frictional resistance of faults during accelerating and decelerating earthquake slip the dynamic friction along faults controls earthquake ruptures in the crust but many previous studies have quantified this value only for constant slip rates experiments accounting for the more realistic condition of changing slip rates suggest that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip the dynamic friction of faults during earthquake slip is a critical control on earthquake ruptures in the crust extrapolation of brittle crack theories to natural earthquakes1 2 3 has led to the commonly held view that fault friction reduces during rapid earthquake slip a process known as slip weakening1 high velocity gouge experiments4 5 and recent analyses of thermal pressurization6 7 and frictional melting8 support such a notion however these studies dealt with constant rates of slip along faults here we present the results of experiments aimed at understanding the frictional behaviour of fault zone materials under variable slip rates conditions that are more representative of natural earthquakes our results show that faults undergo a sequence of strengthening weakening and healing during acceleration and deceleration of slip such a sequence may be explained by the extrapolation of rate and state frictional behaviour9 10 at low slip velocities to more realistic slip rates but involving different physical mechanisms and a different scale the initial strengthening should impose a barrier for rupture growth into large earthquakes the healing on decelerating fault motion may lead to pulse like earthquake ruptures11 12 13 14 and static stress drops that are low in comparison with the dynamic stress changes15

the role of gravity wave breaking in a case of upper level near cloud turbulence abstractan observed turbulence encounter that occurred outside a mesoscale convective system over the central united states on 3 june 2005 is investigated using observations and high resolution num

control of fluid pressures on the formation of listric normal faults abstract listric normal faults are widespread in the extension of the upper crust despite major advances in understanding the formation of listric faults through various experiments the mechanical conditions that allow their formation are highly debated in particular anderson s faulting theory predicts that newly formed normal faults are planar and are dipping at least at 45 and in practice at 60 65 for most rock types here we develop limit analysis to investigate the formation of a listric fault at the onset of slip linking a deep detachment to the topographic surface we find that listric normal faults can occur in the brittle upper crust without appealing to viscous or ductile behaviours nor to flexural stresses the disequilibrium compaction fluid pressures typically observed in many sedimentary basins are essential for the formation of listric faults the fluid pressure is hydrostatic down to the fluid retention depth z f r d and sustains a higher gradient below this depth parametric studies show that the surface slope is also essential for the formation of listric faults even with a gently dipping surface slope 4 whereas a flat topographic surface leads to a simple andersonian geometry at the onset of slip the method is applied to two field examples in order to determine fluid overpressures that best match the fault shapes interpreted from seismic data for the offshore niger delta the simulated normal faults match the observed listric faults with a very shallow z f r d 0 5 0 75 km and below z f r d the fluid pressure has a lithostatic gradient consistent with the observed fluid pressure profiles to reproduce a series of listric faults joining on one common low angle detachment in the nw gulf of mexico we demonstrate that a shallow z f r d 0 7 1 1 km is required below which the fluid pressure increases to the lithostatic pressure on the detachment in agreement with the fluid pressure observations

frictional heat from faulting of the 1999 chi chi taiwan earthquake 1 the frictional heat generated during an earthquake is thought to be a major portion of the total energy release however there have been no direct measurements of the heat generated by a large earthquake we present an estimate of the frictional heat produced by the 1999 chi chi taiwan earthquake mw 7 6 from temperature anomaly that is measured in a borehole penetrating a large slip region 10 m of the fault a local increase in the temperature profile across the fault is interpreted to be the residual heat generated during the earthquake analyses of this temperature anomaly lead to a low estimate of the dynamic shear stress 0 5 to 0 9 mpa and the heat produced in the large slip region of the fault 0 68 to 1 32 1017 j the total frictional energy is estimated as 2 4 to 6 1 1017 j indicating that seismic efficiency is 1 to 3

overpressures in the anadarko basin southwestern oklahoma static or dynamic fluid pressures were estimated from mud weights and wellhead shut in pressures along a north south linear trend through the anadarko basin in southwest oklahoma fluid pressures above hydrostatic start at a depth of about 2 5 km on a normalized scale where hydrostatic pressure equals 0 and lithostatic pressure equals 1 estimates of fluid pressures were found to range from 0 4 to 0 8 over a depth range of 4 7 km using scale analyses and a simple numerical model we evaluated two end member hypotheses compaction disequilibrium and hydrocarbon generation as possible causes of overpressuring in the anadarko basin if compaction disequilibrium is the primary cause of present day overpressures in the anadarko basin the anadarko basin is required to have an average permeability of 10 23 m2 10 8 md or lower if geopressures in the anadarko basin result from hydrocarbon generation average basin permeabilities can be as high as 10 21 m2 10 6 md scaling these average permeabilities down to thicknesses of 100 m or less implies permeabilities lower than 10 25 m2 10 10 md are required in the most optimistic scenario the lowest permeabilities ever measured on sedimentary rocks are in the neighborhood of 10 22 10 23 m2 10 7 10 8 md thus it is not possible to reconcile the existence of overpressures in the anadarko basin with classic hydrodynamic theories that maintain that aquicludes do not exist either some unknown process is generating excess fluid pressures or the anadarko basin contains pressure seals geopressure models that invoke compaction disequilibrium and are commonly applied to cenozoic basins undergoing rapid sedimentation e g the gulf coast basin of the southeastern united states do not appear to apply to the anadarko basin the anadarko basin belongs to a group of cratonic basins that are tectonically quiescent and characterized by the association of abnormal pressures with natural gas begin page 146

