stress strain response of hydrate bearing sands numerical study using discrete element method simulations 1 gas hydrate is a crystalline solid found within marine and subpermafrost sediments while the presence of hydrates can have a profound effect on sediment properties the stress strain behavior of hydrate bearing sediments is poorly understood due to inherent limitations in laboratory testing in this study we use numerical simulations to improve our understanding of the mechanical behavior of hydrate bearing sands the hydrate mass is simulated as either small randomly distributed bonded grains or as ripened hydrate forming patchy saturation whereby sediment clusters with 100 pore filled hydrate saturation are distributed within a hydrate free sediment simulation results reveal that reduced sand porosity and higher hydrate saturation cause an increase in stiffness strength and dilative tendency and the critical state line shifts toward higher void ratio and higher shear strength in particular the critical state friction angle increases in sands with patchy saturation while the apparent cohesion is affected the most when the hydrate mass is distributed in pores sediments with patchy hydrate distribution exhibit a slightly lower strength than sediments with randomly distributed hydrate finally hydrate dissociation under drained conditions leads to volume contraction and or stress relaxation and pronounced shear strains can develop if the hydrate bearing sand is subjected to deviatoric loading during dissociation

change in climate ocean and ice sheet conditions in the ross embayment antarctica at 6 ka evidence from the ross embayment antarctica suggests an abrupt cooling and a concomitant increase in sea ice cover at about 6000 sp 6 ka stable isotope delta d concentrations in the taylor dome ice core at the western edge of the ross embayment decline rapidly after 6 ka and continue to decline through the late holocene methanesulfonic acid concentrations at taylor dome show opposite trends to delta d sediment cores from the western ross sea show a percentage minimum for the sea ice diatom fragilariopsis curta between 9 and 6 ka when taylor dome delta d values are highest followed by an increase through the late holocene radiocarbon dates from raised beach deposits indicate that the retreat of ice shelves in the ross embayment ceased atabout 6 ka coincident with the environmental changes inferred from the sediment and ice core records the similarity in timing suggests an important role for climate in controlling the evolution of ice shelf margins following the end of the last 9 glaciation

the 23 19 aftershock of the 15 october 1979 imperial valley earthquake more evidence for an asperity the well recorded strong ground motion data for the 23 19 aftershock of the 15 october 1979 imperial valley earthquake provide a good opportunity to study the high frequency source characteristics and the path effects at near source distances the best fitting point source model has a strike slip mechanism n40 w which is nearly identical to the main event the estimated stress drop is extremely high roughly 500 bars with a triangular time history 0 1 0 1 sec but with a moment of 1 0 10 24 dyne cm a double source model found by inversion fits the high frequency data better but indicates complex faulting the first source with strike n319 e dip 42 ne and slip angle 165 has a moment of 0 7 10 24 dyne cm the second source with strike n324 e dip 82 sw and slip angle 181 lies about 0 5 km to the north and has a seismic moment twice that of the first source source dimensions appear very small for this amount of energy release many of the anomalous behaviors observed at certain stations for the main event are also present in the aftershock data these features are examined in terms of path effects

constant holocene southern ocean 14c reservoir ages and ice shelf flow rates article i nfo southern ocean radiocarbon reservoir ages i e non zero radiocarbon ages in seawater are the highest in the world s surface ocean constraining these reservoir ages at present and in the past is important not only because unknown reservoir ages limit the interpretation of antarctic radiocarbon chronologies but also because reservoir ages provide information about ocean circulation as a recorder of past circulation and as an end member for major deep water masses in today s ocean in this study we use paired u th and 14 c ages of an unusual set of solitary coral samples trapped by fringing ice shelves in the ross sea to provide the first detailed study of holocene reservoir ages for the southern ocean our results indicate a relatively constant marine radiocarbon reservoir age of 1144 120 years for the past 6000 years these results are consistent with extrapolation of the relationship between 14 c and alkalinity seen elsewhere supporting the use of this empirical relationship in high latitudes the results also suggest constant deep ocean circulation and air sea exchange during the holocene and provide a good target for tuning ocean models of modern circulation combining the new ages for corals with their distance from the modern day ice shelf grounding line provides some of the first long term records of ice shelf velocities for any region and indicates constant flow of the mcmurdo ice shelf during the holocene at a rate similar to that observed today

abandoned penguin rookeries as holocene paleoclimatic indicators in antarctica penguins are sensitive indicators of the antarctic climate and of the environmental parameters that limit their presence and distribution paleoenvironmental data obtained from the study of abandoned penguin rookeries pygoscelis adeliae along the victoria land coast in antarctica indicate 14c date of 11 13 ka for the oldest abandoned rookery and supply new information about the timing of glacier retreat in southern victoria land after the last glacial maximum the continuous presence of the adelie penguins is documented from 7 ka according to our data the limiting factors that control the presence of penguins along the coast of victoria land changed during the holocene whereas several colonies were occupied for very long periods other sites were used for more or less extended periods and then abandoned the greatest diffusion of rookeries occurred between 3 and 4 ka a period of particularly favorable environmental conditions that has never been repeated it was followed by a sudden decrease in the number of penguin rookeries shortly after 3 ka this event has been attributed to an increase of the sea ice extension and may have been correlated to a worldwide phase of climate change near the subboreal subatlantic boundary a minor phase of penguin reoccupation occurred locally in the eighth to fourteenth centuries a d because the presence and number of penguins reflect the state of health of the antarctic marine ecosystem it is important to evaluate the variations in their distribution in the past in the absence of human induced changes

holocene elephant seal distribution implies warmer than present climate in the ross sea we show that southern elephant seal mirounga leonina colonies existed proximate to the ross ice shelf during the holocene well south of their core sub antarctic breeding and molting grounds we propose that this was due to warming including a previously unrecognized period from 1 100 to 2 300 14c yr b p that decreased coastal sea ice and allowed penetration of warmer than present climate conditions into the ross embayment if as proposed in the literature the ice shelf survived this period it would have been exposed to environments substantially warmer than present

investigation of the yellow river buried fault in the wuhai basin northwestern ordos block china using deep shallow seismic reflection and drilling techniques abstract studying the faults in wuhai basin which is located in the northwestern corner of the ordos block in china can not only guide earthquake safe construction in the region but also provide a greater understanding of the structure of the wuhai basin and the dynamic environment of northwestern ordos block in this study we effectively detected the yellow river buried fault yrf which we believe currently presents a risk to human life in the area first we laid out a deep seismic reflection profile dsrp in the north of the wuhai basin and found that the yrf is composed of two subparallel faults the east branch of the yellow river buried fault eyf and the west branch of the yellow river buried fault wyf which formed a y type graben in the section we then used 25 shallow seismic exploration profiles to find out how the faults are distributed finally we used drillings and quaternary dating methods to certify their existence and obtain their activity parameters we used the sequence stratigraphy method to compare sediment strata and identified paleo earthquake events by finding the unequal thickness layers utls on both sides of the fault the drillings revealed that four earthquakes occurred on the yrf around 25 6 0 11 ka bp 39 5 0 45 41 7 0 57 ka bp 58 25 7 13 ka bp and 111 1 21 ka bp since the last activity on the yrf occurred much longer ago than its estimated recurrence cycle we believe that the fault yrf currently presents a dangerous risk our study confirms that the yrf is a normal fault graben and that the wuhai bain is an extensional basin formed by the relative movement of the tibetan plateau the alashan block and the ordos block

cemented sands under static loading cemented sands are found in many areas of the world one of their distinguishing characteristics is their ability to stand in steep natural slopes large deposits are located along the california coast and in a number of areas intense urban development has occurred near the crest of high steep slopes because of the hazards posed by slope failures in the cemented sands a test program was undertaken to define the nature of the cementation and its effect on behavior of the soils a total of 137 laboratory compression and tension load tests were performed on undisturbed samples of naturally cemented sands and artificially prepared cemented sands the materials exhibited friction angles similar to uncemented sands but had a cementation strength intercept and a tensile strength the primary cementing agents of the sands tested were silicates and iron oxides the strength of the cemented sands were found to be a function of density amount of cementing agent grain shape and grain arrangement

a model for a seismic computerized alert network in large earthquakes damaging ground motions may occur at large epicentral distances because of the relatively slow speed of seismic waves it is possible to construct a system to provide short term warning as much as several tens of seconds of imminent strong ground motions from major earthquakes automated safety responses could be triggered by users after receiving estimates of the arrival time and strength of shaking expected at an individual site although warning times are likely to be short for areas greatly damaged by relatively numerous earthquakes of moderate size large areas that experience very strong shaking during great earthquakes would receive longer warning times

