on vertical resolution of seismic acquisition geometries in complex 3d media abstractexploration frequency and spatial sampling can affect the resolution of seismic imaging some factors have a great impact on the horizontal resolution whereas other factors significantly influence the vertical resolution how to quantify these effects still remains controversial for complex media most previous studies on seismic acquisition geometries focus on the horizontal resolution for seismic migration but neglect to measure the vertical resolution especially in complex media the conventional criteria for vertical resolution are based on the theory of geometric seismology with the assumption of a simple medium focal beam analysis can provide comprehensive insight into the combined effects of acquisition geometries band limited frequencies and complex media on vertical resolution we define two parameters to quantify the vertical resolution of acquisition geometry the main lobe width mlw of a focal beam along the vertical direction and the ratio of its main lobe amplitude to the tota

seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

observation of the seismic nucleation phase in the ridgecrest california earthquake sequence near source observations of five m 3 8 5 2 earthquakes near ridgecrest california are consistent with the presence of a seismic nucleation phase these earthquakes start abruptly but then slow or stop before rapidly growing again toward their maximum rate of moment release deconvolution of instrument and path effects by empirical green s functions demonstrates that the initial complexity at the start of the earthquake is a source effect the rapid growth of the p wave arrival at the start of the seismic nucleation phase supports the conclusion of mori and kanamori 1996 that these earthquakes begin without a magnitude scaled slow initial phase of the type observed by iio 1992 1995

small and large earthquakes can have similar starts a long standing question in seismology is whether small and large earthquakes have similar or different onsets an analysis of earthquakes around japan shows that in some cases these onsets are almost identical an analysis of earthquakes along the japan trench

detailed observations of california foreshock sequences implications for the earthquake initiation process we find that foreshocks provide clear evidence for an extended nucleation process before some earthquakes in this study we examine in detail the evolution of six california foreshock sequences the 1986 mount lewis ml 5 5 the 1986 chalfant ml 6 4 the 1986 stone canyon ml 4 7 the 1990 upland ml 5 2 the 1992 joshua tree mw 6 1 and the 1992 landers mw 7 3 sequence typically uncertainties in hypocentral parameters are too large to establish the geometry of foreshock sequences and hence to understand their evolution however the similarity of location and focal mechanisms for the events in these sequences leads to similar foreshock waveforms that we cross correlate to obtain extremely accurate relative locations we use these results to identify small scale fault zone structures that could influence nucleation and to determine the stress evolution leading up to the mainshock in general these foreshock sequences are not compatible with a cascading failure nucleation model in which the foreshocks all occur on a single fault plane and trigger the mainshock by static stress transfer instead the foreshocks seem to concentrate near structural discontinuities in the fault and may themselves be a product of an aseismic nucleation process fault zone heterogeneity may also be important in controlling the number of foreshocks i e the stronger the heterogeneity the greater the number of foreshocks the size of the nucleation region as measured by the extent of the foreshock sequence appears to scale with mainshock moment in the same manner as determined independently by measurements of the seismic nucleation phase we also find evidence for slip localization as predicted by some models of earthquake nucleation

local observations of the onset of a large earthquake 28 june 1992 landers california the landers earthquake mw 7 3 of 28 june 1992 had a very emergent onset the first large amplitude arrivals are delayed by about 3 sec with respect to the origin time and are preceded by smaller scale slip other large earthquakes have been observed to have similar emergent onsets but the landers event is one of the first to be well recorded on nearby stations we used these recordings to investigate the spatial relationship between the hypocenter and the onset of the large energy release and to determine the slip function of the 3 sec nucleation process relative location of the onset of the large energy release with respect to the initial hypocenter indicates its source was between 1 and 4 km north of the hypocenter and delayed by approximately 2 5 sec three station array analysis of the p wave shows that the large amplitude onset arrives with a faster apparent velocity compared to the first arrivals indicating that the large amplitude source was several kilometers deeper than the initial onset an ml 2 8 foreshock located close to the hypocenter was used as an empirical green s function to correct for path and site effects from the first 3 sec of the mainshock seismogram the resultant deconvolution produced a slip function that showed two subevents preceding the main energy release an mw 4 4 followed by an mw 5 6 these subevents do not appear anomalous in comparison to simple moderate sized earthquakes suggesting that they were normal events which just triggered or grew into a much larger earthquake if small and moderate sized earthquakes commonly detonate much larger events this implies that the dynamic stresses during earthquake rupture are at least as important as long term static stresses in causing earthquakes and the prospects of reliable earthquake prediction from premonitory phenomena are not improved

numerical study of generalized lipmann schwinger integral equation including surface topography rugged topographies and general heterogeneities in the near surface sediments have a significant influence on exploration seismic data recorded at the free surface to remove the near surface effect on seismic data a thorough understanding of wave propagation in the shallow subsurface region is needed the physical effect of wave propagation in the near surface region characterized by volume heterogeneities and rugged topographies can be described by a generalized lipmann schwinger integral equation glsie by virtue of the glsie in this paper i develop an efficient numerical method for the study of wave scattering in complex near surface areas

distribution of dynamic and static stress changes during 2000 tottori japan earthquake brief interpretation of the earthquake sequences foreshocks mainshock and aftershocks 1 the dynamic and static stress changes during the 2000 tottori earthquake have been recovered from the results of waveform inversion we use the dem to solve the elastodynamic equation specifying the slip along the fault obtained by a kinematic fault model the resulting shear stress distribution suggests an explanation of the foreshock and aftershock distributions we conclude that the fault zone heterogeneity is strong and most of the foreshocks and aftershocks were located in the zone of negative stress drop and mainly in the area surrounding the asperity this suggests that the asperity behaved as a barrier during the foreshocks and after the main shock the stress in the area surrounding the asperity increased and triggered most of the aftershocks the foreshock distribution was confined to a finite localized zone in the central part of the fault suggesting that this zone was bordered by barriers

statistical physics seismogenesis and seismic hazard the scaling properties of earthquake populations show remarkable similarities to those observed at or near the critical point of other composite systems in statistical physics this has led to the development of a variety of different physical models of seismogenesis as a critical phenomenon involving locally nonlinear dynamics with simplified rheologies exhibiting instability or avalanche type behavior in a material composed of a large number of discrete elements in particular it has been suggested that earthquakes are an example of a self organized critical phenomenon analogous to a sandpile that spontaneously evolves to a critical angle of repose in response to the steady supply of new grains at the summit in this stationary state of marginal stability the distribution of avalanche energies is a power law equivalent to the gutenberg richter frequency magnitude law and the behavior is relatively insensitive to the details of the dynamics here we review the results of some of the composite physical models that have been developed to simulate seismogenesis on different scales during 1 dynamic slip on a preexisting fault 2 fault growth and 3 fault nucleation the individual physical models share some generic features such as a dynamic energy flux applied by tectonic loading at a constant strain rate strong local interactions and fluctuations generated either dynamically or by fixed material heterogeneity but they differ significantly in the details of the assumed dynamics and in the methods of numerical solution however all exhibit critical or near critical behavior with behavior quantitatively consistent with many of the observed fractal or multifractal scaling laws of brittle faulting and earthquakes including the gutenberg richter law some of the results are sensitive to the details of the dynamics and hence are not strict examples of self organized criticality nevertheless the results of these different physical models share some generic statistical properties similar to the universal behavior seen in a wide variety of critical phenomena with significant implications for practical problems in probabilistic seismic hazard evaluation in particular the notion of self organized criticality or near criticality gives a scientific rationale for the a priori assumption of stationarity used as a first step in the prediction of the future level of hazard the gutenberg richter law a power law in energy or seismic moment is found to apply only within a finite scale range both in model and natural seismicity accordingly the frequency magnitude distribution can be generalized to a gamma distribution in energy or seismic moment a power law with an exponential tail this allows extrapolations of the frequency magnitude distribution and the maximum credible magnitude to be constrained by observed seismic or tectonic moment release rates the answers to other questions raised are less clear for example the effect of the a priori assumption of a poisson process in a system with strong local interactions and the impact of zoning a potentially multifractal distribution of epicentres with smooth polygons the results of some models show premonitory patterns of seismicity which could in principle be used as mainshock precursors however there remains no consensus on both theoretical and practical grounds on the possibility or otherwise of reliable intermediate term earthquake prediction

