shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

coseismic slip distribution of the 1999 chi chi taiwan earthquake deduced from inversion analysis of gps data the 1999 chi chi earthquake m w 7 6 was the largest thrust type earthquake that occurred in taiwan in the twentieth century following the event large horizontal and vertical coseismic displacements were observed at gps stations near the fault region the observed maximum horizontal displacement uplift and subsidence were 9 1 4 0 and 0 7 m respectively in order to estimate coseismic slip distribution geodetic data inversion was carried out based on the gps displacement data total numbers of horizontal and vertical data used here are both 118 taking the shape of the surface rupture aftershock distribution and centroid moment tensor solutions into account a gently curved fault plane with a fault size of 70 km 50 km a dip angle of 31 and strike of n9 e was constructed the results show that the amount of average slip is 5 1 m and the average slip direction is n55 w on the fault plane seismic moment estimated from the geodetic data inversion is 5 4 1020 n m the amount of slip gradually increases toward the northwest on the fault plane reaching 13 8 m the spatial distribution of the coseismic slip is consistent with that estimated from inversion analysis of teleseismic and near source strong motion data whereas the amount of slip of the former is larger than that of the latter this may suggest that slow large afterslips occurred on the northwestern part on the fault plane within one month of the event and or the fault dip adopted in this study was larger than the actual dip indicating disagreement of coseismic fault plane with one of the nodal planes estimated from the cmt solutions and the aftershock distribution manuscript received 31 july 2000

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

palaeoearthquake surface rupture in a transition zone from strike slip to oblique normal slip and its implications to seismic hazard north island fault system new zealand

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

mechanical analysis of fault slip data implications for paleostress analysis abstract stress inversions are a useful and popular tool for structural geologist and seismologist alike these methods were first introduced by wallace 1951 and bott 1959 and subsequent studies continue to be based on their assumptions the remote stress tensor is spatially uniform for the rock mass containing the faults and temporally constant over the history of faulting in that region and the slip on each fault surface has the same direction and sense as the maximum shear stress resolved on that surface from the remote stress tensor furthermore successful implementation requires that slip accumulates on faults of diverse orientation many studies employ these methods on isolated faults or on fault systems with limited ranges of orientations which can lead to erroneous results we propose a new method that incorporates the effects of mechanical interaction of the entire fault or fault system and solves the complete mechanical problem rather than employing empirical relationships between slip and stress or strain or strain rate the method requires knowledge of the fault geometry and information on at least one slip vector component along portions of the known fault geometry for example if throw is known the strike slip component can be solved for we test the method using a single synthetic fault with anisotropic roughness similar to that measured at fault outcrops while the orientation of remote stress may be determined precisely the lack of diverse fault orientations introduces a systematic error in the remote stress ratio we further test the effect of diversity of fault orientations and find that wallace bott type inversions do not perform as well for limited ranges of orientations when compared to the proposed method finally we use published data from the 1999 chi chi taiwan earthquake and find that the method using surface data only and surface data with subsurface focal mechanisms produce similar results the resulting stress orientations are in good agreement with results from wallace bott inversions furthermore the slip distribution is in general agreement with kinematic slip inversions using coseismic surface deformation stress inversion methods using fault slip data can thus be improved upon significantly in some cases by solving a mechanical boundary value problem that takes into account the geometry of faults or fault systems as a bonus the solution provides the stress strain and displacement fields throughout the region and the slip distributions on the faults

reconciling seismic and geodetic models of the 1989 kilauea south flank earthquake 1 the inconsistency in depth between geodetic and seismic models of the 1989 kilauea earthquake has long been puzzling previous attempts to incorporate elastic heterogeneity have deepened geodetic models substantially bringing them closer to the seismic depth however recent studies that have included heterogeneity for other faults indicate that the effect is not so great we show here that elastic heterogeneity has a relatively minor effect on the geodetic model depth for this earthquake also however by combining three different sets of geodetic data we are able to get a more accurate estimate of the depth which does in fact coincide with the hypocentral depth at the 95 confidence level when we consider that static elastic parameter values are commonly less than dynamic values the agreement is even better furthermore the depth is consistent with the earthquake having occurred at the interface between the volcanic pile and the pre volcanic seafloor

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

spatio temporal slip and stress level on the faults within the western foothills of taiwan implications for fault frictional properties we use preseismic coseismic and postseismic gps data of the 1999 chi chi earthquake to infer spatio temporal variation of fault slip and frictional behavior on the chelungpu fault the geodetic data shows that coseismic slip during the chi chi earthquake occurred within a patch that was locked in the period preceding the earthquake and that afterslip occurred dominantly downdip from the ruptured area to first order the observed pattern and the temporal evolution of afterslip is consistent with models of the seismic cycle based on rate and state friction comparison with the distribution of temperature on the fault derived from thermo kinematic modeling shows that aseismic slip becomes dominant where temperature is estimated to exceed 200 at depth this inference is consistent with the temperature induced transition from velocity weakening to velocity strengthening friction that is observed in laboratory experiments on quartzo feldspathic rocks the time evolution of afterslip is consistent with afterslip being governed by velocity strengthening frictional sliding the dependency of friction l on the sliding velocity v is estimated to be ol o ln v 8 10 3 we report an azimuthal difference of about 10 20 between preseismic and postseismic gps velocities which we interpret to reflect the very low shear stress on the creeping portion of the decollement beneath the central range of the order of 1 3 mpa implying a very low friction of about 0 01 this study highlights the importance of temperature and pore pressure in determining fault frictional sliding

