recovery of small strain stiffness following blast induced liquefaction based on shear wave velocity measurements changes in soil fabric following liquefaction have been studied using various in situ methods and often return inconclusive or conflicting observations the time rate variation of stiffness when

earthquakes faulting and stress in the los angeles basin since 1920 fourteen moderate sized m l 4 9 6 4 earthquakes have been reported in the los angeles basin these events are associated with both mappable surficial faults and concealed faults beneath the basin sediments to determine the style of faulting and state of stress in the basin single event focal mechanisms for 244 earthquakes of m 2 5 that have occurred during 1977 1989 have been calculated fifty nine percent of the events are strike slip and are mostly located near two of the major northwest striking right lateral strike slip faults in the basin the newport inglewood fault and the palos verdes fault the 1988 pasadena and the 1988 upland earthquakes showed left lateral strike slip on northeast striking faults numerous small earthquakes in the eastern part of the basin show left lateral strike slip faulting and form a northeast trend near yorba linda thirty two percent of the events have reverse mechanisms and are distributed along two broad zones the first the elysian park fold and thrust belt coincides with anticlines along the eastern and northern flank of the los angeles basin extending into santa monica bay the second the torrance wilmington fold and thrust belt coincides with anticlines mapped on the southwest flank of the basin and extends from offshore newport beach to the northwest into santa monica bay oblique faulting that could be inferred by the merging of strike slip and compressional tectonics does not occur in the basin instead the coexistence of zones of thrusting and large strike slip faults in the basin suggests that the thrust and strike slip movements are mostly decoupled a few normal faulting mechanisms appear to be related to faulting orthogonal to the axes of plunging anticlines the trend of the maximum horizontal stress varies from n1 w to n31 e across the basin and consistently forms high angles with the fold axes the stress field that exists along the flanks of the basin has a vertical minimum stress axis this stress field and ongoing folding and thrusting suggest that tectonic deformation is concentrated along the flanks of the deep central basin today the deformation of the basin consists of uplift and crustal thickening and lateral block movement to accommodate the north south compression across the basin

segmented lateral dyke growth in a rifting event at barðarbunga volcanic system iceland crust at many divergent plate boundaries forms primarily by the injection of vertical sheet like dykes some tens of kilometres long1 previous models of rifting events indicate either lateral dyke growth away from a feeding source with propagation rates decreasing as the dyke lengthens2 3 4 or magma flowing vertically into dykes from an underlying source5 6 with the role of topography on the evolution of lateral dykes not clear here we show how a recent segmented dyke intrusion in the bar arbunga volcanic system grew laterally for more than 45 kilometres at a variable rate with topography influencing the direction of propagation barriers at the ends of each segment were overcome by the build up of pressure in the dyke end then a new segment formed and dyke lengthening temporarily peaked the dyke evolution which occurred primarily over 14 days was revealed by propagating seismicity ground deformation mapped by global positioning system gps interferometric analysis of satellite radar images insar and graben formation the strike of the dyke segments varies from an initially radial direction away from the bar arbunga caldera towards alignment with that expected from regional stress at the distal end a model minimizing the combined strain and gravitational potential energy explains the propagation path dyke opening and seismicity focused at the most distal segment at any given time and were simultaneous with magma source deflation and slow collapse at the bar arbunga caldera accompanied by a series of magnitude m 5 earthquakes dyke growth was slowed down by an effusive fissure eruption near the end of the dyke lateral dyke growth with segment barrier breaking by pressure build up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries

prospects for larger or more frequent earthquakes in the los angeles metropolitan region far too few moderate earthquakes have occurred within the los angeles california metropolitan region during the 200 year long historic period to account for observed strain accumulation indicating that the historic era represents either a lull between clusters of moderate earthquakes or part of a centuries long interseismic period between much larger moment magnitude m w 7 2 to 7 6 events geologic slip rates and relations between moment magnitude average coseismic slip and rupture area show that either of these hypotheses is possible but that the latter is the more plausible of the two the average time between m w 7 2 to 7 6 earthquakes from a combination of six fault systems within the metropolitan area was estimated to be about 140 years

the 2004 2008 dome building eruption at mount st helens washington epilogue the 2004 2008 dome building eruption at mount st helens ended during winter 2007 2008 at a time when field observations were hampered by persistent bad weather as a result recognizing the end of the eruption was challenging but important for scientists trying to understand how and why long lived eruptions end and for public officials and land managers responsible for hazards mitigation and access restrictions in hindsight the end of the eruption was presaged by a slight increase in seismicity in december 2007 that culminated on january 12 13 2008 with a burst of more than 500 events most of which occurred in association with several tremor like signals and a spasmodic burst of long period earthquakes at about the same time a series of regular localized small amplitude tilt events thousands of which had been recorded during earlier phases of the eruption came to an end thereafter seismicity declined to 10 20 events per day until january 27 28 when a spasmodic burst of about 50 volcano tectonic earthquakes occurred over a span of 3 h this was followed by a brief return of repetitive drumbeat earthquakes that characterized much of the eruption by january 31 however seismicity had declined to 1 2 earthquakes per day a rate similar to pre eruption levels we attribute the tilt and seismic observations to convulsive stagnation of a semisolid magma plug in the upper part of the conduit the upward movement of the plug ceased when the excess driving pressure which had gradually decreased throughout the eruption as a result of reservoir deflation and increasing overburden from the growing dome was overcome by increasing friction as a result of cooling and crystallization of the plug

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

multidimensional time series analysis of ground deformation from multiple insar data sets applied to virunga volcanic province summary a novel multidimensional small baseline subset msbas methodology is presented for integration of multiple interferometric synthetic aperture radar insar data sets for computation of 2 or 3 d time series of deformation the proposed approach allows the combination of all possible air borne and space borne sar data acquired with different acquisition parameters temporal and spatial sampling and resolution wave band and polarization the produced time series have improved temporal resolution and can be enhanced by applying either regularization or temporal filtering to remove high frequency noise we apply this methodology to map 2003 2010 ground deformation of the virunga volcanic province vvp north kivu democratic republic of congo the horizontal and vertical time series of ground displacement clearly identify lava compaction areas long term deformation of mt nyamuragira and 2004 2006 and 2010 pre and coeruptive deformation providing that enough sar data is available the method opens new opportunities for detecting ground motion in the vvp and elsewhere

effect of aging on the penetration resistance of sands the main objective of this study was to understand the effect of aging on the penetration resistance of freshly deposited sands two types of sand locally available river sand used as masonry sand and beaufort sea sand were selected for the study the sands were allowed to age under a constant stress of 100 kpa in a specially designed apparatus in a dry state as well as submerged in distilled water and in simulated sea water penetration resistance of the sand beds was measured periodically by pushing 4 probes into the sand bed mineralogical and fabric studies on freshly deposited and aged sand samples were conducted to detect the effect of aging if any on sand grains the results indicate that aging significantly increases the penetration resistance of sands the rate of increase in penetration resistance was higher for the submerged sand as compared with the dry sand the increase in penetration resistance of the sand in a dry state was attributed to rearrangement of sand grains in the submerged