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

earthquake nucleation and triggering on an optimally oriented fault seismic surface waves from large distant earthquakes commonly trigger smaller earthquakes however delay times of hours to days between the surface waves and the triggered earthquakes weaken the causal connection furthermore when there is no delay the triggered earthquakes are typically too small or too obscured to obtain reliable source mechanisms we present observations of instantaneous triggering of a strike slip earthquake in central alaska shear strain from the optimally aligned teleseismic love wave induced a 24 s exponential foreshock signal leading to the triggered earthquake this nucleation phase and the alignment of the triggered earthquake source mechanism with the teleseismic stress field reveal the behavior of an existing fault under well calibrated strain conditions the alaska earthquake provides the first observation of combined nucleation and triggering and it suggests that transient stresses during nucleation may influence the subsequent earthquake rupture laboratory and theoretical studies of nucleation and triggering may help discriminate between different interpretations for the alaska earthquake

morphological impacts of the chilean megathrust earthquake mw 8 8 on coastal wetlands of high conservation value abstract the subduction earthquake mw 8 8 on february 27th 2010 which affected chile s south central coast 37 s produced a co seismic uplift of 1 4 m in coastal tubul raqui wetland area with abrupt morphological changes in order to determine the magnitude of the changes in this area of high conservation value salt marsh morphological features were identified and quantified by mapping the changing extent of the coverage of morphological features before 2009 and after 2011 2012 the tectonic disturbance rectified satellite images of seven study sites were created for the three years using google earth images and processed in arcgis the results indicate a total decline of 31 7 in the area of the morphological features and the emergence of 1 25 km2 of dried area salt pans and tidal creeks were severely affected with more than 90 loss in contrast there was a slight recovery of the tubul and raqui main river channel 12 and the tidal channels 8 5 between 2011 and 2012 mainly in the area near the river mouth the salt marsh cover by spartina densiflora showed slight variation after the co seismic uplift 14 6 demonstrating high tolerance in the face of high impact natural disturbances the changes and later evolution may be explained mostly by the action of the seismic cycle in subduction zones continuing to monitor state of the recovery of the salt marsh and other similar environments may help to understand the true role that the seismic cycle plays in the dynamics of coastal ecosystems as well as its incidence in the recovery process

recovery estimates for the rio cruces after the may 1960 chilean earthquake abstract the may 22nd 1960 chilean earthquake was the largest earthquake on record with a magnitude 9 5 the event caused extensive subsidence and uplift over wide areas at least 130 000 km 2 with uplift on the offshore south american plate margin and downwarping in the coastal and landward areas which ranged in magnitude from 1 2 m the subsidence deepened coastal rivers creating extensive shallow banks now wetlands in many rivers including the rio cruces the amount of subsidence was well documented with field measurements recorded soon after the event this study using sediment accumulation histories predicts the recovery time of the rio cruces to pre 1960 conditions an important factor for assessing the fidelity of seismic recorders in the geological record sediment cores n 139 from the subtidal areas of the rio cruces were lithologically logged and selectively analyzed using high resolution particle size distribution psd plots microfossil analysis thecamoebians and 210 pb 137 cs dating documenting the post 1960 thickness of sediment the analysis differentiated four main facies which include 1 floodplain soil horizon 2 tsunami or flood unit 3 post earthquake adjustment and 4 river sedimentation the post 1960 river sediment is clearly demarcated in the cores by highly peaked psds 4 5 phi abundant thecamoebian tests and high diversities compared to the underlying facies species compositions are typical of lacustrine or slow moving river systems cucurbitella tricuspis difflugia oblonga centropyxis constricta centropyxis aculeata lagenodifflugia vas and difflugia protaeiformis based on this core data the shallow banks along the rio cruces will likely shoal in less than 100 yrs

wavefield interpolation in the fourier wavefield extrapolation the computational cost for seismic migration relies heavily on the methods used for wavefield extrapolation in general seismic migration by current industry techniques extrapolates wavefields through a thick slab and then interpolates wavefields in small layers inside the slab in this paper i first optimize practical implementation of the fourier wavefield extrapolation i then design three interpolation algorithms fourier transform kirchhoff and born kirchhoff for mild moderate and large to strong lateral heterogeneities respectively the fourier transform interpolation simultaneously implements wavefield interpolation and imaging without needing to invoke the imaging principle by summing over all frequency components of the interpolated wavefield the kirchhoff interpolation is based on the traditional kirchhoff migration formula and is performed by diffraction summation with a very limited aperture using the average velocity of a laterally heterogeneous slab the born kirchhoff interpolation is based on the lippmann schwinger integral equation it differs from the kirchhoff interpolation in that it accounts not only for the obliquity spherical spreading and wavelet shaping factors but also for the relative slowness perturbation in a laterally heterogeneous slab recursive seismic migration usually accounts for a 20 to 40 ms depth size for wavefield extrapolation in practical applications using the above interpolation techniques fourier depth migration methods are shown to tolerate a 40 to 60 ms depth size with the seg eage salt model therefore the fourier depth migration techniques with thick slab extrapolation plus thin slab interpolation can be used to image structures with salt related complexes

flooding the topography wave equation datuming of land data with rugged acquisition topography wave equation datuming overcomes some of the problems that seismic data recorded on rugged surface topography present in routine image processing the main problems are that 1 standard optimized migration and processing algorithms assume data are recorded on a flat surface and that 2 the static correction applied routinely to compensate for topography is inaccurate for waves that do not propagate vertically wave based processes such as stacking dip moveout correction normal moveout correction velocity analysis and migration after static shift can be severely affected by the nonhyperbolic character of the reflections to alleviate these problems i apply wave equation datuming early in the processing flow to upward continue the data to a flat datum above the highest topography this is what i refer to as flooding the topography this approach does not require detailed a priori knowledge of the near surface velocity and it streamlines subsequent processing because the data are regridded onto a regularly sampled datum wave equation datuming unravels the distortions caused by rugged topography and unlike the static shift method it does not adversely effect subsequent wave based processing the image obtained after wave equation datuming exhibits better reflector continuity and more accurately represents the true structural image than the image obtained after static shift

scaling relationships between sizes of nucleation regions and eventual sizes of microearthquakes abstract we investigate the initial rupture process of microearthquakes to reveal relationships between nucleation region sizes and eventual earthquake sizes in order to obtain high quality waveform data we installed a trigger recording system with a sampling frequency of 10 khz at the base of a deep borehole at the nojima fault japan we analyze waveform data of 31 events around the borehole with seismic moment ranging from 4 2 10 9 nm to 7 1 10 11 nm we use both a circular crack model with an accelerating rupture velocity sk model sato t kanamori h 1999 beginning of earthquakes modeled with the griffith s fracture criterion bull seism soc am 89 80 93 which generates a slow initial phase of velocity pulse and a circular crack model with a constant rupture velocity sh model sato t hirasawa t 1973 body wave spectra from propagating shear cracks j phys earth 21 415 431 which generates a ramp like velocity pulse source parameters of these two models are estimated by waveform inversion of the first half cycle of the observed velocity pulse applying both a grid search and a non linear least squares method 14 of 31 events are never reproduced by the sh model with a constant q operator but sk model with a constant q operator provides a size of the pre existing crack corresponding to the size of the nucleation regions and a size of the eventual crack we recognize that i the eventual seismic moment is approximately scaled as the cube of the size of pre existing cracks ii the eventual seismic moment is scaled as the cube of the size of eventual cracks and iii the size of eventual cracks is roughly proportional to the size of pre existing cracks we thus conclude that the size of eventual earthquakes is controlled by the size of the nucleation regions

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

a new method of quickly estimating epicentral distance and magnitude from a single seismic record rapid estimation of the epicentral distance and magnitude is of fundamental importance for early earthquake detection and warning systems we present a novel method of estimating the epicentral distance from a single seismic record in a short amount of time in order to quantitatively evaluate the difference in observed seismic waveforms we introduced a simple function with the form of bt exp at and determined a and b in terms of the least squares method by fitting this function to the initial part of the waveform envelope we have found that log b is inversely proportional to log where is the epicentral distance this relation holds true regardless of the earthquake magnitude by using this relation we can roughly estimate the epicentral distance nearly immediately after the p wave arrival then we can readily estimate the magnitude from the maximum amplitude observed within a given short time interval after the p wave arrival by using an empirical magnitude amplitude relation that includes the epicentral distance as a parameter manuscript received 11 january 2002

