tectonics of the central zagros iran deduced from microearthquake seismicity summary microearthquakes in central zagros recorded for 7 weeks in 1997 lie in a 6 8 km zone that is likely located beneath 11 km of sediments they are not located on an active decollement between the sediments and the crystalline crust but rather define a pattern of nnw sse trending lineaments parallel to the fold axes observed at the surface the spacing between the seismic lineaments is 15 20 km and therefore different from that between the folds 10 15 km which suggests that there is not a simple relationship between the two focal mechanisms and precise relative locations are consistent with nw se striking reverse faulting connected by nnw sse striking right lateral strike slip faults the dip of the reverse faults is not certain but is likely ne for the northernmost faults the strain pattern deduced from the p axes is remarkably similar to the shortening deduced from gps based geodesy suggesting that microearthquakes are the response of the prefractured brittle crust to strain rather than localized on single active faults

imaging crustal discontinuities and the downgoing slab beneath western crete the migration of teleseismic receiver functions yields high resolution images of the crustal structure of western crete data were collected during two field campaigns in 1996 and 1997 by networks of six and 47 short period three component seismic stations respectively a total of 1288 seismograms from 97 teleseismic events were restituted to true ground displacement within a period range from 0 5 to 7 s the application of a noise adaptive deconvolution filter and a new polarization analysis technique helped to overcome problems with local coda and noise conditions the computation and migration of receiver functions results in images of local crustal structures with unprecedented spatial resolution for this region the crust under crete consists of a continental top layer of 15 20 km thickness above a 20 30 km thick subducted fossil accretionary wedge with a characteristic en echelon fault sequence the downgoing oceanic moho lies at a depth of 40 60 km and shows a topography or undulation with an amplitude of several kilometres as a consequence of slab depth and distribution of local seismicity the mediterranean ridge is interpreted as the recent accretionary wedge

observing coseismic gravity change from the japan tohoku oki 2011 earthquake with goce gravity gradiometry the japan tohoku oki earthquake 9 0 mw of 11 march 2011 has left signatures in the earth s gravity field that are detectable by data of the gravity field recovery and climate experiment grace mission because the european space agency s esa satellite gravity mission gravity field and steady state ocean circulation explorer goce launched in 2009 aims at high spatial resolution its measurements could complement the grace information on coseismic gravity changes although time variable gravity was not foreseen as goal of the goce mission we modeled the coseismic earthquake geoid signal and converted this signal to vertical gravity gradients at goce satellite altitude we combined the single gradient observations in a novel way reducing the noise level required to detect the coseismic gravity change subtracted a global gravity model and applied tailored outlier detection to the resulting gradient residuals furthermore the measured gradients were along track filtered using different gradient bandwidths where in the space domain gaussian smoothing has been applied one year periods before and after earthquake occurrence have been compared with the modeled gradients the comparison reveals that the earthquake signal is well above the accuracy of the vertical gravity gradients at orbital height moreover the obtained signal from goce shows a 1 3 times higher amplitude compared with the modeled signal besides the statistical significance of the obtained signal it has a high spatial correlation of 0 7 with the forward modeled signal we conclude therefore that the coseismic gravity change of the japan tohoku oki earthquake left a statistically significant signal in the goce measured gravity gradients

gravity changes before and after the 2008 m w 7 9 wenchuan earthquake at pixian absolute gravity station in more than a decade absolute gravity repeated measurements at pixian station about 35 km away from the epicenter of the 2008 wenchuan mw 7 9 earthquake have been carried out over more than a decade four pre earthquake measurements at the pixian station show 30 gals increase from 2002 to 2008 but 13 measurements since 2008 shows that the trend of gravity increase ended after the wenchuan earthquake we analyzed the gravity effects from ground vertical motions using data from continuous gps stations collocated with the pixian absolute gravimetry station and surficial and hydrological processes using local hydrological data we found that these effects are much smaller than the observed gravity increase before the earthquakes the continuously gravity increase before the 2008 wenchuan earthquake cannot be explained by the groundwater level change and vertical deformation and related superficial reasons all absolute gravity was measured by the fg 5 gravimeter in this study the high precision gravity change revealed that the pre earthquake gravity increase may be caused by strain and mass fluid transfer in broad seismogenic source regions further studies are needed to validate such pre earthquake gravity changes which however are difficult to be resolved from space based gravity models

crustal dilatation observed by grace after the 2004 sumatra andaman earthquake we report the detection of an earthquake by a space based measurement the gravity recovery and climate experiment grace satellites observed a 15 microgalileo gravity change induced by the great december 2004 sumatra andaman earthquake coseismic deformation produces sudden changes in the gravity field by vertical displacement of earth s layered density structure and by changing the densities of the crust and mantle grace s sensitivity to the long spatial wavelength of gravity changes resulted in roughly equal contributions of vertical displacement and dilatation effects in the gravity measurements the grace observations provide evidence of crustal dilatation resulting from an undersea earthquake

