthetic seismograms waveform modeling and moment tensor inversion commonly assume only the far field response to the seismic source however for certain frequencies and distances the near and intermediate field terms of the earth s response becomes important we developed a criterion to estimate the relative importance of these terms for horizontally layered earth models by comparing reflectivity synthetic seismograms computed with just the far field response far field terms only with the complete response all terms included the frequency and range dependent differences of these two responses are quantified by measuring the difference between synthetics for regional and local earthquake scenarios the 1992 little skull mountain nevada m w 5 7 and 1997 calico hills nevada m w 4 0 earthquakes for these crustal earthquakes we found that the near field term becomes important when the minimum frequency f n hz of the simulation at hypocentral distance r km is f n cr 1 where a reasonable crustal velocity for c is 5 8 km sec and is the fraction of a wavelength estimated in this study to be 0 6 the far field response converges to the complete response for frequencies greater than f n manuscript received 30 september 1999

the effect of velocity structure errors on double difference earthquake location 1 we show that relative earthquake location using double difference methods requires an accurate knowledge of the velocity structure throughout the study region to prevent artifacts in the relative position of hypocenters the velocity structure determines the ray paths between hypocenters and receivers these ray paths and the corresponding ray take off angles at the hypocenters determine the partial derivatives of travel time with respect to the hypocentral coordinates which form the inversion kernel that maps double differences into hypocentral perturbations thus the large scale velocity structure enters into the core of the double difference technique by employing a 1d layered model with sharp interfaces to perform double difference inversion of synthetic data generated using a simple 1d gradient model we show that inappropriate choice of the velocity model combined with unbalanced source receiver distributions can lead to significant distortion and bias in the relative hypocenter positions of closely spaced events

seismic tomography of the southern california crust based on spectral element and adjoint methods we iteratively improve a 3 d tomographic model of the southern california crust using numerical simulations of seismic wave propagation based on a spectral element method sem in combination with an adjoint method the initial 3 d model is provided by the southern california earthquake center the data set comprises three component seismic waveforms i e both body and surface waves filtered over the period range 2 30 s from 143 local earthquakes recorded by a network of 203 stations time windows for measurements are automatically selected by the flexwin algorithm the misfit function in the tomographic inversion is based on frequency dependent multitaper traveltime differences the gradient of the misfit function and related finite frequency sensitivity kernels for each earthquake are computed using an adjoint technique the kernels are combined using a source subspace projection method to compute a model update at each iteration of a gradient based minimization algorithm the inversion involved 16 iterations which required 6800 wavefield simulations the new crustal model m 16 is described in terms of independent shear v s and bulk sound v b wave speed variations it exhibits strong heterogeneity including local changes of 30 per cent with respect to the initial 3 d model the model reveals several features that relate to geological observations such as sedimentary basins exhumed batholiths and contrasting lithologies across faults the quality of the new model is validated by quantifying waveform misfits of full length seismograms from 91 earthquakes that were not used in the tomographic inversion the new model provides more accurate synthetic seismograms that will benefit seismic hazard assessment

simulations of ground motion in the los angeles basin based upon the spectral element method we use the spectral element method to simulate ground motion generated by two recent and well recorded small earthquakes in the los angeles basin simulations are performed using a new sedimentary basin model that is constrained by hundreds of petroleum industry well logs and more than 20 000 km of seismic reflection profiles the numerical simulations account for 3d variations of seismic wave speeds and density topography and bathymetry and attenuation simulations for the 9 september 2001 m w 4 2 hollywood earthquake and the 3 september 2002 m w 4 2 yorba linda earthquake demonstrate that the combination of a detailed sedimentary basin model and an accurate numerical technique facilitates the simulation of ground motion at periods of 2 sec and longer inside the basin model and 6 sec and longer in the regional model peak ground displacement velocity and acceleration maps illustrate that significant amplification occurs in the basin

imaging the complexity of an active normal fault system the 1997 colfiorito central italy case study 1 six moderate magnitude earthquakes 5 mw 6 ruptured normal fault segments of the southern sector of the north apennine belt central italy in the 1997 colfiorito earthquake sequence we study the progressive activation of adjacent and nearby parallel faults of this complex normal fault system using 1650 earthquake locations obtained by applying a double difference location method using travel time picks and waveform cross correlation measurements the lateral extent of the fault segments range from 5 to 10 km and make up a broad 45 km long nw trending fault system the geometry of each segment is quite simple and consists of planar faults gently dipping toward sw with an average dip of 40 45 the fault planes are not listric but maintain a constant dip through the entire seismogenic volume down to 8 km depth we observe the activation of faults on the hanging wall and the absence of seismicity in the footwall of the structure the observed fault segmentation appears to be due to the lateral heterogeneity of the upper crust preexisting thrusts inherited from neogene s compressional tectonic intersect the active normal faults and control their maximum length the stress tensor obtained by inverting the six main shock focal mechanisms of the sequence is in agreement with the tectonic stress active in the inner chain of the apennine revealing a clear ne trending extension direction aftershock focal mechanisms show a consistent extensional kinematics 70 of which are mechanically consistent with the main shock stress field

