deep structures of the palawan and sulu sea and their implications for opening of the south china sea abstract compared to the northern south china sea continental margin the deep structures and tectonic evolution of the palawan and sulu sea and ambient regions are not well understood so far however this part of the southern continental margin and adjacent areas embed critical information on the opening of the south china sea scs in this paper we carry out geophysical investigations using regional magnetic gravity and reflection seismic data analytical signal amplitudes asa of magnetic anomalies are calculated to depict the boundaries of different tectonic units curie point depths are estimated from magnetic anomalies using a windowed wavenumber domain algorithm application of the parker oldenburg algorithm to bouguer gravity anomalies yields a 3d moho topography the palawan continental block pcb is defined by quiet magnetic anomalies low asa moderate depths to the top and bottom of the magnetic layer and its northern boundary is further constrained by reflection seismic data and moho interpretation the pcb is found to be a favorable area for hydrocarbon exploration however the continent ocean transition zone between the pcb and the scs is characterized by hyper extended continental crust intruded with magmatic bodies the nw sulu sea is interpreted as a relict oceanic slice and the geometry and position of extinct trench of the proto south china sea pscs is further constrained with additional age constraints from inverted moho and curie point depths we confirm that the spreading of the se sulu sea started in the early oligocene late eocene due to the subduction of the pscs and terminated in the middle miocene by the obduction of the nw sulu sea onto the pcb

local ice formation via liquid water growth in slowly ascending humid aerosol liquid water layers observed with ground based lidars and radiosondes observations with lidars at wuhan 30 5 n 114 4 e china from 2010 to 2013 captured nine cases of slowly ascending humid aerosol liquid water layers that occurred at altitudes of 2 4 km in winter each of them was almost transparent initially with the backscatter ratio far less than 7 0 and depolarization ratio less than 0 03 with a slow ascent the layer developed into a nearly opaque liquid cloud layer and then ice crystals abruptly formed at the upper edge of the cloud layer with very high liquid water content the ice crystals likely came from water drop freezing the freezing temperatures estimated from radiosonde measurements were 3 to 8 c for two available long lived 16 h cases the layer was observed to always lie just below an inversion layer the ice development on the layer was followed by rainfall

late cretaceous paleomagnetism of the tombstone district and vicinity evidence for a rotational domain boundary in southeastern arizona paleomagnetic data are presented for late cretaceous volcanic and intrusive rocks in the tombstone district and dos cabezas mountains of southeastern arizona the resultant paleopole 73 n 224 e a95 8 is similar to a late cretaceous reference pole for north america 82 n 210 e a95 7 implying that these rocks have not been significantly rotated about vertical or near vertical axes relative to the continental interior generally concordant results have also been published for pennsylvanian terra rosa paleosols within the black prince limestone at localities in the nearby gunnison hills whetstone mountains and naco hills together however these carboniferous data indicate a 9 7 clockwise rotation with respect to north america similar to that determined for the colorado plateau 5 14 since the mid cretaceous published paleomagnetic data for rocks south and west of the tombstone vicinity indicate much larger clockwise rotations ranging from 25 to 60 implying that a rotational domain boundary runs between the mustang mountains and canelo hills to the southeast and between the silver bell and tucson mountains to the northwest this boundary roughly coincides in part with the sawmill canyon fault zone and is parallel to other northwest trending strike slip faults in the region that were active during the laramide orogeny the clockwise rotations in southern arizona are likely part of a larger pattern of dextral shear along the western margin of north america during the late cretaceous and early tertiary caused by northward oblique subduction of oceanic plates relative to the stable craton

composition and structure of the central aleutian island arc from arc parallel wide angle seismic data new results from wide angle seismic data collected parallel to the central aleutian island arc require an intermediate to mafic composition for the middle crust and a mafic to ultramafic composition for the lower crust and yield lateral velocity variations that correspond to arc segmentation and trends in major element geochemistry the 3 d ray tracing 2 5 d inversion of this sparse wide angle data set which incorporates independent phase interpretations and new constraints on shallow velocity structure produces a faster and smoother result than a previously published velocity model middle crustal velocities of 6 5 7 3 km s over depths of 10 20 km indicate an andesitic to basaltic composition high lower crustal velocities of 7 3 7 7 km s over depths of 20 35 km are interpreted as ultramafic mafic cumulates and or garnet granulites the total crustal thickness is 35 37 km this result indicates that the aleutian island arc has higher velocities and thus more mafic compositions than average continental crust implying that significant modifications would be required for this arc to be a suitable building block for continental crust lateral variations in average crustal velocity below 10 km roughly correspond to trends in major element geochemistry of primitive mg 0 6 lavas the highest lower crustal velocities and presumably most mafic material are detected in the center of an arc segment between unmak and unalaska islands implying that arc segmentation exerts control over crustal composition

p wave tomographic imaging of the crust and upper mantle beneath the japan islands more than 50 000 high accuracy arrival times from 1200 shallow and deep earthquakes selected from the japan university network earthquake catalog are used to investigate the three dimensional 3 d seismic velocity structure beneath japan travel times and ray paths are accurately calculated by using an efficient 3 d ray tracing technique p wave tomographic images of the crust and upper mantle to a depth of 500 km beneath the japan islands are determined with spatial resolutions of 25 50 km the obtained p wave velocity in the crust and uppermost mantle is slightly higher and relatively homogeneous in western japan in contrast with an average lower velocity and a large heterogeneity in eastern japan where many active volcanoes exist this feature correlates well with the distributions of heat flow and gravity anomalies low velocity low v zones are imaged in the crust and uppermost mantle beneath active volcanoes the low v zones in the mantle wedge dip toward the west and extend continuously to a depth of about 200 km a high velocity high v zone corresponding to the subducted pacific plate is delineated the thickness of the high v zone is estimated to be 80 90 km in southwestern japan the descending philippine sea plate is also delineated its thickness is estimated to be 30 km

the elkhorn mountains revisited new data for the late cretaceous paleomagnetic field of north america the late cretaceous portion of north america s apparent polar wander apw path is poorly known due to a dearth of suitable post 85 ma reference poles a paleomagnetic re investigation of elkhorn mountains volcanics 80 ma was initiated to fill this void and to determine the degree to which the onset of an apparent rapid episode of apw during this time interval correlates with known late cretaceous tectonic events a total of 249 paleomagnetic samples 30 sites were collected from three separate areas within the elkhorn mountains using both alternating field and thermal demagnetization a characteristic direction of magnetization was isolate at 15 sites a95 15 which passes a fold test at the 95 confidence level the mean pole calculated from site virtual geomagnetic poles is located at 80 3 n 189 5 e n 15 a95 9 6 k 16 8 interestingly the elkhorn mountains pole is not concordant with the cretaceous stillstand poles but is nearly coincident with the paleocene reference pole and the recently published pole for the adel mountains dated at 76 ma these new data suggest the onset of apw which brought the pole from its cretaceous position to near its early tertiary position occurred prior to 80 ma and the transition was exceedingly rapid the onset of this rapid apw now appears to coincide more closely in time with many of the significant late cretaceous tectonic events e g the laramide orogeny however since the elkhorn mountains volcanics are floored by a major east directed thrust and have undergone crustal scale deformation the data should be viewed with caution until more results are available for this time interval

mesozoic ash flow caldera fragments in southeastern arizona and their relation to porphyry copper deposits jurassic and upper cretaceous volcanic and associated granitic rocks in southeast arizona are remnants of large composite silicic volcanic fields characterized by voluminous ash flow tuffs and associated calderas presence of 10 15 large caldera fragments is inferred primarily from 1 ash flow deposits more than 1 km thick having features of intracaldera ponding 2 exotic block breccias within a tuff matrix interpreted as caldera collapse megabreccias and 3 local granitic intrusions along arcuate structural boundaries of the thick volcanic sequences several porphyry copper deposits are associated with late granitic intrusions within the calderas or along their margins

crustal structure and seismicity beneath the forearc off northeastern japan marine seismological and other data in the japan trench area north of 38 5 n were used to infer the relation of subducting plate structure seismicity and focal mechanisms especially at the aseismic to seismogenic zone along the interface between the two interacting plates previous crustal models from ocean bottom seismographic refraction obs surveys were improved by taking into account the relative seismic amplitude characteristics and constraining the shallow structure using multichannel seismic data a wave speed discontinuity in these models is interpreted to be the contact zone of the crust of the overriding plate and the subducting pacific plate crust its dip angle increases to about 7 110 km landward of the trench axis a large increase beneath the deep sea terrace is required to reach the well defined angle of 25 beneath the tohoku east coast a large wave speed gradient within layer 2 commonly observed under normal oceans seems to vanish beneath the inner trench slope at about 10 km depth within the overriding plate apparently brittle material with a p wave speed of 6 km s can be found as near as 35 km from the trench axis the upper limit of the seismogenic zone of interplate low angle thrust events is about 15 km depth from obs seismicity and large event analyses both the strength of the crust of the overriding plate and the characteristics of subducting sediments must be investigated to define the seismic coupling of interacting plates

