dense gps array observations across the atotsugawa fault central japan 1 a cross fault gps array is established to reveal the crustal motion around the atotsugawa fault located in a large strain rate zone in central japan the array has 7 sites along a baseline of 30 km four year observations delineate a characteristic rate field the eastward and the westward motions of 5 mm yr at the sites 25 km apart from the fault gradually decrease and the directions of the motion change towards the ene wsw fault strike as approaching the fault these observations are explained by a simple model two 15 km thick elastic blocks are obliquely colliding along the atotsugawa fault with a rate of 20 mm yr in an ew direction however in the zone sandwiched by the atotsugawa and the ushikubi faults the rates are small and the rate vectors have the fault normal components suggesting that the collision boundary forms a zone with lower elasticity or inelastic property

spatial distribution of focal mechanisms for interplate and intraplate earthquakes associated with the subducting pacific plate beneath the northeastern japan arc a triple planed deep seismic zone the northeastern japan arc is located in one of the most seismically active subduction zones in the world in this study we relocated hypocenters and determined focal mechanisms of small earthquakes m 5 beneath the arc in order to investigate in detail the stress distribution in and around the descending oceanic plate in the hypocenter relocation we adopted a source region station correction method in which station corrections vary with hypocenter locations we have developed a new focal mechanism determination technique named master solution method which is analogous to the master event method in hypocenter determination we applied the method to p and sh wave amplitude data to obtain 1106 focal mechanism solutions from the new mechanism solutions and relocated hypocenters we found that there occur both low angle thrust fault lt type and downdip compression dc type earthquakes at depths from 40 to 70 km near the aseismic front the dc type events are underlying the lt type events almost all the earthquake clusters are composed of lt type events the western limit of the region where lt type events have occurred is subparallel to the trench axis although it undulates considerably it delineates the westernend of the active region of interplate seismicity furthermore we found that normal fault nf type events also occur at depths from 70 km in the upper plane of the double planed deep seismic zone which is characterized mainly by dc type event these nf type events are distributed only in a thin uppermost portion of the slab close to the plate boundary below these in the lower plane are downdip extension de type events this result indicates that the deep seismic zone in the northeastern japan arc is not double planed but triple planed even beneath the land area which cannot be explained by any simple models

time lapse seismic tomography of an underground mining zone abstract in this study we determined p wave tomographic images of the yongshaba deposit an underground mining zone in guizhou province china by inverting arrival time data of micro seismic events and blasts recorded by a passive seismic array consisting of 28 sensors during january to april 2014 using an event location technique and a travel time tomography method that can handle complex seismic discontinuities the damping parameter used in the damped least squares method is determined with the help of trade off curve to reveal internal p wave velocity changes of the study area under severe mining activities a time lapse data partition scheme is used to assess the human influence on the underground structure we introduce a parameter to measure the relative velocity changes in different periods the resolution of the tomographic images and the robustness of the obtained features are examined by conducting a series of checkerboard resolution tests and a restoring resolution test our tomographic results obtained from the entire data set reveal a prominent low velocity low v zone and many obvious high velocity high v zones these features match well with the geological setting and the excavation plan carried out in the mine according to in site surveys the low v zone may reflect empty volumes stress releases and rock breaking and cracking caused by mining activities whereas the high v zones are probably the consequences of local stress concentrations caused by regional stress redistribution the time lapse tomographic images may reveal the process of stress concentrations caused by rock breaking due to the continuing excavations in the entire observation period indicating that the mining activities influenced the rock property and caused complex changes of the underground structure

focal mechanisms of small earthquakes beneath the japanese islands based on first motion polarities picked using deep learning knowledge of crustal stress field is essential for understanding tectonics and earthquake generation one way to estimate the crustal stress field is based on focal mechanisms of earthquakes this

decorrelation in interferometric radar echoes a radar interferometric technique for topographic mapping of surfaces implemented utilizing a single synthetic aperture radar sar system in a nearly repeating orbit is discussed the authors characterize the various sources contributing to the echo correlation statistics and isolate the term which most closely describes surficial change they then examine the application of this approach to topographic mapping of vegetated surfaces which may be expected to possess varying backscatter over time it is found that there is decorrelation increasing with time but that digital terrain model generation remains feasible the authors present such a map of a forested area in oregon which also includes some nearly unvegetated lava flows such a technique could provide a global digital terrain map

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

using microearthquakes to track repeated magma intrusions beneath the eyjafjallajokull stratovolcano iceland 1 we have mapped microearthquakes caused by magma migration preceding and during the flank and summit eruptions in march may 2010 of eyjafjallajokull stratovolcano in iceland using a coalescence microseismic mapping technique spatial and temporal clustering of 5 000 microearthquakes under the eastern flank of the volcano illuminates several northeast southwest striking sub vertical dikes at 2 6 km b s l emplaced before the fimmvor uhals flank eruption in march this intense precursory seismicity had a lateral extent of 6 km east west and 3 km north south a sequence of 386 microearthquakes during the summit eruption refined by double difference relative relocation defines a sub linear trend inclined 5 10 from vertical extending from the upper mantle at 30 km depth to the summit crater this sequence includes two major clusters at 19 km and 24 km b s l each containing 100 earthquakes all microearthquakes display characteristics of brittle fracture with several subsets of events exhibiting closely similar waveforms within clusters this suggests similar repetitive source processes the deeper clusters may be caused by fracturing solidified magma plugs that form constrictions in an otherwise aseismic melt conduit or they may occur at exit points from melt pockets in which case they indicate positions of magma storage at depth the seismicity deeper than 10 km only starts three weeks after the onset of the summit eruption after which the largest clusters occur at progressively greater depths this temporal pattern may result from pressure release at shallow levels in the magmatic plumbing system progressively feeding down to mobilize deeper melt pockets

stress accumulation process in and around the atotsugawa fault central japan estimated from focal mechanism analysis abstract we estimated 275 focal mechanisms from p wave first motion polarities of small earthquakes obtained in an extensive seismic survey during 2004 2008 in and around the atotsugawa fault central japan where ongoing dextral shear strain concentration has been observed along the fault trace the azimuth direction of p axes is oriented wnw ese which agrees well with previous studies the regional stress disturbance is detected by stress inversion analysis the azimuth of the maximum principal stress axis systematically rotates counterclockwise as the distance from the fault trace decreases the regional stress disturbance is explained by a cumulative slip deficit in the shallower portion of the atotsugawa fault relative to the surrounding fault surface i e the eastern western and deeper extensions of the fault plane

intense seismicity during the 2014 2015 barðarbunga holuhraun rifting event iceland reveals the nature of dike induced earthquakes and caldera collapse mechanisms

stress fields in and around metropolitan osaka japan deduced from microearthquake focal mechanisms abstract present day stress fields in and around metropolitan osaka japan have been investigated based on 238 microearthquake focal mechanism solutions from approximately the past 10 years the successful retrieval of the focal mechanisms in the noisy urban area owed much to the clean seismic data recorded at four borehole observatories deeper than 500 m depth in osaka prefecture in which p wave onset polarity of the microearthquake could be clearly identified we found many microearthquakes with a pure reverse faulting mechanism which is consistent with the faulting style of major active faults within the area 42 km long east dipping uemachi and 38 km long east dipping ikoma fault zones however a considerable number of microearthquakes with strike slip components were also found to occur most of the p axes are oriented in the ese wnw to ene wsw directions sub horizontally conforming to the general tectonic trend of the area the analysis of a stress tensor inversion delineated small but noticeable differences in stress regime on a scale of at least 10 km where strike slip faulting prevails throughout the region but the middle and southern sections of the uemachi fault zone contain some reverse faulting components based on the estimated stress fields together with assumptions regarding the deep geometry of the uemachi fault zone we assessed the reactivation potential of the fault zone through slip tendency analysis the results indicate higher potential in the middle and southern sections of the fault zone which is related to the locally increased reverse component detected there

