aftershocks of the 1999 chi chi taiwan earthquake the first hour within the hour immediately after the 1999 chi chi mainshock only 40 aftershocks were located by the taiwan central weather bureau seismic network cwbsn because of the power outage in more than half of the island and the limited dynamic range of the cwbsn high gain instruments here by analyzing 20 near field on scale records from the taiwan strong motion instrumentation program tsmip we determined a catalog of 296 aftershocks with m l 3 4 within the first hour after the chi chi mainshock focal mechanisms were also determined for 24 of these aftershocks the frequency magnitude relation obtained from the 296 aftershocks indicates that the catalog is complete above magnitude m l 4 3 most of the aftershocks occurred in a small slip region of the mainshock immediately to the north of the mainshock epicenter spatially the aftershocks appear to migrate downward from the mainshock hypocenter later in the hour the aftershocks began to concentrate in the fringe area of the main rupture during the first hour the b value as defined by events in the 4 3 m l

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

temporal variation of seismic velocity and anisotropy before the 2009 mw 6 3 l aquila earthquake italy we describe a set of seismological observations of the foreshock sequence preceding the 6 april 2009 m w 6 3 l9aquila earthquake the dense configuration of the seismic network in the epicenter area and the occurrence of a long foreshock sequence provide the opportunity for a detailed reconstruction of the preparatory phase of the main shock approaching the earthquake we observed clear variations in the seismic wave propagation properties the elastic properties of rocks in the fault region underwent a sharp change about a week before the earthquake from our observations we infer that a complex sequence of dilatancy diffusion processes takes place and that fluids play a key role in the fault failure process

unravelling the complexity of apenninic extensional fault systems a review of the 2009 l aquila earthquake central apennines italy the 2009 l aquila sequence activated a normal fault system 50 km long in the central apennines composed of two main nw trending faults 12 16 km long the main high angle l aquila segment and the campotosto listric fault the mw 6 1 l aquila mainshock nucleated on the paganica fault at a depth of 8 6 km and cut through the upper crust producing coseismic surface slip of up to 10 cm observed along a strike length of 13 km analysis of historical seismicity and data collected in paleo seismological trenches suggest that this event filled a 500 year gap in contrast the blind campotosto listric fault is composed of different fault segments displaying abrupt changes in dip at a depth where major events nucleate suggesting a rheological and geometrical control on stress concentration a foreshock sequence that started around 4 months before the l aquila mainshock activated the deepest portion of the paganica fault and marked the onset of large variations in elastic properties of the crustal volume the variations have been modelled in terms of dilatancy and diffusion processes corroborating the hypothesis that fluids play a key role in the nucleation process of extensional faults in the crust

deep structure and tectonics of the northern central apennines as seen by regional scale tomography and 3 d located earthquakes 1 in this study we present new high resolution regional scale vp and vp vs models of the northern central apennines along with accurate 3 d locations of a large set of local earthquakes the main velocity anomalies are consistent with the surface geology in the shallow layers and present evidence for fluids stored within the basement at greater depths beneath the extensional belt the adria and tyrrhenian mantle are defined by positive velocity anomalies below 30 km depth while a low vp high vp vs region in between indicates the existence of a hydrated wedge the results yield new constraints on active processes in the apennines and more generally envisage the evolution of a postcollisional belt velocity anomalies and earthquakes are consistent with a complex system of delamination and sinking of the adria continental lithosphere with the peeling of the crust identified by intermediate depth seismicity change of seismicity and structural patterns along the belt indicates that this tectonic process is diachronous and that fluids released by sunken lithosphere are stored within the crust conditioning the occurrence of seismicity and the onset of extension