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

intensity of thunderstorm generated turbulence revealed by large eddy simulation thunderstorms are characterized by turbulent processes that constitute an important aviation hazard and cause vertical transport of atmospheric constituents turbulence occurs within cloud and in the surrounding clear air but despite its importance the characteristics of thunderstorm generated turbulence and its spatial distribution are poorly understood especially outside of cloud here we use large eddy simulation to characterize turbulence generated by a canonical thunderstorm the simulation identifies regions of notable three dimensional anisotropic turbulence more than 5 km above the storm in a shallow layer above the storm s anvil and a horizontally asymmetric pattern of weaker turbulence that extends more than 50 km horizontally away from the cloud our results provide the first continuous estimate of turbulence intensity in and around thunderstorms and represent a major step toward improved turbulence avoidance methods the results have broader implications for understanding the fundamental aspects of how thunderstorms affect their environment through vertical exchange processes

temperature estimates of coseismic heating in clay rich fault gouges the chelungpu fault zones taiwan abstract to investigate the coseismic frictional temperature in seismogenic fault zones we examine the characteristics of clays in the chelungpu fault zones with isothermal heating experiments scanning electron microscope coupled to an energy dispersive spectrometer sem edx and thermogravimetry analysis tga in the tcdp case taiwan chelungpu fault drilling project three fault zones of the chelungpu fault system were identified at the depth of 1111 m 1153 m and 1222 m described as fz1111 fz1153 and fz1222 hereafter respectively the clay mineral assemblages of fz1111 show evidence of melting and the temperature in a 2 cm band within the black gouge zone is estimated to be from 900 c to 1100 c by comparing the sem images of in situ natural samples with those of heated materials and the finding of no recrystallization of kaolinite amorphous aluminosilicates spinel in the fault samples the clay mineral assemblages of fz1153 suggested that kaolinite has been broken down by the thermal decomposition dehydroxylation but chlorite has not the clay characteristics and results of sem edx and tga constrain the faulting temperature from 500 c to 900 c with a spatial distribution up to 1 3 m the clay characteristics of fz1222 indicated that clays were changed by experiencing high temperature acid fluids instead of thermal decomposition dehydroxylation processes and that the temperature is localized in 2 cm and ranges from 350 c to 500 c the lowest temperature among three fault zones the estimates of temperature ranges and thermal anomaly intervals among three fault zones provide important information and constraints on the physical and chemical processes coseismic dynamic weakening mechanism and earthquake energy budget in the future

quantification of tertiary exhumation in the united kingdom southern north sea using sonic velocity data sonic velocities from the upper and middle chalk upper cretaceous the bunter sandstone and the bunter shale both lower triassic were used to independently quantify apparent exhumation height above maximum burial depth in the united kingdom uk southern north sea apparent exhumation is the displacement on the depth axis of a given velocity depth trend from the normal unaffected by exhumation trend apparent exhumation results derived from the upper and middle chalk the bunter sandstone and the bunter shale are statistically similar the consistency of results from carbonate and clastic units suggests that at a formational and regional scale overcompaction i e anomalously high sonic velocity in all three units analyzed reflects previously greater buria depth rather than sedimentological and or diagenetic processes and validates the use of lithologies other than shale in maximum burial depth studies the consistency of results from units of early triassic to late cretaceous age suggests that tertiary exhumation was of sufficiently great magnitude to mask any earlier mesozoic periods of exhumation and that maximum mesozoic cenozoic burial depth in the southern north sea was attained prior to tertiary exhumation the proposed magnitudes of exhumation are generally greater than those previously published for the southern north sea but they are consistent with recent estimates from apatite fission track analysis the amount of exhumation of the rock column is greatest on the recognized inversion axes i e sole pit cleveland where it reaches approximately 2 5 km however there was a regional component of 1 0 1 5 km exhumation during the tertiary that affected structurally uninverted areas and on which the more localized inversion related exhumation was superimposed cretaceous tertiary burial prior to exhumation must have been of greater magnitude and more rapid than suggested by the preserved stratigraphy the effect of this extra burial and subsequent exhumation on sedimentary rock decompaction procedure and thermal maturation modeling is illustrated for the cleethorpes 1 and 44 7 1 wells and must also be incorporated in modeling reservoir diagenesis the regional tertiary tectonic uplift associated with exhumation must have had a thick skinned origin

regional pore fluid pressures in the active western taiwan thrust belt a test of the classic hubbert rubey fault weakening hypothesis abstract we document regional pore fluid pressures in the active taiwan thrust belt using 55 deep boreholes to test the classic hubbert rubey hypothesis that high static fluid pressures depth normalized as pf rgz account for the extreme weakness of thrust faults since effective friction f f 1 taiwan fluid pressures are dominated by disequilibrium compaction showing fully compacted sediments with hydrostatic fluid pressures at shallow depths until the fluid retention depth zfrd 3 km below which sediments are increasingly undercompacted and overpressured the hubbert rubey fault weakening coefficient is a simple function of depth 1 0 6zfrd z we map present day and pre erosion fluid pressures and weakening 1 regionally and show that active thrusts are too shallow relative to zfrd for the classic hubbert rubey mechanism to be important which requires z 4zfrd 12 km to have the required order of magnitude hubbert rubey fault weakening of 1 0 15 the best characterized thrust is the chelungpu fault that slipped in the 1999 mw 7 6 chi chi earthquake which has a low effective friction f 0 08 0 12 yet lies near the base of the hydrostatic zone at depths of 1 5 km with a modest hubbert rubey weakening of 1 0 4 0 6 overpressured miocene and oligocene detachments at 5 7 km depth have 1 0 3 therefore other mechanisms of fault weakening are required such as the dynamical mechanisms documented for the chi chi earthquake

