applying the coulomb failure function with an optimally oriented plane to the 2008 mw 7 9 wenchuan earthquake triggering the coulomb failure function cff quantitatively describes static stress changes in secondary faults near the source fault of an earthquake cff can be employed to monitor how static stress transfers and then shed some light on the probability of successive events occurring around a source fault in this paper we focus on the cff and particularly on optimally oriented planes we present a unified model to determine an optimally oriented plane and its corresponding coulomb stress then apply the model to the 2003 mw 6 6 bam iran earthquake and the 2008 mw 7 9 wenchuan china earthquake thereby checking its effectiveness our results show that spatial correlation between positive coulomb stress changes and aftershocks are for the 2003 bam earthquake 47 06 when elastic coulomb stress changes are resolved on uniform planes and 87 53 when these are resolved on optimally oriented planes at depth for the 2008 wenchuan earthquake the correlations are 45 68 and 58 20 respectively it is recommended that account be taken of optimally oriented planes when drawing a coulomb stress map for analyzing earthquake triggering effects

surface deformation and stress interactions during the 2007 2010 sequence of earthquake dyke intrusion and eruption in northern tanzania s u m m a r y magma movement and fault slip alter the magnitude and orientation of the stress in the surrounding crust observations of a sequence of events clustered in space and time provide information about the triggering mechanism and stress interactions between magma intrusion earthquakes and eruptions we investigate the synand post intrusion stress changes associated with the 2007 gelei dyke intrusion episode and subsequent eruption of nearby oldonyo lengai previous studies produced a kinematic model of the 2007 june august sequence involving 1m slip on a normal fault followed by the intrusion of the 7 10 km long gelei dyke collapse of a shallow graben and the deflation of the gelei magma chamber immediately following this the volcano oldoinyo lengai 10 km away experienced a new phase of explosive activity lasting for several months here we present new geodetic observations covering gelei and oldoinyo lengai in 2008 september 2010 we show continued slip on graben bounding faults above the gelei dyke the eruption of oldoinyo lengai was accompanied by the intrusion of a 4 km long e w trending dyke followed by deflation of a shallow source directly below the summit of the volcano next we use stress calculations to investigate a number of hypotheses linking these events 1 before the onset of surface deformation a dyke sufficiently deep and narrow to be geodetically undetectable could still have produced sufficient stress changes to trigger slip on the normal fault i e the sequence could have been magmatically driven 2 stresses at the dyke tip would have been sufficient to overcome the effect of continued slip on the normal fault allowing the dyke to propagate upwards into a region of clamping 3 the gelei sequence would have produced a significant stress change on the chamber beneath oldoinyo lengai these static stress calculations allow us to discuss the roles played by dynamic stress deeper magmatic changes and background stresses throughout the sequence with implications for the stress triggering of both seismic and volcanic hazards

role of fluids in the earthquake occurrence around aswan reservoir egypt 1 continuing seismicity for about 30 years near a large western embayment of the lake nasser about 50 km from the aswan high dam in egypt has led to a debate about the possibility of its relation with the reservoir impoundment the largest event in the region occurred on 14 november 1981 m 5 3 20 km beneath the wadi kalabsha embayment a westward extension of the lake aswan since then continuous monitoring of seismic activity has given an excellent opportunity to study the spatiotemporal distribution of seismicity in the area most of the immediate aftershocks of the 1981 main shock were located in the gebel marawa area at depths between 15 and 30 km depths of almost all earthquakes away from this zone were shallower than 12 km to quantify the effect of the reservoir impoundment on the seismicity of the aswan area we calculated changes in stress and pore pressure due to the reservoir impoundment using green s function approach the change in coulomb stress s is calculated on the fault planes responsible for majority of the seismicity of the region we found that for all the seismogenic faults s is negative i e stabilizing when we consider the effect of the reservoir load only whereas it is positive i e destabilizing when we include pore pressure for example at the hypocenter of the main earthquake shear stress normal stress and pore pressure due to reservoir operation are estimated as 5 5 13 2 and 13 5 kpa respectively which suggest that s is 3 1 kpa when we do not consider the effect of pore pressure and 5 7 kpa when contribution from pore pressure is considered hence the seismicity in the aswan lake region is driven by the pore pressure due to reservoir impoundment

link between coulomb stress changes and seismic activation in the eastern marmara sea after the 1999 izmit turkey earthquake 1 we investigate the effect of dynamic and static stress changes produced by the 1999 izmit earthquake on four preexisting seismic clusters located in the eastern marmara sea beyond the western termination of the earthquake rupture these four clusters show long lasting modifications in their seismicity rate we observe that these seismic activity variations are related to stress changes dynamic stress pulses activate strike slip faulting instantaneously but in the absence of a concomitant static coulomb stress increase this activation is short lived indeed a large dynamic stress combined with a negative static coulomb stress may result in an immediate activation followed by the occurrence of a seismicity shadow in contrast the activation of extensional clusters begins slowly and takes a few days to fully develop it is also remarkably long lasting and does not follow a classical omori decay more than 10 years after the earthquake the extensional clusters located near the termination of the rupture where static stress and pressure changes were high are still activated

stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 mw 6 9 zemmouri algeria earthquake stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake 1 the essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated first through idealized examples and then by study of thrust faulting in algeria we calculated coseismic stress changes caused by the 2003 m w 6 9 zemmouri earthquake finding that a large majority of the zemmouri afterslip sites were brought several bars closer to coulomb failure by the coseismic stresses while the majority of aftershock nodal planes were brought closer to failure by an average of 2 bars further we calculated that the shallow portions of the adjacent thenia tear fault which sustained 0 25 m slip were brought 2 bars closer to failure we calculated that the coulomb stress increased by 1 5 bars on the deeper portions of the adjacent boumerdes thrust which lies just 10 20 km from the city of algiers both the boumerdes and thenia faults were illuminated by aftershocks over the next 6 years the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity the stress also increased by 0 4 bar on the east sahel thrust fault west of the zemmouri rupture algiers suffered large damaging earthquakes in a d 1365 and 1716 and is today home to 3 million people if these shocks occurred on the east sahel fault and if it has a 2 mm yr tectonic loading rate then enough loading has accumulated to produce a m w 6 6 6 9 shock today thus these potentially lethal faults need better understanding of their slip rate and earthquake history among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake

trends in uk extreme sea levels a spatial approach the majority of studies of long term sea level change have concentrated on the trend in mean sea level which is just one constituent of the trend in extreme sea level by fitting a spatial model to sea level annual maxima from 62 uk sites extreme sea level trend estimates are obtained for the entire british coastline these estimates exhibit smooth but significant spatial variation which arises from a combination of eustatic extreme sea level change and local vertical land movements once the latter effect is removed eustatic extreme sea level trends are found to have no significant spatial variation and to be similar in value to trends in uk eustatic mean sea level