seismic behavior in central taiwan response to stress evolution following the 1999 mw 7 6 chi chi earthquake abstract following the 1999 mw 7 6 chi chi earthquake a large amount of seismicity occurred in the nantou region of central taiwan among the seismic activities eight mw 5 8 earthquakes took place following the chi chi earthquake whereas only four earthquakes with comparable magnitudes took place from 1900 to 1998 since the seismicity rate during the chi chi postseismic period has never returned to the background level such seismicity activation cannot simply be attributed to modified omori s law decay in this work we attempted to associate seismic activities with stress evolution based on our work it appears that the spatial distribution of the consequent seismicity can be associated with increasing coseismic stress on the contrary the stress changes imparted by the afterslip lower crust upper mantle viscoelastic relaxation and sequent events resulted in a stress drop in most of the study region understanding seismogenic mechanisms in terms of stress evolution would be beneficial to seismic hazard mitigation

the chi chi earthquake sequence active out of sequence thrust faulting in taiwan we combined precise focal depths and fault plane solutions of more than 40 events from the 20 september 1999 chi chi earthquake sequence with a synthesis of subsurface geology to show that the dominant structure for generating earthquakes in central taiwan is a moderately dipping 20 to 30 thrust fault away from the deformation front a second subparallel seismic zone lies about 15 kilometers below the main thrust these seismic zones differ from previous models indicating that both the basal decollement and relic normal faults are aseismic

imaging the ramp decollement geometry of the chelungpu fault using coseismic gps displacements from the 1999 chi chi taiwan earthquake abstract we use coseismic gps data from the 1999 chi chi taiwan earthquake to estimate the subsurface shape of the chelungpu fault that ruptured during the earthquake studies prior to the earthquake suggest a ramp decollement geometry for the chelungpu fault yet many finite source inversions using gps and seismic data assume slip occurred on the down dip extension of the chelungpu ramp rather than on a sub horizontal decollement we test whether slip occurred on the decollement or the down dip extension of the ramp using well established methods of inverting gps data for geometry and slip on faults represented as elastic dislocations we find that a significant portion of the coseismic slip did indeed occur on a sub horizontal decollement located at 8 km depth the slip on the decollement contributes 21 of the total modeled moment release we estimate the fault geometry assuming several different models for the distribution of elastic properties in the earth homogeneous layered and layered with lateral material contrast across the fault it is shown however that heterogeneity has little influence on our estimated fault geometry we also investigate several competing interpretations of deformation within the e w trending rupture zone at the northern end of the 1999 ground ruptures we demonstrate that the gps data require a 22 to 35 km long lateral ramp at the northern end contradicting other investigations that propose deformation is concentrated within 10 km of the chelungpu fault lastly we propose a simple tectonic model for the development of the lateral ramp

quasi static dislocations in three dimensional inhomogeneous media we present an approximate perturbation method for computing surface displacement fields due to quasi static dislocations in inhomogeneous elastic half spaces extending the work of du et al 1994 to three dimensions three dimensional methods are required to model geodetic observations the perturbation method allows one to include more realistic earth structure in the analysis of surface deformation measurements and is computationally efficient enough to be used in inversions for source properties as an example we investigate the effect of material inhomogeneity on the location of the fault plane for the 1989 kalapana hawaii earthquake inversion of coseismic elevation changes assuming a homogeneous half space yielded a finite source depth markedly shallower than the mainshock and principal aftershocks arnadottir et al 1991 incorporation of lateral and vertical variations in shear modulus consistent with velocity and density data yields a source depth more consistent with the seismic results failure to account for variations in elastic properties can bias estimates of source depth and moment

taiwan orogeny thin skinned or lithospheric collision abstract the taiwan orogeny is young and presently very active it provides an excellent environment for studying ongoing orogenic processes especially since the region is monitored intensively with dense seismological and geodetic networks and new studies aiming at deciphering shallow and deep structures in and around taiwan have been recently conducted or are being planned the available data can be used continually to test critically hypotheses of the taiwan orogeny hypotheses dealing with the mechanics of mountain building are basic to the understanding of taiwan orogeny and are particularly amenable to testing the widely cited thin skinned tectonics hypothesis was formulated to explain mainly the geologic and relatively shallow

1999 chi chi earthquake a case study on the role of thrust ramp structures for generating earthquakes the 21 september 1999 chi chi earthquake m w 7 6 occurred on east dipping shallow thrust faults that produced a high relief surface rupture extraordinary surface breaks appeared that could be clearly traced for about 100 km across many counties these thrust faults the chelungpu and shihkang are part of an active fold and thrust belt related to ongoing recent arc continent collision measurement of slip vectors along the earthquake rupture indicates that the orientation of the maximum shear stress changed from a westward direction n70 90 w on the chelungpu fault to a northwestward direction n30 40 w on the shihkang fault the stress field underwent a clockwise rotation of about 40 during the chi chi earthquake near rupture vertical displacements in the hanging wall of the shihkang fault have more cumulative displacement than on the chelungpu fault which is consistent with global positioning system gps measurements maximum vertical offset on the rupture was found to be about 10 m by the surficial rupture and gps measurements in addition analysis of crustal deformation by gps measurements on the hanging wall defines a coseismic uplift related to a fault ramp structure our synthesis of geological and geodetic analyses shows the importance of ramp structures associated with thrust faults for generating large earthquakes and provides a general framework for understanding earthquake in fold and thrust belts large surficial coseismic uplift and strong asperities appear to be a function of fault ramp geometry our analysis also indicates that in general ramp structures in fold and thrust belts may have a high potential in generating large earthquakes manuscript received 14 november 2000

rapid afterslip following the 1999 chi chi taiwan earthquake 1 postseismic displacements of as much as 14 cm were recorded by gps measurements in the 3 months following the mw 7 6 1999 chi chi taiwan earthquake data from 35 continuous and 90 campaign surveyed stations which show continued east over west thrusting are analyzed to estimate the postseismic slip distribution and fault geometry assuming the shallow fault dips 24 e as determined by numerous studies of the mainshock we invert for the deeper fault structure our results show that the fault dip shallows with depth below the hypocenter merging into a nearly horizontal decollement at a depth of 8 12 km the afterslip distribution shows a maximum slip of 25 cm in the hypocentral region at 7 12 km depth as well as significant slip on the lower decollement afterslip is notably absent in the region of maximum coseismic slip consistent with the afterslip being driven by the mainshock stress change

