importance of pre existing oceanic conditions to upper ocean response induced by super typhoon hai tang 1 this study investigates upper ocean response to super typhoon hai tang the most intense typhoon in 2005 in the western north pacific using multi satellite microwave data typhoon data and argo profiles sequential merged microwave sea surface temperature sst images show that hai tang induced four separately cooling responses after its trail in the western north pacific during 11 18 july comparison between upper ocean responses of cooling sst and pre typhoon sea surface height suggests that these cooling responses of the upper ocean to hai tang are closely associated with pre existing cyclonic circulation denoted by pre existing negative sea surface features furthermore applying argo profiles the physical mechanism is confirmed to be associated with pre existing cyclonic circulations provide a relatively unstable thermodynamic structure and therefore cold water would be brought up readily this paper provides the rather convincing evidence that cyclonic flow and uplifted thermocline are the pre existing conditions for intensive cooling following the typhoon passage

crustal extension in the baikal rift zone analysis of the gravity field along four profiles crossing the baikal rift zone permits an estimate of the amount of anomalous mass produced by 1 1 graben fill sediments 2 2 moho uplift and intrusion of mantle sills and dikes 3 3 an asthenospheric bulge crustal extension is evaluated based on the idea of mass and volume balance of material introduced into and removed from the initial volume of the crust extension in the baikal rift increases southwestward from 0 9 km in the chara depression to 19 3 km in the south baikal depression these values generally agree with the position of the euler pole determined from seismic data fault plane solutions average rotation velocity for the lithospheric plates separated by the rift zone is estimated to be 5 93 10 4 rad m y over about 30 m y

comparing e field changes aloft to lightning mapping data 1 a newly developed balloon borne instrument contains electric and magnetic sensors for determining how lightning alters electric field vectors relative to a coordinate system fixed with the earth by combining data from this instrument with results from the compact lightning mapping array lma at langmuir laboratory in central new mexico and the national lightning detection network nldn charge transported to ground by several strokes in a cloud to ground cg lightning flash can be quantified as the flash progresses the locations of the charge centers drained by successive strokes are seen to move further from the ground strike point using this new instrument and two different models to map lma source points onto charge centers the charge transported in an intracloud ic flash is also estimated details of the instrument design and data analysis are also presented

neogene and quaternary faulting in and along the qinling shan the structure of the qinling shan mountain range shaanxi china involves major east south east strike slip faults field observations made during two expeditions in 1983 and 1984 show that the faults are active and may have undergone several tens of kilometres of post eocene left lateral displacement the faults cut the morphology sharply and offset left laterally small channels their trace is marked by cataclastic to mylonitic non coaxial deformation zones at least 50 100 m wide the qinling faults allow the eastward extrusion of south china and may be considered the easternmost continuation of the altyn tagh fault system they link extensional tectonics in northeastern china to the himalayan collision

crustal strains in the japanese islands as deduced from dense gps array data from the nationwide continuous gps network operated by the geographical survey institute of japan were used to estimate crustal strains in the japanese islands we used horizontal velocity vectors at 610 sites for the period april 1996 to march 1997 and employed the least squares prediction method to interpolate the velocities to a uniform 7km 7km grid over japan the gridded velocities were then differentiated in space to calculate principal components of strains results clearly portray tectonic strainings of the japanese islands in one year 1 dilatational strains show that the japanese islands are under a compressive strain regime induced by the subducting oceanic plates 2 distribution of high maximum shear strains coincides with the regions of crustal activities and 3 principal axes of the strains indicate influences of e w and nw se compression due to the converging oceanic plates north south extension in kyushu is also visible

incipient subduction and deduction along the eastern margin of the japan sea the eastern margin of the japan sea has been under convergent tectonics since sometime after the pliocene the suture line is on the ocean continent boundary between the japan yamato basins and the tohoku northeast japan arc incipient subduction and obduction of the oceanic and sub oceanic crust are observed along the suture line with the occurrence of numerous n s trending fault bounded ridges and troughs focal mechanism solutions of several compressional type earthquakes with magnitudes of m 6 9 to 7 7 which have occurred along the zone are consistent with the observation of geological thrust faults the convergent stresses in the japan sea may be due to india eurasia collision and its associated intra plate or inter microplate movements in east asia the eastward movement of the amurian plate causes baikal extension along its western margin and the japan sea convergence along its eastern margin

