prompt identification of tsunamigenic earthquakes from 3 component seismic data abstract an artificial neural network ann based algorithm for prompt identification of shallow focus depth

identification of mantle reflections from a dense linear seismic array tectonic implications to the taiwan orogeny 1 a dense linear seismic array consisting of 18 short period seismic stations is deployed in the western foothills to study deep crustal structures across central taiwan where significant mountain building processes are considered as a result of the oblique convergence between the eurasian and philippine sea plates since a few million years ago the identification of mantle reflections pmp sms and smp from later phases generated by one earthquake ml 4 3 in eastern taiwan and recorded by the linear seismic array shows that crustal thickness gradually increases eastward from 40 km beneath the western central range to 50 km beneath the eastern central range the significant horizontal offset 30 km between the highest mountains and the deepest crust suggests that crustal deformation has not yet reached isostatic equilibrium it is concluded that continental subduction might be acceptable for explaining the dynamic processes in the taiwan orogeny

an energy duration procedure for rapid determination of earthquake magnitude and tsunamigenic potential summary we introduce a rapid and robust energy duration procedure based on the haskell extended source model to obtain an earthquake moment and a moment magnitude med using seismograms at teleseismic distances 30 90 this procedure combines radiated seismic energy measures on the p to s interval of broadband signals and source duration measures on high frequency p wave signals the med energy duration magnitude is scaled to correspond to the global centroid moment tensor cmt moment magnitude mcmtw and can be calculated within about 20 min or less after origin time ot the measured energy and duration values also provide the energy to moment ratio used for identification of tsunami earthquakes the med magnitudes for a set of recent large earthquakes match closely mcmtw even for the largest great earthquakes these results imply that the med measure is accurate and does not saturate after the 2004 december 26 sumatra andaman mega thrust earthquake magnitude estimates available within 1 hr of ot ranged from m 8 0 to 8 5 the cmt magnitude available about 3 hr after ot was mcmtw 9 0 and several months after the event mw 9 1 9 3 was obtained from analysis of the earth normal modes the energy duration magnitude for this event is med 9 2 a measure that is potentially available within 20 min after ot after the 2006 july 17 java earthquake the magnitude was evaluated at m 7 2 at 17 min after ot the cmt magnitude available about 1 hr after ot was mcmtw 7 7 the energy duration results for this event give med 7 8 with a very long source duration of about 160 s and a very low value indicating a possible tsunami earthquake

anisotropy beneath an active collision orogen of taiwan results from across islands array observations 1 we examined shear wave splitting in sks phases from a large event recorded by a temporary array across southern taiwan the span extends from the western plain to the east coast we applied particle motion and cross correlation methods to estimate its polarization directions and delay times analysis shows clear evidence of splitting except stations on the east coast the fast split shear wave along this transect are approximately parallel to the strike of the mountain belt ne sw the delay times show a short wavelength variation and are well correlated to the surface geology the largest split time is about 1 6 sec located at eastern central mountain range and indicates its possible mantle origin implications suggest that anisotropy is related to the collision tectonics which built the taiwan islands and that this tectonic compression involved the lithosphere and is characterized by a strong coherent deformation of the upper mantle and the crust