stress evolution following the 1999 chi chi taiwan earthquake consequences for afterslip relaxation aftershocks and departures from omori decay summary we explore how coulomb stress transfer and viscoelastic relaxation control afterslip and aftershocks in a continental thrust fault system the 1999 september 21 m w 7 6 chi chi shock is typical of continental ramp dsystems throughout the world and so inferences drawn from this uniquely well recorded event may be widely applicable first we find that the spatial and depth distribution of aftershocks and their focal mechanisms are consistent with the calculated coulomb stress changes imparted by the coseismic rupture some 61 per cent of the m 2 aftershocks and 83 per cent of the m 4 aftershocks lie in regions for which the coulomb stress increased by 0 1 bars and there is a 11 12 per cent gain in the percentage of aftershocks nodal planes on which the shear stress increased over the pre chi chi control period second we find that afterslip occurred where the calculated coseismic stress increased on the fault ramp and dsubject to the condition that friction is high on the ramp and low on the d ecollement third viscoelastic relaxation is evident from the fit of the post seismic gps data on the footwall fourth we find that the rate of seismicity began to increase during the post seismic period in an annulus extending east of the main rupture the spatial extent of the seismicity annulus resembles the calculated 0 05 bar coulomb stress increase caused by viscoelastic relaxation and afterslip and we find a 9 12 per cent gain in the percentage of focal mechanisms with 0 01 bar shear stress increases imparted by the post seismic afterslip and relaxation in comparison to the control period thus we argue that post seismic stress changes can for the first time be shown to alter the production of aftershocks as judged by their rate spatial distribution and focal mechanisms

the structure and kinematics of the central taiwan mountain belt derived from geological and seismicity data 1 the structure of the taiwan mountain belt is thought to be that of an imbricate thrust and fold belt developed in a forward breaking sequence above a shallowly dipping basal detachment in recent years however a growing amount of seismicity data from the internal part of the mountain belt indicates the existence of widespread fault activity in the middle and lower crust suggesting that deeper levels of the crust must be involved in the deformation than predicted by the shallow detachment imbricate thrust belt model to address this issue we present new geological mapping together with earthquake focal mechanism and seismic energy release data from the central part of taiwan we concur with the interpretation that the foreland basin part of the western foothills comprises an imbricate thrust system that is developing as a forward breaking sequence that is structurally and kinematically linked to a basal detachment at between 7 and 10 km depth to the east of the foreland basin however in the hsuehshan and central ranges our data show the presence of two fault systems an earlier inactive thrust system with a well developed cleavage is cut by a system of steeply dipping active faults that penetrate to a depth of 25 to 30 km or more in the hsuehshan range the second fault system is best represented by a structural and kinematic model in which this part of the mountain belt forms a zone of transpression with a structural architecture similar to that of a crustal scale positive flower structure eastward in the central range mesozoic basement rocks are over thrusting strongly folded and cleaved deep water sediments of the first now inactive thrust system the involvement of deep crustal levels and mesozoic basement in the second fault system is suggestive of the reactivation of preexisting basin bounding faults that were located on the eurasian continental margin

influence of lithosphere viscosity structure on estimates of fault slip rate in the mojave region of the san andreas fault system 1 it is well known that slip rate estimates from geodetic data are nonunique because they depend on model assumptions and parameters that are often not known a priori estimates of fault slip rate on the mojave segment of the san andreas fault system derived from elastic block models and gps data are significantly lower than estimates from geologic data to determine the extent to which the slip rate discrepancy might be due to the oversimplified models of the rheology of the lithosphere we develop a two dimensional linear maxwell viscoelastic earthquake cycle model and simultaneously estimate fault slip rates and lithosphere viscosity structure in the mojave region the model consists of episodic earthquakes in an elastic crust overlying layers with different viscosities that represent the lower crust uppermost mantle and upper mantle we use gps measurements of postseismic relaxation following the 1992 landers earthquake triangulation measurements spanning 1932 1977 gps measurements of the contemporary velocity field and paleoseismic data along the san andreas fault we infer lower crustal 15 30 km depth viscosity of 1019 10 20 pa s uppermost mantle 30 60 km viscosity of 10 20 22 pa s and underlying upper mantle viscosity of 10 18 10 19 pa s consistent with inferences from laboratory experiments of relatively high viscosity lithospheric mantle and lower viscosity lower crust and underlying asthenospheric mantle we infer a 20 30 mm yr slip rate on the san andreas fault in agreement with the lower end of geologic estimates inversions of geodetic data with models that do not incorporate layered viscosity structure may significantly misestimate slip rates

early jurassic schizosphaerellid crisis in cantabria spain implications for calcification rates and phytoplankton evolution across the toarcian oceanic anoxic event 1 the toarcian oceanic anoxic event 183 myr ago represents a global perturbation marked by increasing organic carbon burial and a general decrease in calcium carbonate production likely triggered by elevated carbon dioxide levels in the atmosphere here we present quantitative analyses of calcareous nannofossil diversity and abundance from the castillo de pedroso section in cantabria northern spain we compare these data with geochemical data c and o isotopes obtained from biogenic and bulk carbonate records in order to highlight the response of calcareous phytoplankton to major climatic and paleoceanographic changes the pliensbachian toarcian boundary is characterized by an abrupt decrease in abundance of schizosphaerella punctulata the most important lithogenic contributor to hemi pelagic carbonates in the early jurassic the early toarcian nannofloral assemblages show an increase in abundance of mitrolithus jansae and small sized r selected taxa and a progressive decrease in s punctulata percentages the deep dwellers m jansae and s punctulata experienced a major crisis slightly prior to the deposition of the toarcian black shales that are characterized by high abundances of eutrophic taxa such as lotharingius spp and biscutum spp the return of s punctulata associated with lower percentages of eutrophic taxa was observed just above the toarcian black shales the toarcian episode reveals that high co2 levels and increasing primary productivity probably triggered a shift in abundance from highly calcified nannoliths such as s punctulata and m jansae to small sized r selected coccoliths that overall record a biocalcification crisis at the onset and during the toarcian episode