sensitivity of coulomb stress change to the parameters of the coulomb failure model a case study using the 2008 mw 7 9 wenchuan earthquake the coulomb stress change has been widely employed to interpret mainshock mainshock and mainshock aftershock triggering as well as interactions amongst earthquake faults and volcanoes this quantitative index is computed based on the coulomb failure criterion and is a function of fault parameters including the source and receiver fault geometries the friction coefficient on the receiver fault and skempton s coefficient of the host rock thus for the robust determination of the coulomb stress change the sensitivity of the coulomb stress change to these model parameters should be thoroughly assessed however notwithstanding numerous case studies almost no systematic investigation of the sensitivity of the coulomb stress change has been performed here we present an error estimator for the coulomb stress change and then quantitatively investigate the sensitivity of the coulomb stress change to the fault model parameters for the 2008 mw 7 9 wenchuan earthquake our results indicate that for this case the coulomb stress change is the most sensitive to the uncertainty in the dip angle of the receiver fault while the influences of the uncertainties in the slip model of the source fault the strike and rake angles of the receiver fault and the friction and skempton s coefficients cannot be neglected accordingly it is crucial to perform a realistic estimate of the uncertainty in the coulomb stress change by performing such calculation future coulomb stress analyses such as the stress triggering of earthquake sequence and the likelihoods of potential earthquakes could be based on more robust coulomb stress change maps

post seismic viscoelastic deformation and stress transfer after the 1960 m9 5 valdivia chile earthquake effects on the 2010 m8 8 maule chile earthquake author posting the authors 2014 this article is posted here by permission of the royal astronomical society for personal use not for redistribution the definitive version was published in geophysical journal international 197 2014 697 704 doi 10 1093 gji ggu048

modeling seismicity rate changes during the 1997 umbria marche sequence central italy through a rate and state dependent model 1 we model the spatial and temporal pattern of seismicity during a sequence of moderate magnitude normal faulting earthquakes which struck in 1997 the umbria marche sector of northern apennines italy by applying the dieterich 1994 rate and state dependent constitutive approach the goal is to investigate the rate of earthquake production caused by repeated coseismic stress changes computed through a 3 d elastic dislocation model in a homogeneous half space the reference seismicity rate is assumed time independent and it is estimated by smoothing the seismicity that occurred in the previous decade without declustering we propose an analytical relation for deriving the stressing rate directly from the reference seismicity rate this allows us to perform a tuning of the constitutive parameter a where a accounts for the direct effect of friction in the rate and state dependent model and is the effective normal stress into the dieterich model through a maximum likelihood method which yields for this seismic sequence a best fitting value equal to 0 04 mpa our computations show that although seven out of eight main shocks are located in areas of increased rate of earthquake production numerous aftershocks are located in seismicity shadows our simulations point out that the adopted value of a strongly affects the pattern of both seismicity shadow and areas of enhanced rate of earthquake production we conclude that solely accounting for static stress changes caused by the main shocks of this seismic sequence is not sufficient to forecast the complex spatial and temporal evolution of seismicity

stress triggering of the great indian ocean strike slip earthquakes in a diffuse plate boundary zone 1 on april 11 2012 two great magnitude 8 earthquakes occurred within a two hour period off the west coast of northern sumatra indonesia in the broadly distributed india australia plate boundary zone the magnitude 8 6 mainshock holds the distinction of being both the largest instrumentally recorded strike slip earthquake and the largest earthquake away from a recognized plate boundary fault the mainshock involved sequential ruptures of multiple fault planes oriented nearly perpendicular to each other the adjacent 2004 megathrust earthquake statically loaded the northern wharton basin oceanic lithosphere on both of the 2012 mainshock fault plane orientations and greatly enhanced the rate of earthquake activity in the region for a year viscoelastic relaxation of the asthenosphere following the 2004 and 2005 megathrust earthquakes continued to positively stress the offshore region correlating with the locations of later strike slip earthquakes including two magnitude 7 and the 2012 magnitude 8 earthquakes

delayed triggering of the 1999 hector mine earthquake by viscoelastic stress transfer stress changes in the crust due to an earthquake can hasten the failure of neighbouring faults and induce earthquake sequences in some cases1 2 3 4 5 the 1999 hector mine earthquake in southern california magnitude 7 1 occurred only 20 km from and 7 years after the 1992 landers earthquake magnitude 7 3 this suggests that the hector mine earthquake was triggered in some fashion by the earlier event but uncertainties in the slip distribution and rock friction properties associated with the landers earthquake have led to widely varying estimates of both the magnitude and sign of the resulting stress change that would be induced at the location of the hector mine hypocentre with estimates varying from 1 4 bar ref 6 to 0 5 bar ref 7 more importantly coseismic stress changes alone cannot satisfactorily explain the delay of 7 years between the two events here we present the results of a three dimensional viscoelastic model that simulates stress transfer from the ductile lower crust and upper mantle to the brittle upper crust in the 7 years following the landers earthquake using viscoelastic parameters that can reproduce the observed horizontal surface deformation following the landers earthquake our calculations suggest that lower crustal or upper mantle flow can lead to postseismic stress increases of up to 1 2 bar at the location of the hector mine hypocentre during this time period contributing to the eventual occurrence of the 1999 hector mine earthquake these results attest to the importance of considering viscoelastic processes in the assessment of seismic hazard8 9 10 11

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

near prospective test of coulomb stress triggering numerous studies retrospectively observed a strong association between earthquake location and increased static coulomb stress in addition to confirming these results for southern california seismicity we observed prospective forecasting potential in static stress evolution with 141 seismic and 98 aseismic stress sources we considered alternate choices of stress components and receiver fault orientations examined the effect of coulomb triggering on earthquake magnitude calculated stress histories for receiver quakes to see if some occurred after their stress had peaked examined whether stress changes from the hector mine earthquake alone changed the earthquake rate as expected and estimated the conditional distribution of earthquake occurrence given resolved coulomb stress change we found that with 95 confidence m 2 8 receiver earthquakes nucleate in areas of shear or coulomb stress change increase on average 59 of earthquakes occurred within stress enhanced zones regardless of the choice of rupture plane or type of stress change the 1999 hector mine california earthquake increased the seismicity in regions of positive and negative stress change but more so in the positive regions earthquakes frequently occur after their calculated peak stress has occurred indicating that elastic calculations do not tell the whole story we found no significant evidence that stress change affects the magnitude of receiver quakes thus instantaneous coulomb and shear stress change apparently influence the locations but not the magnitudes of future earthquakes

