dwindling groundwater resources in northern india from satellite gravity observations 1 northern india and its surroundings home to roughly 600 million people is probably the most heavily irrigated region in the world temporal changes in earth s gravity field in this region as recorded by the grace satellite mission reveal a steady large scale mass loss that we attribute to excessive extraction of groundwater combining the grace data with hydrological models to remove natural variability we conclude the region lost groundwater at a rate of 54 9 km3 yr between april 2002 the start of the grace mission and june 2008 this is probably the largest rate of groundwater loss in any comparable sized region on earth its likely contribution to sea level rise is roughly equivalent to that from melting alaskan glaciers this trend if sustained will lead to a major water crisis in this region when this non renewable resource is exhausted

three dimensional vp and vp vs models in the coso geothermal area california seismic characterization of the magmatic system we combine classic and state of the art techniques to characterize the seismic and volcanic features in the coso area in southern california seismic tomography inversions are carried out to map the variations of vp vs and vp vs beneath coso the velocities in the top layers of our model are correlated with the surface geological features the indian wells valley with high silica content sediment strata shows low velocity anomalies up to 3 km depth whereas the major mountain ranges such as the south sierra nevada and the argus range show higher velocities the resulting three dimensional velocity model is used to improve absolute locations for all local events between january 1981 and august 2011 in our study area we then apply similar event cluster analysis waveform cross correlation and differential time relocation methods to improve relative event location accuracy a dramatic sharpening of seismicity patterns is obtained after using these methods we also estimate high resolution near source vp vs ratio within each event cluster using the differential times from waveform cross correlation the in situ vp vs method confirms the trend of the velocity variations from the tomographic results an anomalous low velocity body with low vp vs and vp vs ratios corresponding to the ductile behavior underlying the coso geothermal field from 6 to 12 km depth can be explained by the existence of frozen felsic magmatic materials with the inclusion of water the material is not likely to include pervasive partial melt due to a lack of high vp vs ratios

monitoring groundwater storage changes in complex basement aquifers an evaluation of the grace satellites over east africa although the use of the gravity recovery and climate experiment grace satellites to monitor groundwater storage changes has become commonplace our evaluation suggests that careful processing of the grace data is necessary to extract a representative signal especially in regions with significant surface water storage i e lakes reservoirs in our study we use cautiously processed datasets including grace lake altimetry and model soil moisture to reduce scaling factor bias and compare grace derived groundwater storage changes to in situ groundwater observations over parts of east africa over the period 2007 2010 a strong correlation between in situ groundwater storage change and grace groundwater estimates spearman s 0 6 is found piecewise trend analyses for the grace groundwater estimates reveal significant negative storage changes that are attributed to groundwater use and climate variability further analysis comparing groundwater and satellite precipitation datasets permits identification of regional groundwater characterization for example our results identify potentially permeable and or shallow groundwater systems underlying tanzania and deep and or less permeable groundwater systems underlying the upper nile basin regional groundwater behaviors in the semi arid regions of northern kenya are attributed to hydraulic connections to recharge zones outside the sub basin boundary our results prove the utility of applying grace in monitoring groundwater resources in hydrologically complex regions that are under sampled and where policies limit data accessibility this article is protected by copyright all rights reserved

local seismicity near the actively deforming corbetti volcano in the main ethiopian rift abstract corbetti is currently one of the fastest uplifting volcanoes globally with strong evidence from geodetic and gravity data for a subsurface inflating magma body a dense network of 18 stations has been deployed around corbetti and hawassa calderas between february 2016 and october 2017 to place seismic constraints on the magmatic hydrothermal and tectonic processes in the region we locate 122 events of magnitudes between 0 4 and 4 2 using a new local velocity model the seismicity is focused in two areas directly beneath corbetti caldera and beneath the city of hawassa the shallower 0 5 km depth below sea level b s l earthquakes beneath corbetti are mainly focused in ew to ns elongated clusters at urji and chabbi volcanic centres this distribution is interpreted to be mainly controlled by a northward propagation of hydrothermal fluids away from a cross rift pre existing fault source mechanisms are predominantly strike slip and different to the normal faulting away from the volcano suggesting a local rotation of the stress field these observations along with a low vp vs ratio are consistent with the inflation of a gas rich sill likely of silicic composition beneath corbetti in contrast the seismicity beneath hawassa extends to greater depth 16 km b s l these earthquakes are focused on 8 10 km long segmented faults which are active in seismic swarms one of these swarms in august 2016 is focused between 5 and 16 km depth b s l along a steep normal fault beneath the city of hawassa highlighting the earthquake hazard for the local population

