paragenesis of sodic pyroxene bearing quartz schists implications for the p t history of the sanbagawa belt sodic pyroxene jadeite content x jd 0 1 0 3 occurs locally as small inclusions within albite porphyroblasts and in the matrix of hematite bearing quartz schists in the sanbagawa sambagawa metamorphic belt central shikoku japan the sodic pyroxene bearing samples are characteristically free from chlorite and their typical mineral assemblage is sodic pyroxene subcalcic or sodic amphibole phengitic mica albite quartz hematite titanite epidote spessartine rich garnet occurs in mn rich samples sodic pyroxene in epidote bearing samples tends to be poorer in acmite content average x acm 0 26 0 50 than that in the epidote free samples x acm 0 45 0 47 x jd shows no systematic relationship to metamorphic grade and is different among the three sampling regions saruta gawa asemi gawa and bessi besshi the average x jd of the saruta gawa samples 0 21 0 29 is higher than that of the asemi gawa 0 13 0 17 and bessi 0 14 0 23 the p t conditions of the asemi gawa and bessi regions are estimated at 5 5 6 5 kbar 360 c in the chlorite zone 7 8 5 kbar 440 15 c in the garnet zone and 8 9 5 kbar 520 25 c in the albite biotite zone metamorphic pressure of the saruta gawa region is systematically 1 1 5 kbar higher than that of the asemi gawa and bessi regions and materials of the saruta gawa region have been subducted to a level 3 5 km deeper than materials that underwent metamorphism at equivalent temperatures and are now exposed in the asemi gawa and bessi regions pressure slightly increases toward the north structurally high levels through the sanbagawa belt of central shikoku two types of zonal structure were observed in relatively coarse grained sodic pyroxenes in the matrix one type is characterized by increasing x jd from core to rim the other type by decreasing x jd from core to rim both types of zoned pyroxenes show an increase in x fe 2 fe2 fe2 mg from core to rim the first type of zoning was observed in a sample from the chlorite zone of lowest grade whereas the latter occurs in the garnet and albite biotite zones of higher grade the contrast in zonal structure implies that dp dt during prograde metamorphism decreased with increasing metamorphic grade and may have been negative in some samples from the higher grade zones the estimated dp dt of the prograde stage of the chlorite zone is 3 2 kbar 100 c and that of the garnet and albite biotite zones is 1 8 to 0 9 kbar 100 c the variation of dp dt at shallow and deep levels of a subduction system probably reflects the difference of heating duration and or change in thermal gradient of the subduction zone by continuous cooling of the surrounding mantle

microstructures and c axis fabrics indicative of quartz dissolution in sheared quartzites and phyllonites abstract quartzites sheared in low metamorphic grade shear zones that extend along the contact with migmatitic gneissic complexes in the quadrilatere ferifero region southeastern brazil show quartz microstructures indicating deformation by dissolution dissolution occurred adjacent to the foliation planes preferentially in quartz porphyroclasts oriented with their 0001 planes parallel to the foliation dissolution worked as an efficient mechanism to remove porphyroclast edges smoothing foliations and enabling strain accommodation both dissolution and crystal plasticity were competitive crystallographically controlled processes operating in different domains of the evolving microstructure dissolution occurred along the foliation planes while isovolume crystal plasticity and accompanying recrystallization operated essentially in the quartzose domains between folia phyllonites formed in the most strained domains of the shear zones fine grained quartz grains in phyllonites show uncommon c axis fabrics c axis oriented at low angles to the stretching lineation which were interpreted to form either by direct reprecipitation or by residual concentration of grains unfavourably orientated to undergo dissolution domainal c axis fabrics reflect a deformation partitioning path with increasing participation of solution transfer strengthening c axis maxima at low angles with the stretching lineation at the expense of crystal plastic processes during progressive phyllonitization

evidence for aseismic deformation in the western transverse ranges southern california implications for seismic risk assessment recent studies in southern california suggest that long term deformation rates are far in excess of that which can be accounted for by historical seismicity and thus a deficit of moderate and or large earthquakes exists in southern california although possible this conclusion is not unique because aseismic deformation may have contributed to bulk regional strain we examined cretaceous to pleistocene sedimentary rocks exposed in the ventura basin along four cross strike traverses to evaluate the possibility that aseismic deformation contributed to regional shortening our field and microstructural investigations suggest that aseismic deformational mechanisms particularly pressure solution contributed significantly to permanent shortening strain during the late neogene and that the proposed seismic deficiency may be overestimated

broadband time domain modeling of earthquakes from friuli italy short period sp and long period lp seismograms written by the main shock and two principal aftershocks of the 1976 friuli italy earthquake sequence are modeled in the time domain using synthetic seismograms the main shock occurred on 6 may 1976 20h 00m m s 6 5 and both aftershocks on 15 september 1976 03h 15m m s 6 0 and 09h 21m m s 5 9 source models were determined initially by trial and error and then refined using a waveform inversion program two point sources of radiation are required to adequately model the aftershock short period records for the 09h 21m aftershock the model derived from short period records also produces good fits to the long period data the seismic moment of this earthquake is found to be 0 8 to 1 0 10 25 dyne cm the sp model for the 03h 15m aftershock on the other hand predicts long period synthetics which do not agree with the observations in particular the sp moment 0 37 10 25 dyne cm is about formula times smaller than the lp moment 1 10 25 dyne cm adding a long period component to the sp model considerably improves lp waveform and moment agreement in the case of the main shock a reasonable fit to the observed sp data is obtained using three point sources of radiation however lp synthetics computed using this model do not agree with the observations and the sp moment 0 65 10 25 dyne cm is a small fraction of the lp moment 3 to 5 10 25 dyne cm time function durations indicate that the individual events inferred from the sp records are radiated from patches of the fault having radii of 2 to 4 km and stress drops in the range 35 to 276 bars in comparison stress drops estimated from lp data are found to be 12 bars main shock and 24 bars 09h 21m aftershock these observations suggest that the short period instruments are sensitive to the high frequency radiation emitted from small high stress drop areas on the fault plane whereas the long period instruments record the overall motion during the earthquake

neotectonics of western india evidence from deformed quaternary fluvial sequences mahi river gujarat a quaternary fluvial sequence along the mahi river gujarat western india shows evidence for a discrete episode of normal faulting and related surface slumping four mapped nw striking faults have throws ranging from 1 m to over 3 m and have related growth folds in synchronous sediment units a slump sheet moved tens of metres northeastward down the 0 7 dip slope of one tilt block during displacement on its bounding fault the exposed part of the internally folded sheet is probably one side of a lobate slump mass several hundred metres in width fault activity began after deposition of a lower gravel which regional correlations suggest is about 300 ka old faulting ended just before deposition of an upper gravel sand complex dated by luminescence techniques in correlated sections at no younger than about 60 ka the mahi river section shows that neotectonic activity in peninsular india exemplified by the 1993 killari latur earthquake has a mid to late pleistocene component

seismicity normal faulting and the geomorphological development of the gulf of corinth greece the corinth earthquakes of february and march 1981 three major destructive earthquakes of m s 6 7 6 4 6 4 occurred in the eastern part of the gulf of corinth in february and march 1981 associated normal faulting was observed on both the north and the south sides of the gulf examination of teleseismic local seismic surface faulting and geomorpbological data suggests that the first and second of these shocks activated major north dipping normal faults these faults control the topography and bathymetry and are related to the recent uplift and subsidence of the coastline it is probable that the first earthquake occurred on a faultwhich outcrops underwater and the second on a fault which is visible on land it appears that the third shock activated an antithetic normal fault dipping southwards on the north side of the gulf and that the overall structure of the gulf of corinth graben is asymmetric the northern antithetic fault clearly demonstrates the geomorphological changes associated with developing young normal faulting in addition we suggest that observations of recent coastline movement provide a powerful tool for identifying major active fault systems and predicting their historical role in the paleogeography of an area

field survey of the 1993 hokkaido nansei oki earthquake tsunami runup data in hokkaido and in three prefectures in the tohoku district are described with a few witnessed arrival times and with comments of tide records the highest runup of 31 7 m was found at the bottom of a narrow valley on the west coast of okushiri island in order to explain high runups of 20 m at hamatsumae in the sheltered area roles of edge waves refraction of the okushiri spur and tsunami generation by causes other than the major fault motion should be understood an early arrival of the tsunami on the west coast of hokkaido suggests another tsunami generation mechanism in addition to the major fault motion

frictional viscous flow of phyllosilicate bearing fault rock microphysical model and implications for crustal strength profiles it is widely believed that around the brittle ductile transition crustal faults can be significantly weaker than predicted by conventional two mechanism brittle ductile strength envelopes factors contributing to this weakness include the polyphase nature of natural rocks foliation development and the action of fluid assisted processes such as pressure solution recently ring shear experiments using halite kaolinite mixtures as an analogue for phyllosilicaterich rocks for the first time showed frictional viscous behavior i e both normal stress and strain rate sensitive behavior involving the combined effects of pressure solution and phyllosilicates this behavior was accompanied by the development of a mylonitic microstructure a quantitative assessment of the implications of this for the strength of natural faults has hitherto been hampered by the absence of a microphysical model in this paper a microphysical model for shear deformation of foliated phyllosilicate bearing fault rock by pressure solution accommodated sliding along phyllosilicate foliae is developed the model predicts purely frictional behavior at low and high shear strain rates and frictional viscous behavior at intermediate shear strain rates the mechanical data on wet halite kaolinite gouge compare favorably with the model when applied to crustal materials the model predicts major weakening with respect to conventional brittle ductile strength envelopes in particular around the brittle ductile transition the predicted strength profiles suggest that in numerical models of crustal deformation the strength of high strain regions could be approximated by an apparent friction coefficient of 0 25 0 35 down to depths of 15 20 km

