causes of unusual distribution of coseismic landslides triggered by the mw 6 1 2014 ludian yunnan china earthquake abstract the mw 6 1 2014 ludian yunnan china earthquake triggered numerous coseismic landslides that do not appear to be associated with any previously known seismogenic fault traditional models of triggering for seismically generated landslides do not provide a reasonable explanation for the landslide pattern observed here here the newmark method is applied to a grid to calculate the minimum accelerations required for slope failures throughout the affected region the results demonstrate that for much of the study area the distribution of failure prone slopes is similar to the actual pattern of coseismic landslides however there are some areas where the model predicts considerably fewer failures than occurred we suggest that this is a result of the complex source faults that generated the ludian earthquake which produced a half conjugate rupture on nearly ew and nnw trending faults at depth the rupture directed much of its seismic moment southeast of the epicenter increasing ground shaking and the number of resulting landslides

ridge offsets normal faulting and gravity anomalies of slow spreading ridges we develop a model relating mid ocean ridge normal faulting and crustal structure by examining recently available high resolution gravity and multibeam bathymetric data of the mid atlantic ridge and other spreading centers results of the analysis reveal a consistent pattern of positive residual gravity anomalies along the crust paralleling all major atlantic offsets studied especially along the inside corner side of the offsets individual residual gravity anomaly spikes local peaks which have amplitudes of up to 20 mgal and typical across axis spacing of 10 30 km often coincide with individual major fault scarps suggesting crust thinned by normal faulting theoretical calculations indicate that the amplitude and spacing of the observed residual gravity spikes are consistent with the presence of successive ridge parallel low angle faults that originate episodically at inside corners of ridge offset intersections fault scarp heights and the amounts of crustal thinning as inferred from gravity anomalies are consistently larger at inside corners than at outside corners supporting a model in which tectonic extension near ridge offsets is asymmetric with low angle faults occurring preferentially at inside corners these results on spatial variations in seafloor morphology and gravity anomalies further support a three dimensional tectonic faulting model at oceanic spreading centers with three major characteristics 1 low angle faults form preferentially at inside corners where the mantle lithosphere is the strongest and the lithospheric plates are sufficiently decoupled across ridge axis offsets 2 low angle faults decrease in throw toward midpoints of long ridge segments where large low angle faults may not be sustained by a weak lithosphere and 3 the residual gravity peaks are statistically larger at transform than near nontransform offsets indicating that the length of a ridge offset and its tectonic style control the development of low angle faults

microearthquake characteristics and crustal velocity structure at 29 n on the mid atlantic ridge the architecture of a slow spreading segment we report the results of a microearthquake and seismic tomography experiment conducted along the southern half of the mid atlantic ridge segment at 29 n and aimed at investigating the relationship of earthquake and seismic structural characteristics to spreading processes the seismic velocity structure is obtained from two dimensional 2 d and three dimensional 3 d tomographic inversions of travel times from shots along an axial refraction line inversion solutions indicate that the velocity structure in the lower crust is heterogeneous with higher velocities and relatively thin crust near the segment end and lower velocities and a thicker layer 3 near the central bathymetrie high the thickness of the lower crust at the segment end is asymmetric across axis with thinner crust beneath the inside corner the indicated variations in crustal thickness are consistent with those inferred from mantle bouguer gravity anomalies the microearthquakes located along axis during the 41 day recording period cluster in three separate along axis regions 1 the southern segment end near 28 55 n 2 the central along axis topographic high at 29 11 n near and north of the broken spur hydrothermal vent field and 3 a region midway between beneath a volcano near 29 02 n the greatest level of microearthquake activity was in a diffuse zone off axis beneath the inside corner of a nontransform offset this pattern of off axis microearthquake activity and the cross axis asymmetry in crustal thickness at the segment end support tectonic models in which normal faulting and consequent crustal thinning occur preferentially at inside corner regions anomalous focal mechanisms for microearthquakes beneath the along axis volcano and the significant seismicity beneath the axial volcanic ridge at the segment center in contrast may be the result of volcanic and hydrothermal processes such as magma movement or thermal stresses generated near cooling plutons a comparison of microearthquake characteristics with residual gravity data and velocity structure leads to the hypothesis that microearthquakes associated with areas of thin crust near the segment end and inside corner are dominantly tectonic in nature whereas microearthquakes associated with volcanic and hydrothermal processes are more likely to occur toward the segment center in areas of greater rates of magma supply and thicker crust along axis well resolved focal depths determined with a 3 d velocity model range from 3 to 6 km beneath the seafloor and do not shoal toward the segment center these observations indicate that the thermal structure of the crust along this slow spreading ridge segment is not in steady state

microearthquakes beneath median valley of mid atlantic ridge near 23 n tomography and tectonics data from a microearthquake experiment in the median valley of the mid atlantic ridge near 23 n in 1982 are used to measure earthquake source parameters to determine the laterally heterogeneous seismic velocity structure across the inner floor and to develop a kinematic tectonic model for this portion of the median valley fifty three microearthquakes occurred over a 10 day period beneath the median valley inner floor and eastern rift mountains twenty of 23 well located inner floor epicenters define a line of activity about 17 km long having a strike of n25 e and located near an along axis depression some 300 400 m deeper than surrounding regions earthquakes with well resolved hypocenters generally have focal depths of 4 8 km beneath the seafloor of both the inner floor and the rift mountains the hypocentral locations are robust with respect to plausible lateral variations in seismic velocity structure composite fault plane solutions for inner floor events indicate normal faulting on planes dipping at angles near 45 normal faulting mechanisms although poorly constrained are also indicated for the rift mountain microearthquakes seismic moments approximate fault dimensions and average stress drops for the largest events recorded are 1019 1020 dyn cm 200 400 m and 1 70 bars respectively a twodimensional tomographic inversion of p wave travel time residuals from microearthquakes and local shots indicates a well resolved lateral heterogeneity in crustal velocity structure across the median valley inner floor p wave velocities at 1 5 km depth within a zone less than 10 km wide beneath the central inner floor are lower by several percent than in surrounding regions the most likely explanation for the low velocities is that the region is the site of the most recent local magmatic injection and remains pervasively fractured as a result of rapid hydrothermal quenching of the newly emplaced crustal column by this view the seismic velocity structure at the ridge axis evolves probably by the sealing of cracks and pores within the first few hundred thousand years of crustal accretion consideration of the detailed sea beam bathymetry in this region of the inner floor the characteristics of large earthquakes that the region has experienced during the past 25 years and the results of the microearthquake and tomography analysis suggests that this section of the median valley has been undergoing continued horizontal extension and block faulting without significant crustal injection of magma for at least the past 104 years

quantitative analysis of abyssal hills in the atlantic ocean a correlation between inferred crustal thickness and extensional faulting a recent cruise to the office of naval research atlantic natural laboratory obtained 100 hydrosweep bathymetrie coverage 200 hawaii mrl hmrl side scan coverage gravity and magnetics over an area spanning three ridge segments along axis 25 25 n to 27 10 n and crustal ages from 0 to 26 30 ma 400 km on the west flank of the mid atlantic ridge this data set represents a first opportunity for an extensive regional analysis of abyssal hill morphology created at a slow spreading ridge the primary purpose of this work is to investigate the relationship between abyssal hill morphology and the properties of the ridge crest at which they were formed we apply the method of goff and jordan 1988 for the estimation of two dimensional statistical properties of abyssal hill morphology from the gridded hydrosweep bathymetry important abyssal hill parameters derived from this analysis include root mean square rms height characteristic width and plan view aspect ratio the analysis is partitioned into two substudies 1 analysis of near axis 7 ma abyssal hills for each of the three segments and 2 analysis of temporal variations 2 29 ma in abyssal hill morphology along the run of the south segment the results of this analysis are compared and correlated with analysis of the gravity data and preliminary determination of faulting characteristics based on hmrl side scan data principal results of this study are 1 abyssal hill morphology within the study region is strongly influenced by the inside outside corner geometry of the mid ocean ridge segments abyssal hills originating at inside corners have larger rms height and characteristic width and smaller plan view aspect ratio than those originating at outside corners 2 the residual mantle bouguer gravity anomaly is positively correlated with intersegment and along flow line variations in rms height and characteristic width and it is negatively correlated with plan view aspect ratio from this result we infer that lower relief narrower and more elongated abyssal hills are produced when the crust being generated is thicker 3 intersegment variations in near axis rms height negatively correlate with average fault density as determined from analysis of hmrl side scan imagery

earthquake driven acceleration of slow moving landslides in the colca valley peru detected from pleiades images abstract major earthquakes in mountainous areas often trigger rapid landslides some observations also suggest that earthquakes can damage landslide prone areas or cause slow moving landslides to accelerate with a risk of evolution to rapid landslides in the following months after the earthquake here we use optical images from the pleiades satellites to detect slow moving landslides and quantify the effect of earthquakes on the landslide motion we process multi temporal pleiades images acquired in march april and july 2013 over an area of 210 km2 in the colca valley south peru to obtain two digital elevation models dem and three displacement fields of the area the processed dems have an uncertainty of 0 6 m 1 an order of magnitude better than two global and freely available dems gdem v2 and srtm whereas the displacement fields have an uncertainty of between 0 11 and 0 18 m 1 in both horizontal directions using these data we detect 9 slow moving landslides and compare their velocities during the march april and april july periods we find that landslide velocities are highest during the wet season which suggests a strong groundwater control and we also highlight a landslide acceleration caused by a regional mw 6 0 earthquake the major parameters controlling the acceleration of the slow moving landslides are the rock type and the distance to the source suggesting that friction at the basal interface in the weeks after the earthquake is dependent on the shaking intensity

mechanisms of lithospheric extension at mid ocean ridges summary we examine the extensional deformation of oceanic plates at mid ocean ridges especially within an axial yield zone where pervasive faulting occurs thermal models of ridges are developed which include the effects of lithospheric thickening on the mantle flow the heat of magmatic crustal accretion at the ridge axis and the hydrothermal cooling due to seawater circulation in the crust when hydrothermal circulation occurs the brittle lithospheric plate at slow spreading ridges could be as thick as 8 9 km thicker than the crust while the plate at fast spreading ridges is only 1 2 km for a typical slow spreading ridge several kilometres of plate thickening are expected within a distance of 15 km from the ridge axis when subjected to the extensional force due to horizontal stretching shear failure by normal faulting will occur pervasively in an axial zone where the lithospheric plate is the thinnest adopting perfectly plastic rheology as a continuum description of deformation on the distributed faults we obtain approximate solutions for the stress distribution in the yield zone within this yield zone sea floor topography increases significantly away from the ridge axis so that the resuiting gravity sliding force balances the differential horizontal extensional force due to the thickening of the lithospheric plate basal stresses induced by the viscously deforming asthenosphere could significantly influence the stresses inside the lithospheric plate only if the mantle viscosity beneath the ridge is on the order of 10 pa s significantly higher than generally accepted values of 10 pa s model calculations reveal that although the seafloor topography at the mid atlantic ridge at 13 15 on is regionally compensated it is locally supported by stresses in the lithospheric plate the deviation of the lithospheric plate from its thermal isostatic equilibrium position can be explained by necking due to plastic stretching in the axial yield zone and elastic deflection of strong plates outside the yield zone the best fit models require the yield zones to have a half width of 10 15 km we find systematic variations in the gravity and topography of the east pacific rise which indicate strong influence of plate spreading rate on the ridge thermal and mechanical structure at the 16 17 on area where the half spreading rate is 4 3 cm yr a prominent axial topographic high and an axial mantle bouguer gravity low exist implying a crustal or sub crustal low density body the gravity low disappears at the 20 21 n area where the half spreading rate is 3 6 cm yr as the plate spreading rate decreases from 4 3 cm yr at the 16 17 on area to 2 7 cm yr at the 22 23 on area axial ridge topography changes from higher than the thermal isostatic equilibrium position to lower than the isostatic position the low axial topography at the 22 23 n area can be explained by the existence of a low amplitude median valley