surface rupture of 1999 chi chi earthquake yields insights on active tectonics of central taiwan the 1999 chi chi earthquake was caused by rupture of the chelungpu fault one of the most prominent active thrust faults of taiwan this largest of taiwan s historical fault ruptures broke the surface for over 90 km at the western base of the rugged mountain range a short right lateral tear extended southwestward from the southern end of the chelungpu fault and a complex assemblage of shallow folds and faults ran northeastward from the northern end vertical offsets averaged about 2 m along the southern half of the chelungpu fault and about 4 m along the northern half and offsets of 5 to 7 m were typical along the northern part of the major thrust the sinuous nature of the surface trace is consistent with seismographic data that indicate a dip of about 30 the 1999 rupture draws attention to the fact that this active fault system is highly segmented and that this segmentation influences the characteristics of seismic ruptures active faults to the south north and west of the chelungpu fault have distinctly different characteristics faults to the south and north broke the surface during earthquakes in 1906 and 1935 the active changhua fault to the west a blind thrust similar in length to the chelungpu has not ruptured in the historical period and should be considered a prime candidate for generating a future earthquake manuscript received 4 october 2000

slip deficit on the san andreas fault at parkfield california as revealed by inversion of geodetic data a network of geodetic lines spanning the san andreas fault near the rupture zone of the 1966 parkfield california earthquake magnitude m 6 has been repeatedly surveyed since 1959 in the study reported here the average rates of line length change since 1966 were inverted to determine the distribution of interseismic slip rate on the fault these results indicate that the parkfield rupture surface has not slipped significantly since 1966 comparison of the geodetically determined seismic moment of the 1966 earthquake with the interseismic slip deficit rate suggests that the strain released by the latest shock will most likely be restored between 1984 and 1989 although this may not occur until 1995 these results lend independent support to the earlier forecast of an m 6 earthquake near parkfield within 5 years of 1988

the ms 7 3 1992 suusamyr kyrgyzstan earthquake 1 constraints on fault geometry and source parameters based on aftershocks and body wave modeling we investigated the suusamyr kyrgyzstan earthquake of 19 august 1992 using aftershock data teleseismic body wave modeling and field observations aftershocks were recorded by the iris kyrgyzstan broadband network a temporary six station aftershock network and a regional network operated by the kyrgyz institute of seismology the aftershocks which range in depth from the surface to 18 km defined a 50 10 km long rupture zone that dips 50 13 to the south and strikes roughly east west the base of the eastern end of the aftershock zone shallowed to the east along strike and may represent a lateral ramp the surface ruptures also had an east west strike and dipped south but the total length less than 4 km was much shorter than the aftershock zone a teleseismic body wave inversion using a point source and a directivity correction yields a focal mechanism with a strike of 221 dip of 46 and a slip of 43 we obtained a moment of 4 1 1019 n m with a centroid depth between 5 and 21 km the rupture propagated along an azimuth of 330 60 which matches the relative location of the mainshock with respect to the aftershock zone the results of the aftershock study and teleseismic inversion yield a clear picture of the fault geometry of a large thrust earthquake

revealing surface deformation of the 1999 chi chi earthquake using high density cadastral control points in the taichung area central taiwan the 1999 chi chi earthquake m w 7 6 ruptured a major thrust fault along the western foothills of the central mountain range of taiwan here we use cadastral control points to detect horizontal displacement in taichung central taiwan the cadastral control points were used to identify the coordinates of buildings and acreage the coordinates of each point are measured by total station and connected to global positioning system gps control points the density of these control points is nearly 36 points km2 and the accuracy of each point is within less than 2 3 cm the government of taiwan measured cadastral control points before and after the chi chi earthquake in the taichung area northern end of the chelungpu fault 1269 control points were measured over a 35 km2 area with most control points being located on the hanging wall of the chelungpu fault on the footwall the displacement is about 1 1 1 2 m toward 123 to 128 which is consistent with gps data at the hanging wall the displacement direction concentrates at 326 to 330 in the eastern section the displacement is from 7 5 to 8 m which is consistent with gps and strong motion data but in the western part displacement changes from 8 m to 4 6 m and then increases again to 8 m along the 326 trending we conclude that the changes in displacements were controlled by the geometry of the fault plane online material horizontal displacement of cadastral control points

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

fault slip inverted from surface displacements during the 1999 chi chi taiwan earthquake we use coseismic surface displacement data to determine the slip distribution on the chelungpu fault during the 1999 chi chi taiwan earthquake the surface displacements were obtained from both gps surveys and integrations of near field strong ground motions the fault rupture is taken as a series of dislocations along the chelungpu fault in a homogeneous elastic half space using this assumption we are able to find both a least squares solution and optimal solutions from genetic algorithm inversion with a step wise rake constraint our results show that with the rake constraint the resulting rupture features are more reasonable and more consistent with geologic observations than with the least squares solution we also evaluate the influence of fault geometry by calculating slip distributions on a simplified 2d fault plane and a more sophisticated 3d fault surface noting that the 3d rupture model can greatly reduce model misfit when compared with the 2d rupture model both models do show however that slip dramatically increases from the hypocenter toward the northern end of the chelungpu fault and that right lateral slip is found at a large asperity near the southern end of the chelungpu fault at depths below 10 km our models predict a much larger average slip than others derived from body wave inversions we interpret this inconsistency to be a result of partitioning of aseismic sliding due to mineral composition state of stress and or frictional heat

