reassessment of the 1907 sumatra tsunami earthquake based on macroseismic seismological and tsunami observations and modeling on 4 january 1907 an earthquake occurred off the west coast of sumatra indonesia with an instrumental surface wave magnitude ms in the range of 7 5 8 0 at periods of 40 s the tsunami it generated was destructive on the islands of nias and simeulue where it killed hundreds and gave rise to the legend of the s mong this tsunami was also observed in other parts of the indian ocean basin relative to its instrumented magnitude the size of the tsunami was anomalous qualifying the event as a tsunami earthquake however unusually for a tsunami earthquake the shaking on nias was severe 7 ems we revisit the 1907 earthquake with a multidisciplinary approach by extracting evidence describing shaking effects or the tsunami from written documents and by acquiring new seismograms combining these we discriminate two large earthquakes within an hour of each other with clear differences in seismological character the first we interpret to be a tsunami earthquake with characteristic low levels of shaking an estimated average seismic moment m0 of 2 5 1028 dyn cm mw 8 2 in the frequency band 6 8 mhz and an epicentral location close to the front of the sunda megathrust the seismograms we analyzed also document a regular growth of moment with period approaching mw 8 4 at the longest resolvable period 170 s for the second earthquake that caused damage on nias we estimate ms 7 based on seismograms and phase data we also identify two ms 6 aftershocks within 24 h of the mainshock additionally we present a dataset of 88 locations within the indian ocean basin where the tsunami was observed using a subset of these we forward modeled the tsunami to propose a seismic rupture model extending along the sunda megathrust for about 220 km 94 7 e to 97 e with a maximum modeled slip of 21 m our new rupture model provides an acceptable fit to our new dataset of tsunami runup and inundation values from 88 local and far field locations in the indian ocean basin we also urge caution against an over reliance on the s mong legend for tsunami evacuation as its premise that a tsunami will only follow an earthquake with very severe ground motions is rendered ineffective for tsunami earthquakes

on the geometric complexity of earthquake focal zone and fault systems a statistical study we discuss various methods used to investigate the geometric complexity of earthquakes and earthquake faults based both on a point source representation and the study of interrelations between earthquake focal mechanisms we briefly review the seismic moment tensor formalism and discuss in some detail the representation of double couple dc earthquake sources by normalized quaternions non dc earthquake sources like the clvd focal mechanism are also considered we obtain the characterization of the earthquake complex source caused by summation of disoriented dc sources we show that commonly defined geometrical fault barriers correspond to sources without any clvd component we analyze the cmt global earthquake catalog to examine whether the focal mechanism distribution suggests that the clvd component is likely to be zero in tectonic earthquakes although some indications support this conjecture we need more extensive and significantly more accurate data to answer this question fully

contemporary stress and strain field in the mediterranean from stress inversion of focal mechanisms and gps data abstract mapping the contemporary stress field of the mediterranean provides fundamental insights on the complexity of plate tectonic forces throughout the region and at different depths despite increased data availability and methodological improvements most recent comprehensive stress field characterization across the entire mediterranean dates back to 1995 to extend the regional stress information we use all earthquake focal mechanisms compiled in the world stress map database release 2016 for a formal stress inversion our main goals are to 1 improve the resolution of the stress field orientation 2 evaluate the performance of the recently refined stress inversion methodology in a tectonically complex region 3 test the hypothesis of a depth dependent stress orientation heterogeneity and 4 compare different types of stress and strain observations from surface using the gps derived information on the strain rate tensor down to the seismogenic crust using summation of normalized seismic potencies the obtained stress orientations generally capture the main seismotectonic features including tectonically complex settings such as the alpine orogeny or the ionian sea the orientation of the maximum horizontal stress shmax tends to be uniform with depth within uncertainties while larger stress heterogeneity quantified by means of the focal mechanism diversity and misfit angles is found between 5 and 14 km both the orientation of the largest horizontal shortening axis of the strain field from potency tensors and horizontal strain rate tensor from gps data are generally sub parallel to shmax orientation indicating a linear stress strain relationship and that the orientations of the co seismic release and interseismic strain accumulation are generally consistent

stress fields in and around metropolitan osaka japan deduced from microearthquake focal mechanisms abstract present day stress fields in and around metropolitan osaka japan have been investigated based on 238 microearthquake focal mechanism solutions from approximately the past 10 years the successful retrieval of the focal mechanisms in the noisy urban area owed much to the clean seismic data recorded at four borehole observatories deeper than 500 m depth in osaka prefecture in which p wave onset polarity of the microearthquake could be clearly identified we found many microearthquakes with a pure reverse faulting mechanism which is consistent with the faulting style of major active faults within the area 42 km long east dipping uemachi and 38 km long east dipping ikoma fault zones however a considerable number of microearthquakes with strike slip components were also found to occur most of the p axes are oriented in the ese wnw to ene wsw directions sub horizontally conforming to the general tectonic trend of the area the analysis of a stress tensor inversion delineated small but noticeable differences in stress regime on a scale of at least 10 km where strike slip faulting prevails throughout the region but the middle and southern sections of the uemachi fault zone contain some reverse faulting components based on the estimated stress fields together with assumptions regarding the deep geometry of the uemachi fault zone we assessed the reactivation potential of the fault zone through slip tendency analysis the results indicate higher potential in the middle and southern sections of the fault zone which is related to the locally increased reverse component detected there

the mw 8 1 2014 iquique chile seismic sequence a tale of foreshocks and aftershocks egu2009 11040 schurr b asch g rosenau m wang r oncken o barrientos s salazar p villotte j p 2012 the 2007m7 7 tocopillanorthernchile earthquake sequence implications for along strike and downdip rupture segmentation and megathrust frictional behaviour j geophys res 117 b05305 doi 10 1029 2011jb009030 schurr b et al 2014 gradual unlocking of the plate boundary controlled the initiation of the 2014 iquique earthquake nature 512 7514 299

seismic moment tensors of the april 2009 l aquila central italy earthquake sequence summary on 2009 april 6 the central apennines were hit by an mw 6 3 earthquake the region had been shaken since 2008 october by seismic activity that culminated in two foreshocks with mw 4 1 week and a few hours before the main shock we computed seismic moment tensors for 26 events with mw between 3 9 and 6 3 using the regional centroid moment tensor rcmt scheme most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively the focal mechanisms are all extensional with a variable and sometimes significant strike slip component this geometry agrees with the ne sw extensional deformation of the apennines known from previous seismic and geodetic observations events group into three clusters those located in the southern area have larger centroid depths and a wider distribution of t axis directions these differences suggest that towards south a different fault system was activated with respect to the sw dipping normal faults beneath l aquila and more to the north

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

spatially heterogeneous stress field in the source area of the 2011 mw 6 6 fukushima hamadori earthquake ne japan probably caused by static stress change

nied seismic moment tensor catalogue for regional earthquakes around japan quality test and application abstract we have examined the quality of the national research institute for earth science and disaster prevention nied seismic moment tensor mt catalogue obtained using a regional broadband seismic network freesia first we examined using synthetic waveforms the robustness of the solutions with regard to data noise as well as to errors in the velocity structure and focal location then to estimate the reliability robustness and validity of the catalogue we compared it with the harvard centroid moment tensor cmt catalogue as well as the japan meteorological agency jma focal mechanism catalogue we found out that the nied catalogue is consistent with harvard and jma catalogues within the uncertainty of 0 1 in moment magnitude 10 km in depth and 15 in direction of the stress axes the nied mt catalogue succeeded in reducing to 3 5 the lower limit of moment magnitude above which the moment tensor could be reliably estimated finally we estimated the stress tensors in several different regions by using the nied mt catalogue this enables us to elucidate the stress deformation field in and around the japanese islands to understand the mode of deformation and applied stress moreover we identified a region of abnormal stress in a swarm area from stress tensor estimates

changes in sediment processes across the western irish sea front abstract sediment characteristics sediment respiration oxygen uptake and sulphate reduction and sediment water nutrient exchange in conjunction with water column structure and phytoplankton biomass were measured at five stations across the western irish sea front in august 2000 the transition from thermally stratified surface to bottom temperature difference of 2 3 c to isothermal water 14 3 c occurred over a distance of 13 km the influence of the front on phytoplankton biomass was limited to a small region of elevated near surface chlorophyll 2 23 mg m 3 50 biomass in mixed waters the front clearly marked the boundary between depositional sediments silt clays with elevated sediment pigment levels 60 mg m 2 on the western side to pigment impoverished 2 sand through to coarse sand and shell fragments on the eastern side maximal rates of sedimentary respiration on the western stratified side of the front e g oxygen uptake s2 852 mol o 2 m 2 h 1 and sulphate reduction at s1 149 mol so 4 2 m 2 h 1 coupled to significant efflux of nitrate and silicate at the western stations indicate closer benthic pelagic coupling in the western irish sea whether this simply reflects the input of phytodetritus from the overlying water column or entrapment and settlement of pelagic production from other regions of the irish sea cannot yet be resolved