the 1983 borah peak idaho earthquake and its aftershocks abstract the 28 october 1983 borah peak idaho earthquake m s 7 3 occurred in an area of low historic seismicity within east central idaho along a segment of the lost river fault active during the holocene a dense network of portable short period seismographs up to 45 stations station spacings of 2 to 10 km was installed beginning several hours after the main shock and operated for 22 days in addition to records from the portable instrumentation data from permanent seismograph stations operating in idaho utah montana oregon washington and wyoming provide a good regional data base no foreshock activity above m c coda magnitude 2 0 was detected for the 2 month period preceding the main shock the epicenter of the main shock is 14 km south southwest of the end of the surface faulting this relationship suggests unilateral rupture propagating to the northwest the distribution of 421 aftershocks of m c 2 defines an epicentral pattern 75 km 10 km trending north northwest parallel to the surface rupture but displaced laterally southwest by 5 to 10 km aftershocks extend to depths of approximately 16 km and in the central and southeastern portion of the aftershock pattern define a zone dipping approximately 45 southwest that intersects the surface near the fault scarp the entire aftershock zone as observed during the first 3 weeks was active shortly after the main shock occurred fault plane solutions for 47 aftershocks show predominantly normal faulting with varying amounts of strike slip motion tension axis orientations indicate a dominant extension direction of nne ssw during the aftershock sequence there is considerable diversity among the aftershock focal mechanisms even along the central and southeast portions of the fault where the hypocenters appear to outline the main fault break we therefore interpret most of the aftershocks to represent complex fracturing on subsidiary structures adjacent to the main fault

a fault model with variable slip duration for the 1989 loma prieta california earthquake determined from strong ground motion data abstract a finite fault model with variable slip duration is inferred from strong ground motion data for the loma prieta earthquake unlike previous models slip duration is found to be consistent with fault width scaling slip duration varies between 1 and 6 sec at points along the fault surface with values between 3 and 6 sec where slip amplitudes obtain or exceed the average slip of 98 cm modest high frequency modifications of the slip function shape greatly enhance the data fit without significantly changing the inferred static offset or rupture characteristics this model exhibits bilateral rupture with the propagation rate of the main energy release of 3 km sec or less the moment is 2 3 10 26 dyne cm and the largest slip amplitudes occur northwest of the hypocenter the rake varies with position along the fault from dominantly strike slip in the southeast to dominantly reverse slip in the northwest

holocene raised beaches at terra nova bay victoria land antarctica abstract more than 40 14c dates for raised beaches at terra nova bay ranging from the present to 7505 230 yr b p supply minimum or maximum limiting ages that bracket a relative sea level curve for this part of victoria land most samples consist of guano and penguin remains collected from abandoned nesting sites on beach deposits up to four 14c dates in stratigraphic sequence have been obtained in two soil profiles other samples consist of marine shells collected both within and on the surface of raised beaches all 14c ages for organisms that lived or fed in circumantarctic waters were corrected for a large reservoir effect the calibrated ages delimit a first relative sea level curve for victoria land rates of uplift ranged from about 10 mm yr following deglaciation to about 2 mm yr in the last 3 millennia widespread presence of adelie penguin nesting sites suggests that terra nova bay was deglaciated before 7065 250 yr b p 7059 6439 cal yr b p when environmental conditions in the coastal area were similar to the present ones

documentation of benchmark photographs that show the effects of the 1983 borah peak earthquake with some considerations for studies of scarp degradation systematic benchmark photography of modern and prehistoric fault scarps provides an accurate and timely method of documenting details of ground breakage related to earthquakes and provides a near permanent record for future quantitative analysis of the degradation of these features during the geologic investigation of surface faulting associated with the 28 october 1983 borah peak earthquake of central idaho i established 14 benchmark stations for repeat photography of selected deformational features about 40 photographs most in stereopairs were made in november 1983 in order to show some of the details of the newly formed fault scarps grabens and an associated landslide one year later october 1984 h e malde and i repeated most of the 1983 photographs and photographed from 14 additional stations this paper provides an account of the location and subject of the photographs that are on file at the u s geological survey photo library in denver hopefully this study will provide the impetus for including systematic benchmark photography in future studies of ground deformation

co seismic ground shortening structures produced by the 2008 mw 7 9 wenchuan earthquake china abstract we observed ground shortening structures produced by the 2008 m w 7 9 wenchuan earthquake along the 285 km long wenchuan co seismic surface rupture zone the structures are characterized by co seismic thrusting and folding structures that include thrust fault scarps flexure slip folds and mole tracks fold structures are generally developed within alluvial deposits river channel deposits and sealed road surfaces mainly restricted to within a

relation between average slip and average stress drop for rectangular faults with multiple asperities abstract it is shown from numerical experiments that the average slip and seismic moment due to the fracture of multiple asperities on a rectangular fault is independent of the distribution of the asperities on the fault for all practical purposes as long as the average stress drop on the fault is the same for the different distributions hence using the relations between average slip and average stress drop for a smooth fault to estimate the stress drop for an earthquake which is due to the failure of a few large asperities gives a sufficiently good estimate of the stress drop relations between the average slip and average stress drop for simple rectangular faults of different length to width ratios are determined numerically both of the cases when the fault slip direction is parallel to the fault length and when it is parallel to the fault width are considered the 1985 mexican earthquake is discussed briefly as an example of this kind of earthquake model

inversion for slip distribution using teleseismic p waveforms north palm springs borah peak and michoacan earthquakes we have inverted the teleseismic p waveforms recorded by stations of the global digital seismograph network for the 8 july 1986 north palm springs california the 28 october 1983 borah peak idaho and the 19 september 1985 michoacan mexico earthquakes to recover the distribution of slip on each of the faults using a point by point inversion method with smoothing and positivity constraints in the inversion procedure a fault plane with fixed strike and dip is placed in the region of the earthquake hypocenter and divided into a large number of subfaults rupture is assumed to propagate at a constant velocity away from the hypocenter and synthetic ground motions for pure strike slip and dip slip dislocations are calculated at the teleseismic stations for each subfault the observed seismograms are then inverted to obtain the distribution of strike slip and dip slip displacement for the earthquake results of the inversion indicate that the global digital seismograph network data are useful for deriving fault dislocation models for moderate to large events however a wide range of frequencies which includes periods shorter than those within the passband of the long period global digital seismograph network instruments is necessary to infer the distribution of slip on the earthquake fault although the long period waveforms define the size dimensions and seismic moment of the earthquake data at shorter periods provide additional constraints on the variation of slip on the fault dislocation models obtained for all three earthquakes are consistent with a heterogeneous rupture process where failure is controlled largely by the size and location of high strength asperity regions

insights into the holocene environmental setting of terra nova bay region ross sea antarctica from oxygen isotope geochemistry of adelie penguin eggshells an oxygen isotope record of adelie penguin pygoscelis adeliae eggshells from terra nova bay victoria land antarctica has been reconstructed in order to provide insights into the palaeoenviroment of this region during the last 8000 years the 18o values measured in eggshell carbonate show a great variability over the course of the studied period with maximum values consistently around 27 5 adopting a metabolic enrichment relative to water source of 28 5 eggshell 18o values can be interpreted in terms of marine water uptake by the penguins the spread in 18o of eggshell carbonate at any given time toward more negative values reflects the existence of a low 18o water end member most plausibly snow or snowmelt samples younger than 2000 years are characterized by a general lack of very negative 18o values as also attested by other proxies this shift toward more positive isotopic values is likely to be related both to a decreasing contribution of snow or meltwater in the seawaters and con

snow accumulation rates in northern victoria land antarctica by firn core analysis a multiparametric chemical isotopic and physical study on three shallow firn cores sampled in northernvictoria land was carried out to obtain glaciological information and climatic data in this antarctic region sampling areas were accurately prospected to identify sites located at different altitudes and distances from the sea where the snow accumulation was not influenced by katabatic wind redistribution or summer melting stratigraphic isotopic 18 o and chemical h 2 o 2 msa and nssso 4 2 profiles were mutually examined for dating purposes and to determine the mean snow accumulation rates at three different stations annual accumulation rates of 85 420 kg m 2 a 1 were determined in the period 1971 92 an inverse pattern between accumulation rate and altitude was shown by the progression of the mean annual rates of 160 203 and 260 kg m 2 a 1 respectively in the highest medium and lowest stations the mean accumulation value of all northern victoria land data available 170 kg m 2 a 1 represents a decrease of up to 35 with respect to the estimated value most widely used until now our accumulation value is very close to that required for a zero net surface mass balance according to ice discharge a linear relationship with a gradient of 0 81 c has been found between mean 18 o values and mean annual surface temperature for different ice cores drilled in northern victoria land