automated seismic event location by waveform coherence analysis summary automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring since microseismic records are generally characterized bylowsignal to noiseratio automated locationmethods arerequested to be noise robust and sufficiently accurate most of the standard automated location routines arebasedontheautomatedpicking identificationandassociationofthefirstarrivalsofpands waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases although current methods can accurately pick p onsets the automatic picking of the s onset is still problematic especially when the p coda overlaps the s wave onset in this paper we propose a picking free earthquake location method based on the use of the short term average long term average sta lta traces at different stations as observed data for the p phases we use the sta lta traces of the vertical energy function whereas for the s phases we use the sta lta traces of a second characteristic function which is obtained using the principal component analysis technique in order to locate the seismic event we scan the space of possible hypocentral locations and origin times and stack the sta lta traces along the theoretical arrival time surface for both p and s phases iterating this procedure on a 3 d grid we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event a pilot application was performed in the campania lucania region southern italy using a seismic network irpinia seismic network with an aperture of about 150km we located 196 crustal earthquakes depth 20km with magnitude range 1 1 ml 2 7 a subset of these locations were compared with accurate manual locations refined by using a double difference technique our results indicate a good agreement with manual locations moreover our method is noise robust and performs better than classical location methods based on the automatic picking of the p and s waves first arrivals

seismic potential around the northeastern edge of the longmenshan fault zone as inferred from seismological observations we assessed the seismic potential around the northeastern edge of the longmenshan fault zone lfz by analyzing the aftershocks of the 2008 mw 7 9 wenchuan earthquake focusing on the right lateral strike slip qingchuan fault qcf the data used in the present study were collected from a dense network of broadband seismographs installed after the mw 7 9 mainshock by the china earthquake administration we analyzed 440 aftershocks that occurred around the northeastern part of the aftershock area between december 2008 and june 2009 the local magnitudes ml of which ranged from 2 0 to 5 2 we determined 127 well constrained focal mechanism solutions for these aftershocks down to ml 2 5 by using p wave polarity data in conjunction with body wave amplitudes an analysis of the stress tensor inversion revealed that upon approaching the qcf from the lfz the stress field changes from a reverse faulting regime to a mixed regime containing strike slip components and the orientation of the maximum compressional stress changes from a nw se to a wnw ese direction this stress field favors a right lateral strike slip movement along the fault the slip tendency analysis revealed that the qcf is regarded as being favorably oriented to the present day stress field the coseismic coulomb stress changes induced by the mainshock increased along the preferred fault plane in the northeastern half of the qcf which is further loaded by viscoelastic relaxation this evidence suggests that the potential for a future earthquake in the qcf is high

joint focal mechanism determination with source region station corrections using short period body wave amplitude data abstract we have developed a method that simultaneously determines focal mechanism solutions of many small earthquakes and source region station corrections for short period body wave amplitudes by inverting amplitude data of p sh and sv waves together with p wave polarity data the observed seismic waveform includes the effects of site amplification and attenuation along its ray path in addition to the radiation pattern of earthquake source the amplitude of seismograms at frequencies higher than a few hertz is extremely sensitive to heterogeneous structure near the ground surface consequently we need to know in detail the effects of site amplification and attenuation in order to estimate focal mechanisms by using short period waveforms however at present we do not know the detailed crustal structure with a resolution necessary for this estimation in the present study we assume that p and s wave attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance backazimuth and incident angle based on this assumption we determined focal mechanism solutions of many earthquakes and the coefficients in the function for each station simultaneously by using p sh and sv wave amplitudes and p wave polarities we applied the present method to 170 aftershocks of the 1996 onikobe earthquake m 5 9 which occurred in the central part of northeastern japan we obtained focal mechanism solutions of many microearthquakes whose mechanism solutions could not be determined by using p wave polarity data alone p axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east west direction t axes are on average near vertical at the shallowest depth as the depth approaches 5 km the t axes become horizontal and then gradually become near vertical again

automatic bayesian polarity determination this work was funded under a natural environment research council nerc studentship as a case award with schlumberger seismometers were borrowed from the nerc seis uk loan 842 who also archive the data

3 d rotation of double couple earthquake sources summary we discuss 3 d rotations by which one double couple earthquake source can be rotated into another arbitrary double couple due to the symmetry of double couple sources there are four such rotations an algorithm is obtained in analytical form which is also available as a computer program solving the inverse problem of 3 d rotation of double couple earthquake sources i e for each pair of focal mechanisms or seismic moment tensor solutions the program finds all four rotations which rotate one mechanism into another this algorithm may be used in a wide variety of studies of stress field causing earthquakes investigations of the relationship between the focal mechanisms and the tectonic features of a seismogenic region etc the same inversion algorithm can be used to study the 3 d rotation of any symmetric second rank tensor such as the stress or strain tensor

mapping stress and structurally controlled crustal shear velocity anisotropy in california we present shear velocity anisotropy data from crustal earthquakes in california and demonstrate that it is often possible to discriminate structural anisotropy polarization of the shear waves along the fabric of major active faults from stress induced anisotropy polarization parallel to the maximum horizontal compressive stress stress directions from seismic stations located near but not on the san andreas fault indicate that the maximum horizontal compressive stress is at a high angle to the strike of the fault in contrast seismic stations located directly on one of the major faults indicate that shear deformation has significantly altered the elastic properties of the crust inducing shear wave polarizations parallel to the fault plane

determination of stress from slip data faults and folds a new technique is derived to invert slickenside data for the stress field that caused the faulting episode this inversion is simplified by the assumption that the magnitude of the tangential traction on the various fault planes at the time of rupture is similar study of three normal faulting regimes shows that the inversion derived with this assumption yields results that closely match older inversions that did not include the assumption hence the assumption may be valid and is shown to be justified by analyzing a simple fracture criterion application of slip data inversions is extended from faulting regimes to the slip on bedding plane faults in folding regimes comparison of the inversion results with the geometry of the folds shows this application to be successful greatly increasing the number of data sets that can be used to find the paleostress field

role of serpentinized mantle wedge in affecting megathrust seismogenic behavior in the area of the 2010 m 8 8 maule earthquake

imaging crustal structure around the western segment of the atotsugawa fault system central japan 1 the velocity structure at the western segment of the atotsugawa fault system is elucidated by inverting arrival times from local earthquakes and explosive sources using double difference tomography bodies with high p wave velocities vp are imaged at depths greater than 2 km beneath surface traces of the atotsugawa fault system the high velocity bodies which tilt gently to the south markedly coincide with zones of high electrical resistivity quite low resistive zones at shallower depths in the vicinity of the fault correspond to bodies with low vp and high vp vs the top of the high velocity bodies is deeper in the northern and southern areas than that in the center of the fault system showing a convex upward shape within the niigata kobe tectonic zone nktz lateral variations in upper crustal structures could partially contribute to the observed large increase in compressional strain within the nktz

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

reverse modelling for seismic event characterization summary the localization of seismic events is of utmost importance in seismology and exploration current techniques rely on the fact that the recorded event is detectable at most of the stations of a seismic network weak events not visible in the individual seismogram of the network are missed out we present an approach where no picking of events in the seismograms of the recording network is required the observed wavefield of the network is reversed in time and then considered as the boundary value for the reverse modelling assuming the correct velocity model the reversely modelled wavefield focuses on the hypocentre of the seismic event the origin time of the event is given by the time where maximum focussing is observed the spatial extent of the focus resembles the resolution power of the recorded wavefield and the acquisition this automatically provides the uncertainty in the localization with respect to the bandwidth of the recorded data the method is particularly useful for the upcoming large passive networks since no picking is required it has great potential for localizing very weak events not detectable in the individual seismogram since the reverse modelling sums the energy of all recorded traces and therefore enhances the signal to noise ratio similar to stacking in seismic exploration the method is demonstrated by 2 d and 3 d numerical case studies which show the potential of the technique events with a s n ratio smaller than 1 where the events cannot be identified in the individual seismogram of the network are localized very well by the method