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

active faulting in and along the qinling range china inferred from spot imagery analysis and extrusion tectonics of south china abstract since the beginning of the india asia collision about 2500 km of convergence has been accommodated by crustal thickening in and around the tibetan plateau and by extrusion of tibetan blocks and of the south china block the relative amounts of convergence accommodated by the two mechanisms are however still largely a matter of debate the main purpose of the present study is to determine the rate of left lateral movement between south china and north china during the late cenozoic this movement is accommodated by offsets along the more than 1000 km long e w trending qinling fault system which separates the south china block from the north china block and terminates to the east in the right lateral ndashs trending tanlu fault zone physiographic features typical of active faulting such as triangular facets along scarps and drainage deviations have been observed on spot images throughout the qinling fault system recent active faulting involves both left lateral strike slip and normal dip slip which are partitioned laterally east of the weihe graben two major faults the luonan and danfeng faults of the qinling fault system slip left laterally a cumulative slip rate of about 7 2 2 2 mm yr between the qinling shan south china and the hua shan north china has been estimated using quaternary morphological offsets in contrast the qinling frontal fault which bounds the cenozoic weihe graben to the south exhibits abundant evidence of normal faulting that accommodated large post early eocene vertical displacement in the graben crustal extension estimated from published seismic profiles and boreholes across the weihe graben contributes to a late cenozoic rate of left lateral movement of 2 0 5 mm yr in a n140 e direction between the hua shan and the ordos block combining these yields a rate of left lateral movement of 8 5 2 5 mm yr in a n100 e direction between south china and the ordos block is achieved additionally the ordos block rotates counterclockwise relative to gobi mongolia resulting in nw se crustal extension along the yinchuandashhetao grabens this is estimated from published seismic sections and adds a component of left lateral movement of 4 1 mm yr in a n125 e direction between south china and gobi mongolia the total rate of left lateral movement of south china with respect to gobi mongolia is 12 4 mm yr in a n110 e direction the eastward decrease of the left lateral strike slip on the active qinling fault system may be explained by the partitioning of left lateral movement on the faults bounding the dabie shan to the south and north and by a book shelf mechanism of counterclockwise rotating blocks separated by active ne sw right lateral faults in the dabie shan

electric fields preceding cloud to ground lightning flashes we analyzed in detail the electric field variations preceding the first return strokes of 80 cloud to ground lightning flashes in nine different storms observed at the nasa kennedy space center during the summers of 1976 and 1977 the electric field variations are best characterized as having two sections preliminary variations and stepped leader the stepped leader electric field change begins during a transition period of a few milliseconds duration marked by characteristic bipolar pulses the durations of stepped leaders lie most frequently in the range 6 20 milliseconds we infer from our measurements and critical review of the previous literature that there is only one type of stepped leader not the two types and often referred to in the literature

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

earthquake strain rates and instantaneous relative motions within central and eastern asia summary we use the spatial distribution of moment tensors of earthquakes in this century to estimate the velocity field in asia within a eurasian reference frame in a least squares inversion strain rates on the surface of the earth are matched with continuous spline functions in order to recover the velocity gradient tensor associated with the seismic moment release in asia earthquakes account for 40 60 per cent of the expected motion of india relative to eurasia with the missing component of strain rate equivalent to about 20 mm yr 1 of n s shortening between siberia and india in this solution south china rotates counterclockwise and moves eastwards relative to siberia using rigid plate constraints we next investigate the characteristics of the complete horizontal strain field in asia that accommodates plate motions our strain rate solutions are analogous to the response of a newtonian thin viscous sheet in which the rate of work done by the straining medium in accommodating the velocity boundary conditions is a minimum in these solutions the euler pole for india relative to eurasia is constrained nuvel 1a demets et al 1994 but in the process of fitting the vlbi velocity at shanghai china ward 1994 heki et al 1995 the euler pole for south china is determined in the inversion a solution that both fits the velocity at shanghai china and yields a strain rate field consistent with the earthquake mechanisms is one where the south china block has a motion relative to siberia described by the pole at 51 n 131 e 0 3 deg myr 1 comparison of the complete strain field that accommodates plate motion with the seismic strains indicates that earthquake moment release rates in this century within mongolia are about a factor of 4 larger than the long term rate within gansu ningxia the earthquake moment rates have been about a factor of 2 higher than the long term rate the strike slip faulting within mongolia gansu ningxia western sichuan and yunnan is possibly a direct result of velocity boundary conditions imposed on the south china block by forces unrelated to continental collision of india and eurasia such as forces associated with subduction along the margins of south eastern asia verification of this requires a better understanding of the role of pre existing zones of weakness within the asian continental lithosphere