determination of earthquake epicentroids by inversion of gravity variation data in the bttz region china abstract during the last decade and a half precise measurements of gravity variations have been carried out in the beijing tianjin tangshan zhangjiakou bttz region in china a possible seismogenic mechanism of a combined dilatancy model cdm for the bttz region has been proposed by kuo and sun 1993 the model consists of the dilatancy diffusion the dilatancy instability and the fault zone dilatancy models gravity variations in space and time associated with the model involve a tectonically stressed volume surrounding a small volume of an impending rupture fault zone they refer to the center of effective mass of the total stress volume which is defined as hypocentroid the projection of which on the earth s surface is defined as epicentroid this paper attempts to confirm the above stated concept of epicentroid associated with the fourteen earthquakes of magnitude mainly 4 5 which occurred in 1981 95 in the bttz region by means of a proposed least squares inversion method using observed gravity variation data on the basis of the 1976 tangshan earthquake the 1989 datong earthquake and these fourteen earthquakes an empirical relationship between the maximum variations of gravity and magnitude was first established iterative inversions of observed gravity variation data were then carried out inversion results show that 1 the separation of the epicentroids and epicenters range from 0 to about 40 km 2 the epicenters of these fourteen earthquakes are generally located at the terminations of the faults or at the intersections of the faults whereas the epicentroids are inevitably located within intact tectonic blocks and 3 the epicentroid of an earthquake at least in the bttz region as attested appears to be determinable

deep crustal structure and flexure of the arabian plate beneath the zagros collisional mountain belt as inferred from gravity observations the zagros mountain belt region a neogene continental collisional zone between arabia and iran that is characterized by a suture a folded belt and a foreland basin is unusual among active mountain belts in that its 6 12 km thick sedimentary cover is shortening predominantly by folding while the basement is apparently thickening along numerous high angle reverse faults we have used over 9000 gravity measurements in the region in conjunction with limited seismological observations and geological cross sections of the uppermost 10 km of crust to infer the deeper crustal structure beneath the region crustal models constrained by the bouguer anomalies and other seismological and geological data are characterized by a moho that dips about 1 to the northeast beneath the folded belt and increases in dip to about 5 near the main zagros thrust mzt the moho depth increases from 40 km beneath the leading edge of the foreland basin the mesopotamian foredeep and persian gulf to as much as 65 km beneath the mzt alternative models that incorporate a subducted oceanic crust that is attached to the underthrusting arabian crust deviate little in their moho configurations from the above simpler models negative isostatic residual anomalies are interpreted to indicate local overcompensation beneath the foreland basin and near the folded belt and beneath the mzt we show that underthrust sedimentary rocks of the converging margins along the suture zone may account for the negative isostatic residual anomalies near the mzt however to explain the rest of the isostatic anomalies requires other forces to be acting on this collisional plate boundary for example elastic flexure models required a combination of topography and subsurface loads or downward force the origin of which is not clear to approximate the bouguer or isostatic residual anomalies associated with the foreland basin and the folded belt the topography load of the zagros mountain belt is insufficient to cause the required deflection of the underthrusting arabian plate a combination of isostatic elastic flexure and horizontal compression forces acting on the edge of the arabian craton and the transitional lithosphere of central iran appears to best model the crust of the zagros region we propose a model in which the lower crust of the converging arabian plate located beneath the zagros is being shortened and thickened plastically between the seismogenic rigid upper crust and a rigid uppermost mantle lid the mantle lid probably decoupled from the lowermost crust un der thrusts the iranian crustal blocks thus confined from below the horizontally compressed plastic lower crust hydraulically depresses the moho and raises the faulted and folded brittle upper crust in isostatic equilibrium

a network of superconducting gravimeters detects submicrogal coseismic gravity changes with high resolution continuous gravity recordings from a regional network of superconducting gravimeters we have detected permanent changes in gravity acceleration associated with a recent large earthquake detected changes in gravity acceleration are smaller than 10 8 meters seconds 2 1 micro galileo about 10 9 times the surface gravity acceleration and agree with theoretical values calculated from a dislocation model superconducting gravimetry can contribute to the studies of secular gravity changes associated with tectonic processes