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

how sensitive are fault slip rates in the los angeles basin to tectonic boundary conditions geodetic studies have produced different interpretations of the relative vertical thickening versus escape tectonics occurring within the los angeles basin based on calculated horizontal strain rates ranging from 56 10 9 yr contraction at n36 et o 85 10 9 yr north south contraction and 60 10 9 yr east west extension three dimensional forward mechanical models of faults in the los an geles basin are used to compare modeled slip rates and slip styles represented as the rakes of average net slip vectors under four representative horizontal strain condi tions with geologically determined late quaternary slip rates and observed slip styles the comparisons strive to identify the most mechanically viable tectonic boundary conditions for the los angeles basin the three dimensional fault surfaces used within the mechanical models have been defined by southern california earthquake center scec workers based on surface geology and subsurface data the model results suggest that northeast southwest principal contraction is inappropriate for the los angeles basin because this tectonic boundary condition produces left lateral slip along the whittier and san gabriel faults in contrast with abundant geologic evidence of right lateral slip of the four tectonic boundary conditions evaluated north south contraction accompanied by either zero or slow east west contraction gives the low est mismatch of modeled and observed fault slip style these results suggest that vertical thickening may be more predominant than escape tectonics in this region

space geodetic observation of expansion of the san gabriel valley california aquifer system during heavy rainfall in winter 2004 2005 1 starting early in 2005 the positions of gps stations in the san gabriel valley region of southern california showed statistically significant departures from their previous behavior station long moved up by about 47 mm and nearby stations moved away from long by about 10 mm these changes began during an extremely rainy season in southern california and coincided with a 16 m increase in water level at a nearby well in baldwin park and a regional uplift detected by interferometric synthetic aperture radar no equivalent signals were seen in gps station position time series elsewhere in southern california our preferred explanation supported by the timing and by a hydrologic simulation is deformation due to recharging of aquifers after near record rainfall in 2004 2005 we cannot rule out an aseismic slip event but we consider such an event unlikely because it requires slip on multiple faults and predicts other signals that are not observed

decadal volcanic deformation in the central andes volcanic zone revealed by insar time series 1 decadal trends of volcanic deformation in the central andes volcanic zone cvz are identified with interferometric synthetic aperture radar insar stacks and time series velocity maps covering an area 19 s 27 s and 66 w 69 w we combine over 750 ers and envisat interferograms from two descending and three ascending tracks these tracks cover 100 000 km 2 and span 1992 2011 our analysis extends observations at cerro blanco uturuncu and lazufre volcanic centers and uncovers two previously undocumented deformation centers cerro overo in northern chile and putana volcano in southwest bolivia cerro overo exhibits a transition from steady 0 4 cm yr deflation to 0 5 cm yr inflation over several years putana volcano underwent a short lived episode of uplift between 13 september 2009 and 31 january 2010 with a maximum uplift of 4 0 cm cerro blanco continues 1 0 cm yr deflation since 1995 uplift at lazufre began between 1997 and 2000 and has gradually accelerated to 3 5 cm yr since 2005 uturuncu volcano continues 1 0 cm yr monotonic uplift since 1992 and shows evidence for a broad moat of subsidence surrounding the uplifting region four of the nine deformation events in the cvz are not obviously associated with a particular volcanic edifice furthermore there is significant spatial and temporal variability of these deformation events within a small geographic area

paleoseismology and geomorphology of the raymond fault los angeles county california the raymond fault extends for 20 km in a broad convex to the south arc across the densely populated san gabriel valley northeast of los angeles although south facing scarps characterize much of the fault geomorphic and seismological evidence indicate a predominance of left lateral motion an apparent 3 4 km left lateral offset of a crystalline basement ridge at the east end of the fault may approximate total slip on the fault data from one of our paleoseismologic trenches in combination with published data indicate that the most recent raymond fault surface rupture occurred 1 2 ka estimates of fault plane area suggest that rupture of the entire raymond fault could generate an earthquake of m w 6 7 the similar kinematics of the raymond fault and the hollywood fault along strike to the west together with a pronounced fault parallel gravity lineament and sparse geomorphic evidence suggests that there may be a through going mechanical connection between the two faults and that they could conceivably rupture together in large earthquakes published data however indicate that the hollywood fault ruptured to the surface most recently 6 9 ka indicating that the most recent raymond fault surface rupture apparently did not extend westward onto the hollywood fault data from another of our paleoseismologic trenches yielded evidence for at least five latest pleistocene earthquakes including at least four surface ruptures that occurred during a brief 10 000 year long period between 31 5 and 41 5 ka the 3300 year long average recurrence interval for these events is much shorter than the interval suggested for the past 40 000 years by the frequency of paleoearthquakes recognized in previous trenches thus either the 31 5 ka to 41 5 ka events represent a temporal cluster and the recurrence interval for the fault is highly irregular or at least half of all raymond fault earthquakes that have occurred since 31 5 ka have not yet been recognized

evolution of dike opening during the march 2011 kamoamoa fissure eruption kīlauea volcano hawai i 1 the 5 9 march 2011 kamoamoa fissure eruption along the east rift zone of k lauea volcano hawai i followed months of pronounced inflation at k lauea summit we examine dike opening during and after the eruption using a comprehensive interferometric synthetic aperture radar insar data set in combination with continuous gps data we solve for distributed dike displacements using a whole k lauea model with dilating rift zones and possibly a deep decollement modeled surface dike opening increased from nearly 1 5 m to over 2 8 m from the first day to the end of the eruption in agreement with field observations of surface fracturing surface dike opening ceased following the eruption but subsurface opening in the dike continued into may 2011 dike volumes increased from 15 to 16 to 21 million cubic meters mcm after the first day eruption end and 2 months following respectively dike shape is distinctive with a main limb plunging from the surface to 2 3 km depth in the up rift direction toward k lauea s summit and a lesser projection extending in the down rift direction toward pu u at 2 km depth volume losses beneath k lauea summit 1 7 mcm and pu u 5 6 mcm crater relative to dike plus erupted volume 18 3 mcm yield a dike to source volume ratio of 2 5 that is in the range expected for compressible magma without requiring additional sources inflation of k lauea s summit in the months before the march 2011 eruption suggests that the kamoamoa eruption resulted from overpressure of the volcano s magmatic system

ground deformation associated with the precursory unrest and early phases of the january 2006 eruption of augustine volcano alaska 1 on january 11 2006 augustine volcano erupted after nearly 20 years of quiescence global positioning system gps instrumentation at augustine consisting of six continuously recording telemetered receivers measured clear precursory deformation consistent with a source of inflation or pressurization beneath the volcano s summit at a depth of around sea level deformation began in early summer 2005 and was preceded by a subtle but distinct increase in seismicity which began in may 2005 after remaining more or less constant deformation rates accelerated on at least three stations beginning in late november 2005 after this date gps data suggest the upward propagation of a small dike into the edifice which based on the style of deformation and high levels of gas emission appears to have ascended to shallow levels by mid december 2005 about four weeks before the eruption began