shumagin seismic gap alaska peninsula history of great earthquakes tectonic setting and evidence for high seismic potential the shumagin seismic gap a segment of the plate boundary along the eastern aleutian arc has not ruptured during a great earthquake since at least 1899 1903 because at least 77 years have elapsed since the shumagin gap last ruptured in a great earthquake and repeat times for the 1938 rupture zone and part of the shumagin gap are estimated to be 50 to 90 years a high probability exists for a great earthquake to occur within the shumagin gap during the next one to two decades reconsideration of the rupture zones of the aleutian earthquakes of 1938 1946 and 1948 suggests that those events did not break the interplate boundary beneath the shumagin islands thus the shumagin seismic gap extends from the western end of the 1938 rupture zone to the eastern end of that of 1946 these boundaries also coincide with transverse structural features at least the eastern half of the shumagin gap broke in great earthquakes in 1788 and 1847 and possibly in 1898 1903 the shumagin gap is probably not the result of aseismic slip rather plate motion is accommodated there seismically and episodically and can be expected to produce large earthquakes in the future although there is no definitive evidence of long term precursors of a possible future earthquake several observations suggest that the shumagin gap is in an advanced stage of the earthquake cycle both teleseismic and local network data indicate a near absence of seismic activity m 2 above a depth of 30 km along the main thrust zone within the gap this is in strong contrast to adjacent portions of the arc where seismic activity is scattered across most of the main thrust zone two earthquakes with high stress drops 600 900 bars which occurred at the base of the main thrust zone may indicate the accumulation of a considerable amount of strain energy within the gap a possible seismic gap at the eastern end of the aftershock zone of the aleutian earthquake of 1957 has been identified near unalaska island an earthquake that nucleates in the shumagin gap could also rupture the possible unalaska gap to the west the 1938 aftershock zone to the east or both with resultant magnitude up to mw 9 0 alternatively the shumagin gap alone or in one of the above combinations could rupture in a series of very large earthquakes instead of a single great shock past alaska aleutian earthquakes including those of 1788 1938 1946 1957 1964 and 1965 have generated very large tsunamis future large earthquakes in the shumagin islands region could generate wave heights of several tens of meters along shorelines near the rupture areas the shumagin gap is one of two major gaps along the united states portion of the alaska aleutian plate boundary and is one of the few areas in the united states where processes leading to a great earthquake are likely to be observed within a reasonable span of time

grace measurements of mass variability in the earth system monthly gravity field estimates made by the twin gravity recovery and climate experiment grace satellites have a geoid height accuracy of 2 to 3 millimeters at a spatial resolution as small as 400 kilometers the annual cycle in the geoid variations up to 10 millimeters in some regions peaked predominantly in the spring and fall seasons geoid variations observed over south america that can be largely attributed to surface water and groundwater changes show a clear separation between the large amazon watershed and the smaller watersheds to the north such observations will help hydrologists to connect processes at traditional length scales tens of kilometers or less to those at regional and global scales

teleseismic time functions for large shallow subduction zone earthquakes broadband vertical p wave records are analyzed from 63 of the largest shallow subduction zone earthquakes which have occurred in the circum pacific in the last 45 yr most of the records studied come from a common instrument the pasadena california benioff 1 90 seismometer propagation and instrument effects are deconvolved from the p wave records using a damped least squares inversion to obtain the teleseismic source time function the inversion has the additional constraint that the time function be positive everywhere the period band over which the time functions are considered reliable is from 2 5 to 50 sec fourier displacement amplitude spectra computed for each of the 1 90 p wave trains indicate spectral slopes measured between 2 and 50 sec of 1 0 to 2 25 with an average value of 1 5 these values assume an average attenuation of t 1 0 the seismic moments derived from the p wave time functions compare well with other published values for earthquakes having moments smaller than 2 5 10 28 dyne cm m w 8 2 because the 1 90 seismometer has little response at very long periods this technique underestimates the moments of the very largest events the time functions are characterized using five parameters 1 spectral slope between 2 and 50 sec 2 roughness of the time function 3 multiplicity of sources 4 pulse widths of individual sources and 5 overall signal duration the 63 earthquakes studied come from 15 subduction zones with a wide range in the ages of subducted lithosphere convergence rates and maximum size of earthquakes comparing the time function parameters with age rate and m w of the subduction zone does not yield obvious global trends however most of the subduction zones do behave characteristically and can be grouped accordingly

