the critical slip distance for seismic faulting experimentally based friction laws1 2 have been found to predict virtually the entire range of observed behaviour of natural faults3 4 these laws contain a critical slip distance l which plays a key role in determining the degree of fault instability the size of the zone of earthquake nucleation the frictional breakdown width and the proportion of pre and post seismic slip to co seismic slip in laboratory measurements l is found to be about 10 5m but modelling results show that it must be about 10 2m if natural earthquake behaviour is to be simulated the discovery that fault surfaces are fractal over the scale range 10 5 105 refs 5 6 even for faults with large net slip has confused the problem of scaling this parameter from laboratory experiments to natural faults because fractal surfaces have no characteristic length here i show that geometrically unmated fractal surfaces when in contact under a normal load develop a characteristic length in their contact because long wavelength apertures close under load whereas short wavelength apertures may remain open this critical distance may be identified with l and calculations based on fault topography data show that at seismogenic depths it will be in the range anticipated from the earthquake modelling studies

deformation enhanced fluid distribution in feldspar aggregates and implications for ductile shear zones experiments at 900 c and 1 4 gpa show that the distribution of aqueous fluid in fine grained feldspar aggregates changes from isolated pores under hydrostatic conditions to mostly wetted grain boundaries during deformation the isolated pore distribution is rapidly regained during annealing following deformation the deformation enhanced fluid distribution causes a switch from dislocation creep to diffusion creep accompanied by a significant decrease in strength it also increases the bulk transport rate through the aggregate by more than an order of magnitude a change in fluid distribution is not observed in fine grained quartz aggregates deformed at similar conditions if deformation enhanced fluid distribution occurs in naturally deformed feldspathic rocks it could help to explain the localization of strain and enhancement of bulk transport in ductile shear zones

estimation of gas hydrate concentration and free gas saturation at the norwegian svalbard continental margin we estimate the concentration of gas hydrate and free gas at an area located to the north of the knipovich ridge western svalbard margin the method is based on p wave velocities computed by reflection tomography applied to multicomponent ocean bottom seismometer data the tomographic velocity field is fitted to theoretical velocities obtained from a poro elastic model based on a biot type approach the interaction between the rock frame gas hydrate and fluid is modelled from first physical principles we obtain average hydrate concentrations of 7 and maximum free gas saturations of 0 4 and 9 depending on the saturation model

fluid generation and pathways beneath an active compressional orogen the new zealand southern alps inferred from magnetotelluric data 1 forty one wideband magnetotelluric mt soundings were collected in a 150 km long transect across the southern alps of the central south island of new zealand an active compressional orogen decomposed mt impedance tensors vertical magnetic field relations and reconnaissance soundings at two locations off line imply an approximately two dimensional geometry here with average regional geoelectric strike of n40 e similar to surface geologic trends two independent two dimensional inversion algorithms were applied to the mt data and both imply a concave upward u shaped middle to lower crustal conductive zone beneath the west central portion of the island the average conductivity of this zone in the strike direction appears to be much higher than that required across strike and may represent anisotropy or along strike conductive strands narrower than the transverse magnetic cross strike mode mt data can resolve the deep crustal conductor under the southern alps is interpreted to represent mainly a volume of fluids arising from prograde metamorphism within a thickening crust fluid interconnection and electrical conduction are promoted by shear deformation the conductor rises northwestward toward the trace of the alpine fault but attains a near vertical configuration at a depth of 10 km and reaches close to the surface 5 10 km inland of the fault trace itself the transition to vertical orientation at this depth is interpreted to occur as fluids ascend across the brittle ductile transition in uplifting schist and approach the surface through induced hydrofractures the high grade schist becomes resistive after depletion of fluids and continues to extrude toward the alpine fault shallow extensions of the deep high conductivity are coincident with modern hydrothermal veining and gold mineralization interpreted to be of deep crustal provenance to the southeast high conductivity also reaches the surface coincident with a major back thrust fault zone of the doubly vergent southern alps orogen which also exhibits evidence for expulsion of high temperature fluids the higher conductivity inferred along strike possible anisotropy could reflect more efficient fluid interconnection in this higher strain direction as well as possible contributions by sheared fluid deposited graphite conductivity of the uppermost mantle of the south island is low consistent with advection of cold mantle lithosphere into the underlying asthenosphere as suggested by p wave delay studies