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

lightning subsequent stroke electric field peak greater than the first stroke peak and multiple ground terminations for 46 multiple stroke flashes in which each stroke ground termination was located using a tv camera network and thunder ranging 15 flashes 33 had one or more subsequent return strokes whose initial electric field peak normalized to 100 km was greater than the first stroke field peak of the flash in 9 of these 15 flashes the subsequent strokes with field peaks greater than the first stroke followed the same channel as the first stroke in five flashes the subsequent strokes with the greater peaks followed a different channel to ground and in one flash the subsequent strokes with the greater peaks occurred both in the first stroke channel and in a different channel the interstroke intervals immediately preceding the 13 larger subsequent strokes that followed the first stroke channel had a geometric mean gm duration of 98 ms 1 7 times greater than the gm of 57 ms for all 199 interstroke intervals 46 flashes without any selection eight of the 13 larger subsequent strokes for which leader durations were measurable had a gm leader duration of 0 55 ms 3 3 times smaller than the gm of 1 8 ms for 117 subsequent leaders with measurable duration in a previously formed channel of the 46 multiple stroke flashes for the six larger subsequent strokes that created a new channel to ground the preceding interstroke interval had a gm of 130 ms and the leader duration had a gm of 15 ms no subsequent stroke with peak field exceeding the first in any category had a preceding interstroke interval less than 35 ms analysis of direct current measurements from switzerland shows that subsequent stroke currents exhibit many features similar to those of florida subsequent stroke electric fields in 22 florida single stroke and multiple stroke ground flashes the distances between multiple channel terminations in a given flash 33 measurements ranged from 0 3 km to 7 3 km with a gm of 1 7 km

present day kinematics of asia derived from geologic fault rates active fault geometry available quaternary rates on major faults and the far field plate motion are used to determine crustal kinematics in the collision zone between india and asia using a finite element formalism to construct a spherical shell model of the asian continent with embedded faults we seek a velocity solution approaching the motion of rigid blocks by minimizing the elastic strain energy in the fault bounded blocks by doing so we test the assumption that long term deformation within continents is mostly localized into major faults in the solution fault motion accounts for more than 80 of the deformation allowing us to describe our velocity model in terms of quasi rigid block rotations on the sphere south china is rotating clockwise about a pole located southwest of borneo implying an e ese velocity vector of 11 mm yr for a point at shanghai in agreement with the velocity vector determined by very long baseline interferometry heki et al 1995 the eastward movement of south china is accommodated by oblique extension along the red river fault at a rate of 10 5 mm yr in the south and by the combination of left lateral strike slip motion on the qinling dabie shan fault and the counterclockwise rotation of the ordos and adjacent blocks in the north the tarim rotates clockwise with respect to dzungaria about a pole located at 44 n 92 e consistent with increasing crustal shortening toward the west throughout the tien shan assuming incompressibility a crustal volume budget over a domain encompassing the tertiary mountain ranges in asia shows that over the last 10 000 years 73 4 of the north south shortening between india and asia has been absorbed by thickening of the lithosphere and 27 has been accommodated by lateral extrusion of continental blocks the present day predominance of thickening in asia results from the relatively slow eastward motion of south china controlled by strike slip faulting in the qinling shan and oblique extension in northeastern china

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

crustal deformation in the baikal rift from gps measurements three years and four campaigns of global positioning system gps measurements 1994 1997 in the baikal rift zone largest active continental rift system in eurasia show crustal extension at a rate of 4 5 1 2 mm yr in a wnw ese direction a comparison with moment release of large historical earthquakes suggests that elastic strain is currently accumulating in the baikal rift zone along active faults that currently have the potential for a m 7 5 earthquake the gps derived extension rate in the baikal rift zone is at least two times greater than the prediction of most deformation models of asia this result could reflect the dynamic contribution of the pacific eurasia subduction to intracontinental deformation in asia in addition to the effect of the india eurasia collision

horizontal and vertical crustal movements from three dimensional very long baseline interferometry kinematic reference frame implication for the reversal timescale revision three dimensional kinematic reference frame of geodetic very long baseline interferometry vlbi stations tied to a geologic plate motion model was established using the glb907 solution by first selecting globally distributed stable plate interior stations and then applying a small translation and a rotation for the entire network in a three dimensional space so that the differences in the horizontal velocities between the vlbi observations and the model predictions are minimized since the vlbi network is global we only assume that the horizontal movements of technically stable stations obey a plate motion model we need not introduce any unwarranted constraints to the vertical velocities of specific stations to realize the frame a suggestive correlation was found between the estimated vertical velocities of north american stations and those predicted by a postglacial rebound model the revision of the magnetic polarity timescale mpts causes a uniform increase or decrease of the predicted velocities which could be detected as the small difference between the measured and the predicted relative plate velocities direct estimation of the correction suggests that the vlbi data fit best to the model when the nuvel1 model is corrected by 3 4 1 2 which differs significantly from the 4 5 deduced from the astronomical mpts calibration this was further confirmed by estimating the rotation rates for individual plate pairs