a midcrustal ramp fault structure beneath the taiwan tectonic wedge illuminated by the 2013 nantou earthquake series 1 taiwan s active mountain belt is a spotlight for orogenic studies and was first used to test the critical taper wedge mechanics the concept of an orogenic wedge above a shallow detachment surface has been highly influential on current understanding of orogenic processes in taiwan however the recent ml 6 2 and ml 6 5 2013 nantou reverse faulting earthquakes in central taiwan have nucleated below the proposed detachment indicating that active mountain building is occurring below the orogenic wedge we estimate the coseismic slip distributions and fault geometry using the uniform stress drop slip inversions the earthquakes occur on essentially the same 30 dipping fault plane ramping up from 20km depth near a cluster of 1999 chi chi earthquake aftershocks to the shallow detachment and the chi chi fault plane the fault could be a deep extension of a mature shallow fault or a newly developed deep ramp fault that is not reflected in the surface geology

calcareous nannoplankton changes across the early toarcian oceanic anoxic event in the western tethys 1 calcareous nannoplankton were profoundly affected by environmental perturbations coincident with the early toarcian oceanic anoxic event t oae we quantify the abundance of nannofossils across the t oae at three locations in western europe where the event is marked by a prominent negative carbon isotope excursion cie data were treated by statistical analysis and the shannon diversity index was applied in order to describe nannofossil assemblage changes related to paleoenvironmental evolution in the basal toarcian before the t oae high proportions of taxa with an affinity for low temperature e g p liasicus t patulus bussonius occurred this observation is consistent with interpretations of published oxygen isotope records during the t oae the lowest abundance of nannofossils is observed but there is a peak of a coccolith calyculus from an organism that probably thrived in low saline surface waters depleted of nitrate at the end of the perturbation the lowest diversities of nannofossils occurred and assemblages are dominated by crepidolithus crassus a deep dweller this interval corresponded to progressive reoxygenation of deep water and the reoccupation of the deep photic zone by nannoplankton the highest abundance of nannofossils is recorded above the cie and testifies to the recovery of the entire nannoplankton community the t oae was widespread perhaps global and probably linked to major changes in the atmosphere and hydrosphere however the record of this event varies in the basins surrounding the western tethys suggesting regional imprints on the global signal the regional variability may attest to establishment of effective connections between the arctic and tethys oceans which allowed cool low saline water formed at high latitudes to stream toward the western tethys

temporal and spatial variations of post seismic deformation following the 1999 chi chi taiwan earthquake summary we use gps displacements collected in the 15 months after the 1999 chi chi taiwan earthquake m w 7 6 to evaluate whether post seismic deformation is better explained by afterslip or viscoelastic relaxation of the lower crust and upper mantle we find that all viscoelastic models tested fail to fit the general features in the post seismic gps displacements in contrast to the satisfactory fit obtained with afterslip models we conclude that afterslip is the dominant mechanism in the 15 month period and invert for the space time distribution of afterslip using the extended network inversion filter our results show high slip rates surrounding the region of greatest coseismic slip the slip rate distribution remains roughly stationary over the 15 month period in contrast to the limited coseismic slip on the

a calcareous nannofossil and organic geochemical study of marine palaeoenvironmental changes across the sinemurian pliensbachian early jurassic 191 ma in portugal the sinemurian pliensbachian boundary 191 ma is acknowledged as one of the most important steps in the radiation of planktonic organisms especially primary producers such as dinoflagellates and coccolithophores to date there is no detailed study documenting changes in planktonic assemblages related to palaeoceanographic changes across this boundary the aim of this study is to characterize the palaeoenvironmental changes occurring across the sinemurian pliensbachian boundary at the sao pedro de moel section lusitanian basin portugal using micropalaeontology and organic geochemistry approaches combined calcareous nannofossil assemblage and lipid biomarker data document for a decrease in primary productivity in relation to a major sea level rise occurring above the boundary the lusitanian basin was particularly restricted during the late sinemurian with a relatively low sea level a configuration that led to the recurrent development of black shales after a sharp sea level fall the basin became progressively deeper and more open during the earliest pliensbachian subsequently to a major transgression this sea level increase seems to have been a global feature and could have been related to the opening of the hispanic corridor that connected the tethys and palaeo pacific oceans the palaeoceanographic and palaeoclimatic changes induced by this opening may have played a role in the diversification of coccolithophores with the first occurrence or colonization of tethyan waters by placolith type coccoliths

conditions of high grade metamorphism in the dalradian of connemara ireland in e connemara ireland dalradian metasediments were initially metamorphosed to kyanite staurolite grade at pressures above 7kbar the subsequent emplacement of basic to intermediate magmas accompanied by uplift and erosion produce a steepening of the geothermal gradient and led to the formation of migmatitic garnet cordierite sillimanite gneisses in the highest grade regions in the s cation exchange equilibria between coexisting mineral pairs suggest that partial melting took place under high temperatures 750 c and moderate pressures 4 5 6 kbar fluid inclusion studies and andalusite occurrences from migmatite leucosomes suggest that crystallization of the melts occurred at lower pressures

slip distribution and tectonic implication of the 1999 chi chi taiwan earthquake we report on the fault complexity of the large m w 7 6 chi chi earthquake obtained by inverting densely and well distributed static measurements consisting of 119 gps and 23 doubly integrated strong motion records we show that the slip of the chi chi earthquake was concentrated on the surface of a wedge shaped block the inferred geometric complexity explains the difference between the strike of the fault plane determined by long period seismic data and surface break observations when combined with other geophysical and geological observations the result provides a unique snapshot of tectonic deformation taking place in the form of very large 10m displacements of a massive wedge shaped crustal block which may relate to the changeover from over thrusting to subducting motion between the philippine sea and the eurasian plates