location and size of the shallow magma reservoir beneath kīlauea caldera constraints from near source vp vs ratios we present high resolution compressional wave to shear wave velocity ratios vp vs beneath k lauea s summit caldera by applying an in situ estimation method using waveform cross correlation data for three similar earthquake clusters we observe high vp vs ratios 1 832 and 1 852 for two event clusters surrounded by the low background vp vs value of 1 412 at 2 1 km depth below the surface these high and low vp vs ratios can be explained by melt and co2 filled cracks respectively based on a theoretical crack model the event cluster with the highest vp vs ratio consists of long period events that followed the 1997 east rift zone eruption indicating their association with fluid and magma movement the depths of the two clusters with high vp vs ratios are consistent with the magma reservoir location inferred from geodetic observations their locations east and north of halema uma u crater suggest a horizontal extent of a few kilometers for the reservoir

time variability of the earth s gravity field hydrological and oceanic effects and their possible detection using grace the grace satellite mission scheduled for launch in 2001 is designed to map out the earth s gravity field to high accuracy every 2 4 weeks over a nominal lifetime of 5 years changes in the gravity field are caused by the redistribution of mass within the earth and on or above its surface grace will thus be able to constrain processes that involve mass redistribution in this paper we use output from hydrological oceanographic and atmospheric models to estimate the variability in the gravity field i e in the geoid due to those sources we develop a method for constructing surface mass estimates from the grace gravity coefficients we show the results of simulations where we use synthetic grace gravity data constructed by combining estimated geophysical signals and simulated grace measurement errors to attempt to recover hydrological and oceanographic signals we show that grace may be able to recover changes in continental water storage and in seafloor pressure at scales of a few hundred kilometers and larger and at timescales of a few weeks and longer with accuracies approaching 2 mm in water thickness over land and 0 1 mbar or better in seafloor pressure

seismic velocity variations along the rupture zone of the 1989 loma prieta earthquake california 1 we revisit the rupture zone of the 1989 mw6 9 loma prieta earthquake central california by developing high resolution three dimensional 3 d vp and vp vs models we apply the simul2000 inversion method and algorithm to a set of composite events which have greater number of picks per event and reduced random picking errors compared with traditional master events our final p wave velocity model generally agrees with previous studies showing a high velocity body of above 6 7 km s in the southeast rupture zone of the main shock the 3 dvp vs model however has different features with low vp vs in the upper crust and high vp vs anomalies in deeper layers of the rupture zone we interpret the low vp vs at shallow depths to be granitic rocks whereas at greater depths the areas of higher vp vs around 1 725 1 75 presumably are mafic rocks the resulting 3 d velocity model was used to improve absolute locations for all local events between 1984 and 2010 in our study area we then applied a similar event cluster analysis waveform cross correlation and differential time relocation methods to improve relative event location accuracy over 88 of the seismicity falls into similar event clusters a dramatic sharpening of seismicity patterns is obtained after using these methods the medians of the relative location uncertainties calculated by using the bootstrap approach are 5 m for horizontal and 8 m for vertical differential times from cross correlation are used to estimatein situnear sourcevp vsratio within each event cluster the high resolutionvp vs method confirms the trend of the velocity variations from the tomographic results although absolute values are slightly different

seismically triggered anomalies in the isotope signatures of mantle derived gases detected at degassing sites along two neighboring faults in nw bohemia central europe the vogtland and nw bohemia region is known for its earthquake swarms the most intensive swarm since 1985 86 occurred in october 2008 to find further indications for the interaction of ascending mantle derived fluids and the occurrence of earthquake swarms detailed fortnightly studies of gas compositions co2 n2 ar he h2 and ch4 and isotope ratios 13c 15n and 3he 4he were carried out between october 2008 and april 2011 at four locations close to the nov kostel focal zone and at the wettinquelle spring bad brambach from the start of the 2008 earthquake swarm seismically induced isotope geochemical anomalies were recorded at locations along the pocatky plesna fault zone ppz and were for the first time also found at degassing locations on the marianske lazn fault zone mlf variations were observed in both the temporal and spatial distributions of the anomalies as well in anomaly strengths probably due to the positions of these fault zones relative to the focal zone and to differences in fluid migration pathways prior to both the 2000 and 2008 swarms 3he 4he ratios 6 ra were recorded at the bublak mofette these anomalous pre seismic 3he 4he ratios suggest that both the 2000 and 2008 swarms may have been associated with the supply of fresh magma from a less degassed reservoir in the lithospheric mantle the temporal 13cco2 pattern from detailed studies at bublak between 2005 and 2011 indicates progressive magma degassing as well as seismically induced variations in the 13c providing additional support to the interpretation derived from the 3he 4he ratios