unpairing metamorphic belts p t paths and a tectonic model for the ryoke belt southwest japan southwest japan is divided into outer and inner zones by the median tectonic line mtl a major transcurrent fault the outer zone is composed of the sambagawa high pressure intermediate or high p t type metamorphism chichibu and shimanto belts in the inner zone the ryoke belt andalusite sillimanite or low p t type metamorphism was developed mainly within a jurassic accretionary complex this spatial relationship between high p t type and low p t type metamorphic belts led miyashiro to the idea that metamorphic belts were developed as paired systems textural relationships and petrogenetically significant mineral assemblages in pelites from the ryoke belt imply peak p t conditions of 5 kbar and up to 850 c in migmatitic garnet cordierite rocks from the highest grade metamorphic zone it is likely that the thermal anomaly responsible for metamorphism of the ryoke belt was related to a segment of the farallon izanagi ridge as it subducted under the eastern margin of the asian continent during the cretaceous the sequence of mineral assemblages developed in pelites implies a metamorphic field gradient with shallow dp dt slope inferred to have been generated by a nested set of hairpin like clockwise p t paths these p t paths are characterized by limited prograde thickening minor decompression at peak t and near isobaric cooling features that may be typical of p t paths in low p t type metamorphic belts caused by ridge subduction a ridge subduction model for the ryoke belt implies that juxtaposition of the high p t metamorphic rocks of the sambagawa belt against it was a result of terrane amalgamation belt parallel ductile stretching recorded as syn metamorphic predominantly constrictional strain in both ryoke and sambagawa belt rocks and substantial sinistral displacement on the mtl are consistent with left lateral oblique convergence diachroneity in fast cooling of the ryoke belt is implied by extant thermochronological data and is inferred to relate to progressive sw to ne docking of the sambagawa belt thus an alternative interpretation of paired metamorphic belts in japan is that they represent laterally contemporaneous terranes rather than outboard and inboard components of a trench arc paired system amalgamation of laterally contemporaneous terranes during large translations of forearcs along continental margins may explain other examples of paired metamorphic belts in the geological record

intermediate high pressure exhumation of the northern segment of the sanbagawa belt saruta gawa area central shikoku japan abstract the retrograde chemical zonal structure of amphibole in hematite bearing basic and quartz schists from the higher grade zone in the saruta gawa area of the sanbagawa belt was studied to investigate the relationships between the prograde and retrograde p t paths of the sanbagawa metamorphism this amphibole coexists with chlorite epidote muscovite albite quartz and hematite and is composed of al rich core and al poor mantle the core is fairly homogeneous and has a barroisitic composition in the mantle part b na increases with decreasing 4 al towards the margins which have winchite magnesioriebeckite compositions the barroisite winchite magnesioriebeckite composite crystal is sometimes rimmed by actinolite and or winchite with low 4 al and b na the al rich core and al poor mantle are regarded as prograde and retrograde products respectively the retrograde mantle in the saruta gawa area 1 is systematically richer in b na 0 40 1 73 per formula unit pfu for o 23 than that from the same grade zone in the asemi gawa area 0 19 0 78 pfu about 8 km south of the studied area 2 tends to be b na poorer less than 1 73 pfu than prograde sodic amphibole up to 1 93 b na pfu produced in the peak temperature stage from the lower grade zone in the same and other areas and 3 extends its compositional range towards higher b na and lower 4 al than prograde formed amphibole from the same grade zone in the same area these zonal characteristics imply that 1 the saruta gawa samples experienced retrograde metamorphism under higher p t conditions than the asemi gawa samples 2 the retrograde p t path of the saruta gawa area passes on the lower pressure side of the metamorphic field gradient and 3 the saruta gawa samples underwent retrograde metamorphism under higher p t conditions than the prograde metamorphism the higher p t conditions of the retrograde metamorphism suggests an increasing dp dt of the geotherm during exhumation retrograde p t conditions during the formation of magnesioriebeckite can be roughly estimated at 7 8 kbar 400 450 c based on semi quantitative phase relations of actinolite winchite magnesioriebeckite barroisite series associated with chlorite epidote muscovite albite quartz and hematite

brittle normal faulting in the highest grade sambagawa metamorphic rocks of central shikoku southwest japan indication of the exhumation into the upper crustal level abstract analysis of fault system in the high p t type sambagawa metamorphic rocks of central shikoku southwest japan shows that conjugate normal faults pervasively developed in the highest grade biotite zone upper structural level in three study areas asemi river oriu and niihama areas these conjugate normal faults consist of ne sw to e w striking and moderately north dipping set a and nnw sse striking and moderately east dipping set b faults the fault set a is dominant compared to the fault set b and hence most of deformation is accommodated by the fault set a leading to non coaxial deformation the sense of shear is inferred to be a top to the wnw to nnw based on the orientations of striation or quartz slickenfibre and dominant north side down normal displacement these transport direction by normal faulting is significantly different from that at d1 penetrative ductile flow i e top to the w to wnw it has also been found that these conjugate normal faults are openly folded during the d3 phase about the axes trending nw se to e w and plunging west at low angles or horizontally indicating that normal faulting occurred at the d2 phase d2 normal faults along which actinolite breccia derived from serpentinite by metasomatism sometimes occurs perhaps formed under subgreenschist conditions ca 250 c in relation to the final exhumation of sambagawa metamorphic rocks into the upper crustal level the pervasive development of d2 normal faults in the upper structural level suggests that the final exhumation of sambagawa metamorphic rocks could be caused by distributed extension and normal faulting removal of overburden in the upper crust

multiscaling of shear zones and the evolution of the brittle to viscous transition in continental crust 1 a new method is introduced for quantifying the scale and the intensity of strain localization from maps of natural shear zones the method employs autocorrelation functions to determine local areal scales of geometric homogeneity these homogenization scales are used to calculate scale dependent localization fractions of deformed rock the strain localization intensity is quantified from measurements of mean relative to maximum shear strain this approach is used to analyze shear zones on different scales from an exposure cap de creus spain of the fossil brittle to viscous transition bvt changes in the scaling characteristics of shear zones are interpreted to reflect a time sequence of localization during the evolution of the continental bvt we show that shear zone scaling is related to inherited anisotropies older schistosity lithological layering pegmatite bodies and to the predominant mode of deformation brittle viscous the length to width ratio of shear zones increases with their length up to the meter scale and decreases for larger length scales as they evolve from isolated shear fractures to interconnected mylonitic shear zones variations in strain localization intensity calculated along a single shear zone indicate that such shear zones weakened from their brittle tips to their mylonitic centers thus driving their propagation and growth to larger scales our results imply that the bvt evolves by network widening a process whereby strain localizes on progressively larger scales until a dense network of weak mylonitic layers tens to hundreds of meters wide and hundreds to thousands of meters long forms subparallel to the regional shearing plane

deep lower crustal earthquakes in central india inferences from analysis of regional broadband data of the 1997 may 21 jabalpur earthquake summary the only instance of a confirmed deep lower crustal earthquake occurrence in the indian shield region has been that of the 1938 satpura earthquake m 6 3 of central india reportedly at a depth of about 40 km moment tensor inversion of regional broadband waveform data of the 1997 may 21 jabalpur earthquake mw 5 7 confirms yet another such earthquake at about 35 km depth in the central part of the narmada son lineament nsl zone the study is based on a refined velocity model obtained using a traveltime grid search method a reverse fault mechanism is obtained which for a palaeo rift valley zone indicates the possibility of reactivation of a pre existing fault under the influence of the ambient stress field due to the india eurasia plate collision forces the occurrence of earthquakes at lower crustal depths quite unusual for the indian shield region indicates a possible causative mechanism related to crust mantle interaction based on the close proximity of the two deep earthquakes and their disposition with respect to the local trend of the central part of the nsl we suggest a model of stress accumulation due to horizontally elongated or elliptical possibly serpentinized mafic intrusives in the lower crust to explain the occurrence of deep earthquakes in the heart of the indian shield

compaction of granular quartz under hydrothermal conditions controlling mechanisms and grain boundary processes 1 we report isostatic compaction experiments performed on granular quartz under hydrothermal conditions 3 129 m of initial grain size 300 600 c 200 mpa of fluid pressure and 25 100 mpa of effective pressure from microstructural evidence it was determined that whereas microcracking controlled precompaction at room temperature pressure solution was the main mechanism during hydrothermal compaction although a role of microcracking could not be excluded entirely our mechanical data together with theoretical pressure solution rate models further indicated that pressure solution was controlled by interface kinetics dissolution being the most likely rate controlling mechanism an empirical relation of the form 10 7 8 0 10 0 3 4d 1 exp 105 000 rt was fitted to our data to describe experimental compaction rates electron backscatter diffraction ebsd analysis performed on one sample showed limited evidence for plastic deformation dauphine twinning and lattice bending at grain contact points under high stress contact microstructures formed during compaction were studied using quartz single crystal discs or a mica plate as reference surfaces this showed that in all contacts microstructures were rough with a micrometer scale roughness many contacts also showed internal microcracking and it is inferred that microcracking is likely an important mechanism for creating and maintaining rough contacts during quartz pressure solution at least under the present experimental conditions extrapolation of our empirical equation for compaction rates to natural conditions is consistent with previous observations that during burial and diagenesis of a sandstone pressure solution starts to operate at depths of about 1 5 2 km becoming the dominant compaction mechanism at depths greater than 2 5 3 km the extrapolation gives good agreement with porosity depth trends reported for natural arenitic sandstones

focal depths and mechanisms of shallow earthquakes in the himalayan tibetan region abstract the complexity of the himalayan tibetan lithospheric deformation is evident from widespread seismicity and diverse focal mechanism solutions here we investigate the focal depths and fault plane solutions of 97 moderate and shallow earthquakes in the himalayan tibetan region by modeling teleseismic p wave and its tailing surface reflections pp and sp earthquakes in central tibet are restricted to the upper crust and originate dominantly by strike slip faulting in agreement with the low p wave velocity layers in the lower crust and the strong s wave attenuation zones in the uppermost mantle in northern and southern tibet where the asian and indian plates descend beneath central tibet earthquakes appear to be distributed throughout the thickness of the crust and exhibit dominantly reverse faulting we incorporate well estimated focal depths of 127 additional earthquakes from previous studies to estimate the seismogenic thickness ts of the study region the resulting pattern of ts is found to be rather flat for central and northeastern tibet and highly variable along the strike of the himalayan foreland

source modeling of the hsingtai china earthquakes of march 1966 abstract the hsingtai china earthquakes of march 1966 were a series of destructive earthquakes associated with the shu lu graben five strong shocks of ms 6 occurred within a period of less than a month the largest of which was ms 7 2 body and surface waves over the period range from several to 100 s have been modeled for the four largest events using synthetic seismograms in the time domain and spectral analysis in the frequency domain data from ground deformation local geology regional seismic network and teleseismic joint epicenter determination have also been used to constrain the source model and the rupture process the fault mechanism of the hsingtai sequence was mainly strike slip with a small component of normal dip slip the strikes of the four largest shocks range from n26 to 30 e approximately along strike of the major faults of the shu lu graben and the aftershock distribution the source mechanisms can be explained with a nnw sse extensional stress and a nee sww compressional stress acting in the area the major shocks all had focal depths 10 km the four largest shocks in the sequence were characterized by a relatively simple and smooth dislocation time history the durations of the far field source time functions ranged from 3 5 to 5 s while the rise times were all 1 s the seismic moments of the four largest earthquakes ranged from 1 43 1025 to 1 51 1026 dyne cm 1 the fault sizes of the four events were very close assuming circular faults the diameters of the four events were determined to be between 10 and 14 km stress drops varied from 52 to 194 bars a trend of increasing stress drop with earthquake size was observed a survey of stress drop determinations for 15 major intraplate earthquakes shows that on the average the magnitude of stress drop of oceanic intraplate earthquakes and passive continental margin events is higher 200 to several hundred bars than that of continental intraplate earthquakes 100 bars or less

