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

neogene stratigraphy and the sedimentary and oceanographic development of the nw european atlantic margin a regional correlation of neogene stratigraphy has been attempted along and across the nw european atlantic continental margin between mid norway and sw ireland two unconformity bounded successions are recognised these are referred to as the lower and upper neogene successions and have been dated as miocene early pliocene and early pliocene holocene respectively in age their development is interpreted to reflect plate wide tectonically driven changes in the sedimentary oceanographic and latterly climatic evolution of the ne atlantic region the lower neogene succession mainly preserves a record of deep water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities within this succession on both sides of the eastern greenland scotland ridge from the mid miocene this is interpreted to record enhanced deep water exchange through the faroe conduit deepest part of the southern gateway and can be linked to compressive inversion of the wyville thomson ridge complex thus a pervasive interconnected arctic north atlantic deep water circulation system is a neogene phenomenon the upper neogene succession records a regional change at about 4 ma in the patterns of contourite sedimentation submarine erosion new depocentres coeval with the onset of rapid seaward progradation of the continental margin by up to 100 km this build out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin associated changes in deep water circulation may be part of an atlantic wide reorganisation of ocean bottom currents glacial sediments form a major component of the prograding shelf margin shelf slope sediment wedges but stratigraphic data indicate that the onset of progradation pre dates significant high latitude glaciation by at least 1 ma and expansive northern hemisphere glaciation by at least 3 ma

giant carbonate mud mounds in the southern rockall trough seismic profiles sidescan sonar data bottom photography and sampling proved for the first time that there are giant carbonate mounds bioherms in the rockall trough the pelagia mounds on the northern porcupine bank are relatively isolated whereas most of the logachev mounds on the southeast rockall bank form a field of closely spaced contiguous mounds they are all found on the upper slope at depths between about 500 and 1200 m and as a result of this study about 500 have been mapped they have a variety of shapes and the larger ones are very steep sided up to 350 m high and 2 km wide at the base sediment samples show that the mounds consist of pale coloured muds mainly aragonite usually with live and or dead cold water corals at the seafloor and with buried dead corals coral thickets appear to be detected as a brush like signature on high resolution profiles and as a speckled pattern on high resolution sidescan sonar records shelly sands are found on the seabed between the mounds currents in the mound areas are strong enough to transport sands along slope as medium sized sand waves and to prevent pelagic deposition thus providing surfaces for initial coral settlement by the winnowing of fines to leave glacial dropstones and exposed rocks these observations show that the poleward directed upper slope current of the eastern north atlantic extends further south than hitherto known and that there is a southwesterly directed current on rockall bank there are waves on the logachev mounds with a wavelength of about 20 30 m that are thought to be moulded in carbonate muds by across slope directed internal tidal currents and or cascading currents mounds develop above erosional surfaces seen on seismic data the huge amount of carbonate mud seems to be produced by the rapid growth and breakdown of cold water corals living in a very favourable environment intermediate nepheloid layers formed upstream by the strong currents may provide the food source for the deep water suspension feeders conditions for giant mound growth require an ideal balance between current speed and sedimentation rate among other factors no evidence for the suggested link to methane seepage has been found so far

fossil fluid reservoir beneath a duplex fault structure within the central range of taiwan implications for fluid leakage and lubrication during earthquake rupturing process in order to understand the kinematics which likely facilitated the speedy rupturing process of the 1999 mw 7 6 taiwan chichi earthquake we examined exposed rocks in the taiwan slate belt where the pressure and temperature conditions most resembled the hypocentre of the chi chi earthquake i e subgreenschist facies field observations and composition analyses of the silicified vein rich zones beneath the duplex structure suggest that impermeable slate layers may serve as cap rocks for confining deep seated fluids these fluids most likely come from the taiwan metamorphic complex at deeper depths by the dehydration and decarbonation reactions or partial melting in addition the gouge zone of a link fault above the detachment also indicates the presence of overpressured fluids during faulting it is probable that episodic leakage of the confined fluid reservoirs may provide essential fluids for fault lubrication during earthquake ruptures

