constraining spatiotemporal characteristics of magma migration at piton de la fournaise volcano from pre eruptive seismicity volcano tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis we explore the seismicity that occurred before eruptions at piton de la fournaise in the last 5 years using template matching and relocation techniques we produce a refined image of the summit seismicity demonstrating that most earthquakes are located on a ring structure however only a portion of this structure is activated before each eruption which provides an indication as to the direction of the future eruptive site furthermore we show that the delay between the pre eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone this reveals that the beginning of the intrusion already bears information regarding the future eruption location

strong shaking in los angeles expected from southern san andreas earthquake 1 the southernmost san andreas fault has a high probability of rupturing in a large greater than magnitude 7 5 earthquake sometime during the next few decades new simulations show that the chain of sedimentary basins between san bernardino and downtown los angeles form an effective waveguide that channels love waves along the southern edge of the san bernardino and san gabriel mountains earthquake scenarios with northward rupture in which the guided wave is efficiently excited produce unusually high long period ground motions over much of the greater los angeles region including intense localized amplitude modulations arising from variations in waveguide cross section

uncovering the hidden signature of a magmatic recharge at piton de la fournaise volcano using small earthquakes we apply a template matching method to detect and locate preeruptive earthquakes at piton de la fournaise volcano in 2014 and 2015 this approach enabled the detection of many events and unveiled persistent seismicity features through multiple eruptions shallow earthquakes define a ring shaped structure beneath the main crater the repetitive occurrence of events along this structure suggests that it corresponds to a preexisting zone of weakness within the edifice we also show evidence of deep magma transfer in 2015 more than 5000 deep earthquakes define an upward migration immediately followed by the occurrence of shallow events leading to an eruption 20 days later this suggests the creation of a hydraulic connection between the lower part of the volcanic system and a magma reservoir located near sea level we can envisage than such replenishments of the shallow reservoir occurred in the past but were undetected because of limited deep earthquake detections

shear wave velocity characteristics of geological units throughout tehran city iran abstract one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity vs in the shallow subsurface to classify materials we used the average shear wave velocity to a depth of 30 m v s 30 to develop site categories for tehran this parameter can further be used for modifying a calculated ground motion to account for site conditions the national earthquake hazard reduction program nehrp classification was used to group sites into different classes our classification was based on v s 30 values measured in 188 seismic profiles and on the assumption of similar values for similar geological materials for each geological unit characteristics of shear wave velocity distribution including histograms of shear wave velocity and variation of vs versus depth were calculated and shown this study reveals that the v s 30 of the mountainous zones fall into categories a and b of nehrp site classification but in the tehran plain the northern alluvium tends to have v s 30 values which fall into range of category c of the nehrp site classification whereas those in the southern alluvium would be categorized as nehrp d

dynamic triggering by strong motion p and s waves evidence from the 1999 chi chi taiwan earthquake high frequency band pass filtering of acceleration records from the 1999 chi chi taiwan earthquake m w 7 6 resolves the continuous signal into a series of relatively short duration discrete energy bursts we hypothesize that these bursts originate near the individual stations as small shallow events that have been dynamically triggered by the p and s waves generated by the chi chi mainshock however we cannot rule out the possibility that they originate from some nonseismic source associated with the surface such as buildings or trees bursts are observed only during the seismic signal and not in the pre or postsignal noise the bursts are not likely to be generated by the instruments because groupings of three colocated individual instruments record identical bursts also we show that the bursts are not due to the band pass filtering of instrumentally generated step functions the hypothesis that they are local events is supported by the observation of bursts in the 40 hz frequency band at distances up to 170 km from the epicenter if the bursts originated on the chi chi fault plane as hypothesized by chen et al 2006 based on their analysis of recordings within 20 km from the chelungpu fault then they should not be observable at this distance assuming any reasonable value of crustal attenuation assuming a local origin we estimate an average local event magnitude of m w 0 2 and a source receiver distance of approximately 1 km we extended our analysis to lower stress levels by analyzing records from a smaller m w 5 3 event that was recorded by many of the same instruments used in the chi chi analysis for this event bursts are observed only on the accelerograms from stations relatively close to the mainshock hypocenter analysis of the combined data set from both mainshocks suggests a stress threshold for triggering in the range 0 03 0 05 mpa for s wave triggering and 0 0013 0 0033 mpa for p wave triggering consistent with prior observations of surface wave triggering

landscape form and millennial erosion rates in the san gabriel mountains ca abstract it has been long hypothesized that topography as well as climate and rock strength exert first order controls on erosion rates here we use detrital cosmogenic 10 be from 50 basins ranging in size from 1 to 150 km 2 to measure millennial erosion rates across the san gabriel mountains in southern california where a strong e w gradient in relief compared to weak variation in precipitation and lithology allow us to isolate the relationship between topographic form and erosion rate our erosion rates range from 35 to 1100 m ma and generally agree with both decadal sediment fluxes and long term exhumation rates inferred from low temperature thermochronometry catchment mean hillslope angle increases with erosion rate until 300 m ma at which point slopes become invariant with erosion rate although this sort of relation has been offered as support for non linear models of soil transport we use 1 d analytical hillslope profiles derived from existing soil transport laws to show that a model with soil flux linear in slope but including a slope stability threshold is indistinguishable from a non linear law within the scatter of our data catchment mean normalized channel steepness index increases monotonically though non linearly with erosion rate throughout the san gabriel mountains even where catchment mean hillslope angles have reached a threshold this non linearity can be mostly accounted for by a stochastic threshold incision model though additional factors likely contribute to the observed relationship between channel steepness and erosion rate these findings substantiate the claim that the normalized channel steepness index is an important topographic metric in active ranges

structural and sedimentological development of footwall growth synclines along an intraforeland uplift east central bighorn mountains wyoming structural sedimentological and provenance data from paleogene synorogenic deposits of the east central flank of the bighorn mountains provide new information about the development of footwall growth synclines the evolution of fault related folds and the erosional unroofing history of intraforeland uplifts three conglomerate units the upper conglomerate member of the fort union formation and the kingsbury and moncrief members of the wasatch formation are incorporated within an asymmetric east verging growth syncline in the footwall of the main range bounding thrust system three stages of footwall deformation are recorded within these conglomerates analysis of mapped progressive unconformities retrodeformed balanced cross sections and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines development of an anticline syncline pair marked the earliest stage of growth syncline formation stage i rotation of the shared fold limb resulted in amplification of the growth syncline fine grained synorogenic sediment derived from easily eroded mesozoic mudstone bypassed the growth syncline during this stage by the end of lebo shale deposition an average of 12 1 of shortening and 6 46 km of uplift had occurred along the range margin continued growth syncline development was marked by the deposition of the kingsbury conglomerate the kingsbury conglomerate was derived from resistant middle and lower paleozoic carbonate strata in the uplifted source terrane intraformational unconformities recording as much as 55 of bed rotation were developed within the kingsbury conglomerate as fold limb rotation occurred coeval with deposition cross sections indicate that during this early stage of fault related folding an average of 16 9 shortening and 8 12 km of uplift occurred along the eastern flank of the bighorn mountains end of stage i the intermediate stage stage ii of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the moncrief conglomerate the lower portion of the moncrief conglomerate was rotated basinward in the developing growth syncline the final stage of deformation stage iii was dominated by the thrust faulting of middle and lower paleozoic strata eastward over steeply dipping mesozoic strata and rotated eocene synorogenic conglomerate during this stage of deformation the moncrief conglomerate was deformed as the initially blind thrusts propagated into the near surface conglomerate deposits truncated the entire footwall syncline and overrode the synorogenic conglomerate package cross sections in areas where this final stage of deformation is well developed indicate that an average of 24 1 shortening and 9 7 km of uplift had occurred along the eastern margin of the bighorn mountains the caliber of synorogenic deposition in the powder river basin was linked directly to the lithologic composition of the bighorn mountains approximately half of the 3 6 km thick source stratigraphic section of the eastern bighorn mountains was eroded prior to accumulation of conglomerate the majority of this eroded material was derived from mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus the first paleogene conglomerates deposited along the east central bighorn mountains therefore do not represent the initiation of laramide uplift but instead represent the exposure of coarse clast forming rock types from the lower half of the hanging wall stratigraphic section i e the mississippian madison limestone and ordovician bighorn dolomite

