recurrence behavior of short term slow slip and correlated nonvolcanic tremor episodes in western shikoku southwest japan 1 from the national research institute for earth science and disaster prevention hi net tiltmeter data we determine time dependent source processes of seven repeating short term slow slip events sse in the western shikoku region southwest japan over the period from 2002 to 2007 the tiltmeters record clear signals of sses characterized by a slow rise a week long duration and a magnitude on the order of 10 2 10 1 rad we apply a time dependent slip inversion method to the tilt records for the seven sses for each sse a slip area migrates in the strike direction of the subducting slab at a rate of 10 km d 1 comparing the slow slip area with epicenters of accompanying nonvolcanic tremors in subday time resolution we find that the two phenomena are located on a smaller area than previously reported and migrate as a group a moment rate function for each sse exhibits good correlation with the temporal change in tremor activity a comparison of the slip distributions of all of the analyzed sses shows that there is a patch of slow slip area 30 km in diameter that is shared by all of the episodes in addition the location of the slip patch is in good agreement with the epicenters of tremors and very low frequency earthquakes these lines of evidence suggest that the identified slip patch is one of the main slow slip patches in the region and a recurrence of sses may be controlled by the patch and that these slow earthquakes might be different manifestations of a single slip process on the deep plate interface

paleomagnetic investigation of the early permian panjal traps of nw india regional tectonic implications abstract the 289 ma panjal traps of nw india kashmir are part of a series of rift related mafic suites abor sikkim etc that were erupted onto northern india present day coordinates around the same time as separation of the cimmerian blocks of qiangtang and sibumasu we report new data from only the second paleomagnetic investigation of this unit standard alternating field and thermal demagnetization methods were used to isolate characteristic magnetizations from seven outcrops at three locations within the kashmir valley nw india analysis of four sections 14 individual cooling units from close to srinagar that together form a tectonically coherent sequence spanning 3 km of stratigraphy yield a single component primary magnetization with a mean direction of dec 134 8 inc 55 3 95 8 9 k 21 0 an inclination only mean of 52 5 95 8 9 k 47 2 gives a paleolatitude of 33 s 5 a paleopole of 110 5 e 8 4 s a 95 10 7 is also calculated assuming the magnetization records a portion of the reverse polarity kiaman superchron the new result indicates extrusion of the panjal traps basalts at mid latitudes in the southern hemisphere by inference this constrains the location of central gondwana and informs debates related to cimmeria s detachment from gondwana

source parameters and time dependent slip distributions of slow slip events on the cascadia subduction zone from 1998 to 2008 1 we invert for the time dependent slip history of slow slip events on the cascadia subduction zone using gps data from 1998 to 2008 the 16 slip transients have sufficient station coverage to solve for the slip distribution on the plate interface gps time series are inverted for fault slip using the extended network inversion filter limited station coverage south of portland 45 5 n latitude restricts our analysis to events on the northern half of the subduction zone slip is resolved at the base of the seismogenic zone and the slip distributions suggest a potential segment boundary near seattle 47 6 n that correlates roughly with geologic and tectonic boundaries events that initiate to the north and south tend to overlap at about this latitude we compile statistics on source parameters such as propagation rate recurrence interval and stress drop which can be used to constrain proposed models of the source mechanics over a 10 year period total strain release from slow slip events is nonuniform along strike with the greatest cumulative slip 27 cm centered beneath port angeles 48 1 n this slip patch also exhibits the most regular recurrence of mw 6 events relative to other locations along strike the spatial extent of the slip patch beneath port angeles correlates with the along strike bend of the cascadia subduction zone in northwestern washington suggesting that plate geometry plays an important role in controlling the along strike characteristics of slow slip

time dependent inversion of three component continuous gps for steady and transient sources in northern cascadia 1 an approach to invert gps time series to estimate crustal block rotations fault locking and strain rates while simultaneously solving for transient slow slip events is described and applied to the northern cascadia subduction zone the method can use continuous or survey mode gps time series or both i invert 5 6 years of 3 component continuous gps time series at 53 sites from cascadia to estimate simultaneously the block motions and strains locking on the subduction zone and source parameters of the four most recent slow slip events over the time period and section of the cascadia margin sampled the strain released in slow slip was 7 to 10 of the accumulated subduction strain but at the base of and immediately downdip of the locked zone beneath the olympic peninsula

along strike variations in short term slow slip events in the southwest japan subduction zone 1 short term slow slip events accompanied by nonvolcanic deep low frequency tremors and deep very low frequency earthquakes in southwest japan were investigated systematically by means of ground tilting studies the change in tilt usually lasts for several days by using a genetic algorithm and a least squares method we inverted the data for tilt steps that were caused by slow slip events and were detected by at least four stations situated near the source of the tremor fault parameters were estimated for 54 slow slip episodes that occurred mainly in the western shikoku northeastern kii and tokai regions from 2001 to 2008 in eastern shikoku two slow slip episodes were detected quantitatively for the first time the fault geometries of all the slow slip events were located within the belt like distribution of tremors in the transition zone between the locked and aseismic slip zones at the plate interface of the subducting philippine sea plate the spatial extent of the fault geometry corresponds roughly to the distribution of clusters of nonvolcanic tremors and very low frequency earthquakes the moment magnitudes ranged from 5 4 to 6 2 and the slip was 1 cm for each slow slip event the rate of moment release by the detected slow slip events was 40 60 of the moment accumulation expected from the relative plate motion and it showed regional differences they may reflect the along strike variations in plate convergence and or the characteristic size of the slow slip fault plane on the plate interface

