scale dependence of seismic energy to moment ratio for strike slip earthquakes in japan we analyzed four pairs of a large m w 6 and a small m w 3 5 to 4 shallow strike slip earthquakes to investigate the scale dependence of the seismic energy to moment ratio an important macroscopic parameter which reflects the basic physical process of seismic slip these earthquakes occurred in the south western part of japan and high quality close in records epicentral distance 50 km are available for both the small and large earthquakes the paired events have almost the same focal mechanism and hypocenter location we used the spectral ratio of the paired events in order to remove the effects of attenuation along the wave propagation path and the station site response we then estimated the seismic energy from the source spectra estimated from the spectral ratio the energy to moment ratio increases with the earthquake size this scale dependence is very similar to that found earlier for earthquakes in southern california

radiated energy from the mid niigata japan earthquake of october 23 2004 and its aftershocks 1 the mid niigata earthquake of october 23 2004 is a shallow reverse faulting event with mw 6 6 we analyze transverse component accelerograms of the main shock and four aftershocks mw 4 0 5 5 recorded at 29 strong motion observation stations the epicenters of the four aftershocks are located within 5 km from that of the main shock the stations are well distributed around the epicenters and their epicentral distances are between 15 and 60 km we calculate spectral ratio between records of the main shock and each of the aftershocks in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations thus obtained source spectral ratio is inconsistent with that expected from the self similar omega square model fitting omega square source spectral ratio with variable corner frequency to the observed spectral ratio radiated energy and corner frequency are estimated radiated energy from the main shock is 3 2 1014 j although energy to moment ratios for the main shock and the aftershocks are all distributed within a narrow range from 8 10 6 to 4 10 5 they definitely increase with the event size this scale dependence is quite similar to that obtained previously for strike slip events in japan the relationship between the seismic moment m0 and the corner frequency f0 is m0 f0 3 3 0 2 these results suggest a break in self similarity

acceleration source spectra anticipated for large earthquakes in northeastern north america a set of 16 large intraplate earthquakes are considered on the basis of their tectonic settings compressive focal mechanisms and shallow focal depths as possible analogs for large earthquakes that may be anticipated to occur in northeastern north america the earthquakes range in seismic moment from 5 1023 to 3 1026 dyne cm and include the mainshocks and largest aftershocks of the 1982 miramichi canada the 1985 to 1988 nahanni canada and the 1988 tennant creek australia earthquake sequences the teleseismic recordings of these earthquakes are spectrally analyzed by correcting the logarithmically averaged acceleration spectra for the frequency dependent effects of attenuation and interference of the depth and direct phases the resulting acceleration source spectra are generally flat at high frequencies the mainshock spectra exhibit intermediate spectral falloffs that is u where 1 over frequencies that characteristically extend from 0 1 to 0 5 hz in contrast the largest aftershocks of the three sequences named above exhibit 2 spectral shapes the high frequency source spectral levels increase with seismic moment approximately as ru m 1 3 the 1988 saguenay canada earthquake which occurred significantly deeper than the other earthquakes exhibits an anomalous spectral shape combining the teleseismic data with strong motion recordings indicates that the intermediate spectral falloff for this earthquake extends from 0 2 to 3 hz the spectral amplitude at 3 hz is a factor of 3 higher than the amplitude anticipated for an earthquake of this size from the other 15 earthquakes

long range triggered earthquakes that continue after the wave train passes 1 large earthquakes can trigger distant earthquakes in geothermal areas some triggered earthquakes happen while the surface waves pass through a site but others occur hours or even days later does this prolonged seismicity require a special mechanism to store the stress from the seismic waves that differs from ordinary aftershock mechanisms these questions have driven studies of long range triggering since the phenomenon s discovery here i attempt to answer the questions by examining the statistics of triggered sequences two separate observations are consistent with the prolonged sequences being simply local aftershocks of earthquakes triggered early in the wave train first the sequences obey omori s law over both short 1 hour and longer 5 day time intervals secondly the number of observed triggered earthquakes in the first hour after the wave train can be predicted from the number of earthquakes triggered during the wave train even the very vigorous 10 day triggering at long valley from the 1992 landers mw 7 3 earthquakes can be interpreted as the aftershocks of either a local m 4 1 earthquake or an equivalent combination of several smaller mainshocks therefore long range triggering does not need to include a mechanism to produce sustained stresses other than the process that generates aftershocks of the earthquakes that occur while the wave train is passing

triggered surface slips in the salton trough associated with the 1999 hector mine california earthquake surface fracturing occurred along the southern san andreas superstition hills and imperial faults in association with the 16 october 1999 mw 7 1 hector mine earthquake making this at least the eighth time in the past 31 years that a regional earthquake has triggered slip along faults in the salton trough fractures associated with the event formed discontinuous breaks over a 39 km long stretch of the san andreas fault from the mecca hills southeastward to salt creek and durmid hill a distance from the epicenter of 107 to 139 km sense of slip was right lateral only locally was there a minor 1 mm vertical component of slip dextral slip ranged from 1 to 13 mm maximum slip values in 1999 and earlier triggered slips are most common in the central mecca hills field evidence indicates a transient opening as the hector mine seismic waves passed the southern san andreas fault comparison of nearby strong motion records indicates several periods of relative opening with passage of the hector mine seismic wave a similar process may have contributed to the field evidence of a transient opening slip on the superstition hills fault extended at least 9 km at a distance from the hector mine epicenter of about 188 to 196 km this length of slip is a minimum value because we saw fresh surface breakage extending farther northwest than our measurement sites sense of slip was right lateral locally there was a minor 1 mm vertical component of slip dextral slip ranged from 1 to 18 mm with the largest amounts found distributed or skewed away from the hector mine earthquake source slip triggered on the superstition hills fault commonly is skewed away from the earthquake source most notably in 1968 1979 and 1999 surface slip on the imperial fault and within the imperial valley extended about 22 km representing a distance from the hector mine epicenter of about 204 to 226 km sense of slip dominantly was right lateral the right lateral component of slip ranged from 1 to 19 mm locally there was a minor 1 2 mm vertical component of slip larger proportions of vertical slip up to 10 mm occurred in mesquite basin where scarps indicate long term oblique slip motion for this part of the imperial fault slip triggered on the imperial fault appears randomly distributed relative to location along the fault and source direction multiple surface slips both primary and triggered slip indicate that slip repeatedly is small at locations of structural complexity

earthquake stress via event ratio levels application to the 2011 and 2016 oklahoma seismic sequences we develop a new methodology for determining earthquake stress drop and apparent stress values via spectral ratio asymptotic levels with sufficient bandwidth the stress ratio for a pair of events can be directly related to these low and high frequency levels this avoids the need to assume a particular spectral model and derive stress drop from cubed corner frequency measures the method can be applied to spectral ratios for any pair of closely related earthquakes and is particularly well suited for coda envelope methods that provide good azimuthally averaged point source measures we apply the new method to the 2011 prague and 2016 pawnee earthquake sequences in oklahoma the sequences show stress scaling with size and depth with the largest events having apparent stress levels near 1 mpa and smaller and or shallower events having systematically lower stress values

ground motion variability and implementation of a probabilistic deterministic hazard method abstract a key step in probabilistic seismic hazard assessment is the prediction of expected ground motions produced by the seismic sources most probabilistic studies use a ground motion prediction model to perform this estimation the present study aims at testing the use of simulations in the probabilistic analysis instead of ground motion models the method used is the empirical green s function method of kohrs sansorny et al 2005 which takes into account the characteristics of the source propagation paths and site effects the recording of only one small event is needed for simulating a larger event the small events considered here consist of aftershocks from the m 6 4 les saintes earthquake which struck the guadeloupe archipelago french antilles in 2004 the variability of the simulated ground motions is studied in detail at the sites of the french permanent accelerometric array intrinsic variability is quantified ground motions follow lognormal distributions with standard deviations between 0 05 and 0 18 log units depending on the spectral frequency one input parameter bearing large uncertainties is the ratio of the stress drop of the target event to the small event therefore overall sigma values and medians are recomputed varying stress drop ratio values between 1 and 15 sigma values increase but remain in general lower or equal to the sigma values of current ground motion prediction models a simple application of this hybrid deterministic probabilistic method is carried out at several sites in guadeloupe for the estimation of the hazard posed by an m 6 4 occurring in the rupture zone of the les saintes event

source parameters for small events associated with the 1986 north palm springs california earthquake determined using empirical green functions using small events as empirical green functions which include path site and instrument effects on the p waveforms source parameters were estimated for 25 ml 3 4 to 4 4 events associated with the 1986 north palm springs earthquake the static stress drops ranged from 3 to 80 bars for moments of 0 7 to 11 1021 dyne cm there was a spatial pattern to the stress drops of the aftershocks which showed increasing values along the fault plane toward the northwest compared to relatively low values near the hypocenter of the mainshock the highest values were outside the main area of slip and are believed to reflect a loaded area of the fault that still has an higher level of stress which was not released during the main shock the relatively high stress drop of a preshock in 1983 located close to the hypocenter of the main shock is also interpreted as evidence that stress drops of magnitude 3 and 4 events can be used as indicators of the stress level in a particular area

a new spectral ratio method using narrow band coda envelopes evidence for non self similarity in the hector mine sequence 1 the use of local and regional s wave coda is shown to provide stable amplitude ratios that better constrains source differences between event pairs we first compared amplitude ratio performance between local and near regional s and coda waves in the san francisco bay region for moderate sized events then applied the coda spectral ratio method to the 1999 hector mine mainshock and its larger aftershocks we find 1 average amplitude ratio standard deviations using coda are 0 05 to 0 12 roughly a factor of 3 smaller than direct s waves for 0 2 f 15 0 hz 2 coda spectral ratios for the mw 7 0 hector mine earthquake and its aftershocks show a clear departure from self similarity consistent with other studies using the same datasets and 3 event pairs green s function and target events can be separated by 25 km for coda amplitudes without any appreciable degradation in sharp contrast to direct waves

