segmentation of the himalayan megathrust around the gorkha earthquake 25 april 2015 in nepal abstract we put the 25 april 2015 earthquake of nepal mw 7 9 into its structural geological context in order to specify the role of the segmentation of the himalayan megathrust the rupture is mainly located nw of kathmandu at a depth of 13 15 km on a flat portion of the main himalayan thrust mht that dips towards the n ne by 7 10 the northern bound of the main rupture corresponds to the transition towards a steeper crustal ramp this ramp which is partly coupled during the interseismic period is only locally affected by the earthquake the southern bound of the rupture was near the leading edge of the lesser himalaya antiformal duplex and near the frontal footwall ramp of the upper nawakot duplex the rupture has been affected by transversal structures on the western side the judi lineament separates the main rupture zone from the nucleation area on the eastern side the gaurishankar lineament separates the 25 april 2015 rupture from the 12 may 2015 mw 7 2 rupture the origin of these lineaments is very complex they are probably linked to pre himalayan faults that extend into the indian shield beneath the mht these inherited faults induce transverse warping of the upper lithosphere beneath the mht control the location of lateral ramps of the thrust system and concentrate the hanging wall deformation at the lateral edge of the ruptures the mht is therefore segmented by stable barriers that define at least five patches in central nepal these barriers influence the extent of the earthquake ruptures for the last two centuries the 1833 mw 7 6 earthquake was rather similar in extent to the 2015 event but its rupture propagated south westwards from an epicentre located ne of kathmandu the patch south of kathmandu was probably affected by at least three earthquakes of mw 7 that followed the 1833 event a few days later or 33 years 1866 event mw 7 2 later the 1934 earthquake mw 8 4 had an epicentre 170 km east of kathmandu may have propagated as far as kathmandu and jumped the gaurishankar lineament this combined structural approach and earthquake study allows us to propose that the mht in the central eastern himalaya is segmented by stable barriers that define barrier type earthquake families however for each individual earthquake within a family the rupture histories could be different furthermore the greatest earthquakes could have broken the barriers and affected the patches of several families the concept of a regular recurrence of characteristic earthquakes is therefore misleading to describe the succession of himalayan earthquakes

magnitude scale and quantification of earthquakes despite various shortcomings the earthquake magnitude scale is one of the most fundamental earthquake source parameters to be used for catalogs although use of a uniform scale is desirable it is not always possible because of changes in instrumentation the data reduction method and the magnitude formula the station distribution etc as a result various magnitude scales have been developed and are currently in use recent developments in seismometry and earthquake source theories provide more quantitative source parameters than the magnitude in order to maintain continuity and uniformity of the data it is important to relate these magnitude scales and the new parameters in view of this importance relations between different magnitude scales are examined with an emphasis on the difference in the period of the waves used for the magnitude determination use of several magnitude scales determined at different periods provides a convenient method for characterizing earthquakes the moment magnitude can be used to quantify both shallow and deep earthquakes on the basis of wave energy radiated and provides a uniform scheme

earthquake magnitude potential of the intermountain seismic belt usa from surface parameter scaling of late quaternary faults two of the largest historical earthquakes documented for the united states occurred within the past four decades in a zone of anomalous seismicity in the western interior of the country known as the intermountain seismic belt isb paleoseismology has revealed the presence of major active faults throughout this region some of them extending through densely populated area this study presents mean value estimates of the maximum earthquake magnitudes that can be expected from 65 of the most prominent late quaternary fault segments of the isb using surface rupture parameters linear least squares regressions of magnitude on surface rupture length l maximum surface displacement d and dl respectively were computed for an updated worldwide set of historical normal slip earthquakes these were compared with similar regressions from other publications and it was found that a dl based formula restricted to normal faulting mechanisms has a relatively high correlation low standard deviation and tends to yield magnitudes between those given by d and l alone this last property is useful for applications to the isb prehistoric data where the record of historical ground rupturing earthquakes is too sparse to estimate the proportions in which d and l are likely to contribute to seismic energy release of a fault application of regressions to published paleoseismic displacements and estimated earthquake segment lengths for the isb faults shows that d consistently scales a larger magnitude than the corresponding single segment l by an average of 0 2 to 0 3 magnitude unit after accounting for bias from the regressions considerations of uncertainties in paleoseismic displacements suggest that they cannot fully explain the discrepancy since it is known that large earthquakes often encompass multiple segments of a fault these observations indicate that longer rupture lengths should be used to estimate maximum magnitudes for isb faults a dual segment rupture scenario produces better agreement between d and l based magnitudes and is supported by historical and paleoseismic earthquake data from the region magnitudes scaled by the dl based regression for dual segment rupture range from ms 6 8 to 7 5 m 0 20 and the largest are associated with the central segments of the wasatch fault and the swan grand valley teton madison and east bear lake faults

magnitudes of future large earthquakes near istanbul quantified from 1500 years of historical earthquakes present day microseismicity and gps slip rates abstract in the past 1500 years seven sequences of significant earthquakes have occurred on a 160 km long segment of the north anatolian fault zone nafz centered on istanbul the most recent of these sequences will be complete with the future occurrence of one or more mw 7 0 earthquakes near the city from a summation of the seismic moment released by historical earthquakes between 500 and 2000 ce we calculate a mean slip deficit rate of 9 9 mm year our moment summation procedure sums the seismic moment associated with known historical earthquakes in the past 1500 years based on rupture length and assumed seismogenic depth we observed that in the 1999 izmit earthquake strongly coupled fault patches were associated with the highest co seismic slip in our calculated map of present day slip potential we recognize several such patches from their low present day rate of microseismicity e g segments beneath the kumburgaz and eastern cinarcik marmara basins in contrast intervening weakly coupled patches host high present day background seismicity e g the segment beneath the western tekirdag basin this lends credibility to an interpretation of future earthquakes occurring in three seismogenic segments of the nafz corresponding to three deep basins in the sea of marmara the present day slip deficits reach up to 1 7 m beneath the western tekirdag basin segment and 4 0 m and 5 4 m beneath the central central high and kumburgaz basin and eastern cinarcik basin segments respectively these segments most recently ruptured in august 1766 may 1766 and october 1509 and currently have a potential to generate mw 7 2 mw 7 4 and mw 7 5 earthquakes respectively although contiguous ruptures have not occurred historically ruptures of contiguous segments could occur as a mw 7 5 earthquake in the west or a mw 7 6 earthquake in the east or as a single through going mw 7 7 rupture

homogeneous moment magnitude calibration in switzerland an earthquake catalog containing a uniform size estimate is important for long term seismic hazard assessment in regions of low to moderate seismicity during the update of the earthquake catalog of switzerland ecos we performed regression analyses to convert all earthquake size information in ecos to physically meaningful moment magnitude m w for 34 events in and near switzerland we determined seismic moment thus m w by regional waveform inversion independent m w estimates for the same events do not exist however m w from european mediterranean events obtained in the same way agree with m w from harvard cmt solutions all other size estimates m l m d m b m s and intensities are calibrated relative to these 34 events teleseismic m s and m b from international data centers are directly regressed against m w most observations in ecos consist of local magnitudes m l m d and intensities for local magnitudes we first calibrated the swiss seismological service s m l then we calibrated magnitudes from observatories in neighboring countries france germany italy using only events in the border region e g france switzerland modern instrumental records exist only since the mid 1970s we calibrated the macroseismic dataset which represents by far the largest period in the catalog by determining surface wave magnitude m s for stronger twentieth century swiss earthquakes from analog seismograms these m s which were converted to m w connect intensities and m w after calibration all 20 300 events in ecos have a unified m w including a class type uncertainty estimate based on the original magnitude scale ecos covers the period 250 2001 from 44 n to 51 n and 4 e to 13 e the largest event in ecos is the 1356 m w 6 9 basle earthquake

attenuation of high frequency seismic waves beneath the central andean plateau observed patterns of high frequency seismic wave attenuation suggest that near 22 s the upper mantle structure beneath the central andean plateau changes along strike to the south contrasting regions of high and low upper mantle seismic wave attenuation beneath the plateau are identified based on striking azimuthal variations in the character and frequency content of p and s waves propagating beneath the plateau to a portable seismic network deployed in jujuy province argentina 24 s 65 w ray paths from intermediate depth earthquakes located north and northwest of the network transmit seismic waves with a higher frequency content than ray paths from earthquakes at similar depths and distances but located west and south of the network the estimated apparent q values fall into two categories qp 500 and qs 350 for the high q paths and qp 350 and qs 200 for the low q paths in addition sn phases from regional crustal earthquakes in the subandean foreland fold thrust belt to the north propagate efficiently to the jujuy network while sn is not observed from foreland earthquakes located at similar distances to the south of the network these observations combined with data from previously reported wave propagation studies suggest that south of about 22 s the upper mantle beneath the plateau and its adjacent foreland thrust belt is more highly attenuating than the upper mantle farther north forward modeling of the q measurements made at jujuy indicates that the observations can be explained either by a variable thickness high q upper plate beneath the plateau or by a thin variable width very low q zone in the asthenospheric wedge above the subducted slab this lateral variation in upper mantle structure coincides with two physiographically distinct segments of the central andean plateau and its adjacent foreland thrust belt to the east the bolivian altiplano and subandean ranges in the north and the argentine puna and santa barbara system in the south we interpret the north south change in upper mantle attenuation and the corresponding changes in physiography topography and tectonic style at the surface to be due to a mantle lid that is thicker beneath the altiplano and the subandean belt than beneath the puna and the santa barbara ranges