permanent scatterers analysis for atmospheric correction in ground based sar interferometry ground based synthetic aperture radar gb sar interferometry has already been recognized as a powerful tool complementary or alternative to spaceborne sar interferometry for terrain monitoring and for detecting structural changes in buildings it has been noted that in spite of the very short range compared with the satellite configuration in gb sar measurement the disturbances due to atmospheric effects cannot be neglected either the analysis of the interferometric phases of very coherent points called permanent scatterers pss allows the evaluation of the atmospheric disturbance and the possibility of removing it in this paper the ps analysis is carried out both on a test site facility and on a real campaign citrin valley italy that provided data with a temporal baseline of about ten months

the source scanning algorithm mapping the distribution of seismic sources in time and space summary we introduce a new method which we call the source scanning algorithm ssa for imaging the distribution of seismic sources in both time and space using trial locations and origin times the method calculates the brightness function by summing the absolute amplitudes observed at all stations at their respective predicted arrival times the spatial and temporal distribution of sources is then identified by a systematic search throughout the model space and time for the maximum brightness the greatest advantages of this method are that 1 it exploits waveform information both arrival times and relative amplitudes without the need to calculate highfrequency synthetic seismograms and 2 it requires neither pre assembled phase picking data nor any a priori assumptions about the source geometry a series of tests using synthetic data have shown that this method is robust and can faithfully recover the input source configuration to within 1 grid interval finally we demonstrate the value of the algorithm by locating a typical tremor event with emergent waveforms that occurred during the recent episodic tremor and slip ets sequence in the northern cascadia subduction zone

depth dependent stress field in and around the atotsugawa fault central japan deduced from microearthquake focal mechanisms evidence for localized aseismic deformation in the downward extension of the fault 1 focal mechanisms have been determined from p wave polarity data as well as body wave amplitudes for 154 microearthquakes that occurred around the atotsugawa fault in central japan between 2002 and 2004 while we found many microearthquakes with a pure strike slip mechanism that is similar to the faulting style of the atotsugawa fault a considerable number of microearthquakes with reverse faulting components are also occurring most of the p axes are horizontal and oriented in the wnw ese direction which conforms to the general tectonic trend in this area in contrast the t axes have a wide range of plunge suggesting that reverse faulting type earthquakes as well as strike slip ones are occurring the most conspicuous feature in the focal mechanism distribution is the depth dependence where shallow earthquakes are primarily reverse faulting and strike slip earthquakes become predominant with depth a stress tensor inversion reveals that the shallower part is characterized by a mixture of reverse and strike slip faulting regimes and that a pure strike slip faulting regime appears only around the bottom of the seismogenic zone together with other geophysical observational evidence for the fault we suggest that the existence of a localized aseismic deformation below the atotsugawa fault is the simplest scenario that can explain the observed stress fields this scenario provides a stress accumulation mechanism of disastrous shallow inland earthquakes in which the localized aseismic deformation accumulates stress onto the fault plane in the seismogenic zone during an earthquake cycle and the main shock would occur when the failure stress is reached on the fault

atmospheric effects in interferometric synthetic aperture radar surface deformation and topographic maps interferogram images derived from repeat pass spaceborne synthetic aperture radar systems exhibit artifacts due to the time and space variations of atmospheric water vapor other tropospheric variations such as pressure and temperature also induce distortions but the effects are smaller in magnitude and more evenly distributed throughout the interferogram than the wet troposphere term spatial and temporal changes of 20 in relative humidity lead to 10 cm errors in deformation products and perhaps 100 m of error in derived topographic maps for those pass pairs with unfavorable baseline geometries in wet regions such as hawaii these are by far the dominant errors in the spaceborne imaging radar c and x band synthetic aperature radar sir c x sar interferometric products the unknown time delay from tropospheric distortion is independent of frequency and thus multiwavelength measurements such as those commonly used to correct radar altimeter and global positioning system gps ionospheric biases cannot be used to rectify the error in the topographic case the errors may be mitigated by choosing interferometric pairs with relatively long baselines as the error amplitude is inversely proportional to the perpendicular component of the interferometer baseline for the sir c x sar hawaii data we found that the best longest baseline pair produced a map supporting 100 m contouring whereas the poorest baseline choice yielded an extremely noisy topographic map even at this coarse contour interval in the case of deformation map errors the result is either independent of baseline parameters or else very nearly so here the only solution is averaging of independent interferograms so in order to create accurate deformation products in wet regions many multiple passes may be required rules for designing optimal data acquisition and processing sequences for interferometric analyses in nondesert parts of the world are 1 to use the longest radar wavelengths possible within ionospheric scintillation and faraday rotation limits 2 for topography maximize interferometer baseline within decorrelation limits and 3 for surface deformation use multiple observations and average the derived products following the above recipe yields accuracies of 10 m for digital elevation models and 1 cm for deformation maps even in very wet regions such as hawaii

ductile fracture of fine grained plagioclase in the brittle plastic transition regime implication for earthquake source nucleation abstract crush zones along strain localized zones of plastic deformation were found in a small natural brittle plastic shear zone in the abukuma mountains ne japan the optical microstructures indicate that crush zones are developed where plastic deformation is strong scanning electron microscopy sem revealed the presence of microvoids which connect together to form intergranular fractures in fine grained plagioclase layers in strain localized zones with crush zones this suggests that the microvoids coalesce in the fine grained plagioclase layers allowed ductile fracture to form crush zones during plastic deformation transmission electron microscopy tem revealed that the dislocation densities of all grains in fine grained plagioclase layers in strain localized zones with crush zones are high while evidence for grain boundary migration and dynamic recrystallization is found away from crush zones during plastic deformation of plagioclase in the brittle plastic transition regime strong plastic deformation with insufficient recrystallization may have resulted in the nucleation of microvoids which link together to form intergranular fractures this process may be an important mechanism during earthquake source nucleation

earthquake source mechanism determination by use of body wave amplitudes an application to swedish earthquakes abstract a method for earthquake source studies based on a combined use of polarity and amplitude observations is proposed it makes use of the impulses of the observed body waves to avoid the introduction of additional source parameters besides the orientation angles and seismic moments a statistical model is proposed and the method is applied to five small earthquakes in sweden recorded by 3 to 5 stations in the distance range of 20 to 100 km the seismic moments of these earthquakes are in the range of 0 6 to 10 10 11 n m 1 n m 10 7 dyne cm the resulting mechanisms are statistically significant and well defined in spite of the fact that for four of the earthquakes only two or less polarities are used furthermore the solutions are close to the mechanism of the major m o 3 5 10 15 n m earthquake in the gulf of finland 1976 they all indicate horizontal principal compressive stresses in the sector e w to sse nnw the successful use of amplitude observations presented in this paper shows that source mechanism inversion can be made based on recordings at only a very few close stations

remote monitoring of the comba citrin landslide using discontinuous gbinsar campaigns this paper describes the use of the discontinuous ground based interferometric synthetic aperture radar technique gbinsar to monitor the displacement of the comba citrin landslide in the north western italian alps two gbinsar surveys were carried out respectively during the summer and the fall of 2015 separated by a temporal baseline of 63 days for each gbinsar survey which lasted respectively 166 2 h 6 dd 22 h 12 and 238 3 h 9 dd 22 h 18 two sets of 139 and 275 sar images were acquired after the selection of a specific stack of persistent scatterers the sar images of each survey were analyzed separately and in combination with the images of the other survey to detect the possible displacements occurred both in every single survey as well as in the elapsed time between the two different campaigns the displacement maps showed that two different sectors of the monitored slope were affected by millimetres to centimetres movements during the monitoring period the results obtained for the comba citrin landslide show that the discontinuous gbinsar can be reliably adopted to monitor the displacement of landslides moving at an average rate of few centimetres per year