an observation of rupture pulses of the 20 september 1999 chi chi taiwan earthquake from near field seismograms the ground velocity recordings of the 20 september 1999 chi chi taiwan earthquake recorded at stations near the ruptured fault trace show a simple large amplitude and long period pulse following the s wave which is closely associated with the surface faulting and the rupture process of thrust faulting the conspicuous pulse on the ground velocity seismogram following the s wave arrival called the s 1 phase is interpreted as the superposition of the rupture pulses that nucleate at an asperity near and underneath the station and propagate up dip and laterally along the fault plane toward the surface stations the arrival times of the s 1 phase and the onsets of the permanent displacement at stations near and along the ruptured fault trace increase with hypocentral distance suggesting that the rupture of the chi chi earthquake might have initiated at the hypocenter of the mainshock and propagated both upward and laterally from south to north on the basis of the travel time differences between the s 1 phase and the direct s wave at the stations near and along the ruptured fault trace the rupture velocities varied from 2 28 to 2 69 km sec with an average rupture velocity of about 2 49 km sec the rupture velocities decreased from south to north

nondestructive continuous physical property measurements of core samples recovered from hole b taiwan chelungpu fault drilling project 1 the taiwan chelungpu fault drilling project was undertaken in 2002 to investigate the faulting mechanism of the 1999 mw 7 6 taiwan chi chi earthquake hole b penetrated the chelungpu fault and core samples were recovered from between 948 42 and 1352 60 m depth three major zones designated fzb1136 fault zone at 1136 m depth in hole b fzb1194 and fzb1243 were recognized in the core samples as active fault zones within the chelungpu fault nondestructive continuous physical property measurements conducted on all core samples revealed that the three major fault zones were characterized by low gamma ray attenuation gra densities and high magnetic susceptibilities extensive fracturing and cracks within the fault zones and or loss of atoms with high atomic number but not a measurement artifact might have caused the low gra densities whereas the high magnetic susceptibility values might have resulted from the formation of magnetic minerals from paramagnetic minerals by frictional heating minor fault zones were characterized by low gra densities and no change in magnetic susceptibility and the latter may indicate that these minor zones experienced relatively low frictional heating magnetic susceptibility in a fault zone may be key to the determination that frictional heating occurred during an earthquake on the fault

conjugate thrust faulting associated with the 1999 chi chi taiwan earthquake sequence 1 the geometrical structure of the responsible faults of the 20 september 1999 chi chi taiwan earthquake ml 7 3 mw 7 6 and its aftershocks can be clearly depicted by well located hypocenters and focal mechanisms of large aftershocks the mainshock and two large aftershocks with ml 6 8 were characterized by thrust faulting along a n s striking fault plane dipping to the east the underground structure of the chelungpu fault which is probably merging with the decollement beneath the western foothills can be clearly associated with the seismicity pattern and the focal mechanisms of the three largest events a group of deeper aftershocks including two moderate events ml 6 3 and 6 0 respectively were located to the southeast of the mainshock along a fault plane dipping steeply to the west down to a depth of about 30 km our results suggest that the spatial pattern of the aftershocks in the southern part of the source area can be interpreted by a conjugate fault system this conjugate fault system is comprised of the gently east dipping chelungpu fault and a steeply west dipping deeper fault zone

a high frequency view of the 1999 chi chi taiwan source rupture and fault mechanics high frequency bandpass filtering of broadband strong motion seismograms recorded immediately adjacent to the fault plane of the 1999 chi chi taiwan earthquake reveals a sequence of distinct bursts many of which contain quasi periodic subbursts with repeat times on the order of a few tenths of a second the subevents that produce these bursts do not appear in conventional slip maps presumably because of the low pass filtering used in the waveform inversions the origin times locations and magnitudes of of about 500 of these subevents were determined those closest to the hypocenter appear to have been triggered by the p wave while the earliest subevents at greater distances are consistent with a rupture front propagating at about 2 0 km sec later subevents at a given distance follow omori9s law and may be interpreted as aftershocks that begin before the chi chi rupture has terminated the frequency magnitude distribution of these subevents has a b value equal to 1 1 the subevents are clustered in space with most clusters located at shallow depth along the chelungpu surface rupture the larger subevents tend to occur at greater depth while the small subevents are only located at shallower depths cluster locations generally coincide with the large amplitude slip patches found by source inversions at lower frequencies relocation of the deeper subevents suggests a nonplaner rupture surface where dip increases with depth at the southern end