three dimensional p wave velocity structure beneath the indonesian region abstract we present the p wave seismic tomography image of the mantle to a depth of 1200 km beneath the indonesian region the artb inversion method is applied to a dataset of 118 203 p wave travel times of local and teleseismic events taken from isc bulletins although the resolution is sufficient for detailed discussion in only a limited part of the study region the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle structures beneath the philippine islands and the molucca sea region are well resolved and high velocity zones corresponding to the slabs of the molucca sea and philippine sea plates are well delineated seismic zones beneath the manila negros and cotabato trenches are characterized by high velocity anomalies although shallow structures were not resolved the molucca sea collision zone and volcanic zones of the sangihe and philippine arcs are dominated by low velocity anomalies the philippine sea slab subducts beneath the philippine islands at least to a depth of 200 km and may reach depths of 450 km the southern end of the slab extends at least to about 6 n near southern mindanao in the south the two opposing subducting slabs of the molucca sea plate are clearly defined by the two opposing high velocity zones the eastward dipping slab can be traced about 400 km beneath the halmahera arc and may extend as far north as about 5 n unfortunately resolution is not sufficient to reveal detailed structures at the boundary region between the halmahera and philippine sea slabs the westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved this slab trends n s from about 10 n in the philippine islands to northern sulawesi a ne sw trending high velocity zone is found in the lower mantle beneath the molucca sea region this high velocity zone may represent a remnant of the former subduction zone which formed the sulawesi arc during the miocene the blocks along the sunda and banda arcs are less well resolved than those in the philippine islands and the molucca sea region nevertheless overall structures can be inferred the bowl shaped distribution of the seismicity of the banda arc is clearly defined by a horseshoe shaped high velocity zone the tomographic image shows that the indian oceanic slab subducts to a depth deeper than 300 km i e deeper than its seismicity beneath andaman islands and sumatra and may be discontinuous in northern sumatra along southern sumatra java and the islands to the east the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity where it appears to penetrate into the lower mantle

cenozoic thermotectonic history of the sunda asri basin southeast sumatra new insights from apatite fission track thermochronology abstract the tectonic and thermal history of cenozoic rocks from four wells asri 1 ne ria 1 hariet 1 and yani 2 in the sunda asri basin has been reconstructed using apatite fission track aft analysis combined with modelling of previously determined vitrinite reflectance vr measurements the wells all penetrate recent to middle eocene successions in which only the eocene to oligocene successions have been subjected to temperatures suitable for partial annealing due to rapid late miocene to recent burial with respect to organic thermal maturities the zone of minimum annealing coincides with undermature heating and records provenance aft ages whilst the zone of partial annealing agrees well with mature heating suitable for generation of hydrocarbons the integrated aft and vr data suggest that the sunda asri basin continues subsiding probably due to extension initiated in the late eocene and the successions near the base of the wells were recently exposed to the high present day temperatures the recent heating of rocks is consistent with up to 800 m of plio pleistocene burial both the aft and vr results indicate that geothermal gradients remained relatively constant through the cenozoic

three dimensional p wave velocity structure beneath central japan low velocity bodies in the wedge portion of the upper mantle above high velocity subducting plates abstract the three dimensional 3 d p wave velocity structure beneath central japan has been investigated in detail by an inversion method 7490 p wave arrival times from 120 shallow and intermediate depth earthquakes that have occurred in this region are used to estimate velocity anomalies in 3 d subdivided blocks and hypocentral perturbations simultaneously the results reveal complex 3 d structures with low velocity zones in the wedge portion of the upper mantle above the high velocity philippine sea and pacific plates subducting beneath this region prominent low velocity bodies exist just beneath active volcanoes particularly in the hida mountain range low velocity bodies are spatially correlated with the low q zones estimated from seismic intensity data one low velocity body coincides with an anisotropic body detected from the study of shear wave splitting dome shaped low velocity masses seem to represent partially melted mantle diapirs no clear evidence on velocity contrast has been identified across the fossa magna which is a tectonic boundary between northeast and southwest japan

heat flow distribution in southeast asia with consideration of volcanic heat abstract as of 1995 in southeast asia from 15 s to 25 n and from 90 to 160 e 2539 heat flow measurements are available despite a recent increase in the number of measurements still important data gaps exist in the region especially around the volcanic regions so far the contribution of heat flux from active volcanoes has largely been overlooked in regional heat flow maps because of uncertainties surrounding it we have tried to estimate the volcanic heat in this region with the assumption that these volcanoes emit a similar amount of heat as those in northeast honshu japan where heat flow studies and seismic tomography enable us to estimate that as a first approximation a volcano can be represented by 140 mw m 2 of heat flow a heat flow map including volcanic heat estimated in this way makes the heat flow in the sunda arc and the philippines where conventional heat flow data are scarce much higher than on a map without the volcanic heat

the 1989 1990 seismic swarm in the alban hills volcanic area central italy abstract a long seismic swarm has been recorded by a digital microseismic network that the istituto nazionale di geo fisica ing deployed from april 1989 to march 1990 in the alban hills quaternary volcanic region about 20 km southeast of rome the network consisted of thirteen digital stations equipped with four six component weak motion and strong motion sensors three three component and six vertical weak motion seismometers including both broad band and short period sensors more than 3000 earthquakes were detected during about one year of operation the data recorded during the sequence provided an unprecedented opportunity to resolve details of the seismogenic features of this area that has experienced earthquakes since the roman age although the temporal distribution of seismicity reveals a volcanic type swarm activity the recorded seismic signals show medium high frequency waveforms and clear s wave arrivals typical of tectonic earthquakes about 1100 earthquakes in a magnitude range between m d 1 5 and md 4 0 have been located the seismicity delineates a 6 12 km 2 nw se elongated region that corresponds to the area where the most recent 0 027 ma phreato magmatic activity took place almost no earthquakes occurred beneath the central cone and the eastern side of the caldera the seismicity is shallow and is mostly concentrated in two clusters that are offset laterally and are at sligthly different depths 3 5 and 4 6 km the fault plane solutions of the strongest earthquakes reveal a ne sw extension consistent with the regional orientation of the stress field along the apenninic chain as obtained by other seismo logical data

mid cretaceous paleomagnetic reference field for north america restudy of 100 ma intrusive rocks from arkansas we have obtained new paleomagnetic data from three middle cretaceous alkalic intrusive complexes in central arkansas magnet cove and potash sulfur springs intrusions about 100 ma 20 sites and granite mountain stock about 88 ma 6 sites out of 254 specimens measured 147 from 20 sites were accepted the remainders have scattered magnetization directions which experiments indicate were caused by lightning occurring during frequent electrical storms in this region the geologic evidence indicates that the intrusions have not been tilted since emplacement the directions of magnetization calculated with respect to present day horizontal yield a mean paleopole at 192 5 e 74 1 n n 20 k 34 a95 5 7 this does not differ at 95 confidence from that determined previously by scharon and hsu but the error is diminished by half the angular dispersion sd of site virtual geomagnetic poles vgps is 13 6 similar to the value of sd about 15 predicted by current paleosecular variation models the revised arkansas paleopole is combined with four other cratonic north american paleopoles of mid cretaceous age to yield a revised middle cretaceous reference pole at 196 e 71 n a95 4 9 the mean of nine paleopoles derived from overprints in rock units from the craton and craton margin which range in age from proterozoic to jura cretaceous is 202 e 68 n a95 8 2 this is not different from the reference paleopole indicating that overprinting was very widespread across north america in mid cretaceous time

tomographic inversion for three dimensional velocity structure at mount st helens using earthquake data tomographic inversion is applied to 17 659 p phase observations at 21 stations from 2023 earthquakes in the vicinity of mount st helens to study the three dimensional velocity structure block size for the inversion is 2 km horizontally and 2 km or more vertically locations of hypocenters are assumed known and are based on a reference one dimensional layered velocity structure a conjugate gradient technique lsqr is used to invert the large sparse system of equations augmented by regularization with a laplacian roughening matrix resolution is estimated by computing the impulse response of the inversion for various critical locations and uncertainties of the estimates are determined by a jackknife approach the results of the inversion show a remarkable correlation with known geological and geophysical features the spirit lake and spud mt plutons are characterized by high velocity regions extending to approximately 9 km depth the st helens seismic zone a band of diffuse seismicity extending nnw from the volcano is evident as a prominent low velocity lineation the change in character of the velocity anomalies south of st helens corresponds well with the near cessation of seismic activity there a low velocity anomaly beneath the crater from 6 to 16 km depths may represent modern magma accumulations