structural heterogeneity of the longmenshan fault zone and the mechanism of the 2008 wenchuan earthquake ms 8 0 we determined detailed 3 d images of p and s wave velocity vp vs and poisson s ratio in and around the longmenshan lms fault zone by using a large number of p and s wave arrival times from the aftershocks of the 2008 wenchuan earthquake ms 8 0 and other local events our results show that the structure of the lms fault zone north of the wenchuan main shock is very different from that south of the main shock the southern section of the lms fault zone contains a broad zone with low vp low vs and high anomalies while the northern segment exhibits more scattered heterogeneities corresponding to most of the aftershocks which occurred there a prominent low vp low vs and high anomaly exists directly beneath the wenchuan main shock hypocenter suggesting that in addition to compositional variations fluid filled fractured rock matrices may exist in the lms fault zone which may have influenced the generation of the large wenchuan earthquake our tomographic results provide sound seismic evidence for the hypothesis that an upward intrusion of lower crustal flow occurred along the lms fault zone in addition most small earthquakes before the 2008 wenchuan main shock occurred around the guanxian jiangyou fault while the wenchuan aftershocks were mainly concentrated on the yingxiu beichuan fault suggesting that the rupture process of the wenchuan earthquake may belong to an out of sequence thrusting event a suggestion which is in good agreement with the results from geological surveys and also quite similar to the rupture processes of the 1999 chi chi earthquake m 7 5 and the 2005 kashmir earthquake m 7 6 a few aftershocks occurred close to the blind guangyuan dayi fault in the sichuan basin suggesting that this blind fault was also ruptured by the wenchuan earthquake consistent with geological surveys

altimeter sampling characteristics using a single satellite altimetric satellites have characteristic sampling patterns in both space and time based on their repeat period and orbit inclination aliased phenomena measured by altimetric measurements can appear as propagating waves with both wavelength and direction of propagation different from the underlying phenomena all signals that contribute to the altimetric measurement can be aliased and produce such patterns not just tidal signals for example mesoscale energy will be aliased as will unmodeled atmospheric variations past discussions of aliasing have only considered spatially homogeneous signals this paper extends this work to phenomena with finite wavelengths and considers both the north south and east west components of the resulting aliases

a fault zone conductor beneath a compressional inversion zone northeastern honshu japan 1 a resistivity section based on magnetotelluric data was obtained for the shonai plain fault in northeastern honshu japan faults in this area were created as normal faults during the opening of the japan sea in the miocene but are now reactivated as high angle reverse faults under compressional tectonics geological interpretations of the resistivity section support the proposed fault reactivation an estimated east dipping conductor along a deep part of the shonai plain fault system probably represents a fluid rich zone around the fault zone the high 3he 4he ratio near the fault indicates transportation of mantle fluid through this fluid rich zone these evidences may reflect the development of pronounced fracture permeability after fault rupturing as in the fault valve hypothesis

electrical imaging of narmada son lineament zone central india from magnetotellurics the narmada son lineament nsl zone is the second most important tectonic feature after himalayas in the indian geology magnetotelluric mt studies were carried out in the nsl zone along a 130 km long nne ssw trending profile the area of investigation extends from edlabad 20 46 16 7 5 59 05 in the south to khandwa 21 53 51 7 6 18 05 i n the north the data shows in general the validity of a two dimensional 2d approach besides providing details on the shallow crustal section the 2d modeling results resolved four high conductive zones extending from the middle to deep crust spatially coinciding with the major structural features in the area namely the gavligarh tapti barwani sukta and narmada south faults the model for the shallow section has brought out a moderately resistive layer 30 150 m representing the exposed deccan trap layer overlying a conductive layer 10 30 m inferred to be the subtrappean gondwana sediments the latter resting on a high resistive basement upper crust the deccan trap thickness varies from around a few hundred meters to as much as 1 5 km along the traverse a subtrappean sedimentary basin like feature is delineated in the northern half of the traverse where a sudden thickening of subtrappean sediments amounting to as much as 2 km is noticed the high resistive upper crust is relatively thick towards the southern end and tends to become thinner towards the middle and northern part of the traverse the lower crustal segment is conductive over a major part of the profile considering the generally enhanced heat flow values in the nsl region coupled with characteristic gravity highs and enhanced seismic velocities coinciding with the mid to lower crustal conductors delineated from mt presence of zones of high density mafic bodies intrusives with fluids presumably associated with magmatic underplating of the crust in the zone of major tectonic faults in nsl region are inferred 2004 elsevier b v all rights reserved

