groundwater electromagnetic imaging in complex geological and topographical regions a case study of a tectonic boundary in the french alps very low frequency vlf audiomagnetotelluric amt and water geochemistry surveys were performed on the sur fretes ridge in the french alps to evaluate the groundwater circulation system within the ridge at this site temporal variations of the electric field have been observed in association with water level variations of neighboring artificial lakes the sur fretes ridge is 1 km wide and trends east west water samples were collected at 52 points distributed throughout the area vlf soundings were carried out along three parallel east west profiles and 7 amt soundings were carried out along an east west profile on the top of the ridge this site is characterized by a rugged topography of the ridge where geological and topographic trends are almost perpendicular making the structure fully three dimensional we constructed a 2 d resistivity model of the ridge from 2 d and 3 d analyses of the vlf and amt data associating geology and topography models when combined with the water chemistry data a m

source characteristics of the 2017 ms 7 0 jiuzhaigou china earthquake and implications for recent seismicity in eastern tibet

surface deformation and lower crustal flow in eastern tibet field observations and satellite geodesy indicate that little crustal shortening has occurred along the central to southern margin of the eastern tibetan plateau since about 4 million years ago instead central eastern tibet has been nearly stationary relative to southeastern china southeastern tibet has rotated clockwise without major crustal shortening and the crust along portions of the eastern plateau margin has been extended modeling suggests that these phenomena are the result of continental convergence where the lower crust is so weak that upper crustal deformation is decoupled from the motion of the underlying mantle this model also predicts east west extension on the high plateau without convective removal of tibetan lithosphere and without eastward movement of the crust east of the plateau

indian punch rifts tibet the strikes of late cenozoic normal faults in tibet fan systematically from a northwesterly to northeasterly direction from west to east they exhibit an axis of symmetry that bisects the himalayan arc and trends subparallel to india asia motion the two dimensional stress field inferred from the spatial pattern of normal fault orientations can be explained solely by collisional stresses localized along a southern part of the himalayan arc continued insertion of indian crust into tibet can explain the persistence of extension and may be increasing plateau crustal thickness and elevation coeval with rifting

synthetic normal faulting of the 9 january 2008 nima tibet earthquake from conventional and along track sar interferometry 1 we use synthetic aperture radar interferometry insar to derive the coseismic deformation field of the 9 january 2008 nima tibet earthquake the results show an asymmetric deformation pattern consistent with normal faulting on a nw dipping fault plane the complex line of sight los fringe pattern suggests that a second synthetic fault in the hanging wall of the mainshock rupture slipped during the event most likely during the largest aftershock we use conventional and along track insar data to invert for the geometry and the slip distribution on the two fault planes the focal mechanisms of the mainshock and its largest aftershock show normal faulting with a small left lateral strike slip component near the ne trending riganpei cuo fault which is consistent with our insar observation and inversion result this event suggests that normal faulting in addition to previously established conjugate strike slip deformation in the region contributes to the internal deformation of central tibet

mantle dynamics uplift of the tibetan plateau and the indian monsoon convective removal of lower lithosphere beneath the tibetan plateau can account for a rapid increase in the mean elevation of the tibetan plateau of 1000 m or more in a few million years such uplift seems to be required by abrupt tectonic and environmental changes in asia and the indian ocean in late cenozoic time the composition of basaltic volcanism in northern tibet which apparently began at about 13 ma implies melting of lithosphere not asthenosphere the most plausible mechanism for rapid heat transfer to the midlithosphere is by convective removal of deeper lithosphere and its replacement by hotter asthenosphere the initiation of normal faulting in tibet at about 8 3 ma suggests that the plateau underwent an appreciable increase in elevation at that time an increase due solely to the isostatic response to crustal thickening caused by india s penetration into eurasia should have been slow and could not have triggered normal faulting another process such as removal of relatively cold dense lower lithosphere must have caused a supplemental uplift of the surface folding and faulting of the indo australian plate south of india the most prominent oceanic intraplate deformation on earth began between about 7 5 and 8 ma and indicates an increased north south compressional stress within the indo australian plate a tibetan uplift of only 1000 m if the result of removal of lower lithosphere should have increased the compressional stress that the plateau applies to india and that resists india s northward movement from an amount too small to fold oceanic lithosphere to one sufficient to do so the climate of the equatorial indian ocean and southern asia changed at about 6 9 ma monsoonal winds apparently strengthened northern pakistan became more arid but weathering of rock in the eastern himalaya apparently increased because of its high altitude and lateral extent the tibetan plateau provides a heat source at midlatitudes that should oppose classical symmetric hadley circulation between the equator and temperate latitudes and that should help to drive an essentially opposite circulation characteristic of summer monsoons for the simple case of axisymmetric heating no dependence on longitude of an atmosphere without dissipation theoretical analyses by hou lindzen and plumb show that an axisymmetric heat source displaced from the equator can drive a much stronger meridianal monsoonlike circulation than such a source centered on the equator but only if heating exceeds a threshold whose level increases with the latitude of the heat source because heating of the atmosphere over tibet should increase monotonically with elevation of the plateau a modest uplift 1000 2500 m of tibet already of substantial extent and height might have been sufficient to exceed a threshold necessary for a strong monsoon the virtual simultaneity of these phenomena suggests that uplift was rapid approximately 1000 m to 2500 m in a few million years moreover nearly simultaneously with the late miocene strengthening of the monsoon the calcite compensation depth in the oceans dropped plants using the relatively efficient c4 pathway for photosynthesis evolved rapidly and atmospheric co2 seems to have decreased suggesting causal relationships and positive feedbacks among these phenomena both a supplemental uplift of the himalaya the southern edge of tibet and a strengthened monsoon may have accelerated erosion and weathering of silicate rock in the himalaya that in turn enhanced extraction of co2 from the atmosphere thus these correlations offer some support for links between plateau uplift a downdrawing of co2 from the atmosphere and global climate change as proposed by raymo ruddiman and froehlich mantle dynamics beneath mountain belts not only may profoundly affect tectonic processes near and far from the belts but might also play an important role in altering regional and global climates