revealing the deep structure and rupture plane of the 2010 maule chile earthquake mw 8 8 using wide angle seismic data the 27 february 2010 maule earthquake mw 8 8 ruptured 400 km of the nazca south america plate boundary and caused hundreds of fatalities and billions of dollars in material losses here we present constraints on the fore arc structure and subduction zone of the rupture area derived from seismic refraction and wide angle data the results show a wedge shaped body 40 km wide with typical sedimentary velocities interpreted as a frontal accretionary prism fap landward of the imaged fap the velocity model shows an abrupt velocity contrast suggesting a lithological change which is interpreted as the contact between the fap and the paleo accretionary prism backstop the backstop location is coincident with the seaward limit of the aftershocks defining the updip limit of the co seismic rupture and seismogenic zone furthermore the seaward limit of the aftershocks coincides with the location of the shelf break in the entire earthquake rupture area 33 s 38 5 s which is interpreted as the location of the backstop along the margin published seismic profiles at the northern and southern limit of the rupture area also show the presence of a strong horizontal velocity gradient seismic backstop at a distance of 30 km from the deformation front the seismic wide angle reflections from the top of the subducting oceanic crust constrain the location of the plate boundary offshore dipping at 10 the projection of the epicenter of the maule earthquake onto our derived interplate boundary yielded a hypocenter around 20 km depth this implies that this earthquake nucleated somewhere in the middle of the seismogenic zone neither at its updip nor at its downdip limit

examination of scaling between proposed early signals in p waveforms and earthquake magnitudes summary we examine seismic waveforms generated by clusters of similar earthquakes and additional events located on the karadere duzce branch of the north anatolian fault to investigate possible scaling between proposed early signals in the p waveforms and magnitudes the employed signals can be divided into two classes the first is associated with ellsworth beroza and iio type signals that are assumed to reflect signatures of seismic nucleation phases the second are associated with nakamura type period and wu zhao type maximum displacement in the early waveforms that are related to measures of the corner frequency and local magnitude respectively the impact on each signal of artefacts generated by the finite impulse response fir filter is also examined the use of repeating event clusters reduces considerably the variability of path and site effects compared to previous regional and global studies this allows us to focus more accurately on variations of the potential scaling parameters with the source magnitude however the magnitude range of the employed events is limited to about 4 units the fir filter artefacts can generate spurious signals prior to the p wave arrival potentially affecting the ellsworth beroza type signals but are not a significant influence on any of the other measurements the results indicate that candidates for the ellsworth beroza signals associated with identification of a weak arrival before the main p phase exist in less than 20 per cent of the cases the iio type signals can be determined by definition on all waveforms both of these potential signatures of nucleation phases show little or no scaling with the final event size in the examined data in contrast the nakamura and wu zhao type signals in the first few seconds which can also be determined by definition on all waveforms appear to scale with the final event magnitude albeit with large scatter the relatively large time windows used in the analysis compared to the rupture time of the employed events implies that the results provide little if any information on the physical process of the rupture initiation the scaling of the nakamura and wu zhao type early signals with the final event size may be explained by statistical tendency of stronger initial rupture phases to propagate larger distances

initial rupture of earthquakes in the 1995 ridgecrest california sequence close examination of the p waves from earthquakes ranging in size across several orders of magnitude shows that the shape of the initiation of the velocity waveforms is independent of the magnitude of the earthquake a model in which earthquakes of all sizes have similar rupture initiation can explain the data this suggests that it is difficult to estimate the eventual size of an earthquake from the initial portion of the waveform previously reported curvature seen in the beginning of some velocity waveforms can be largely explained as the effect of anelastic attenuation thus there is little evidence for a departure from models of simple rupture initiation that grow dynamically from a small region the results of this study indicate that any precursory radiation at seismic frequencies must emanate from a source region no larger than the equivalent of a m0 5 event i e a characteristic length of 10 m the size of the nucleation region for magnitude 0 to 5 earthquakes thus is not resolvable with the standard seismic instrumentation deployed in california

rising slope of moment rate functions the 1989 earthquakes off east coast of honshu a series of large earthquakes occurred off east coast of honshu japan during the period of october to november 1989 mechanisms were studied for the foreshock m 6 5 the mainshock m 7 1 and the two aftershocks m 5 2 and 5 3 using the sts i broadband records at station inu about 700km away from the epicenters the lowpass filtered seismograms of these earthquakes show mutually very similar waveforms in good agreement with those calculated for a known mechanism by an extended reflectivity method the mainshock is 10 times as large as the foreshock and 2000 times as large as the aftershocks in terms of seismic moment assuming that the mainshock or foreshock is a collection of some elementary sources at a focal point and that aftershock seismograms represent the responses to such elementary sources the broadband seismogram of the mainshock or foreshock for the first 60s was deconvolved with that of an aftershock to obtain the moment rate function the moment rate functions of the mainshock and foreshock are both triangle like with durations of 14 and 9s respectively their rising slopes are mutually very different a greater slope is associated with the greater shock this and the similar results for other pairs of earthquakes suggest that the rising slope of moment rate function is causaly related to the eventual size of seismic rupture

vertical deformation through a complete seismic cycle at isla santa maria chile records of complete earthquake cycles are rare analysis of historical nautical charts and modern gps data that record a full earthquake cycle in chile show that great earthquakes can create small amounts of permanent uplift

earthquakes as multiscale dynamic ruptures with heterogeneous fracture surface energy 1 we propose a model of the wide scale growth of dynamic rupture during an earthquake based on our multiscale simulation of a planar crack in a three dimensional homogeneous elastic space a simple slip weakening law governs the fracture friction processes and its characteristic parameters slip weakening distance and fracture surface energy have multiscale heterogeneous distributions we consider a set of randomly distributed circular patches whose diameter is proportional to the fracture surface energy each patch represents an asperity between irregular fault surfaces and the size number relation of the patches obeys power law statistics we assess rupture propagation from a small instability using a boundary integral equation method with a renormalization technique although most events stop shortly after their initiation some grow triggering neighboring patches of similar size small and large events show statistically self similar properties of rupture growth and stop spontaneously without requiring a special stopping mechanism the rupture velocity locally exceeds the shear wave speed but globally remains subshear speed due to the increase of the average fracture energy as the rupture grows the relation between size and frequency of events is a power law which is explained by the triggering probability between patches as a consequence of statistically self similar random triggering growth we observe a distinct main phase in seismic waves similar to those of natural earthquakes but we cannot estimate the final size of the event from the initial part of the seismic waves if this is true for the real earthquakes predicting the size of a future earthquake would be quite difficult

nucleation of rupture under slip dependent friction law simple models of fault zone the initiation of frictional instability is investigated for simple models of fault zone using a linearized perturbation analysis the fault interface is assumed to obey a linear slip weakening law the fault is initially prestressed uniformly at the sliding threshold in the case of antiplane shear between two homogeneous linearly elastic media space time and spectral solutions are obtained and shown to be consistent the nucleation is characterized by 1 a long wavelength unstable spectrum bounded by a critical wave number 2 an exponential growth of the unstable modes and 3 an induced off fault deformation that remains trapped within a bounded zone in the vicinity of the fault these phenomena are characterized in terms of the elastic parameters of the surrounding medium and a nucleation length that results from the coupling between the frictional interface and the bulk elasticity these results are extended to other geometries within the same formalism and implications for three dimensional rupture are discussed finally internal fault structures are investigated in terms of a fault parallel damaged zone spectral solutions are obtained for both a smooth and a layered distribution of damage for natural faults the nucleation is shown to depend strongly on the existence of a internal damaged layer this nucleation can be described in terms of an effective homogeneous model in all cases frictional trapping of the deformation out of the fault can lead to the property that arbitrarily long wavelengths remain sensitive to the existence of a fault zone

scaling of earthquake rupture growth in the parkfield area self similar growth and suppression by the finite seismogenic layer 1 we propose a new framework on the scaling of earthquake rupture growth time history and we scale the moment rate and the cumulative moment functions of earthquakes over a wide magnitude range mw 1 7 6 0 in parkfield california the moment rate and the cumulative moment functions of the small and medium earthquakes mw 1 7 4 6 are derived by slip inversion analyses with the empirical green s function technique the moment rate functions of the investigated earthquakes except the mw 6 0 event are similar to each other increasing rapidly in the first half growth stage and decelerating in the latter half decline stage in the growth stage the cumulative moment functions are approximated by mo t nm 2 1017 t s 3 independent of the final size of the earthquakes the proportionality of the cumulative moment to the cube of time implies self similarity during earthquake rupture growth in the decline stage the cumulative moment function veers off the common rupture curve the mw 6 0 event also grows along the same rupture curve until 1 s after which the cumulative moment function is proportional to time from the onset itself this is because the finite seismogenic layer limits the vertical extent of dynamic rupture our method and results contribute to our understanding of earthquake source physics especially on earthquake rupture growth processes which may help to improve earthquake early warning techniques