ramp flat basement structures of the zagros mountains inferred from co seismic slip and afterslip of the 2017 mw7 3 darbandikhan iran iraq earthquake abstract the november 2017 mw7 3 darbandikhan earthquake in the northern zagros mountains of iran iraq was the largest instrumentally recorded earthquake to date in this mountain belt despite extensive research in this region the nature of active faults in the arabian basement beneath the zagros mountains is largely unresolved additionally there is active debate regarding the interaction of thin and thick skin shortening of the zagros and whether these processes are accommodated seismogenically here we use interferometric synthetic aperture radar insar of co and post seismic surface displacements to document the source of the darbandikhan earthquake and the first 120 days of afterslip following the earthquake we apply a fault inversion approach that finds permissible geometries locations and slip depths as a means to image subsurface structure with remote sensing geodesy we find that the darbandikhan earthquake ruptured the shallowly dipping 14 19 mountain front fault within the arabian crystalline basement 12 22 km deep we additionally find that afterslip propagated up dip of the earthquake onto the nearly horizontal dip 1 5 basal decollement of the zagros mountains indicating that the earthquake and its initial afterslip activated a ramp flat structure we also inverted co seismic insar displacements of the january 11 2018 mandali earthquake sequence that occurred 80 km south of the darbandikhan earthquake and find that these moderate magnitude events mw5 0 5 5 ruptured the lower phanerozoic cover of the zagros together the darbandikhan and mandali sequences demonstrate that the zagros mountains actively shorten via both thin and thick skin styles and that these modes of shortening are accommodated in part by earthquakes moreover the darbandikhan earthquake and afterslip highlight the presence of seismically active low angle thrust faults beneath the zagros that were not previously recognized highlighting sources for potential future large earthquakes we compare these results to the 2015 gorkha nepal earthquake to argue that frictional characteristics of decollement govern spatial relationships between seismic and aseismic slip in ramp flat geometries

the fractal geometry of the surface ruptures of the 1999 chi chi earthquake taiwan summary the 1999 september 20 chi chi earthquake is the largest seismic event which occurred in the island during the twentieth century available seismic data relative to this earthquake are of high quality and surface ruptures identified as features associated to the chelungpu fault can be clearly observed at the surface and precisely mapped we calculated the fractal dimension d and b value of gutenberg richter law for 6 month aftershocks of the chi chi earthquake for the fault area and find that the surface ruptures exhibit self similar geometry only within specific ruler intervals the d values of the surface ruptures reflect the fault slip and geometry at depth more importantly the small size aftershocks seem more likely to occur within high d value and high b value areas whereas small d value and small b value areas have a high potential for medium and large size aftershocks

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

environmental controls on clay mineralogy of an early jurassic mudrock blue lias formation southern england we present a dataset including clay mineralogy gamma ray spectrometry organic matter content and magnetic susceptibility of the hettangian to lowest sinemurian successions of dorset and somerset southern uk blue lias formation bristol channel and wessex basins in both areas the clay assemblages comprise predominantly detrital illite kaolinite and illite smectite mixed layers clays probably originated from the erosion of the hercynian massifs the relative proportions of kaolinite and illite being modulated by arid humid climatic fluctuations the organic matter om content types ii to iv ranges up to 12 in both areas a clear stratigraphical trend in clay mineral assemblages is apparent in somerset whereas in dorset sharp contrasts between adjacent horizons and a greater dilution by carbonate mask the long term evolution correlations between both areas based on similar vertical trends in clay mineral abundance support the suggestion of a hiatus within the angulata zone of the dorset succession as expected the kaolinite illite ratio correlates with the th k ratio deduced from gamma ray spectrometry however significant departures from the correlation occur in om rich intervals suggesting that th may be partly adsorbed on to om particles surprisingly high magnetic susceptibility correlates with abundant kaolinite not with fe rich clays indicating either that kaolinite is accompanied by a soil inherited magnetisable phase possibly iron oxide or that illite rich rocks are more strongly diluted by carbonate than are kaolinite rich strata

two dimensional crustal structures of taiwan from gravity data to delineate the tectonic character of taiwan an island wide gravity survey of taiwan was conducted between 1980 and 1987 the bouguer anomaly map shows that in general isogals trend nne in consonance with the overall structural trend of the island with seismic and other geophysical data as constraints the subsurface density structures were modeled along three profiles across the major structural trends the gravity data are consistent with average continental moho depths of 26 km in the coastal plain and the western foothills 28 km underneath the coastal range in eastern taiwan and 33 km under the central range a lack of significant correlation of the bouguer anomalies with the topography implies dynamic rather than isostatic support of topography in the taiwan region

a blind thrust and overlying folding earthquake of the 2016 mw 6 0 hutubi earthquake in the northern tien shan fold and thrust belts china

spatial and temporal evolution of b values before large earthquakes in taiwan abstract we investigate the spatial and temporal variations of b values before twenty three earthquakes with ml 6 0 in the taiwan region from 1999 to 2009 we estimate the spatial distribution of b values within a one year period before the occurrence of investigated earthquakes it shows that the epicenters of those earthquakes are located predominately in the regions with low b values relative to the entire study area in terms of temporal evolutions the b values are slightly lower during the year prior to the investigated earthquakes in comparison to the periods two to five years earlier we propose that these anomalies may offer spatiotemporal constraints for the earthquake forecasting in taiwan in the future