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

gravity anomalies flexure and deformation of the converging indian lithosphere in nepal and sikkim darjeeling himalayas researchers ubiquitously noted that the common processes of partitioning oblique convergence in response to drag from the trench hanging plate simultaneously produce radial slips along strike translation and extension parallel to the deformation front here we focus on the area between nepal and sikkim darjeeling himalayas and carry out gravity and finite element stress modeling of the strike orthogonal converging indian lithosphere we delineate the geometries of different layers and their interfaces through gravity modeling the optimum model parameters along with rheological parameters of different layers are used for finite element modeling finite element modeling is done with boundary conditions of keeping the upper surface free and rigidly fixing the section of the northern boundary below the main himalayan thrust we impart on its frontal section an amount of 6 1012 n m force equivalent to resistive force of the himalayan tibet system and analyze the maximum and minimum compressive stress fields evolved in the lithosphere we testify our observations with earthquake database and other geophysical and geological studies we note that an increasing flexing of the indian lithosphere beyond the main boundary thrust becomes maxima between the main central thrust and south tibetan detachment in both the areas however more steepening of the moho boundary is identified in the sikkim darjeeling himalaya this abrupt change in lithospheric geometry beneath the greater himalaya is likely correlated with the sharp elevation changes in the topography although the highest seismicity concentration is dominant in this zone the lesser and the tethys himalayas in sikkim darjeeling area also record relatively fair seismic activity more compressive stress field in different layers right within the sharp bending zone supports this observation we thus propose that the sharp bending zone beneath the greater himalaya is suffering maximum deformation and the deformation is continued in the mantle too we also identify both right lateral shear and radial vergence slip which are presumably associated with the general dynamics and kinematics of the himalaya

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

seismotectonics of the zagros continental collision zone and a comparison with the himalayas accurate focal depths of 16 medium to large zagros earthquakes were determined from identification of surface reflected phases by comparing observed long period p waves with synthetic seismograms all events are shallow 6 12 km and show no tendency to deepen toward the main zagros thrust geological and geophysical evidence suggests that most of these earthquakes probably occurred within the uppermost precambrian basement because the focal mechanisms of these events indicate high angle reverse faulting the events do not occur on a single detachment surface but rather reflect horizontal shortening of the basement on numerous short segmented 8 probably occurred along this detachment a comparative study of the zagros with the himalayas suggests that the active tectonics of the zagros continental collision zone and the iranian blocks arc similar to those of the himalayas and the tibetan terranes in oligocene time

seismic structure of iran from surface and body wave data summary an investigation of the lithospheric structure of the iranian plateau has been undertaken in order to find complementary information bearing on the tectonic evolution of the plateau the phase velocity dispersion of the fundamental mode rayleigh waves between the wwssn stations shiraz tabriz and mashad and between the sites of the iranian long period array and maio sro have been obtained from well dispersed wavetrains generated by eight great circle earthquakes the aftershocks of the destructive tabas earthquake in central iran which were accurately located by a field survey recorded clear p and s phases at maio providing supplementary travel time information for the interpretation of the phase velocity data the uppermost mantle p wave velocities beneath iran obtained in a previous study asudeh were also used in the analysis an alpine type crust was found for the iranian plateau while uppermost mantle velocities ranging from low velocity mantle in eastern iran to a high velocity shield like structure in the west of the country

grace detects coseismic and postseismic deformation from the sumatra andaman earthquake 1 we show that spherical harmonic sh solutions of the gravity recovery and climate experiment grace are now of sufficient quality to observe effects of co seismic and post seismic deformation due to the rupture from the mw 9 3 sumatra andaman earthquake on december 26 2004 and its companion nias earthquake mw 8 7 on march 28 2005 the improved ggm 03 sh level 2 solutions and improved filtering methods provide estimates with spatial resolution comparable to earlier estimates from range rate level 1 grace data the gravityfield disturbance extends over 1800 km along andaman and sunda subduction zones and changes with time following events gravity changes may be due to afterslip viscoelastic relaxation or other processes associated with dilatation satellite gravity measurements from grace provide a unique new measure of deformation and post seismic processes associated with major earthquakes especially in areas which are primarily oceanic citation chen j l c r wilson b d tapley and s grand 2007 grace detects coseismic and postseismic deformation from the sumatraandaman earthquake geophys res lett 34 l13302

is it possible that a gravity increase of 20 μgal yr 1 in southern tibet comes from a wide range density increase with absolute gravimetric observations from 2010 to 2013 in the southern tibet chen et al 2016 reported a gravity increase of up to 20 gal yr and concluded that it is possible if there was a density increase in a disk range of 580 km in diameter here we used observations from the gravity satellites gravity recovery and climate experiment grace over 12 years to evaluate whether the model was practical because a mass accumulation in such a large spatial range is well within the detectability ability of grace the gravity trend based on their model is orders of magnitude larger than the grace observation thus negating its conclusions we then evaluated contributions from seasonal variation lakes glaciers rivers precipitation and snowfall and concluded that these factors cannot cause such a large gravity signal finally we discussed some possible explanations for the gravity increase of 40 gal in two years

numerical simulations of global scale high resolution hydrological crustal deformations 1 high resolution load induced crustal deformations calculated from numerical models are tested for their ability to predict hydrologically induced station height variability as they are known to be large enough to affect epoch wise parameters obtained from the analysis of global geodetic networks loading contributions due to terrestrial water storage as given by global hydrological models are calculated on a 0 5 global regular grid with daily temporal resolution apart from the dominant seasonal variations the hydrological loading signal discloses also rapid changes exceeding 1 mm in several regions that can be associated with major precipitation events and river floods locally strong loading signals with exceptionally high amplitudes in many cases even with nonseasonal nature occur along the major river channels only high resolution loading calculations considering also the water mass anomalies stored in the model river flow can resolve the correct amplitudes in the surrounded area up to 100 km distance the comparison of the modeled hydrological surface deformation with gps station time series shows that high resolution hydrological loading estimates based on global scale models are able to explain a considerable fraction up to 54 of the observed vertical station movements caused by continental water storage variations