3 d magnetotelluric imaging of the phayao fault zone northern thailand evidence for saline fluid in the source region of the 2014 chiang rai earthquake abstract seismicity in thailand had been relatively low for decades prior to the mw 6 5 earthquake of 5 may 2014 which came as a surprise and was followed by thousands of aftershocks most of the epicenters were located in the transition region between the mae lao segment mls and the pan segment ps of the phayao fault zone pfz we conducted a 3 d magnetotelluric mt survey 31 sites to image the deep pfz structure the shallow 3 d resistivity structure matches very well with the surface geology while the deeper structures disclose many interesting resistive and conductive anomalies however the most interesting feature of this study is the large conductive anomaly ml located at a depth of 4 km to the mid crust beneath the mls near the seismogenic zone our current hypothesis is that the ml conductor has a highly interconnected aqueous fluid content and also plays crucial role in the earthquake sequence of the 5 may 2014 event as our previous seismic waveform study revealed that the mls has a relatively high fault plane instability the fluid within the fractured fault would further reduce the fault strength the accumulated pre existing tectonic stress from the north can therefore overcome the maximum frictional strength of the mls and hence cause it to slip and produce the main shock with the local structural heterogeneities and fluid in the fractured fault zones the aftershocks then occurred on both the ps and mls this is in contrast to the mae chan fault zone mcfz in the north which many scientists expected to generate a larger magnitude earthquake than any other faults since instrumental record it has only generated a few mw 4 earthquakes some of our mt stations were located within the mcfz however there is no deep conductor as the conductor lies beneath the mls a lack of interconnected fluid within the deep fault beneath the mcfz might be one of the reasons for the lower seismic activity from the mcfz other geophysical methods such as seismic tomography are necessary in order to confirm the presence of the fluid beneath the mls and also the lack of a deep conductor beneath the mcfz

magnetotelluric imaging of the creeping segment of the san andreas fault near hollister 1 fluids may play a significant role in the earthquake rupture process since fluids can dramatically change the electrical resistivity of crustal rocks electromagnetic exploration methods can image in situ fault zone fluids magnetotelluric mt data has been collected on segments of the san andreas fault saf in central california exhibiting a range of seismic behavior from locked to creeping this paper describes mt data from the creeping segment of the saf near hollister california inversion models image a zone of enhanced conductivity beneath the surface trace of the saf that has similar geometry and greater depth extent than the fault zone conductor at parkfield comparison with geologic and seismic tomographic studies show this zone is bounded by the san andreas and calaveras faults and coincident with a zone of low seismic p wave velocities combined with previous mt studies this indicates a correlation between seismicity and the presence of fault zone fluids

combined escape tectonics and subduction rollback back arc extension a model for the evolution of tertiary rift basins in thailand malaysia and laos the tertiary rift basins of thailand and adjacent countries show considerable variability in the timing of rift initiation termination the timing and magnitude of thermal subsidence and the timing and intensity of inversion episodes the rift basins developed on continental blocks that were extruded southeastwards hence their development must be tied into himalayan extrusion tectonics current tectonic models propose that the tertiary basins opened up as pull apart basins associated with strike slip faults published geochronology of strike slip fault zone rocks mapping of fault patterns in the tertiary basins and mapped releasing restraining bend geometries all indicate that in thailand major sinistral strike slip motion ceased at about 30 ma prior to the formation of most rift basins the thailand the effects of later dextral slip were minor and probably a result of reactivation during episodes of inversion during nw se to ne sw himalayan compression dextral slip was not responsible for opening most of the rift basins in thailand an alternative mechanism to open the rift basins is subduction rollback of the indian plate to the west of thailand it is proposed that subuction rollback can help explain some of the characteristics of the rift basins such as non uniform lithospheric extension deep sag basins and the diachronous onset and termination of rifting