implications of the 26 december 2004 sumatra andaman earthquake on tsunami forecast and assessment models for great subduction zone earthquakes results from different tsunami forecasting and hazard assessment mod els are compared with observed tsunami wave heights from the 26 december 2004 indian ocean tsunami forecast models are based on initial earthquake information and are used to estimate tsunami wave heights during propagation an empirical forecast relationship based only on seismic moment provides a close estimate to the observed mean regional and maximum local tsunami runup heights for the 2004 indian ocean tsunami but underestimates mean regional tsunami heights at azimuths in line with the tsunami beaming pattern e g sri lanka thailand standard forecast models developed from subfault discretization of earthquake rupture in which deep ocean sea level observations are used to constrain slip are also tested forecast models of this type use tsunami time series measurements at points in the deep ocean as a proxy for the 2004 indian ocean tsunami a transect of deep ocean tsunami amplitudes recorded by satellite altimetry is used to constrain slip along four subfaults of the m 9 sumatra andaman earthquake this proxy model performs well in comparison to observed tsunami wave heights travel times and inundation patterns at banda aceh hypothetical tsunami hazard assessments models based on end member estimates for average slip and rupture length m w 9 0 9 3 are compared with tsunami observations using average slip low end member and rupture length high end member m w 9 14 consistent with many seismic geodetic and tsunami inversions adequately estimates tsunami runup in most regions except the extreme runup in the western aceh province the high slip that occurred in the southern part of the rupture zone linked to runup in this location is a larger fluctuation than expected from standard stochastic slip models in addition excess moment release 9 deduced from geodetic studies in comparison to seismic moment estimates may gen erate additional tsunami energy if the exponential time constant of slip is less than approximately 1 hr overall there is significant variation in assessed runup heights caused by quantifiable uncertainty in both first order source parameters e g rupture length slip length scaling and spatiotemporal complexity of earthquake rupture

application of mwp to tsunami earthquake tsunami earthquake produces anomalously strong tsunamis for their surface wave magnitude to issue accurate early tsunami warnings for tsunami earthquakes it is critical to identify them as tsunamigenic events as early as possible here we show that a pulse width of p wave which we use to calculate broadband moment magnitude mwp gives accurate estimates of source duration time we find that we may identify 1992 nicaragua earthquake as a possible tsunamigenic earthquake by using a combination of both mwp and the source duration our result suggests that the combination of mwp and the source duration will provide an effective tool to issue early tsunami warnings even for tsunami earthquakes which have anomalously long source duration

near real time magnitude determination for large crustal earthquakes abstract we introduce an empirical method of near real time near field magnitude determination for large m 6 5 crustal earthquakes time integration over the strong shaking duration on the absolute values of the acceleration records is carried out for nearby stations surrounding many large earthquake sources in taiwan the integrated quantity here denoted as total effective shaking is used in a regression process to derive an empirical relationship for a quick mw determination useful for a reliable real time operation in earthquake rapid reporting and earthquake early warning systems ewss

wind induced eddy motion in the lower st lawrence estuary the lower st lawrence estuary is a wide estuary in the sense of being several internal rossby radii in breadth thus the coriolis effects are significant and complex circulation patterns are to be expected we analyse the response of this body to a strong up channel pulse of wind using data from an array of current meters and sea level gauges interesting features of the flow are found such as coastal jets accelerating into the wind as the wind speed relaxes apparently due to the establishment of an along channel pressure gradient and a pair of synoptic scale eddies developing in the current pattern

tsunami early warning within five minutes tsunamis are most destructive at near to regional distances arriving within 20 30 min after a causative earthquake effective early warning at these distances requires notification within 15 min or less the size and impact of a tsunami also depend on sea floor displacement which is related to the length l width w mean slip d and depth z of the earthquake rupture currently the primary seismic discriminant for tsunami potential is the centroid moment tensor magnitude m w cmt representing the product lwd and estimated via an indirect inversion procedure however the obtained m w cmt and the implied lwd value vary with rupture depth earth model and other factors and are only available 20 30 min or more after an earthquake the use of more direct discriminants for tsunami potential could avoid these problems and aid in effective early warning especially for near to regional distances previously we presented a direct procedure for rapid assessment of earthquake tsunami potential using two simple measurements on p wave seismograms the predominant period on velocity records t d and the likelihood t 50 ex that the high frequency apparent rupture duration t 0 exceeds 50 55 s we have shown that t d and t 0 are related to the critical rupture parameters l w d and z and that either of the period duration products t d t 0 or t d t 50 ex gives more information on tsunami impact and size than m w cmt m wp and other currently used discriminants these results imply that tsunami potential is not directly related to the product lwd from the seismic faulting model as is assumed with the use of the m w cmt discriminant instead information on rupture length l and depth z as provided by t d t 0 or t d t 50 ex can constrain well the tsunami potential of an earthquake we introduce here special treatment of the signal around the s arrival at close stations a modified real time m wpd rt magnitude and other procedures to enable early estimation of event parameters and tsunami discriminants we show that with real time data currently available in most regions of tsunami hazard event locations m b and m wp magnitudes and the direct period duration discriminant t d t 50 ex can be determined within 5 min after an earthquake occurs and t 0 t d t 0 and m wpd rt within approximately 10 min this processing is implemented and running continuously in real time within the early est earthquake monitor at ingv rome http early est rm ingv it we also show that the difference m b log10 t d t 0 forms a rapid discriminant for slow tsunami earthquakes the rapid availability of these measurements can aid in faster and more reliable tsunami early warning for near to regional distances