automatic seismic phase picking and consistent observation error assessment application to the italian seismicity summary accuracy of seismic phase observation and consistency of timing error assessment define the quality of seismic waves arrival times high quality and large data sets are prerequisites for seismic tomography to enhance the resolution of crustal and upper mantle structures in this paper we present the application of an automated picking system to some 600 000 seismograms of local earthquakes routinely recorded and archived by the italian national seismic network the system defines an observation weighting scheme calibrated with a hand picked data subset and mimics the picking by an expert seismologist the strength of this automatic picking is that once it is tuned for observation quality assessment consistency of arrival times is strongly improved and errors are independent of the amount of data to be picked the application to the italian local seismicity documents that it is possible to automatically compile a precise homogeneous and large data set of local earthquake pg and pn arrivals with related polarities we demonstrate that such a data set is suitable for high precision earthquake location focal mechanism determination and high resolution seismic tomography

unified structural representation of the southern california crust and upper mantle we present a new 3d description of crust and upper mantle velocity structure in southern california implemented as a unified structural representation usr the usr is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity vp vs measurements and incorporates the locations and displacement of major fault zones that influence basin structure these basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure which were subsequently iterated and improved using 3d waveform adjoint tomography a geotechnical layer gtl based on vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component the resulting model provides a detailed description of the structure of the southern california crust and upper mantle that reflects the complex tectonic history of the region the crust thickens eastward as moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust deep sedimentary basins and underlying areas of thin crust reflect neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late pliocene to illustrate the impact of this complex structure on strong ground motion forecasting we simulate rupture of a proposed m 7 9 earthquake source in the western transverse ranges the results show distinct basin amplification and focusing of energy that reflects crustal structure described by the usr that is not captured by simpler velocity descriptions we anticipate that the usr will be useful for a broad range of simulation and modeling efforts including strong ground motion forecasting dynamic rupture simulations and fault system modeling the usr is available through the southern california earthquake center scec website http www scec org

stability of premonitory seismicity pattern and intermediate term earthquake prediction in central italy the algorithm cn makes use of normalized functions therefore the original algorithm developed for the california nevada region can be directly applied without adjustment of the parameters to the determination of the time of increased probability tip of strong earthquakes for central italy the prediction is applied to the events with magnitudem m0 5 6 which in central italy have a return period of about six years the routinely available digital earthquake bulletins of the istituto nazionale di geofisica ing rome permits continuous monitoring here we extend to november 1994 the first study made by keilis boroket al 1990b on the basis of the combined analysis of seismicity and seismotectonic we formulate a new regionalization which reduces the total alarm time and the failures to predict and narrows the spatial uncertainty of the prediction with respect to the results ofkeilis boroket al 1990b

seismotectonic models and cn algorithm the case of italy the cn algorithm is utilized here both for the intermediate term earthquake prediction and to validate the seismotectonic model of the italian territory using the results of the analysis made through the cn algorithm and taking into account the seismotectonic model three main areas one for northern italy one for central italy and one for southern italy are defined two transition areas between the three main areas are delineated the earthquakes which occurred in these two areas contribute to the precursor phenomena identified by the cn algorithm in each main area

rupture process of four medium sized earthquakes that occurred in the gulf of california 1 four medium sized earthquakes m w global cmt project 5 5 5 6 5 9 6 3 hereinafter named topolobampo angel de la guarda san lorenzo and loreto earthquakes respectively located in the gulf of california extensional province were studied to obtain their kinematic rupture processes a network of broadband seismic stations located around the gulf of california recorded the events network of autonomously recording seismographs baja and red sismica de banda ancha inversion of the seismic moment tensor and body waveform modeling were used to obtain the fault geometry and slip distribution on the fault plane respectively from these analyses we obtained source depths of the order of 5 5 0 5 km we found also that the source rupture processes of the topolobampo and angel de la guarda events have simple moment rate functions and source time durations of 5 0 1 2 and 4 2 1 2 s respectively the topolobampo event was a right lateral strike slip event and angel de la guarda was a normal event the san lorenzo and loreto shocks show a rather complex rupture with source time durations of 7 5 1 2 and 9 0 1 2 s respectively for these earthquakes we tested the resolution of numerical results performing an extra inversion with smoother waveforms the new inversions do not show the separated patches of slip as in the first analysis but the slip distribution has an elongated shape not characteristic of simple events we cannot therefore conclude rupture propagation for the san lorenzo event although the extent of the patch for the loreto earthquake agrees with aftershock locations estimates of source time durations for these earthquakes are at the upper limit of the values found for earthquakes elsewhere directions of p axes are in the same order of magnitude as the maximum horizontal stress obtained for the socalled gulf of california stress province from borehole elongations focal plane solutions and fault slip data

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

detailed kinematics structure and recurrence of micro seismicity in the safod target region 1 large numbers of small earthquakes recorded over 2 decades and analyzed with advanced techniques are used to characterize the detailed kinematics structure and recurrence interval scaling properties of micro seismicity in a 4 4 km lateral and 6 km deep crustal volume encompassing the region of the safod deep drilling experiment the characterization reveals that the seismically active san andreas fault in the vicinity of safod s repeating magnitude 2 target earthquakes is composed of two sub parallel fault strands that are creeping at comparable rates and that one of the strands lies between the safod drilling platform and safod s target events in the region 55 of the earthquakes are members of 52 characteristically repeating earthquake sequences the recurrence intervals of the repeating target events are consistent with the interval scaling of the other sequences however this scaling is contrary to that expected from standard constant stress drop theory