morphology and tectonics of the kane transform from sea beam bathymetry data high resolution sea beam data have been used to construct an accurate regional scale bathymetric map of the kane transform a large offset slowly slipping 30 mm yr central north atlantic transform the kane transform trends about 100 nearly orthogonal to the regional trend of the adjacent mid atlantic ridge mar rift valley the transform valley walls are composed of an alternating series of ridges and troughs which parallel the regional trend of the mar the ridges narrow and deepen toward the transform valley over distances of 10 20 km and the intervening troughs widen into distinct closed contour depressions that appear to be relict nodal basins the morphologic elements found on either side of the transform valley exhibit along strike continuity and represent undisrupted displacement markers the swath of terrain sandwiched between these markers is only several kilometers wide and is made up of elongate basins and ridges that integrate to create a distinctive transform parallel grain this interval the transform tectonized zone ttz marks the time averaged location of strike slip tectonism as parcels of crust move from each intersection along the transform interface the ttz is widest 6 km near the eastern ridge transform intersection rti and narrows to a strand less than 3 km wide along the central and western portions of the transform along the eastern portion of the transform valley a narrow 3 km median ridge several hundred meters high can be traced for more than 40 km along the valley floor and a similar but shorter feature is also present near the western rti at both rtis the neovolcanic zone from the adjacent rift valley can be traced as a series of constructional edifices across the entire intersection area to the opposing transform valley wall at the eastern rti the neovolcanic zone wraps around the eastern edge of the nodal basin while at the western rti it appears to bisect a paired nodal basin located in the intersection area a line drawn connecting the ends of each neovolcanic zone lies within the narrow ttz and has a strike of 098 using the bathymetric map of the kane transform as a record of the time integrated tectonic evolution of this large slowly slipping ridge transform ridge plate boundary we have constructed a simple model for the evolution of rtis our model emphasizes the interplay between temporal variations in crustal production rates i e variations in the volume of basaltic melt production along oceanic spreading centers and extensional tectonism this model can explain the existence of nodal basins at rtis and relict nodal basins along transforms and fracture zones as well as the occurrence of regularly spaced ridge and trough topography on the ridge flanks

spatial and temporal variations in crustal production at the mid atlantic ridge 25 n 27 30 n and 0 27 ma we use high resolution multibeam bathymetry shipboard gravity side scan sonar images and magnetic anomaly data collected on conjugate flanks of the mid atlantic ridge at 25 n 27 30 n and out to 27 ma crust to investigate the crustal evolution of the ridge substantial variations in crustal structure and thickness are observed both along and across isochrons along isochrons within spreading segments there are distinct differences in seafloor morphology and gravity derived crustal thickness between inside and outside corners inside corners are associated with shallow depths thin crust and enhanced normal faulting while outside corners have greater depths thicker crust and more limited faulting across isochrons systematic variations in crustal thickness are observed at two different timescales one at 2 3 myr and another at 10 myr and these are attributed to temporal changes in melt supply at the ridge axis the shorter term variations mostly are in phase between conjugate ridge flanks although the actual crustal thickness can be significantly different on the two flanks at any given time we observe no correlation between crustal thickness and spreading rate thus during periods of low melt supply tectonic extension must increase to accommodate the full plate separation rate this extension commonly is concentrated in long lived faults on only one side of the axial valley resulting in strong across axis asymmetries in crustal thickness and seafloor morphology the thin crust flank has few volcanic features and exhibits elevated blocky topography with large offset often irregular faults while the conjugate thicker crust flank shows shorter offset regular faulting and common volcanic features the variations in melt supply at the ridge axis most likely are caused either by episodic convection in the subaxial mantle or by variable melting of chemically heterogeneous mantle

causes and consequences of variations in faulting style at the mid atlantic ridge both volcanism and faulting contribute to the rugged topography that is created at the mid atlantic ridge mar and preserved off axis in atlantic abyssal hill terrain distinguishing volcanic from fault generated topography is essential to understanding the variations in these processes and how these variations are affected by the three dimensional pattern of mantle upwelling ridge segmentation and offsets here we describe a new quantitative method for identifying fault generated topography in swath bathymetry data by measuring topographic curvature the curvature method can distinguish large normal faults from volcanic features whereas slope methods cannot because both faults and volcanic constructs can produce steep slopes the combination of curvature and slope information allows inward and outward facing fault faces to be mapped we apply the method to sea beam data collected along the mar between 28 and 29 30 n the fault styles mapped in this way are strongly correlated with their location within the ridge segmentation framework long linear small throw faults occur toward segment centers while shorter larger throw curved faults occur toward ends these variations reflect those of active faults within the axial valley we investigate two different physical mechanisms that could affect fault interactions and thus underlie variations in abyssal hill topography at the mar in the first model only one fault is active at a time on each side of the rift valley each fault grows while migrating away from the volcanic center due to dike injection extension across the fault causes a flexural rotation of nearby inactive faults the amount of stress necessary to displace the fault increases as the fault grows when reaching a critical size the fault stops growing as fault activity jumps inward as a new fault starts its growth near the rift valley this model yields a realistic terracelike morphology from the rift valley floor into the rift mountains the relief is caused by the net rotation accumulated in the lithosphere from the active faults e g 10 reached 20 km from the active fault fault spacing is controlled by lithospheric thickness fault angle and the ratio of amagmatic to magmatic extension we hypothesize that this mechanism may be dominant toward ridge segment offsets an alternative model considers multiple active faults each fault relieves stresses as it grows and inhibits the growth of nearby faults causing a characteristic fault spacing such fault interactions would occur in a region of necking instability involving deformation over an extended area this mode of extension would drive a feedback mechanism that would act to regulate the size of nearby faults we hypothesize that this mechanism may be active in the relatively weak regions of strong mantle upwelling near segment midpoints causing the homogeneous abyssal hill fabric in these regions

three dimensional gravity and bathymetry analysis of the mid atlantic ridge between 20 n and 24 n flow geometry and temporal evolution of the segmentation bathymetry and gravity data covering 10 m y on both flanks of the mid atlantic ridge south of the kane fracture zone reveal a complex segmentation pattern well correlated with short scale temporal variations in crustal production segment and paleosegment centers are associated with crustal thickening while their extremities appear as elongated bands of thin crust subsidence rates vary between centers and extremities of a segment with higher than world average values at segmert midpoints and closer to average values at the edges this is consistent with segment centers being the site of focused mantle upwellings with associated thin lithosphere and with thick crust a pronounced circular minimum in the long wavelength of the mantle bouguer anomaly associated to a maximum in the long wavelength of the bathymetry marks the site of a mantle upwelling associated with a particularly robust segment located north of a small fracture zone 21 20 n an offset is often observed between extreme values of topography and crustal thickness resulting in a lack of isostatic equilibrium for off axis short wavelength features an obliquity between maxima of crustal thickening associated with active segments and the topographic axial domain suggests that the shift between topography and crustal structure may arise partly from a decoupling between crust and topography formation processes

spatial and temporal distribution of seismicity along the northern mid atlantic ridge 15 35 n 1 a detailed investigation of the relationship between the spatial and temporal patterns of the seismic activity recorded by six autonomous hydrophones and the structure of the northern mid atlantic ridge between 15 and 35 n is presented two years of monitoring yielded a total of 3485 hydroacoustically detected events within the array recorded by four or more hydrophones the seismically active zone extends 20 km to either side of the ridge axis consistent with earlier results from studies of fault morphology along the axis hydrophone recorded activity shows important variations areas with intense and persistent seismic activity stripes stand in sharp contrast to areas that lack seismicity gaps the regions of persistent activity are a new observation at mid ocean ridges in general the patterns of seismically active inactive regions are also recognized in the 28 year teleseismic record implying that these patterns are maintained at timescales between a few years and a few decades we find no simple relationship between individual segment variables e g length or trend of the segment maximum offset of discontinuities or along axis change in mantle bouguer anomaly mba and water depths and number of hydrophone recorded events there does appear to be a correlation between axial thermal structure and seismicity regions of low and high numbers of events would thus correspond to thinner hotter and thicker colder lithosphere respectively seismicity may reflect thermal structure at short timescales decadal or longer while relief and inferred crustal thickness may integrate this structure over longer periods of time order of 1 myr

a systematic analysis of the mid atlantic ridge morphology and gravity between 15 n and 40 n constraints of the thermal structure multibeam bathymetry data obtained along a 2400 km long section of the mid atlantic ridge mar from 15 n to the azores platform 40 n and satellite derived gravity data were used to calculate the mantle bouguer anomaly mba along this portion of the mar both data sets were used to determine the relations between gravity anomalies and topographic variations and discuss these in terms of thermal difference a long wavelength influence of the azores hot spot is characterized by a gentle continuous slope of the average ridge axial depth and a general gradient in the along axis mba profile this thermal influence of the azores hot spot controls a systematic southward propagation of the spreading segments at least to 26 30 n south of 26 30 n the direction of the segment propagation is controlled by the local difference in thermal state between adjacent segments except on the azores platform the systematic along axis 11 90 km long wavelength segmentation is independent of the long wavelength influence of the azores at the segment center the axial morphology is linked to the thermal state of the segments between 1 hotter segments characterized by a smooth axial morphology a well defined shallow inner valley high mba and a long length 2 colder segments which present a rough axial morphology with a deep wide and well defined rift valley a low mba and a small length for hotter segments the formation of the abyssal hills is mainly due to a magmato tectonic cycle over periods of 0 3 to 1 myr whereas on colder segments the axial morphology is mainly controlled by a tectonic rift valley formation we propose that these different segment types correspond to a temporal evolution of the rift valley morphology over periods of several million years

variation in landslide affected area under the control of ground motion and topography abstract earthquake induced landslide eqil inventories are the key to improve our understanding of the relationship between landslides and their causes including environmental settings and ground shaking parameters however creating a high quality inventory can take years as a result reliable information on landslide affected areas typically remains unknown until a complete inventory is compiled in this paper we analyze 20 digital eqil inventories of varying quality and completeness that represent a range of geologic and climatic settings around the globe we examine the landslide affected area with respect to peak ground acceleration pga and topography and develop a statistical model to estimate the landslide distribution without prior knowledge of the actual landslide triggering locations for each eqil inventory we initially calculated the pga contours where 90 of the total landslide population fell into subsequently we define landslide susceptible areas as those pixels with slope 5 and local relief 100 m the latter is used to normalize the total landslide affected area and to compute correlations with local pga values we find that the landslide affected area may be predicted from pga values only with the mean error ranging from 20 0 to 7 1 with respect to total landslide population this relationship can be used immediately following a disaster to identify areas of greatest landslide impact and to prioritize emergency response actions even without a landslide inventory

discrete characterization of abyssal hills unraveling temporal variations in crustal accretion processes at the 10 30 n segment east pacific rise abstract the morphology of abyssal hills provides important information on the crustal accretion processes acting at mid ocean ridges discretely characterizing abyssal hill shape is challenging and therefore the study of abyssal hill morphology is often approached by examining the average properties of relatively wide regions containing multiple hills however this averaging process removes any spatial trends in abyssal hill shape that may reflect temporal variations in crustal accretion processes here we present an automated approach for analyzing the shape of individual abyssal hills which we detect using the ridgelet transform method of downey and clayton 2007 we first analyze seafloor morphologies as revealed in multibeam bathymetry surveys across 16 mid ocean ridge segments with varying spreading rates the results of this analysis display the known negative correlation between the width and height of abyssal hills and the spreading rate thus validating our approach our results also show that the fraction of inward facing abyssal hills exhibits a simple linear trend across all spreading rates suggesting a property that could be used to determine the spreading rate at which the seafloor formed we then apply our technique to study a flow line transect collected across the fast spreading 10 30 n segment of the northern east pacific rise revealing temporal changes in the shape of the abyssal hills formed during the last 3 8 myr the youngest part of the flow line coincides with a location where basaltic glasses were previously sampled the abyssal hill morphology and mgo content of the glass samples share mutual trends over 105 106 yrs suggesting that abyssal hill morphology is sensitive to the rate at which magma is supplied to the ridge axis finally a 1 myr cyclic variation in seafloor morphology is observed this periodicity is attributed to temporal changes in magma supply at the ridge axis possibly related to upper mantle dynamics or the presence of chemical heterogeneities