mode of cenozoic east west extension in tibet suggesting a common origin of rifts in asia during the indo asian collision cenozoic rifts in tibet were traditionally interpreted as a result of topographic collapse of the tibetan plateau reaching the maximum elevation that can be supported by its mechanical strength recent studies have emphasized possible similarities between rifting in tibet and extension in the basin and range of the western united states however when examined in detail one finds that spacing of long 100 km rifts in tibet 100 300 km is significantly greater than that in the basin and range 20 40 km from south to north rift spacing decreases systematically from 191 67 km in the himalaya south of the indus yalu suture to 146 34 km in south tibet between the indus yalu and bangong nujiang sutures and farther north to 101 31 km in central tibet between the bangong nujiang and jinsha sutures instability analysis suggests that the mantle lithosphere must have been involved in east west tibetan extension specifically the widely spaced rifts in the himalaya and tibet may have been related to the presence of a relatively light crust density 2 90 g cm 3 and a strong mantle lithosphere 40 km thick and a factor of 5 stronger than the upper crust the observed systematic decrease in rift spacing can be explained by the known decrease in the crustal thickness in tibet from 70 80 km in the himalaya in the south to 50 55 km in central tibet in the north a regional comparison of rifts in east asia suggests that both the involvement of the mantle lithosphere and the age of rift initiation are similar for tibetan rifts the baikal rift and the shanxi graben this implies that topographic collapse or a convective event in the mantle cannot be the sole cause for the development of the tibetan rifts a regional boundary condition applied throughout east asia must be required

the displacement field of the landers earthquake mapped by radar interferometry geodetic data obtained by ground or space based techniques can be used to infer the distribution of slip on a fault that has ruptured in an earthquake although most geodetic techniques require a surveyed network to be in place before the earthquake1 3 satellite images when collected at regular intervals can capture co seismic displacements without advance knowledge of the earthquake s location synthetic aperture radar sar interferometry first introduced4 in 1974 for topographic mapping5 8 can also be used to detect changes in the ground surface by removing the signal from the topography9 10 here we use sar interferometry to capture the movements produced by the 1992 earthquake in landers california11 we construct an interferogram by combining topographic information with sar images obtained by the ers 1 satellite before and after the earthquake the observed changes in range from the ground surface to the satellite agree well with the slip measured in the field with the displacements measured by surveying and with the results of an elastic dislocation model as a geodetic tool the sar interferogram provides a denser spatial sampling 100 m per pixel than surveying methods1 3 and a better precision 3 cm than previous space imaging techniques12 13

variation of the electrical resistivity of large rock samples with stress many experimental and theoretical efforts have been devoted to the study of the electrical properties of rocks e g brace et al 1965 madden 1982 parkhomenko 1982 yamazaki 1966 special attention has been paid to possible relationships between variations of mechanical stresses inside the rock and variations of its electrical properties in reference to a possible technique of predicting earthquakes raleigh et al 1977 these studies were generally performed on small decimeter sized samples but the complexity of the physical processes involved and the heterogeneity of rocks in the field make it necessary to try to get results from larger blocks with dimensions of several decimeters sobolev et al 1983 or of meters this study it also appears quite desirable to look for information on the electrical properties of rocks at different scales from a centimeter to a kilometer say to see if some scaling laws could be experimentally established these scaling laws would allow inference of electrical properties at a given scale from the knowledge of the electrical properties at a smaller scale madden 1976 scaling law methods seem to be promising in seismogenesis studies e g allegre et al 1984 turcotte 1986

nyainqentanglha shan a window into the tectonic thermal and geochemical evolution of the lhasa block southern tibet 1 in the nyainqentanglha nqtl massif southern tibet a late cenozoic se dipping normal fault exhumed an oblique section of crust in its footwall u th pb dating of zircon and monazite from footwall exposures reveals a collage of felsic intrusions including cretaceous early tertiary and miocene granitoids ages of the latter span 10 m y suggesting semicontinuous or episodic miocene magmatism geochemical and isotopic analyses show a gangdese arc affinity indicating significant mantle heat and mass transfer in their formation and semicontinuous calc alkaline magmatism throughout the cenozoic indo asian collision the undeformed nature of the footwall cretaceous and miocene granitoids suggests that mesozoic cenozoic lhasa block deformation was thin skinned being concentrated in supracrustal assemblages this coupled with the lack of migmatites exposed in the nqtl implies the exposed crust was not a partial melt zone nor involved in large scale channel flow some 40ar 39ar thermochronologic studies of footwall k feldspars reveal that samples collected within several kilometers below the normal fault cooled prior to emplacement of young leucogranites indicating little perturbation of the background thermal structure since 15 ma this plus high melting temperatures and the lack of penetrative granitoid deformation requires that the melts formed at lower crustal levels and were emplaced rapidly to the midcrust seismic reflection results showing high bright spot anomalies in the midcrust along the nqtl rift may have imaged the youngest magmatic episode or its associated hydrothermal system