shakeout d ground motion estimates using an ensemble of large earthquakes on the southern san andreas fault with spontaneous rupture propagation 1 we simulate ground motion in southern california from an ensemble of 7 spontaneous rupture models of large mw7 8 northwest propagating earthquakes on the southern san andreas fault shakeout d compared to long period spectral accelerations from the next generation attenuation nga empirical relations shakeout d predicts similar average rock site values i e within roughly their epistemic uncertainty but significantly larger values in los angeles and ventura basins due to wave guide focusing effects the shakeout d ground motion predictions differ from those of a kinematically parameterized geometrically similar scenario rupture 1 the kinematic rock site predictions depart significantly from the common distance attenuation trend of the nga and shakeout d results and 2 shakeout d predictions of long period spectral acceleration within the basins of the greater los angeles area are lower by factors of 2 3 than the corresponding kinematic predictions we attribute these differences to a less coherent wavefield excited by the complex rupture paths of the shakeout d sources

new perspectives on volcano monitoring in a tropical environment continuous measurements of soil co2 flux at piton de la fournaise la reunion island france detecting renewal of volcanic activity is a challenging task and even more difficult in tropical settings continuous measurements of soil co2 flux were carried out at the piton de la fournaise volcano during 2013 2016 since this site is in the tropics periods of heavy rainfall are in the norm measurements covered volcanic unrest after a hiatus of 3 5 years we find that while temperature has the strongest effect extreme rainfall causes short term noise when corrected and filtered from the environmental influence soil co2 time series permit to detect a major deep magmatic event during march april 2014 three months before the first eruption of the new activity phase correlation with geophysical datasets allow timing of further stages of upward fluid ascent our study validates soil co2 flux monitoring in tropical environments as a valuable tool to monitor magma transfer and to enhance understanding of volcano unrest down to the lithospheric mantle

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

shattered rock and precarious rock evidence for strong asymmetry in ground motions during thrust faulting recent thrust faulting models both physical and numerical have indicated very high ground motions on the hanging wall and relatively low motions on the footwall of thrust faults in this article recent field evidence supporting this strong asymmetry is described earlier field observations of objects thrown in the air also suggest that ground motions must have exceeded 1 g and 100 cm sec new shattered rock evidence on the hanging wall of thrust faults in southern california supports the occurrence of intense ground motions on the other hand the lack of shattered rock and the presence of precariously balanced rocks on the footwall of two thrust faults in southern california indicate relatively low ground motions thus indicating strong asymmetry in ground motions near the fault trace for thrust faults some current ground motion attenuation curves and hazard maps may give too low values on the hanging wall and too high values on the footwall this could be of critical importance to estimating earthquake hazard from potentially large thrust fault earthquakes in the los angeles basin and elsewhere in the world the new evidence also supports the idea that dynamic inertial detachment of the hanging wall from the footwall occurs in nature in the manner suggested by some recent physical and numerical models if such detachment occurs it could also have important implications for understanding thrust fault rupture mechanics for example the paradox of large overthrusts and the heat flow paradox for thrusts

the effects of topography on magma chamber deformation models application to mt etna and radar interferometry we have used a three dimensional elastic finite element model to examine the effects of topography on the surface deformation predicted by models of magma chamber deflation we used the topography of mt etna to control the geometry of our model and compared the finite element results to those predicted by an analytical solution for a pressurized sphere in an elastic half space topography has a significant effect on the predicted surface deformation for both displacement profiles and synthetic interferograms not only are the predicted displacement magnitudes significantly different but also the map view patterns of displacement it is possible to match the predicted displacement magnitudes fairly well by adjusting the elevation of a reference surface however the horizontal pattern of deformation is still significantly different thus inversions based on constant elevation reference surfaces may not properly estimate the horizontal position of a magma chamber we have investigated an approach where the elevation of the reference surface varies for each computation point corresponding to topography for vertical displacements and tilts this method provides a good fit to the finite element results and thus may form the basis for an inversion scheme for radial displacements a constant reference elevation provides a better fit to the numerical results

broadband simulations for mw 7 8 southern san andreas earthquakes ground motion sensitivity to rupture speed using the high performance computing resources of the southern california earthquake center we simulate broadband 0 10 hz ground motions for three m w 7 8 rupture scenarios of the southern san andreas fault the scenarios incorporate a kinematic rupture description with the average rupture speed along the large slip portions of the fault set at 0 96 0 89 and 0 84 times the local shear wave velocity consistent with previous simulations a southern hypocenter efficiently channels energy into the los angeles region along the string of basins south of the san gabriel mountains however we find the basin ground motion levels are quite sensitive to the prescribed rupture speed with peak ground velocities at some sites varying by over a factor of two for variations in average rupture speed of about 15 these results have important implications for estimating seismic hazards in southern california and emphasize the need for improved understanding of earthquake rupture processes

late cretaceous to middle tertiary basin evolution in the central tibetan plateau changing environments in response to tectonic partitioning aridification and regional elevation gain located in the bangong suture zone between the lhasa and qiangtang terranes of central tibet the nima basin records cretaceous late miocene sediment accumulation during a period of drastically changing paleogeography and paleoelevation the bangong suture zone originally formed during late jurassic early cretaceous time as the lhasa terrane collided with the qiang tang terrane during early to middle cretaceous time the region lay at northern near equatorial paleolatitudes near sea level by aptian time the nima basin was above sea level and was strongly influenced by nearby volcanic activity and crustal shortening in the reactivated bangong suture zone in the southern nima basin an 50 m y late cretaceous eocene depositional hiatus correlates with major crustal shortening and ensuing voluminous ignimbrite eruptions in the lhasa terrane in the northern nima basin deposition continued during latest cretaceous time recording arid paleoclimate in evaporitic lacustrine and eolian dunefield deposits by oligocene time the nima basin comprised two independent depocenters that accumulated coarse grained alluvial fluvial lacustrine evaporitic and fan delta deposits in close association with reactivated thrusts in the bangong suture zone carbon and oxygen isotope data from oligocene paleosol carbonate reported elsewhere indicate that regional paleoelevation during the late oligocene was 4 6 km as it is today overall the depositional record of the nima basin combined with ongoing structural and geochronologic studies demonstrates that the bangong suture zone was reactivated during middle cretaceous and middle tertiary time that the intervening 50 m y interval was a time of regional upper crustal shortening in the lhasa terrane followed by regional ignimbrite eruptions and that arid paleoclimate and high paleoelevation were established by the late cretaceous and late oligocene respectively within the context of other data sets from the lhasa terrane the record of deposition in the nima basin is consistent with low angle subduction of neotethyan oceanic lithosphere and reactivation of the bangong suture zone during the early cretaceous followed by shortening within the gangdese retroarc and northern lhasa terrane thrust belts during the late cretaceous lithospheric delamination dripping and regional magmatic flare up during latest cretaceous through early tertiary time and underthrusting of indian lower crust and lithosphere as far north as the bangong suture zone during late oligocene time

basin formation in the high himalaya by arc parallel extension and tectonic damming zhada basin southwestern tibet 1 the late miocene pleistocene zhada basin in southwestern tibet provides a record of subsidence and basin formation within an active collisional thrust belt the 800 m thick basin fill is undeformed and was deposited along an angular unconformity on top of tethyan strata that were previously shortened in the himalayan fold thrust belt modal sandstone petrographic data conglomerate clast count data and detrital zircon u pb age spectra indicate a transition from detritus dominated by a distal northern source to a local southern source this transition was accompanied by a change in paleocurrent directions from uniformly northwestward to basin centric at the same time the depositional environment in the zhada basin changed from a large braided river to a closed basin lake sedimentation in the zhada basin was synchronous with displacement on the qusum and gurla mandhata detachment faults which root beneath the basin and exhume midcrustal rocks along the northwestern and southeastern flanks of the basin respectively these observations indicate that accommodation for zhada basin fill was produced by a combination of tectonic subsidence and damming as midcrustal rocks were evacuated from beneath the zhada basin in response to arc parallel slip on crustal scale detachment faults