slip maxima at fault junctions and rupturing of barriers during the 2008 wenchuan earthquake the devastating wenchuan earthquake in 2008 struck along a fault zone that showed low rates of deformation analysis of gps and insar data suggests that as structural barriers failed during a single earthquake the rupture cascaded across multiple fault segments which may explain the high magnitude of the event

the 2011 m 9 0 tohoku oki earthquake more than doubled the probability of large shocks beneath tokyo 1 the kanto seismic corridor surrounding tokyo has hosted four to five m 7 earthquakes in the past 400 years immediately after the tohoku earthquake the seismicity rate in the corridor jumped 10 fold while the rate of normal focal mechanisms dropped in half the seismicity rate decayed for 6 12 months after which it steadied at three times the pre tohoku rate the seismicity rate jump and decay to a new rate as well as the focal mechanism change can be explained by the static stress imparted by the tohoku rupture and postseismic creep to kanto faults we therefore fit the seismicity observations to a rate state coulomb model which we use to forecast the time dependent probability of large earthquakes in the kanto seismic corridor we estimate a 17 probability of a m 7 0 shock over the 5 year prospective period 11 march 2013 to 10 march 2018 two and a half times the probability had the tohoku earthquake not struck

rupture of deep faults in the 2008 wenchuan earthquake and uplift of the longmen shan the longmen shan mountains rise up 6 000 m over a distance of just 100 km but the mechanisms driving formation of this striking topography are debated analyses of crustal movements during the 2008 wenchuan earthquake suggest that fault induced uplift plays a role in building the high topography

aftershock modeling based on uncertain stress calculations 1 we discuss the impact of uncertainties in computed coseismic stress perturbations on the seismicity rate changes forecasted through a rate and state dependent frictional model we aim to understand how the variability of coulomb stress changes affects the correlation between predicted and observed changes in the rate of earthquake production we use the aftershock activity following the 1992 m7 3 landers california earthquake as a case study to accomplish these tasks we first analyze the variability of stress changes resulting from the use of different published slip distributions we find that the standard deviation of the uncertainty is of the same size as the absolute stress change and that their ratio the coefficient of variation cv is approximately constant in space this uncertainty has a strong impact on the forecasted aftershock activity if a rate and state frictional model is considered we use the early aftershocks to invert for friction parameters and the coefficient of variation by means of the maximum likelihood method we show that when the uncertainties are properly taken into account the inversion yields stable results which fit the spatiotemporal aftershock sequence the analysis of the 1992 landers sequence demonstrates that accounting for realistic uncertainties in stress changes strongly improves the correlation between modeled and observed seismicity rate changes for this sequence we measure a friction parameter asn 0 017 mpa and a coefficient of stress variation cv 0 95

stress coupling between earthquakes in northwest turkey and the north aegean sea we have investigated the coulomb stress interactions of 29 earthquakes m s greater than or equal to 6 0 that have occurred in the region of northwest turkey and north aegean sea since 1912 of these events 23 may be related to earlier events and 16 are clearly related to earlier events all events after 1967 are related to previous events events in the early part of our time interval that show no correlation could be related to historical events as yet unidentified in some cases faults that have received a stress reduction from earlier events are prepared for an event by an earthquake occurring a few years before that creates a local coulomb stress rise thus regions of coulomb stress shadow can become regions where a damaging earthquake may occur the relation between smaller events and the coulomb stress distribution is less clear but may be related to poor data quality and practical limitations of our modeling technique nonetheless there are 4 times as many events per unit area in regions of enhanced stress than where stress is reduced we discuss the contemporary distribution of coulomb stress and argue that it is possible to identify the likely locations of future damaging earthquakes including identifying the most likely candidate faults

static stress interactions in extensional earthquake sequences an example from the south lunggar rift tibet 1 an extensional earthquake sequence occurred in 2004 8 across a graben in the south lunggar rift on the tibetan plateau we use insar data to determine the location fault geometry and slip distribution of these earthquakes and to test whether the sequence is compatible with static stress triggering the mw 6 2 and 6 3 earthquakes in 2004 and 2005 both ruptured west dipping faults on the east side of a graben in 2008 a mw 6 7 earthquake ruptured a pair of east dipping fault segments on the other side of the graben offset from the earlier ruptures we compute first order dislocation models of stress change and demonstrate that the order and spatial configuration of this sequence of events is compatible with triggering by static stress transfer a continuation of the sequence would be most likely to occur on the northern extension of the 2008 rupture although variable slip rate along the rift may mean that the sequence has run its course the insar data for the 2008 earthquake also reveal slip on a fault that cuts the graben at a highly oblique angle we suggest that this is a release fault accommodating differential throw in the hanging wall and associate the deformation with a mw 6 0 aftershock activity on such a release fault has not been directly imaged before the zhongba sequence is one of several examples of recent clustered normal fault earthquakes on the plateau and may be an example of phase locking of similar faults

assessing elastic coulomb stress transfer models using seismicity rates in southern california and southwestern japan 1 we investigated whether observed changes in seismicity rate following the 1992 landers and 1995 kobe earthquakes correspond with predictions from coulomb stress transfer models to quantify the relationship between coulomb stress change and seismicity rate change we compared spatial changes in observed seismicity rates to the modeled changes in coulomb failure stress cfs for the two subject earthquakes we begin with the simplest and most common cfs model which assumes that regional stress orientations are uniform and the stress change is resolved on optimally oriented strike slip planes we then extended the cfs models to include the more geophysically realistic assumptions of spatially varying regional stress orientations and optimally oriented planes in three dimensions for all the tested cfs models we found that virtually everywhere seismicity rate changes could be resolved the rate increased regardless of whether the cfs theoretically promoted or inhibited failure and that we were not able to reliably resolve seismicity rate decreases an improvement in the correlation between the sign of the cfs and where rate increases occur when estimating the cfs on optimally oriented planes in three dimensions rather than two dimensions is a consequence of using optimally oriented planes and the ability to primarily observe rate increases the region of positive cfs increases by allowing more degrees of freedom so the correlation with positive rate change appears to increase the areas of highest seismicity rate following the main shock did not correlate with the sign or the magnitude of the cfs rather the areas most active after the main shock were also the most active before the main shock