present day crustal motion within the tibetan plateau inferred from gps measurements 1 using the measurements of 726 gps stations around the tibetan plateau we determine the rigid rotation of the entire plateau in a eurasia fixed reference frame which can be best described by an euler vector of 24 38 0 42 n 102 37 0 42 e 0 7096 0 0206 ma the rigid rotational component accommodates at least 50 of the northeastward thrust from india and dominates the eastward extrusion of the northern plateau after removing the rigid rotation to highlight the interior deformation within the plateau we find that the most remarkable interior deformation of the plateau is a glacier like flow zone which starts at somewhere between the middle and western plateau goes clockwise around the eastern himalayan syntaxis ehs and ends at the southeast corner of the plateau with a fan like front the deformation feature of the southern plateau especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau the first order feature of crustal deformation of the northeastern plateau can be well explained by a three dimensional elastic half space dislocation model with rates of dislocation segments comparable to the ones from geological observations in the eastern plateau although gps data show no significant convergence between the eastern margin of the plateau and the sichuan basin a small but significant compressional strain rate component of 10 5 2 8 nstrain yr exists in a relatively narrow region around the eastern margin in addition a large part of the eastern plateau northeast of the ehs is not undergoing shortening along the northeastward convergence direction of the ehs but is stretching

field evidence for active normal faulting in tibet crustal thickening does not now occur in southern tibet field observations made during the chinese french expedition of 1980 support an earlier hypothesis based on a combined analysis of satellite images and fault plane solutions of earthquakes immediately north of the highest peaks of the himalayas the tectonic regime is dominated by east west extension we have mapped a large number of north south normal faults which sharply cut the glacial and post glacial morphology and followed several recent earthquake breaks along faults detected on satellite and aerial photographs microtectonic measurements in the quaternary suggest that the maximum principal stress is vertical

monitoring resistivity changes prior to earthquakes in parkfield california with telluric arrays a telluric array has been designed to monitor long period changes of resistivity in parkfield prior to the next characteristic earthquake there the array straddles the san andreas fault and utilizes dipoles which range from 5 to 18 km long a method of data analysis using robust processing in the time domain and singular value decomposition yields daily estimates of telluric coefficients which are stable to within 1 the array has detected several fluctuations above the noise level of the measurements most of these fluctuations are uncorrelated with bursts of seismic activity changes in water levels anomalous strain and creep or magnetic storms however the largest fluctuation in 2 years coincided with a tensor strain anomaly and both of these preceded a m 3 7 earthquake by approximately 1 month this is the largest earthquake to occur in parkfield since the array was installed

seismic resistivity changes observed at aburatsubo central japan revisited abstract earth s resistivity variation has been continuously recorded in a vault at aburatsubo central japan since 1967 in the previous works tidal coseismic and precursory resistivity variations were reported which were explained by strain induced changes based on the recent data obtained by a digital recorder and laboratory experiments newly conducted on the rock s electrical properties we have reexamined the nature of the seismic resistivity changes new findings so far obtained from in situ observation are as follows 1 a coseismic step takes place on arrival of the s wave rather than that of the p wave 2 the polarity of the coseismic step shows no correlation to the source mechanism of the earthquake but shows a clear seasonal variation i e positive steps appear in summer but are negative in winter 3 there is a seasonal variation in the earth s resistivity with minimum and maximum in october and in april respectively the polarity of coseismic resistivity steps has a good correlation with the rate of seasonal variation of the ground resistivity itself combining these observations with results of recently made laboratory experiments we present a tentative model for coseismic resistivity step generation which proposes mixing of temperature stratification in the shallow ground due to ground oscillation by seismic s waves

seismic and electrical properties of sandstones at low saturations laboratory measurements of elastic wave velocities attenuation and electrical resistivity of sandstones all show distinct changes in the measured properties at very low levels of water saturation velocity decreases attenuation reaches a maximum and electrical resistivity decreases over a limited range in saturation we assume that all the water at low saturations is present in the rock as a layer of uniform thickness covering the entire internal surface area of the sample with this model we calculate the thickness of surface water that corresponds to the distinct low saturation region in all cases for both the seismic and the electrical data the thickness is equal to one to four monolayers of water this is interpreted as marking the transition in the behavior of water in a sandstone from that of a surface adsorbed phase to a bulk water phase the changes in seismic properties can be modeled by considering the effect of adding surface and bulk water to grain contacts in a similar treatment the role of contacts is shown to be a dominant factor in the electrical resistivity of sandstones at low saturations such that the addition of water to the contact area causes a dramatic decrease in the electrical resistivity