statistical methods for comparing directions to the orientations of focal mechanisms and wadati benioff zones we propose simple graphical methods for evaluating whether a set of direction vectors are clustered with respect to particular directions axes or planes as examples of these techniques we present data concerning the relationship between 1 aftershock initial event geometry and nodal planes of focal mechanisms 2 aftershock initial event geometry and the plane of the wadati benioff zone and 3 b axes of focal mechanisms and the plane of the wadati benioff zone

effects of long term fluid injection on induced seismicity parameters and maximum magnitude in northwestern part of the geysers geothermal field the long term temporal and spatial changes in statistical source and stress characteristics of one cluster of induced seismicity recorded at the geysers geothermal field u s are analyzed in relation to the field operations fluid migration and constraints on the maximum likely magnitude two injection wells prati 9 and prati 29 located in the northwestern part of the field and their associated seismicity composed of 1776 events recorded throughout a 7 year period were analyzed the seismicity catalog was relocated and the source characteristics including focal mechanisms and static source parameters were refined using first motion polarity spectral fitting and mesh spectral ratio analysis techniques the source characteristics together with statistical parameters b value and cluster dynamics were used to investigate and understand the details of fluid migration scheme in the vicinity of injection wells the observed temporal spatial and source characteristics were clearly attributed to fluid injection and fluid migration toward greater depths involving increasing pore pressure in the reservoir the seasonal changes of injection rates were found to directly impact the shape and spatial extent of the seismic cloud a tendency of larger seismic events to occur closer to injection wells and a correlation between the spatial extent of the seismic cloud and source sizes of the largest events was observed suggesting geometrical constraints on the maximum likely magnitude and its correlation to the average injection rate and volume of fluids present in the reservoir

the effect of acid rain and altitude on concentration δ34s and δ18o of sulfate in the water from sudety mountains poland abstract the analyses of sulfate content 34s and 18o of dissolved sulfate and 18o of water were carried out in a 14 km2 crystalline massif located in the sudety mountains sw poland to 1 assess the amount of the sulfate delivered to the surface and groundwater systems by modern atmospheric precipitation 2 determine the effect of altitude on these parameters and 3 investigate their seasonal variations in april and november of 2002 august 2003 and march and september of 2005 samples of water were collected from springs and streams of the massif during these seasons sulfate contents and 18o so42 values varied from 5 80 to 18 00 mg l and from 3 96 to 8 23 respectively showing distinctively higher values of 18o so42 in wet seasons the 34s so42 values had a relatively narrow range from 4 09 to 5 28 and were similar to those reported for organic matter in soil and the canopy throughfall in the sudety mountains sulfate content 34s so42 18o so42 and 18o h2o values revealed a remarkable dependence on the altitude the calculated altitude effects for five season averages of these parameters were 1 00 mg l 100 m 0 18 100 m 0 27 100 m and 0 17 100 m respectively this dependence on the altitude resulted mainly from the mixing of sulfates of different origins such as anthropogenic sulfate sulfate produced in the soil within the weathered zone of the massif and that one from the tree canopy the oxygen isotope mass balance indicates that in the study area about one third of the sulfate delivered to the surface and groundwater by modern precipitation comes from anthropogenic pollution further interaction of meteoric water within the weathered rocks causes a continuous decrease of 18o so42 values resulting from biological transformation of the sulfate due to plant vegetation and decomposition of organic matter

fault plane solutions for the 1984 morgan hill california earthquake sequence evidence for the state of stress on the calaveras fault fault plane solutions for 946 aftershocks of the april 24 1984 morgan hill california m6 2 earthquake reveal a pattern of complex faulting within a 10 km wide zone surrounding the calaveras fault the fault plane solutions fall into three groups strike slip mechanisms located along the calaveras fault with north northwest striking dextral slip planes nearly parallel to the fault strike slip mechanisms located northeast of the calaveras fault with north striking dextral slip planes and reverse mechanisms located southwest of the calaveras fault with northeast or southwest dipping slip planes the average azimuth of p axes for aftershocks located on the calaveras fault is n10 1 e in contrast the average azimuths of p axes for aftershocks northeast and southwest of the calaveras fault are n49 7 e and n37 3 e respectively by assuming that the earthquakes occur on preexisting cracks in response to a uniformly oriented regional stress field we are able to infer from the observed average slip directions an orientation for 1 the axis of maximum horizontal compression 63 80 from the local strike of the calaveras fault such a high angle orientation of 1 is incompatible with the classical andersonian model of strike slip faulting but is consistent with an alternate model in which a weak calaveras fault is driven by plate motion slightly convergent with respect to the san andreas fault system in central california if this inferred high angle uniform stress field is combined with the changes in the static stress field calculated with elastic dislocation theory for the 1984 morgan hill main shock the resulting stress field predicts most of the observed spatial pattern of the aftershocks and their fault plane solutions the orientations of the inferred aftershock slip planes are generally consstent with the fracture orientations predicted by the coulomb failure criterion areas with predicted increases in the coulomb failure function of only a few tenths of a megapascal correspond to areas of intense aftershock activity the invariance of focal mechanisms in the vicinity of the south end of the main shock rupture before and after the main shock suggests that the magnitude of compressive stress in this area is at least 10 mpa in addition to explaining a preponderance of the seismic observations of the aftershock sequence the presence of a predominantly fault normal compressive regional stress field accounts for the contemporary development of folds reverse faults and topographic relief observed throughout the central california coast ranges

detached deep earthquakes are they really abstract we use primarily the generation of acoustic t waves into the ocean by deep seismic sources to investigate the propagation of high frequency seismic energy from the bottom of subduction zones to the shoreline at the earth s surface conversion from shear waves to oceanic acoustic waves can be used as a proxy for the existence of a continuous slab featuring low anelastic attenuation with the help of other techniques such as the estimation of q from s to p spectral amplitude ratios we examine systematically a number of regions where earthquakes have been described as detached we establish the mechanical continuity of the slab to the hypocenters of the 1990 sakhalin and 1982 bonin events which occurred several hundred kilometers in front of the mainstream seismic zone the study of the 1989 paraguay shock is inconclusive probably due to its much smaller size the vertical continuity of the south american slab through its aseismic depth range is verified and a similar situation probably exists in java attenuation data suggests that the deep spanish earthquakes occur within a vertically large segment of colder material and a similar situation may exist in colombia the only clearly detached deep events with no mechanical connection to the surface make up the vityaz cluster under the north fiji basin based on a variety of geophysical evidence the small deep earthquakes under new zealand are likely to take place in a detached blob at least 350 km below the termination of mainstream seismicity these results support a model integrating buoyancy forces over a long continuous slab as the source of the down dip compressional stresses observed in large earthquakes at the bottom of the transition zone

benthic mineralization and solute exchange on a celtic sea sand bank jones bank benthic carbon mineralization and solute exchange was investigated on a celtic sea sandbank during july 2008 the sediment on the top of the bank consisted of consolidated sand characterized by advective porewater transport and was difficult to sample this to some extent compromised the investigations at this site however intact sediment cores were sampled at 4 stations at the slopes base of the bank and off the bank reference site this sediment was used to assess rates and pathways for benthic diagenesis total sediment o2 uptake tou ranged from 5 8 to 9 0 mmol m 2 d 1 and total sediment release rates of dissolved inorganic carbon dic ranged between 8 60 and 13 8 mmol m 2 d 1 microbial denitrification and sulfate reduction accounted for 2 and 12 28 of the total benthic carbon mineralization respectively the remaining mineralization is ascribed to o2 and fe mn respiration respectively activity profiles of unsupported 210pb from all stations indicated deep mixing presumably caused by intense trawling activity in the area calculation based on satellite tracking of fishing vessels suggest that on average 33 of the sediment is affected by trawling activity every year this is presumed to facilitate high metal respiration rates by continuously oxidizing reduced fe that would otherwise accumulate in the sediment extracted porewater profiles reflected elevated no3 levels as compared to microsensor determined no3 profiles that were measured in parallel we suggest that this reflects no3 leakage from meiofauna and that the intracellular no3 pool in the top 5 cm of the sediment exceeds the porewater pool up to a factor of 45 however this intracellular pool is presumably turned over at very slow rates compared to the porewater pool subject to microbial denitrification