late pleistocene holocene marine conditions in the ross sea antarctica evidence from the diatom record statistical analyses of diatom assemblages from radiocarbon dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west central ross sea antarctica from c 12 14c kyr bp to the present data from three kasten cores support a north to south time transgressive glacial interglacial transition assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late pleistocene increasing biogenic silic and decreasing per centages of reworked species suggest that upper water column productivity instead of preservational processes increasingly dominates diatom assemblages during grounding line recession c 12to c 6 14c kyr bp a warm ing during the middle to late holocene c 6to c 3 14c kyr bp may have resulted in a spring sea ice melting prior to the annual inception of the ross sea polynya in the west central ross sea and b increased plateletice delivery due to increased melting beneath t

a 45 000 yr record of adelie penguins and climate change in the ross sea antarctica well preserved remains of bone tissue and eggshell of adelie penguin pygoscelis adeliae have been recovered from numerous abandoned colonies in the ross sea region antarctica radiocarbon dates on these remains provide an occupation history for this species ranging from hundreds to tens of thousands of years ago we completed 62 new radiocarbon dates on these remains which now indicate that an open water marine environment existed in the ross sea from ca 45 000 to 27 000 14 c yr before present b p and provide constraints for the timing of the last advance of the ross ice sheet penguins did not recolonize the ross sea until ca 8000 calendar years cal yr b p after the early holocene retreat of the ross ice sheet two subsequent periods of abandonment at 5000 4000 and 2000 1100 cal yr b p correlate with cooling episodes that caused unfavorable marine conditions for breeding penguins most modern colonies were established only within the past 2000 yr

a new holocene relative sea level curve for terra nova bay victoria land antarctica more than 100 radiocarbon dates of penguin guano and remains shells and seal skin afford ages for raised beaches adjacent to terra nova bay antarctica these dates permit construction of a new relative sea level curve that bears on the timing of deglaciation recession of the ross sea ice sheet grounding line from terra nova bay occurred no earlier than 7200 14c yr 8000 cal yr bp retreat along the victoria land coast may have been rapid possibly contributing to eustatic sea level rise centred at ca 7600 cal yr bp the presence of a significant amount of ice remaining in the ross sea embayment in holocene time lessens the chance that antarctica contributed significantly to meltwater pulse 1a several thousand years earlier copyright 2004 john wiley sons ltd

comparison of seismic waveform inversion results for the rupture history of a finite fault application to the 1986 north palm springs california earthquake the july 8 1986 north palm springs earthquake is used as a basis for comparison of several different approaches to the solution for the rupture history of a finite fault the inversion of different waveform data is considered both teleseismic p waveforms and local strong ground motion records linear parametrizations for slip amplitude are compared with nonlinear parametrizations for both slip amplitude and rupture time inversions using both synthetic and empirical green s functions are considered in general accurate green s functions are more readily calculable for the teleseismic problem where simple ray theory and flat layered velocity structures are usually sufficient however uncertainties in the variation in t with frequency most limit the resolution of teleseismic inversions a set of empirical green s functions that are well recorded at teleseismic distances could avoid the uncertainties in attenuation in the inversion of strong motion data the accurate calculation of propagation path effects other than attenuation effects is the limiting factor in the resolution of source parameters the assumption of a laterally homogeneous velocity structure is usually not a good one and the use of empirical green s functions is desirable considering the parametrization of the problem any degree of fault rupture complexity can be described in terms of a linear parametrization for slip amplitudes however a nonlinear parametrization for rupture times and slip amplitudes can have a distinct advantage over a simple linear one by limiting the number of unknown parameters regardless of the choice of data or the type of parametrization the model or solution will be affected by the choice of minimization norm and the type of stabilization used

modeling the evolution of natural cliffs subject to weathering 2 discrete element approach the evolution of slopes subjected to weathering has been modeled by assuming mohr coulomb behavior and by using a numerical approach based on the discrete element method dem according to this method soil and or rock are represented by an assembly of bonded particles particle bonds are subject to progressive weakening and so the material weathering and removal processes are modeled slope instability and material movement follow the decrease of material strength in space and time with the only assumption concerning the weathering distribution within the slope first the case of cliffs subject to strong erosion weathering limited conditions and uniform weathering was studied to compare the results of the dem approach with the limit analysis approach second transport limited slopes subject to nonuniform slope weathering were studied results have been compared with experimental data and other geomorphologic models from the literature fisher lehmann and bakker le heux the flux of material from the slope is modeled assuming degradation both in space and time

stiffness evolution in frozen sands subjected to stress changes abstractsampling affects all soils including frozen soils and hydrate bearing sediments the authors monitor the stiffness evolution of frozen sands subjected to various temperature and stress con

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

observed source parameters for dynamic rupture with non uniform initial stress and relatively high fracture energy we have conducted dynamic rupture propagation experiments to establish the relations between insource stress drop fracture energy and the resulting particle velocity during slip of an unconfined 2 m long laboratory fault at normal stresses between 4 and 8 mpa to produce high fracture energy in the source we use a rough fault that has a large slip weakening distance an artifact of the high fracture energy is that the nucleation zone is large such that precursory slip reduces fault strength over a large fraction of the total fault length prior to dynamic rupture making the initial stress non uniform shear stress particle velocity fault slip and acceleration were recorded coseismically at multiple locations along strike and at small fault normal distances stress drop increases weakly with normal stress average slip rate depends linearly on the fault strength loss and on static stress drop both with a nonzero intercept a minimum fracture energy of 1 8 j m 2 and a linear slip weakening distance of 33 mm are inferred from the intercept the large slip weakening distance also affects the average slip rate which is reduced by in source energy dissipation from on fault fracture energy because of the low normal stress and small per event slip w86 mm no thermal weakening such as melting or pore fluid pressurization occurs in these experiments despite the relatively high fracture energy and the very low heat production energy partitioning during these laboratory earthquakes is very similar to typical earthquake source properties the product of fracture energy and fault area is larger than the radiated energy seismic efficiency is low at w2 the ratio of apparent stress to static stress drop is w27 consistent with measured overshoot the fracture efficiency is w33 the static and dynamic stress drops when extrapolated to crustal stresses are 2e7 3 mpa and in the range of typical earthquake stress drops as the relatively high fracture energy reduces the slip velocities in these experiments the extrapolated average particle velocities for crustal stresses are 0 18e0 6 m s that these experiments are consistent with typical earthquake source properties suggests albeit indirectly that thermal weakening mechanisms such as thermal pressurization and melting which lead to near complete stress drops dominate earthquake source properties only for exceptional events unless crustal stresses are low published by elsevier ltd

displaced rocks strong motion and the mechanics of shallow faulting associated with the 1999 hector mine california earthquake the paucity of strong motion stations near the 1999 hector mine earthquake makes it impossible to make instrumental studies of key questions about near fault strong motion patterns associated with this event however observations of displaced rocks allow a qualitative investigation of these problems by observing the slope of the desert surface and the frictional coefficient between these rocks and the desert surface we estimate the minimum horizontal acceleration needed to displace the rocks combining this information with observations of how many rocks were displaced in different areas near the fault we infer the level of shaking given current empirical shaking attenuation relationships the number of rocks that moved is slightly lower than expected this implies that slightly lower than expected shaking occurred during the hector mine earthquake perhaps more importantly stretches of the fault with 4 m of total displacement at the surface displaced few nearby rocks on 15 slopes suggesting that the horizontal accelerations were below 0 2 g within meters of the fault scarp this low level of shaking suggests that the shallow parts of this rupture did not produce strong accelerations finally we did not observe an increased incidence of displaced rocks along the fault zone itself this suggests that despite observations of fault zone trapped waves generated by aftershocks of the hector mine earthquake such waves were not an important factor in controlling peak ground acceleration during the mainshock

discrete element method simulations of analogue reservoir sandstones abstract the discrete element method was used to model the behaviour of two natural sandstones that are commonly used as analogues for oil reservoir sandstones with a relatively large number of parameters needed to define the model and few micro scale data on which to base them a parametric study was first carried out to identify how each parameter affects the overall macroscopic behaviour this study highlighted the importance of the load share between the particle contacts and the bonds the model for the more strongly cemented sandstone was calibrated against the response observed at a single stress level and predictions at other stress levels were then found to be good a second more weakly cemented sandstone was also modelled it was found that while this sandstone had a very much lower cement content by weight only minor modifications were needed to the bond strengths and the proportion of bonded contacts compared to the more strongly bonded material this may be because of the failure to model the natural fabric of the sandstones in general the post peak regime was not modelled well nor was the volumetric response the latter as a result of the failure to achieve the in situ porosities in the model