earthquake induced chains of geologic hazards patterns mechanisms and impacts large earthquakes initiate chains of surface processes that last much longer than the brief moments of strong shaking most moderate and large magnitude earthquakes trigger landslides ranging from small failures in the soil cover to massive devastating rock avalanches some landslides dam rivers and impound lakes which can collapse days to centuries later and flood mountain valleys for hundreds of kilometers downstream landslide deposits on slopes can remobilize during heavy rainfall and evolve into debris flows cracks and fractures can form and widen on mountain crests and flanks promoting increased frequency of landslides that lasts for decades more gradual impacts involve the flushing of excess debris downstream by rivers which can generate bank erosion and floodplain accretion as well as channel avulsions that affect flooding frequency settlements ecosystems and infrastructure ultimately earthquake sequences and their geomorphic consequences alter mountain landscapes over both human and geologic time scales two recent events have attracted intense research into earthquake induced landslides and their consequences the magnitude m 7 6 chi chi taiwan earthquake of 1999 and the m 7 9 wenchuan china earthquake of 2008 using data and insights from these and several other earthquakes we analyze how such events initiate processes that change mountain landscapes highlight research gaps and suggest pathways toward a more complete understanding of the seismic effects on the earth s surface

imaging the source region of the 2004 mid niigata prefecture earthquake and the evolution of a seismogenic thrust related fold 1 the velocity structure and accurate aftershock distributions of the 2004 mid niigata prefecture earthquake are elucidated by inverting the arrival times from 716 aftershocks using double difference tomography fourteen temporal seismic stations were immediately deployed in and around the source region within 46 h of the occurrence of mainshock the seismic velocities in a hanging wall are lower than those in a footwall and the velocity contrast extends to a depth of approximately 10 km the aftershocks associated with the mainshock are distributed around the clear boundary between the low and high velocity structures it is interpreted that the mainshock fault plane of the mid niigata prefecture earthquake was reactivated as a reverse fault since the crustal shortening initiated at 3 5 ma crustal stretching or shortening along the japan coastline has created complex structures such as low velocity zones which can potentially control the seismic activities around the source region

asymmetric generation of oceanic crust at the ultra slow spreading southwest indian ridge 64 e we describe topographic gravity magnetic and sonar data from a southwest indian ridge spreading segment near 64 e 28 s we interpret these to reveal crustal structure spreading history and volcanic and tectonic processes over the last 12 myr we confirm that the crust is some 2 km thicker north of the ridge axis though it varies along and across axis on scales of 10 km and 4 myr the plate separation rate remained approximately constant at 13 1 km myr 1 but half spreading rates were up to 40 asymmetric varying between faster to the north and faster to the south on a 4 myr timescale topography shows a dominant e w lineation normal to the n s spreading direction this is superficially similar to faulted abyssal hill terrain of the mid atlantic ridge mar but inferred fault scarps are 3 4 times more widely spaced and have greater offsets conjugate pairs of massifs on either plate are interpreted as volcanic constructions similar to the large volcano currently filling the median valley at the segment center they have temporal spacings of 4 myr and are thought to reflect episodic melt focusing along an otherwise melt poor ridge additionally there are places mainly on the southern plate where lineated topography is replaced by a much blockier topography and embryonic ocean core complexes similar to those recently reported on the mar near 13 n there is generally more extrusive volcanism on the northern plate and more tectonism on the southern one extrusive volcanism has propagated westward from the segment center since 2 ma the fuji dome core complex and adjacent seafloor to its east and west appear to be part of a single coherent block capped by extrusive rock near the segment center exposing gabbro via a detachment fault over the dome and probably exposing deeper crust or upper mantle farther west near the segment end magnetic anomalies are continuous along this block we suggest that at its eastern boundary the detachment is simply welded onto magmatically emplaced crust to the east in a similar way to young crust being welded to the old plate at ridge transform intersections

lake sediments record high intensity shaking that provides insight into the location and rupture length of large earthquakes on the alpine fault new zealand abstract understanding the seismic hazard posed by large earthquakes requires paleoseismic investigation because most faults have not ruptured repeatedly during the period of historic records however determining the location and length of fault ruptures using paleoseismic data remains challenging our study demonstrates that lake sediments record the high intensity shaking that occurs proximal to fault rupture allowing the location and length of ruptures to be reconstructed in two lakes adjacent to the alpine fault new zealand seismic shaking is recorded as subaqueous mass wasting derived turbidites formed by coseismic subaqueous slope failures which are overlain by sets of hyperpycnites representing elevated fluvial sediment fluxes from earthquake induced landslides precise radiocarbon age models show that shaking events are synchronous between the two lake sites and correlate with the timing of known alpine fault earthquakes modelled shaking intensities for the last two alpine fault earthquakes show that subaqueous mass wasting occurs when shaking intensities exceed modified mercalli scale mm vi vii and that fluvial sediment fluxes from earthquake induced landslides occur when shaking intensities exceed mm ix the data demonstrate that lake records distinguish between strong mm vi and violent mm ix shaking at a lake site the ability to map the spatial extent of mm ix shaking provides new insights into the timing and extent of rupture for the last five earthquakes on the alpine fault the study demonstrates that lake deposits constrain the spatial extent of rupture during large earthquakes and may yield long records of the spatial and temporal patterns of fault rupture

spatial and temporal evolution of co seismic landslides after the 2005 kashmir earthquake abstract large earthquakes in mountainous regions often trigger widespread landslides some of which remain active for years to decades this study has evaluated the spatial and temporal evolution of the 2005 kashmir earthquake induced landslides using pre earthquake and post earthquake landslide inventories temporal landslide inventories were developed from the spot satellite images using the visual image interpretation supported with field validation it is observed that after the earthquake the landslide area and number showed a surge however decays in the subsequent years the rate of decline in the landslide area was relatively slower until 2010 however it dropped considerably during 2010 2018 the spatial variation of the landslides was traced and analyzed to classify them based on the activity the temporal evolution of the landslides was compared with the geology earthquake triggering fault and topographic attributes of slope aspect and elevation to evaluate their influence on the distribution of landslides the landslide inventories were related to the major triggering factors including rainfall and earthquakes to determine their impact on the temporal dynamics of the landslides regeneration of vegetation is analyzed using the temporal ndvi images as one of the drivers for the decline in the landslide area the knowledge of temporal dynamics of landslides and their major contributing factors shall assist to understand their triggering mechanism and effective mitigation measures

database and spatial distribution of landslides triggered by the lushan china mw 6 6 earthquake of 20 april 2013 abstract on 20 april 2013 an earthquake with mw 6 6 ms 7 0 hit lushan county sichuan province of china 30 3 n 103 e only 85 km southwest of the 2008 wenchuan mw 7 9 event the lushan shock triggered a large number of landslides with various types including highly disrupted shallow slides and rock falls deep seated landslides and large scale rock avalanches post earthquake high resolution aerial photographs and satellite images as well as a series of pre earthquake high resolution satellite images were collected to construct a detailed accurate objective and complete coseismic landslide database inventory which was validated by field investigation in selected areas based on the aerial photographs 0 2 or 0 6 m resolution that partly cover the affected area and pre earthquake satellite images 14 580 coseismic landslides were recognized and mapped in those areas without post earthquake aerial photographs coverage we mapped 7 948 more coseismic landslides based on post earthquake satellite images rapideye images with 5 m resolution and zy 3 images including panchromatic images with 2 1 m resolution and multi spectral images with 5 8 m resolution and pre earthquake satellite images the 22 528 coseismic landslides with a horizontal projection area of 18 88 km 2 and an estimated total volume of 41 56 10 6 m 3 were distributed in a nearly elliptic area of about 5 400 km 2 correlations between coseismic landslide abundances and topographic geologic and seismic factors were analyzed on 15 546 landslides of area 100 m 2 scatter plots between regional slope angle and landslide abundances in generalized homogeneous lithology combinations show no obvious relationship is present between them which challenges the conclusions of previous studies combining the lushan earthquake triggered landslides with other events on reverse and or thrust faults such as the 1999 chi chi and 2008 wenchuan shocks we found that coseismic landslides tend to occur in areas enveloped by two or more imbricated reverse and or thrust faults rather than only along the seismogenic fault the lushan event shows a higher ability of triggering landslides compared with other earthquakes of similar magnitudes which is likely due to the steep and rugged topography and fractured and densely jointed lithology resulted from long term tectonic activity the blind reverse seismogenic fault is likely also another significant factor based on detailed coseismic landslide inventory maps and databases of several recent major earthquakes such as the 2008 wenchuan 2010 haiti 2010 yushu and 2013 lushan temblors we suggest that the empirical correlations between earthquake magnitude and coseismic landslides need to be updated

effects of serpentinization on the lithospheric strength and the style of normal faulting at slow spreading ridges rock deformation experiments indicate that serpentinization can strongly influence the strength and tectonics of the oceanic lithosphere strength versus depth profiles calculated for conditions appropriate for slow spreading ridges indicate that the presence of serpentinite can reduce the integrated strength of the lithosphere by up to 30 results from flexural fault models indicate that if serpentinization is isolated to fault zones strain localization should be enhanced providing an explanation for the variations in the style of normal faulting along slow spreading ridge segments at segment centers where serpentinites are scarce deformation is accommodated on closely spaced faults with small throws at the segment ends where serpentinites are most abundant faults are widely spaced and have large throws q 1997 elsevier science b v

a simple model for the fault generated morphology of slow spreading mid oceanic ridges we postulate that fluctuations in magmatic activity at mid oceanic ridges perturb the horizontal least principal stress across rift bounding normal faults leading to alternating phases of magmatic accretion which increases valley width and tectonic extension which results in the growth of inner rift wall topography fine scale bathymetrie surveys and earthquake fault plane solutions show that active normal faults at slow spreading ridges are moderately dipping approximately 45 planar features throughout the seismogenic oceanic lithosphere a simple quantitative model that includes flexural deformation of a 10 km thick elastic plate by slippage on 45 dipping normal faults can match the bathymetrie profiles across several slow spreading ridge segments comparison among dip distributions of normal faulting earthquakes at mid ocean ridges in the trench outer rise region and on continents suggests that most events from these three tectonic environments initiated at dips close to 45 raising unanswered questions about the mechanical conditions under which the faults originated

segmentation and morphotectonic variations of the central indian ridge 21 10 s 22 25 s bathymetric magnetic and petrographic data have been used to analyze the segmentation and the morphotectonic variations on the central indian ridge cir between 21 10 s and 22 25 s volcanoes abyssal hills and steep slopes corresponding to fault scarps and to volcanic constructional slopes have been obtained by image processing methods applied to sea beam data in the survey area segmentation of the cir is similar to that of a slow spreading ridge the plate boundary morphology is defined by a linear zone composed of an ensemble of median ridges and elongate depressions hourglass shaped valleys are bounded by second and third order discontinuities located at local along axis depth maxima 400 700 m depth variations and marked by oblique extensional basins and en echelon jogs respectively large throw faults are prevalent toward segment ends and suggest greater amagmatic extension in these places along the axial valley the petrographic characteristics of the dredged basalts are correlated with the morphotectonic segmentation and suggest different magma reservoirs the morphology and structure of the rift valley reflect the three dimensional structure of the axial lithosphere and the geometry of mantle upwelling beneath the spreading center abyssal hills are bounded by both inward and outward facing faults in 1 5 ma crust indicating that the formation of abyssal hills is not solely resulting from a combination of volcanic and tectonic processes within the central part of the ridge but that tectonic processes may also occur as far as 20 40 km from the axis by initiating or reactivating some faults at the outward facing slope of the abyssal hills reconstructions of the plate boundary geometry through time using abyssal hills as isochrons provide evidence to show that the nontransform discontinuity located at 21 47 s with an offset as small as 2 3 km is associated with v shaped off axis traces in the form of alignments of disrupted abyssal hill lineations these reconstructions suggest that a small ridge jump is responsible for the initiation of this discontinuity and that this latter migrates away from areas of higher melt delivery three dimensional inversion of magnetic data shows that this discontinuity has been initiated between 0 780 and 0 984 ma and suggests postaccretionary crustal block rotations within the discordant zones