formation of eddies and transverse currents in a two layer channel of variable bottom with application to the lower st lawrence estuary abstract baroclinic shelf waves and kelvin waves in a two layer channel of variable bottom are discussed using a simple numerical model two different propagation directions are shown to be possible analogous to the existence of shelf waves and trench waves in an ocean bounded by a coast with a trench described by mysak et al the eigenfunctions of baroclinic shelf wave modes are quite different from the barotropic eigenfunctions that is each of the baroclinic modes shows a pattern similar to the first mode with the exception of small scale structures near the coast the model also shows the formation of a series of eddies with alternating rotation sense accompanied by transverse currants between two successive eddies eddies and transverse currants were observed in the upper layer of the lower st lawrence estuary based on four months of direct measurements taken in 1979 the observed wavelike motion with a period of about 80 days and a wavelength of 75 km corresponded to the fourth baroclinic shelf

lateral stratification and dynamic balance at the matane transect in the lower saint lawrence estuary abstract the lateral stratification and momentum balance in the lower saint lawrence estuary lsle were investigated over a period of six days from current temperature and salinity measurements taken in 1979 at the matane transect asymptotic singular decomposition analysis was used to show that the spatial variability of hydrodynamic parameters at that cross section was more pronounced than their temporal or tidal variability classification of the section in the lateral circulation stratification diagram revealed that the lsle is one of the most laterally stratified estuaries examined in the world estimates of various acceleration terms in the lateral dynamic balance equation showed that when averaged over many tidal cycles the motion can be considered as being quasigeostrophic to a first approximation with contributions of the same order of magnitude from the baroclinic and the barotropic pressure gradients convection accelerations were found to be important only near the north shore where strong cross channel currents were recorded whilst local and centrifugal accelerations were found to be of secondary importance

upper mantle seismic velocity anomaly beneath southern taiwan as revealed by teleseismic relative arrival times article i nfo probing the lateral heterogeneity of the upper mantle seismic velocity structure beneath southern and central taiwan is critical to understanding the local tectonics and orogeny a linear broadband array that transects southern taiwan together with carefully selected teleseismic sources with the right azimuth provides useful constraints they are capable of differentiating the lateral heterogeneity along the profile with systematic coverage of ray paths we implement a scheme based on the genetic algorithm to simultaneously determine the relative delayed times of the teleseismic first arrivals of array data the resulting patterns of the delayed times systematically vary as a function of the incident angle ray tracing attributes the observed variations to a high velocity anomaly dipping east in the mantle beneath the southeast of taiwan combining the ray tracing analysis and a pseudo spectral method to solve the 2 d wave propagations we determine the extent of the anomaly that best fits the observations via the forward grid search the east dipping fast anomaly in the upper mantle beneath the southeast of taiwan agrees with the results from several previous studies and indicates that the nature of the local ongoing arc continent collision is likely characterized by the thin skinned style