interplate coupling in the kanto district central japan and the boso peninsula silent earthquake in may 1996 i studied crustal deformation in the kanto district central japan based on continuous gps data horizontal as well as vertical displacement rate demonstrate significant interaction between the landward kanto block and the philippine sea plate although the subduction effect of the pacific plate is not apparent it is reasonable to consider the entire kanto district is displaced westward due to the interaction with the pacific plate the gps velocity data were inverted to estimate the slip deficit distribution on the sagami trough subduction zone the result delineates a strongly coupled region on the plate interface part of which corresponds to the 1923 kanto earthquake the strongly coupled region is located shallower than 20 km in addition the plate interaction is laterally heterogeneous even in the same depth range implying thermal structure is not the only factor controlling interplate coupling the gps data also detected a silent earthquake event on the interface of the philippine sea slab east of the boso peninsula in the middle of may 1996 the silent rupture propagated over a 50 km 50 km wide area during about a week the maximum slip was approximately 50 mm and the released seismic moment was 4 7 1018nm mw 6 4 there was a small seismicity triggered by this silent event the silent slip was located in the peripheral of the strongly coupled area suggesting that frictional properties and or stress conditions are inhomogeneous on the plate boundary interface

crustal block kinematics and seismic potential of the northernmost philippine sea plate and izu microplate central japan inferred from gps and leveling data 1 we clarify the contemporary deformation observed by gps and leveling for the greater tokyo kanto eastern tokai and the izu islands region where the izu ogasawara bonin arc is subducting and colliding with the central part of the japan arc from these data we develop a kinematic model of fault sources with variable components of seismic and aseismic slip under the assumption that the contemporary deformation during 1995 2000 is representative of the long term interseismic strain field the geodetic data are inverted to estimate the rotation poles of the crustal blocks the degree of elastic strain accumulation on faults and the volumetric inflation sources beneath volcanoes the present crustal movements are explained by four crustal blocks the izu microplate the central japan block the pacific plate and the philippine sea plate along the suruga and sagami margins of the philippine sea plate lie strongly coupled faults which include sites of the 1854 m 8 4 tokai 1923 m 7 9 kanto and 1703 m 8 2 genroku kanto earthquakes in contrast the philippine sea plate boundary immediately north of the izu peninsula site of m 7 5 collisional earthquakes is only weakly coupled the boundary between the izu microplate and the philippine sea plate experiences left lateral motion with the rate of 30 mm yr most of this boundary is locked and thus has a large potential of future earthquakes the izu microplate is found to rotate rapidly clockwise at 10 myr with a rotation pole relative to the central japan block located just north of its northern boundary the pole and angular velocity of the izu microplate depends however on the assumed location of the boundary with the exception of the site of the 1938 m 7 earthquake swarm which we infer has the current potential to produce a m 8 1 earthquake the pacific megathrust has a very low seismic potential although the geodetic data have little resolving power for much of the pacific plate interface east of tokyo

detection of a hidden boso slow slip event immediately after the 2011 mw 9 0 tohoku oki earthquake japan utilizing a cross correlation detector technique we discovered an increase in swarm like seismicity within the source area of the boso slow slip events sses immediately after the 2011 tohoku oki earthquake the epicentral distribution of the detected seismicity was similar to that of previously recognized boso sses in addition small repeating earthquakes were identified within this seismic swarm sequence these seismic observations indicate that a hidden sse occurred along the top surface of the subducting philippine sea plate immediately after the tohoku oki earthquake we propose that external stress transfer by the coseismic slip of the tohoku oki earthquake and the following afterslip could have led to the occurrence of the newly detected boso sse in contrast to previous work we demonstrate that the recurrence interval of the boso sses has not shortened over time but has shown a more complex evolution as a result of external stress perturbations imposed by the tohoku oki earthquake

noble gas isotopic systematics of fe ti v oxide ore related mafic ultramafic layered intrusions in the panxi area china the role of recycled oceanic crust in their petrogenesis olivine and clinopyroxene grains have been separated from four large fe ti v oxide ore bearing intrusions panzhihua hongge baima and taihe in the panxi area emeishan large igneous province southwest china for he and ar isotope studies the samples examined revealed extremely low 3 he 4 he ratios 0 078 4 34 ra with the mean value 0 78 ra for gases extracted by stepwise heating this feature combined with low 40 ar 36 ar ratios can be interpreted as due to addition of subduction related fluids and melts that had been stored in the lithospheric mantle for long periods considering the regional geologic history such addition can be attributed to the paleo subduction that occurred along the western margin of the yangtze block during the neoproterozoic the subducted oceanic crust beneath the panxi area underwent eclogite facies metamorphism and subsequent exhumation the infiltration of subduction related melts and fluids into the lithospheric mantle led to enriched isotopic signatures from that of the slightly depleted asthenopheric mantle which has been suggested by the sr nd and pb isotopic data of the emeishan basalts and picrites in addition considerable amounts of eclogitic melts produced by partial melting of eclogite facies oceanic crust extensively contaminated the lithospheric mantle during the late permian partial melting of an upwelling mantle plume that contained an eclogite or pyroxenite component generated the parental fe rich magma that supplied the ore bearing intrusions the combination of these factors may have been the crucial reason that many world class fe ti v oxides deposits are clustered in the panxi area