gps and seismic constraints on the m 7 3 2009 swan islands earthquake implications for stress changes along the motagua fault and other nearby faults summary we use measurements at 35 gps stations in northern central america and 25 seismometers at teleseismic distances to estimate the distribution of slip source time function and coulomb stress changes of the mw 7 3 2009 may 28 swan islands fault earthquake this event the largest in the region for several decades ruptured the offshore continuation of the seismically hazardous motagua fault of guatemala the site of the destructive ms 7 5 earthquake in 1976 measured gps offsets range from 308 millimetres at a campaign site in northern honduras to 6 millimetres at five continuous sites in el salvador separate inversions of geodetic and seismic data both indicate that up to 1 m of coseismic slip occurred along a 250 km long rupture zone between the island of roatan and the eastern limit of the 1976 m 7 5 motagua fault earthquake in guatemala evidence for slip 250 km west of the epicentre is corroborated independently by aftershocks recorded by a local seismic network and by the high concentration of damage to structures in areas of northern honduras adjacent to the western limit of the rupture zone coulomb stresses determined from the coseismic slip distribution resolve a maximum of 1 bar of stress transferred to the seismically hazardous motagua fault and further indicate unclamping of normal faults along the northern shore of honduras where two m 5 normal faulting earthquakes and numerous small earthquakes were triggered by the main shock

the stress shadow induced by the 1975 1984 krafla rifting episode 1 it has been posited that the 1975 1984 krafla rifting episode in northern iceland was responsible for a significant drop in the rate of earthquakes along the husavik flatey fault hff a transform fault that had previously been the source of several magnitude 6 7 earthquakes this compelling case of the existence of a stress shadow has never been studied in detail and the implications of such a stress shadow remain an open question according to rate state models intense stress shadows cause tens of years of low seismicity rate followed by a faster recovery phase of rate increase here we compare the long term predictions from a coulomb stress model of the rifting episode with seismological observations from the sil catalog 1995 2011 in northern iceland in the analyzed time frame we find that the rift induced stress shadow coincides with the eastern half of the fault where the observed seismicity rates are found to be significantly lower than expected given the historical earthquake activity there we also find that the seismicity rates on the central part of the hff increased significantly in the last 17 years with the seismicity progressively recovering from west to east our observations confirm that rate state theory successfully describes the long term seismic rate variation during the reloading phase of a fault invested by a negative coulomb stress coincident with this recovery we find that the b value of the frequency magnitude distribution changed significantly over time we conclude that the rift induced stress shadow not only decreased the seismic rate on the eastern part of the hff but also temporarily modified how the system releases seismic energy with more large magnitude events in proportion to small ones this behavior is currently being overturned as rift induced locking is now being compensated by tectonic forcing

improving empirical aftershock modeling based on additional source information 1 several mechanisms are proposed to underlie earthquake triggering including static stress interactions and dynamic stress transfer significant differences of these mechanisms are particularly expected in the spatial distribution of aftershocks however testing the different hypotheses is challenging because it requires the consideration of the large uncertainties involved in stress calculations as well as the appropriate consideration of secondary aftershock triggering which is related to stress changes induced by smaller pre and aftershocks in order to evaluate the forecast capability of different mechanisms we take the effect of smaller magnitude earthquakes into account by using the epidemic type aftershock sequence etas model where the spatial probability distribution of direct aftershocks if available is correlated to alternative source information and mechanisms we test surface shaking rupture geometry and slip distributions as an approximation of the shaking level we use shakemap data which are available in near real time after a main shock and thus could be used for first order forecasts of the spatial aftershock distribution alternatively we test the use of empirical decay laws related to minimum fault distance and coulomb stress change calculations based on published and random slip models for comparison we analyze the likelihood values of the different model combinations in the case of several well known aftershock sequences 1992 landers 1999 hector mine 2004 parkfield our test shows that the fault geometry is the most valuable information for improving aftershock forecasts furthermore we find that static stress maps can additionally improve the forecasts of off fault aftershock locations while the integration of ground shaking data could not upgrade the results significantly

stress triggering and the canterbury earthquake sequence the canterbury earthquake sequence which includes the devastating christchurch event of 2011 february has to date led to losses of around 40 billion nz dollars the location and severity of the earthquakes was a surprise to most inhabitants as the seismic hazard model was dominated by an expected mw 8 earthquake on the alpine fault and an mw 7 5 earthquake on the porters pass fault 150 and 80 km to the west of christchurch the sequence to date has included an mw 7 1 earthquake and 3 mw 5 9 events which migrated from west to east here we investigate whether the later events are consistent with stress triggering and whether a simple stress map produced shortly after the first earthquake would have accurately indicated the regions where the subsequent activity occurred we find that 100 per cent of m 5 5 earthquakes occurred in positive stress areas computed using a slip model for the first event that was available within 10 d of its occurrence we further find that the stress changes at the starting points of major slip patches of post darfield main events are consistent with triggering although this is not always true at the hypocentral locations our results suggest that coulomb stress changes contributed to the evolution of the canterbury sequence and we note additional areas of increased stress in the christchurch region and on the porters pass fault

impact of the receiver fault distribution on aftershock activity 1 aftershock models are usually based either on purely empirical relations ignoring the physical mechanism or on deterministic calculations of stress changes on a predefined receiver fault orientation here we investigate the effect of considering more realistic fault systems in models based on static coulomb stress changes for that purpose we perform earthquake simulations with elastic half space stress interactions rate and state dependent frictional earthquake nucleation and extended ruptures with heterogeneous fractal slip distributions we find that the consideration of earthquake nucleation on multiple receiver fault orientations does not influence the shape of the temporal omori type aftershock decay but changes significantly the predicted spatial patterns and the total number of triggered events so called stress shadows with decreased activity almost vanish and activation decays continuously with increasing distance from the main shock rupture the total aftershock productivity which is shown to be almost independent of the assumed background rate increases significantly if multiple receiver fault planes exist the application to the 1992 m7 3 landers california aftershock sequence indicates a good agreement with the locations and the total productivity of the observed directly triggered aftershocks

large extensional aftershocks in the continental forearc triggered by the 2010 maule earthquake chile summary the mw 8 8 maule earthquake occurred off the coast of central chile on 2010 february 27 and was the sixth largest earthquake to be recorded instrumentally this subduction zone event was followed by thousands of aftershocks both near the plate interface and in the overriding continental crust here we report on a pair of large shallow crustal earthquakes that occurred on 2010 march 11 within 15 min of each other near the town of pichilemu on the coast of the o higgins region of chile field and aerial reconnaissance following the events revealed no distinct surface rupture we infer from geodetic data spanning both events that the ruptures occurred on synthetic sw dipping normal faults the first larger rupture was followed by buried slip on a steeper fault in the hangingwall the fault locations and geometry of the two events are additionally constrained by locations of aftershock seismicity based on the international maule aftershock data set the maximum slip on the main fault is about 3 m and consistent with field results the onshore slip is close to zero near the surface satellite radar data also reveal that significant aseismic afterslip occurred following the two earthquakes coulomb stress modelling indicates that the faults were positively stressed by up to 40 bars as a result of slip on the subduction interface in the preceding megathrust event in other words the pichilemu earthquakes should be considered aftershocks of the maule earthquake the occurrence of these extensional events suggests that regional interseismic compressive stresses are small several recent large shallow crustal earthquakes in the overriding plate following the 2011 mw 9 0 tohoku oki earthquake in japan may be an analogue for the triggering process at pichilemu