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

a re assessment of focal depth distributions in southern iran the tien shan and northern india do earthquakes really occur in the continental mantle summary we investigate the depth distribution of earthquakes within the continental lithosphere of southern iran the tien shan and northern india by using synthetic seismograms to analyse p and sh body waveforms in the zagros mountains of southern iran earthquakes are apparently restricted to the upper crust depths of 20 km whereas in the tien shan and northern india they occur throughout the thickness of the continental crust to depths of 40 45 km we find no convincing evidence for earthquakes in the continental mantle of these regions in spite of previous suggestions to the contrary and question whether seismicity in the continental mantle is important in any part of the world in some regions such as iran the aegean tibet and california seismicity is virtually restricted to the upper continental crust whereas in others including parts of east africa the tien shan and northern india the lower crust is also seismically active although usually less so than the upper crust such variations cannot reliably be demonstrated from published catalogue or bulletin locations even from ones in which depth resolution is generally improved in contrast to the oceanic mantle lithosphere in which earthquakes certainly occur the continental mantle lithosphere is we suggest virtually aseismic and may not be significantly stronger than the lower continental crust these variations in continental seismogenic thickness are broadly correlated with variations in effective elastic thickness suggesting that the strength of the continental lithosphere resides in the crust and require some modification to prevalent views of lithosphere rheology

separating climate induced mass transfers and instrumental effects from tectonic signal in repeated absolute gravity measurements we estimate the signature of the climate induced mass transfers in repeated absolute gravity measurements based on satellite gravimetric measurements from the gravity recovery and climate experiment grace mission we show results at the globe scale and compare them with repeated absolute gravity ag time behavior in three zones where ag surveys have been published northwestern europe canada and tibet for 10 yearly campaigns the uncertainties affecting the determination of a linear gravity rate of change range 3 4 nm s 2 a in most cases in the absence of instrumental artifacts the results are consistent with what is observed for long term repeated campaigns we also discuss the possible artifact that can result from using short ag survey to determine the tectonic effects in a zone of high hydrological variability we call into question the tectonic interpretation of several gravity changes reported from stations in tibet in particular the variation observed prior to the 2015 gorkha earthquake

the crustal and upper mantle structure of the interior arabian platform summary the crustal and upper mantle velocity structure of the interior arabian platform is derived using the spectral analysis of long period p wave amplitude ratios the ratio of the vertical to the horizontal component is utilized to obtain crustal transfer functions using the thomson haskell matrix formulation for horizontally layered crustal models 20 earthquakes recorded at the long period station ryd between azimuths n20 w and n150 e were selected for the analysis based on the following criteria focal depths in the range 5 to 215 km body wave magnitudes greater than 5 0 and epicentral distances in the range 7 to 97 a careful quality check of the data left us with six events out of 29 that had short epicentral distances 20 to be analysed the selection criterion for the final model in the forward modelling process was based on the correlation coeycient between observed and theoretical transfer function the model suggested that the crust consists of five distinct layers the upper crustal layer has a p wave velocity of about 5 6 km s 1 and is about 3 km thick the second layer has a velocity of about 6 3 km s 1 and is 10 km thick the third layer has a velocity of 6 6 km s 1 and is 8 km thick the fourth layer has a velocity of 6 9 km s 1 and is 15 km thick the lower layer has a velocity of about 7 6 km s 1 and is 10 km thick for the mohorovicic discontinuity a velocity of 8 3 km s 1 for the upper mantle and 46 km depth are indicated

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

statistical evaluation of efficiency and possibility of earthquake predictions with gravity field variation and its analytic signal in western china this paper aimed at assessing gravity variations as precursors for earthquake prediction in the tibet xizang qinghai xinjiang sichuan region western china we here take a statistical approach to evaluate efficiency and possibility of earthquake prediction we used the most recent spatiotemporal gravity field variation datasets of 2002 2008 for the region that were provided by the crustal movement observation network of china cmonc the datasets were space sparse and time discrete in 2007 2010 13 earthquakes ms 6 0 occurred in the region the observed gravity variations have a statistical correlation with the occurrence of these earthquakes through the molchan error diagram tests that lead to alarms over a good fraction of space time the results show that the prediction efficiency of amplitude of analytic signal of gravity variations is better than seismicity rate model and thd and absolute value of gravity variation implying that gravity variations before earthquake may include precursory information of future large earthquakes