the characteristics of the landslides triggered by the wenchuan ms 8 0 earthquake from anxian to beichuan abstract this paper presents a quantitative analysis of the number and area of the landslides triggered by the wenchuan ms 8 0 earthquake from anxian to beichuan in this study the controlling factors of landslides are obtained from geological maps relief amplitude slope and topographic roughness calculated from dem data in arcgis 9 2 a total of 4134 landslides are identified from digital aero image of 1 m resolution covering 19 7 km2 that accounts for 6 4 of the study area the number of landslides with areas less than 5000 m2 is up to 85 22 the smallest landslide is 6 m2 and the largest 1515 000 m2 the number of landslides which have occurred is 1 6 times more prevalent at hanging walls as opposed to foot walls also the relationship between the numbers of landslides and the distances to an earthquake rupture at a hanging wall is linear but exponential at a footwall these results prove that landslide activity is more severe at hanging walls than at foot walls the outcrop area of geologic unit is proportional to the number of landslides except the jurassic triassic and quaternary units r2 0 952 in the study area and landslide density is 19 meanwhile the area of a landslide is linearly proportional to outcrop area of geologic unit except jurassic lower cambrian and quaternary unit r2 0 8279 in the study area and appear to indicate that the lithology does not play an important role in landslides in the study area earthquake triggered landslides tend to be concentrated in specific zones associated with the event controlling parameters such as reliefs slopes and topographic roughness the landslides occurred particularly in the range of 600 1293 m relief amplitudes and the number in this range amounts to 90 of total slides in the studied region moreover landslides easily occurred in the curvature 1 15 with slope between 5 and 55 in addition landslides also usually occurred in the range of 1 1 5 topographic roughness therefore these correlations provide a way to assess regional landslide hazards and are of great significance to regional geohazard planning and prediction

a seismologically consistent expression for the total area and volume of earthquake triggered landsliding we present a new seismologically consistent expression for the total area and volume of populations of earthquake triggered landslides this model builds on a set of scaling relationships between key parameters such as landslide spatial density seismic ground acceleration fault length earthquake source depth and seismic moment to assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow continental earthquakes low landscape steepness causes systematic overprediction of the total area and volume of landslides when this effect is accounted for the model predicts the total landslide volume of 63 of 40 cases to within a factor 2 of the volume estimated from observations r2 0 76 the prediction of total landslide area is also sensitive to the landscape steepness but less so than the total volume and it appears to be sensitive to controls on the landslide size frequency distribution and possibly the shaking duration some outliers are likely associated with exceptionally strong rock mass in the epicentral area while others may be related to seismic source complexities ignored by the model however the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate despite the variety of lithologies and tectonic settings covered this makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes

rupture processes of the 2004 chuetsu mid niigata prefecture earthquake japan a series of events in a complex fault system 1 we relocated the hypocenters of the 2004 chuetsu earthquake sequence niigata japan using the double difference method the distribution of aftershocks reveals a complex fault system consisting of five different fault planes inversions of strong motion records for the five major events within the sequence indicate that the mainshock mw 6 6 and the largest aftershock mw 6 3 occurred on parallel wnw dipping fault planes the zones of large slip asperities of these two events are located near the hypocenters in contrast the three other large earthquakes mw 5 9 5 7 and 5 9 occurred on east dipping fault planes oriented perpendicular to the fault plane of the mainshock we used slip distributions deduced from waveform inversions to estimate the coulomb failure stress changes that occurred immediately prior to each event cff values were positive at the hypocenters and within the asperities of the major aftershocks these results suggest that stress changes resulting from individual earthquakes led directly to the occurrence of subsequent earthquakes within the complex fault system

landslides triggered by the 1994 northridge california earthquake abstract the 17 january 1994 northridge california earthquake m w 6 7 triggered more than 11 000 landslides over an area of about 10 000 km 2 most of the landslides were concentrated in a 1000 km 2 area that included the santa susana mountains and the mountains north of the santa clara river valley we mapped landslides triggered by the earthquake in the field and from 1 60 000 nominal scale aerial photography provided by the u s air force and taken the morning of the earthquake these mapped landslides were subsequently digitized and plotted in a gis based format most of the triggered landslides were shallow 1 to 5 m thick highly disrupted falls and slides within weakly cemented tertiary to pleistocene clastic sediment average volumes of these types of landslides were less than 1000 m 3 but many had volumes exceeding 100 000 m 3 the larger disrupted slides commonly had runout paths of more than 50 m and a few traveled as far as 200 m from the bases of steep parent slopes deeper 5 m thick rotational slumps and block slides numbered in the tens to perhaps hundreds a few of which exceeded 100 000 m 3 in volume most of these were reactivations of previously existing landslides the largest single landslide triggered by the earthquake was a rotational slump block slide having a volume of 8 10 6 m 3 analysis of the mapped landslide distribution with respect to variations in 1 landslide susceptibility and 2 strong shaking recorded by hundreds of instruments will form the basis of a seismic landslide hazard analysis of the los angeles area

attenuation and scattering of broadband p and s waves across north america differential attenuation deltat italic measurements of teleseismic p italic and s italic waves are made in the frequency range 0 05 5 0 hz across north america using broadband seismic data from the department of energy s regional seismic test network and lawrence livermore national laboratory s basin and range network data from four events have been analyzed by first assuming frequency independent q italic the observed regional variations for deltat italic are consistent with previous studies and show greater attenuation for stations in the basin and range relative to those in shield regions of north america

the crownpoint new mexico earthquakes of 1976 and 1977 abstract in 1976 and 1977 two unusually deep earthquakes of m l 4 6 and 4 2 respectively occurred near the town of crownpoint in northwestern new mexico both events were felt extensively in the four corners region with maximum reported modified mercalli intensities of vi these earthquakes are two of the larger earthquakes observed within the colorado plateau and are among the strongest earthquakes reported in new mexico outside the rio grande rift relocations of the events placed them within the chaco slope along the southern portion of the san juan basin an area that appears to have exhibited a low level of historical seismicity and tectonism possibly since laramide times the most significant aspect of the 1976 and 1977 crownpoint earthquakes is their focal depths of 41 and 44 km respectively such depths would locate the events in the lowermost crust in the vicinity of the moho in sharp contrast to the upper crustal origin of most intraplate earthquakes although located within the colorado plateau revised fault plane solutions exhibit normal faulting along northwest trending planes and northeast southwest trending minimum compression which are characteristic of basin and range rio grande rift extension this observation suggests that this portion of the colorado plateau is located within a tectonic transition zone between the basin and range rio grande rift and colorado plateau stress provinces

flexural uplift of rift flanks due to mechanical unloading of the lithosphere during extension we suggest that the uplift of rift flanks results from mechanical unloading of the lithosphere during extension and consequent isostatic rebound this mechanism is presented as an alternative to explanations for rift flank uplift involving thermal or dynamic processes and magmatic thickening of the crust our hypothesis is based on two critical concepts first the lithosphere retains finite mechanical strength or flexural rigidity during extension second isostatic rebound uplift of the lithosphere follows when the kinematics of extension produces a surface topographic depression that is deeper than the level to which the surface of the extended lithosphere would subside assuming local isostatic compensation we develop and analyze two kinematic models for instantaneous extension of the lithosphere to show that flexural rebound is a viable explanation for the uplift of rift flanks we first investigate the isostatic consequences of finite simple slip on an initially planar dipping normal fault cutting the entire lithosphere when the lithosphere retains flexural rigidity during extension the topography resulting from this model resembles a half graben and the footwall rift flank is flexurally uplifted this simple normal faulting model explains free air gravity anomalies and topography observed at rift flanks in oceanic lithosphere such as broken ridge in the eastern indian ocean the caroline ridges sorol trough in the western equatorial pacific and the coriolis trough behind the new hebrides island arc we then investigate a general kinematic model for lithospheric extension where simple slip on a surface of arbitrary shape is accompanied by pure shear extension in the upper and lower plates when the simple slip component is not zero or the distribution of pure shear in the upper and lower plates is not identical the surface of slip can be regarded as a detachment by simplification our general model accounts for pure shear extension of the lithosphere that is uniform with depth in this case detachments have no meaning in the geologic sense however the kinematics of depth independent pure shear may nevertheless be described in terms of a surface which we term a kinematic reference surface at some depth in the lithosphere we speculate that the depth of this surface may be rheologically controlled the magnitude of rift flank uplift by flexure depends critically on the depth of this reference surface in contrast if local isostasy is assumed when the lithosphere undergoes a given amount of depth independent pure shear the resulting topography will be the same regardless of how the kinematics of that extension are formulated the basin and rift flank topography and free air gravity anomaly over young continental rifts such as the rhine graben can be satisfied using our general extensional model with a small amount 5 km of extension along a listric shaped detachment soling into the crust mantle boundary because the flexural rebound mechanism explains the observed topography and gravity anomaly over both oceanic and continental extensional domains we suggest that rheological differences between the two lithospheric types may not be important in their overall response to extension

isostatic compensation of tectonic features of the mid atlantic ridge 25 27 30 s we investigate the isostatic compensation of tectonic features along the mid atlantic ridge 25 27 30 s through a detailed examination of the relationship between bathymetry and gravity anomalies the study area includes three ridge segments spreading at an average full rate of 35 mm yr their flanks out to about 6 m y old crust and the intervening rio grande and moore fracture zones in a three dimensional analysis of gravity and sea beam bathymetry data we focus on crustal thickness variations and mantle density anomalies by removing from the observed fields the predicted contribution of simple crustal and mantle models positive residual gravity anomalies over the northern wall of the rio grande fracture zone indicate that in spots the crust is 2 3 km thinner than average there in contrast to the moore fracture zone where little thinning is observed the greater than average depths of the fracture zones as a whole are not locally compensated by thin crust but the deepest basins within the active transform parts of the fracture zones are partially compensated by thin crust or cooler mantle a narrow linear ridge that crosses one of the inactive branches of the moore fracture zone had been suggested to be the product of an episode of excess volcanism but is found to be underlain by thinner not thicker crust there is no indication of thicker crust beneath topographic highs at the inside corners of ridge transform intersections presumably these highs are dynamically maintained as must be the median valleys characteristic of most the length of the ridge segments judging from the absence of axial residual gravity anomalies there is a residual gravity low associated with an unusually shallow 15 to 20 km section of the ridge segment between the rio grande and moore offsets where the median valley virtually disappears our analysis suggests that while part of the anomalous elevation of this section of the ridge axis is attributable to excess volcanism and a thicker crust much of the elevation contrast is simply caused by the diminution of the dynamic mechanism responsible for median valley formation two dimensional fourier transforms of the gravity and bathymetry fields show that seafloor topography is strongly aligned parallel to either ridges or transforms while density anomalies are more randomly oriented this implies that the tectonic processes that control the gross ridge transform topography are not the dominant control on the magmatic processes that determine the upper mantle and crustal density structure statistical analysis of the coherence between the gravity and bathymetry fields indicates that the average effective elastic plate thickness in the study area is about 6 km