oxygen isotope variations in phosphate of biogenic apatites iv mammal teeth and bones groups of rats grown from birth to death in identical conditions but with different 18o of drinking water w were studied for variations of 18o of their body water bw and bone phosphate p there is a high linear correlation r 0 99 between bw and between p and w the regression lines have similar slope coefficients 0 53 and 0 49 values of p of different teeth and bones are the same within the precision of the method 0 5 the isotopic fractionation coefficient between phosphate and body water is 1 0178 and close to the estimated value of 1 0173 derived from the phosphate paleotemperature equation deviations from constant fractionation between bone phosphate and environmental drinking water depend primarily on rates of drinking and metabolism environment conditions have relatively little effect on oxygen isotope fractionation between water sources and bone phosphate

surface faulting accompanying the borah peak earthquake and segmentation of the lost river fault central idaho on the morning of 28 october 1983 the ms 7 3 borah peak earthquake struck central idaho and formed a y shaped zone of surface faults that is divided into a southern a western and a northern section the total length of the surface faults is 36 4 3 1 km and the maximum net throw is 2 5 to 2 7 m the near surface net slip direction determined from the rakes of striations in colluvium averaged 0 17 m of sinistral slip for 1 00 m of dip slip the 20 8 km long southern section is the main zone of surface faulting and coincides with the thousand springs segment of the lost river fault it has the largest amount of net throw most complex rupture patterns and best evidence of sinistral slip the surface faults include zones of ground breakage as much as 140 m wide en echelon scarps with synthetic and antithetic displacements and individual scarps that are nearly 5 m high the 14 2 km long western section diverges away from the lost river fault near the northern end of the southern section the net throw on this section is generally less than 0 5 m but locally is as much as 1 6 m the new ruptures are poorly developed across the crest and north flank of the willow creek hills they are mostly downhill facing arcuate scars perhaps incipient landslides that may overlie a deeper zone of tectonic movement the northern section at least 7 9 km long is on the warm spring segment of the lost river fault and has a maximum net throw of about 1 m the pattern of surface faulting on this section is simple compared to the other sections a 4 7 km long gap in 1983 surface faults separates the northern and southern sections but contains an older scarp of late pleistocene age geologic seismologic and geodetic data from the earthquake suggest that barriers confined the primary coseismic rupture to the thousand springs segment of the fault the rupture propagated unilaterally to the northwest from a hypocenter near the southeastern end of the segment the southeastern boundary of the segment is marked by an abrupt bend in the range front a 4 km long gap in late quaternary scarps and transverse faults of eocene age that intersect the lost river fault the northwestern boundary of the thousand springs segment is at the junction of the willow creek hills and the lost river fault here the southern and western sections of surface faults diverge and there is a gap in the 1983 scarps during the first few weeks after the main shock the large magnitude and large stress drop aftershocks clustered near this barrier later aftershocks were mainly northwest of the barrier on the warm spring and challis segments and showed that strain adjustments eventually affected the entire northern part of the lost river fault fault scarp morphology and the bedrock geology suggest that the boundary between the thousand springs and warm spring segments has probably ruptured less frequently and had less net slip during much of the late cenozoic than the interior of the adjacent segments the 1983 faulting shows that although segment boundaries can stop or deflect primary ruptures secondary surface faulting can occur on adjacent segments of the main fault a late pleistocene scarp in the 1983 gap suggests that infrequent earthquakes perhaps larger than the 1983 event might break through a segment boundary and thus release strain on two adjacent segments

what the exercise of the spice source inversion validation blindtest 1 did not tell you summary uncertainties of earthquake finite fault inversions based upon strong motion data are investigated using the source inversion validation blindtest 1 exercise of the spice seismic wave propagation and imaging in complex media a european network project motivated by previous counterintuitive results the distribution of slip and the shapes of asymmetric slip rate functions are simultaneously inverted by matching 10 or 33 broad band three component velocity waveforms within the period ranging from 0 02 to 2hz using a finite fault method that carries out the waveform inversion in the wavelet domain the effects of subfault size data noise and the number of stations have been explored our results suggest 1 although there are inevitable discrepancies between the inverted model and the target model because of ignoring the spatial slip variations within individual subfaults the fault slip and rise time distributions can be well constrained even with the data including large gaussian noise 2 it is crucial for source studies to develop new inversion schemes that can properly honour the frequency and time dependent energy distribution of seismic radiation and data noise for instance inversions using the variance reduction function of velocity waveforms as the objective function have low sensitivities to the total seismic moment and peak slip 3 although the relative value of the objective function is guided in the inversion the absolute value of the objective function cannot be used to evaluate the quality of an inverted model 4 because the source inversion is based on surface observations the spatiotemporal resolution of source inversion is affected not only by the data quality but also by the earthquake itself for vertical strike slip faults the along strike resolution is better than that along the downdip direction

linearized inversion for fault rupture behavior application to the 1984 morgan hill california earthquake we present a technique to infer the rupture history of an earthquake from near source records of ground motion unlike most previous studies each point on the fault is assumed to slip only once when the rupture front passes with a spatially variable slip intensity in this parameterization the data are linearly related to slip intensity but nonlinearly related to rupture time we perform a linearized inversion for slip intensity and rupture time by iteratively perturbing an assumed starting model the inverse problem for the model perturbation is solved using a tomographic back projection technique smoothing and inequality constraints are applied to ensure that the resulting solution is stable and feasible asymptotic ray theory is used to calculate theoretical seismograms and partial derivatives with respect to model parameters in test cases with noisy synthetic data sets we found that it is possible to distinguish between rupture models having variable slip amplitude and models having variable rupture velocity provided the station coverage is adequate we apply the technique to recordings of the april 24 1984 morgan hill earthquake the results indicate that slip amplitude on the fault plane was extremely variable and that the rupture front did not propagate uniformly away from the hypocenter in particular rupture was delayed on a 12 km2 section of the fault approximately 14 km to the southeast of the hypocenter the rupture front surrounded the region which subsequently failed with a component of rupture propagation back toward the hypocenter similar behavior has been observed in dynamic rupture models with stress or strength inhomogeneities this segment of the fault ruptured with a large slip amplitude releasing 12 of the total seismic moment from 4 of the total area of the aftershock zone the surface trace of this section of the fault is characterized by a complex left step that could act to increase the normal stress acting across the fault however the distribution of aftershocks suggests that the fault at depth is simpler and that it may bend to the right in either case our rupture model suggests that this segment of the fault represents an asperity which initially resisted rupture but eventually ruptured massively we estimate the shear fracture energy for this earthquake to be 2 106 j m2

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

source parameters and rupture velocity of small m 2 1 reservoir induced earthquakes summary we calculate stress drop and rupture speed for ml 2 1 shallow reservoir induced earthquakes and find them to be similar to those of large natural earthquakes previous studies have suggested that hydrofractures mining and reservoir induced earthquakes have lower average stress drop than natural tectonic earthquakes this difference might result from the different tectonic setting or the shallower hypocentral depths of induced earthquakes alternatively difficulties in correcting for attenuation and site effects in earlier studies may lead to underestimation of stress drop in addition most studies assume the rupture velocity of small reservoir induced earthquakes to be the same as for the large earthquakes we analyse a set of 101 ml 2 1 earthquakes induced by changing water level in the acu reservoir ne brazil the earthquakes are shallow depth 5 km and the region has negligible natural seismicity we use three different approaches to calculate the source parameters of the six largest 1 9 ml 2 1 earthquakes we model the individual spectra to find corner frequency frequency independent q and long period amplitude we use collocated small earthquakes as empirical green s functions to calculate the spectral ratios and determine the relative source time functions estimates of the source duration and corner frequency imply stress drops in the range of 26 179 mpa these are similar to or higher than tectonic earthquakes suggesting that the shallow hypocentral depth and the presence of water do not affect stress drop we observe clear directivity for one of the earthquakes and use the azimuthal variation in pulse width to estimate a rupture velocity of 0 6

adelie penguin dietary remains reveal holocene environmental changes in the western ross sea antarctica carbon and nitrogen stable isotope analyses were performed on modern and holocene adelie penguin guano samples collected from ornithogenic soils along the scott coast southern victoria land antarctica from cape irizar to dunlop island and at cape bird ross island guano samples also were sieved and sorted under stereomicroscope in order to select penguin dietary remains such as fish bones and otoliths carbon and nitrogen stable isotope composition coupled with the taxonomic identification of fish otoliths from scott coast holocene samples indicated a mainly fish based diet for this area with pleuragramma antarcticum as the most eaten prey throughout the investigated period from 390 cal bp to ca 7300 cal bp the isotopic values of ross island samples from modern to 3850 cal bp showed a krill consumption increase in the samples younger than 2000 cal bp with the maximum in modern samples scott coast and ross island holocene samples showed 13c and 15n trends similar to those previously published from terra nova bay northern victoria land whereas modern samples from ross island have similar 15n composition but different 13c values this 13c divergence started at ca 2000 bp and follows the abandonment of the scott coast colonies the 13c trend observed in ross island and terra nova bay samples and the abandonment of the scott coast colonies could suggest the stability and the persistence of the previous oceanographic conditions i e polynya for the terra nova bay area and the establishment of new conditions for water circulation in the southern ross sea since 2000 bp when persistent sea ice sealed the scott coast