observations of static coulomb stress triggering of the november 2011 m5 7 oklahoma earthquake sequence in november 2011 a m5 0 earthquake occurred less than a day before a m5 7 earthquake near prague oklahoma which may have promoted failure of the mainshock and thousands of aftershocks along the wilzetta fault including a m5 0 aftershock the m5 0 foreshock occurred in close proximity to active fluid injection wells fluid injection can cause a buildup of pore fluid pressure decrease the fault strength and may induce earthquakes keranen et al 2013 links the m5 0 foreshock with fluid injection but the relationship between the foreshock and successive events has not been investigated here we examine the role of coseismic coulomb stress transfer on earthquakes that follow the m5 0 foreshock including the m5 7 mainshock we resolve the static coulomb stress change onto the focal mechanism nodal plane that is most consistent with the rupture geometry of the three m 5 0 earthquakes as well as specified receiver fault planes that reflect the regional stress orientation we find that coulomb stress is increased e g fault failure is promoted on the nodal planes of 60 of the events that have focal mechanism solutions and more specifically that the m5 0 foreshock promoted failure on the rupture plane of the m5 7 mainshock we test our results over a range of effective coefficient of friction values hence we argue that the m5 0 foreshock induced by fluid injection potentially triggered a cascading failure of earthquakes along the complex wilzetta fault system

stress perturbations and seismic response associated with the 2011 m9 0 tohoku oki earthquake in and around the tokai seismic gap central japan 1 the m9 0 tohoku oki event is the largest earthquake in japan s modern history social concerns and scientific interests require an urgent evaluation of this event s impact on other megathrust zones nearby japan here we investigate the stress transfer from the tohoku oki event on the tokai subduction zone where an m8 class megathrust earthquake has been long time anticipated first we demonstrate that the clear increase of crustal seismicity around izu peninsula near the tokai gap is the consequence of a coulomb static stress increase due to the tohoku oki earthquake calculated using a variable slip model for the mainshock and regional focal mechanisms of events occurred before and after the m9 0 earthquake the largest stress increase is of about 1 0 bar as estimated on earthquake nodal planes of maximum stress change the time decay characteristics of the activated seismicity favor the triggering by static stresses such validations of the coulomb hypothesis support our stress perturbation assessment on the tokai gap to precisely calculate the stress changes on the tokai source we use the curved plate interface and plate motion inferred rake directions the computed stress changes are predominantly positive but have relatively small values of less than 0 1 bar the large afterslip mw8 6 and the aftershocks following the tohoku oki earthquake caused additional but minor stress increases our results imply that the stress state on the tokai plane did not change significantly after the tohoku oki event however static stress driven seismic activation in neighboring areas can bring a secondary impact on the interplate seismicity

april 2012 intra oceanic seismicity off sumatra boosted by the banda aceh megathrust the two earthquakes of respective magnitudes 8 6 and 8 2 that occurred off the coast of the sumatra subduction zone on 11 april 2012 are shown to be part of a continuing boost of the intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes on 11 april 2012 two of the largest strike slip earthquakes ever recorded at magnitudes of 8 7 and 8 2 occurred in the northeastern indian ocean a few hundred kilometres off the coast of sumatra three groups now report the analysis of seismic data from the days and months before and after these events as well as the events themselves matthias delescluse and co authors show that these earthquakes are part of the ongoing boost of intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes they conclude that the australian plate driven by slab pull forces at the sunda trench is gradually detaching from the indian plate han yue and colleagues show that the 11 april event involved a complex four fault rupture lasting several minutes followed two hours later by a magnitude 8 2 aftershock these great ruptures on a lattice of strike slip faults that extends through the crust and into the upper mantle represent large lithospheric deformation that may eventually create a localized boundary between the indian and australian plates fred pollitz and colleagues show that in the six days following 11 april the global rate of remote earthquakes with magnitudes greater than 5 5 increased nearly fivefold and events up to magnitude 7 seem to have been triggered the unprecedented delayed triggering power of this earthquake may arise from its strike slip source geometry or because it struck at a time of an unusually low global earthquake rate and increased the number of nucleation sites that were very close to failure large earthquakes nucleate at tectonic plate boundaries and their occurrence within a plate s interior remains rare and poorly documented especially offshore the two large earthquakes that struck the northeastern indian ocean on 11 april 2012 are an exception they are the largest strike slip events reported in historical times1 2 and triggered large aftershocks worldwide3 yet they occurred within an intra oceanic setting along the fossil fabric of the extinct wharton basin rather than on a discrete plate boundary4 5 6 7 8 here we show that the 11 april 2012 twin earthquakes are part of a continuing boost of the intraplate deformation between india and australia that followed the aceh 2004 and nias 2005 megathrust earthquakes subsequent to a stress transfer process recognized at other subduction zones9 10 using coulomb stress change calculations we show that the coseismic slips of the aceh and nias earthquakes can promote oceanic left lateral strike slip earthquakes on pre existing meridian aligned fault planes we further show that persistent viscous relaxation in the asthenospheric mantle several years after the aceh megathrust explains the time lag between the 2004 megathrust and the 2012 intraplate events on a short timescale the 2012 events provide new evidence for the interplay between megathrusts at the subduction interface and intraplate deformation offshore on a longer geological timescale the australian plate driven by slab pull forces at the sunda trench is detaching from the indian plate which is subjected to resisting forces at the himalayan front6 8 11

indonesian earthquake earthquake risk from co seismic stress last year s indonesian earthquake has increased seismic hazard in the region the scale of death and destruction caused by the recent sumatra andaman islands earthquake and its tsunami has raised concerns that another earthquake might be triggered on the contiguous sunda trench subduction zone a new calculation of stress distribution here and on the neighbouring sumatra fault reveals stress build up on both structures severe enough to increase the already high earthquake hazard this finding makes the need for an indian ocean tsunami warning system all the more pressing following the massive loss of life caused by the sumatra andaman earthquake in indonesia and its tsunami the possibility of a triggered earthquake on the contiguous sunda trench subduction zone is a real concern we have calculated the distributions of co seismic stress on this zone as well as on the neighbouring vertical strike slip sumatra fault and find an increase in stress on both structures that significantly boosts the already considerable earthquake hazard posed by them in particular the increased potential for a large subduction zone event in this region with the concomitant risk of another tsunami makes the need for a tsunami warning system in the indian ocean all the more urgent