tomography of the 1995 kobe earthquake area comparison of finite frequency and ray approaches summary we determined a detailed 3 d crustal model in the 1995 kobe earthquake m 7 2 area in southwest japan using both finite frequency and ray tomography methods our finite frequency tomography technique is based on the single scattering theory the finite frequency sensitivity kernel derived in this study reflects correctly the sensitivity of the heterogeneity off the geometrical ray path and the existence of fresnel volume and the kernel depends on the dominant frequency of the observed wave the dominant frequency is estimated directly from the earthquake magnitude based on a relation that is obtained by regressively analyzing the displacement spectra of 20 earthquakes in the study area we used 141 118 p wave and 133 648 s wave high quality arrival time data from 2813 kobe aftershocks and 3140 other local earthquakes during 1995 2010 the tomographic images obtained with the finite frequency and ray tomography methods show a high level of similarity which is verified quantitatively by adopting the structural similarity index our results show that the kobe main shock hypocentre is located in a distinctive zone characterized by a high poisson s ratio and a low product vp vs of p and s wave velocities which is interpreted as a fluid filled fractured rock matrix that may have triggered the 1995 kobe earthquake

holocene pool formation in oligotrophic fens from boreal quebec in northeastern canada at the biogeographical limit between the boreal and the subarctic domain in northeastern canada peatlands are mainly oligotrophic fens characterized by a dominance of aquatic microforms such as pools and wet hollows these peatlands present similar features as the appa mires in scandinavia they show evidence for recent water table rise indicated by tree mortality physical degradation of strings and pool expansion this study aims to evaluate the timing of pool inception and their impact on the long term dynamics of these microforms within two patterned oligotrophic fens in the laforge region northern quebec plant macrofossil and testate amoeba analyses from sediment underneath pools were used along with radiocarbon dating to reconstruct peatland pool dynamics over the holocene our data indicate that wet hollows or shallow pools developed at minimal ages between 4200 and 2500 cal a bp pool initiation in the peatlands of the laforge region corresponds to the climate shift toward cooler and wetter

high frequency borehole seismograms recorded in the san jcinto fault zone southern california part 2 attenuation and site effects we examine surface and downhole p and s wave spectra from local earthquakes recorded at two borehole seismometer arrays knw bh and pfo bh installed in the southern california batholith region of the san jacinto fault zone by the u s geological survey to assess the influence of the weathered layer on the spectral content of high frequency 2 to 200 hz seismic signals earthquake signals recorded downhole at both sites show significantly improved seismic bandwidth due to both a reduction in ambient noise levels and especially to dramatically increased levels of high frequency signal significant seismic signal is observed up to approximately 190 hz for p waves at knw bh stacked spectral ratios from these signals indicate that the highly weathered near surface between 0 and 150 m at knw bh and pfo bh exerts a much larger influence on seismic signals than deeper between 150 and 300 m material modeling of uphole downhole spectral ratio data suggests q 6 5 and q 9 between 0 and 150 m increasing to q 27 and q 26 between 150 and 300 m an outcrop mounted anza network station deployed approximately 0 4 km from knw bh displays roughly similar high frequency content to the knw bh downhole sensors but it exhibits spectra that are significantly colored by directional resonances low q and low velocity near surface material forms a lossy boundary layer at these borehole sites that is advantageous to the high frequency downhole environment not only are noise levels reduced but reflections from the surface and near surface are greatly attenuated as a result high frequency recordings from below the weathered zone more nearly resemble those recorded in a whole space than would otherwise be expected

the dynamics of the formation and development of hollows in raised bogs in estonia hollow ridge microrelief is a typical surface pattern of raised bogs in the boreal zone it may play an essential role in maintaining the balance between bog ecosystems and changing environmental conditions the data of the location depth approximate age area and length width ratio of 225 hollows and reconstructions of the shape dynamics of eight hollows from six bogs in estonia were used to study the dynamics of the formation and development of hollows the approximate age of hollows was established according to their depth and peat age isolines calculated by the bulk density method and based on radiocarbon dating the first period of intensive hollow formation in the bogs studied occurred 3200 2800 years ago the second still continuing period of intensive hollow formation started c 1800 years ago no correlation was detected between the temporal distribution of hollows on different profiles within one bog or in different bogs therefore the formation of the hollows could have been initiated by ext

development history and carbon accumulation of a slope bog in oceanic british columbia canada palaeoecological techniques and radiocarbon datings were used to reconstruct the initiation and development of a sloping bog system near prince rupert british columbia canada peat initiation began around 12 000 cal bp possibly as a result of a cool wet climate prior to the insolation maximum a picea sitchensis tsuga heterophylla alnus minerotrophic wet fern forest occupied the study site from 9300 to 8300 cal bp between 8300 and 7500 cal bp cooler and wetter climatic conditions promoted increased organic matter accumulation and paludification by sphagnum species subsequent lateral expansion has been very slow in the later holocene paludification resulted in a shift to a scrubby less productive pinus contorta t heterophylla cupressaceae cyperaceae bog woodland around approximately 7500 3000 cal bp the modern cupressaceae pinus contorta t heterophylla ericaceae cyperaceae mire was well established by 2000 cal bp and a modern oceanic climate was predominant the initiation and development

thermal regime of peatlands in subarctic eastern canada temperatures were measured to 2 m depth at six peatland sites in the schefferville area northern quebec from july 1982 to september 1984 the sites varied in their plant cover type of peat and

empirical green s function study of the january 17 1994 northridge california earthquake the january 17 1994 northridge main shock was analyzed using an empirical green s function approach to estimate the spatial and temporal distribution of fault slip far field source time functions obtained from seismograms recorded by the berkeley digital seismic network bdsn and terrascope stations reveal the distributed nature of the source and the presence of a second large subevent the location of the fault beneath the san fernando valley as well as the updip directivity of the rupture contributed to the locally heavy damage due to this earthquake

attenuation and source properties at the coso geothermal area california we use a multiple empirical green s function method to determine source properties of small m 0 4 to 1 3 earthquakes and p and s wave attenuation at the coso geothermal field california source properties of a previously identified set of clustered events from the coso geothermal region are first analyzed using an empirical green s function egf method stress drop values of at least 0 5 1 mpa are inferred for all of the events in many cases the corner frequency is outside the usable bandwidth and the stress drop can only be constrained as being higher than 3 mpa p and s wave stress drop estimates are identical to the resolution limits of the data these results are indistinguishable from numerous egf studies of m 2 5 earthquakes suggesting a similarity in rupture processes that extends to events that are both tiny and induced providing further support for byerlee s law whole path q estimates for p and s waves are determined using the multiple empirical green s function megf method of hough 1997 whereby spectra from clusters of colocated events at a given station are inverted for a single attenuation parameter with source parameters constrained from egf analysis the estimates which we infer to be resolved to within 0 01 sec or better exhibit almost as much scatter as a function of hypocentral distance as do values from previous single spectrum studies for which much higher uncertainties in individual estimates are expected the variability in estimates determined here therefore suggests real lateral variability in q structure although the ray path coverage is too sparse to yield a complete three dimensional attenuation tomographic image we invert the inferred value for three dimensional structure using a damped least squares method and the results do reveal significant lateral variability in q structure the inferred attenuation variability corresponds to the heat flow variations within the geothermal region a central low q region corresponds well with the central high heat flow region additional detailed structure is also suggested

remotely triggered seismicity in continental china following the 2008 mw 7 9 wenchuan earthquake we perform a systematic search of remotely triggered seismicity in con tinental china following the 2008 mw 7 9 wenchuan earthquake we visually identify earthquakes as impulsive seismic energy with clear p and s arrivals on 5 hz high pass filtered three component velocity seismograms 1 hr before and after the wenchuan earthquake out of the 271 stations in the updated chinese digital seismic network csn 17 stations show statistically significant seismicity increase with statistic values larger than 2 following the wenchuan earthquake these include 11 stations in the north china block which is seismically active and is in the rupture propagation direction of the wenchuan earthquake three stations along the coastal lines in the relatively stable south china block one station near the haiyuan fault zone in north west china and two stations near the tanlu fault zone and the longgang volcano in northeast china these observations suggest that dynamic triggering in intraplate regions tends to occur near active faults that have ruptured in historic times and in the rupture propagation directions of the mainshock however it is worth noting that many sites that satisfy the criteria are not triggered suggesting that these conditions would help but are not sufficient enough to guarantee remote triggering in intraplate regions the tectonic environments near the sites with clear triggered activity range from transpressional to tranextentional and most regions are not associated with active geothermal or volcanic activity indicating that dynamic triggering could occur in a wide range of tectonic environments online material tables of station information and measured parameters and two supplementary figures showing locally triggered earthquakes

southern surface rupture associated with the 1992 m7 4 landers earthquake did it all happen during the mainshock approximately three minutes after the magnitude 7 4 landers mainshock on 28 june 1992 a m5 7 aftershock occurred south of the mainshock epicenter with a location of 34 7 65 n 116 23 82 w this aftershock was recorded on an array of portable digital seismic instruments deployed in morongo valley 21 km southwest of the event although peak accelerations are found to differ by approximately 50 at stations with similar general site conditions within 500 m of each other there is good coherence of arrivals across the array for frequencies 1 hz we use the recordings to determine the apparent phase velocity and azimuth of propagation across the array and show that the event clearly ruptured to the south with a rupture length of 11 km and a rupture velocity of approximately 3 0 km s our results suggest that at least some of the mapped surface rupture south of the town of yucca valley 11 km in extent maximum displacement of 20 cm may have been associated with this aftershock if this is the case then the fault that produced the southern end of the landers mainshock the johnson valley fault need not continue at depth across the active left lateral east west trending pinto mountain fault