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

magnetotelluric imaging beneath the taiwan orogen an arc continent collision 1 the taiwan orogen has formed since the late miocene by oblique collision between the luzon volcanic arc on the philippine sea plate and the eurasian continental margin this oblique collision has produced an orogen that decreases in age from north to south and permits study of the temporal evolution of an arc continent collision these factors make taiwan a favorable location to study the process of arc continent collision the first long period magnetotelluric mt measurements were recorded in taiwan as part of the taiwan integrated geodynamics research taiger project in 2006 7 measurements were made at 82 sites on three transects across south central and north taiwan that span the breadth of the orogen and cross all major tectonic boundaries robust remote reference processing of the mt time series data resulted in high quality soundings that were modeled in both 2 and 3 dimensions these mt models support predictions of lithospheric deformation i e thick skinned tectonics beneath the central ranges in south and central taiwan but are inconsistent with predictions of orogen scale thin skinned models the mt resistivity model for northern taiwan is consistent with dewatering of the subducting philippine slab and with deformation described by the subducting indenter tectonic model modeling the taiger mt data has definitively shown that conductive and seismically active crustal structures exist to 30 km beneath the orogen these conductive regions interpreted as interconnected fluid map pervasive zones of collisional deformation that are lithospheric in scale

electromagnetic heterogeneity of the seismogenic region of 1962 m6 5 northern miyagi earthquake northeastern japan magnetotelluric surveys were carried out to in vestigate the electrical resistivity structure of the seismo genic region of the 1962 northern miyagi earthquake m6 5 in miyagi prefecture northeastern japan a 2 d inversion reveals the existence of a deep conductive zone and overly ing re sistivezonein theuppe r crust a positiveae romag netic anomaly is also recognized above the resistive zone which is interpreted as a buried kitakami granitoid pluton by comparison with these ismicity wefound that themi croearthquakes occur just above the deep conductor and in the resistive zone and that several s wave reflectors are just above the deep conductor since the s wave reflectors sug gest the existence of fluid beneath them the deep conduc tor can be interpreted as a fluid filled zone moreover we suggest that the seepage of the fluid from the conductive fluid filled zone to the resistive granitoid pluton can become a trigger of the earthquakes

variations in late cenozoic recent strike slip and oblique extensional geometries within indochina the influence of pre existing fabrics abstract from yunnan to northern thailand late cenozoic recent faults strike predominantly nne ssw n s to nne ssw and ne sw to ene wsw associated sedimentary basins are aligned ne sw to n s the regional fault patterns are commonly interpreted as strike slip dominated deformation throughout the area releasing bend and en echelon stepping patterns on faults bounding sedimentary basins indicate sinistral displacement on ne sw to ene wsw trending faults yet in the escape tectonics model left lateral displacement on the ne sw to ene wsw faults is thought to have occurred late in the miocene whilst earlier motion was dextral however in yunnan the ne sw shmax direction required for dextral motion on the n s sagaing nanting and gaoligong fault zones is consistent with sinistral motion on ene wsw striking faults which is still their sense of motion today in northern thailand the dextral sinistral switch model during the miocene is not tenable because the fang basin is of late oligocene pliocene age and requires similar age sinistral motion on the ene wsw mae chan fault in order to have opened in an alternative model northern thailand is interpreted to have evolved predominantly by oblique extension the golden triangle area marks a transition from transtensional deformation in the north to oblique extension in the south the activation of pre existing fabrics strongly affects both strike slip and extensional faults and has given rise to the similar extensional and strike slip fault patterns multiple episodes of basin inversion in northern thailand during the miocene require short term changes in stress pattern to produce the inferred changes in stress pattern it is suggested that stresses radiating out from the himalayan syntaxis exert a strong influence but were not the only important forces acting on the region

crustal heterogeneity in the 2000 western tottori earthquake region effect of fluids from slab dehydration abstract in order to understand the generating mechanism of the western tottori earthquake m 7 3 that occurred on 6 october 2000 in southwest japan we determined high resolution 3d p and s wave velocity and poisson s ratio structures in the epicentral area we used 17 542 p and 13 831 s wave high quality arrival times from 721 tottori aftershocks and other local microearthquakes recorded by the dense high sensitivity seismic network hi net installed recently on the japan islands significant variations of up to 4 for seismic velocity and 9 for poisson s ratio are revealed in the aftershock area areas with large coseismic slips and high aftershock activity are associated with high p wave velocity v p high poisson s ratio and high electrical conductivity which may represent strong and competent parts of the fault zone containing fluids the western tottori mainshock hypocenter is located in a boundary zone where both velocity and poisson s ratio change drastically both p and s wave velocities are slower in the lower crust under the mainshock hypocenter and low frequency microearthquakes were detected within the slow anomalies around the moho discontinuity before and after the occurrence of the 2000 western tottori earthquake these results and other related evidence suggest that the strong crustal heterogeneity in the western tottori source area is associated with fluids and arc magma under nearby the daisen volcano which may have influenced the nucleation and rupture process of the western tottori earthquake the arc magma and fluids are thought to result from the dehydration reactions of the subducting philippine sea slab in this region these results suggest that the nucleation of shallow earthquakes could be controlled by a deep structure and regime and so it is important to study the deeper crust and upper mantle structure and processes for clarifying the generating mechanism of large crustal earthquakes

