seismic evidence for an earthquake nucleation phase near source observations show that earthquakes initiate with a distinctive seismic nucleation phase that is characterized by a low rate of moment release relative to the rest of the event this phase was observed for the 30 earthquakes having moment magnitudes 2 6 to 8 1 and the size and duration of this phase scale with the eventual size of the earthquake during the nucleation phase moment release was irregular and appears to have been confined to a limited region of the fault it was characteristically followed by quadratic growth in the moment rate as rupture began to propagate away from the nucleation zone these observations suggest that the nucleation process exerts a strong influence on the size of the eventual earthquake

finite faults and inverse theory with applications to the 1979 imperial valley earthquake abstract using a representation theorem from elastodynamics subsurface slip on a known fault is formulated as the solution to an inverse problem in which recorded surface ground motion is the data two methods of solution are presented the least squares method which minimizes the squared differences between theory and data and the constrained least squares method which simultaneously maintains a set of linear inequalities instabilities in the solution are effectively eliminated in both methods and the sensitivity of the solution to small changes in the data is quantitatively stated the inversion methodology is applied to 77 components of near field ground acceleration recorded during the 15 october 1979 imperial valley earthquake the faulting is constrained to propagate bilaterally away from the epicenter at an average velocity of 90 per cent of the shear wave speed on a vertical fault plane extending from the surface to 10 km depth inequality constraints are used to keep the faulting sequence physically reasonable by maintaining right lateral motion and positive slip velocity the preferred solution is stable and provides a good fit to the data it is also realistic and consistent with observed surface offsets and independent estimates of seismic moment

observation of the seismic nucleation phase in the ridgecrest california earthquake sequence near source observations of five m 3 8 5 2 earthquakes near ridgecrest california are consistent with the presence of a seismic nucleation phase these earthquakes start abruptly but then slow or stop before rapidly growing again toward their maximum rate of moment release deconvolution of instrument and path effects by empirical green s functions demonstrates that the initial complexity at the start of the earthquake is a source effect the rapid growth of the p wave arrival at the start of the seismic nucleation phase supports the conclusion of mori and kanamori 1996 that these earthquakes begin without a magnitude scaled slow initial phase of the type observed by iio 1992 1995

new insights on 3 d plates interaction near taiwan from tomography and tectonic implications abstract recent tomographic results are used to trace the south china sea and philippine sea subducting slabs south and northeast of taiwan along the manila and ryukyu trenches respectively in particular the 3 d plates interaction beneath taiwan is discussed based on a close up view of the tomographic sections together with earthquake hypocenters distribution our study indicates that 1 the east dipping south china sea slab can be followed to the north up to the latitude of hualien 2 the eurasian plate subducts beneath most part of the taiwan island down to the 670 km depth discontinuity 3 the north dipping philippine sea slab can be followed slightly west of the longitude of hualien both plates thus interact beneath northern taiwan where the arc continent collision is paroxysmal 4 slab detachment is envisaged at the northern edge of the subducted eurasian plate beneath the coastal range of taiwan which may facilitate the northwestward motion of the philippine sea plate with respect to eurasia slabs geometries obtained from tomographic sections allow us to reconstruct the late neogene plate kinematics and dynamics in this region our main conclusions are 1 the size of the original south china sea was about twice its present size 2 the subducted part of the west philippine basin i e the largest oceanic basin of the philippine sea plate extends only 400 km north of the ryukyu trench 3 slab detachment might have occurred 3 5 my ago beneath the central and northern ryukyu arc along a weak zone that is aligned with the gagua ridge an ancient plate boundary 4 the ryukyu trench has propagated westward from 126 e of longitude southeast of miyako island to the locus of the present arc continent collision along a major lithospheric tear that cut through the continent ocean boundary first and then through the continental lithosphere as a consequence the southern ryukyu margin developed progressively from east to west as a subduction zone during the last 8 my it has been elaborated onto a passive margin which corresponded to the edge of the eurasian continental shelf bordering the south china sea prior to pliocene 5 the southern okinawa trough rifted during the last 2 1 ma following the propagation of the subduction zone 6 subduction of the eurasian margin probably stopped recently beneath northern taiwan and a flip of subduction from west to east is being initiated near hualien