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

seismicity of central tibet from project indepth iii seismic recordings as part of project international deep profiling of tibet and the himalaya iii a 400 km long densely spaced array of 57 broadband and short period seismic stations was deployed in central tibet from august 1998 through may 1999 although originally designed to image the lithosphere with teleseismic events the array also recorded numerous local and regional seismic events more than 900 local and regional events were detected on at least 10 stations during the 1 year deployment and we were able to locate 267 local earthquakes a substantial number of the events were found to cluster in or near large grabens and along known strike slip faults while other events show no obvious correlation with known structures in addition to spatial clustering at least one of the large clusters also exhibits temporal clustering that may be associated with magmatic or geothermal activity in the upper crust the average v p and v s are estimated to be 5 85 and 3 35 km sec for the upper crust and 7 0 and 3 9 km sec for the lower crust respectively the 50 focal mechanisms computed from this set of events are consistent with north south shortening and east west extension there are no clear indications of significant local perturbations in the regional stress field induced by the collision between india and eurasia the majority of the focal mechanisms indicate normal and strike slip faulting at least six of the newly computed focal mechanisms however indicate thrust faulting which is a phenomenon not well documented previously ninety nine percent of the local earthquakes have focal depths shallower than 25 km and the locations of the few deeper events are poorly constrained the shallow earthquake focal depths are consistent with high temperatures and proposed ductile or aseismic behavior in the middle to lower crust of central tibet figure 6 1 figure 6 a earthquake locations computed from this study shown on shaded topographic data triangles are indepth iii seismic stations circles are events and are scaled by magnitude graphic 2 a color version of this figure is available online at the ssa web site b earthquake locations shown with major geologic structures from taylor et al 2003 3 reproduced with permission m h taylor personal comm 2002 triangles are indepth iii seismic stations geologic structures are as in figure 2 4 1 pending yes 2 f1 embed inline graphic 1 gif 3 ref 46 4 f3

shallow structure of the yadong gulu rift southern tibet from refraction analysis of project indepth common midpoint data refracted arrivals on international deep profiling of tibet and the himalaya indepth common midpoint cmp data provide insight into the shallow structure of the yadong gulu rift in southern tibet this is the first such in formation available for the neogene quaternary rifts on the tibetan plateau geologic cross sections across three separate valleys within the rift have been constructed from these data and available surface geological information in each case the valleys are floored by asymmetric low velocity sedimentary fills ranging from 100 m to 1 5 km in thickness beneath all three the basement appears to dip gently to the east 5 seismic reflection data from one of these valleys nyinzhong show a 30 east dipping reflector within the basement beneath the valley that projects upward to the normal sense nyainqentanglha detachment exposed in the range immediately to the west field investigations by indepth personnel have additionally shown the existence of previously unrecognized normal sense shear zones bordering the other two valleys the newly discovered shear zones are 200 to 500 m thick and in both instances are characterized by moderately to steeply west dipping mylonites with top to west shear sense metamorphic minerals within the shear zones indicate at least amphibolite grade metamorphism with increasing metamorphic grade down section the seismic data coupled with the new geologic information and geomorphologic data from landsat imagery suggest that the structure of the northern yadong gulu rift is comparable to other well documented rift systems in which steep range front normal faults terminate at or sole into moderately dipping normal sense detachments at depth that have undergone substantial footwall uplift and rotation during extension this geometry implies that the extension of the tibetan plateau crust has been accommodated at depth by lateral flow within the middle crust it also suggests that e w extension of the plateau may have been substantially greater than has generally been presumed

postseismic strain following the 1989 loma prieta earthquake from gps and leveling measurements postseismic deformation in the 5 years following the 1989 loma prieta earthquake has been measured with the global positioning system and precise leveling postearthquake velocities at distances greater than 20 km from the coseismic rupture are not significantly different from those observed in the 20 years prior to the earthquake however velocities at stations within 20 km of the rupture exceed preearthquake rates and exhibit unanticipated contraction normal to the strike of the san andreas fault system a combination of forward modeling and nonlinear optimization suggests that the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2 9 cm yr on the san andreas fault and or the loma prieta rupture zone and 2 4 cm yr reverse slip along a buried fault within the foothills thrust belt the best fitting sources of postseismic deformation are all located at depths of less than 15 km we find no evidence for accelerated flow or shear below the loma prieta rupture in the first 5 years following the earthquake the inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture

radar interferometry and its application to changes in the earth s surface geophysical applications of radar interferometry to measure changes in the earth s surface have exploded in the early 1990s this new geodetic technique calculates the interference pattern caused by the difference in phase between two images acquired by a spaceborne synthetic aperture radar at two distinct times the resulting interferogram is a contour map of the change in distance between the ground and the radar instrument these maps provide an unsurpassed spatial sampling density 100 pixels km 2 a competitive precision 1 cm and a useful observation cadence 1 pass month 1 they record movements in the crust perturbations in the atmosphere dielectric modifications in the soil and relief in the topography they are also sensitive to technical effects such as relative variations in the radar s trajectory or variations in its frequency standard we describe how all these phenomena contribute to an interferogram then a practical summary explains the techniques for calculating and manipulating interferograms from various radar instruments including the four satellites currently in orbit ers 1 ers 2 jers 1 and radarsat the next chapter suggests some guidelines for interpreting an interferogram as a geophysical measurement respecting the limits of the technique assessing its uncertainty recognizing artifacts and discriminating different types of signal we then review the geophysical applications published to date most of which study deformation related to earthquakes volcanoes and glaciers using ers 1 data we also show examples of monitoring natural hazards and environmental alterations related to landslides subsidence and agriculture in addition we consider subtler geophysical signals such as postseismic relaxation tidal loading of coastal areas and interseismic strain accumulation we conclude with our perspectives on the future of radar interferometry the objective of the review is for the reader to develop the physical understanding necessary to calculate an interferogram and the geophysical intuition necessary to interpret it