aragonite cycles diagenesis caught in the act organic biomarker and nannofossil assemblages are used in combination with sedimentary petrology to identify the role of diagenesis for the formation of a rhythmic calcareous succession a record from the early pliocene of the maldives ocean drilling program odp leg 115 is presented containing precession and eccentricity cycles expressed as variable aragonite content additional sub milankovitch cycles are caused by rhythmic precipitation of calcite cement in the lower part of the interval comparison with palaeo productivity indicators nannofossils chlorin total organic carbon suggests that cementation occurs preferentially in intervals characterized by increasing or decreasing productivity the coupled variability in productivity and carbonate diagenesis is attributed to the effect of organic matter degradation in the sediment the observed combination of primary and diagenetic factors hampers the interpretation of the cyclicity on milankovitch and sub milankovitch scales diagenetically stable proxies for palaeo productivity such as nannofossil assemblage data were used to distinguish between palaeoclimate and diagenetic influences

the evolution of the porcupine and rockall basins offshore ireland the geological template for carbonate mound development the margins of the deep water sedimentary basins west of ireland contain a number of large clusters provinces of spectacular carbonate mounds and build ups these basins have a complex development history involving the interplay of rift tectonics thermal subsidence igneous activity and oceanographic variations the porcupine and rockall basins both rest upon thin continental crust the consequence of major rift episodes in permo triassic late jurassic and early cretaceous times phases of volcanism occurred in the early cretaceous and especially in the early cenozoic fluid flow within the basins is likely to have been controlled by the overall basin geometry and by the distribution and linkage of permeable strata with fault systems stratal surfaces and unconformities a number of regional unconformities controlled by both basin tectonic and regional oceanographic effects can be mapped and correlated throughout the porcupine and rockall basins the youngest of these unconformities c10 early pliocene can be traced throughout much of the nw european atlantic margin it forms the horizon on which virtually all the carbonate mounds in the basins develop suggesting a geologically instantaneous mound nucleation and growth event although the control on their development is uncertain the mound clusters show a spatial association with lithified strata buried contourite and deltaic deposits slope failure features and with the basin margins analysis of these relationships points to a combination of geological and oceanographic processes controlling mound initiation and growth

analyses of pseudotachylyte from hole b of taiwan chelungpu fault drilling project tcdp their implications for seismic slip behaviors during the 1999 chi chi earthquake abstract the seismic slip behavior during the 1999 chi chi taiwan earthquake m w 7 6 was contrastive between the northern and southern segments of the activated chelungpu fault large fast and smooth slips with large stress drop in the north while smaller slower and irregular slips with smaller stress drop in the south we analyzed the pseudotachylyte samples recovered from 1194 m 1243 m and 1314 m depths of hole b of taiwan chelungpu fault drilling project tcdp to reveal the spatial difference in friction mechanism all pseudotachylyte layers are thin 0 7 2 8 cm the volume fraction of protoliths is very large more than 63 and the estimated temperature distribution is very heterogeneous from ca 750 1750 c these observations suggest that these pseudotachylyte melts were in the partial melting regime of montgomery montgomery r s 1976 friction and wear at high sliding speeds wear 36 275 298 where friction coefficient is abnormally large similar pseudotachylyte was found already in the core sample from 175 m depth of the nanto borehole penetrating the southern fault since both pseudotachylyte samples from the two boreholes are older than the 1999 chi chi event and have been uplifted from depths farther down dip of their current locations it is likely that recent seismic ruptures also would have encountered these mechanical barriers of viscous melt patches at deeper parts in the north than in the south elastohydrodynamic lubrication of clayey gouge worked effectively at the shallower parts of the northern segment however there is no evidence that it played an important role in the south these differences are the plausible causes of the contrastive local slip behaviors during the chi chi earthquake

analysis of the ground accelerations radiated by the 1980 livermore valley earthquakes for directivity and dynamic source characteristics the strong motion accelerograph recordings of the 24 january 1980 main shock and the 27 january 1980 aftershock of the livermore valley earthquake sequence are analyzed for systematic variations with azimuth or station location the variation of the peak accelerations with epicentral azimuth is apparently reversed for the two events the main shock accelerations are larger to the south and the aftershock accelerations are larger to the northwest we eliminate the site effects by forming the ratio of the peak accelerations recorded at the same station after correcting for the epicentral distance this analysis indicates that source directivity caused a total variation of a factor of 10 in the peak accelerations comparison of this variation with the spatial extent of the aftershock sequences suggests that the strong directivity in the radiated accelerations is the result of unilateral ruptures in both events the accelerograms recorded at 10 stations within 35 km of the events were digitized to analyze the azimuthal variation of the rms acceleration the peak velocity and the radiated energy flux the variation of rms acceleration correlates almost exactly with the variation of the peak accelerations this correlation is analyzed using both deterministic and stochastic models for the acceleration waveforms the peak velocities corrected for epicentral distance vary with azimuth by a factor of 5 for both events while the radiated energy flux varies by a factor of 30 for the main shock and 15 for the aftershock the peak velocities are strongly correlated with the radiated energy flux the radiated seismic energies are estimated to be 2 6 0 9 1020 dyne cm for the main shock and 1 5 0 3 1020 dyne cm for the aftershock