correlation distance of waveforms for closely located events i implication of the heterogeneous structure around the source region of the 1995 hyogo ken nanbu japan earthquake mw 6 9 summary the way in which cross correlation coefficients of seismograms for closely located events change with frequency and event separation was investigated by using records of aftershocks of the 1995 hyogo ken nanbu japan earthquake m w 6 9 for 11 master events m between 2 9 and 3 5 on the mainshock fault plane and smaller events m greater than 2 0 within 5 km of the master events the relative hypocentre was determined with respect to each master event and cross correlation coefficients of seismograms were calculated for a time window of 2 s including direct p waves for pairs of events in each cluster at two stations with an average hypocentral distance of 36 km and 42 km relative hypocentres were located within errors of several hundred metres for most of the earthquakes cross correlation coefficients are high for frequencies below 8 hz and decrease with increasing frequency above 8 hz at both stations it was also found that cross correlation coefficients decay with increasing event separation if the source time function is assumed to be simple for small earthquakes it may be said that dependence of cross correlation coefficients on event separation below 8 hz is mainly influenced by the heterogeneous structure around the earthquake source we introduce a correlation distance where cross correlation coefficients first become lower than 0 6 with increasing event separation the correlation distance exhibits a clear regional difference it is less than 4 5 km in the awaji region and more than 4 5 km in the kobe region this result implies that heterogeneity of velocity structure around the earthquake source is stronger in the awaji region than in the kobe region it is notable that both low and high frequency seismic waves radiated strongly from the awaji region at the time of the mainshock the correlation distance may be an indicator of heterogeneous structure around an earthquake source which may have a close relationship to the rupture process itself

stress release process along an intraplate fault analogous to the plate boundary a case study of the 2017 m5 2 akita daisen earthquake ne japan stress accumulation and release in the crust remains poorly understood compared to that at the plate boundaries spatiotemporal variations in foreshock and aftershock activities can provide key con

a focal mechanism solution catalog of earthquakes m 2 0 in and around the japanese islands for 1985 1998 abstract we determined focal mechanism solutions for 14 544 earthquakes that occurred in and around the japanese islands from july 1985 to december 1998 using first motion polarities reported by the japan university seismic network and compiled by the japan university seismic network earthquake catalog of first motion focal mechanisms junec fm 2 this catalog covers small magnitude earthquakes m 2 0 prior to the recent development of seismic observation networks and automated waveform data processing systems this catalog will prove helpful in understanding the spatial and temporal heterogeneities of stress fields by combining recent focal mechanism solutions and also will be useful for statistical analyses online material figures of velocity structure focal mechanisms magnitude frequency distributions and temporal changes in station locations

preliminary determination of focal mechanisms from the inversion of spectral amplitudes of mantle waves abstract we present a method for the preliminary determination of focal mechanisms pdfm based on the inversion of deviatoric moment tensor components from depleted datasets of mantle wave spectral amplitudes the latter are found to be largely insensitive to errors in epicentral estimates which can hamper the inversion of the full complex spectrum under real time operational conditions robust solutions can be obtained from rayleigh wave spectra at as few as three stations and from a combination of rayleigh and love waves at only two stations provided they sample 60 in azimuth the systematic application of this method to a dataset of 43 large earthquakes during 1996 1999 yielded mechanisms rotated an average of only 17 from the published harvard cmt a figure comparing favorably with the case of other catalogues such as the usgs moment tensor solutions

state of stress and modern deformation of the northern basin and range province constraints on the current stress regime of the actively extending northern basin and range province are provided by deformation data focal mechanisms and fault slip studies hydraulic fracturing in situ stress measurements borehole elongation breakouts analyses and alignment of young volcanic vents the integrated data indicate significant variations both in principal stress orientations and magnitudes an approximately e w least principal stress direction appears to characterize both the eastern and western margins of the basin and range province whereas in the active interior parts of the province extension occurs in response to a least principal stress oriented nw to n60 w the contrast in stress orientations between the province boundaries and in the interior suggests that along the margins the least principal stress direction may be locally controlled by the generally northerly trending profound lithospheric discontinuities associated with these margins active deformation along the southeastern and western province margins is characterized by a combination of strike slip and normal faulting focal mechanisms along northeastern province margin wasatch front and in central nevada indicate a combination of normal and oblique normal faulting temporal regional and depth dependent variations in the relative magnitudes of the vertical and maximum horizontal stresses can explain much of the observed variations in deformation styles however some depth variation in faulting style inferred from focal mechanisms may be apparent and simply a function of the attitude of fault planes being reactivated evidence for significant temporal variation or multiple cycles of variation in relative stress magnitude comes from the sierran front basin and range boundary region where recent earthquakes are predominantly strike slip whereas the profound relative vertical relief across the sierra frontal fault zone in the last 9 10 m y implies a normal faulting stress regime using the best data on stress orientation relative stress magnitudes are constrained from slip vectors of major earthquakes and young fault displacements analysis of well constrained slip vectors in the owens valley california area indicate that large temporal variations in the magnitude of the approximately n s oriented maximum horizontal stress are required to explain dominantly dip slip and strike slip offsets on subparallel faults similar faulting relations are observed throughout much of the boundary zone between the basin and range sierra nevada including the walker lane belt along the eastern province margin in the wasatch front area in utah available data suggest that the maximum and minimum horizontal stresses may be approximately equal at depths of 4 5 km earthquake focal mechanisms in this area suggest more variability in relative magnitude of the two horizontal stresses with depth furthermore superimposed sets of young fault striae along a segment of the wasatch fault also indicate temporal variations of relative stress magnitudes sources of regional and temporal variations in the stress field may be linked to variable shear tractions applied to the base of the brittle crust related to intrusion thermally induced flow and the influence of the san andreas plate boundary although difficult to date accurately the fault slip data suggest that the temporal variations in relative magnitudes stress may occur on the time scale of both a single major earthquake cycle 1000 5000 years and multiple earthquake cycles 10 000 years

spatial distribution of the faulting types of small earthquakes around the 2011 tohoku oki earthquake a comprehensive search using template events we developed a new method to classify the faulting types of small earthquakes using interevent waveform similarity and applied it to earthquakes in the northeast japan subduction zone in the method we used separate time windows for p and s waves and established a relationship between waveform similarity and differences in focal mechanisms from event pairs whose focal mechanisms we know then we applied the relationship to many pairs of such focal mechanism known events 5607 from the moment tensor catalogue and 3623 events from the interplate repeating earthquakes catalogue and focal mechanism unknown events for the period from 1984 to 2013 as a result 8984 earthquakes were newly classified into interplate n 5401 noninterplate thrust n 631 normal n 1070 and strike slip faulting earthquakes n 165 from the new data set which doubles the number of mechanism types we confirmed that there have been almost no interplate earthquakes in the area of large coseismic slip of the tohoku oki earthquake since that event we also saw that this trend continued until at least the end of 2013 suggesting a nearly complete stress release and slow interplate stress recovery the abundant interplate aftershocks also indicate the precise spatial extent of postsesimic slip which is usually difficult to obtain from land based geodetic data the postseismic slip also suggests stress concentration at the asperities of the 1968 tokachi oki m7 9 and 1994 sanriku oki m7 6 earthquakes the present day faulting types offshore tohoku correlated well with the static stress change from the tohoku oki earthquake suggesting a stress state change during the earthquake cycle of megathrust earthquakes

deep seismicity and modes of deformation in tonga subduction zone the geometry of deep 400 km earthquakes in the subducting western edge of the pacific plate when related to the local distribution of seismic activity reveals a complex pattern of planes of shear failure enabling the modes of deformation by which the descending plate shortens and thickens to be identified the deepest part of the slab is displaced laterally suggesting that it fails to penetrate the discontinuity at 670 km

seasonal evolution of the cold pool gyre in the western irish sea an extensive cruise program during 1994 1995 and 1996 provided observations that describe the seasonal evolution of the three dimensional density field in the western irish sea a cold dense pool flanked by strong nearbed density gradients was present from may until october in spring salinity had a dominant influence on the density structure but from june until october temperature controlled the density stratification the trajectories of 55 satellite tracked argos drifters demonstrated the existence of the cyclonic circulation pattern that constitutes the western irish sea gyre and defined the gyre s spatial extent several distinct recirculation paths were observed and the implications for planktonic organisms of the seasonal variability in the recirculation are discussed drifter speeds were in good agreement with geostrophic calculations based on the observed density field and with de tided acoustic doppler current profiler adcp measurements the dynamical significance of strong nearbed gradients bottom fronts is highlighted the location of the dynamically significant baroclinicity below the level of wind mixing explains the persistence of the cold pool and cyclonic circulation until late october the dataset described here is valuable for environmental management purposes and it facilitates testing of the prognostic capabilities of the present generation of density advecting numerical models

moment tensor resolvability application to southwest iberia abstract we present a method to assess the uncertainty of earthquake focal mechanisms based on the standard theory of linear inverse problems we compute the uncertainty of the moment tensor m then map it into uncertainties of the strike dip and rake the inputs are source and station locations crustal model frequency band of interest and an estimate of data error the output is a six dimensional 6d error ellipsoid which shows the uncertainty of the individual parameters of m we focus on the double couple dc part of m the method is applicable both with and without waveforms the latter is particularly useful for network design as an example we present maps of dc resolvability for earthquakes in southwest europe computed without waveforms we find that the resolvability depends critically on frequency range and source depth shallow dc sources 10 km are theoretically better resolved than deeper sources 40 km and 60 km the dc resolvability of a 40 km deep event improves considerably when the portuguese network is supplemented by stations in spain and morocco the dc resolvability can be further improved by using a few ocean bottom seismometer obs stations or a dense land network a dense land network is able to resolve m well in spite of the large azimuthal gap which spans 200 the theoretical resolution analysis also explains the success of single station inversions when using a broad frequency range as exemplified by an application using waveforms of a m w 6 earthquake offshore iberia