integration between ground based and satellite sar data in landslide mapping the san fratello case study abstract the potential use of the integration of psi persistent scatterer interferometry and gb insar ground based synthetic aperture radar interferometry for landslide hazard mitigation was evaluated for mapping and monitoring activities of the san fratello landslide sicily italy intense and exceptional rainfall events are the main factors that triggered several slope movements in the study area which is susceptible to landslides because of its steep slopes and silty clayey sedimentary cover in the last three centuries the town of san fratello was affected by three large landslides developed in different periods the oldest one occurred in 1754 damaging the northeastern sector of the town in 1922 a large landslide completely destroyed a wide area in the western hillside of the town in this paper the attention is focussed on the most recent landslide that occurred on 14 february 2010 in this case the phenomenon produced the failure of a large sector of the eastern hillside causing severe damages to buildings and infrastructures in particular several slow moving rotational and translational slides occurred in the area making it suitable to monitor ground instability through different insar techniques ps insar permanent scatterers sar interferometry techniques using ers 1 ers 2 envisat radarsat 1 and cosmo skymed sar images were applied to analyze ground displacements during pre and post event phases moreover during the post event phase in march 2010 a gb insar system able to acquire data continuously every 14 min was installed collecting ground displacement maps for a period of about three years until march 2013 through the integration of space borne and ground based data sets ground deformation velocity maps were obtained providing a more accurate delimitation of the february 2010 landslide boundary with respect to the carried out traditional geomorphological field survey the integration of gb insar and psi techniques proved to be very effective in landslide mapping in the san fratello test site representing a valid scientific support for local authorities and decision makers during the post emergency management

local stress concentration in the seismic belt along the japan sea coast inferred from precise focal mechanisms implications for the stress accumulation process on intraplate earthquake faults 1 spatial changes in the azimuth of the maximum principal stress 1 axis are found in the intraplate region of southwest japan it is inferred from stress inversions of numerous precise focal mechanisms that the azimuths of the 1 axis in the seismic belt along the japan sea coast are oriented in n110 e n130 e directions while in the surrounding region they are aligned in almost the ew direction n90 e n100 e maximum horizontal compressional stresses in an ew direction are widely observed in the shallow crust in the inland plate along the nankai trough however the maximum horizontal stress in a wnw ese direction is seen only in the seismic belt this spatial change in the stress field in and around the seismic belt is explained by the deformation of an aseismic fault or a ductile fault zone in the lower crust beneath the seismic belt

delineation of probable asperities on the atotsugawa fault central japan using a dense temporary seismic network 1 we elucidate the velocity structure along the atotsugawa fault by inverting arrival times from local earthquakes and explosive sources using double difference tomography high p wave vp and s wave vs velocity bodies are located in the western and eastern sections with depths greater than 2 km most earthquake hypocenters are distributed at the periphery of the high velocity bodies at the western section high vp body extends for 20 km along fault strike and 10 km perpendicular to strike we suggest that the high velocity body imaged at the western section is an asperity that ruptured in the 1858 hietsu earthquake in contrast the central section of the atotsugawa fault is characterized by low vp and low vp vs values the extremely low seismicity and the creep like movements observed at the central section are attributed to this local crustal heterogeneity associated with crustal fluids

non self similar source property for microforeshocks of the 2014 mw 6 2 northern nagano central japan earthquake foreshocks are considered a part of the preparation process for large earthquakes and as such can provide important constraints on earthquake generation we examine the characteristics of the four day long foreshock sequence of the 2014 northern nagano earthquake mw 6 2 using seismograms recorded by a dense seismic observation network including data from a deep borehole closest to the foreshock region the improved earthquake catalog shows a slow speed migration of the sequence toward the mainshock hypocenter implying possible slow slip transients which should have caused stress loading at the mainshock hypocenter analysis of source spectra reveals that foreshocks for mw 1 5 display a weaker dependence of corner frequency on magnitude than expected for self similar scaling suggesting that these micro foreshocks can be regarded as small low frequency earthquakes so far we might have missed the expected weak low frequency pre seismic signals because they emerge only below a certain magnitude and are generally embedded in background noise

aftershock seismicity of the 27 february 2010 mw 8 8 maule earthquake rupture zone on 27 february 2010 the mw 8 8 maule earthquake in central chile ruptured a seismic gap where significant strain had accumulated since 1835 shortly after the mainshock a dense network of temporary seismic stations was installed along the whole rupture zone in order to capture the aftershock activity here we present the aftershock distribution and first motion polarity focal mechanisms based on automatic detection algorithms and picking engines by processing the seismic data between 15 march and 30 september 2010 from stations from iris ipgp gfz and university of liverpool we determined 20 205 hypocentres with magnitudes mw between 1 and 5 5 seismic activity occurs in six groups 1 normal faulting outer rise events 2 a shallow group of plate interface seismicity apparent at 25 35 km depth and 50 120 km distance to the trench with some variations between profiles along strike the aftershocks occur largely within the zone of coseismic slip but extend 50 km further north and with predominantly shallowly dipping thrust mechanisms along dip the events are either within the zone of coseismic slip or downdip from it depending on the coseismic slip model used 3 a third band of seismicity is observed further downdip at 40 50 km depth and further inland at 150 160 km trench perpendicular distance with mostly shallow dipping 28 thrust focal mechanisms indicating rupture of the plate interface significantly downdip of the coseismic rupture and presumably above the intersection of the continental moho with the plate interface 4 a deep group of intermediate depth events between 80 and 120 km depth is present north of 36 s within the maule segment a large portion of events during the inter seismic phase originated from this depth range 5 the magmatic arc exhibits a small amount of crustal seismicity but does not appear to show significantly enhanced activity after the mw 8 8 maule 2010 earthquake 6 pronounced crustal aftershock activity with mainly normal faulting mechanisms is found in the region of pichilemu 34 5 s these crustal events occur in a 30 km wide region with sharp inclined boundaries and oriented oblique to the trench the best located events describe a plane dipping to the southwest consistent with one of the focal planes of the large normal faulting aftershock mw 6 9 on 11 march 2010

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

stress directions in the shallow part of the hikurangi subduction zone new zealand from the inversion of earthquake first motions the numerous earthquakes recorded during recent dense seismograph deployments in the northern south island and southernmost north island and in the raukumara peninsula of new zealand provide an opportunity to investigate stress directions in the shallow part of the hikurangi subduction zone here we invert for the stress tensor orientation for regions within both the subducted and overlying plates using a new method that invokes the coulomb failure criterion and considers all p wave first motions together regardless of whether or not they are sufficient to define single event focal mechanisms the inversion also provides information on which of the two planes with maximum coulomb failure stress is the preferred fault plane in the crust of the subducted plate the least compressive stress 3 is closely aligned with the dip of the plate the subducted plate is acting as an efficient stress guide with slab pull from the deeper part of the plate being transmitted to shallow depths normal faulting on steeply dipping fault planes is favoured suggesting that bending of the crust of the subducted plate is accomplished through bulk simple shear akin to shuffling a vertical deck of cards in the overlying plate in the northeastern south island the greatest and least compressive stresses 1 and 3 are horizontal thus favouring strike slip faulting the orientation of 1 is close to that expected if the overlying plate is contracting in response to coupling at the underlying plate interface however sinistral motion on nw faults is favoured whereas motion on the major ne ene surface faults is predominantly dextral in the raukumara peninsula thrust faulting on steeply dipping planes is favoured in the lower part of the overlying plate and near the plate interface the stress regime at the plate interface does not favour interplate thrusting and a weak interface is required for this to occur it appears that strain in the overlying plate in both the northeastern south island and raukumara peninsula is partitioned in time conjugate faults may be active in taking up strain in the interseismic period between large events on the major faults

temporal analysis of a landslide by means of a ground based sar interferometer a ground based synthetic aperture radar gb sar interferometer is used to retrieve the velocity field of a landslide high resolution images are obtained by means of a time domain sar processor an in depth analysis of the sequence of sar interferograms enables the recognition of a slowly deforming upper scarp in the scene and a debris flow that feeds the accumulation zone of the landslide where a fast change in terrain morphology is observed the estimated deformation map is in agreement with the available measurements obtained by means of global positioning system receivers results show that gb sar interferometry is a cost effective solution for the monitoring of landslides the proposed method is shown to be a valid complement to space and airborne sar and to the traditional geodetic instruments