time functions of deep earthquakes from broadband and short period stacks to constrain dynamic source properties of deep earthquakes we have systematically constructed broadband time functions of deep earthquakes by stacking and scaling teleseismic p waves from u s national seismic network terrascope and berkeley digital seismic network broadband stations we examined 42 earthquakes with depths from 100 to 660 km that occurred between july 1 1992 and july 31 1995 to directly compare time functions or to group them by size depth or region it is essential to scale them to remove the effect of moment which varies by more than 3 orders of magnitude for these events for each event we also computed short period stacks of p waves recorded by west coast regional arrays the comparison of broadband with short period stacks yields a considerable advantage enabling more reliable measurement of event duration a more accurate estimate of the duration better constrains the scaling procedure to remove the effect of moment producing scaled time functions with both correct timing and amplitude we find only subtle differences in the broadband time function shape with moment indicating successful scaling and minimal effects of attenuation at the periods considered here the average shape of the envelopes of the short period stacks is very similar to the average broadband time function the main variations seen with depth are 1 a mild decrease in duration with increasing depth 2 greater asymmetry in the time functions of intermediate events compared to deep ones and 3 unexpected complexity and late moment release for events between 350 and 550 km with seven of the eight events in that depth interval displaying markedly more complicated time functions with more moment release late in the rupture than most events above or below the first two results are broadly consistent with our previous studies while the third is reported here for the first time the greater complexity between 350 and 550 km suggests greater heterogeneity in the failure process in that depth range

magnitude determination using initial p waves a single station approach 1 prompted by recent success in the research and application of earthquake early warning systems we conducted an investigation into the relationship between the magnitudes of earthquakes and the properties of the first three seconds of the p waves at a single station using waveforms at station nacb of the broadband array in taiwan for seismology from 46 earthquakes within 100 km epicentral distance we found a linear correlation between the magnitudes and the logarithmic characteristic periods of the initial p waves for earthquakes up to magnitude 6 5 we also detected a deterministic relationship between the magnitudes and the peak amplitudes of the initial p waves for earthquakes of magnitude m 6 5 while further study needs to be done on the behavior of the initial p wave peak amplitudes from larger earthquakes we propose here that the characteristic periods and peak amplitudes of the first three seconds of the p waves be used jointly in onsite single station earthquake early warning operations

split step fourier migration the split step fourier method is developed and applied to migrating stacked seismic data in two and three dimensions this migration method which is implemented in both the frequency wavenumber and frequency space domains takes into account laterally varying velocity by defining a reference slowness reciprocal of velocity as the mean slowness in the migration interval and a perturbation term that is spatially varying the mean slowness defines a reference vertical wavenumber which is used in the frequency wavenumber domain to downward continue the data across a depth interval as in constant velocity phase shift migration the perturbation term is used to define a source contribution that is taken into account by the application of a second phase shift in the frequency space domain since the method does not include the effects of second and higher order spatial derivatives of the slowness field the method theoretically is accurate only when there are no rapid lateral slowness variations combined wi

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

an egf technique to infer the rupture velocity history of a small magnitude earthquake 1 an empirical green s function egf technique has been developed to detect the rupture velocity history of a small earthquake the assumed source model is a circular crack that is characterized by a single and unipolar moment rate function mrf the deconvolution is treated as an inverse problem in the time domain which involves an assumed form of the moment rate function mrf the source parameters of the mrf are determined by adopting a global nonlinear inversion scheme a thorough synthetic study on both synthetic and real seismograms allowed us to evaluate the degree of reliability of the retrieved model parameters the technique was applied to four small events that occurred in the umbria marche region italy in 1997 to test the hypothesis of a single rupture process the inversion results were compared with those arising from another egf technique which assumes a multiple rupture process for each event the best fit model was selected using the corrected akaike information criterion for all the considered events the most interesting result is that the selected best fit model favors the hypothesis of a single faulting process with a clear variability of the rupture velocity during the process for the studied events the maximum rupture speed can even approach the p wave velocity at the source as theoretically foreseen in studies of the physics of the rupture and recently observed for high magnitude earthquakes

single and double asperity failures in a large scale biaxial experiment stick slip experiments were performed in a direct shear apparatus using large inada granite blocks the dimensions of the pre existing fault surface were 100 cm length 10cm width by applying heterogeneous normal stress using three actuators by which forces could be independently controlled two asperities with different strengths were formed on a fault plane under a certain normal stress distribution single asperity failure and double asperity failure occurred alternately the single asperity failure refers to a stick slip event in which a weaker asperity ruptures alone without triggering the rupture of a stronger asperity the double asperity failure is an event in which a rupture of a weak asperity triggers the rupture of a strong asperity resulting in a failure of the whole fault for triggering of a rupture it is necessary that stress at the strong asperity is accumulated to a certain level just prior to the failure of the weak asperity

correlation of p wave amplitudes and travel time residuals for teleseisms recorded on the southern california seismic network p waves from 13 teleseismic events well distributed in azimuth and recorded on a large short period network in southern california show a positive correlation between travel time residuals and relative amplitudes slower arrivals are consistently larger than faster arrivals although there is a large amount of scatter the data show an amplitude increase of about a factor of 2 for a 1 s increase in travel time the correlation can be seen in various subsets of the data individual earthquakes single stations recording 10 or more earthquakes and data averaged over all recorded events at each station because the variations in amplitude and travel time can be associated with surface geology much of the data recorded at non bedrock sites can be explained in terms of a near surface layer of varying velocity the travel time residual would then be directly proportional to the velocity in the layer and the amplitude proportional to the square root of the velocity contrast at the base of the layer however some stations show azimuthally varying travel time residuals that are attributed to upper mantle velocity structures we use a two dimensional finite difference calculation to show that velocity anomalies in the upper mantle can also contribute to the observed correlation of travel time and amplitude

beginning of earthquakes modeled with the griffith s fracture criterion we present a source model for the beginning of earthquakes based on the griffith s fracture criterion the initial state is a critical state of pre existing circular fault which is on the verge of instability after the onset of instability the fault grows with a progressively increasing rupture speed satisfying the condition of fracture energy balance at the crack tip we investigate the difference in rupture growth patterns in two classes of models that are considered to represent end member cases in the first model spontaneous model we assume that the surface energy varies smoothly as a function of position in the crust in this model faults with small initial dimensions grow in regions with small surface energy and those with large initial dimensions in large surface energy the rupture velocity increases progressively until it reaches its limiting value the synthetic velocity seismogram at far field shows a weak initial phase during the transitional stage to limiting velocity the time taken to reach the limiting velocity is proportional to the initial length of pre existing fault therefore the duration of the weak initial phase scales with the initial length of fault in the second model trigger model we envisage that there are many pre existing faults in the crust with various lengths these faults are stable because they encounter some obstacle at their ends e g fault segmentation strong asperity etc this situation is modeled with a local increase of surface energy near the ends of fault an earthquake is triggered when the obstacle is suddenly removed i e sudden weakening or the stress is suddenly increased locally to overcome the obstacle once an earthquake is triggered the fault growth is governed by the ambient surface energy in this model the rupture speed attains its limiting velocity almost instantly the synthetic velocity seismogram at far field shows an abrupt linear increase in amplitude without the weak initial phase that appears in the spontaneous model both models can be unified using a trigger factor defined as a fractional perturbation of the surface energy at the ends of fault relative to the ambient surface energy the spontaneous model is characterized by a small trigger factor and the trigger model by a large trigger factor thus the seismic initiation phase with and without the slow initial phase can both occur depending on the trigger factor the variability in the observed seismic initiation phase may represent a variation surface energy strength distribution surrounding the pre existing cracks a theoretical consideration of rupture arrest by barriers using the griffith s fracture criterion does not support the scaling relation between the nucleation moment and the eventual size of earthquake

rupture nucleations in the 1995 hyogo ken nanbu earthquake and its large aftershocks summary local seismograms of the hyogo ken nanbu earthquake m 7 2 and its largest aftershocks show that a slow rising initial phase precedes the main p phase high dynamic range short period seismograms of the foreshocks mainshock and aftershocks were recorded by the japan meteorological agency jma network and the net hyogo using these seismograms we investigate the initial rupture process of the mainshock and large aftershocks using an empirical green s function method the deconvolved moment rate function of the mainshock shows that it begins with a small pre event mw 4 0 then the moment releases gradually and after about 0 6 s it increases rapidly the first 0 7 s of the deconvolved moment rate functions are inverted to obtain the spatio temporal images of the initial rupture process the results show that at the hypocentral area less than 1 km from the hypocentre slip velocity rises slowly with a low peak in the surrounding area 1 km east and downward from the hypocentre slip velocity rises rapidly with a high peak it is also found that during the initial rupture process the slip velocity pulse grows continuously these observations are in accord with a theoretical model of the transition process from nucleation to high speed dynamic rupture in which slip velocity rises slowly at the nucleation zone we also analyse the initiation and the main dynamic rupture of large aftershocks spatio temporal images of the largest aftershocks m 5 1 and m 4 8 show that there is a clear initial rupture process with a low moment release and after about 0 2 s slip velocity increases rapidly we compare the initial rupture process of the mainshock with those of the large aftershocks m 4 0 5 1 the duration 0 6 s of the initial phase of the mainshock is longer than those 0 02 0 3 s of the large aftershocks furthermore the slip velocity of the initial rupture process of the mainshock is several times larger than those of the two largest aftershocks these results suggest that the mainshock starts in the region where the stress drop and fracture energy is higher