terrain attributes of earthquake and rainstorm induced landslides in orogenic mountain belt taiwan landsliding induced by earthquakes and rainstorms in montane regions is not only a sculptor for shaping the landscape but also a driver for delivering sediments and above ground biomass downstream however the terrain attributes of earthquake and rainstorm induced landslides are less discussed comprehensively in taiwan as part of an island wide inventory we here compare and contrast the landslide terrain attributes resulting from two catastrophic events the chi chi earthquake mw 7 6 september 1999 and typhoon morakot rainfall 2500 mm august 2009 results show that the earthquake induced landslides are relatively small round shaped and prone to occur primarily in middle and toe of slopes in contrast the rainstorm induced landslides are larger horseshoe shaped and preferentially occurring in slope toes also earthquake induced landslides particularly large landslides are usually found at steeper gradients whereas rainstorm induced landslides aggregate at gradients between 25 and 40 lithologic control plays a secondary role in landsliding from an island wide perspective high landslide density locates in the region of earthquake intensity vi or one day rainfall 600 mm day 1 through the landslide patterns and their terrain attributes our retrospective approach shed lights on accessing the historical and remote events for close geophysical investigations finally we should bear in mind that the landslide location size and terrain attributes varying with triggers may affect the landscape evaluation or biogeochemical processes in landslide dominated regions this article is protected by copyright all rights reserved

active faulting and seismicity in a prefractured terrane grand canyon arizona structural and seismic data for the eastern grand canyon were analyzed to determine the relationship between basement fractures surface faulting and seismicity published structural data were compared with the results of focal mechanism analysis of tremors occurring in the eastern canyon region during the period 1989 2004 previous studies of the geology of this area indicate that the fault and joint trends exposed in the surface rocks and through the entire sedimentary section were first established with predominant northeast and northwest trends in precambrian time the northwest trends of this prefractured terrane correlate with a dominant northwest trend of nodal planes in the seismic data suggesting that the present stress system in the region is favoring the reactivation of the preferentially oriented pre existing northwest trending fractures

segmentation and crustal structure of the western mid atlantic ridge flank 25 25 27 10 n and 0 29 m y we conducted a detailed geological geophysical survey of the west flank of the mid atlantic ridge between 25 25 n and 27 10 n and from the ridge axis out to 29 ma crust acquiring hydrosweep multibeam bathymetry hawaii mr1 sidescan sonar imagery gravity magnetics and single channel seismic reflection profiles the survey covered all or part of nine spreading segments bounded by mostly nontransform right stepping discontinuities which are subparallel to flow lines but which migrated independently of one another some discontinuities alternated between small right and left stepping offsets or exhibited zero offset for up to 3 4 m y despite these changes the spreading segments have been long lived and extend 20 m y or more across isochrons a large shift 9 in relative plate motion about 24 22 ma caused significant changes in segmentation pattern the nature of this plate boundary response together with the persistence of segments through periods of zero offset at their bounding discontinuities suggest that the position and longevity of segments are controlled primarily by the subaxial position of buoyant mantle diapirs or focused zones of rising melt within segments there are distinct differences in seafloor depth morphology residual mantle bouguer gravity anomaly and apparent crustal thickness between inside corner and outside corner crust this demands fundamentally asymmetric crustal accretion and extension across the ridge axis which we attribute to low angle detachment faulting near segment ends cyclic variations in residual gravity over the crossisochron run of segments also suggest crustal thickness changes of at least 1 2 km every 2 3 m y these are interpreted to be caused by episodes of magmatic versus relatively amagmatic extension controlled by retention and quasiperiodic release of melt from the upwelling mantle detachment faulting appears to be especially effective in exhuming lower crust to upper mantle at inside corners during relatively amagmatic episodes creating crustal domes analogous to turtleback metamorphic core complexes that are formed by low angle detachment faulting in subaerial extensional environments

reconstruction of the flanks of the mid atlantic ridge 28 to 29 n implications for evolution of young oceanic lithosphere at slow spreading centers mar flank reconstruction

seismically induced mass movements and volumetric fluxes resulting from the 2010 mw 7 2 earthquake in the sierra cucapah mexico the observation that sediment flux from mountain ranges struck by high magnitude earthquakes can be strongly influenced by coseismic mass movements brings into question the nature of coseismic deformation as a net contributor to mountain building to better constrain the role of high magnitude earthquakes in orogenesis high resolution data of earthquake induced mass wasting is required for areas of differing tectonic morphological and climatic settings here we compare the erosional flux to the tectonic flux associated with the 2010 mw 7 2 sierra el mayor earthquake in mexico and examine the landslide patterning of coseismic mass movements associated with this event the ruptured fault system has a significant strike slip component with subsidence along the eastern flank and uplift on the western flank of the range peak ground acceleration was highest along the steepest sections of the range such that the frequency of landslide occurrence was strongly correlated to slope gradient both vertical and horizontal coseismic displacement demonstrated a strong control over landslide initiation this result suggests that strike slip systems experience very different landslide patterning to thrust faults during earthquakes based on interferometric analysis of synthetic aperture radar images the earthquake resulted in a total uplifted volume of 41 6 106 m3 and a loss of 95 2 106 m3 due to subsidence this suggests a net tectonic volumetric flux of 53 6 106 m3 sediment mobilisation by coseismic landslides is estimated at 2 7 106 m3 derived from a manually mapped inventory using spot 5 multispectral imagery thus the net volume loss through coseismic subsidence of the mountain range generated a strongly negative mass flux which was only marginally enhanced by mass wasting

mechanisms for the origin of mid ocean ridge axial topography implications for the thermal and mechanical structure of accreting plate boundaries to better understand the implications of ridge axis morphology for the thermal and mechanical structure of accreting plate boundaries we examine mechanisms for the creation of stress supported axial topography and its dependence on parameters such as spreading rate asthenosphere viscosity and plate thickness near the ridge axis three basic mechanisms are considered 1 asthenospheric upwelling in a narrow steady state conduit beneath a ridge axis 2 mantle flow stresses due to plate spreading extending ridge axis lithosphere or melt segregation and associated mantle compaction and 3 topography supported by moments due to horizontal extensional stresses in a thickening lithosphere if mid ocean ridge topography is due to asthenosphere rising in a narrow conduit at the ridge axis then the conduit structure cannot be thermally controlled as the associated thermal structure has relatively broad flat isotherms instead of a conduitlike shape mantle flow associated with plate spreading alone induces no stress supported topography thus the intuitive notion that diverging flow at the ridge axis due solely to plate spreading produces the axial valley is incorrect vertical mantle flow at the base of a stretching accreting lithosphere and mantle flow associated with melt segregation can however lead to stress supported axial topography however for these mantle flow related processes to produce significant amounts of axial relief the mantle viscosity beneath the ridge axis must be on the order of 1020 pa s 1021 p poise significantly higher than generally accepted values of 1018 pa s 1019 p horizontal extensional stresses in a strong brittle lithosphere that thickens with distance from the ridge axis can produce axial topography of the form and amplitude observed on slow spreading ridges a continuum idealization of deformation due to faulting is used to examine this mechanism this model predicts the axial valley width is controlled by the plate thickness near the ridge axis an 8 km thick plate near the ridge axis would produce the 30 km wide axial valley observed at slow spreading ridges an increased lithosphere thickness of only several kilometers over the half width of the axial valley can produce kilometer scale relief to examine whether a plate 8 10 km thick at the ridge axis that thickens by several kilometers within 15 km of the axis is plausible at a slow spreading ridge thermal models that include both the heat of magmatic crustal accretion on the ridge axis and upwelling mantle flow beneath the axis are formulated hydrothermal cooling that increases the effective conductivity by about a factor of 10 is required for an 8 km thick plate to exist at a slow spreading ridge axis however even with this enhanced hydrothermal cooling the plate thickness at a fast spreading ridge axis and the resulting horizontal force in the plate are too small to result in appreciable topography while mid ocean ridge axial topography is strongly influenced by spreading rate other factors also shape axial structure for example the anomalously shallow slow spreading reykjanes ridge has an axial structure more like that of a fast spreading ridge and the anomalously deep intermediate spreading australian antarctic discordance has a median valley axial structure typical of a slower spreading ridge in addition within a given spreading segment there is often a systematic deepening of the ridge axis toward transform offsets these non spreading rate dependent axial topographic variations may be produced by variations in magmatic heat input associated with crustal emplacement which shapes the thermal structure and lithosphere thickness near the ridge axis

rupture process of the 2008 iwate miyagi nairiku japan earthquake derived from near source strong motion records abstract we derive the rupture process of the 2008 iwate miyagi nairiku japan earthquake m jma 7 2 during which the largest ground acceleration to date namely 4022 cm sec 2 was recorded at a hanging wall station iwth25 station of kik net just above the hypocenter velocity waveform data 0 1 1 hz at 14 strong motion stations of k net and kik net including the borehole records of iwth25 are inverted using the multi time window linear waveform inversion method we assume a horizontally layered velocity structure model having low velocity subsurface layers for each station in order to calculate the green s functions the waveform inversion indicates that there are two major slip patches one patch extends from the hypocenter to the southern shallower part of the fault a particularly large slip area in this patch is centered approximately 8 km to the south of the hypocenter with a maximum slip of 6 2 m the area ruptured between 4 and 9 sec after the initial break the other patch with smaller slip is located in the northern part which broke after the rupture of the southern slip patch the initial 0 4 sec rupture occurred beneath iwth25 contributing to the synthesis of a distinctive upward velocity pulse at this station examination of the slip contribution to the synthetic velocity waveforms and comparison of the isochrones with the slip distribution suggest that a peak acceleration greater than 4000 cm sec 2 observed at iwth25 was generated from the area that is closest to the hypocenter in the southern particularly large slip area

three dimensional gravity study of the mid atlantic ridge evolution of the segmentation between 28 and 29 n during the last 10 m y during the high resolution survey sara segmentation ancienne de la ride atlantique sea beam bathymetry magnetic gravity and seismic reflection data were collected on the flanks of the mid atlantic ridge between 28 and 29 n this survey was designed to provide off axis information up to approximately 10 m y and to complement a detailed on axis survey carried out in 1988 and 1989 sempere et al 1990 between the atlantis and kane fracture zones a previous gravity study had revealed the existence of bulls eye shaped gravity lows centered on the axial segments and gravity highs centered on the non transform discontinuities lin et al 1990 we carried out a three dimensional calculation of the mantle bouguer anomaly in order to investigate if the axial pattern of circular anomaly lows can be followed on the flanks of the spreading center the off axis gravity anomalies are characterized by anomaly lows over the centers of the segments and anomaly highs over the discontinuities after correcting for the gravity effect of lithospheric cooling away from the ridge the segmentation configuration determined from gravity data appears to be very similar to that deduced from bathymetry off axis bathymetry is characterized by southward pointing v shaped basins which indicate that the traces of the nontransform discontinuities do not follow plate motion flow lines and that each ridge segment advances and retreats continuously however the gravity trace of the discontinuities is always slightly offset with respect to the bathymetric lows northward on the western flank and southward on the eastern flank the sense of offset between the gravity and bathymetric traces appears to be related to the right stepping nature of the axial discontinuities

seismicity and active faulting of the kanab fredonia area of the southern colorado plateau 1 detailed study of the historic seismicity of the kanab fredonia area adds information to the location of the colorado plateau tectonic boundary in this area and to the nature of contemporary seismicity and faulting on this part of the colorado plateau historic seismicity over 45 years 1959 2004 defines a band of activity which extends through fredonia arizona and into southern utah around kanab the area is dominated by north trending high angle normal faults the spatial distribution of epicenters consists of clusters associated with the west kaibab big springs and toroweap sevier faults indicating that these faults may be active four focal mechanism solutions show basin range style high angle normal faulting on north to north northwest trending surfaces that are parallel to subparallel in most cases to mapped quaternary faults this suggests a present east west extension occurring on the southern colorado plateau for the kanab fredonia area and an expansion of the adjacent basin range province eastward into the plateau as far as the west kaibab big springs faults the west kaibab big springs faults are proposed to be the tectonic boundary of the southern colorado plateau in this area since they mark the limit of significant seismic activity that is combined with basin range type faulting

evidence for ascending upper mantle derived melt beneath the cheb basin central europe 1 we present new 3he 4he data of co2 rich gas exhalations of three presently nonvolcanic areas in europe the 3he 4he ratios from the cheb basin czech republic are clearly higher than data obtained ten years ago whereas the 3he 4he ratios from the other areas laacher see germany and marianske lazn cr have remained nearly constant no other locality showing such high 3he 4he ratios in free gases supplied by continental mantle degassing is known in the european cenozoic rift system at the northeastern edge of the cheb basin swarm earthquakes repeatedly occur in the context of contemporaneous periods of seismicity the increased 3he 4he ratios are interpreted as the first geochemical evidence for ascending mantle derived melt beneath the cheb basin which is related to the triggering of earthquake swarms