source parameters of loma prieta aftershocks and wave propagation characteristics along the san francisco peninsula from a joint inversion of digital seismograms abstract aftershock recordings from 10 digital seismographs deployed along the axis of the san francisco peninsula from the epicenter of the 18 october 1989 loma prieta earthquake to san francisco provide the data for a joint inversion for source wave propagation and site effects the inversion procedure is a least squares method using the singular value decomposition algorithm and is done in two parts the first solves only for the source and attenuation terms for all events and the second projects the residuals from the first inversion onto the site terms the coefficient of geometrical spreading is solved for as part of the model of attenuation residuals plotted versus distance and frequency provide a check on the appropriateness of the attenuation model the earthquakes are all located near the san andreas fault mostly in the aftershock zone of the loma prieta mainshock but some area near daly city on the peninsula the data set provided by geos recorders consists of 148 digital seismograms for 33 events from 10 sites that form a linear profile from the epicentral region to the city of san francisco a distance of approximately 100 km strong motion accelerograms are also available for the larger events body wave spectra are fit surprisingly well by our model especially at distances beyond about 20 km where differences due to radiation pattern effects and changes in angle of incidence become less important results from the inversion show that estimates of moment are only 1 higher for the p waves compared to the s waves apparently there are no major biases in the estimates as each is determined independently of the other p wave corner frequencies are 1 5 times higher than s wave corner frequencies on average stress drops with an average of 176 bars for events that range in magnitude from 1 7 to 4 2 are higher than those found in previous studies where site and path were not explicitly taken into account the exponents of geometrical spreading are very close to one 1 019 for p waves and 1 017 for s waves for this data set which extends to about 100 km the whole path q assumed to be frequency independent was about 800 for both p and s waves specifically 790 for p waves and 830 for s waves the average p wave attenuation at all sites is quantified by a t of 0 020 sec which compares to 0 03 sec for s waves t determined for each site range from a low of 0 008 sec at san bruno mountain a hard rock site to a high of 0 065 sec at corralitos in the epicentral area residuals of the model fits which are distance dependent show larger amplitudes near the epicenter but fall off with a minimum at about 30 km where amplitudes are about 30 to 60 lower than average at distances farther than 30 km amplitudes rise out to the limit of the data at about 105 km where amplitudes are about average at frequencies less than 10 hz but are slightly above average for higher frequencies the location of this low in amplitude can be explained as the boundary between the amplitude decay of direct arrivals and the emergence of wide angle reflections from the lower crust and moho which increase in amplitude beyond 30 km these amplitudes correlate with damage patterns from the mainshock as less damage was observed along the peninsula but appeared to increase towards san francisco even when damage in the marina and china basin districts of san francisco are not included in the damage census

seismicity rate changes in the salton sea geothermal field and the san jacinto fault zone after the 2010 mw 7 2 el mayor cucapah earthquake

aftershocks and triggered events of the great 1906 california earthquake the san andreas fault is the longest fault in california and one of the longest strike slip faults in the world yet little is known about the aftershocks following the most recent great event on the san andreas the m w 7 8 san francisco earthquake on 18 april 1906 we conducted a study to locate and to estimate magnitudes for the largest aftershocks and triggered events of this earthquake we examined existing catalogs and historical documents for the period april 1906 to december 1907 compiling data on the first 20 months of the aftershock sequence we grouped felt reports temporally and assigned modified mercalli intensities for the larger events based on the descriptions judged to be the most reliable for onshore and near shore events a grid search algorithm derived from empirical analysis of modern earthquakes was used to find the epicentral location and magnitude most consistent with the assigned intensities for one event identified as far offshore the event s intensity distribution was compared with those of modern events in order to constrain the event s location and magnitude the largest aftershock within the study period an m 6 7 event occurred 100 km west of eureka on 23 april 1906 although not within our study period another m 6 7 aftershock occurred near cape mendocino on 28 october 1909 other significant aftershocks included an m 5 6 event near san juan bautista on 17 may 1906 and an m 6 3 event near shelter cove on 11 august 1907 an m 4 9 aftershock occurred on the creeping segment of the san andreas fault southeast of the mainshock rupture on 6 july 1906 the 1906 san francisco earthquake also triggered events in southern california including separate events in or near the imperial valley the pomona valley and santa monica bay in western nevada in southern central oregon and in western arizona all within 2 days of the mainshock of these triggered events the largest were an m 6 1 earthquake near brawley and an m 5 0 event under or near santa monica bay 11 3 and 31 3 hr after the san francisco mainshock respectively the western arizona event is inferred to have been triggered dynamically in general the largest aftershocks occurred at the ends of the 1906 rupture or away from the rupture entirely very few significant aftershocks occurred along the mainshock rupture itself the total number of large aftershocks was less than predicted by a generic model based on typical california mainshock aftershock statistics and the 1906 sequence appears to have decayed more slowly than average california sequences similarities can be drawn between the 1906 aftershock sequence and that of the 1857 m w 7 9 san andreas fault earthquake

the seismic spectrum radiated energy and the savage and wood inequality for complex earthquakes abstract we have integrated velocity squared spectra in order to determine the seismic energy radiated during fault rupture the high frequency spectral fall off and the shape of the spectrum at the corner frequency are critical to the energy calculation high frequency spectral fall offs of 2 beyond the corner frequency in a brune 1970 source model return radiated energies approximately equal to that of an orowan 1960 type fault failure where the final stress level is equal to the dynamic frictional stress any spectra with an extended intermediate slope of 1 would therefore result in higher radiated energies savage and wood 1971 proposed a model in which the final stress level was less than the dynamic stress level and that this was the result of overshoot they based their model on the observation that the ratio of twice the apparent stress to the stress drop was typically around 0 3 we show that for such a ratio to exist high frequency spectral fall offs of 3 would be required composite spectra have been constructed for several moderate to large earthquakes these spectra have been compared to that predicted by the haskell 1966 model and velocity squared spectra have been integrated to determine the radiated energy in all cases this ratio twice the apparent stress to the stress drop is greater than or equal to one violating the savage and wood 1971 inequality and provides evidence against overshoot as a source model

empirical green s function analysis of recent moderate events in california i use seismic data from portable digital stations and the broadband terrascope network in southern california to investigate radiated earthquake source spectra and discuss the results in light of previous studies on both static stress drop and apparent stress applying the empirical green s function egf method to two sets of m 4 6 1 events i obtain deconvolved source spectra estimates and corner frequencies the results are consistent with an 2 source model and constant brune stress drop however consideration of the raw spectral shapes of the largest events provides evidence for a high frequency decay more shallow than 2 the intermediate f 1 slope cannot be explained plausibly with attenuation or site effects and is qualitatively consistent with a model incorporating directivity effects and a fractional stress drop rupture process as suggested by haddon 1996 however the results obtained in this study are not consistent with the model of haddon 1996 in that the intermediate slope is not revealed with egf analysis this could reflect either bandwidth limitations inherent in egf analysis or perhaps a rupture process that is not self similar i show that a model with an intermediate spectral decay can also reconcile the apparent discrepancy between the scaling of static stress drop and that of apparent stress drop for moderate to large events

analysis of broadband records from the 28 june 1992 big bear earthquake evidence of a multiple event source the 28 june 1992 big bear earthquake occurred at 15 05 21 gmt and is considered to be an aftershock of the earlier m w 7 3 landers earthquake from overall aftershock locations and long period focal studies rupture is generally assumed to have propagated northeast no surface rupture was found however and the mainshock locations determined from both strong motion and terrascope data are mutually consistent and do not lie on the assumed fault plane further directivity analysis of records from the terrascope array suggests significant short and long period energy propagating northwest along the presumed antithetic fault plane this observation is supported by significant early aftershocks distributed along both the presumed rupture plane and the antithetic plane to the northwest an empirical green s function egf approach using both the m w 5 2 28 june 1992 14 43 gmt foreshock and the m w 5 0 17 august 1992 aftershock produces consistent results and suggests that the big bear event comprised at least two substantial subevents from the egf results we infer that the second and possibly a third subevent occurred on the presumed northeast striking mainshock rupture surface but that significant moment release occurred on the antithetic northwest striking surface we present results from line source fault modeling of broadband displacement recordings of the big bear mainshock which indicate that a two fault event is necessary to produce the observed waveforms the limitations imposed by the mainshock location and directivity analysis require that the initial rupture be towards the northwest striking 320 this was followed approximately 4 sec later by bilateral rupture along a northeast southwest fault that strikes 50 east of north

site resonance from strong ground motions at lucerne california during the 1992 landers mainshock analog station luc near lucerne california recorded strong motions from the nearby 1 25 km fault rupture during the 28 june 1992 landers mainshock the records illustrate general issues that can arise at near field stations in the area of the station weathered granite regolith with 400 m s s wave velocity overlies intact granite with 3000 m s s wave velocity a strongly reverberating signal persisted for several seconds after near field velocity pulse passed recovery of the vertical record in digital form provided calibration of resonant site properties and qualitative separation of site and source effects the dominant signal on the vertical spectrum arises from vertically reverberating p waves in an 13 5 m thick layer horizontal spectra marginally resolve the analogous resonance for vertical s waves and coupling of vertical p waves into horizontal motion here resonant amplification of a broad high frequency band 5 40 hz by a factor of a few over lower frequencies sufficed to dominate acceleration records and to make velocity records jittery conversely the amplitude damping times of these resonances are much less than 1 s indicating that the time domain decay of the acceleration signal over 8 s is an incident wave effect overall the raw seismograms represent incident incoming high frequency 5 40 hz signals but poorly resolved directional effects preclude straightforward determination of the incident body waves

