some key features of the strong motion data from the m 6 0 parkfield california earthquake of 28 september 2004 the 2004 parkfield california earthquake was recorded by an extensive set of strong motion instruments well positioned to record details of the motion in the near fault region where there has previously been very little recorded data the strong motion measurements obtained are highly varied with significant variations occurring over only a few kilometers the peak accelerations in the near fault region range from 0 13 g to over 1 8 g one of the highest acceleration recorded to date exceeding the capacity of the recording instrument the largest accelerations occurred near the northwest end of the inferred rupture zone these motions are consistent with directivity for a fault rupturing from the hypocenter near gold hill toward the northwest however accelerations up to 0 8 g were also observed in the opposite direction at the south end of the cholame valley near highway 41 consistent with bilateral rupture with rupture southeast of the hypocenter several stations near and over the rupturing fault recorded relatively weak motions consistent with seemingly paradoxical observations of low shaking damage near strike slip faults this event had more ground motion observations within 10 km of the fault than many other earthquakes combined at moderate distances peak horizontal ground acceleration pga values dropped off more rapidly with distance than standard relationships at close in distance the wide variation of pga suggests a distance dependent sigma may be important to consider the near fault ground motion variation is greater than that assumed in shakemap interpolations based on the existing set of observed data higher density of stations near faults may be the only means in the near future to reduce uncertainty in the interpolations outside of the near fault zone the variance is closer to that assumed this set of data provides the first case where near fault radiation has been observed at an adequate number of stations around the fault to allow detailed study of the fault normal and fault parallel motion and the near field s wave radiation the fault normal motions are significant but they are not large at the central part of the fault away from the ends the fault normal and fault parallel motions drop off quite rapidly with distance from the fault analysis of directivity indicates increased values of peak velocity in the rupture direction no such dependence is observed in the peak acceleration except for stations close to the strike of the fault near and beyond the ends of the faulting

syndepositional tectonics and extension compression relationships at the front of the taiwan collision belt a case study in the pleistocene reefal limestones near kaohsiung sw taiwan in the kaohsiung area sw taiwan large lenses of pleistocene reef limestones interbedded in clastic layers of the gutingkeng formation cover the crest of the takangshan and panpingshan anticlines tectonic analyses carried out on these limestones provide evidence that these anticlines developed during deposition of the reefs this is supported by synsedimentary normal faulting related to tensional stresses at the hinge of the anticlines this synsedimentary extension is subperpendicular to the local trends of fold axes and parallel to the compression responsible for fold development and which is mainly marked by strike slip faults these observations lead us to propose a model of extension compression relationships and reef development during quaternary folding in the foreland of the taiwan collision belt

a viscoelastic earthquake cycle model for taiwan 1 while recent geophysical measurements including global positioning system gps surveys have clarified the mechanisms of active mountain building in the taiwan arc continent collision the geometry of faults beneath the island remains unclear in this paper we use gps data collected before the 1999 chi chi earthquake to image the geometry of active faults under taiwan and estimate slip rates on these faults we invert the data using kinematic and mechanical earthquake cycle models consisting of faulting in an elastic lithosphere overlying a viscoelastic asthenosphere in the kinematic model uniform slip is prescribed on the faults at a constant rate while in the mechanical model the faults slip in response to shear stresses in the lithosphere these models explain the essential features of both the horizontal and vertical gps velocity fields we find a 27 39 km thick elastic lithosphere overlying a viscoelastic asthenosphere with maxwell relaxation time of 15 80 years or viscosity of 0 5 4 1019 pa s the models produce a combined slip rate of 30 50 mm yr on the frontal thrusts in western taiwan and 60 80 mm yr of slip on the longitudinal valley fault inversion of the data using both models indicates a decollement dipping 10 under western taiwan and increasing in dip by no more than 10 under the central ranges and eastern taiwan

structural petrological and thermal evolution of a tertiary ductile strike slip shear zone diancang shan yunnan the diancang shan a horst massif within the red river fault zone in yunnan people s republic of china preserves a structural petrological and thermal record of two distinct phases of tectonic activity a left lateral ductile shear that terminated between 20 and 17 ma and a ductile to brittle phase of normal faulting which began at 4 7 ma and remains active mylonitic rocks in the core of the range display an early steep high temperature ht schistosity and a horizontal stretching lineation that are both parallel to the trend of the belt kinematic indicators indicate that shear was left lateral the complex shape of the ht schistosity at the southern termination of the massif likely results from a large scale oblique left lateral c shear plane that dismembered the shear zone and separated the ailao shan and the diancang shan as left lateral deformation terminated thermochronological and thermobarometric results suggest that the gneisses were partially unroofed during this event along the eastern edge of the diancang shan the ht fabrics were overprinted by low temperature structures during activation of east dipping normal faults cooling associated with this normal right lateral faulting along the diancang shan and perhaps activation of the right lateral normal movement on the range front fault farther south along the ailao shan began at 4 7 0 1 ma these results tend to support the view that extrusion of indochina occurred along the left lateral red river shear zone between 35 and 19 17 ma initiation of right lateral normal slip during the late miocene may relate to eastward extensional collapse of the thickened tibetan crust or more probably to initiation of the second phase of extrusion