remotely triggered seismic activity in hakone volcano during and after the passage of surface waves from the 2011 m9 0 tohoku oki earthquake abstract immediately after the march 11 2011 m9 0 tohoku oki earthquake seismic activity increased remarkably beneath hakone volcano central japan at an epicentral distance of 450 km the heightened seismicity was initiated during the passage of the large amplitude surface waves from the main shock and continued over the subsequent 2 months we obtained hypocenters and focal mechanisms of the seismic sequence with the aim of clarifying the physical mechanism responsible for the remotely triggered seismicity we used data from a dense seismic network containing 56 online permanent and offline temporary stations in and around the hakone volcano we found that the earthquakes that occurred during the passage of the surface waves are located at the lower depth limit of ordinary seismicity in the caldera these earthquakes have larger magnitudes than both the ordinary seismicity prior to the tohoku oki earthquake and the seismicity triggered after the passage of the surface waves the focal mechanism that we determined is a strike slip fault type with the p axis in the nw se direction which is consistent with the focal mechanisms of earthquakes that occurred after the passage of the surface waves and the tectonic stress field in the region we also tried to detect missing events that occurred immediately after the passage of the surface waves by using a waveform correlation technique the detected events are distributed near the hypocenters of the earthquakes that occurred during the passage of the surface waves the origin times of the first four events after the arrival of surface waves are consistent with the phases of the decrease in normal stress generated by the surface waves the results suggest that the changes in dynamic stress due to the surface waves from the 2011 tohoku oki earthquake contributed significantly to the initiation of the sequence of triggered seismic activity assuming that normal stress changes on the faults did play an important role in the triggering of earthquakes we propose that fluid flow induced by the oscillation of permeability on the faults is the main mechanism for the initiation of post tohoku oki earthquakes beneath the hakone volcano

resolution of non double couple components in the seismic moment tensor using regional networks i a synthetic case study summary we perform a detailed synthetic study on the resolution of non double couple non dc com ponents in the seismic moment tensors from short period data observed at regional networks designed typically for monitoring aftershock sequences of large earthquakes in addition we test two different inversion approaches a linear full moment tensor inversion and a non linear moment tensor inversion constrained to a shear tensile source model the inversions are applied to synthetic first motion p and s wave amplitudes which mimic seismic observa tions of aftershocks of the 1999 mw 7 4 izmit earthquake in northwestern turkey adopting a shear tensile source model to analyse the resolution capability for the obtained non dc components inverted we contaminate synthetic amplitudes with random noise and incorporate realistic uncertainties in the velocity model as well as in the hypocentre locations we find that the constrained moment tensor inversion yields significantly smaller errors in the non dc components than the full moment tensor inversion in particular the errors in the compensated linear vector dipole clvd component are reduced if the constrained inversion is applied furthermore we show that including the s wave amplitudes in addition to p wave amplitudes into the inversion helps to obtain reliable non dc components for the studied station config urations the resolution remains limited due to the lack of stations with epicentral distances less than 15km assuming realistic noise in waveform data and uncertainties in the velocity model the errors in the non dc components are as high as 15 percent for the isotropic and clvd components respectively thus being non negligible in most applications however the orientation of p and t axes is well determined even when errors in the modelling procedure are high

the 1956 earthquake and tsunami in amorgos greece summary we conduct a comprehensive study of the amorgos greece earthquake and tsunami of 1956 july 09 the largest such event in the aegean sea in the 20th century systematic relocation of the main shock and 34 associated events defines a rupture area measuring 75 40 km the use of the preliminary determination of focal mechanism algorithm resolves the longstanding controversy about the focal geometry of the event yielding a normal faulting mechanism along a plane dipping to the southeast which expresses extensional tectonics in the back arc behind the hellenic subduction zone the seismic moment of 3 9 10 27 dyn cm is the largest measured in the past 100 yr in the mediterranean basin a quantitative database of 68 values of tsunami run up was built through the systematic interview over the past 5 yr of elderly eyewitness residents of 16 aegean islands and the turkish coast of asia minor it confirms values of up to 20 m on the southern coast of amorgos 10 m on astypalaia and up to 14 m on the western coast of folegandros 80 km to the west of the epicentre these values largely in excess of the inferred seismic slip at the source and their concentration along isolated segments of fault are incompatible with the generation of the tsunami by the seismic dislocation and require an ancillary source in the form of a series of landslides triggered by the earthquake and or its main aftershocks a model confirmed by hydrodynamic simulations using both the dislocation source and models of landslide sources

bacterial sulphate reduction in sediments of a european salt marsh acid volatile and tin reducible products abstract the products of 35s sulphate reduction by sedimentary bacteria were measured at two sites in a salt marsh on the east coast of england non acid volatile products were measured after acid volatile sulphide was removed by their reduction to sulphide by digestion with tin the proportion of the sulphate reduced to tin reducible products varied between 25 in a salt marsh pan and 61 in creek sediment over a 0 25 cm depth profile there were also variations with depth at each site in the proportions of sulphate reduced to tin reducible products further examination revealed differences in the proportions of sulphate which were reduced to free sulphide acid volatile sulphide sulphur or pyrite at the two sites the data suggest that previous work which did not measure non acid volatile products underestimated sulphate reduction rates by three fold in the creek site but by only one third in the pan

random stress and earthquake statistics spatial dependence summary we calculate the 3 d stochastic rotations of focal mechanisms disorientations caused by stresses arising from the presence of many small random point defects that may surround the tip of an earthquake fault these random stresses can be shown to be distributed according to a cauchy distribution as a consequence the next episode of fracture of a fault cannot be planar the disorientation of focal mechanisms of these new rupture episodes is closely approximated by a rotational cauchy distribution as observed previously the geometry of fault systems for natural earthquakes is consistent with these observations since it too can be modelled by the cauchy distribution these observations indicate how the 3 d rupture process in rocks and other materials can be modelled we also calculate distributions of disorientations caused by a uniformly random 3 d rotation of sources these distributions are governed by symmetry properties of earthquake focal mechanisms to take into account the source symmetry we compare the cauchy distribution which is due to influence of random stresses to the distributions caused by random rotations

imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres application to the azores western mediterranean region abstract the matching between linear trends of hypocentres and fault planes indicated by focal mechanisms fms is frequently used to infer the location and geometry of active faults this practice works well in regions of fast lithospheric deformation where earthquake patterns are clear and major structures accommodate the bulk of deformation but typically fails in regions of slow and distributed deformation we present a new joint fm and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and fms even in regions of distributed deformation we apply the method to the azores western mediterranean region with particular emphasis on western iberia the analysis relies on a compilation of hypocentres and fms taken from regional and global earthquake catalogues academic theses and technical reports complemented by new fms for western iberia the joint clustering algorithm images both well known and new seismo tectonic features the azores triple junction is characterised by fms with vertical pressure p axes in good agreement with the divergent setting and the iberian domain is characterised by nw se oriented p axes indicating a response of the lithosphere to the ongoing oblique convergence between nubia and eurasia several earthquakes remain unclustered in the western mediterranean domain which may indicate a response to local stresses the major regions of consistent faulting that we identify are the mid atlantic ridge the terceira rift the trans alboran shear zone and the north coast of algeria in addition other smaller earthquake clusters present a good match between epicentre lineations and fm fault planes these clusters may signal single active faults or wide zones of distributed but consistent faulting mainland portugal is dominated by strike slip earthquakes with fault planes coincident with the predominant nne ssw and wnw ese oriented earthquake lineations clusters offshore sw iberia are predominantly strike slip or reverse confirming previous suggestions of slip partitioning

regional w phase source inversion for moderate to large earthquakes in china and neighboring areas earthquake source characterization has been significantly speeded up in the last decade with the development of rapid inversion techniques in seismology among these techniques the w phase source inversion method quickly provides point source parameters of large earthquakes using very long period seismic waves recorded at teleseismic distances although the w phase method was initially developed to work at global scale within 20 to 30 min after the origin time faster results can be obtained when seismological data are available at regional distances i e 12 in this study we assess the use and reliability of regional w phase source estimates in china and neighboring areas our implementation uses broadband records from the chinese network supplemented by global seismological stations installed in the region using this data set and minor modifications to the w phase algorithm we show that reliable solutions can be retrieved automatically within 4 to 7 min after the earthquake origin time moreover the method yields stable results down to mw 5 0 events which is well below the size of earthquakes that are rapidly characterized using w phase inversions at teleseismic distances