paleomagnetism of the roskruge and gringo gulch volcanics southeast arizona paleomagnetic data were obtained from nine cooling units of the late cretaceous 72 ma roskruge volcanics and from 25 flows in the lower paleocene gringo gulch volcanics both from southeastern arizona alternating field demagnetization successfully erased the infrequent secondary components of magnetization the paleomagnetic pole position obtained from the roskruge volcanics is at 73 6 n 176 0 e with dp 6 2 and dm 8 8 the gringo gulch volcanics pole position is at 77 0 n 201 0 e with dp 1 2 and dm 1 7 in conjunction with other recently published paleocene and eocene paleomagnetic poles these data provide details of north american apparent polar wander during the laramide orogeny 80 to 40 ma an episode of rapid apparent polar wander from the cretaceous pole position in the bering strait to the eocene pole position near the present rotation axis occurred during that interval of time the initiation of this episode of apparent polar wander appears to be coincident with the major plate reorganizations which occurred at the onset of the laramide orogeny

arctic multilayered mixed phase cloud processes revealed in millimeter wave cloud radar doppler spectra 1 cloud radar doppler velocity spectra lidar backscattering coefficients and depolarization ratios and aircraft in situ measurements are used to investigate microphysical processes occurring in a case of multilayered mixed phase clouds over the north slope of alaska some liquid cloud layers were observed to exist in well mixed atmospheric layers but others were found in absolutely stable atmospheric layers the observations suggest that strong cloud top cooling was necessary to produce the well mixed cloud layers clouds shielded from radiative cooling by overlaying clouds more frequently existed in absolutely stable layers the in situ measurements revealed that most liquid layers contained drizzle the production process of which was shown from the radar and lidar measurements to have been interrupted only during heavier ice precipitation events different layers interacted with one another by changing the radiative heating profile and by precipitation which changed the growth paths available to cloud particles and even initiated new hydrometeor classes

lithospheric structure beneath nw iran using regional and teleseismic travel time tomography we compute a 2 d tomogram using the p wave arrival time readings from a temporary seismic experiment to study the seismic structure of the crust and upper mantle in nw iran the study area includes the western margins of the south caspian basin scb and the sahand and sabalan post collisional volcanoes in nw iran we invert 2780 regional and teleseismic relative p wave arrival times recorded by 23 stations along the seismic profile extending from the western shoreline of the caspian sea to lake urumieh our tomographic results show a higher velocity region beneath the scb the observed higher velocities strongly correlate with the observed positive gravity anomalies over the southwestern margins of the caspian sea suggesting an oceanic like nature for the scb lithosphere the tomographic results also show several lower velocity anomalies in the crust the sabalan volcano is underlain by a low velocity zone in the lower crust which is most likely thermal in nature in the sahand region the lower velocities are considerably shallower in depth and might be controlled by shallow sedimentary structures as well as an anomalously warm upper crust the shallow low velocity regions are connected with deeper low velocity zones 60 100 km deep in the upper mantle this pattern points to a possible mantle source of post collisional volcanism in nw iran i e the melting of a subducted slab

seismic activity and deformation process of the overriding plate in the northeastern japan subduction zone abstract we estimated the temperature distribution within the crust of the northeastern japan arc from p wave velocity perturbations obtained by travel time tomography by comparing the estimated temperature distribution with the focal depth distribution of shallow precisely relocated microearthquakes we found that the brittle to ductile or stick slip to stable sliding transition occurs at the 400 c isotherm and that the transition depth has considerable lateral variations the brittle seismogenic zone the upper portion of the crust becomes locally thin in the p wave low velocity areas where the temperature is estimated to be relatively high concentration of shallow microearthquakes high topography and relatively large contractile deformation of the crust are also observed in these low velocity areas active faults are not distributed in the low velocity areas but lie just along the edge of those areas or outside them all these observations suggest that earthquake occurrence and deformation within the crust is governed to a considerable degree by the thermal regime of this volcanic arc which is characterized by a horizontally inhomogeneous distribution of temperature

deep structure of arc volcanoes as inferred from seismic observations possible evidence for deep seated magmatic activity beneath the northeastern japan arc has been obtained from micro earthquake observations tomographic inversions for p wave velocity clearly delineate low velocity zones which are inclined to the west and continuously distributed from the uppermost mantle to the upper crust beneath active volcanoes exceptionally deep 22 40 km micro earthquakes are found at 10 locations around the low velocity zones beneath active volcanoes all these events have extremely low predominant frequencies suggesting a close relation to the magmatic activity in this depth range at shallower depths 8 15 km distinct reflectors of s waves from shallow events are found at five locations in or around the low velocity zones their locations and reflection coefficients suggest that the reflectors are very thin magma bodies existing in the mid crust these observations shed some light on the state of magma at depths beneath volcanic arcs

whole mantle p wave travel time tomography abstract a method of tomographic inversion to obtain three dimensional velocity perturbations in the earth s whole mantle has been developed and applied to more than two million p wave arrival time data reported by international seismology center isc the model is parameterized with 32 768 blocks the divisions in latitude longitude and radius are 32 64 and 16 respectively horizontal cell size is 5 6 5 6 the layer thicknesses vary with depth 29 km just below the surface and 334 km just above the core mantle boundary starting from a spherically symmetric earth model we obtained a three dimensional model using the following iterative procedures first we relocated all the events second we backprojected the residual into the whole mantle third we refined the spherically symmetric earth model the solutions have been converged in five iterations we adopted the following techniques in the backprojection procedure the first order smoothness was introduced as a damping which makes the solution independent of the starting model and its apparent fluctuation minimal the basic equations for delay times and smoothness are solved using the conjugate gradient method an iterative method which guarantees the convergence of solution into the exact least squares solution the weight on the smoothness i e the damping factor was objectively determined by a simplified cross validation technique the final solution was obtained as an average of the ten solutions each of which was derived from one tenth of the total data set the reliability of the solution is examined in two ways 1 mapping the resolution given by the reconstruction of checkerboard patterns and 2 mapping the variance given from the gaussian noise input this is the first result which delineates the whole mantle structure with its reliability mapping the longest wavelength anomalies of the lower mantle are similar to those of previous studies by dziewonski 1984 and hager and clayton 1989 however the shorter wavelength patterns have many discrepancies the fast anomalies of the uppermost mantle beneath the shield and the slow anomalies beneath the active tectonic regions are clearly seen we also revealed the l 2 pattern at the transition zone reported by the previous surface wave and free oscillation studies the most striking feature is that of the fast anomalies lying along the extension of the large subducting plate up to depths of about 1000 km or more the resolving powers in these regions are generally good

development of a new system for shallow sea heat flow measurement and its test application in the gulf of thailand abstract a new technique has been developed for the heat flow measurement in shallow seas the temperature in the sediment is measured at every 10 cm to the depth of 5 m by only one thermistor which moves up and down in the probe from the temperature data thus obtained the geothermal gradient is calculated in the least square sense by solving the thermal diffusion equation that is assuming an annual sinusoidal temperature variation at the sea bottom of which amplitude and initial phase are parameterized this system was used in the gulf of thailand and detailed temperature distributions were obtained in the future however to obtain more accurate heat flow values it is considered necessary to measure the temperature to at least the depth of 7 10 m

new results on the resistivity structure of merapi volcano indonesia derived from three dimensional restricted inversion of long offset transient electromagnetic data three long offset transient electromagnetic lotem surveys werecarried out at the active volcano merapi in central java indonesia during the years 1998 2000 and 2001 the measurements focused on the general resistivity structure of the volcanic edifice at depths of 0 5 2 km and the further investigation of a southside anomaly the measurements were insufficient for a full 3d inversion scheme which could enable the imaging of finely discretized resistivity distributions therefore a stable damped least squares joint inversion approach is used to optimize 3d models with a limited number of parameters the mode ls feature the realistic simulation of topography a layered background structure and additional coarse 3d blocks representing conductivity anomalies twenty eight lotem transients comprising both horizontal and vertical components of the magnetic induction time derivative were analyzed in view of the few unknowns we were able to achieve reasonable data fits the inversion results indicate an upwelling conductor below the summit suggesting hydrothermal activity in the central volcanic complex a shallow conductor due to a magma filled chamber at depths down to 1 km below the summit suggested by earlier seismic studies is not indicated by the inversion results in conjunction with an anomalous density model derived from arecent gravity study our inversion results provide information about the southern geological structure resulting from a major sector collapse during the middle merapi period the density model allows to assess a porosity range andthus an estimated vertical salinity profile to explain the high conductivities on a larger scale extending beyond the foothills of merapi

the late cretaceous paleomagnetic field in north america a south american perspective determining the late cretaceous paleomagnetic pole for north america has been difficult because of the lack of suitable rocks of that age in cratonic areas to provide the necessary data as an alternative different studies have appealed to paleomagnetic data from rocks in western north america using paleopoles from stable areas in neighboring continents it is suggested that the available late cretaceous paleomagnetic record in western north america should be analyzed in terms of rigid body deformations rather than be used to represent the cratonic reference field