state of stress in the southern tyrrhenian subduction zone from fault plane solutions summary in this paper we present revised locations and original focal mechanisms computed for intermediate and deep earthquakes that occurred within the southern tyrrhenian subduction zone between 1988 and 1994 in order to improve our knowledge of the state of stress for this compressional margin in particular we define the stress distribution within a large portion of the descending slab between 40 and about 450 km depth the seismicity distribution reveals a continuous 40 50 km thick slab that abruptly increases its dip from subhorizontal in the ionian sea to a constant 70 dip in the tyrrhenian we computed focal mechanisms for events with magnitudes ranging from 2 7 and 5 7 obtaining the distribution of p and t axes for many events for which centroid moment tensor cmt solutions are not available thus enabling the sampling of a larger depth range compared to previous studies we define three portions of the slab characterized by different distributions of p and t axes a general down dip compression is found between 165 and 370 km depth whereas in the upper part of the slab 40 165 km depth the fault plane solutions are strongly heterogeneous below 370 km the p axes of the few deep events located further to the north have a shallower dip and are not aligned with the 70 dipping slab possibly suggesting that they belong to a separated piece of subducted lithosphere there is a good correspondence between the depth range in which the p axes plunge closer to the slab dip 70 and the interval characterized by the highest seismic energy release 190 370 km

scaling law and its applications to earthquake statistical relations abstract the spectra of the far field body wave displacement for earthquakes of various magnitudes have been obtained using a two dimensional faulting model on a rectangular fault there are three corner frequencies f c 1 f c 2 and f c 3 in the displacement spectra f c 1 and f c 2 relate to faulting times for the long and wide directions on the rectangular fault respectively and f c 3 corresponds to the rise time of the source time function according to these three corner frequency values four spectral regions are defined u u 0 f 0 f f c 1 in the first region u 1 f f c 1 f f c 2 in the second region u 1 f 2 f c 2 f f c 3 in the third region and u 1 f 3 f f c 3 in the fourth region this results in different source parameter relations for different magnitude ranges i e different seismic moment ranges because the attenuation rates depend on frequency it is supposed that earthquake faulting is satisfied by three conditions of geometrical similarity stress environment and dynamic similarity therefore seismic moment faulting time along the length and width of the fault and rise time can all be scaled with fault length the constants in the scaling relations can be determined from seismic moment data for about 800 earthquakes that occurred during 1981 1983 and are given by dziewonski and woodhouse 1983 and m s and m b data from the isc bulletin thus the source parameter relations between m s and m b m s and m l m b and m l log m o and log s fault area log s and m s log l fault length and m s and log d average dislocation and m s can be deduced from the scaling law rather than from pure statistical relations these relations are statistically consistent with the observed data the average rupture velocity of the fault can also be estimated from the scaling law it is 2 65 km s the total time of rupture is 0 35 s km l km which is close to that estimated by kanamori 1981 and the dislocation slip rate is 287 1143 cm s

systematic analysis of deep seismicity 200 centroid moment tensor solutions for earthquakes between 1977 and 1980 summary a systematic study of deep seismicity is performed using waveform data from the gdsn between 1977 and 1980 and the centroid moment tensor method of dziewonski et al two hundred new cmt solutions are found for events deeper than 100km their moments obtained using the same algorithm range between 7 x and 1 4 x lo2 dyne cm a factor of 20 000 a statistical analysis of the cmt parameters provides important conclusions among these the shift in origin time for deep events is found to be almost independent of the seismic moment providing an indication of the complexity of deep earthquakes the deviation from the double couple model appears to be correlated to the state of stress of the subducting slabs mechanisms showing down dip compression are generally dominated by the eigenvalue corresponding to the compression axis and down dip tension correlates with the predominance of the tensional eigenvalue comparison with moment tensors obtained by other authors using different waveform data shows good agreement between different methods comparison with published focal plane mechanisms confirms the precision and reliability of the cmt method examples of cmt solutions used to identify patterns of seismicity associated with deep fault planes are shown

crustal and upper mantle structure of peninsular india and source parameters of the 21 may 1997 jabalpur earthquake mw 5 8 results from a new regional broadband network abstract in the past two years a permanent network of 10 broadband seismographs has become operational in the indian peninsular shield region in this article we analyze the data recorded by this network with two goals 1 to lay ground for a quick estimation of source parameters of future earthquakes in the region and 2 to estimate the source parameters of the destructive jabalpur earthquake of 21 may 1997 mw 5 8 which occurred within the network toward these goals we measure rayleigh and love wave group velocity dispersion curves in the period range of 10 to 75 sec and invert these curves to estimate the crustal and the upper mantle structure below the indian shield region our best model consists of a two layer crust the upper layer is 14 km thick with a shear wave velocity v s of 3 55 km sec the corresponding values for the lower layer are 25 km and 3 85 km sec v s for the upper mantle is 4 65 km sec based on this structure we perform a moment tensor mt inversion of the bandpassed 0 05 0 02 hz seismograms of the jabalpur earthquake the best fit is obtained for a source located at a depth of 42 km with a seismic moment m 0 of 7 7 10 24 dyne cm and a focal mechanism with strike 61 dip 64 and rake 74 these source parameters are similar to those previously reported in the literature demonstrating that a routine mt inversion of moderate and large indian penisular earthquakes is now possible a careful examination of the seismograms and modeling of the two closest records reveal that the jabalpur earthquake nucleated in the lower crust at a depth of 36 km it consisted of two subevents separated in time by 0 65 sec with the second subevent located 2 km above the first one the total source duration was 1 4 sec

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

seismic hazard reappraisal from combined structural geology geomorphology and cosmic ray exposure dating analyses the eastern precordillera thrust system nw argentina because earthquakes on large active thrust or reverse faults are not always accompanied with surface rupture paleoseismological estimation of their associated seismic hazard is a difficult task to improve the seismic hazard assessments in the andean foreland of western argentina san juan province this paper proposes a novel approach that combines structural geology geomorphology and exposure age dating the eastern precordillera of san juan is probably one of the most active zones of thrust tectonics in the world we concentrated on one major regional active reverse structure the 145 km long villic um pedernal thrust where this methodology allows one to 1 constrain the quaternary stress regime by inversion of geologically determined slip vectors on minor or major fault planes 2 analyse the geometry and the geomorphic characteristics of the villic um pedernal thrust and 3 estimate uplift and shortening rates through determination of in situ produced 1 0 be cosmic ray exposure cre ages of abandoned and uplifted alluvial terraces from a structural point of view the villic um pedernal thrust can be subdivided into three thrust portions constituting major structural segments separated by oblique n40 e trending fault branches along the three segments inversion of fault slip data shows that the development of the eastern precordillera between 31 s and 32 s latitude is dominated by a pure compressive reverse faulting stress regime characterized by a n110 10 e trending compressional stress axis 1 a geomorphic study realized along the 18 km long las tapias fault segment combined with cre ages shows that the minimum shortening rate calculated over the previous 20 kyr is at least of the order of 1 mm yr 1 an earthquake moment tensor sum has also been used to calculate a regional shortening rate caused by seismic deformation this analysis of the focal solutions available for the last 23 yr shows that the seismic contribution may be three times greater than the shortening rate we determined for the las tapias fault i e 3 mm yr 1 suggesting that the san juan region may have experienced a seismic crisis during the 20th century moreover the ramp that controls the development of the eastern precordillera appears to be one of the main seismic sources in the san juan area particularly the 65 km long villic um las tapias segment a first order evaluation of the seismic hazard parameters shows that this thrust segment can produce a maximum earthquake characterized by a moment magnitude of 7 3 0 1 and a recurrence interval of 2 4 1 5 kyr this part of the villic um pedernal ramp may have ruptured during the ms 7 4 1944 san juan earthquake producing very few surface ruptures and only distributed flexural slip deformation on to the neogene foreland bedding planes between the eastern precordillera and pie de palo

lattice preferred orientation and microstructure of peridotites from odp hole 1274a 15 39 n mid atlantic ridge testing models of mantle upwelling and tectonic exhumation abstract eleven harzburgites and one dunite from ocean drilling program leg 209 hole 1274a preserve high temperature mantle textures electron backscatter diffraction ebsd analysis shows moderately developed crystal lattice preferred orientations lpos in olivine and orthopyroxene m indices 0 1 indicative of crystal plastic deformation at 1250 c these rocks preserve a protogranular texture with a weak olivine foliation a very weak or absent orthopyroxene foliation that may be decoupled from the orthopyroxene lpo and minor interstitial clinopyroxene and spinel olivine grain size distributions along with melt related microstructures in orthopyroxene clinopyroxene and spinel suggest that high temperature deformation textures have been overprinted by pervasive post deformation melt rock interaction paleomagnetic data constrain the olivine 100 axes to be subhorizontal and oriented at low angle 28 6 10 6 to the ridge axis at the onset of serpentinization this orientation is consistent with either complex 3 d mantle upwelling or 2 d mantle upwelling coupled with complex 3 d tectonic emplacement to the seafloor