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

tectonics of the san gabriel basin and surroundings southern california the sangabriel basin is a pliocene pleistocene transverse ranges structure bounded by the san gabriel mountains on the north the san jose and puente hills on the east and the repetto and montebello hills on the west a basement boundary between gneissoid rocks of san gabriel mountains aspect and peninsular ranges rocks strikes east across the basin and connects with the san jose fault this boundary may represent the eastward continuation of the canton fault a middle miocene precursor of the san gabriel fault system with up to 30 km of right slip canton fault displacement is largely canceled by 22 5 km of left slip on a precursor to the raymond fault such that an oligocene dacite in the san jose hills and clasts derived from it show little evidence of large horizontal displacement between the san gabriel mountains and puente hills clockwise rotation in the middle miocene probably influenced the distribution of lateral slip the fill in the northeast trending pliocene pleistocene san gabriel basin is a basal shallow marine sequence overlain by the nonmarine duarte conglomerate in contrast to the deep water fernando formation of the los angeles basin the paleoslope trends south in the direction of the repetto and puente hills evidence that uplift of these hills postdated deposition the triangular san gabriel basin is currently a stable block bounded by the right slip northwest striking east montebello fault on the west and the left slip northeast striking walnut creek fault on the east farther east the san jose and puente hills are underlain by an east trending active fold belt including the san jose reverse fault and anticline the walnut anticline and the puente hills anticline adjacent to the right lateral whittier fault the east montebello fault is bounded on the west by the elysian park anticlinorium a fold belt in downtown los angeles the left slip holocene raymond fault joins the sierra madre reverse fault at its segment boundary marked by the clamshell sawpit fault the triangular stable block between east trending fold belts is bounded on the south by the puente hills blind thrust and on the north by the sierra madre fault documenting north south quaternary convergence east west extension is also indicated although not confirmed by geodetic measurements

properties of aftershock sequences in southern california the temporal behavior of 39 aftershock sequences in southern california 1933 1988 was modeled by the modified omori relation minimum magnitudes for completeness of each sequence catalog were determined and the maximum likelihood estimates of the parameters k p and c with the standard errors on each were determined by the ogata algorithm the b value of each sequence was also calculated many of the active faults in the region both strike slip and thrust were sampled the p values were graded in terms of the size of the standard error relative to the p value itself most of the sequences were modeled well by the omori relation many of the sequences had p values close to the mean of the whole data set 1 11 0 25 but values significantly different from the mean as low as 0 7 and as high as 1 8 exist no correlation of p with either the b value of the sequence or the mainshock magnitude was found the results suggest a direct correlation of p values is with surface heat flow with high values in the salton trough high heat flow and one low value in the san bernardino mountains and on the edge of the ventura basin both low heat flow the large fraction of the sequences with p values near the mean are at locations where the heat flow is near the regional mean 74 mw m2 if the hypothesis that aftershock decay rate is controlled by temperature at depth is valid the effects of other factors such as heterogeneity of the fault zone properties are superimposed on the background rate determined by temperature surface heat flow is taken as an indicator of crustal temperature at hypocentral depths but the effects on heat flow of convective heat transport and variations in near surface thermal conductivity invalidate any simple association of local variations in heat flow with details of the subsurface temperature distribution the interpretation is that higher temperatures in the aftershock source volume caused shortened stress relaxation times in the fault zone materials leading to a faster decay rate higher p value in 1967 mogi proposed such a relation on the basis of japanese data seismic velocity distributions published for southern california generally support the hypothesis with low velocities higher temperatures corresponding to high p values and vice versa

use of explosives to investigate liquefaction resistance of aged sand deposits abstract current methods of predicting liquefaction potential were largely developed using data from relatively young deposits or deposits that have been frequently disturbed i e areas of high seismicity while engineers recognize that these prediction methods are overly conservative for assessing liquefaction potential in geologically aged deposits there is no widely accepted method for quantitatively accounting for age in these assessments because a major disturbance such as an earthquake or explosion that causes liquefaction resets a deposit s geological age data from explosive compaction projects in aged deposits are used herein to provide information about both the aged and fresh deposits a recent explosive compaction project performed in griffin in as well as four other explosive compaction projects is used to develop an aging correction relationship for liquefaction resistance using a log linear trend frequently proposed in previous studies the method proposed herein predicts an approximate 20 gain in liquefaction resistance per time log cycle the proposed relationship can be used directly if the time since deposition or last disturbance is known or in conjunction with the measured to estimated velocity ratio mevr relationship proposed by andrus et al if the deposit s age is unknown

digital photogrammetry and gis based analysis of the bio geomorphological evolution of sakurajima volcano diachronic analysis from 1947 to 2006 abstract the sakurajima volcano is one of the most active volcanoes in the world with regular activity dominated by vulcanian eruptions since 1955 located in kagoshima prefecture kyushu island japan the sakurajima volcano is a stratovolcano with two main vents at the summit the kitadake and the minamidake and a third smaller central vent the nakadake the two firsts peak at 1117 and 1060 m dominate the slopes mainly composed of lava flow deposits secondary volcaniclastic material and recent ejectas from the vulcanian eruptions although the volcano has been very closely monitored by japanese universities mostly kyoto university and kagoshima university and governmental agencies there has been very little geomorphological investigation of the structure of the volcano using the digital photogammetric method sfm mvs structure from motion and multiple view stereophotogrammetry applied to historical aerial photographs the present contribution aims to provide an analysis of the volcanic structure and the recent bio geomorphological evolution for the period 1947 2006 first the results have proved that sfm mvs is a method that can be successfully applied to aerial photographs for diachronic reconstruction of geomorphological landscape evolution this method is especially important in active volcanic areas as the geomorphology can change very rapidly within the historical period secondly the results have shown that during the last 60 years the summit area of the sakurajima has greatly evolved the morpholology of the minamidake crater has changed due to its regular explosive activity the upper slopes have been covered in ejecta modifying their elevation and their smoothness the lower slopes have seen the apparition of lahar deposition areas while valleys upslope have widened due to the lahar activity and the upward progression of the deposits the 3d derived from sfm mvs has also shown how the lahar deposits are using the topographic low created on top of the lava deposits and in between lava deposit to accumulate mid slopes rather than accumulating on the lower volcanic apron this is accentuated by the construction of sabo dams that keep a large amount of the material on the slopes finally as this publication has been carried out using the freely available imagery from the gsi geospatial information authority of japan at 200 dpi higher resolution imagery can even open further possibilities for the monitoring of volcano evolution in japan and in countries providing long series of historical imagery

compaction of alluvial sands by deep blasting the jebba hydroelectric development nigeria presently under construction features a 42 m high zoned rockfill embankment founded on river alluvium up to 70 m in depth the riverbed alluvium comprises fine to medium to coarse grained quartzitic sands with traces of gravel the relative densities of the sands vary appreciably in both the vertical and horizontal directions during the dam design it was found that it would be necessary to densify the loose to medium dense portion of the river sands to maintain settlements within acceptable limits and to withstand design earthquake forces the top 25 m of the river alluvium is densified by the vibrocompaction method and below this level down to depths of 40 m the alluvium is densified by blasting there is no precedent found in the literature for densification by blasting at such depth this paper presents details of a test program and the production work test results conclusively show increases in static cone penetration resistance in loose sand layers