southern california hypocenter relocation with waveform cross correlation part 1 results using the double difference method we present the results of relocating 327 000 southern california earthquakes that occurred between 1984 and 2002 we apply time domain waveform cross correlation for p and s waves between each event and 100 neighboring events identified from the catalog based on a 3d velocity model to simplify the computation we first divide southern california into five polygons such that there are 100 000 events or less in each region the polygon boundaries are chosen to lie in regions of sparse seismicity we calculate and save differential times from the peaks in the cross correlation functions and use a spline interpolation method to achieve a nominal timing precision of 0 001 sec these differential times together with existing p and s phase picks are input to the double difference program of waldhauser and ellsworth 2000 2002 to calculate refined hypocenters we divide the southern california region into grid cells and successively relocate hypocenters within each grid cell the overall resulting pattern of seismicity is more focused than the previously determined pattern from 1d or 3d models the new improved locations are more clustered in many cases by a factor of two or three and often show clear linear alignments in particular the depth distribution is improved and less affected by layer boundaries in velocity models or other similar artifacts

estimating the diminution of shear wave amplitude with distance application to the los angeles california urban area the rate of decay with distance of shear wave amplitude computed from 20 sec s wave spectra is determined from terrascope records of small earthquakes in the greater los angeles area piecewise log linear interpolation functions and traditional diminution functions are used to fit spectral decay to a maximum distance of 150 km simultaneously isotropic source and receiver terms are determined separate branches of the spectral decay function are found for two categories of source depth greater than 10 km and less than 10 km in the hypocentral distance range of 20 to 150 km and in the frequency range of 0 5 to 8 0 hz an important result of the investigation is that the horizontal component decay rate associated with deeper crustal sources is generally greater than that associated with shallower sources and is greater than that which is estimated using more traditional models of spectral decay with distance the same behavior generally holds for vertical component spectra the variation in apparent attenuation rate with source depth should affect seismic hazard estimates associated with the rupture of blind thrust faults in the los angeles basin and vicinity the results of the inversions suggest that interpolation function representations of spectral decay are sensitive to perturbations of s wave amplitude due to crustal reflectors such as post critical s wave arrivals from mid crustal to deep crustal velocity interfaces

prediction of strong earthquakes in vrancea romania using the cn algorithm the application of the cn algorithm to a new earthquake catalogue for the period from 1932 to 1993 obtained by merging romanian and u s s r data allows us to monitor on the intermediate time scale the preparation of strong intermediate depth earthquakes in the vrancea region four of the five strong earthquakes with a magnitude above 6 4 are predicted the total duration of the time of increased probability of the occurrence of an earthquake tip occupies 21 7 of the time interval under consideration i e about 2 5 years for each strong earthquake

investigation of the rupture process of the 28 june 1992 landers earthquake utilizing terrascope abstract displacement seismograms recorded by terrascope for the 28 june 1992 landers earthquake m w 7 3 are deterministically modeled using a forward point source summation technique although the data set is sparse it was possible to robustly determine important rupture parameters such as gross slip distribution rupture velocity rise time and total source duration the relatively simple approach lends itself to rapid application following large earthquakes provided that a catalog of green9s functions appropriate for the region is available the fault used in the modeling of the landers mainshock has a length of 70 km along strike and a width of 15 km along dip a model was found in which the distribution and amplitude of slip at the surface matches the observed surface slip and provides a very good level of fit to the seismic data seismically the landers earthquake is characterized as two subevents the peak slip of the first subevent is 10 km north of the epicenter and the second is 40 km northwest along strike from the epicenter the seismic moment is distributed as 2 10 26 dyne cm to the first and 6 10 26 to the second subevent respectively it was assumed in our modeling that the distribution of seismic moment along strike was the same at all depths this assumption implies that slip at depth is 69 of that at the surface as a result of differences in the material properties in the velocity model the sensitivities of the source model to rupture velocity and dislocation rise time were examined a rupture velocity of 2 9 km sec 80 of the shear wave velocity and a rise time of 1 to 3 sec were found to satisfy the data the rise time is only a fraction of the total source process time of 24 sec and implies that slip on the fault occurred within a narrow band 3 to 10 km at any instant during the rupture

accurate hypocentre determination in the seismogenic zone of the subducting nazca plate in northern chile using a combined on offshore network the coupled plate interface of subduction zones commonly called the seismogenic zone has been recognized as the origin of fatal earthquakes a subset of the after shock series of the great antofagasta thrust type event 1995 july 30 mw 8 0 has been used to study the extent of the seismogenic zone in northern chile to achieve reliable and precise hypocentre locations we applied the concept of the minimum 1 d model which incorporates iterative simultaneous inversion of velocity and hypocentre parameters the minimum 1 d model is complemented by station corrections which are influenced by near surface velocity heterogeneity and by the individual station elevations by relocating mine blasts which were not included in the inversion we obtain absolute location errors of 1 km in epicentre and 2 km in focal depth a study of the resolution parameters ale and dspr documents the importance of offshore stations on location accuracy for offshore events based on precisely determined hypo centres we calculate a depth of 46 km for the lower limit of the seismogenic zone which is in good agreement with previous studies for this area for the upper limit we found a depth of 20 km our results of an aseismic zone between the upper limit of the seismogenic zone and the surface correlates with a detachment zone proposed by other studies the results are also in agreement with thermal studies for the antofagasta forearc region