applying a three dimensional velocity model waveform cross correlation and cluster analysis to locate southern california seismicity from 1981 to 2005 we compute high precision earthquake locations using southern california pick and waveform data from 1981 to 2005 our latest results are significantly improved compared to our previous catalog by the following 1 we locate events with respect to a new crustal p and s velocity model using three dimensional ray tracing 2 we examine six more years of waveform data and compute cross correlation results for many more pairs than our last analysis and 3 we compute locations within similar event clusters using a new method that applies a robust fitting method to obtain the best locations satisfying all the differential time constraints from the waveform cross correlation these results build on the relocated catalogs of hauksson and shearer 2005 and shearer et al 2005 and provide additional insight regarding the fine scale fault structure in southern california and the relationship between the san andreas fault saf and nearby seismicity in particular we present results for two regions in which the seismicity near the southern saf seems to align on dipping faults

seismic image of a co2 reservoir beneath a seismically active volcano mammoth mountain is a seismically active volcano 200 000 to 50 000 years old situated on the southwestern rim of long valley caldera california since 1989 it has shown evidence of unrest in the form of earthquake swarms hill et al 1990 volcanic long period earthquakes pitt hill 1994 increased output of magmatic 3he sorey et al 1993 and the emission of about 500 tonnes day 1 of co2 farrar et al 1995 hill 1996 m sorey personal communication 1997 which has killed trees and poses a threat to human safety local earthquake tomography shows that in mid 1989 areas of subsequent tree kill were underlain by extensive regions where the ratio of the compressional and shear elastic wave speeds vp vs was about 9 per cent lower than in the surrounding rocks theory mavko mukerji 1995 experiment ito devilbiss nur 1979 and experience at other geothermal volcanic areas julian et al 1996 and at petroleum reservoirs harris et al 1996 indicate that vp vs is sensitive to pore fluid compressibility through its effect on vp the observed vp vs anomaly is probably caused directly by co2 and seismic vp vs tomography is thus a promising tool for monitoring gas concentration and movement in volcanoes which may in turn be related to volcanic activity

the 1989 earthquake swarm beneath mammoth mountain california an initial look at the 4 may through 30 september activity abstract mammoth mountain is a 50 000 to 200 000 year old cumulovolcano standing on the southwestern rim of long valley in eastern california on 4 may 1989 two m 1 earthquakes beneath the south flank of the mountain marked the onset of a swarm that has continued for more than 6 months in addition to its longevity noteworthy aspects of this persistent swarm include 1 an exponential like increase in the rate of activity through the first month 2 a vertically oriented planar distribution of hypocenters at depths between 6 and 9 km with a north northeast strike roughly perpendicular to the average t axis orientation for the swarm earthquakes 3 recurring spasmodic bursts rapid fire sequences of similar sized earthquakes with overlapping coda and occasional earthquakes with enhanced low frequency energy 4 a uniform temporal distribution of the four largest m 3 events over the first 4 months of the swarm with a cumulative seismic moment for the entire sequence through 30 september corresponding to a single m 4 earthquake 5 a b value of 1 2 and 6 submicrostrain perturbations on the nearby borehole dilatometer the first of which led the onset of swarm activity by more than 2 weeks these aspects of the swarm together with its location along the southern extension of the youthful mono inyo volcanic chain which last erupted 500 to 600 years ago point to a magmatic source for the modest but persistent influx of strain energy into the crust beneath mammoth mountain

three dimensional seismic velocity structure of mauna loa and kilauea volcanoes in hawaii from local seismic tomography we present a new three dimensional seismic velocity model of the crustal and upper mantle structure for mauna loa and kilauea volcanoes in hawaii our model is derived from the first arrival times of the compressional and shear waves from about 53 000 events on and near the island of hawaii between 1992 and 2009 recorded by the hawaiian volcano observatory stations the vp model generally agrees with previous studies showing high velocity anomalies near the calderas and rift zones and low velocity anomalies in the fault systems the most significant difference from previous models is in v p vs structure the high vp and high v p vs anomalies below mauna loa caldera are interpreted as mafic magmatic cumulates the observed low vp and high v p vs bodies in the kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments the high vp and moderate to low vp vs anomalies beneath kilauea caldera can be explained by a combination of different mafic compositions likely to be olivine rich gabbro and dunite the systematically low vp and low vp vs bodies in the southeast flank of kilauea may be caused by the presence of volatiles another difference between this study and previous ones is the improved vp model resolution in deeper layers owing to the inclusion of events with large epicentral distances the new velocity model is used to relocate the seismicity of mauna loa and kilauea for improved absolute locations and ultimately to develop a high precision earthquake catalog using waveform cross correlation data 2014 american geophysical union all rights reserved