a 3d seismic study of the morphology and spatial distribution of buried coral banks in the porcupine basin sw of ireland an industrial 3d seismic data volume supplemented by high resolution 2d seismics was used to study part of a province of buried mound structures in the porcupine basin southwest of ireland these magellan mounds and their associated moat structures interpreted as scour marks were mapped semi automatically from time structure and isopach maps image analysis techniques such as a tophat transformation mathematical morphology were applied for feature extraction size measures of both mounds and moats were derived from the resulting maps and summarised by means of some descriptive statistics spatial variability in mound occurrence and characteristics was investigated comparison with other mound structures in the area allowed the magellan mounds to be identified as coral banks associated with the growth of cold water deep sea coral species such as lophelia pertusa l and madrepora oculata l mound growth clearly started in a single event confined in time and space bottom currents and oceanographic characteristics of the surrounding water masses influenced this sudden process and the further mound development however the analysis of the 3d seismic data set did not allow us to identify unambiguously the actual cause for the sudden mound start up the mounds appear to have formed a dense cluster of structures of moderate size which are significantly elongated in a n s direction they are associated with even more elongated moats implying a periodically reversing n s directed current influence a spatial density of one mound per km2 was measured which remains more or less constant over the area investigated mound width and cross sectional area and moat shape gradually change across the mound province due to spatially changing environmental conditions at the initial growth stages of the mounds and during their further development interplay between current regime and sedimentation

characteristics of strong ground motion across a thrust fault tip from the september 21 1999 chi chi taiwan earthquake near fault tip strong motion records from the northern part of the major earthquake mw 7 6 namely the chi chi earthquake on september 21 1999 in central taiwan demonstrated systematic differences on the hanging wall and footwall and simulated by the finite element method the extraordinary ground motion differences on either side of the northern fault tip can be explained by a 2 dimension kinematic source model with fault rupture breaking to surface in this study the earthquake faulting was considered as bilateral from the center of a low angle thrust fault which is 30 km in length with a dip angle of 31 based on waveform modeling the source rupture velocity rise time and dislocation of 2 0 km sec 5 sec and 6 meters respectively are suggested the results of this study show that on the northern part of the chi chi earthquake fault there was lower rupture velocity and longer rise time of the fault slip than that previously reported furthermore the effects of surface breaking from the fault movement contributed large ground deformations near the fault tip and consequently induced extensive damage

effects of fault dip and slip rake angles on near source ground motions why rupture directivity was minimal in the 1999 chi chi taiwan earthquake we study how the fault dip and slip rake angles affect near source ground velocities and displacements as faulting transitions from strike slip motion on a vertical fault to thrust motion on a shallow dipping fault ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip the nature of the shear wave directivity is the key factor in determining the size and distribution of the peak velocities and displacements strong shear wave directivity requires that 1 the observer is located in the direction of rupture propagation and 2 the rupture propagates parallel to the direction of the fault slip vector we show that predominantly along strike rupture of a thrust fault geometry similar in the chi chi earthquake minimizes the area subjected to large amplitude velocity pulses associated with rupture directivity because the rupture propagates perpendicular to the slip vector that is the rupture propagates in the direction of a node in the shear wave radiation pattern in our simulations with a shallow hypocenter the maximum peak to peak horizontal velocities exceed 1 5 m sec over an area of only 200 km 2 for the 30 dipping fault geometry similar to the chi chi earthquake whereas for the 60 and 75 dipping faults this velocity is exceeded over an area of 2700 km 2 these simulations indicate that the area subjected to large amplitude long period ground motions would be larger for events of the same size as chi chi that have different styles of faulting or a deeper hypocenter