resistivity structure of the central indian tectonic zone citz from multiple magnetotelluric mt profiles and tectonic implications the central indian tectonic zone citz is a major tectonic feature extending across the indian subcontinent it was formed in the paleoproterozoic when the bastar craton and the bundelkhand craton were sutured together this region is recognized in the geological record as a persistent zone of weakness with many tectonothermal events occurring over geologic time the weakness of this region may have caused the late cretaceous early tertiary deccan volcanism to have been localized in the citz the zone is still tectonically active as evidenced by sustained levels of seismic activity this paper presents the first systematic investigation of the resistivity structure of the citz using multiple magnetotelluric mt transects two dimensional 2d resistivity models were generated for five north south profiles that cross the citz and encompass an area of 60 000 km2 the models were based on the joint inversion of transverse electric te transverse magnetic tm and tipper hz data all the profiles showed a low resistive 10 80 m middle to lower crust beneath the citz with a crustal conductance of 300 800 s the presence of an interconnected fluid phase and or hydrous metallic minerals appears to be the most likely explanation for the elevated conductivity that is observed beneath the citz the presence of fluids is significant because it may indicate the cause of persistent weakness at crustal depths a northward dip of both the crustal conductive layer and coincident seismic reflections favor a northward polarity of the subduction process associated with the formation of the citz

electrical resistivity cross section across the garhwal himalaya proxy to fluid seismicity linkage abstract magnetotelluric mt measurements along a profile cutting across the garhwal himalaya of india are inverted to obtain 2 d electrical resistivity structures of the himalayan wedge and of the underthrusting indian plate the imaged resistivity cross section is dominated by a low angle north east dipping intra crustal high conducting layer ic hcl with an average thickness of 5 km at transition from the lesser himalaya to the higher himalaya the ic hcl is marked by a ramp structure across which its top jumps from a depth of 8 km to 13 km high conductivity of the layer is caused by pounding of upward propagating metamorphic fluids trapped by tectonically induced neutral buoyancy in compression regime of the himalaya the mechanical weakening effects of the fluids counteract the fault normal stresses thereby facilitating thrust type earthquakes on a plane imaged as the top of the ic hcl it is suggested that in the himalaya collision belt like the active subduction zone the active seismic plane forming seat of large and great earthquakes is located a few kilometers above the top of the down going plate in this tectonic setting the high conductance ramp symbolizes a block of low shear strength and high strain which under the deviatoric stresses release accentuated stresses into the brittle crust thereby generating small but more frequent earthquakes in the narrow himalayan seismic belt in response to either the co seismic pumping or the stress transfer during inter seismic period the upward infiltration of fluid fluxes into the over pressurized zones sufficiently reduces the shear strength of local thrusts and shear zones turning these into locales of concentrated seismicity

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

crustal and uppermost mantle structure and seismotectonics of north china craton abstract we determined a 3 d p wave anisotropic tomography of the crust and uppermost mantle beneath north china craton ncc using 107 976 p wave arrival times from 16 073 local earthquakes recorded by 380 seismic stations our results show significant lateral heterogeneities beneath ncc the lower crust and uppermost mantle beneath the north china basin show widespread low velocity anomalies which may reflect high temperature materials caused by the late mesozoic basaltic magmatism in the ncc low velocity anomalies also exist beneath the trans north china orogen which may reflect asthenospheric upwelling since late mesozoic large crustal earthquakes generally occurred in high velocity zones in the upper to middle crust while low velocity and high conductivity anomalies that may represent fluid filled fractured rock matrices exist in the lower crust to the uppermost mantle under the source zones of the large earthquakes the crustal fluids may lead to the weakening of the seismogenic layer in the upper and middle crust and hence cause the large crustal earthquakes the nw se p wave fast velocity directions seem to be dominant in the uppermost mantle under the central parts of eastern ncc suggesting that these mantle minerals were possibly regenerated but keep the original fossil anisotropy formed before the new lithospheric mantle was produced during the mesozoic to cenozoic