seismogenic magma intrusion before the 2010 eruption of eyjafjallajokull volcano iceland we present relatively relocated earthquake hypocentres for 1000 microearthquakes ml 3 that occurred during the 2 weeks immediately prior to the 2010 march 20 fissure eruption at fimmvor uhals on the flank of eyjafjallajokull volcano in iceland our hypocentre locations lie predominantly in horizontally separated clusters spread over an area of 10 km2 and approximately 4 km below sea level 5 km below the surface seismic activity in the final 4 d preceding the eruption extended to shallower levels 2 km below sea level and propagated to the surface at the fimmvor uhals eruption site on the day the eruption started we demonstrate using synthetic data that the observed apparent 1 km vertical elongation of seismic clusters is predominantly an artefact caused by only small errors 0 01 0 02 s in arrival time data where the signal to noise ratio was sufficiently good to make subsample arrival time picks by cross correlation of both p and s wave arrivals the mean depth of 103 events in an individual cluster were constrained to 3 84 0 06 km epicentral locations are significantly less vulnerable to arrival time errors than are depths for the seismic monitoring network we used within clusters of typically 100 recorded earthquakes most of the arrivals exhibit similar waveforms and identical patterns of p wave first motion polarities across the entire monitoring network the clusters of similar events comprise repetitive sources in the same location with the same orientations of failure probably on the same rupture plane the epicentral clustering and similarity of source mechanisms suggest that much of the seismicity was generated at approximately static constrictions to magma flow in an inflating sill complex these constrictions may act as a form of valve in the country rock which ruptures when the melt pressure exceeds a critical level then reseals after a pulse of melt has passed through this would generate recurring similar source mechanisms on the same weak fault plane as the connection between segments of the sill system is repeatedly refractured in the same location we infer that the magmatic intrusion causing most of the seismicity was likely to be a laterally inflating complex of sills at about 4 km depth with seismogenic pinch points occurring between aseismic compartments of the sills or between adjacent magma lobes as they inflated during the final 4 d preceding the eruption onset between 22 30 and 23 30 utc on 2010 march 20 the seismicity suggests that melt progressed upwards to a depth of 2 km this seismicity was probably caused by fracturing of the country rock at the margins of the propagating dyke subsequently on the morning of the eruption a dyke propagated eastward from the region of precursory seismic activity to the fimmvor uhals eruption site

nonlinear subsidence rate estimation using permanent scatterers in differential sar interferometry discrete and temporarily stable natural reflectors or permanent scatterers ps can be identified from long temporal series of interferometric sar images even with baselines larger than the so called critical baseline this subset of image pixels can be exploited successfully for high accuracy differential measurements the authors discuss the use of ps in urban areas like pomona ca showing subsidence and absidence effects a new approach to the estimation of the atmospheric phase contributions and the local displacement field is proposed based on simple statistical assumptions new solutions are presented in order to cope with nonlinear motion of the targets

automatic seismic event detection using migration and stacking a performance and parameter study in hengill southwest iceland we investigate the performance of a seismic event detection algorithm using migration and stacking of seismic traces the focus lies on determining optimal data dependent detection parameters for a

surface microseismic imaging in the presence of high velocity lithologic layers surface microseismic monitoring above regions containing high velocity units will be influenced by a reduction in the effective array aperture and contain significant seismic coda due to an increase in reflected and converted wave energy which can influence the capability of surface arrays to image microseismic events we have examined the imaging difficulties due to the reduction of the effective array aperture and increased coda within microseismic data caused by the presence of a fast anhydrite layer we have generated and used finite difference full waveform microseismic synthetics derived from 1d sonic log data taken from an unconventional shale reservoir in complex anhydrite geology two imaging techniques are used to locate the synthetic microseismic events we use a simplistic and easily reproducible standard diffraction imaging procedure and a more sophisticated technique moment tensor microseismic imaging mtmi we have confirmed that the presence of high velocity layers such as anhydrite reduce the overall aperture of a surface array which result in poor resolution of imaged events and reduction in the accuracy of event locations more importantly we have determined that the coda in the microseismic data can isolate itself from the direct arrival stacked into the final imaging result and it can be misinterpreted as separate events located directly below the true source location which is unavoidable given the ambiguity between event location and time comparison of the two imaging procedures found that even though the more sophisticated mtmi was able to better cope with the effects caused by high velocity layers it still demonstrated a significant reduction in resolution of imaged events a reduction in accuracy and evidence of multiple and converted energy still present in the final imaging result

no frictional heat along the san gabriel fault california evidence from fission track thermochronology large earthquakes generate frictional heat and the magnitude of heating is related to the slip magnitude the applied effective normal stress and the frictional strength of the fault we looked for evidence of this heating in apatite fission track age and track length distributions of samples from adjacent to and within the san gabriel fault zone in southern california the fault is thought to be an abandoned major trace of the san andreas fault system active from 13 to 4 ma and has since been exhumed from depths of 2 5 km at our sample locality as much as 40 km of total slip is thought to have accumulated along a localized ultracataclasite layer just 1 8 cm thick we see no evidence of a localized thermal anomaly in either fission track ages or track lengths even in samples within just 2 cm of the ultracataclasite because of the absence of any measurable impact on fission tracks we have been able to use forward modeling of heat generation heat transport and fission track annealing to constrain the frictional properties of the fault we find that either there has never been an earthquake with 4 m of slip at this locality or the average apparent coefficient of friction must have been 0 4

a multiple regression model considering deformation information for atmospheric phase screen compensation in ground based sar the accuracy of ground based synthetic aperture radar gb sar interferometry is highly affected by the atmospheric phase screen aps a multiple regression model mrm for aps estimation with two parameters line of sight los distance and the height difference between the targets and the gb sar sensor was proposed however this mrm is inapplicable if the los deformation of the observed objects has similar behavior to that of the aps for example both the aps and the los deformation of observed objects can have an increasing trend along the los direction in this article an improved mrm imrm that considers the spatial pattern of the los deformation of observed objects was proposed the spatial pattern can be expressed by the location information of the observed objects the applicability of this improved model was demonstrated in a deformation measured campaign carried out on a high loess cut slope using 285 images obtained by the gb sar sensor during a three day measurement the similarity and dissimilarity between the aps and the behavior of the los deformation of the slope were illustrated and used to estimate the aps the accuracy of this imrm was verified using deformation data measured by a displacement meter this imrm will be helpful in aps estimation and compensation in gb sar interferometry in case studies where the aps and the los deformation of observed objects have similar behavior

a new method for measuring deformation on volcanoes and other natural terrains using insar persistent scatterers 1 we present here a new insar persistent scatterer ps method for analyzing episodic crustal deformation in non urban environments with application to volcanic settings our method for identifying ps pixels in a series of interferograms is based primarily on phase characteristics and finds low amplitude pixels with phase stability that are not identified by the existing amplitude based algorithm our method also uses the spatial correlation of the phases rather than a well defined phase history so that we can observe temporally variable processes e g volcanic deformation the algorithm involves removing the residual topographic component of flattened interferogram phase for each ps then unwrapping the ps phases both spatially and temporally our method finds scatterers with stable phase characteristics independent of amplitudes associated with man made objects and is applicable to areas where conventional insar fails due to complete decorrelation of the majority of scatterers yet a few stable scatterers are present

source parameters of a m4 8 and its accompanying repeating earthquakes off kamaishi ne japan implications for the hierarchical structure of asperities and earthquake cycle 1 we determine the source parameters of a m4 9 0 1 characteristic earthquake sequence and its accompanying microearthquakes at 50 km depth on the subduction plate boundary offshore of kamaishi ne japan the microearthquakes tend to occur more frequently in the latter half of the recurrence intervals of the m4 9 0 1 events our results show that the microearthquakes are repeating events and they are located not only around but also within the slip area for the 2001 m4 8 event from the hierarchical structure of slip areas and smaller stress drops for the microearthquakes compared to the m4 8 event we infer the small repeating earthquakes rupture relatively weak patches in and around the slip area for the m4 8 event and their activity reflects a stress concentration process and or change in frictional property healing at the area we also infer the patches for the m4 9 0 1 and other repeating earthquakes undergo aseismic slip during their interseismic period