thermal history estimation of the taiwan chelungpu fault using rock magnetic methods 1 to investigate the cause of high magnetic susceptibility in disk shaped black materials bm disks within core samples of hole b the taiwan chelungpu fault drilling project we carried out magnetic analyses of samples from the bm disks and surrounding gouge zones frequency dependence of low temperature magnetic susceptibility and thermal demagnetization of low temperature remanent magnetization revealed lower amounts of superparamagnetic grains in the bm disks than in the surrounding gouges magnetic grain size reduction by shearing is therefore not a plausible explanation for the high magnetic susceptibility of the bm disks thermomagnetic analyses of the gouge samples showed that above 400 c magnetization could be increased by thermal decomposition of paramagnetic minerals whereas analyses of the bm disks showed a much smaller increase in magnetization thus formation of ferrimagnetic magnetite or maghemite by thermal decomposition of paramagnetic minerals was inferred to be the cause of the high magnetic susceptibility of the bm disks indicating that the bm disks but not the gouges have experienced temperatures of at least 400 c

fault zone geology lessons from drilling through the nojima and chelungpu faults several drilling projects have been conducted through active faults with the aim of learning about the geology of the fault zones and tentatively correlating the structure and mineralogy of the fault zones with their seismological behaviour during recent earthquakes here we present the major results obtained from structural and mineralogical studies of core samples retrieved from the dextral reverse strike slip nojima fault japan within granitic rocks following the kobe earthquake 1995 and from the chelungpu thrust fault taiwan within alternating silts and shales following the chi chi earthquake 1999 we show how these projects despite not fullfilling all their objectives have still contributed to a better geological knowledge of the fault zones to a better characterization of the slip zones related to the recent earthquakes particularly of their thickness microstructures and deformation mechanisms and to a better understanding of the nature and role of fluids within the fault zone they have also led to new questions and to new approaches for studying fault rock samples for all of these reasons they have stimulated international scientific research into fault zone geology

carbonate budget of a cold water coral carbonate mound propeller mound porcupine seabight high resolution studies from the propeller mound a cold water coral carbonate mound in the ne atlantic show that this mound consists of 50 carbonate justifying the name carbonate mound through the last 300 000 years approximately one third of the carbonate has been contributed by cold water corals namely lophelia pertusa and madrepora oculata this coral bound contribution to the carbonate budget of propeller mound is probably accompanied by an unknown portion of sediments buffered from suspension by the corals however extended hiatuses in propeller mound sequences only allow the calculation of a net carbonate accumulation thus net carbonate accumulation for the last 175 kyr accounts for only 0 3 g cm2 kyr which is even less than for the off mound sediments these data imply that propeller mound faces burial by hemipelagic sediments as has happened to numerous buried carbonate mounds found slightly to the north of the investigated area

carbonate mound development at the sw rockall trough margin based on high resolution tobi and seismic recording abstract in 2002 high resolution sidescan sonar images of a mound area at the sw rockall trough margin were recorded with the tobi deep towed sidescan sonar processed tobi images with a pixel resolution of 6 m provide a unique overview of the carbonate mound distribution and related sedimentary features around the mounds three morphologically distinct areas can be recognised on the tobi mosaic in area i between 500 and 600 m water depth upslope of the mounds giant sediment waves are found with wavelengths up to 500 m with wave crests of more than 10 km long and with an amplitude of up to 30 m reflected with a high backscatter on the tobi image area ii between 600 and 1000 m water depth along the upper margin flank is characterised by clustered and isolated carbonate mounds forming elongated ridges with an orientation perpendicular to the slope sedimentary structures such as flow ridges sediment waves local scouring at the foot of some mounds and draping of sediment around mounds indicate the influence of strong near bed currents oriented in two main current directions parallel to the margin as well as in a similar direction as the mound clusters the mound clusters are several kilometres long can be over 380 m high and are dissected by downslope directed channels on the tobi image the mounds appear as regions of high backscatter caused by the presence of cold water coral colonies on the sediment and by distinct shadows all mounds have their tops at a specific depth level 500 600 m water depth area iii between 900 and 1200 m water depth below the mounds is characterised by disturbed sediments with distinct slump scars and flow ridges 2d high resolution seismic profiling perpendicular and parallel to the slope across the mounds does in general not reveal strong internal reflectors within the mounds in contrast three strong reflectors can be observed in the sedimentary sequence underneath the mounds the upper reflector c10 of early pliocene age is an erosional unconformity above which most of the mounds and sediment waves seem to have developed the second erosional unconformity c20 of middle miocene age is formed by an apparent irregular surface that locally is dissected by some small faults reflectors c10 and c20 have been found in two different mound clusters in the mound area indicating that mound development possibly started after formation of reflector c20 the third reflector forms the acoustic basement which is locally dissected by some small faults that are located below the mounds at least two stages of mound formation are recognised on the seismic profiles