quaternary extension in southern tibet field observations and tectonic implications we summarize evidence for quaternary and active faulting collected in the field during three sino french expeditions to southeastern tibet 1980 1982 detailed mapping of quaternary and active faults as well as microtectonic measurements indicate that normal faulting has been the dominant tectonic regime north of the himalayas in the last 2 0 5 m y the maximum horizontal principal stress in south tibet appears to be only the intermediate principal stress 2 1 being vertical south of the chord joining the eastern and western syntaxes of the himalayan arc extensional strains are principally localized within seven regularly spaced rift zones three of which have been studied in some detail the extension direction is determined to be n96 e 7 mainly from statistical averaging of strikes of newly formed normal faults throw rates on normal faults are evaluated for different time spans 2 0 5 m y 60 40 kyr and 10 2 kyr b p using structural and topographic reliefs as well as synglacial and postglacial vertical offsets the rate of quaternary extension is about 1 m y 1 along an 1100 km long ese traverse across south tibet this corresponds to a spreading rate of 1 0 6 cm yr this rate and the divergent horizontal projections of slip vectors of earthquakes along the himalayan front constrain the rate at which rigid india underthrusts southern tibet to be 2 1 cm yr although most of the normal faults appear to be independent of and nearly orthogonal to the e w mesozoic tertiary tectonic fabric the yadong gulu rift appears to be guided for over 130 km by the older oblique ne sw nyainqentanglha range and fault zones along it this reactivated zone is the most prominent left lateral strike slip fault system in se tibet excepting this zone and the vicinity of the se extremity of the karakorum fault quaternary strike slip faulting is rare in south tibet i e south of the chord between the syntaxes of the himalayan arc north of the chord the tectonic style is different there minor conjugate strike slip faulting is widespread and appears to control quaternary normal faulting which is more diffuse and subdued than in south tibet along the chord the presence of a major zone of active right lateral en echelon strike slip faults karakorum jiali fault zone probably reflects the greater facility of eastward extrusion in north central tibet in response to the northward push of india the eastern himalayan syntaxis may be an obstacle to such extrusion movements south of the chord

role of oblique convergence in the active deformation of the himalayas and southern tibet plateau noting similarities with subduction along curved oceanic trenches and using a simple block model we show that radial vergence evident in earthquake slip vectors along the himalayan deformation front east west extension on north trending normal faults in the himalayas and southern tibet and right lateral strike slip on the karakorum jiali fault zone can all result from basal shear caused by the indian plate sliding obliquely beneath tibet along a gently dipping arcuate plate boundary within the framework of this mechanism the normal faults in the himalayas and southern tibet are not proxies for the uplift history of tibet the distribution and style of the faults in the himalayas and southern tibet suggest that the basal drag from the underthrusting indian lithosphere extends northward beneath most of southern tibet

locations of selected small earthquakes in the zagros mountains the zagros mountains of southern iran are marked by a zone of high seismicity and accommodate a significant portion of the convergence between arabia and eurasia due to the lack of dense local seismic or geodetic networks the inferred kinematics of the collision in iran is mainly based on catalogs of teleseismically determined earthquake locations we surveyed all mw 4 5 earthquakes in the harvard centroid moment tensor hcmt and international seismological centre isc catalogs that occurred in the zagros mountains during the period 1992 2002 and that were spanned by interferometric synthetic aperture radar insar images from the ers 1 and 2 satellites we invert the observed deformation for the best fitting point source single fault plane and distributed fault slip for four earthquakes and one unexplained deformation event we find that we can precisely locate earthquakes that are too small to be well located by either the hcmt or isc catalogs allowing us to tie specific earthquakes to active geologic structures

surface deformation detected by alos palsar small baseline sar interferometry over permafrost environment of beiluhe section tibet plateau china abstract the evolution of permafrost and the active layer is highly related to biological diversity and climate change because of its feedback effects involving water and carbon storage in this study we firstly examined the relationship of active layer variation geomorphological processes and anthropogenic activities by means of small baseline synthetic aperture radar interferometry in beiluhe hoh xil natural reserve in tibet plateau tp china 3 5 yr observation span of l band alos palsar data june 2007 to december 2010 was used the estimated surface displacements primarily in the range of 20 mm yr 1 to 20 mm yr 1 and time series implied evolution of the active layer and permafrost beneath the motion trend along slopes was complicated due to the geomorphological processes and thus interdisciplinary interpretations were needed anthropogenic influences on this frail permafrost environment were significant as evident from the remarkable surface settlement along the embankment of qinghai tibet railway it is crucial and necessary to monitor this permafrost plateau owing to the consequences arising from a combination of factors related to climate change geo hazard prediction nature conservation and regional sustainable development

continuous deformation of the tibetan plateau from global positioning system data global positioning system velocities from 553 control points within the tibetan plateau and on its margins show that the present day tectonics in the plateau is best described as deformation of a continuous medium at least when averaged over distances of 100 km deformation occurs throughout the plateau interior by ese wnw extension and slightly slower nne ssw shortening relative to eurasia material within the plateau interior moves roughly eastward with speeds that increase toward the east and then flows southward around the eastern end of the himalaya crustal thickening on the northeast ern and eastern margins of the plateau occurs over a zone 400 km wide and cannot be the result of elastic strain on a single major thrust fault shortening there accommodates much of india s penetration into eurasia a description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field