simultaneous long term and short term slow slip events at the hikurangi subduction margin new zealand implications for processes that control slow slip event occurrence duration and migration 1 we document a sequence of simultaneous short term and long term slow slip events sses at the hikurangi subduction zone during the 2010 2011 period the sequence of short term events each 2 3 weeks in duration ruptured much of the shallow plate interface 15 km at central and northern hikurangi over a 6 month period was accompanied by microseismicity and involved patchy irregular migration of sse slip we suggest that the patchy migration of the short term sse is due to large scale 100 3500 km heterogeneities on the plate interface related to seamount subduction and sediment subduction and or underplating this is in contrast to a 2010 2011 long term sse at the central hikurangi margin which evolved steadily over 1 5 years and ruptured much of the plate interface between 20 and 70 km depth we suggest that the occurrence of long term versus short term sses at hikurangi is related to differences in effective normal stresses and relative heterogeneity of the subduction interface the long term sse sequence began 1 year before the short term sequence coulomb stress change models suggest that the long term sse may have triggered initiation of the subsequent short term sse sequence initiation of the short term sequence occurred in a region just updip of or within an interseismically locked portion of the plate interface and may be located within the updip transition from seismic to aseismic behavior alternatively it could be characteristic of a region undergoing partial interseismic coupling this is in contrast to sses observed elsewhere in the world that typically occur within the downdip transition from seismic to aseismic behavior

interseismic coupling stress evolution and earthquake slip on the sunda megathrust 1 the extent to which interseismic coupling controls the slip distribution of large megathrust earthquakes is unclear with some authors proposing that it is the primary control and others suggesting that stress changes from previous earthquakes are of first order importance here we develop a detailed stress history of the sunda megathrust modified by coupling and compare the correlation between slip and stress with that of slip versus coupling we find that the slip distributions of recent earthquakes are more consistent with the stress field than with the coupling distributions but observe that in places the stress pattern is strongly dependent on poorly constrained values of slip in historical earthquakes we also find that of the 13 earthquakes in our study for which we have hypocentral locations only two appear to have nucleated in areas of negative stress and these locations correspond to large uncertainties in the slip distribution of pre instrumental events citation nalbant s j mccloskey s steacy m nicbhloscaidh and s murphy 2013 interseismic coupling stress evolution and earthquake slip on the sunda megathrust geophys res lett 40 4204 4208

coseismic deformation from the 2008 wenchuan china earthquake derived from alos palsar images abstract we analyzed alos palsar images along eight paths acquired before and after the mainshock of an earthquake in wenchuan in the sichuan province of china may 12 2008 we found entire coseismic deformation features and detected many fringes in an approximately 100 km wide region surrounding the longmen shan fault zone we found 6 7 broad elliptic fringes north of the epicenter which indicated around 70 80 cm increase in range distance between the ground and satellite this pattern corresponded to subsidence or eastward shift of ground which is often seen above the lower margin of a low angled thrust we also counted 8 9 fringes i e 90 100 cm range decrease between the fault zone and chengdu chengdu is located roughly 50 km away from the pengguan fault which is the southernmost trace of the longmen shan fault zone as this area is located on the footwall side the pattern suggested a westward shift of the earth s surface however we could not obtain high correlations due to large displacements in the about 240 km long belt along the surface faults several concentric fringes were found along the beichuan fault which is the central trace of the longmen shan fault zone this implied that the rupture process of this earthquake was complicated we also performed pixel matching to estimate offsets in the region of low correlation positive and negative range offsets larger than 2 m were found on the north and south sides of the beichuan fault respectively we observed a belt of negative range and azimuth offsets between the beichuan and pengguan faults we calculated an interferogram using a multi segment fault model with uniform slip along the beichuan and pengguan faults and estimated the slip distribution based on previous seismological studies we assumed that the southwestern part dipped toward the northwest by 33 degrees whereas the central and northeastern parts had a much steeper dip angle we found two regions of slips larger than 4 m in the southwest and central parts of the beichuan fault the pengguan segments may have much smaller slips around 1 m the southwestern segments of the beichuan fault and the entire pengguan fault had dominant thrust components whereas dextral slip prevailed in the central and northeastern segments of the beichuan fault the estimated geodetic moment was 5 87 1020nm mw 7 78

structural constraints on the spatial distribution of aftershocks 1 calculations of static stress changes due to large earthquakes have shown that the spatial distribution of aftershocks is predictable to first order with aftershocks primarily occurring in areas experiencing positive stress changes delineation of these areas relies on resolving the stress perturbation onto planes with known orientations common practice is to use poorly constrained regional stress information to compute optimally oriented failure planes assuming that they exist everywhere here we show that this assumption is not supported by observation but rather that aftershock failure planes are controlled by geological structure we argue that useful aftershock hazard estimates are better made by replacing information on regional stress with statistical measures of structural orientations

onto what planes should coulomb stress perturbations be resolved 1 coulomb stress maps are produced by computing the tensorial stress perturbation due to an earthquake rupture and resolving this tensor onto planes of a particular orientation it is often assumed that aftershock fault planes are optimally oriented in other words the regional stress and coseismic stress change are used to compute the orientation of planes most likely to fail and the coseismic stress is resolved onto these orientations this practice assumes that faults capable of sustaining aftershocks exist at all orientations an assumption contradicted by the observation that aftershock focal mechanisms have strong preferred orientations consistent with mapped structural trends here we systematically investigate the best planes onto which stress should be resolved for the landers hector mine loma prieta and northridge earthquakes by quantitatively comparing observed aftershock distributions with stress maps based on optimally oriented planes two and three dimensional main shock orientation and regional structural trend we find that the best model differs between different tectonic regions but that in all cases models that incorporate the regional stress field tend to produce stress maps that best fit the observed aftershock distributions although not all such models do so equally well our results suggest that when the regional stress field is poorly defined or in structurally complex areas the best model may be to fix the strike of the planes upon which the stress is to be resolved to that of the main shock but allow the dip and rake to vary

triggered aseismic slip adjacent to the 6 february 2013 mw 8 0 santa cruz islands megathrust earthquake abstract aseismic or slow slip events have been observed in many subduction zones but whether they affect the occurrence of earthquakes or result from stress changes caused by nearby events is unclear in an area lacking direct geodetic observations inferences can be made from seismological studies of co seismic slip associated stress changes and the spatiotemporal nature of aftershocks these observations indicate that the february 2013 mw 8 0 santa cruz islands earthquake may have triggered slow or aseismic slip on an adjacent section of the subduction thrust over the following hours to days this aseismic event was equivalent to mw 7 6 significantly larger than any earthquakes in the aftershock sequence the aseismic slip was situated within the seismogenic portion of the subduction interface and must have occurred to the south of the main seismic slip and most aftershocks in order to promote right lateral faulting in the upper plate the dominant deformation style of the aftershock sequence this plate boundary segment can support either stable sliding aseismic or stick slip seismic deformation in response to different driving conditions the complete lack of aftershocks on the thrust interface implies this pair of megathrust slip episodes seismic and aseismic released a substantial portion of the stored strain on the northernmost section of the vanuatu subduction zone