the mantle magnitude mm and the slowness parameter θ five years of real time use in the context of tsunami warning we study a database of more than 119 000 measurements of the mantle magnitude mm introduced by okal and talandier 1989 obtained since 1999 as part of the operational procedures at the pacific tsunami warning center the perfor mance of this method is significantly affected by the seismic instrumentation at the recording station with the very broadband sts 1 and ks54000 systems offering the lowest residuals between measured values of mm and those predicted from the har vard centroid moment tensor cmt catalog and also by the period at which spec tral amplitudes are measured with the best results between 70 and 250 sec with such mild restrictions estimates of seismic moments can be obtained in real time by retaining either the maximum value of mm measured on each record or its average over the various mantle frequencies with the resulting residuals on the order of 0 1 0 2 moment magnitude units mm deficiencies in the case of the two large earthquakes of peru 2001 and hokkaido 2003 are attributed to azimuthal bias from an excess of stations principally in north america in directions nodal for the focal mechanism and directivity patterns we further study a group of more than 3000 measurements of the energy to moment ratio h introduced by newman and okal 1998 which allows the real time identification of teleseismic sources violating scaling laws and in particular of so called tsunami earthquakes the use of a sliding window of analysis in the computation of h allows the separation of late earthquakes characterized by a delayed but fast moment release from truly slow earthquakes many such events are recognized notably on major oceanic and con tinental strike slip faults introduction and background we present detailed analyses of a large dataset resulting from implementation as part of the operational procedures of the pacific tsunami warning center ptwc of the real time calculation of the mantle magnitude mm and of the slowness parameter h as defined and introduced by okal and talandier 1989 and newman and okal 1998 re spectively during the past five years more than 119 000 individual measurements of mm and 3000 values of h have been computed through automated algorithms these values contribute to the estimation of the source characteristic of distant earthquakes in the framework of the real time as sessment of their tsunamigenic potential this study offers a progress report on the performance of the algorithms and in particular discusses the influence of instrumentation at the various reporting stations as the final revision of this article was being prepared the occurrence of the great sumatra earthquake on 26 de cember 2004 provided an opportunity to extend the concepts of mm and h to a range of magnitudes unexplored for the

rapid determination of mw from broadband p waveforms we analyze broadband seismograms for magnitude 5 to 7 earthquakes which occurred in and around japan to develop a technique to determine moment magnitude from first arrival p waveforms we theoretically consider displacements of the p wave portion on broadband seismograph record as an approximate source time function and integrate them to obtain scalar moments at each station we show that a combination of multiple records will give a good estimation of moment magnitude without correcting for the source mechanism this technique is quite simple and robust so it will be effective for a rapid evaluation of the tsunami potential of a large earthquake

a synthesis of the geologic evolution of taiwan abstract the island arc of taiwan is composed of cenozoic geosynclinal sediments more than 10 000 m thick lying on a pre tertiary metamorphic basement pleistocene to miocene andesitic islands surround the main island and are related mostly to arc magmatism the penghu island group in the taiwan strait is covered with pleistocene flood basalt neogene shallow marine clastic sediments are exposed mainly in the western foothills with pleistocene andesitic extrusives at the northern tip and the northeastern offshore islands a thick sequence of paleogene to miocene argillitic to slaty metaclastic rocks underlies the western central range and forms the immediate sedimentary cover on the pre tertiary metamorphic complex to the east which represents an older mesozoic arc trench system the coastal range in eastern taiwan is a neogene andesitic magmatic arc including also a large variety of volcaniclastic and turbiditic sediments cenozoic taiwan is the site of arc continent collision where the luzon arc on the philippine sea plate overrides the chinese continental margin on the eurasian plate east and northeast of taiwan the polarity of subduction changes whereby the oceanic philippine sea plate is subducting beneath the ryukyu arc system on the eurasian plate continent arc collision in taiwan island is anomalous and may occur in a broad belt of deformation rather than along a well defined plate boundary or subduction zone