quasi static propagator matrices creep on strike slip faults abstract this paper presents a method for computing viscoelastic flow in a layered earth by means of quasi static propagator matrices the method has advantages over approximate or purely numerical attacks in that exact semi analytical solutions are obtained the procedure enables a more rapid calculation than is possible with finite elements yet it does not sacrifice exactness as do analytical approximations to illustrate the technique i constructed a plausible model of the san andreas fault and investigated the time and space behavior of displacement displacement rate shear stress and shear strain rate at depth as well as at the surface viscoelastic relaxation speeds the restressing of the fault for events of magnitude 6 2 and 6 9 viscoelasticity reduces recharge time relative to the base strain rate by 15 and 50 respectively for events of magnitude 6 2 and less viscoelasticity has only a small influence and a linear extrapolation of stress accumulation will predict the time of recharge reasonably well relative plate velocities measured within 400 km of the fault are highly variable in space and time direct plate velocity measurements made as far as 100 km from a major fault could differ by a factor of two from the average rate features of the fault model at depth include stresses and strain rates which exceed surface values by a factor of three sign reversals in strain rates and positive coseismic stress drops induced for limited periods in narrow thin zones the latter feature could initiate and terminate aftershock sequences stress recharge does not occur simultaneously at all depths on the fault for all magnitude events recurrence times of earthquakes estimated from surface observations may thus be biased

effects of superficial layers on coseismic displacements for a dip slip fault and geophysical implications summary we study the effect of a superficial layer overlying a half space on the surface displacements created by a dip slip dislocation on a planar rectangular fault using a 2 d finite element model the effect of the density and poisson s ratio is negligible on the other hand the contrast in young s modulus between the top layer and the half space below significantly affects the modelled coseismic displacements the horizontal displacements are more sensitive than the vertical displacements to the existence of the top layer near the fault a low rigidity layer with a young s modulus of 10 gpa can increase the horizontal displacements by up to 40 per cent an analytical 3 d half space model is used to interpret this effect in terms of an equivalent homogeneous model the presence of a top layer can be partly simulated in a homogeneous half space by perturbing the depth and the slip on the fault from their real values to equivalent values for a given displacement field observed at the surface the perturbations in fault depth and slip can reach 1 km and 25 per cent respectively the fault dip angle is not model dependent we conclude that for the accurate estimation of fault depth and slip from coseismic geodetic data rigidity contrasts existing within the upper crust must be taken into account not taking into account the effect of an existing low rigidity layer also leads to an underestimation of seismic moment release this may in part be the cause of apparent discrepancies between seismic and geodetic moment releases in particular areas such as the gulf of corinth greece

fault rupture process of the 20 september 1999 chi chi taiwan earthquake we modeled the source rupture process of the 20 september 1999 chi chi taiwan earthquake mw 7 6 using an integrated dataset of near field strong ground motion and global positioning system observations this large inland thrust earthquake produced a surface break more than 80 km long along the chelungpu fault the event triggered over 700 strong motion instruments on the island of tai wan this large ground motion dataset provides the best opportunity to date to un derstand earthquake source processes in a major earthquake first we develop a 3d curved fault model consistent with the surface rupture data and aftershock distribu tion the subsurface fault plane has an average dip of 30 to the east and measures 96 km along strike and 40 km down dip next we applied a genetic algorithm to reconstruct the source rupture process the inversion results indicate a complex slip distribution with a generally broad triangular shaped slip zone that points down dip most of the displacement occurred over a 15 km depth range in the northern segment of the fault with the maximum slip exceeding 20 m the average slip is 3 8 m and the average rupture velocity is 2 6 km sec the mainshock slip distribution clearly complements the aftershock location distribution slip rise times range from 8 to 6 sec over most of the primary slip area and decrease slightly as rupture propagates south to north this relatively long rise time resulted in a low dynamic stress drop and low peak ground accelerations observed at surface stations the rake angle rotates across the rupture plane from predominantly dip slip in the southern segment to mostly left lateral oblique slip in the north we find that geometrical irregularities over the fault plane played an important role in controlling the temporal rupture behavior at fault bends rupture tends to decelerate the rake angle rotates to a near dip slip orientation and the shear stress increases as rupture tries to overcome the bending barriers the total seismic moment from our inversion is 2 9 10 27 dyne cm in good agreement with the harvard and the u s geological survey moment estimation

increased capture of magma in the crust promoted by ice cap retreat in iceland retreating ice caps overlying volcanoes are thought to relieve surface pressure causing enhanced magma generation and volcanic activity analysis of crustal stress during a dyke intrusion event associated with retreat of iceland s largest ice cap indicates that ice retreat could instead promote storage of magma in the crust rather than eruption at the surface

preseismic deformation and coseismic displacements associated with the 1999 chi chi taiwan earthquake the destructive 1999 chi chi taiwan earthquake m w 7 5 produced an approximately 100 km long surface rupture mostly along the previously recognized north south trending chelungpu fault preseismic deformation in central taiwan is realized from annually repeated global positioning system gps data acquired during the 1992 1999 period the total wnw ese shortening rate in the vicinity of the epicentral region that is from the west coast to the western boundary of the central range is up to 25 mm yr the crustal deformation before the chi chi earthquake was essentially a uniaxial compressional strain of 0 36 strain yr in the direction of 114 the gps measurements taken 0 2 2 7 yr before and within 3 months after the mainshock were utilized to estimate the coseismic displacements horizontal movements of 1 1 9 1 m in the nw nnw directions are observed on the hanging wall eastern side of the fault there is a northward increasing trend in the magnitude of the displacement vectors and a dramatic change in the direction of about 50 toward the east along the fault strike in contrast much smaller se see movements of 0 1 1 5 m are found on the footwall western side of the fault the gps data show 2 4 10 1 m of total horizontal offsets across the chelungpu fault vertical offsets of 1 2 4 4 m with the eastern side up are also observed along the surface rupture the uplift on the hanging wall decreases rapidly toward the east it becomes subsidence at sun moon lake and in the puli wushe area the stations on the footwall show subsidence of 0 02 0 26 m the width of the uplift zone increases from about 10 km in the south to approximately 30 km in the north manuscript received 13 october 2000

time lapse imaging of coseismic ruptures for the 2019 ridgecrest earthquakes using multiazimuth backprojection with regional seismic data and a 3 d crustal velocity model