coulomb stress evolution along xianshuihe xiaojiang fault system since 1713 and its interaction with wenchuan earthquake may 12 2008 abstract the curved left lateral strike slip xianshuihe xiaojiang fault system xxfs in southwestern china extends at least 1400 km in the eastern margin of the tibetan plateau fieldworks confirm that the xxfs is one of the longest and most seismically active faults in china the strain released by the slip motion on the xxfs is related to the convergence between the indian and eurasian plates the entire fault system has experienced at least 35 earthquakes of m 6 in the recent 300 years and almost all segments of the system have been the locus of major historical earthquakes since the xxfs region is heavily populated over 50 million people understanding the migration of the large earthquakes in space and time is of crucial importance for the seismic hazard assessment in this region we analyze a sequence of 25 earthquakes m 6 5 that occurred along the xxfs since 1713 and investigate their influence on the 2008 mw7 9 wenchuan earthquake occurred on the adjacent longmenshan fault in our analysis the relevant parameters for the earth crust are constrained by seismic studies the locations and geometries of the earthquake faults as well as the rupture distributions are taken from field observations and seismological studies results from the coulomb failure stress modeling indicate significant interactions among the earthquakes after the 1713 earthquake 19 out of 24 earthquakes occurred in the positive stress zone of the preceding earthquakes the other 5 earthquakes located in the area without significant stress changes induced by the preceding events in particular we can identify 4 visible earthquake gaps with increasing seismic hazard along the xxfs consistent with the findings from the paleo seismological studies the seismic activity and tectonic motion on the xxfs reduced the coulomb stress accumulation at the hypocenter of 2008 mw7 9 wenchuan earthquake implying that the wenchuan earthquake might not be triggered directly by the seismic activities on the xxfs on the other hand the coulomb failure stress induced by the wenchuan earthquake has increased in a region of 125 km long segment of the xxfs northwest of kangding city

the 1999 mw 7 1 hector mine california earthquake a test of the stress shadow hypothesis we test the stress shadow hypothesis for large earthquake interactions by examining the relationship between two large earthquakes that occurred in the mojave desert of southern california the 1992 m w 7 3 landers and 1999 m w 7 1 hector mine earthquakes we want to determine if the 1999 hector mine earthquake occurred at a location where the coulomb stress was increased earthquake advance stress trigger or decreased earthquake delay stress shadow by the previous large earthquake using four models of the landers rupture and a range of possible hypocentral planes for the hector mine earthquake we discover that most scenarios yield a landers induced relaxation stress shadow on the hector mine hypocentral plane although this result would seem to weigh against the stress shadow hypothesis the results become considerably more uncertain when the effects of a nearby landers aftershock the 1992 m l 5 4 pisgah earthquake are taken into account we calculate the combined static coulomb stress changes due to the landers and pisgah earthquakes to range from 0 3 to 0 3 mpa 3 to 3 bars at the possible hector mine hypocenters depending on choice of rupture model and hypocenter these varied results imply that the hector mine earthquake does not provide a good test of the stress shadow hypothesis for large earthquake interactions we use a simple approach that of static dislocations in an elastic half space yet we still obtain a wide range of both negative and positive coulomb stress changes our findings serve as a caution that more complex models purporting to explain the triggering or shadowing relationship between the 1992 landers and 1999 hector mine earthquakes need to also consider the parametric and geometric uncertainties raised here

static stress changes induced by the magmatic intrusions during the 2002 2003 etna eruption 1 the shallow intrusive processes that occurred during 2002 2003 etna eruption as well as the complex interaction between the magma intrusive events and the tectonic response of the volcano s eastern flank are investigated with numerical deformation modeling and the estimation of changes in the static coulomb stress ground deformation and volcanologic evidence clearly indicate a composite mechanism of intrusion on both the southern and northeastern flanks of the volcano geodetic data inversions have been based on a homogeneous elastic half space model although geological data and seismic tomography indicate that mt etna is elastically inhomogeneous and that rigidity layering and heterogeneities are likely to affect the magnitude and pattern of the deformation field to account for topographic effects as well as a complicated distribution of material properties we use the finite element method fem to provide a more realistic model the presence of medium heterogeneity strongly affects the amplitudes of the static stress changes seismicity matches well the areas of positive increase in the static stress caused by the intrusive events along the southern and northeastern flanks the changes in the state of stress generated by the southern dike produce an extensional stress field that favors magma propagation along the north east rift the highest seismic releases were associated with the activation of two fault systems the timpe fault system and the pernicana fault the static stress changes resolved onto these faults indicate that the magma intrusions on the southern and northeastern flanks encouraged these seismogenic structures to slip

stress evolution before and after the 2008 wenchuan china earthquake abstract we examine the distribution of coulomb stress before and following the m 7 9 wenchuan earthquake and model the time dependent components of the stress field into the future our modelling shows that the combined coseismic plus postseismic viscoelastic stress change due to the preceding large events m 6 7 at the hypocentral area of the wenchuan earthquake is negative which may have led to a delay on its occurrence between 16 and 95 yr depending on the rake of the rupture on the other hand coseismic stress modelling of the wenchuan earthquake shows strong interaction particularly with the faults close to its sw and ne ends such interactions have previously been shown to trigger further large earthquakes in addition redistribution of stresses due to continuing postseismic deformation will potentially increase the stress levels not only on these faults but also on the distant faults such as the xianshuihe kunlun and tazang faults postseismic viscoelastic stress load on these distant faults over the next 22 yr since the earthquake could be up to 2 5 times larger than that of the coseismic stress increase alone this would potentially advance these faults in their seismic cycle and thereby encourage future earthquakes resulting in clustering of large earthquakes in the region this behaviour however strongly depends on the stage that these faults are in their seismic cycle which is not known currently given the high density of population in the area with several cities chengdu guangyuan and hanzhong of more than 1 million inhabitants our results indicate a need for detailed paleoseismic studies to help elucidate the state of the stressed faults