pn velocities beneath iran abstract in active tectonic areas like iran where the coverage of seismograph stations is inadequate but earthquakes occur frequently uppermost mantle body wave velocities are conventionally determined by using a single station and an array of earthquake sources this method fails when earthquakes are mislocated or source areas have varied structures an extension of the traditional surface wave two station method is developed for body waves and shown to be independent of mislocation errors it thus gives accurate estimates of body wave velocities along two station paths with greatly reduced errors uppermost mantle p wave p n velocities are determined along several paths in iran using this method and show zones of low velocity corresponding to zones of high attenuation and quaternary volcanic activity in the country a remarkably high p n velocity of 8 30 km s is found for the zagros area of western iran more typical of shield like structures than that of tectonic areas

dynamical forcing and mesoscale organization of precipitation bands in a midwest winter cyclonic storm abstract a winter snowstorm developed on 10 11 february 1988 over the midwestern united states and produced several inches of snowfall locally over east central illinois analysis of the mesoscale organization of the storm revealed the presence of complex banded structure throughout its 17 h evolution three distinct types of mesoscale precipitation bands were identified during the course of the storm using a 10 cm doppler radar as part of the university of illinois winter precipitation program the bands had different orientations directions of movement relationships to synoptic scale frontal zones and mechanisms for development the mesoscale organization of this storm system is reviewed mesoscale synoptic scale and doppler analyses of the storm structure are presented the role of boundary layer convergence conditional symmetric instability and frontogenetical forcing in the formation and maintenance of the different mesoscale precipitation bands is discussed

lithospheric structure of the arabian shield and platform from complete regional waveform modelling and surface wave group velocities summary regional seismic waveforms reveal significant differences in the structure of the arabian shield and the arabian platform we estimate lithospheric velocity structure by modelling regional waveforms recorded by the 1995 1997 saudi arabian temporary broadband deployment using a grid search scheme we employ a new method whereby we narrow the waveform modelling grid search by first fitting the fundamental mode love and rayleigh wave group velocities the group velocities constrain the average crustal thickness and velocities as well as the crustal velocity gradients because the group velocity fitting is computationally much faster than the synthetic seismogram calculation this method allows us to determine good average starting models quickly waveform fits of the jon and sn body wave arrivals constrain the mantle velocities the resulting lithospheric structures indicate that the arabian platform has an average crustal thickness of 40 km with relatively low crustal velocities average crustal p and s wave velocities of 6 07 and 3 50 km s 1 respectively without a strong velocity gradient the moho is shallower 36 km and crustal velocities are 6 per cent higher with a velocity increase with depth for the arabian shield fast crustal velocities of the arabian shield result from a predominantly mafic composition in the lower crust lower velocities in the arabian platform crust indicate a bulk felsic composition consistent with orogenesis of this former active margin p and s wave velocities immediately below the moho are slower in the arabian shield than in the arabian platform 7 9 and 4 30 km s 1 and 8 10 and 4 55 km s respectively this indicates that the poisson s ratios for the uppermost mantle of the arabian shield and platform are 0 29 and 0 27 respectively the lower mantle velocities and higher poisson s ratio beneath the arabian shield probably arise from a partially molten mantle associated with red sea spreading and continental volcanism although we cannot constrain the lateral extent of a zone of partially molten mantle

modeling gravity variations caused by dilatancies abstract one postulated earthquake mechanism is the dilatancy model the dilatations due to deformation microfracture fracture and stress relaxation either accompanied by fluid invasion or not change the density the geometrical configuration in space and the porosity and the contents of the stressed volume of a tectonically active region observed gravity therefore is expected to respond to the sequence of events in the deformation cycle of dilatation in this paper a formulation of the gravity variations associated with the dilatation processes based on a combined dilatancy model is given the combined dilatancy model consists of the dilatancy diffusion the dilatancy instability and the fault zone dilatancy models for numerical calculations the total tectonically active region involved is represented by a vertical finite right circular cylinder within which the fault zone volume of the potential hypocentral region represented by a disk is embedded the cylinder has a radius of 40 km and thickness of 15 km with the bottom of the cylinder coinciding with the depth of a tectonically detached zone the disk is 2 km thick and 11 km in radius with the bottom of the disk at a depth of 15 km this representation is compatible with that of earthquakes of magnitude 4 5 that frequently occurred through the last decade or so in the beijing tianjin tangshan zhangjiakou bttz region in china the results of the calculations show that the variation forms of gravity changes are a function of space and time depending upon the size and shape of both the total tectonically active region and the fault zone volume therefore the calculation of theoretical gravity variations for a specific region comparable to that of the bttz region may be made on the basis of a thorough prior knowledge of the geological setting and the tectonic stress distribution of that region