a reexamination of the bucaramanga colombia earthquake nest the bucaramanga earthquake nest is situated at a depth of about 160 km beneath colombia at 6 8 n 73 w and it produces about eight earthquakes of mb 4 7 or more each year from a source region having dimensions of about 10 km or less in this study we evaluate nest properties using reported locations focal mechanisms and moment tensors as well as relocations determined from teleseismic p pp and pkp arrivals we also introduce a novel method for determining the volume of a group of hypocenters and use this volume as a statistic for evaluating the accuracy of nest hypocenters we have relocated 26 nest earthquakes occurring between 1964 and 1986 using the jhd method and carefully reread teleseismic p pp and pkpdf arrivals the relocated earthquakes cluster within a region having a volume of 776 km3 and east west north south and vertical dimensions of 13 18 12 km a smaller region than any found previously from analysis of teleseismic data in practical terms this represents an approximate upper bound on the accuracy of relative earthquake locations possible using teleseismic data and standard relocation methods this compares with a volume of 11 km3 and dimensions of 5 1 3 4 3 8 km as determined by schneider et al 1987 from observations of microearthquakes collected over 16 days with a temporary local network these dimensions are comparable to those of the rupture dimensions of the largest observed nest earthquakes as determined from an analysis of their seismic moments 5 1024 dyne cm furthermore an evaluation of cumulative moment rate since 1964 indicates that strain rates within the nest volume must be between 10 13 sec and 10 11 sec the b values 2 0 and values 0 9 determined from available magnitudes and moments are remarkably high suggesting that earthquakes of all observed sizes 3 1020 to 5 1024 dyne cm contribute significantly to the moment release focal mechanisms determined from teleseismic observations exhibit a consistent pattern most having westward dipping p axes and eastward dipping t axes this differs from the more varied pattern reported by schneider et al 1987 for microseismic earthquakes

source solutions and station residuals from long period waveform inversion of deep events deep earthquakes of up to moderate size have been analyzed by a long period waveform inversion of global digital seismographic network data where the use of a point source model proved to be adequate but the use of a standard earth model was inadequate without modification modifications include calculations in an earth model based on prem but with different source and receiver structures and the introduction of time delays which were determined together with the moment tensor components of the source by an iterative correlation method the moment tensor components are in accordance with the pattern of stress release in other work but results for the seismic moment differ somewhat and there is no compelling evidence for deviations from a double couple mechanism the time delays were inverted to find the source centroid depths and time shifts and the station residuals there is no baseline effect in the times of source duration which could be explained by a simple circular source model but there is such an effect in the station residuals together with a distance trend especially for s part of the baselines may be an effect of bias in origin times but the pattern of s residuals in particular suggests also possible modifications of the standard model

structural setting along the western north anatolian fault and its influence on the 2014 north aegean earthquake mw 6 9 abstract we investigated microseismicity geodetic slip and structural setting along the western north anatolian fault naf to characterize their influence on pre co and post seismic stages of the 2014 north aegean earthquake m 6 9 we identified that the naf in north aegean sea nas operates beneath three basins and two transpressional ridges rather than a single through going basin refined hypocenters indicate that naf is a narrow shear zone in the east and systematically expands towards the west microseismicity has a wide spread epicentral pattern at pre seismic stage of the 2014 earthquake but later tightens during post seismic stage this suggests that pre seismic strain accumulation was completed on the main fault and transferred to surrounding secondary structures and the slip returned back to the main fault following the mainshock overall microseismicity pattern shows that seismogenic zone becomes deeper to the west and shallower to the east three fault segments merged with two step overs have failed during the 2014 north aegean earthquake rupturing a 90 km section of the naf the co seismic slips reach 90 cm beneath western step over and remains below 60 cm beneath eastern step over along fault pre and co seismic geodetic slips show a complementary pattern verifying that the 2014 mainshock generated the highest slip at pre seismically locked patches located beneath transpressive ridges hosting two step overs the existence of high pre shock concentrations underneath suggests fracturing at seismogenic basement overcoming frictional strength at these two fault step overs

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

microseismicity of the mid atlantic ridge at 7 s 8 15 s and at the logatchev massif oceanic core complex at 14 40 n 14 50 n lithospheric formation at slow spreading rates is heterogeneous with multiple modalities favoring symmetric spreading where magmatism dominates or core complex and inside corner high formation where tectonics dominate we report microseismicity from three deployments of seismic networks at the mid atlantic ridge mar two networks surveyed the mar near 7 degrees s in the vicinity of the ascension transform fault three inside corner high settings were investigated however they remained seismically largely inactive and major seismic activity occurred along the center of the median valley in contrast at the logatchev massif core complex at 14 degrees 45n seismicity was sparse within the center of the median valley but concentrated along the eastern rift mountains just west of the serpentine hosted logatchev hydrothermal vent field to the north and south of the massif however seismic activity occurred along the ridge axis emphasizing the asymmetry of seismicity at the logatchev segment focal mechanisms indicated a large number of reverse faulting events occurring in the vicinity of the vent field at 3 5 km depth which we interpret to reflect volume expansion accompanying serpentinization at shallower depth of 2 4 km some earthquakes in the vicinity of the vent field showed normal faulting behavior suggesting that normal faults facilitates hydrothermal circulation feeding the vent field further a second set of cross cutting faults occurred indicating that the surface location of the field is controlled by local fault systems

stage dependent variability in tractive force distribution through a riffle pool sequence high resolution data on spatial and temporal variability in flow hydraulics and sediment transport within riffle pool sequences are required to improve understanding of how fluvial processes maintain these meso scale bedforms this paper addresses this issue by providing velocity and boundary shear stress data over a range of discharges from base flow 0 07 m3 s 1 to just over bankfull 8 52 m3 s 1 from a sequence of four pools and three riffles in the river rede northumberland the data supports the reversal hypothesis of keller geol soc am bull 87 1971 753 as the primary explanation for the maintenance of the riffle pool sequence although they also indicate that spatial variability in tractive force is highly stage dependent and complex section averaged velocity data indicate reversal to be evident at four out of six riffle pool units an equalisation in velocity was found for the other two riffle pool units close to bankfull stage the spatial patterns of tractive force exhibited in the study reach as a result of increased discharge demonstrate that riffle pool units operate independently of one another shear stress reversals were observed in individual riffle pool units at different river stages during a flood hydrograph and in some instances two occurred in the same riffle pool unit during a single flow event pools were characterised by coarser bed sediments and narrower channel widths in comparison to riffles increasing the likelihood of tractive force reversal in the river rede areas of predicted bed sediment entrainment obtained from o c matched observed channel changes in the upper part of the study reach but over estimated change in the middle portion of the reach

constraints on present day shortening rate across the central eastern andes from gps data two years of continuous gps data from several sites in south america indicate that arequipa in the southern peruvian andes has a velocity of 13 3 mm yr two standard errors to the northeast with respect to stable south america we interpret these data as reflecting a combination of elastic strain accumulation associated with a locked nazca south america subduction zone and a small amount of crustal shortening across the fold and thrust belt on the eastern margin of the andes models of elastic strain accumulation for fully locked and partly locked subduction zones constrain shortening in the eastern andes to 0 3 mm yr fully locked and 0 12 mm yr partly locked slower than some geologic estimates averaged over millions of years

probabilistic forecasting of tsunami occurrences across various tsunamigenic zones of the earth stochastic tools have been developed to estimate the potential for tsunami generation in a particular region under consideration this paper identifies 13 probable zones on the earth where there is a high likelihood for tsunami generation in the future the conditional probabilities for future tsunami and earthquake occurrences are estimated for all the identified zones also total probabilities for future tsunami events are computed forecasting is done on the basis of conditional probability obtained using the best fit model among lognormal gamma log logistic and weibull distributions the obtained probabilities of tsunami are validated by calculating the region specific threshold probabilities also a country wise expectation of anticipated tsunami is developed for each zone zones 5 northwest u s a and bering sea islands 6 kuril kamchatka islands and 7 japan northeast china and korea have the highest ratio of tsunamigenic earthquakes to the total number of earthquakes the zone 7 has the highest probability of tsunami occurrence in the near future as calculated from the total probability theorem however zones 1 southwest coast of south american continent 7 and 11 papua new guinea and solomon islands are expected to experience a tsunami in the near future before 2022 as per the current forecasting study

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

distribution of the late quaternary deformation in northwestern himalaya abstract three main cenozoic thrusts at the front of northwestern himalaya have accommodated most of the india eurasia convergence across the belt over the last million years and produced the present relief their recent tectonic activity is poorly known because of the long period of inaccessibility of the jammu and kashmir state and because the latest and only large earthquake recorded in the region occurred in 1555 ad we show where the deformation is localized during the late quaternary and determine shortening rates across the structures by analyzing the geometry and chronology of geomorphic markers the main boundary thrust in this region ceased moving at least 30 ka ago on the contrary the more external medlicott wadia thrust and main frontal thrust both merging at depth on the sub flat detachment of the main himalayan thrust exhibit hectometric scale deformations accumulated during the last thousands of years the total shortening rate absorbed by these faults over the last 14 24 ka is between 13 2 and 27 2 mm yr 11 2 3 8 and 9 0 3 2 mm yr respectively part of this deformation may be associated to the geometry of the chenab reentrant which could generate an extra oblique component however the lower bound of our shortening rates is consistent with previously determined geodetic rates active deformation on these structures follows an in sequence out of sequence pattern with breaking of both ramps being possible for earthquakes triggered on the main detachment