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

on homogeneous ice formation in liquid clouds primary ice formation by homogeneous freezing of supercooled cloud droplets in moist adiabatic air parcels is investigated theoretically and by means of numerical simulations dependencies of nucleated ice crystal number and size and associated freezing temperatures are systematically studied as functions of updraught speed and cloud droplet number and size droplet freezing temperatures range between 235 and 239 k depending on dynamical forcing and liquid water content vertical resolutions on the order of 10 m are required in numerical cloud models to resolve the thin layers in which homogeneous ice formation processes unfold only a fraction of droplets freeze in weakly forced clouds small scale variability in updraught speeds encountered by air parcels containing supercooled cloud droplets results in broad ice crystal number distributions when sampled across a parcel ensemble the strong dynamical control of ice initiation in tropospheric clouds initiates homogeneous freezing in the presence of heterogeneous ice nuclei even at moderate mean updraught speeds suggesting that such particles play a limited role in affecting droplet freezing in cold convective cloud outflow regions these findings have important implications for microphysical and optical properties of condensed phase convective detrainment setting the stage for the evolution of anvil cirrus

a new late cretaceous paleomagnetic pole from the adel mountains west central montana north america s apparent polar wander path has been poorly defined between the mid cretaceous and paleocene reference pole positions existing data allowed 13 of apparent polar motion over about 22 m y 87 65 ma roughly coinciding with the beginning of laramide deformation 80 ma we report on a paleomagnetic study of the adel mountain volcanic rocks to refine the north american apparent polar wander path for this interval the shonkinite rocks of the adel mountain volcanic field are on the eastern edge of the cretaceous paleocene fold and thrust belt some of these structures disturb the western edge of the volcanic pile we obtained two new k ar dates from the adel rocks one date on biotite from a shonkinite dike that crosscuts most of the volcanic rocks is 71 2 2 7 ma the other a whole rock date from a flow deep in the volcanic pile is 81 1 3 5 ma we collected six to nine paleomagnetic samples from each of 34 sites in roadcuts and natural outcrops of flows dikes and laccoliths positive fold and conglomerate tests along with alternating field and thermal demagnetization indicate that our characteristic remanent directions are primary magnetizations acquired before late cretaceous to paleocene thrust belt deformation averaging the virtual geomagnetic poles from 26 reliable sites all of normal polarity yields a paleopole at 82 2 n 209 9 e 95 6 80 k 18 38 this pole is concordant with the paleocene reference pole 82 0 n 170 2 e 95 3 5 k 18 6 diehl et al 1983 and is 11 6 from the globerman and irving 1988 mid cretaceous pole at 71 n 196 e the youngest information in the cretaceous stillstand pole is from the niobrara formation shive and frerichs 1974 at about 85 89 ma if we take the average age of the adel mountain volcanics to be 76 ma then 12 of apparent polar motion occurred between 87 ma and 76 ma thus rapid apparent polar motion correlates well with the onset of laramide deformation

microphysical properties of cold frontal rainbands observations have been obtained within an intense precipitation rates 50 mm h 1 narrow cold frontal rainband ncfr embedded within a broader region of stratiform precipitation in situ data were obtained from an aircraft which flew near a steerable dual polarisation doppler radar the observations were obtained to characterise the microphysical properties of cold frontal clouds with an emphasis on ice and precipitation formation and development primary ice nucleation near cloud top 55 degrees c appeared to be enhanced by convective features however ice multiplication led to the largest ice particle number concentrations being observed at relativelyhigh temperatures 10 degrees c the multiplication process most likely rime splintering occurs when stratiform precipitation interacts with supercooled water generated in the ncfr graupel was notably absent in the data obtained ice multiplication processes are known to have a strong impact in glaciating isolated convective clouds but have rarely been studied within larger organised convective systems such as ncfrs secondary ice particles will impact on precipitation formation and cloud dynamics due to their relatively small size and high number density further modelling studies are required to quantify the effects of rime splintering on precipitation and dynamics in frontal rainbands available parametrizations used to diagnose the particle size distributions do not account for the influence of ice multiplication this deficiency in parametrizations is likely to be important in some cases for modelling the evolution of cloud systems and the precipitation formation ice multiplication has significant impact on artefact removal from in situ particle imaging probes

evidence of liquid dependent ice nucleation in high latitude stratiform clouds from surface remote sensors 1 ground based lidar radar and microwave radiometer observations at eureka canada barrow alaska and over the western arctic ocean measure physical characteristics and morphology of stratiform clouds despite transition of a cold atmosphere 15 c through ice supersaturated conditions ice is not observed until soon after a liquid layer several cases illustrating this phenomenon are presented in addition to long term observations from three measurement sites characterizing cloud phase frequency this analysis demonstrates that clouds composed entirely of ice occur less frequently than liquid topped mixed phase clouds at temperatures warmer than 25 to 30 c these results indicate ice formation generally occurs in conjunction with liquid at these temperatures and suggest the importance of liquid dependent ice nucleation mechanisms

paleomagnetism stratigraphy and petrology of the upper cretaceous roskruge volcanics at bell mountain southeast arizona reconnaissance geologic mapping and petrologic study of the upper cretaceous roskruge volcanics at bell mountain in the roskruge mountains southeastern arizona have identified five compositionally distinct ash flow tuffs including the basal red viopuli tuff which comprise six or seven separate cooling units previous paleomagnetic investigators inferred eleven cooling units at bell mountain but insufficient information was given to determine which tuffs had been sampled this study was undertaken therefore to establish characteristic remanence directions for each tuff sheet the available paleomagnetic data corroborate the identification of five map units in the bell mountain area but the number of independent observations is too few for the calculation of a reliable paleopole paleosecular variation of the geomagnetic field would probably not be averaged out no correctable tuffs are present at bell mountain so relative vertical axis rotations cannot be determined although they are probably not large the absence of regionally correctable tuffs suggests the presence of additional potentially mineralized volcanic centers perhaps farther north in the roskruge mountains or buried nearby beneath cenozoic basin fill

3 d seismic velocity structure of the crust and the uppermost mantle in the northeastern japan arc 3 d seismic velocity structure of the crust and the uppermost mantle beneath the northeastern japan arc is investigated by using arrival time data from local earthquakes we use a velocity model composed of three layers corresponding to the upper crust the lower crust and the uppermost mantle respectively taking into account the observed regional variation of pn velocity the uppermost mantle is further divided into three parts by two pn velocity boundaries near the coasts of the japan sea and the pacific ocean the velocities within the upper crust the lower crust and the three parts of the uppermost mantle are assumed to be constant locations of two pn velocity boundaries and depth distributions of the conrad and the moho discontinuities are expressed by continuous functions of unknown parameters station corrections and hypocenters are also introduced to be unknowns these unknown parameters are determined by inverting arrival time data of p and s wave first arrivals and clear later arrivals of pg and p waves the pn velocity boundary between the land and the pacific ocean is located approximately along the pacific coastline and that between the land and the japan sea is nearly along the japan sea coastline the conrad and the moho discontinuities are at depths ranging from 14 to 20 km and from 27 to 36 km respectively the conrad and the moho depths have similar spatial distributions they are deep beneath the land and become shallower toward the western and the eastern coastlines beneath the land they are shallow in the central part of the tohoku district and become deeper toward both the north and the south directions in the north they become shallow again

seismic tomography of northern tibet and kunlun evidence for crustal blocks and mantle velocity contrasts although the crust and mantle of the tibet plateau reveal vital information for understanding the interplay of dynamic processes that has governed its recent uplift and growth their deep physical and thermal structure remains poorly understood in order to throw light on the structure and hence to constrain the processes and models tied to them we performed a teleseismic experiment on a 600 km long profile across the northern part of the plateau the kunlun range and the qaidam basin the 400 km deep tomographic image we obtain has a resolution 50 km over one order of magnitude better than achieved in previous broader scale studies at relatively shallow depth 100 km the tomographic cross section clearly reveals that the mid lower crust and upper lithosphere of northern tibet is an assemblage of blocks with different velocities and thicknesses hence different natures histories and ages the crust of the qiantang block appears to be thickest 70 km with the lowest velocity along the north edge of that block the jinsha suture although not remarkable in the local geology and topography stands as a particularly sharp and prominent crustal boundary the crust and lithosphere of the region between that suture and the qaidam bayan har songpan south kunlun appear to be thinnest 50 km and with the highest velocity at greater depth 150 km our experiment confirms the existence of a bulky low velocity zone in the mantle beneath the northernmost reaches of the plateau the tomogram helps assess with unprecedented accuracy the location and shape of this low velocity anomaly which forms a 250 300 km wide dome rising to about 150 200 km south of the kunlun range roughly coincident with the region where the strongest shear wave splitting hence horizontal anisotropy has recently been found that dome lies between two relatively high velocity zones with opposite dips one towards the north under the qaidam basin the other towards the south beneath the quangtang platform the implications that this new detailed image of the deep structure of northern tibet has upon the uplift and thermo mechanical evolution of the plateau are discussed