detection of a locked zone at depth on the parkfield california segment of the san andreas fault the parkfield california segment of the san andreas fault is transitional in character between the creeping segment of the fault to the northwest and the locked carrizo plain segment to the southeast the rate of shallow fault slip decreases from 25 30 mm yr northwest of the epicenter of the 1966 parkfield earthquake to zero at the southeastern end of the 1966 rupture zone data from a network of trilateration lines spanning the san andreas fault near parkfield and extending to the pacific coast near san luis obispo shed light on the rate of fault slip at depth since the 1966 earthquake in this study average rates of line length change and shallow fault slip were inverted to determine the slip rate at depth on the parkfield fault segment the fault is taken to be a vertical surface with unknown distribution of strike slip displacement in an elastic half space a striking result of the inversions is that all solutions providing acceptable fits to the data exhibit a locked zone essentially coincident with the rupture surface of the 1966 parkfield earthquake the data require that the locked zone extend nearly as far north as the 1966 epicenter however the vertical extent of the locked zone is not well resolved over much of the parkfield segment the fault is slipping faster at the earth s surface than it is at seismogenic depths in order to fit the trilateration measurements it is necessary to include a component of contraction normal to the trend of the san andreas the inversion results suggest a spatially uniform normal strain of 0 06 strain yr the orientation of the contraction is compatible with geologic and seismic evidence of active folding and reverse faulting in the region the magnitude of the contraction is consistent with convergence rates inferred from global plate motion models

coseismic source model of the 2003 mw 6 8 chengkung earthquake taiwan determined from gps measurements 1 a coseismic source model of the 2003 mw 6 8 chengkung taiwan earthquake was well determined with 213 gps stations providing a unique opportunity to study the characteristics of coseismic displacements of a high angle buried reverse fault horizontal coseismic displacements show fault normal shortening across the fault trace displacements on the hanging wall reveal fault parallel and fault normal lengthening the largest horizontal and vertical gps displacements reached 153 and 302 mm respectively in the middle part of the network fault geometry and slip distribution were determined by inverting gps data using a three dimensional 3 d layered elastic dislocation model the slip is mainly concentrated within a 44 14 km slip patch centered at 15 km depth with peak amplitude of 126 6 cm results from 3 d forward elastic model tests indicate that the dome shaped folding on the hanging wall is reproduced with fault dips greater than 40 compared with the rupture area and average slip from slow slip earthquakes and a compilation of finite source models of 18 earthquakes the chengkung earthquake generated a larger rupture area and a lower stress drop suggesting lower than average friction hence the chengkung earthquake seems to be a transitional example between regular and slow slip earthquakes the coseismic source model of this event indicates that the chihshang fault is divided into a creeping segment in the north and the locked segment in the south an average recurrence interval of 50 years for a magnitude 6 8 earthquake was estimated for the southern fault segment

character of seismic motion at a location of a gas hydrate bearing mud volcano on the sw barents sea margin the hakon mosby mud volcano hmmv at 1270 m water depth on the sw barents sea slope has been intensively studied since its discovery in 1989 a variety of sensors monitored morphological hydrological geochemical and biological parameters in the hmmv area an ocean bottom seismometer deployment allowed us to register seismic motion for 2 years from october 2008 to october 2010 the analysis of seismic records documents two types of seismic signals the first type are harmonic tremors with frequency peaks around 4 5 and 8 10 hz that occur in swarms their origin could be from fluid flow circulation or resonant vibrations of gas bubbles or from delayed movement of fluid rich sediments in the conduit or in a deeper pseudo mud chamber of the hmmv because swarms occur with a periodicity of 6 h tide related effects are suspected to influence the mechanism originating the tremors the second type of signals are regional earthquakes that were in 15 cases recognized in seismic records the activity of harmonic tremors was not significantly affected by earthquakes

origin of the west taiwan basin by orogenic loading and flexure of a rifted continental margin 1 seismic and well data suggest that the west taiwan basin developed by orogenic loading and flexure of a rift type continental margin the most likely source of the loading is taiwan where oblique convergence between the eurasian and philippine sea plates has produced an orogenic belt up to 300 km in length 100 km in width and 4 km in height flexure modeling shows that surface loading is unable to explain the depth of the west taiwan basin other subsurface or buried loads are required combined surface and buried loading explains the depth and width of the basin it also accounts for a bouguer gravity anomaly high and flanking low over the orogenic belt a lateral offset of 20 30 km between the peak topography and the maximum depth to the seismic moho and evidence for tectonic uplift in the penghu islands the depth of the base of the foreland sequence in the northern part of the west taiwan basin can be explained well by an elastic plate model with an effective elastic thickness te of 13 km while this value is low when compared to most other foreland basins it is within the range of values derived from rifted continental margins the northern part of the west taiwan basin unconformably overlies a passive margin sequence and therefore appears to have inherited the long term 1 myr flexural properties of the margin in the southern part of the basin however the depth to the base of the foreland sequence dips too steeply to be explained by elastic plate models this part of the basin therefore appears to be yielding rather than flexing differences in the flexural behavior along strike of the west taiwan foreland basin lithosphere are reflected in seismicity patterns west of the thrust front the northern part of the basin is associated with a low level of seismic activity while the south correlates with an abundance of earthquakes especially at shallow 25 km depths there is a cluster of earthquakes along two extensional faults that were active during rifting of the underlying margin therefore lithospheric flexure and fault reactivation may be important contributors to the seismicity of the taiwan region