relationship between the deformation characteristics and microscopic properties of sandstone explored by the bonded particle model abstract previous research shows that the mechanical properties of sandstone are strongly influenced by porosity and grain area ratio gar this study explores how these microscopic factors affect the elasto plastic deformation of sandstone and adopts a modified bonded particle model to study the deformation behavior of sandstone under biaxial loading compared with the natural sandstone the analysis model can effectively capture the elasto plastic behavior of sandstone including non linear elasticity and the variations of plastic flow furthermore the simulated results of biaxial compressive tests show that the mechanical behavior of sandstone with different porosities and gars possesses the following characteristics the cohesion is significantly influenced by both gar and porosity greater gar and porosity values lead to a lesser cohesion however the influence of gar on the friction angle is insignificant and a lower porosity leads to a higher friction angle for elastic deformation the elastic shear and bulk modulus increase with decreasing porosity and increasing gar for plastic deformation the influence of porosity and gar on the variations of plastic angle under different shear stress ratios seems insignificant on the other hand the plastic strain trajectory increases with increasing porosity but the influence of gar is insignificant

dynamics of penguin population size and food availability at prydz bay east antarctica during the last millennium a solar control abstract the paleoecology of the adelie penguin pygoscelis adeliae is controlled by multiple factors in this study we analyzed two millennial scale ornithogenic sediment cores rnl and rl from the vestfold hills east antarctica using the al normalized phosphorus content of the bulk sediment and carbon nitrogen fractions in penguin remains we reconstructed relative changes in the penguin population size of each sub colony and relative krill abundance in the summer prydz bay polynya both records are correlated to solar irradiance at the centennial scale the penguin population recorded in core rnl decreased from 1120 860 yr bp reached a peak from 860 630 yr bp remained at a low level from 630 320 yr bp and then increased with large fluctuations during the past 400 years these changes are all in phase with the trend of solar irradiance at the decadal scale penguin population minima correspond to solar minima from 490 400 yr bp sporer minimum 290 220 yr bp maunder minimum and from 160 120 yr bp dalton minimum whereas population maxima correspond to solar maxima from 1030 980 yr bp 350 290 yr bp 210 160 yr bp 120 70 yr bp the population recorded in core rl exhibited the same changes as in rnl during the last 480 years the reconstructed krill abundance also corresponds to these trends when data are available this correspondence demonstrates a food chain mechanism that is related to solar activity and light availability at the ocean surface which influence the intensity of photosynthesis and phytoplankton productivity and thus the abundance of krill and apex predators such as penguins our findings highlight the fact that despite the various climatic impacts on penguin populations their effects on the base of the food chain are usually the direct drive

seismic gap hypothesis ten years after the seismic gap hypothesis states that earthquake hazard increases with time since the last large earthquake on certain faults or plate boundaries one of the earliest and clearest applications of the seismic gap theory to earthquake forecasting was by mccann et al 1979 who postulated zones of high medium and low seismic potential around the pacific rim in the 10 years since there have been over 40 large m 7 0 earthquakes enough to test statistically the earlier forecast we also analyze another forecast of long term earthquake risk that by kelleher et al 1973 the hypothesis of increased earthquake potential after a long quiet period can be rejected with a large confidence the data suggest that contrary to these forecasts places of recent earthquake activity have larger than usual seismic hazard whereas the segments of the circum pacific belt with no large earthquakes in recent decades have remained relatively quiet the clustering of earthquake times does not contradict the plate tectonic model which constrains only the long term average slip rate not the regularity of earthquakes

relationships between the average offset and the stress drop for two and three dimensional faults abstract finite element results for c the nondimensional shape factor which relates stress drop to fault offset are presented for rectangular strike slip and two dimensional strike slip and dip slip faults at various depths of burial all faults were oriented vertically except for a two dimensional fault which was dipped at 10 the finite element meshes were constructed to limit the error in c to 1 per cent as demonstrated by comparison with the analytical solution for a circular fault in an infinite region attainment of such accuracy results in large finite element matrix equations which were solved by a fast iterative technique the multi grid method for the rectangular faults significant differences were seen in values of c between the finite element results and some previously reported solutions which were obtained by a different numerical technique

micromechanical modeling of cracking and failure in brittle rocks dynamic micromechanical models are used to analyze crack nucleation and propagation in brittle rock models of rock are created by bonding together thousands of individual particles at points of contact the feasibility of using these bonded particle models to reproduce rock mechanical behavior is explored by comparing model behavior to results from actual laboratory tests on different rock types the behavior of two granite models are examined in detail to study cracking and failure patterns that occur during compressional loading because discontinuum models are being used the rock models are free to crack and break apart under stress such that the micromechanics of cracking can be examined stress waves are allowed to propagate outward from each crack and it is shown that these dynamic waves significantly affect the rock behavior as the peak stress in the modeled rock is approached and many of the bonds are close to breaking a passing wave from a nearby crack is sufficient to break more bonds this causes clusters of cracks to be created and then eventual macroscopic shear failure occurs as these clusters connect to bisect the sample the failure patterns observed in the granite models are similar to those observed in actual laboratory tests

evidence for and implications of self healing pulses of slip in earthquake rupture dislocation time histories of models derived from waveforms of seven earthquakes are discussed in each model dislocation rise times the duration of slip for a given point on the fault are found to be short compared to the overall duration of the earthquake 10 however in many crack like numerical models of dynamic rupture the slip duration at a given point is comparable to the overall duration of the rupture i e slip at a given point continues until information is received that the rupture has stopped propagating alternative explanations for the discrepancy between the short slip durations used to model waveforms and the long slip durations inferred from dynamic crack models are 1 the dislocation models are unable to resolve the relatively slow parts of earthquake slip and have seriously underestimated the dislocations for these earthquakes 2 earthquakes are composed of a sequence of small dimension short duration events that are separated by locked regions barriers 3 rupture occurs in a narrow self healing pulse of slip that travels along the fault surface evidence is discussed that suggests that slip durations are indeed short and that the self healing slip pulse model is the most appropriate explanation a qualitative model is presented that produces self healing slip pulses the key feature of the model is the assumption that friction on the fault surface is inversely related to the local slip velocity the model has the following features high static strength of materials kilobar range low static stress drops in the range of tens of bars and relatively low frictional stress during slip less than several hundreds of bars it is suggested that the reason that the average dislocation scales with fault length is because large amplitude slip pulses are difficult to stop and hence tend to propagate large distances this model may explain why seismicity and ambient stress are low along fault segments that have experienced large earthquakes it also qualitatively explains why the recurrence time for large earthquakes may be irregular

stable isotope analyses of dinosaur eggshells paleoenvironmental implications well preserved clutches of dinosaur sauropod eggshells and skeletal remains have been discovered in the upper cretaceous lameta limestones of the kheda district gujarat india indicating a dinosaur nesting site oxygen isotope analyses of the eggs show that the dinosaurs drank from a variety of freshwater bodies such as rivers and small evaporative pools whereas the carbon isotope values indicate that the reptiles were consuming plants that utilize the c 3 photosynthetic pathway e g small palms shrubs conifers etc similar analyses of the host limestones suggest that they were deposited in a freshwater environment that provided the niche for large scale breeding and nesting of the dinosaurs

oxygen isotope compositions of phosphate from middle miocene early pliocene marine vertebrates of peru phosphatic remains of marine vertebrates recovered from five fossil sites of the pisco formation ranging from the latest middle earliest late miocene ca 11 13 ma to the early pliocene ca 3 5 ma have been analysed for their oxygen isotope compositions 18op coexisting seals dolphins whales penguins and sharks from each locality have distinct 18op values reflecting ecology and physiology differences ranging from 18 2 to 21 4 for marine mammals from 19 5 to 21 5 for marine birds and from 20 9 to 23 1 for sharks systematic offsets observed between dolphin teeth and bones as well as between dolphin and whale bones indicate that the fractionation equation established by using data from extant cetaceans may not be directly applicable to miocene cetaceans in order to estimate water 18ow values assuming that polar ice caps were not totally developed during this time interval marine palaeotemperatures ranging from 13 0 1 3 c to 17 2 1 3 c were estimated comparison of our results with those obtained in other world s areas suggests that the oxygen isotope ratios of pisco vertebrates reflect the influence of both global and local events such as the setting of the atacama desert the cold humboldt current or the global phases of ice cap growth and decay