seismicity precursors to large earthquakes unified in a stress accumulation framework 1 various seismicity patterns before large earthquakes have been reported in the literature they include foreshocks medium term acceleration and short term activation quiescence doughnut patterns and event migration the existence of these precursory patterns is however debated here we develop an approach based on the concept of stress accumulation to unify and categorize all claimed seismic precursors in a same physical framework we first extend the non critical precursory accelerating seismicity theory n c past which already explains most precursors to additionally include short term activation theoretical results are then compared to the time series observed prior to the 2009mw 6 3 l aquila italy earthquake we finally show that different precursory paths are possible before large earthquakes with possible coupling of different patterns or non occurrence of any this is described by a logic tree defined from the combined probabilities of occurrence of the mainshock at a given stress state and of precursory silent slip on the fault in the case of the l aquila earthquake the observed precursory path is coupling of quiescence and accelerating seismic release followed by activation these results provide guidelines for future research on earthquake predictability

precursory seismic quiescence seventeen cases of precursory seismic quiescence to mainshocks with magnitudes fromml 4 7 toms 8 0 are summarized the amount of rate decrease ranges from 45 to 90 the significance of these changes varies between 90 and 99 99 the assumption that the background rate is approximately constant is fulfilled in most crustal volumes studied all quiescence anomalies seem to have abrupt beginnings and the rate during the anomalous period is fairly constant the duration of the precursors ranges from 15 to 75 months and it is not clear what factors determine that time at least three successful predictions have been based on seismic quiescence these cases have shown that mainshocks can be predicted based on quiescence but they have also shown that the interpretation of the data in real time is difficult and nonunique if a false alarm is defined as a period of quiescence with a significance level larger than a precursory quiescence in the same tectonic area then we estimate based on searches in four areas that the false alarm rate may be on the order of 50 failure to predict may be expected in perhaps 50 of mainshocks even in carefully monitored areas quiescence cannot be used as a precursor in tectonic environments with low seismic activity most characteristics of the phenomenon are still poorly defined but data exist which probably permit at least a doubling of the presently available data on case histories

seismic quiescence as an indicator for large earthquakes in a system of self organized criticality seismically active fault systems may be in a state of self organized criticality soc investigations of simple soc models have suggested that earthquakes might be inherently unpredictable in this paper we analyze the question of predictability in a more complex and realistic soc model which consists of a spring block system with transient creep characteristics additionally to the power law distribution of earthquake sizes this model reproduces also foreshock and aftershock sequences aside from a short term increase of seismicity immediately prior to large model earthquakes these events are preceded on average by an intermediate term period of reduced seismicity the stronger and the longer the duration of this period the larger on average is the subsequent mainshock we find that the detection of seismic quiescence can improve the time independent hazard assessment the improvement is most significant for the largest target events

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

risk and return evaluating reverse tracing of precursors earthquake predictions summary in 2003 the reverse tracing of precursors rtp algorithm attracted the attention of seismologists and international news agencies when researchers claimed two successful predictions of large earthquakes these researchers had begun applying rtp to seismicity in japan california the eastern mediterranean and italy they have since applied it to seismicity in the northern pacific oregon and nevada rtp is a pattern recognition algorithm that uses earthquake catalogue data to declare alarms and these alarms indicate that rtp expects a moderate to large earthquake in the following months the spatial extent of alarms is highly variable and each alarm typically lasts 9 months although the algorithm may extend alarms in time and space we examined the record of alarms and outcomes since the prospective application of rtp began and in this paper we report on the performance of rtp to date to analyse these predictions we used a recently developed approach based on a gambling score and we used a simple reference model to estimate the prior probability of target earthquakes for each alarm formally we believe that rtp investigators did not rigorously specify the first two successful predictions in advance of the relevant earthquakes because this issue is contentious we consider analyses with and without these alarms when we included contentious alarms rtp predictions demonstrate statistically significant skill under a stricter interpretation the predictions are marginally unsuccessful