structural geodetic and seismological evidence for tectonic escape in sw taiwan abstract recent structural geodetic and seismological data in sw taiwan are analysed and discussed in terms of present day tectonic escape occurring in response to the active n100 collisional shortening the escaping area corresponds to the onland extension of the manila accretionary wedge this region comprises a rheologically weak thick muddy cover which is decoupled from the underlying basement by a decollement and which deforms mainly by aseismic creep it is separated from the northern actual collisional area by a major wnw to nw trending structural and kinematic transition zone oblique to the structural grain of the belt the chishan transfer fault zone geodetic data are further used to define several poorly deforming blocks undergoing nearly uniform displacement velocities and bounded by kinematic discontinuities that fit the major faults and to determine the present day across strike and along strike motions on these major faults although direct onland structural evidence of tectonic escape is poor reconstruction of quaternary paleostress patterns demonstrate that this escape probably began during the late pleistocene later than in northeastern taiwan as a result of the southward migration of the collision through time offshore structural data help to constrain the geometry and the southern extension of the escaping blocks finally a tentative model of lateral extrusion in sw taiwan is proposed

significance of mud volcanism 1 mud volcanism and diapirism have puzzled geoscientists for 2 centuries they have been described onshore and offshore in many places on earth and although they occur in various tectonic settings the majority of the features known to date are located in compressional tectonic scenarios this paper summarizes the main thrusts in mud volcano research as well as the various regions in which mud volcanism has been described mud volcanoes show variable geometry up to tens of kilometers in diameter and several hundred meters in height and a great diversity regarding the origin of the fluid and solid phases gas predominantly methane water and mud may be mobilized at subbottom depth of only a few meters but in places can originate from several kilometers depth with minor crustal or mantle input the possible contribution of mud extrusion to global budgets both from quiescent fluid emission and from the extrusive processes themselves is important in regions where mud volcanoes are abundant such as the collision zones between africa and eurasia fluid flux through mud extrusion exceeds the compaction driven pore fluid expulsion of the accretionary wedge also quiescent degassing of mud volcanoes may contribute significantly to volatile budgets and hence to greenhouse climate

kinematic inversion of the 2004 m 6 0 parkfield earthquake including an approximation to site effects the 2004 m 6 0 parkfield earthquake yielded one of the largest amounts of near source strong ground motion seismic data ever we invert strong motion seismograms to obtain a model for the space time distribution of coseismic slip on the fault to reduce noise in the inversion we take into account local amplifications that affect each station by using records of the 1983 m 6 5 coalinga earthquake site amplification correlates well with large peak ground velocities registered during the 2004 parkfield mainshock the inversion for a kinematic rupture model yields a nonunique solution we therefore analyze various rupture models that explain the data equally well our preferred rupture model identifies a primary zone of high slip surrounding the hypocenter where the maximum slip is 57 cm a secondary slip area over which contours are not well resolved is located northwest of the hypo center the rupture speed is highly heterogeneous we infer an average rupture ve locity of 2 8 km sec close to the hypocenter and of 3 3 km sec in the secondary region of large slip to the northwest of the hypocenter by correlation of our rupture model with both microseismicity and velocity structure we identify six patches on the fault plane that behave in seismically distinct ways online material kinematic rupture model parameters

surface deformation and tectonic setting of taiwan inferred from a gps velocity field 1 we have determined the present day surface deformation of taiwan by computing the velocity gradient field and fault slip from 143 gps velocity vectors in southern taiwan the derived strain and rotation rates and fault slips are indicative of lateral extrusion toward the south in northern taiwan we infer the onset of gravitational collapse which is induced by the on land extension of the okinawa trough in the eastern central range the observed inverted nw se extension is consistent with geological observations and high heat flow measurements this could be the result of exhumation of crustal material the model further shows a significant decrease in slip rate northward along the longitudinal valley fault at 23 7 n the northern coastal range shows high strain rates and two oppositely rotating blocks by combining the surface deformation model with seismicity data and seismic tomography we are able to propose a coherent model for the present day tectonic activity both seismicity and tomography show further evidence for active southward propagating exhumation of a crustal slice in the eastern central range offshore east taiwan we deduce strong evidence of a southward propagating crustal tear fault accommodating most of the philippine sea plate eurasian plate convergence the tear is the crustal response to incipient northwestward subduction of the philippine sea plate thus the ryukyu trench is bending southward becoming almost perpendicular to the convergence direction while subduction of the philippine sea plate continues in this setting a sudden rapid southward propagation of the afore mentioned tear is conceivable

introduction to the special issue on the 2004 parkfield earthquake and the parkfield earthquake prediction experiment the 28 september 2004 m 6 0 parkfield earthquake a long anticipated event on the san andreas fault is the world s best recorded earthquake to date with state of the art data obtained from geologic geodetic seismic magnetic and electrical field networks this has allowed the preearthquake and postearthquake states of the san andreas fault in this region to be analyzed in detail analyses of these data provide views into the san andreas fault that show a complex geologic history fault geometry rheology and response of the nearby region to the earthquake induced ground movement although aspects of san andreas fault zone behavior in the parkfield region can be modeled simply over geological time frames the parkfield earthquake prediction experiment and the 2004 parkfield earthquake indicate that predicting the fine details of future earthquakes is still a challenge instead of a deterministic approach forecasting future damaging behavior such as that caused by strong ground motions will likely continue to require probabilistic methods however the parkfield earthquake prediction experiment and the 2004 parkfield earthquake have provided ample data to understand most of what did occur in 2004 culminating in significant scientific advances