joint vp and vs tomography of taiwan implications for subduction collision orogeny abstract the taiwan orogen sitting at the pre rifted eurasian margin and bracketed by two sub orthogonal subduction systems is subject to complicated geotectonics motivating numerous seismic tomographic studies in local and regional scale most of them obtained p wave velocities vp or with vp vs ratio jointly but few were for s wave velocities vs with unprecedented amount of s wave data in this study a new set of well tuned vp vs and vp vs models were determined by an elaborate joint inversion scheme integrating the data of p and s wave travel times s p times and the borehole logging data for near surface correction into one system this allowed us to revisit the subduction collision process in detail by comparing vp vs and vp vs ratio simultaneously with enhanced slab imaging of philippine sea plate psp under northeast taiwan we are able to discriminate the plausible missing luzon forearc basement along the plate boundary and propose a skateboarding edge model in which the westernmost psp rides on the east subducted forearc basement and subducts northward underneath the eurasian lithosphere the underlain forearc basement along with the psp subduction then results in the anomalous shallow double seismic zone observed only near taiwan island meanwhile at around 121 e the north subducting psp seems dipping west to collide with the deep eurasian lithosphere shaping an irregular corner wedge structure in addition we evaluate our model with previous ones by waveform modeling approach and show the current performance of travel time tomography in taiwan region

environment and mechanisms of severe turbulence in a midlatitude cyclone abstracta large midlatitude cyclone occurred over the central united states from 0000 to 1800 utc 30 april 2017 during this period there were more than 1100 reports of moderate or greater turbulence at commercial aviation cruising altitudes east of the rocky mountains much of this turbulence was located above or otherwise outside the synoptic scale cloud shield of the cyclone thus complicating its avoidance in this study we use two way nesting in a numerical model with finest horizontal spacing of 370 m to investigate possible mechanisms producing turbulence in two distinct regions of the cyclone in both regions model parameterized turbulence kinetic energy compares well to observed turbulence reports despite being outside of hazardous large radar reflectivity locations in deep convection both regions experienced strong modification of the turbulence environment as a result of upper tropospheric lower stratospheric utls convective outflow for one region where turbulence was isolated and short lived simulations revealed breaking of 100 km horizontal wavelength lower stratospheric gravity waves in the exit region of a utls jet streak as the most likely mechanism for the observed turbulence although similar waves occurred in a simulation without convection the altitude at which wave breaking occurred in the control simulation was strongly affected by utls outflow from distant deep convection in the other analyzed region turbulence was more persistent and widespread there overturning waves of much shorter 5 10 km horizontal wavelengths occurred within layers of gradient richardson number 0 25 which promoted kelvin helmholtz instability associated with strong vertical shear in different horizontal locations both above and beneath the convectively enhanced utls jet

microseismicity and permeability enhancement of hydrogeologic structures during massive fluid injections into granite at 3 km depth at the soultz hdr site summary a high rate injection of 20 000 m3 of water into granite between 2 8 and 3 4 km depth at the soultz hot dry rock hdr test site in france in 1993 september led to a 200 fold increase in borehole transmissivity and produced a subvertical cloud of microseismicity of dimensions 0 5 km wide 1 2 km long 1 5 km high and oriented 25 nw the resulting data set is unusually complete and well suited to studying permeability creation enhancement processes in crystalline rock and the utility of microseismic data for revealing them although the microseismic cloud defined using joint hypocentre determination jhd locations was diffuse and showed little structure application of the collapsing method showed it to be composed largely of discrete tubes and planes that propagated coherently one prominent structure that extended 350 m downwards from the vicinity of a flow inlet early in the injection and that appears to contain a major flow path was subjected to detailed investigation to establish its hydrogeologic nature and the mechanisms underpinning its inferred permeability enhancement high resolution microseismic mapping techniques i e multiplets and clustering showed it to be a subvertical nnw sse striking fracture zone of width 10 20 m the strike and scale of the structure identifies it as a member of a family of hydrothermally altered cataclastic shear structures that constitute the primary permeable paths for fluid migration within the rock mass both under ambient and forced fluid flow conditions the microseismicity occurred on subvertical small scale fractures within the cataclastic shear zone whose azimuths scatter within 22 of parallel to the parent structure although the structure is likely to have been naturally permeable to some degree its permeability appears to have been significantly enhanced as a consequence of the injection the most likely mechanism of permeability enhancement which is in accord with the strong preference for the microseismicity to grow downwards involves strike slip shearing which produced the opening of vertical tubes at along strike jogs in the fault the so called hill mesh seismic moment release averaged over the structure suggests shear displacements of at least 0 3 mm occurred which are sufficient to generate aperture changes that are hydraulically significant the preponderance of discrete structures within the microseismic cloud after collapsing suggests that significant flow and permeability enhancement i e stimulation within the rock mass is largely confined to the interiors of shear zones that appear to have a spacing of approximately 100 m

permeability creation and damage due to massive fluid injections into granite at 3 5 km at soultz 2 critical stress and fracture strength 1 the stress acting on fractures in a 3 5 km deep borehole in granite is examined to place constraints on fracture strength and to evaluate whether permeable fractures tended to be critically stressed two data sets consisting of some 500 fractures are analyzed the first considers the permeable impermeable fracture populations in their natural state the second considers the populations after the hole had been subject to a prolonged 9 mpa overpressure in two major injections which increased the number of permeable fractures from 18 to more than 95 for both data sets it is found that permeable fractures are critically stressed inasmuch as they support levels of shear stress that would be verging on failure if their strength were governed by a coulomb friction law with a coefficient of 0 6 1 0 however the vast majority of impermeable fractures are also critically stressed implying that critical stressing is a necessary but not a sufficient condition for permeability to develop most permeable fractures showed evidence of shear failure after the injections and tended to occur in hydrothermally altered cataclastic shear zones suggesting that they may have been relatively weak because of the presence of illite to prevent failure of the impermeable fractures during the injections requires a cohesion of at least 6 5 mpa to augment a maximum allowable friction coefficient of 1 0 these are probably early mode 1 fractures that are sealed primarily with calcite the strength of the shear zones appears to be significantly greater than the illite rich fractures from which they are composed this imposes constraints on their internal architecture