the geology of the persian gulf gulf of oman region a synthesis during the mesozoic most of the arabian peninsula persian gulf south western iran and eastern iraq constituted the arabian platform deformation of the musandam peninsula in the late cretaceous and mid tertiary by compression subduction from the east and southwest collision of the arabian platform and eurasian plate along the zagros crush zone during the oligocene or early miocene and emplacement of the zagros mountains by gravitational sliding during the neogene and pleistocene have reduced the platform area to the persian gulf other factors that contributed to the reduction of the arabian platform include the uplift of the arabian peninsula during the opening of the red sea in the tertiary tectonism of the infracambrian hormuz salt upwarp of the platform sediment cover by basement uplift and or salt tectonics and a 600 to 400 m drop in sea level since the cretaceous at present tectonism in the region is restricted to the northern edge of the gulf of oman where the arabian plate is subducting the eurasian plate from the south and to the zagros crush zone where the arabian and eurasian plates are colliding with one another

the structure and evolution of a continental winter cyclone part ii frontal forcing of an extreme snow event abstract the production of a narrow heavy occasionally convective snowband that fell within a modest surface cyclone on 19 january 1995 is examined using gridded model output from a successful numerical simulation performed using the university of wisconsin nonhydrostatic modeling system it is found that the snowband was produced by a thermally direct vertical circulation forced by significant lower tropospheric warm frontogenesis in the presence of across front effective static stability differences as measured in terms of the equivalent potential vorticity pve the sometimes convective nature of the snowband resulted from the development of freely convective motions forced by frontal lifting of the environmental stratification model trajectories demonstrate that a stream of warm moist air ascended through the trowal portion of the warm occluded structure that developed during the cyclone life cycle the lifting of air in the trowal was in this case forced by lower tropospheric frontogenesis occ

mesoscale dynamics in the palm sunday tornado outbreak abstract radar and satellite imagery suggest that strong mesoscale forcing occurred in the palm sunday tornado outbreak on 27 march 1994 parallel lines of severe thunderstorms within each of three mesoscale convective systems developed just ahead of a cold front in mississippi and alabama on this date analyses of routine meteorological observations barograph data and forecasts from the eta and ngm models and a mesoscale research model mass are used to examine the relative roles of large scale dynamics and mesoscale processes in triggering and organizing the mesoscale convection quasigeostrophic forcing was absent in the outbreak region likewise a thermally direct circulation system transverse to the upper level jet that was present to the northwest of the outbreak region was decoupled from the strong low level ascent occurring in northern alabama and mississippi at the time of the outbreak strong ageostrophic frontogenesis in the presence of conditional symmetric instability csi was the chief

saudi arabian seismic refraction profile a traveltime interpretation of crustal and upper mantle structure abstract the crustal and upper mantle compressional wave velocity structure across the southwestern arabian shield has been investigated by a 1000 km long seismic refraction profile the profile begins in mesozoic cover rocks near riyadh on the arabian platform trends southwesterly across three major precambrian tectonic provinces traverses cenozoic rocks of the coastal plain near jizan and terminates at the outer edge of the farasan bank in the southern red sea more than 500 surveyed recording sites were occupied and six shot points were used including one in the red sea two dimensional ray tracing techniques used to analyze amplitude normalized record sections indicate that the arabian shield is composed to first order of two layers each about 20 km thick with average velocities of about 6 3 km s and 7 0 km s respectively west of the shield red sea margin the crust thins to a total thickness of less than 20 km beyond which the red sea shelf and coastal plain are interpreted to be underlain by oceanic crust a major crustal inhomogeneity at the northeast end of the profile probably represents the suture zone between two crustal blocks of different composition elsewhere along the profile several high velocity anomalies in the upper crust correlate with mapped gneiss domes the most prominent of which is the khamis mushayt gneiss based on their velocities these domes may constitute areas where lower crustal rocks have been raised some 20 km two intracrustal reflectors in the center of the shield at 13 km depth probably represent the tops of mafic intrusives the mohorovicic discontinuity beneath the shield varies from a depth of 43 km and mantle velocity of 8 2 km s in the northeast to a depth of 38 km and mantle velocity of 8 0 km s depth in the southwest near the shield red sea transition two velocity discontinuities occur in the upper mantle at 59 and 70 km depth the crustal and upper mantle velocity structure of the arabian shield is interpreted as revealing a complex crust derived from the suturing of island arcs in the precarnbrian the shield is currently flanked by the active spreading boundary in the red sea

crustal uplift and sea level rise in northern cascadia from gps absolute gravity and tide gauge data we combine data from nine gps absolute gravity and tide gauge stations to estimate the relation between sea level rise vertical motion and solid earth processes in the pacific northwest gps vertical velocities in itrf2000 and absolute gravity rates are well correlated with a gradient of 0 2 0 1 gal mm 1 but show a significant offset of 0 53 0 30 gal yr 1 2 2 1 3 mm yr 1 95 confidence tide gauge and gps data indicate a northeast pacific regional sea level rise of 1 7 0 5 mm yr 1 aligned to itrf2000 or an unlikely regional sea level fall of 0 5 0 5 mm yr 1 aligned to absolute gravity although we cannot rule out a bias in the gps reference frame alignment our results suggest a possible absolute gravity bias by a long period mass increase from an unknown near surface or deep seated source the impact of such a mass increase on gravity vertical motion and sea level remains to be defined