foreshock and aftershock sequence of the 1998 m 5 0 sendai northeastern japan earthquake and its implications for earthquake nucleation we investigated foreshock and aftershock sequences of a m 5 0 earthquake that occurred on 15 september 1998 near the nagamachi rifu fault an active fault crossing the urban area of sendai city northeastern japan the focal mechanism of this event was a reverse fault type with a nearly horizontal p axis parallel to the plate conversion direction aftershock distribution located by the homogeneousstation method delineates the fault plane of this event dipping to the northwest at an angle of 30 in the depth range of 10 12 km the location of the fault plane and the slip direction thus estimated suggest that this event was a slip at a deep portion of the nagamachi rifu fault three days prior to the mainshock many foreshocks with similar waveforms started to occur very close to the mainshock hypocenter we estimated relative locations of these similar foreshocks based on crossspectrum analyses of waveforms recorded at nearby stations they are located at the deepest portion of the mainshock fault plane and just above the mainshock hypocenter migration of the foreshocks is observed from deeper to shallower depths cumulative coulomb stress changes caused by preceding events show negative values at hypocenters of similar waveform foreshocks our results do not support the cascade model for the process of foreshock generation nucleation phase prior to the high speed rupture of the mainshock is observed in seismograms at nearby stations the initial point of the nucleation phase is located on a deeper extension of the foreshock area the high speed breakout point is located in the area where a large amount of seismic moment release was estimated from waveform inversions these observations probably reflect an underlying aseismic nucleation process preceding the main dynamic rupture of the m 5 0 event

slow initial phase and nucleation process of microearthquakes in western nagano central japan 1 we investigated the slow initial phase of small earthquakes m 0 0 3 6 in western nagano central japan by deconvolution with causal attenuation operators and empirical green s functions to determine whether the slow initial phase is caused by propagation effects along the raypath or source effects we investigated whether all earthquakes begin as shear cracks with a constant stress drop and rupture velocity whether the path effect can be represented by a constant attenuation operator and whether the seismograms of the smallest earthquakes are empirical green s functions for the path effect of larger earthquakes we found that the larger earthquakes m 1 9 have complicated source processes in combination with linear growth while smaller earthquakes show simple linear increases in moment accelerations it is possible that the larger earthquakes are fundamentally different from the smaller earthquakes it also appears that the complex waveforms observed in the larger earthquakes can be explained by multiple rupture processes although the slow initial phase of m 1 9 events at the very least must be explained as a source effect

slow initial phase generated by microearthquakes occurring in the western nagano prefecture japan the source effect near source observations of microearthquakes occurring in the western nagano prefecture show that durations of recorded slows initial phases were almost constant independently of focal distance although a closer inspection revealed that the durations of the slow initial phases slightly increased with focal distance they were not proportional to focal distance thus it is concluded that the slow initial phases do not mainly reflect the whole path q if the slow initial phases were attributed to the strong anelastic attenuation in the surface layer combined with that of the whole path q the rise time of the p wave velocity pulse at the source for a m2 4 event would be estimated as about 3 ms and the source radius of the m2 4 event would be estimated as about 10 m this value of the source radius is too small for m2 4 this suggests that the slow initial phase does not arise from the strong anelastic attenuation in the surface layer it is likely that the slow initial phase does not mainly reflect a path effect but a source effect

can we image beneath salt a decade has passed since petroleum geologists first recognized that jurassic salt in the extensional gulf of mexico often appeared to be thrust between layers of younger sediments since then many teams of geoscientists have been faced with the problems of either 1 improving subsalt quality through better data collection or 2 making subsalt interpretations from data of very poor quality these problems aren t new in fact they have faced the seismic industry from the beginning in the gulf of mexico however the cause of the problem salt is obvious in particular high velocity structurally contoured salt bodies act as sonic lenses that disperse or concentrate seismic signals in haphazard ways many advances in seismic imaging technology have been in response to these salt related problems of velocity and structure

wavefield interpolation in 3d large step fourier wavefield extrapolation extrapolating wavefields and imaging at each depth during three dimensional recursive wave equation migration is a time consuming endeavor for efficiency most commercial techniques extrapolate wavefields through thick slabs followed by wavefield interpolation within each thick slab in this article we develop this strategy by associating more efficient interpolators with a fourier transform related wavefield extrapolation method first we formulate a three dimensional first order separation of variables screen propagator for large step wavefield extrapolation which allows for wide angle propagations in highly contrasting media this propagator significantly improves the performance of the split step fourier method in dealing with significant lateral heterogeneities at the cost of only one more fast fourier transform in each thick slab we then extend the two dimensional kirchhoff and born kirchhoff local wavefield interpolators to three dimensional cases for each slab the three dimensional kirchhoff interpolator is based on the traditional kirchhoff formula and applies to moderate lateral velocity variations whereas the three dimensional born kirchhoff interpolator is derived from the lippmann schwinger integral equation under the born approximation and is adapted to highly laterally varying media numerical examples on the three dimensional salt model of the society of exploration geophysicists european association of geoscientists demonstrate that three dimensional first order separation of variables screen propagator born kirchhoff depth migration using thick slab wavefield extrapolation plus thin slab interpolation tolerates a considerable depth step size of up to 72 ms eventually resulting in an efficiency improvement of nearly 80 without obvious loss of imaging accuracy although the proposed three dimensional interpolators are presented with one way fourier extrapolation methods they can be extended for applications to general migration methods

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

properties of the seismic nucleation phase abstract near source observations show that earthquakes begin abruptly at the p wave arrival but that this beginning is weak with a low moment rate relative to the rest of the main shock we term this initial phase of low moment rate the seismic nucleation phase we have observed the seismic nucleation phase for a set of 48 earthquakes ranging in magnitude from 1 1 8 1 the size and duration of the seismic nucleation phase scale with the total seismic moment of the earthquake suggesting that the process responsible for the seismic nucleation phase carries information about the eventual size of the earthquake the seismic nucleation phase is characteristically followed by quadratic growth in the moment rate consistent with self similar rupture at constant stress drop in this paper we quantify the properties of the seismic nucleation phase and offer several possible explanations for it

implications of a composite source model and seismic wave attenuation for the observed simplicity of small earthquakes and reported duration of earthquake initiation phase an examination of p waves recorded on near source velocity seismograms generally shows that most small earthquakes mw 2 to 3 are simple on the other hand larger earthquakes mw 4 are most often complex the simplicity of the seismograms of mw 2 to 3 events may reflect the simplicity of the source and hence may imply that smaller and larger earthquakes are not self similar or may be a consequence of attenuation of seismic waves to test whether the attenuation is the cause we generated synthetic p wave seismograms from a composite circular source model in which subevent rupture areas are assumed to follow a power law distribution the rupture of an event is assumed to initiate at a random point on the fault and to propagate with a uniform speed as the rupture front reaches the center of a subevent patch all of which are circular a p pulse is radiated that is calculated from the kinematic source model of sato and hirasawa 1973 synthetic p wave seismograms which are all complex are then convolved with an attenuation operator for different values of t the results show that the observed simplicity of small events mw 2 to 3 may be entirely explained by attenuation if t 0 02 sec the composite source model predicts that the average time delay between the initiation of the rupture and the rupture of the largest patch scales as m 1 3 such that log 1 3 log m 8 462 this relation is very similar to that reported by umeda et al 1996 between m and the observed time difference between the initiation of the rupture and the rupture of the bright spot it roughly agrees with the relation between m and the duration of the initiation phase reported by ellsworth and beroza 1995 and beroza and ellsworth 1996 the relation also fits surprisingly well the data on duration of slow initial phase t sip and m reported by iio 1995 one possible explanation of this agreement may be that the composite source model which is essentially the cascade model successfully captures the evolution of the earthquake source process and that the rupture initiation and the abrupt increase in the velocity amplitude observed on seismograms by previous researchers roughly corresponds to the rupture of the first subevent and the breaking of the largest subevent in the composite source model