seismotectonics and fault geometries of the 2019 ridgecrest sequence insight from aftershock moment tensor catalog using 3 d green s functions the 2019 m w 7 1 ridgecrest earthquake occurred on july 6th preceded by the m w 6 4 foreshock on july 4th 2019 these two earthquakes occurred close in space and time with partially overlapping surface ruptures and aftershock patterns raising the question of the relationship between the two events geological surveys and satellite observations provide important constraints on the surface traces of faulting however the subsurface fault geometries which are important for understanding the regional stress field earthquake initiation propagation and termination are not well resolved in this study moment tensor solutions for 256 earthquakes in the 2019 ridgecrest sequence were determined by waveform inversion using 3d velocity model the obtained moment tensor solutions show rotations of the stresses after mainshock indicating the ratio of mainshock stress drop to the background stress to be 0 5 0 9 the obtained moment tensor catalog also facilitates a better understanding of the sub surface fault geometries including 1 splay faults and antithetic faults in the northwest aftershock zone 2 shallow flower structures near the m w 7 1 epicenter 3 sub parallel faults in the southeast aftershock zone the aftershocks studies suggest the very complex surface ruptures near the 2019 ridgecrest m w 7 1 epicenter are near surface features that linked to a simple large through going fault at 5 km depth we also found that the southeastern most aftershocks which are located less than a kilometer from the garlock fault trace have significant different strike directions from that of the garlock fault indicating the central garlock fault remains seismically quiet

spatial patterns of aftershocks of shallow focus earthquakes in california and implications for deep focus earthquakes previous workers have pioneered statistical techniques to study the spatial distribution of aftershocks with respect to the focal mechanism of the main shock application of these techniques to deep focus earthquakes failed to show clustering of aftershocks near the nodal planes of the main shocks to better understand the behavior of these statistics this study applies them to the aftershocks of six large shallow focus earthquakes in california august 6 1979 coyote lake may 2 1983 coalinga april 24 1984 morgan hill august 4 1985 kettleman hills july 8 1986 north palm springs and october 1 1987 whittier narrows the large number of aftershocks accurately located by dense local networks allows us to treat these aftershock sequences individually instead of combining them as was done for the deep earthquakes the results for individual sequences show significant clustering about the closest nodal plane and the strike direction for five of the sequences and about the presumed fault plane for all six sequences this implies that the previously developed method does work properly nonrandom behavior was also found about the slip directions the p axis the t axis and the b axis but this is probably caused by the lack of independence between these axes and the previously mentioned features of the focal mechanisms given that the method does work and that deep aftershocks were not shown to cluster about the main shock nodal planes the shallow focus data were used to simulate the deep focus study the goal is to determine if there are artificial factors that make clustering in the deep focus data unobservable to more closely mimic the work on deep earthquakes the largest aftershocks from each of the six sequences were combined and studied with respect to their respective main shock focal mechanisms this reduced the significance of the clustering about the focal mechanism parameters but not below 95 confidence gaussian noise was then added to the aftershock hypocenters in order to determine if the larger hypocentral and focal mechanism errors in the deep focus data could account for the previous negative result the conclusion is that the following reasons are sufficient to explain the lack of clustering about the main shock nodal planes for the deep focus aftershocks the need to combine aftershocks from several sequences the size of the hypocentral location and focal mechanism errors and the alignment of distant aftershocks with the wadati benioff zone

iranian regional centroid moment tensor catalog solutions for 2012 2017 abstract in 2012 the installation of broadband seismic stations in iran allowed the beginning of the moment tensor project of iranian earthquakes by the iranian seismological center irsc in a period of five years 194 moment tensors with 3 7 mw 7 6 were computed based on analysis of seismograms recorded at local and regional distances included in the catalog are the moment tensors of 83 events not modeled by gcmt a reasonable consistency exists between the mechanisms of common events in the two catalogs the average moment magnitude difference is 0 1 and the kagan angle is below 20 for 61 of the earthquakes the p b and t axes difference is up to 15 the moment tensor catalog of iran shows a decrease of the magnitude of completeness by 0 3 after this study the number of accepted solutions as a fraction of attempts of the project with the average of 55 increased from 40 in 2012 to 68 in 2016 due to the expansions of the seismic networks in iran the dataset includes earthquakes from all seismic zones in iran with the dominance of thrust faulting the calculated depths in this study are consistent with the subregion seismotectonic conditions of iran the information on seven earthquakes with mw 6 0 and 53 events with 5 0 mw

intensity based source inversion of the destructive earthquake of 1694 in the southern apennines italy 1 we inverted the regional pattern of intensities of the catastrophic earthquake of 1694 in the southern apennines and determined the geometrical and kinematic characteristics of its source including the double couple orientation strike angle 299 10 dip 54 12 and rake 309 11 pure dip slip solution not precluded the objective nonlinear inversion was performed using the simple 11 parameter kinematic function model kf with a niching genetic algorithm technique the similarity between the pattern of the field intensities of the 1694 earthquake and the synthetic pattern is striking this result is supported by the fact that our inversion technique was verified in the study area where it was able to again find the source of the ms 6 9 irpinia 1980 earthquake known from instruments and from field surveys of the rupture this type of inversion enables researchers to exploit the extensive intensity data from italy and other countries to extend the knowledge of seismotectonic activity to preinstrumental times new paleoseismological evidence and even published descriptions of the fault rupture by witnesses of the 1694 earthquake were found confirming our results we also present and apply a new algorithm of general interest to calculate disorientations between double couples via standard linear algebra the 3 d rotations that bring the pairwise orthogonal unit vectors that were estimated by our intensity inversion into the instrumental triples of the 1980 irpinia earthquake assumed as benchmarks provide verification of our algorithm

rupture process and aftershocks relocation of the 8 june 2008 mw 6 4 earthquake in northwest peloponnese western greece on 8 june 2008 at 12 25 gmt an m w 6 4 strong earthquake occurred in the area of northwest peloponnese western greece causing the death of two people and extensive damage to the surrounding area the main event and its aftershocks were recorded by one nationwide and three regional networks equipped with three component broadband seismometers initial locations of the earthquake sequence comprising 438 aftershocks showed a linear northeast southwest trend and that the mainshock was located at 22 km depth after the relocation using catalog and differential travel times most events form three distinct clusters at depths 15 25 km moment tensor solutions for the main event and its largest aftershocks exhibited a pure strike slip mechanism with one nodal plane orientated northeast southwest in accordance with the relocated seismicity a parallel nonnegative least squares inversion technique utilizing multiple time windows was used to derive the spatiotemporal slip distribution of the main event the resulting slip distribution model revealed a large slip patch maximum slip 150 cm between 10 and 20 km depth at the northeast part of the fault that also coincides with the area that suffered most of the damage another patch exhibiting smaller amounts of slip 20 50 cm is located to the southwest direction at the same depth range and smaller patches exist at 25 30 km depth most aftershocks are located in areas of low slip 25 cm filling the regions of slip deficit the 8 june earthquake occurred at an area where no previous seismological or other observations indicated the existence of a seismogenic fault at that depth and with this strike this and the fact that the event nucleated in the middle to lower crust may be interpreted as the reactivation of a fault structure that was inherited from previous tectonic phases

pre and postseismic slow slip surrounding the 2011 tohoku oki earthquake rupture abstract slow aseismic slip that accommodates part of the long term plate motion on subduction megathrusts is thought to be strongly related to the occurrence of large earthquakes on the same fault zone however the temporal evolution and spatial distribution of the aseismic slip before major earthquakes and of accelerated postseismic afterslip are largely unconstrained we estimate cumulative offsets of small repeating earthquakes that are interpreted to reflect the in situ aseismic slip history on the subduction zone offshore northeastern japan these data reveal contrasting aseismic slip patterns between the coseismic rupture area of the mw 9 0 tohoku oki earthquake and surrounding portions of the subduction thrust the rupture area is characterised by low and variable slip rates before 2008 and the slip stopped almost completely after the earthquake the region surrounding the rupture area exhibited higher aseismic fault slip rates before the earthquake and clear postseismic slip of up to 1 6 m within 9 months following the main shock the frictional fault properties and complete relief of ambient stress in the central rupture zone of the main shock probably control the observed distribution the postseismic slip shows a more abrupt increase in the region closer to the source suggesting outwards propagation of afterslip small but distinct increases in the slip rate in the 3 yr before the earthquake near the area of large coseismic slip suggests preseismic unfastening of the locked area in the last stage of the earthquake cycle