spatial and temporal evolution of stress and slip rate during the 2000 tokai slow earthquake 1 we investigate an ongoing silent thrust event in the tokai seismic gap along the suruga nankai trough central japan prior to the event continuous gps data from april 1996 to the end of 1999 show that this region displaced 2 cm yr to the northwest relative to the landward plate the gps time series show an abrupt change in rate in mid june 2000 that continues as of mid 2005 we model this transient deformation which we refer to as the tokai slow thrust slip event as caused by slip on the interface between the philippine sea and amurian plates the spatial and temporal distribution of slip rate is estimated with kalman filter based inversion methods our inversions reveal two slow subevents the first initiated in late june 2000 slightly before the miyake jima eruption the locus of slip then propagated southeast in the second half of 2000 with maximum slip rates of about 15 cm yr through 2001 a second locus of slip initiated to the northeast in early 2001 the depth of the slip zone is about 25 km which may correspond to the transition zone from a seismogenic to a freely sliding zone the cumulative moment magnitude of the slow slip event up to november 2002 is mw 6 8 we calculate shear stress changes on the plate interface from the slip histories stress change as a function of slip rate shows trajectories similar to that inferred for high speed ruptures however the maximum velocity is 8 orders of magnitude less than in normal earthquakes

mesoscopic and magnetic fabrics in arcuate igneous bodies an example from the mandi karsog pluton himachal lesser himalaya field microstructural and anisotropy of magnetic susceptibility ams data from the palaeozoic mandi karsog pluton in the lesser himalayan region reveal a concordant relationship between fabric of the proterozoic host rock and the granite the pluton displays a prominent arcuate shape on the geological map the margin parallel mesoscopic and magnetic fabrics of the granite and warping of the host rock fabric around the pluton indicate that this regional curvature is either synchronous or pre dates the emplacement of the granite body mesoscopic fabric magnetic fabric and microstructures indicate that the northern part of the pluton preserves its pre himalayan magmatic fabric while the central and southern part shows tectonic fabric related to the tertiary himalayan orogeny the presence of nw se trending aplitic veins within the granite indicates a post emplacement stretching in the ne sw direction shear sense indicators in the mylonites along the margin of the pluton suggest top to the sw shearing related to the himalayan orogeny based on these observations it is envisaged that the extension that gave rise to this rift related magmatism had a ne sw trend that is normal to the trend of the aplite veins subsequently during the himalayan orogeny compression occurred along this same ne sw orientation these findings imply that the regional curvature present in the himachal lesser himalaya is in fact a pre himalayan feature and the pluton has formed by filling a major pre himalayan arcuate extension fracture

petrogenesis of the flood basalts from the early permian panjal traps kashmir india geochemical evidence for shallow melting of the mantle article i nfo the early permian panjal traps of northern india represent a significant eruption of volcanic rocks which occurred during the opening of the neotethys ocean basaltic basaltic andesites dacitic and rhyolitic rocks collected from guryal ravine and pahalgam show evidence for subaerial and subaqueous eruptions indicating that they are contemporaneous with the formation of a shallow marine basin the major and trace element geochemistry of the basalts is consistent with a within plate setting and there are basalts which have high ti tio2 n 2 0 wt and low ti tio2 b 1 8 wt compositions the high ti basalts are similar to oib whereas the low ti basalts are similar to continental tholeiites the identification of high and low ti basalts within the panjal traps is analogous to other large igneous provinces e g karoo deccan parana emeishan the sr nd isotopic values end t 5 3 to 1 3 isr 0 70432 to 0 71168 of both types of basalts overlap indicating that the rocks may have originated from the same ancient subcontinental lithospheric i e emii like mantle source tdm 2000 ma the two groups of basalts can be modeled by using a primitive mantle source and different degrees of partial melting where the high tirocksare producedby 1 partial melting of a spinel peridotite source where as the low ti rocks are produced by 8 partial melting trace elemental and isotope modeling indicatesthat some of the basalts assimilated 10 crustal material in contrast the basaltic andesites are likely formed by mixing be tween basaltic magmas and crustal melts which produced rocks with higher sio2 55 wt content and enriched isotopic signatures end t 6 1 isr 0 70992 the panjal trap volcanism was likely due to partial melting of the sclm within a passive extensional setting related to the rifting of cimmeria from gondwana contemporaneous volcanic and plutonic granitic rocks throughout the himalaya are probably not petrogenetically related but are likely part of the same regional tectonic regime