critical state soil constitutive model for methane hydrate soil 1 this paper presents a new constitutive model that simulates the mechanical behavior of methane hydrate bearing soil based on the concept of critical state soil mechanics referred to as the methane hydrate critical state mhcs model methane hydrate bearing soil is under certain geological conditions known to exhibit greater stiffness strength and dilatancy which are often observed in dense soils and also in bonded soils such as cemented soil and unsaturated soil those soils tend to show greater resistance to compressive deformation but the tendency disappears when the soil is excessively compressed or the bonds are destroyed due to shearing the proposed model represents these features by introducing five extra model parameters to the conventional critical state model it is found that for an accurate prediction of ground settlement volumetric yielding plays an important role when hydrate soil undergoes a significant change in effective stresses and hydrate saturation which are expected during depressurization for methane gas recovery

short slip duration in dynamic rupture in the presence of heterogeneous fault properties recent studies of strong motion data consistently show that the risetime duration of slip at particular locations on the fault is significantly shorter than the overall rupture duration the physical explanation for this observation and its implications have become central issues in earthquake source studies two classes of mechanisms have been proposed to explain short risetimes one explanation is that velocity weakening frictional behavior on the fault surface causes the fault to self heal this possibility is suggested by rate dependent friction observed in laboratory experiments and by some two dimensional dynamic numerical simulations of earthquake rupture it has recently been demonstrated however that the velocity dependence of friction observed in the laboratory is too weak to cause faults to self heal an alternative explanation for short risetimes is that spatially heterogeneous fault strength e g barriers limit the slip duration in this paper we investigate this second explanation for short risetimes by constructing a three dimensional dynamic rupture model for the 1984 morgan hill california earthquake mw 6 2 using a kinematic model previously obtained from waveform inversion of strong motion data we assume velocity independent friction and a critical stress fracture criterion and derive a dynamic model specified by the spatial distribution of dynamic stress drop and strength excess that reproduces the slip and rupture time of the kinematic model the slip velocity time functions calculated from this dynamic model are then used in a subsequent inversion to fit the strong motion data by alternating between dynamic and kinematic modeling we obtain a dynamic model that provides an acceptable fit to the recorded waveforms in this dynamic model the risetime is short over most of the fault which is attributable entirely to the short scale length slip stress drop heterogeneity required by the strong motion data a self healing mechanism such as strongly velocity dependent friction is not required to explain the short risetimes observed in this earthquake

the rupture mechanism of the coyote lake earthquake of 6 august 1979 inferred from near field data the coyote lake earthquake ml 5 7 occurred within the dense network of seismic instruments of central california and was recorded by numerous accelerograph stations two of these stations located within the fault zone itself provide particularly remarkable records of the rupture process we use these data obtained in the immediate vicinity of the fault and the broadband seismograms recorded at berkeley about 100 km away from the epicenter to infer the velocity of propagation of the rupture the extent of the fractured area the rupture front geometry and other characteristics of the fracture mechanism in order to extract this information from the data we model the earthquake as a propagating dislocation starting at the hypocenter and spreading radially we compute the resulting ground motion at the receiver sites using the discrete wavenumber representation of green s functions bouchon 1981 the results yield a rupture velocity of 2 6 km sec a fault length of about 14 km and a fault slip of 15 to 20 cm they also show that the fault extends to shallower depth than indicated by the aftershocks the most important result is the finding that slip at any given location on the fault takes place in a very short time span and that simple uniform dislocation models give a good description of the rupture process

the 1971 san fernando earthquake a double event evidence is presented which suggest that the 1971 san fernando earthquake may have been a double event that occurred on two separate subparallel thrust faults it is postulated that the initial event took place at depth on the sierra madre fault zone which runs along the base of the san gabriel mountains rupture is postulated to have occurred from a depth of about 15 km to a depth of about 3 km a second event is thought to have initiated about 4 sec later on another steeply dipping thrust fault which is located about 4 km south of the sierra madre fault zone the surface trace of this fault coincides with the san fernando fault zone which was the principal fault associated with surface rupture it is postulated that rupture propagated from a depth of 8 km to the free surface the moments of the first and second events are approximately 0 7 10 26 dyne cm and 1 0 10 26 dyne cm respectively this model is found to explain the combined data sets of strong ground motions teleseismic p and s waveforms and static offsets better than previous models which consist of either a single fault plane or a plane having a dip angle which shallows with decreasing depth nevertheless many features of the observed motions remain unexplained and considerable uncertainty still exists regarding the faulting history of the san fernando earthquake

strain budget of the ecuador colombia subduction zone a stochastic view the 2016 pedernales earthquake m w 7 8 ruptured a portion of the colombia ecuador subduction interface where several large historical earthquakes have been documented since the great 1906 earthquake m 8 6 considering all significant ruptures that occurred in the region it has been suggested that the cumulative moment generated co seismically along this part of the subduction over the last century exceeds the moment deficit accumulated inter seismically since 1906 such an excess challenges simple models with earthquakes resetting the elastic strain accumulated inter seismically in locked asperities these inferences are however associated with large uncertainties that are generally unknown the impact of spatial smoothing constraints on co seismic and inter seismic models also prevents any robust assessment of the strain budget we propose a bayesian kinematic slip model of the 2016 pedernales earthquake using the most comprehensive dataset to date including insar and gps offsets tsunami waveforms and kinematic records from high rate gps and strong motions in addition we use inter seismic geodetic velocities to produce a probabilistic inter seismic coupling model of the subduction interface our stochastic co seismic and inter seismic solutions include the ensemble of all plausible models consistent with our prior information and that fit the observations within uncertainties the analysis of these model ensembles indicates that an excess of co seismic moment during the 1906 2016 period is likely in central ecuador only if we assume that 1942 and 2016 earthquakes are colocated if this assumption is relaxed we show that this conclusion no longer holds given uncertainties in co and inter seismic processes the comparison of 1942 and 2016 teleseismic records reveals large uncertainties in the location of the 1942 event hampering our ability to draw strong conclusions on the unbalanced moment budget in the region our results also show a heterogeneous coupling of the subduction interface that coincides with two slip asperities in our co seismic model for the 2016 pedernales earthquake and with the location of historical ruptures in 1958 1979 and 1998 the spatial variability in coupling and complexity in earthquake history suggest strong heterogeneities in frictional properties of the subduction megathrust

modelling of multiple events using empirical green s functions method application to swarm earthquakes and implications for their rupture propagation summary recent studies of source time functions stfs of small earthquakes have shown that some of the ml 3 events may display complicated waveforms indicating multiple rupturing episodes the stfs of such earthquakes consist of several pulses whose relative positions provide information on the mutual position of the subevents i have used the waveform modelling method to analyse multiple events in order to disclose the geometry of the rupture the p and s waveforms of multiple events mes are modelled as the sum of waveforms of single subevents with different hypocentre coordinates and scalar moments to construct the waveform of each single event composing the me the waveform of a co located small event is used as an empirical green s function egf assuming similar focal mechanisms of the subevents and of the egf the method seeks the coordinates and origin times of the subevents and their relative seismic moments the non linear problem is solved using the genetic algorithms method synthetic tests have shown that the method is capable of locating reliably up to three subevents with an accuracy better than 40 m the method was applied to the records of the 2000 earthquake swarm in nw bohemia vogtland in central europe by the egf deconvolution 54 mes were identified in the magnitude range from 1 2 to 3 3 and 18 of them were successfully modelled as double or triple events with separate rupture positions the separation of subsources reached 100 ms in time and 320 m in space the relative positions of the subevents with respect to the orientation of the fault indicate that most of them occurred on a common fault plane the space time separation of the subevents corresponds to a speed of 3 0 0 9 km s 1 a value typical for rupture propagation of large earthquakes the later subevents occur farther than the nominal rupture radius of the first subevent and their mutual distance scales with magnitude these observations suggest that the analysed mes share a common fault surface and that their subevents represent individual rupture episodes the angular distribution of the position vectors of later subevents indicates that many of them result from slip parallel rupture growth while some of the ruptures propagate upwards