temporal changes in the cumulative piecewise gradient of a variant of the gutenberg richter relationship and the imminence of extreme events abstract it is generally found that the relative frequencies of occurrence of earthquakes of different magnitudes in seismogenic zones have a power law distribution for a long term dataset the overall slope of this logarithmically transformed distribution is usually indicated by a best fit straight line and expressed as a b value this slope is stable and normally lies between 0 8 and 1 2 the actual value depending on the region examined and the threshold selected for data completeness the linearity of the distribution can be used to make statistical inferences about the potential for larger events over the long run and with appropriate reservations may even be extrapolated to magnitudes that are beyond recent experience we suggest the same information can also be viewed over shorter intervals in terms of an empirical piecewise distribution with relative frequencies of occurrence at adjacent magnitude steps controlling the local slope of the distribution an emergence through time of an excess number of lower magnitude earthquakes causes temporal changes to appear in the low end piecewise gradients of this distribution a marked excursion away from an overall uniform trend for the particular zone may be indicative of an imminent larger event on two separate occasions in 1982 and 1997 such temporal variations were seen in the magnitude distributions of sequences of events near tobago west indies and used to anticipate subsequent damaging mainshocks the recognition of temporal departures from overall linearity of the magnitude frequency relation in a suitable dataset may thus provide an evidential element that can contribute to earthquake forecasting this phenomenological approach was used in the analysis of the neic global dataset of earthquakes of magnitude 6 1 and bigger for the period 1973 2003 to explore its wider applicability trends in the piecewise gradients of the global data were interpreted as pointing to an imminent great earthquake perhaps exceeding magnitude 8 5 such an event did occur shortly afterwards in the form of the great sumatran earthquake of 2004 12 26 following that event global magnitude production continued to exhibit sharp imbalances in the lower magnitude bins indicating that another similar event was likely the second sumatran earthquake on 2005 03 28 satisfied that projection since that time a magnitude production imbalance persists in the global dataset suggesting the system could be poised to output an earthquake or earthquakes in the magnitude range 8 6 9 0 or even greater this contribution describes the piecewise gradient approach and examines its application to global earthquake data

measurements of coseismic deformation in southern california 1972 1982 since 1972 a number of static strain changes have been measured at pinon flat observatory southern california as a result of regional faulting as recorded by a collection of long baselength strainmeters and tiltmeters these signals are in good quantitative agreement with the deformation calculated for a dislocation in an elastic half space in contrast colocated short baselength sensors are found to produce spurious results whose size is much larger than expected theoretically and well correlated with peak site acceleration calculations show that the root mean square rms of the coseismic signals from several different instruments at one site or from several sites at known hypocentral distances provide a good estimate of the seismic moment a result confirmed by the observations static moment estimates for the four largest events in this period are imperial valley 1979 m0 9 0 1018nm mexicali valley 1980 m0 6 1 1018nm westmorland 1981 m0 5 3 1017nm and brawley 1979 m0 2 3 1017 nm these estimated moments generally exceed those determined seismically by about 25 which is as expected since they include some postseismic deformation results from the mexicali valley earthquake are particularly interesting indicating an average fault strike approximately 9 different from the historic fault trace several small to moderate earthquakes ml 3 7 5 2 were also well enough recorded to estimate source parameters for the only other detectable events in the period 1972 1982 a total of three others for which the strain change erms was greater than 0 4 ne high accelerations caused most of the instruments at the site to malfunction no precursory signals were evident for any of the earthquakes recorded at this site

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

spatial and temporal distribution of deformation at the front of the andean orogenic wedge in southern bolivia new observations from an active orogenic wedge help link the seismotectonic behavior of individual faults to wedge deformation rates and patterns over multiple timescales we provide the first detailed constraints on the distribution and timing of deformation at the front of the andean orogenic wedge in southern bolivia where a recent study suggests that great mw 8 earthquakes could rupture the master fault underlying the wedge we use stratigraphic relationships across fault related folds and elastic dislocation modeling of seismic reflection horizons to obtain probabilistic estimates of wedge front fault ages and slip rates our analyses reveal that at least half of the previously determined gps based wedge loading and quaternary whole wedge shortening rates are absorbed across a 20 40 km wide wedge front zone consisting of 1 4 en echelon and partially to fully overlapping faults and folds associated with blind thrust faults the difference between our slip rates and the geodetic geologic observations combined with evidence for activity across internal wedge structures supports the notion that nonsteady state mass balance conditions coupled with elevated erosional efficiency result in distributed wedge deformation the orogenic wedge in southern bolivia behaves in a similar fashion to the taiwanese and himalayan ranges slip accumulates at downdip locations along the master fault and is released incrementally by earthquakes that rupture the wedge front fault zone the faults and folds comprising this zone pose a major source of seismic hazard accumulating slip is also released in the wedge interior and older internal wedge faults must be considered in any future assessment of regional earthquake risk

evidence for a great medieval earthquake 1100 a d in the central himalayas nepal the himalayan orogen has produced three thrust earthquakes with moment magnitude m w 7 8 to 8 5 during the past century yet no surface ruptures associated with these great earthquakes have been documented here we present paleoseismic evidence from east central nepal that since 700 a d a single earthquake ruptured the frontal thrust fault at 1100 a d with a surface displacement of 17 5 3 meters and a lateral extent and size that could have exceeded 240 kilometers and m w 8 8 respectively ruptures associated with m w

intensity attenuation relationship for the south china region and comparison with the component attenuation model abstract the paper utilises seismic intensity information from historical pre instrumental earthquakes in the south china region to evaluate the mean attenuation relations the formulation of these attenuation relations accounts for the seismic waveguide effects in delineating three parts of the geometrical attenuation relationship the derived relations are then compared with the intensity attenuation predictions implied by the newly developed component attenuation model cam which is considered to be particularly applicable in regions of low or moderate seismicity that typically have limited earthquake records recognising that the observed intensities from historical earthquake events may implicitly incorporate some site effects the incremental difference between the two models between 0 and 1 unit of intensity is found to be accountable in terms of average regional site effects arising due to the near surface geology or soils it is therefore concluded that the cam model gives remarkably accurate predictions of ground motion and implied seismic intensity across a large range of earthquake magnitudes and at site source distances ranging up to 500 km the larger site source distances representing far field and very far field events are particularly important in the south china region including hong kong hk due to the large disparity in seismic activity rates in the region surrounding hk which is rather seismically stable and at distances 300 km from hk where some relatively active seismic zones exist

the susceptibility of oklahoma s basement to seismic reactivation recent widespread seismicity in oklahoma is attributed to the reactivation of pre existing critically stressed and seismically unstable faults due to decades of wastewater injection however the structure and properties of the reactivated faults remain concealed by the sedimentary cover here we explore the major ingredients needed to induce earthquakes in oklahoma by characterizing basement faults in the field in seismic surveys and via rock mechanics experiments outcrop and satellite mapping reveal widespread fault and fracture systems with trends that display a marked similarity to the trends of recent earthquake lineaments our three dimensional seismic analyses show steeply dipping basement rooted faults that penetrate the overlying sedimentary sequences representing pathways for wastewater migration experimental stability analysis indicates that oklahoma s basement rocks become seismically unstable at conditions relevant to the dominant hypocentral depths of the recent earthquakes these analyses demonstrate that the geometry structure and mechanical stability of oklahoma s basement make it critically susceptible to seismic reactivation seismicity induced by wastewater injections is widespread in oklahoma probably because its basement is susceptible to the reactivation of basement rooted faults according to three dimensional seismic analyses rock mechanics experiments and field surveys

spatial patterns of aftershocks of deep focus earthquakes this paper presents precise relative relocations for aftershocks of 59 intermediate and deep earthquakes using p pp and pkp arrival times read by us or reported in the literature these aftershocks included 36 rupture subevents occurring within 1 min of the initial event and 71 true aftershocks occurring later and identified statistically as being related to the initial event we compare the relative locations with the orientations of the wadati benioff zones and with the available focal mechanisms using statistical methods not previously applied to earthquake data surprisingly neither true aftershocks nor rupture subevents cluster along the nodal planes of intermediate or deep earthquake focal mechanisms aftershocks more than 20 km from the initial events occur preferentially in the plane of the wadati benioff zone while those lying closer have isotropically distributed directions rupture subevents occur after the travel time of the s wave from the initial event larger magnitude earthquakes generally possess rupture subevents lying farther from the initial event whereas true aftershocks can occur 50 km or more from initial events having magnitudes as small as 5 3 except following a few unusually large earthquakes with focal depths of about 100 km we find no rupture subevents or true aftershocks more than about 80 km from the initial hypocenter the existence of many aftershocks far from nodal planes does not favor models in which deep earthquake failure is simply slip along a planar fault rather the aftershocks may occur in response to a general redistribution of stress caused either by the occurrence of the initial event or possibly by nearby continuing phase transitions alternatively the failure zones of deep earthquakes may be surfaces which are frequently curved by 40 or more from the orientation of the initial nodal plane perhaps due to inhomogeneous stress distributions

seismotectonics of the bitlis zagros fold and thrust belt in northern iraq and surrounding regions from moment tensor analysis northern iraq represents part of the convergent plate boundary between the arabian and eurasian plates the collision zone between these two plates is manifested by the bitlis zagros fold and thrust belt this belt is one of the most seismically active regions among the present active belts this study intends to improve our knowledge on the seismotectonic activities in northern iraq and the surrounding areas to reach this goal we used the waveform moment tensor inversion method to determine the focal depths moment magnitudes fault plane solutions and directions of the principal stress axes of 25 events with magnitudes 3 5 the seismic data of these events were collected from 54 broadband stations which belong to the kandilli observatory and earthquake research institute the incorporated research institutions for seismology the observatories and research facilities for european seismology and the iraqi seismological network computer programs in seismology version 3 30 herrmann and ammon2004 was used for analysis the results show that the focal depth of these events ranged from 15 to 25 km in general the fault plane solutions show that the strike slip mechanism is the most dominant mechanism in the study area usually with a reverse component the stress regime shows three major directions north south northeast southwest and east west these directions are comparable with the tectonic regime in the region