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

near surface velocities and attenuation at two boreholes near anza california from logging data to investigate near surface site effects in granite rock we drilled 300 m deep boreholes at two sites which are collocated with stations from the digital array at anza california the first borehole was sited at station knw keenwild fire station which is located along a ridge line about 8 7 km east of the san jacinto fault zone station pfo pinon flat observatory chosen for the second site is another 6 km further to the east of station knw and is located on a gently sloping hillside we logged each borehole for p and s wave velocities as well as for crack density and orientation p waves were generated by striking a plate with a hammer at the surface a tool consisting of weighted anvils driven by compressed air against end plates along a 3 5 m beam was used to generate shear waves signals were recorded downhole with a three component sensor package at 2 5 m intervals from the surface to 50 m depth and at 5 m intervals from 50 m depth to the bottom of the hole velocities were determined by differencing the measured arrival times of first arrivals or peaks over each interval in depth travel times were computed for the first breaks at shallow depths however below about 100 m depth times were computed for the first peaks rather than for first breaks since the first arrival was no longer clearly distinguishable the knw site yielded a shear velocity of 1 9 km sec by only 30 m in depth and reached close to 2 6 km sec at the bottom of the hole p wave velocities at knw were also high at 5 4 km sec starting at 120 m depth the pfo site had similar but slightly higher shear wave velocities the bottom hole shear wave velocity reached 3 0 km sec and the p wave velocity was 5 4 km sec shear wave attenuation was computed using both the pulse rise time and spectral ratio methods at station knw attenuation was significant only in an interval between 17 5 and approximately 40 m in depth over the top 50 m attenuation corresponding to a q of about 8 was obtained a total t of 0 004 sec was measured for this interval pulse rise times also increased rapidly in this zone the spectral ratio data for station pfo yields two peaks in attenuation above 50 m similar to the attenuation found for station knw the peak in attenuation corresponds to a q of about 11 averaged over the top 50 m spectra of the seismic pulses produced by the hammer give good signal between 20 to 80 hz significant motion perpendicular to the polarizations of the first shear wave arrival was recorded within a few meters of the surface apparently the rock structure is sufficiently complicated that body waves are being converted sh to sv at oblique incidence very close to the surface the presence of these elliptical particle motions within a mere few m of the pure shear wave source suggests that the detection of polarizations perpendicular to the main shear arrival at a single location at the surface is not by itself a good method for detecting shearwave splitting within the upper few tens of kilometers of the earth s crust crack densities and orientations were determined from televiewer records these records showed cracks with a preferred direction at station knw and of a greater density than at station pfo at station pfo crack densities were smaller and more diffuse in orientation

simulating strong motions of large earthquakes using recordings of small earthquakes the loma prieta mainshock as a test case abstract a simple method is developed for predicting ground motions for future large earthquakes for specific sites by summing and filtering recordings of adjacent small earthquakes this method is tested by simulating strong motion records for the loma prieta earthquake m 7 0 using aftershocks m 3 7 to 4 0 recorded at the same sites i use an asperity rupture model where the rms stress drop averaged over the fault plane is constant with moment the observed spectra indicate that stress drop remains constant from the m 3 aftershocks up to the m 7 mainshock about six orders of magnitude in seismic moment each simulation sums the seismogram of one aftershock with time delays appropriate for propagating rupture and incorporates directivity and site response the simulation scales the spectrum in accordance with a constant stress drop 2 source model in this procedure the high frequency energy of the aftershock sum above the corner frequency of the aftershock is not reduced when it is convolved with the mainshock slip velocity function unlike most previous methods of summation for most cases the spectra 0 6 to 20 hz peak accelerations and durations of the simulated mainshock records are in good agreement with the observed strong motion records even though only one aftershock waveform was used in each simulation this agreement indicates that the response of these soil sites is essentially linear for accelerations up to about 0 3 g the summed aftershock records display the same site dependent values of f max as the mainshock records implying that f max is a site effect rather than a property of the mainshock rupture process

comprehensive analysis of earthquake source spectra and swarms in the salton trough california 1 we study earthquakes within california s salton trough from 1981 to 2009 from a precisely relocated catalog we process the seismic waveforms to isolate source spectra station spectra and travel time dependent spectra the results suggest an average p wave q of 340 agreeing with previous results indicating relatively high attenuation in the salton trough stress drops estimated from the source spectra using an empirical green s function egf method reveal large scatter among individual events but a low median stress drop of 0 56 mpa for the region the distribution of stress drop after applying a spatial median filter indicates lower stress drops near geothermal sites we explore the relationships between seismicity stress drops and geothermal injection activities seismicity within the salton trough shows strong spatial clustering with 20 distinct earthquake swarms with at least 50 events they can be separated into early mmax and late mmax groups based on the normalized occurrence time of their largest event these swarms generally have a low skew value of moment release history ranging from 9 to 3 0 the major temporal difference between the two groups is the excess of seismicity and an inverse power law increase of seismicity before the largest event for the late mmax group all swarms exhibit spatial migration of seismicity at a statistical significance greater than 85 a weighted l1 norm inversion of linear migration parameters yields migration velocities from 0 008 to 0 8 km hour to explore the influence of fluid injection in geothermal sites we also model the migration behavior with the diffusion equation and obtain a hydraulic diffusion coefficient of approximately 0 25 m2 s for the salton sea geothermal site which is within the range of expected values for a typical geothermal reservoir the swarms with migration velocities over 0 1 km hour cannot be explained by the diffusion curve rather their velocity is consistent with the propagation velocity of creep and slow slip events these variations in migration behavior allow us to distinguish among different driving processes

earthquake source spectra in eastern north america abstract a new model for average earthquake s wave source spectra in eastern north america ena is derived the model is consistent with fundamental elasto dynamic principles as well as the familiar spectral scaling laws appropriate to sources having geometrical and dynamical similarity observed characteristics of s wave spectra in ena are fully explained as simple consequences of directivity effects entailed by the classical crack rupture model kostrov 1964 madariaga 1976 with normal effective stresses of the order of 100 bars and fractional stress drop brune 1970 abnormally high stress drops are not required recognition of the fundamental role of directivity explains most features of observed data that are currently interpreted as anomalous among other things neglect of such effects is shown to be responsible for the conclusion by boatwright and choy 1992 and boore and atkinson 1992 that high frequency spectral levels for the magnitude 6 saguenay earthquake of 1988 are anomalously large other important implications of the new model are that some previously inferred systematic variations in brune stress drop with magnitude are simply artifacts of the invalid use of the standard brune 1970 1971 model assumption and that current estimates of q in ena which depend on this assumption are likely to be significantly too large for high frequencies associated uncertainties allow the possibility that effective stress does not vary significantly with magnitude for earthquakes having magnitudes in the range of 4 to 7 the new model suggests that some currently favored source spectra may under estimate spectral amplitudes of future larger earthquakes in ena by as much as a factor of 6 for some frequencies the proposed new spectra are practically identical with those of the brune standard model for an effective stress of 100 bars for frequencies up to about twice the brune corner frequency but then increase to values 3 times larger over a range of about 4 in frequency as such the high frequency spectral levels are equivalent to standard brune model values for earthquakes of one full magnitude unit larger with consequent important implications for seismic hazard estimates in the region

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

observational constraints on earthquake source scaling understanding the limits in resolution abstract i examine the resolution of the type of stress drop estimates that have been used to place observational constraints on the scaling of earthquake source processes i first show that apparent stress and brune stress drop are equivalent to within a constant given any source spectral decay between 1 5 and 3 i e any plausible value and so consistent scaling is expected for the two estimates i then discuss the resolution and scaling of brune stress drop estimates in the context of empirical green s function results from recent earthquake sequences including the 1992 joshua tree california mainshock and its aftershocks i show that no definitive scaling of stress drop with moment is revealed over the moment range 1019 1025 within this sequence however there is a tendency for moderate sized m 4 5 events to be characterized by high stress drops however well resolved results for recent m 6 events are inconsistent with any extrapolated stress increase with moment for the aftershocks focusing on corner frequency estimates for smaller m

source parameters of small earthquakes recorded at 2 5 km depth cajon pass southern california implications for earthquake scaling a 2 5 km deep triaxial seismometer at cajon pass in southern california has recorded several hundred earthquakes ml4 0 occurring within the san andreas fault system at 2 5 km seismic background noise is below amplifier sensitivity and the 2 250 hz spectral range of recorded seismic motion is wider and higher than that of most natural event catalogs compared with downhole recorded motion seismic amplitudes at the surface are amplified below 10 hz and severely attenuated above 30 hz we estimate that qs is at least 1000 for wave motion at 2 5 km and below and qp is over 2000 the range of source dimensions in the downhole recorded catalog is 10 m to 70 m ml 2 0 mo 108 nm to ml 2 7 mo 1013 nm the plot of log source radius vs log moment has a straight line trend compatible with earthquake scaling at constant stress drop inferred stress drops are scattered between 1 and 500 bars there is no evidence in the catalog for the proposed minimum source dimension at 100 m when the cajon pass borehole catalog containing some of the smallest recorded natural earthquakes is combined with 800 larger events from previous studies the moment radius trend suggests that natural earthquakes are self similar over a magnitude range m 2 to 8 we suggest that inferences of minimum source dimension are more likely due to bias in bandlimited individual catalogs than to properties of the seismic crust

high frequency directivity effect for an mw 4 1 earthquake widely felt by the population in southeastern france abstract we document a moderate earthquake in the french alps 26 february 2012 m w 4 1 that has been much more distinctly felt south of the event than north of it this discrepancy was especially clear in the two large cities of nice and grenoble both situated at 100 km from the epicenter this observation was confirmed by ground motion measurements that were eight times larger in one city than in the other one for the same site conditions using a time domain deconvolution between the broadband recordings of the mainshock and an aftershock used as empirical green s functions we show that the rupture process of this event had a strong directivity effect toward a direction of n155 5 on an 2 km long fault detectable only at frequencies higher than 1 hz the fault size and direction are in good accordance with the location of the aftershocks despite the various possible contributions leading to high frequency amplification we show here that this simple directivity effect controlled the intensity felt by the population and the acceleration measured in the cities