historical seismicity of peninsular india abstract well documented historical earthquake data from 1340 to 1983 has been analyzed and reported in this work so as to understand the seismicity and associated phenomena of peninsular india it has been the belief among earth scientists that the peninsular shield is aseismic as the region attained stability long ago however the earthquake at koyna 10 december 1967 bhadrachalam 13 april 1969 broach 23 march 1970 hyderabad 30 june 1983 etc altered this concept and it has now widely accepted that seismic activity is still continuing on a mild scale as such a need has arisen to take into consideration historical as well as recent seismological data to study the seismic status of peninsular india using the well known frequency magnitude relation of gutenberg and richter 1954 an attempt has been made to derive a and b and the ratio a b the values as obtained for peninsular india are 4 4 0 85 and 5 17 which are typical of moderately active zones the world over recurrence periods of earthquake magnitude 6 75 and 7 0 are calculated to be 21 and 35 yr respectively further the historical seismicity correlates well with the protocontinents such as dharwar aravalli and singhbhum in the peninsular shield it is observed that seismicity in a broad sense is defined by the protocontinents with low intracontinental seismicity while the lineaments and rift valleys are from zones of moderate seismicity

simulation of tsunami induced by dynamic displacement of seabed due to seismic faulting in conventional tsunami simulation techniques simplifications have been employed by neglecting the dynamic seabed displacement resulting from fracturing of a seismic fault and considering only the static contribution the water layer is also assumed to be incompressible regardless of its acoustic effects they should be reconsidered in light of the state of the art technology because considerable discrepancies between numerical simulations and actual observation have been pointed out regarding for example arrival time and wave height in the present study tsunami simulation is conducted without using these kinds of simplification taking into account both the dynamic displacement and acoustic effects as a result thus simulated tsunamis are found to be remarkably larger in the wave height especially in the near fault area where these two effects are superposed in far field however tsunamis thus simulated are likely to show little difference in the wave height but show considerable difference in the arrival time in addition the present dynamic analysis is capable of simulating the water wave induced by the rayleigh wave propagated along the seabed

buckle controlled seismogenic faulting in peninsular india as intraplate earthquakes are often not associated with major known faults their location as well as their timing is unpredictable in peninsular india the larger mx5 0 events occur mainly on reverse faults in a series of belts b400 km apart which are aligned roughly normal to the azimuth of convergence between the indian and eurasian plates the location of the belts is controlled largely by the buckling wavelength of the lithosphere and the seismogenic faults do not generate folding and sometimes result from it there is consequently no need to postulate the creation of regularly spaced normal faults in an antecedent extensional phase and the deformation is consistent with a plate driving force such as gravity glide which is unlikely to reverse its polarity and which creates structures that are influenced by plate geometry at the leading edge the thesis is potentially of value to seismic hazard mitigation as it identifies the zones that are most at risk r 2004 published by elsevier ltd

the high p t sambagawa extrusional wedge japan abstract a metamorphic inversion along the asemigawa section of the besshi unit in the sambagawa high p t metamorphic zone has been explained previously by s vergent major recumbent folding or thrusting through careful structural field investigations however we recognize the d2 asemigawa detachment fault at the boundary of the highest grade oligoclase biotite zone thermal culmination in the belt we have also discovered a series of normal faults in the hanging wall of the major detachment in the upper domain and a series of thrust faults bounding every metamorphic mineral zone of the footwall in the lower domain outcrop scale d2 asymmetric folds are closely associated with axial planar pressure solution cleavages and are genetically related to the above d2 normal faulting and thrusting as fault propagation folds northward fold vergence is found only in the upper domain and southward vergence is found only in the lower domain exceptions to this rule occur only for parasitic folds in the overturned limbs of mesoscopic folds which indicates flexural slip as a likely fold mechanism we propose an extrusion wedge model for the inverted metamorphism and accordingly this mechanism may also account for a large part of the exhumation of the sambagawa metamorphic rocks although westward shear at the time of d1 stretching lineation has partly contributed to the exhumation by counter flow in the accretionary wedge we infer that m1 with its retrograde actinolite schists represents a d1 ductile shear zone but it contributes as much as a component of the d2 asemigawa detachment other normal and thrust faults and asymmetric folds as reactivated brittle shear zones thus shear direction had changed orthogonally and drastically between ductile d1 stretching and ductile brittle transition to brittle d2 extrusion we infer that this transition reflects the collision of an actively spreading mid ocean ridge and is a consequence of increased coupling of plates and orogen normal stress followed by oblique subduction d0 and d 1 record eastward down flow during the oblique underthrusting of oceanic plate before peak metamorphism m1

faulting mechanisms of the liyang china earthquakes of 1974 and 1979 from regional and teleseismic waveforms evidence of tectonic inversion under a fault bounded basin abstract the liyang earthquakes of 1974 and 1979 were two moderately sized but destructive events in eastern china the first shock m s 5 5 occurred on 22 april 1974 in a densely populated area and the second one m s 5 7 took place on 9 july 1979 near the same location the epicenters were located near the intersection of two faults and inside a late mesozoic to late tertiary sedimentary extensional basin in this article long period p and sh waveforms between 2 and 90 and short period teleseismic p waveforms were used to determine strike slip source mechanisms with large reverse faulting components that occurred for both events these mechanisms are significantly different from earlier determined solutions reached through p wave first motions which found strike slip and normal slip components for the two events the solution of the 1974 event obtained from this study strikes 126 dips 71 and slips 33 the focal depth seismic moment and stress drop are determined to be 12 km 8 4 10 23 dyne cm and 41 bars respectively the mechanism of the 1979 event strikes 41 dips 64 and slips 147 the focal depth seismic moment and stress drop are found to be 7 5 km 1 6 10 24 dyne cm and 152 bars respectively seismic data and local observations suggest that the 1974 event ruptured a wnw striking fault for the 1979 event the fault plane is difficult to resolve the observed oblique reverse faulting is relatively rare for major earthquakes in eastern china and probably represents a reactivated and inverted fault motion beneath a structural basin under the present day e w to ene wsw compressional stress field

microstructural development of fine grained quartz aggregates by syntectonic recrystallization abstract experimental study of syntectonic recrystallization of fine grained quartz aggregates was carried out in order to simulate the development of some natural microstructures of quartz tectonites and to understand their formation condition agate was axially compressed with a constant strain rate apparatus experiments were conducted at 4 kbar solid confining pressure 700 1000 c and 10 4 10 6 sec 1 to 10 45 strain in all runs deformation has proceeded under wet condition caused by dehydration of pyrophyllite used as pressure medium two different types of microstructure were distinguished in the deformed specimens one is p type which is characterized by equant equidimensional and polygonal grains the other is s type which is characterized by the highly oblate grains with the largest dimension perpendicular to the compression axis the p type microstructure is developed at higher temperatures and slower strain rates while the s type developed at lower temperatures and faster strain rates the transition between the s and p types is found to be very sharp

periodic variation of stress field in the koyna warna reservoir triggered seismic zone inferred from focal mechanism studies abstract the koyna warna region in western india is globally recognized as the premier site of reservoir triggered seismicity rts associated with the koyna and warna reservoirs the region is characterized by continuous seismic activity observed since several decades including the world s largest triggered earthquake of m6 3 which occurred in koyna in 1967 while the role of reservoirs in triggering earthquakes has been widely discussed the actual tectonic mechanism controlling earthquake genesis in this region is hardly understood the koyna warna region is exclusively governed by earthquakes of strike slip and normal fault mechanism distinct from the thrust faulting seen in other active zones in the indian region in the present study a comprehensive catalog of 50 focal mechanism solutions of earthquakes that occurred during the last 45 years in the koyna warna region is developed both from previous literature and from moment tensor inversion studies by the authors using broadband data from a local seismic network operating since 2005 the seismicity and fault plane data have enabled precise delineation of trends of the major causative faults which are further accentuated using the double difference technique stress inversion of the focal mechanism data has provided the best fitting principal compressive and tensile stress field of the region which in conjunction with the deciphered fault zones provides a feasible model of seismogenesis in this region based on the observed temporal variation of faulting mechanism a model of alternating cycles of predominantly strike slip and normal faulting is proposed which is attributed to a periodic peaking and relaxation respectively of the horizontal compressive stress field in this region due to the indian plate collision with eurasia

microtectonic evidence for eastward ductile shear in the jurassic orogen of sw japan abstract two jurassic deformation phases are responsible for the thrust and nappe structures in the infrastructure of the outer belt of the mesozoic chain of sw japan the first phase was synmetamorphic and took place under hp lt conditions microtectonic analysis shows that the penetrative deformation corresponded to a ductile shear directed from w to e parallel to the stretching and mineral lineation at the regional scale the first phase corresponded to the obduction of the greenschist nappes upon the kurosegawa continent during the second phase the greenschist nappes were sliced leading to an apparent reverse metamorphic zoning the first phase structures were then locally reworked by folds giving rise to an apparent westwards sense of shear

offshore geodetic data conducive to the estimation of the afterslip distribution following the 2003 tokachi oki earthquake a cable based seafloor observatory located offshore of hokkaido japan provides the world s first direct observation of offshore post seismic displacement after removing thermal noise this data is used to constrain the distribution of offshore afterslip from a great interplate earthquake mw 8 0 that occurred during 2003 along the southern kuril trench a checkerboard resolution test showed a great contribution of the offshore data to improving the spatial resolution on the plate interface slip near the trench the 1 yr afterslip is distributed in a u shaped pattern encircling its co seismic slip area this result indicates that the stick slip frictional properties of the plate interface are distributed in a patch like pattern as opposed to a banding pattern as previously assumed in young subduction zones

pressure temperature trajectory of the sanbagawa metamorphism deduced from garnet zoning abstract most garnets in a small volume of the pelitic sanbagawa schists nucleated simultaneously grew and then ceased with their growth maintaining near equilibrium with coexisting minerals such as chlorite and biotite during the prograde metamorphism chemical trends of zoned garnets systematically shift from the pyrope poor to pyrope rich portions in a ternary mn fe mg system in order of ascending metamorphic grade a ternary mn fe mg model system suggests that the higher grade garnets started to grow at lower pressures and higher temperatures than the lower grade ones during prograde metamorphism it follows that high grade metamorphism took place at lower pressures in the garnet to oligoclase biotite zones of the sanbagawa metamorphic terrain in central shikoku

a procedure for modelling shallow dislocation sources summary expressions for displacements on the surface of a layered half space due to an arbitrary oriented shear dislocation are given in terms of generalized ray expansions useful approximations of these expressions for shallow events as recorded at teleseismic distances for realistic earth models are presented the results of this procedure are used to generate synthetic p sv and sh waveforms for various assumptions of stress drop