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

abyssal hill characterization at the ultraslow spreading southwest indian ridge 1 the morphology of the flanks of the southwest indian ridge holds a record of seafloor formation and abyssal hill generation at an ultraslow spreading rate statistical analysis of compiled bathymetry and gravity data from the flanks of the southwest indian ridge from 54 e to 67 e provides estimates of abyssal hill morphologic character and inferred crustal thickness the extent of the compiled data encompasses a spreading rate change from slow to ultraslow at 24 ma a significant inferred variation in sub axis mantle temperature and a patchwork of volcanic and non volcanic seafloor making the southwest indian ridge an ideal and unique location to characterize abyssal hills generated by ultraslow spreading and to examine the effect of dramatic spreading rate change on seafloor morphology root mean square abyssal hill height in ultraslow spreading seafloor ranges from 280 m to 320 m and is on average 80 m greater than found for slow spreading seafloor ultraslow spreading abyssal hill width ranges from 4 km to 12 km averaging 8 km abyssal hill height and width increases west to east in both slow and ultraslow spreading seafloor corresponding to decreasing inferred mantle temperature abyssal hills persist in non volcanic seafloor and extend continuously from volcanic to non volcanic terrains we attribute the increase of abyssal hill height and width to strengthening of the mantle portion of the lithosphere as the result of cooler sub axial mantle temperature and conclude that abyssal hill height is primarily controlled by the strength of the mantle component of the lithosphere rather than spreading rate

a review of the 2005 kashmir earthquake induced landslides from a remote sensing prospective abstract the 8th october 2005 kashmir earthquake in northern pakistan has triggered thousands of landslides which was the second major factor in the destruction of the build up environment after earthquake induced ground shaking subsequent to the earthquake several researchers from home and abroad applied a variety of remote sensing techniques supported with field observations to develop inventories of the earthquake triggered landslides analyzed their spatial distribution and subsequently developed landslide susceptibility maps earthquake causative fault rupture geology anthropogenic activities and remote sensing derived topographic attributes were observed to have major influence on the spatial distribution of landslides these were subsequently used to develop a landslide susceptibility map thereby demarcating the areas prone to landsliding temporal studies monitoring the earthquake induced landslides shows that the earthquake induced landslides are stabilized contrary to earlier belief directly after the earthquake the biggest landslide induced dam as a result of the massive hattian bala landslide is still posing a threat to the surrounding communities it is observed that remote sensing data is effectively and efficiently used to assess the landslides triggered by the kashmir earthquake however there is still a need of more research to understand the mechanism of intensity and distribution of landslides and their continuous monitoring using remote sensing data at a regional scale this paper provides an overview of remote sensing and gis applications for the kashmir earthquake triggered landslides derived outputs and discusses the lessons learnt advantages limitations and recommendations for future research

quantifying tectonic strain and magmatic accretion at a slow spreading ridge segment mid atlantic ridge 29 n high resolution deep towed side scan sonar data are used to characterize faulting and variations in tectonic strain along a segment of the slow spreading mid atlantic ridge near 29 n sonar data allow us to identify individual fault scarps to measure fault widths and spacing and to calculate horizontal fault displacements heave and tectonic strain we find that over long periods of time 1 myr on average tectonic strain is 10 on average and does not vary significantly along axis there is a marked asymmetry in tectonic strain that appears to be linked to asymmetric accretion along the whole segment indicated by 50 lower tectonic strain on the east flank than on the west flank these variations in tectonic strain do not correlate directly with changes in fault spacing and heave fault spacing and heave increase from the center of the segment toward the end inside corner on the west flank and from the outside to the inside corner across the axis these parameters remain relatively constant along the segment on the east flank and across the axis at the segment center tectonic strain appears to be decoupled from magmatic accretion at timescales 1 myr as the decrease in magma supply from the segment center toward the end inferred from variations in crustal thickness along the axis is not correlated with a complementary increase in tectonic strain instead tectonic strain remains relatively constant along the axis at 7 on the east flank and at 15 on the west flank these results indicate that variations in fault development and geometry may reflect spatial differences in the rheology of the lithosphere and not changes in tectonic strain or magma supply along axis

seismic and geological controls on earthquake induced landslide size abstract landslide size controls the destructive power of landslides and is related to the frequency of occurrence with larger landslides being less frequent than smaller ones for this reason the analysis of landslide size is essential for landslide hazard assessment we analyse six earthquake induced landslide inventories with earthquake magnitude ranging between 6 6 and 7 9 mw papua new guinea 1993 chichi 1999 northridge 1994 niigata chuetsu 2004 iwate miyagi nairiku 2008 wenchuan 2008 for each inventory we developed magnitude frequency curves to analyse the size distribution of landslides as a function of ground motion distance from the seismic source both fault trace and epicentre local relief and lithology for three earthquakes we observed a clear relationship between the landslide size and ground motion with larger landslides associated with higher ground motion we investigate different possible causes for such observation and propose that the main mechanical reason is that stronger shaking induces higher stresses that may overcome the strength which increases with depth triggering larger landslides we also show that landslide size decreases with distance from the fault trace whereas this trend is not clear for distance from the epicentre local relief does not seem a first order control on landslide size for the earthquake induced landslides considered here some lithologies do influence landslide size but we were unable to identify a general behaviour for different lithologies

coseismic velocity change in and around the focal region of the 2008 iwate miyagi nairiku earthquake 1 the 2008 m7 2 iwate miyagi nairiku earthquake occurred in ne japan where dense seismic networks exist using the data from these networks we determined the coseismic seismic velocity change associated with this earthquake by two different methods ambient noise interferometry and vertical array interferometry of coda wave the purpose of this article is to reveal the spatial distribution and the cause of the velocity change by integrating these two approaches ambient noise interferometry revealed a coseismic velocity decrease of rayleigh wave by 0 1 0 5 at 0 25 0 5 hz we also estimated the spatial distribution of the velocity change by a tomographic inversion the velocity decrease was distributed in and around the focal area in the second method we applied cross correlation analysis to coda waves observed by the kik net vertical array we detected a shear velocity decrease of approximately 5 in shallow layers up to a few hundred meters depth quantitative comparison of the two results reveals that the 5 shear velocity decrease in shallow layers can explain the 0 1 0 5 decrease of rayleigh wave velocity the distribution of the velocity decrease is similar to that of the strong ground motion and the static stress change however a significant velocity increase is not observed in the compression area where a velocity increase is expected based on the observations we consider that the primary factor affecting the velocity change is damage in shallow layers due to strong motion the effect of the static stress change might be masked by the larger effect of the strong motion

landslide distribution and size in response to quaternary fault activity the peloritani range ne sicily italy landslides contribute to dismantle active mountain ranges and faults control the location of landslides yet evidence of the long term regional dependency of landslides on active faults is limited previous studies focused on the transient effects of earthquakes on slope stability in compressive and transcurrent regimes here we show that in the peloritani range ne sicily italy one of the fastest uplifting areas in the mediterranean a clear geographical association exists between large bedrock landslides and active normal faults of the messina straits graben by interpreting aerial photographs we mapped 1590 landslides and sackungs and 626 fault elements and their facets in a 300 km2 area in the eastern part of the range we used the new landslide and fault information in combination with prior geological and seismic information to investigate the association between bedrock landslides and faults we find that the distribution and abundance of landslides is related to the presence of large active normal faults and matches the pattern of the local historical seismicity landslide material is more abundant along the east peloritani fault system where the long term activity of the faults measured by the average yearly geological moment rate is larger than in the west peloritani fault system where landslides are less abundant along the fault systems landslide material concentrates where the cumulated fault throws are largest we conclude that large landslides and their cumulated volume are sensitive to local rates of tectonic deformation and discriminate the deformation of the single fault segments that dissect the peloritani range our findings are a direct test of landscape evolution models that predict higher rates of landslide activity near active faults our work opens up the possibility of exploiting accurate landslide and fault maps in combination with geological and seismic information to characterize the long term seismic history of poorly instrumented active regions copyright 2015 the authors earth surface processes and landforms published by john wiley sons ltd

the paradox of the axial profile isostatic compensation along the axis of the mid atlantic ridge mantle bouguer gravity anomalies mba and bathymetry on three profiles covering more than 1000 km along the axis of the mid atlantic ridge mar are highly correlated suggesting that along axis topographic relief is locally compensated by variations in crustal thickness and or mantle density structure the quantitative relationship between topography and gravity on these profiles could be explained by the flexure of a thin narrow elastic strip representing the response to isostatic loads of an inner rift valley isolated from the rest of the plate by weak bounding normal faults the paradox is that across axis profiles show that the median valley is an uncompensated feature apparently created by a dynamic mechanism new extensive off axis coverage of the mar from 31 to 36 s shows that the high correlation does not persist outside the axial zone we suggest that the on axis correlation exists because the mechanism creating the median valley is controlled by the mantle thermal structure and along axis variations in crustal thickness both of which contribute to the mba if the mechanism is extension of a brittle ductile lithosphere the critical parameter controlling topographic relief is the thickness of the relatively stiff mantle layer immediately beneath the crust at the ridge axis a three dimensional 3 d thermal model incorporating passive mantle flow hydrothermal circulation the plate boundary geometry and variable magmatic heating associated with observed variations in crustal thickness predicts variations in the thickness of the stiff mantle layer that correlate with the observed axial topography we model the expected topography using cross axis sections of the 3 d thermal model and a 2 d finite element model of an extending lithosphere that incorporates temperature and strain dependent rheology as well as the flexural response of a thickening plate the predicted topographic signal produced by the combined dynamic and isostatic effects matches the amplitude of the observed axial bathymetry at the 18 mm yr 1 spreading half rate in our south atlantic survey the 2 d models also reproduce the observed rapid transition along the axis between rift valley no rift valley morphology we conclude that extensional forces acting on segmented oceanic lithosphere with varying rates of crustal production produce the highly variable morphology of the southern mar and the along axis correlation between mba and bathymetry

effect of lithospheric geometry on rift valley relief 1 continental and mid oceanic rifts commonly show a rift valley bounded by normal faults and uplifted shoulders in this paper we numerically model the evolution of rift valley relief in a notched brittle lithosphere results show that the rift valley has a maximum valley relief which is controlled by the competition between isostasy and lithospheric geometry if the axial lithosphere is much thinner than the flanking lithosphere the isostatic force will break outward dipping faults on the axis and stop the deepening of the rift valley we call this the axial failure mode on the other hand if the thickness of axial lithosphere is close to that of the flanks flexural bending will break new faults on the flanks and stop the valley deepening we call this the flanking failure mode triggering of either mode gives the maximum valley depth and the selection is controlled by the interplay between isostasy and lithospheric geometry on the basis of these mechanisms we propose a scaling equation that relates the maximum valley depth to the geometry flanking thickness axial thickness and notch width and strength friction angle and cohesion of the lithosphere the model explains along axis variation of valley relief at mid oceanic ridges by changes of the axial lithosphere thickness

coseismic landslides reveal near surface rock strength in a high relief tectonically active setting we present quantitative estimates of near surface rock strength relevant to landscape evolution and landslide hazard assessment for 15 geologic map units of the longmen shan china strength estimates are derived from a novel method that inverts earthquake peak ground acceleration models and coseismic landslide inventories to obtain material properties and landslide thickness aggregate rock strength is determined by prescribing a friction angle of 30 and solving for effective cohesion effective cohesion ranges are from 70 kpa to 107 kpa for 15 geologic map units and are approximately an order of magnitude less than typical laboratory measurements probably because laboratory tests on hand sized specimens do not incorporate the effects of heterogeneity and fracturing that likely control near surface strength at the hillslope scale we find that strength among the geologic map units studied varies by less than a factor of two however increased weakening of units with proximity to the range front where precipitation and active fault density are the greatest suggests that climatic and tectonic factors overwhelm lithologic differences in rock strength in this high relief tectonically active setting