tsunami early warning using earthquake rupture duration and p wave dominant period the importance of length and depth of faulting summary after an earthquake rapid real time assessment of hazards such as ground shaking and tsunami potential is important for early warning and emergency response tsunami potential depends on seafloor displacement which is related to the length l width w mean slip d and depth z of earthquake rupture currently the primary discriminant for tsunami potential is the centroid moment tensor magnitude mcmtw representing the seismic potency lwd and estimated through an indirect inversion procedure the obtained mcmtw and the implied lwd value vary with the depth of faulting assumed earth model and other factors and is only available 30 min or more after an earthquake the use of more direct procedures for hazard assessment when available could avoid these problems and aid in effective early warning here we present a direct procedure for rapid assessment of earthquake tsunami potential using two simple measures on p wave seismograms the dominant period on the velocity records td and the likelihood that the high frequency apparent rupture duration t0 exceeds 50 55 s t0 can be related to the critical parameters l and z while td may be related to w d or z for a set of recent large earthquakes we show that the period duration product tdt0 gives more information on tsunami impact and size than mcmtw and other currently used discriminants all discriminants have difficulty in assessing the tsunami potential for oceanic strike slip and backarc or upper plate intraplate earthquake types our analysis and results suggest that tsunami potential is not directly related to the potency lwd from the seismic faulting model as is assumed with the use of the mcmtw discriminant instead knowledge of rupture length l and depth z alone can constrain well the tsunami potential of an earthquake with explicit determination of fault width w and slip d being of secondary importance with available real time seismogram data rapid calculation of the direct period duration discriminant can be completed within 6 10 min after an earthquake occurs and thus can aid in effective and reliable tsunami early warning

on the application of mwp in the near field and the march 11 2011 tohoku earthquake tsunami warning centers issue rapid and accurate tsunami warnings to coastal populations by estimating the location and size of the causative earthquake as soon as possible after rupture initiation both us tsunami warning centers have therefore been using mwp to issue tsunami warnings 5 10 min after earthquake origin time since 2002 however because mwp tsuboiet al bulletin of the seismological society of america 85 606 613 1995 is based on the far field approximation to the p wave displacement due to a double couple point source we should only very carefully apply mwp to data obtained in the near field at distances of less than a few wavelengths from the fault on the other hand the surface waves from great earthquakes including those that occur just offshore of populated areas such as the 2011 tohoku earthquake clip seismographs located near the fault because the first arriving p waves from such large events are often on scale mwp should provide useful information even for these great earthquakes we therefore calculate mwp from 18 unclipped sts 1 broadband p wave seismograms recorded at 2 15 distance from the tohoku epicenter to determine if mwp can usefully estimate mw for this earthquake using data obtained close to the epicenter in this case there should be a good chance to get reliable mwp values for stations at epicentral distances of 9 10 since the source duration for the tohoku earthquake is less than 200 s and the time window used to estimate mwp is 120 s in duration our analysis indicates that mwp does indeed give reliable results mw 9 1 beginning at about 11 distance from the epicenter the values of mwp from seismic waveforms obtained at 11 15 epicentral distance from the mw 9 1 off the east coast of tohuku earthquake of march 11 2011 fell within the range 9 1 9 3 and were available within 4 5 min after origin time even the mwp values of 7 7 8 4 obtained at less than 5 epicentral distance exceed the ptwc s threshold of mw 7 6 for issuing a regional tsunami warning to coastal populations within 1 000 km of the epicenter and of mw 6 9 for issuing a local tsunami warning to the coastal populations of hawaii