the izmit kocaeli turkey earthquake of 17 august 1999 previous seismicity aftershocks and seismotectonics a field experiment carried out from 17 july to 2 november 1999 with a dense seismic network surrounding the marmara sea region and including the rupture zone of the izmit kocaeli destructive earthquake of 17 august 1999 m w 7 6 harvard centroid moment tensor delouis et al 2002 permitted the collection of precise seismic data and the quantitative evaluation of the associated set of surface ruptures a previous experiment conducted in 1995 had already given reliable information about the distribution of seismicity in space focal mechanisms and the regional stress regime aftershock distribution and clustering together with the variations of slip amplitude along the fault allow the identification of at least five segments a maximum horizontal displacement of about 5 m is observed in golcuk and east of sapanca lake the rupture is extremely linear but its complexity increases toward the western end including the bifurcation the stress field associated with the aftershocks is compared with the one obtained in 1995 showing the invariance of the smallest principal axis lack of definition of the other principal axes suggests a transition from shear to extension a clear quiescence period of 18 days preceded the izmit earthquake a precursor which occurred 100 sec before had the same epicenter as the mainshock manuscript received 30 august 2000

earthquake mechanisms from linear programming inversion of seismic wave amplitude ratios the amplitudes of radiated seismic waves contain far more information about earthquake source mechanisms than do first motion polarities but amplitudes are severely distorted by the effects of heterogeneity in the earth this distortion can be reduced greatly by using the ratios of amplitudes of appropriately chosen seismic phases rather than simple amplitudes but existing methods for inverting amplitude ratios are severely nonlinear and require computationally intensive searching methods to ensure that solutions are globally optimal searching methods are particularly costly if general moment tensor mechanisms are allowed efficient linear programming methods which do not suffer from these problems have previously been applied to inverting polarities and wave amplitudes we extend these methods to amplitude ratios in which formulation on inequality constraint for an amplitude ratio takes the same mathematical form as a polarity observation three component digital data for an earthquake at the hengill grensdalur geothermal area in southwestern iceland illustrate the power of the method polarities of p sh and sv waves unusually well distributed on the focal sphere cannot distinguish between diverse mechanisms including a double couple amplitude ratios on the other hand clearly rule out the double couple solution and require a large explosive isotropic component

transient and permanent deformation of central japan estimated by gps 2 strain partitioning and arc arc collision abstract deformation of central japan can be divided into two main components elastic deformation due to the interseismic locking of subduction thrusts and deformation associated with intra arc tectonics in a companion paper henry et al earth planet sci lett 2000 this issue we estimated an elastic deformation field based on the modeling of global positioning system gps strain rates in this study we show that the corrected field gps minus predicted elastic deformation is consistent with geological and seismological observations and should represent long term plastic deformation we use this corrected gps deformation field to describe the kinematics of partitioning of the philippine sea plate amurian plate amu convergence in relation with the izu bonin arc collision about one third of the relative philippine sea amur motion is transferred to the central japan crust north of the collision front this transfer induces high strain rates in southern kanto and in the northern japanese alps the latter region corresponds to the eastern boundary of the amu we propose that the independent motion of central japan results from the delamination and the underthrusting of the izu bonin arc lower crust and the upward bent oceanic slab

analysis of ground based sar data with diverse temporal baselines in this paper the algorithms developed for satellite synthetic aperture radar sar interferometry were adapted to the ground based sar gb sar configuration and used for detecting the displacements of an alpine landslide which have occurred over many years indeed gb sar interferometry is based on the same principles as satellite sar techniques but benefits from the gb sar s versatility and capability of gathering many images per day in monitoring applications of landslides moving only few centimeters per year as the case here reported the gb sar sensor is installed at repeated intervals several months apart over the observation period although the revisiting time is very similar to the satellite one for each survey lasting two or three days more than ten images are available they are analyzed separately and in combination with images from other surveys for coherent pixel selection interferograms are formed by cross combining images from different surveys finally the evolution of the deformation across the surveys is retrieved in a least square sense without any assumptions on its regularity the used gb sar technique is described in detail in this paper and the results obtained with regard to a landslide in the italian alps that has been monitored over a period of about three years are discussed

use of fault striations and dislocation models to infer tectonic shear stress during the 1995 hyogo ken nanbu kobe earthquake dislocation models of the 1995 hyogo ken nanbu kobe earthquake derived by yoshida et al 1996 show substantial changes in direction of slip with time at specific points on the nojima and rokko fault systems as do striations we observed on exposures of the nojima fault surface on awaji island spudich 1992 showed that the initial stress that is the shear traction on the fault before the earthquake origin time can be derived at points on the fault where the slip rake rotates with time if slip velocity and stress change are known at these points from yoshida s slip model we calculated dynamic stress changes on the ruptured fault surfaces to estimate errors we compared the slip velocities and dynamic stress changes of several published models of the earthquake the differences between these models had an exponential distribution not gaussian we developed a bayesian method to estimate the probability density function pdf of initial stress from the striations and from yoshida s slip model striations near toshima and hirabayashi give initial stresses of about 13 and 7 mpa respectively we obtained initial stresses of about 7 to 17 mpa at depths of 2 to 10 km on a subset of points on the nojima and rokko fault systems our initial stresses and coseismic stress changes agree well with postearthquake stresses measured by hydrofracturing in deep boreholes near hirabayashi and ogura on awaji island our results indicate that the nojima fault slipped at very low shear stress and fractional stress drop was complete near the surface and about 32 below depths of 2 km our results at depth depend on the accuracy of the rake rotations in yoshida s model which are probably correct on the nojima fault but debatable on the rokko fault our results imply that curved or cross cutting fault striations can be formed in a single earthquake contradicting a common assumption of structural geology

the occurrence of graphite bearing fault rocks in the atotsugawa fault system japan origins and implications for fault creep abstract graphite in fault zones has received little attention even though it is a well known solid lubricant that could affect frictional properties of faults dramatically this paper reports the presence of abundant graphite in fault zones of the atotsugawa fault system central japan mesoscopic and microscopic observations of fault rocks revealed two processes of carbon enrichment in fault zones one is a pressure solution process or diffusive mass transfer in general which removes water soluble minerals such as quartz and carbonates from rocks resulting in the enrichment of insoluble minerals including carbon the other process is precipitation of graphite from a high temperature carbon rich fluid forming graphite filling fractures within cataclasitic fault zones the two processes have led to the concentration up to 12 wt of graphite in the atotsugawa fault zones compared to 0 to 3 wt of carbonaceous materials in the host rocks this concentration is high enough for graphite to affect frictional properties at wide range of slip rates the presence of graphite may provide an explanation for the low resistivity the patterns of microearthquakes and fault creep along the western part of the atotsugawa fault system graphite should receive more attention as a weakening and stabilizing agent of faults

coalescence microseismic mapping earthquakes are commonly located by linearized inversion of discrete arrival time picks made from signals recorded at a network of seismic stations if mis picks are made these will contribute to the location therefore causing potential bias for data recorded by a dense seismic array direct imaging methods can be applied instead we describe the coalescence microseismic mapping method which is a bridge between the two approaches and will operate with seismic data recorded continuously on a sparse array by continuously mapping scalar signals derived from the envelope of seismic arrivals we derive robust estimates of the spatio temporal coordinates of the origins of seismic events noisy data are migrated away from the correct origin so do not contribute to errors in location the method is rooted in a bayesian formulation of event location traveltime inversion allows imaging of source locations and has the capacity to handle errors in modelled traveltimes it has the advantage of working with any 3 d velocity model which therefore may include anisotropy it also automatically incorporates both p and s wave data a multiresolution grid search leads to an efficient implementation with a search over a larger domain including joint inversion for location and velocity structure possible where warranted by the data quality we discuss the theory and implementation of this method and illustrate it with real data from microseismic events in iceland caused by melt intrusion in the crust

recurrence interval of big earthquakes along the atotsugawa fault system central japan results of seismo geological survey 1 the atotsugawa fault system afs characterized by high seismicity of micro earthquakes is an active zone of right lateral strike slip faults in central japan we carried out seismo geological studies of three sites on the system one is in the middle of the master atotsugawa fault agf one is at the end and another is on a branching mozumi sukenobe fault msf trenching surveys demonstrated a maximum recurrence interval of 3 000 years which is similar to that of the central agf 2 500 years this might indicate a uniform behavior in the seismogenic zone despite the apparent segmentation in the shallower agf another geo slicing survey at msf depicted a scarce interval of 13 500 years about six times longer than that of the master fault two simultaneous events on both agf and msf occurred in 1858 a d and at about 17 300 years ago suggesting an intermittent cooperation between the master and branch faults of afs