horizontal electric fields from lightning return strokes measurements are presented of simultaneous horizontal and vertical electric fields from 42 lightning return strokes in 27 flashes at distances from 7 to 43 km the data were obtained at the nasa kennedy space center florida using an elevated spherical antenna having a system bandwidth of 3 hz to 4 mhz the strokes studied occurred in a 6 min interval from 1850 to 1856 ut on august 11 1984 the 42 measured horizontal fields exhibited initial peaks having a mean half width of 0 52 s the ratio of the amplitude of the peak horizontal field to the associated vertical field peak had a mean value of 0 030 with a standard deviation of 0 007 the measured horizontal field wave shapes are compared with those obtained from calculations using the measured vertical fields and theory the wavetilt formula that models the fields as plane wave radiation over a homogeneous ground of uniform conductivity and permittivity the local ground conductivity measured as a function of depth using the wenner four probe method was found to increase with depth within the region relevant to this study from the surface to a depth of a few meters the conductivity was 8 2 10 3 mho m between the surface and a depth of 2 2 m and 3 1 10 2 mho m below this layer to a depth of 11 m if a ground conductivity equal to that of the top layer is used in the wavetilt formula the calculated horizontal field peaks are found to be on average about 33 wider and larger than the measured field peaks errors and compensation procedures for tilt of the spherical antenna for electronic system distortion and for electric field distortion at the antenna due to proximity of the ground and of the antenna support structure are described

interplate coupling along the nankai trough off southwest japan derived from gps measurements we investigate interplate coupling between the philippine sea and the eurasian plates at the nankai trough off southwest japan during the interseismic period plate coupling is modeled by imaginary backward normal slip superposed on the steady state subduction we divide the plate interface into several segments and estimate coupling on each segment from gps horizontal velocity data estimated coupling is in general agreement with the rate of steady state subduction predicted from a plate motion model this implies that current coupling at the nankai trough is so strong that much of the relative plate motion is taken up by shortening of the leading edge of the overriding plate it seems that stronger interseismic coupling is realized on the segment where larger coseismic dislocation occurred and vice versa time fluctuation of plate coupling from 1995 to 1996 is found on a small segment

a test of present day plate geometries for northeast asia and japan alternative geometries for the present day configuration of plate boundaries in northeast asia and japan are tested using nuvel 1 and 256 horizontal earthquake slip vectors from the japan and northern kuril trenches statistical analysis of the slip vectors is used to determine whether the north american eurasian or okhotsk plate overlies the trench along the northern kuril trench sup vectors are well fit by the nuvel 1 pacific north america euler pole but are poorly fit by the pacific eurasia euler pole results for the japan trench are less conclusive but suggest that much of honshu and hokkaido are also part of the north american plate the simplest geometry consistent with the trench slip vectors is a geometry in which the north american plate extends south to 41 n and possibly includes northern honshu and southern hokkaido although these results imply that the diffuse seismicity that connects the lena river delta to sakhalin island and the eastern sea of japan records motion between eurasia and north america onshore geologic and seismic data define an additional belt of seismicity in siberia that cannot be explained with this geometry assuming that these two seismic belts constitute evidence for an okhotsk block two published kinematic models for motion of the okhotsk block are tested the first model which predicts motion of up to 15 mm yr 1 relative to north america is rejected because kuril and japan trench slip vectors are fit more poorly than for the simpler geometry described above the second model gives a good fit to the trench slip vectors but only if okhotsk north america motion is slower than 5 mm yr 1

crustal deformation at the nankai subduction zone southwest japan derived from gps measurements the interseismic strain accumulation process at the nankai subduction zone the plate boundary region between the philippine sea and the eurasian plates off southwest japan has been revealed by gps measurements spanning five years large strains characterized by a contraction of 2 2 3 4 10 7 yr have accumulated in a narrow region extending parallel to the strike of the plate boundary the contraction axes lie in a northwest southeast direction nearly parallel to the direction of relative motion of the philippine sea plate with respect to the eurasian plate gps derived deformation data including both rate and direction are consistent with the expected earthquake deformation cycle at the nankai subduction zone current interplate coupling in this zone is strong much of the relative plate motion has been taken up by deformation of the marginal parts of the eurasian plate