a preliminary assessment of internal deformation in the indian plate from gps measurements abstract the rate of convergence of the indian plate with respect to eurasia has been obtained using igs gps stations at hyderabad hyde and bangalore iisc in conjunction with a select set of other igs stations the rates obtained for hyde and iisc are 37 09 1 4 and 35 68 1 7 mm yr respectively the difference in the velocities of these two peninsular indian stations with respect to eurasia necessitated a fresh investigation into possible deformation between hyde and iisc separate processing of the baseline with ambiguity resolution suggests a differential motion of 5 01 0 6 mm yr between the two gps sites with hyde moving s68 e relative to iisc the available geological and geophysical data also suggest that this part of peninsular india is undergoing internal deformation

magnetotelluric studies in the central india tectonic zone implications for intraplate stress regimes and generation of shallow earthquakes abstract the central india tectonic zone citz dissects the indian peninsula into the northern and southern crustal blocks the citz has been a seismically active region since the precambrian whereas the relatively deep crustal earthquakes near the narmada faults in the eastern part of the citz have been well investigated the mechanisms for the shallow earthquakes in the western part remain unknown here we present results from a new magnetotelluric study to derive the crustal structure and to understand its implications our data show a thick and highly resistive 500 ohm m crust in the south of tapti river as against a less resistive one in the north these results in conjunction with heat flow values indicate that the crust below the southern part has stable continental cratonic signatures on the northern side of the tapti river we infer the ascent of basaltic magmas from the mantle into the shallow crust and crystallization into layered intrusions these mafic ultramafic bodies could be a potential cause for the shallow earthquakes in the western part of the citz the mafic ultramafic bodies below the crust of citz would locally modify the intraplate stresses which in turn would facilitate the occurrence of earthquakes due to reactivation of pre existing faults thus the large accumulation of strain energy in the deep crust beneath the region can be attributed to the presence of high stress bodies emplaced at depth during the deccan volcanic activity

the 1984 southern yellow sea earthquake of eastern china source properties and seismotectonic implications for a stable continental area on 21 may 1984 a strong shock ms 6 3 mb 5 7 occurred in the southern yellow sea which shook the densely populated coastal area of eastern china about 1 min before the main shock a foreshock of mb 5 4 occurred because of interference from the foreshock no reliable p wave first motions or focal mechanisms have been obtained for the main shock from local seismic data in this paper long period teleseismic data have been used to investigate the source mechanism fault plane solutions determined from first motions as well as p and sh waveforms show a predominant strike slip motion with a small dip slip component on a steeply dipping plane the tectonic environment of this event supports the observation that margins of former rifts tend to be sites of midplate seismic source regions the yellow sea developed in a cratonic environment due to early cenozoic rifting the major graben faults strike nne ssw to ne sw and are intersected by second order faults trending wnw ese aftershock distribution suggests that the fault which generated the main shock probably strikes wnw ese the mechanism determined in this paper strikes 120 dips 88 and slips 28 this solution suggests that the earthquake ruptured along a secondary fault near the intersection of a more major nne ssw trending fault the epicentral area is subject to to an ene wsw compression and a nnw sse extension the seismic moment and focal depth are determined to be 1 09 1025 dyne cm and 12 4 km respectively relative hypocentral locations indicate that the focal depth of the foreshock is similar to that of the main shock and the hypocenter of the foreshock is located very close to the wnw ese striking nodal plane of the main shock mechanism and is about 20 km away from the main shock hypocenter source properties of the southern yellow sea earthquake have been compared with those of three major earthquakes of north china the stress drop of the yellow sea earthquake is determined to be about 42 bars this value is much lower than the stress drops computed for the 1966 hsingtai and the 1975 haicheng earthquakes of north china the southern yellow sea is characterized by short recurrence intervals while the hsingtai and haicheng areas have very long recurrence intervals the short recurrence intervals and low stress drop may reflect a lower material strength at the source region in the yellow sea

dynamic analysis of deformed quartz grains from the folded middle miocene momonoki subgroup of central japan origin of healed microcracks abstract dynamic analyses have been performed on quartz detrital grains from the sandstones of folded middle miocene strata momonoki subgroup found along the itoigawa shizuoka tectonic line istl central japan these quartz grains contain numerous deformation lamellae kink bands and healed microcracks in this study in addition to the dynamic analysis using deformation lamellae the arrow method of carter and friedman the c axis preferred orientations of kinked and unkinked grains and the preferred orientations of healed microcracks in individual grains are analyzed in order to test if these fabrics can be used to determine the palaeostress field in the case of basal a slip being dominant which probably holds for the analyzed quartz the principal stress axes can be inferred from the c axis preferred orientations of kinked and unkinked grains referred to as the kink method here because the preferred orientations indicate the favourable and unfavourable orientations respectively under stress for basal a slip results of the dynamic analyses of deformed quartz by the arrow method and by the kink method are consistent with each other and presumably indicate the palaeostress field associated with the macroscopic folding of the momonoki subgroup although the origin and timing of healed microcracking in the deformed quartz are not completely resolved the preferred orientation of poles to healed microcracks seems to consist of two or three sets of orthogonally disposed maxima whose directions coincide with the principal stress axes responsible for the crystal plasticity i e the lamellae and kinks in the quartz it is suggested that the successive release of residual tectonic stresses in the principal stress directions led to this orthogonal orientation pattern of healed microcracks in the present study then combined dynamic analyses of deformed quartz using deformation lamellae kink bands and healed microcracks provide a more complete quantitative picture of the bulk stress field during deformation particularly the combination of the arrow method with the kink method the latter applied to naturally deformed quartz for the first time in this study provides an indication of the relative magnitude of principal stresses finally in the context of the influence of fluids on the deformation processes in rocks i would like to stress that microcracking in crystalline or consolidated rocks is essential for the incorporation of enough fluid into the constituent crystals to activate fluid assisted deformation processes such as solution precipitation creep and that the regional development of microcracks may be controlled by the stress field associated with the fold development in layered consolidated rocks

three dimensional modeling of intraplate stresses in the epicentral zone of the 21 may 1997 jabalpur earthquake of mw 5 8 central india abstract three dimensional intraplate stresses induced by topography and crustal density heterogeneities have been modeled for a region in central india latitude 21 26 n longitude 77 82 e that was affected by the 1927 son valley m w 6 4 and the 1997 jabalpur m w 5 8 earthquakes the modeled stresses show that these two events occurred in the zones of significant increase in gradients of the principal stress difference 1 3 contours the highest value of these differential stresses 90 mpa is obtained at 5 km depth beneath the epicentral zone of 1927 son valley earthquake whereas a value of 35 mpa is obtained at the focal depth 35 km of the 1997 jabalpur mainshock further depth sections of estimated differential stresses delineate a south dipping high stress body penetrating the whole crust probably a mafic intrusive intruded during the deccan volcanism episode beneath a zone bounded by narmada north fault in the north and narmada south fault in the south within which all aftershocks including mainshocks of the 1997 jabalpur and the 1927 son valley have occurred the modeled direction of principal stresses as well as inferred mode of faulting at 5 20 35 and 40 km depths correlates strongly with the long period 20 50 s centroid moment tensor solutions for the broadband recordings of the m w 5 8 jabalpur mainshock results suggest that estimated large intraplate stresses associated with an inferred mafic intrusive in the presence of high pore pressure resulted from the dehydration of the serpentinite minerals and deep brittle ductile transition may contribute to the failure of rock along the pre existing weak narmada south fault leading to the earthquakes in the deep crust it is proposed that the causal association of large intraplate stresses and the pre existing deep crustal faults would control the future locales of earthquakes in the narmada son lineament

crustal channel flows 1 numerical models with applications to the tectonics of the himalayan tibetan orogen 1 plane strain thermal mechanical numerical models are used to examine the development of midcrustal channel flows in large hot orogens in the models radioactive self heating reduces the viscosity of tectonically thickened crust and increases its susceptibility to large scale horizontal flow channels can be exhumed and exposed by denudation focused on the high relief transition between plateau and foreland we interpret the himalaya to have evolved in this manner channel flows are poorly developed if the channel has a ductile rheology based on wet quartz flow laws and well developed if there is an additional reduction in viscosity to 1019 pa s this reduction occurs from 700 c to 750 c in the models and is attributed to a small percentage of in situ partial melt melt weakening model ht1 provides an internally consistent explanation for the tectonic evolution of many features of the himalayan tibetan orogenic system erosional exhumation exposes the migmatitic channel equivalent to the greater himalayan sequence ghs between coeval normal and thrust sense ductile shear zones corresponding to the south tibetan detachment and the main central thrust systems outward flow of unstable upper crust rotates these shears to low dip angles in the model both the ghs and the lesser himalayan sequence are derived from indian crust with the latter from much farther south similar models exhibit a range of tectonic styles including the formation of domes resembling north himalayan gneiss domes model results are relatively insensitive to channel heterogeneities and to variations in the behavior of the mantle lithosphere beneath the model plateau

40ar 39ar mineral ages within metamorphic clasts from the kuma group eocene central shikoku japan implications for tectonic development of the sambagawa accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku records a high p t metamorphism it is comprised by the oboke nappe and the structurally overlying internally imbricated besshi nappe complex the besshi nappe complex locally is unconformably overlain by the kuma group eocene which consists of conglomerates and subordinate sandstones and mudstones clasts within kuma conglomerates exposed in the kamegamori district include low grade schists derived from the unconformably underlying sambagawa complex and high grade metamorphic rocks of uncertain provenance including garnet amphibolite and oligoclase bearing pelitic schist 36 ar 40 ar vs 39 ar 40 ar isotope correlation ages recorded by hornblende from two amphibolite clasts are 131 1 4 9 ma and 156 8 4 3 ma these are interpreted to date post metamorphic cooling through temperatures required for intracrystalline retention of argon and are older than cooling ages previously reported from any presently exposed segments of the sambagawa terrane plateau ages of 108 8 0 7 ma and 115 7 0 6 ma are recorded by muscovite from two clasts of schist muscovite within a proximal basement exposure of unconformably underlying sambagawa pelitic schist records a plateau age of 78 7 0 5 ma combined with isotopic ages previously reported for the sambagawa terrane 40 ar 39 ar data from clasts in the kuma group suggest that metamorphic culmination within a high grade source terrane occured at c 185 145 ma sectors of this complex cooled through c 500 c at c 150 ma other portions cooled through c 500 c at c 130 ma contrasts in the cooling ages likely reflect internal imbrication within the source terrane the besshi nappe complex reached peak metamorphic conditions at c 100 90 ma and experienced relatively rapid uplift and cooling at c 85 75 ma the besshi nappe complex was structurally emplaced onto the oboke nappe which attained peak metamorphic conditions at c 75 ma subsequently the entire sambagawa section was exhumed and most high grade metamorphic rocks were removed the eocene kuma group was unconformably deposited over the sambagawa terrane at c 50 ma