seismic evidence for an ancient rift beneath the cumberland plateau tennessee a detailed analysis of broadband teleseismic p waveforms broadband receiver functions developed from teleseismic p waveforms recorded on the midperiod passband of regional seismic test network station rscp are inverted for vertical velocity structure beneath the cumberland plateau tennessee the detailed broadband receiver functions are obtained by stacking source equalizd horizontal components of teleseismic p waveforms the resulting receiver functions are most sensitive to the shear velocity structure near the station a time domain inversion routine utilizes the radial receiver function to determine this structure assuming a crustal model parameterized by many thin flat lying homogeneous layers lateral changes in structure are identified by examining azimuthal variations in the vertical structure the results reveal significant rapid lateral changes in the midcrustal structure beneath the station that are interpreted in relation to the origin of the east continent gravity high located northeast of rscp the results from events arriving from the northeast show a high velocity midcrustal layer not present in results from the southeast azimuth this velocity structure can be shown to support the idea that this feature is part of a keweenawan rift system another interesting feature of the derived velocity models is the indication that the crust mantle boundary beneath the cumberland plateau is a thick probably laminated transition zonemore between the depths of 40 and 55 km a result consistent with interpretations of early refraction work in the area less

basement faulting and the focal depths of the larger earthquakes in the zagros mountains iran summary the present day seismicity of the zagros seems to occur on high angle reverse faults distributed across the whole width of the belt it does not indicate activity on a single inclined thrust surface and there do not seem to have been any well located events at intermediate depths modelling of the long period teleseismic body waves of seven large earthquakes presented here shows their focal depths to be in the range 8 15 km this is thought to indicate faulting in the uppermost basement beneath the sedimentary cover though the absence of published seismic refraction results renders the sediment thickness uncertain faulting of this type and depth may occur on inherited normal faults which have subsequently been reactivated as thrusts such reactivation allows considerable shortening to take place in the early stages of continental collision without the subduction or excessive thickening of continental crust

absolute gravity monitoring of water storage variation in a karst aquifer on the larzac plateau southern france in this study we attempt to understand the water storage variations in a karst aquifer on the larzac plateau south of france using absolute gravimetry on this karst system water input is exclusively rainfall and draining occurs at the durzon perennial spring in a karstic valley our basis assumption is that water storage in the vadose zone epikarst and infiltration zone has a significant effect on surface gravity through newtonian attraction the karst aquifer is hence being monitored since january 2006 with monthly absolute gravity measurements at three sites the gravity measurements are corrected for regional scale gravity using water storage models in order to obtain gravity variations related exclusively to the local water storage variations the gravity variations exhibit an important seasonal component 10 15 mu gal corresponding to a variation of equivalent water stab thickness of similar to 24 36 cm water storage variation seen by gravimetry is not spatially uniform on the studied karst system corroborating current geomorphologic observations and interpretations finally we use a global mass balance consideration linking rainfall evapotranspiration and spring discharge to provide a conceptual framework for the understanding of observed gravity variations

coseismic and postseismic deformation of the 2011 tohoku oki earthquake constrained by grace gravimetry 1 spaceborne gravimetry data from the gravity recovery and climate experiment grace are processed using spatio spectral slepian localization analysis enabling the high resolution detection of permanent gravity change associated with both coseismic and postseismic deformation resulting from the great 11 march 2011 mw 9 0 tohoku oki earthquake the grace observations are then used in a geophysical inversion to estimate a new slip model containing both coseismic slip and after slip the grace estimated moment for the total slip up to the end of july 2011 is estimated as 4 59 0 49 1022 n m equivalent to a composite mw of 9 07 0 65 if the moment for the tohoku oki main shock is assumed to be 3 8 1022 n m the contribution from the after slip is estimated to be 3 0 1021 12 8 1021 n m in good agreement with a postseismic slip model inverted from gps data we conclude that grace data provide an independent constraint to quantify co and post seismic deformation for the tohoku oki event

earthquakes on the kazerun line in the zagros mountains of iran strike slip faulting within a fold and thrust belt summary the kazerun line is a transverse valley of about 200 km long that obliquely crosses the regular anticlines of the zagros fold belt in sw iran at its northern end it is a clear fault which can be mapped on the surface anticline axes die out or bend towards this valley but do not cross it six moderate sized earthquakes that occurred close the the kazerun line and within a 25 km area involved right lateral strike slip motion parallel to the strike of the valley they indicate that the kazerun line is the surface expression of a buried strike slip fault slip vectors in these strike slip earthquakes are different from those of neighbouring reverse fault earthquakes suggesting that the kazerun line accommodates some of the shortening between arabia and central iran by an elongation of the zagros mountains parallel to strike the centroid depths and the source dimensions of these earthquakes combined with the lack of seismogenic surface faulting in the zagros suggest to us that all these earthquakes involve faulting in the metamorphic basement beneath the sedimentary cover the sedimentary cover is almost certainly decoupled from the basement by several thick evaporite horizons the seismicity of the kazerun line thus demonstrates how lateral interruptions to the regularity of a fold belt can arise from faulting in the basement and not just from lateral ramps between the thrust sheets that deform the sedimentary cover