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

the egf method for dissimilar focal mechanisms the athens 1999 earthquake abstract the empirical green s function method egf is innovated to examine the rupture nucleation and propagation during the disastrous athens earthquake of september 7 1999 ml 5 4 waveforms recorded at seven regional broadband stations are studied one of the two strongest aftershocks ml 4 was selected as the egf but its focal mechanism differs from the mainshock mechanism therefore the paper suggests an innovation of the classical egf method the assumption of the similarity of the mainshock and aftershock focal mechanisms is relaxed as follows the mainshock is modeled by an egf like method using synthetic weak events computed by discrete wave number method dw two times once with the focal mechanism of the mainshock and again with the assumed focal mechanism of the aftershock these computations are used to determine the subset of the stations at which the disparate focal mechanism results in a station dependent multiplicative factor only with minimum waveform distortion real data from that station subset are then inverted as if the mainshock and aftershock mechanisms were the same the egf synthetics are produced for constant velocity radial rupture propagation starting at 36 trial grid points regularly distributed on the fault plane and the grid point providing the best fit to the observed waveforms is assumed to be the nucleation point synthetic tests show that success of the method strongly depends on the exact knowledge of the mainshock true fault plane orientation but that is fairly well known from the aftershocks distribution in this case the aftershock sequence suggests two possible sizes of the fault a large fault 20 16 km along strike and dip respectively and a small fault 8 10 km that fills in the gap identified during the first 12 observation days between two aftershock clusters the egf modeling does not resolve a preferred fault dimension however for both sizes the method locates the nucleation point at the western part of the fault plane thus clearly indicating the rupture propagation toward athens

origin of string patterns in boreal peatlands the detailed stratigraphical analyses supported by field observations on mires in labrador and northern minnesota reported here provide the basis for an explanation of the development of the surface pattern of alternating peat ridges strings and linear depressions or pools flarks in boreal fens the developmental sequence involves drainage impediment and the concomitant initiation of peat accumulation development of linear patterns as a result of changing hydrological conditions and differential rates of peat accumulation of hummock and hollow plant communities and subsequent enlargement and coalescence of pools through the degradation of the underlying peat and the intervening ridges we show here that many of the processes may be active in the development of the pool patterns on raised bogs as well as on fens

rupture characteristics and tomographic source imaging of ml 3 earthquakes near anza southern california the rupture characteristics of several ml 3 earthquakes near anza california are determined from time domain analysis of path corrected displacement pulses these pulses are corrected for propagation effects apparent attenuation scattering site resonance using the waveforms of adjacent small events ml 2 1 as empirical green s functions the earthquakes studied occurred during two swarm sequences near cahuilla in an area characterized by swarm activity at shallow depth 5 km the data consist of seismograms recorded by the anza seismic network a high dynamic range local array with digital telemetry the waveforms of adjacent small events ml 2 1 are deconvolved from those of the ml 3 events to yield the source time functions of the larger earthquakes the ml 3 earthquakes display a variety of rupture modes similar to those reported for large shocks but over much shorter time scales and distances events with single and multiple ruptures are observed relative locations of the subevents are obtained from azimuthal differences in the time separation of pulses in the deconvolved displacement waveforms some events as small as ml 2 4 display unilateral rupture propagation as manifested by azimuthal variations in the pulse widths of the deconvolved displacement pulses a tomographic back projection technique is applied to the deconvolved displacement pulses to image the slip velocity on the fault as a function of time after nucleation and distance along the fault using a one dimensional fault model the tomographic inversion for one of the events ml 2 4 reveals a unilateral rupture with rupture velocity about equal to the shear wave velocity vs and fault length of 300 m a similar inversion for an ml 3 7 event resolves two subevents separated by about 200 m and yields an average rupture velocity of 0 8vs these rupture velocities are similar to those reported for large earthquakes indicating that rupture velocity is independent of seismic moment down to 3 1 1019 dyn cm the smallest event studied there are clear variations in pulse width for neighboring events with similar seismic moments implying significant differences in static stress drops factor of five variations in stress drop 11 61 bars are calculated for events within 200 m of each other thus the stress and or strength along this fault zone varies considerably over distances of hundreds of meters

source parameters of the 23 april 1992 m 6 1 joshua tree california earthquake and its aftershocks empirical green s function analysis of geos and terrascope data source parameters of the m 6 1 23 april 1992 joshua tree mainshock and 86 m 1 8 to 4 9 aftershocks are determined using an empirical green s function methodology for the aftershocks deconvolved p and s wave spectra are calculated for 126 pairs of closely spaced events recorded on portable geos stations s wave spectra from the two horizontal components are averaged the deconvolved spectra are fit by a ratio of omega square source models yielding an optimal least squares corner frequency for both the large and the small event in each pair we find no resolved difference between the inferred p and s wave corner frequencies using the standard brune model for stress drop we also find no resolved nonconstant scaling of stress drop with moment although we also conclude that detailed scaling systematics would be difficult to resolve in particular a weak increase of stress drop with moment over a limited moment magnitude cannot be ruled out for magnitudes smaller than m 3 to 3 5 the inferred stress drop values will be limited by the maximum observable corner frequency value of 60 hz for the mainshock source time functions are obtained from mainshock recordings at three terrascope stations pfo pas and gsc using an m 4 3 foreshock as an empirical green s function the results indicate a fairly simple single pulse source time function with clear south to north directivity and an inferred rupture radius of 5 to 6 km the deconvolved source time functions are inverted to obtain a finite rupture model that gives a robust estimate of rupture dimension early aftershocks are found to lie along the perimeters of regions with high mainshock slip the inferred mainshock stress drop value 56 bars is within the range determined for the aftershocks our derived mainshock source spectra do not show resolvable deviation from the omega square model

high frequency spectral falloff of earthquakes fractal dimension of complex rupture b value and the scaling of strength on faults the high frequency falloff omega sup minus gamma of earthquake displacement spectra and the b value of aftershock sequences are attributed to the character of spatially varying strength along fault zones the author assumes that the high frequency energy of a main shock is produced by a self similar distribution of subevents where the number of subevents with radii greated than r is proportional to r sup minus d d being the fractal dimension in this model an earthquake is composed of a hierarchical set of smaller earthquakes the static stress drop is parameterized to be proportional to r sup eta and strength is assumed to be proportional to static stress drop he finds that a distribution of subevents with d 2 and stress drop independent of seismic moment eta 0 produces a main shock with an omega sup minus 2 falloff if the subevent areas fill the rupture area of the main shock by equating subevents to islands of high stress of a random self similar stress field on a fault he relates d to the scaling of strength on a fault such that d 2 minus eta thus d 2 corresponds to constant stress drop scaling eta 0 and scale invariant fault strength amore self similar model of aftershock rupture zones on a fault is used to determine the relationship between the b value the size distribution of aftershock rupture zones and the scaling of strength on a fault the b value for aftershock sequences on a fault is found to equal 3 minus 1 5 eta 3 eta therefore this model indicates that the typically observed spectral falloffs of omega sup minus 2 and b values of 1 can be entirely caused by scale invariant strength eta 0 along fault zones less

seismic source parameters from the guerrero subduction zone abstract a method to systematically determine seismic moment and corner frequency from shear wave spectra has been applied to strong motion data recorded in guerrero mexico the method determines a model spectrum that minimizes the misfit from the observed spectrum after a correction for frequency dependent site response has been applied the calculated moments for larger events in guerrero are consistent with moments determined from teleseismic body waves adjusted for differences in focal depth and consequent assumed differences in the velocity and density structure in the source region the average stress drop for the 82 earthquakes with magnitudes from 3 to 7 is 150 bars the spatial distribution of the stress drops shows a distinctive pattern at the northwest end of the guerrero gap adjacent to the aftershock zones of large earthquakes in 1979 and 1985 there is a mix of low and high stress drop events at the southeast end of the guerrero gap where the most recent large earthquake occurred in 1957 there are predominantly high stress drop events this pattern might be caused by the different relative positions of these two active regions in the earthquake cycle although several other explanations cannot be ruled out

the anza array a high dynamic range broadband digitally radiotelemetered seismic array a small aperture seismic array has been deployed along a 30 km stretch of the san jacinto fault in the vicinity of the town of anza california the array was installed to study specifically the scaling laws of body wave spectra the character of high frequency ground motion the physical interpretation of seismic stress drops and the interaction of earthquakes this region was chosen for these studies due to its high rate of seismic activity in the 2 m 4 5 range the likelihood of a m 6 event in the next decade and the existence of the southern california batholith on either side of the fault reducing problems associated with attenuation and large scale anisotropy these studies employ an instrument package with a frequency response of 100 hz a dynamic range of 138 db a sampling rate of 250 times per second per component and a 16 bit a d converter the array consists of 10 three component stations telemetered via digital vhf radio to a nearby mountain peak and thence via a microwave link to la jolla california a minicomputer system monitors the array s performance detects events and records data upon demand initial results demonstrate the feasibility of digital transmission with an inherent increase in data quality over analog systems