computations of the viscoelastic response of a 3 d compressible earth to surface loading an application to glacial isostatic adjustment in antarctica and canada s u m m a r y we develop a 3 d finite element model to study the viscoelastic response of a compressible earth to surface loads the effects of centre of mass motion polar wander feedback and selfconsistent ocean loading are implemented to assess the model s accuracy we benchmark the numerical results against a semi analytic solution for spherically symmetric structure we force our model with the ice 5g global ice loading history to study the effects of laterally varying viscosity structure on several glacial isostatic adjustment gia observables including relative sea level rsl measurements incanada and present day time variable gravity and uplift rates in antarctica canadian rsl observations have been used to determine the earth s globally averaged viscosity profile antarcticgps uplift rates have been used to constrainantarcticgia models and gia time variable gravity and uplift signals are error sources for grace and altimeter estimates of present day antarctic ice mass loss and must be modelled and removed from those estimates computinggia results for a 3 d viscosity profile derived from a realistic seismic tomography model and comparing with results computed for 1 d averages of that 3 d profile we conclude that 1 a gia viscosity model based on canadian relative sea level data is more likely to represent a canadian average than a true global average 2 the effects of 3 d viscosity structure on grace estimates of present day antarctic mass loss are probably smaller than the difference between gia models based on different antarctic deglaciation histories and 3 the effects of 3 d viscosity structure on antarctic gps observations of present day uplift rate can be significant and can complicate efforts to use gps observations to constrain 1 d gia models

body wave and surface wave analysis of large and great earthquakes along the eastern aleutian arc 1923 1993 implications for future events the 500 km long alaska peninsula and shumagin islands segments of the aleutian arc have a moderate to high probability of rupturing in one or more large or great earthquakes in the next few decades to understand the likely modes of rupture in the next sequence of large and great events and to delineate the current geometry of the plate interface we determine focal mechanisms depths and source time functions from seismic records for the largest events since 1917 the great earthquake of november 10 1938 and seven events with surface wave magnitude ms of 6 9 to 7 5 teleseismic body waves and surface waves are used to estimate the seismic moment and gross rupture characteristics of the great earthquake of november 10 1938 along the alaska peninsula body wave inversion of five p and four sh waves gives a duration of about 110 s in which moment was released in two episodes each of about 50 s duration with the second being larger than the first the first source was located in the general vicinity of the epicenter of the mainshock and the second which occurred about 60 s later was centered about 180 km to the northeast the body wave derived seismic moment is 3 7 1021 n m mw 8 3 we corroborate the body wave results by calculating surface waves by normal mode summation and comparing them with data at periods greater than 50 s an adequate fit to observed seismograms is obtained for either a single point source or two point sources with one located about 180 km northeast of the mainshock epicenter rupture in 1938 appears to have been confined to the alaska peninsula segment uniform rupture into the shumagin region is not supported by the data the ms 6 9 earthquake of may 13 1993 ruptured a small portion of the shumagin gap the earthquake of may 14 1948 ms 7 5 occurred on a shallow dipping thrust fault with a depth of about 31 km not 60 km as originally suggested five ms 7 events in the 1938 rupture zone have locations depths and mechanisms that define a shallow dipping 16 19 plate interface which shallows to 8 under kodiak island subduction of seamounts of the gulf of alaska seamount province may explain the location moment focal mechanism and depth of the five ms 7 events the plate interface dips nearly uniformly between the alaska peninsula and shumagin segments indicating that segmentation if any is not controlled by the orientation of the plate interface a slight warp of the plate interface may form the boundary between rupture zones of great earthquakes along the kodiak and alaska peninsula segments of the arc and may explain why rupture zones of large to great earthquakes rarely cross this tectonic boundary

seismic investigation of magmatic unrest beneath mammoth mountain california usa i present a reinvestigation of the seismic activity during an 11 mo long seismic swarm between 1989 and 1990 beneath mammoth mountain in eastern california united states this swarm believed to be the result of a shallow intrusion of magma beneath mammoth mountain was followed by the emission of magmatic co 2 gas resulting in tree die off in 1990 and posing a signifi cant human health risk around mammoth mountain in this study i apply a state of the art approach to estimate the ratio of compressional to shear wave velocity vp vs within similar event clusters using differential times from waveform crosscorrelation a high resolution three dimensional seismic velocity model and a precise earthquake location catalog are obtained to complement the analysis of the in situ vp vs ratios the majority of the relocated seismicity below sea level is distributed in an anomalous body with low vp and high vp vs consistent with the seismic expression of the magma body that triggered the seismic swarm abrupt changes in vp vs ratios with lower values for the shallow depths are observed near sea level indicating the source of the 1989 co 2 fl ux is a shallow co 2 reservoir instead of the hypothesized basaltic magma at mid crustal depths of 10 25 km from sea level to the surface low vp vs ratios in a near vertical zone suggest involvement of fl uid in the upward migration of the seismicity