the anatomy of the 2009 l aquila normal fault system central italy imaged by high resolution foreshock and aftershock locations 1 on 6 april 01 32 utc 2009 a mw 6 1 normal faulting earthquake struck the axial area of the abruzzo region in central italy we study the geometry of fault segments using high resolution foreshock and aftershock locations two main sw dipping segments the l aquila and campotosto faults forming an en echelon system 40 km long nw trending the 16 km long l aquila fault shows a planar geometry with constant dip 48 through the entire upper crust down to 10 km depth the campotosto fault activated by three events with 5 0 mw 5 2 shows a striking listric geometry composed by planar segments with different dips along depth rather than a smoothly curving single fault surface the investigation of the spatiotemporal evolution of foreshock activity within the crustal volume where the subsequent l aquila main shock nucleated allows us to image the progressive activation of the main fault plane from the beginning of 2009 the foreshocks activated the deepest portion of the fault until a week before the main shock when the largest foreshock mw 4 0 triggered a minor antithetic segment seismicity jumped back to the main plane a few hours before the main shock secondary synthetic and antithetic fault segments are present both on the hanging and footwall of the system the stress tensor obtained by inverting focal mechanisms of the largest events reveals a ne trending extension and the majority of the aftershocks are kinematically consistent deviations from the dominant extensional strain pattern are observed for those earthquakes activating minor structures

high pressure fluid at hypocentral depths in the l aquila region inferred from earthquake focal mechanisms we apply a new analysis technique using earthquake focal mechanisms to infer the 3 d fluid pressure field at depth in the source region of the a d 2009 l9aquila earthquake aftershock sequence the technique termed focal mechanism tomography inverts for fluid pressure by examining the fault orientation relative to the regional tectonic stress pattern we identify three large scale pockets of high fluid pressure up to 50 mpa above hydrostatic pressure at depths of 7 10 km that strongly correlates with an independent data set of well located foreshocks and aftershocks the shape of overpressured regions and the evolution of seismicity indicate a plausible scenario that this sequence is being driven in part by the poro elastic response of trapped reservoirs of high pressure fluid presumably co 2 and postseismic fluid flow initiated by the main shock

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

loading rate variations along a midcrustal shear zone preceding the m w 6 0 earthquake of 24 august 2016 in central italy

juvenile crustal recycling in an accretionary orogen insights from contrasting early permian granites from central inner mongolia north china abstract coeval high k calc alkaline to alkaline granites constitute important components of post collisional to post orogenic igneous suites in most orogenic belts of various ages on earth and their genesis harbors a key to ascertaining critical geodynamic controls on continental crustal formation and differentiation this zircon u pb dating and geochemical study documents three contrasting early permian granites from erenhot of central inner mongolia eastern central asian orogenic belt caob and reveals concurrent high k calc alkaline to alkaline granite association derived from successive partial melting of distinct protoliths the ca 280 ma gancihuduge gcg pluton shows a calc alkaline i type character with initial 87 sr 86 sr ratios of 0 7035 to 0 7039 e nd t of 1 87 to 4 70 zircon e hf t of 8 0 to 13 2 and 18 o from 7 4 to 8 7 the ca 276 ma cailiwusu cls pluton is magnesian and peraluminous with initial 87 sr 86 sr ratios of 0 7036 to 0 7040 e nd t of 1 9 to 2 4 zircon e hf t of 6 5 to 12 1 and 18 o from 9 7 to 10 9 these features are consistent with partial melts of mixed sources composed of newly underplated meta basaltic to andesitic protoliths and variable supracrustal components with distinctively higher proportion of the latter in the cls pluton by contrast the ca 279 ma kunduleng kdl suite exhibits an a type magmatic affinity with typical enrichment in alkalis ga zr nb and y e nd t of 2 39 to 3 55 zircon e hf t from 8 3 to 12 3 and 18 o values from 6 8 to 7 5 these features suggest that they stem from high temperature fusion of dehydrated k rich mafic to intermediate protoliths besides presenting a snapshot into a stratified crustal architecture in 18 o these contrasting granites could not only serve as a temporal marker for monitoring post collisional extension in the aftermath of a retreating subduction zone but also present spatial magmatic proxy for tracing crustal formation and differentiation within back arc basin environments in the caob