nucleation phase and high speed rupture propagation of faulting at mt etna volcano southern italy a detailed analysis of microearthquake waveforms recorded at mt etna shows with some exceptions that first pulse of events with magnitude m 2 5 is consistent with the presence of a slow initial phase which precedes a phase of high speed rupture propagation this is in agreement with experimental results theoretical models and laboratory experiments which considered gradually increasing rupture velocity or slip in order to investigate the dependence of the pulse shapes on the azimuth we analyze recordings for six earthquakes m 2 7 3 7 with well constrained focal mechanisms computed by a high number of observations 21 27 for each earthquake we observe that the values of the slow phase duration tsip and those of the high speed rupture duration tris compared over the focal sphere exhibit a spatial distribution which seem to depend strictly on the type of rupture mechanism moreover waveforms of very closely located earthquakes do not exhibit similar characteristics in the pulse shapes which would exclude that the waveforms of analyzed earthquakes are influenced drastically by attenuation effects and that the slow initial phase is the result of the propagation path these and other evidence suggest that i the nucleation phases are mainly a source effect and ii directivity effects must be adequately considered on pulse width measurements

seismicity on a fault controlled by rate and state dependent friction with spatial variations of the critical slip distance 1 we perform systematic simulations of slip using a quasi dynamic continuum model of a two dimensional 2 d strike slip fault governed by rate and state dependent friction the depth dependence of the a b and l frictional parameters are treated in an innovative way that is consistent with available laboratory data and multidisciplinary field observations various realizations of heterogeneous l distributions are used to study effects of structural variations of fault zones on spatiotemporal evolution of slip we demonstrate that such realizations can produce within the continuum class of models realistic features of seismicity and slip distributions on a fault we explore effects of three types of variable l distributions 1 a depth dependent l profile accounting for the variable width of fault zones with depth 2 uncorrelated 2 d random distributions of l with different degrees of heterogeneity and 3 a hybrid distribution combining the depth dependent l profile with the 2 d random l distributions the first type of l distribution with relatively small l over the depth range corresponding to the seismogenic zone and larger l elsewhere generates stick slip events in the seismogenic zone and ongoing creep above and below that region the 2 d heterogeneous parameterizations generate frequency size statistics with event sizes spanning 4 orders of magnitude our results indicate that different degrees of heterogeneity of l distributions control 1 the number of simulated events and 2 the overall stress level and fluctuations other observable trends are 3 the dependency of hypocenter location on l and 4 different nucleation phases for small and large events in heterogeneous distributions

what controls an earthquake s size results from a heterogeneous cellular automaton the controls on an earthquake s size are examined in a heterogeneous cellular automaton that includes stress concentrations which scale with rupture size large events only occur when stress is highly correlated with strength over the entire fault although the largest events occur when this correlation is the highest the magnitude of the correlation has no predictive value as events of all magnitudes occur during times of high stress strength correlation rather the size of any particular event depends on the local stress heterogeneity encountered by the growing rupture patterns of energy release with time for individual ruptures reflect this heterogeneity and many show nucleation type behaviour although there is no relation between the duration of nucleation phase and the size of the event these results support the view that earthquake size is determined by complex interactions between previous event history and dynamic stress concentrations and suggest that deterministic earthquake prediction based on monitoring nucleation zones will not be possible

beginnings of earthquakes in the mexican subduction zone on strong motion accelerograms abstract the guerrero mexico accelerograph network has recorded at short distances earthquakes with magnitudes from 3 0 to 8 1 in this article the initial 3 5 sec of the p waves on the vertical component are compared in addition to unfiltered accelerograms several causal bandpass filters are applied we do not see significant differences in either original or filtered records between the initial e g 0 5 sec seismograms of moderate and large earthquakes in the original and 2 to 5 hz passband the main differences among events with magnitudes over about 4 5 is in the duration of shaking the initial ground motions of all the large events have very small amplitudes which gradually get larger at lower frequencies seismograms of the largest events show a complex series of multiple pulses assumed related to failure of numerous asperities in our lowest frequency band 0 2 to 0 5 hz most of the large events that we examined begin with rupture of asperities that are not necessarily larger and are sometimes smaller than the asperities that fail during smaller events the observations are consistent with a model of faulting in which the largest asperities are located at random on the eventual fault plane and fail when the rupture front propagating from the hypocenter reaches them this allows the largest asperities to occasionally be at the hypocenter and to fail immediately but for a large fault it is more likely that they will be located elsewhere and fail later

continuous borehole strain in the san andreas fault zone before during and after the 28 june 1992 mw 7 3 landers california earthquake abstract high precision strain was observed with a borehole dilational strainmeter in the devil9s punchbowl during the 11 58 ut 28 june 1992 m w 7 3 landers earthquake and the large big bear aftershock m w 6 3 the strainmeter is installed at a depth of 176 m in the fault zone approximately midway between the surface traces of the san andreas and punchbowl faults and is about 100 km from the 85 km long landers rupture we have questioned whether unusual amplified strains indicating precursive slip or high fault compliance occurred on the faults ruptured by the landers earthquake or in the san andreas fault zone before and during the earthquake whether static offsets for both the landers and big bear earthquakes agree with expectation from geodetic and seismologic models of the ruptures and with observations from a nearby two color geodimeter network and whether postseismic behavior indicated continued slip on the landers rupture or local triggered slip on the san andreas we show that the strain observed during the earthquake at this instrument shows no apparent amplification effects there are no indications of precursive strain in these strain data due to either local slip on the san andreas or precursive slip on the eventual landers rupture the observations are generally consistent with models of the earthquake in which fault geometry and slip have the same form as that determined by either inversion of the seismic data or inversion of geodetically determined ground displacements produced by the earthquake finally there are some indications of minor postseismic behavior particularly during the month following the earthquake

post earthquake coastal evolution and recovery of an embayed beach in central southern chile abstract earthquakes and tsunamis are significant factors for change along active margin shores and influence coastal evolution the chilean coast was affected in 2010 by a subduction earthquake with a magnitude of mw 8 8 and also by a trans pacific tsunami which generated violent geomorphologic changes and damaged homes following these events the magnitude of the changes which affect chile s central southern coast 37 s and the role of subduction earthquakes in coastal evolution on a historical scale were investigated at lebu bay an embayed beach data were generated for variations in time and space along the shoreline topographical and bathymetric changes in the bay and for morphodynamic littoral processes logarithmic and parabolic models were applied to the shoreline along with map overlays in order to determine changes the shoreline processes were analyzed based on statistics for waves tides and sediment transport for pre and post tsunami conditions an average accretion rate of 2 80 m year 1984 2010 was established for the shoreline with a strong trend towards accretion in the last 30 years a parabolic function best represented the general form of the shoreline although the presence of a river in the concave zone affected the fit in this sector two factors controlled historical changes on the beach one of anthropic origin in addition to the earthquake and tsunami on february 27th 2010 the post earthquake recovery was fast and currently the beach is in a stable condition despite the inter seismic subsidence process previous to the event this coastal system showed a high resilience in the face of coastal geomorphological changes induced by high impact natural disturbances however the opposite occurred in relation to changes induced by anthropogenic disturbances

quick estimation of the magnitude and epicentral distance using the p wave for earthquakes in iran abstract a reliable estimation of the earthquake magnitude and epicentral distance within a few seconds after the p wave arrival is of great importance for earthquake early warning systems this study aims to investigate the relations between the envelope of the initial part of the p wave with epicentral distance and magnitude of the earthquakes related to the tectonic conditions of iran to this end the accelerometer waveforms of 17 earthquakes with moment magnitudes less than 7 8 and epicentral distances less than 150 km are considered a simple function with the form of y bt exp at is fitted to the initial part of the waveform envelope on time windows of 2 3 4 and 5 s by the least squares method which is constructed simply by keeping the past maximum amplitude at every moment parameters a and b are obtained to scale magnitude and epicentral distance as well the results show that log is proportional to log b in which denotes the epicentral distance the distance scaling relations for all of the time windows indicate standard deviations between 0 16 and 0 17 km for log comparing to the adopted relation in the early warning system of the japan meteorological agency results illustrate a relatively distinct slope and intercept which arises from differences in tectonic structure and features of the earthquake sources in two areas the same process for records with epicentral distances less than 50 km is also repeated results indicate smaller standard deviations between 0 13 and 0 14 km for four time windows considering the arrangement of hazardous faults in many populated districts of iran including tehran utilization of the obtained relations is recommended for distances less than 50 km moreover the current study represents two distance dependent relations between magnitudes with p max and a p max within the initial 3 s of p wave arrivals with standard deviations of 0 42 and 0 46 magnitude units respectively