imaging of the early acceleration phase of the 2013 2014 boso slow slip event we analyze gps and seismic data to examine the spatiotemporal evolution of a slow slip event sse near boso peninsula central japan from december 2013 to january 2014 the evolution of this sse and its associated seismicity is divided into two distinct phases slip initially accelerated slowly with low slip rates low propagation speeds and no accompanying seismicity during the early phase and then accelerated more rapidly with higher slip rates a higher propagation speed and local earthquake swarm activity during the later phase the seismicity was highly correlated in space and time with slip rate suggesting that the swarm activity was triggered by stress loading due to the slow slip the transition from the slow to faster phase shares some similarities with the nucleation of megathrust earthquakes inferred from foreshock activities suggesting that sses may provide insights into the nucleation of large earthquakes

slow slip events and strain accumulation in the guerrero gap mexico 1 global positioning system gps time series in guerrero mexico reveal the existence of large slow slip events sses at the boundary between the cocos and north american plates in this study we examined the last three sses that occurred in 2001 2002 2006 and 2009 2010 and their impact on the strain accumulation along the guerrero subduction margin gps displacements were inverted to retrieve the slip distribution during each sse and the inter sse coupling of the subduction interface the three analyzed sses have equivalent moment magnitudes of between 7 50 and 7 65 their lateral extents are variable and they all show significant slip in the guerrero seismic gap during the inter sse epochs the interplate coupling is high in the area where slow slip subsequently occurs in the guerrero gap the shallow portion of the plate interface from the trench to the coast is weakly coupled the average slip deficit accumulated in the guerrero gap over a period of 12 years which corresponds to three cycles of sse is only 1 4 of the slip deficit accumulated on both sides of the gap moreover the regions of large slip deficit coincide with the rupture areas of recent large earthquakes we conclude that the sses in the guerrero gap release a significant part of the strain accumulated during the inter sse period if large subduction thrust earthquakes occur in the guerrero gap their recurrence time is probably increased compared to adjacent regions

postseismic response of repeating earthquakes around the 2011 tohoku oki earthquake moment increases due to the fast loading rate we examined the temporal variation of the size of repeating earthquakes related to the 2011 tohoku oki earthquake m9 0 in the northeastern japan subduction zone for the period from july 1984 to the end of 2011 the repeaters m2 5 6 1 show postseismic magnitude increases for most sequences located in the area of large postseismic slip at the downdip extension of the m9 source region the magnitudes of the first events after the m9 earthquake increased by an average of about 0 3 for sequences having three or more earthquakes over the 9 months following it we also examined the slip area in detail for kamaishi repeaters whose magnitudes had been m4 9 0 2 but which increased by about 1 after the m9 earthquake waveform modeling shows that the slip area for the post m9 kamaishi earthquakes overlaps with that before the tohoku oki earthquake but enlarged by about 6 times until the occurrence time of the last event september 2011 in the analysis period the rupture area remained larger than before but appeared to shrink over time the enlargement of the rupture area suggests that an aseismic to seismic transition occurred in the region surrounding the pre m9 repeaters and is most likely related to fast loading of the repeaters due to rapid postseismic slip estimated to have occurred in the area the existence of conditionally stable regions around the repeating earthquakes and or patches slightly larger than the earthquake nucleation sizes may explain such behavior the temporal change of loading rate is an important factor in determining earthquake size in this case

origin of the silicic volcanic rocks of the early permian panjal traps kashmir india abstract the panjal traps of kashmir india represent a significant outpouring of mafic and silicic volcanic rocks during the early permian and are synchronous with the opening of the neotethys ocean previous studies have suggested that the silicic volcanic rocks are derived by differentiation of mafic magmas dacites and rhyolites collected from the lower portions of the volcanic pile near pampore kashmir are peraluminous anck 1 0 in composition their calculated whole rock i sr values are variable i sr 0 69307 to 0 71825 and indicate open system behavior of either rb or sr or both whereas their nd isotope compositions end t 8 6 to 8 9 are nearly uniform the end t values and trace element th nb pm 4 nb u 8 ratios suggest the rocks are derived partially or wholly from the crust least squares and melts modeling indicate that the likely source of the silicic rocks is the middle crust rather than the lower or upper crust furthermore the silicic panjal traps have trace element compositions similar to some felsic volcanic rocks and a type granitic rocks from other large igneous provinces e g karoo parana and camp the paleoproterozoic t dm ages t dm 1836 to 1937 ma indicate that the rocks were likely derived from an ancient crustal source which experienced multiple episodes of recycling in contrast to silicic volcanic rocks from other lips the silicic panjal traps are unusual in that they did not involve mantle source material the heat required to melt the crust was likely due to the continuous injection of contemporaneous basaltic magmas which formed the majority of the mafic panjal traps

slip rate and tremor genesis in cascadia at many plate boundaries conditions in the transition zone between seismogenic and stable slip produce slow earthquakes in the cascadia subduction zone these events are consistently observed as slow aseismic slip on the plate interface accompanied by persistent tectonic tremor however not all slow slip at other plate boundaries coincides spatially and temporally with tremor leaving the physics of tremor genesis poorly understood here we analyze seismic geodetic and strainmeter data in cascadia to observe for the first time a large tremor generating slow earthquake change from tremor genic to silent and back again the tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure the finding suggests that rheology and slip speed regulated stressing rate control tremor genesis and the same section of fault can slip both with and without detectable tremor limiting tremor s use as a proxy for slip