velocity field of gps stations in the taiwan area abstract the 131 stations of the taiwan gps network were surveyed 4 6 times from 1990 to 1995 with dual frequency geodetic receivers the standard deviation of an observed baseline length with its linear trend removed is in the range of 6 10 mm for a 3 120 km long baseline the average rates of length change for all baselines of the network and those from nine continuously monitoring permanent stations are used in a least squares adjustment to estimate the velocities of the gps stations relative to paisha penghu situated at the chinese continental margin to the south of fengping in the northern coastal range the velocity vectors of stations in lanhsu lutao and the coastal range trend in the directions of 306 322 with rates of 56 82 mm yr in contrast there is a dramatic decrease in the rates to the north of fengping this may be caused by the motion along the ne sw trending thrusts which obliquely cut the northern coastal range a discontinuity of about 30 mm yr in the rates along with a remarkable change in the directions of station velocity is observed across the longitudinal valley then the moving directions gradually shift to the west for the stations in the western foothills in the kaohsiung pingtung coastal area the station velocities are even directed toward the southwest to the north of the peikang high the velocity vectors of the stations change direction from the west gradually to the north and finally to the east and southeast significant nw se extensional deformation is found in the ilan plain and northern taiwan in general the pattern of the velocity field for gps stations in the taiwan area is quite consistent with the directions of present day tectonic stress

source and site characteristics of earthquakes that have caused exceptional ground accelerations and velocities abstract this study investigates the characteristics of the free field strong motion records that have yielded the 100 largest peak accelerations and the 100 largest peak velocities in a relatively complete database of accelerograms recorded through the summer of 2007 the peak is defined as the maximum zero to peak amplitude of the acceleration or velocity vector during the strong shaking this compilation includes 35 records with peak acceleration greater than 1 g 980 cm sec 2 and 40 records with peak velocities greater than 100 cm sec the results sample an estimated 150 000 instrument years of strong motion recordings the geometric mean of the two horizontal components of acceleration or velocity as used in many ground motion prediction equations is typically 0 76 times the magnitude of this vector peak accelerations in the top 100 come from earthquakes as small as magnitude 4 8 while velocities in the top 100 all come from earthquakes with magnitude 5 7 or larger these records are dominated by crustal earthquakes with thrust oblique thrust or strike slip mechanisms normal faulting mechanisms in crustal earthquakes constitute under 5 of the records in the databases searched and an even smaller percentage of the 100 largest acceleration or velocity records all national earthquake hazard reduction program site categories have contributed exceptional records in proportions similar to the extent that they are represented in larger databases

spatial distribution of earthquake potential along the himalayan arc abstract to determine the spatial distribution of earthquake potential along the active himalayan arc we utilize gps measurements and earthquake data we derive horizontal velocity field and 2 d strain rates from a new set of 41 regional gps stations along with 446 published velocities we convert these strain rate tensors to geodetic moment rate build up within 24 contiguous segments and compare to the seismic moment rate release derived from a reassessed earthquake catalog of 900 years the geodetic to seismic moment rate ratio an indicator of stored strain energy varies from below unity to more than 50 in different segments the estimated geodetic moment rate ranges from 1 7 1018 nm yr to 10 2 1018 nm yr whereas the seismic moment rate ranges from 3 7 1016 nm yr to 5 1 1019 nm yr this variation between the geodetic and seismic moment rate corresponds to a moment deficit rate of 1 15 1017 nm yr to 7 97 1018 nm yr along various segments of the study region the above moment deficit rate provides an equivalent earthquake potential of magnitude 5 7 8 2 in different segments specifically the higher earthquake potential mw 8 0 corresponds to the segments in the central seismic gap and the northeast part of himalaya whereas the lower earthquake potential mw

production of brief extreme ground acceleration pulses by nonlinear mechanisms in the shallow subsurface 1 a brief pulse of extreme acceleration 20 m s 2 was recorded at station fz16 during the 2004 mw 6 0 parkfield california earthquake the sustained acceleration at the dominant frequency is a factor of 2 below the maximum here we show that the pulses of extreme acceleration might originate in the shallow subsurface rather than on the main fault plane two nonlinear mechanisms can feasibly convert low frequency energy of the incident wave into high frequency pulses with extreme acceleration 1 dynamic stress carried by strong seismic waves causes small shallow cracks to slip in secondary earthquakes 2 the elasticity of the shallow subsurface is nonlinear the relationship between dynamic shear stress and strain is linear at small strains at the large strains associated with strong ground motion shear deformation locks compliant cracks by bringing their asperities into contact the locking increases the instantaneous shear modulus of the cracked rock computations indicate that both mechanisms produce high accelerations in the later part of the strong ground motion these testable hypotheses imply that brief pulses of extreme acceleration are likely not a property of the main fault and hence not harbingers of prolonged pulses of extreme acceleration