evidence for water filled cracks in earthquake source regions 1 we identify lowered vp vs ratios near earthquake source regions in southern california using observations from a seismic tomography model and high resolution local vp vs estimates using waveform cross correlation data from within similar event clusters the median tomographic vp vs ratio is 1 716 0 008 at all the relocated crustal earthquake locations compared to the background median value of 1 729 0 007 for the tomography model although the error estimates overlap slightly the median in situ vp vs ratio of 1 673 0 022 within the similar event clusters suggests that tomographic studies are overestimating vp vs at source regions interpretation of vp vs anomalies is complicated by the scatter in values obtained for individual clusters and in comparisons to absolute vp and vs velocities in the tomography model however the low vp vs ratios measured for the seismicity clusters are hard to explain with known rocks and suggest the presence of water filled cracks with several percent porosity in earthquake source regions in southern california which likely has an effect on faulting and earthquake activity

an efficient repeating signal detector to investigate earthquake swarms repetitive earthquake swarms have been recognized as key signatures in fluid injection induced seismicity precursors to volcanic eruptions and slow slip events preceding megathrust earthquakes we investigate earthquake swarms by developing a repeating signal detector rsd a computationally efficient algorithm utilizing agglomerative clustering to identify similar waveforms buried in years of seismic recordings using a single seismometer instead of relying on existing earthquake catalogs of larger earthquakes rsd identifies characteristic repetitive waveforms by rapidly identifying signals of interest above a low signal to noise ratio and then grouping based on spectral and time domain characteristics resulting in dramatically shorter processing time than more exhaustive autocorrelation approaches we investigate seismicity in four regions using rsd 1 volcanic seismicity at mammoth mountain california 2 subduction related seismicity in oaxaca mexico 3 induced seismicity in central alberta canada and 4 induced seismicity in harrison county ohio in each case rsd detects a similar or larger number of earthquakes than existing catalogs created using more time intensive methods in harrison county rsd identifies 18 seismic sequences that correlate temporally and spatially to separate hydraulic fracturing operations 15 of which were previously unreported rsd utilizes a single seismometer for earthquake detection which enables seismicity to be quickly identified in poorly instrumented regions at the expense of relying on another method to locate the new detections due to the smaller computation overhead and success at distances up to 50 km rsd is well suited for real time detection of low magnitude earthquake swarms with permanent regional networks

the gravity recovery and climate experiment mission overview and early results 1 the grace mission is designed to track changes in the earth s gravity field for a period of five years launched in march 2002 the two grace satellites have collected nearly two years of data a span of data available during the commissioning phase was used to obtain initial gravity models the gravity models developed with this data are more than an order of magnitude better at the long and mid wavelengths than previous models the error estimates indicate a 2 cm accuracy uniformly over the land and ocean regions a consequence of the highly accurate global and homogenous nature of the grace data these early results are a strong affirmation of the grace mission concept

geometric effects of global lateral heterogeneity on long period surface wave propagation long period rayleigh waves from iranian earthquakes have large amplitude asymmetries between minor arc and major arc arrivals e g r 2 and r 3 at digital stations in the azimuth range n20 w to n60 e these asymmetries are as large as a factor of 2 at a period of 256 s and persist to periods greater than 300 s in some cases the entire rayleigh wave group arrival spanning periods from 100 to 300 s is either uniformly enhanced in amplitude or diminished to such a degree that the group arrival appears to be missing the amplitude anomalies are generally not accompanied by significant phase anomalies the irregular azimuthal distribution of the amplitude asymmetries and their occurrence for events with different focal mechanisms and epicentral separations of several hundred kilometers preclude an explanation of these observations by source complexity events in the mediterranean and nepal do not produce similar amplitude asymmetries at the same stations the anomalies are thus most likely due to focusing and defocusing propagation effects as a preliminary investigation of the effects of lateral heterogeneity of upper mantle velocity structure on long period surface wave amplitudes surface wave ray tracing calculations are performed using recently proposed global phase velocity distributions dramatic deviations from great circle paths are predicted for long propagation paths e g r 3 the particular spatial distribution of lateral velocity gradients around a given source location determines whether substantial amplitude asymmetries will be observed between minor arc and major arc arrivals and whether these will persist for sequential great circle orbits the 200 s period amplitude asymmetry observed at kip for the iranian source region r 2 4 r 3 is well predicted by the ray tracing results the absence of this anomaly for the other source regions is also predicted other observed anomalies are not all well predicted but it is clear that geometric effects can contribute significantly to the observed variations of rayleigh and love wave amplitudes this is the probable explanation for the instability of q estimates made from surface waves other source regions producing large surface wave amplitude anomalies include japan and southeastern alaska