the magnitude 6 7 northridge california earthquake of january 17 1994 the most costly american earthquake since 1906 struck los angeles on 17 january 1994 the magnitude 6 7 northridge earthquake resulted from more than 3 meters of reverse slip on a 1 5 kilometer long south dipping thrust fault that raised the santa susana mountains by as much as 70 centimeters the fault appears to be truncated by the fault that broke in the 1971 san fernando earthquake at a depth of 8 kilometers of these two events the northridge earthquake caused many times more damage primarily because its causative fault is directly under the city many types of structures were damaged but the fracture of welds in steel frame buildings was the greatest surprise the northridge earthquake emphasizes the hazard posed to los angeles by concealed thrust faults and the potential for strong ground shaking in moderate earthquakes

site amplification from coda waves validation and application to s wave site response abstract the subject of this article is to see if the response to s waves at a specific site can be determined from coda waves we used aftershock records of the 1992 landers and big bear earthquakes observed at four terrascope stations pas pfo svd and gsc in southern california the wide dynamic range of the terrascope instrument provided a broadband seismogram for s waves and at the same time coda waves over a long lapse time window we analyzed a total of 708 three component waveforms from 65 events whose magnitudes ranged from 3 3 to 5 4 the station svd is located on quaternary alluvium and the remaining stations are on rocks of cretaceous age we first evaluated the coda site amplification factor using a spectral ratio method may eda et al 1991 koyanagi et al 1992 for frequency bands centered at 0 75 1 0 1 5 2 0 3 0 4 0 and 6 0 hz for lapse time windows after 70 sec from the origin time we found that the site amplification factor for the radial component is similar to that for the transverse component this similarity was expected because codas consist of backscattered waves coming from all directions into the station resulting in a directionally averaged site response we then evaluated the s wave site amplification factor using an inversion method andrews 1986 on the direct s wave portion of the same data set we found that the coda site response agrees with the s wave site response within a factor of about 1 5 supporting the earlier findings by tsujiura 1978 and justifying the use of coda waves in determining site specific amplification for s waves this agreement between s wave site response and coda site response is understandable if we assume that coda waves are dominated by s waves as theoretically predicted by aki 1992 and zeng 1993

dynamic triggering of shallow earthquakes near beijing china summary we perform a comprehensive analysis of dynamic triggering around the babaoshan and huangzhuang gaoliying faults near beijing china the triggered earthquakes are identified as impulsive seismic arrivals with clear p and s waves in 5 hz high pass filtered three component velocity seismograms during the passage of large amplitude body and surface waves of large teleseismic earthquakes we find that this region was repeatedly triggered by four earthquakes in east asia including the 2001 mw 7 8 kunlun 2003 mw 8 3 tokachi oki 2004 mw 9 2 sumatra and 2008 mw 7 9 wenchuan earthquakes in most instances the microearthquakes coincide with the first few cycles of the love waves and more are triggered during the large amplitude rayleigh waves such an instantaneous triggering by both the love and rayleigh waves is similar to recent observations of remotely triggered non volcanic tremor along major plate boundary faults and can be explained by a simple coulomb failure criterion we are able to locate five of the earthquakes triggered by the kunlun and tokachi oki earthquakes these events occurred at shallow depth 5 km above the background seismicity near the boundary between nw striking babaoshan and huangzhuang gaoliying faults and the fangshan pluton we suggest that these triggered earthquakes occur near the transition between the velocity strengthening and weakening zones in the top few kilometres of the crust and are likely driven by relatively large dynamic stresses on the order of few tens of kpa

the 1992 landers earthquake sequence seismological observations the m w 6 1 7 3 6 2 1992 landers earthquakes began on april 23 with the m w6 1 1992 joshua tree preshock and form the most substantial earthquake sequence to occur in california in the last 40 years this sequence ruptured almost 100 km of both surficial and concealed faults and caused aftershocks over an area 100 km wide by 180 km long the faulting was predominantly strike slip and three main events in the sequence had unilateral rupture to the north away from the san andreas fault the m w6 1 joshua tree preshock at 33 n58 and 116 w19 on 0451 ut april 23 was preceded by a tightly clustered foreshock sequence m 4 6 beginning 2 hours before the mainshock and followed by a large aftershock sequence with more than 6000 aftershocks the aftershocks extended along a northerly trend from about 10 km north of the san andreas fault northwest of indio to the east striking pinto mountain fault the m w7 3 landers mainshock occurred at 34 n13 and 116 w26 at 1158 ut june 28 1992 and was preceded for 12 hours by 25 small m 3 earthquakes at the mainshock epicenter the distribution of more than 20 000 aftershocks analyzed in this study and short period focal mechanisms illuminate a complex sequence of faulting the aftershocks extend 60 km to the north of the mainshock epicenter along a system of at least five different surficial faults and 40 km to the south crossing the pinto mountain fault through the joshua tree aftershock zone towards the san andreas fault near indio the rupture initiated in the depth range of 3 6 km similar to previous m 5 earthquakes in the region although the maximum depth of aftershocks is about 15 km the mainshock focal mechanism showed right lateral strike slip faulting with a strike of n10 w on an almost vertical fault the rupture formed an arclike zone well defined by both surficial faulting and aftershocks with more westerly faulting to the north this change in strike is accomplished by jumping across dilational jogs connecting surficial faults with strikes rotated progressively to the west a 20 km long linear cluster of aftershocks occurred 10 20 km north of barstow or 30 40 km north of the end of the mainshock rupture the most prominent off fault aftershock cluster occurred 30 km to the west of the landers mainshock the largest aftershock was within this cluster the m w6 2 big bear aftershock occurring at 34 n10 and 116 w49 at 1505 ut june 28 it exhibited left lateral strike slip faulting on a northeast striking and steeply dipping plane the big bear aftershocks form a linear trend extending 20 km to the northeast with a scattered distribution to the north the landers mainshock occurred near the southernmost extent of the eastern california shear zone an 80 km wide more than 400 km long zone of deformation this zone extends into the death valley region and accommodates about 10 to 20 of the plate motion between the pacific and north american plates the joshua tree preshock its aftershocks and landers aftershocks form a previously missing link that connects the eastern california shear zone to the southern san andreas fault

an empirical study of earthquake source spectra for california earthquakes we generalize source path and site effects for california earthquakes as functions of magnitude and distance based on regression analysis of 1000 fourier acceleration spectra from 43 california earthquakes in the moment magnitude range from 4 4 to 7 4 recorded at rupture distances from 1 to 200 km empirically derived source spectra for california earthquakes are generally inconsistent with the spectral shape implied by a brune omega squared point source model this is manifested by magnitude and frequency dependence of the brune model parameters for ex ample the brune stress parameter that best matches the data at high frequencies decreases from a value of about 120 bars at m5 5 to a value near 50 bars at m7 5 at frequencies below 1 hz though source spectra have much lower spectral ampli tudes than predicted by the brune point source model for these values of stress this discrepancy grows with increasing magnitude finite fault simulations indicate that this is a consequence of the breakdown of the validity of the point source approxi mation for large ruptures a stochastic finite fault model in which the fault is dis cretized as a number of subfaults each of which is represented by a brune omega squared point source correctly matches the observed spectral shapes and amplitudes the spectral decay parameter kappa representing average near surface attenuation of high frequency motion at rock sites increases with increasing magnitude from values near 0 035 sec at m5 5 to 0 050 sec at m7 5 magnitude dependence of kappa may be interpreted as evidence of nonlinearity for typical california sites subjected to strong ground motion comparisons of our empirical source spectra for california to corresponding spec tra for eastern north america suggest that the spectral amplitudes are similar in the two regions for low frequency motions f 2 hz for m5 5 f 0 5 hz for m7 5 for equivalent crustal conditions the eastern events appear to have enhanced high frequency near source amplitudes relative to the california events this is particularly pronounced for large magnitude earthquakes

quantifying landscape morphology influence on peatland lateral expansion using ground penetrating radar gpr and peat core analysis 1 northern peatlands contain vast amounts of organic carbon large scale datasets have documented spatial patterns of peatland initiation as well as vertical peat accumulation rates however the rate pattern and timing of lateral expansion across the northern landscape remain largely unknown as peatland lateral extent is a key boundary condition constraining the dynamics of peatland systems understanding this process is essential here we use ground penetrating radar gpr and peat core analysis to study the effect of local slope and topography on peatland development at a site in south central alaska the study site is unique in that a thick tephra volcanic ash layer visible in the gpr data interrupted the peatland development for about one thousand years during the mid holocene in our analysis this tephra layer serves as a re initiation point for peatland development by comparing the initial mineral basin vs the post tephra surfaces the influence of topography and slope on peatland expansion rate and peat carbon sequestration was analyzed our results show that 1 peatland surface slope becomes progressively shallower over the holocene 2 slope affects peatland lateral expansion nonlinearly 3 the relationship between lateral expansion rate and slope follows a power law behavior and 4 peatland expansion becomes slope limited above a threshold 0 5 furthermore we propose a conceptual model linking slope to peatland lateral expansion where slope gradient and basin topography exert deterministic controls on peatland lateral expansion directly or through hydrology and vertical accumulation rates