prograde amphiboles in hematite bearing basic and quartz schists in the sanbagawa belt central shikoku relationship between metamorphic field gradient and p t paths of individual rocks the prograde amphibole that coexists with chlorite epidote muscovite albite quartz and hematite in sanbagawa schists was examined to investigate the relationship between the prograde p t paths of individual rocks and the metamorphic field gradient in the sanbagawa metamorphic belt central shikoku the amphibole changes from actinolite through ferri winchite and crossite to barroisite and hornblende with increasing grade along the metamorphic field gradient however the sequence of prograde amphibole compositions in each sample varies in different mineral zones the general scheme can be summarized as magnesioriebeckite riebeckite crossite in the upper chlorite zone of lower grade rocks crossite or glaucophane barroisite in the garnet zone of medium grade rocks and actinolite or winchite barroisite hornblende in the albite biotite zone of higher grade rocks changes of amphibole composition indicate that the prograde p t path recorded in the higher grade rocks was situated on the higher temperature side of that of the lower grade rocks and on the lower pressure side of the metamorphic field gradient the systematic change of p t paths implies an increasing dp dt during continuous subduction these features can be interpreted as documenting prograde metamorphism within a young subduction zone that has a non steady state geotherm

kinematic earthquake source inversion and tsunami runup prediction with regional geophysical data rapid near source earthquake source modeling relying only on strong motion data is limited by instrumental offsets and magnitude saturation adversely affecting subsequent tsunami prediction seismogeodetic displacement and velocity waveforms estimated from an optimal combination of high rate gps and strong motion data overcome these limitations supplementing land based data with offshore wave measurements by seafloor pressure sensors and gps equipped buoys can further improve the image of the earthquake source and prediction of tsunami extent inundation and runup we present a kinematic source model obtained from a retrospective real time analysis of a heterogeneous data set for the 2011 mw9 0 tohoku oki japan earthquake our model is consistent with conceptual models of subduction zones exhibiting depth dependent behavior that is quantified through frequency domain analysis of slip rate functions the stress drop distribution is found to be significantly more correlated with aftershock locations and mechanism types when off shore data are included the kinematic model parameters are then used as initial conditions in a fully nonlinear tsunami propagation analysis notably we include the horizontal advection of steeply sloping bathymetric features comparison with post event on land survey measurements demonstrates that the tsunami s inundation and runup are predicted with considerable accuracy only limited in scale by the resolution of available topography and bathymetry we conclude that it is possible to produce credible and rapid kinematic source models and tsunami predictions within minutes of earthquake onset time for near source coastal regions most susceptible to loss of life and damage to critical infrastructure regardless of earthquake magnitude

nappe structure of the sambagawa belt the thermal structure of the sambagawa belt which is reflected by minerals produced during the highest temperature of metamorphism generally is characterized by the occurrence of the highest grade schists in the middle of the structural pile the origin of this structure has been analysed in the upper horizon of the sambagawa schist sequence in central shikoku as an example for the structure of the whole belt the upper horizon of the sambagawa schist sequence in central shikoku consists of three nappes the saruta nappe ii the saruta nappe i and the fuyunose nappe in descending order of structural level the saruta nappe ii shows a downward increase of metamorphic grade from the garnet zone through the albite biotite zone to the oligoclase biotite zone the saruta nappe i consists mainly of rocks in the albite biotite zone and partly in the oligoclase biotite zone but the direction of the increase of metamorphic grade is not clear the fuyunose nappe shows an upward increase in metamorphic grade which changes from the glaucophane zone to the barroisite zone it is concluded that the saruta nappe ii and saruta nappe i were overturned and then mechanically coupled with the fuyunose nappe the sambagawa metamorphic field which is of the highest temperature phase of metamorphism appears to have had an inverted thermal gradient and a thermal structure comparable with that expected in the deeper parts of a subduction complex

source parameters of two rift associated intraplate earthquakes in peninsular india the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 abstract the bhadrachalam earthquake of april 13 1969 and the broach earthquake of march 23 1970 are two major intraplate earthquakes associated with paleorift zones in the stable continental region of peninsular india these two events shook very large portions of the peninsula and casualties were reported for the broach earthquake ancient rifts have recently been identified as a major seismogenic tectonic feature for intraplate seismicity in stable continental regions p wave first motions and waveforms of long period teleseismic p and sh waves have been modeled to constrain the focal mechanisms and to determine the source parameters for the earthquakes previous investigators proposed multiple fault plane solutions for each of the events in this paper some of the early solutions are eliminated and the best source mechanism is derived for each earthquake for the bhadrachalam earthquake the focal mechanism determined is predominantly strike slip strike 245 dip 72 rake 358 the strike direction of the ne sw trending nodal plane is in good agreement with the trend of the observed isoseismals and is probably the fault plane the seismic moment is 4 59 1024 dyne cm and the moment magnitude mw is determined to be 5 7 the focal depth and the static stress drop are estimated to be 10 km and 17 bar respectively the strike slip motion represents a reactivated fault motion under the present day stress field for the broach earthquake the focal mechanism determined is reverse faulting with a strike slip component strike 273 dip 58 rake 130 the direction of the e w striking nodal plane is in good agreement with the mapped narmada fault dislocation direction of fissures and the trend of the isoseismals the seismic moment and moment magnitude are determined to be 1 39 1024 dyne cm and 5 4 respectivety the focal depth and the stress drop are estimated to be 11 km and 9 bar respectively the reverse motion of this event represents an inverted slip or tectonic inversion within a rift zone under the present day compressional stress field some rift associated earthquakes are characterized by large multiple shocks with significant strike slip motions the two indian earthquakes however occurred as regular main shock aftershock sequences and represent a different mode of strain release these two earthquakes also represent events with low stress drops and relatively long recurrence intervals the interpretation of this last observation is uncertain and needs more study in the future

earthquake depth distributions in central asia and their relations with lithosphere thickness shortening and extension this paper examines the relationship between seismogenic thickness lithosphere structure and rheology in central and northeastern asia we accurately determine earthquake depth distributions which reveal important rheological variations in the lower crust these variations exert a fundamental control on the active tectonics and the morphological evolution of the continents we consider 323 earthquakes across the tibetan plateau the tien shan and their forelands as well as the baikal rift ne siberia and the laptev sea and present the source parameters of 94 of these here for the first time these parameters have been determined through body wave inversion the identification of depth phases or the modelling of regional waveforms lower crustal earthquakes are found to be restricted to the forelands in areas undergoing shortening and to locations where rifting coincides with abrupt changes in lithosphere thickness such as the ne baikal rift and w laptev sea the lower crust in these areas is seismogenic at temperatures that may be as high as 600 c suggesting that it is anhydrous and is likely to have great long term strength lower crustal earthquakes are therefore a useful proxy indicating strong lithosphere in places that are too small in areal extent for this to be confirmed independently by estimating effective elastic thickness from gravity topography relations the variation in crustal rheology indicated by the distribution of lower crustal earthquakes has many implications ranging from the support of mountain belts and the formation of steep mountain fronts to the localization and orientation of rifting in combination these processes can also be responsible for the separation of the front of the thin skinned mountain belts from their hinterlands when continents separate

body waveforms and source parameters of some moderate sized earthquakes near north island new zealand p wave first motion and synthetic seismogram analysis of p and sh waveforms recorded at teleseismic distances on the wwssn are used to estimate source parameters of seven of the largest earthquakes 6 1 mb 6 3 that occurred in the vicinity of north island new zealand since 1965 the source parameters of three other mb 6 1 events determined outside of this study are included and considered in the final analysis four of the earthquakes occurred at shallow depths 20 km of which three were located within and to the north of north island two of the shallow events show strike slip and normal focal mechanisms with t axes oriented in a manner consistent with their location in an area of known back arc extension one of the shallow events occurred in northern south island and shows a reverse type mechanism indicating horizontal contraction of the crust in an easterly azimuth six events occurred at intermediate depths h 39 to 195 km of which five exhibit thrust mechanisms with t axes consistently oriented near vertical in the light of previously published plate tectonic models the near vertical orientation of t axes of the intermediate depth events may be used to infer that the southern kermadec plate boundary immediately north of north island is not strongly coupled and hence not likely capable of producing great earthquakes a similar inference cannot be made for the section of the hikurangi margin adjacent to north island since the intermediate depth events considered in this study lie to the north of this segment of the plate boundary

high frequency radiation process during earthquake faulting envelope inversion of acceleration seismograms from the 1993 hokkaido nansei oki japan earthquake we investigate the process of high frequency 1 to 10 hz radiation on the fault plane of the 1993 hokkaido nansei oki japan earthquake mw 7 5 from the envelope inversion of strong motion acceleration seismograms for the analysis empirical green s functions are used because theoretical approach is not available for such high frequencies the source is modeled with two fault planes with different strike angles the rupture process of this earthquake is very complex in terms of high frequency wave generation the rupture which started on the northern fault plane had a delay of about 10 sec or propagated very slowly between the northern and southern fault planes high frequency wave radiation is large at the northern and southern edges of the source region deceleration of rupture is also observed there this is interpreted to be associated with stopping of rupture another high frequency wave radiation area is found at the center of the northern fault plane where discontinuity in the depth distribution of aftershocks suggests an existence of a barrier the areas of high and low frequency wave radiation are not correlated this is considered to result from the complexity of rupture process we cannot distinguish between westward and eastward dip of the southern fault plane because of one sided station distribution

shear wave attenuation characteristics over the central india tectonic zone and its surroundings abstract the study area lies between latitude 18 26 n and longitude 73 83 e and mainly covers the central india tectonic zone citz the frequency dependent shear wave quality factor qs has been estimated over the citz and its surroundings using double spectral ratio dsr method we have considered 25 local earthquakes with magnitude ml varies from 3 0 to 4 7 recorded at 11 stations running under national seismic network the fast fourier transformed fft spectra were computed from the recorded waveform having time window from onset of s phase to 1 0 s and for a frequency band of 0 1 10 hz three different shear wave velocities i e 3 87 3 39 and 3 96 km s were obtained over the study area based on a pair of earthquakes recorded at a pair of stations the low qs values of 51 96 at 1 hz i e qs 51f0 49 qs 90f0 488 and qs 96f0 53 were found in the area covering the son narmada tapti sonata lineament citz eastern part of the satpura fold belt vindhyan and gondwana basins godavari and mahanadi grabens and southern part of gangetic plain intermediate qs values of the order of 204 277 i e qs 204f0 56 and qs 277f0 55 were noted in the cartonic areas namely bundelkhand dharwar bhandara and bastar while the higher qs values of 391 628 at 1 hz i e qs 391f0 49 qs 409f0 48 qs 417f0 48 qs 500f0 66 qs 585f0 65 and qs 628f0 69 were found in the eastern part of the sonata citz and the northeastern part of the satpura fold belt the low qs values might be attributing to the more heterogeneous sonata rift system low qs values further may presumably be associated with lower level of seismicity and apparently account for higher tectonic stress accumulation over long duration the long term accumulated stress is generally released through occasional triggering of moderate magnitude earthquakes in the sonata zone surrounding the sonata region the higher qs values possibly accounts for a more homogeneous subsurface structure along the sonata zone