oblique stepwise rise and growth of the tibet plateau two end member models of how the high elevations in tibet formed are i continuous thickening and widespread viscous flow of the crust and mantle of the entire plateau and ii time dependent localized shear between coherent lithospheric blocks recent studies of cenozoic deformation magmatism and seismic structure lend support to the latter since india collided with asia 55 million years ago the rise of the high tibetan plateau likely occurred in three main steps by successive growth and uplift of 300 to 500 kilometer wide crustal thrust wedges the crust thickened while the mantle decoupled beneath gently dipping shear zones did not sediment infilling bathtub like of dammed intermontane basins formed flat high plains at each step the existence of magmatic belts younging northward implies that slabs of asian mantle subducted one after another under ranges north of the himalayas subduction was oblique and accompanied by extrusion along the left lateral strike slip faults that slice tibet s east side these mechanisms akin to plate tectonics hidden by thickening crust with slip partitioning account for the dominant growth of the tibet plateau toward the east and northeast

some thoughts on the use of insar data to constrain models of surface deformation noise structure and data downsampling repeat pass interferometric synthetic aperture radar insar provides spatially dense maps of surface deformation with potentially tens of millions of data points here we estimate the actual covariance structure of noise in insar data we compare the results for several independent interferograms with a large ensemble of gps observations of tropospheric delay and discuss how the common approaches used during processing of insar data affects the inferred covariance structure motivated by computational concerns associated with numerical modeling of deformation sources we then combine the data covariance information with the inherent resolution of an assumed source model to develop an efficient algorithm for spatially variable data resampling or averaging we illustrate these technical developments with two earthquake scenarios at different ends of the earthquake magnitude spectrum for the larger events our goal is to invert for the coseismic fault slip distribution for smaller events we infer the hypocenter location and moment we compare the results of inversions using several different resampling algorithms and we assess the importance of using the full noise covariance matrix

global seismicity of 2003 centroid moment tensor solutions for 1087 earthquakes abstract centroid moment tensor cmt solutions are presented for 1087 earthquakes that occurred during 2003 the solutions are obtained using the method of dziewonski et al dziewonski a m chou t a woodward j h 1981 determination of earthquake source parameters from waveform data for studies of global and regional seismicity j geophys res 86 2825 2852 and applying corrections for aspherical earth structure as represented by the whole mantle shear velocity model sh8 u4l8 of dziewonski and woodward dziewonski a m woodward r l 1992 acoustic imaging at the planetary scale in emert h harjes h p eds acoustical imaging vol 19 plenum press new york pp 785 797 the model of inelastic attenuation of durek and ekstrom durek j j ekstrom g 1996 a radial model of inelasticity consistent with long period surface wave attenuation bull seism soc am 86 144 158 is used to predict the decay of the waveforms the focal mechanisms of the largest or otherwise significant earthquakes of 2003 are reviewed

surface displacement of the 17 may 1993 eureka valley california earthquake observed by sar interferometry satellite synthetic aperture radar sar interferometry shows that the magnitude 6 1 eureka valley earthquake of 17 may 1993 produced an elongated subsidence basin oriented north northwest parallel to the trend defined by the aftershock distribution whereas the source mechanism of the earthquake implies a north northeast striking normal fault the 3 millimeter accuracy of the radar observed displacement map over short spatial scales allowed identification of the main surface rupture associated with the event these observations suggest that the rupture began at depth and propagated diagonally upward and southward on a west dipping north northeast fault plane reactivating the largest escarpment in the saline range

ferrihydrite and allophane in four andepts from hawaii and implications for their classification abstract the mineralogy and composition of the waimea kukaiau akaka and hilo soils on the island of hawaii were studied using methods which included moessbauer spectroscopy and chemical dissolution the hilo soil which experiences 3000 mm year rainfall and the akaka soil 3800 mm year rainfall both contain large amounts about 25 of iron oxides of short range order together with other iron oxides gibbsite and allophane the iron oxides of short range order have characteristics similar to those of the reactive mineral ferrihydrite which is known to occur in a wide range of soils these characteristics however in two respects x ray diffraction and acid oxalate solubility do not rule out the presence or admixture of the much less known feroxyhite another closely related iron oxide of short range order most samples from these two soils dry irreversibly to give hard aggregates a property probably related to the presence of the iron oxides of shortrange order both the hilo and the akaka soils are classified as hydrandepts in the current usda soil taxonomy in the new proposed order of andisols these two soils would become hydrudands it is desirable to recognise the presence of short range order iron oxides in these soils the kukaiau soil currently classified as a dystrandept which occurs in a lower rainfall zone 1500 mm year contains about 25 allophane and lesser amounts of ferrihydrite other iron oxides and gibbsite the waimea soil occurs in the lowest rainfall zone 1000 mm year and the dominant mineral is halloysite but some allophane ferrihydrite and hematite are also present this soil is currently classified as a eutrandept under the andisol proposal the kukaiau and waimea soils would be a hapludand and a haplustand respectively quartz mica and other layer silicates were present in all four of the soils suggesting that there have been additions of eolian material