ground motion modelling in the gujarat region of western india using empirical green s function approach abstract in this study ground motions are estimated for scenario earthquakes of mw 6 0 6 5 and 7 0 at 17 sites in gujarat region using empirical green s function technique the dholavira earthquake of june 19 2012 mw 5 1 which occurred in the kachchh region of gujarat is considered as an element earthquake we estimated the focal mechanism and source parameters of the element earthquake using standard methodologies the moment tensor inversion technique is used to determine the fault plane solution strike 8 dip 51 and rake 7 the seismic moment and the stress drop are 5 6 10 16 nm and 120 bars respectively the validity of the approach was tested for a smaller earthquake a few possible directivity scenarios were also tested to find out the effect of directivity on the level of ground motions our study reveals that source complexities and site effects play a very important role in deciding the level of ground motions at a site which are difficult to model by gmpes our results shed new light on the expected accelerations in the region and suggest that the kachchh region can expect maximum acceleration of around 500 cm s 2 at few sites near source and around 200 cm s 2 at most of the sites located within 50 km from the epicentre for a mw 7 0 earthquake the estimated ground accelerations can be used by the administrators and planners for providing a guiding framework to undertake mitigation investments and activities in the region

assessment of ground motion in palermo italy during the 6 september 2002 mw 5 9 earthquake using source scaling law in calderoni et al 2005 a section of text that was present in the original manuscript was inadvertently deleted during composition the section entitled random summation of aftershocks rnds is printed correctly below rnds joyner and boore 1986 generates synthetic seismograms of the target earthquake at

spatial and temporal distribution of slip for the 1992 landers california earthquake we have determined a source rupture model for the 1992 landers earthquake m w 7 2 compatible with multiple data sets spanning a frequency range from zero to 0 5 hz geodetic survey displacements near field and regional strong motions broadband teleseismic waveforms and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface our fault parameterization involves a variable slip multiple segment finite fault model which treats the diverse data sets in a self consistent manner allowing them to be inverted both independently and in unison the high quality data available for the landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern in all models consistent features include the following 1 similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 10 26 dyne cm seismic potency of 2 3 to 2 7 km 3 2 very heterogeneous unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km though slip is limited to shallower regions in some areas 3 a total rupture duration of 24 sec and an average rupture velocity of 2 7 km sec and 4 substantial variations of slip with depth relative to measured surface offsets the extended rupture length and duration of the landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter duration strike slip events our imaging allows visualization of the rupture evolution including local differences in slip durations and variations in rupture velocity rupture velocity decreases markedly at shallow depths as well as near regions of slip transfer from one fault segment to the next as rupture propagates northwestward along the multiply segmented fault length the rupture front slows as it reaches the northern limit of the johnson valley landers faults where slip is transferred to the southern homestead valley fault an abrupt acceleration is apparent following the transfer this process is repeated and is more pronounced as slip is again passed from the northern homestead valley fault to the emerson fault although the largest surface offsets were observed at the northern end of the rupture our modeling indicates that substantial rupture was also relatively shallow less than 10 km in this region

southern surface rupture associated with the m 7 3 1992 landers california earthquake although most evidence suggests that the 28 june 1992 m 7 3 landers earthquake ruptured unilaterally north significant surface rupture was mapped on the eureka peak and burnt mountain faults to the south of the landers epicenter an eyewitness account reports that surface rupture occurred on the northern eureka peak fault within approximately 35 sec of the mainshock initiation array analysis of the landers mainshock provides evidence in support of this report a significant southern subevent in the early mainshock coda i also analyze dense array recordings of a m 5 6 aftershock that occurred 3 min after the mainshock at 34 7 65 n 116 23 82 w and show that there is strong evidence that this event was also associated with significant rupture on the eureka peak fault this analysis thus suggests that the eureka peak fault rupture was not caused by direct bilateral mainshock rupture but instead was initially triggered less than a minute after the mainshock and reruptured by the m 5 6 aftershock results for the evolution of the landers sequence suggest that mainshock subevents may in some cases be accurately described as aftershocks i e disjoint triggered events that occur within the duration of mainshock strong ground motion

moment energy stress drop and source spectra of western united states earthquakes from regional coda envelopes we present a new method to estimate stable seismic source parameters such as energy moment and orowan stress drop using regional coda envelopes from as few as one broadband station we use the method to compute path and site corrected seismic moment rate spectra for 117 recent western united states earthquakes empirical green s function corrections were applied to our surface and body wave coda envelope measurements to generate s wave source spectra these source spectra provide stable single station estimates of radiated seismic energy es and seismic moment mo that for common events are in excellent agreement with network averaged estimates obtained using local and regional data teleseismic moment estimates are compatible with our regional results but teleseismic energy estimates appear to be nearly an order of magnitude low we estimated the seismic moment of events ranging between mw 2 2 and 7 3 and energy estimates for which we had measured at least 70 of the total energy generally events above mw 3 3 we use these estimates to examine the behavior of derived parameters such as the orowan stress drop 2 es mo while the earthquakes we studied have a small range in orowan stress drop generally between 0 1 and 20 mpa they show a strong tendency for orowan stress drop to increase with moment approximately as mo0 25 we believe this is a source effect and is not due to inadequate bandwidth or attenuation correction and note that this trend appears to continue for microearthquakes as described in a recent deep borehole study in southern california many of the large high stress drop earthquakes show complexity in their moment rate spectra near the corner frequency and cannot be fit by a simple square model instead above the first corner frequency the spectral decay ranges between f 1 0 and f 1 5 this leads to larger estimates of radiated energy than predicted with a simple square model and has implications for seismic hazard estimation coda envelopes have three main advantages over direct arrivals for estimating seismic moment and energy 1 coda amplitudes vary little with geology and source radiation anisotropy and allow accurate single station applications 2 path corrected coda amplitude measurements can be applied to very large regions allowing a comparison of source parameters throughout the western united states using a common methodology and stations 3 because long period coda can last for hours for large local and regional events it allows the analysis of seismograms with clipped early arrivals

geophysical and hydrological evaluation of two bog complexes in a northern peatland implications for the distribution of biogenic gases at the basin scale 1 ground penetrating radar gpr was used to determine peat basin geometry and the spatial distribution of free phase biogenic gasses in two separate units of a northern peatland central and southern unit of caribou bog maine the central unit is characterized by a deep basin structure 15 m maximum depth and a raised eccentric bog topographic profile up to 2 m topographic variation here numerous regions of electromagnetic em wave scattering are considered diagnostic of the presence of extensive free phase biogenic gas in contrast the southern unit is shallower 8 m maximum depth and has a slightly convex upwards bog profile less than 1 m topographic variation and areas of em wave scattering are notably absent the biogenic gas zones interpreted from gpr in the central unit are associated with 1 wooded heath vegetation at the surface 2 open pools at the surface 3 high water table elevations near the center of the basin and 4 a region of overpressure at approximately 5 m depth immediately below the zone of free phase gas accumulation the latter suggests 1 a transient pressure head associated with low hydraulic conductivity resulting from the biogenic gasses themselves or confining layers in the peat that restrict both gas release and groundwater flow and or 2 overpressure in the peat column as a result of the gas buildup itself in contrast the southern unit where zones of em scattering are absent is characterized by 1 predominantly shrub vegetation 2 a lack of open pools 3 only minor variations less than 1 m in water table elevation throughout the entire unit and 4 generally upward groundwater flow throughout the basin the results illustrate the nonuniformity of free phase biogenic gas distribution at the peat basin scale and provide insights into the processes and controls associated with ch4 and co2 accumulation in peatlands

regionalization of crustal coda q in the continental united states a contour map of crustal q sub 0 values for the entire united states is presented based on a scattering model to explain the coda waves of local and near regional earthquakes these coda q sub 0 values are in good agreement with q of lg waves data are obtained from over 250 local earthquakes with most magnitudes between 3 0 and 5 0 recorded by 25 wwssn and 27 lrsm stations throughout the continental united states these two sets of data provide a range of frequencies from 0 5 to 3 5 hz a frequency dependence of q is observed in the range of frequencies considered a power law dependence of the form q q sub 0 f f sub 0 sup eta is assumed the value of frequency dependence eta is found to be maximum in the tectonically active western united states and least in the stable regions of the central and south central united states the lowest q sub 0 values are obtained in the western united states with values ranging from 140 to 200 in the coastal plains average crustal q sub 0 values for the basin and range province vary from 200 to 300 increasing gradually to 400 in the colorado plateau region q sub 0 valuesmore in the columbia plateau vary from 200 to 400 q sub 0 values increase very rapidly along the central and southern rocky mountains from 400 to 800 east of the rocky mountains q sub 0 values increase gradually in the interior plains to a maximum value of around 1300 in the mississippi embayment region farther east q sub 0 values decrease gradually to an almost constant value of 1000 along the appalachian mountains coastal regions of eastern and northeastern united states have a crustal q sub 0 value between 900 to 700 regions of north central and gulf coastal plains show low q sub 0 values ranging from 600 to 400 and less the source factor b f sub p a measure of the intensity of scattering was obtained for several different regions of the continental united states regions of high q sub 0 values exhibit low intensity of scattering less

empirical green function deconvolution of broadband surface waves rupture directivity of the 1992 landers california mw 7 3 earthquake we present a simple method to determine gross temporal and spatial characteristics of faulting that can uniquely define the fault plane for a relatively large earthquake the technique involves deconvolution of teleseismic and regional broadband surface waves and or body waves of a small event an empirical green function from the corresponding signals at the same stations for a large mainshock this deconvolution corrects each mainshock seismic record for propagation and instrument response and if the focal mechanisms and centroid depths are identical deconvolution provides relative source time functions for the mainshock azimuthal variations of source time function width or subevent interference reveal the mainshock rupture directivity changes in the source mechanism during rupture can be evaluated for some classes of events our empirical green function procedure is novel in its application to surface waves and its use for large m 7 earthquakes we perform synthetic tests to establish intrinsic limitations of the method the procedure requires very little data processing and can be applied in near real time with the current distribution of seismic stations that have dial up data retrieval capability it also provides a straightforward procedure for reducing bias in source duration estimates resulting from aspherical heterogeneity and for detecting anomalous long period radiation we apply the procedure to the 28 june 1992 landers california mw 7 3 earthquake the landers earthquake source duration lasted about 25 sec and was dominated by two subevents with predominantly north northwestward rupture extending 60 to 70 km the subevents show counter clockwise rotations of at least 12 in strike that correlate well with mapped surface rupture