a seismologically consistent expression for the total area and volume of earthquake triggered landsliding we present a new seismologically consistent expression for the total area and volume of populations of earthquake triggered landslides this model builds on a set of scaling relationships between key parameters such as landslide spatial density seismic ground acceleration fault length earthquake source depth and seismic moment to assess the model we have assembled and normalized a catalog of landslide inventories for 40 shallow continental earthquakes low landscape steepness causes systematic overprediction of the total area and volume of landslides when this effect is accounted for the model predicts the total landslide volume of 63 of 40 cases to within a factor 2 of the volume estimated from observations r2 0 76 the prediction of total landslide area is also sensitive to the landscape steepness but less so than the total volume and it appears to be sensitive to controls on the landslide size frequency distribution and possibly the shaking duration some outliers are likely associated with exceptionally strong rock mass in the epicentral area while others may be related to seismic source complexities ignored by the model however the close match between prediction and estimate for about two thirds of cases in our database suggests that rock mass strength is similar in many cases and that our simple seismic model is often adequate despite the variety of lithologies and tectonic settings covered this makes our expression suitable for integration into landscape evolution models and application to the anticipation or rapid assessment of secondary hazards associated with earthquakes

trampoline effect in extreme ground motion in earthquake hazard assessment studies the focus is usually on horizontal ground motion however records from the 14 june 2008 iwate miyagi earthquake in japan a crustal event with a moment magnitude of 6 9 revealed an unprecedented vertical surface acceleration of nearly four times gravity more than twice its horizontal counterpart the vertical acceleration was distinctly asymmetric the waveform envelope was about 1 6 times as large in the upward direction as in the downward direction which is not explained by existing models of the soil response we present a simple model of a mass bouncing on a trampoline to account for this asymmetry and the large vertical amplitude the finding of a hitherto unknown mode of strong ground motion may prompt major progress in near source shaking assessments

contrasting tectonic and sedimentary history of the central and eastern parts of the polish carpathian foredeep basin results of seismic data interpretation polish carpathian foredeep basin pcfb is located at the junction between western and eastern european platforms such location caused different evolution of various parts of this basin in the central part of the pcfb growth fault propagation folds related to latest badenian stages of thrusting in this segment of the carpathians developed only minor normal faulting related to miocene reactivation of older basement faults was detected paleovalleys mapped within the mesozoic basement were interpreted as palaeogene tectonically controlled erosional features developed after inversion of the polish trough in the central pcfb post evaporitic sediments were supplied into the foredeep basin from south from the eroded carpathians in the eastern part of the pcfb a system of large normal faults related to miocene flexure induced reactivation of inherited mesozoic faults was identified within the hangingwall of this system reverse faults rotated blocks and basement pop up structures were described their formation was related to combined effect of compressional stresses transferred from the carpathian collision zone and reactivation of older large scale fault caused by both flexural extension and strike slip movements during deposition of the miocene foredeep sediments differential compaction also played an important role gentle onlap of the middle badenian evaporites by post evaporitic sediments towards the nw was interpreted as a result of tectonically driven relative sea level rise and re establishment of marine connections with eastern paratethys

thrust generated fan delta deposition little muddy creek conglomerate sw wyoming abstract the upper cretaceous little muddy creek conglomerate in southwestern wyoming is an often cited example of a thin skinned thrust derived conglomerate that has been used to date absolute and relative timing of thrust sheet motion in the idaho wyoming utah fold and thrust belt despite the regional tectonic significance of the little muddy creek conglomerate no quantitative sedimentological or compositional analyses are available in the literature sedimentological analysis indicates that the little muddy creek conglomerate was produced by forelandward eastward progradation of a marine fan delta that emanated from the thrust ridge above the old absaroka thrust fan delta deposits are overlain by nearshore inner shelf outer shelf and slope deposits which record sedimentation as motion on the old absaroka thrust began to wane a two dimensional provenance modeling technique described herein compares hypothetical synorogenic sediment compositions with actual compositional data from the little muddy creek conglomerate the two dimensional modeling is a refinement of previous one dimensional models in that it is based upon the reconstruction of syn thrusting hanging wall and footwall geometries the provenance mod ling shows that compositional data from the little muddy creek conglomerate record uplift followed by gradual cessation thereof on the old absaroka thrust sedimentological and compositional interpretations are integrated allowing for an evaluation of the tectonic controls on deposition of this thin skinned thrust derived conglomerate

a site conditions map for california based on geology and shear wave velocity one simple way of accounting for site conditions in calculating seismic hazards is to use the shear wave velocity in the shallow subsurface to classify materials the average shear wave velocity to 30 m v 30s has been used to develop site categories that can be used for modifying a calculated ground motion to account for site conditions we have prepared a site category map of california by first classifying the geologic units shown on 1 250 000 scale geologic maps our classification of geologic units is based on v 30s measured in 556 profiles and geological similarities between units for which we have v s data and the vast majority of units for which we have no data we then digitized the geologic boundaries from those maps that separated units with different site classifications v s data for california shows that several widespread geologic units have ranges of v 30s values that cross the boundaries between nehrp ubc site categories the franciscan complex has v 30s values across ubc categories b and c with a mean value near the boundary between those two categories older alluvium and late tertiary bedrock have v 30s values that range from about 300 to about 450 m sec across the boundary between categories c and d to accommodate these units we have created intermediate categories which we informally call bc and cd geologic units that have or are interpreted to have v 30s values near the boundary of the ubc categories are placed in these intermediate units in testing our map against the available v 30s measurements we have found that 74 of the measured v 30s values fall within the range assigned to the v s category where they fall on the map this ratio is quite good considering the inherent problems in plotting site specific data on a regional map and the variability of physical properties in geologic units we have also calculated the mean and distribution of v 30s for each of our map units and prepared composite profiles showing the variation of v s in the upper 100 m from the available v s data these data show that the map categories that we have defined based on geologic units have different v s properties that can be taken into account in calculating seismic hazards

microcracking during triaxial deformation of porous rocks monitored by changes in rock physical properties ii pore volumometry and acoustic emission measurements on water saturated rocks abstract we report results from a series of laboratory triaxial deformation experiments performed on samples of darley dale sandstone at servo controlled constant strain rate and constant pore fluid pressure during deformation the volume of water either expelled from the samples during compaction or injected into the samples during dilatancy in order to maintain a constant pore fluid pressure was continuously monitored throughout each experiment in addition the parameters of differential axial stress axial strain and acoustic emission ae characteristics were also recorded complete ae waveforms were also captured and stored by means of a transient recorder and fourier analysis of these waveforms was subsequently carried out the reported experiments were all performed in a conventional high pressure gas medium triaxial cell but with the pore fluid pressure maintained constant using a new servo controlled fluid pressure intensifier and pore volumometer the ae and pore volumometry measurements on water saturated rocks reported in this paper are complementary to the measurements of elastic wave propagation parameters made on dry rocks and reported in a companion paper in this issue the two suites of data have been integrated to infer relations between crack density parameters calculated from elastic wave velocity measurements and the directly measured pore volume during deformation our results show a distinct positive correlation between changes in the axial crack density parameter x and changes in the pore volume during deformation once fluid expulsion due to elastic pore collapse has been corrected for these two parameters have then been combined to obtain an estimate of changes in the mean aspect ratio of propagating dilatant cracks the results suggest that under moderate confining pressures axially aligned dilatant cracks are likely to bow open elastically prior to significant crack extension and growth