discrete element modeling of indentation tests to investigate mechanisms of co2 related chemomechanical rock alteration during co2 injection into geological formations petrophysical and geomechanical properties of host formations can be altered due to mineral dissolution and precipitation field and laboratory results have shown that sandstone and siltstone can be altered by co2 water mixtures but few quantitative studies have been performed to fully investigate underlying mechanisms based on the hypothesis that co2 water mixtures alter the integrity of rock structure by attacking cements rather than grains we attempt to explain the degradation of cementation due to long term contact with co2 and water and mechanisms for changes in rock mechanical properties many sandstones including calcite cemented quartzitic sandstone chlorite cemented quartzitic sandstone and hematite cemented quartzitic sandstone contain interparticle cements that are more readily affected by co2 water mixtures than grains a model that couples the discrete element method dem and the bonded particle model bpm is used to perform simulations of indentation tests on synthetic rocks with crystal and random packings the model is verified against the analytical cavity expansion model cem and validated against laboratory indentation tests on entrada sandstone with and without co2 alteration sensitivity analysis is performed for cementation microscopic parameters including stiffness size axial and shear strength the simulation results indicate that the co2 related degradation of mechanical properties in bleached entrada sandstone can be attributed to the reduction of cement size rather than cement strength our study indicates that it is possible to describe the co2 related rock alteration through particle scale mechanisms

fiber bundle model for multiscale modeling of hydromechanical triggering of shallow landslides 1 sudden and rapid mass movements associated with landslides and snow avalanches present a hazard to life and infrastructure yet their predictions and triggering mechanisms remain poorly understood statistical methods and correlative studies have been used to produce landslide or avalanche susceptibility maps often with limited physical basis mechanistic approaches based on factor of safety computation seldom represent the progressive transition from local failure events to a landslide and in general do not include heterogeneities associated with land cover or with subsurface material properties and hydrologic pathways focusing on rainfall induced shallow landslides we propose the use of the fiber bundle model fbm a generic yet powerful and adaptable model used in modeling fatigue and fracture of complex and disordered materials the primary strength of the fbm is its ability to represent the progressive failure of cracks and shear zones and the ruptures of highly heterogeneous bonding elements that are present in soils at all scales the model also provides a natural framework for interpretation of acoustic emission signatures from failing slopes which may form the basis of a monitoring and warning system

a particulate scale investigation of cemented sand behavior in this paper triaxial tests and numerical simulations using the discrete element method dem are combined to explore the underlying mechanisms of the unique behavior of artificially cemented sands the experimental results show that strength enhancement volumetric dilation and the shear banding associated failure mode are observed in portland cement sand these features become more pronounced with increasing cement content different responses are found in gypsum cemented sand even though both types of cemented sand specimens were prepared under very similar void ratios before shearing the dem simulations on the portland cement sand were carried out under two particular arrangements i e the use of small cementing particles and flexible membrane boundaries the simulation results reveal that particles in the bonding network jointly share the loading and many micro force chains associated with cementation are created compared with uncemented sand a more stable and stronger force chain complex su

stability and localization of rapid shear in fluid saturated fault gouge 1 linearized stability analysis field observations of major earthquake fault zones show that shear deformation is often confined to principal slipping zones that may be of order 1 100 m wide located within a broader gouge layer of order 10 100 mm wide this paper examines the possibility that the extreme strain localization observed may be due to the coupling of shear heating thermal pressurization and diffusion in the absence of a stabilizing mechanism shear deformation in a continuum analysis will collapse to an infinitesimally thin zone two possible stabilizing mechanisms studied in this paper are rate strengthening friction and dilatancy for rate strengthening friction alone a linear stability analysis shows that uniform shear of a gouge layer is unstable for perturbations exceeding a critical wavelength using this critical wavelength we predict a width for the localized zone as a function of the gouge properties taking representative parameters for fault gouge at typical centroidal depths of crustal seismogenic zones we predict localized zones of order 5 40 m wide roughly consistent with field and experimental observations for dilatancy alone linearized strain rate perturbations with a sufficiently large wavelength will undergo transient exponential growth before decaying back to uniform shear the total perturbation strain accumulated during this transient strain rate localization is shown to be largely controlled by a single dimensionless parameter e which is a measure of the dilatancy of the gouge material due to an increase in strain rate

the general and congruent effects of structure in natural soils and weak rocks the engineering properties of naturally occurring sedimentary and residual deposits which are usually treated in geotechnical engineering as soils are reviewed and it is shown that usually they have characteristics due to bonded structure which are similar to those of porous weak rock while this structure can arise from many causes its effects follow a simple general pattern that involves stiff behaviour followed by yield this yield can be described in a similar way to that occurring due to overconsolidation although it is a separate phenomenon the effects of structure are as important in determining engineering behaviour as are the effects of initial porosity and stress history which are the basic concepts of soil mechanics as it can be described in a general way it is concluded that structure and its effects should be treated as a further basic concept of equal importance l article passe en revue les proprietes des depots sedimentaires et residuels naturels qui sont nor malement traites comm

the near source ground motion of the 6 august 1979 coyote lake california earthquake a finite fault striking n24 w and extending to a depth of 10 km is proposed to explain the strong ground motion data for the 6 august 1979 coyote lake california earthquake m l 5 9 our source model suggests that right lateral faulting initiated at a depth of 8 km and ruptured toward the south with a velocity of 2 8 km sec this unilateral rupture can explain the large displacement recorded south of the epicenter however the waveform coherency across an array south and southwest of the epicenter suggests that the rupture length is less than 6 km the maximum dislocation is about 120 cm in a small area near the hypocenter and the total moment is estimated to be 3 5 10 24 dyne cm an abrupt stopping phase which corresponds to a deceleration of right lateral motion can explain the high peak acceleration recorded at array station 6 the stress drop in the hypocentral area is about 140 bars the average stress drop over the entire rupture surface is 30 bars the preferred finite source model can predict the p n1 waveforms and the beginning features in the teleseismic seismograms no clear arrivals can be observed in the near source data for the possible second and third smaller events suggested by nabelek personal communication

geologic context of geodetic data across a basin and range normal fault crescent valley nevada geodetic strain and late quaternary faulting in the basin and range province is distributed over a region much wider than historic seismicity which is localized near the margins of the province in the relatively aseismic interior both the magnitude and direction of geodetic strain may be inconsistent with the holocene faulting record we document the best example of such a disagreement across the ne striking 55 nw dipping crescent normal fault where a nw oriented 70 km geodetic baseline records contemporary shortening of 2 mm yr orthogonal to the fault trace in contrast our geomorphic paleoseismic and geochronologic analyses of the crescent fault suggest that a large extensional rupture occurred during the late holocene epoch an excavation across the fault at fourmile canyon reveals that the most recent event occurred at 2 8 0 1 ka with net vertical tectonic displacement of 4 6 0 4 m at this location corresponding to the release of 3 m of accumulated nw se extension measured alluvial scarp profiles suggest a minimum rupture length of 30 km along the range front for the event implying a moment magnitude m w of at least 6 6 no prior event occurred between 2 8 ka and 6 4 0 1 ka the 14 c calender age of strata near the base of the exposed section assuming typical slip rates for basin and range faults 0 3 mm yr these results imply that up to one third or 1 m of the extensional strain released in the previous earthquake could have reaccumulated across the fault since 2 8 ka however the contemporary shortening implies that the fault is unloading due to a transient process whose duration is limited to between 6 years geodetic recording time and 2 8 ka the age of the most recent event these results emphasize the importance of providing accurate geologic data on the timescale of the earthquake cycle in order to evaluate geodetic measurements

slip distribution of the 19 september 1985 michoacan mexico earthquake near source and teleseismic constraints we simultaneously invert the strong motion velocity records and the long and intermediate period teleseismic p waveforms of the 19 september 1985 michoacan mexico earthquake to recover the distribution of slip on the fault using a point by point constrained and stabilized least squares inversion method a fault plane with strike fixed at 300 and dip fixed at 14 is placed in the region of the earthquake hypocenter and divided into 120 subfaults rupture is assumed to propagate at a velocity of 2 6 km sec away from the hypocenter synthetic near source ground motions and teleseismic p waveforms for pure strike slip and dipslip dislocations are calculated for each subfault the observed data are then inverted to obtain the amount of strike slip and dip slip displacement required of each subfault we also invert the data sets using a time window procedure where the subfaults are allowed to slip up to three times this approach relaxes the constraint of fixed subfault rupture time imposed by a constant rupture velocity inversion of the strong motion data alone yields a slip model similar to the solution previously obtained using only teleseismic waveforms this result supports the use of teleseismic waveform data for the derivation of fault dislocation models in the absence of strong motion recordings our simultaneous inversion of both data sets suggests that rupture during the michoacan earthquake was controlled largely by the failure of three major asperities located along the length and down the dip of a 150 km segment of the cocos north america plate boundary the solution contains three major source regions including an 80 km by 55 km source near the hypocenter with a peak slip of 6 5 meters two additional sources are present on the southeast portion of the fault about 70 km away from the hypocenter one of these sources with a peak slip of 5 meters covers a 45 km by 60 km area and extends downdip from a depth of about 10 km to 24 km the third source region is somewhat smaller 30 km by 60 km area 3 1 meters peak slip and extends further downdip at depths between 27 km and 39 km aftershock activity following the earthquake was associated mainly with the two shallow sources these two sources are separated by the aftershock zone of the 1981 playa azul earthquake

inversion of strong ground motion and teleseismic waveform data for the fault rupture history of the 1979 imperial valley california earthquake a least squares point by point inversion of strong ground motion and teleseismic body waves is used to infer the fault rupture history of the 1979 imperial valley california earthquake the imperial fault is represented by a plane embedded in a half space where the elastic properties vary with depth the inversion yields both the spatial and temporal variations in dislocation on the fault plane for both right lateral strike slip and normal dip slip components of motion inversions are run for different fault dips and for both constant and variable rupture velocity models effects of different data sets are also investigated inversions are compared which use the strong ground motions alone the teleseismic body waves alone and simultaneously the strong ground motion and teleseismic records the inversions are stabilized by adding both smoothing and positivity constraints the moment is estimated to be 5 0 10 25 dyne cm and the fault dip 90 5 dislocation in the hypocentral region south of the united states mexican border is relatively small and almost dies out near the border dislocation then increases sharply north of the border to a maximum of about 2 m under interstate 8 dipslip motion is minor compared to strike slip motion and is concentrated in the sediments the best fitting constant rupture velocity is 80 per cent of the local shear wave velocity however there is a suggestion that the rupture front accelerated from the hypocenter northward the 1979 imperial valley earthquake can be characterized as a magnitude 5 earthquake at the hypocenter which then grew into or triggered a magnitude 6 earthquake north of the border

microearthquake spectra from the anza california seismic network site response and source scaling abstract we analyzed spectra of local microearthquakes recorded by the anza california seismic network to isolate the effects of site response and to investigate the scaling of source parameters for small earthquakes spectra of microearthquakes m m o 19 dyne cm at anza have shapes characteristic of the receiver sites and are generally independent of the source region thus the site response is a major conditioner of the observed spectral shape to remove the effects of site response from the spectra of a m 3 event and isolate its source spectrum we divided by the spectra of an adjacent aftershock used as an empirical green9s function event the spectral ratios indicate that the apparent corner frequencies of small earthquakes m o 19 dyne cm observed at even the high f max stations on hard rock are much lower than the source corner frequencies the spectral ratios are consistent with stress drop remaining constant with decreasing seismic moment for events with moments as small as 10 18 dyne cm the spectral ratios display remarkable agreement between sites which showed vast differences in their original spectra indicating that the spectral division effectively removed the site response the source spectrum of the m 3 event has a high frequency spectral fall off of about 2 an apparent dependence of high frequency fall off with seismic moment in the original spectra can also be explained by the effects of site response the difference between the p and s wave corner frequencies and high frequency roll offs in the observed spectra for these events is the result of the site response and is not a source property the shapes of the spectra of microearthquakes at anza can largely be explained by attenuation at shallow depth with a frequency independent q for some sites near surface resonances are also apparent in the spectra of microearthquakes it is indicated by t values determined for each site that q p q s for the shallow low q layer further evidence of low near surface q is observed in the anomalous spectra of an unusually shallow earthquake source depth 1 km in the network the spectra from this shallow event are depleted in high frequency energy at most stations relative to those of deeper events this observation can be explained by a low q surficial zone for stations of the network situated on alluvium this low q layer has a maximum thickness of about 3 km and maximum p and s wave q values of 30 to 50

rupture history of the 1984 morgan hill california earthquake from the inversion of strong motion records near source strong motion velocity records and teleseismic short period p waveforms are modeled to obtain the spatial and temporal distribution of slip for the 1984 morgan hill earthquake both forward modeling and constrained least squares inversion techniques are used to interpret the strong motion velocity waveforms in the frequency range of approximately 0 2 to 2 0 hz these data support a nearly unilateral rupture to the southeast with a rupture propagation velocity of nine tenths of the local s wave velocity the majority of the slip occurs over a fault length of 25 km and to a first approximation can be interpreted as two main source regions each with an extent of about 5 km with their centers separated by about 12 km however each of the sources has detailed structure of its own and a simple two point source model is not an accurate representation of the morgan hill earthquake the second source occurs about 4 5 sec after the first and is approximately 3 times larger the maximum dislocation on the fault plane is about 1 m the total moment of the earthquake is estimated to be 2 1 10 25 dyne cm the morgan hill earthquake offers convincing evidence for very inhomogeneous slip and stress distributions on shallow strike slip faults

spontaneous growth and autonomous contraction of a two dimensional earthquake fault abstract we numerically study a model of an earthquake as a spontaneous rupture on a fault we assume that a two dimensional antiplane shear crack initiates at a point in an infinite homogeneous and isotropic elastic medium and subsequently propagates with variable velocity under the influence of nonuniform stress drop on the crack and nonuniform cohesive resistance at the crack edges to begin with we analyze the dynamical rupture process immediately after nucleation we determine the subsequent extension of each edge by solving an ordinary differential equation of the first order as well as the dynamical stress in the regions between each edge and the nearest wave front application of this procedure to both edges of the crack in an alternating manner yields the complete history of extension of the crack we use the critical stress intensity fracture criterion to determine the conditions on propagation and arrest of the crack to verify the accuracy and the stability of our numerical technique we compare it with some special cases in which analytical solutions are available the comparison indicates that the numerical results are in good agreement with the analytical ones obtained previously by knopoff and chatterjee 1982 and chatterjee and knopoff 1983 we apply this technique to the computation of the dynamical extension of the crack for several representative cases among them are 1 1 uniform stress drop but nonuniform cohesion a barrier model 2 2 nonuniform stress drop but uniform cohesion an asperity model and 3 3 nonuniform stress drop and nonuniform cohesion a combination of both the barrier and the asperity models the numerical results indicate that the heterogeneities of both the stress drop and the cohesion are the main factors which control the growth cessation and healing of the crack and that the complexities in the seismic radiation are caused by the complex healing process as well as by the complex rupture propagation in contrast to the asperity model the barrier model is characterized by abrupt changes in the slope of the source time function and the theoretical seismogram the collision of the stress pulses from each pair of barriers is the potential source of the crack fission in the general model the fission process occurs in a complex sequence and the effects of this process have to be taken into account in the interpretation of observations

three dimensional finite difference simulation of fault dynamics rectangular faults with fixed rupture velocity we analyze three dimensional finite difference solutions for a simple shear crack model of faulting to determine the effects of fault length and width on the earthquake slip function the fault model is dynamic with only rupture velocity fault dimensions and dynamic stress drop prescribed the numerical solutions are accurate for frequencies up to 5 hz and are combined with asymptotic results for shear cracks in order to characterize the slip function at higher frequencies near the hypocenter the slip velocity exhibits a square root singularity whose intensity increases with hypocentral distance at distances greater than the fault width w growth of the velocity intensity ceases and the slip function becomes nearly invariant with distance along the fault length closed form expressions are developed for the dependence of static slip s slip rise time tr and slip velocity intensity v on fault geometry along the center line of a long narrow fault at hypocentral distances exceeding w these expressions reduce to s w tr 0 5 w vr and v w 2 vr where is the dynamic stress drop the shear modulus and vr the rupture velocity the numerical results imply that uniform dislocation kinematic earthquake models in which slip is represented by a ramp time function will underpredict high frequency ground motion relative to low frequency ground motion a further implication of the numerical solutions is that the nature of inelastic processes at the advancing edge of a long fault will depend on fault width but will be independent of rupture length

large slip velocity of the surface rupture associated with the 1990 luzon earthquake we found more than fifty people who provided important information on coseismic fault motion of the 1990 luzon the philippines earthquake about thirty of them witnessed coseismic fault motion close to less than 30 m the surface rupture the average slip duration reported was about 1 s and some reported much less than 1 s which is surprisingly short compared with the predicted value of about 10 s for its size e g fault length 120 km slip 5 m according to scaling laws obtained from teleseismic studies teleseismic studies only obtain spatially and temporally averaged values of fault motion but actual coseismic fault slip has a high degree of spatial heterogeneity the large slip velocity over 10 m s obtained by our study suggests a very high local stress drop 100 mpa other important information from the eyewitness accounts is that the slip velocity seems to have been nearly constant implying that the fault slip is well described by a ramp function proposed by haskell