global evaluation of large earthquake energy from 1997 through mid 2010 1 we develop an updated radiated seismic energy e catalog of global earthquakes with seismic moment m0 1019 nm mw 6 7 from 1997 through mid 2010 recording 342 events using 17849 seismograms station specific corrections and event duration dependent total p wave group calculations allow for improved e determinations for large and long duration earthquakes we find the global mean energy to moment ratio log10 e m0 4 59 0 36 robust deviations are found for thrust t 4 74 strike slip ss 4 44 and normal n 4 51 faulting events for two regions with recent energy deficient tsunami earthquakes tse we examine all large thrust earthquakes with m0 5 1017 nm mw 5 7 to identify a regional characterization in their relative radiated energy to moment ratio while thrust events along java indonesia the site of two tse events in 1994 and 2006 are comparable t jv 4 91 to the global thrust average events along the middle america trench mat the site of the 1992 nicaragua tse are consistently deficient t mat 5 15 along the mat a trend of increased deficiency in radiated energy to the southeast occurs in the direction of more rapid plate convergence global thrust mechanisms become increasingly deficient in radiated seismic energy at shallow depths with tse events representing the shallowest and most energetically deficient end member of the events in the study results suggest thrust events are highly variable but tend to increase in apparent stress from about 15 kpa near the surface to 2 mpa near 70 km depth

tsunami early warning using earthquake rupture duration 1 effective tsunami early warning for coastlines near a tsunamigenic earthquake requires notification within 5 15 minutes we have shown recently that tsunamigenic earthquakes have an apparent rupture duration t0 greater than about 50 s here we show that t0 gives more information on tsunami importance than moment magnitude mw and we introduce a procedure using seismograms recorded near an earthquake to rapidly determine if t0 is likely to exceed t 50 or 100 s we show that this duration exceedance procedure can be completed within 3 10 min after the earthquake occurs depending on station density and that it correctly identifies most recent earthquakes which produced large or devastating tsunamis this identification forms a complement to initial estimates of the location depth and magnitude of an earthquake to improve the reliability of tsunami early warning and in some cases may make possible such warning

seismogenic structures of the 1999 mw 7 6 chi chi taiwan earthquake and its aftershocks abstract high resolution 3 d vp and vs velocity models around the source region of the mw7 6 chi chi taiwan earthquake show significant lateral and vertical variations the mainshock occurred within a narrow low velocity zone along the chelungpu fault a sudden increase of velocity and seismicity took place across the shuilikeng fault to the east most aftershocks were located in areas of high vp and vs a sharp east dipping zone extending from the shuilikeng fault on the surface to a depth of about 15 km separates the low velocity region in the west from the high velocity region in the east an apparent high angle west dipping seismic zone lies at depths of 15 30 km beneath the western central range numerous aftershocks with normal faulting were located west of the middle segment of the chelungpu fault

variability of the near surface residual current in the lower st lawrence estuary current measurements of 1 and 4 month duration from may 1979 taken at 10 stations in the lower st lawrence estuary were subject to time series analysis we find that the spectral energy density of the near surface current in the sub inertial frequency range is comparable to the energy concentrated in the semi diurnal frequency band the strong residual current decreases rapidly with depth while the tidal current is more or less uniform from surface to bottom a cross spectral analysis showed that the longshore current at a station near the south shore was negatively correlated to the current at a north shore station with high coherence in the period range greater than 7 days evidence was found for the existence of a cross channel current at stations in the center of the channel the near surface circulation system in the area can be classified into three types of patters 1 one anticyclonic eddy centered between the estuary gulf boundary and the baie comeau cross section region i accompanied by a cyclonic eddy located to the landward between the two cross sections at baie comeau and pointe au pere region ii 2 a cyclonic eddy in region i with an anti cyclonic eddy in region ii and 3 the transition phase between phases 1 and 2 the intensity of these eddies and cross channel currents is related to sea level changes in the estuary