the 20 january 2007 odaesan korea earthquake sequence reactivation of a buried strike slip fault the m w 4 6 odaesan korea earthquake of 20 january 2007 11 hr 56 min had nine locatable foreshocks in the previous 67 hours and nine aftershocks during the 11 hours after the main event we obtained accurate locations of this sequence by employing the double difference earthquake relocation method with differential travel time measurements using waveform cross correlation we found that 19 accurately relocated foreshocks mainshock and aftershocks aligned along a 1 2 km long lineation with an azimuth of west northwest east southeast 115 which coincides with a nodal plane of the mainshock focal mechanism that strikes 114 regional waveform modeling of the mainshock constrained a focal depth of 11 1 km and the focal mechanism is a pure strike slip faulting along the vertical nodal planes with a horizontal p axis plunge 1 trending east northeast 69 the pulse rise time of the mainshock source time function estimated from an empirical green s function analysis ranges from 0 1 to 0 16 sec which yields a source radius of 0 6 km and is consistent with the spatial distribution of the foreshock and aftershock sequences the stress drop of graphic 1 is obtained for the mainshock using a radius of 0 6 km for a circular rupture and seismic moment graphic 2 the 20 january 2007 odaesan earthquake may be the first significant earthquake in southern korea to date where the fault plane is constrained by accurate locations of the foreshock and aftershock sequences its source mechanism vertical strike slip fault at depth suggests that the event represents reactivation of a buried high angle fault in the precambrian basement by the contemporary east east northeast trending regional horizontal compressive stress 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif

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

source inversion of the 1988 upland california earthquake determination of a fault plane for a small event abstract we examined short period p waves to investigate if waveform data could be used to determine which of two nodal planes was the actual fault plane for a small m l 4 6 earthquake near upland california we removed path and site complications by choosing a small aftershock m l 2 7 as an empirical green function the main shock p waves were deconvolved by using the empirical green function to produce simple far field displacement pulses we used a least squares method to invert these pulses for the slip distribution on a finite fault both nodal planes strike 125 dip 85 and strike 221 dip 40 of the first motion focal mechanism were tested at various rupture velocities the southwest trending fault plane consistently gave better fitting solutions than the southeast trending plane we determined a moment of 4 2 10 22 dyne cm the rupture velocity and thus the source area could not be well resolved but if we assume a reasonable rupture velocity of 0 87 times the shear wave velocity we obtain a source area of 0 97 km 2 and a stress drop of 38 bars choice of a southwest trending fault plane is consistent with the trend of the nearby portion of the transverse ranges frontal fault zone and indicates left lateral motion this method provides a way to determine the fault plane for small earthquakes that have no surface rupture and no obvious trend in aftershock locations

a method for calibration of the local magnitude scale based on relative spectral amplitudes and application to the san juan bautista california area we develop and use a spectral empirical green s function approach to estimate the relative source amplitudes of earthquakes near san juan bautista california we isolate the source amplitudes from path effects by comparing the recorded spectra of pairs of events with similar location and focal mechanism without computing the path effect with this method we estimate the relative moments of 1600 m 1 5 4 local earthquakes and we use these moments to recalibrate the duration magnitude scale in this region the estimated moments of these small earthquakes increase with catalog magnitude m d roughly proportionally to 101 1 m d slightly more slowly than a moment magnitude scaling of 101 5 m w this more accurate magnitude scaling can be used in analyses of the local earthquakes such as comparisons between the seismic moments and geodetic observations electronic supplement 1 additional description and figures showing estimated source amplitudes obtained with different parameters and observed amplitudes of some earthquakes with large misfits 1 http www bssaonline org lookup suppl doi 10 1785 0120160141 dc1

earthquake spatial distribution the correlation dimension summary we review methods for determining the fractal dimensions of earthquake epicentres and hypocentres paying special attention to the problem of errors biases and systematic effects among effects considered are earthquake location errors boundary effects inhomogeneity of depth distribution and temporal dependence in particular the correlation dimension of earthquake spatial distribution is discussed techniques for its evaluation presented and results for several earthquake catalogues are analysed we show that practically any value for the correlation dimension can be obtained if many errors and inhomogeneities in observational data as well as deficiencies in data processing are not properly considered it is likely that such technical difficulties are intensified when one attempts to evaluate multifractal measures of dimension taking into account possible errors and biases we conclude that the fractal dimension for shallow seismicity asymptotically approaches 2 20 0 05 for a catalogue time span of decades and perhaps centuries the value of the correlation dimension declines to 1 8 1 9 for intermediate events depth interval 71 280 km and to 1 5 1 6 for deeper ones

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

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

community fault model cfm for southern california we present a new three dimensional model of the major fault systems in southern california the model describes the san andreas fault and associated strike slip fault systems in the eastern california shear zone and peninsular ranges as well as active blind thrust and reverse faults in the los angeles basin and transverse ranges the model consists of triangulated surface representations t surfs of more than 140 active faults that are defined based on surfaces traces seismicity seismic reflection profiles wells and geologic cross sections and models the majority of earthquakes and more than 95 of the regional seismic moment release occur along faults represented in the model this suggests that the model describes a comprehen sive set of major earthquake sources in the region the model serves the southern california earthquake center scec as a unified resource for physics based fault systems modeling strong ground motion prediction and probabilistic seismic hazards assessment