shortening of recurrence interval of boso slow slip events in japan a slow slip event occurred off the coast of the boso peninsula japan from approximately 28 december 2013 to 10 january 2014 the estimated aseismic slip expanded slightly southward and westward over time with a moment magnitude of 6 5 which was the smallest value since 1996 the recurrence interval has decreased from approximately 6 4 to 2 2 years from 1996 to 2014 one explanation of this shortening is the change in coulomb failure stress due to the 2011 mw9 0 tohoku earthquake and its afterslip another interpretation is related to a scenario observed in several numerical simulation studies in which the recurrence interval of slow slip becomes shorter as the time nears a large earthquake this case will constrain the physical processes of a slip cycle the boso slow slip events together with the tohoku earthquake and its afterslip changed the stress state for the anticipated interplate earthquake near the sagami trough

role of inversion tectonics in structural development of the himalaya abstract analysis of surface and subsurface structures variation of shortening amounts obtained by restoration of deformed cross sections and occurrence of younger hangingwall rocks over the older footwall rocks across the vaikrita thrust in the higher himalaya suggests reactivation of early normal faults as thrusts based on this an inversion tectonics model is proposed for structural development of the himalaya the model explains the geometrical shape of the himalaya as primary arcuation and helps in resolving superimposed deformation in the region

kilauea slow slip events identification source inversions and relation to seismicity 1 several slow slip events beneath the south flank ofkilauea volcano hawaii have been inferred from transient displacements in daily gps positions to search for smaller events that may be close to the noise level in the gps time series we compare displacement fields on kilauea s south flank with displacement patterns in previously identified slow slip events matching displacement patterns are found for several new candidate events although displacements are much smaller than previously identified events one of the candidates 29 may 2000 is coincident with a microearthquake swarm as are all of the previously identified slow slip events the microearthquakes follow the onset of slow slip implying that they are triggered by stress changes during slip the new slow slip event brings the total number of events on kilauea between 1997 and 2007 to eight the smallest having m w 5 3 and the largest having m w 6 0 while the recurrence time between the four largest events is 2 11 0 01 years the repeat time for all eight events is 0 9 0 6 years we invert for the fault geometry and distribution of slip during the slow slip events the optimal source depths of 5 km assuming uniform slip dislocations in an elastic half space are considerably shallower than the accompanying swarm earthquakes 6 5 8 5 km which would place the earthquakes in a zone of decreased coulomb stress inversions including the effects of topography and layered elastic structure in the forward models favor depths comparable to microearthquake depths such that the earthquakes are located in a region of increased coulomb stress we also invert for time dependent fault slip directly from the 30 s gps phase observations constraining the source to the optimal uniform slip geometry on the basis of these inversions the larger events last between 1 5 2 2 days the data are unable to resolve migration of slip along the fault the temporal pattern of accompanying microearthquakes is consistent with the fault slip history assuming a seismicity rate theory based on rate and state friction making the swarm earthquakes coshocks and aftershocks of the slow slip events

late paleozoic rifting in northern pakistan metasedimentary rocks exposed in the eastern peshawar basin and the southern swat region of northern pakistan provide evidence for late paleozoic continental rifting the onset of extensional tectonics in the early carboniferous is indicated by north derived clasts in the jafar kandao formation eroded from thermally induced uplifts of parts of the formerly passive margin of gondwana rift highlands were eroded until they were inundated during the middle carboniferous renewed uplift accompanied the eruption of basaltic lava flows during the early permian uplift along south dipping northeast striking normal faults during the carboniferous was accompanied by alkaline magmatism represented by the shewa shahbazgarhi and warsak porphyries and koga syenite geochemistry of basaltic flows now amphibolites and intrusions associated with permian uplift is similar to the coeval panjal volcanics of northwestern india and indicates rift zone magmatism postrifting thermal subsidence led to the deposition of upper triassic marine carbonate rocks which unconformably overlie the rift basalts a similar tectonic history in central afghanistan suggests continuity between the two regions prior to the opening of the neo tethys

gps constraints on 34 slow slip events within the cascadia subduction zone 1997 2005 1 refinements to gps analyses in which we factor geodetic time series to better estimate both reference frames and transient deformation resolve 34 slow slip events located throughout the cascadia subduction zone from 1997 through 2005 timing of transient onset is determined with wavelet transformation of geodetic time series thirty continuous stations are included in this study ranging from northern california to southwestern british columbia our improvements in analysis better resolve the largest creep events and also identify many smaller events at 48 5 n latitude a 14 month average recurrence interval has been observed over eight events since 1997 farther north along vancouver island a host of smaller events with a distinct 14 month periodicity also occurs in southern washington state some of the largest transient displacements are observed but lack any obvious periodicity in their recurrence along central oregon an 18 month recurrence is evident while in northern california an 11 month periodicity continues through 2005 we invert gps offsets of the 12 best recorded events for thrust slip along the plate interface using a cross validation scheme to derive optimal smoothing parameters these 12 events have equivalent moment magnitudes between 6 3 and 6 8 and have 2 3 cm of slip unlike other subduction zones no long duration events are observed and cumulative surface deformation is consistently less than 0 6 cm the many newly resolved smaller transient events in cascadia show that slow slip events occur frequently with gps best capturing only the largest events it is likely that slow slip events occur more frequently at levels not detectable with gps