present day crustal motion along the longitudinal valley fault eastern taiwan abstract the nne striking longitudinal valley fault lvf in eastern taiwan is an extremely active high angle thrust fault it bounds the coastal range and the longitudinal valley which is considered a collision boundary between the philippine sea and the eurasian plates repeated gps data in the longitudinal valley area from 1992 to 1999 are utilized to study the spatial variation of crustal motion along the lvf with respect to penghu in the chinese continental margin velocities for stations on the western side of the lvf longitudinal valley and eastern central range are 18 35 mm yr in directions 283 311 whereas those on the eastern side of the lvf the coastal range are 28 68 mm yr in directions 303 324 a major discontinuity of about 30 mm yr on the rate of crustal motion across the longitudinal valley is attributed to the aseismic slip along the lvf as revealed by trilateration data previously to the south of fengping the block motions of the coastal range are 31 40 mm yr in 317 330 relative to the central range while the near fault motions are 13 33 mm yr in 309 336 various partitions on the left lateral strike slip and convergent components along the lvf are found in the southern longitudinal valley crustal motion is mainly accommodated on the lvf and the luyeh fault in contrast those in the central and northern longitudinal valley are partly taken up on the faults to the east of the lvf or result in the elastic deformation of the coastal range the crustal motion in the northern longitudinal valley area is likely to be distributed in the several ne striking thrusts in a horsetail pattern and obliquely cut the northern coastal range with a small portion of fault slips along the lvf data from dense deployed gps networks across the lvf can be employed to give better estimates of near fault motions and delineate the surface traces of the lvf repeated gps and leveling data from two stations on both ends of the yuli bridge that are 575 m apart clearly indicate that the surface trace of the lvf passes beneath the bridge with oblique horizontal motion of 23 mm yr in 306 and uplift rate of 24 mm yr

2003 mw6 8 chengkung earthquake and its related seismogenic structures abstract the mw 6 8 chengkung earthquake on december 10 2003 in eastern taiwan was associated with abundant aftershocks to explore the seismogenic mechanism and its causative fault system we relocated the aftershocks determined the focal mechanisms from p wave polarities and used the finite dimension source model method to identify the fault plane based on our results the earthquake can be divided into three seismic clusters one is located in the east of the southern longitudinal valley one on the chihshang fault and the other on the western side of the luyeh fault to the south both the seismic distribution and finite dimension source model method show that east dipping fault planes with thrust mechanisms coincide with previous studies based on background seismicity the third seismic cluster suggests thrust mechanism along west dipping fault plane that was not recognized by background seismicity this seismic cluster occurred along the central range fault previously proposed as active by geomorphic and geologic evidence

hypocenter locations in finite source rupture models we use a database of more than 80 finite source rupture models for more than 50 earthquakes m w 4 1 8 1 with different faulting styles occurring in both tectonic and subduction environments to analyze the location of the hypocenter within the fault and to consider the correlation between hypocenter location and regions of large slip rupture in strike slip and crustal dip slip earthquakes tends to nucleate in the deeper sections of the fault subduction earthquakes do not show this tendency ratios of the hypocentral slip to either the average or the maximum slip show that rupture can nucleate at locations with any level of relative displacement rupture nucleates in regions of very large slip d 2 3 d max in only 16 of the events in regions of large slip 1 3 d max d d max in 35 of the events and in regions of low slip d 1 3 d max in 48 of the events these percentages significantly exceed the percentages of fault area with very large 7 and large 28 slip ruptures that nucleate in regions of low slip however tend to nucleate close to regions of large slip and encounter a zone of very large slip within half the total rupture length applying several statistical tests we conclude that hypocenters are not randomly located on a fault but are located either within or close to regions of large slip

seismogenic structure in a tectonic suture zone with new constraints from 2006 mw6 1 taitung earthquake 1 a mw 6 1 earthquake occurred on april 1st 2006 near taitung eastern taiwan it produced significant coseismic ground displacements and a large number of aftershocks in the ensuing month this event provides an opportunity to diagnose the seismogenic structure in the southern longitudinal valley lv of eastern taiwan long viewed as one of the collision sutures between the philippine sea and the eurasian plates with precisely relocated main and aftershock hypocenters focal mechanisms for m 3 8 events and coseismic ground displacements from strong motion records we determine a main shock dislocation model our results indicate that the main shock occurred on a high angle fault azimuth 198 dip 77 the model comprises a fault with two segments the main shock and a large number of aftershocks are associated with the northern segment that exhibited predominantly left lateral strike slip motion in agreement with p wave first motions and waveform usgs solutions the southern segment exhibits a slightly larger thrust component in agreement with cmt solutions tectonically this event highlights a nne trending fault on the west side of the lv which is predominantly strike slip the aftershocks clustered to the east of the main shock which exhibit mainly thrust mechanisms indicate that shortening is still acting on the sedimentary materials deposited between the coastal and central ranges prior to collision as a result the southern lv is undergoing slip partitioning along different faults which has never been specified before

