apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

paleomagnetism of the late precambrian fourchu group cape breton island nova scotia volcanogenic sediments of the fourchu group and a gabbroic intrusion which are found in the avalonian terrane of south eastern cape breton island have been sampled for paleomagnetic analysis upo

paleomagnetism of the little dal lavas mackenzie mountains northwest territories canada the proterozoic stratigraphic column of the mackenzie mountains is dominated by two main successions the platformal mackenzie mountains supergroup beneath and the windermere equivalent rapitan

three dimensional velocity structures of mount fuji and the south fossa magna central japan 1 we present the three dimensional structures of the p wave velocity vp s wave velocity vs as well as the p wave to s wave velocity ratio vp vs beneath mount fuji and the south fossa magna japan using arrival time data collected from 2002 to 2005 by a dense seismograph array the high resolution data set and improved methodology reveal not only several velocity features that are consistent with previous studies but also important new details that clarify the velocity structures associated with volcanic processes beneath mount fuji and the collision tectonics of the south fossa magna one such particular feature is a low vp low vs and low vp vs anomaly at depths of 7 17 km beneath mount fuji that corresponds with the locations of deep low frequency dlf earthquakes the coincidence of the velocity anomaly and the dlf locations suggests that supercritical volatile fluid such as h2o and co2 may be abundant in the low vp vs region and may play an important role in generating dlf earthquakes this anomaly overlies a deeper low vp low vs and high vp vs anomaly at depths of 15 25 km that may represent a zone of basaltic partial melt a low vp low vs and low vp vs anomaly is seen at depths of 6 14 km beneath mount hakone isovelocity surfaces vp 6 0 km s and vs 3 5 km s corresponding to the upper limit of hypocenter distribution below mount fuji may define the upper surface of the philippine sea plate whose existence in a seismic gap beneath mount fuji has been controversial

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

pull aparts shear fractures and pressure solution vein arrays are often composed of pull aparts which are linked by shear fractures good examples of which occur in the lower jurassic limestones of somerset southwestern england such pull apart arrays have displacement distance characteristics which are similar to fault zones with maximum displacement indicated by the largest pull apart widths near the centre of the array and with displacement decreasing towards the tips pull apart arrays usually die out into enechelon or pinnate veins evidence for pressure solution along the shear fractures which connect pull aparts include their dark and braided nature their obliquity to the displacement direction the high dihedral angles often 90 between conjugate shear fractures and the dissolution of earlier structures a range of geometries occurs with varying relative amounts of veins and pressure solution being related to varying amounts of transtension or transpression there is a general trend for an increase in the angle between vein segments and the shear fractures as contraction increases there is therefore a trend for increased pressure solution on the shear fractures in more contractional arrays the concentration of insoluble material along shear fractures has important implications for the mechanics and sealing of faults

fine fracture structures in the geothermal region of hakone volcano revealed by well resolved earthquake hypocenters and focal mechanisms abstract we investigated precise hypocentral distribution and the mechanisms of small earthquakes in the geothermal region of hakone volcano central japan where swarm activity has been frequently observed earthquake swarms were remarkably prevalent in 2001 and 2006 and were accompanied by crustal deformation we first determined initial hypocenters using station corrections and one dimensional velocity structures as estimated by the joint hypocenter determination method then we applied the double difference method to relocate the initial hypocenters using the differential arrival time obtained by both manual picking and waveform cross correlation analysis subsequently we determined the focal mechanisms from the absolute p and sh wave amplitudes and p wave polarities from the relocated hypocenter distribution we found that most swarm earthquakes are distributed on thin plane like zones with width length of 100 m to 1 km we found that these plane like hypocentral distributions range from the e w to n s strikes and are consistent with one of the nodal planes of the focal mechanism it is likely that most swarm earthquakes occurred on pre existing fracture planes shaping the plane like hypocenter distributions previous studies suggested that a highly permeable fracture system has developed in the fault interaction area and these highly permeable fractures affect the occurrence of swarm earthquakes and surface geothermal activity since hakone volcano is located in the interaction area of the active tanna and hirayama faults it is suggested that the fracture planes revealed by the relocated hypocenter distribution have been developed by the activity of the two faults the fracture planes in the caldera might be channels for the hydrothermal water of hot springs in the caldera of hakone volcano which are rich in sodium chloride and considered to be composed of fluid heated by a deep seated magma the strike of the fracture plane on which the swarm earthquakes of the 2001 activity occurred is inconsistent with the orientation of open crack models estimated from geodetic data it is therefore possible that the hydrothermal fluid aseismically intruded the open cracks during the 2001 activity