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

no link between the panjal traps kashmir and the late permian mass extinctions 1 voluminous late permian flood basalt eruptions are contemporaneous with the mid capitanian 260 ma and end permian 251 ma mass extinction events the panjal traps of kashmir are thought to be correlative to the mid capitanian mass extinction however no radiometric age has been determined we report a single zircon u pb laser ablation icp ms date of a rhyolite from the lower middle part of the volcanic sequence twenty four individual zircon crystals yield a mean 206u 238pb age of 289 3 ma the results show that the panjal traps are considerably older than previously interpreted and not correlative to post neo tethys rifting of the gondwanan margin or the mid capitanian mass extinction and are in fact correlative to the opening of the neo tethys ocean in contrast to other similarly size large igneous provinces the panjal traps are not coincident with a mass extinction event and therefore casts doubt on the direct relationship between continental flood basalt volcanism and ecosystem collapse

crustal growth and two stage india eurasia collision in ladakh abstract the post palaeozoic history of crustal growth between india and the karakoram lhasa accreted southern margin of asia begins with the creation of the oceanic crust during the northward drift of the karakoram lhasa block away from the northern margin of india after permo triassic rifting data suggest initiation of northward subduction and the development of the island arc close to the southern margin of asia sometime in upper jurassic 160 m y the northward retreat of the overriding eurasian plate due to movements along transform faults which subsequently changed into transcurrent faults resulted in the opening of the shyok back arc basin in the kohistan ladakh region during pre upper cretaceous time the mature and thickened tholeiitic island arc lying between the subducting indian plate and the spreading shyok back arc basin suffered compression deformation emplacement of ophiolitic melanges and metamorphism during the upper cretaceous 80 m y the intrusion of the calc alkaline magma into the deformed rocks of the island arc and the back arc basin during the paleocene eocene 60 40 m y was followed by explosive calc alkaline volcanism 40 25 m y resulting in further crustal growth in this part of the trans himalaya the collision of the dras island arc with the approaching margins of the indian and eurasian plates took place in two stages in the first stage it collided with the northern margin of india during the paleocene along the indus suture the final collision of the island arc accreted northern margin of india with the eurasian plate took place along the shyok suture during the early oligocene 30 m y

inverting for slip on three dimensional fault surfaces using angular dislocations the increasing quality of geodetic data synthetic aperture radar interferometry insar dense global positioning system gps arrays now available to geophysicists and geologists are not fully exploited in slip inversion procedures most common methods of inversion use rectangular dislocation segments to model fault ruptures and therefore oversimplify fault geometries these geometric simplifications can lead to inconsistencies when inverting for slip on earthquake faults and they preclude a more complete understanding of the role of fault geometry in the earthquake process we have developed a new three dimensional slip inversion method based on the analytical solution for an angular dislocation in a linear elastic homogeneous isotropic half space the approach uses the boundary element code poly3d that employs a set of planar triangular elements of constant displacement discontinuity to model fault surfaces the use of triangulated surfaces as discontinuities permits one to construct fault models that better approximate curved three dimensional surfaces bounded by curved tiplines shapes that commonly are imaged by three dimensional reflection seismic data and inferred from relocated aftershock data we demonstrate the method s ability to model three dimensional rupture geometries by inverting for slip associated with the 1999 hector mine earthquake the resulting model avoids displacement anomalies associated with the overlapping rectangular dislocations used in previous models improving the fit to the geodetic data by 32 and honors the observed surface ruptures thereby allowing more direct comparisons between geologic and geodetic data on slip distributions online material hector mine input files and file format description

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

collision tectonics in the himalaya as evidenced by the indus and shyok rock assemblages abstract the himalayan orogeny is closely associated with the tectonic developments which occurred along the indus suture zone during the last decade many new data on sediment stratigraphy and volcanic plutonic suites have been obtained these data have been interpreted in terms of plate tectonics the meso tethys was generated following the permo triassic rifting and spreading during the jurassic the tethys ocean is postulated in accordance with geophysical data to have been consumed during northward subduction along the indus suture resulting in the himalayan orogeny through collision between india and eurasia however the nature of tectonic processes and their chronology appear to be different in the western and eastern himalayan segments in the western himalaya subduction in an island arc setting and eocene collision are evident mainly by the occurrence of the island arc dras volcanics the sangeluma group srikantia and rajdhan 1980 trench deposits ophiolitic blocks older 60 m y calc alkaline plutons and blueschist facies rocks the indus group srikantia and rajdhan 1980 continental deposits and the younger