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

seismic scaling relations and aftershock activity from the sequences of the 2004 mid niigata and the 2005 west off fukuoka earthquakes mw 6 6 in japan 1 we investigate seismic scaling relations and seismic activity using two japanese earthquake sequences the 2004 mid niigata prefecture earthquake mnpe and the 2005 west off fukuoka prefecture earthquake wofe sequences although the mainshocks of the two sequences have the same mw of 6 6 the aftershock activities are different from each other in term of moment release the mnpe produced a large number of aftershocks including six events with mw 5 5 over a period of about two weeks on the other hand the wofe sequence did not produce aftershocks that exceeded mw 5 5 in the scaling relationship of seismic moment m0 versus corner frequency fc obtained from the mnpe sequence the fc s tend to decrease with decreasing m0 between mw 3 5 and 6 6 and the best fit line determined in a least squares sense is m0 fc 3 41 in the wofe sequence the best fit line is m0 fc 3 06 in the same mw range the fc range of small aftershocks is lower in the mnpe sequence than in the wofe sequence moreover the m0 fc relations for small events 3 5 mw 4 0 in the mnpe sequence are different between the events on the main faults m0 fc 3 53 and the off main fault events m0 fc 4 44 these results suggest that there is difference or variation in the scaling relation even in the same mw range probably reflecting different tectonic or seismogenic conditions

hydrological processes and chemical characteristics of low alpine patterned wetlands south central new zealand summary patterned wetlands in new zealand are not only rare but they are distinguished from their northern hemisphere counterparts by their vegetation and the supply of rainfall which is relatively free of pollution hydrological processes in two low alpine patterned wetlands 5 and 220 ha on block faulted uplands in south central south island new zealand were investigated using hydraulic head gradients and chemical and isotope data there was no significant spatial variability in chemical parameters within either wetland although the larger wetland is characterised by a lower trophic status than the smaller one ca2 concentrations and ph of surface water of both wetlands are within the range of that of northern hemisphere ombrotrophic mesotrophic bogs and poor fens pool water chemistry only partially overlaps with the lower end of the ca2 distribution for the northern hemisphere wetlands likely to be caused by the low level of ca2 in aeolian dust the ph in the pools of the small wetland was generally higher probably as a result of differing organic acid production by the sphagnum and sedge species both of which were common and dominant or sub dominant in the wetlands some temporal variability was observed possibly due to seasonal variations in plant uptake and or rainfall a steady increase in na concentrations in the pools over 4 years was tentatively attributed to an excess of supply from rainfall and or groundwater cation and stable isotope data indicate strong evaporation in pools and surface water despite the high ambient relative humidity and mixing within the top of the wetland sequence stratigraphy indicates that peat formation has been interrupted by flooding or runoff bringing mineral matter into the wetlands particularly in the earlier development stages of the larger wetland the peat sequence is thicker in the smaller wetland reaching up to 2 8 m with limited mineral input during wetland development the relatively low ph and ionic concentrations in the contemporary water and peat sequence of the larger wetland indicate that it has become isolated from runoff and mineral input

remotely triggered seismicity in yunnan southwestern china following the 2004 mw9 3 sumatra earthquake 1 following the 2004 mw9 3 sumatra earthquake seismicity rate increased sharply over a wide area of up to 2700 km away in yunnan province southwestern china raised seismicity lasts for 14 days during this period more than 800 earthquakes with magnitude between 1 5 and 5 1 occurred this is perhaps the most impressive example of remotely triggered seismicity yet observed major events were clustered at several sites that exhibit complex fault geometries such as step overs and junctures we use statistic approaches including the statistics to examine the statistical significance of the seismic rate increases associated with the sumatra main shock and conclude that there is a reasonable probability that the raised seismicity was remotely triggered by the sumatra earthquake both rapid onset of dynamic triggering the very first event is a m4 6 earthquake occurred during the passage of the rayleigh wave from the sumatra earthquake and delayed response activated a few hours to a few days after the sumatra earthquake are well established the triggered activities show more earthquake swarm like characteristics as indicated by the epidemic type aftershock sequence modeling results large percentage of random components and less magnitude dependence in omori law type self triggering multiple sources of evidence including intensive hydrothermal activities and low velocity and high vp vs zones in the lower to middle crust suggests that magma mantle generated fluids have a role in the region high fluid pressure in branched fault zones weakened the faults making them sensitive to external disturbances and leading to fluid driven seismicity

3 d velocity structure of the san jacinto fault zone near anza california i p waves summary seismic arrival times from microearthquakes ml 4 on the san jacinto fault near anza california are used to find spatial variations in the seismic velocity that are related to the crustal structure of the fault zone preliminary modelling of the 1 d p wave velocity structure of the upper 25 km of crust reveals that most of the variation in velocity is lateral rather than depth dependent the traveltime anomalies due to lateral structure can be partially compensated for by applying station corrections however the variance of the traveltime residuals is still 2 25 times larger than the variance of the picking error the spatially correlated residuals show that this variance is due to localized velocity anomalies and that the data require further modelling using a 3 d velocity structure because the 3 d inverse problem is non unique smoothness constraints are applied to find the model that has the minimum structure required to fit the data to the picking error where a smooth model is defined such that the gradient of the velocity perturbation from the original 1 d model is small with small non zero station corrections a 3 d velocity model can be found that fits the data well the structure is well resolved from 3 to 9 km depth where lateral perturbations of up to 7 per cent are determined independently of the trade off between station corrections and poorly resolved near surface structure the model shows a horizontal gradient with overall faster velocities in the north east side of the fault zone at 3 6 km depth the signature of the fault zone is evident in the lower velocities beneath the surface trace of the fault however at 9 km depth higher seismic velocities are found extending into the fault zone from the north east block this higher velocity region occurs where there is a distinct lack of seismicity on the fault there is also a localized feature in the south west of the modelled region that is more than 10 km from the main trace of the fault with velocities 3 per cent slower than average

radiated energy of great earthquakes from teleseismic empirical green s function deconvolution we expand on the empirical green s function deconvolution method of ide et al 2011 to estimate radiated energy for the six largest earthquakes worldwide over the last 10 years 2011 m w 9 0 tohoku oki 2004 m w 9 1 sumatra 2010 m w 8 8 maule 2005 m w 8 7 nias 2007 m w 8 5 bengkulu and 2012 m w 8 6 off sumatra deconvolution of p sv and sh components gives consistent energy results that are comparable to estimates found independently by other researchers apparent stress for the five great thrust earthquakes is between 0 4 and 0 8 mpa while the 2012 off sumatra strike slip earthquake has a higher apparent stress of 3 mpa which is consistent with other studies that find a tendency for strike slip events to be more energetic our results are within the spread of apparent stress from the wider global earthquake population over a large magnitude range the azimuthal distribution of energy in each case shows signs of directivity and in some cases shows less energy radiated in the trench ward direction which may suggest enhanced tsunami potential we find that egfs as small as m 6 5 can be used for teleseismic deconvolution and that an egf mainshock magnitude difference of 1 5 units yields stable results this implies that m 8 is the minimum mainshock size for which teleseismic egf deconvolution will work well we propose that a database of egf events could be used to calculate radiated energy and apparent stress of great hazardous events in near real time i e promptly enough that it could contribute to rapid response measures

apparent stress and corner frequency variations in the 1999 taiwan chi chi sequence evidence for a step wise increase at mw 5 5 1 apparent stress and corner frequencies are measured for the chi chi taiwan sequence beginning with the mw 7 6 mainshock on 20 september 1999 using the coda source ratio method we obtained stable source ratio estimates using broadband stations on taiwan we find the following 1 for the mainshock and 3 of the larger aftershocks apparent stress is clustered around 0 8 mpa 0 1 mpa 2 events below mw 5 5 exhibit lower apparent stress with larger scatter ranging between 0 08 and 0 8 mpa and are spatially variable 3 the brune 1970a 1970b omega square source model fits the spectral shape for events 4 7 mw 7 6 however a step wise break in self similarity exists at mw 5 5 we hypothesize that larger events are subject to the regional state of stress whereas smaller aftershocks are sensitive to the local state of stress from stress field redistribution following the mainshock and or fault zone lubrication that affects only larger events

ground penetrating radar and spring formation in a groundwater dominated peat wetland summary ground penetrating radar gpr was used to identify the thickness and geometry of peat in a groundwater fed wetland in northern wisconsin the low electrical conductivity of the water saturated peat permitted high resolution imaging to a depth of 16 m the gpr survey results delineated a break in slope in the interface between peat and the underlying sand gravel springs and ponds are located above the break in slope suggesting that thinning of the sand and gravel may focus groundwater flow upward to the wetland surface with emergence as springs the results of the gpr surveys suggests a potential mechanism that controls the formation of large springs and pools above the break in slope