experimental hydration of natural volcanic clinopyroxene phenocrysts under hydrothermal pressures 0 5 3 kbar water is a key parameter in mantle rheology magma genesis magma evolution and resulting eruption styles because it controls the density and the viscosity as well as the melting and crystallization behavior of a melt the water content in nominally anhydrous minerals nams such as clinopyroxene recently has been used as a proxy for magmatic water contents nams however may dehydrate during magma degassing and eruption we performed rehydration experiments on potentially degassed clinopyroxene phenocrysts from various volcanic settings the experiments were conducted in hydrogen gas at 1 atm or hydrothermal pressures ranging from 0 5 to 3 kbar to test the incorporation of water into natural clinopyroxene under water fugacities similar to those in a volcanic system our results show a dependence of the water content in the clinopyroxene crystals with pressure as the phenocrysts begin to dehydrate upon lower water fugacities in the experiments water loss or gain in a crystal occurs according to the relatively fast redox reaction oh fe 2 o 2 fe 3 h 2 which was confirmed by mossbauer spectroscopy the kinetics of this redox process are independent of pressure and thus water fugacity water contents in rehydrated clinopyroxene crystals can be related to magmatic water contents at various levels in a volcanic system our results thus show that the water content in erupted clinopyroxene phenocrysts cannot be taken for granted to be representative of magmatic water contents prior to magma degassing the conducted experiments indicate the simultaneous dehydration of clinopyroxene along with magma ascent and degassing rehydration experiments under hydrothermal pressures however may be able to reconstruct clinopyroxene water contents at crystallization prior to dehydration

geomorphology of the southernmost longitudinal valley fault implications for evolution of the active suture of eastern taiwan in order to understand fully the deformational patterns of the longitudinal valley fault system a major structure along the eastern suture of taiwan we mapped geomorphic features near the southern end of the longitudinal valley where many well developed fluvial landforms record deformation along multiple strands of the fault our analysis shows that the longitudinal valley fault there comprises two major strands the luyeh strand on the west has predominantly reverse motion the peinan strand on the east has a significant left lateral component between the two strands late quaternary fluvial sediments and surfaces exhibit progressive deformation the luyeh strand dies out to the north where it steps to the east and joins the peinan strand to become the main strand of the reverse sinistral longitudinal valley fault to the south the luyeh strand becomes an e w striking monocline this suggests that the reverse motion on the longitudinal valley system decreases drastically at that point the longitudinal valley fault system is therefore likely to terminate abruptly there and does not seem to connect to any existing structure further to the south this abrupt structural change suggests that the development of the longitudinal valley suture occurs through discrete structural jumps rather than by a continuous northward maturation

continuous monitoring of an active fault in a plate suture zone a creepmeter study of the chihshang fault eastern taiwan abstract data from continuously monitored creepmeters across the active chihshang fault in eastern taiwan are presented the chihshang fault is an active segment of the longitudinal valley fault the main suture between the converging philippine and eurasian plates in taiwan since the 1951 earthquake mw 7 0 no earthquake larger than magnitude 6 0 occurred in the chihshang area at least during the last 20 years the chihshang fault underwent a steady creep movement resulting in numerous fractures at the surface five creepmeters were installed in 1998 at two sites tapo and chinyuan within the chihshang active fault zone one year results from august 1998 to july 1999 show a horizontal shortening of 19 4 0 3 mm and 17 3 0 7 mm at tapo and chinyuan respectively these annual shortening rates are in a good agreement with other estimates of strain rate independently obtained from geodetic measurements and geological site investigation the creepmeter measurements were made on a daily basis providing accurate information on the previously unknown evolution of creep during the year the records of fault creep at the tapo site thus revealed close seasonal correlation with average rainfall the period of high creep rate coincides with the wet season whereas that of low creep rate coincides with the dry season also in comparison with the tapo site the creep behaviour as a function of time is complex at the chinyuan site possible factors of irregularity are under investigation thermal effect acting on the concrete basement of the creepmeters earth tide effect water table variations in a nearby rice field and rainfall the comparison between gps measurements across the longitudinal valley 31 mm year of horizontal displacement and the creepmeter measurement across the chihshang fault zone 17 19 mm year of horizontal displacement suggests that there exists other shortening deformation across the active fault zone in addition to those we have measured from the creepmeters