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

rapid deformation rates due to development of diapiric anticline in southwestern taiwan from geodetic observations abstract we adopted 106 campaign mode gps observations and 310 precise leveling measurements between 2002 and 2010 to understand the present day crustal deformation in mudstone area and to estimate the earthquake potential of the hsiaokangshan hksf and the chishan faults chnf in southwest taiwan horizontal velocities east of the chnf are 66 mm yr 270 and gradually decrease westward to 15 mm yr n259 a horizontal velocity gradient of 15 mm yr is shown between the hksf and chnf subsidence rates west of the hksf and east of the chnf are 5 10 mm yr while the uplift is observed between these two faults in the highest elevation with the maximum rate of 18 mm yr the observed deformation patterns are difficult to be fully modeled by 2d kinematic fault model field relationships within the vertical shear zones of the mudstone therefore indicate that the deformation pattern may be also controlled by a relic onshore mud diapir that is still experiencing vertical uplift consistency between the geological and geodetic vertical velocities weak rock strength and no destructive earthquakes over the last 100 years imply that faults hksf within the mudstone area are creeping however the chnf or the associated decollement may still have earthquake potential

strain and stress field in taiwan oblique convergent system constraints from gps observation and tectonic data abstract this paper focuses on the stress and strain rate field of the taiwan area the strain rate field in the taiwan region is studied qualitatively and quantitatively based on the gps observation in 1990 1995 it reflects the accommodation of the ongoing lithospheric deformation within the seismogenic portion of lithosphere and exhibits zones with contrasting deformation modes and amounts we then compare the obtained strain rate field with the tectonic information provided by studies of borehole breakouts and earthquake focal mechanisms for the present and by fault slip data analyses for the quaternary period in the first approximation the stress and strain rate fields show spatial similarity the orientation of principal shortening is generally consistent with the compressive stress orientation that reflects the oblique indentation of the luzon arc into the eurasian continental margin in more detail significant anomalies in the deformation pattern deserve consideration in that they may reveal ongoing stress accumulation despite the short term variations related to the earthquake cycle some major features of the strain rate field including the distribution of extension and compression highlight the long term tectonic behavior of the mountain belt at the lithospheric scale the time and space variations of strain should be a function of local heterogeneity and be transferred between interseismic and coseismic periods

the flexural slip mechanism abstract detailed field studies of turbiditic sequences from south georgia south atlantic north devon england and cardigan bay wales show that flexural slip occurs on discrete movement horizons between rock packets in which the beds have welded contacts stair stepping displacements of sedimentary dykes and of early quartz veins show that the movement horizons generally have a decimetre to metre spacing and are marked by bedding parallel quartz veins these veins are from 1 mm to several cm thick and can be used to identify movement horizons in the absence of displaced markers they consist of several sheets of quartz fibres which each carry a slickenfibre lineation and which together preserve a record of the displacements on an individual surface complex slickenfibre patterns and departures from ideal behaviour in which slip occurs orthogonal to the fold hinge probably result from changes in slip vector on the limbs of growing non cylindrical folds movement horizons show many of the features associated with large scale thrusting such as ramps duplexes and imbricate structures and the shear sense given by fibre steps on these surfaces and by duplexes within stratigraphically restricted packages changes across fold hinges chevron folds are thought to develop mainly by flexural flow in the early stages with flexural slip becoming dominant later as the beds become lithified new slip surfaces are generated as the dip of the fold limbs increases

modern vertical deformation rates and mountain building in taiwan from precise leveling and continuous gps observations 2000 2008 1 to characterize the present day vertical displacement field in the active taiwan orogenic belt 1843 precise leveling and 199 continuous gps measurements from 2000 to 2008 are collected and analyzed in this study vertical velocities derived from the leveling data are placed in a reference frame of the chinese continental margin using continuous gps observations at nearby sites the leveling and gps vertical velocities generally reveal a dome shaped pattern with uplift of 0 2 18 5 mm yr in the interior of the mountain range and subsidence on the flanks of the mountains and coastal plains modern uplift rates in the active fold and thrust belt are generally consistent with geologic uplift rates however present day uplift rates in the central range are faster than the million years averaged exhumation rates the modern subsidence rates are generally consistent with geologic rates except for the rates in western coastal areas due to groundwater pumping present day subsidence in the southern central range and northern coastal range is however inconsistent with long term uplift which may reflect interseismic elastic strain accumulation across faults present day subsidence in northern taiwan occurs in a region of postcollisional orogenic collapse we model the present day and geologic vertical velocities and published gps horizontal velocity data across southern taiwan using a 2 d lithospheric model the model suggests a combined slip rate of 40 mm yr on the frontal thrusts and 45 mm yr on the longitudinal valley fault the model requires an additional source of crustal thickening under the central range to match the observed present day uplift rates

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

present day kinematics of active mountain building in taiwan from gps observations during 1995 2005 1 we characterize the kinematics of modern crustal deformation in taiwan and evaluate the potential for large earthquakes by computing tectonic block motions and fault slip rates from 531 gps horizontal velocities these new gps velocity field indicates that lateral extrusion in the southern transition from collision to subduction is primarily achieved by motion along several major reverse faults and internal distortion of blocks the northern transition is characterized by asymmetric opening of the okinawa trough and collision induced rotation between the ryukyu trench and okinawa trough we suggest that the differences in style of deformation in northern and southern taiwan are a result of differences in trenchward motions between the overriding plate and forearc sliver along strike variations in basin thickness and the presence of foreland basement obstacles in central taiwan result in clockwise rotation with sinistral motion on faults and counterclockwise rotation with dextral motion on faults north and south of the obstacle respectively in eastern taiwan high slip rate of 43 mm yr on the southern longitudinal valley fault lvf is responsible for the full collision of taiwan orogeny e w syn orogenic extension in the southern central range has been inferred by our model patches with high slip rate deficits on the lvf and the chelungpu fault from our model respectively mainly correspond to the source areas of the 1951 m 7 1 longitudinal valley earthquake sequence and of the 1999 mw 7 6 chi chi earthquake