chemical and physical characteristics of pulverized tejon lookout granite adjacent to the san andreas and garlock faults implications for earthquake physics we present new detailed analyses of samples of pulverized tejon lookout granite collected from sections adjacent to the san andreas and garlock faults in southern california the tejon lookout granite is pulverized in all exposures within about 100 m from both faults chemical analyses indicate no or little weathering in the collected samples although xrd analysis shows the presence of smectite illite and minor kaolinite in the clay size fraction weathering products may dominate in the less than 1 micron fraction the average grain size in all samples of pulverized tejon lookout granite ranges between 26 and 208 microns silt to fine sand with the particle size distribution in part a function of proximity to the primary slip zone the san andreas fault samples that we studied are generally finer grained than those collected from adjacent to the garlock fault the particle size distribution for each studied sample from both faults follows a pseudo power law with a continuously changing exponent which suggests that pulverization is not simply a consequence of direct shear the average particle size that we determined for our samples is considerably coarser than reported in previous investigations which we attribute to possible measurement errors in the prior work our data and observations suggest that dynamic fracturing in the wall rock of the san andreas and garlock faults only accounts for about 1 or less of the earthquake energy budget

microcracking during triaxial deformation of porous rocks monitored by changes in rock physical properties i elastic wave propagation measurements on dry rocks we present results from two series of triaxial deformation experiments performed on dry samples of two sandstones darley dale and gosford carried out at confining pressures from 25 mpa to 200 mpa over this pressure range the mode of failure in both these sandstones passes from localized brittle failure with a clear through going fault to distributed cataclastic flow during these experiments stress strain compressional wave velocity vp and shear wave velocity vs measurements were made simultaneously in the direction of the maximum principal compressive loading axis initial application of the hydrostatic confining pressure causes both vp and vs to increase and upon raising the axial stress above the confining pressure both velocities increase further at first generally by only a few percent but then decrease as dilatant crack growth commences during dilatancy vs decreases proportionately more than vp and this decrease is generally of the order of 10 15 these velocity measurements allow changes in rock physical properties to be calculated along with the axial and transverse crack volume density parameters x and z the results from two selected tests are analysed in detail these tests were chosen because they exhibit a typical brittle shear failure and b typical ductile cataclastic flow respectively the full interrogating elastic waveforms were also recorded during testing and these have been used to calculate the seismic quality factors qp and qs to our knowledge this is the first time this has been reported for rock samples undergoing triaxial deformation the changes in q values generally exhibit similar trends to those observed in the velocity measurements but the percentage changes in q are an order of magnitude greater suggesting that this parameter is a more sensitive measure of dilatant crack damage the measurements on dry rock samples reported here provide the basis for comparison with measurments of changes in complementary physical properties made on water saturated rock samples under the same experimental conditions and reported in a companion paper in this issue read et al 1995

a physical model for widespread near surface and fault zone damage induced by earthquakes 1 i present a rigorous unifying interpretation of the well documented widespread near surface and fault zone damage induced by earthquakes by simulating three dimensional dynamic rupture propagation on a vertical strike slip fault stresses in the crust are depth dependent and material response is governed by the drucker prager yielding criterion i show that material yielding induced by seismic waves under the low confining pressure causes widespread near surface damage because the confining pressure increases with depth the yielding zone at depth is narrowly confined near the fault but its thickness broadens dramatically near the surface forming a flower like damage zone the fault zone damage at depth is induced by large dynamic stresses associated with the rupture front while is induced by strong seismic waves ahead of the rupture front near the earth s surface these results have important implications for the formation and evolution of fault zones and possibly for the dynamic triggering of earthquakes as well

magma transport and storage at piton de la fournaise la reunion between 1972 and 2007 a review of geophysical and geochemical data abstract since the middle of the 20th century improvement in volcano monitoring techniques has provided large data sets that can be used to evaluate the evolution of magma plumbing systems at piton de la fournaise volcano abundant eruptive activity and a dense monitoring network are especially conducive to such research analysis of the extensive set of geophysical and geochemical data associated with the last 35 years of activity provides new insights into magma transport and storage at piton de la fournaise two periods of frequent eruptions separated by 6 years of inactivity can be distinguished 1972 1992 and 1998 2007 considering these two periods we show evidence of major changes in the shallow plumbing system in 2000 during 1972 1992 and 1998 2000 lava compositions and weak long term eruptive precursors lasting few days to three weeks characterized by no significant summit inflation and about ten volcano tectonic earthquakes per day suggest that eruptions were fed by the progressive drainage of an occasionally recharged shallow magma reservoir geophysical evidence of shallow magma reservoir recharge was only recorded in 1986 and 1998 in contrast from 2000 to 2007 geophysical data highlight the appearance of long term precursors 1 to 5 months of summit inflation and strong seismicity up to one hundred events per day preceding cycles of successive eruptions each cycle of eruptions was characterized by a sequence 3 to 10 months in duration of summit and near summit proximal eruptions and ended with a distal low altitude oceanite olivine abundances 20 vol eruption on the eastern flank of the volcano within each of these eruptive cycles lavas became progressively more magnesian over time the preferential motion of the eastern flank caused by continuous recharging of the shallow reservoir since 2000 would favour the occurrence of distal eruptions towards this flank at the end of a cycle

production of brief extreme ground acceleration pulses by nonlinear mechanisms in the shallow subsurface 1 a brief pulse of extreme acceleration 20 m s 2 was recorded at station fz16 during the 2004 mw 6 0 parkfield california earthquake the sustained acceleration at the dominant frequency is a factor of 2 below the maximum here we show that the pulses of extreme acceleration might originate in the shallow subsurface rather than on the main fault plane two nonlinear mechanisms can feasibly convert low frequency energy of the incident wave into high frequency pulses with extreme acceleration 1 dynamic stress carried by strong seismic waves causes small shallow cracks to slip in secondary earthquakes 2 the elasticity of the shallow subsurface is nonlinear the relationship between dynamic shear stress and strain is linear at small strains at the large strains associated with strong ground motion shear deformation locks compliant cracks by bringing their asperities into contact the locking increases the instantaneous shear modulus of the cracked rock computations indicate that both mechanisms produce high accelerations in the later part of the strong ground motion these testable hypotheses imply that brief pulses of extreme acceleration are likely not a property of the main fault and hence not harbingers of prolonged pulses of extreme acceleration

microscopic elasticity and rate and state friction evolution laws 1 rate and state friction formalism represents the dependence of macroscopic shear traction m on sliding velocity v and the history of the sliding surface in macroscopic terms m pn 0 a ln v vref b ln norm where pn is normal traction 0 is the coefficient of friction a b 0 01 are small dimensionless parameters vref is a reference velocity is the state variable that depends on history and norm represents the effect of changes in normal traction this representation does not consider microscopic elasticity and is inadequate over very small times the apparent value of a just after a small decrease in shear traction is a factor of a few larger than its traditional value of 0 01 changes of microscopic elastic strain energy may cause this effect microscopic elasticity affects friction after changes in normal traction shear traction does not change instantly after a sudden change in normal traction because time is required for real contact area to change a hybrid of the aging law where increases linearly with time during holds and the slip law behavior where the state variable does not change in the limit of zero sliding velocity is necessary slip law behavior dominates near steady state and also applies to sudden initial sliding where the state variable and porosity are far from steady state porosity increases from its initial value toward the steady state value over slip scaling with the critical displacementdc the ratio of dilatant to shear strain in low porosity material is a modest fraction of 1 and related to the construct of dilatancy angle in engineering