some seismological and geometric features of intraplate earthquakes to understand the nature and cause of intraplate earthquakes we carried out a systematic search for common features associated with them various geological geophysical and seismic data were analyzed and geometric and seismic parameters were compared for 29 intraplate events m 4 5 occurring worldwide the results suggest that intraplate earthquakes occur by the reactivation of pre existing zones of weakness in a compressional stress regime which is generally oriented parallel to the absolute direction of plate motion two styles of faulting were observed for type a earthquakes observed in the eastern united states eastern china western europe and west africa deformation occurs by strike slip motion on steeply dipping faults type b events are usually associated with thrust or normal faulting and were observed in eastern canada fennoscandia australia and peninsular india focal depths did not explain the differences between type a and type b earthquakes rather the differences are due to the perturbation of a regional stress field by a local stress field the regional stress field for type a events is primarily due to ridge push forces the method of stress perturbation varied from region to region the earthquakes in the type b category were further divided into three subcategories type b1 occurring in eastern canada and fennoscandia type b2 occurring in australia peninsular india and central brazil and type b3 occurring in the gulf coast of the u s the inferred causes of the perturbing stresses are deglaciation intracontinental resistive forces resulting from the collision of plates and the deposition of a large thickness of sediments respectively type a events were found to be associated with intersecting faults and generally supported the intersection model of talwani 1988 and had analogs in plate boundary events

seismogenesis in the stable continental interiors an appraisal based on two examples from india characteristics of two recent moderate earthquakes from india 1993 killari mw 6 1 and 1997 jabalpur mw 5 8 are presented in this paper to illustrate the influence of geologic and tectonic setting on the nature of seismicity in stable continental regions scrs the killari event which occurred in the middle of a cratonic region of low background seismicity long recurrence interval and poorly developed neotectonic features may be qualified as a common type of scr event this earthquake is also characterized by a shallow focal depth and a long sequence of aftershocks in contrast the jabalpur earthquake shows a spatial association with a well defined tectonic structure with significant background seismicity a remarkable feature of this earthquake is its deep focus not commonly observed in scr seismicity this event was associated with fewer aftershocks unlike most other scr earthquakes analogous events are found in other shield regions as well based on their general characteristics a broad classification of moderate scr earthquakes is attempted here two broad groups have been identified in this study 1 a set of deep focus earthquakes that are related to intracratonic paleorifts and 2 shallow focus earthquakes associated with discrete faults in the less deformed precambrian terrains a synthesis of earthquake data from different geologic environments will improve our understanding of the seismogenesis in the shield regions 1999 elsevier science b v all rights reserved

microstructures and flow mechanisms in regional metamorphic rocks of japan a number of microstructural features indicate a difference in the dominant deformation mechanism between the higher temperature ryoke and the lower temperature sambagawa and shimanto metamorphic belts of japan the microstructures of metacherts containing deformed radiolaria are divided into two types in both the sambagawa and shimanto belts the quartz grains are tabular while in the ryoke belt they are equiaxed tem studies of these metacherts revealed that the tabular grains contain abundant subboundaries consisting of large numbers of network dislocations and bowe out dislocations while the equiaxed grains contain no subboundaries and have low densities of dislocations which are not bowed out there is a corresponding difference in the textures lattice preferred orientation of quartz the ryoke metacherts display randomly distributed c axes of quartz while the sambagawa and shimanto metacherts show conspicuous crossed girdle patterns with some asymmetry there is a third difference between these regions in the metacherts of the ryoke metamorphic belt the strain magnitudes determined from deformed radiolaria increase with increasing volume fraction of mica in the same metamorphic p and t conditions while in the sambagawa and the shimanto metamorphic cherts the strain magnitudes decrease with increasing the mica fraction

active faulting in apparently stable peninsular india rift inversion and a holocene age great earthquake on the tapti fault we present observations of active faulting within peninsular india far from the surrounding plate boundaries offset alluvial fan surfaces indicate one or more magnitude 7 6 8 4 thrust faulting earthquakes on the tapti fault maharashtra western india during the holocene the high ratio of fault displacement to length on the alluvial fan offsets implies high stress drop faulting as has been observed elsewhere in the peninsula the along strike extent of the fan offsets is similar to the thickness of the seismogenic layer suggesting a roughly equidimensional fault rupture the subsiding footwall of the fault is likely to have been responsible for altering the continental scale drainage pattern in central india and creating the large west flowing catchment of the tapti river a preexisting sedimentary basin in the uplifting hanging wall implies that the tapti fault was active as a normal fault during the mesozoic and has been reactivated as a thrust highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere the slip sense of faults and earthquakes in india suggests that deformation south of the ganges foreland basin is driven by the compressive force transmitted between india and the tibetan plateau the along strike continuation of faulting to the east of the holocene ruptures we have studied represents a significant seismic hazard in central india

body wave waveform constraints on the source parameters of the yangjiang china earthquake of july 25 1969 a devastating earthquake in a stable continental region on july 25 1969 anm s 5 9 earthquake shook the kwangtung province near yangjiang china casualties and extensive damage were reported in the epicentral area the yangjiang earthquake occurred within the passive margin located along china s southeast coast this stable continental setting is seismically one of the most quiet regions of china historic records indicate this earthquake to have been the first devastating one in the area a remarkable feature of this earthquake sequence is that its foreshocks and aftershocks are relatively small in terms of number and magnitude despite the relatively large main shock waveforms of long and short period teleseismicp and long period teleseismicsh waves have been modeled to estimate the source parameters for this earthquake the focal mechanism determined is predominately strike slip with a small normal component strike 263 dip 79 rake 194 and is in good agreement with observations in the epicentral area regarding dislocation direction of fissures distribution of aftershocks and isoseismals the average seismic moment is 5 15 1024 dyne cm and the focal depth is estimated to be 9 km the earthquake is characterized by a rather short source time function and a high stress drop of approximately 380 bars the observed pattern of the foreshock main shock aftershock sequence is interpreted in terms of the large stress drop associated with the main shock and the material properties at and near the source thep axis orientation lies roughly nw se and is consistent with the maximum compressive stress observed along the coast of southeast china this stress orientation is consistent with the nw subducting philippine sea plate and the se ward push from central china due to the convergence between indian and eurasian subcontinents

chronology of sanbagawa metamorphism by collating age data based on the fossil age of the protoliths radiometric dating of the metamorphic minerals and sedimentary records of erosion at the earth s surface the history of the sanbagawa metamorphism can be summarized as follows 1 the pre metamorphic sedimentary rocks carboniferous jurassic early cretaceous became mixed and formed a thickened packet in the vicinity of an ancient trench through a variety of subduction related tectono sedimentary processes probably in early cretaceous time c 130 120 ma 2 the subducted protoliths underwent progressive metamorphism reaching a maximum depth of c 30 km in late early cretaceous time c 116 10 ma 3 the high p t metamorphic rocks began to rise toward the surface during the interval 110 50 ma with minimum estimates for the average cooling rate around 9 12 c ma and an average uplift rate around 0 4 0 5 mm year 4 finally at some stage after reaching the erosional surface the high p t metamorphic rocks were covered unconformably by the middle eocene c 50 42 ma kuma group on the basis of the present chronological summary of the sanbagawa metamorphism the areal extent of the sanbagawa metamorphism is also discussed with respect to the weakly metamorphosed subduction accretion complex of the next tectonic belt to the south the northern chichibu belt

coupled micro faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the sambagawa metamorphic rocks southwest japan abstract in the sambagawa schist southwest japan while ductile deformation pervasively occurred at d 1 phase during exhumation low angle normal faulting was locally intensive at d 2 phase under the conditions of frictional viscous transition of quartz c 300 c during further exhumation into the upper crustal level accordingly the formation of d 2 shear bands was overprinted on type i crossed girdle quartz c axis fabrics and microstructures formed by intracrystalline plasticity at d 1 phase in some quartz schists the quartz c axis fabrics became weak and finally random with increasing shear accompanied by the decreasing degree of undulation of recrystallized quartz grain boundaries which resulted from the increasing portion of straight grain boundaries coinciding with the interfaces between newly precipitated quartz and mica we interpreted these facts as caused by increasing activity of pressure solution the quartz grains were dissolved mostly at platy quartz mica interface and precipitated with random orientation and pinned by mica thus having led to the obliteration of existing quartz c axis fabrics in the sheared quartz schist the strength became reduced by the enhanced pressure solution creep not only due to the reduction of diffusion path length caused by increasing number of shear bands but also to enhanced dissolution at the interphase boundaries

shrimp u pb zircon dating of quartz bearing eclogite from the sanbagawa belt south west japan implications for metamorphic evolution of subducted protolith in order to decipher the origin of eclogite in the high p t sanbagawa metamorphic belt shrimp u pb ages of zircons from quartz bearing eclogite and associated quartz rich rock metasandstone were determined one zircon core of the quartz rich rock yields an extremely old provenance age of 1899 79 ma suggesting that the core is of detrital origin eight other core ages are in the 148 134 ma range and are older than the estimated age for trench sedimentation as indicated by the youngest radiolarian fossil age of 139 135 ma from the sanbagawa schists ages of metamorphic zircon rims 132 112 ma from the quartz rich rock are consistent with metamorphic zircon ages from the quartz bearing eclogite indicating that eclogite facies metamorphism peaked at 120 110 ma these new data are consistent with both the iratsu eclogite body and surrounding highest grade sanbagawa schists undergoing coeval subduction zone metamorphism and subsequent re equilibration under epidote amphibolite facies conditions during exhumation