numerical experiments to investigate the accuracy of broad band moment magnitude mwp summary we perform numerical experiments to investigate the accuracy of broad band moment magnitude mwp we conduct these experiments by measuring mwp from synthetic seismograms and comparing the resulting values to the moment magnitudes used in the calculation of synthetic seismograms in the numerical experiments using point sources we have found that there is a significant dependence of mwp on focal mechanisms and that depths phases have a large impact on mwp estimates especially for large shallow earthquakes numerical experiments using line sources suggest that the effects of source finiteness and rupture propagation on mwp estimates are on the order of 0 2 magnitude units for vertical fault planes with pure dip slip mechanisms and 45 dipping fault planes with pure dip slip thrust mechanisms but that the dependence is small for strike slip events on a vertical fault plane numerical experiments for huge thrust faulting earthquakes on a fault plane with a shallow dip angle suggest that the mwp estimates do not saturate in the moment magnitude range between 8 and 9 although they are underestimates our results are consistent with previous studies that compared mwp estimates to moment magnitudes calculated from seismic moment tensors obtained by analyses of observed data

geochronologic evidence for a cold arc continent collision the taiwan orogeny abstract in order to constrain the tectonic consequences of the collision of the luzon arc with the se chinese continental margin during the neogene taiwan orogeny we assess the thermal history of the poly metamorphic para autochtthonous rocks of the continental margin in taiwan to accomplish this we report a new sims u pb age of prograde metamorphic zircons and interpret this age in the context of existing geochronology and thermochronology zircons extracted from the fenniaolin amphibolite near nanao taiwan in the contact aureole of a granodiorite are interpreted to have crystallized during the first lower amphibolite facies prograde metamorphism based on 1 their equant shape rather than the prismatic shape typical of magmatic zircon 2 their microcrystalline or micro saccharoidal aggregate structure and patchy and sector zoning rather than oscillatory zoning visible in cathodoluminescent imaging 3 their low concentrations of u most 206 pb 238 u age of 86 1 ma analytically indistinguishable from the age of the adjacent pluton that caused the contact metamorphism we thus conclude that the contact metamorphism of this intrusion caused the first lower amphibolite facies metamorphism of these rocks in the mid cretaceous existing 40 ar 39 ar and rb sr cooling ages of both amphibole and muscovite at 80 ma e g lan 1990 lo and onstott 1995 show that the granodiorite and its contact aureole cooled rapidly from 700 to the crustal history reconstructed from these data shows that the regional gneissic terrane of the northern tananao complex may have been caused by coalescing contact aureoles of multiple mid cretaceous intrusions the nanao intrusive event and not by the neogene taiwan orogeny on the contrary the tananao rocks probably achieved middle greenschist conditions and 15 20 km depth in a forearc setting in the early cretaceous this intrusive event caused regional contact metamorphism at about 85 ma after which the passive margin setting preserved these rocks at mid crustal depths until the beginning of the taiwan orogeny 5 ma these depths 10 12 km and temperatures 200 250 c were high enough to account for the late miocene lower greenschist facies cleavages and the pliocene pleistocene fission track cooling ages without additional loading and heating from the taiwan orogeny

automated determination of magnitude and source length of large earthquakes using backprojection and p wave amplitudes fast estimates of magnitude and source extent of large earthquakes are fundamental for disaster mitigation however resolving these estimates within 10 20 min after origin time remains challenging here we propose a robust algorithm to resolve magnitude and source length of large earthquakes using seismic data recorded by regional arrays and global stations we estimate source length and source duration by back projecting seismic array data then the source duration and the maximum amplitude of the teleseismic p wave displacement waveforms are used jointly to estimate magnitude we apply this method to 74 shallow earthquakes that occurred within epicentral distances of 30 85 degrees to hi net 2004 2014 the estimated magnitudes are similar to moment magnitudes estimated from w phase inversions usgs with standard deviations of 0 14 0 19 depending on the global station distributions application of this method to multiple regional seismic arrays could benefit tsunami warning systems and emergency response to large global earthquakes