characteristics of surface heat flow in the south china sea a total of 592 heat flow measurements ranging from 8 to 192 mw m 2 78 percent of which are between 50 and 100 mw m 2 have been collected in the south china sea scs to overcome shortcomings such as the uneven distribution of the measurements and the occurrence of abnormal heat flow values the tectonic evolution of different areas and their crustal thickness have been combined in analyzing geothermal characters the results show that the oceanic basins where they are floored by oceanic crust the western part of the southern margin and the western fault system have high heat flow values heat flow along the northern margin of the scs increases from 61 mw m 2 on the shelf to 73 80 mw m 2 in the slope area and in the xisha zhongsha area increases from about 70 mw m 2 to about 85 mw m 2 from the nw to the se heat flow in the nansha spratley islands is about 60 mw m 2 or even higher and decreases from the nw to se the average heat flow of the mekong basin is about 60 mw m 2 which is similar to that of the beibuwan basin on the northern margin heat flow on the eastern margin and on the eastern part of the southern margin is lower especially in the luzon trough where the average heat flow is lower than 40 mw m 2 observed heat flow values in the sw subbasin are generally lower than predicted theoretically from the age of the ocean floor unlike values in the eastern subbasin a high heat flow zone in the lower slope area of the northern margin is recognized for the first time c 2003 elsevier ltd all rights reserved

fine structure beneath the tohoku district northeastern japan arc as derived by an inversion of p wave arrival times from local earthquakes abstract three dimensional p wave velocity structure beneath the tohoku district northeastern japan arc is investigated by an inversion of arrival times from local earthquakes using the method originally due to aki and lee 1976 in the crust 0 32 km depth a low velocity region is found along the volcanic front and its vicinity velocities at depths of 32 65 km are low beneath the regions where many quaternary volcanoes and geothermal areas are distributed in the region deeper than 65 km the subduction of the pacific plate is clearly revealed and the mantle structure above the descending plate is rather uniform these features suggest that volcanic activities have relation to the upper mantle structure the results obtained in this study will be helpful in investigating the mechanism of magma generation in a subduction zone

origin of low k intermediate lavas at nekoma volcano ne honshu arc japan geochemical constraints for lower crustal melts at lower crustal depths beneath the frontal arc is suggested by extremely low k basaltic andesite to andesite lavas at nekoma geophysical observations these observations further support lowervolcano situated in the frontal volcanic zone of the ne honshu crustal melting beneath nekoma as the origin of the intermediate arc were produced from melts that originated in the lower crust low k lavas multiple incompatible trace element model calculations suggest that extremely low k basalt found in the same arc is a natural analog for the source composition however fractional crystallization magma mixing and crustal contamination models of primary lowk basalt cannot reproduce the nekoma chemical composition

the method for consecutive subtraction of selected anomalies the estimated crustal velocity structure in the 1996 onikobe m 5 9 earthquake area northeastern japan summary the consecutive subtraction of selected anomalies cssa method has been presented to provide a new opportunity to improve the quality of inversion results in seismic tomography the basic idea of the iterative method is to determine in each step a parameter that subtracts the total largest square residuals the criteria proposed control the selection of the best solution from all candidates by inspecting their convergence to the accurate solution in the lsq sense resolution measures were defined by estimating the convergence degree the matching of the lanczos lsqr and cssa methods has been demonstrated from the perspective of the projection technique the storage and work requirements for both algorithms were compared revealing that cssa is also efficient for large and sparse systems synthetic models were reconstructed comparing cssa and lsqr and indicating that cssa gives us more reliable results when large sized structures are considered at the same time the simultaneous subtraction of the selected anomalies algorithm was examined numeral tests revealed that this algorithm is able to produce results that are similar to those obtained by lsqr complicated velocity structure can lead to ambiguous results a problem that can be solved by setting the appropriate starting vector for the cssa inversion the difference between the starting vector and the starting or reference model is discussed the cssa method was applied to p wave arrival times from shallow earthquakes to determine deep structure in the focal area of the onikobe m 5 9 earthquake 1996 in the northern part of honshu japan a specific feature of the traveltime residuals is a set of positive values corresponding to late p wave arrivals tomography revealed a low velocity body in the focal area from the surface down to the hypocentres local anomalies with the lowest perturbations were found in the surface layer of 0 2 km around the onikobe epicentre to the north of the focal area and to the northeast of naruko volcano

late cretaceous paleomagnetism of the tucson mountains implications for vertical axis rotations in south central arizona the tucson mountains of southern arizona are the site of an upper cretaceous caldera from which the rhyolitic cat mountain tuff was erupted at about 72 ma two magnetic units within the cat mountain tuff are distinguished by paleomagnetic data in both the northern and southern tucson mountains the resurgent amole pluton 72 ma in the northern tucson mountains was emplaced soon after eruption of the cat mountain tuff but cooled and was magnetized after northeastward tilting 50 85 of the adjacent caldera fill sequence petrologic and paleomagnetic data indicate that the lower magnetic unit of the cat mountain tuff caps the silver bell mountains to the northwest a previous paleomagnetic investigation n 34 indicates that the silver bell mountains have been rotated clockwise 30 16 95 confidence level about a vertical axis relative to cratonic north america a similar paleomagnetic study of upper cretaceous volcanic volcaniclastic and intrusive units in the tucson mountains n 26 indicates that these rocks have been rotated 7 14 clockwise relative to stable north america a direct comparison of paleomagnetic directions for the lower unit of the cat mountain tuff shows a 17 10 clockwise rotation between the silver bell mountains and the tucson mountains which supports the relative accuracy of the absolute rotations determined for these two mountain ranges preliminary paleomagnetic directions for middle tertiary units from the silver bell and tucson mountains are consistent with clockwise rotation having occurred prior to deposition of these rocks clockwise rotation of crustal blocks in southern arizona likely was associated with strike slip movement on major northwest trending faults in the region and this movement may have been related to oblique subduction of oceanic plates along the western continental margin in late cretaceous and early tertiary time the available paleomagnetic data indicate that rocks in southern arizona have not remained unrotated with respect to north america since late cretaceous time and that vertical axis rotations may have played an important role in the region during laramide deformation

late cretaceous paleomagnetism and clockwise rotation of the silver bell mountains south central arizona late cretaceous ash flow volcanism in the silver bell mountains of southern arizona 32 3 n 248 5 e was associated with caldera formation and porphyry copper mineralization oriented samples from 34 sites in volcanic volcaniclastic and intrusive units related to this episode of igneous activity 73 69 ma yield a mean paleomagnetic direction of i 61 2 d 24 0 95 7 6 primary remanent magnetizations are indicated by the presence of both normal and reversed polarities and by the significantly improved grouping 95 confidence level of site mean directions for a widespread tuff unit after structural correction a comparison of this direction with a direction at silver bell calculated from contemporaneous units for stable north america i 58 8 d 342 3 95 7 7 indicates a late cretaceous paleolatitude anomaly of 2 4 7 6 not significant at the 95 confidence level and a declination anomaly of 41 7 14 3 for the silver bell mountains previously determined paleomagnetic data for southeastern arizona suggest that this apparent clockwise rotation in the silver bell mountains is a local phenomenon although preliminary the average paleomagnetic direction for oligocene and lower miocene rocks in the silver bell area i 43 8 d 357 3 95 16 5 is similar to that calculated for stable north america i 50 2 d 352 2 95 3 9 implying that the observed rotation in the silver bell mountains occurred before 26 ma and was most likely associated with dextral strike slip movement along the ragged top and related wnw trending faults bounding the silver bell mountain block these data in conjunction with plate reconstructions and other paleomagnetic data from southwestern north america imply that wnw trending strike slip faults may have played an important role during late cretaceous to early tertiary deformation in southern arizona