paleomagnetic data support early permian age for the abor volcanics in the lower siang valley ne india significance for gondwana related break up models confusion exists as to the age of the abor volcanics of ne india some consider the unit to have been emplaced in the early permian others the early eocene a difference of 230 million years the divergence in opinion is significant because fundamentally different models explaining the geotectonic evolution of india depend on the age designation of the unit paleomagnetic data reported here from several exposures in the type locality of the formation in the lower siang valley indicate that steep dipping primary magnetizations mean 72 7 6 2 equating to a paleo latitude of 58 1 are recorded in the formation these are only consistent with the unit being of permian age possibly artinskian based on a magnetostratigraphic argument plate tectonic models for this time consistently show the ne corner of the sub continent 50 s in the early eocene it was just north of the equator which would have resulted in the unit recording shallow directions the mean declination is counter clockwise rotated by 94 around half of which can be related to the motion of the indian block the remainder is likely due local himalayan age thrusting in the eastern syntaxis several workers have correlated the abor volcanics with broadly coeval mafic volcanic suites in oman ne pakistan nw india and southern tibet nepal which developed in response to the cimmerian block peeling off eastern gondwana in the early middle permian but we believe there are problems with this model instead we suggest that the abor basalts relate to india antarctica india australia extension that was happening at about the same time such an explanation best accommodates the relevant stratigraphical and structural data present day position within the himalayan thrust stack as well as the plate tectonic model for permian eastern gondwana

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

abor volcanics further evidence for the birth of the tethys ocean in the himalayan segment the himalayan region has a record of several phases of igneous activity which indicate a continued n s orientated tensional regime since at least late precambrian time though the earlier volcanic eruptions were restricted both in time and space the late carboniferous triassic activity was widespread in terms of both the time interval and area covered the abor volcanic activity in the eastern syntaxial bend of the himalayan fold belt is coeval with the initiation of late carboniferous triassic panjal trap volcanism of the western syntaxial bend and eruption of the sikkim lavas chemical characters of the abor volcanics indicate 1 a within plate rift tectonic setting of the lava eruptions 2 a transitional nature between tholeiitic and alkalic compositions 3 relative enrichment in incompatible elements and 4 high fe ti values similar to many such basalts erupted in the regions of active lithospheric rifting the olivine free nature a linear trend for mgo and low co contents of the studied rocks are suggestive of high pressure olivine fractionation for the generation of the bulk chemistry however large variations in the incompatible element abundances and ratios of rocks at a similar fractionation stage discount the evolution of the lava chemistry exclusively by simple fractionation or partial melting processes instead these characters together with the low zr nb ratio and within plate rift tectonic setting suggests the modification of an upper mantle source region possibly by fluid phase co 2 immediately before the partial melting and lithospheric rifting combining geology of the region with the geochemistry and inferred tectonic setting of these rocks the lava eruptions are suggested to have been associated with the 9rift valley stage9 of the tethys ocean formation in the present himalayan region

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

thermal and tectonic evolution of the kashmir basin vis a vis petroleum prospects abstract investigation of the formation of peri atlantic basins and evaluation of the mechanism of lithospheric break up provide a guide for understanding the pre collision history of the himalayan region as an example the kashmir basin is discussed the present form of the kashmir basin is that of a graben bounded by two horsts the stratigraphic succession shows a complete record of shallow marine sedimentation from the cambrian to middle carboniferous in the upper carboniferous the depositional environment changed to continental type accompanied by large scale erosion especially on the western side and the deposition of agglomeratic slate and then in the lower permian by the panjal trap volcanism whilst the eastern side after this continental phase again subsided and received marine sediments until the end of the triassic the western side experienced repeated uplift and volcanism gravity and seismic data indicate the presence of high density material and a shallow depth of the moho beneath the basin and also the eruption of the panjal trap lava along two deep seated faults f1 and f2 on the flanking horsts with dips towards the present indus tsangpo suture after the upper carboniferous a continental phase is noted all over the himalaya this is thought to mark the initiation of the break up of the indian plate from the siberian cathysian block which finally occurred at the end of the triassic based on the stratigraphie and tectonic set up of kashmir in particular and the whole himalaya in general a model is presented to explain the formation of the kashmir basin good compatibility of the model with observed tectonic and stratigraphie aspects of kashmir and the whole himalaya is found the geothermal history of different strata in this basin indicates promising conditions for hydrocarbon generation a few of the more promising strata are identified for intensive investigations

revel a model for recent plate velocities from space geodesy 1 we present a new global model for recent plate velocities revel describing the relative velocities of 19 plates and continental blocks the model is derived from publicly available space geodetic primarily gps data for the period 1993 2000 we include an independent and rigorous estimate for gps velocity uncertainties to assess plate rigidity and propagate these uncertainties to the velocity estimates the velocity fields for north america eurasia and antarctica clearly show the effects of glacial isostatic adjustment and australia appears to depart from rigid plate behavior in a manner consistent with the mapped intraplate stress field two thirds of tested plate pairs agree with the nuvel 1a geologic 3 myr average velocities within uncertainties three plate pairs caribbean north america caribbean south america and north america pacific exhibit significant differences between the geodetic and geologic model that may reflect systematic errors in nuvel 1a due to the use of seafloor magnetic rate data that do not reflect the full plate rate because of tectonic complexities most other differences probably reflect real velocity changes over the last few million years several plate pairs arabia eurasia arabia nubia eurasia india move more slowly than the 3 myr nuvel 1a average perhaps reflecting long term deceleration associated with continental collision several other plate pairs including nazca pacific nazca south america and nubia south america are experiencing slowing that began 25 ma the beginning of the current phase of andean crustal shortening