fault geometry and slip distribution of the 1999 chi chi taiwan earthquake imaged from inversion of gps data gps measurements of coseismic displacements from the 1999 chi chi taiwan earthquake are modeled using elastic dislocation theory we find that a single fault plane cannot fit the data but rather a curved fault surface consisting of multiple segments dipping 20 25 best fits the observations the model fault exhibits reverse and left lateral slip on a 75 km long n s trending segment and reverse and right lateral slip on a 25 km e w trending segment at the northern end of the rupture the 21 dipping e w segment is inconsistent with previous interpretations of high angle tear faulting

why does the co seismic slip of the 1999 chi chi taiwan earthquake increase progressively northwestward on the plane of rupture the chi chi 1999 earthquake ruptured the out of sequence chelungpu thrust fault ctf in the fold and thrust belt in western central taiwan an important feature of this rupture is that the calculated slip increases approximately linearly in the se nw convergence plate direction from very little at its deeper edge to a maximum near the surface we propose here a new explanation for this co seismic slip distribution based on the study of both stress and displacement over the long term as well as over a seismic cycle over the last 0 5 my the convergence rate in the mountain front belt is accommodated by the frontal changhua fault ch f the ctf and the shuangtung fault sh f based on previously published balanced cross sections we estimate that the long term slip of the ch f and of the ctf accommodate 5 30 and 30 55 of the convergence rate respectively this long term partitioning of the convergence rate and the modeling of inter seismic and post seismic displacements suggest that the peculiar linear co seismic slip distribution is accounted for by a combination of the effect of the obliquity of the ctf to the direction of inter seismic loading and of increasing aseismic creep on the deeper part of the ch f and ctf many previous interpretations of this slip distribution have been done including the effects of material properties lubrication site effect fault geometry and dynamic waves the importance of these processes with respect to the effects proposed here is still unknown taking into account the dip angle of the ctf asperity dynamic models have been proposed to explain the general features of coseismic slip distribution in particular recent works show the importance of heterogeneous spatial distribution of stress prior to the chi chi earthquake our analysis of seismicity shows that previous large historic earthquakes cannot explain the amplitude of this heterogeneity based onour approach we rather think that the highstress in the northern part ofthe ctf proposed by oglesby and day oglesby d d day s m 2001 fault geometry and the dynamics of the 1999 chi chi taiwan earthquake bull seismol soc am 91 1099 1111 reflects the latitudinal variation of inter seismic coupling due to the obliquity of the ctf d 2004 elsevier b v all rights reserved

fault related folding a review of kinematic models and their application abstract folding that is directly related to fault activity is an important deformation feature that occurs all over the world in mountain belts accretionary wedges fold and thrust belts and intra plate settings in either strike slip compressional or extensional regimes due to their widespread occurrence knowledge about the development of these structures is important to a broad spectrum of geoscience sub disciplines such as structural geology seismology geomorphology petroleum geology and quaternary geology fault related folding has been analyzed intensively over the last 140 years for the sake of this review we divide the folds according to the way the faults and the folds form that is into detachment fault bend and fault propagation folds all fault related folds are caused by changes in fault parameters the simplest method to produce folds is to transport material along faults that have stepped flat ramp flat geometries fault bend fold alternatively the slip can decrease along the length of the fault and depending on whether the fault remains within a detachment layer or steps up through mechanical stratigraphy either a detachment fold or a fault propagation fold is formed respectively detachment folding was first investigated in the early 20th century whereas the full significance of fault propagation folds was recognized quite late in the 1980s seminal work on fault related folding was carried out in the 1930s but quantitative kinematic models have only been available in the last 30 years these models are extremely valuable because they allow a comprehensive understanding of the evolution of fault related folds and lead to more accurate predictions of the sub surface structure from the mid 1990s onwards numerical simulations have been used to identify how fault parameters such as dip and fault bend angle propagation to slip ratio and shape of the trishear zone influence the geometry of the related folding this is directly applicable to the analysis of the shape of anticlines produced however this does not mean that fold geometry is uniquely related to fault geometry on the contrary different kinematic approaches can lead to a similar fold shape

inflation detected at mount veniaminof alaska with campaign gps 1 in 2005 a repeat gps campaign was conducted at 12 sites on mt veniaminof volcano and the surrounding region a previous survey in 2002 provided initial locations for the sites the deformation that occurred in the three years between the two surveys consist of 2 4 cm of displacement caused by the northwest convergence of the pacific and north america plates and 0 5 1 cm displacements caused by a deep intrusion that may be associated with eruptive activity in 2003 2005 the site velocities are corrected for compression using a pre existing model for a locked subduction zone and the residuals modeled with volcanic sources in homogeneous and layered material although the data are fit equally well by several source models we nevertheless gain important information about the deformation source the best fitting models have depths that range from 3 to 17 km

source process of the chi chi earthquake a joint inversion of strong motion data and global positioning system data with a multifault model the chi chi taiwan earthquake of 21 september 1999 was a large thrust earthquake that caused disastrous damage the surface fracture trace runs along the chelungpu fault which strikes n5 e along most of the faulting area but turns to the northeast while approaching its northern end it finally presents a horsetaillike faulting system and bends to an east northeast direction at the northern end both strong motion and global positioning system gps data recorded large displace ments in the northern part in this study we use a multifault model to simulate the observed large strong motion and gps data the results of the joint inversion reveal that in the southern part slip occurred mainly in the shallow portion reaching a maximum about 20 m on the ene fault where the rupture propagated to the deep part of the fault there was obviously slip vector rotation from south to north such that the slip on the branched fault plane was almost purely reverse faulting the seismic moment a total of 2 7 10 20 n m was released in less than 40 sec during the mainshock aftershocks occurred mainly in areas where little or no slip occurred slip vector rotation can be explained by the complexity of regional tectonic stress changes in tectonic stress at the northern end of the fault inhibited the northward propagation of the rupture and favored the rupturing of the ene fault