kinematics of the north american african plate boundary between 28 and 29 n during the last 10 ma evolution of the axial geometry and spreading rate and direction abstract a high resolution survey sara segmentation ancienne de la ride atlantique collected sea beam bathymetry magnetic gravity and seismic reflection data on the flanks of the mid atlantic ridge between 28 and 29 n this survey was designed to complement a portion of an on axis study carried out between the atlantis and kane transform faults which revealed the configuration of the spreading axis the sara survey extends this coverage to an age of approximately 10 ma on either flank a sinuous isochron pattern was established from anomaly identification made using a two dimensional model the plate tectonic reconstruction based solely on this isochron pattern provides an accurate kinematic description of the relative motion between the african and north american plates within the zone our results confirmed by data from the famous area and a flowline comparison with the trend of the kane fracture zone show that a change in axial orientation spreading direction and spreading rate occurred at approximately anomaly 4 time 7 01 ma this was coincident with the appearance of a new axial segment all the axial segments observed have changed length continously during the last 10 ma by advancing or retreating at one or both ends in any combination so as to leave non parallel trails on the flanks that do not align with either the spreading direction or with the absolute plate motion factors contributing to the sinuous magnetic anomaly pattern are discussed

the mass balance of earthquakes and earthquake sequences large compressional earthquakes cause surface uplift as well as widespread mass wasting knowledge of their trade off is fragmentary combining a seismologically consistent model of earthquake triggered landsliding and an analytical solution of coseismic surface displacement we assess how the mass balance of single earthquakes and earthquake sequences depends on fault size and other geophysical parameters we find that intermediate size earthquakes mw 6 7 3 may cause more erosion than uplift controlled primarily by seismic source depth and landscape steepness and less so by fault dip and rake such earthquakes can limit topographic growth but our model indicates that both smaller and larger earthquakes mw 7 3 systematically cause mountain building earthquake sequences with a gutenberg richter distribution have a greater tendency to lead to predominant erosion than repeating earthquakes of the same magnitude unless a fault can produce earthquakes with mw 8 or more

regional patterns of earthquake triggered landslides and their relation to ground motion 1 we have documented patterns of landsliding associated with large earthquakes on three thrust faults the northridge earthquake in california chi chi earthquake in taiwan and two earthquakes on the ramu markham fault bounding the finisterre mountains of papua new guinea in each case landslide densities are shown to be greatest in the area of strongest ground acceleration and to decay with distance from the epicenter in california and taiwan the density of co seismic landslides is linearly and highly correlated with both the vertical and horizontal components of measured peak ground acceleration based on this observation we derive an expression for the spatial variation of landslide density analogous with regional seismic attenuation laws in its general form this expression applies to our three examples and we determine best fit values for individual cases our findings open a window on the construction of shake maps from geomorphic observations for earthquakes in non instrumented regions

generation of morphotectonic fabric on the mid atlantic ridge flanks 28 to 29 n implications for the limits of tectonic deformation and abyssal hill formation 1 high resolution multibeam bathymetry is used to analyze the morphotectonic fabric of a 35 000 km2 zone of the mid atlantic ridge crest between 28 and 29 n interpolated isochrons at 1 myr intervals derived from a kinematic reconstruction provide a temporal framework for the structural analysis the axial valley within the survey area is offset by three non transform discontinuities dividing the axis into en echelon segments the flanks display a predominantly ridge parallel fabric of elongate abyssal hills crosscut by several discordant zones throughout the zone faulting is the predominant factor in generating the morphotectonic fabric analysis of fault scarp distribution places the limit of active tectonic deformation between 2 and 3 ma 25 to 35 km on either side of the spreading axis fault scarp relief on the ridge flanks varies with a period of approximately 2 myr which corresponds to the wavelength of abyssal hills within the area we propose an interpretation in which abyssal hill formation occurs periodically 2 myr within the ridge mountains as the lithosphere transitions from the dynamic supported regime near the axis to the isostatic regime of the flanks at 2 3 ma 25 35 km from the axis

the relationship between late cenozoic tectonic events and stress field and basin development in northeast japan the regional tectonic stress field basin development and crustal deformation of the ne japan arc in the interval between 32 ma to the quaternary can be synthesized based on dike vein and fault orientation data as well as on the compilation of the regional geology an extensional stress field became prevalent from 32 ma and major normal faulting started at 25 20 ma which resulted from back arc rifting normal faulting trending nearly parallel to the arc propagated from the present japan sea coast to the forearc side following the trenchward migration of the main volcanic field from 20 to 15 ma normal faults with an oblique trend to the arc developed due to the counterclockwise rotation of ne japan the rapid clockwise rotation of sw japan since 16 ma produced a nw se directed transtensional stress regime in the ne japan arc due to crustal stretching associated with this pull apart movement the back arc side of the ne japan arc subsided rapidly to middle bathyal environments after the termination of the opening of the japan sea at about 14 ma a neutral stress regime prevailed which included phases of both weak extension and compression lithospheric cooling eventually led to thermal subsidence of the back arc region and igneous underplating caused uplift of the axial zone of the volcanic arc the increase in velocity of the westward motion of the pacific plate at around 4 ma produced strong compression across the arc reactivating most of the miocene normal faults and uplifting the volcanic arc the greatest crustal shortening occurred in areas that were stretched the most in the miocene within the volcanic arc which implies tectonic inversion

segmentation of the mid atlantic ridge between 24 n and 30 40 n the mid atlantic ridge mar extends for over 12 000 km from iceland to the bouvet triple junction in the south atlantic most of our knowledge of the geology of this slow spreading centre comes either from widely spaced low resolution echo sounding lines or from detailed studies of small areas using deep towed instruments or submarines high resolution multibeam bathy metry1 2 has been insufficient to define the variability of accretionary processes along this plate boundary here we present the results of a recent investigation of a 800 km long section of the mar carried out using the multibeam echo sounder seabeam3 analysis of these data reveals the scale and nature of the segmentation of the mar between the kane fracture zone 24 n and latitude 30 40 n

geostatistical modeling to capture seismic shaking patterns from earthquake induced landslides we investigate earthquake induced landslides using a geostatistical model featuring a latent spatial effect lse the lse represents the spatially structured residuals in the data which remain after adjusting for covariate effects to determine whether the lse captures the residual signal from a given trigger we test the lse in reproducing the pattern of seismic shaking from the distribution of seismically induced landslides without prior knowledge of the earthquake being included in the model we assessed the landslide intensity that is the expected number of landslides per mapping unit for the area in which landslides triggered by the wenchuan and lushan earthquakes overlap we examined this area to test our method on landslide inventories located in near and far fields of the earthquake we generated three models for both earthquakes i seismic parameters only proxy for the trigger ii the lse only and iii both seismic parameters and the lse the three configurations share the same morphometric covariates this allowed us to study the lse pattern and assess whether it approximated the seismic effects our results show that the lse reproduced the shaking patterns for both earthquakes in addition the models including the lse perform better than conventional models featuring seismic parameters only due to computational limitations we carried out a detailed analysis for a relatively small area 2 112 km2 using a data set with higher spatial resolution results were consistent with those of a subsequent analysis for a larger area 14 648 km2 using coarser resolution data

rupture process of the 1944 tonankai earthquake ms 8 1 from the inversion of teleseismic and regional seismograms 1 we digitized teleseismic and regional records of the 1944 tonankai earthquake we used the multiple time window method to invert these records for the spatial and temporal distribution of slip and rake we assume a 220 140 km fault with a spacing of 20 20 km and a maximum rupture velocity of 2 5 km s the inversion resolved an asperity along the accretionary wedge and under the shima and atsumi peninsulas the rupture propagated from southwest to northeast and there was little slip near the hypocenter consistent with the absence of uplift in the overlying submarine forearc basin the peak slip is 2 3 m and the total seismic moment is 2 4 1028 dyn cm mw 8 2 we compared the predicted and observed vertical geodetic displacements and inferred that the limit of rupture is consistent with the change from subsidence to uplift west of the atsumi peninsula this suggested that the earthquake did not rupture the plate interface in the tokai gap we modeled the tsunami using sea bottom displacements generated from this slip model the tide gauge amplitudes and frequency content are consistent with those predicted resolution tests from inverting synthetic seismograms computed using a simplified slip model indicated that the combination of teleseismic and regional data sets best recovers the asperity locations and peak slips given similar station geometry and degrees of freedom an inversion of the synthetic regional data set indicates that slip artifacts can occur early in the rupture process due to many clipped records while the inversion of synthetic teleseismic data set had less resolution and recovered only 50 of the peak slip

fault structure and detailed evolution of a slow spreading ridge segment the mid atlantic ridge at 29 n we present preliminary results of a detailed near bottom study of the morphology and tectonics of the 29 n broken spur segment on the slow spreading mid atlantic ridge using principally the tobi deep towed instrument the survey covered two thirds of the segment length including all of its southern non transform boundary and extended off axis of 40 km 3 3 ma on either side we obtained nearly complete near bottom sidescan sonar coverage and deep towed three component magnetic observations along 2 km spaced e w tracks sidescan data reveal new details of fault structure and evolution faults grow by along axis linkage in the inside corner they also link in the axis normal direction by curving to meet the next outer older fault this leads to wider spaced faults compared to segment centre or outside corner outward facing faults exist but are rare the non transform offset is characterised by faults that are highly oblique not parallel to the spreading direction and show cross cutting relations with ridge parallel faults to the north suggesting along axis migration of the offset almost all volcanic activity occurs within 5 km of the axis most fault growth is complete within 15 km of the axis 1 2 ma though large scarps continue to be degraded by mass wasting beyond there crustal magnetisation is strongly three dimensional the current neovolcanic zone is slightly oblique to earlier reversal boundaries and its magnetisation rises to a maximum of 30 a m 1 near its southern tip the central magnetisation high tapers southwards and is asymmetric with a sharp western but gradual eastern boundary we infer a highly asymmetric accretion of layer 2 near the segment end older magnetic anomalies are kinked and sometimes missing we interpret these observations as evidence of a rapid 18 km southward migration of the segment boundary during the past 1 8 ma and present a series of reconstructions illustrating this tectonic history

evidence from gravity data for focused magmatic accretion along the mid atlantic ridge gravity data from the mid atlantic ridge between latitudes 27 50 n and 30 40 n show that the accretion of magma at the ridge is focused at discrete centres along the spreading axis large positive gravity anomalies equivalent to reductions of almost 50 in crustal thickness are observed over non transform discontinuities bounding spreading segments

earthquakes on dipping faults the effects of broken symmetry dynamic simulations of earthquakes on dipping faults show asymmetric near source ground motion caused by the asymmetric geometry of such faults the ground motion from a thrust or reverse fault is larger than that of a normal fault by a factor of 2 or more given identical initial stress magnitudes the motion of the hanging wall is larger than that of the footwall in both thrust reverse and normal earthquakes the asymmetry between normal and thrust reverse faults results from time dependent normal stress caused by the interaction of the earthquake generated stress field with earth s free surface the asymmetry between hanging wall and footwall results from the asymmetric mass and geometry on the two sides of the fault

correction to reconstruction of the flanks of the mid atlantic ridge 28 to 29 n implications for evolution of young oceanic lithosphere at slow spreading centers 1 we reconstruct the flanks of the mid atlantic ridge mar between 28 and 29 n from 1 to 10 ma at intervals of 1 myr for the purpose of investigating evolution of young oceanic lithosphere morphology and its variation through time using an innovative method that combines seafloor subsidence correction with interpolated isochrons and rotation poles reconstruction results are consistent with formation of abyssal hills every 1 to 2 myr in 2 3 myr old lithosphere at the outer edge of the ridge mountains as a result of transition from dynamic regime near the axis to isostatic regime of the flanks the oblique passage of structures formed at the axial valley walls through this transition zone may play a role in the development of inside corner high bathymetry asymmetric juxtaposition of abyssal hill morphology in reconstruction is indicative of independent formation and evolution of the morphotectonic fabric on opposing flanks the two major factors affecting asymmetric ridge flank morphology are found to be sense of axial offset and fluctuation of magmatic activity at the segment scale sense of axial offset determines the relative distribution of inside and outside corner bathymetry on the flanks enhanced magma supply and associated segment propagation may contribute to half spreading rate asymmetry accretion of thicker crust and formation of larger abyssal hills on the faster spreading flank consistent alignment in reconstruction of the base of the steep walls bounding inside corner bathymetry confirms that they mark the boundaries between segments on the flanks and that the deep sediment filled basins typically identified as discordant zones are attributable to outside corner bathymetry