precursory inflation of shallow magma reservoirs at west sunda volcanoes detected by insar 1 we use 2006 2009 alos interferometric synthetic aperture radar data over the entire west sunda arc indonesia home of 13 of the world s active volcanoes to derive arc wide time dependent ground deformation data we present unambiguous evidence of inflation at six volcanoes three of which erupted after the observation period we show that these volcanoes have shallow magma reservoirs at 1 3 km depth below the average regional elevation a global comparison of reservoir depths at arc volcanoes suggests that volcanoes in extensional and strike slip settings west sunda can develop shallow reservoirs whereas volcanoes in compressional settings may lack them thus magma ascend through the upper crust could be influenced by intra arc tectonic settings

fractal analysis of three dimensional spatial distributions of earthquakes with a percolation interpretation although many studies have shown that faults and fractures are self similar over a large range of scales none have tested the fault structure for self similarity in three dimensions in this study earthquake hypocentral locations in central and southern california were used to illuminate three dimensional 3 d fault structures for which we measured the fractal capacity dimension d0 3 d hypocentral distributions from the joshua tree big bear and upland aftershock sequences as well as background seismicity at parkfield were found to be fractal where d0 3 d increased with increasing event density asymptotically approaching a stable value the joshua tree data set stabilized at d0 3 d 1 92 0 02 the parkfield data set asymptotically approached d0 3 d 1 82 and the big bear data set approached d0 3 d 2 01 as a test of the effects of location errors upon the measured value of d0 3 d the upland aftershock data were located with both the southern california hadley and kanamori 1977 h k velocity model and the more accurate hauksson and jones 1991 h j velocity model events located with the h k model asymptotically approached d0 3 d 2 07 and events located with the h j model approached d0 3 d 1 79 suggesting that improved hypocentral locations may decrease the measured fractal dimension one interpretation of our results of d0 3 d 2 0 for all of the hypocentral data is that earthquakes only occur on the percolation backbone of a fault network i e the active part of the network that accommodates finite strain deformation sahimi et al 1993 we show that a percolation model that allows for healing of previously broken bonds is consistent with this interpretation

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

earthquake source zones in northeast india seismic tomography fractal dimension and b value mapping we have imaged earthquake source zones beneath the northeast india region by seismic tomography fractal dimension and b value mapping 3d p wave velocity vp structure is imaged by the local earthquake tomography let method high precision p wave 3 494 and s wave 3 064 travel times of 980 selected earthquakes m d 2 5 are used the events were recorded by 77 temporary permanent seismic stations in the region during 1993 1999 by the let method simultaneous inversion is made for precise location of the events as well as for 3d seismic imaging of the velocity structure fractal dimension and seismic b value has been estimated using the 980 let relocated epicenters a prominent northwest southeast low vp structure is imaged between the shillong plateau and mikir hills that reflects the kopili fault at the fault end a high vp structure is imaged at a depth of 40 km this is inferred to be the source zone for high seismic activity along this fault a similar high vp seismic source zone is imaged beneath the shillong plateau at 30 km depth both of the source zones have high fractal dimension from 1 80 to 1 90 indicating that most of the earthquake associated fractures are approaching a 2d space the spatial fractal dimension variation map has revealed the seismogenic structures and the crustal heterogeneities in the region the seismic b value in northeast india is found to vary from 0 6 to 1 0 higher b value contours are obtained along the kopili fault 1 0 and in the shillong plateau 0 9 the correlation coefficient between the fractal dimension and b value is found to be 0 79 indicating that the correlation is positive and significant to the south of shillong plateau a low vp structure is interpreted as thick 20 km sediments in the bengal basin with almost no seismic activity in the basin

volcano geodesy recent developments and future challenges abstract ascent of magma through earth s crust is normally associated with among other effects ground deformation and gravity changes geodesy is thus a valuable tool for monitoring and hazards assessment during volcanic unrest and it provides valuable data for exploring the geometry and volume of magma plumbing systems recent decades have seen an explosion in the quality and quantity of volcano geodetic data new datasets some made possible by regional and global scientific initiatives as well as new analysis methods and modeling practices have resulted in important changes to our understanding of the geodetic characteristics of active volcanism and magmatic processes from the scale of individual eruptive vents to global compilations of volcano deformation here we describe some of the recent developments in volcano geodesy both in terms of data and interpretive tools and discuss the role of international initiatives in meeting future challenges for the field

triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke the role of static versus dynamic stresses in earthquake clusters is unclear analysis of earthquakes triggered by a dyke intrusion at an icelandic volcano unambiguously demonstrates that static stresses are important for earthquake clustering large earthquakes can generate small changes in static stress increases that trigger aftershock swarms or reductions that create a region of reduced seismicity a stress shadow1 2 however seismic waves from large earthquakes also cause transient dynamic stresses that may trigger seismicity3 4 this makes it difficult to separate the relative influence of static and dynamic stress changes on aftershocks dyke intrusions do not generate dynamic stresses so provide an unambiguous test of the stress shadow hypothesis here we use gps and seismic data to reconstruct the intrusion of an igneous dyke that is 46 km long and 5 m wide beneath bar arbunga volcano central iceland in august 2014 we find that during dyke emplacement bursts of seismicity at a distance of 5 to 15 km were first triggered and then abruptly switched off as the dyke tip propagated away from the volcano we calculate the evolving static stress changes during dyke propagation and show that the stressing rate controls both the triggering and then suppression of earthquake rates in three separate areas adjacent to the dyke our results imply that static stress changes help control earthquake clustering similar small static stress changes may be important for triggering seismicity near geothermal areas regions being hydrofractured and deflating oil and gas fields

determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

abrupt magma chamber contraction and microseismicity at campi flegrei italy cause and effect determined from strainmeters and tiltmeters in march 2010 two borehole strainmeters and three michelson tiltmeters within the campi flegrei volcanic system italy registered an abrupt deformation signal that was followed 20 min later by seismic slip on a pair of onshore normal faults we demonstrate that the observed strain changes were caused by a small but rapid volume decrease in a previously identified offshore ellipsoidal magma source or part of it although the total deflation was below the detectability of interferometric synthetic aperture radar and gps deflation observed rates were briefly 2 orders of magnitude more rapid than decadal inflation rates we conclude that this high dilatational contraction rate was responsible for triggering seismicity and that this process may be responsible for the normal faulting often observed in the campi flegrei region our study quantifies the crucial role played by a transient minor reduction in dilatational stress in triggering slip on a fault near critical failure our subsurface measurements of strain and tilt registered anomalous deformation three sigma above background noise levels 17 min before the onset of microseismicity suggesting strain measurements have potential utility as an early warning system for the city of naples