rupture behavior of a moderate earthquake mw 5 9 april 2006 and its close relation with the 2003 chengkung earthquake mw 6 8 at the southern termination of the plate boundary southeast taiwan the taiwanese orogen is the result of the active and vigorous collision between the eurasian and the philippine sea plates in this strong convergence context a one month long earthquake sequence composed of two mainshocks of magnitude 6 occurred in april 2006 in the taitung area the first mainshock t1 mobilized a structure just west to the plate boundary while the second one t2 is located on the other side in order to retrieve the exact fault geometry of t2 we inverted waveforms from stations located at local and teleseismic distances we performed a grid search on strike and dip each strike dip couple defining a geometry considering the source as a point source then as an extended source in the last case a simple average over stations misfit failed to isolate a precise geometry to overcome this problem we used a more statistical approach on the distribution of misfits to define the best geometry comparing the best model to local structures it appears the generative fault was the plate boundary that rotates from a strike pointing at n20 e north of the event to n0 e in t2 area with an identical eastward dip of 35 for this model the fault slip inversion provides a critical slip of 3 5 cm above which slip rake and rupture time are constrained with uncertainties of 29 14 and 0 47 s respectively the average slip along the rupture was 20 cm with a maximum of 46 13 cm the movement was inverse with a minor left lateral component similar to the faulting behavior of the plate boundary in addition the slip pattern of t2 is contained within the southern portion of the deepest segment of the plate boundary and at the edge of the rupture area of the 2003 chengkung earthquake mw 6 8 a large event also generated by the plate boundary but 2 5 years earlier after 1 s of aseismic spreading the rupture propagated seismically and circularly outward before being stopped by the fault bending

examination of scaling between earthquake magnitude and proposed early signals in p waveforms from very near source stations in a south african gold mine 1 we analyze near source seismograms recorded in a deep south african mine for scaling between signals early in p waveforms and the magnitude m of the events the data consist of recordings at 26 stations of 122 events with 1 5 0 implying that the final earthquake size is affected statistically by the initial rupture process if these correlations hold for larger earthquakes as suggested by other studies the early predominant period and peak displacement are useful for early warning systems

rupture process of the 2014 iquique chile earthquake in relation with the foreshock activity the rupture process of the 2014 iquique chile earthquake is inverted from teleseismic p wave data applying a novel formulation that takes into account the uncertainty of green s function which has been a major error source in waveform inversion the estimated seismic moment is 1 5 1021 nm mw 8 1 associated with a 140 km long and 140 km wide fault rupture along the plate interface the source process is characterized by unilateral rupture propagation during the first 20 s the dynamic rupture front propagated from the hypocenter to the large asperity located about 50 km southward crossing a remarkably active foreshock area at high velocity of about 3 0 km s but small and irregular seismic moment release rate our result may suggest that the 20 s long initial phase was influenced by the stress drop due to the foreshock activity near the main shock hypocenter moreover the 2 week long swarm like foreshock activity migrating roughly at 5 km day toward the main shock hypocenter and possibly associated slow slip contributed to the stress accumulation prior to the mw 8 1 megaquake the main shock initial rupture phase might have triggered the rupture of the large asperity which had large fracture energy

frequent observations of identical onsets of large and small earthquakes every gigantic earthquake begins as a tiny rock failure at almost a point followed by successive slip of the complex fault system before radiating strong shaking from a vast rupture area extending over hundreds of kilometres whether the growth process of the rupture of a large earthquake is predictable and whether it produces observable signatures different from that of smaller events1 5 are fundamental questions related to the potential for earthquake early warning and probabilistic forecasting inspired by a recent discovery that large earthquakes might have seismic waves and probably rupture processes that are almost identical to those of smaller events6 8 we show that such similarity characterized by large cross correlation is a common feature of earthquakes in the tohoku hokkaido subduction zone japan a systematic comparison of 15 years of high sensitivity seismograph records for approximately 100 000 events reveals 80 extremely similar and 390 very similar pairs of large moment magnitude m 4 5 and small m 4 0 earthquakes co located within about 100 metres an extremely high similarity is observed for pairs of subduction type earthquakes 170 of 899 large events separated by a long period of up to 15 years whereas for pairs of other types of large earthquakes only the foreshocks and aftershocks are similar this frequently occurring similarity between different sized subduction type earthquakes suggests repeated cascading rupture processes in a widespread hierarchical structure9 12 along the plate interface and indicates a specific but probabilistically limited predictability of the final size of the earthquake that is the location and a set of possible sizes of an earthquake are well predicted but its final size is not at all well constrained analysis of a dataset of high sensitivity tohoku hokkaido seismograph records shows that pairs of subduction type earthquakes of different sizes have very similar initial characteristics implying that the final size of an earthquake cannot be reliably predicted from these

scaling relationship of initiations for moderate to large earthquakes 1 we investigate the initiation sizes of earthquakes over a wide range of moderate to large events using the model of sato and kanamori which is based on griffith crack theory for a circular fault we estimate the initial crack sizes of earthquakes using high quality data recorded at close hypocentral distances taking into account the local attenuation and the dynamic stress drop of the earthquakes we estimate trigger factors and initial crack radii for 35 events in japan and taiwan with magnitudes of 3 5 to 7 9 our results show that all of the earthquakes can be explained with a small trigger factor and initial crack sizes of 12 96 m for the large range of earthquake sizes this is a small range of initial crack sizes there does not appear to be a clear scaling relationship between initial crack size and final earthquake size instead our results show that all the moderate to large earthquakes initiate with initial crack radii on the order of tens of meters

nucleation and early seismic propagation of small and large events in a crustal earthquake model 1 earthquake nucleation and early seismic propagation are studied in a two dimensional strike slip fault model with depth variable properties the fault is governed by the dieterich ruina rate and state friction law we use an efficient and rigorous numerical procedure for elastodynamic analysis of earthquake sequences on slowly loaded faults developed by lapusta et al 2000 we find that for decreasing values of the characteristic slip distance of the friction law small events appear at the transition from the locked to creeping behavior toward the bottom of the seismogenic zone small and large events have very similar nucleation phases in our simulations here by nucleation phase we mean gradually accelerating aseismic slip in a small slowly expanding zone before the breakout of the dynamic seismically detectable event moment acceleration to which velocity seismograms are proportional in early stages of seismic propagation exhibits irregular fluctuations in the form of speedups and slowdowns in the moment release rate consistently with observations as reported by ellsworth and beroza 1995 our simulations show that such irregular moment acceleration can at least in part be due to the heterogeneous stress distribution imprinted on the fault by the arrest of previous small events and by stress concentrations at the borders of creeping regions and to partial arrest of the rupture in velocity strengthening fault regions which inhibit seismic slip index terms 7209 seismology earthquake dynamics and mechanics 7260 seismology theory and modeling 3220 mathematical geophysics nonlinear dynamics 7230 seismology seismicity and seismotectonics 3230 mathematical geophysics numerical solutions 8164 tectonophysics stresses crust and lithosphere keywords earthquake nucleation phase event clustering irregular moment release stress concentrations rate and state friction earthquake sequences

segmentation of megathrust rupture zones from fore arc deformation patterns over hundreds to millions of years arauco peninsula chile 1 this work explores the control of fore arc structure on segmentation of megathrust earthquake ruptures using coastal geomorphic markers the arauco nahuelbuta region at the south central chile margin constitutes an anomalous fore arc sector in terms of topography geology and exhumation located within the overlap between the concepcion and valdivia megathrust segments this boundary however is only based on 500 years of historical records we integrate deformed marine terraces dated by cosmogenic nuclides syntectonic sediments published fission track data seismic reflection profiles and microseismicity to analyze this earthquake boundary over 10 2 10 6 years rapid exhumation of nahuelbuta s dome like core started at 4 1 2 ma coeval with inversion of the adjacent arauco basin resulting in emergence of the arauco peninsula here similarities between topography spatiotemporal trends in fission track ages pliocene pleistocene growth strata and folded marine terraces suggest that margin parallel shortening has dominated since pliocene time this shortening likely results from translation of a fore arc sliver or microplate decoupled from south america by an intra arc strike slip fault microplate collision against a buttress leads to localized uplift at arauco accrued by deep seated reverse faults as well as incipient oroclinal bending the extent of the valdivia segment which ruptured last in 1960 with an mw 9 5 event equals the inferred microplate we propose that mechanical homogeneity of the fore arc microplate delimits the valdivia segment and that a marked discontinuity in the continental basement at arauco acts as an inhomogeneous barrier controlling nucleation and propagation of 1960 type ruptures as microplate related deformation occurs since the pliocene we propose that this earthquake boundary and the extent of the valdivia segment are spatially stable seismotectonic features at million year scale