intense interface seismicity triggered by a shallow slow slip event in the central ecuador subduction zone we document a 1 week long slow slip event sse with an equivalent moment magnitude of 6 0 6 3 which occurred in august 2010 below la plata island ecuador south of the rupture area of the 1906 mw 8 8 megathrust earthquake gps data reveal that the sse occurred at a depth of about 10 km within the downdip part of a shallow 15 km isolated locked patch along the subduction interface the availability of both broadband seismometer and continuous geodetic station located at the la plata island 10 km above the sse enables a careful analysis of the relationships between slow and rapid processes of stress release along the subduction interface during the slow slip sequence the seismic data show a sharp increase of the local seismicity with more than 650 earthquakes detected among which 50 have a moment magnitude between 1 8 and 4 1 however the cumulative moment released through earthquakes accounts at most for 0 2 of the total moment release estimated from gps displacements most of the largest earthquakes are located along or very close to the subduction interface with focal mechanism consistent with the relative plate motion while the earthquake sizes show a classical distribution gutenberg richter law with a b value close to 1 the space time occurrence presents a specific pattern first the largest earthquakes appear to occur randomly during the slow slip sequence which further evidence that the seismicity is driven by the stress fluctuations related to aseismic slip moreover the seismicity observed during the sse consists in individual events and families of repeating earthquakes these observations indicate that the stress increment induced by the episodic aseismic slip may lead both to sudden seismic moment release and to progressive rupture within small locked patches this study offers an a posteriori interpretation of the seismogenesis in the central ecuador subduction zone where intense seismic swarms have been regularly observed 1977 1998 2002 and 2005 these swarms have likely been triggered by large magnitude slow slip events

small particles in plumes of mount st helens particles in the size range of 0 1 25 micrometers were sampled by aircraft carrying a quartz crystal microcascade in the mount st helens plume on three dates in august and september 1980 two of the sampling dates represented typical emissions of the volcano between plinian eruptions one sampling flight was made 1 4 hours before the small plinian eruption of august 7 1980 when the plume had become discontinuous and visibly darker size distributions were determined and individual particles were studied by using scanning electron microscopy the plume sampled on august 7 before the eruption contained mainly approximately 2 micrometer diameter silicic glass particles fragments of the mount st helens magma the typical plumes sampled on september 22 and august 6 had much smaller concentrations of particles trimodal size distributions with peaks at 10 0 4 and 0 1 micrometers the particles were largely nonsilicate and apparently represented cu zn oxide 10 micrometer peak al sulfate chloride and oxide and sulfuric acid smallest size peak the characterization of small particles in the plume may give information about approaching activity and possibly about changing conditions in the subsurface magma body

microseismicity but no tremor accompanying slow slip in the hikurangi subduction zone new zealand abstract geodetically detected episodes of slow slip appear in several subduction zones to be accompanied by bursts of low frequency coherent noise known as seismic tremor but whether a single physical process governs this association or even whether slow slip is invariably accompanied by tremor remains unresolved detailed analysis of broadband seismic data spanning a slow slip episode in the hikurangi subduction zone new zealand reveals that slow slip was accompanied by distinct reverse faulting microearthquakes rather than tremor the timing location and faulting style of these earthquakes are consistent with stress triggering down dip of the slow slip patch either on the subduction interface or just below it these results indicate that tremor is not ubiquitous during subduction zone slow slip and that slow slip in subduction zone environments is capable of triggering high frequency earthquakes near the base of the locked subduction thrust in this and other locations hawaii boso peninsula where slow slip is accompanied by triggered microseismicity the estimated upper extent of the slow slip is shallower less than 20 km than in those locations from which tremor has been reported this suggests that ambient temperature or pressure dependent factors govern the character of the seismic response to slow slip on subduction thrusts and other large faults with rheological or lithological conditions at shallow depths triggering high frequency microearthquakes and those at greater depths triggering seismic tremor

spatiotemporal evolution of a transient slip event on the san andreas fault near parkfield california 1 in 1993 several baselines of the two color electronic distance meter edm network at parkfield california deviated from their long term rates coincident with anomalous observations from nearby strain meters and a creep meter as well as an increase in microseismicity between october 1992 and december 1994 three m 4 5 earthquakes occurred beneath middle mountain near the hypocenter of the 1934 and 1966 parkfield m6 events we analyzed the two color edm data using a kalman filtering based technique to image the spatiotemporal evolution of slip on the fault at parkfield between the mid 1980s and 2003 this method accounts for localized random walk motion of the geodetic monuments and a prominent seasonal signal that affects many baselines we find that a slip rate increase occurred between january 1993 and july 1996 on the upper 8 km of the fault near middle mountain the peak estimated slip rate during this time was 49 mm yr which exceeds the long term geologic rate of 35 mm yr the slip rate evolution appears episodic with an initial modest increase after the m4 3 earthquake and a much larger jump following the shallower m4 7 event in december 1994 this temporal correlation between inferred slip and seismicity suggests that the moderate earthquakes triggered the aseismic fault slip the edm data cannot resolve whether transient slip propagated across the nucleation zone of the 1934 and 1966 m6 parkfield earthquakes however transient slip and its associated stress release in the hypocentral area of previous parkfield events is consistent with the nucleation of the 2004 m6 parkfield earthquake elsewhere on the fault