application of high resolution dem data to detect rock damage from geomorphic signals along the central san jacinto fault abstract we analyze geomorphic properties extracted from lidar and srtm shuttle radar topography mission data to test whether the damage zone along the central san jacinto fault sjf zone can be resolved with remotely sensed data in a quantitative fashion the sjf is one of the most active faults in southern california with well expressed geomorphology and a fast slip rate as seen in the geology and by gps we use arcmap and the taudem toolbox to compare several morphometric parameters including drainage density dd on both sides of the fault using a 1 km and a 5 km buffer for the lidar and srtm data respectively we also analyze the spatial patterns of dd near the fault using two different definitions of spatial dd the high resolution of the lidar data allows us to focus on a single fault eliminating the effects of parallel nearby faults from the lidar data we find that the highest dd values occur in areas between two fault strands followed generally by rocks on the northeast side of the fault with the lowest dd values occurring on the southwest side of the fault the srtm data shows a band of high dd values centered on the main fault trace with 1 km width our results indicate that there is a strong correlation between drainage density and proximity to the fault with zones of structural complexity along the fault displaying the highest dd we interpret this to largely be an effect of degree of rock damage as these are areas that are expected to be more damaged and field observations support this contention if we are correct then it appears that the northeast side of the sjf is generally more damaged south of the trifurcation area there is evidence that the signal is reversed on the larger scale with more damage on the southwest side of the fault inferred from the srtm data possibly caused by extension between the coyote creek and clark faults the implications of the observed asymmetry could be geological evidence for rupture propagation direction because a preferred propagation direction is predicted to produce asymmetric damage structure that would be recorded in the volume of rock surrounding a fault

depth of rock damage from strong seismic ground motions near the 2004 parkfield mainshock changes in the s p delay of repeating earthquakes near parkfield california after strong shaking in the 2004 mainshock occur at surface stations but not at borehole stations this result indicates that rock damage occurs mainly in the upper few tens of meters in fractured rock with a low seismic velocity in addition changes in coda primary delay are comparable to changes in s p delay this observation along with the lack of s p delay changes at borehole stations yields a simple model for the coda direct waves pass through the shallow damaged layer once coda waves scatter or refract in the deep undamaged subsurface and hence also pass through the subsurface just once the coda however contains some brief reverberations within the shallow subsurface where the additional path length scales to the thickness of the shallow layer the coda primary delay measured by correlation includes both the zero delay change of direct coda and the increased delay of reverberating coda published changes in rayleigh wave group velocity before and after the parkfield mainshock are compatible with their main cause being from the shallow velocity changes inferred from repeating earthquakes but have little spatial resolution stacking of earthquake seismograms resolved surface reflections at one shallow 63 m deep borehole station ghib a change in p wave travel time body of 8 msec was marginally resolved and is compatible with the repeating earthquake s p delay changes autocorrelation passive seismology resolved 32 msec p wave reverberation delay change above the 251 m deep borehole station ccrb

geological and geomorphologic asymmetry across the rupture zones of the 1943 and 1944 earthquakes on the north anatolian fault possible signals for preferred earthquake propagation direction summary the east and west rupture directions of the 1943 and 1944 earthquakes on the north anatolian fault naf are hypothesized to represent respectively long term preferred propagation directions on the corresponding sections of the naf fault sections with preferred rupture direction are expected to have an asymmetric damage structure with respect to the slipping zone to test the above hypothesis we study geological and geomorphologic manifestations of structural asymmetry with respect to the active trace of the naf along the 1943 and 1944 sections the following fault zone elements are mapped gouge fabric in the cm scale fault core structure in a metre scale and secondary faults and fault rocks in tens of metres scale mapping results at three sites on the 1943 rupture and one site on the 1944 rupture are consistent with accumulation of more rock damage on the south side of the 1943 section and on the north side of the 1944 section erosion patterns adjacent to the fault that are not correlated with the distribution of intrinsic and extrinsic erosion controlling variables e g rock type are interpreted as morphologic responses to the damage content of rocks and its impact on rock erodibility the valleys of 11 rivers are parallel to the studied fault sections about 75 per cent of the total river valleys length along the 1943 rupture is on the south side of the fault and about 89 per cent of the total river valleys length along the 1944 rupture is on the north side of the fault morphometric analysis of watersheds in two correlative terrains displaced along the 1944 rupture section shows that stream erosion is considerably more intense in the terrain north of the fault with drainage density values almost double in the north compare to the south badland topography at two sites along the 1943 rupture section is substantially more developed at the 100 m scale on the south side of fault our observations along the 1943 1944 rupture sections including various types of signals that span a large range of scales are systematically compatible with an opposite sense of damage asymmetry between the two fault sections these observations are consistent with opposite preferred direction of ruptures for the two sections similar to the propagation directions of the two recent earthquakes if those rupture directions are dictated by the velocity structure at depth we infer that the south side of the 1943 rupture has faster seismic velocity at seismogenic depth than the north side and that the sense of velocity contrast is reversed along the 1944 rupture zone

deep fluid transfer evidenced by surface deformation during the 2014 2015 unrest at piton de la fournaise volcano abstract identifying the onset of volcano unrest and providing an unequivocal identification of volcano reawakening remain challenging problems in volcanology at piton de la fournaise renewal of eruptive activity in 2014 2015 after 41 months of quiescence and deflation was associated with long term continuous edifice inflation measured by gnss inflation started on june 9 2014 and its rate progressively increased through 2015 inflation onset was rapidly followed by an eruption on june 20 21 2014 showing that volcano reactivation can be extremely fast even after long non eruptive phases this short lived eruption involved a shallow source 1 3 1 9 km depth below the summit the inflation that followed and eruptions in 2015 involved a larger depth range of fluid accumulation constrained by inverse modeling at ca 3 9 to 1 2 1 7 km depth this time evolution reveals that volcano reawakening was associated with continuous pressurization of the shallowest parts of its plumbing system triggered by progressive upwards transfer of magma from greater depth a deep magma pulse occurred in mid april 2015 and was associated with deep seismicity 3 to 9 5 km depth and co 2 enrichment in fluids emitted by summit fumaroles from this date ground deformation accelerated and the output rates of eruptions increased culminating in the long lasting large volume august october eruption 36 mm 3 this evolution suggests that deep magma fluid transfer through an open conduit system first provoked the expulsion of the top of the plumbing system in june 2014 and then induced the progressive vertical transfer of the entire plumbing system down to 9 km four eruptions in 2015 the new sustained feeding of the volcano was also at the origin of the hydrothermal system perturbation and the acceleration of the eastern flank motion which favor lateral dike propagation and the occurrence of frequent and increasingly large eruptions our results highlight the fast and progressive way in which basaltic magmatic systems can wake up

interferometric multichannel analysis of surface waves imasw abstract refraction microtremor remi and multichannel analysis of surface waves masw are effective approaches to estimate shallow shear wave velocity v s structure often needed to estimate ground motions using recent ground motion prediction relations interferometric masw imasw uses slowness frequency slant stack analyses combined with interferometric time domain dispersion analyses to improve resolution of lower frequency rayleigh wave dispersion to better constrain v s cross correlation interferometry is used to obtain deterministic correlation green s function cgf imasw seismograms from ambient noise and or active source wave fields contained in remi and or masw data the cgfs are processed using the multiple filter technique to estimate phase and group dispersion in the imasw approach active seismic sources ensure that the stationary phase contributions to cross correlations dominate cgf responses in a single imasw profile each geophone represents a virtual source and the imasw approach stacks cgf common offset data from all virtual sources to obtain a single averaged forward and reverse record section cgf time domain and slowness frequency phase slowness estimates are combined with cgf time domain group slowness estimates for a consistency check on dispersion picks a multistate monte carlo approach is used to estimate mean slowness depth and slowness uncertainties imasw is evaluated with passive remi data from two sites and active source imasw at six sites with independent downhole velocity depth logs comparison of six p s suspension log imasw profile pairs across the van norman complex in northern san fernando valley shows that on average 30 m depth shear wave velocity estimates between the two methods differed by p s suspension log measurements of v s were made at the imasw profile midpoint the imasw v s depth inversions resolve 3 m thickness v s variations accurately to the bottom of one borehole at 40 m depth and to 100 m depth at a 200 m deep borehole site