p t deformation fe3 fe2 mapping at the thin section scale and comparison with xanes mapping application to a garnet bearing metapelite from the sambagawa metamorphic belt japan quantitative x ray maps of composition from a chlorite k white mica albite quartz and garnet bearing thin section from a sambagawa blueschist facies metapelite were combined with a multiequilibrium calculation method to calculate a p t fe3 fe2 deformation map at the millimetre scale the studied sample was chosen because elongated chlorite crystallization tails pressure shadows rimmed by phengite are present which is an appropriate assemblage for the quantification of the p t evolution chlorite temperature and fe3 content maps were calculated by successive iterations for each pixel analysis of fe3 until convergence of the four chlorite quartz h2o equilibria that can be written using the fe and mg amesite clinchlore daphnite and sudoite chlorite end members the calculated map of fe2 fe3 in chlorite is in good qualitative agreement with the in situ mapping of this ratio using xanes x ray absorption near edge structure techniques the temperature map indicates that high temperature chlorite zones with low fe3 contents alternate with lower temperature zones and higher fe3 contents in the crystallization tail late fractures perpendicular to the elongation axis of the tail are filled by very low temperature chlorite 250 c showing fe3 fetotal up to 0 4 groups of chlorite and mica pixels were then identified based on compositional and structural criteria and a p tdeformation map was calculated using representative analyses of these groups the calculated p tdeformation map suggests that in contrast to chlorite the composition of most mica did not change significantly during exhumation mica reequilibrated in late ew shear bands only ew shearing was already active at 0 1 gpa 500 c which corresponds to the peak temperature and probably pressure conditions at reduced redox conditions the intensity of deformation probably decreased with decrease in temperature to 350 400 c at this temperature a second main deformation event corresponding to a further ew stretching occurred and was still active below 250 c and more oxidizing conditions these results indicate that the scale at which p t data can be obtained is now close to the scale of observation of structural geologists a close link between deformation and mineral reaction is therefore possible at the microscopic scale which provides information about the relationship between deformation and mineral reactivity the modalities of deformation with time and the p t conditions at which it occurred

fdm simulation of seismic waves ocean acoustic waves and tsunamis based on tsunami coupled equations of motion we have developed a new unified modeling technique for the total simulation of seismic waves ocean acoustic waves and tsunamis resulting from earthquakes based on a finite difference method simulation of the 3d equations of motion using the equilibrium between the pressure gradient and gravity in these equations tsunami propagation is naturally incorporated in the simulation based on the equations of motion the performance of the parallel computation for the newly developed tsunami coupled equations using a domain partitioning procedure shows a high efficiency coefficient with a large number of cpu cores the simulation results show how the near field term associated with seismic waves produced by shallow earthquakes leads to a permanent coseismic deformation of the ground surface which gives rise to the initial tsunami on the sea surface propagation of the tsunami along the sea surface as a gravity wave and ocean acoustic waves in seawater with high frequency multiple p wave reflections between the free surface and sea bottom are also clearly demonstrated by the present simulations we find a good agreement in the tsunami waveform between our results and those obtained by other simulations based on an analytical model and the navier stokes equations demonstrating the effectiveness of the tsunami coupling simulation model based on this simulation we show that the ratio of the amplitude of ocean acoustic waves to the height of the tsunami both of which are produced by the earthquake strongly depends on the rise time of the earthquake rupture this ratio can be used to obtain a more detailed understanding of the source rupture processes of subduction zone earthquakes and for implementing an improved tsunami alert system for slow tsunami earthquakes

c axis fabrics and microstructures in a recrystallized quartz vein deformed under fluid rich greenschist conditions the quartz v axis orientations and microstructures have been analyzed in an originally single crystal buckled quartz vein of greenschist metamorphic grade from the sambagawa metamorphic belt southwest japan the basal 0001 plane was inclined by ca 10 20 to the quartz vein surface before deformation and the flexure essentially kink which produced the fold was accomplished by basal 0001 slip alone in the hinges i e flexural slip folding in addition to crystal plasticity dissolution microstructures are ubiquitous in the quartz vein dynamic recrystallization resulted from both subgrain rotation and grain boundary migration rotation recrystallization associated with basal 0001 slip resulted in host controlled v axis orientation distribution along a great circle whereas migration recrystallization perhaps assisted by intergranular fluid resulted in a penetrative development of a weak x elongation maximum v axis fabric nowhere rotated by the folding the migration recrystallization is evidenced by large v axis misorientations across the grain boundaries as well as irregular grain shape based on the weak v axis fabric development and lack of grain shape fabric solution precipitation creep may have dominated in the fluid assisted grain boundary migration regime and hence it is inferred that the transition from rotation to migration recrystallization was caused by a local decrease of differential stress in the buckled quartz vein

mode of strain release of three graben associated earthquakes the nature of graben associated earthquakes has been investigated through a study of three earthquake sequences using various seismological geophysical and geological data the three earthquake sequences are the hsingtai china earthquakes maximum magnitude ms 7 2 of march 1966 the nevada earthquakes maximum m 7 1 of 1954 and the new madrid earthquakes maximum ms 8 8 of 1811 1812 these earthquake sequences represent a unique mode of strain release away from plate margins and have bearings on earthquake hazard evaluation a number of similarities have been observed during these earthquake sequences for instance all the three sequences are characterized by large multiple shocks or swarms which last from several weeks to several months among the large multiple shocks in each sequence the largest one usually is not the first one migrations of epicenters were observed during the hsingtai and the new madrid earthquakes significant amount of strike slip motion was associated or inferred with all these three sequences in particular for the hsingtai earthquakes the swarm of multiple shock activities is probably due to induced instability or strong coupling and interactions among a series of adjacent faults in a heterogeneous graben the strike slip motion can be explained by a change or a rotation of stress orientation after the formation of a graben the graben events are similar to the earthquake swarms associated with spreading oceanic ridges but with significant differences available data indicate that the recurrence intervals for the three graben earthquake sequences studied are of the order of thousands of years

tectonics and thermal structure of western satpura india abstract increased seismicity and occurrences of hot springs having surface temperature of 36 58 c are observed in the central part of india 74 81 e 20 25 n where the ne trending middle proterozoic aravalli mobile belt meets the ene trending satpura mobile belt earlier deep seismic sounding dss studies along thuadara sendhwa sindad profile in the area has showed mesozoic sediments up to around 4 km depth covered by deccan trap and the moho depth with a boundary velocity p n of 8 2 km s in the present study surface heat flow of 48 4 mw m 2 has been estimated based on p n velocity which agrees with the value of heat flow of 52 4 mw m 2 based on curie point isotherms estimates the calculated temperature depth profile shows temperature of 80 120 c at the basement which is equivalent to oil window temperature in mesozoic sediments and around 570 635 c at moho depth of 38 43 km and the thermal lithosphere is about 110 km thick which is comparatively higher than those of adjoining regions the present study reveals the brittle ductile transition zone at 14 41 km depth temperature around 250 600 c where earthquake nucleation takes place

on the mechanism and source parameters of the deep crustal jabalpur earthquake india of 1997 may 21 constraints from aftershocks and changes in static stress summary the 1997 may 21 jabalpur earthquake mb 6 0 occurred in the lower crust of the ene wswtrending narmada son palaeorift zone in central india known as the narmada son lineament nsl we correlate the aftershock distribution of this earthquake with the computed changes in static stress caused by slip on the earthquake rupture in order to constrain some of the source parameters of the main event we estimate that the downdip edge of the earthquake rupture extended up to a depth of about 38 km and that the majority of the aftershocks occurred due to unclamping in the hangingwall near the downdip edge of the rupture considering the intermediate to moderately high heat flow in the region we suggest that 1 high pore pressure in the lower crust which developed due to the dehydration of the serpentinite body during previous episodes of thermo tectonic processes 2 a lower frictional coefficient possibly arising due to fractured rocks at depth 3 a higher strain rate and 4 the favourable influence of n s compression due to the motion of the indian plate are responsible for the infrequent earthquakes in the lower crust of the nsl zone

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

occurrences of large magnitude earthquakes in the kachchh region gujarat western india tectonic implications abstract moderate to large damaging earthquakes in the peninsular part of the indian plate do not support the long standing belief of the seismic stability of this region the historical record shows that about 15 damaging earthquakes with magnitudes from 5 5 to 8 0 occurred in the indian peninsula most of these events were associated with the old rift systems our analysis of the 2001 bhuj earthquake and its 12 year aftershock sequence indicates a seismic zone bound by two linear trends nnw and nne that intersect an e w trending graben the bouguer gravity values near the epicentre of the bhuj earthquake are relatively low 2 mgal the gravity anomaly maps the distribution of earthquake epicentres and the crustal strain rate patterns indicate that the 2001 bhuj earthquake occurred along a fault within strain hardened mid crustal rocks the collision resistance between the indian plate and the eurasian plate along the himalayas and anticlockwise rotation of the indian plate provide the far field stresses that concentrate within a fault bounded block close to the western margin of the indian plate and is periodically released during earthquakes such as the 2001 m w 7 7 bhuj earthquake we propose that the moderate to large magnitude earthquakes in the deeper crust in this area occur along faults associated with old rift systems that are reactivated in a strain hardened environment

three dimensional tsunami generation simulation due to sea bottom deformation and its interpretation based on the linear theory summary the present study investigates the tsunami generation process by using 3 d numerical simulations and the linear potential theory first we evaluate the relation between sea bottom elevation and sea surface elevation as function of source size l sea depth h and source duration t based on 3 d numerical simulations the surface elevation decreases with increasing sea depth and source duration the difference between the sea bottom and the sea surface elevation appears when the source size is smaller than approximately 10 times the sea depth for a short source duration the linear potential theory can precisely predict the numerical simulation results based on the theory we can consider the tsunami generation as two spatial lowpass filter processes in which the cut off wavenumbers are given by the sea depth and the source duration the criteria for small source size and short source duration are given as l 13h and t l 8c respectively where c is the phase velocity of the tsunami we then simulate the tsunami generation of the 1896 sanriku tsunami earthquake japan the simulated sea surface elevation is significantly different from the sea bottom elevation which suggests the need for correction of the sea depth and source duration for the precise evaluation of the initial water height distribution to include these effects in 2 d simulations we can use the impulse response function and add the fractional sea surface uplift within the time step to the sea surface for each time step

evolution of the sambagawa metamorphic belt japan abstract the high pressure sambagawa metamorphic belt evolved within a mesozoic accretionary prism that developed in the convergent margin along the east of the eurasian continent although extensively researched recent studies in this region have revealed a number of important features that allow more complete reconstruction of the tectonic history i the grouping of radiometric ages suggests the existence of three major structural units with distinct metamorphic histories one of these has since been completely eroded away ii the difference of ages recorded by different minerals is in many cases small suggesting rapid exhumation after reaching peak metamorphic conditions iii the dominant ductile deformation of the sanbagawa belt representing major orogen parallel flow is commonly related to retrograde metamorphic reactions this shows that the associated fabric developed during exhumation not subduction iv kinematic studies suggest that the main ductile deformation caused major ductile thinning of the region which was probably a significant factor in causing exhumation of the region

muscovite k ar ages of the sanbagawa schists japan and argon depletion during cooling and deformation seventy muscovites from schists in the sanbagawa terrain in central shikoku were dated by the k ar method the muscovite ages are consistently older with increasing metamorphic grade within the same zone the ages are significantly younger in schists which have been more severely deformed these k ar age variations could be due to systematic argon depletion during deformation i e to the dynamic recrystallization of muscovites during ductile deformation that formed a large scale recumbent fold during the uplift and cooling argon loss was greater in schists that were more extensively deformed and in the lower grade zone that experienced a longer period of low temperature deformation than the higher grade zone the relationships between age and grain size in a pelitic schist suggest that coarse grained muscovites lost more argon than the finegrained ones there was no significant resetting of ages in the vicinity of major strike slip faults such as the median tecotonic line or near thrust faults the combination of geochronological and geological data constrains the cooling rate of the sanbagawa schists to 9 12 c ma in the oligoclase biotite zone in central shikoku japan