reinvestigation of the 1989 mammoth mountain california seismic swarm and dike intrusion abstract during the period of unrest and inflation beneath long valley east central california between 1988 and 1992 a swarm of seismic activity occurred beneath mammoth mountain on the caldera rim in 1989 followed by the onset of diffuse co 2 degassing these events combined with elevation changes along a leveling line north of mammoth mountain suggested a dike intrusion an early inversion of deformation data resulted in a dike model with an unrealistically small amount of opening 13 cm for the proposed dimensions the current reinvestigation of the 1989 seismic event at mammoth mountain ca incorporates relocated earthquakes prejean et al 2003 and ellipsoidal inflation sources beneath the caldera to the east langbein 2003 to better constrain the location and dimensions of a proposed dike intrusion beneath mammoth mountain assuming that the dike coincides with a keel of seismicity at 7 9 km depth most of the dislocation parameters can be constrained fixing all dike parameters except opening to coincide with the keel inversion of the local leveling data yields a dike with 3 3 m of opening allowing the dike height to vary as well improves the fit to the data significantly and results in a dike 1 m wide and nearly 7 m high these results indicate that the intruded dike had significantly more opening than previously modeled magma volumes for reasonable models center around 0 015 km 3 suggesting a small likely basaltic intrusion

deceleration in the earth s oblateness 1 for over three decades satellite laser ranging slr has recorded the global nature of the long wavelength mass change within the earth system analysis of the most recent time series of 30 day slr based estimates of earth s dynamical oblateness characterized by the gravitational degree 2 zonal spherical harmonic j2 indicates that the long term variation of j2 appears to be more quadratic than linear in nature the superposition of a quadratic and an 18 6 year variation leads to the unknown decadal variation reported by cheng and tapley 2004 although the primary trend is expected to be linear due to global isostatic adjustment there is an evident deceleration j 2 18 1 10 13 yr2 in the rate of the decrease in j2 during the last few decades likely due to changes in the rate of the global mass redistribution from melting of the glaciers and ice sheets as well as mass changes in the atmosphere and ocean

estimating geocenter variations from a combination of grace and ocean model output 1 in this study we estimate a time series of geocenter anomalies from a combination of data from the gravityrecoveryandclimateexperiment grace satellitemissionandthe outputfromoceanmodels amatrixequationisderivedrelating totalgeocentervariations to the grace coefficients of degrees two and higher and to the oceanic component of the degree one coefficients we estimate the oceanic component from two state of the art ocean models results are compared to independent estimates of geocenter derived from other satellite data such as satellite laser ranging and gps finally we compute degree one coefficients that are consistent with the processing applied to the grace level 2 gravity field coefficients the estimated degree one coefficients can be used to improve estimates of mass variability from grace which alone cannot provide them directly

seismic velocity structure and earthquake relocation for the magmatic system beneath long valley caldera eastern california abstract a new three dimensional 3 d seismic velocity model and high precision location catalog for earthquakes between 1984 and 2014 are presented for long valley caldera and its adjacent fault zones in eastern california the simul2000 tomography algorithm is applied to derive the 3 d vp and vp vs models using first arrivals of 1004 composite earthquakes obtained from the original seismic data at the northern california earthquake data center the resulting vp model reflects geological structures and agrees with previous local tomographic studies the simultaneously resolved vp vs model is a major contribution of this study providing an important complement to the vp model for the interpretation of structural heterogeneities and physical properties in the study area the caldera is dominated by low vp anomalies at shallow depths due to postcaldera fill high vp and low vp vs values are resolved from the surface to 3 4 km depth beneath the center of the caldera corresponding to the structural uplift of the resurgent dome an aseismic body with low vp and high vp vs anomalies at 4 2 6 2 km depth below the surface is consistent with the location of partial melt suggested by previous studies based on vp models only and the inflation source locations based on geodetic modeling the sierran crystalline rocks outside the caldera are generally characterized with high vp and low vp vs values the newly resolved velocity model improves absolute location accuracy for the seismicity in the study area and ultimately provides the basis for a high precision earthquake catalog based on similar event cluster analysis and waveform cross correlation data the fine scale velocity structure and precise earthquake relocations are useful for investigating magma sources seismicity and stress interaction and other seismological studies in long valley