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

determining fault geometry from the distribution of coseismic fault slip related to the 2006 taitung earthquake eastern taiwan on 1 april 2006 the taitung earthquake m w 6 1 occurred in taiwan at the boundary between the philippine sea and eurasian plates where high convergence rates contributed to the development of plio pleistocene orogeny in the region from the joint inversion of seismic and geodetic data we identified the event s fault geometry and reconstructed the distribution of coseismic fault slip we modeled fault geometries with increasing complexity and selected the model that best reproduced all datasets simultaneously even though the earthquake magnitude was moderate rupturing occurred in two steps the initial rupture was generated on a listric north south trending fault for which dip decreases with increasing depth and was immediately followed by movement along a perpendicular structure that cross cuts the main fault at 5 km south of the earthquake hypocenter the average slip along the rupture was 30 cm with a maximum of 87 cm oblique reverse fault movement was characterized by a predominant left lateral component the amount of slip is well constrained for offsets of more than 5 cm with an associated uncertainty of 32 for slip amounts greater than 5 cm uncertainties on rake and rupture time are 11 and 0 54 s respectively the rupture propagated from the hypocenter bilaterally moving slightly faster toward the south 2 5 0 4 km s than to the north 1 7 0 1 km s to the south the rupture was rapidly transmitted upward at the junction with the cross cutting east west segment whereas in the north the rupture remained confined to the lower segment of the main fault from global positioning systems gps and seismic data time window 1 min we infer that the cross cutting segment was activated following coseismic rupture on the main north south fault yet close enough in time to be associated with coseismic movement acquired by gps daily solutions

fmnear determination of focal mechanism and first estimate of rupture directivity using near source records and a linear distribution of point sources abstract the fmnear method is based on both the waveform inversion of near source seismic records and on a linear finite source model the primary source parameters that are determined are the moment magnitude m w the double couple focal mechanism strike dip and rake and the distribution of seismic moment along strike which provides a first order estimate of rupture length and directivity source depth is also explored an advantage of the approach is the use of the finite source model directly within the search of the focal mechanism this strategy allows the inclusion of strong motion records at short distances for moderate to very large earthquakes m w 5 5 however for moderate to small earthquakes m w m w 4 5 to 9 0 test cases incorporate continental events recorded by a large number of well distributed stations and less favorable cases in its present form the fmnear approach is very well adapted to continental earthquakes surrounded by seismic stations but it can also give informative results in more difficult configurations the fmnear method is now ready for fully automated determinations and is already implemented in near real time online material details on inversion parameters flow charts of the fmnear method figures of waveform modeling and sensitivity for selected events and table of velocity models

shear concentration in a collision zone kinematics of the chihshang fault as revealed by outcrop scale quantification of active faulting longitudinal valley eastern taiwan abstract repeated measurements of active deformation were carried out at three sites along the active chihshang fault a segment of the longitudinal valley fault zone of eastern taiwan the present day plate boundary between the philippine sea plate and eurasia reliable annual records of displacement along an active fault were obtained based on detailed surveys of faulted concrete structures along the active chihshang fault striking n18 e we determined average motion vectors trending n37 w with an average shortening of 2 2 cm yr thus the transverse component of motion related to westward thrusting is 1 8 cm yr whereas the left lateral strike slip component of motion is 1 3 cm yr the fault dips 39 45 to the east so that the vertical displacement is 1 5 3 cm yr and the actual oblique offset of the fault increases at a rate of 2 7 3 7 cm yr this is in good agreement with the results of regional geodetic and tectonic analyses in taiwan and consistent with the n54 w trend of convergence between the northernmost luzon arc and south china revealed by gps studies our study provides an example of extreme shear concentration in an oblique collision zone at chihshang the whole horizontal shortening of the longitudinal valley fault 2 2 cm yr on average occurs across a single narrow fault zone so that the whole reverse slip about 2 7 3 7 cm yr depending on fault dip was entirely recorded by walls 20 200 m long where faults are tightly localized this active faulting accounts for more than one fourth 27 of the total shortening between the luzon arc and south china recorded through gps analyses further surveys should indicate whether the decreasing shortening velocity across the fault is significant revealing increasing earthquake risk due to stress accumulation or not revealing continuing fault creep and weak behaviour of the chihshang fault