deep water niger delta fold and thrust belt modeled as a critical taper wedge the influence of elevated basal fluid pressure on structural styles we use critical taper wedge mechanics theory to show that the niger delta toe thrust system deforms above a very weak basal detachment induced by high pore fluid pressure the niger delta exhibits similar rock properties but an anomalously low taper sum of the bathymetric slope and dip of the basal detachment compared with most orogenic fold belts this low taper implies that the niger delta has a very weak basal detachment which we interpret to reflect elevated pore fluid pressure 0 90 within the akata formation a prodelta marine shale that contains the basal detachment horizon the weak basal detachment zone has a significant influence on the structural styles in the deep water niger delta fold belts the overpressured and thereby weak akata shales ductilely deform within the cores of anticlines and in the hanging walls of toe thrust structures leading to the development of shear fault bend folds and detachment anticlines that form the main structural trap types in the deep water fold belts moreover the low taper shape leads to the widespread development of backthrust zones as well as the presence of large relatively undeformed regions that separate the deep water fold and thrust belts this study expands the use of critical taper wedge mechanics concepts to passive margin settings while documenting the influence of elevated basal fluid pressures on the structure and tectonics of the deep water niger delta

earthquakes injection wells and the perry nuclear power plant cleveland ohio on january 31 1986 an earthquake of richter magnitude 4 9 occurred in northeastern ohio some 17 0 km south of the perry nuclear power plant pnpp and 12 0 km south of the calhio injection wells accelerometers on site at the pnpp recorded accelerations as high as 0 19 to 0 23 g many instruments tripped due to high amplitude vibrations microearthquake networks have recorded 16 microearthquakes within 5 0 km of the injection wells with focal depths ranging from 1 0 to 3 0 km a hydrological model of an anisotropic reservoir 7 2 km wide and 18 4 km long indicates a pressure buildup of 5 3 mpa at the epicenter and 11 8 mpa at the injection well the assumption of an anisotropic reservoir is consistent with available geophysical and geologic data a pressure increase of 11 8 mpa based on stress ratio estimates in crustal rocks in the region is more than sufficient to induce failure to a depth of 5 0 km furthermore brittle faults and extensive fracture permeability within the basement rocks would allow for the migration of pressure transients to hypocentral distances the indicated pressure buildup of 5 3 mpa at the epicenter may have been sufficient to trigger the january 31 1986 earthquake

coseismic thickness of principal slip zone from the taiwan chelungpu fault drilling project a tcdp a and correlated fracture energy abstract direct observations of the physical structures of the seismogenic zones of active faults are rare due to the difficulty in reaching the fault zone at depth current geological evidences mostly from the surface suggest that principal slip zone psz accommodated most shear displacement and was the place where physico chemical processes occurred during an individual coseismic event and the thickness of psz is a few millimeter to tens of centimeter wide however the actual thickness of psz of a large earthquake a key parameter of seismology in understanding energy dissipation and rupture processes remains largely unknown the chelungpu fault that ruptured during the 1999 mw 7 6 chi chi earthquake taiwan was drilled to a depth of 2003 m providing a unique opportunity to sample an active fault that slipped in a recent large earthquake the psz corresponding to the 1999 chi chi earthquake was well characterized within cores at a borehole depth of 1111 m from the taiwan chelungpu fault drilling project a tcdp a here we determine the interval of clay anomaly that resulted from frictional melting thermal decomposition process by state of art in situ synchrotron xrd analysis providing very high spatial resolution for mineralogy combined with the interval of the presence of vesicles from microstructural observation the thickness of chi chi psz is estimated to be 1 mm thus the correlated contribution of surface fracture energy to earthquake breakdown work at least in this locality is quantified to be 1 9 the huge remaining part of the breakdown work seems to be turned into heat associated with fault dynamic processes during the 1999 chi chi earthquake

active detachment of taiwan illuminated by small earthquakes and its control of first order topography we use 110 000 small earthquakes to locate and map active faults in three dimensions within the taiwan arc continent collision the structure is dominated by a nearly horizontal band of small earthquakes at 10 km depth that is interpreted to seismically illuminate the main detachment zone of the mountain belt with other illuminated fault zones abutting the detachment zone the zone steepens below eastern taiwan to 30 90 and reaches depths of 30 60 km the three dimensional shape of the detachment zone in relation to topography allows a new test of critical taper wedge mechanics and suggests that the reversal of topographic slope across taiwan is controlled by the shape of the detachment