the chanthaburi terrane of southeastern thailand stratigraphic confirmation as a disrupted segment of the sukhothai arc a permo triassic volcanic arc system the sukhothai arc is recognised between the indochina and sibumasu continental blocks the chanthaburi terrane is here interpreted as a fault detached highly disrupted southern segment of the sukhothai arc occupying part of southeastern thailand and extending into cambodia the klaeng tectonic line is defined as the boundary between the chanthaburi terrane and sibumasu block the stratigraphy of the chanthaburi terrane is compared with that of the sukhothai terrane in northern thailand the late palaeozoic mesozoic sequences of these two volcanic arc terranes in the sukhothai zone share important similarities but show marked contrasts to those of the sibumasu and indochina blocks where the late permian triassic is largely absent due to the indosinian i unconformity western indochina or is dominantly carbonates with little terrigenous clastic input sibumasu there is no clear evidence of pre carboniferous sedimentary rocks for either the sukhothai or chanthaburi terranes late permian lyttoniid brachiopod shale near klaeng in the chanthaburi terrane was revisited the brachiopod previously reported as leptodus is re identified to oldhamina the genus previously known elsewhere in southeast asia only in the huai tak formation of the sukhothai terrane oldhamina in thailand is confined to the sukhothai arc the marine stratigraphy of the sukhothai arc is represented by a permian triassic lithological succession of mixed carbonates and siliciclastics with common volcanic material the late permian and triassic litho and biostratigraphy of the chanthaburi terrane are comparable with the upper ngao and lampang groups of the sukhothai terrane in particular they share similar successions from oldhamina brachiopod bearing shale to palaeofusulina colaniella foraminifer bearing limestone in the latest permian marine depositional conditions were terminated on the sukhothai arc by end triassic times later than on the indochina block late permian but earlier than on the sibumasu block jurassic cretaceous

tomography of the source area of the 1995 kobe earthquake evidence for fluids at the hypocenter seismic tomography revealed a low seismic velocity 5 and high poisson s ratio 6 anomaly covering about 300 square kilometers at the hypocenter of the 17 january 1995 magnitude 7 2 kobe earthquake in japan this anomaly may be due to an overpressurized fluid filled fractured rock matrix that contributed to the initiation of the kobe earthquake

fluid driven earthquakes in the chamoli region garhwal himalaya evidence from local earthquake tomography summary the chamoli region within the 700 km seismic gap of the seismically active region of the central himalaya has been site of moderate sized earthquakes in recent past viz 1999 march 29 mb 6 3 2005 december 14 mb 5 3 and very recently 2011 june 20 m 4 6 to understand the process of earthquake generation in the region we constrain earthquake distribution pattern and determine the crustal seismic wave velocity variation using local earthquake data recorded by the kumaon garhwal himalaya seismic network that was operated during 2005 2008 also we included aftershocks data from the 1999 chamoli earthquake we infer that the earthquakes are mainly clustered near the munsiary thrust marking the southern part of the main central thrust zone and in depth above the main himalayan thrust the chamoli earthquake source region is characterized by low p wave velocity vp and high vp vs this could be expression of possible presence of fluids because of metamorphic dehydration reaction by the underthrusting indian crust the released fluid percolates upwards into the brittle portion of the crust reducing the fault zone friction leading to generation of crustal earthquakes

evidence for middle triassic to miocene dual subduction zones beneath the shan thai terrane western thailand from magnetotelluric data abstract kanchanaburi province western thailand is in the middle of shan thai terrane paleomagnetic and geological data support the hypothesis of dual subduction zones beneath the shan thai terrane during the late triassic there was a westward subduction in the east where the lampang chiang rai block subducted beneath the shan thai terrane in addition in the early tertiary the western burma terrane subducted underneath the shan thai in the west resulting in an eastward subduction a pioneer survey of this region was therefore conducted using magnetotelluric mt techniques with the aim of finding deep structures associated with these ancient subduction zones 39 mt stations were deployed to cover most of the province resistivity structures are obtained from the 3 d inversion the near surface resistivity structures correspond well with the surface geology the mid and lower crusts are conductive and this is interpreted as the crusts being composed of mafic granulites of 3 porosity in which the remnant dehydrated fluid was accumulated during the subduction in addition the westward and eastward subduction zones generated mafic ultramafic intrusions which appear as two conductive zones on the east and west respectively these two conductors and the conductive lower crust support the hypotheses of the middle triassic to miocene dual subduction zones