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

three dimensional p and s wave velocity structures beneath the japan islands obtained by high density seismic stations by seismic tomography abstract we construct fine scale 3d p and s wave velocity structures of the crust and upper mantle beneath the whole japan islands with a unified resolution where the pacific pac and philippine sea phs plates subduct beneath the eurasian eur plate we can detect the low velocity low v oceanic crust of the pac and phs plates at their uppermost part beneath almost all the japan islands the depth limit of the imaged oceanic crust varies with the regions high vp vs zones are widely distributed in the lower crust especially beneath the volcanic front and the high strain rate zones are located at the edge of the extremely high vp vs zone however vp vs at the top of the mantle wedge is not so high beneath northern japan we can image the high v subducting pac plate using the tomographic method without any assumption of velocity discontinuities we also imaged the heterogeneous structure in the pac plate such as the low v zone considered as the old seamount or the highly seismic zone within the double seismic zone where the seismic fault ruptured by the earthquake connects the upper and lower layer of the double seismic zone beneath central japan thrust type small repeating earthquakes occur at the boundary between the eur and phs plates and are located at the upper part of the low v layer that is considered to be the oceanic crust of the phs plate in addition to the low v oceanic crust the subducting high v pac plate is clearly imaged to depths of approximately 250 km and the subducting high v phs zone to depths of approximately 180 km is considered to be the phs plate beneath southwestern japan the iso depth lines of the moho discontinuity in the phs plate derived by the receiver function method divide the upper low v layer and lower high v layer of our model at depths of 30 50 km beneath kyushu the steeply subducting phs plate is clearly imaged to depths of approximately 250 km with high velocities the high vp vs zone is considered as the lower crust of the eur plate or the oceanic crust of the phs plate at depths of 25 35 km and the partially serpentinized mantle wedge of the eur plate at depths of 30 45 km beneath southwestern japan the deep low frequency nonvolcanic tremors occur at all parts of the high vp vs zone within the zone the seaward side and the landward side where the phs plate encounters the mantle wedge of the eur plate we prove that we can objectively obtain the fine scale 3d structure with simple constraints such as only 1d initial velocity model with no velocity discontinuity

a review of terrestrial radar interferometry for measuring surface change in the geosciences this paper presents a review of the current state of the art in the use of terrestrial radar interferometry for the detection of surface changes related to mass movement different hardware types and acquisition concepts are described which use either real or synthetic aperture for radar image formation we present approaches for data processing procedures paying special attention to the separation of high resolution displacement information from atmospheric phase variations recent case studies are used to illustrate applications in terrestrial radar interferometry for change detection applications range from detection and quantification of very slow moving millimeters to centimeters per year displacements in rock walls from repeat monitoring to rapid processes resulting in fast displacements 50 m yr acquired during single measurement campaigns with durations of only a few hours fast and episodic acting processes such as rockfall and snow avalanches can be assessed qualitatively in the spatial domain by mapping decorrelation caused by those processes a concluding guide to best practice outlines the necessary preconditions that have to be fulfilled for successful application of the technique as well as in areas characterized by rapid decorrelation empirical data from a ku band sensor show the range of temporal decorrelation of different surfaces after more than two years for rock surfaces and after a few seconds to minutes in vegetated areas during windy conditions the examples show that the displacement field can be measured for landslides in dense grassland ice surfaces on flowing glaciers and snowpack creep copyright 2014 john wiley sons ltd

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

estimates of stress and strain rate in mylonites based on the boundary between the fields of grain size sensitive and insensitive creep 1 microstructural analyses of mylonites next to the median tectonic line mtl sw japan reveal a transition in the dominant deformation mechanism of quartz from grain size insensitive dislocation creep to grain size sensitive grain boundary sliding gbs the transition occurred under greenschist facies conditions 300 400 c during grain size reduction by dynamic recrystallization the stereologically corrected grain size for the transition is approximately 4 3 m at the boundary between the fields of dislocation creep and gbs as calculated from creep constitutive relations the differential stress and strain rate for this corrected grain size are estimated to be 280 mpa and 1 2 10 11 s 1 for 300 c and 110 mpa and 1 0 10 10 s 1 for 400 c the strain rates estimated for the mylonites next to the mtl are much higher than those estimated for the surrounding metamorphic rocks 10 14 s 1 and the displacement rates calculated based on the thickness of high strain mylonites and their strain rates are comparable with the average slip rates of the most active intraplate faults in japan these inferences suggest that the high strain mylonite zones next to the mtl are the exhumed downward extension of a seismogenic fault in the ductile region the zones were highly localized 10 m and experienced very high strain rates 10 11 to 10 10 s 1

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

calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor calculating horizontal stress orientations with full or partial knowledge of the tectonic stress tensor

structure related and stress induced shear wave velocity anisotropy observations from microearthquakes near the calaveras fault in central california we attempt to distinguish between structure related and stress induced shear wave velocity anisotropy in the upper crust using microearthquakes m 2 6 that occurred before and after the tres pinos california earthquake m 5 5 of 26 january 1986 the tres pinos earthquake occurred on the quien sabe fault a northwest southeast trending right lateral strike slip fault approximately 10 km east of the calaveras fault in central california digital three component seismograms are available from 1984 to 1992 from the quien sabe ranch station hqr located only 7 3 km north northeast of the epicenter of the main event we studied polarization directions and delay times using a method that combines cross correlation techniques and particle motion plots to enhance the significance of our interpretations we reduced uncertainties related to the hypocenter location of the earthquakes by source relocation based on joint hypocenter determination and cross correlation in the study area we found two zones with different but stable polarization directions around the quien sabe fault system shear wave polarizations of over 30 microearthquakes clearly indicate that the slow shear wave direction is normal to the northwest southeast trend of this vertical right lateral strike slip fault thus velocity anisotropy appears to be caused by the fault system itself however anisotropy associated with a cluster of microearthquakes located about 4 km to the east is quite different in this zone the fast and slow shear polarization directions are correlative with the maximum and minimum horizontal stress directions respectively thus in this case it appears the crustal velocity anisotropy is controlled by the state of stress in the crust the observation of these two polarization directions at one station suggests that the shallow crust below the station hqr does not influence shear wave polarization directions

seismic evidence for a slab tear at the puerto rico trench 1 the fore arc region of the northeast caribbean plate north of puerto rico and the virgin islands has been the site of numerous seismic swarms since at least 1976 a 6 month deployment of five ocean bottom seismographs recorded two such tightly clustered swarms along with additional events joint analyses of the ocean bottom seismographs and land based seismic data reveal that the swarms are located at depths of 50 150 km focal mechanism solutions found by jointly fitting p wave first motion polarities and s p amplitude ratios indicate that the broadly distributed events outside the swarm generally have strike and dip slip mechanisms at depths of 50 100 km while events at depths of 100 150 km have oblique mechanisms a stress inversion reveals two distinct stress regimes the slab segment east of 65 w longitude is dominated by trench normal tensile stresses at shallower depths 50 100 km and by trench parallel tensile stresses at deeper depths 100 150 km whereas the slab segment west of 65 w longitude has tensile stresses that are consistently trench normal throughout the depth range at which events were observed 50 100 km the simple stress pattern in the western segment implies relatively straightforward subduction of an unimpeded slab while the stress pattern observed in the eastern segment shallow trench normal tension and deeper trench normal compression is consistent with flexure of the slab due to rollback these results support the hypothesis that the subducting north american plate is tearing at or near these swarms the 35 year record of seismic swarms at this location and the recent increase in seismicity suggest that the tear is still propagating