nonlinear attenuation of s waves and love waves within ambient rock we obtain scaling relationships for nonlinear attenuation of s waves and love waves within sedimentary basins to assist numerical modeling these relationships constrain the past peak ground velocity pgv of strong 3 4 s love waves from san andreas events within greater los angeles as well as the maximum pgv of future waves that can propagate without strong nonlinear attenuation during each event the shaking episode cracks the stiff shallow rock over multiple events this repeated damage in the upper few hundred meters leads to self organization of the shear modulus dynamic strain is pgv divided by phase velocity and dynamic stress is strain times the shear modulus the frictional yield stress is proportional to depth times the effective coefficient of friction at the eventual quasi steady self organized state the shear modulus increases linearly with depth allowing inference of past typical pgv where rock over the damaged depth range barely reaches frictional failure still greater future pgv would cause frictional failure throughout the damaged zone nonlinearly attenuating the wave assuming self organization has taken place estimated maximum past pgv within greater los angeles basins is 0 4 2 6 m s 1 the upper part of this range includes regions of accumulating sediments with low s wave velocity that may have not yet compacted rather than having been damaged by strong shaking published numerical models indicate that strong love waves from the san andreas fault pass through whittier narrows within this corridor deep drawdown of the water table from its currently shallow and preindustrial levels would nearly double pgv of love waves reaching downtown los angeles

strong motion from surface waves in deep sedimentary basins it is widely recognized that long period surface waves generated by conversion of body waves at the boundaries of deep sedimentary basins make an important contribution to strong ground motion the factors controlling the amplitude of such motion however are not widely understood a study of pseudovelocity response spectra of strong motion records from the los angeles basin shows that late arriving surface waves with group velocities of about 1 km sec dominate the ground motion for periods of 3 sec and longer the rate of amplitude decay for these waves is less than for the body waves and depends significantly on period with smaller decay for longer periods the amplitude can be modeled by the equation batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document mathrm log y f mathbf m r mathrm e c br mathrm b end document where y is the pseudovelocity response f m r e is an attenuation relation based on a general strong motion data set m is moment magnitude r e is the distance from the source to the edge of the basin r b is the distance from the edge of the basin to the recording site and b and c are parameters fit to the data the equation gives values larger by as much as a factor of 3 than given by the attenuation relationships based on general strong motion data sets for the same source site distance it is clear that surface waves need to be taken into account in the design of long period structures in deep sedimentary basins the ground motion levels specified by the earthquake provisions of current building codes in california at least accommodate the long period ground motions from basin edge generated surface waves for periods of 5 sec and less and earthquakes with moment magnitudes of 7 5 or less located more than 20 km outside the basin there may be problems at longer periods and for earthquakes located closer to the basin edge the results of this study suggest that anelastic attenuation may need to be included in attempts to model long period motion in deep sedimentary basins to obtain better data on surface waves in the future operators of strong motion networks should take special care for the faithful recording of the long period components of ground motion it will also be necessary to insure that at least some selected recorders once triggered continue to operate for a time sufficient for the surface waves to traverse the basin with velocities of about 1 km sec that time will be as long as 100 sec for a basin the size of the los angeles basin

investigating the deepest part of a volcano plumbing system evidence for an active magma path below the western flank of piton de la fournaise la reunion island abstract peripheral diffuse degassing of co 2 from the soil occurs across the western flank of piton de la fournaise volcano la reunion island indian ocean along a narrow zone in this area carbon isotopic analysis on soil gas samples highlights significant mixing between magmatic and organic end members the zones with the strongest magmatic signature highest 13 c overlap spatial distribution of hypocenters recorded shortly before and during volcano reactivation and allow discriminating a n135 degassing lineament with a minimum length of 11 km and 140 20 m width such orientation is in accordance with that of an old dyke network along the rift zone and with n120 130 and n140 155 lineaments related to the inheritance of oceanic lithosphere structures our findings show that this n135 lineament represents a preferential magmatic pathway for deep magma transfer below the volcano flank moreover spatial distributions of recent eccentric cones indicate a well founded possibility that future eruptions may by pass the shallow plumbing system of the central area of the volcano taking a lateral pathway along this structure our results also confirm that piton de la fournaise activity is linked to a laterally shifted plumbing system and represent a major improvement in identifying the main high risk area on the densely populated western flank of the volcano

cyclic ground tilt associated with the 2004 2008 eruption of mount st helens 1 the long term behavior of the 2004 2008 effusive eruption of mount st helens was characterized by a gradual decline in the rates of seismicity dome growth and broad scale ground deformation but shallow near periodic drumbeat earthquakes over timescales of minutes indicated episodic short term behavior in part to better characterize this behavior and any associated ground deformation a network of tiltmeters was installed and recorded thousands of cyclic tilt events within the crater the duration of these events from minutes to hours was too long for them to be directly caused by the drumbeat seismicity tilt events were characterized by a recoverable asymmetric pattern of rapid tilt away from the vent followed by a more gradual reversal were highly correlated between different tiltmeters in the crater sometimes occurred in association with volcanic seismicity and ceased at the end of the eruption tilt vectors converged on a point just south of the center of the preexisting 1980s lava dome and the absence of detectable tilt outside the crater suggests a shallow source 1 km we examine several models including cycles of conduit pressurization and plug slip or gas loss and stick slip behavior on the interface between the ascending plug and the 1980s lava dome the small number of stations within the crater prevents a unique determination of source type or geometry but results are consistent with a mechanism involving extrusion of the semisolid dacite plug and or cycles of conduit pressurization

dynamic triggering of high frequency bursts by strong motions during the 2004 parkfield earthquake sequence high pass filtering 20 hz of acceleration records from the usgs parkfield dense seismograph array upsar reveals a series of bursts that occur only during strong shaking from the 2004 mw6 parkfield california earthquake and its immediate aftershocks because there is no correlation between these high frequency bursts observed at closely spaced stations we hypothesize that they are associated with dynamically triggered events occurring within 20 meters of the stations in the highly fractured shallow crust the triggering threshold was found to be 0 02 mpa consistent with a previous estimate based on a similar analysis of high frequency bursts observed in strong motion data from the 1999 chi chi earthquake in taiwan fischer et al 2008 the consistent observation of high frequency bursts at both parkfield and taiwan suggest that they may be a common phenomenon associated with strong motion in the very shallow crust

an unusual occurrence of probable pleistocene corestone within a cretaceous dioritic enclave peninsular ranges california abstract we here document an unusual occurrence of probable pleistocene corestone within an 5 m by 5 m dioritic enclave contained within a cretaceous tonalitic pluton santa margarita ecological reserve sw california the enclave lies within 3 5 km of the seismically active 1 5 2 ma elsinore fault zone and may have been subjected to 70 90 ground shaking events since 22 000 18 000 years ago the studied corestone is elliptical with major axis measuring 55 cm and minor axis 26 cm in length it is surrounded by a discontinuous 7 cm thick rind that breaks apart under slightly greater finger pressure than does the surrounding saprolite in order to assess changes in the physical and chemical properties of the corestone rind and saprolite we collected along an 66 5 cm long traverse 4 samples from the corestone 1 from the rind and 5 from the saprolite for bulk and grain density porosity and major and trace element analyses textural and clay mineral data along with the redistribution of elemental mass indicate that the weathering of biotite and to much lesser degrees apatite and the an rich cores of plagioclase played critical roles in the production of saprolite especially in a narrow 20 cm wide zone adjacent to the rind of the corestone within this zone bulk densities reach their minimum values while porosities and positive volume strains reach their maximums in addition the maximum loss of k fe mn and ca mass occurred just inside this region and is paralleled by the highest cia values and highest additions of si and rb mass in contrast the masses of na and sr are progressively increased and decreased respectively along the entire sampling traverse while the loss of mg ti and p mass is episodic with the greatest losses occurring within the narrow zone adjacent to the rind and at the end of the traverse the above observations indicate that the conversion of biotite to expandable mixed layered clay minerals aided by the alteration of the an rich cores of plagioclase produced sufficient stress on grain boundaries that a weakening or loss of intercrystalline cohesion occurred however unlike the well documented isovolumetric development of saprolite in other areas at the study site saprolitization was accompanied by a volume expansion we speculate that repeated ground shaking in response to earthquakes generated in the nearby elsinore fault zone may be responsible for this difference important byproducts of ground shaking would include additional weakening or loss of intercrystalline cohesion and the production and enhancement of new and older fluid pathways respectively the fact that the most intensely altered material at the study site lies adjacent to the boundary between the rind and saprolite suggests that this interface acted to guide fluid flow around the corestone and rind and into the adjacent saprolite where elemental mass was redistributed down various paths leading to the underlying water table most of the leached elemental mass was removed from the area of the sampling traverse but small increases in si rb and na mass suggest redistribution of these elements from elevated areas outside the area sampled during this study the result of the above complex set of processes is a variably porous and chemically altered saprolitic enclave that is still undergoing modification as it adjusts to the vicissitudes of the paralithic environment and continuing ground shaking during earthquakes generated along the elsinore fault