late cenozoic right lateral strike slip faulting in southern tibet field observations collected during the sino french himalaya tibet cooperation project 1980 1982 show that right lateral faulting between southern and northern tibet roughly along the chord joining the eastern and western syntaxes of the himalayan arc is a major component of the active tectonics north of the himalayas just north of the well developed rifts of southern tibet we studied three right lateral 100 200 km long strike slip faults forming an en echelon array along that chord evidence for earthquake surface breaks was found on each of these faults for the m 8 beng co or damxung strike slip earthquake of november 18 1951 rupture parameters could be constrained to be 8 2 m and l 90 km offset glacial and postglacial morphological markers 105 years and 104 years b p imply displacement rates of the order of 1 2 cm yr on the three faults the en echelon fault zone appears to extend westward 2000 km across the plateau to the karakorum fault and is thus referred to as the karakorum jiali fault zone kjfz fast rates of slip on it and on faults along the northern rim of tibet appear to contrast with the slower rates of deformations in the interior of the plateau our estimates of slip rates on the strike slip and normal faults of southeastern tibet suggest that eastward extrusion of north tibet between the right lateral kjfz and the left lateral altyn tagh and kun lun faults absorbs at least 30 of the present convergence between india and asia we propose an instantaneous velocity model of the active tectonics of asia compatible with such faulting rates and geometries evidence for tertiary right lateral strike slip movements in southern tibet and around the eastern syntaxis of the himalayas is also found in the structural record offsets of various large scale geological features imply that these movements have been large

characterization of a weathering sequence of soils derived from volcanic ash in cameroon taxonomic mineralogical and agronomic implications the characteristics of eight pedons developed in quaternary basaltic pyroclasts in western cameroon under humid tropical conditions are reported the soil weathering sequence consists of an andept tropept udalf udult association andic properties physico chemical characteristics and weathering stage clearly distinguish the taxonomic units the total reserve in bases trb and the clay content measured after adequate h2o dispersion with na resins both appear to be suitable weathering indices clay mineralogy of non andic soils shows direct relationships between interstratified halloysite smectite content cec of the clay fraction and weathering stage the weathering stage of the investigated soils is reflected not only in their components and classification but also in their nutrient status and banana crop performance

temporal variations in the electrical resistivity of the earth s crust an electrical resistivity monitoring experiment was conducted on a portion of the san andreas fault near hollister california in 1979 and early 1980 receiving dipoles up to 20 km away from a 140 a 2 km transmitting dipole were used to monitor apparent resistivities with accuracies as high as 0 1 for some of the sites several of the transmitter receivers clearly show long term changes in resistivity greater than the data errors annual variations at a site outside the fault zone exceed 10 and sites in the fault zone show month to month changes of a few percent there are also significant variations in the vicinity of the transmitter which would be expected to produce correlated changes at other sites but this was not observed in the data there were no earthquakes of magnitudes greater than 3 0 during this period of high accuracy monitoring so that no conclusions can be drawn about changes in resistivity associated with major strain events future experiments to relate resistivity changes to earthquakes must not only have high sensitivity but must also be designed to distinguish such an event from normal background fluctuations that we have measured unless the resistivity variations associated with the event are of the order of several percent their detection will be a truly formidable task

pressure induced temperature variations in an underground quarry abstract temperature measurements have been performed in the rock and atmosphere of an underground limestone quarry in vincennes france in the atmosphere temperature variations associated with variations of the atmospheric pressure are continuously observed with an average coupling of 70 m c hpa at a period of 4 min 35 m c hpa at 1 h and 3 m c hpa at 1 day and an increasing phase advance for increasing period at the highest frequencies the coupling is close to its adiabatic value of 80 m c hpa the reduction of coupling with decreasing frequency is interpreted as diabatic thermal stabilisation of the atmosphere by heat flow and coupled feedback due to phase changes of water during extreme events such as the tempests that occurred in france in december 1999 additional effects were observed in the atmosphere and in the rock material as well pressure induced temperature variations may be important to study in underground monitoring experiments and may be a useful tool for the characterisation of nuclear waste storage sites

radar interferogram filtering for geophysical applications the use of sar interferometry is often impeded by decorrelation from thermal noise temporal change and baseline geometry power spectra of interferograms are typically the sum of a narrow band component combined with broad band noise we describe a new adaptive filtering algorithm that dramatically lowers phase noise improving both measurement accuracy and phase unwrapping while demonstrating graceful degradation in regions of pure noise the performance of the filter is demonstrated with sar data from the ers satellites over the jakobshavns glacier of greenland

coseismic slip from the 6 october 2008 mw6 3 damxung earthquake tibetan plateau constrained by insar observations coseismic deformation fields of the 6 october 2008 m w6 3 damxung earthquake were obtained from interferometric synthetic aperture radar by using three descending and two ascending envisat images significant coseismic surface deformation occurred within 20 km 20 km of the epicenter with a maximum displacement of 0 3 m along the satellite line of sight we model a linear elastic dislocation in a homogeneous half space and use a nonlinear constraint optimized algorithm to estimate the fault location geometry and slip distribution the results indicate a moment magnitude m w6 3 and the earthquake is dominated by oblique normal and right lateral slip with a maximum slip of 2 86 m at depth of 8 km the rupture plane is about 15 km 14 km with strike s190 w and dip 55 to nw located at a secondary fault of the southeastern piedmont of the nyainqentanglha mountains slip on normal faults in the tibetan plateau contributes to the rift evolution