stress induced spatiotemporal variations in anisotropic structures beneath hakone volcano japan detected by s wave splitting a tool for volcanic activity monitoring hakone volcano located at the northern tip of the izu mariana volcanic arc japan has a large caldera structure containing numerous volcanic hot springs earthquake swarms have occurred repeatedly within the caldera the largest seismic swarm since the commencement of modern seismic observations in 1968 occurred in 2001 we investigated the anisotropic structure of hakone volcano based on s wave splitting analysis and found spatiotemporal changes in the splitting parameters accompanying the seismic swarm activity depth dependent anisotropic structures are clearly observed a highly anisotropic layer with a thickness of 1 5 km is located beneath the koziri kzr and kozukayama kzy stations the anisotropic intensity in the region reaches a maximum of 6 7 at a depth of 1 km and decreases markedly to less than 1 at a depth of 2 km the anisotropic intensity beneath komagatake station kom decreases gradually from a maximum of 6 at the surface to 0 at a depth of 5 km but is still greater than 2 5 at a depth of 3 km at kzy the anisotropic intensity along a travel path of which the back azimuth was the south decreased noticeably after the 2001 seismic swarm activity during the swarm activity tilt meters and gps recorded the crustal deformation the observed decrease in anisotropic intensity is presumed to be caused by the closing of microcracks by stress changes accompanying crustal deformation near the travel path

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

earthquake source fault beneath tokyo devastating earthquakes occur on a megathrust fault that underlies the tokyo metropolitan region we identify this fault with use of deep seismic reflection profiling to be the upper surface of the philippine sea plate the depth to the top of this plate 4 to 26 kilometers is much shallower than previous estimates based on the distribution of seismicity this shallower plate geometry changes the location of maximum finite slip of the 1923 kanto earthquake and will affect estimations of strong ground motion for seismic hazards analysis within the tokyo region

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

a magma hydrothermal system beneath hakone volcano central japan revealed by highly resolved velocity structures high resolution images of subsurface structures are necessary to understand the transport processes of crustal fluids from deep magma sources and their relationship to earthquake swarms in active volcanic regions based on a seismic tomography approach we have developed a new model for the magma hydrothermal system beneath hakone volcano central japan where shallow earthquake swarms and crustal deformation associated with inflation of an open crack source are often observed by applying travel time data for local earthquakes to a tomographic inversion we obtained highly resolved seismic velocity structures that show a region of low p wave velocity vp low s wave velocity vs and high vp vs ratios at depths of 10 20 km beneath the volcano corresponding to the location of the open crack source we suggest that the high vp vs ratios represent a deep magma chamber with a high concentration of melt and or fluids deep low frequency earthquakes located just beneath this high vp vs zone may indicate that magmatic fluids are supplied from below above the high vp vs zone a region of low vp low vs and low vp vs ratios exists at depths of 3 10 km suggesting the presence of crack filled water or co2 supplied from the inferred deep magma chamber many earthquake swarms occur in this low vp vs zone indicating that crustal fluids play an important role in generating the swarms similar relationships between magma reservoirs overlying hydrothermal systems and swarm activity have been reported from other volcanic areas and thus may be a ubiquitous feature beneath active volcanoes