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

venus surface thermal emission at 1 μm in virtis imaging observations evidence for variation of crust and mantle differentiation conditions 1 the venus express spacecraft images the nightside thermal emissions using the visible and infrared thermal imaging spectrometer virtis at 1 02 1 10 and 1 18 m thermal emission from the surface is observed the signal is attenuated by scattering and absorption in the dense atmosphere the measured flux at the top of the atmosphere is positively correlated with surface temperature and surface emissivity the surface temperature of venus is relatively well constrained as being mainly a function of altitude with a gradient lesser or equal to the adiabatic lapse rate this study examines the correlation of virtis images showing a signal of the surface at 1 02 m with viewing geometry stray sunlight cloud opacity and topography and applies semiempirical relations to remove their influence the remaining contrast can be either ascribed to surface emissivity or unexpected temperature variations temperature variations due to active volcanism are unlikely to be persistent over the time of observations therefore the mosaic of all processed images is here interpreted in terms of surface emissivity variation the emissivity variation found is correlated with geomorphological features established from magellan synthetic aperture radar images it is generally lower at tessera terrain some but not all volcanic edifices show increased emissivity large lava flows in the lada terra lavinia planitia region also show an increased thermal emission this might indicate a more felsic surface composition of tessera highlands and large scale extrusive volcanism of ultramafic composition

numerical simulation of radial cloud bands within the upper level outflow of an observed mesoscale convective system abstract turbulence affecting aircraft is frequently reported within bands of cirrus anvil cloud extending radially outward from upstream deep convection in mesoscale convective systems mcss a high resolution convection permitting model is used to simulate bands of this type observed on 17 june 2005 the timing location and orientation of these simulated bands are similar to those in satellite imagery for this case the 10 20 km horizontal spacing between the bands is also similar to typical spacing found in a recent satellite based climatology of mcs induced radial outflow bands the simulated bands result from shallow convection in the near neutral to weakly unstable mcs outer anvil the weak stratification of the anvil the ratio of band horizontal wavelength to the depth of the near neutral anvil layer 5 1 to 10 1 and band orientation approximately parallel to the vertical shear within the same layer are similar to corresponding aspects of horizontal convective rolls in the atmospheric boundar

frictional strength of fault gouge in taiwan chelungpu fault obtained from tcdp hole b abstract three fault zones fzb1136 fzb1194 and fzb1243 are found in core samples in hole b borehole penetrating through the chelungpu fault central taiwan that activated at the 1999 taiwan chi chi earthquake each fault zone is composed of a black gouge zone bgz and a gray gouge zone ggz surrounded by a fault breccia zone bz and or fracture damaged zone fz we conducted tri axial friction experiments on samples collected from subzones of the above three fault zones under the 1 km depth ambient condition with axial shortening rates of 0 1 to 10 m s to investigate frictional strength and its velocity dependence we found that the coefficient of friction is 0 3 for the bgz at fzb1136 1136bgz which is lower than those at other fault zones this result indicates that fault slip at the chi chi earthquake occurred at the 1136bgz the estimated frictional strength profile across fzb1136 was that the frictional strength was the lowest the coefficient of friction was 0 3 for the bgz and increased up to 0 5 for undeformed host rock with increasing distance from the bgz presence of the intermediate frictional strength zone consisting of the ggz and the bz suggests a development of off fault damage zone where deformation occurred not only in the bgz but also in the intermediate zone this feature should be important to estimate total fracture energy released during earthquakes we also suggest that coefficients of friction and the velocity dependences of the samples are closely related to localization of shear deformation and clay content respectively

regional velocity depth anomalies north sea chalk a record of overpressure and neogene uplift and erosion a normal velocity depth trend for the upper cretaceous danian chalk group is determined by identifying interval velocity data that represent maximum burial in areas unaffected by overpressuring these data are derived from 845 wells throughout the north sea basin data from pelagic carbonate deposits on a stable plateau constrain the trend for shallow depths positive velocity anomalies relative to the trend are mapped along the western and eastern margins of the north sea basin and reflect regional neogene uplift and erosion of up to 1 km along the present day limit of the chalk a hiatus at the base of the quaternary increases in magnitude away from the basin center where a complete cenozoic succession is found this hiatus is consistent in size with the missing section estimated from chalk velocities when allowance is made for the quaternary reburial of the chalk negative velocity anomalies in the central and southern parts of the basin outline an area within which overpressures in the chalk exceed 10 mpa equivalent to a burial anomaly greater than 1 km relative to the normal trend the chalk pressure system is primarily dependent on overburden properties because retention of overpressure generated by the load of the upper overburden depends on the thickness and sealing quality of the lower overburden therefore the chalk is considered to represent a regional aquitard and the hydrodynamic model of long distance migration within the chalk is rejected the neogene uplift and erosion of the margins of the north sea basin and the rapid late cenozoic subsidence of its center fit into a pattern of late cenozoic vertical movements around the north atlantic

overpressuring mechanisms in the yinggehai basin south china sea yinggehai basin is an elongate cenozoic rift basin on the northwestern margin of the south china sea continental shelf its thick 17 km basin fill is characterized by high geothermal gradient and high overpressure overpressure associated with nonequilibrium compaction mainly occurs at depths more than 2800 m at the basin center and more than 4000 m at the basin margin because the shallow buried neogene and quaternary strata lack effective seals this regional overpressure distribution however is disrupted at basin center where high overpressure occurs in permeable formations at a depth as shallow as 1400 m on top of a series of deep seated faults and fractures we studied the processes and mechanisms of overpressuring via numerical modeling that couples basin filling sediment compaction and thermal and pressure fields to approach the origin of the shallow high overpressure model results indicated that an increase of fluid volume due to natural gas generation by organic cracking is not large enough to generate the overpressure because of the limited amount of organic matter the shallow overpressure has probably been generated allogenically deep open faults have served as vertical hydraulic conduits and channeled the deep high pressure into shallow permeable formations