cleavage fronts and fans as reflections of orogen stress and kinematics in taiwan recent observations of cleavage patterns strain histories and kinematics across the taiwan mountain belt depict systematic orogen scale variations with respect to the synorogenic divide and suggest that the pattern of cleavage development is a predictable consequence of orogen stresses and kinematics in taiwan continental crust within the collision is accreted in the prowedge facing asia but is advected eastward into the east verging retrowedge where the most deeply exhumed rocks are exposed wedge mechanics predict a reversal in the direction of plunge of the principal compressive stress at the topographic divide between the opposing wedges the observation of a single cleavage in western taiwan suggests that the cleavage in the prowedge remains stable with respect to the stress orientation in contrast the existence of a second crenulation cleavage in the retrowedge is evidence for an abrupt change in stress orientation and unstable buckling of preexisting prowedge fabrics advection of a fabric across a topographic divide in a doubly vergent wedge provides an explanation for the occurrence of cleavage fronts and fans in natural systems such as taiwan

application of mwp to deep and teleseismic earthquakes the broadband moment magnitude m wp tsuboi et al 1995 allows for the effective determination of earthquake magnitude by using broadband p waveforms it was developed to determine moment magnitude of shallow earthquakes around the japanese islands for early tsunami warnings tsuboi et al 1995 demonstrated that m wp shows good agreement with the m w from harvard centroid moment tensor cmt solutions in the present study we show that m wp is also applicable to deep earthquakes and earthquakes recorded at teleseismic distances the m wp proves to be useful for quick accurate size estimates of earthquakes recorded at both regional and teleseismic distances occurring at any depth

compelling evidence of an aseismic slab beneath central taiwan from a dense linear seismic array abstract from a dense linear seismic array consisting of 15 short period seismic stations deployed across the suture zone an aseismic slab subducted beneath central taiwan was clearly detected in addition to the direct p waves the identification of the mantle refracted phases generated by an intermediate depth earthquake m l 5 8 in southeastern taiwan and recorded by the linear array as well as some seismic stations cwbsn along the eastern central range shows that a subducted crust with a low velocity exists down at the depth of at least 89 km this strongly suggests that the subduction of the eurasian plate in southern taiwan most likely extends to central taiwan where there has been an absence of mantle earthquakes in the wadati benioff zone what the subduction slab without mantle earthquakes could very well be attributed to is the subducted continental crust where the rock strength is totally different from that of the oceanic crust

structure of the upper mantle and transition zone beneath southeast asia from traveltime tomography 1 tomographic images of the mantle beneath east asia were obtained from the inversion of traveltime data from global and regional seismograph networks and from temporary arrays on and around the tibetan plateau our results are consistent with previous studies but the unprecedented resolution of mantle heterogeneity provides new insight into the large scale tectonic framework of the continental india asia collision in the western part of the study region and subduction of the oceanic lithosphere in the east in the realm of continental collision west of 100 e a relatively slow p wave speed characterizes the upper mantle beneath much of the tibetan plateau but the wave speed is high beneath cratonic india the southern and western part of the tibetan plateau hindu kush and the tian shan in the subduction realm east of 110 e the main structures are i pronounced low wave speed anomalies at a depth of between 100 and 400 km beneath asia s southeastern seaboard and the back arc regions of ongoing subduction ii narrow fast anomalies in the upper mantle beneath major subduction zones and iii widespread fast anomalies at a depth of 500 700 km beneath the sea of japan the northern part of the philippine sea plate and southeastern china if the latter anomalies represent stagnant slabs their fragmented nature and large lateral extent suggest that they are produced by different episodes of subduction beneath western pacific island arcs along the old se margin of asia or during the mesozoic collision of cratonic units in southeast asia attribution to ancient subduction systems implies that slab fragments can reside in the transition zone for at least several tens of millions of years shallow slow anomalies beneath the red river fault region connect to deep anomalies beneath the south china fold belt and south china sea suggesting a causal relationship between the evolution of the continental lithosphere of sw china and deeper mantle processes between the collision and the subduction realms tomography reveals high wave speed continental roots beneath the western part of the north china craton ordos block and the south china or yangtze craton sichuan basin to a depth of 300 km