the vertical cloud structure of the west african monsoon a 4 year climatology using cloudsat and calipso the west african summer monsoon wam is an important driver of the global climate and locally provides most of the annual rainfall a solid climatological knowledge of the complex vertical cloud structure is invaluable to forecasters and modelers to improve the understanding of the wam in this paper 4 years of data from the cloudsat profiling radar and calipso are used to create a composite zonal mean vertical cloud and precipitation structure for the wam for the first time the near coincident vertical radar and lidar profiles allow for the identification of individual cloud types from optically thin cirrus and shallow cumulus to congestus and deep convection a clear diurnal signal in zonal mean cloud structure is observed for the wam with deep convective activity enhanced at night producing extensive anvil and cirrus while daytime observations show more shallow cloud and congestus a layer of altocumulus is frequently observed over the sahara at night and day extending southward to the coastline and the majority of this cloud is shown to contain supercooled liquid in the top the occurrence of deep convective systems and congestus in relation to the position of the african easterly jet is studied but only the daytime cumulonimbus distribution indicates some influence of the jet position

tertiary tectonic and magmatic evolution of western sulawesi and the makassar strait indonesia evidence for a miocene continent continent collision

an investigation of the relationship between the geology of indonesian sedimentary basins and heat flow density abstract geothermal data collected from 929 wells drilled by oil companies in 20 tertiary basins of indonesia have been related to the geology and tectonics of the area it is found that the thermal conductivity increases with the depth of burial and degree of compaction in both transgressive and regressive sediments but decreases with increases in impurities and heterogeneous grain sizes the temperature gradient is controlled mainly by the depth and temperature of a heat source beneath a basin very high heat flow densities 125 mw m 2 found in central sumatra south sumatra salawati basin and bintuni basin may be caused by relatively shallow magmatic diapirism

a neogene history of mantle convective support beneath borneo abstract most but not all geodynamic models predict 1 2 km of mantle convective draw down of the earth s surface in a region centered on borneo within southeast asia nevertheless there is geomorphic geologic and geophysical evidence which suggests that convective uplift might have played some role in sculpting bornean physiography for example a long wavelength free air gravity anomaly of 60 mgal centered on borneo coincides with the distribution of neogene basaltic magmatism and with the locus of sub plate slow shear wave velocity anomalies global positioning system measurements an estimate of elastic thickness and crustal isostatic considerations suggest that regional shortening does not entirely account for kilometer scale regional elevation here we explore the possible evolution of the bornean landscape by extracting and modeling an inventory of 90 longitudinal river profiles misfit between observed and calculated river profiles is minimized by smoothly varying uplift rate as a function of space and time erosional parameters are chosen by assuming that regional uplift post dates eocene deposition of marine carbonate rocks the robustness of this calibration is tested against independent geologic observations such as thermochronometric measurements offshore sedimentary flux calculations and the history of volcanism a calculated cumulative uplift history suggests that kilometer scale bornean topography grew rapidly during neogene times this suggestion is corroborated by an offshore miocene transition from carbonate to clastic deposition co location of regional uplift and slow shear wave velocity anomalies immediately beneath the lithospheric plate implies that regional uplift could have been at least partly generated and maintained by temperature anomalies within an asthenospheric channel

high heat flow effects on a coalbed methane reservoir east kalimantan borneo indonesia abstract the balikpapan formation miocene age in sangatta east kalimantan is thick 1500 m containing abundant coal seams that range in thickness from less than a meter to over 5 m coal seams are distributed throughout the section and may represent 5 to 7 of the total formation thickness measured gas contents range from

subducting plate boundary beneath the northeastern japan arc estimated from sp converted waves abstract in the tohoku district the northeastern part of honshu japan a conspicuous phase is frequently observed between p and s phases in seismograms for events in the lower seismic plane of the double planed deep seismic zone this phase is dominant in the vertical component and has an apparent velocity almost equal to or slightly smaller than the p phase we have never found this phase in seismograms for events in the upper seismic plane from these characteristics the phase is interpreted as sp converted from s to p at the upper boundary of the descending oceanic plate ubp using the travel times of the sp waves we estimated the location of the ubp beneath the tohoku district to be just above the upper seismic plane of the double planed deep seismic zone this position is consistent with those determined from the analyses of the travel times of the scsp and ps waves which are respectively the seismic wave converted from scs to p and that from p to s at the ubp

lateral variation of the cutoff depth of shallow earthquakes beneath the japan islands and its implications for seismogenesis abstract we estimated the spatial distribution of the cut off depth of shallow seismicity beneath the japan islands based on data from a recently constructed nationwide dense seismic network in order to avoid the effect of heterogeneous seismic velocity structure we determined the 3d seismic velocity structure for the whole of japan which was then used to relocate the hypocenters the cut off depth was determined by calculating d90 the depth above which 90 of the earthquakes occur a spatial distribution of estimated d90 values shows a considerable lateral variation ranging from about 5 km to about 40 km the d90 s are deep along the pacific coast of eastern japan locally shallow d90 s extend along belt like stretches of volcanic areas heat flow is low along the pacific coast in eastern japan and high in the volcanic areas this indicates that the lateral variation of d90 s is formed mainly by lateral geotherm variation cooling by the subducting old very cold pacific plate may cause the deep d90 s along the pacific coast in eastern japan heating by magma supplied from the mantle wedge below is considered to be the main cause of the shallow d90 s in the volcanic areas magma and or aqueous fluids derived from solidified magma contribute not only to locally shallow d90 s but also to the weakening of ambient rocks in the lower crust resulting in stress concentrations in the upper crust just above them large shallow inland earthquakes tend to occur in such areas suggesting that a model of shallow earthquake generation applied to tohoku can be used in other areas in japan as well

mantle structure and seismotectonics of the sunda and banda arcs abstract we have examined the mantle structure and seismotectonic features of the sunda and banda arcs indonesia based on the p wave tomographic images focal mechanism solutions gravity anomaly and heat flow data on the basis of slab morphology and seismicity we can divide the arcs into three parts the western sunda eastern sunda and banda arc the slab like tomographic image penetrates to a depth of about 500 km below the western sunda arc where seismicity does not exceed a depth of 250 km in the eastern sunda arc where a seismic gap exists between 300 and 500 km depths the slab appears to be continuous and to penetrate into the lower mantle beneath the banda arc with seismicity down to a depth of about 650 km the slab dips gently and does not appear to penetrate into the lower mantle the positive gravity anomaly shows a systematic pattern namely the anomaly along the eastern sunda arc is larger than that in the western sunda and the banda arcs along the back arc side of the sunda and banda arcs the heat flow decreases from the west to the east seismic strain release from the shallow earthquakes calculated from the cmt solutions show the strain axes to be oblique to the structural trends the cmt solutions show that the eastern sunda arc is characterized by normal earthquakes along the trench and back arc thrusting earthquakes north of the volcanic line in the western sunda and the eastern sunda arcs earthquakes of the down dip extension type dominate the slab down to a depth of 200 km while down dip compression earthquakes occur below 500 km depth in the banda arc deep earthquakes show down dip extension to a depth of 500 km below this depth the state of stress is not clearly defined

paleomagnetism of the late cretaceous early tertiary north central montana alkalic province paleomagnetic results have been obtained from the late cretaceous early tertiary igneous complexes of the north central montana alkalic province data from 94 sites in eocene volcanic and intrusive rocks give a paleomagnetic pole located at 82 0 n 170 2 e a95 3 5 k 18 6 while 36 sites in paleocene intrusions yield a paleomagnetic pole at 81 8 n 181 4 e a95 5 4 k 20 2 these poles differ by only 1 6 and are not significantly different statistically the 130 site virtual geomagnetic poles show no significant elongation and suggest no significant apparent polar wander apw during the period of magnetization of the igneous centers postmagnetization structural complications in these rocks are minimal the presence of a single predominant polarity in these intrusive complexes reinforces the radiometric age data that suggest that igneous activity within individual centers was of short duration the northcentral montana data together with other early tertiary cretaceous and mid tertiary paleomagnetic results require modification of our earlier apw chronology diehl et al 1980 it now appears that apw relative to north america since the early cretaceous consists of a polar still stand during much of the cretaceous 120 75 m y b p a period of rapid movement in latest cretaceous time 75 65 m y b p and a period of slow polar movement thereafter the onset of this period of rapid apw correlates well with a major change in plate motions at 80 m y and the beginning of the laramide orogeny