observed structure of mesoscale convective systems and implications for large scale heating mesoscale convective cloud systems that produce large amounts of rain in mid latitudes and most of the rain in the tropics consist of a combination of convective and stratiform cloud the convective regions contain numerous deep cells that are often but not always arranged in lines the stratiform region is an outgrowth of the convective ensemble it lies adjacent to the convective region and is seeded by ice particles detrained from convective towers sometimes it lies to the rear of a propagating convective line while on other occasions it surrounds the convection the heating of the large scale environment by a mesoscale convective system is affected by both the convective and stratiform regions although processes such as melting and radiation are important the net heating by a system is dominated by condensation and evaporation associated with vertical air motions this paper reviews recent observational evidence regarding the mean vertical motion profiles in the convective and stratiform regions of mesoscale convective systems and the implications of these mean motions for the vertical distribution of heating of the large scale environment in both the convective and the stratiform regions vertical motions have been determined by various techniques including composites of rawinsonde and aircraft wind data single and dual doppler precipitation radar analyses and wind profiler observations in stratiform regions these data consistently show mean vertical velocity that is upward in the upper troposphere and downward in the lower troposphere the level separating upward from downward motion is located from 0 to 2 km above the 0 c level depending on location within the stratiform region diagnostic calculations show that these vertical motion profiles imply heating of the upper troposphere and cooling of lower levels by stratiform region processes data on vertical motions in the convective regions are less consistent from case to case these data sometimes indicate that the mean vertical velocity in convective regions is maximum in the lower troposphere in other cases the data indicate a maximum in the high troposphere diagnostic calculations show that heating profiles diagnosed from these two types of profile are quite different the first having a maximum of heating in the lower troposphere while the second has a maximum in the middle troposphere although it is difficult to determine whether or not the differences in estimates arise from different types of observations analysis methods or sampling strategies it seems likely that they stem from differences in the large scale environment of the different mesoscale systems the ubiquitous occurrence of stratiform regions in mesoscale convective systems and hurricanes together with their consistent heating profiles which systematically concentrate heating in upper levels while cooling lower levels are a major consideration in evaluating the interaction of mesoscale systems with the large scale environment however the consistency of the stratiform profiles from case to case indicates that the variability of net convective plus stratiform heating profiles from case to case lies primarily in the variation of the convective region profiles from one case to another it is suggested that future work should focus on the convective region vertical profiles of vertical motion and heating and on the large scale environmental factors that may control the variation of these profiles from case to case

the role of vertical shear on aviation turbulence within cirrus bands of a simulated western pacific cyclone abstractat 0300 utc 9 september 2010 commercial aircraft traveling between tokyo and hawaii encountered regions of moderate and severe intensity turbulence at about 12 km elevation in or just above banded structures in the cirrus anvil associated with an oceanic cyclone located off the east coast of japan the generation mechanisms of the cirrus bands and turbulence are investigated using the advanced research weather research and forecasting model with five nested domains having a finest horizontal grid spacing of 370 m the simulation reproduces the satellite observed patterns of cloud brightness including the bands and suggests that synoptic scale vertical shear within the anvil cloud layer and radiative effects including longwave cooling at cloud top and warming at cloud base act together to produce banded structures within the southern edge of the cirrus cloud shield the character of the bands within the nearly neutral or convectively unstable layer of the cirrus shield is similar to boundary l

evolution of structures and fabrics in the barbados accretionary prism insights from leg 110 of the ocean drilling program the microstructures and crystal fabrics associated with the development of an amphibolite facies quartzo feldspathic mylonitic shear zone torridon nw scotland have been investigated using sem electron channelling our results illustrate a variety of microstructures and fabrics which attest to a complex shear zone deformation history microstructural variation is particularly pronounced at low shear strains significant intragranular deformation occurs via a domino faulting style process whilst mechanical incompatibilities between individual grains result in characteristic grain boundary deformation accommodation microstructures a sudden reduction in grain size defines the transition to medium shear strains but many of the boundaries inherited from the original and low shear strain regions can still be recognized and define distinctive bands oriented at low angles to the shear zone margin grains within these bands have somewhat steeper preferred dimensional orientations these domains persist into the high shear strain mylonitic region where they are oriented subparallel to the shear zone margin and consist of sub 20 m grains the microstructures suggest that the principal deformation mechanism was intracrystalline plasticity with contributions from grain size reduction via dynamic recrystallization grain boundary migration and grain boundary sliding crystal fabrics measured from the shear zone vary with position depending on the shear strain involved and are consistent with the operation of several crystal slip systems e g prism basal rhomb and acute rhomb planes in a consistent direction probably parallel to a and or m they also reveal the presence of dauphine twinning and suggest that this may be a significant process in quartz deformation a single crystal fabric evolution path linking the shear zone margin fabric with the mylonitic fabric was not observed rather the mylonitic fabric reflects the instantaneous fabric which developed at a particular location for a particular shear strain and original parental grain orientation the mature shear zone therefore consists of a series of deformed original grains stacked on top of each other in a manner which preserves original grain boundaries and intragranular features which develop during shear zone evolution the stability of some microstructures to higher shear strains the exploitation of others at lower shear strains and a continuously evolving crystal fabric mean that the strain gradient observed across many shear zones is unlikely to be equivalent to a time gradient

slip vectors of the surface rupture of the 1999 chi chi earthquake western taiwan about 100 slip vectors were surveyed along the 1999 chi chi earthquake rupture 100 km long western taiwan to understand the coseismic reverse faulting processes the surveyed slip azimuths vary locally over 80 where the rupture is irregular or associated with flexure even where the rupture is straight and has consistent slip azimuths the fault scarp heights horizontal slips and fault dip angles oscillate in a distance of hundreds of meters along the rupture despite these local variations the net slip up to 11 5 m vertical and horizontal slips are significant greater in the north on which maximum shortening 6 m by pure thrust and strike slip 8 m by left lateral fault occur in association with the bend of the rupture the slip azimuths also progressively rotate from north northwest in the north to west southwest in the south these patterns generally agree with those revealed by gps surveys except that the slips by gps in the south move to the west northwest and have values unexpectedly smaller than our measurements our obtained sw directed slips resulted in dominantly right lateral faulting up to 2 4 m where the rupture ends to the southeast this however does not correspond to focal mechanisms of any main shocks or aftershocks