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

step like migration of early aftershocks following the 2007 mw 6 7 noto hanto earthquake japan seismic data reveal that the aftershock zone expands with time after a main shock event here we examine the aftershock sequence recorded during the first 32 days following the 2007 noto hanto earthquake japan by applying a matched filter technique to the data we detected about 10 times more events than those listed in the routinely constructed earthquake catalog the aftershock area expanded along the fault strike as a logarithmic function of time beginning immediately after the main shock aftershock expansion toward the sw was especially extensive and developed more rapidly than toward the ne interestingly the aftershock area expanded in a step like manner by the activation of a series of spatially clustered seismic bursts spatial correlation between the aftershock extension and the afterslip distribution suggests that the expansion of the aftershock area could be mainly driven by aseismic afterslip the aftershock area continues to expand even though 7 years have now passed since the main shock

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

the preparatory phase of the 2009 mw 6 3 l aquila earthquake by improving the detection capability of low magnitude foreshocks we explored the detection capability of low magnitude earthquakes before the 6 april 2009 mw 6 3 l aquila event by using a matched filter technique and 512 foreshocks as templates we analyzed continuous waveforms from 10 broadband seismic stations in a 60 km radius from the epicenter and for 3 months before the main shock more than 3000 new events mostly located on the main shock fault were detected to define the spatial temporal evolution of micro seismicity the foreshock sequence was active northwest of the mw 6 3 hypocenter in january then migrated toward it at a speed of 0 5 km day in middle of february at that time in a 4 km2 patch close to the main shock nucleation point the cumulative number of earthquakes gradually increased until the mw 6 3 event this patch characterized by a low b value played a key role in controlling the preparation stage to the 2009 l aquila main rupture

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

spatial temporal evolution of early aftershocks following the 2010 ml 6 4 jiashian earthquake in southern taiwan chi chia tang 1 2 cheng horng lin2 and zhigang peng3 1hubei subsurface multi scale imaging lab institute of geophysics and geomatics china university of geosciences 388 lumo rd wuhan hubei 430074 p r china e mail iori897 gmail com 2institute of earth sciences academia sinica 128 sec 2 academia rd nangang taipei 11529 taiwan 3school of earth and atmospheric sciences georgia institute of technology 311 ferst drive atlanta ga 30332 usa

a constitutive law for rate of earthquake production and its application to earthquake clustering seismicity is modeled as a sequence of earthquake nucleation events in which the distribution of initial conditions over the population of nucleation sources and stress ing history control the timing of earthquakes the model is implemented using solutions for nucleation of unstable fault slip on faults with experimentally derived rate and state dependent fault properties this yields a general state variable constitutive formulation for rate of earthquake production resulting from an applied stressing history to illustrate and test the model some characteristics of seismicity following a stress step have been explored it is proposed that various features of earthquake clustering arise from sensi tivity of nucleation times to the stress changes induced by prior earthquakes the model gives the characteristic omori aftershock decay law and interprets aftershock parameters in terms of stress change and stressing rate earthquake data appear to support a model prediction that aftershock duration defined as the time for rates to return to the back ground seismicity rate is proportional to mainshock recurrence time observed spatial and temporal clustering of earthquake pairs arises as a consequence of the spatial depen dence of stress changes of the first event of the pair and stress sensitive time dependent nucleation applications of the constitutive formulation are not restricted to the simple stress step models investigated here it may be applied to stressing histories of arbitrary complexity the apparent success at modeling clustering phenomena suggests the possibil ity of using the formulation to estimate short to intermediate term earthquake probabil ities following occurrence of other earthquakes and for inversion of temporal variations of earthquake rates for changes in driving stress