estimated dynamic shear stress and frictional heat during the 1999 taiwan chi chi earthquake a chemical kinetics approach with isothermal heating experiments abstract we performed isothermal heating experiments on samples from a breccia zone adjacent to the slip zone of the taiwan chelungpu fault that slipped during the 1999 chi chi earthquake to determine the chemical kinetics function and parameters for thermal decomposition of carbonate minerals in the fault zone we found that a zero order reaction was the most likely reaction mechanism for thermal decomposition of these samples and determined an activation energy for the reaction of 137 kj mol 1 and a pre exponential term of 1 15 10 4 s 1 we applied these parameters in chemical kinetics calculations taking into account the temperature change over time caused by frictional heating and heat conduction energy conservation and energy taken up by the endothermic reaction to estimate the dynamic shear stress and maximum temperature reached in the slip zone and found them to be 6 62 mpa and 1079 c respectively

high magnetic susceptibility of fault gouge within taiwan chelungpu fault nondestructive continuous measurements of physical and chemical properties in fault rocks recovered from hole b tcdp 1 the taiwan chelungpu fault drilling project tcdp was undertaken in 2002 to investigate the faulting mechanism of the 1999 taiwan chi chi earthquake hole b penetrated the chelungpu fault and recovered core samples from between 948 42 m and 1352 60 m depth three zones marked 1136mfz 1194mfz and 1243mfz were recognized in the core samples as active fault zones within the chelungpu fault multi sensor core logger measurements revealed lower densities and higher magnetic susceptibilities within the black gouge zones in all three fault zones even though the fault zone that slipped during the 1999 earthquake has not been identified higher magnetic susceptibilities indicate that frictional heating has taken place in the chelungpu fault

structure and development of giant carbonate mounds at the sw and se rockall trough margins ne atlantic ocean abstract high resolution seismic reflection profiling carried out in 1997 1999 showed that giant carbonate mounds occur between 500 and 1200 m water depth along both the se and sw margins of rockall trough the mounds rise 5 300 m above the surrounding seafloor and have diameters at their bases of up to 5 km buried mounds at relatively shallow depths below the seafloor are also found both individual and complex clusters of mounds can be recognized smaller and individual sometimes buried mounds are found at the upper slope on the sw rockall trough margin higher steeper and individual mounds are found deeper downslope 900 1100 m at the middle slope the mounds merge into a complex structure and form complex clusters with a very irregular upper surface and an apparent lack of internal reflectors 600 1000 m depth initial results of high resolution 3d seismic profiling at 30 m line spacing in august 2000 in two boxes of 750 m 14 5 km covering a small central part of the sw rockall trough mound area indicate two stages of mound development here the latest probably of pliocene holocene age this age based on the presence of a regionally recognizable unconformity below the mounds is also assumed for the mounds of the se rockall trough porcupine bank margin

near fault peak ground velocity from earthquake and laboratory data we test the hypothesis that peak ground velocity pgv has an upper bound independent of earthquake magnitude and that this bound is controlled primarily by the strength of the seismogenic crust the highest pgvs ranging up to several meters per second have been measured at sites within a few kilometers of the causative faults because the database for near fault pgv is small we use earthquake slip models laboratory experiments and evidence from a mining induced earthquake to investigate the factors influencing near fault pgv and the nature of its scaling for each earthquake slip model we have calculated the peak slip rates for all subfaults and then chosen the maximum of these rates as an estimate of twice the largest near fault pgv nine slip models for eight earthquakes with magnitudes ranging from 6 5 to 7 6 yielded maximum peak slip rates ranging from 2 3 to 12 m sec with a median of 5 9 m sec by making several adjustments pgvs for small earthquakes can be simulated from peak slip rates measured during laboratory stick slip experiments first we adjust the pgv for differences in the state of stress i e the difference between the laboratory loading stresses and those appropriate for faults at seismogenic depths to do this we multiply both the slip and the peak slip rate by the ratio of the effective normal stresses acting on fault planes measured at 6 8 km depth at the ktb site germany deepest available in situ stress measurements to those acting on the laboratory faults we also adjust the seismic moment by replacing the laboratory fault with a buried circular shear crack whose radius is chosen to match the experimental unloading stiffness an additional less important adjustment is needed for experiments run in triaxial loading conditions with these adjustments peak slip rates for 10 stick slip events with scaled moment magnitudes from 2 9 to 1 0 range from 3 3 to 10 3 m sec with a median of 5 4 m sec both the earthquake and laboratory results are consistent with typical maximum peak slip rates averaging between 5 and 6 m sec or corresponding maximum near fault pgvs between 2 5 and 3 m sec at seismogenic depths independent of magnitude our ability to replicate maximum slip rates in the fault zones of earthquakes by adjusting the corresponding laboratory rates using the ratio of effective normal stresses acting on the fault planes suggests that the strength of the seismogenic crust is the important factor limiting the near fault pgv