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

a two dimensional dislocation model for interseismic deformation of the taiwan mountain belt we use a global positioning system gps derived surface velocity field of taiwan for the time period between 1993 and 1999 to infer interseismic slip rates on subsurface faults we adopt a composite elastic half space dislocation model constrained by the observed horizontal velocities projected into the direction of plate motion 306 the gps data are divided into northern and southern regions and the velocities in each region are projected into single profiles the model fault geometry includes a shallowly dipping decollement based on the balanced geological cross sections in the coastal plain and western foothills and a two segment fault representing the longitudinal valley fault lvf in eastern taiwan the decollement is composed of two fault segments one extending west under the central range cr and one extending east of the lvf with estimated slip rates of about 35 and 80 mm yr respectively the optimal geometry of decollement is subhorizontal 2 v11 at a depth of 8v9 km the inferred surface location of the western end point of dislocation in the northern profile is located 15 km east of the chelungpu fault while in the southern section it is located beneath the chukou fault the elastic dislocation model successfully matches the horizontal velocity data and predicts elastic strain accumulation in the western foothills that will presumably be released in future earthquakes however considered over multiple earthquake cycles our model cannot explain the topography of the cr and thus fails to predict the active mountain building process in taiwan this failure indicates that both horizontal and vertical velocity fields require a more complex rheological model that incorporates inelastic behavior

inversion of gps data for spatially variable slip rate on the san andreas fault near parkfield ca we analyze gps data collected from 1991 1998 at 35 sites near the parkeld segment of the san andreas fault inverting the resultant site velocities for the distri bution of interseismic slip rate on the san andreas reveals an area of low slip rate on thefault extendingfrom between middle mountain and carr hill to southeast of gold hill this slip rate patternis similar to thatfoundbyharris and segall 1987 using trilateration data collected between 1966 and 1984 we infer a deep slip rate 33 mm yr and depth of the transition between seismogenic and non seismogenic slip 14km thatagree betterwithindependentgeologic ev idence than those found in the 1987 study in contrast to harris and segall 1987 wendnoevidenceoffault normal contraction

geology and geochemistry of the shuanggou ophiolite ailao shan ophiolitic belt yunnan province sw china evidence for a slow spreading oceanic basin origin abstract the early carboniferous shuanggou ophiolite lies in the middle segment of the ailao shan orogenic belt between the south china block to the north and the indochina block to the south the ophiolite consists of meta peridotite gabbro diabase and basalt capped by radiolarian bearing siliceous rocks no layered gabbros or sheeted dikes have been observed the meta peridotite underwent low degrees of partial melting consistent with the low magma budget of this oceanic lithosphere whole rock rare earth element analyses of gabbro indicate a geochemical affinity with normal mid ocean ridge basalts consistent with the crystallization order of plagioclase followed by clinopyroxene recognized in the gabbros the ophiolite is believed to have formed in a small slow spreading oceanic basin collision of the indochina block with the south china block in the late paleozoic was responsible for the closure of the oceanic basin and emplacement of the ophiolite in the ailao shan orogenic belt

nonlinear attenuation and rock damage during strong seismic ground motions strong seismic waves cause nonlinear behavior in the shallow subsurface in fractured rocks seismologists use low amplitude signals from small repeating earthquakes to measure s wave velocity decrease after strong motion the 2004 parkfield california earthquake provides examples of such velocity changes in fractured sandstone with an s wave velocity of 300 m s 1 this nonlinear behavior occurred around the wave number depth of the incident waves 30 m for the 10 s 1 dominant angular frequency on a velocity seismogram the low amplitude s wave velocity gradually recovered with the logarithm of time the attenuation of strong waves in general depends nonlinearly on their amplitude high dynamic stress triggered small very shallow earthquakes at sites including parkfield the theoretical frictional behavior of a fractured medium with heterogeneous prestress relates these phenomena failure occurs in the highly prestressed domains causing small earthquakes and opening mode cracks the energy to dilate the cracks dissipates a significant fraction of the incoming seismic energy the local high porosity domains close with the logarithm of time as expected from the aging law of rate and state friction increasing the s wave velocity the domain model indicates that nonlinear effects increase gradually over a range of dynamic coulomb stresses as observed and as included in the widely used masing rules the linker and dieterich 1992 relationship provides the maximum sustainable dynamic coefficient of friction needed to utilize the masing rules this parameter is the coefficient of friction at a laboratory normal traction plus a constant 0 15 times the logarithm of the ratio of field normal traction to the laboratory normal traction it is helpful to relate s wave velocity to starting frictional strength as coefficient of friction near the quarter wavelength depth determines nonlinear behavior then the dynamic coefficient of friction and equivalently the maximum sustainable acceleration at the dominant frequency depend weakly on s wave velocity for example the coefficient of friction at an angular frequency of 10 s 1 is less than 1 5 for rocks ranging from parkfield sandstone to intact granite