subregional scale groundwater depletion detected by grace for both shallow and deep aquifers in north china plain this study explores the capability of gravity recovery and climate experiment grace to detect heterogeneous groundwater storage gws variations in two subregions of the north china plain the piedmont plain pp 54 000 km2 mainly exploiting shallow groundwater and east central plain ecp 86 000 km2 mainly exploiting deep groundwater results show that the gws anomalies estimated from grace data 2003 2013 agree well with those estimated from in situ observations 2005 2010 for both pp r2 0 91 and ecp r2 0 75 the shallow gws 2003 2013 in pp declines faster 46 5 6 8 mm yr than the deep gws in ecp 16 9 1 9 mm yr however the shallow gws in pp recovered more quickly especially during the 2008 2011 drought period despite its lower magnitude the grace derived gws depletion in ecp reveals the overexploitation of deep gws this study demonstrated that the heterogeneous gws variations can potentially be detected by grace at the subregional scale smaller than the typical grace footprint 200 000 km2

tomographic image of a seismically active volcano mammoth mountain california high resolution tomographic p wave s wave and vp vs velocity structure models are derived for mammoth mountain california using phase data from the northern california seismic network and a temporary deployment of broadband seismometers an anomalous volume 5 1 109 to 5 9 1010m3 of low p and low s wave velocities is imaged beneath mammoth mountain extending from near the surface to a depth of 2 km below sea level we infer that the reduction in seismic wave velocities is due to the presence of co2 distributed in oblate spheroid pores with mean aspect ratio 1 6 10 3 to 7 9 10 3 crack like pores and mean gas volume fraction 8 1 10 4 to 3 4 10 3 the pore density parameter 3 4 na3 0 11 where n is the number of pores per cubic meter and a is the mean pore equatorial radius the total mass of co2 is estimated to be 4 6 109 to 1 9 1011 kg the local geological structure indicates that the co2 contained in the pores is delivered to the surface through fractures controlled by faults and remnant foliation of the bedrock beneath mammoth mountain the total volume of co2 contained in the reservoir suggests that given an emission rate of 500 tons day 1 the reservoir could supply the emission of co2 for 25 1040 years before depletion continued supply of co2 from an underlying magmatic system would significantly prolong the existence of the reservoir

estimating the human contribution to groundwater depletion in the middle east from grace data land surface models and well observations data from the gravity recovery and climate experiment grace satellite mission are used to estimate monthly changes in total water storage across the middle east during february 2003 to december 2012 the results show a large negative trend in total water storage centered over western iran and eastern iraq subtracting contributions from the caspian sea and two large lakes tharthar and urmiah and using output from a version of the clm4 5 land surface model to remove contributions from soil moisture snow canopy storage and river storage we conclude that most of the long term water loss is due to a decline in groundwater storage by dividing the region into seven mascons outlined along national boundaries and fitting them to the data we find that the largest groundwater depletion is occurring in iran with a mass loss rate of 25 3 gt yr during the study period the conclusion of significant iranian groundwater loss is further supported by in situ well data from across the country anthropogenic contributions to the groundwater loss are estimated by removing the natural variations in groundwater predicted by clm4 5 these results indicate that over half of the groundwater loss in iran 14 3 gt yr may be attributed to human withdrawals

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

seismological evidence for magmatic and hydrothermal structure in long valley caldera from local earthquake attenuation and velocity tomography we compare the results of six different tomographic inversions for the three dimensional seismic attenuation and velocity structure in long valley caldera california in order to constrain interpretations on the location and character of magmatic and geothermal structure in the caldera crust p and s wave amplitudes and arrival times obtained in previous studies from seismograms of local earthquakes recorded on vertical and three component seismographis were inverted for q sv 1 q sh 1 q s 1 q p 1 and v p v s in the upper 9 km of teh caldera crust detailed comparisons of the results of the inversions suggest significant locations of high temperatures and perhaps magma and hydrothermal zones in the caldera a region of low q s with locally variable q p and v p v s is imaged in the 7 9 km depth range beneath the resurgent dome overlying and adjacent to this anomaly are significant low q p and low v p v s anomalies as well as smaller zones of low q s and high v p v s together these suggest zones of high temperature magma below and adjacent to zones of supercritical hydrothermal fluids at 4 5 km depth along the southern rim of the caldera just east of mammoth mountain a significant anomaly with relatively low q p and relatively low v p v s is imaged and is interpreted as a supercritical hydrothermal zone poorly resolved relatively low q p and relatively high v p v s are seen at 4 5 km depth beneath the inyo craters suggesting possible high temperatures and perhaps magma because of lack of data in the individual inversions the resultant images have spatially variable error and resolution however by comparing multiple images of different seismic parameters we have improved our ability to determine the significance of an constrain interpretation of seismic structure anomalies