an overview of geodetic volcano research in the canary islands the canary islands are mostly characterized by diffuse and scattered volcanism affecting a large area with only one active stratovolcano the teide pico viejo complex tenerife more than 2 million people live and work in the 7 447 km2 of the archipelago resulting in an average population density three times greater than the rest of spain this fact together with the growth of exposure during the past 40 years increases volcanic risk with respect previous eruptions as witnessed during the recent 2011 2012 el hierro submarine eruption therefore in addition to purely scientific reasons there are economic and population security reasons for developing and maintaining an efficient volcano monitoring system in this scenario geodetic monitoring represents an important part of the monitoring system we describe volcano geodetic monitoring research carried out in the canary islands and the results obtained we consider for each epoch the two main existing constraints the level of volcanic activity in the archipelago and the limitations of the techniques available at the time theoretical and observational aspects are considered as well as the implications for operational volcano surveillance current challenges of and future perspectives in geodetic volcano monitoring in the canaries are also presented

active parasitic folds on the elysian park anticline implications for seismic hazard in central los angeles california we characterize the seismic hazard of the elysian park fault a blind reverse fault beneath central los angeles by analysis of the elysian park anticline which overlies it new shallow subsurface geotechnical data combined with other surficial stratigraphy and geomorphology reveal that the elysian park anticline is an active 20 km long structure from the style and rates of deformation of parasitic folds on the southern limb of the anticline we estimate a contraction rate of 0 6 1 1 mm yr this rate provides a basis for estimating a rate of contraction of the entire elysian park anticline which in turn allows us to estimate a 0 8 2 2 mm yr time averaged rate of slip on the underlying fault at this rate of slip rupture of the elysian park fault could produce a nominal mw 6 2 to 6 7 earthquake every 500 to 1300 yr on average although this elysian park earthquake would recur infrequently its size and recurrence interval may be similar to those estimated for the sources of the destructive 1971 san fernando and 1994 northridge earthquakes

the 3 december 1988 pasadena california earthquake evidence for strike slip motion on the raymond fault the pasadena earthquake m l 4 9 occurred on 3 december 1988 at a depth of 16 km the hypocenters of the earthquake and its aftershocks define a east northeast striking steeply northwest dipping surface that projects up to the active surficial trace of the raymond fault one of the nodal planes of the focal mechanism of the earthquake parallels the raymond fault with left lateral strike slip movement on that plane and is consistent with geomorphic and paleoseismic evidence that the raymond fault is dominantly a left lateral strike slip fault the existence of a component of sinistral slip along the raymond fault had been suspected prior to the earthquake but the northward dip of the fault and the prominent scarp along the western portion of its trace had led most workers to conclude that slip along the fault was dominantly reverse

the 1987 whittier narrows earthquake in the los angeles metropolitan area california the whittier narrows earthquake sequence local magnitude m l 5 9 which caused over 358 million damage indicates that assessments of earthquake hazards in the los angeles metropolitan area may be underestimated the sequence ruptured a previously unidentified thrust fault that may be part of a large system of thrust faults that extends across the entire east west length of the northern margin of the los angeles basin peak horizontal accelerations from the main shock which were measured at ground level and in structures were as high as 0 6g where g is the acceleration of gravity at sea level within 50 kilometers of the epicenter the distribution of the modified mercalli intensity vii reflects a broad north south elongated zone of damage that is approximately centered on the main shock epicenter

multiscale seismic imaging of active fault zones for hazard assessment a case study of the santa monica fault zone los angeles california high resolution seismic reflection profiles at two different scales were acquired across the transpressional santa monica fault of north los angeles as part of an integrated hazard assessment of the fault the seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies the trench shows a series of near vertical strike slip faults beneath a topographic scarp inferred to be caused by thrusting on the santa monica fault analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike slip faults within the past 50 000 years with the latest being 1000 to 3000 years ago a 3 8 km long high resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the santa monica fault upper 300 m to dip northward between 30 and 55 most likely 30 to 35 in contrast to the 60 to 70 dip interpreted for the deeper portion of the fault pr

spatiotemporal analysis and interpretation of 1993 2013 ground deformation at campi flegrei italy observed by advanced dinsar campi flegrei is one of the most hazardous volcanic areas in the world because of its close proximity to the city of naples here we apply the multidimensional small baseline subset msbas differential interferometric synthetic aperture radar dinsar technique to obtain vertical and horizontal components of ground deformation for campi flegrei at high spatial and temporal resolutions that span for the first time 20 years the area underwent continuous subsidence from 1993 through 1999 moderate uplift began in 2010 and substantially increased through 2012 reaching approximately 13 cm by 2013 we model the observed deformation to determine source parameters for subsidence and uplift epochs both the inflation and deflation mechanisms involve large extended sources in a layered hydrothermal system whose location is controlled by the caldera structure and stratigraphy the temporal resolution of msbas approaches that of gps daily time series with superior precision and spatial resolution making it an excellent alternative for volcano monitoring

paleoseismologic evidence for a 8 ka age of the most recent surface rupture on the eastern sierra madre fault northern los angeles metropolitan region california paleoseismologic data from the sierra madre fault a major north dipping reverse fault that extends for 75 km across the northern edge of the los angeles metropolitan region indicate that the most recent surface rupture on the eastern part of the fault occurred more than 8000 years ago coupled with evidence for a minimum reverse slip rate of 0 6 0 9 mm yr on the strand that we trenched the long elapsed interval since the most recent event suggests that the sierra madre fault breaks during very infrequent large magnitude m w 7 earthquakes events of such large magnitude are much larger than the largest earthquakes that have occurred on any of the los angeles area urban faults during the 200 year long historic period e g the 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes and must be considered in future seismic hazard analyses for southern california although more paleoseismologic data are needed to determine whether or not the sierra madre fault ruptures together with adjacent faults available data already show that the raymond fault a west southwest trending left lateral strike slip fault that intersects the central sierra madre fault has ruptured to the surface at least once and possibly several times since the most recent surface rupture on the eastern sierra madre fault moreover if the san andreas fault saf and the sierra madre fault ever rupture together then such events must be exceedingly rare with at least 50 100 saf m w 8 so called big ones occurring between every possible combined saf sierra madre fault event

late quaternary activity and seismic potential of the santa monica fault system los angeles california the santa monica fault is a 40 km long oblique left lateral reverse fault that extends through the densely urbanized northwestern los angeles california area and offshore parallel to the malibu coast the fault exhibits near surface strain partitioning in paleoseismologic trenches and has undergone at least six surface ruptures during the past 50 k y although events may be missing from the older part of the record and the ages of older events are based on poorly constrained soil age estimates at least two and probably three events occurred after the well dated burial of a prominent paleosol ca 16 17 ka the resulting 7 8 k y latest pleistocene holocene average recurrence interval for events large enough to cause surface rupture is much longer than the 1 9 3 3 k y maximum interval we calculate for hypothetical m w 6 9 7 0 earthquakes generated by rupture of the entire santa monica fault the pronounced disparity between the measured and calculated average recurrence intervals suggests that the santa monica fault undergoes infrequent and therefore probably very large earthquakes m w 7 0 if such large earthquakes have occurred we speculate that they may have been generated by simultaneous rupture of the santa monica fault with other faults in the transverse ranges southern boundary fault system such as the hollywood or anacapa dume faults the most recent definite santa monica fault surface rupture occurred between ca 10 and 17 ka although a more recent event probably occurred between ca 1 and 3 ka