quaternary crusts on slopes of the mediterranean sea a tentative explanation for their genesis abstract quaternary deep sea crusts i e lithified omission surfaces are widespread on slopes and subsea relief features in the western and especially the eastern mediterranean sea the lithification is induced by the early precipitation of a magnesian calcite cement in the uppermost few centimetres of a calcareous ooze based on their thickness and degree of hardening the collected samples have been divided into three main types each of them corresponding to a different degree of lithification except in rare probably old crusts collected at water depths below 2000 2500 m and in infills of some sponge skeletons or in the case of inferred internal tension recrystallization and generally mineral alterations are very limited the precipitation mechanisms appear to be essentially physicochemically controlled and ions involved in cementation come from the seawater reservoir by means of an inward diffusion of solutions diffusion is enhanced by bottom currents these currents maintaining a low or zero rate of sedimentation moreover lithification also depends on the chemical characteristics of the seawater i e supersaturation with respect to low magnesian calcite and low contents of phosphates and dissolved organic matter which would inhibit crystal growth local factors and primary composition of the original sediment also appear to influence the speed of early lithification when conditions of lithification are favourable a few hundreds of years to a few thousand years at the most seem sufficient for the first two stages of lithification to be reached the submarine lithification was active during the last glacial episode and as exhibited by numerous samples especially towards the end of this period the previous cold stages were probably also episodes of efficient lithification this correlation with quaternary climatic cycles certainly reflects an intensification of thermohaline and bottom current circulations during periods of severe climatic conditions there is also some evidence of holocene and even present day crusts

investigation of the records of earthquake slip in carbonaceous materials from the taiwan chelungpu fault by means of infrared and raman spectroscopies this research was supported by a grant in aid for young scientists a from the japan ministry of education science sports and culture 23684039 2013

characterization of slip zone associated with the 1999 taiwan chi chi earthquake x ray ct image analyses and microstructural observations of the taiwan chelungpu fault abstract to characterize the fault related rocks within the chelungpu fault we performed x ray computed tomography ct image analyses and microstructural observations of hole b core samples from the taiwan chelungpu fault drilling project we identified the slip zone associated with the 1999 chi chi earthquake within the black gouge zone in the shallowest major fault zone by comparison with previous reports the slip zone was characterized by low ct number cataclastic or ultracataclastic texture and high possibility to have experienced a mechanically fluidized state taking these characteristics and previous reports of frictional heating in the slip zone into consideration we suggested that thermal pressurization was the most likely dynamic weakening mechanism during the earthquake

diagenetic processes in carbonate mound sediments at the south west rockall trough margin cold water coral covered carbonate mounds at the south west margin of the rockall trough form ridges several kilometres long and up to 380 m high piston cores obtained at three mound crests reveal the complex internal structure of the mound build up with alternating unlithified coral dominated intervals and lithified intervals the most recent lithified interval is covered by corals embedded in a fine grained matrix comprising ca 11 000 years of continuous mound evolution before this time 230th u dating shows the presence of several hiatuses in mound build up aragonitic coral material is absent or only present as mouldic porosity in the lithified intervals and coccoliths display widespread overgrowth downcore x ray fluorescence scanning computer tomography scan images and petrographic observations indicate different degrees of diagenetic alteration the upper boundary of the most recent lithified interval shows some erosional features but petrographic observations indicate that initial lithification of the sediments is not related to this erosive event or to long term non sedimentation but to earlier sub surface diagenesis organic matter oxidation and the subsequent lowering of the saturation state of the carbonate system drives dissolution of the unstable aragonitic coral skeletons depending on the openness of the system this can lead to precipitation of a more stable low magnesium carbonate a model is presented describing the sedimentary and diagenetic processes leading to the formation of lithified intervals