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

40ar 39ar mineral age constraints for the tectonothermal evolution of the sambagawa metamorphic belt central shikoku japan a cretaceous accretionary prism abstract the sambagawa metamorphic belt exposed in central shikoku japan is tectonostratigraphically represented by the oboke and structurally overlying besshi nappe complexes oboke units consist of metamorphic rocks largely derived from clastic protoliths sandstone and conglomerate whereas besshi units are dominated by rocks with oceanic protolith affinities shale chert and greenstone whole rock schist samples from low grade oboke units record intermediate temperature 40 ar 39 ar plateau ages of 70 77 ma which are interpreted to closely date attainment of maximum metamorphic conditions whole rock schist samples from besshi units chlorite zone record plateau ages of 85 94 ma suggesting an earlier metamorphic climax within this structural level amphibole within the albite biotite zone in besshi records 36 ar 40 ar vs 39 ar 40 ar plateau isotope correlation ages of 84 87 ma which are interpreted as dating the post metamorphic cooling through temperatures required for intracrystalline retention of argon a slightly older isotope correlation age 94 ma is recorded by amphibole from the higher grade oligioclase biotite zone contrasts in amphibole cooling ages are interpreted as reflecting thrust related metamorphic inversion and resultant earlier cooling of higher grade structural units muscovite from all structural levels of the besshi nappe complex records 40 ar 39 ar plateau ages of 76 89 ma these are interpreted to date post metamorphic cooling through appropriate closure temperatures following structural assembly of the besshi nappe complex protoliths of the besshi units originated at approx 130 ma and attained maximum metamorphic conditions during entrainment in an accretionary complex at approx 90 100 ma higher grade sequences developed at deeper levels along the hanging wall of the accretionary complex during subsequent structural uplift to shallower crustal levels the besshi nappe complex was tectonically emplaced over oboke units

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

the july 12 1993 hokkaido nansei oki japan earthquake coseismic slip pattern from strong motion and teleseismic recordings we employ a finite fault inversion scheme to infer the distribution of coseismic slip for the july 12 1993 hokkaido nansei oki earthquake using strong ground motions recorded by the japan meteorological agency within 400 km of the epicenter and vertical p waveforms recorded by the global digital seismograph network at teleseismic distances the assumed fault geometry is based on the location of the aftershock zone and comprises two fault segments with different orientations a northern segment striking at n20 e with a 30 dip to the west and a southern segment with an n20 w strike for the southern segment we use both westerly and easterly dip directions to test thrust orientations previously proposed for this portion of the fault the variance reduction is greater using a shallow west dipping segment suggesting that the direction of dip did not change as the rupture propagated south from the hypocenter this indicates that the earthquake resulted from the shallow underthrusting of hokkaido beneath the sea of japan static vertical movements predicted by the corresponding distribution of fault slip are consistent with the general pattern of surface deformation observed following the earthquake fault rupture in the northern segment accounts for about 60 of the total p wave seismic moment of 3 4 1020 n m and includes a large circular slip zone 4 m peak near the earthquake hypocenter at depths between 10 and 25 km slip in the southern segment is also predominantly shallower than 25 km but the maximum coseismic displacements 2 0 2 5 m are observed at a depth of about 5 km this significant shallow slip in the southern portion of the rupture zone may have been responsible for the large tsunami that devastated the small offshore island of okushiri localized shallow faulting near the island however may require a steep westerly dip to reconcile the measured values of ground subsidence

modeling of the hydroacoustic signal and tsunami wave generated by seafloor motion including a porous seabed 1 within the framework of a 2 d compressible tsunami generation model with a flat porous seabed acoustic waves are generated and travel outward from the source area the effects of the porous seabed during tsunami generation and propagation processes include wave amplitude attenuation and low pass filtering of both the hydroacoustic signal and tsunami wave the period of the acoustic wave generated by the seafloor motion depends on water depth over the source area and is given by four times the period of time required for sound to travel from the seabed to the surface these waves carry information about seafloor motion the semianalytical solution of the 2 d compressible water layer model overlying a porous seabed is presented and discussed furthermore to include the effects generated by the coupling between compressible porous sedimentary and water layers a simplified two layer model with the sediment modeled as a compressible viscous fluid is presented

source parameters of the anjar earthquake of july 21 1956 india and its seismotectonic implications for the kutch rift basin abstract the kutch rift basin is a major seismic region in india characterized by a low earthquake occurrence rate but a very high maximum intensity the largest event in the region is the great kutch earthquake of 1819 estimated m w 7 8 however lacking instrumental data its exact source parameters are not well known the anjar or rann of kutch earthquake of july 21 1956 m w 6 0 took place very close to the 1819 kutch event and caused considerable damage and casualties our modeled waveforms of teleseismic p and sh waves and p wave first motions determine a reverse faulting mechanism strike 235 dip 46 5 and rake 85 as well as source parameters for the anjar earthquake a previous strike slip mechanism for this event has been eliminated on the basis of waveform constraints the two nodal planes of our solution both strike northeast sub parallel to the trend of the kutch rift very close to the trend of the isoseismals the seismic moment is 1 19 10 25 dyne cm the focal depth and the stress drop are 15 km and 162 bar respectively the anjar reverse fault may represent a reactivated normal fault undergoing tectonic inversion in the kutch rift zone under present day compressional stress two larger earthquakes adjacent to anjar but outside of the kutch rift are also found to be mainly reverse faulting with a minor strike slip component judging from available information the great kutch event of 1819 is most likely a reverse faulting event

three dimensional simulation of tsunami generation and propagation application to intraplate events 1 a parallel finite difference numerical simulation program based on the navier stokes ns equations is developed for simulating 3 d tsunami generation and propagation we can simulate tsunami propagation over more than 1000 km using this program although such tsunami propagation over long distances has usually been conducted on the basis of on 2 d simulations some 2 d simulations have assumed that the initial tsunami distribution is identical to the sea bottom deformation caused by the earthquake the 3 d simulations however indicate that this assumption is inappropriate when the source width 2ax is less than 10 times the sea depth h 2ax 10h for a source process time of 20 s dispersion of tsunami appears when the source is of small size and the dispersion is more apparent in a direction perpendicular to the fault strike we also conduct tsunami simulations for two intraplate events the 2004 off kii peninsula m 7 4 and the 2007 off kuril islands m 8 1 events the 3 d tsunami simulation has successfully simulated the offshore tsunami and we obtained good agreement between the observations and the calculations for both events in particular for the 2004 off kii peninsula event although the 2 d linear long wave theory cannot simulate important characteristics in the record such as the arrival time of the peak amplitude and the dispersive tsunami the 3 d ns simulation is well able to model those characteristics

deformation processes and weakening mechanisms within the frictional viscous transition zone of major crustal scale faults insights from the great glen fault zone scotland abstract the great glen fault zone ggfz scotland is a typical example of a crustal scale reactivated strike slip fault within the continental crust analysis of intensely strained fault rocks from the core of the ggfz near fort william provides a unique insight into the nature of deformation associated with the main phase of sinistral movements along the fault zone in this region an exhumed sequence of complex mid crustal deformation textures that developed in the region of the frictional viscous transition ca 8 15 km depth is preserved fault rock fabrics vary from mylonitic in quartzites to cataclastic in micaceous shear zones and feldspathic psammites protolith mineralogy exerted a strong control on the initial textural development and distribution of the fault rocks at lower strains crystal plastic deformation occurred in quartz dominated lithologies to produce mylonites simultaneously with widespread fracturing and cataclasis in feldspar and mica dominated rocks at higher strains shearing appears to increasingly localise into interconnected networks of cataclastic shear zones many of which are strongly foliated textures indicative of fluid assisted diffusive mass transfer mechanisms are widespread in such regions and suggest that a hydrous fluid assisted grainsize controlled switch in deformation behaviour followed the brittle comminution of grains the fault zone textural evolution implies that a strain induced fluid assisted shallowing and narrowing of the frictional viscous transition occurred with increasing strain it is proposed that this led to an overall weakening of the fault zone and that equivalent processes may occur along many other long lived crustal scale dislocations

interactions between active faulting volcanism and sedimentary processes at an island arc insights from les saintes channel lesser antilles arc new high resolution marine geophysical data allow to characterize a large normal fault system in the lesser antilles arc and to investigate the interactions between active faulting volcanism sedimentary and mass wasting processes les saintes fault system is composed of several normal faults that form a 30 km wide half graben accommodating ne sw extension it is bounded by the roseau fault responsible for the destructive mw6 3 21 11 2004 earthquake the roseau fault has been identified from the island of basse terre to dominica it is thus 40 km long and it could generate mw7 earthquakes in the future several submarine volcanoes are also recognized we show that the fault system initiated after the main volcanic construction and subsequently controls the emission of volcanic products the system propagates southward through damage zones at the tip of the damage zones several volcanic cones were recently emplaced probably due to fissures opening in an area of stress increase a two way interaction is observed between active faulting and sedimentary processes the faults control the development of the main turbiditic system made of kilometer wide canyons as well as the location of sediment ponding in turn erosion and sedimentation prevent scarp growth at the seafloor faulting also enhances mass wasting processes since its initiation the fault system has consequently modified the morphologic evolution of the arc through perturbation of the sedimentary processes and localization of the more recent volcanic activity this article is protected by copyright all rights reserved

introduction to tsunamis 1992 94 tsunamis have caused extensive human and property damage in the world there had not been a tsunami disaster since 1983 when the japan sea earthquake tsunami caused 100 fatalities in the three year period 1992 94 however several destructive tsunamis occurred in the world and caused more than 1 500 casualties after each of these tsunami disasters field survey teams consisting of scientists and engineers from various fields and countries were dispatched they measured tsunami runup heights and estimated the velocity direction and other local behavior in addition to such hydrodynamic features they searched for evidence of coseismic ground deformation and tsunami depositions and erosions the first goal of this topical issue is to document data from these tsunamis for later use in various tsunami related research