deep seated downslope slip during strong seismic shaking 1 strong seismic waves cause frictional failure within regolith on hillslopes the material responds anelastically to the combined oscillating dynamic and static gravitational stresses gravity drives preferential downslope movement of the transiently weakened material the net effect over many earthquake cycles is a tens of meter thick slow landslide that is a sackung the classical approach to hillside failure involves downslope dynamic accelerations or equivalently downslope dynamic shear tractions rate and state friction quantifies that the starting coefficient of friction is a few tenths higher that the apparent long term coefficient of friction from the angle of repose 0 96 1 25 in the calculations retaining an extra digit furthermore the dynamic coulomb stress ratio for dynamic to lithostatic stress for s waves refracted toward vertical paths is the dynamic acceleration in g s above the scale depth 1 k the inverse of the wave number in more detail a dynamic acceleration of 0 13 0 35 g destabilizes slopes near the angle of repose seismologists expect such acceleration near active major faults compatible with the widespread occurrence of sackungen on steep slopes accelerations of 0 96 1 25 1 g destabilize shallow slopes leading to net downhill movement analogous to the movement of an object down a vibrating ramp however sackungen are rare or even absent on shallow slopes in california indicating the rarity of sustained 1 g accelerations a second mechanism may drive downhill movement on modest 19 slopes as observed in the san gabriel mountains of california near the san andreas fault the near field velocity pulse on strike slip faults produces only a few tenths g acceleration but particle velocities of over 1 m s 1 persisting over 1 s dynamic stresses and strains scale with this velocity and extend all the way to the free surface coulomb failure criteria are exceeded at shallow depths failure greatly weakens the regolith allowing it to move downhill in response to gravity this mechanism appears capable of producing prehistoric 1 m per event slip on modest slopes observed in the san gabriel mountains

nonlinear attenuation and rock damage during strong seismic ground motions strong seismic waves cause nonlinear behavior in the shallow subsurface in fractured rocks seismologists use low amplitude signals from small repeating earthquakes to measure s wave velocity decrease after strong motion the 2004 parkfield california earthquake provides examples of such velocity changes in fractured sandstone with an s wave velocity of 300 m s 1 this nonlinear behavior occurred around the wave number depth of the incident waves 30 m for the 10 s 1 dominant angular frequency on a velocity seismogram the low amplitude s wave velocity gradually recovered with the logarithm of time the attenuation of strong waves in general depends nonlinearly on their amplitude high dynamic stress triggered small very shallow earthquakes at sites including parkfield the theoretical frictional behavior of a fractured medium with heterogeneous prestress relates these phenomena failure occurs in the highly prestressed domains causing small earthquakes and opening mode cracks the energy to dilate the cracks dissipates a significant fraction of the incoming seismic energy the local high porosity domains close with the logarithm of time as expected from the aging law of rate and state friction increasing the s wave velocity the domain model indicates that nonlinear effects increase gradually over a range of dynamic coulomb stresses as observed and as included in the widely used masing rules the linker and dieterich 1992 relationship provides the maximum sustainable dynamic coefficient of friction needed to utilize the masing rules this parameter is the coefficient of friction at a laboratory normal traction plus a constant 0 15 times the logarithm of the ratio of field normal traction to the laboratory normal traction it is helpful to relate s wave velocity to starting frictional strength as coefficient of friction near the quarter wavelength depth determines nonlinear behavior then the dynamic coefficient of friction and equivalently the maximum sustainable acceleration at the dominant frequency depend weakly on s wave velocity for example the coefficient of friction at an angular frequency of 10 s 1 is less than 1 5 for rocks ranging from parkfield sandstone to intact granite

quantitative models of sediment generation and provenance state of the art and future developments abstract an overview of quantitative approaches to analysis and modelling of sediment generation and provenance is presented with an emphasis on major framework components as determined by means of petrographic techniques conceptual models of sediment provenance are shown to be consistent with two classes of numerical statistical models i e linear mixing models and compositional linear models these cannot be placed within a common mathematical framework because the former requires that sediment composition is expressed in terms of proportions whereas the latter requires that sediment composition is expressed in terms of log ratios of proportions additivity of proportions a fundamental assumption in linear mixing models cannot be readily expressed in log ratio terms linear mixing models may be used to describe compositional variability in terms of physical and conceptual un mixing models of physical un mixing are appropriate for describing compositional variation within transport invariant subpopulations of grains as a result of varying rates of supply of detritus from multiple sources conceptual un mixing governs the relations among chemical mineralogical and petrographic characteristics of sediments which represent different descriptive levels within a compositional hierarchy compositional linear process models may be used to describe compositional and or textural evolution resulting from selective modifications induced by sediment transport as well as chemical and mechanical weathering current approaches to modelling of surface processes treat the coupled evolution of source areas and sedimentary basins in terms of bulk mass transfer only and do not take into account compositional and textural sediment properties moving from the inverse modelling approach embodied in provenance research to process based forward models of sediment generation which provide detailed predictions of sediment properties meets with considerable albeit not insurmountable problems strategies for developing more advanced parameterizations of sediment properties and for simulating their evolution are proposed and expansion of current data acquisition protocols is discussed in the light of data requirements for such advanced sediment generation models inclusion of sediment generation modules in models of landscape evolution and basin filling will mark a significant step towards full fledged source to sink simulations of earth surface processes

strong seismic shaking of randomly prestressed brittle rocks rock damage and nonlinear attenuation strong seismic waves produce frequent episodes of transient oscillating dynamic stress in the shallow subsurface within seismically active areas dynamic stress drives slip on a network of preexisting small fracture planes and leaves residual stresses once shaking ceases the residual stresses act as prestresses during the next strong earthquake local failure occurs on fractures at low dynamic stresses where the prestresses are favorably aligned while most of the bulk rock remains intact hence nonlinear attenuation of strong seismic waves commences at dynamic stresses well below those for pervasive coulomb failure consideration of the fractal distribution of prestresses indicates that nonlinear attenuation increases rapidly with dynamic stress vertically propagating shear waves provide simple scaling relationships for quick application 1 nonlinear attenuation is concentrated near the quarter wavelength depth 2 the coulomb stress ratio dynamic lithostatic stress above the quarter wavelength depth scales with the sustained dynamic acceleration in g s rate and state friction thus provides estimates of the maximum sustained acceleration from coulomb stress ratio at failure 1 for regolith that has repeatedly failed 1 5 for shallow intact sandstone and 2 for shallow intact granite a potentially observable effect occurs with shallow brittle regolith on hillslopes where gravity causes net downslope creep during strong shaking analogous crack network behavior with prestress occurs in the damage zone surrounding the rupture zone of major faults pulverized rock forms at shallow depths when rock is repeatedly deformed in strong shaking to just beyond the elastic limit but strain does not localize into a crack network