nitrogen isotope analysis of groundwater nitrate in carbonate aquifers natural sources versus human pollution abstract results of nitrogen isotope analyses of nitrate in the waters of the cretaceous edwards aquifer in texas u s a indicate that the source of the nitrate is naturally occurring nitrogen compounds in the recharge streams in contrast nitrogen isotopes of nitrate in the fresh waters of the pleistocene ironshore formation on grand cayman island west indies indicate that human wastes are the source of the nitrate the cretaceous edwards limestone is a prolific aquifer that produces principally from fracture porosity along the balcones fault zone recharge is primarily by streams crossing the fault zone rainfall is 70 cm yr 1 and the water table is generally deeper than 30 m below land surface the 15 n of 73 samples of nitrate from edwards waters ranged from 1 9 to 10 with an average of 6 2 this 15 n range is within the range of nitrate in surface water in the recharge streams 15 n range 1 to 8 3 and within the range of nitrate in surface water from the colorado river texas 15 n range 1 to 11 no sample was found to be enriched in 15n which would suggest the presence of nitrate from animal waste 15 n range 10 to 22 the ironshore formation contains a small freshwater lens that is recharged entirely by percolation through the soil average rainfall is 165 cm yr 1 and the water table is within 3 m of land surface the 15 n of four nitrate samples from water samples of the ironshore formation ranged from 18 to 23 9 which indicates a cesspool septictank source of the nitrate limestone aquifers in humid environments that are recharged by percolation through the soil appear to be more susceptible to contamination by septic tanks than are aquifers in subhumid environments that feature thick unsaturated sections and are recharged by streams

dynamics of thrust faulting 2d lattice model particle motions in a foam rubber model of shallow angle thrust faulting show many features different from those commonly assumed in dislocation models of subduction thrusts brune 1996 as a complement to a physical foam rubber experiment we have carried out dynamic simulation using a 2d lattice numerical model the model is constructed as a triangular block sliding over a rectangular elastic block it consists of a 2d set of particles interacting with each other by nonlinear hooke s forces and obeying newton s equations of motion rough surfaces are introduced on the contact plane of the two blocks to simulate realistic friction the numerical simulations demonstrate several key features of thrust faulting including stick slip fault opening and strong breakout and shaking at the hanging wall toe the wedge shaped tip of the outcropping hanging wall block of the thrust fault all consistent with the foam rubber experiments the stick slip motion shows an approximate time and slip repeatable behavior each slip event is characterized by a self healing pulse associated with fault opening and frictional locking the rupture pulse propagates steadily along the fault when rupture reaches the toe of the fault outcrop the hanging wall breaks away from the foot wall and creates a large opening vibration of the hanging wall the peak acceleration observed at the hanging wall toe of the fault outcrop is about 3 to 4 times the peak acceleration in the center part of the fault and about 2 to 3 times the motion of the foot wall such a large increase in peak acceleration at the toe is caused mainly by multiply reflecting stress waves trapped in the wedge shaped hanging wall of the fault the strong asymmetry of the particle velocity between the hanging wall and foot wall is an important feature of the results consistent with the foam rubber model but different from standard dislocation models this dynamic result illustrates the important effects of thrust faulting geometry on fault slip and ground motion

slip history and dynamic implications of the 1999 chi chi taiwan earthquake we investigate the rupture process of the 1999 chi chi taiwan earthquake using extensive near source observations including three component velocity waveforms at 36 strong motion stations and 119 gps measurements a three plane fault geometry derived from our previous inversion using only static data ji et al 2001 is applied the slip amplitude rake angle rupture initiation time and risetime function are inverted simultaneously with a recently developed finite fault inverse method that combines a wavelet transform approach with a simulated annealing algorithm ji et al 2002b the inversion results are validated by the forward prediction of an independent data set the teleseismic p and sh ground velocities with notable agreement the results show that the total seismic moment release of this earthquake is 2 7 10 20 n m and that most of the slip occurred in a triangular shaped asperity involving two fault segments which is consistent with our previous static inversion the rupture front propagates with an average rupture velocity of 2 0 km s 1 and the average slip duration risetime is 7 2 s several interesting observations related to the temporal evolution of the chi chi earthquake are also investigated including 1 the strong effect of the sinuous fault plane of the chelungpu fault on spatial and temporal variations in slip history 2 the intersection of fault 1 and fault 2 not being a strong impediment to the rupture propagation and 3 the observation that the peak slip velocity near the surface is in general higher than on the deeper portion of the fault plane as predicted by dynamic modeling