tectonic stress state in ne japan as part of the okhotsk plate abstract an existing geodetic flow velocity model obtained by using an internal free network adjustment technique is used to derive estimates for various strain rates parameters in ne japan the greatest shortening rates of the principal strains trending e w are located in regions where much steady internal frame invariant plastic flow deformation is observed to be taking place the internal geodetic adjustment technique yielded the internal deformation in the tohoku arc most of the intraplate deformations including the much folding deformations observed in the inner zone are produced from within an interseismic transient elastic loading at a strongly coupled locked japan trench would not be needed the observed ongoing extensive ductile folding deformation in the inner zone of tohoku may mean that the geodetic strain rates causing shortening at 2 3 cm yr probably reflect the more correct level of the deformation which is steady permanent in ne japan as compared with seismic faulting data which indicate 0 5 cm yr shortening the calculated principal strain rates are used to make an interpretation for the origin of the deviatoric principal stresses within the greater regional plate tectonic framework the tectonic stress state in ne japan as part of the okhotsk plate could mostly be influenced by the okhotsk plate which is extruding southward to lessen the significant accumulated contractional deformation in ne asia in the verkhoyansk cherskii mountains the principal strain rates are n s extensional essentially everywhere in ne japan as a result of the southerly extrusion except in its southernmost leading edge in the uetsu fossa magna province where the japan alps rampart rises in front of the extrusion here an e w compressional stress state prevails a second e w contractional zone is found in north central tohoku extending from the sanriku province in the outer zone to the inner zone in the japan sea side being more prevalent in the latter zone the calculated rotation rates from the geodetic flow model are clockwise cw in both of the e w contractional regions ne japan extruding southward faces buttresses in 1 the oga ojika line ool and or a crustal weakness zone between the northern and the southern halves of tohoku approx at 38 5 n latitude and especially 2 the japanese alps rampart these obstacles cause the northern and southernmost tohoku to veer to its right and rotate cw thereby setting up the e w trending compressional deformation in their respective inner zones between the ool or the 38 5 n boundary and the kanto tectonic line ktl the sense of the differential rotations is counterclockwise ccw towards the ocean to the se the northern tohoku north of the ool and the southernmost tohoku south of the ktl cannot rotate ccw towards the ocean because of the izu block s collision in the south and the relatively strong coupling along the subduction interface beneath the japan trench in the north off sanriku the relatively stronger long term coupling between the northern tohoku and the pacific plate at the sanriku coast with respect to that in off fukushima is due to a flatter subduction of the pacific slab there increasing the plates interface contact area the flattening of the subduction dip angle was caused by ccw rotation and shifting of the northern tohoku along the dextral honjo matsushima line roughly corresponding to the ool towards the pacific and overriding of the subduction zone during the formation of the japan sea

crustal structure in an onshore offshore transitional zone near hong kong northern south china sea to study the crustal structure beneath the onshore offshore transitional zone a wide angle onshore offshore seismic experiment was carried out in northern south china sea near hong kong using large volume airgun sources at sea and seismic stations on land the crustal velocity model constructed from traveltime fitting shows that the sedimentary thickness abruptly increases seaward of the dangan islands based on the characteristics of pg and multiple pg and the crustal structure beneath the sedimentary layer is relatively simple the moho depth is about 25 28 km along the profile and the p wave velocity increases gradually with depth the velocities in the upper crust range from 5 5 to 6 4 km s while that in the lower crust is 6 4 6 9 km s it also reveals a low velocity zone with a width of more than 10 km crossing the crust at about 75 90 km distance which suggests that the littoral fault zone lfz exists beneath the onshore offshore transitional zone the magnetism anomalies bouguer gravity anomalies and active seismic zone along the coastline imply the lfz is a main tectonic fault in the onshore offshore area combined with two previously published profiles in the continental south china l g profile and in the northern margin of south china sea obs1993 respectively we constructed a land sea super cross section about 1000 km long the results show the onshore offshore transitional zone is a border separating the unstretched and the stretched continental crust the low velocity layer lvl in the middle crust was imaged along l g profile however the high velocity layer hvl in the lower crust was detected along obs 1993 by analyzing the mechanisms of the lvl in the middle crust and hvl in the base of crust we believe the crustal structures had distinctly different attributes in the continental south china and in the northern scs which indicates that the lfz could be the boundary fault between them c 2009 elsevier ltd all rights reserved

crustal structure across the xisha trough northwestern south china sea located at the northwestern part of the south china sea scs between the hainan and xisha paracel islands the xisha trough represents a failed rift in conjunction with the opening of the scs between 32 and 17 ma from west towards east within a scale of several hundred kilometers it presents all major stages of the rifting process and thus provides an ideal place to study the rifting process in great details in the autumn of 1996 a joint team of sino german scientists carried out a wide angle seismic experiment across the xisha trough with 10 ocean bottom hydrophones obh along a 237 km nnw sse oriented profile which was surveyed in 1987 with multi channel seismic mcs method by bgr of germany and soa of china favorable weather conditions and the powerful 4 x 12 1 air gun array rendered very good quality data with seismic signals observed at the offset of up to 110 km a detailed velocity depth model was obtained by using an interactive trial and error 2d ray tracing method interpretation of the nics data published by bgr provides very good geometrical constraints of the complex upper crustal structure which is characterized by fault blocks half horsts and half grabens filled with syn and post rift cenozoic sediments the velocity model in turn confirms the major structure outlined by the interpretation of the mcs data showing a varying sedimentary layer between i and 4 km of thickness and velocities between 1 7 and 4 5 km s the p wave velocity of 5 5 km s on the top of the crystalline basement is relatively low suggesting strong weathering within the crystalline crust the velocity increases downward continuously to 6 8 km s at the bottom of the crust without a clear differentiation in the middle crust showing clearly its continental nature even beneath the xisha trough the moho is marked by a sharp first order interface with a velocity of 8 0 8 1 km s at the uppermost mantle the moho depth is 15 km beneath the center of the trough and increases gradually to more than 25 kin towards north and south corresponding to an extreme thinning of the pre rift continental crust from more than 25 kin under the coast line to only 8 kin beneath the xisha trough the similar velocity structure of the continental nature on both sides of the xisha trough suggests a homogeneous pre rift continental setting the sharp moho and the lack of high velocity body hvb in the lower crust imply no magmatic underplating which is very different to interpretations across the eastern part of the continental margin in northern south china sea the intense faulting in the upper crust the strong but rather symmetrical crustal thinning centered at the xisha trough and the close neighborhood to the open scs nw subbasin suggest a pure shear rifting which failed most likely at the phase shortly before the continental breakup c 2001 elsevier science b v all rights reserved

permeability distribution in the lahendong geothermal field a blind fault captured by thermal hydraulic simulation subsurface fluid flow of reservoirs in active tectonic regions is mainly controlled by permeability of fault zones therefore the characterization of fault zones is an important step toward performance assessment of a reservoir the fluid flow is controlled also by pressure and temperature conditions in this context we simulated pressure and temperature fields to elaborate on the influence of permeability on subsurface fluid flow in the lahendong geothermal reservoir thermal hydraulic simulation is performed using a finite element approach adjusting the permeability through 370 different cases modeling results converged to the observed data within a misfit range of 0 7 the best fitting models identified a deep seated fault that has previously not been traced at the surface simulated temperature distribution suggests a prominent convective heat flow driven by an upward migrating and sw ne oriented fluid flow this hydraulic gradient causes a pressure drop along the reservoir high pressure patterns are used to constrain recharge areas in addition to infiltration measurements discharge flow occurs from sw to ne migrating also upward toward the hot springs in that frame thermal hydraulic simulations identified previously unresolved subsurface faults which now allow a better understanding of the subsurface permeability and its influence on fluid flow

new evidence for the existence and internal structure of a thin layer of magma at mid crustal depths near socorro new mexico the characteristics of a strong mid crustal reflector in the rio grande rift southwest of socorro new mexico were studied using high quality digital seismograms of microearthquakes the data are from a tight cluster of hypocenters located almost directly beneath the recording station 2 km cross correlation of the direct and reflected microearthquake s phases yields coefficients which are positive and large in absolute value average 0 79 because these two phases leave the focal region 180 out of phase for this swarm reflection must occur at a discontinuity where a 180 phase shift occurs waveforms for the p wave reflections are not identical from event to event within the swarm the character of the p reflection indicates a magma body with rapid lateral changes in internal structure the spectral characteristics of the reflected p phase are suggestive of constructive interference the near normal incidence geometry of both the reflected and direct p phase implies an essentially common path through the upper crust and near surface phanerozoic rocks for these two phases the earthquakes examined in this study are quite small ml 0 hence the initial portion of the direct p phase may be used as the response function for the path through the upper crust during modeling of the reflected p phase synthetic seismograms which include attenuation effects and interbed multiples were calculated and compared to the observed waveforms the results of modeling the stacked spectra of the pzp phase indicate a thin 70 m layer of nonrigid low velocity material underlain by a second thin 60 m layer of slightly higher velocity material this second layer may be an earlier partially solidified intrusion or a crystalline mush at the base of a single magma chamber the total thickness of the magma body is estimated to be 150 m