large earthquakes and crustal deformation near taiwan source parameters of 15 large mb 6 earthquakes which occurred near taiwan during the last 25 years are determined by synthetic seismogram analysis of teleseismic p and s waveforms source depths range from 13 to 88 km three earthquakes of intermediate depth are located within the southernmost limit of the ryukyu arc and show thrust type mechanisms with t axes subparallel to a northward dipping wadati benioff zone shallow earthquakes 30 km are distributed over a broad region along and off the east coast of taiwan and show both high angle reverse and strike slip mechanisms the p axes of the shallow events located off the east coast of northern taiwan are oriented near horizontal trend south to southwest and may reflect relative motion between the okinawa platelet and taiwan or complex deformation at the southwest limit of the ryukyu trench in contrast p axes of shallow earthquakes both onshore and off the east coast of central and southern taiwan consistently trend northwest and are interpreted to reflect relative convergence between the philippine sea and eurasian plates summation of the seismic moment tensors of eight large shallow earthquakes that occurred along and off the central and southern coast of taiwan shows that relative plate motion between the eurasian and philippine sea plates when averaged over the last 25 years has been accommodated by crustal contraction at a rate of 2 6 5 4 cm yr along an azimuth of about 290 o

source mechanism of vulcanian eruption at tungurahua volcano ecuador derived from seismic moment tensor inversions source mechanisms of explosive volcanic eruptions are critical for understanding magmatic plumbing systems and magma transport tungurahua is a large andesitic stratovolcano where seismoacoustic data has been recorded over several years in may 2010 an energetic eruption cycle began with a midsize vulcanian explosion followed by swarms of explosive eruptions the five station seismoacoustic network recorded significant seismic and infrasonic signals from the explosions source mechanisms of 50 explosion earthquakes associated with vulcanian explosions during this eruptive period are investigated here the source centroid locations and geometries of explosive signals in the 10 2 s band were determined by full waveform moment tensor inversion the observed waveforms are well explained by a combination of volumetric moment tensor components and a single vertical downward force component the source centroids are positioned about 1 5 km below and about 320 m north of the active crater eigenvalue and eigenvector analysis indicates that the source geometries can be described by a subhorizontal thin ellipsoid representing a sill like magma accumulation resultant source time histories show a repetitive sequence of inflation and deflation from event to event indicating identical source processes frequently occurred over the period the inflation deflation in the deep source region may be the result of crack opening volatile bubble growth at depth opens a pathway for gases to escape and triggers shallow explosions at the summit crater the associated downward single force is interpreted as an exchange of linear momentum between the source and the surrounding region during the escaping gas flow

a local magnitude scale for crustal earthquakes in italy abstract in this study a new local magnitude m l scale is derived for the italian region from the analysis of seismic signals recorded by a dense broadband network between 2003 and 2009 the m l computation is performed by measuring peak amplitudes of synthetic wood anderson seismograms based on the original definition by richter 1935 these amplitudes are inverted for earthquake magnitudes site corrections and the distance dependent term that corrects amplitudes for geometrical spreading and scattering anelastic attenuation the latter is expressed as a function of r hypocentral distance and log r by means of a two parameter linear form and is constrained at the distance of 100 km in accordance with richter s definition using the newly derived distance dependent term and site corrections magnitudes are consistently estimated for the stations recording each earthquake within an overall root mean square residual of 0 18 no anomalous trend with distance is appreciable in the magnitude residuals for the italian region as a whole or for smaller areas along the italian peninsula the only exception is represented by northeastern italy where increasingly negative residuals are observed for distances decreasing below 100 km the spatial pattern of site corrections reveals contrasting attenuation properties of the crust between the tyrrhenian side of the italian peninsula high attenuation west of the apennines and the adriatic side low attenuation east of the apennines as previously found in other studies finally the magnitudes computed with the new m l scale are compared with global estimates of body wave magnitude m b and with local and regional estimates of moment magnitude m w they display a satisfactory agreement in most of the magnitude range considered roughly from 3 to 5 5 online material tables of station parameters maximum amplitudes and magnitude

average seismic source parameter relations for plate margin earthquakes abstract empirical mb ms and mo data are used to develop an average spectral scaling relation for plate margin earthquakes using equations based upon a rectangular bilateral dislocation model with uniform rupture velocity the spectra give values of fault rupture length and width static stress drop and average fault displacement as a function of mb ms and mo compared to mid plate earthquakes of the same seismic moment the large average plate margin earthquake has a bigger rupture length rupture area and average fault displacement and a smaller rupture width and static stress drop

a complex thrust sequence in western himalaya the active medlicott wadia thrust the recent activity of the medlicott wadia thrust mwt is investigated by geomorphic and tectonic studies in the riasi zone south of the pir panjal range india jammu kasmir state of western himalaya in the riasi area the mwt forms a splay of five faults that dip northward the recent activity of the splay is quantified using a set of deformed quaternary alluvial units the central branch of the thrust splay moved precambrian limestones above quaternary sediments and is sealed by 36 3 ka youngest osl age deposits the other branches offset the top of a 15 1 ka youngest osl age alluvial fan by 180 to 120 m the two southernmost branches form 17 34 m high non cylindrical scarps and the two northernmost branches also offset the fan by 8 m and 54 m respectively a balanced cross section parallel to the n210 e thrust motion suggests that the sequence of activity is complex an in sequence propagation is found for the three southern tea scorpion and rain faults and an out of sequence reactivation for the northern pillar fault furthermore several thrusts simultaneously activated for intervals of a few thousand years whereas others are episodically inactive nearly 10 mm yr of india eurasia convergence is regularly absorbed by the mwt a value greater than the one estimated for the western segment of the mwt affected by the 2005 kashmir earthquake where the thrust tectonics interacts with the complex kinematics of the syntax this work indicates that the mwt is very active and might be related to thick skinned tectonics in the western himalaya

extension rates across the northern shanxi grabens china from quaternary geology seismicity and geodesy discrepancies between geological seismic and geodetic rates of strain can indicate that rates of crustal deformation and hence seismic hazard are varying through time previous studies in the northern shanxi grabens at the northeastern corner of the ordos plateau in northern china have found extension rates of anywhere between 0 and 6 mm a at an azimuth of between 95 and 180 in this paper we determine extension rates across the northern shanxi grabens from offset geomorphological features and a variety of quaternary dating techniques including new irsl and ar ar ages a kostrov summation using a 700 year catalogue of historical earthquakes and recent campaign gps measurements we observe good agreement between quaternary seismic and geodetic rates of strain and we find that the northern shanxi grabens are extending at around 1 to 2 mm a at an azimuth of 151 the azimuth of extension is particularly well constrained and can be reliably inferred from catalogues of small earthquakes we do not find evidence for any substantial variations in extension rate through time though there is a notable seismic moment rate deficit since 1750 this deficit could indicate complex fault interactions across large regions aseismic accommodation of deformation or that we are quite late in the earthquake cycle with the potential for larger earthquakes in the relatively near future

microseismicity tectonics and seismic potential in the western himalayan segment nw himalaya india abstract the tectonics and seismic potential of the western himalayan segment 30 33 n 76 80 e of the nw himalayan india region have been determined in this study 423 earthquakes were located in the nw himalaya between 2004 and 2013 using more than 4495 p and 4453 s differential travel times to determine the moment tensors for 8 mw 4 0 of these earthquakes using their broadband regional waveforms the geometry of the main himalayan thrust mht plane which varies along the strike of the himalaya in flat and ramp segments with a dip ranging between 2 5 to 4 to 19 below the himalayan frontal thrust hft in the south to the south tibetan detachment std in the north has also been deduced in this study two crustal ramps were reported in this study with a depth variance below the main central thrust mct and to the south tibetan detachment std between 12 to 22 km and 28 to 40 km depth respectively the estimated earthquake potential prevailing in the western himalayan seismic gap lying between the epicentral zone of the 1905 kangra earthquake and the 1975 kinnaur earthquake reveals that the total amount of energy released since the last great event is only a fraction 3 5 of the accommodated energy i e 1 1e 28 dyne cm yr this suggests that if an earthquake hits this nw himalayan segment in the future its magnitude might be around mw 8 0

earthquake rate analysis abstract earthquake rate analysis explores the quantitative relationship between earthquake occurrence rates and geological deformation rates one application is the estimation of tectonic deformation rates from seismicity for comparison with tectonic models another application is the use of geological models to help quantify seismic hazards seismicity is described by a catalog of the largest earthquakes in the region the contribution of small earthquakes towards causing geological deformation is insignificant although the occurrence rate of small events may be predictable from the occurrence rate of large events by a b value relationship the critical information about each earthquake is its seismic moment or better still its seismic moment tensor when moment is not available directly it can be estimated from the earthquake magnitude although this increases uncertainties considerably the average annual moment from all the earthquakes in the catalog is the seismic moment rate uncertainties in seismic estimates of moment rate arise from the short time period of observations from the magnitude moment relationship from the shape of the distribution function giving number of earthquakes as a function of magnitude and from uncertainties in the physical properties of the earth near the source geological models for deformation rates are described by slip rates on individual faults or by regional strain rates a regional strain rate can be derived as a limiting case where there are numerous individual faults such a strain rate is a particularly useful concept where information about each of the faults is limited in the case of either faulting or regional strain the average seismic moment rate is proportional to the deformation rate geological uncertainties arise from difficulties in estimating slip rates or strain rates from fault creep and other aseismic deformation from uncertainty in the part of the fault that fails during earthquakes and boundaries of the deforming region and from uncertainty about the earth s physical properties the seismic moment rate is the critical factor for relating the earthquake occurrence rate and the geological deformation rate using this intermediate parameter one can infer earthquake occurrence rates from deformation rates or infer deformation rates from earthquake occurrence rates generally it is found that deformation rates and earthquake occurrence rates are consistent within uncertainties where both are well constrained they are generally consistent within a factor of two or three