hydrocarbon generation as a mechanism for overpressuring in rocky mountain region overpressured reservoirs are present in the deeper parts of most basins in the rocky mountain region a variety of conditions can cause overpressuring however most high pressures in the region are caused by present day or recently active oil and gas generation or generation in the last few million years in low permeability rock successions that still contain organic matter capable of yielding thermally generated hydrocarbons rocks with above normal pressure range from devonian to tertiary and commonly are associated with low permeability tight reservoirs most of the overpressuring occurs in cretaceous and tertiary rocks overpressuring in rocks older than cretaceous is rare and where present only occurs in strata with very rich hydrocarbon source beds such as the d vonian mississippian bakken formation most organically lean pre cretaceous source beds are no longer capable of yielding enough hydrocarbons to maintain abnormal pressure nearly all overpressured reservoirs and source rocks have temperatures of approximately 200 f 93 c or higher in addition available data indicate that hydrocarbon related overpressuring does not generally occur if vitrinite reflectance ro values are less than 0 6 in oil prone strata or less than 0 7 in gas prone strata overpressured gas bearing strata generally have ro values of 0 8 or higher maximum reservoir pressures are about equal to the fracture gradient pressure in the reservoir rocks some vertical fractures in reservoir rocks are probably caused by rapid expulsion of hydrocarbons from the source beds high pressures in the rocky mountain region means that the rock succession is gas or oil saturated and discrete hydrocarbon water contacts are generally not present classical concepts of hydrodynamics do not appear to be applicable to these overpressured successions the optimum depths for exploration are generally the upper 1 000 2 000 ft 305 610 m of the overpressured succession

changes in paleostress and its magnitude related to seismic cycles in the chelung pu fault taiwan paleostress analysis was conducted through a multiple stress inversion method using slip data recoded for the core samples from the taiwan chelung pu fault drilling project tcdp two stress fields were obtained one of these had horizontally plunging 1 and the other has horizontally plunging 2 or 3 in the compressional stress direction of the chi chi earthquake stress magnitude for both the stress fields was constrained by stress polygons which indicated larger shmax for horizontally plunging 1 than that in the case of horizontally plunging 2 or 3 these differences in stress orientations and stress magnitude suggest that the change in stress filed can be caused by stress drop and stress buildup associated with seismic cycles the seismic cycles recoded in the core samples from tcdp could include many events at geological timescale and not only the 1999 chi chi earthquake

convection permitting simulations of the environment supporting widespread turbulence within the upper level outflow of a mesoscale convective system abstract widespread moderate turbulence was recorded on three specially equipped commercial airline flights over northern kansas near the northern edge of the extensive cirrus anvil of a nocturnal mesoscale convective system mcs on 17 june 2005 a noteworthy aspect of the turbulence was its location several hundred kilometers from the active deep convection i e large reflectivity regions of the mcs herein the mcs life cycle and the turbulence environment in its upper level outflow are studied using rapid update cycle ruc analyses and cloud permitting simulations with the weather research and forecast model wrf it is demonstrated that strong vertical shear beneath the mcs outflow jet is critical to providing an environment that could support dynamic e g shearing type instabilities conducive to turbulence comparison of a control simulation to one in which the temperature tendency due to latent heating was eliminated indicates that strong vertical shear and corresponding reductions in the l

pore pressure generation in sedimentary basins overloading versus aquathermal the principal mechanism for abnormally high pore pressure generation has been an important matter of debate for more than a decade among the various mechanisms proposed mechanical overloading and aquathermal pressuring have probably received the greatest attention most previous discussions however have been based upon qualitative conceptual models here we propose a quantitative analysis by first examining the basic principles of porous flow and the fundamental properties of sediments and second by comparing the relative importance of the overloading versus the aquathermal mechanisms the coupling between pore pressure and compaction as well as the nonlinear and path dependent material properties are found to be critical in the present analysis we find that although changes in stress and temperature both contribute to pressure generation mechanical overloading is the main mechanism under normal geological conditions and is capable of producing the observed pore pressure profiles

an investigation of turbulence generation mechanisms above deep convection abstract an investigation of the generation of turbulence above deep convection is presented this investigation is motivated by an encounter between a commercial passenger aircraft and severe turbulence above a developing thunderstorm near dickinson north dakota on 10 july 1997 very high resolution two and three dimensional numerical simulations are used to investigate the possible causes of the turbulence encounter these simulations explicitly resolve the convection and the turbulence causing instabilities the configurations of the models are consistent with the meteorological conditions surrounding the event the turbulence generated in the numerical simulations can be placed into two general categories the first category includes turbulence that remains local to the cloud top and the second category includes turbulence that propagates away from the convection and owes its existence to the breakdown of convectively generated gravity waves in both the two and three dimensional calculations th

geopressuring mechanism of organic matter cracking numerical modeling since the 1950s hydrocarbon generation has been considered as one of the most important abnormal pressuring mechanisms hydrocarbon generation effects on pore pressure evolution 1 it increases the pore fluid volume through the conversion of solid kerogen into liquid or gaseous hydrocarbon and 2 it decreases the sediment permeability because hydrocarbons remain an immiscible phase in pore water in this paper the two products of organic matter decomposition liquid hydrocarbon oil and gaseous hydrocarbon methane are assumed to occur in sequence as a supplementary phase in pores as a basis for evaluating the effect of this pressuring mechanism a simplified three stage first order kinetic reaction model is applied to simulate the generation of oil and gas we u e a numerical basin model with a two phase hydrodynamic formulation to calculate the effect of organic maturation on geopressure evolution oil generation does not play an important role except when the organic matter content of rocks is relatively large 5 however the generation of gas has a large influence the results show that beneath a certain depth oil to gas cracking strongly influences overpressuring the effect of this mechanism becomes more important with increasing organic matter content of rocks several environmental conditions such as kerogen type temperature gradient and lithological characteristics influence to various degrees the effect of organic matter maturation on overpressure development