weathering sequence of soils from volcanic ash involving allophane and halloysite new zealand abstract the clay minerals in a series of soils from rhyolitic ash having the same stratigraphy but different leaching environments were estimated quantitatively by oxalate dissolution infrared spectroscopy differential thermal analysis electron microscopy and x ray diffraction three soils were studied in detail these were the kereone soil mean annual rainfall 1200 mm the ohaupo soil 1400 mm and the mairoa soil 2600 mm the kereone soil contained halloysite as the predominant clay mineral whereas the mairoa soil was mainly allophanic the ohaupo soil contained considerable amounts of both allophane and halloysite thus the allophane content of the soils increased as rainfall increased reflecting a sequence of increased l leaching the si concentration in soil solution decreased as rainfall increased also reflecting increasing leaching of the soils at mairoa si is rapidly removed and allophane al si 2 1 with monomeric silicate is formed whereas at kereone less leaching occurs si levels are higher and halloysite al si 1 1 with polymeric silicate is formed at intermediate sites either allophane or halloysite may form the often reported situation of younger allophanic beds overlying older 10 000 year halloysitic beds may not be due to allophane weathering to halloysite but may result from lower temperature and drier climate during the last glacial maximum between 10 000 and 26 000 years before present bp a new weathering scheme for volcanic ash in new zealand is presented

a deforming block model for the present day tectonics of tibet 1 we use gps data from 45 sites across the tibetan plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the india eurasia collision zone the plateau is cut by a few major rapidly slipping strike slip fault zones with broadly distributed strain between those zones the gps velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau the boundaries of the four blocks in this model correspond to the major rapidly slipping faults a rigid block model with a smaller number of blocks fits the data poorly and can be rejected we estimate that 5 9 0 7 mm yr of extension in the n69 w direction occurs on the yadong gulu rift south of the plateau localized extension may extend as far north as the nyainqentanglha range we find 7 4 0 7 mm yr of right lateral slip on the karakorum jiali fault zone significantly slower than that previously estimated from offset geologic features our deforming block model and a two dimensional single fault screw dislocation model give lower and upper bounds of 4 4 1 1 and 10 3 0 4 mm yr on the slip rate on the kunlun fault respectively comparable in its highest to the long term slip rate observed geologically the distributed deformation is surprisingly uniform over the tibetan plateau qaidam basin and qilian shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction n32 e this strain field is a combination of shortening and extension that produces little net dilatation 1 area loss per million years at present the broadly distributed strain most likely represents slip on many faults each with a relatively low slip rate distributed conjugate strike slip faulting is the most plausible mechanism to produce the observed strains as supported by the record of medium to large earthquakes within the plateau the distributed deformation is just as important in the accommodation of the total india eurasia convergence as is slip on the major faults the eastward motion of central tibet is as large as 50 of the convergence rate between india and eurasia however this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike slip faults as suggested by past extrusion models instead much of this eastward extrusion is driven by the internal extension of the plateau our inference is in agreement with the model of f shen et al 2001 that suggested east west extension north south contraction and eastward plateau growth dominate the present tectonics of the tibetan plateau

insar observations of low slip rates on the major faults of western tibet two contrasting views of the active deformation of asia dominate the debate about how continents deform i the deformation is primarily localized on major faults separating crustal blocks or ii deformation is distributed throughout the continental lithosphere in the first model western tibet is being extruded eastward between the major faults bounding the region surface displacement measurements across the western tibetan plateau using satellite radar interferometry insar indicate that slip rates on the karakoram and altyn tagh faults are lower than would be expected for the extrusion model and suggest a significant amount of internal deformation in tibet

coseismic deformation from the 1999 mw 7 1 hector mine california earthquake as inferred from insar and gps observations we use interferometric synthetic aperture radar insar and global positioning system gps observations to investigate static deformation due to the 1999 m w 7 1 hector mine earthquake that occurred in the eastern california shear zone interferometric decorrelation phase and azimuth offset measurements indicate regions of surface and near surface slip which we use to constrain the geometry of surface rupture the inferred geometry is spatially complex with multiple strands the southern third of the rupture zone consists of three subparallel segments extending about 20 km in length in a n45 w direction the central segment is the simplest with a single strand crossing the bullion mountains and a strike of n10 w the northern third of the rupture zone is characterized by multiple splays with directions subparallel to strikes in the southern and central the average strike for the entire rupture is about n30 w the interferograms indicate significant along strike variations in strain which are consistent with variations in the ground based slip measurements using a variable resolution data sampling routine to reduce the computational burden we invert the insar and gps data for the fault geometry and distribution of slip we compare results from assuming an elastic half space and a layered elastic space results from these two elastic models are similar although the layered space model predicts more slip at depth than does the half space model the layered model predicts a maximum coseismic slip of more than 5 m at a depth of 3 to 6 km contrary to preliminary reports the northern part of the hector mine rupture accommodates the maximum slip our model predictions for the surface fault offset and total seismic moment agree with both field mapping results and recent seismic models the inferred shallow slip deficit is enigmatic and may suggest that distributed inelastic yielding occurred in the uppermost few kilometers of the crust during or soon after the earthquake