the pucallpa nest and its constraints on the geometry of the peruvian flat slab abstract seismic nests or clusters are typically defined as regions of high seismic activity at intermediate depths that do not move over time and are not associated with volcanic activity at the surface e g zarifi and havskov 2003 zarifi et al 2007 prieto et al 2012 in this study we focus on a seismic nest located in central peru beneath the amazon basin city of pucallpa the location of this nest is just beyond the eastern most extent of the peruvian flat slab similar to the settings of two other south american clusters the bucaramanga and pipanaco nests while the pucallpa nest is visible in the figures of many earlier papers on intermediate depth south american seismicity it has not to our knowledge been described as a seismic nest before we present the first detailed description of the pucallpa nest compare it to other established nests and discuss its implications for our understanding of the peruvian flat slab our results indicate that the pucallpa nest demarcates the northern margin of a sag in the horizontally subducting nazca plate in central peru the position of the nest along the projected location of the downgoing mendana fracture zone is consistent with local variations in b values and could help to explain both the nest s genesis and the co located change in slab geometry the nest is also spatially well correlated with the northern margin of the thick skinned shira mountains and with the high heat flow associated with the agua caliente dome hermoza et al 2006 navarro comet 2018 further study is needed to understand the effects of the complex peruvian slab geometry on the formation of thick skinned deformation and heat flow anomalies on the overriding south american continent

the large andaman islands earthquake of 26 june 1941 why no significant tsunami we present a modern seismological study of the earthquake of 26 june 1941 in the andaman islands the largest pre 2004 event along that section of the india burma plate boundary despite a large conventional magnitude m text pas 8 1 it generated at best a mediocre tsunami for which no definitive quantitative reports are available we show that the 1941 earthquake took place under the andaman accretionary prism and consisted of a composite event whose nucleating phase had a strike slip mechanism incompatible with a data set of spectral amplitudes of mantle rayleigh and love waves combining this initial phase with a larger normal faulting mechanism can reconcile them with p wave first motions reports of subsidence on the eastern coast of the andaman islands and the small amplitudes of any putative tsunami the small tsunami results from a combination of that mechanism and of a source located under the islands themselves and in shallow water implying a reduction in amplitude under green s law when transitioning to a deeper basin

tsunamigenic predecessors to the 2009 samoa earthquake abstract we analyze historical earthquakes of the past century having generated regional tsunamis in samoa by means of epicentral relocation and quantification of spectral amplitudes of waveforms from historical seismograms the only tsunami with a level of destruction comparable to the 2009 event was generated by the earthquake of 26 june 1917 in the samoa corner yet a memory of this event is largely absent from the ancestral heritage of the present population of samoa which we tentatively attribute to the nearly simultaneous occurrence of the influenza epidemic in 1918 while not able to fully resolve focal geometries we document a diversity of mechanisms which add an element of unpredictability to the forecast of any future tsunami in the region

spatial variations in the similarity of earthquake populations the case of the 1997 colfiorito sellano northern apennines italy seismic sequence abstract the spatial properties of events in the 1997 colfiorito sellano seismic sequence northern apennines italy were investigated using coherence a parameter derived from seismic moment tensors that quantifies the kinematic similarity between focal mechanisms the 1997 colfiorito sellano seismic sequence predominantly consists of normal faulting earthquakes with a few strike slip and reverse faulting episodes this kinematic heterogeneity is possibly related to the contemporaneous activity of two different sets of faults nw se normal faults and nne ssw sub vertical faults the latter inherited from the previous miocene compressional phase the study used two independently derived data sets of the same seismic sequence characterized by a different number of events and by different precision of spatial localisation their statistical significances assessed through a reshuffling procedure reveal that data sets with at least some hundreds of events and good positional precision are required to obtain significant results through coherence analysis results from the better quality data set indicate that this seismic sequence is characterized by a rapid decrease in the kinematic similarity between earthquake pairs within 2 km of separation particularly along directions sub perpendicular to the normal fault strike the decrease rate seems to be controlled by the geometric characteristics of the normal faults given that the mean along dip distance between fault segments is 2 km in proximity to pre existing tectonic lineaments the relative abundance of strike slip and reverse faults tends to decrease the kinematic similarity between events but does not influence the coherence decrease rate the presence of mixed focal mechanisms normal reverse and strike slip in a single seismic phase implies that mixed fault types are not restricted to polyphase tectonic histories such heterogeneous kinematics during a single phase may be induced by the presence of inherited discontinuities

systematic changes of earthquake rupture with depth a case study from the 2010mw 8 8 maule chile earthquake aftershock sequence the very shallow part of subduction megathrusts occasionally hosts tsunami earthquakes with unusually slow rupture propagation the aftershock sequence of the 2010 mw 8 8 maule earthquake offshore chile provides us with the opportunity to study systematic changes in source properties for smaller earthquakes within a single segment of a subduction zone we invert amplitude spectra for double couple moment tensors and centroid depths of 71 aftershocks of the maule earthquake down to magnitudes mw 4 0 in addition we also derive average source durations we find that shallower earthquakes tend to have longer normalized source durations on average similar to the pattern observed previously for larger magnitude events this depth dependence is observable for thrust and normal earthquakes the normalized source durations of normal faulting earthquakes are at the lower end of those for thrust earthquakes probably because of the higher stress drops of intraplate earthquakes compared to interplate earthquakes we suggest from the similarity of the depth dependence of normal and thrust events and between smaller and larger magnitude earthquakes that the depth dependent variation of rigidity rather than frictional conditional stability at the plate interface is primarily responsible for the observed pattern tsunami earthquakes probably require both low rigidity and conditionally stable frictional conditions the presence of longduration moderate magnitude events is therefore a helpful but not sufficient indicator for areas at risk of tsunami earthquakes

centroid moment tensor catalogue for indonesia abstract we developed a centroid moment tensor cmt catalogue of earthquakes in and around indonesia inacmt using data from the nationwide broadband seismograph network in indonesia we obtained cmt solutions for about 500 earthquakes that occurred in and around indonesia between 2006 and 2009 the moment magnitudes ranged from 4 5 to 8 3 we examined the accuracy of the cmt solutions of the inacmt catalogue by comparing them with those obtained by the global cmt gcmt project the seismic moments and focal mechanisms of these catalogues were highly consistent with each other but we found systematic differences between the catalogues in the source centroid locations of earthquakes off sumatra the inacmt source centroid locations were closer to the hypocenter locations in the preliminary determination of earthquakes pde of the u s geological survey compared to those of gcmt the systematic deviations in the gcmt source centroid locations may mainly reflect insufficient azimuthal coverage of the stations used for the inversions as well as uncertainties in the earth model using the inacmt catalogue we investigated seismic activity related to the off bengkulu seismic sequence on 12 september 2007 mw 8 3 7 9 and 6 8 southwest of sumatra and the earthquakes northwest of the island of new guinea on 3 january 2009 mw 7 7 and 7 4 in the aftershock activity of the 2007 off bengkulu seismic sequence we found that shallow earthquakes were aligned along the eastern coast of siberut island located between the sunda trench and sumatra these earthquakes may have occurred along the mentawai fault or another unknown fault the focal mechanisms of the earthquakes were dominantly reverse slip although the mentawai fault has been considered to be a strike slip fault shallow large earthquakes along this fault may cause damage above the source region and generate large tsunamis we found that the 2009 earthquakes northwest of new guinea occurred along the manokwari trough and that the aftershocks were aligned along a plane dipping about 30 to the south indicating that the pacific and or philippine sea plate subducts below the australian plate at the manokwari trough the inacmt catalogue enables us to perform detailed analyses of seismic activity in and around indonesia which contributes to better understanding of tectonic features and potential seismic and tsunami hazards in indonesia as well as the coastal regions of the pacific and indian oceans

focal mechanisms and the state of stress on the san andreas fault in southern california focal mechanisms have been determined from p wave first motion polarities for 138 small to moderate 2 6 m 4 3 earthquakes that occurred within 10 km of the surface trace of the san andreas fault in southern california between 1978 and 1985 on the basis of these mechanisms the southern san andreas fault has been divided into five segments with different stress regimes earthquakes in the fort tejon segment show oblique reverse sup on east west and northwest striking faults the mojave segment has earthquakes with oblique reverse and right lateral strikesup motion on northwest strikes the san bernardino segment has normal faulting earthquakes on north south striking planes while the banning segment has reverse strike sup and normal faulting events all occurring in the same area the earthquakes in the indio segment show strike slip and oblique normal faulting on northwest to north south striking planes these focal mechanism data have been inverted to determine how the stresses acting on the san andreas fault in southern california vary with position along strike of the fault one of the principal stresses is vertical in all of the regions the vertical stress is the minimum principal stress in fort tejon and mojave the intermediate principal stress in banning and indio and the maximum principal stress in san bernardino the orientations of the horizontal principal stresses also vary between the regions the trend of the maximum horizontal stress rotates over 35 from n15 w at fort tejon to n20 at indio except for the san bernardino segment the trend of the maximum horizontal stress is at a constant angle of about 65 to the local strike of the san andreas fault implying a weak fault the largest change in the present stress state occurs at the end of the rupture zone of the 1857 fort tejon earthquake it appears that the 1857 rupture ended when it propagated into an area of low stress amplitude possibly caused by the 15 angle between the strikes of the san jacinto and san andreas faults the strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation

spatial structures in earthquakes and faults quantifying similarity in simulated stress fields and natural data sets abstract this paper presents an adaptation for fault analysis of the coherence method of kagan and knopoff kagan y y knopoff l 1985b the two point correlation function of the seismic moment tensor geophysical journal of the royal astronomical society 83 637 656 understanding coherence as a measure of the similarity between fault slip data for two faults which can be analytically computed from earthquake or fault moment tensors through the use of a customized gis routine the degree and distribution of similarity in synthetic and natural fault populations can be calculated as a function of distance between fault earthquake pairs and their relative orientation stress simulations using synthetic data sets reveal that fault populations which developed under homogeneous stress fields have a high degree of similarity that increases with the slip tendency of faults stress ratio variations and especially stress axis rotations lower the coherence values spatial analysis of natural earthquake and fault data sets from the umbria marche region northern apennines italy reveals a common pattern of coherence spatial cyclicities in faults earthquakes controlled by two consecutive tectonic phases miocene compression and plio pleistocene extension the proposed interpretation attributes the spatial cyclicities of miocene data to syn to post faulting folding in agreement with wavelengths derived from field data the observed periodicities in earthquakes 1997 colfiorito sellano umbria marche seismic sequence could in turn have been controlled by the miocene thrust structures with possible spatial stress field axis rotations and or stress ratio variations the spatial characteristics of younger fault earthquake populations are thus possibly controlled by the characteristics of older tectonic structures such as fold wavelength or fault spacing

new tsunami forecast tools for the french polynesia tsunami warning system this paper presents the tsunami warning tools which are used for the estimation of the seismic source parameters these tools are grouped under a method called preliminary determination of focal mechanism 2 pdfm2 that has been developed at the french polynesia warning center in the framework of the seiscomp3 system as a plug in concept the first tool determines the seismic moment and the focal geometry strike dip and slip and the second tool identifies the tsunami earthquakes earthquakes that cause much bigger tsunamis than their magnitude would imply in a tsunami warning operation initial assessment of the tsunami potential is based on location and magnitude the usual quick magnitude methods which use p waves work fine for smaller earthquakes for major earthquakes these methods drastically underestimate the magnitude and its tsunami potential because the radiated energy shifts to the longer period waves since french polynesia is located far away from the subduction zones of the pacific rim the tsunami threat is not imminent and this luxury of time allows to use the long period surface wave data to determine the true size of a major earthquake the source inversion method presented in this paper uses a combination of surface waves amplitude spectra and p wave first motions the advantage of using long period surface data is that there is a much more accurate determination of earthquake size and the advantage of using p wave first motion is to have a better constrain of the focal geometry than using the surface waves alone the pdfm2 method routinely gives stable results at t 0 45 minutes with t 0 being the origin time of an earthquake our results are then compared to the global centroid moment tensor catalog for validating both the seismic moment and the source geometry the second tool discussed in this paper is the slowness parameter theta and is the energy to moment ratio it has been used to identify tsunami earthquakes which are characterized by having unusual slow rupture velocity and release seismic energy that has been shifted to longer periods and therefore have low theta values the slow rupture velocity would indicate weaker material and bigger uplift and thus bigger tsunami potential the use of the slowness parameter theta is an efficient tool for monitoring the near real time identification of tsunami earthquakes

very fast characterization of focal mechanism parameters through w phase centroid inversion in the context of tsunami warning most of the tsunami potential seismic sources in the neam region are in a magnitude range of 6 5 le m w le 7 5 e g the tsunami triggered by the boumerdes earthquake of 2003 with m w 6 9 the centre d alerte aux tsunamis cenalt in operation since 2012 as the french national tsunami warning centre ntwc and candidate tsunami service provider ctsp has to issue warning messages within 15 min of earthquake origin time these warnings are based on the seismic source parameters m w magnitude focal depth and type of fault which are computed by focal mechanisms and centroid inversion methods the w phase method developed by kanamori and rivera allows quick computation of seismic source parameters due to the early arrival time between p waves and surface waves and is therefore particularly useful for monitoring we assess the w phase method with 29 events of magnitude m w ge 5 8 for the period 2010 2015 in the neam region results with 10 min of signal length are in good agreement compared to the global centroid moment tensor gcmt catalog

moment tensor solutions along the central lesser antilles using regional broadband stations abstract using waveform data gathered from the seismological networks of the lesser antilles we calculate 38 moment tensors for earthquakes with m 3 from 2013 to middle of 2015 by full waveform inversion nine of these moment tensor solutions are in good agreement with those previously reported by other institutions it provides some guarantee for 29 new moment tensors for the central region of the lesser antilles for earthquakes within the upper caribbean lithosphere our results evidence that extensional and strike slip focal mechanisms are predominant resulting from the intra plate deformation produced by the subduction of the north america and south american plates under the caribbean plate whereas very few thrust events are observed for deeper earthquakes 90 km our results compare well with older focal mechanisms from previous studies showing normal oblique or strike slip faulting within the subducted slab however the inversion for most of the deeper events is less reliable as documented for example by their larger condition numbers we use the newly obtained moment magnitudes to estimate the scaling relationship with the local magnitude mlv computed by the regional seismic network the two magnitudes are consistent for earthquakes with magnitudes m 4 with a slope close to unity further work is needed to precise the scaling relation for m

do intermediate and deep focus earthquakes occur on preexisting weak zones an examination of the tonga subduction zone it has been proposed that intermediate and deep focus earthquakes occur on preexisting planes of weakness that were created at shallow depth the purpose of this study is to test this hypothesis we examined fault plane solutions for 360 events that occurred in the tonga subduction zone from january 1976 to february 1999 for events in the slab each fault plane solution is rotated by the slab dip angle so that the slab is in its original horizontal position we then compare fault plane solutions for events in the slab with those for events at the outer rise we find that an asymmetric fault system corresponding to that found for outer rise events persists down to about 450 km depth this suggests that earthquakes down to this depth are caused by the reactivation of preexisting faults created in the oceanic plate before subduction a similar pattern though less well constrained is found in the kurile subduction zone down to 200 km depth for earthquakes deeper than 450 km the fault plane solutions are much more scattered in some places the fault plane pattern suggests the creation of new fault planes along orientations of maximum shear with zero internal friction the pattern of fault plane solutions in particular localized volumes cannot be easily explained by the creation of new faults in the direction of maximum shear under a coherent regional tectonic stress field thus either a highly heterogeneous stress field exists or preexisting planes of weakness also account for some deep earthquakes

seismicity induced by hydraulic fracturing in shales a bedding plane slip model passive seismic monitoring of microseismic events induced in oil or gas reservoirs is known as microseismic monitoring microseismic monitoring is used to understand the process of hydraulic fracturing which is a reservoir stimulation technique we use a new geomechanical model with bedding plane slippage induced by hydraulic fractures within shale reservoirs to explain seismicity observed in a typical case study of hydraulic fracturing of a shale gas play in north america microseismic events propagating from the injection point are located at similar depths within the uncertainty of their locations and their source mechanisms are dominated by shear failure with both dip slip and strike slip senses of motion the prevailing dip slip mechanisms have one nearly vertical nodal plane perpendicular to the minimum horizontal stress axis while the other nodal plane is nearly horizontal such dip slip mechanisms can be explained by slippage along bedding planes activated by the aseismic opening of vertical hydraulic fractures the model explains the observed prevailing orientation of the shear planes of the microseismic events as well as the large difference between seismic and hydraulic energy

an implosive component to the source of the deep sea of okhotsk earthquake of 24 may 2013 evidence from radial modes and cmt inversion abstract we study the spectral amplitudes of the first two earth radial modes 0 s 0 and 1 s 0 excited by the sea of okhotsk earthquake of 24 may 2013 the largest deep event ever recorded in the search for an isotropic component to its source in contrast to the case of the 1994 bolivian earthquake we detect an implosive component m i 1 1 10 27 dyn cm equivalent to 3 of the full scalar moment but 14 of the lone deviatoric component exciting the earth s radial modes an independent moment tensor inversion using the standard globalcmt algorithm but after relaxing its zero trace constraint similarly yields an implosive isotropic component albeit with a larger amplitude while it fails to document one in the case of the 1994 bolivian deep earthquake an implosive component to the source is expected in the model of transformational faulting in which deep earthquake rupture nucleates and grows upon transformation of metastable olivine to ringwoodite in the cold subducting slab this interpretation is supported by quantitative estimates 0 9 4 m of the thickness of the transformed shear zone which scale favorably relative to earthquake fault length with the upper end of the range of laboratory results reported for ices germanates and silicates the resulting extent of the transformation in the metastable wedge is consistent with the local geometry of the deep slab as recently determined by rupture modeling and aftershock distribution our results are in contrast to those for the two runner up largest deep earthquakes the 1994 bolivian and 1970 colombian shocks for which a similar isotropic component could not be detected we attribute this difference to variability in the ratio of isotropic to deviatoric components which combined with the smaller size of the 1970 and 1994 events would make any putative implosive component fall below detection levels especially in the case of the 1970 colombian earthquake for which only analog narrow band records were available

computing a large refined catalog of focal mechanisms for southern california 1981 2010 temporal stability of the style of faulting using the method developed by hardebeck and shearer 2002 2003 termed the hash method we calculate focal mechanisms for earthquakes that occurred in the southern california region from 1981 to 2010 when available we use hypocenters refined with differential travel times from waveform cross correlation using both the p wave first motion polarities and the s p amplitude ratios computed from three component seismograms we determine mechanisms for more than 480 000 earthquakes and analyze the statistical features of the whole catalog we filter the preliminary catalog with criteria associated with mean nodal plane uncertainty and azimuthal gap and obtain a high quality catalog with approximately 179 000 focal mechanisms as more s p amplitude ratios become available after 2000 the average nodal plane uncertainty decreases significantly compared with mechanisms that include only p wave polarities in general the parameters of the focal mechanisms have been stable during the three decades the dominant style of faulting is high angle strike slip faulting with the most likely p axis centered at n5 e for earthquakes of m 2 5 events using the 210 moment tensor solutions in tape et al 2010 as benchmarks we compare the focal plane rotation angles of common events in the catalog seventy percent of common earthquakes match well with rotation angles less than the typical nodal plane uncertainty the common events with relatively large rotation angles are either located around the edge of the scsn network or poorly recorded