heat signature on the chelungpu fault associated with the 1999 chi chi taiwan earthquake 1 we have made observations of a heat signature that is associated with the frictional heat generated at the time of faulting for a large earthquake temperature measurements in a borehole that intersects the chelungpu fault at a depth of about 1100 m show a small increase near the fault even six years after the earthquake the temperature signature has a symmetric shape with a width of about 40 m and is centered on the fault that slipped about 5 m during the 1999 chi chi taiwan earthquake the small amplitude of 0 06 c for the observed temperature anomaly indicates a very low level of friction that generated heat at the time of the earthquake

early post rift sequence stratigraphy of a mid tertiary rift basin in taiwan insights into a siliciclastic fill up wedge abstract in order to scrutinize the development process and control of an early post rift siliciclastic fill up wedge sequence stratigraphy was applied to the oligo miocene coastal shelf strata of a mid tertiary rift basin in taiwan four sequences at the million year 3rd order scale constrained by microfossil biohorizons and radioactive dates were identified and correlated regionally the lower sequence belongs to the fault bounded oligocene syn rift wedge the middle two comprise the lower miocene early post rift wedge onlapping onto the mesozoic basement highs the upper sequence is the lower miocene late post rift drape on the continental margin the middle two sequences record a process of active topographic transformation through successive coastal shelf progradations at first the remnant rift topographic low received drastic progradations from both the inner and outer highs during the later progradations principally from the inner high the topographic low was filled up for the successive drape this wedge formation was characteristically short lived and high in sedimentation rate when accommodation space and sediment supply both increased the initial accommodation space of the remnant rift deep shelf was augmented by rapid thermal subsidence and long term eustatic sea level rise the sediment supply in spite of a decrease in provenance exposure due to onlapping was promoted by periodic exposures due to 3rd order eustatic sea level falls and additionally by a warm and humid climate these falls are age concordant with the sequence boundaries and thus evidently important for the sequence boundary formations and sediment dispersal

analysis of data from aquifer and well tests in intrusive dikes abstract approximate solutions to the problem of groundwater flow in a composite dike aquifer system are presented for the case that a well in the dike is pumped at a constant rate these solutions yield curve fitting procedures to evaluate the drawdown behaviour of wells drilled in a dike procedures based on the authors previous work are described these contained a distance drawdown analysis of observation wells with two particular type curves and a time drawdown analysis of the pumped well they were tested for validity with model and field tests in this study the authors develop a method to analyze the time drawdown behaviour of individual observation wells in the dike in addition general type curves are presented which allow the distance drawdown behaviour at any time to be analyzed a computer program is presented to construct time drawdown type curves it can be run on a pocket calculator or small computer sufficient data are tabulated to construct distance drawdown type curves with common type curve matching procedures early time transient drawdown data can be analyzed to obtain the hydraulic characteristics of the dike and the product of the storativity and the transmissivity of the country rock the methods described are illustrated by aquifer test data from two field tests

mechanisms supporting long lived episodes of propagating nocturnal convection within a 7 day wrf model simulation abstract a large domain explicit convection simulation is used to investigate the life cycle of nocturnal convection for a one week period of successive zonally propagating heavy precipitation episodes occurring over the central united states similar to climatological studies of phase coherent warm season convection the longest lived precipitation episodes initiate during the late afternoon over the western great plains 105 100 w reach their greatest intensity at night over the central great plains 100 95 w and typically weaken around or slightly after sunrise over the midwest 95 85 w the longest lived episodes exhibit average zonal phase speeds of 20 m s 1 consistent with radar observations during the period composite analysis of the life cycle of five long lived nocturnal precipitation episodes indicates that convection both develops and then propagates eastward along an east west oriented lower tropospheric frontal zone an elevated 2 km deep layer of high e air helps sustain convect

neotectonic architecture of taiwan and its implications for future large earthquakes the disastrous effects of the 1999 chi chi earthquake in taiwan demonstrated an urgent need for better knowledge of the island s potential earthquake sources toward this end we have prepared a neotectonic map of taiwan the map and related cross sections are based upon structural and geomorphic expression of active faults and folds both in the field and on shaded relief maps prepared from a 40 m resolution digital elevation model augmented by geodetic and seismologic data the active tandem suturing and tandem disengagement of a volcanic arc and a continental sliver to and from the eurasian continental margin have created two neotectonic belts in taiwan in the southern part of the orogen both belts are in the final stage of consuming oceanic crust collision and suturing occur in the middle part of both belts and postcollisional collapse and extension dominate the island s northern and northeastern flanks both belts consist of several distinct neotectonic domains seven domains kaoping chiayi taichung miaoli hsinchu ilan and taipei constitute the western belt and four domains lutao lanyu taitung hualien and ryukyu make up the eastern belt each domain is defined by a distinct suite of active structures for example the chelungpu fault source of the 1999 earthquake and its western neighbor the changhua fault are the principal components of the taichung domain whereas both its neighboring domains the chiayi and miaoli domains are dominated by major blind faults in most of the domains the size of the principal active fault is large enough to produce future earthquakes with magnitudes in the mid 7 values