contemporary deformation of tectonic escape in sw taiwan from gps observations 1995 2005 abstract the gps velocity field in sw taiwan inferred by 103 stations from 1995 to 2005 provides an opportunity to better recognize the contemporary crustal deformation under escaping tectonics horizontal velocities relative to the chinese continental margin from east to west rotate counterclockwise from 42 0 mm yr to 13 0 mm yr along azimuths from 246 to 265 across sw taiwan the vertical velocity field in sw taiwan shows a subsidence rate of 5 to 20 mm yr concentrated on the coastal area of the pingtung plain and an uplift rate of 10 to 20 mm yr distributed along the mountain belt spatial velocity variation indicates the ne sw striking chishan fault chnf acting as reverse faulting with dextral motion the n s trending chaochou fault as nearly pure reverse faulting and the fengshan transfer fault zone ftfz as left lateral shearing intersecting the aforementioned faults the dominant wnw ese shortening and ne sw dextral shear strain are subject to the fold and thrust belt of the western foothills west of the chnf a ne sw extension and nw se contraction are represented near the ftfz along the sw coastal area showing a nw se sinistral shear strain our gps data show that the movement of ftfz greatly enhances the velocities of sw taiwan rotating from nearly westward direction to wsw direction sub parallel to the edge of the basement high i e the rigid indenter of the chinese continental margin the chishan fault as a boundary fault separates the sw taiwan into a western deforming domain and an eastern quasi rigid block a nearly e w contraction and n s extension escaping stress regime is accommodated by n s trending ductile flow within the upper mantle and by brittle conjugated type fracture formed by the chnf and the ftfz within the crust the different directions between n s trending upper mantle flow and southwestward crustal escape indicate that the crust and upper mantle are decoupled in the tectonic escape process of sw taiwan

exceptional ground motions recorded during the 26 april 2008 mw 5 0 earthquake in mogul nevada abstract an unusually shallow swarm of earthquakes in mogul a suburb in west reno nevada started 28 february 2008 and continued for several months temporary instruments in the epicentral region constrained event depths and locations and provided onscale recordings of the strong ground motions and supplemented a network of over 21 permanent advanced national seismic system anss strong motion stations deployed throughout the metropolitan reno area by the end of august the swarm had produced over 200 earthquakes with magnitude m l greater than 2 0 the largest earthquake in the sequence occurred at 06 40 utc on 26 april 2008 11 40 p m on 25 april local time with magnitude m l 4 7 m w 5 0 and a hypocentral depth of about 3 1 km in the m w 5 0 mainshock mean horizontal peak ground acceleration exceeded 0 6 g at three stations the strongest peak vector acceleration was 1164 cm sec 2 or about 1 19 g at the station mogl 0 4 km from the epicenter at a frequency of about 3 hz the mean horizontal peak velocity exceeded 12 cm sec at the four nearest stations and the peak vector velocity at the strongest was 54 cm sec the duration of the strongest shaking was about 2 sec at these stations the observed peak accelerations and peak velocities decreased more rapidly with distance than predicted to values below the median predictions at most stations in the reno metropolitan area the shallow source depth is to some degree a likely contributing factor to these unusual observations the motions in the residential neighborhood near the epicenter are significantly greater than the seismic forces required by the 1985 uniform building code zone 3 that was in effect when the mogul neighborhood was developed but damage to the wood frame structures in the neighborhood was minimal

fault activity and lateral extrusion inferred from velocity field revealed by gps measurements in the pingtung area of southwestern taiwan abstract four campaigns of dense gps measurements have been conducted since 1995 to investigate crustal deformation patterns in sw taiwan the station velocities decrease westwards from 42 2 to 55 5 mm yr along the azimuths from 247 1 to 272 5 in central part of the study area gps stations move nearly toward the west whereas in the pingtung kaohsiung coastal area displacement vectors demonstrate a clear counter clockwise deviation toward the sw the transtensional deformation and the along strike variation of southward increase of extensional deformation is due to the low lateral confining conditions related to the manila subduction zone as a free boundary or and the presence of the prominent peikang high as a rigid indentor the chishan fault is dominated by right lateral motion with a fault slip rate 7 mm yr in a n50 w direction the kaoping fault is dominated by left lateral motion with a 4 8 mm yr in a n s direction the significant right lateral component of motion of 24 30 mm yr is accommodated along the active structures west of the chishan fault the right lateral and left lateral structures facilitate the southwestward extrusion the velocity gradients of the gps stations across the chaochou fault are not significant this implies that the chaochou fault is locked along the fault plane

plate collision and paleostress trajectories in a fold thrust belt the foothills of taiwan abstract field analyses of compressional faulting and folding in the foothills of western taiwan enable us to reconstruct paleostress trajectories over a large area and to establish the relative chronology of tectonic events two main compressional events have contributed to the present structure of the fold thrust belt stratigraphic data show that these events are plio pliocene in age older normal faulting indicates nnw sse extension across the chinesse passive continental margin during the neogene the two main compressional events of the taiwan collision correspond to similar fan shaped distributions of maximum compressive stress trajectories with a counterclockwise shift of 30 50 between the two events using the relationship between recent stress trajectories and the direction of recent plate motion as a guide we reconstruct the direction of plate convergence for the older event we suspect that the relative motion philippine sea plate eurasia has rotated counterclockwise of at least 35 45 in taiwan during collision this conclusion is in agreement with independent plate tectonic reconstructions several problems provide objectives to further tectonic and paleomagnetic studies including the duration and diachronism of compressional events as well as possible clockwise rotation of northernmost taiwan