teleseismic p wave crustal tomography of the weifang segment on the tanlu fault zone a case study based on short period dense seismic array experiment abstract the 1896 high quality relative travel time residuals are collected by applying the multi channel cross correlation technique to the waveform data of teleseismic events recorded by a short period dense seismic array consisting of 302 stations in the weifang segment of the tanlu fault zone using the fast marching teleseismic tomography technique these residuals are inverted for a fine p wave crustal velocity model under the study region down to 30 km depth with the resolution of 20 km in horizontal directions and 30 km in depth we image obvious high velocity anomalies to the west of the fault zone from the surface down to a depth of 30 km and striking low velocity anomalies appear within the fault zone around 36 5 n where the changle volcano exists on the surface whilst to the east velocity anomalies exhibit a complicated pattern meanwhile our tomographic images roughly show a boundary between the fault zone and its surrounding areas we infer that the fault zone provides a plausible channel for continuous upwelling of hot and wet materials from the mantle to the surface when it intruded into the crust the process of upwelling of hot and wet materials from the mantle could be associated with mantle dynamics of the big mantle wedge due to the stagnation and dehydration of the subducted pacific slab in the mantle transition zone under the region our present study demonstrates that it is possible that a fine crustal velocity structure can be obtained by teleseismic tomography with a short period dense seismic array

migration of early aftershocks following the 2004 parkfield earthquake a significant number of the early aftershocks following large shallow earthquakes are missing in existing earthquake catalogues an analysis of the waveforms of 3 647 relocated earthquakes along the parkfield section of the san andreas fault reveals 11 times more aftershocks within three days of the 2004 parkfield earthquake than listed in a standard catalogue large shallow earthquakes are immediately followed by numerous aftershocks a significant portion of these events is missing in existing earthquake catalogues mainly because seismicity after the mainshock can be masked by overlapping arrivals of waves from the mainshock and aftershocks1 2 3 4 however recovery of the missing early aftershocks is important for understanding the physical mechanisms of earthquake triggering2 3 4 and for tracking postseismic deformation around the rupture zone associated with the mainshock5 6 7 here we use the waveforms of 3 647 relocated earthquakes8 along the parkfield section of the san andreas fault as templates9 10 to detect missing aftershocks within three days of the 2004 magnitude 6 0 parkfield earthquake we identify 11 times more aftershocks than listed in the standard catalogue of the northern california seismic network we find that the newly detected aftershocks migrate in both along strike and down dip directions with logarithmic time since the mainshock consistent with numerical simulations of the expansion of aftershocks caused by propagating afterslip11 12 the cumulative number of early aftershocks increases linearly with postseismic deformation in the first two days supporting the view that aftershocks are driven primarily by afterslip13 14

fault plane determination of the 18 april 2008 mount carmel illinois earthquake by detecting and relocating aftershocks we developed a sliding window cross correlation scc detection technique and applied the technique to continuous waveforms recorded by the cooperative new madrid seismic network stations following the 18 april 2008 illinois earthquake the technique detected more than 120 aftershocks down to m l 1 0 in the 2 week time window following the mainshock which is three times more than the number of aftershocks reported by the seismic network most aftershocks happened within 24 hrs of the mainshock we then relocated all events by the double difference relocation algorithm accurate p and s wave differential arrival times between events were obtained by waveform cross correlation after relocation we used the l1 norm to fit all located events by a plane to determine the mainshock fault plane the best fit plane has a strike of 292 11 and dips 81 7 to the northeast this plane agrees well with the focal mechanism solutions of the mainshock and four largest aftershocks by combining the aftershock locations and focal mechanism solutions we conclude that the 18 april earthquake occurred on a nearly vertical left lateral strike slip fault orienting in the west northwest east southeast direction the fault coincides with the proposed left stepping divide accommodation zone in the la salle deformation belt and indicates reactivation of old deformation zone by contemporary stresses in the midcontinent

foreshocks explained by cascades of triggered seismicity 1 the observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock when averaging over many sequences using southern california seismicity we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes without arbitrary distinction between foreshocks aftershocks and mainshocks we find that foreshock precursory properties are independent of the mainshock size this implies that earthquakes large or small are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering the cascades of triggering give rise naturally to long range and long time interactions which can explain the observations of correlations in seismicity over surprisingly large length scales