seismological constraints on the crustal structure beneath the zagros mountain belt iran summary the zagros mountain belt of western iran results from the collision of the arabian and central iran continental blocks the stage of the collision is unclear and the crustal structure of the zagros is rather poorly known in this study we investigate the velocity structure of the crust and upper mantle beneath the ghir region located in the central zagros using data collected by a temporary local seismological network including a broad band instrument the structures of the sedimentary cover and the upper crystalline crust are estimated from the inversion of p and s traveltimes of local earthquakes recorded on a dense seismological network the upper crust consists of an 11 km thick sedimentary layer v p 4 70 km s 1 above a 8 km thick upper crystalline crust v p 5 85 km s 1 the velocity of the lower crust and the depth of the moho are found using receiver function analysis of teleseismic earthquakes the lower crystalline crust is unusually slow v p 6 5 km s 1 and 27 km thick the upper bound for the total crustal thickness beneath the ghir region is 46 2 km a comparison of the thickness of the crystalline crust of the zagros with available information for the thickness of the crystalline crust of the arabian platform shows that at present the zagros has a thinner crust the current crustal thickness beneath the zagros is comparable to the pre collision crustal thickness of the arabian platform suggesting that the zagros is now in a very early stage of continental collision

measuring lithospheric stretching on tethyan passive margins preliminary estimates of lithospheric stretching have been made by examining 63 stratigraphic sections from the northern and southern tethyan margins southeast france to bulgaria the study was centred on the italian southern alps the dolomites a portion of the southern margin within the external zones of the alpine orogen sections were decompacted and backstripped using the standard procedure allowing for errors in palaeowater depth estimates theoretical subsidence curves based on the finite duration stretching model were then fitted to the resultant water loaded subsidence curves in an attempt to clarify the pre compressional tectonic history of the region according to our results stretching started in the early to mid triassic and lasted 30 40 ma this conclusion is broadly in agreement with some previously published estimates the stretching factor is generally small 1 1 1 3 especially in southeast france and northern italy larger values of occur in the balkans c 1 5 to our knowledge the finite duration stretching model has not yet been applied to water loaded stratigraphic sections from the tethyan belt theory and observation appear to agree well

gravity increase before the 2015 mw 7 8 nepal earthquake the 25 april 2015 nepal earthquake mw 7 8 ruptured a segment of the himalayan front fault zone four absolute gravimetric stations in southern tibet surveyed from 2010 2011 to 2013 and corrected for secular variations recorded up to 22 40 1 11 gal yr of gravity increase during this period the gravity increase is distinct from the long wavelength secular trends of gravity decrease over the tibetan plateau and may be related to interseismic mass change around the locked plate interface under the himalayan tibetan plateau we modeled the source region as a disk of 580 km in diameter which is consistent with the notion that much of the southern tibetan crust is involved in storing strain energy that drives the himalayan earthquakes if validated in other regions high precision ground measurements of absolute gravity may provide a useful method for monitoring mass changes in the source regions of potential large earthquakes

gravity measurements and their variations before the 2008 wenchuan earthquake it was recognized 50 years ago that coseismic gravity changes take place during a large earthquake in the past 30 years there have been research efforts devoted to investigating possible associations between gravity variations and earthquakes in china before the wenchuan m w 7 9 earthquake a group of researchers at the second crust monitoring and application center of china earthquake administration noticed significant gravity changes in a region covering the well known south north earthquake belt in china and suggested in 2006 that the possibility for a major earthquake to occur near wenchuan in either 2007 or 2008 was high these researchers used gravity changes as the primary earthquake precursor to make the suggestion in this article we report the method used for repeated regional gravity survey the procedures for gravity survey data analysis and the characteristics of gravity variations before the wenchuan earthquake that ruptured on 12 may 2008 although gravity changes at a number of locations in the region surrounding wenchuan were significant more research is needed to investigate whether these gravity variations could be viewed as a precursor of the wenchuan earthquake uncertainties in the reported gravity variations include inevitable measurement errors related to ground gravity surveys covering a large region hydrologic effects on gravity and the effects of vertical crustal movements on gravity other limitations of the data are that the density of the gravity observation stations is coarse and that the time intervals of the surveys were two to three years long based on these observations we make several recommendations about data collection and data analysis procedures that would enhance future earthquake research using gravity monitoring data in china