is there a link between faulting and magmatism in the south central aegean sea a distinct spatial relationship between surface faulting magmatic intrusions and volcanic activity exists in the aegean continental crust in this paper we provide detailed structural observations from key onshore areas as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship although pluton emplacement was associated with low angle extensional detachments the nne to ne trending strike slip faults also played an important role in localizing the middle miocene plutonism providing ready pathways to deeper magma batches and controlling the late stage emplacement and deformation of granites in the upper crust additionally the linear arrangements of volcanic centres from the quaternary volcanoes along the active south aegean volcanic arc are controlled primarily by ne trending faults and secondarily by nw trending faults these volcanic features are located at several extensional settings which are associated with the main ne trending faults such as i in the extensional steps or relay zones between strike slip and oblique normal fault segments ii at the overlap zones between oblique normal faults associated with an extensional strike slip duplex and iii at the tip zone of a ne trending divergent dextral strike slip zone the ne trend of volcano tectonic features such as volcanic cone alignments concentration of eruptive centres hydrothermal activity and fractures indicates the significant role of tectonics in controlling fluid and magma pathways in the aegean upper crust furthermore microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these ne trending faults

possible role of fluids in the process of earthquake swarm generation in the west bohemia vogtland seismoactive region abstract the west bohemia vogtland region in the western part of the bohemian massif known for periodic occurrence of earthquake swarms is also characterised by 0 2 0 5 ma old quaternary volcanoes rich co2 emissions anomalies of mantle derived he mineral springs and moffets the detailed analysis of the time space pattern of seismicity during the january 1997 swarm demonstrates the gradual and ordered migration of micro seismic activity suggesting the step by step penetration of fluids into a small fractured volume this scenario is supported by the similarity of the source mechanisms of the natural events of the january 1997 swarm with artificial injection induced micro earthquakes during the german deep drilling project ktb in neighbouring ne bavaria also the comparison of the west bohemia vogtland earthquake swarm region with other intraplate earthquake swarm regions and with earthquake swarms induced by current volcanic processes indicates a role of intrusions of magma and related fluids in generation process of earthquake swarms

the 2013 earthquake swarm in helike greece seismic activity at the root of old normal faults the corinth rift in central greece has been studied extensively during the past decades as it is one of the most seismically active regions in europe it is characterized by normal faulting and extension rates between 6 and 15 mm yr 1 in an approximately n10e direction on 2013 may 21 an earthquake swarm was initiated with a series of small events 4 km southeast of aigion city in the next days the seismic activity became more intense with outbursts of several stronger events of magnitude between 3 3 and 3 7 the seismicity migrated towards the east during june followed by a sudden activation of the western part of the swarm on july 15th more than 1500 events have been detected and manually analysed during the period between 2013 may 21 and august 31 using over 15 local stations in epicentral distances up to 30 km and a local velocity model determined by an error minimization method waveform similarity based analysis was performed revealing several distinct multiplets within the earthquake swarm high resolution relocation was applied using the double difference algorithm hypodd incorporating both catalogue and cross correlation differential traveltime data which managed to separate the initial seismic cloud into several smaller densely concentrated spatial clusters of strongly correlated events focal mechanism solutions for over 170 events were determined using p wave first motion polarities while regional waveform modelling was applied for the calculation of moment tensors for the 18 largest events of the sequence selected events belonging to common spatial groups were considered for the calculation of composite mechanisms to characterize different parts of the swarm the solutions are mainly in agreement with the regional nne ssw extension representing typical normal faulting on 30 50 north dipping planes while a few exhibit slip in an nne ssw direction on a roughly subhorizontal plane moment magnitudes were calculated by spectral analysis of s waves yielding b values between 1 1 and 1 2 in their frequency magnitude distribution the seismic moment release history indicates swarm like activity during the first phase which could have acted as a preparatory stage for the second phase after 12 july that presented a more typical main shock aftershock behaviour the spatiotemporal analysis reveals that the swarm has occurred in a volume that is likely related with the extension at depth of the nne dipping pirgaki normal fault outcropping 8 km to the south the slow velocity of eastward migration of the epicentres during june implies triggering by fluids the situation appears different in the second phase of the sequence which was probably triggered by a build up of stress during the first one the relatively deep hypocentres of the 2013 swarm compared to the shallower seismic layer within the rift and their coincidence with the steeply dipping pirgaki fault favour an immature rift detachment model previous results from instrumental data indicate that approximately the same region had been activated during july august 1991 the availability of the dense permanent seismological network data thus allowed for a detailed analysis of this crisis a better understanding of its mechanical context and of the earlier events