quantitative analysis of surface coseismic faulting and postseismic creep accompanying the 2003 mw 6 5 chengkung earthquake in eastern taiwan 1 on the basis of field observations and geodetic measurements we analyzed coseismic and postseismic deformation of the 2003 mw 6 5 chengkung earthquake across the rupture trace of the chihshang fault which lies along the suture zone between the philippine sea plate and the eurasian plate in eastern taiwan at three of our investigation sites along the chihshang fault the earthquake deformation was exhibited by fresh fractures within the 150 to 200 m wide surface fault zone reactivating preexisting fractures in most cases in addition to daily recorded creep meter data geodetic measurements including leveling distance and angle electronic distance meters and gps measurements were carried out during surveys 20 25 days before 20 25 days after and 120 125 days after the earthquake the near fault surface deformation is mainly characterized by anticlinal folding in the hanging wall and minor gentle synclinal folding in the footwall the geodetic data show that within our 150 to 250 m wide networks the coseismic deformation of the main shock produced only about 1 2 cm of horizontal shortening and vertical offset across the fault zone a larger additional displacement of about 7 9 cm for both the horizontal shortening and the vertical offset occurred as postseismic creep during the 120 125 days following the main shock we interpret the predominant folding and the rather large postseismic creep as a result of strong velocity strengthening along the fault plane near the surface which caused locking or coupling effect during the coseismic rupturing the depth of locked segment along which the coseismic and postseismic slip decreased dramatically upward is estimated to be 25 100 m depending on the site we interpreted the velocity strengthening and coupling effect at the shallow level as viscoelastic behavior of unconsolidated deposits in the footwall and melange mudstone in the hanging wall by incorporating far fault continuous gps data it was found that minor but significant deformation occurred outside of the surface ruptures zone of the chihshang fault in addition a possible back thrust or back fold might have occurred in the hanging wall we note that the chengkung earthquake occurred during the dry season this is consistent with the fact that the mechanical coupling of the fault at shallow depth is higher during drier periods inferred from the previous seasonal creep data at outcrop scale regarding damage of construction such as a concrete retaining wall most of the coseismic and postseismic horizontal shortening was essentially absorbed by multiple distributed brittle ruptures which deserves attention in terms of earthquake hazard mitigation

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

geomorphic analysis of the central range fault the second major active structure of the longitudinal valley suture eastern taiwan numerous landforms along the longitudinal valley suture of eastern taiwan indicate that two opposing reverse faults currently dominate the suturing process between the luzon volcanic arc and the central range of taiwan the east dipping longitudinal valley fault on the eastern flank of the valley is well known the west dipping central range reverse fault on the western flank of the valley is more obscure nonetheless it has produced many uplifted lateritic fluvial terraces along the eastern flank of the central range in the central reach of the valley from just north of the wuhe tableland to near chihshang the fault appears to be active but blind south of chihshang and inactive along the northern part of the longitudinal valley the late quaternary slip rate of the fault is less than 12 8 mm yr this constraint means that the fault is absorbing far less than half of the horizontal shortening across the longitudinal valley suture however the late quaternary slip rate along the fault may be comparable to the uplift and exhumation rate of the central range this suggests that localized brittle slip along the central range fault is an important component of crustal thickening and uplift of the range even though additional shortening and crustal thickening may be occurring because of pervasive deformation beneath the range

moment tensor inversion from mednet data 1 large worldwide earthquakes of 1990 we develop a method for the rapid determination of the moment tensor of large worldwide earthquakes by inversion of long period data recorded by the mednet regional network and we apply it to the most significant events of 1990 march 3 fiji and 25 costa rica may 12 sakhalin 20 sudan and 30 romania june 20 iran july 16 luzon and december 30 new britain the comparison with cmts and moment tensors by usgs shows that an advanced regional seismic network is capable of providing reliable and rapid control of the seismic source for worldwide seismicity

seismic cycle and plate margin deformation in costa rica gps observations from 1994 to 1997 global positioning system gps observations in costa rica from 1994 to 1997 reveal a complex pattern of motion consistent with the superposition of seismic cycle and secular plate margin deformation in the south velocity vectors are consistent with motion of the panama block plus postseismic deformation following the 1991 limon earthquake and interseismic strain due to partial locking of the middle america trench mat thrust in the northwest sites west of the volcanic arc are moving to the nw as a forearc sliver superimposed on this sliver motion are vertical and horizontal interseismic deformations from the adjacent nicoya segment of the mat we apply two different inverse methods to understand the source of the seismic strain in nw costa rica we compare fault locking models derived using a singular value decomposition inversion with that of a simulated annealing global optimization approach both methods yield similar models for partial locking of the thrust interface beneath the nicoya peninsula our results define an area of nearly fully locked fault beneath the outer coast of the southern portion of the peninsula with somewhat lower coupling beneath the northern half and with low coupling elsewhere these initial results show the promise for detailed imaging of the locked portion of a thrust interface responsible for future large subduction zone earthquakes