note on the very high acceleration fault zone 16 record from the 2004 parkfield earthquake a very high acceleration recording was obtained at station fault zone 16 near parkfield california during the m 6 0 parkfield earthquake of 28 september 2004 this note documents key aspects of the station the instrument and the record a preliminary reconstruction of the record is performed to produce an estimate of the true acceleration which is then integrated to obtain the estimated velocity the strong motion accelerograph at fault zone 16 is deployed at a soil site in a light fiberglass housing common in the parkfield array postearthquake testing indicates that the accelerograph operated normally instrument shake table tests indicate that the recorded acceleration is relatively accurate even at the high accelerations involved in this record that is the very high accelerations in the record are a reasonably accurate reflection of the accelerations that occurred at the site during the parkfield earthquake although the peak motion was not recorded the record itself has several unusual features the trace was lost at the top edge of the film where the excursion went beyond the recordable part of the film most unusually the traces of two accelerometers recorded on top of one another during the positive highest amplitude part of the record the accelerograph did not record the peak accelerations of the components which occurred during this time an additional aspect is that for the largest amplitude component the negative part of the acceleration was affected by momentary stalling of the recording film during the strongest shaking the constraint for the mean of the acceleration over the whole record to be zero and detailed analysis of the time trace leads to a reconstruction of the record the peak acceleration on this component is over 1 8 g and most likely over 2 g the peak velocity is estimated to be about 80 cm sec the other horizontal component goes off the film at the same time combined the horizontals yield a fault normal acceleration of over 2 2 g and most likely over 2 5 g this record is a challenge to interpret an important practical lesson is that given what has been learned about near fault accelerations any instrument deployed in the region should have a recording capacity well in excess of 2 g

geometry and quaternary kinematics of fold and thrust units of southwestern taiwan structural and paleostress analyses provide new insights into the quaternary kinematics of the outermost fold and thrust units of southwestern taiwan foothills the frontal folds are interpreted as fault related folds and their tectonic evolution through space and time is tightly constrained fold development is correlated with reef building on top of the anticlines moreover we provide field evidence that nw se fault zones oblique to the structural grain of the belt probably acted as transfer fault zones during the the quaternary fold thrust emplacement two successive quaternary stress regimes are evidenced in southwestern taiwan a nw se compression followed by a recent nearly e w compression the latter shows an along strike change from pure e w contraction to the north to perpendicular n s extension in the south this southward decrease in n s confinement probably represents the on land signature of the incipient quaternary tectonic escape predicted by analogue and numerical modelling and evidenced at present day by global positioning system data

multiscale site response mapping a case study of parkfield california the scale of previously proposed methods for mapping site response ranges from global coverage down to individual urban regions typically spatial coverage and accuracy are inversely related we use the densely spaced strong motion stations in parkfield california to estimate the accuracy of different site response mapping methods and demonstrate a method for integrating multiple site response estimates from the site to the global scale this method is simply a weighted mean of a suite of different estimates where the weights are the inverse of the variance of the individual estimates thus the dominant site response model varies in space as a function of the accuracy of the different models for mapping applications site response models should be judged in terms of both spatial coverage and the degree of correlation with observed amplifications performance varies with period but in general the parkfield data show that 1 where a velocity profile is available the square root of impedance sri method outperforms the measured v s 30 30 m divided by the s wave travel time to 30 m depth and 2 where velocity profiles are unavailable the topographic slope method outperforms surficial geology for short periods but geology outperforms slope at longer periods we develop new equations to estimate site response from topographic slope derived from the next generation attenuation nga database

interseismic crustal deformation of frontal thrust fault system in the chiayi tainan area taiwan abstract we derive a velocity field using gps data between 1993 and 2007 in the chiayi tainan area located in the deformation front of the taiwan mountain belt the crustal motion with respect to penghu shows large velocities of about 33 44 mm yr in the west northwest to west directions in the western foothills and the velocities decrease westward to 0 5 mm yr in the coastal area significant uplift rates of 5 20 mm yr are observed at sites to the east of the jiuchiunken muchiliao liuchia fault jmlf system we use a block model a buried dislocation model and a two dimensional fault model to invert for fault geometries and slip rates on major frontal thrust faults modeling results from a block model show the inferred long term slip rate of 42 mm yr in the direction of 280 and the maximum back slip rate of 38 mm yr on a 23 east dipping fault extending to 13 km at depth on the other hand the buried dislocation model results in a horizontal decollement at a depth of 8 km with a uniform slip rate of 41 6 mm yr if we connect the top edge of decollement to the surface trace of jmlf as a potential future rupture a 22 east dipping fault is required results from both block model and buried dislocation model suggest the jmlf is nearly fully locked the results of two dimensional fault models show the frontal thrust faults have slip rates of less than 2 mm yr at shallow depths and the inferred decollement is sub horizontal 5 7 at a depth of 10 km with slip rates of 44 46 mm yr results of various approaches show general agreement on fault geometries and slip rates and reveal that the frontal thrust fault system has a high potential for large earthquakes