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

localized ductile shear below the seismogenic zone structural analysis of an exhumed strike slip fault austrian alps 1 the miocene salzachtal ennstal mariazell puchberg semp strike slip fault in austria allows study of the internal structure of a fault zone from the near surface to 30 km depth as it enters the tauern window along the rinderkarsee shear zone the semp fault passes from a dominantly brittle to a dominantly ductile structure the shear zone consists of three 1 to 100 m wide zones of brittle ductile and ductile deformation separated by 500 m wide zones of less deformed rocks the southern shear zone is mylonitic with ductile amphibole and plagioclase weak crystal preferred orientations imply that the main deformation mechanism was dislocation accommodated grain boundary sliding the northern and central shear zones are characterized by discrete millimeter wide shear zones with ductile quartz muscovite and biotite and brittle feldspar shear zone nucleation at the grain scale involved dislocation creep and the transformation of plagioclase to muscovite strain then localized in muscovite rich grain boundary shear zones that linked to form throughgoing shear zones

tectonic evolution of a crustal scale oblique ramp hellenides thrust belt greece abstract this study investigates the tectonic evolution of the omalos transverse zone which served as a crustal scale oblique ramp in the external hellenides thrust belt on crete island the omalos oblique ramp developed above an inherited mesozoic fault zone that strikes ne sw oblique to the regional ssw directed tectonic transport during the early miocene pleistocene evolution of the thrust belt the oblique ramp was repeatedly reactivated localizing deformation above the inherited structure geological and structural mapping combined with kinematic analysis of ductile and brittle structures suggest that the omalos oblique ramp generated a local kinematic field which deviated significantly from the regional kinematic pattern in the thrust belt the most conspicuous feature in the tectonic evolution of the oblique ramp is a change from a ductile wrench dominated to a brittle primarily reverse faulting regime across the brittle ductile transition followed by brittle wrench deformation after the final exhumation of high pressure hp rocks deflections of transport and compression orientations from the regional pattern are attributed to buttressing against basement cover offsets produced by the pre existing fault zone to oblique ramping and to transfer faulting respectively our findings are potentially applicable to other examples of crustal scale oblique thrust ramps in various tectonic settings

deep structure of the northeastern japan arc and its implications for crustal deformation and shallow seismic activity abstract seismic tomography studies in the northeastern japan arc have revealed the existence of an inclined sheet like seismic low velocity and high attenuation zone in the mantle wedge at depths shallower than about 150 km this sheet like low velocity high attenuation zone is oriented sub parallel to the subducted slab and is considered to correspond to the upwelling flow portion of the subduction induced convection the low velocity high attenuation zone reaches the moho immediately beneath the volcanic front or the ou backbone range running through the middle of the arc nearly parallel to the trench axis which suggests that the volcanic front is formed by this hot upwelling flow aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the backbone range where they are expelled from solidified magma and migrate further upward the existence of aqueous fluids may weaken the surrounding crustal rocks resulting in local contractive deformation and uplift along the backbone range under the compressional stress field of the volcanic arc a strain rate distribution map generated from gps data reveals a notable concentration of east west contraction along the backbone range consistent with this interpretation shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone based on these observations a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern japan arc

real time earthquake location using kirchhoff reconstruction real time location of earthquakes can be achieved by using direct imaging of the recorded wave field based on a kirchhoff reconstruction method similar to that used in the migration of seismic reflection data the standard method of event location requires the wave arrival at each sensor to be picked and associated with an event by using direct imaging the event is identified once in the imaged wave field the computation is independent of the level of seismic activity and can be carried out on a typical desktop computer the procedure has been successfully demonstrated in two and three dimensions using data from the southern california seismic network trinet at higher resolutions the reconstruction method can identify finite source effects further work considers extending the method by implementing full elastic theory and solving for moment tensors at all locations in the mesh

seismotectonics of the hida region central honshu japan abstract seismotectonic features of the northern hida region central honshu japan have been investigated in some detail mainly on the basis of the last 6 years of observations of seismicity and focal mechanism of a large number of earthquakes with reference to the geological and tectonic setting and evidence of a large earthquake in the past it was found that high seismicity is concentrated with a remarkably clear lineation but with a relatively low activity in the central section along the atotsugawa fault extending for about 70 km this is one of major quaternary faults in this region the high seismicity with spatially nonuniform distribution may be related to postseismic stress concentration after the 1858 hida earthquake m 7 0 and to heterogeneous fault strength seismicity is also high with belt like extension beneath the hida mountain range which is the highest mountain system in the japan islands the depth distribution of seismicity is clearly bounded at 15 km below the atotsugawa fault and 8 km beneath the hida mountains the local variations can be interpreted as being due to the difference in the brittle ductile transition depth which suggests higher temperature beneath the mountains involving active volcanoes the focal mechanism solutions indicate that the maximum compressive stress is oriented in an ese wnw direction which is more consistent with the direction of motion of the pacific plate relative to the eurasian plate rather than the suggested relative motion between the north america and eurasian plates the magnitude of the shear stress working in this region is estimated to be less than 700 bar

deep roots of upper plate faults and earthquake generation illuminated by volcanism 1 for many years the generation mechanism of disastrous intraplate earthquakes in the upper plate of a subduction zone have remained unclear largely because the roots of upper plate intraplate faults have particularly quiet inter seismic nature and limited visibility here we propose that the 2008 mw 6 9 iwate miyagi nairiku japan earthquake occurred on a dipping fault in a volcanic region contains previously unreported co seismic evidence of a ductile shear zone dsz present on the down dip fault extension beneath the seismogenic layer and dsz plays a dominant role in the seismogenesis we found the evidence in the spatial pattern of the co seismic ground displacement which was well captured by synthetic aperture radar reflecting geothermal anomalies there a dynamic forward model including the inter seismic deformation of dsz naturally reproduced this displacement pattern without kinematic inversions and consistently explained other independent observations this finding should make breakthroughs in observational and theoretical studies of earthquake generation

spatial variation of shear wave splitting across an active fault and its implication for stress accumulation mechanism of inland earthquakes the atotsugawa fault case 1 we analyzed shear wave splitting of small earthquakes around the atotsugawa fault central japan to infer a spatial variation in the direction of maximum horizontal compression shmax while the angle between the shmax direction and fault strike ranges approximately from 55 to 80 at the stations 2 to 8 km from the fault it approaches 45 at the stations within 1 km from the fault the present result indicates the local stress accumulation due to the localized flow or slip along the deep extension of the fault the finite element modeling of the stress field around the fault suggests that the present existing stress field can be explained by the superposition of the stress field associated with regional deformation and the stable slip along the deep extension of the fault

stressing of the new madrid seismic zone by a lower crust detachment fault a new mechanical model for the cause of the new madrid seismic zone in the central united states is analyzed the model contains a subhorizontal detachment fault which is assumed to be near the domed top surface of locally thickened anomalous lower crust rift pillow regional horizontal compression induces slip on the fault and the slip creates a stress concentration in the upper crust above the rift pillow dome in the coseismic stage of the model earthquake cycle where the three largest magnitude 7 8 earthquakes in 1811 1812 are represented by a single model mainshock on a vertical northeast trending fault the model mainshock has a moment equivalent to a magnitude 8 event during the interseismic stage corresponding to the present time slip on the detachment fault exerts a right lateral shear stress on the locked vertical fault whose failure produces the model mainshock the sense of shear is generally consistent with the overall sense of slip of 1811 1812 and later earthquakes predicted rates of horizontal strain at the ground surface are about 10 7 year 1 and are comparable to some observed rates the model implies that rift pillow geometry is a significant influence on the maximum possible earthquake magnitude

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses