strength of plate coupling in the southern ryukyu subduction zone abstract understanding the strength of a plate coupling is critical for assessing potential seismic and tsunamic hazards in subduction zones the interaction between an overriding plate and the associated subducting plate can be used to evaluate the strength of plate coupling by examining the mantle lithospheric buoyancy here we calculate the mantle lithosphere buoyancy across the northern portion of the southern ryukyu subduction zone based on gravity modeling with the constraints from a newly derived p wave seismic velocity model the result indicates that the strength of the plate coupling in the study area is relatively strong which is consistent with previous observations in the southernmost ryukyu subduction zone because few large earthquakes mw 7 have occurred in the southern ryukyu subduction zone a large amount of energy is locked and accumulated by plate coupling that could be released in the near future

three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

a 3000 years old sequence of extreme events revealed by marine and shore deposits east of taiwan we have discovered in a marine core located 20 km east of the coastal range of taiwan at the top of a 1200 m deep submarine high sheltered from rivers discharges and gravitational flows a 23 cm thick anomalous sequence topped with broken bivalves and wood fragments based on radiocarbon dating we distinguish five sub events within 100 yrs about 3000 years ago the oldest four sub events are interpreted as the record of local submarine landslides likely triggered by clustered earthquakes that are common in this tectonically active area the last event including shells and wood has a different origin despite the high level of climatic and tectonic recent activity no comparable event has been observed at the same site since that time making it unique during the last 3 75 ka hydrodynamical modeling stimulated with a set of submarine landslide triggered tsunami sources and combined with the regional oceanic circulation dominated by the kuroshio current allow us to better constrain the transport paths of the suspended material the expected run up at the coast and ultimately the trigger and source that best fit our observations the kuroshio current appears as a strong constraint that generally prevents cross shore transport of suspended material even during a major tsunami since the largest aerial debris flow observed along the east coast of taiwan during the last 4 ka was synchronous with the marine deposit our preferred scenario starts with the occurrence of four distinct large earthquakes within less than a century triggering both submarine and aerial landslides in the study area then a giant typhoon reworked the nearshore material as well as the slided material stored upstream resulting in a debris flow it deeply modified the surface current allowing the wood debris and shells to fastly reach the core site

reconstructing subducted oceanic lithosphere by reverse engineering slab geometries the northern philippine sea plate subducting slabs commonly acquire complex geometries from the migration of subduction trenches slab mantle interaction slab tearing and collision of slabs at depth although it is possible to construct three dimensional models of subducted slabs using earthquake hypocenter locations and tomographic models it is often not possible to rigorously test their accuracy here we present a methodology for performing such a test by reverse engineering the presubduction configuration of a slab of oceanic lithosphere from interpretations of its present day morphology we illustrate our approach for the ryukyu and shikoku slabs northwest philippine sea having simulated them as viscoelastic sheets that we unfolded and floated to the surface the net strain distribution of the floated mesh indicated which parts of the original slab model were geometrically viable minimal net strain and which parts of the mesh required additional tears and or zones of localized ductile extension to have enabled the slab to deform during subduction in the instance of the ryukyu and shikoku slabs the palau kyushu and gagua ridges are shown to have both acted as planes of weakness that broke into major vertical slab tears these subducted ridges are connected by a trench parallel tear that represented the former contact between the huatung and west philippine basins the fossil spreading center of the shikoku basin formed a separate slab window upon subduction along the nankai trough the methodology presented herein is a powerful tool to evaluate complex slab morphologies infer the locations of slab tears and therefore reconstruct intricate configurations of subducted oceanic lithosphere

paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone an example of decreasing plate coupling abstract the okinawa trough is a backarc basin located behind the ryukyu arc trench system the southernmost part of the okinawa trough spot displays different tectonic features from the rest of the okinawa trough the spot area includes abundant seamounts with active hydrothermal venting and high heat flow values to understand better the rifting and magmatism context of the spot area we examine the lithospheric structure buoyancy and coupling across the southernmost ryukyu subduction zone the results show that beneath the spot area the continental crust and mantle lithosphere thickness of 25 30 and 120 km respectively are thick with little continental thinning the analysis of mantle lithosphere buoyancy across the southernmost ryukyu subduction zone shows strong plate coupling between the overriding and subducting plates however the two plates are actually decoupled as indicated by present day interface earthquakes this situation indicates that the southernmost ryukyu subduction zone displays a transitory case of a changing plate coupling from a strong to a weak plate coupling such a coupling decoupling transition is probably associated with the collision of the luzon arc with the asian continental margin additionally the curve of the mantle lithosphere buoyancy across the southernmost ryukyu subduction zone indicates that the submarine magmatism in the spot area is located within the volcanic arc area suggesting early arc magmatism in the spot area

deformation structures from splay and decollement faults in the nankai accretionary prism sw japan iodp nantroseize expedition 316 evidence for slow and rapid slip in fault rocks

climatic dependence of stable carbon and oxygen isotope signals recorded in speleothems from soil water to speleothem calcite abstract understanding the relationship between stable isotope signals recorded in speleothems 13 c and 18 o and the isotopic composition of the carbonate species in the soil water is of great importance for their interpretation in terms of past climate variability here the evolution of the carbon isotope composition of soil water on its way down to the cave during dissolution of limestone is studied for both closed and open closed conditions with respect to co 2 the water entering the cave flows as a thin film towards the drip site co 2 degasses from this film within approx 10 s by molecular diffusion subsequently chemical and isotopic equilibrium is established on a time scale of several 10 100 s the 13 c value of the drip water is mainly determined by the isotopic composition of soil co 2 the evolution of the 18 o value of the carbonate species is determined by the long exchange time t ex between oxygen in carbonate and water of several 10 000 s even if the oxygen of the co 2 in soil water is in isotopic equilibrium with that of the water dissolution of limestone delivers oxygen with a different isotopic composition changing the 18 o value of the carbonate species consequently the 18 o value of the rainwater will only be reflected in the drip water if it has stayed in the rock for a sufficiently long time after the water has entered the cave the carbon and oxygen isotope composition of the drip water may be altered by co 2 exchange with the cave air exchange times ex co 2 of about 3000 s are derived thus only drip water which drips in less than 3000 s onto the stalagmite surface is suitable to imprint climatic signals into speleothem calcite deposited from it precipitation of calcite proceeds with time constants p of several 100 s different rate constants and equilibrium concentrations for the heavy and light isotopes respectively result in isotope fractionation during calcite precipitation since t ex p exchange with the oxygen in the water can be neglected and the isotopic evolution of carbon and oxygen proceed analogously for drip intervals t d p the isotopic compositions of both carbon and oxygen in the solution evolve linearly in time the calcite precipitated at the apex of the stalagmite reflects the isotopic signal of the drip water for long drip intervals when calcite is deposited from a stagnant water film long drip intervals may have a significant effect on the isotopic composition of the dic in this case the isotopic composition of the calcite deposited at the apex must be determined by averaging over the drip interval such processes must be considered when speleothems are used as proxies of past climate variability

the composition and its impact on the methane sorption of lacustrine shales from the upper triassic yanchang formation ordos basin china abstract the organic geochemistry mineralogy and methane sorption of lacustrine shales of the upper triassic yanchang formation collected from the south eastern ordos basin were investigated to characterize them and clarify the effects of shale composition on their sorbed gas capacity these yanchang shales have recently been selected as a target area for shale gas exploration in typical terrestrial strata in china the two main sections of these shales containing type ii organic matters chang 7 and chang 9 have relatively high total organic carbon content toc of 2 10 the two shales also have similar mineralogies mainly comprising quartz clay minerals and feldspars both the chang 7 and chang 9 shales are generally in the oil window chang 9 is slightly more mature than chang 7 higher methane sorption capacity was observed for chang 9 than for chang 7 shales determined on a dried basis at 50 c methane sorption measurements were further performed on three samples from which the residual bitumen had been extracted and their corresponding kerogen fractions to gain insight into the effects of shale composition on methane sorption this was significantly higher in solvent extracted samples than in raw samples indicating that residual bitumen largely restricts methane sorption on such shales a positive correlation between the amount of clay minerals and methane sorption capacity of bulk rocks was evident suggesting that clay mineral content is relevant to methane sorption this result was also supported by the much higher methane sorption capacity of solvent extracted shales compared to the extracted kerogen from those shales when measured sorption data was normalized to toc values the effects of both residual bitumen and clay mineral on the methane sorption of bulk rocks have complicated the evaluation of methane sorption on organic matter in these mature shales

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

strike slip intraplate earthquakes in the western philippine sea plate abstract on 26 april 2010 a strike slip earthquake mw 6 5 occurred in the western philippine sea plate we deployed 14 ocean bottom seismometers to record the corresponding aftershocks to acquire information regarding these intraplate events our results show that the aftershocks were located along two linear features that intersect with an angle of approximately 120 and are considered a conjugate fault set the p axis of the mainshock focal mechanism is consistent with the compressive stress direction induced by the arc continent collision occurring in eastern taiwan the pre existing oceanic fracture zones and tectonic fabrics do not appear to be reactivated based on the distinct rupture directions determined from the relocated aftershocks however the abrupt halt of the aftershocks at the border of the fracture zone suggests that pre existing weak zones could act as a barrier to rupture propagation moreover most large earthquakes have occurred near fracture zones indicating that the pre existing weakness may favor the generation of earthquakes compared to the other portion of the oceanic plate due to the relatively low rock strength of this zone

the importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs abstract the effect of shale composition and fabric upon pore structure and ch 4 sorption is investigated for potential shale gas reservoirs in the western canadian sedimentary basin wcsb devonian mississippian d m and jurassic shales have complex heterogeneous pore volume distributions as identified by low pressure co 2 and n 2 sorption and high pressure hg porosimetry thermally mature d m shales 1 6 2 5 vro have dubinin radushkevich d r co 2 micropore volumes ranging between 0 3 and 1 2 cc 100 g and n 2 bet surface areas of 5 31 m 2 g jurassic shales which are invariably of lower thermal maturity ranging from 0 9 to 1 3 vro than d m shales have smaller d r co 2 micropore volumes and n 2 bet surface areas typically in the range of 0 23 0 63 cc 100 g co 2 and 1 9 m 2 g n 2 high pressure ch 4 isotherms on dried and moisture equilibrated shales show a general increase of gas sorption with total organic carbon toc content methane sorption in d m shales increases with increasing toc and micropore volume indicating that microporosity associated with the organic fraction is a primary control upon ch 4 sorption sorption capacities for jurassic shales however can be in part unrelated to micropore volume the large sorbed gas capacities of organic rich jurassic shales independent of surface area imply a portion of ch 4 is stored by solution in matrix bituminite solute ch 4 is not an important contributor to gas storage in d m shales structural transformation of d m organic matter has occurred during thermal diagenesis creating and or opening up microporosity onto which gas can sorb as such d m shales sorb more ch 4 per weight percent wt toc than jurassic shales inorganic material influences modal pore size total porosity and sorption characteristics of shales clay minerals are capable of sorbing gas to their internal structure the amount of which is dependent on clay type illite and montmorillonite have co 2 micropore volumes of 0 78 and 0 79 cc 100 g n 2 bet surface areas of 25 and 30 m 2 g and sorb 2 9 and 2 1 cc g of ch 4 respectively dry basis a reflection of microporosity between irregular surfaces of clay platelets and possibly related to the size of the clay crystals themselves mercury porosimetry analyses show that total porosities are larger in clay rich shales compared to silica rich shales due to open porosity associated with the aluminosilicate fraction clay rich sediments low si al ratios have unimodal pore size distributions

submarine active normal faults completely crossing the southwest ryukyu arc abstract several identified active faults located in the southwest ryukyu area may be an origin of m5 class earthquakes taking place frequently every year sometimes of m7 class earthquakes which cause a severe geohazard in this area the east ishigaki fault one of the officially identified active faults was studied precisely by multibeam echo sounding and the in situ rov observation the survey expedition figured the topographic feature of the fault clearly and more precisely than that mapped by the hydrographic department of japan the survey also identified the locations of northwestern and southeastern termini of the fault which revealed the total length to be 44 km corresponding to a m7 4 earthquake the new topographic map shows that the fault is composed of four or five segments with maximum vertical offset of 80 m in the southernmost segment not all of the segment can slip at once a reconnaissance survey of three of these segments by the rov hyper dolphin dives during the same expedition revealed that the headwall scarp is an outcrop made up of the ryukyu limestone of the middle pleistocene and that the lower scarp and the trough are covered with mostly talus apparently from the headwall at least two of these segments look fresher in fault activity rather than the others though all the observations show very recent activities along the fault based on these results the east ishigaki fault at least some of the segments might cause the 1771 tsunami and also future tsunamis with the similar magnitude

estimation of marine shale methane adsorption capacity based on experimental investigations of lower silurian longmaxi formation in the upper yangtze platform south china abstract methane adsorption experiments were performed on eight lower silurian longmaxi moisture equilibrated shale samples from the upper yangtze platform south china at pressures up to 12 mpa at 20 c 40 c 60 c 80 c and 100 c to investigate the effects upon methane adsorption capacity and to estimate the variation of methane adsorption capacity as a function of depth and burial history the methane adsorption capacity of the longmaxi shale shows a significant positive correlation with total organic carbon toc content which is accompanied by an increase in bet brunauer emmett teller surface area and total pore volume a quadratic relationship was observed between clay content and methane adsorption capacity there is a threshold clay content 42 3 44 4 in this trend methane adsorption capacity declines with increasing clay content below the threshold and later increases with increasing clay content the langmuir pressure decreases exponentially with the reciprocal of temperature and the langmuir volume decreases linearly with temperature the isosteric heat of adsorption and standard entropy for the longmaxi shale ranges from 10 34 to 11 67 kj mol and from 57 04 to 61 32 j mol k respectively which are clustered around kerogen type i using these relationships a computational scheme was developed to calculate methane adsorption capacity as a function of toc content temperature and pressure based on the langmuir equation this algorithm was applied to estimate methane adsorption capacity of the longmaxi shale as a function of depth due to the dominating effect of pressure methane adsorption capacity increases initially with depth through a maximum and then decreases as a result of increasing temperature at a greater depth the maximum gas adsorption capacity is typically located at a depth range between 800 and 1350 m with toc content increasing the curves shift continuously towards higher adsorption capacity furthermore the maximum methane adsorption capacity moves higher and shifts to a deeper depth as toc content increases ultimately four principal dynamic evolutionary stages of methane adsorption capacity of the longmaxi shale over geologic time as a function of burial history were reconstructed

seafloor morphology and sediment magnetic fabric in a putative 1771 meiwa tsunami source region in the southern ryukyu islands southwest japan

26th december 2004 great sumatra andaman earthquake co seismic and post seismic motions in northern sumatra trench parallel thrust faults verging both landward and seaward were mapped in the portion of wedge located between northern sumatra and the indian indonesian boundary the spatial aftershocks distribution of the 26th december 2004 earthquake shows that the post seismic motion is partitioned along two thrust faults the lower and median thrust faults the latter being right laterally offset by a n s lower plate fracture zone located along the 93 6 n meridian between february 2005 and august 2005 the upper plate aftershock activity shifted from southeast of this fracture zone to northwest of it suggesting that the lower plate left lateral motion along the fracture zone may have induced a shift of the upper plate post seismic activity along the median thrust fault based on swath bathymetric and 3 5 khz data co seismic deformations were weak close to the trench joint seismic geodetic determination of slip distribution and time arrivals and heights of tsunami waves suggest that the co seismic slip was maximum along a portion of the upper thrust fault located north of the tuba ridge suggesting that the upper thrust fault might be a splay fault originated at the interplate fault plane as the upper thrust fault is steeper than the slab the vertical motion of the adjacent outer arc and overlying water is much larger compared to the one resulting from slip on the megathrust alone increasing tsunamogenic effects

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

the evolution of 13 c and 18 o isotope composition of dic in a calcite depositing film of water with isotope exchange between the dic and a co 2 containing atmosphere and simultaneous evaporation of the water implication to climate proxies from stalagmites a theoretical model abstract the most widely applied climate proxies in speleothems are the isotope compositions of carbon and oxygen expressed by 13c and 18o values however mechanisms which are not related to climate changes overlay the climate signal one is the temporal increase of both 13c and 18o values by kinetic processes during precipitation of calcite isotope exchange between dic in the water and the co2 in the surrounding cave atmosphere can also change isotope composition here we present a theoretical model of the temporal isotope evolution of dic in a thin water layer during precipitation of calcite and simultaneous isotope exchange with the cave atmosphere and simultaneous evaporation of water the exchange of oxygen isotopes in the dic with those in the water is also considered for drip times for tdrip dic t drip e c eq c 0 e t drip eq atm 0 t drip in atm eq water 0 e w t drip t ev t drip water the first term on the right hand side is the contribution from precipitation of calcite the second stems from isotope exchange with the co2 of the cave atmosphere and the third results from isotope exchange between oxygen in the dic and the oxygen in the water e are kinetic parameters is the time scale of precipitation eq atm 0 and eq water 0 are the differences between the corresponding initial value 0 and the value eq atm water if dic were in isotope equilibrium with the atmosphere or in the case of oxygen with the water respectively in atm and water are the time scales of approach to isotope equilibrium by the exchange reactions ceq is the concentration of dic in chemical equilibrium with the co2 in the cave atmosphere and c0 is the initial concentration when the water drips to the stalagmite tev is the time needed for complete evaporation of the water layer ew is the fractionation between water vapor and fluid water for times tdrip 0 2 we find a further increase of dic tdrip until a maximum is passed and a final value is reached if eq atm 0 and eq water 0 are both zero exchange has no influence on the isotope composition for drip times tdrip eq atm 0 is about zero in summer time when most of the co2 comes from the vadose zone ground air and about 12 in winter time in well ventilated caves when most of the co2 stems from earth s atmosphere outside the cave therefore 13c may be affected by isotope exchange for the 18o equilibrium between the dic and the oxygen in the water as well as the oxygen in the co2 of the atmosphere is likely in summer time in winter time co2 from the atmosphere outside the cave with of about 6 vpdb may imprint small signals

fluid overpressure along an oligocene out of sequence thrust in the shimanto belt sw japan abstract out of sequence thrusts osts exposed in ancient accretionary prisms are considered as fossil analogs of present day megasplay faults in subduction margins and can provide direct information about the conditions of deformation during thrust activity in modern as well as in ancient accretionary prisms first order megasplay faults or osts truncate or merge with faults of lesser importance called second order osts structural analysis of the makinokuchi fault a branch of an oligocene to lower miocene second order ost in the tertiary shimanto belt of central kyushu sw japan brings information about the conditions of deformation at the time of thrusting the studied exposure shows that the fault footwall and to a much lesser extent the fault hanging wall consist of quartz cemented syntectonic dilatant hydraulic breccias testifying to pore fluid pressures larger than the least principal stress component the footwall sandstones are crossed by several centimeters thick quartz veins that merge with the footwall breccias the continuity between the veins and the breccias suggest that the veins acted as conduits which likely collected fluids from the footwall side sandstones upward and toward the fault fluid inclusions indicate that the quartz cementing the breccias and that filling the feeder veins crystallized from similar fluids and under similar pressure and temperature conditions 245 285 c and 5 8 km depth these similarities suggest that the fluids responsible for syn tectonic hydraulic brecciation were collected from the footwall through the conduits the fluid inclusion trapping temperatures are close to the temperatures expected to be reached along the seismogenic zone our analysis shows that fluid overpressures can play a key role in the growth and activity of second order osts in accretionary prisms and suggests that fluids collected along second order osts or splay faults may flow upward along first order osts or megasplay faults

response of forearc crustal faults to the megathrust earthquake cycle insar evidence from mejillones peninsula northern chile abstract we report on a rare example of aseismic response of a creeping fault to the earthquake cycle of a nearby megathrust interferometric synthetic aperture radar insar is used to detect and analyze shallow creep of two crustal faults at mejilones peninsula northern chile located in the hanging wall of the 2007 mw 7 7 tocopilla subduction earthquake we generate two independent time series of surface deformation spanning 3 5 yr of late interseismic and 1 5 yr early postseismic deformation associated with this event the analysis reveals creep on the mejillones fault as well as on a previously unmapped fault to the west of the mejillones fault the insar deformation maps and distributed slip models obtained from the data reveal that fault creep reversed between the interseismic and postseismic periods given the regional stress field perturbations due to interseismic and coseismic deformation we argue that the observed shallow creep and its slip reversal are directly linked to the megathrust seismic cycle moreover from similar eastward dips but opposite slip directions of the two faults we infer that fault strength must be very low and that the kinematics is controlled by crustal flexure associated with the seismic cycle on the underlying megathrust

source mechanism of the 1998 mw 7 4 intraplate strike slip earthquake in the west philippine basin revealed by coulomb stress changes abstract on april 11 2012 mw 8 6 and mw 8 2 earthquakes occurred off the west coast of northern sumatra as a result of strike slip type events within the indo australia plate it is suggested that these two earthquakes were linked to the occurrence of the 2004 great sumatra andaman earthquake over the last few decades several strike slip type earthquakes have been observed within the west philippine basin wpb however little investigation has been conducted to understand these strike slip earthquakes and the possible geohazard potential that they may bring in our study to determine the rupture plane for these strike slip events we calculated the static coulomb failure stress changes cfs induced by the 1998 mw 7 4 strike slip earthquake and compared them with the distribution of aftershocks our results show that when the fault plane is trending in the nw se direction the aftershocks that occurred in the region show a good agreement with the maximal positive cfs consequently instead of sliding along the pre existing oceanic fracture zones the 1998 strike slip event that occurred in the wpb should have ruptured in the nw se direction moreover we also observed a correlation between the activities of the normal faulting type earthquakes along the trench and the positive cfs induced by the 1998 mw 7 4 event which suggests that the occurrence of intraplate strike slip events in oceanic plates might affect the distribution of earthquakes along the nearby subduction systems

spatial variation of the crustal stress field along the ryukyu taiwan luzon convergent boundary 1 we applied an improved stress inversion method to a comprehensive data set of earthquake focal mechanisms to depict the pattern of crustal stress along the western convergent boundary of the philippine sea plate our results indicate that the crustal stress along the ryukyu fore arc is segmented with boundaries at or near the places of seamount subduction including the tokara channel an extensional stress regime is observed along the entire ryukyu back arc implying that back arc rifting may have extended northward to kyushu a triangular area near the southernmost terminus of the ryukyu arc is characterized by a unique stress signature the eastern boundary of this ryukyu taiwan stress transition coincides with the 123 e meridian where the gagua ridge intercepts the ryukyu trench whereas its western boundary agrees remarkably well with the border between the postcollision and waning collision domains in northern taiwan the taiwan collision zone is dominated by compression that rotates locally according to the structural configuration of the lukang magnetization high lmh suggesting that the lmh may be critical in controlling the local stress distribution the stress signature of the luzon arc taiwan collision reaches as far south as 19 5 n the tectonic stress along the manila trench luzon fore arc is dominated by a complex regime of extension that cannot be explained by simple plate bending or in slab membrane stress since this extensional regime is observed only south of 22 n it probably marks the northern limit of the contemporary boundary between the subduction along the manila trench and the collision in taiwan

characterization of pore systems in seal rocks using nitrogen gas adsorption combined with mercury injection capillary pressure techniques abstract porous microstructure parameters of seal rock samples originating from different depths within brazilian geological formations were correlated to empirical models which predict the intrinsic permeability mercury injection capillary pressure micp and nitrogen gas adsorption n 2 ga were applied in combination as complementary techniques micp to obtain the porosity values and the size distribution of meso and macropores and n 2 ga associated with the brunauer emmett and teller bet theory to determine the specific surface area s o the barret joyner and hallenda bjh theory was applied to find the size distribution of the micro and mesopores the combination of the micp and n 2 ga curves showed that the samples analyzed present a polymodal pore size distribution psd and a total porosity ranging from 0 33 to 10 44 the s o values measured by n 2 ga were higher than those calculated by micp due to the majority of the samples having a mean pore size of 20 1000 a the intrinsic permeability could also be predicted applying the measured parameters s o psd curves and total porosity in the carman kozeny and series parallel models the ranges of permeability values obtained were 4 09 10 24 4 96 10 21 m 2 and 9 48 10 27 9 14 10 22 m 2 respectively these results were compared with values reported in the related literature and those obtained for four samples submitted to pressure pulse decay permeability pdp tests

accretionary prisms in subduction earthquake cycles the theory of dynamic coulomb wedge 1 we expand the theory of critically tapered coulomb wedge for accretionary prisms by considering stress changes in subduction earthquake cycles building on the coulomb plasticity of the classical theory we assume an elastic perfectly coulomb plastic rheology and derive exact stress solutions for stable and critical wedges the new theory postulates that the actively deforming most seaward part of an accretionary prism the outer wedge overlies the updip velocity strengthening part of the subduction fault and the less deformed inner wedge overlies the velocity weakening part the seismogenic zone during great earthquakes the outer wedge is pushed into a compressively critical state with an increase in basal and internal stresses and pore fluid pressure after the earthquake the outer wedge returns to a stable state the outer wedge geometry is controlled by the peak stress of the updip velocity strengthening part of the subduction fault achieved in largest earthquakes the inner wedge generally stays in the stable regime throughout earthquake cycles acting as an apparent backstop and providing a stable environment for the formation of forearc basins the new theory has important implications for the studies of the updip limit of the seismogenic zone the evolution of accretionary prisms and forearc basins activation of splay faults and tsunami generation evolution of the fluid regime and mechanics of frontal prisms at margins dominated by tectonic erosion

the effect of seamount subduction on seismic coupling it has long been speculated that the subduction of seamounts may have profound mechanical consequences particularly on the generation of large subduction zone earthquakes we consider this problem as a special case of the seismic coupling model of scholz and campos the model predicts that the subduction of a large seamount will increase the normal stress across the subduction interface and hence will enhance seismic coupling in the case of coupled arcs this increased coupling will result in a large increase in the recurrence intervals of earthquakes such events will therefore appear rare in the instrumental record as is observed for decoupled arcs the subduction of a large seamount should cause them to become locally coupled three of the latter localities have been found with satellite altimetry data two on the tonga kermadec trench and one on the izu bonin trench the diagnostic feature is a shallowing or obstruction of the trench axis adjacent to a chain or group of large seamounts on the subducting plate in each case the small to moderate plate interface seismicity typical of decoupled seismic zones is almost completely absent in a 100 200 km arc segment indicating that the subduction zone is locally locked as predicted by the model the occurrence of large interplate earthquakes at both tonga sites confirms that they are seismically coupled

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

frictional afterslip following the 2005 nias simeulue earthquake sumatra continuously recording global positioning system stations near the 28 march 2005 rupture of the sunda megathrust moment magnitude m w 8 7 show that the earthquake triggered aseismic frictional afterslip on the subduction megathrust with a major fraction of this slip in the up dip direction from the main rupture eleven months after the main shock afterslip continues at rates several times the average interseismic rate resulting in deformation equivalent to at least a m w 8 2 earthquake in general along strike variations in frictional behavior appear to persist over multiple earthquake cycles aftershocks cluster along the boundary between the region of coseismic slip and the up dip creeping zone we observe that the cumulative number of aftershocks increases linearly with postseismic displacements this finding suggests that the temporal evolution of aftershocks is governed by afterslip

seismic record of tectonic evolution and backarc rifting in the southern ryukyu island arc system abstract the southern ryukyu island arc system is located at a convergent plate margin where the philippine sea plate is subducting under the eurasia plate we have conducted multi channel seismic reflection surveys to study tectonic evolution and backarc rifting of the southern ryukyu island arc system using the r v tansei maru of the ocean research institute university of tokyo in june 1993 and 1994 we describe systematically a complete cross section from the east china sea continental shelf to the ryukyu trench from the viewpoint of seismic stratigraphy seven major seismic units and three stages in the tectonic evolution of the system are identified 1 during stage 1 from late miocene to earliest pleistocene pre rift deposits of the shimajiri group accumulated over a wide region from the east china sea continental shelf to the forearc region 2 stage 2 is defined by a series of tectonic processes involving crustal doming erosion subsidence and sedimentation in association with initial rifting of the southern okinawa trough during most of early pleistocene time and 3 the backarc rifting is still in progress and syn rift sedimentation has been under way since the late pleistocene stage 3 a new significant observation lies in the fact that the pliocene shimajiri group is not distributed in most of the present day southern okinawa trough this implies that the backarc rifting of the southern okinawa trough was probably initiated after the deposition of the shimajiri group that is during the early pleistocene crustal scale simple shear allowing an asymmetrical half graben structure rather than pure shear governed the initial rifting of the southern okinawa trough the possibility however cannot be excluded that pure shear associated with symmetrical rifting may be predominant in the present day rifting of the southern okinawa trough as a result of northwestward migration of the rifting axis the average extension rate of the southern okinawa trough is estimated to be approximately 1 2 cm year on the basis of fault geometry observed on the acoustic basement

geological records of western pacific tsunamis in northern taiwan ad 1867 and earlier event deposits abstract located in the western circum pacific seismic zone taiwan is an ideal area for recording tsunamis that originate in the tectonically and volcanically active systems of the ryukyu arc okinawa trough and luzon arc however because of taiwan s short historical record there is only credible evidence for one disastrous tsunami which occurred in northern taiwan in ad 1867 to better understand the western pacific tsunamis an upper holocene deposit of a coastal plain inundated by the ad 1867 tsunami was investigated to search for geological evidence of tsunamis based on facies characteristics and sediment composition we identified two sharp based decimetre thick marine quartzose sandy layers that fine upward and landward intercalated with floodplain marsh sand and mud the fluvium are rusty red rich in volcanic clasts and fe and comparable to modern riverine sediments of local andesitic provenance extending 0 8 km inland the marine quartzose sandy layers are light coloured and rich in quartz and si have high ca ti values and are comparable to the modern beach dune sediments of regional siliciclastic provenance radiocarbon dating indicates that the marine sandy layers are correlated with the ad 1867 tsunami and an older event at the boundary between the 17th and 18th centuries both events were probably associated with reported earthquakes involving normal faulting in addition the distribution patterns of the two marine sandy layers are similar suggesting that the inundation distances run ups and flow heights of the two events are comparable this indicates that the disastrous tsunamis were frequent in the area between northern taiwan and the okinawa trough of the western circum pacific seismic zone

the role of the residual bitumen in the gas storage capacity of mature lacustrine shale a case study of the triassic yanchang shale ordos basin china abstract the role of the residual bitumen in the shale gas storage capacity is investigated for potential terrestrial shale gas reservoirs in the yanchang area southern ordos basin china the upper triassic organic rich yanchang shales comprise of thermally mature chang 7 shale average toc 5 12 wt type i ii1 kerogen tmax 443 458 c ro 0 83 1 02 and relatively mature chang 9 shale average toc 4 40 wt type i ii1 kerogen tmax 443 476 c ro 0 88 1 10 the mineralogy of yanchang shales is dominated by clay minerals average 48 85 and quarts average 31 7 a series of low pressure nitrogen adsorption desorption and high pressure methane sorption experiments were conducted on pretreated fresh drilling cores including three groups of core samples one original group one group extracted by dichloromethane and the other group extracted by trichloromethane selected from yanchang shales to demonstrate the role of the residual bitumen in the shale gas potential low pressure nitrogen sorption method was used to elucidate the effect of the residual bitumen on the pore structure of yanchang shales the results show that the specific surface area and pore volume and pore surface area of shale samples after the extraction greatly increase and their growth was closely related with pores of 30 nm and

effect of pore structure on shale oil accumulation in the lower third member of the shahejie formation zhanhua sag eastern china evidence from gas adsorption and nuclear magnetic resonance abstract as shale oil occurs primarily in micro nano pores and fractures research about the effect of pore structure on shale oil accumulation has great significance for shale oil exploration and development the effect of pore structure on shale oil accumulation in the lower third member of the shahejie formation es 3 l zhanhua sag eastern china was investigated using gas adsorption soxhlet extraction nuclear magnetic resonance nmr analysis and field emission scanning electron microscope fe sem observation the results indicated that the samples contained a larger amount of ink bottle shaped and slit shaped pores after extraction than before extraction the pore volume and specific surface area of the samples were approximately 2 5 times larger after extraction than before extraction residual hydrocarbon occurred primarily in the free state form in pores with diameters of 10 1000 nm which can provide sufficient pore volume for free hydrocarbon accumulation therefore pores with diameters of 10 1000 nm were regarded as oil enriched pores which are effective pores for shale oil exploration whereas pores with diameters smaller than 10 nm were regarded as oil ineffective pores samples with only well developed small pores with diameters smaller than 1000 nm showed high oil saturation whereas samples with both small pores and also relatively large pores and micro fractures presented low oil saturation as the minimum pore size allowing fluid expulsion is 1000 nm pores with diameters greater than 1000 nm were considered as oil percolated pores large pores and micro fractures are generally interconnected and may even form a complex fracture mesh which greatly improves the permeability of shale reservoirs and is beneficial to fluid discharge

impact of hydrocarbon expulsion efficiency of continental shale upon shale oil accumulations in eastern china abstract core samples were taken from two formations the qingshankou formation in northern songliao basin and the third member of the shahejie formation of zhanhua sag to carry out a study of impact of hydrocarbon expulsion from continental shale upon shale oil accumulations in eastern china total organic carbon toc and pyrolysis data of these samples were used to establish an evaluation criterion with absolute and relative oil content indexes for determining oil potential of shale as a result a correspondence relationship between shale oil content and organic types was established factors that may affect oil content of shale were discussed through study of fractures pore development minerals and lithological assemblage of the samples the results show that oil content of mature petroleum source rocks is firstly controlled by fracture growth and secondly by pore development they played both negative and positive roles in hydrocarbon flow and accumulation in shale overpressure caused by hydrocarbon generation and existence of organic acid corrosion are two important factors affecting the formation of fractures and pores in shale respectively intervals with type i organic matter are not favorable shale oil exploration targets because they contain little oil shale with type i organic matter tends to generate large amount of hydrocarbon but these hydrocarbon will escape with a high efficiency through over pressurized fractures caused by hydrocarbon generation and lack of pore space which in turn is the result of absence of oxygen that is essential for forming organic acid to create secondary pores in shale on the contrary intervals with type ii organic matters are potential shale oil exploration targets for that they offered just right conditions for oil to stay inside higher content of oxygen that is helpful in forming organic acid moderate hydrocarbon generation capacity that will not cause over pressurized fractures in shale with secondary pores while intervals with type iii organic matter bear no exploration significance due to the fact that this type of kerogen produces less oil because of low hydrocarbon generation capacity and unfavorable molecular configuration shale intervals with thin sandstone interbeds provide favorable passageways for dissolved carbonate by organic acid to flow out avoiding secondary precipitation the pores left behind can be excellent space for generated hydrocarbon to linger around these interbeds are also favorable for later reservoir stimulation measures such as hydraulic fracturing shale oil exploration shall be focused on finding sweet spots with greater pores which are the main reservoir space

are rupture zone limits of great subduction earthquakes controlled by upper plate structures evidence from multichannel seismic reflection data acquired across the northern ecuador southwest colombia margin 1 subduction of the nazca plate beneath the ecuador colombia margin has produced four megathrust earthquakes during the last century the 500 km long rupture zone of the 1906 mw 8 8 event was partially reactivated by three thrust events in 1942 mw 7 8 1958 mw 7 7 and 1979 mw 8 2 whose rupture zones abut one another multichannel seismic reflection and bathymetric data acquired during the sisteur cruise show evidence that the margin wedge is segmented by transverse crustal faults that potentially correlate with the limits of the earthquake coseismic slip zones the paleogene neogene jama quininde and esmeraldas crustal faults define a 200 km long margin crustal block that coincides with the 1942 earthquake rupture zone subduction of the buoyant carnegie ridge is inferred to partially lock the plate interface along central ecuador however coseismic slip during the 1942 and 1906 earthquakes may have terminated against the subducted northern flank of the ridge we report on a newly identified manglares crustal fault that cuts transversally through the margin wedge and correlates with the limit between the 1958 and 1979 rupture zones during the earthquake cycle the fault is associated with high stress concentration on the plate interface an outer basement high which bounds the margin seaward of the 1958 rupture zone may act as a deformable buttress to seaward propagation of coseismic slip along a megathrust splay fault coseismic uplift of the basement high is interpreted as the cause for the 1958 tsunami we propose a model of weak transverse faults which reduce coupling between adjacent margin segments together with a splay fault and an asperity along the plate interface as controlling the seismogenic rupture of the 1958 earthquake

the organic matter distribution and methane capacity of the lower cretaceous strata of northeastern british columbia canada abstract the methane sorption capacity of a succession of sandstone siltstone shale and coal from the lower cretaceous fort st john group of northeastern british columbia was investigated average organic matter om content for all formations is 2 3 wt with a minimum of 0 6 wt and maximum of 10 1 wt the methane sorption capacity ranges between 0 19 and 2 74 cm3 g at 6 mpa and at 30 c total gas capacity free and sorbed gas ranges between 2 2 and 16 6 cm3 g at 6 mpa micropore volumes range between 0 43 and 1 69 cm3 100 g a positive correlation exists between the om content micropore volume and the methane capacity of shales shales with high methane capacities have either high contents of inertodetrinite or vitrinite moisture content shows a positive relationship with om content micropore volume and methane capacity the negative relationship between moisture and surface area derived from n2 adsorption suggests the moisture is located within the microporosity of the om and also explains the positive relationship between methane capacity and moisture the high inertodetrinite and vitrinite contents correlate with sea level regressions that delivered terrestrial om from coastal plains located south of the study area into the basin

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

geological controls and estimation algorithms of lacustrine shale gas adsorption capacity a case study of the triassic strata in the southeastern ordos basin china abstract high pressure methane adsorption experiments on a series of triassic lacustrine shale moisture equilibrated samples from the southeastern ordos basin china were conducted at pressure up to 20 mpa two of which were measured at 30 c 40 c 50 c 60 c and 70 c and seven were performed under reservoir temperature from 48 c to 62 c to investigate the effect of organic matter content maturity mineralogical compositions and reservoir conditions temperature and pressure on the methane sorption capacity the total organic carbon contents tocs range from 0 91 wt to 6 11 wt the thermal maturities as inferred from rock eval analysis range from low mature to high mature the minerals of the shale samples are dominated by clays 36 57 wt and quartz 19 44 wt for the entire shale samples the dominant clay minerals are mixed layer illite smectite with some illite and no smectite exists corresponding to a stage of late diagenesis the studied samples have n2 bet surface areas ranging between 1 47 and 9 21 m2 g and pore volumes of 0 013 0 034 cm3 g the methane sorption capacities of moisture equilibrated shale samples show a positive correlation with toc contents and bet surface areas no relationship was observed between the clay contents and methane sorption capacities indicating that clay minerals do not significantly contribute to methane sorption capacity in these organic shales the langmuir pressure pl increases exponentially with temperature and the langmuir volume vl decreases linearly with temperature a computational scheme has been developed to calculate the methane sorption capacity of shales as a function of toc content temperature and pressure based on langmuir sorption isotherm function using this algorithm methane sorption capacity of organic shales as function of depth can be obtained due to the predominating effect of pressure the methane sorption capacity increases with depth initially through a maximum and then decreases due to the influence of increasing temperature at a greater depth the maximum gas sorption capacity typically occurs at a depth range between 400 and 900 m with toc content increasing the maximum methane sorption capacities of organic shales and the corresponding depths increase

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

seismically inferred dilatancy distribution northern barbados ridge decollement implications for fluid migration and fault strength a 5 x 25 km three dimensional seismic survey of the lower part of the northern barbados ridge accretionary prism creates a three dimensional image of a major active decollement fault the fault is usually a compound negative polarity reflection modeled as a low velocity high porosity zone less than 14 m thick this thickness is significantly less than that defined by drilling of a 40 m zone of deformation at ocean drilling program odp site 671b located within the surveyed area we infer that the seismically defined fault is a thin high porosity zone and is thus an undercompacted high fluid pressure dilatant section if these inferences are correct then map view variations in seismic reflection waveform and amplitude illustrate complex patterns of fault zone fluid content and fluid migration paths the amplitude map suggests kilometre wide channels of locally high porosity and thus focused fluid flow these paths are only subparallel to the expected minimum head as inferred from the shape of the overlying sediment wedge other factors must modify fluid concentrations and ultimately migration several areas of positive polarity fault reflections define square kilometre sized regions inferred to be lower porosity sections producing strong asperities in an otherwise weak fault one coincident with site 671b may explain the success of drilling through the fault here all other holes drilled in the area were within the negative polarity regions and were unsuccessful in penetrating through the entire fault zone possibly because of instability associated with high fluid pressures and a weak fault odp leg 156 planned for 1994 will test inferences related to fault permeability and fluid pressures

activation of very low frequency earthquakes by slow slip events in the ryukyu trench long term activity of shallow very low frequency earthquakes vlfes in the ryukyu trench unassociated with recent large thrust earthquakes was analyzed using a broadband seismometer network the distribution of shallow vlfes was divided into three large clusters the activity of the vlfes is modulated by repetitive slow slip events and the activity of these vlfes increases to 2 3 times its ordinary rate at 10 20 days after the onset of the slow slip events the activation of vlfes could be generated by small increases on the order of approximately 0 1 0 5 kpa in coulomb failure stress suggesting that stress in the plate interface where the vlfes occur is frequently released in small amounts moreover the distribution of vlfes is complementary to the historical tsunami source area and locked area the distribution of the vlfes indicates heterogeneity in interplate coupling along the trench

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

source fault model of the 1771 yaeyama tsunami southern ryukyu islands japan inferred from numerical simulation the 1771 yaeyama tsunami is successfully reproduced using a simple faulting model without submarine landslide the yaeyama tsunami m 7 4 which struck the southern ryukyu islands of japan produced unusually high tsunami amplitudes on the southeastern coast of ishigaki island and caused significant damage including 12 000 casualties previous tsunami source models for this event have included both seismological faults and submarine landslides however no evidence of landslides in the source has been obtained despite marine surveying of the area the seismological fault model proposed in this study describing a fault to the east of ishigaki island successfully reproduces the distribution of tsunami runup on the southern coast of the ryukyu islands the unusual runup heights are found through the numerical simulation attributable to a concentration of tsunami energy toward the southeastern coast of ishigaki island by the effect of the shelf to the east thus the unusual runup heights observed on the southeastern coast of ishigaki island can be adequately explained by a seismological fault model with wave ray bending on the adjacent shelf

fault model of the 1771 yaeyama earthquake along the ryukyu trench estimated from the devastating tsunami 1 the 24 april 1771 yaeyama earthquake generated a large tsunami with a maximum runup of 30 m causing significant damage in south ryukyu japan despite the weak ground shaking previously proposed mechanisms of the tsunami include intraplate faulting or submarine landslide in the forearc slope in this study i estimate the fault parameters of the 1771 earthquake by numerically computing the tsunami heights and comparing them with the recorded heights the result indicates that the source fault of the tsunami is very close to the ryukyu trench the results are consistent with a thrust faulting earthquake that had a fault width of less than 50 km the 1771 yaeyama tsunami was caused by a tsunami earthquake mw 8 0 that occurred in the subducted sediments beneath the accretionary wedge

a mega splay fault system and tsunami hazard in the southern ryukyu subduction zone abstract in april 1771 a subduction earthquake generated a great tsunami that struck the south ryukyu islands and killed 12 000 people whereas its mechanism is still enigmatic nakata and kawana 1995 nakamura 2006 matsumoto et al 2009 in this paper we show its probable source on a mega splay fault system existing along the southern ryukyu forearc analyses of deep multi channel seismic reflection profiles indicate that the mega splay fault system is rising from the summit of a 1 km high ridge situated at a 5 landward dipping plate interface an outer ridge marks the seafloor outcrop of the splay fault system and separates the landward inner wedge and the oceanward outer wedge the inner wedge is uplifting and exhibits widespread normal faulting while the outer wedge shows folded structures the mega splay fault system is parallel to the ryukyu trench east of 125 5 e and is estimated to be 450 km long the origin of this south ryukyu mega splay fault system is ascribed to a resistant subduction of the elevated transverse ridges associated with the subducting portion of the trench parallel luzon okinawa fracture zone in contrast no similar splay fault is found west of 125 5 e where the oblique subduction has produced large shear zones along the south ryukyu forearc we infer that a thrust earthquake linked to the mega splay fault system is responsible for the south ryukyu tsunami however another possible scenario of generating a large tsunami affecting the south ryukyu islands is that the subducted ridge in the western end of the mega splay fault system nucleated a large earthquake and simultaneously triggered the 100 km long e w trending strike slip fault west of 125 5 e and induced a southward dipping tsunami genic subsidence in any case after a quiescence of 241 yr a large earthquake and tsunami is anticipated in the south ryukyu forearc in the near future

a preliminary study on the pore characterization of lower silurian black shales in the chuandong thrust fold belt southwestern china using low pressure n2 adsorption and fe sem methods although lower silurian black shales within and around the sichuan basin have received renewed attention during the past few years because of their potential prospectivity for shale gas studies associated with shale gas reservoir evaluation are still rare in this study eight black shale core samples were collected from a well drilled recently in the chuandong thrust fold belt southwestern china and their geochemistry and pore structures were investigated using low pressure n2 adsorption analysis and field emission scanning electron microscopy fe sem observations the results show that the black shales have total organic carbon toc values ranging from 1 01 to 3 98 and their equivalent vitrinite reflectance values are in the range of 2 84 3 05 both mineral matrix and organic matter pores are well developed with pore sizes ranging from several to several hundred nanometers the total porosity for the eight samples ranges from 2 60 to 4 74 and the percentages of organic matter pores are estimated to be in the range of 31 62 the total surface area ranges from 5 06 m2 g to 19 32 m2 g and the micropore 2 nm surface area estimated by the t plot method ranges from 3 13 m2 g to 9 27 m2 g the toc values have positive relationships with the total porosity total surface area and the micropore 2 nm volume and surface area indicating toc may be an effective parameter for shale gas reservoir evaluation in the studied area

spatial variation of seismogenic depths of crustal earthquakes in the taiwan region implications for seismic hazard assessment abstract this paper presents the first whole taiwan scale spatial variation of the seismogenic zone using a high quality crustal seismicity catalog the seismicity onset and cutoff depths i e seismogenic depths are determined by the earthquake depth moment distribution and used to define the upper and lower boundaries of the seismogenic zone respectively together with the published fault geometries and fault area moment magnitude relations the depth difference in the onset and cutoff depths i e seismogenic thickness is used as the fault width to determine the moment magnitudes of potential earthquakes for the major seismogenic faults results show that the largest mw7 9 8 0 potential earthquake may occur along the changhua fault in western taiwan where the seismic risk is relatively high and seismic hazard mitigation should be a matter of urgent concern in addition the first motion focal mechanism catalog is used to examine the relation between the seismogenic depths and earthquake source parameters for crustal earthquakes 50 km the shallowest onset and cutoff depths are observed for normal and strike slip events respectively this observation is different from the prediction of the conventional continental rheology model which states that thrust events have the shallowest cutoff depth thus a more sophisticated rheology model is necessary to explain our observed dependence of the seismogenic depths on faulting types meanwhile for intermediate to large crustal mw 4 depth 50 km earthquakes thrust events tend to occur at the bottom region of the seismogenic zone but normal and strike slip events distribute at a large depth range

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

benham rise unveiled morphology and structure of an eocene large igneous province in the west philippine basin abstract the benham rise is an oceanic large igneous province at the western margin of the philippine sea it has an ocean island basalt geochemistry a surface area of 0 11 mkm2 and a volume of 0 13 mkm3 a crustal thickness of 15 km is estimated from gravity anomalies volcanism was most active in the early stages of its formation during the lutetian from 47 9 ma to 41 3 ma although volcanic activity extended to 26 ma multibeam bathymetry with almost 100 coverage has revealed the morphology of benham rise for the first time it consists of a main body 310 km by 330 km with the narra loro and molave spurs extending 100 200 km from its eastern side the main body is built on a shield platform from 5200 m to 3800 m sub sea the platform flanks consist of 3 15 km wide terraces with scarps as high as 100 m to 300 m the platform is surmounted by a crest exhibiting caldera morphology at an average depth of 2500 m the crest is named apolaki caldera and may be the world s largest known caldera with a diameter of 150 km features like a breached rim intra caldera benches and a resurgent dome indicate a multi phase volcanic history consisting of both quiet and explosive eruptions the bathymetry and publicly available geological and geophysical data record three main stages in the tectonic history of benham rise shield building caldera formation and post caldera late stage volcanism the platform base is interpreted to have formed over a hotspot beneath the central basin spreading center during the shield building phase between 47 9 ma to 42 5 ma the arrowhead shaped molave spur is interpreted to have formed late in this stage along a ridge that propagated away from the hotspot the caldera formation followed and is interpreted to have occurred before 41 3 41 5 ma when benham rise was still joined with urdaneta plateau the narra spur was formed by late stage hotspot related volcanism as benham rise and urdaneta plateau separated and ended with the eruptions of the vinogradov seamount at 26 ma

weak interplate coupling by seamounts and repeating m 7 earthquakes subducting seamounts are thought to increase the normal stress between subducting and overriding plates however recent seismic surveys and laboratory experiments suggest that interplate coupling is weak a seismic survey in the japan trench shows that a large seamount is being subducted near a region of repeating earthquakes of magnitude m 7 both observed seismicity and the pattern of rupture propagation during the 1982 m 7 0 event imply that interplate coupling was weak over the seamount a large rupture area with small slip occurred in front of the seamount its northern bound could be determined by a trace of multiple subducted seamounts whereas a subducted seamount itself may not define the rupture area its width may be influenced by that of the seamount

transition from oblique subduction to collision earthquakes in the southernmost ryukyu arc taiwan region tectonic characteristics of the region between taiwan and the southernmost ryukyu arc are inferred from a detailed analysis of local seismicity and source parameters of 62 recent earthquakes of 5 5 mb 6 6 five major seismogenic structures can be delineated the collision seismic zone csz the interface seismic zone isz the wadati benioff seismic zone wbsz the lateral compression seismic zone lcsz and the okinawa seismic zone osz in the csz located along the east coast of taiwan and offshore earthquake focal mechanisms show horizontal p axes distributed in two directions 287 10 and 333 16 possibly reflecting a strain partition associated with the relative plate convergence between the eurasia plate and the philippine sea plate the corresponding seismic strain tensor indicates a maximum compressive strain rate of 1 2 10 7 yr 1 along 293 and a comparable extension in vertical direction presumably resulted from plate collision in the region the geometry of the isz which is distorted significantly at its westernmost end can be approximated by a north dipping plane that is gradually pushed northward with increasing dip the seismogenic portion of the interface spans a short depth range from 10 km to 35 km a clear pattern of earthquake slip partition is observed the average slip vector residual is as large as 35 seismic strain patterns within the subducted philippine sea slab show predominantly downdip extension between 80 and 120 km and downdip compression at 270 km different from the pattern of strain segmentation observed for the rest of the ryukyu arc where the northern and southern portions are dominated by downdip extension and compression respectively owing to the large convergence obliquity the slab is descending at a rate significantly slower near taiwan than in the southern ryukyu thus we interpret the appearance of downdip extension within the subducted lithosphere as a combined result of oblique subduction and the slab s negative buoyancy a number of thrust or oblique strike slip earthquakes between isz and wbsz show a consistent pattern of lateral compression with p axes oriented roughly parallel to the local strike of the trench arc system they are probably due to the compressive strain originated from the collision and transmitted laterally within the lithosphere shallow normal faulting earthquakes show successive rotation of t axes from approximately n s in the okinawa trough to approximately e w in northeast taiwan possibly as a result of interaction between the extension from the opening of the okinawa trough and the compression from collision one normal event january 18 1991 mb 5 9 occurred in the central range with t axis roughly parallel to the structural trend of taiwan implying that the nature of the orogeny in taiwan has changed from thin skinned deformation to lithospheric collision involving the whole crust and uppermost mantle

simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 abstract here we present novel cave analogue experiments directly investigating stable carbon and oxygen isotope fractionation between the major involved species of the carbonate system hco3 co2 caco3 and h2o in these experiments which were performed under controlled conditions inside a climate box a thin film of solution flew down an inclined marble or glass plate after different distances of flow and thus residence times on the plate ph electrical conductivity supersaturation with respect to calcite precipitation rate as well as the 18o and 13c values of the dissolved inorganic carbon dic and the precipitated caco3 were obtained progressive precipitation of caco3 along the plate is accompanied by degassing of co2 and stable isotope fractionation and the system is driven out of isotope equilibrium we observe a strong enrichment of the 13c values with increasing residence time and a smaller enrichment in 18o the temporal evolution of the 18o and 13c values of both the dic and the precipitated caco3 can be explained by a rayleigh fractionation model but the observed enrichment in 13c values is much larger than expected based on isotope equilibrium fractionation factors our setup enables to determine the fractionation between caco3 and hco3 i e ecaco3 hco3 carbon isotope fractionation 13ecaco3 hco3 is strongly negative for all experiments and much lower than equilibrium isotope fractionation 0 1 in addition 13ecaco3 hco3 decreases with increasing residence time on the plate and thus decreasing supersaturation with respect to calcite thus isotope fractionation depends on precipitation rate and consequently occurs under kinetic conditions this is in contrast to previous studies which found no rate dependence and no or even a positive carbon isotope fractionation between caco3 and hco3 oxygen isotope fractionation 18ecaco3 hco3 is also negative and dependent on precipitation rate since no literature values for 18ecaco3 hco3 are available we calculated 18ecaco3 hco3 using equilibrium oxygen isotope fractionation factors between water and calcite and water and hco3 respectively at the beginning of the plate the fractionation is in agreement with the fractionation calculated using fractionation factors determined in cave systems the observed fractionation between caco3 and water 1000ln18 is also in good agreement with the values determined in cave systems and shows a very similar temperature dependence 1000 ln 18 16 516 1 267 10 3 t 26 141 4 356 however with progressive precipitation of caco3 along the plate the system is forced out of isotope equilibrium with the water and 1000ln18 increases the large negative rate dependent isotope fractionations observed in this study suggest that precipitation of speleothem calcite is strongly kinetically controlled and may thus have a large effect on speleothem 18o and 13c values since these values may erroneously be interpreted as reflecting changes in past temperature precipitation and or vegetation density these results have important implications for paleoclimate reconstructions from speleothems

trench parallel stretching and folding of forearc basins and lateral migration of the accretionary wedge in the southern ryukyus a case of strain partition caused by oblique convergence detailed seafloor mapping in the area east of taiwan revealed trench parallel stretching and folding of the ryukyu forearc and lateral motion of the accretionary wedge under oblique convergence east of 122 40 e a steep accretionary wedge is elongated in an e w direction a major transcurrent right lateral strike slip fault accommodates the strain partitioning caused by an oblique convergence of 40 a spectacular out of sequence thrust may be related to the subduction of a structural high lying in the axis of the n s trending gagua ridge this asperity is likely responsible for the uplift of the accretionary wedge and forearc basement and may have augmented strain partitioning by increasing the coupling between the two plates west of 122 40 e the low taper accretionary wedge is sheared in a direction subparallel to the convergence vector with respect to the ryukyu arc the bayonet shape of the southern ryukyu arc slope partly results from the recent re opening of the southern okinawa trough at a rate of about 2 to 4 cm yr right lateral shearing of the sedimentary forearc with respect to the nonlinear ryukyu backstop generates trench parallel extension in the forearc sediment sequence at dilational jogs and trench parallel folding at compressive jogs the hoping basin lies above a diffuse trench trench fault ttf or tff unstable triple junction moving toward the south along a n s transform zone which accommodates the southward drift of the ryukyu arc with respect to eurasia

differential subsidence of the forearc wedge of the ryukyu nansei shoto arc caused by subduction of ridges on the philippine sea plate abstract the philippine sea plate psp carrying several ridges has been sudbucting under the ryukyu nansei shoto arc since middle miocene because no extensive accretionary prism has been growing along the ryukyu trench the arc provides an opportunity to examine effects of ridge subduction on structure of the forearc wedge and a clue to reconstruct ancient plate motion of the psp that is inferred to have changed between nw and nnw to examine this perspective we clarified structure of the ryukyu forearc wedge based on seismic profiles and bathymetric data and related them to ridge subduction an erosional unconformity between pre neogen and neogene rocks is widely recognized through the ryukyu arc and we divided the forearc wedges into zones i to iv from southwest to northeast by difference of depth of the erosional unconformity we correlated these four zones to the locations of ridge subduction that have been shifting ne or sw along the ryukyu trench zone i is underlain by the largely subsided unconformity and we attributed the structure to tearing of the eurasia plate due to subduction of the western margin of the psp including the luzon arc zone ii consists of a wide terrace on the shallow erosional unconformity and no ridge that was subducting in this zone is known zone iii is characterized by the seaward descending unconformity covered with a thick sequence of neogene sediments and is related to subduction of the nw se trending daito ridge and the e w trending amami plateau zone iv has the deeper unconformity and slope geometry and corresponds to subduction of the nnw sse trending kyushu palau ridge the structure of the ryukyu forearc is consistently related to subduction of ridges on the psp suggesting that the change of the plate motion of the psp can be precisely reconstructed by further detailed survey

comment on maximilian hansen denis scholz bernd r schone christoph spotl simulating speleothem growth in the laboratory determination of the stable isotope fractionation δ13c and δ18o between h2o dic and caco3 chemical geology 509 2019 20 44 abstract in this comment it is shown that analysis of the fractionation constants of the dic describing the enrichment of 13c and 18o along the flow path of a thin water layer flowing down an inclined marble plate precipitating calcite in analogy to precipitation to speleothems enables one to decide whether the rayleigh distillation model or the kinetic model is valid appropriate analysis of etot values for carbon and oxygen as reported by hansen et al 2019 reveals the validity of the kinetic model and allows determining the constants ekin and this is in contrast to findings of hansen and coauthors and gives a deeper understanding of the meaning of kinetic fractionation during precipitation of calcite