recent unrest of changbaishan volcano northeast china a precursor of a future eruption 1 over 12 years of continuous monitoring of changbaishan volcano in the border region of china and north korea by means of volcanic seismicity ground deformation and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006 in this so called active period the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background inactive periods the active period was also accompanied by ground inflation high values of co2 he h2 and high ratios of n2 o2 and 3he 4he in volcanic gases released from three hot springs near the caldera rim the monitoring evidence implies pressurization of the magma chamber possibly caused by incremental magma recharge the ground deformation data from both gps and precise leveling are modeled to suggest the corresponding deformation source is at 2 60 km depth beneath the volcano s summit where earthquake swarms were detected in 2002 and 2003 our findings suggest that the magma chamber beneath changbaishan volcano has awakened and resumed activity after remaining dormant since ad 1903 there is an urgent need to keep close watch on this active and very hazardous volcano in northeast china

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

pcaim joint inversion of insar and ground based geodetic time series application to monitoring magmatic inflation beneath the long valley caldera this study demonstrates the interest of using a principal component analysis based inversion method pcaim to analyze jointly insar and ground based geodetic time series of crustal deformation a major advantage of this approach is that the insar tropospheric biases are naturally filtered out provided they do not introduce correlated or high amplitude noise in the input times series this approach yields source models which are well constrained both in time and space due to the temporal resolution of the ground based geodetic data and the spatial resolution of the insar data the technique is computationally inexpensive allowing for the inversion of large datasets to demonstrate the performance of this approach we apply it to the 1997 98 magmatic inflation event in the long valley caldera california

precise relocations and stress change calculations for the upland earthquake sequence in southern california we relocate earthquakes that occurred near the 1988 ml 4 7 and the 1990 ml 5 5 upland california earthquakes to map the fault geometry of the poorly defined san jose fault and to test the static stress triggering hypothesis for this sequence we adopt the l1 norm waveform cross correlation method of shearer 1997 to obtain precise relocations for 1573 events between 1981 and 1997 in the upland area to limit computation time we only perform waveform cross correlation on 60 of the nearest neighbors of each relocated event our final relocations show two linear features the first is imaged by the locations of the initial month of aftershocks of the 1988 upland earthquake which delineate a fault with a dip angle of 45 between 7 and 9 km depth consistent with the mainshock focal mechanism the second linear feature is a plane dipping at about 74 from 2 to 9 km depth which is illuminated by both the 1988 and 1990 upland sequences in agreement with the inferred location of the san jose fault at depth however below 9 km the event locations become more diffuse giving rise to two different interpretations of the fate of the san jose fault at depth one possibility is that the fault shallows at depth consistent with our relocations but not with the focal mechanism of a ml 4 7 deep aftershock alternatively the fault may be offset at depth by the more shallow dipping fault strand broken during the 1988 earthquake using these inferred fault geometries we compute stress changes resulting from slip during the mainshocks to test whether the relocated aftershocks are consistent with the hypothesis that more aftershocks occur where the change in static coulomb failure stress is positive on faults optimally oriented for failure this requires an extension of previous models of changes in the failure stress to three dimensions and arbitrary fault orientation we find that patterns of change in coulomb failure stress differ little between the different fault geometries all are nearly symmetric about the fault and so do not match the aftershock distribution in which most of the off fault events occur to one side of the fault plane

blast densification multi instrumented case history a comprehensive blast densification field study was conducted at a test site in south carolina to densify a loose soil layer at a depth between z 8 13 m the study included extensive laboratory and field characterizations and four carefully monitored blast events results revealed that densification is not an instantaneous phenomenon underlying time dependent processes involve resedimentation drainage of excess pore pressure as the granular skeleton deforms and the effective stress recovers and secondary settlement effects which do not involve excess pore pressure dissipation the degree of densification decreased in successive blasting events and the soil gradually evolved toward an asymptotical terminal density associated with blast densification the blasting sequence and detonation delays appeared to have a minor effect on shear induced movements the increase in penetration resistance manifested 2 years after four blasting drainage events instead surface settlement using standard surveying te

aftershock sequence of the 3 december 1988 pasadena earthquake the pasadena earthquake m l 4 9 of 3 december 1988 occurred at a depth of 16 km probably on the santa monica raymond fault which is recognized as one of the most important faults in the los angeles basin for its potential seismic hazard prior to this event no earthquake larger than magnitude 4 had been recorded since 1930 in this area high quality seismograms were recorded with the pasadena very broadband vbb system iris terrascope station not only for the mainshock but also for the aftershocks at epicentral distances of 3 to 4 km we determined the focal mechanisms of 9 aftershocks using these data for most of the aftershocks the first motion data are too sparse to determine the mechanism we combined the first motion data and the waveform data of p sv and sh waves recorded with the vbb instrument to determine the mechanism and seismic moment of nine aftershocks the average orientations of the p and t axes of the aftershocks are consistent with the strike of the raymond fault the ratio of the logarithm of cumulative seismic moment of aftershocks to that of the seismic moment of the mainshock is significantly smaller than commonly observed

terrasar x interferometry reveals small scale deformation associated with the summit eruption of kīlauea volcano hawai i 1 on 19 march 2008 a small explosive eruption at the summit of k lauea volcano hawai i heralded the formation of a new vent along the east wall of halema uma u crater in the ensuing years the vent widened due to collapses of the unstable rim and conduit wall some collapses impacted an actively circulating lava pond and resulted in small explosive events we used synthetic aperture radar data collected by the terrasar x satellite a joint venture between the german aerospace center dlr and eads astrium to identify and analyze small scale surface deformation around the new vent during 2008 2012 lidar data were used to construct a digital elevation model to correct for topographic phase allowing us to generate differential interferograms with a spatial resolution of about 3 m in k lauea s summit area these interferograms reveal subsidence within about 100 m of the rim of the vent small baseline subset time series analysis suggests that the subsidence rate is not constant and over time may provide an indication of vent stability and potential for rim and wall collapse information with obvious hazard implications the deformation is not currently detectable by other space or ground based techniques