development of multiscale slip inversion method and its application to the 2004 mid niigata prefecture earthquake 1 we present a multiscale slip inversion method for earthquakes as a first attempt to analyze an initial rupture process on a small scale and a whole one on a large scale a multiscale source model is constructed by renormalizing slip rate distributions on different scales a multiscale observation equation includes a renormalized kernel matrix using the new method and employing theoretical and empirical green s functions with two small events mw 2 3 and 3 3 we analyze the 2004 mid niigata prefecture earthquake mw 6 6 following a preliminary deconvolution analysis suggesting a complexity of the initial phase the multiscale analysis reveals details of the initial stage of the rupture process the first 1 s successfully in the multiscale model the estimated source process is consistent for all scales while independent slip inversion analyses on three scales monoscale analysis result in inconsistent slip distributions with large errors the maximum slip rate is about 1 0 m s and the rupture velocity is 2 5 3 0 km s in the initial rupture process four stages of rupture growth with different rupture directivities are found the first 0 4 s with northeastward directivity from 0 6 s to 1 0 s with southward directivity until 2 0 s with northeastward directivity again and after 2 0 s with southwestward directivity these stages may represent cascading ruptures evolving into a large earthquake the image of the whole rupture process implies self similarity of the dynamic rupture process and is a breakthrough in the complete realization of earthquake source scaling

depth dependence of earthquake frequency magnitude distributions in california implications for rupture initiation statistics of earthquakes in california show linear frequency magnitude relationships in the range of m2 0 to m5 5 for various data sets assuming gutenberg richter distributions there is a systematic decrease in b value with increasing depth of earthquakes we find consistent results for various data sets from northern and southern california that both include and exclude the larger aftershock sequences we suggest that at shallow depth 0 to 6 km conditions with more heterogeneous material properties and lower lithospheric stress prevail rupture initiations are more likely to stop before growing into large earthquakes producing relatively more smaller earthquakes and consequently higher b values these ideas help to explain the depth dependent observations of foreshocks in the western united states the higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock at greater depth 9 15 km any rupture initiation is more likely to continue growing into a larger event so there are fewer foreshocks if one assumes that frequency magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake then a small m2 rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a m5 5 or larger event compared to the same small rupture initiation at 0 to 3 km

initial rupture process of microearthquakes recorded by high sampling borehole seismographs at the nojima fault central japan abstract we analyze high sampling waveforms of the initial part of p wave recorded at the 1800 m deep borehole seismographs at the nojima fault from december 1999 to may 2000 to clarify the initial rupture process of microearthquakes we select 12 events with high s n whose magnitudes range from 0 3 to 2 2 and hypocentral distances from 1 to 11 km we adopt the two different source models by sato and hirasawa 1973 and by sato and kanamori 1999 the former model by sato and hirasawa sh model generates only a ramp like onset of velocity pulse the later model by sato and kanamori sk model is able to generate a weak initial phase that is controlled by a trigger factor and the length of pre existing crack we perform the waveform inversion to estimate the optimum source parameters of each model waveforms of 5 of the 12 events are clearly reproduced by both sh model and sk model with a large trigger factor and a small length of pre existing crack the others are explained by not sh model but only sk model with a small trigger factor and a large length of the pre existing crack indicating that the weak initial phase is a nucleation phase and reflects the source process these seven events satisfy roughly a relation that a large event has a large length of the pre existing crack the final crack length is proportional to the length of the pre existing crack

empirical green s function analysis taking the next step an extension of the empirical green s function egf method is presented that involves determination of source parameters using standard egf deconvolution followed by inversion for a common attenuation parameter for a set of colocated events recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate i apply this method to recordings from the 1995 1996 ridgecrest california earthquake sequence i analyze four clusters consisting of 13 total events with magnitudes between 2 6 and 4 9 i first obtain corner frequencies which are used to infer brune stress drop estimates i obtain stress drop values of 0 3 53 mpa with all but one between 0 3 and 11 mpa with no resolved increase of stress drop with moment with the corner frequencies constrained the inferred attenuation parameters are very consistent they imply an average shear wave quality factor of approximately 20 25 for alluvial sediments within the indian wells valley although the resultant spectral fitting using corner frequency and is good the residuals are consistent among the clusters analyzed their spectral shape is similar to the the theoretical one dimensional response of a layered low velocity structure in the valley an absolute site response cannot be determined by this method because of an ambiguity between absolute response and source spectral amplitudes i show that even this subtle site response can significantly bias estimates of corner frequency and if it is ignored in an inversion for only source and path effects the multiple egf method presented in this paper is analogous to a joint inversion for source path and site effects the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates especially if data are from a single site or sites with similar site response

3 d modeling project 3rd report the two geologic models overthrust and salt dome are now finalized the acquisition phases are defined and doe laboratories have started the computations simulation for phase a is expected to be completed during the first quarter of 1995

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

triggering of the 1999 mw 7 1 hector mine earthquake by aftershocks of the 1992 mw 7 3 landers earthquake 1 there is strong observational evidence that the 1999 mw 7 1 hector mine earthquake in the mojave desert california was triggered by the nearby 1992 mw 7 3 landers earthquake many authors have proposed that the landers earthquake directly stressed the hector mine fault our model of the landers aftershock sequence however suggests there is an 85 chance that the hector mine hypocenter was actually triggered by a chain of smaller earthquakes that was initiated by the landers main shock we perform our model simulations using the monte carlo method based on the gutenberg richter relationship omori s law bath s law and assumptions that all earthquakes including aftershocks are capable of producing aftershocks and that aftershocks produce their own aftershocks at the same rate that other earthquakes do in general our simulations show that if it has been more than several days since an m 7 main shock most new aftershocks will be the result of secondary triggering these secondary aftershocks are not physically constrained to occur where the original main shock increased stress this may explain the significant fraction of aftershocks that have been found to occur in main shock stress shadows in static coulomb stress triggering studies

high amplitude seismic waves radiated from the bright spot of an earthquake abstract in the source region of a large shallow earthquake there is likely to be a small spot characterized by the production of high accelerations and a gap in the aftershocks on the seismograms of most large shallow earthquakes and on some seismograms of moderate main shocks two types of p waves may be detected the relatively low amplitude waves following phase p 1 and the predominant high frequency waves following phase p 2 the duration of the seismic waves following phase p 1 the p 1 p 2 time increases proportionately with the earthquake magnitude this fact strongly suggests that the preliminary rupture period is closely related to the radiation of the predominant high frequency seismic waves to explain the above observation the shear strain waves radiated from a moving rupture are calculated because the seismic wave velocity is generally higher than the rupture propagation velocity maximum shear strains by seismic waves usually precede the rupture front if the total shear strain which is equal to the static pre earthquake shear strain plus dynamic shear strain excited by seismic waves exceeds the critical shear strain 10 4 the secondary ruptures break out in the forward direction from the initial rupture the rupture processes of large or moderate earthquakes occur in two stages one is the initiation of rupture corresponding to phase p 1 and the other is the development of secondary ruptures triggered by seismic shear strain waves the latter process generates an earthquake bright spot which radiates high amplitude seismic waves

coastal uplift and mortality of intertidal organisms caused by the september 1985 mexico earthquakes coastal uplift associated with the great mexican earthquake of 19 september 1985 and its principal aftershock produced widespread mortality of intertidal organisms along the coast of the states of michoacan and guerrero mexico measurements of the vertical extent of mortality at ten sites provided estimates of the magnitude of the vertical component of deformation along the coast within the affected area uplift ranged from about 12 centimeters to about 1 meter and no subsidence was observed the observations are consistent with models of the tectonic deformation that results from buried slip on a shallow dipping underthrust fault

theory of time dependent rupture in the earth at a velocity x which is a well defined function of k this propagation is stable and quasi static and is referred to as subcritical crack growth we shall use the terms stable quasistatic and subcritical to mean propagation at velocities much less than the sonic velocities of the medium this behavior results from stress induced corrosion at the crack tip the principal corrodent for the present application being h20 this behavior has been firmly established in the laboratory for mode i tensile cracks in a wide variety of materials ineluding silicates and silicate glasses see cholz 1968a 1972a martin 1972 wiederhorn and bolz 1970 atkinson 1979 lawn and wilshaw 1975 knott 1973 the form of the relationship between k and x does not vary significantly with the material only the parameters in the law vary as an example we show in figure 1 data on subcritical crack growth in quartz after atkinson 1979 the empirical relationship is found to take the form