long term evolution of intraplate seismicity in stress shadows after a megathrust abstract megathrusts produce large permanent lithospheric displacements as well as strong transient ground shaking up to regional distances the influence of the 2011 m9 0 tohoku oki earthquake on the seismicity in stable intraplate regions around the korean peninsula is investigated the differential lateral displacements by the megathrust build transient radial tension field over the backarc lithosphere constructing stress shadows for all types of faults in optimal orientation over the wide backarc region including the southern korean peninsula a characteristic seismic velocity decrease after the megathrust supports the medium relaxation the number of earthquakes with magnitudes greater than or equal to 2 5 was increased by 61 after the megathrust the earthquakes occurred episodically a series of unusual earthquake swarms and a temporal cluster of moderate size earthquakes were observed in the yellow sea region the significant seismicity increase since the megathrust may be due to the fluid diffusion during the transient tension field and the pore fluid pressure increase during the ambient compressional stress field recovery by tectonic loading the induced seismicity may continue until the ambient stress field is fully recovered

magnetostratigraphy of the hominin sites and paleolakes drilling project hspdp baringo tugen hills barsemoi core kenya abstract the principal objective of the hominin sites and paleolakes drilling project hspdp is to study the relationship between climate and environmental change and the implications on human evolution in eastern africa for this purpose hspdp has recovered a 228 m core in the chemeron formation of the baringo basin kenya the chemeron formation spans approximately 3 7 myr from around 1 6 to 5 3 ma and has yielded many vertebrate fossils including fossil hominins the magnetostratigraphy of the baringo core contributes to the chronological framework a total of 567 individual paleomagnetic samples were collected from 543 levels at regular intervals throughout the core and 264 were processed using thermal and alternative field stepwise demagnetizations in most samples distinct low temperature lt 20 150 c and high temperature ht 150 550 c characteristic remanent magnetization chrm could be determined typical demagnetization behaviors and some rock magnetic experiments suggest titanomagnetite acts as the main carrier of the ht chrm with pervasive secondary overprints in normal polarity expressed by the lt component normal and reversed polarities were identified based on the secondary overprints lt chrm directions either parallel or antiparallel to the ht chrm directions respectively our study identified four paleomagnetic reversals interpreted as the matuyama gauss gauss kaena kaena gauss and the gauss mammoth transitions these boundaries provide chronostratigraphic tie points that can be combined with those derived from 40ar 39ar dating of tuffs deino et al this issue and together indicate that the hspdp baringo core has an age range of 3 3 ma to 2 6 ma the consistent paleomagnetic and radioisotopic age constraints are incorporated into a bayesian age model of the core deino et al this issue

broadband modelling of regional seismograms imperial valley to pasadena summary this paper addresses broadband wave propagation along a corridor from imperial valley to pasadena california the path consists of 50 km of slow basin structure with a shallow moho followed by 250 km of relatively normal southern california structure approaching pasadena events occurring in the valley produce extended body wave codas which carry a dispersive waveform imprint along with longer period rayleigh waves many features of these seismograms at periods greater than a few seconds can be modelled by applying a finite difference technique to a 2 d structure shorter periods display complex behaviours not easily modelled by present techniques especially for shallow events events occurring in the normal structure produce broadband sh waveforms that can be modelled analytically if some extra empirically derived alignment parameters determined from calibration events are used these parameters are determined by adjusting traveltime differentials between the decomposed wavefield s ss etc for example delays in ss relative to s correspond to local corrections for sediment cover for a particular source region source complexity such as asperities and directivity become increasingly important at shorter periods as demonstrated by numerical experiments and observation

stress in the descending relic slab beneath the vrancea region romania we examine the effects of viscous flow phase transition and dehydration on the stress field of a relic slab to explain the intermediate depth seismic activity in the vrancea region a 2 d finite element model of a slab gravitationally sinking in the mantle predicts 1 downward extension in the slab as inferred from the stress axes of earthquakes 2 the maximum stress occurring in the depth range of 70 km to 160 km and 3 a very narrow area of the maximum stress the depth distribution of the annual average seismic energy released in earthquakes has a shape similar to that of the depth distribution of the stress in the slab estimations of the cumulative annual seismic moment observed and associated with the volume change due to the basalt eclogite phase changes in the oceanic slab indicate that a pure phase transition model cannot solely explain the intermediate depth earthquakes in the region we consider that one of the realistic mechanisms for triggering these events in the vrancea slab can be the dehydration of rocks which makes fluid assisted faulting possible

waveform relocated earthquake catalog for southern california 1981 to june 2011 we determine a new relocated catalog hys catalog 2011 for southern california from 1981 through june 2011 about 75 3 of the hypocenters are calculated with absolute and differential travel time picks and 24 7 could be relocated only by using absolute travel time picks with 3d or 1d velocity models the total catalog consists of more than 502 000 earthquakes in the region extending from baja california in the south to coalinga and owens valley in the north the catalog consists of three m 7 1 m 7 2 and m 7 3 mainshocks their foreshocks and aftershocks and background seismicity caused by tectonic and other processes in the southern california crust hypocenters in the new relocated catalog exhibit tighter spatial clustering of seismicity than does the routinely generated catalog and the depth distribution is tighter and reflects the thickness of the seismogenic zone more accurately compared to the standard catalog the relocated hypocenters are more easily related to other data sets such as mapped late quaternary faults