reliability of coulomb stress changes inferred from correlated uncertainties of finite fault source models 1 static stress transfer is one physical mechanism to explain triggered seismicity coseismic stress change calculations strongly depend on the parameterization of the causative finite fault source model these models are uncertain due to uncertainties in input data model assumptions and modeling procedures however fault model uncertainties have usually been ignored in stress triggering studies and have not been propagated to assess the reliability of coulomb failure stress change cfs calculations we show how these uncertainties can be used to provide confidence intervals for co seismic cfs values we demonstrate this for the mw 5 9 june 2000 kleifarvatn earthquake in southwest iceland and systematically map these uncertainties a set of 2500 candidate source models from the full posterior fault parameter distribution was used to compute 2500 cfs maps we assess the reliability of the cfs values from the coefficient of variation cv and deem cfs values to be reliable where they are at least twice as large as the standard deviation cv 0 5 unreliable cfs values are found near the causative fault and between lobes of positive and negative stress change where a small change in fault strike causes cfs values to change sign the most reliable cfs values are found away from the source fault in the middle of positive and negative cfs lobes a likely general pattern using the reliability criterion our results support the static stress triggering hypothesis nevertheless our analysis also suggests that results from previous stress triggering studies not considering source model uncertainties may have lead to a biased interpretation of the importance of static stress triggering

long term changes in the coulomb failure function on inland active faults in southwest japan due to east west compression and interplate earthquakes inland earthquake activity in and around the kinki region southwest japan increases in the period from several decades before to about a decade after the occurrence of great interplate earthquakes along the nankai trough to quantitatively investigate this relationship we calculated long term changes in the coulomb failure function cff on inland active faults in this region with viscoelastic slip response functions as sources for the change in cff we investigated east west compression within the niigata kobe tectonic zone nktz historical interplate earthquakes and interseismic locking along the nankai trough subduction zone and historical inland earthquakes in this region among these sources the nktz east west compression is the primary cause of the long term changes in cff the changes in cff due to interplate earthquakes are mostly negative on reverse faults and positive on strike slip faults this result suggests that the inland reverse faulting activity mostly increases before interplate earthquakes and decreases after the earthquakes whereas strike slip activity is mostly suppressed before interplate earthquakes and increases thereafter this suggestion is supported by spatiotemporal pattern of historical inland earthquakes if focal mechanisms of historical earthquakes correspond to fault geometries in the region the calculated changes in cff are usually consistent with the occurrence of historical inland earthquakes if we use the change in shear stress instead of the change in cff this consistency is enhanced which suggests low apparent coefficients of friction in this region

extending earthquakes reach through cascading earthquakes whatever their size can trigger other earthquakes mainshocks cause aftershocks to occur which in turn activate their own local aftershock sequences resulting in a cascade of triggering that extends the reach of the initial mainshock a long lasting difficulty is to determine which earthquakes are connected either directly or indirectly here we show that this causal structure can be found probabilistically with no a priori model nor parameterization large regional earthquakes are found to have a short direct influence in comparison to the overall aftershock sequence duration relative to these large mainshocks small earthquakes collectively have a greater effect on triggering hence cascade triggering is a key component in earthquake interactions

stress interaction between magma accumulation and trapdoor faulting on sierra negra volcano galapagos abstract understanding the state of stress within volcanoes and how it changes with active geophysical processes is important to assess when and where magma may propagate to the surface and initiate an eruption observations of volcanic deformation help to constrain parameters of models that can be used to describe these processes and to calculate the resulting stress changes within volcanoes here i use geodetic observations to constrain elastic dislocation models of magma accumulation and faulting at sierra negra volcano galapagos in the years before the october 2005 eruption which was the first eruption at sierra negra since 1979 both insar and gps data document a remarkable story of 5 m pre eruption uplift during 1992 2005 which was accompanied by at least three trapdoor faulting events on an intra caldera fault system in january 1998 april 2005 and just before the eruption in october 2005 the pattern of uplift observed in the insar data from different time periods during 1992 2005 is consistent with filling and pressurization of a 2 2 km deep sill under the caldera modeling results for the trapdoor faulting in april 2005 on the other hand indicate that slip occurred on a thrust fault that dips steeply 71 in towards the center of the caldera and extends from the surface down to the sill at 2 2 km depth independently the calculated stress changes caused by the inflating sill show that the coulomb failure stress change cfs at the fault s location is maximized on a 72 dipping thrust fault agreeing almost exactly with the deformation modeling result and implying that the inflation triggered the faulting the calculations also show that the cfs for optimally oriented faults any strike and dip is significantly larger in the southern part of the caldera where the faulting took place than at any other location the trapdoor faulting in turn relieved the pressure within the sill but caused compression to the south of the faults this suggests that while the faulting provides a mechanism for the sill to thicken and postpone eruptions it also prevents the sill from growing to the south

widespread seismicity excitation throughout central japan following the 2011 m 9 0 tohoku earthquake and its interpretation by coulomb stress transfer 1 we report on a broad and unprecedented increase in seismicity rate following the m 9 0 tohoku mainshock for m 2 earthquakes over inland japan parts of the japan sea and izu islands at distances of up to 425 km from the locus of high 15 m seismic slip on the megathrust such an increase was not seen for the 2004 m 9 1 sumatra or 2010 m 8 8 chile earthquakes but they lacked the seismic networks necessary to detect such small events here we explore the possibility that the rate changes are the product of static coulomb stress transfer to small faults we use the nodal planes of m 3 5 earthquakes as proxies for such small active faults and find that of fifteen regions averaging 80 by 80 km in size 11 show a positive association between calculated stress changes and the observed seismicity rate change 3 show a negative correlation and for one the changes are too small to assess this work demonstrates that seismicity can turn on in the nominal stress shadow of a mainshock as long as small geometrically diverse active faults exist there which is likely quite common

aftershock triggering by complete coulomb stress changes 1 we examine the correlation between seismicity rate change following the 1992 m7 3 landers california earthquake and characteristics of the complete coulomb failure stress cfs changes cfs t that this earthquake generated at close distances the time varying dynamic portion of the stress change depends on how the rupture develops temporally and spatially and arises from radiated seismic waves and from permanent coseismic fault displacement the permanent static portion cfs depends only on the final coseismic displacement cfs diminishes much more rapidly with distance than the transient dynamic stress changes a common interpretation of the strong correlation between cfs and aftershocks is that load changes can advance or delay failure stress changes may also promote failure by physically altering properties of the fault or its environs because it is transient cfs t can alter the failure rate only by the latter means we calculate both cfs and the maximum positive value of cfs t peak cfs t using a reflectivity program input parameters are constrained by modeling landers displacement seismograms we quantify the correlation between maps of seismicity rate changes and maps of modeled cfs and peak cfs t and find agreement for both models however rupture directivity which does not affect cfs creates larger peak cfs t values northwest of the main shock this asymmetry is also observed in seismicity rate changes but not in cfs this result implies that dynamic stress changes are as effective as static stress changes in triggering aftershocks and may trigger earthquakes long after the waves have passed