spatial distribution and b value of intermediate depth earthquakes beneath central peru we have investigated the spatial distribution of microseismicity at intermediate depth in the wadati benioff w b zone beneath central peru within a 100 to 150 km depth range in the subducting nazca plate 67 event hypocenters define a horizontally subducting zone horizontal zone 450 to 600 km from the trench and a zone of increasing dip resubduction zone 600 to 700 km from the trench although the shape of the w b zone is generally consistent with previous observations from teleseismic data the distribution of seismicity is not in a 550 km wide band extending from 400 to 750 km from the trench the density of teleseismicity mb 4 1971 1981 increases as a function of distance from the trench while the density of microseismicity 1 6 mb 4 2 decreases combining local and teleseismic data the b value changes from 84 in the horizontal zone to 57 in the resubduction zone this result suggests that the minimum earthquake size and or stress drop increases in the resubduction zone low b values may also be intrinsic to proximity to the seismic cut off at 150 km depth

geological constraints on the kinematics and fault plane solution of the quiches fault zone reactivated during the 10 november 1946 ancash earthquake northern peru the ancash earthquake of 10 november 1946 mw 6 8 produced surface faulting along the quiches normal slip fault field studies reported discontinuous nw se to nnw sse striking seismic scarps that displace quaternary glacial moraines and outwash as well as mesozoic sedimentary rocks structural analyses show that the 1946 normal displacement was accompanied by a small left lateral slip component morphological analysis of the fault scarp and observations in a trench excavated across the scarp show evidence of a single normal fault displacement before the 1946 seismic event that offset late pleistocene glacial moraines this indicates an approximate recurrence interval of more than 13 000 1 000 years for the major events suggesting a rate of net vertical displacement on the fault of less than 0 25 mm yr kinematic analysis along the quiches fault in comparison with other regional studies suggests that the state of stress in the high andes is regionally and locally homogeneous with only minor changes in the stress directions adjacent to major structures such as the maranon thrust and fold belt the minimum horizontal stress 3 axis is oriented n10 25 e the intermediate horizontal stress 2 axis is oriented n100 115 e and the maximum stress 1 axis is vertical we suggest that the 60 sw dipping quiches surface fault plane is connected at depth to a low angle dipping fault plane this seismic fault is a reactivated thrust fault of the tertiary maranon thrust and fold belt

global pattern of earthquakes and seismic energy distributions insights for the mechanisms of plate tectonics article i nfo in this paper we analyse the distributions of number of events n and seismic energy e on the earth s surface and along its radius as obtained from the global declustered catalogue of large independent events m 7 0 dissipating about 95 of the earth s elastic budget the latitude distribution of the seismic event density is almost symmetric with respect to the equator and the seismic energy flux distribution is bimodal both have their medians near the equator so that they are equally distributed in the two hemispheres this symmetry with respect to the equator sug gests that the earth s rotational dynamics contributes to modulate the long term tectonic processes the distributions of number and energy of earthquakes versus depth are not uniform as well 76 of the total earth quakes dissipates about 60 of the total energy in the first 50 km only 6 of events dissipates about 20 of the total amount of energy in a narrow depth interval at the lower boundary of the upper mantle 550 680 km therefore only the remaining 20 of energy is released along most of the depth extent of subduction zones 50 550 km since the energetic release along slabs is a minor fraction of the total seismic budget the role of the slab pull appears as ancillary if any in driving plate tectonics moreover the concentration of seismic release in the not yet subducted lithosphere suggests that the force moving the plates acts on the uppermost lithosphere and contemporaneously all over the earth s outer shell again supporting a rotational tidal modulation

regional relationships among earthquake magnitude scales various magnitude scales commonly used and the interrelationships among them are reviewed it is shown that problems exist with all of the magnitude scales being used in the united states when using regional catalogs for example it is often necessary to determine how the reported magnitudes were determined often such information is not available although the potential errors are quite large both the ms and the mb scales were designed to be universal scales however both ms and mb magnitudes are often determined beyond the applicable range of the equations used to define the two scales furthermore the ms magnitudes are not generally available for moderate to small earthquakes in most earthquake catalogs the mb magnitudes are more generally available than ms values however there is also much greater variation in the way mb is determined in particular a significant change in the mb scale occurred in the early 1960 s when the world wide standard seismograph network wwssn was established this change in instrumentation used to determine mb values had a significant effect on estimated magnitudes post 1960 values are lower and the saturation level of the mb scale the older longer period instruments recorded larger mb magnitudes than can be recorded with the wwssn instruments in addition great care must be taken when selecting the mb magnitudes of western u s earthquakes because the values are often in considerable error owing to the fact that they were determined at distances less than 25 and were not properly corrected for attenuation in the upper mantle or asthenosphere the seismic body wave magnitude mb of an earthquake is strongly affected by regional variations in the q structure composition and physical state within the earth therefore because of differences in attenuation of p waves between the western and eastern united states a problem arises when comparing mb values for the two regions a regional mb magnitude bias exists which depending on where the earthquake occurs and where the p waves are recorded can lead to magnitude errors as large as unit there is also a significant difference between mb and ml values for earthquakes in the western united states an empirical link between the mb of an eastern u s earthquake and the ml of an equivalent western earthquake is given by ml 0 57 0 92 mb east this result is important when comparing ground motion between the two regions and for choosing a set of real western u s earthquake records to represent eastern earthquakes

gravity anomalies crustal structure and seismicity at subduction zones 2 interrelationships between fore arc structure and seismogenic behavior an ensemble averaging technique is used to remove the long wavelength topography and gravity field associated with subduction zones short wavelength residual anomalies are attributed to the tectonic structure of subducting and overthrusting plates a paired positive negative fore arc anomaly is observed consisting of a long 1000 km linear trench parallel ridge landward of the deep sea terrace basin ridges have amplitudes of 1500 3000 m and 160 240 mgal wavelengths of 150 200 km and high gravity anomaly to topography ratios 50 75 mgal km 1 the ridge crests correlate with the downdip limit of coseismic slip and strong interplate coupling and in cascadia the updip limit of tremor epicenters the ridge crest may be interpreted as defining the boundary between the velocity weakening and seismogenic region of the subduction interface and the downdip frictional transition zone in tonga kermadec the kuril islands and chile landward ridges are associated with extinct volcanic arcs paired anomalies are attributed to the preferential subduction erosion of the outer fore arc and a spatially varying combination of a lower crustal underplating beneath the inner fore arc b the transformation of interseismic strain into permanent geologic strain via faulting folding or buckling of the inner fore arc and c the relative trenchward migration of extinct volcanic arcs in regions operating with a net crustal deficit along strike transitions in fore arc morphology and seismogenic behavior are related to preexisting crustal structure of subducting and overthrusting plates fore arcs have the added potential of recording the time integrated response of the upper plate to subduction processes and fore arc structure should be considered in tandem with seismological observations

single link cluster analysis of earthquake aftershocks decay laws and regional variations using single link cluster analysis the authors investigate how various properties of aftershock sequences depend on their tectonic regime and focal depth for international seismological centre earthquakes of m sub b ge 4 8 they find that earthquakes deeper than 70 km have the fewest and smallest aftershock sequences even after accounting for differences in detectability and maximum magnitude they find that ridge transform earthquakes have smaller aftershock sequences that shallow subduction zone earthquakes among different subduction zones they find that zones with high moment release rates possess larger aftershock sequences comparing ridge transform zones they find those with slower spreading rates possess larger aftershock sequences by transposing origin times of several different aftershock sequences as if all had main shocks occurring at time zero they are able to study the properties of aftershock sequences which individually have too few aftershocks to study by other means secondary events determined by single link cluster analysis follow a modified omori s power law decay for time separations of 0 1 day to 20 days from the parent event with p values ranging from 0 539 plus minus 0 022 intermediate and deep focus earthquakes to 0 928 plus minus 0 024 ridge transform earthquakes they find that earthquake foreshocks and multiplets also follow a modified omori s law atmore greater times from the main shock the decay is steeper than a power law decay more like an exponential decay aftershocks in the adak catalog m sub b ge 2 0 show a marked decrease in activity between 40 and 50 km depth they speculate that the observed differences in number of aftershocks and p values may be caused by variations in fault heterogeneity or in fluid pressures less