fault structure and mechanics of the hayward fault california from double difference earthquake locations 1 the relationship between small magnitude seismicity and large scale crustal faulting along the hayward fault california is investigated using a double difference dd earthquake location algorithm we used the dd method to determine high resolution hypocenter locations of the seismicity that occurred between 1967 and 1998 the dd technique incorporates catalog travel time data and relative p and s wave arrival time measurements from waveform cross correlation to solve for the hypocentral separation between events the relocated seismicity reveals a narrow near vertical fault zone at most locations this zone follows the hayward fault along its northern half and then diverges from it to the east near san leandro forming the mission trend the relocated seismicity is consistent with the idea that slip from the calaveras fault is transferred over the mission trend onto the northern hayward fault the mission trend is not clearly associated with any mapped active fault as it continues to the south and joins the calaveras fault at calaveras reservoir in some locations discrete structures adjacent to the main trace are seen features that were previously hidden in the uncertainty of the network locations the fine structure of the seismicity suggests that the fault surface on the northern hayward fault is curved or that the events occur on several substructures near san leandro where the more westerly striking trend of the mission seismicity intersects with the surface trace of the aseismic southern hayward fault the seismicity remains diffuse after relocation with strong variation in focal mechanisms between adjacent events indicating a highly fractured zone of deformation the seismicity is highly organized in space especially on the northern hayward fault where it forms horizontal slip parallel streaks of hypocenters of only a few tens of meters width bounded by areas almost absent of seismic activity during the interval from 1984 to 1998 when digital waveforms are available we find that fewer than 6 5 of the earthquakes can be classified as repeating earthquakes events that rupture the same fault patch more than one time these most commonly are located in the shallow creeping part of the fault or within the streaks at greater depth the slow repeat rate of 2 3 times within the 15 year observation period for events with magnitudes around m 1 5 is indicative of a low slip rate or a high stress drop the absence of microearthquakes over large contiguous areas of the northern hayward fault plane in the depth interval from 5 to 10 km and the concentrations of seismicity at these depths suggest that the aseismic regions are either locked or retarded and are storing strain energy for release in future large magnitude earthquakes

pliocene and pleistocene hominid bearing sites from west of lake turkana kenya pliocene and pleistocene fossil localities near the western shoreline of lake turkana ranging in age between 1 million and 3 5 million years in age have produced important new hominid specimens including most of a homo erectus skeleton and a relatively complete early robust australopithecine cranium the lacustrine fluviatile and terrestrial strata are designated the nachukui formation which is subdivided into eight members the distribution of sedimentary facies within the nachukui formation suggests that as today the labur and murua rith ranges formed the western margin of the basin and were drained by eastward flowing rivers that fed into the forerunner of the present lake or a major river system there is also stratigraphic evidence for tectonic movement during the deposition of these sediments twenty three of the tuffs observed in the succession occur also in the koobi fora formation east of the lake and in the shungura formation of the lower omo valley and permit precise correlation among these three localities fortyseven fossiliferous sites from west turkana have yielded more than 1000 specimens of 93 mammalian species the mammalian fossils represent nine sequential assemblages that augment information about faunal and environmental change from elsewhere in the basin

the world s oldest stone artefacts from gona ethiopia their implications for understanding stone technology and patterns of human evolution between 2 6 1 5 million years ago the systematic archaeological and geological survey and excavations at gona between 1992 1994 led to the discovery of well flaked stone artefacts which are currently the oldest known from anywhere in the world more than 3000 surface and excavated artefacts were recovered at 15 localities documented east and west of the kada gona river based on radioisotopic dating 40 ar 39 ar and magnetostratigraphy the artefacts are dated between 2 6 2 5 million years ago ma eg10 and eg12 from east gona are the most informative with the highest density providing the best opportunity for characterizing the oldest assemblages and for understanding the stone working capability of the earliest tool makers slightly younger artefact occurrences dated to 2 4 2 3 ma are known from hadar and omo in ethiopia and from lokalalei in kenya cut marked bones dated to 2 5 ma from bouri in ethiopia are now providing important clues on the function of these artefacts in addition australopithecus garhi known from contemporary deposits at bouri may be the best candidate responsible for the oldest artefacts surprisingly the makers of the gona artefacts had a sophisticated understanding of stone fracture mechanics and control similar to what is observed for oldowan assemblages dated between 2 0 1 5 ma this observation was corroborated by the recent archaeological discoveries made at lokalalei because of the similarities seen in the techniques of artefact manufacture during the late pliocene early pleistocene it is argued here that the stone assemblages dated between 2 6 1 5 ma group into the oldowan industry the similarity and simplicity of the artefacts from this time interval suggests a technological stasis in the oldowan 2000 academic press

the oroville earthquakes a study of source characteristics and site effects half space modeling in the time domain of broadband seismic records from the oroville aftershock sequence demonstrates that these events have simple sources systematic scaling between the far field source duration and seismic moment for the aftershocks studied here and other california earthquakes confirms brune s 1970 source model and shows that the stress drops for california earthquakes range between 10 and 100 bars these events also show no trend in stress drop as a function of size for 3 0 or m sub l or 6 4 analysis of the static deformation associated with the main shock shows that the slip occurred on a fault 81 km sup 2 in area corresponding to the zone defined by the first 3 days of aftershocks teleseismic studies indicate that the seismic source area was 50 km sup 2 corresponding to a zone completely free of aftershocks in the middle of the aftershock zone both results imply a stress drop of 29 39 bars and seismic moment between 5 7 and 8 7 x 10 sup 24 dyn cm the evidence suggests that faulting occurred seismically on the central portion of the fault and propagated out slowly enlarging the fault plane complicated waveforms recorded for the same events at nearby sites on alluvium indicatemore the critical role that propagation through complex structure plays in determining the character of the observed seismic signal at close in stations modeling of these records show that dipping structure may account for the observed waveform complexities less