remotely triggered seismic activity in hakone volcano during and after the passage of surface waves from the 2011 m9 0 tohoku oki earthquake abstract immediately after the march 11 2011 m9 0 tohoku oki earthquake seismic activity increased remarkably beneath hakone volcano central japan at an epicentral distance of 450 km the heightened seismicity was initiated during the passage of the large amplitude surface waves from the main shock and continued over the subsequent 2 months we obtained hypocenters and focal mechanisms of the seismic sequence with the aim of clarifying the physical mechanism responsible for the remotely triggered seismicity we used data from a dense seismic network containing 56 online permanent and offline temporary stations in and around the hakone volcano we found that the earthquakes that occurred during the passage of the surface waves are located at the lower depth limit of ordinary seismicity in the caldera these earthquakes have larger magnitudes than both the ordinary seismicity prior to the tohoku oki earthquake and the seismicity triggered after the passage of the surface waves the focal mechanism that we determined is a strike slip fault type with the p axis in the nw se direction which is consistent with the focal mechanisms of earthquakes that occurred after the passage of the surface waves and the tectonic stress field in the region we also tried to detect missing events that occurred immediately after the passage of the surface waves by using a waveform correlation technique the detected events are distributed near the hypocenters of the earthquakes that occurred during the passage of the surface waves the origin times of the first four events after the arrival of surface waves are consistent with the phases of the decrease in normal stress generated by the surface waves the results suggest that the changes in dynamic stress due to the surface waves from the 2011 tohoku oki earthquake contributed significantly to the initiation of the sequence of triggered seismic activity assuming that normal stress changes on the faults did play an important role in the triggering of earthquakes we propose that fluid flow induced by the oscillation of permeability on the faults is the main mechanism for the initiation of post tohoku oki earthquakes beneath the hakone volcano

fluid induced swarm earthquake sequence revealed by precisely determined hypocenters and focal mechanisms in the 2009 activity at hakone volcano japan 1 a swarm earthquake sequence is often assumed to be triggered by fluid flow within a brittle fault damage zone which is assumed to be highly permeable however there is little seismological evidence of the relation between the fluid flow within the fault damage zone and the occurrence of swarm earthquakes here we precisely determine the hypocenters and focal mechanisms of swarm earthquakes that occurred in the caldera of hakone volcano central japan using data from a dense seismic network we demonstrate that the swarm earthquakes are concentrated on four thin plane like zones each of which has a thickness of approximately 100 m one of the nodal planes of the focal mechanisms agrees with the planar hypocenter distribution the swarm earthquakes that occurred during the initial stage of the activity exhibited a migration of hypocenters that appears to be represented by the diffusion equation based on the spatiotemporal distribution of the earthquakes the hydraulic diffusivity is estimated to be approximately 0 5 1 0 m2 s the observations imply that swarm earthquakes were triggered by the diffusion of highly pressured fluid within the fault damage zone a burst like occurrence of the swarm earthquakes is also observed in the later stage these swarm earthquakes are thought to have been triggered primarily by local stress changes caused by the preceding activity the complicated spatiotemporal pattern is thought to have been caused by the effect of the fluid flow within the high permeability damage zones as well as the stress perturbations generated by the swarm earthquakes themselves