2019 m6 7 yamagata oki earthquake in the stress shadow of 2011 tohoku oki earthquake was it caused by the reduction in fault strength abstract earthquake occurrence in the stress shadow provides a unique opportunity for extracting information about the physical processes behind earthquakes because it highlights processes other than the ambient stress change in earthquake generation in this study we examined the fault structure and the spatiotemporal distribution of the aftershocks of the 2019 m6 7 yamagata oki earthquake which occurred in the stress shadow of the 2011 m9 0 tohoku oki earthquake to better understand the earthquake generation mechanism the detection and hypocenter relocation of the aftershocks led to the delineation of three planar earthquake structures consitent with their focal mechanisms the results suggest that individual aftershocks were caused by a slip on these macroscopic planar structures aftershock hypocenters rapidly migrated upward from the deeper part of the major plane fault similar to the recent earthquake swarm sequences following the tohoku oki earthquake in the upper plate moreover we investigated the temporal evolution of the surface strain rate distribution in the source region using gnss data the east west contraction strain rate in the source region of the yamagata oki earthquake with an e w compressional reverse fault mechanism changed to an e w extension as a result of the tohoku oki earthquake and it continued until the occurrence of the yamagata oki earthquake the upward hypocenter migrations together with the earthquake occurrence in the stress shadow and in the e w extension strain rate field suggest that a reduction in the fault strength due to uprising fluids contributed to the occurrence of this earthquake sequence localized aseismic deformations such as aseismic creeps beneath the fault zone may also have contributed to the earthquake occurrence the results support the hypothesis that aseismic processes in the deeper part of the fault play crucial roles in the occurrence of shallow intraplate earthquakes

the ahar varzeghan earthquake doublet mw 6 4 and 6 2 of 11 august 2012 regional seismic moment tensors and a seismotectonic interpretation abstract on 11 august 2012 an earthquake doublet m w 6 4 and 6 2 occurred near the city of ahar northwest iran both events were only 6 km and 11 minutes apart producing a surface rupture of about 12 km in length historical and modern seismicity has so far been sparse in this area spatially the region represents a transitional zone between different tectonic domains including compression in iran westward extrusion of the anatolian plate and thrusting beneath the caucasus in this study we inverted the surface waveforms of the two mainshocks and 11 aftershocks m w 4 3 to obtain regional seismic moment tensors the earthquakes analyzed can be grouped into pure strike slip including the first mainshock and oblique reverse mechanisms including the second mainshock the sequence provides information about faulting mechanisms at the spatial scale of the entire rock volume affected by the earthquake doublet including coinciding deformation on minor faults sub parallel to the main fault and riedel shears it occurred on a so far unknown fault structure which we call the ahar fault alongside the seismological data we used geological maps satellite images and digital elevation data to analyze the geomorphology of the region our analysis suggests that the adjacent north tabriz fault which accomodates up to 7 mm yr of right lateral strike slip faulting does not compensate the entire lateral shear strain and that part of it is compensated farther north combined our results suggest a temporally and spatially complex style of deformation reverse and strike slip overprinting older reverse deformation

spatial and temporal variations of stress field in the longmenshan fault zone after the 2008 wenchuan china earthquake summary we investigate the temporal and spatial patterns of the regional stress field along the longmenshan fault zone lfz following the 2008 wenchuan mw7 9 earthquake regional broadband seismic records are used to determine the focal mechanisms and centroid source depths of 400 aftershocks of magnitudes 3 3 mw 5 9 the focal mechanisms are then used to invert for the temporal and spatial variations of the regional stress field results show clear spatial changes in the directions of principle stress axes as well as the faulting types along the lfz the regional stress field is in an overall thrust regime with nearly horizontal maximum compressional axis in the southern section of the lfz in addition to the primarily thrust background with maximum compressional axis perpendicular to the main fault zone strike slip component is also present in the middle section the maximum compressional axis varies spatially changing abruptly from perpendicular to parallel to the lfz in the northernmost section the stress environment becomes primarily strike slip our result suggests that the collision of indian and eurasian plates led to the first order feature of the stress field in the study area the geometry of blocks and faults the lower crustal flow as well as the shallow crustal property difference are the major factors to controlling the local stress field temporal variations of stress field suggest that the mainshock caused a large stress disturbance at early stage in certain areas of lfz and the stress field variations with depth imply a different deformation pattern and different stress background in the shallow and lower crust

quantifying focal mechanism heterogeneity for fault zones in central and southern california summary we present a statistical analysis of focal mechanism orientations for nine california fault zones with the goal of quantifying variations of fault zone heterogeneity at seismogenic depths the focal mechanism data are generated from first motion polarities for earthquakes in the time period 1983 2004 magnitude range 0 5 and depth range 0 15 km only mechanisms with good quality solutions are used we define fault zones using 20 km wide rectangles and use summations of normalized potency tensors to describe the distribution of double couple orientations for each fault zone focal mechanism heterogeneity is quantified using two measures computed from the tensors that relate to the scatter in orientations and rotational asymmetry or skewness of the distribution we illustrate the use of these quantities by showing relative differences in the focal mechanism heterogeneity characteristics for different fault zones these differences are shown to relate to properties of the fault zone surface traces such that increased scatter correlates with fault trace complexity and rotational asymmetry correlates with the dominant fault trace azimuth these correlations indicate a link between the long term evolution of a fault zone over many earthquake cycles and its seismic behaviour over a 20 yr time period analysis of the partitioning of san jacinto fault zone focal mechanisms into different faulting styles further indicates that heterogeneity is dominantly controlled by structural properties of the fault zone rather than time or magnitude related properties of the seismicity

present day crustal stress field in greece inferred from regional scale damped inversion of earthquake focal mechanisms in this study we utilize regional and teleseismic earthquake moment tensor solutions in order to infer the contemporary crustal stress in the greek region we focus on crustal earthquakes and select only solutions with good waveform fits and well resolved nodal planes a data set of 1614 focal mechanisms is used as input to a regional scale damped stress inversion algorithm over a grid whose node spacing is 0 35 several resolution and sensitivity tests are performed in order to ascertain the robustness of our results our findings show that for most of the greek region the largest principal stress 1 is vertically oriented and that the minimum principal stress axis 3 are subhorizontal with a predominant n s orientation in the sw peloponnese the orientation of 3 axes rotates clockwise and in se aegean counterclockwise these results are in agreement with the generally accepted model that slab rollback combined with gravitational spreading of the aegean lithosphere are the main causes of the extension transitions between different faulting types in nw greece or in the aegean occur within narrow zones in the order of tens of kilometers a visual comparison of the principal horizontal stress axes and the principal strain axes derived from gps observations shows good agreement suggesting that the crust in the greek region behaves largely in an elastic manner

the south of java earthquake of 1921 september 11 a negative search for a large interplate thrust event at the java trench summary we present a detailed study of the earthquake of 1921 september 11 located between the two anomalous tsunami earthquakes of 1994 and 2006 south of java based on modern relocation techniques a compilation of focal mechanism constraints from historical seismograms a quantification of mantle surface waves and a numerical simulation of its mediocre tsunami only 10 cm at cilacap we conclude that the 1921 earthquake occurred at a depth of 30 km as an intraplate earthquake in the outer rise featuring a mostly strike slip mechanism expressing tensional stress parallel to the direction of convergence with a moment of 5 1027 dyn cm two other large historical earthquakes south of java in 1937 and 1943 are also shown to be intraplate shocks so that the java subduction zone lacks large interplate thrust events for the entire era of instrumental seismicity however this does not violate the extrapolation to large sources of the frequency moment characteristics of modern digital data 1976 2011 thus leaving open the possibility that the java trench might entertain occasional if rare mega thrust events