the 4 january 2006 mw 6 6 san pedro martir earthquake example of an earthquake for calibrating excitation and attenuation studiesthe mw 6 6 san pedro martir earthquake for calibrating excitation and attenuation studies

geodynamics and intermediate depth seismicity in vrancea the south eastern carpathians current state of the art abstract the vrancea region of the south eastern carpathians is a remarkable site of intra continental intermediate depth seismicity a large set of geological geophysical and geodetic observations has been accumulated for the last few decades and utilised to improve our knowledge of the shallow and deep structures beneath vrancea the crustal and mantle dynamics and the linkage between deep and surface processes in the region in this article we review geology and tectonics of the vrancea region including post collisional to recent deformations syn to post collisional magmatism and orogenic exhumation along the east and south carpathians the regional seismicity is analysed and the recent seismic studies including reflection refraction body and surface wave tomography are reviewed we discuss new geodetic measurements of horizontal and vertical movements in the region geoelectric studies density gravity and thermal modelling qualitative and quantitative including retrospective geodynamic models developed for vrancea are analysed the knowledge of regional tectonics geodynamics seismicity lithospheric deformation and stress regime in the vrancea earthquake prone region assists in an assessment of strong ground motion seismic hazard and risk the earthquake simulation seismic hazard and earthquake forecasting models have also been reviewed providing a link between deep geodynamic processes and their manifestation on the surface finally we discuss unresolved problems in vrancea in order to improve our understanding of the regional evolution present tectonics mantle dynamics intermediate depth seismicity and surface manifestations of the lithosphere dynamics and to enhance our ability to forecast strong earthquakes in the vrancea region the problems to be solved include i the origin of the high velocity body revealed by seismic tomography studies oceanic versus continental ii the lithospheric scale mechanism driving the miocene subsidence of the transylvania basin iii sub crustal structure between 40 and 70 km iv contemporary regional horizontal and vertical movements and v a comprehensive seismic hazard assessment in the region

moment tensor inversion from mednet data 2 regional earthquakes of the mediterranean we present a method for the rapid determination of the moment tensor suitable for application to regional earthquakes up to 3000 km distance the algorithm is based on the inversion of long period waveforms in the time domain and is routinely applied to significant events of the mediterranean from iran to the azores using digital data recorded by the mednet regional network we show results for 20 significant earthquakes of 1990 1992 including the large shocks in romania may 30 1990 iran june 20 1990 caucasus april 29 1991 turkey march 13 1992 and egypt october 12 1992 the damaging italian earthquakes of potenza may 5 1990 and siracusa december 13 1990 unusual events in the southern mediterranean november 11 1990 and holland april 13 1992 and the recent shocks of october 23 1992 in morocco and caucasus the comparison with published focal mechanisms and centroid moment tensors show our results to be consistent with those retrieved using global data and local networks proving that an advanced regional seismic network is capable of providing accurate rapid control of regional seismicity

plio pleistocene sedimentation in west turkana turkana depression kenya east african rift system paleolake fluctuations paleolandscapes and controlling factors abstract pliocene and pleistocene sediments from west turkana kenya east african rift system form emblematic syn rift successions for understanding the evolution of extensional basin and continental rifting they also constitute world renowned fossil bearing strata from which 500 hominin fossils were discovered over the past decades with 100 inventoried archeological sites however associated sedimentary dynamics and architectures as well as paleoenvironments are only partially reconstructed and the relative contribution of climate and tectonism to paleoenvironmental change over time remains unclear here through the interpretation of sedimentary facies the delineation of sequences and the analysis of 13c in soil carbonates we provide the first exhaustive reconstruction from 4 00 to 0 75 ma of i fluctuations of the paleolake that occupied the turkana depression ii the successive sedimentary dynamics and related paleolandscapes that characterized the west turkana area and iii respective roles of climate and tectonism in the sedimentation we show evidence for seven major transgression regression t r cycles between 4 00 and 0 75 ma superimposed locally by lower amplitude t r cycles comparing the sedimentological interpretations and the 13c values in soil carbonates literature data we reveal that fluctuations of rainfall over the ethiopian dome which hosts the drainage basin of the omo river the main tributary of lake turkana controlled high amplitude lake level fluctuations during the plio pleistocene period we also demonstrate that vegetation and tree cover evolved differently in the omo valley and west turkana furthermore we outline that two different sedimentary systems reflecting two distinct modes of sedimentation alternated through times in the west turkana area as a response to the variations in sediment supply coming from the western rift shoulder i e lapurr range that alternatively generated wave or river dominated sedimentary systems in conclusion we reveal that climate regulated water input paleolake water level fluctuations and vegetation tectonism determined sediment supply to the basin controlled in west turkana by pulses of increased activity of the main border fault i e the murua rith lapurr fault

crustal structure in southern korea from joint analysis of regional broadband waveforms and travel times regional broadband waveforms and travel times of seismic phases are combined to model crustal structure in regions where the signal to noise ratio snr of waveforms is low the utilization of travel time data enables us to overcome the problem occurring in waveform inversion with low snr data the distortion of deep velocity structure the genetic algorithm ga adopted as a search algorithm is useful in regions where there is little a priori information about crustal structure after verifying the robustness of the joint inversion technique by numerical tests we applied the technique to southern korea in order to get a simple one dimensional average crustal model using broadband waveforms bandpassed between 0 03 and 0 3 hz and travel times of pg pmp and pn waves recorded at ten broadband and five short period stations from the 2 june 1999 gyeongju earthquake m l 3 4 korea the p wave velocities in the resulting three layered crustal model are 5 67 0 06 6 05 0 05 6 67 0 02 and 7 88 0 02 km sec from the top layer to the half space respectively and the depths of layers are 5 1 0 8 16 7 1 0 and 31 9 1 0 km synthetic waveforms and travel time curves corresponding to the resulting velocity model fit observed seismograms generally well the synthetics are preceded by the observed waveforms in the southwestern part of korean peninsula inferring the presence of a high velocity zone in that area

earthquake locations and three dimensional crustal structure in the coyote lake area central california previous work on the simultaneous inversion method has been improved and extended to incorporate iterative solution for earthquake locations and laterally heterogeneous structure approximate ray tracing and parameter separation are important elements of the improved method application of the method to p wave arrival time data recorded by stations of the u s geological survey central california network yields a three dimensional model for the velocity structure of the upper crust in an area encompassing the rupture zone of the coyote lake earthquake of august 1979 very strong correlations between the velocity model and the geology and gravity and magnetic anomalies are observed improved estimates of the locations of earthquakes in the study area are also determined the relocation of explosions indicates epicentral accuracies of the order of a kilometer or better based on the revised hypocentral locations it is concluded that the san andreas fault is vertical in this area with no actual offset between the epicenters and the fault trace in contrast the calaveras has two or more active fault surfaces one nearly vertical and another dipping 75 to the northeast

2 5 myr australopithecus boisei from west of lake turkana kenya specimens of australopithecus boisei have been found in 2 5 myr old sediments west of lake turkana kenya the primitive morphology of these early a boisei suggests that robust and hyper robust australopithecus developed many of their common features in parallel and further that a africanus is unlikely to have been ancestral to a boisei

a reanalysis of the hypocentral location and related observations for the great 1906 california earthquake we determine probabilistic hypocentral locations for the foreshock and mainshock of the great 1906 california earthquake through reanalysis of arrival time observations in conjunction with modern velocity models and advanced event location techniques we obtain two additional observations for the mainshock and one for the foreshock that were not used in previous location studies using a robust likelihood function for event location we generate a usable subset of the predominantly unreliable teleseismic readings and determine new wave type identifications for some of the local and teleseismic readings our locations are much better constrained than those of earlier studies even though we do not assume that the epicenter lies on the san andreas fault as did previous authors we confirm the conclusions of earlier studies that the local and teleseismic arrival time observations can be explained by a single foreshock focus and a single mainshock focus on the san andreas fault and that there is no single unique hypocenter that satisfies all available local observations the maximum likelihood point latitude 37 78 n longitude 122 51 w for our preferred mainshock location indicates a hypocenter to the west of san francisco close to the san andreas fault zone this hypocenter has a 68 confidence error of about 8 km parallel to the san andreas fault and about 24 km perpendicular to the fault and a depth in the midcrust of about 12 7 km the closest point on the san andreas fault to this hypocenter lies about 10 km to the northwest of the widely accepted mainshock epicenter of bolt 1968 our mainshock location is consistent with the association of initial rupture of the 1906 mainshock with a dilatational right bend or step over in the submerged san andreas fault system offshore of the golden gate our foreshock location is less well constrained than our mainshock location but is consistent with the foreshock hypocenter being at the same location as the mainshock hypocenter online material visualization of 3d probabilistic hypocentral locations associated with the 1906 earthquake

a terrestrial auxiliary stratotype point and section for the plio pleistocene boundary in the turkana basin east africa abstract the turkana basin of northern kenya and southern ethiopia preserves an extensive record of terrestrial sediments and fossils dating from the oligocene through the holocene of particular significance is the plio pleistocene omo group which documents changes in environments and faunas through the pli pleistocene omo group strata have been intensively studied for nearly three decades and a tightly constrained stratigraphic framework has been developed the lithostratigraphic sequence shows that a fluvial system dominated the basin for most of the past five million years with six relatively short but significant intervals of lacustrine deposition the sequence is punctuated by some 130 tephra most of which have been geochemically characterized and can be used as a basis for local and inter basinal correlation these tephra reach as far as the gulf of aden and the indian ocean providing a means of tightly correlating the marine and terrestrial records isotopic dating and magnetic polarity stratigraphy allow good temporal control on the sequence with over 30 control points in the interval from 4 35 to 0 6 ma extensive paleontological collections from this context provide critical calibration of east african biostratigraphic markers the plio pleistocene boundary can be closely constrained in the omo group deposits based on magnetic polarity stratigraphy this allows the boundary to be related to components of the stratigraphic framework recognized in the terrestrial sequence there and thence related to other east african terrestrial localities by a variety of correlation tools establishment of the omo group sequence as an auxiliary stratotype point for the plio pleistocene boundary will thus allow close relation of these terrestrial localities on the basis of tephro and biostratigraphy the most useful correlation tools in the east african terrestrial record