the ms 8 tensional earthquake of 9 december 1950 of northern chile and its relation to the seismic potential of the region abstract the only known great m s 8 intermediate depth earthquake localized downdip of the main thrust zone of the chilean subduction zone occurred landward of antofagasta on 9 december 1950 in this paper we determine the source parameters and rupture process of this shock by modeling long period body waves the source mechanism corresponds to a downdip tensional intraplate event rupturing along a nearly vertical plane with a seismic moment of m 0 1 10 28 dyn cm of strike 350 dip 88 slip 270 m w 7 9 and a stress drop of about 100 bar the source time function consists of two subevents the second being responsible for 70 of the total moment release the unusually large magnitude m s 8 of this intermediate depth event suggests a rupture through the entire lithosphere the spatial and temporal stress regime in this region is discussed the simplest interpretation suggests that a large thrust earthquake should follow the 1950 tensional shock considering that the historical record of the region does not show large earthquakes a slow earthquake can be postulated as an alternative mechanism to unload the thrust zone a weakly coupled subduction zone within an otherwise strongly coupled region as evidenced by great earthquakes to the north and south or the existence of creep are not consistent with the occurrence of a large tensional earthquake in the subducting lithosphere downdip of the thrust zone the study of focal mechanisms of the outer rise earthquakes would add more information which would help us to infer the present state of stress in the thrust region

moment magnitude determination for local and regional earthquakes based on source spectra we investigated the use of an automated routine to determine moment magnitudes from the displacement spectra of local and regional earthquakes two algorithms a genetic algorithm and a converging grid search were developed and tested with earthquake data from mexico norway and deception island antarctica it was found that compared with manual analysis the algorithms give reliable automatic moment magnitude m w estimates in the range 1 m 8 the converging grid search appeared to be more cost effective than the genetic algorithm m w at local and regional distances seems superior to amplitude based magnitudes that saturate for large earthquakes the application of the automated algorithm in near real time may help to obtain a nonsaturated magnitude estimate in the case of a large earthquake immediately after the earthquake has occurred also the method can be useful for processing large amounts of data manuscript received 27 july 2001

earthquake magnitude recent research and current trends abstract the magnitude recommendations adopted by the iaspei assembly at zurich in 1967 have had both a stabilizing and a stimulating effect on magnitude determinations and related research from 1967 onwards one magnitude research paper has appeared on the average almost every week thus making this parameter the most studied one in seismology new facilities and more accurate methods e g concerning instrumental equipment and interpretation techniques have made it possible to improve earlier achievements the application of magnitude scales has been extended in all respects e g with regard to epicentral distances focal depths wave types and wave periods magnitude frequency relations have become the most investigated equations within seismology observationally as well as theoretically they have wide applications e g for estimating the maximum magnitudes of future earthquakes an important item in earthquake prediction the magnitudes provide significant information on other source parameters such as wave energy fault length seismic moment relations between different types of magnitude yield valuable information on source properties for instance relations between magnitudes based on body and surface waves are used for efficient discrimination between earthquakes and underground explosions it is our purpose to review the magnitude development in the post zurich period 1967 1980 partly for geologists tectonophysicists and engineers who need an overview partly for seismologists who need an introduction to an overwhelmingly comprehensive literature

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

empirical relationships between aftershock area dimensions and magnitude for earthquakes in the mediterranean sea region fault dimension estimates derived from the aftershock area extent of 36 shallow depth v31 km earthquakes that occurred in the mediterranean sea region have been used in order to establish empirical relationships between length width area and surface wave moment magnitude this dataset consists of events whose aftershock sequence was recorded by a dense local or regional network and the reported location errors did not exceed on average 3 5 km surface wave magnitudes for these events were obtained from the neic database and or published reports while moment magnitudes as well as focal mechanisms were available from the harvard usgs catalogues contrary to the results of some previously published studies we found no evidence in our dataset that faulting type may have an effect on the fault dimension estimates and therefore we derived relationships for the whole of the dataset comparisons by means of statistical f tests of our relationships with other previously published regional and global relationships were performed in order to check possible similarities or differences most such comparisons showed relatively low significance levels b95 since the differences in source dimension estimates were large mainly for magnitudes lower than 6 5 becoming smaller with increasing magnitude some degree of similarity however could be observed between our fault length relationship and the one derived from aftershock area lengths of events in greece while a difference was found between our regional and global fault length relationships a calculation of the ratio defined as the fault length derived from our relationships to the length estimated from regional empirical relationships involving surface ruptures showed that it can take a maximum value of about 7 for small magnitudes while it approaches unity at ms 7 2 when calculating the same ratio using instead global empirical relationships we see the maximum value not exceeding 1 8 while unity is reached at mw 7 8 indicating the existence of a strong regional variation in the fault lengths of earthquakes occurring in the mediterranean sea region also a relationship between the logarithms of the rupture area and seismic moment is established and it is inferred that there is some variation of stress drop as a function of seismic moment in particular it is observed that for magnitudes

a local magnitude relation for earthquakes in the western canada sedimentary basin a local magnitude m l relation for the western canada sedimentary basin wcsb is developed using a rich ground motion dataset compiled from local and regional networks in the area the assessment of amplitude decay with distance suggests that joining direct waves with postcritical reflections from moho discontinuity modifies the attenuation pattern in the 100 200 km distance range the m l distance correction is parameterized using a trilinear function that accounts for the observed attenuation attributes regression of ground motion amplitudes results in the following distance correction model log a for earthquakes in wcsb graphic 1 in which r is the hypocentral distance km the standard m l relations fail to capture the rates and shape of amplitude attenuation in the region resulting in overestimated magnitudes by 0 3 0 6 units the overestimation is larger for local networks due to the increased discrepancy between standard m l relations and actual attenuation properties at close distances the derived relationship results in unbiased m l magnitude estimates in wcsb over a wide distance range 2 600 km which ensures consistent magnitude estimates from local and regional networks 1 embed inline graphic 1 gif

lacustrine turbidites as a tool for quantitative earthquake reconstruction new evidence for a variable rupture mode in south central chile understanding the long term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions south central chilean lakes are typically characterized by laminated sediments providing a quasi annual resolution our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes among others the 2010 and 1960 events furthermore we found that a turbidite s spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo intensities consequently our multilake turbidite record aids in pinpointing magnitudes rupture locations and extent of past subduction earthquakes in south central chile comparison of the lacustrine turbidite records with historical reports a paleotsunami subsidence record and a marine megaturbidite record demonstrates that the valdivia segment is characterized by a variable rupture mode over the last 900 years including i full ruptures mw 9 5 1960 1575 1319 9 1127 44 ii ruptures covering half of the valdivia segment mw 9 1837 and iii partial ruptures of much smaller coseismic slip and extent mw 7 5 8 1737 1466 4 also distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values for instance the 2010 event at the maule segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near concepci n

the nature of deep focus earthquakes wadati 1928 first proved convincingly that some earthquakes occur at depths well beneath the earth s crust he essentially proposed the nomenclature used today by the international seismological centre isc i e earthquakes with focal depths exceeding 300 km are deep earthquakes and those with depths between 70 and 300 km are intermediate earth quakes however when there is little reason to distinguish between the two groups both types are called simply deep earthquakes to avoid confusion in this paper we refer to those with focal depths exceeding 300 km as very deep earthquakes and those with focal depths between 70 and 300 km as intermediate earthquakes deep earthquakes are of interest for at least four reasons first they are exceedingly common between 1964 and 1986 they constituted no less than 22 of all earthquakes having mb greater than 5 0 in the isc catalog second they most often occur in association with deep ocean trenches and volcanic island arcs in subduction zones one of the great achievements of twentieth century geophysics was the recognition that their occurrence in inclined planar groups or wadati benioff zones apparently delineates the cold down going cores of convection cells in the uppermost mantle third seismologists use body waves of deep earthquakes dispro portionately more often than those of shallow earthquakes to inves tigate core mantle and crustal structure this is because a deep earth quakes often possess relatively more impulsive sources b their body phases traverse the heterogeneous uppermost mantle only once on the ray path from hypocenter to station and c surface waves do not contaminate these body phase arrivals on seismograms finally deep earthquakes are

new insights on the offshore extension of the great sumatran fault nw sumatra from marine geophysical studies 1 over the last 20 years the great sumatran fault gsf has been studied on land but we have very little information about its offshore extension nw of sumatra and its link with the west andaman fault to the north the problem is further complicated by its vicinity to the volcanic arc here we present detailed analyses of the offshore extension of the gsf based on recently acquired high resolution bathymetry multichannel seismic reflection data and some old single channel seismic reflection data our findings demonstrate that the branches of the gsf near banda aceh proceed further northwestward producing two 15 20 km wide adjacent basins the southwestern transpressional breueh basin is 1 2 km deep and has a flower structure with a push up ridge in the center suggesting the presence of an active strike slip fault the presence of strike slip earthquakes beneath this basin further suggests that one active branch of the gsf passes through this basin the northeastern transtensional weh basin is up to 3 4 km deep and the absence of recent sediments on the basin floor suggests that the basin is very young the presence of a chain of volcanoes in the center of the basin suggests that the sumatran volcanic arc passes through this basin the anomalous depth of the weh basin might be a site of early back arc spreading or may have resulted from pull apart extension we examine all these new observations in the light of plate motion local deformation and possible seismic risk

magnitude the relation of ml to mblg abstract the m blg magnitude developed by nuttli 1973 for the central united states is adapted to other regions of the world by incorporating a specific term for the spatial coefficient of anelastic attenuation using region specific values m blg values are determined for earthquakes occurring near the wwssn stations bks gsc and dug a comparison of the m blg values with published m l magnitudes shows that these two magnitude scales are essentially equivalent between magnitudes 3 to 5 because of this observation we now have a direct way of comparing eastern and western united states earthquake sizes for the purpose of adapting western strong motion data bases to the east and also for understanding teleseismic magnitude biases