joint inversion of insar gps teleseismic and strong motion data for the spatial and temporal distribution of earthquake slip application to the 1999 izmit mainshock the space time distribution of slip of the 17 august 1999 izmit earthquake is investigated by inverting synthetic aperture radar sar interferometry and global positioning system gps data together with teleseismic broadband and near field strong motion records surface offsets are used as an added constraint special emphasis is given to analysis of the resolution of the different data sets we use a four segment finite fault model and a nonlinear inversion scheme allowing slip to vary in amplitude direction and duration as well as variable rupture velocity from the inversion of synthetic data we find that the best spatial resolution can be expected in the upper half of the fault model above 12 km where coverage of the interferometric sar data is good western half of the rupture and near the gps and strong motion stations teleseismic data are found to have a lower resolution that is more evenly distributed over the fault model the joint inversion of all the data sets has an increased resolving power compared with the separate inversions and gives a more robust description of the space and time distribution of slip our study shows the importance of resolution tests in evaluating the reliability of earthquake kinematic models and it confirms that an excellent fit of a single kind of data does not necessarily imply a good retrieval of the kinematic properties of an earthquake the izmit rupture which is almost pure right lateral strike slip faulting is dominated by the bilateral breaking of a central asperity located between 29 7 e about 10 km west of the city of golcuk and 30 4 e eastern margin of sapanka lake with slip reaching 6 8 m in the depth range 6 12 km the western termination of the rupture is found near the city of yalova but large slip ends around 29 7 e about 10 km east of hersek delta a second area of large slip is required by all the data sets further east toward the city of duzce between 30 7 e and 31 1 e karadere and duzce faults this eastern slip zone which is separated from the main central asperity by an area of greatly reduced slip is less well constrained by the data however a strong motion station near the city of duzce helps to locate a high slip patch near 31 1 e in the depth range 6 12 km the total seismic moment resulting from the joint inversion is 2 4 1027 dyne cm most of the energy release occurred in a short time less than 15 sec corresponding to the bilateral breaking of the central asperity rupture propagation is relatively uniform and fast toward the west with a rupture velocity close to 3 5 km sec propagation of large slip toward the east is initially slower but it accelerates during a short time interval about 10 sec after rupture nucleation eastward progression then slows down to less than 2 km sec after 15 sec and rupture almost vanishes in amplitude ca 20 sec after initiation rupture propagation then proceeds on the easternmost karadere and duzce fault segments east of 30 7 e from 22 to ca 50 sec supershear rupture propagation is not required for modeling the waveforms considered in this study the hypocenter of the duzce earthquake which occurred 3 months later 12 november 1999 m w 7 2 is located in the immediate vicinity of the easternmost slip patch of the izmit earthquake manuscript received 28 july 2000

plate boundary strain partitioning along the sinistral collision suture of the philippine and eurasian plates analysis of geodetic data and geological observation in southeastern taiwan crustal deformation and strain partitioning of oblique convergence between the philippine sea plate and the eurasian plate in the southern longitudinal valley of eastern taiwan were characterized based on geodetic analysis of trilateration network and geological field investigation the longitudinal valley fault one of the most active faults on taiwan branches into two individual faults in the southern longitudinal valley these two active faults bound the plio pleistocene pinanshan conglomerate massif between the coastal range the luzon island arc belonging to the philippine sea plate and the central range the metamorphic basement of the eurasian plate a geodetic trilateration network near the southern end of the valley shows a stable rate of the annual length changes during 1983 1990 the strain tensors for polygonal regions including triangular regions of the taitung trilateration network reveal that there are two distinct zones of deformation a zone of shortening thrusting between the pinanshan massif and the central range on the west and a strike slip movement between the pinanshan massif and the coastal range on the east the analysis of a discontinuity model consisting of three rigid blocks separated by two discontinuities has been carried out the results show that the deformation in this region can be characterized by two major faults a reverse fault is located between the plio pleistocene pinanshan massif and the metamorphic basement of the central range with a shortening rate of about 12 mm yr in the direction n280 e a strike slip fault is located principally along the river between the pinanshan massif and island arc system of the coastal range with a purely strike slip component of about 22 mm yr in the direction n353 e the analysis of the geodetic data further suggests that substantial deformation probably strike slip in type occurs within the pinanshan massif geological evidence of deformation in the plio pliestocene pinanshan conglomerate includes regional folding a conjugate set of strike slip fractures at the outcrop scale and morphological lineaments related to fracturing all indicating that the pinanshan massif is being deformed within a transpressive stress regime regional kinematic data indicate that a significant portion of the 82 mm yr of motion between the eurasian plate and the philippine sea plate is absorbed in the southern longitudinal valley by the decoupling of two distinct major faults the geometry of the oblique convergence and the rheology of the rock units the well consolidated plio pleistocene conglomerate and the sheared melange formation play the two important roles in the partitioning of crust deformation