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

landslide patterns reveal the sources of large earthquakes the distribution of fault slip in an earthquake controls seismic surface deformation and ground shaking and is the most direct record of fault response to tectonic stress detailed information about slip patterns in large earthquakes is only available where a dense local network of seismometers is in place elsewhere the evaluation of earthquake source and mechanism relies on observation of proxies such as surface change or damage intensity in upland areas the density of seismically induced landslides is strongly influenced by the intensity and duration of strong ground motion and therefore contains information about the earthquake source mechanism here we show that density patterns of co seismic landslides closely track the distribution of fault slip in two large thrust earthquakes in japan when adjusted for site effects landslide distributions readily obtained from remote sensed images can supplement or replace instrumental records of earthquakes opening historical and remote events for close geophysical investigation

statistical analysis of an earthquake induced landslide distribution the 1989 loma prieta california event the 1989 loma prieta california earthquake moment magnitude m 6 9 generated landslides throughout an area of about 15 000 km2 in central california most of these landslides occurred in an area of about 2000 km2 in the mountainous terrain around the epicenter where they were mapped during field investigations immediately following the earthquake the distribution of these landslides is investigated statistically using regression and one way analysis of variance anova techniques to determine how the occurrence of landslides correlates with distance from the earthquake source slope steepness and rock type the landslide concentration defined as the number of landslide sources per unit area has a strong inverse correlation with distance from the earthquake source and a strong positive correlation with slope steepness the landslide concentration differs substantially among the various geologic units in the area the differences correlate to some degree with differences in lithology and degree of induration but this correlation is less clear suggesting a more complex relationship between landslide occurrence and rock properties

a quantitative study of the axial topography of the mid atlantic ridge some basic characteristics of ridge axis topography are related to spreading rate and distance from neighboring transform faults for example the presence of an axial depression coincides in most cases with slow spreading rates and the overall depth of the ridge axis increases toward ridge transform intersections rtis on the other hand it is also well known that the relief and width of the axial valley on say the mid atlantic ridge mar vary along strike in an unpredictable manner the purpose of the present study is to quantify how much of the observed variation in the first order topography at the axis is related to changes in other parameters such as spreading rate and distance from rtis to carry out this test the zero age depth and the relief and width of the axial valley have been estimated on 46 profiles that cross the axis of the mar between the equator and 50 n full spreading rates 22 36 km ma zero age depth is here defined to be the depth at age zero of the best fit thermal subsidence trend axial valley relief and width have been measured with respect to the ridge flanks by the least squares fit of a gaussian bell the measured axial valley relief varies between 600 and 2100 m average 1300 m while the valley width varies between 16 and 62 km average 35 km the correlation between zero age depth axial valley relief and width latitude of axial crossing spreading rate distance from nearest rtt and offset on the nearby transforms has been investigated using linear regression techniques the main results of the present study are that 1 zero age depth significantly correlates with latitude of crossing distance from nearest rti and offset on the nearby transforms and 2 the variation in axial valley relief and width is essentially uncorrelated with spreading rate zero age depth distance from nearest rtt and offset on nearby transforms the preferred explanation for the observed spatial variation in axial valley geometry is that it reflects a temporal variation in fact if the rough abyssal hill topography typical of the mar flanks is created within the axial valley the shape of the axial valley cannot be steady state although the existence of an axial valley may be a steady state phenomenon this hypothesis is supported by the observation that the variability in axial valley relief is similar to the overall amplitude of abyssal hill topography measured as the residual on the thermal subsidence trend

models of ocean ridge lithospheric deformation dependence on crustal thickness spreading rate and segmentation we use three dimensional 3 d temperature and rheology models to investigate the effects of crustal thickness and ridge segmentation on mid ocean ridge lithospheric structure we find that crustal thickness variations associated with focused magma accretion at a slow spreading ridge segment can cause significant along axis gradients in crustal temperature and a pita pocket shaped weak zone in the lower crust that decouples brittle upper crust from upper mantle in contrast fast spreading ridge segments with little crustal thickness variation are found to be uniformly weak along axis the overthickened crust produced by ridge hotspot interaction alters the heat balance between magma emplacement and hydrothermal cooling creating an extremely weak lithosphere in a steady state model we apply a simple two dimensional 2 d cyclic faulting model to across axis sections of temperature and rheological structure slow spreading segments are predicted to have relatively large along axis variations in fault height and spacing in contrast fast spreading and hotspot affected segments are predicted to have much smaller variations in faulting styles except in the immediate vicinity of a major transform fault the presence or lack of a steady state axial rift valley is also predicted to depend on crustal thickness spreading rate and the ability of rift bounding normal faults to propagate along axis for fast spreading and hotspot affected segments the sizes of axial rift valleys are predicted to be small and may not be distinguishable from those of neovolcanic or magma chamber supported isostatic features this is in contrast to most slow spreading segments where axial rift valleys are predicted to be a dominant morphological feature for a slow spreading segment of great length however the axial rift valley size is predicted to diminish toward the segment center because large faults formed at segment distal ends cannot propagate through a large decoupling zone created by locally thickened crust at the segment center

on origin of near axis volcanism and faulting at fast spreading mid ocean ridges at fast and superfast spreading mid ocean ridges such as the east pacific rise a plate boundary is defined by a narrow tens to hundreds of meters wide neovolcanic zone within which the bulk of the upper oceanic crust is created however detailed near bottom observations indicate that the volcanic construction may occasionally persist several kilometers off of the ridge axis it has been proposed that off axis volcanism manifests tapping of a wide melting region that supplies magma to the ridge axis or spatial migration of magmatic sources in the crust and upper mantle we demonstrate that off axis eruptions may be a natural consequence of variations in magma supply rate even if the ridge axis is stationary in space and the magma delivery is perfectly focussed at the ridge axis theoretical modeling and field observations indicate that off axis volcanism may result from magma emplacement in sills that propagate toward the surface after their characteristic horizontal size exceeds their emplacement depth volcanic construction and faulting due to sill intrusions may contribute to the formation of abyssal hills arguably the most abundant relief form on earth fl 2001 elsevier science b v all rights reserved

landslide susceptibility mapping using geological data a dem from aster images and an artificial neural network ann an efficient and accurate method of generating landslide susceptibility maps is very important to mitigate the loss of properties and lives caused by this type of geological hazard this study focuses on the development of an accurate and efficient method of data integration processing and generation of a landslide susceptibility map using an ann and data from aster images the method contains two major phases the first phase is the data integration and analysis and the second is the artificial neural network training and mapping the data integration and analysis phase involve gis based statistical analysis relating landslide occurrence to geological and dem digital elevation model derived geomorphological parameters the parameters include slope aspect elevation geology density of geological boundaries and distance to the boundaries this phase determines the geological and geomorphological factors that are significantly correlated with landslide occurrence the second phase further relates the landslide susceptibility index to the important geological and geomorphological parameters identified in the first phase through ann training the trained ann is then used to generate a landslide susceptibility map landslide data from the 2004 niigata earthquake and a dem derived from aster images were used the area provided enough landslide data to check the efficiency and accuracy of the developed method based on the initial results of the experiment the developed method is more than 90 accurate in determining the probability of landslide occurrence in a particular area

detailed geological mapping of two contrasting second order segments of the mid atlantic ridge between oceanographer and hayes fracture zones 33 30 n 35 n we present detailed geological mapping of the axial valley floor and ridge flanks of two neighboring but contrasting spreading segments oh1 and oh3 of the mid atlantic ridge between oceanographer and hayes fracture zones new in situ observations from the submersible nautile correlated with swath bathymetry and acoustic backscattering data from these segments reveal that the along and across axis volcanic tectonic variability within second order segments is larger than commonly acknowledged segment oh1 is a long and robust segment with a narrow and shallow axial valley the most intense magmatic activity is found at the segment center where the thickest crust has been imaged suggesting focused magma supply away from this part of the segment faulting and sedimentary cover predominate in contrast the center of segment oh3 is dominated by extensive sedimentary cover fissuring and faulting furthermore the most recent constructional volcanism is located away from the segment center in a region of greater depth and thinner crust this relocation of volcanism suggests either a recent shift in the magmatic source or the last vestige of a centrally located source fed by lateral dike injection segment tip magmatic oscillations are suggested by the distribution of rock types at both segment ends serpentinized peridotites and associated dolerites are exposed at the massifs located at the intersection with nontransform offsets ntos whereas only basaltic rocks crop out on the nodal basin floors we suggest that the combination of low magmatic budget and extension taking place at the ntos during a segment retreat favors the uplift and exposure of ultramafic massifs

fault strain and seismic coupling on mid ocean ridges the contribution of extensional faulting to seafloor spreading along the east pacific rise epr axis near 3 s and between 13 n and 15 n is calculated using data on the displacement and length distributions of faults obtained from side scan sonar and bathymetric data it is found that faulting may account for of the order of 5 10 of the total spreading rate which is comparable to a previous estimate from the epr near 19 s given the paucity of normal faulting earthquakes on the epr axis a maximum estimate of the seismic moment release shows that seismicity can account for only 1 of the strain due to faulting this result leads us to conclude that most of the slip on active faults must be occurring by stable sliding laboratory observations of the stability of frictional sliding show that increasing normal stress promotes unstable sliding while increasing temperature promotes stable sliding by applying a simple frictional model to mid ocean ridge faults it is shown that at fast spreading ridges 90 mm yr the seismic portion of a fault ws is a small proportion of the total downdip width of the fault w the ratio ws w interpreted as the seismic coupling coefficient x and in this case x 0 in contrast at slow spreading rates 40 mm yr ws w and therefore x 1 which is consistent with the occurrence of large magnitude earthquakes mb 5 0 to 6 0 occurring for example along the mid atlantic ridge axis

magmato tectonic cyclicity at the ultra slow spreading southwest indian ridge evidence from variations of axial volcanic ridge morphology and abyssal hills pattern on axis deep tow side scan sonar data are used together with off axis bathymetric data to investigate the temporal variations of the accretion processes at the ultra slow spreading southwest indian ridge differences in the length and height of the axial volcanic ridges and various degrees of deformation of these volcanic constructions are observed in side scan sonar images of the ridge segments we interpret these differences as stages in an evolutionary life cycle of axial volcanic ridge development including periods of volcanic construction and periods of tectonic dismemberment using off axis bathymetric data we identify numerous abyssal hills with a homogeneous size for each segment these abyssal hills all display an asymmetric shape with a steep faulted scarp facing toward the axis and a gentle dipping volcanic slope facing away we suggest that these hills are remnants of old split axial volcanic ridges that have been transported onto the flanks and that they result from successive periods of magmatic construction and tectonic dismemberment i e a magmato tectonic cycle we observe that large abyssal hills are in ridge sections of thicker crust whereas smaller abyssal hills are in ridge sections of thinner crust this suggests that the magma supply controls the size of abyssal hills the abyssal hills in ridge sections of thinner crust are regularly spaced indicating that the magmato tectonic cycle is a pseudoperiodic process that lasts 0 4 m y about 4 to 6 times shorter than in ridge sections of thicker crust we suggest that the regularity of the abyssal hills pattern is related to the persistence of a nearly constant magma supply beneath long lived segments by contrast when magma supply strongly decreases and becomes highly discontinuous regular abyssal hills patterns are no longer observed