an indication of time dependent seismic behavior an assessment of paleoseismic evidence from the arava fault israel abstract we discuss the implications of 56 kyr of paleoseismic data from a fault on the southern segment of the arava fault system in israel at least nine events are evident beginning 37 ka we study in detail the frequency magnitude relation for the fault and develop a bayesian analysis to compare the characteristic earthquake ce model and the gutenberg richter gr model our analysis leads to the conclusion that there was a change in seismic behavior at about 14 ka from 37 ka to 14 ka the seismic activity is best described by the ce model from 14 ka to the present there is no strong indication favoring one model over the other the earthquake record is somewhat more consistent with the classical gr equation than with the ce model if one does assume that the ce model is appropriate for the younger episode then there is evidence of a change in the characteristic magnitude thus there is evidence of a change in earthquake behavior on the fault segment 14 ka

suitability of rapid energy magnitude determinations for emergency response purposes summary it is common practice in the seismological community to use especially for large earthquakes the moment magnitude mw as a unique magnitude parameter to evaluate the earthquake s damage potential however as a static measure of earthquake size mw does not provide direct information about the released seismic wave energy and its high frequency content which is the more interesting information both for engineering purposes and for a rapid assessment of the earthquake s shaking potential therefore we recommend to provide to disaster management organizations besides mw also sufficiently accurate energy magnitude determinations as soon as possible after large earthquakes we developed and extensively tested a rapid method for calculating the energy magnitude me within about 10 15 min after an earthquake s occurrence the method is based on pre calculated spectral amplitude decay functions obtained from numerical simulations of green s functions after empirical validation the procedure has been applied offline to a large data set of 767 shallow earthquakes that have been grouped according to their type of mechanism strike slip normal faulting thrust faulting etc the suitability of the proposed approach is discussed by comparing our rapid me estimates with mw published by gcmt as well as with mw and me reported by the usgs mw is on average slightly larger than our me for all types of mechanisms no clear dependence on source mechanism is observed for our me estimates in contrast me from the usgs is generally larger than mw for strike slip earthquakes and generally smaller for the other source types for 67 per cent of the event data set our me differs 0 3 magnitude units m u from the respective me values published by the usgs however larger discrepancies up to 0 8 m u may occur for strike slip events a reason of that may be the overcorrection of the energy flux applied by the usgs for this type of earthquakes we follow the original definition of magnitude scales which does not apply a priori mechanism corrections to measured amplitudes also since reliable fault plane solutions are hardly available within 10 15 min after the earthquake origin time notable is that our uncorrected me data show a better linear correlation and less scatter with respect to mw than me of the usgs finally by analysing the recordings of representative recent pairs of strong and great earthquakes we emphasize the importance of combining mw and me in the rapid characterization of the seismic source they are related to different aspects of the source and may differ occasionally even more than 1 m u this highlights the usefulness and importance of providing these two magnitude estimates together for a better assessment of an earthquake s shaking potential and or tsunamigenic potential

use of seismotectonic information for the seismic hazard analysis for surat city gujarat india deterministic and probabilistic approach surat the financial capital of gujarat india is a mega city with a population exceeding five millions the city falls under zone iii of the seismic zoning map of india after the devastating 2001 bhuj earthquake of mw 7 7 much attention is paid towards the seismic microzonation activity in the state of gujarat in this work an attempt has been made to evaluate the seismic hazard for surat city 21 170 n 72 830 e based on the probabilistic and deterministic seismic hazard analysis after collecting a catalogue of historical earthquakes in a 350 km radius around the city and after analyzing a database statistically deterministic analysis has been carried out considering known tectonic sources a further recurrence relationship for the control region is found out probabilistic seismic hazard analyses were then carried out for the surat region considering five seismotectonic sources selected from a deterministic approach the final results of the present investigations are presented in the form of peak ground acceleration and response spectra at bed rock level considering the local site conditions rock level peak ground acceleration pga and spectral acceleration values at 0 01 s and 1 0 s corresponding to 10 and 2 probability of exceedance in 50 years have been calculated further uniform hazard response spectrum uhrs at rock level for 5 damping and 10 and 2 probability of exceedance in 50 years were also developed for the city considering all site classes these results can be directly used by engineers as basic inputs in earthquake resistant design of structures in and around the city

depth extent and kinematics of faulting in the southern tanganyika rift africa unusually deep earthquakes occur beneath rift segments with and without surface expressions of magmatism in the east african rift system ears the tanganyika rift is part of the western rift and has no surface evidence of magmatism the tang14 array was deployed in the southern tanganyika rift where earthquakes of magnitude up to 7 4 have occurred to probe crust and upper mantle structure and evaluate fault kinematics 474 earthquakes detected between june 2014 and september 2015 are located using a new regional velocity model the precise locations magnitudes and source mechanisms of local and teleseismic earthquakes are used to determine seismogenic layer thickness delineate active faults evaluate regional extension direction and evaluate kinematics of border faults the active faults span more than 350 km with deep normal faults transecting the thick bangweulu craton indicating a wide plate boundary zone the seismogenic layer thickness is 42 km spanning the entire crust beneath the rift basins and their uplifted flanks earthquakes in the upper mantle are also detected deep earthquakes with steep nodal planes occur along subsurface projections of tanganyika and rukwa border faults indicating that large offset 5 km faults penetrate to the base of the crust and are the current locus of strain the focal mechanisms continuous depth distribution and correlation with mapped structures indicate that steep deep border faults maintain a half graben morphology over at least 12 my of basin evolution fault scaling based on our results suggests m 7 earthquakes along tanganyika border faults are possible

frequency distribution and quantification of deep earthquakes the frequency distribution of deep earthquakes d 350 km is analyzed on a regional scale using magnitude data from 4660 events reported in the international seismological center bulletin 1964 1982 and 391 centroid moment tensor solutions 1977 1987 we use the moment magnitude mw to define b values comparable with studies of shallow seismicity scaling laws relating mw mb and mo are derived mw 1 6mb 3 2 mb log mo 4 3 2 4 which compare very favorably with published laws uncertainties and biases of the mb and mo data sets are considered the slope of the frequency distribution is evaluated over a restricted magnitude range the results are very robust and independent from the magnitude range used from the mb magnitude data we obtain regional b values in the range 0 4 b 1 22 with a worldwide average value b 0 87 these results are confirmed by the analysis of the seismic moment data the steepest frequency distribution is observed in the tonga islands region b 1 22 although 60 of the worldwide deep seismicity occurs here only few events since 1977 had seismic moment exceeding 1019 n m the high fractal dimension d 2 4 implies a volume partially filled with fault planes in agreement with the observations on the seismic morphology of the region at the other extreme south america is characterized by the largest recorded deep events and an almost complete absence of small ones b 0 4

paleoseismic evidence of a surface rupture along the northwestern himalayan frontal thrust hft abstract new paleoseismic evidence is presented from the bhatpur n 31 18 16 28 e 76 9 50 00 trench site along the himalayan frontal thrust hft on western margin of the janauri anticline in nw himachal himalaya india the latest surface rupture at this site demonstrates coseismic displacement of at least 9 3 m radiocarbon dating of trench samples indicates that the surface ruptures occurred at a d 1400 1460 after comparison with other trench results along the himalayan front two scenarios are presented of the latest surface rupturing earthquake event in the northwestern indian himalaya 1 a single event surface rupturing for a minimum fault length of 450 km or 2 two events of different lateral extent according to the former scenario the latest surface rupture occurred between a d 1404 and 1422 the latter scenario suggests the latest surface rupture occurred between a d 1404 and a d 1460 in the northwestern extent from kala amb to hajipur with 9 0 m of coseismic displacement over a minimum fault length of 200 km yet another surface rupture event in the southeastern extent from kala amb to ramnagar has occurred between a d 1282 and a d 1422 with displacement ranging from 16 0 m to 26 0 m and a minimum surface rupture length of 230 km on the basis of these observations and historical earthquakes it is suggested that the potential for earthquakes larger than those in the historical records are capable of producing surface rupture lengths greater than the 200 to 230 km or 450 km in the northwestern indian himalayan front

evaluation of precursory seismic quiescence in sixteen subduction zones using single link cluster analysis this paper describes a new method single link cluster analysis slc to evaluate percursory quiescence for shallow earthquakes in sixteen subduction zones using data from the isc catalog to define quiescent regions we divided the catalog into time intervals with a durationt overlapping byt 2 we considered all earthquakes having magnitudes larger than some magnitudemmin lying within a specified distance of a great circle which is approximately coincident with the trench near a subduction zone within each time interval we connected or linked all earthquakes lying within some cutoff distanced of one another we then projected all these links onto the great circle and defined a region to be quiescent if it was not covered by the projection of any links for this study t was two years mmin wasmb 4 9 and we variedd from 100 to 400 km we defined an earthquake as following quiescence if it occurred within two years following and within 75 km of a quiescent zone as defined above the primary conclusion of this study was that earthquakes with surface wave magnitudes 7 2 and greater were about 5 15 more likely to follow quiescence than were the smaller background earthquakes withmb 4 9 a chi squared analysis shows that this result is significant at the 99 level in contrast earthquakes with surface wave magnitude of 6 7 to 7 1 were no more likely to follow quiescence than were background earthquakes of sixteen individual regions central america japan and peru chile were the only regions where large earthquakes were more likely to occur following quiescence than were background earthquakes for a cutoff link length of 300 km only in central america was the difference between large earthquakes and background earthquakes significant at the 95 level of significance for a cutoff link length of 250 km the significance level exceeded 95 only in japan the slc method is an objective quantitative method for evaluating large data catalogs or for monitoring quiescence in regions where quiescence is conjectured to precede large earthquakes