active fault creep variations at chihshang taiwan revealed by creep meter monitoring 1998 2001 1 the daily creep meter data recorded at chihshang in 1998 2001 are presented the chihshang creep meter experiment was set up across the chihshang thrust fault the most active segment of the longitudinal valley fault which is the present day plate suture between the eurasian and the philippine sea plates in eastern taiwan near continuous data recording at two sites revealed different surface fault motions yet similar annual shortening rates 16 2 mm at the tapo site comprising two connected creep meters and 15 0 mm at the chinyuan site three creep meters straddling parallel fault branches four of the five creep meters showed a seasonal variation with the fault moving steadily during the rainy season from april to october and remaining quiescent during the rest of the year the only exception was recorded by the creep meter located on a melange composed hillslope where local gravitational landsliding played an additional role other than tectonic faulting through comparison with daily precipitation data we inferred that moderate rainfall suffices to trigger or facilitate slippage on the surface fault during the transition period of the dry wet season during the observation period from 1998 to 2001 the subsurface seismicity exhibited clusters of microearthquakes on the chihshang fault at depths of 10 25 km recurrent earthquakes occurred regardless of whether the season was wet or dry indicating that the stress relaxation associated with seismicity in the seismogenic zone did not transfer immediately up to the surface the accumulated strain on the chihshang fault at shallow surface levels was released through creep during the wet season in addition to these short term seasonal variations an apparent decrease in the annual slipping rate on the chihshang fault during the last few years deserves further investigation in order to mitigate against seismic hazard

rupture behavior of a moderate earthquake mw 5 9 april 2006 and its close relation with the 2003 chengkung earthquake mw 6 8 at the southern termination of the plate boundary southeast taiwan the taiwanese orogen is the result of the active and vigorous collision between the eurasian and the philippine sea plates in this strong convergence context a one month long earthquake sequence composed of two mainshocks of magnitude 6 occurred in april 2006 in the taitung area the first mainshock t1 mobilized a structure just west to the plate boundary while the second one t2 is located on the other side in order to retrieve the exact fault geometry of t2 we inverted waveforms from stations located at local and teleseismic distances we performed a grid search on strike and dip each strike dip couple defining a geometry considering the source as a point source then as an extended source in the last case a simple average over stations misfit failed to isolate a precise geometry to overcome this problem we used a more statistical approach on the distribution of misfits to define the best geometry comparing the best model to local structures it appears the generative fault was the plate boundary that rotates from a strike pointing at n20 e north of the event to n0 e in t2 area with an identical eastward dip of 35 for this model the fault slip inversion provides a critical slip of 3 5 cm above which slip rake and rupture time are constrained with uncertainties of 29 14 and 0 47 s respectively the average slip along the rupture was 20 cm with a maximum of 46 13 cm the movement was inverse with a minor left lateral component similar to the faulting behavior of the plate boundary in addition the slip pattern of t2 is contained within the southern portion of the deepest segment of the plate boundary and at the edge of the rupture area of the 2003 chengkung earthquake mw 6 8 a large event also generated by the plate boundary but 2 5 years earlier after 1 s of aseismic spreading the rupture propagated seismically and circularly outward before being stopped by the fault bending

slip distribution on a thrust fault at a plate boundary the 2003 chengkung earthquake taiwan summary the 2003 chengkung earthquake mw 6 8 occurred on the east dipping chihshang fault of eastern taiwan a listric fault with dominant reverse motion a joint inversion taking into account geodetic gps and seismological accelerometric and teleseismic data is performed this modelling highlights the rupture process behaviour on the fault plane at depth the coseismic rupture developed essentially between 12 and 26 km depth expanding laterally by about 30 km towards the ssw two slip patches dominated with slip values exceeding 1 5 m during the 30 s of the whole process the rupture propagation decelerated with time starting at 3 4 0 3 km s 1 in the two main slip patches and ending with velocities below 1 6 0 1 km s 1 the 48 hr of aftershocks that followed the main shock are distributed essentially inside the coseismic slip patches on the fault surface except in the deepest southern part of the fault where slip is less resolved the results of our modelling illustrate the particular behaviour of the 2003 chengkung earthquake where the coseismic slip rapidly diminished towards the surface in good agreement with the observation of fast post seismic slip followed by interseismic creep along the chihshang fault