paleomagnetic results from the upper cretaceous maudlow and livingston formations southwest montana a paleomagnetic investigation of welded tuff units from the late cretaceous livingston and maudlow formations was undertaken to refine the late cretaceous to paleocene apwp for cratonic north america after progressive af and thermal demagnetization the maudlow formation 46 1 n 248 9 e yields a paleomagnetic pole at 70 n 208 e 11 sites a95 9 k 22 tectonic correction improves the directional grouping and the change is statistically significant two normal polarity intervals bounding a single reversed polarity interval are present we interpret the reversed interval to be chron 33r on the basis of 1 stratigraphic correlation of the maudlow formation with the campanian sedan formation located 40 km to the east and 2 k ar dates of 83 2 ma at the middle of the sampled section and 74 9 1 ma near the top of the sampled section the livingston formation 45 5 n 250 1 e yields a high hc magnetization with a negative fold test suggesting a post folding secondary magnetization the livingston mean direction yields a paleomagnetic pole at 72 n 218 e 10 sites a95 4 k 107 and is clearly distinguishable from a co existing lower hc component reflecting a recent viscous overprint we interpret the high hc magnetization as late cretaceous to paleocene in age neither the maudlow formation pole nor the pole derived from the high hc overprint in the livingston formation agree with previously published poles for either the late cretaceous or tertiary but they do lie on a simple continuation of the apwp between late cretaceous and paleocene mean poles secondary magnetizations found in the franciscan complex of california also yield poles which lie on a proposed extension of the apwp if the franciscan secondary poles represent an overprint event associated with early tertiary accretion and if the livingston secondary pole represents a deformational event related to laramide uplift of the nearby beartooth range then together these three poles suggest that the north american apwp may continue farther to the east and south to define a cretaceous tertiary cusp

deep structure of the northeastern japan arc and its relationship to seismic and volcanic activity evidence for possible deep seated magmatic activity beneath northeastern japan can be obtained from seismic observations tomographic inversions of p wave velocity data show low velocity zones distributed in the crust and upper mantle beneath active volcanoes in or around these zones anomalously low frequency micro earthquakes perhaps caused by magmatic activity are found at depths of 25 40 km distinct s wave reflectors corresponding to the upper surfaces of magma bodies are found at depths of 10 18 km large crustal earthquakes also occur around the low velocity zones these observations reveal the distribution of magma reservoirs at depths and elucidate its relation with shallow seismicity beneath volcanic arcs

deep structure of the northeastern japan arc and its implications for crustal deformation and shallow seismic activity abstract seismic tomography studies in the northeastern japan arc have revealed the existence of an inclined sheet like seismic low velocity and high attenuation zone in the mantle wedge at depths shallower than about 150 km this sheet like low velocity high attenuation zone is oriented sub parallel to the subducted slab and is considered to correspond to the upwelling flow portion of the subduction induced convection the low velocity high attenuation zone reaches the moho immediately beneath the volcanic front or the ou backbone range running through the middle of the arc nearly parallel to the trench axis which suggests that the volcanic front is formed by this hot upwelling flow aqueous fluids supplied by the subducted slab are probably transported upward through this upwelling flow to reach shallow levels beneath the backbone range where they are expelled from solidified magma and migrate further upward the existence of aqueous fluids may weaken the surrounding crustal rocks resulting in local contractive deformation and uplift along the backbone range under the compressional stress field of the volcanic arc a strain rate distribution map generated from gps data reveals a notable concentration of east west contraction along the backbone range consistent with this interpretation shallow inland earthquakes are also concentrated in the upper crust of this locally large contraction deformation zone based on these observations a simple model is proposed to explain the deformation pattern of the crust and the characteristic shallow seismic activity beneath the northeastern japan arc

along arc variation in seismic velocity structure related to variable growth of arc crust in northern izu bonin intraoceanic arc the izu bonin arc is an intraoceanic island arc where the pacific plate subducts beneath the philippine sea plate along arc variation in thickness of the arc crust has been observed by previous active seismic surveys beneath the izu bonin arc we have imaged three dimensional 3 d seismic velocity structures in the northern izu bonin arc using arrival time data of the earthquakes during 80 days of observations by ocean bottom seismographs and three permanent island seismic stations our 3 d velocity model indicates heterogeneous structure in the mantle wedge along the arc low velocity anomalies related to upwelling flow in the mantle wedge are not uniform beneath the volcanic front low velocity anomalies extending down to the subducting slab beneath the volcanic front coincide with thicker parts of the arc crust north of aoga shima and south of sumisu jima this coincidence suggests that heterogeneous mantle upwelling flow fundamentally controls the growth of the arc crust along topographic highs in the forearc low velocity anomalies in the crust and uppermost mantle coincide with positive magnetic anomalies suggesting the presence of a remnant arc providing further evidence of this view of arc crust formation

evidence that ice forms primarily in supercooled liquid clouds at temperatures 27 c using 4 years of radar and lidar observations of layer clouds from the chilbolton observatory in the uk we show that almost all 95 ice particles formed at temperatures 20 c appear to originate from supercooled liquid clouds at colder temperatures there is a monotonic decline in the fraction of liquid topped ice clouds 50 at 27 c falling to zero at 37 c where homogeneous freezing of water droplets occurs this strongly suggests that deposition nucleation plays a relatively minor role in the initiation of ice in mid level clouds it also means that the initial growth of the ice particles occurs predominantly within a liquid cloud a situation which promotes rapid production of precipitation via the bergeron findeison mechanism

low frequency earthquakes observed in close vicinity of repeating earthquakes in the brittle upper crust of hakodate hokkaido northern japan we conducted a detailed investigation of an earthquake cluster distributed from the lower crust to the upper crust beneath hakodate hokkaido which included both low frequency earthquakes lfes a

crustal structure of central japan and its petrological implications the crustal structure of central honshu japan has been influenced by several tectonic events a series of collision processes during the late tertiary extensive faulting highly compressive deformation and quaternary volcanism the southern part of the study area is covered by various granitic rocks which intrude into old palaeozoic formations quaternary volcanoes occupy the northern part and cover the basement which is mainly composed of granitic rocks and tertiary formations a traveltime inversion for velocity and interface depth was applied to the seismic data together with constraints from amplitude forward modelling to produce a seismic velocity model of the crust in central honshu in this experiment both refracted p and s waves are clearly recorded along a 110 km profile these provide constraints on the 2 d p and s wave velocity structure down to a depth of about 10 km moreover clear p wave reflections from intracrustal interfaces provide constraints on deeper parts of the crust down to about 25 km for the p wave velocity model the velocities of near surface layers show large lateral variations from 3 7 to 4 4 km s 1 increasing towards the south underlying layers have velocities ranging from 4 85 to 5 6 km s 1 velocities in the range 5 85 6 2 km s 1 characterize the upper crust that extends to a depth of about 15 km for the s wave velocity model the near surface layer velocities change from 1 7 to 2 55 km s 1 showing remarkable lateral heterogeneity whilst the upper crust is characterized by velocities of 3 4 3 6 km s 1 the deeper parts are modelled by two prominent reflectors in the mid crust the shallower one which delineates the bottom of the upper crust dips southwards from 14 to 16 km the deeper reflector lies between 20 and 24 km depth and dips northwards the velocity in this mid crustal layer is 6 35 km s 1 at the top and 6 7 km s 1 at the bottom the crustal thickness under the profile could not be determined because of a lack of pn and or pm p phases this study also presents the vp vs ratio and the poisson s ratio distribution and gives the probable composition of the upper crust poisson s ratio varies from 0 29 to 0 34 which can be ascribed to a porous and water saturated structure for the near surface layers in the northern part of the region poisson s ratios of about 0 24 0 25 in the southern part and 0 22 0 24 in the upper crust together with the geological data show that the upper crust has a felsic content and is formed by granite granodioritic rocks with a high quartz content the changes in the quartz content explain the lateral variations of vp vs and poisson s ratio in the model the higher velocities in the middle crust suggest a more mafic structure probably composed of diorites

reflection imaging of deep structure beneath montserrat using microearthquake sources 1 the sea calipso experiment was designed to image structure related to active volcanism beneath the island of montserrat in the caribbean as part of that experiment over 200 texan recorders with 5 hz geophones were deployed in 3 linear arrays at a nominal spacing of 100m primarily to record an airgun source towed offshore around the island because the recorders were operating in continuous mode for three days a number of shallow microearthquakes under the active summit of soufriere hills volcano shv were also recorded 20 events were sufficiently well recorded and located that they could be used to identify and map reflections from deep subsurface structure here we report on the processing of those recordings as multichannel cmp reflection sources with emphasis on careful statics correction and coherency enhancement the resulting reflection images indicate subhorizontal layering at depths between 6 and 19km which we interpret as sills