an insar based survey of volcanic deformation in the central andes we extend an earlier interferometric synthetic aperture radar insar survey covering about 900 remote volcanos of the central andes 14 27 s between the years 1992 and 2002 our survey reveals broad 10s of km roughly axisymmetric deformation at 4 volcanic centers two stratovolcanoes are inflating uturuncu bolivia and hualca hualca peru another source of inflation on the border between chile and argentina is not obviously associated with a volcanic edifice here called lazufre and a caldera cerro blanco also called robledo in northwest argentina is subsiding we explore the range of source depths and volumes allowed by our observations using spherical ellipsoidal and crack like source geometries we further examine the effects of local topography upon the deformation field and invert for a spherical point source in both elastic half space and layered space crustal models we use a global search algorithm with gradient search methods used to further constrain best fitting models inferred source depths are model dependent with differences in the assumed source geometry generating a larger range of accepted depths than variations in elastic structure source depths relative to sea level are 8 18 km at hualca hualca 12 25 km for uturuncu 5 13 km for lazufre and 5 10 km at cerro blanco deformation at all four volcanoes seems to be time dependent and only uturuncu and cerro blanco were deforming during the entire time period of observation inflation at hualca hualca stopped in 1997 perhaps related to a large eruption of nearby sabancaya volcano in may 1997 although there is no obvious relation between the rate of deformation and the eruptions of sabancaya we do not observe any deformation associated with eruptions of lascar chile at 16 other volcanoes that had recent small eruptions or fumarolic activity or associated with a short lived thermal anomaly at chiliques volcano we posit a hydrothermal system at cerro blanco to explain the rate of subsidence there for the last decade we calculate the ratio of the volume of magma intruded to extruded is between 1 10 and that the combined rate of intrusion and extrusion is within an order of magnitude of the inferred geologic rate

retrieving 65 years of volcano summit deformation from multitemporal structure from motion the case of piton de la fournaise la reunion island the structure from motion photogrammetry technique enables use of historical airborne photography to achieve high resolution 3d terrain models we apply this method on piton de la fournaise volcano la reunion which allows a unique opportunity to retrieve high resolution 1 5 0 11 m digital elevation models and precise deformation maps of the volcano since 1950 our results provide evidence that the summit volume increased throughout the study period at a stable rate of 2 2 mm3 yr between 1950 and 2000 increasing by a factor of four to 8 0mm3 yr prior to the major 2007 eruption which was accompanied by summit caldera collapse at the same time summit deformation was asymmetric with 9 2 2 5 m of eastward seaward displacement and 1 3 2 5 m to the west during 1950 2015 our results reveal a temporal evolution in the volcano magma influx rate and deformation tracking these fluxes and the long lived preferential eastern motion is crucial to mitigate risks associated to flank destabilization

detailed multidisciplinary monitoring reveals pre and co eruptive signals at nyamulagira volcano north kivu democratic republic of congo this paper presents a thorough description of nyamulagira s january 2010 volcanic eruption north kivu democratic republic of congo based on a combination of field observation and ground based and space borne data it is the first eruption in the virunga volcanic province that has been described by a combination of several modern monitoring techniques the 2010 eruption lasted 26 days and emitted 45 5 106 m3 of lava field observations divided the event into four eruptive stages delimited by major changes in effusive activity these stages are consistent with those described by pouclet 1976 for historical eruptions of nyamulagira co eruptive signals from ground deformation seismicity so2 emission and thermal flux correlate with the eruptive stages unambiguous pre eruptive ground deformation was observed 3 weeks before the lava outburst coinciding with a small but clear increase in the short period seismicity and so2 emission the 3 weeks of precursors contrasts with the only precursory signal previously recognized in the virunga volcanic province the short term increase of tremor and long period seismicity which for example were only detected less than 2 h prior to the 2010 eruption the present paper is the most detailed picture of a typical flank eruption of this volcano it provides valuable tools for re examining former mostly qualitative descriptions of historical nyamulagira eruptions that occurred during the colonial period

the 1991 sierra madre earthquake sequence in southern california seismological and tectonic analysis the m l 5 8 sierra madre earthquake of 28 june 1991 occurred at a depth of 12 km under the san gabriel mountains of the central transverse ranges since at least 1932 this region had been quiescent for m 3 the mainshock focal mechanism derived from first motion polarities exhibited almost pure thrust faulting with a rake of 82 on a plane striking n62 e and dipping 50 to the north the event appears to have occurred on the clamshell sawpit fault a splay of the sierra madre fault zone the aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes having a b value of 0 6 twenty nine single event focal mechanisms were determined for aftershocks of m 1 5 the 4 km long segment of the clamshell sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east northeast striking fault plane dipping to the north to the west several thrust aftershocks with east striking nodal planes suggest some complexity in the aftershock faulting such as a curved rupture surface in addition several strike slip and normal faulting events occurred along the edges of the mainshock fault plane indicating secondary tear faulting the tectonic stress field driving the coexisting left lateral strike slip and thrust faults in the northern los angeles basin is north south horizontal compression with vertical intermediate or minimum principal stress axis

on the effects of 3 d mechanical heterogeneities at campi flegrei caldera southern italy 1 campi flegrei caldera located near the highly populated city of naples southern italy is characterized by long term subsidence punctuated by fast uplift phases most of the interpretations of the ground deformation are still based on standard models that assume the lithosphere to behave as a homogeneous half space however several geophysical investigations show the presence of vertical and lateral heterogeneities especially in the shallow subsurface which might have an effect on the interpretation of the surface displacements our 3 d finite element models constrained by seismic tomography to take into account the realistic distribution of mechanical heterogeneities demonstrate that at campi flegrei the assessment of the source location is independent of the consideration of 3 d heterogeneities while the evaluation of its strength is overestimated thus we propose an approach that still allows use of standard homogeneous half space models but accounts for 3 d heterogeneity effects this procedure applied to the deformation field revealed by differential synthetic aperture radar interferometry dinsar over the past 16 years provides new insights for the understanding of the ground displacements observed at campi flegrei caldera this work provides an approach for a quantitative evaluation of the effects of mechanical heterogeneities on surface deformation analogous procedures can be also applied in other volcanic areas where similar to campi flegrei caldera a priori information on the mechanical heterogeneities distribution is available

evolution of unrest at laguna del maule volcanic field chile from insar and gps measurements 2003 to 2014 the laguna del maule ldm volcanic field in the southern volcanic zone of the chilean andes exhibits a large volume of rhyolitic material erupted during postglacial times 20 2 ka since 2007 ldm has experienced an unrest episode characterized by high rates of deformation analysis of new gps and interferometric synthetic aperture radar insar data reveals uplift rates greater than 190 mm yr between january 2013 and november 2014 the geodetic data are modeled as an inflating sill at depth the results are used to calculate the temporal evolution of the vertical displacement the best time function for modeling the insar data set is a double exponential model with rates increasing from 2007 through 2010 and decreasing slowly since 2010 we hypothesize that magma intruding into an existing silicic magma reservoir is driving the surface deformation modeling historical uplift at yellowstone long valley and three sisters volcanic fields suggests a common temporal evolution of vertical displacement rates

the 1987 whittier narrows earthquake sequence in los angeles southern california seismological and tectonic analysis the october 1 1987 whittier narrows earthquake m l 5 9 was located at 34 2 96 n 118 4 86 w at a depth of 14 6 0 5 km in the northeastern los angeles basin the focal mechanism of the mainshock derived from first motion polarities shows pure thrust motion on west striking nodal planes with dips of 25 5 and 65 5 respectively the aftershocks define an approximately circular surface that dips gently to the north centered at the hypocenter of the mainshock with a diameter of 4 6 km hence the spatial distribution of the mainshock and aftershocks as well as the focal mechanisms of the mainshock indicate that the causative fault was a 25 north dipping thrust fault striking west and is confined to depths from 10 to 16 km although most of the 59 aftershock focal mechanisms presented here document a complex sequence of faulting they are consistent with deformation of the hanging wall caused by the thrust faulting observed in the mainshock a cluster of reverse faulting events on north striking planes occurred within hours after the mainshock 2 km to the west of the mainshock the largest aftershock m l 5 3 occurred on october 4 and showed mostly right lateral faulting on the same north northwest striking plane within the hanging wall similarly several left lateral focal mechanisms are observed near the eastern edge of the mainshock rupture the earthquake and calibration blast arrival time data were inverted to obtain two refined crustal velocity models and a set of station delays when relocating the blast using the new models and delays the absolute hypocentral location bias is less than 0 5 km the mainshock was followed by nearly 500 locatable aftershocks which is a small number of aftershocks for this magnitude mainshock the decay rate of aftershock occurrences with time was fast while the b value was low 0 67 0 05 for a los angeles basin sequence