source tomography by simulated annealing using broad band surface waves and geodetic data application to the mw 8 1 chile 1995 event summary we invert surface wave and geodetic data for the spatio temporal complexity of slip during the mw 8 1 chile 1995 event by simulated annealing this quasi global inversion method allows for a wide exploration of model space and retains the non linearity of the source tomography problem complex source spectra are obtained from 5 to 45 mhz from first and second orbit fundamental mode rayleigh waves using an empirical green s function cross correlation technique coseismic displacement vectors were measured at 10 gps sites near antofagasta they are part of a french chilean experiment which monitors the northern chile seismic gap the spectra together with the geodetic data are inverted for the moment distribution on a 2 d dipping fault under the physical constraints of slip positivity and causality marginal a posteriori distributions of the model parameters are obtained from several independently inverted solutions in general features of the slip model are well resolved data are well fitted by a purely unilateral southward rupture with a nearly uniform velocity around 2 5 3 0 km s 1 and a total duration of 65 s several regions of moment release were imaged one near the hypocentre a major one 80 km south of it and a minor one 160 km south of it the major patch of moment release seemed to have propagated to relatively shallow depths near the trench 100 km ssw of the epicentre the region of major slip is located updip of the 1987 mw 7 5 earthquake suggesting a causal relationship most of the slip occurred updip of the hypocentre 36 km but the entire coupled plate interface 20 40 km ruptured during the chile 1995 event

focal mechanism determination and identification of the fault plane of earthquakes using only one or two near source seismic recordings a waveform inversion scheme was developed in order to explore the resolving power of one or two seismic recordings at short epicentral distance for the determination of focal mechanisms and the identification of the fault plane of earthquakes two key features are used to constrain the fault parameters with a reduced number of stations 1 a simple finite dimension source model and 2 the modeling of the complete displacement field including the near field waves the identification of the fault plane should be possible even with a single station as soon as the seismograms produced by the two nodal planes of a same focal mechanism are significantly different which is the general case when waveforms are controlled by source finiteness seven parameters including the strike dip rake and dislocation are explored with a grid search and the minima of the misfit error between the observed and calculated seismograms are mapped with such an approach it is possible to conclude about the uniqueness or nonuniqueness of the solutions the method is tested with three earthquakes of moderate to large size for which the fault plane is well established and for which strong motion records are available at maximum distances of a few tens of kilometers test events are the 1994 northridge m w 6 7 california the 1996 copala m w 7 3 mexico and the 1996 pinotepa nacional m w 5 4 mexico earthquakes in the case of inversions with two stations we find a unique solution or a group of similar solutions with a good estimation of the focal mechanism and the proper selection of the fault plane our results also show that in some cases a single station may be enough to recover the fault parameters the inversion scheme presented here may be systematically applied to future earthquakes especially to those recorded by few stations it should be particularly useful in the case of blind faults for which the fault plane may not be identified with the help of other data

seismotectonics of taiwan abstract high quality seismicity data and focal mechanism solutions obtained during 1973 1983 by the permanent taiwan telemetered seismographic network and several temporary local seismographic networks are used for a detailed study of the seismotectonics of the taiwan area seismicity distribution in southern taiwan clearly reveals an east dipping benioff zone which has a thickness of about 30 km and begins to deepen along 121 e at a dip angle of 55 60 the leading edge of this benioff zone reaches a depth of about 180 km between 21 n and 22 n but tapers off to a shallower depth of about 100 km from 22 n to 23 n the presence of this seismic zone implies that subduction of the south china sea plate under the philippine sea plate extends from luzon northward to about 23 n the position of the northern boundary of the south china sea plate as tentatively defined according to the seismicity distribution passes through southern taiwan from the offshore area in the taiwan strait west of kaohsiung in an east northeast direction to the taitung area where a triple junction probably lies seismicity is found to disappear abruptly below a certain depth in many parts of taiwan this phenomenon may be attributed to the frictional to quasiplastic transition in the crust or upper mantle comparison of shallow seismicity with surface faults and fractures shows that all areas of active shallow seismicity are marked by densely developed faults and fractures however the converse is not necessarily true this may be partly due to the relatively short duration of seismicity data and partly due to excessive weakening of some of the severely faulted and fractured areas finally focal mechanism solutions for west central taiwan and the kuangfu fuli area in eastern taiwan predominantly show a maximum horizontal compression in the se nw direction which can be related to collision between the eurasian and philippine sea plates however focal mechanism solutions for both the hualien area in eastern taiwan and the tainan area in southwestern taiwan show remarkable irregularities which may result from local tectonic complexities