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

gravity changes and deformation at kīlauea volcano hawaii associated with summit eruptive activity 2009 2012 analysis of microgravity and surface displacement data collected at the summit of k lauea volcano hawaii usa between december 2009 and november 2012 suggests a net mass accumulation at 1 5 km depth beneath the northeast margin of halema uma u crater within k lauea caldera although residual gravity increases and decreases are accompanied by periods of uplift and subsidence of the surface respectively the volume change inferred from the modeling of interferometric synthetic aperture radar deformation data can account for only a small portion as low as 8 of the mass addition responsible for the gravity increase we propose that since the opening of a new eruptive vent at the summit of k lauea in 2008 magma rising to the surface of the lava lake outgasses becomes denser and sinks to deeper levels replacing less dense gas rich magma stored in the halema uma u magma reservoir in fact a relatively small density increase 200 kg m 3 of a portion of the reservoir can produce the positive residual gravity change measured during the period with the largest mass increase between march 2011 and november 2012 other mechanisms may also play a role in the gravity increase without producing significant uplift of the surface including compressibility of magma formation of olivine cumulates and filling of void space by magma the rate of gravity increase higher than during previous decades varies through time and seems to be directly correlated with the volcanic activity occurring at both the summit and the east rift zone of the volcano

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

geotechnical analysis of paleoseismic shaking using liquefaction features a major updating a new methodology is proposed for the geotechnical analysis of strength of paleoseismic shaking using liquefaction effects the proposed method provides recommendations for selection of both individual and regionally located test sites provides techniques for validation of field data for use in back analysis and presents a recently developed energy based solution to back calculate paleoearthquake magnitude and strength of shaking the proposed method allows investigators to qualitatively assess the influence of post earthquake density change and aging the proposed method also describes how the back calculations from individual sites should be integrated into a regional assessment of paleoseismic parameters

the 1988 and 1990 upland earthquakes left lateral faulting adjacent to the central transverse ranges two earthquakes m l 4 6 and m l 5 2 occurred at almost the same location in upland southern california in june 1988 and february 1990 and had similar strike slip focal mechanisms with left lateral motion on a northeast striking plane the focal mechanisms and aftershock locations showed that the causative fault was the san jose fault an 18 km long concealed fault that splays west southwest from the frontal fault of the central transverse ranges left lateral strike slip faults adjacent to the frontal faults may play an important role in the deformation of the transverse ranges and the los angeles basin as suggested by these upland earthquakes the left lateral strike slip 1988 m l 4 9 pasadena earthquake on the raymond fault 30 km to the west of upland and scattered background seismicity along other active left lateral faults these faults may transfer slip away from part of the frontal fault toward the south alternatively these faults could represent secondary faulting related to the termination of the northwest striking right lateral strike slip faults to the south of the range front the 1988 and 1990 upland earthquakes ruptured abutting or possibly overlapping segments of the san jose fault the edges of the overlapping aftershock zones which are sharply defined together with background seismicity outline a 14 km long aseismic segment of the san jose fault the 1988 mainshock originated at 9 5 km depth and caused aftershocks between 5 and 12 km in contrast the 1990 mainshock focus occurred at the top of its aftershock zone at 5 km and caused aftershocks down to 13 km depth these deep aftershocks tapered off within 2 weeks the rate of occurrence of aftershocks in magnitude time space was the same for both sequences the state of stress reflected in the focal mechanisms of the aftershocks is identical to that determined from background activity and did not change with time during the aftershock sequence the constant stress state suggests that the 1988 and 1990 events did not completely release all the stored slip on that segment of the fault the presence of 14 km of unbroken fault the abrupt temporal termination of deep aftershocks and the constant stress state all suggest that a future moderate sized earthquake m l 6 0 6 5 on the san jose fault is possible with a rupture length of at least 14 km and possibly 18 km

active tectonics paleoseismology and seismic hazards of the hollywood fault northern los angeles basin california data from geotechnical boreholes and trenches in combination with geomorphologic mapping indicate that the hollywood fault is an oblique reverse left lateral fault that has undergone at least one surface rupturing earthquake during latest pleistocene to middle or late holocene time geomorphologic observations show that the fault extends for 14 km along the southern edge of the eastern santa monica mountains from the los angeles river westward through downtown hollywood to northwestern beverly hills where the locus of active deformation steps 1 2 km southward along the west beverly hills lineament to the santa monica fault rupture of the entire hollywood fault by itself could produce a m w 6 6 earthquake similar in size to the highly destructive 1994 northridge earthquake but even closer to more densely urbanized areas assuming a 0 35 mm yr minimum fault slip rate consistent with available geologic data we calculate an average maximum recurrence interval for such moderate events of 4000 yr although occurrence of such moderate events is consistent with the elapsed time since the poorly constrained age of the most recent surface rupture the data do not preclude a longer quiescent interval suggestive of larger earthquakes if earthquakes much larger than m w 6 6 occurred in the past we speculate that they may have been generated by the hollywood fault together with other faults in the transverse ranges southern boundary fault system

densification of pond ash by blasting fly ash from thermal power plants is disposed in huge quantities in ash ponds which occupy large land areas otherwise useful for agriculture housing or other development for effective rehabilitation of ash ponds densification of the slurry deposit is essential to increase the bearing capacity and to improve its resistance to liquefication extensive field trials were carried out to evaluate the effectiveness of deep blasting for densification of deposited fly ash ninety explosions comprising 15 single blasts with varying depths and quantities of charges and 3 group blasts each having 25 charges placed at various spacings were carried out the compaction achieved in terms of an increase in relative density was evaluated from surface settlement measurements extensive field monitoring was undertaken through pore water pressure measurements vibration measurements penetration tests and block vibration tests for the average charge of 2 4 g of explosive per cubic meter of untreated deposit the average relative density was found to improve from 50 to 56 58 analysis of the test results indicates that deep blasting may be an effective technique for modest compaction of loose fly ash deposits the field testing program presented in this paper provides valuable information that can be used for planning blast densification of fly ash deposits