physics of crustal fracturing and chert dike formation triggered by asteroid impact 3 26 ga barberton greenstone belt south africa archean asteroid impacts reflected in the presence of spherule beds in the 3 2 3 5 ga barberton greenstone belt bgb south africa generated extreme seismic waves spherule bed s2 provides a field example it locally lies at the contact between the onverwacht and fig tree groups in the bgb which formed as a result of the impact of asteroid possibly 50 km diameter scaling calculations indicate that very strong seismic waves traveled several crater diameters from the impact site where they widely damaged onverwacht rocks over much of the bgb lithified sediments near the top of the onverwacht group failed with opening mode fractures the underlying volcanic sequence then failed with normal faults and opening mode fractures surficial unlithified sediments liquefied and behaved as a fluid these liquefied sediments and some impact produced spherules filled near surface fractures today represented by swarms of chert dikes strong impact related tsunamis then swept the seafloor p waves and rayleigh waves from the impact greatly exceeded the amplitudes of typical earthquake waves the duration of extreme shaking was also far longer probably hundreds of seconds than that from strong earthquakes dynamic strains of 10 3 occurred from the surface and downward throughout the lithosphere shaking weakened the onverwacht volcanic edifice and the surface layers locally moved downhill from gravity accommodated by faults and open mode fractures coast parallel opening mode fractures on the fore arc coast of chile formed as a result of megathrust events are the closest modern analogs it is even conceivable that dynamic stresses throughout the lithosphere initiated subduction beneath the onverwacht rocks

shallow s wave well logs as an indicator of past strong shaking from earthquakes on the newport inglewood fault numerical calculations assuming linear elasticity by bose et al 2014 indicate that an m w 7 75 earthquake on the newport inglewood fault would cause 5 m s of horizontal peak ground velocity pgv within the los angeles basin however the dynamic strain from this event would take much of the uppermost few hundred meters of basin rock beyond its frictional elastic limit stiff quartz rich beds within the basin are fragile geological features that would fail and crack before the rest of the clay rich rock mass repeated cracking would reduce the shear modulus of the quartz rich beds to the level that cracking barely occurred during strong events when interpreted in this way data from such stiff beds near the los angeles international airport indicate past pgv of 1 6 m s comparable with near field records from the strike slip 2002 denali and 1992 landers earthquakes numerical calculations capable of representing nonlinear failure within shallow bedded rocks are warranted online material digital rosrine s wave borehole logs

physical limits on ground motion at yucca mountain abstract physical limits on possible maximum ground motion at yucca mountain nevada the designated site of a high level radioactive waste repository are set by the shear stress available in the seismogenic depth of the crust and by limits on stress change that can propagate through the medium we find in dynamic deterministic 2d calculations that maximum possible horizontal peak ground velocity pgv at the underground repository site is 3 6 m sec which is smaller than the mean pgv predicted by the probabilistic seismic hazard analysis psha at annual exceedance probabilities less than 10 6 per year the physical limit on vertical pgv 5 7 m sec arises from supershear rupture and is larger than that from the psha down to 10 8 per year in addition to these physical limits we also calculate the maximum ground motion subject to the constraint of known fault slip at the surface as inferred from paleoseismic studies using a published probabilistic fault displacement hazard curve these calculations provide a probabilistic hazard curve for horizontal pgv that is lower than that from the psha in all cases the maximum ground motion at the repository site is found by maximizing constructive interference of signals from the rupture front for physically realizable rupture velocity from all parts of the fault vertical pgv is maximized for ruptures propagating near the p wave speed and horizontal pgv is maximized for ruptures propagating near the rayleigh wave speed yielding in shear with a mohr coulomb yield condition reduces ground motion only a modest amount in events with supershear rupture velocity because ground motion consists primarily of p waves in that case the possibility of compaction of the porous unsaturated tuffs at the higher ground motion levels is another attenuating mechanism that needs to be investigated

a magnetostratigraphic age constraint for the proximal synorogenic conglomerates of the late cretaceous cordilleran foreland basin northeast utah usa

the scec southern california reference three dimensional seismic velocity model version 2 we describe version 2 of the three dimensional 3d seismic velocity model of southern california developed by the southern california earthquake center and designed to serve as a reference model for multidisciplinary research activities in the area the model consists of detailed rule based representations of the major southern california basins los angeles basin ventura basin san gabriel valley san fernando valley chino basin san bernardino valley and the salton trough embedded in a 3d crust over a variable depth moho outside of the basins the model crust is based on regional tomographic results the model moho is represented by a surface with the depths determined by the receiver function technique shallow basin sediment velocities are constrained by geotechnical data the model is implemented in a computer code that generates any specified 3d mesh of seismic velocity and density values this parameterization is convenient to store transfer and update as new information and verification results become available

kinematic history of the meade thrust based on provenance of the bechler conglomerate at red mountain idaho sevier thrust belt with up to 45 km of slip the meade thrust fault in southeastern idaho is one of the major thrusts in the sevier thrust belt yet its age of displacement has remained enigmatic because of the lack of a derivative synorogenic deposit we propose that the synorogenic conglomerate produced by initial meade thrusting crops out on red mountain in southeastern idaho 1 5 km east of the present trace of the meade thrust this conglomerate historically has been considered part of the ephraim formation of the lower cretaceous gannett group but we suggest that it is a conglomeratic facies of the bechler formation localized to the area of red mountain regional stratigraphic considerations and paleontological dates from underlying and overlying strata indicate that the bechler conglomerate facies bcf is aptian in age the bcf is 850 m thick and consists of pebble to boulder conglomerate sandstone and mudrock deposited by fluvial and mass flow processes on medial to distal parts of an alluvial fan paleocurrent data indicate an eastward fan shaped dispersal pattern the bcf contains clasts of micritic limestone chert pebble conglomerate and cherty litharenite that were derived from the ephraim formation in addition the conglomerate contains abundant clasts of ordovician carboniferous and lower mesozoic rocks that crop out on both the meade thrust sheet and the paris thrust sheet 25 30 km to the west the base of the bcf is marked by a local 27 angular unconformity on top of the ephraim formation the bcf contains intraformational progressively rotated angular unconformities internal growth folds and minor dip discontinuities that were produced by simultaneous folding and sediment accumulation on the proximal footwall of the meade thrust provenance modeling indicates that the bcf was derived from mesozoic strata that were exposed along the frontal part of the meade thrust sheet and from paleozoic strata that were coevally exposed in the hindward located paris thrust sheet topography on the paris sheet was rejuvenated as it was carried passively over a major ramp in the meade thrust provenance and structural data are combined to produce an incremental bulk rock retrodeformation of initial meade displacement clasts of jurassic twin creek limestone with pressure solution cleavage in the lower part of the bcf indicate that an episode of layer parallel shortening occurred in the meade hanging wall prior to meade displacement this may have been related to emplacement of the paris thrust sheet the bcf recorded 6 km of initial meade related shortening by thrust slip and fault propagation folding during aptian time illite crystallinity systematic fracture sets in the ephraim formation and bcf finite strain in meade footwall and hanging wall rocks and thermal models by previous workers indicate that the meade thrust sheet ultimately overrode the bcf and other footwall rocks probably during albian cenomanian time the bcf and the meade thrust were folded during slip on thrust faults related to the northern crawford thrust during coniacian time a revised interpretation of gannett group provenance throughout the thrust belt suggests that the ephraim formation was derived from both the paris thrust sheet and an older hindward located thrust sheet the bechler was derived from the meade and paris sheets

compound dislocation models cdms for volcano deformation analyses volcanic crises are often preceded and accompanied by volcano deformation caused by magmatic and hydrothermal processes fast and efficient model identification and parameter estimation techniques for various sources of deformation are crucial for process understanding volcano hazard assessment and early warning purposes as a simple model that can be a basis for rapid inversion techniques we present a compound dislocation model cdm that is composed of three mutually orthogonal rectangular dislocations rds we present new rd solutions which are free of artefact singularities and that also possess full rotational degrees of freedom the cdm can represent both planar intrusions in the near field and volumetric sources of inflation and deflation in the far field therefore this source model can be applied to shallow dikes and sills as well as to deep planar and equidimensional sources of any geometry including oblate prolate and other triaxial ellipsoidal shapes in either case the sources may possess any arbitrary orientation in space after systematically evaluating the cdm we apply it to the co eruptive displacements of the 2015 calbuco eruption observed by the sentinel 1a satellite in both ascending and descending orbits the results show that the deformation source is a deflating vertical lens shaped source at an approximate depth of 8 km centred beneath calbuco volcano the parameters of the optimal source model clearly show that it is signicantly different from an isotropic point source or a single dislocation model the calbuco example reflects the convenience of using the cdm for a rapid inter pretation of deformation data

three dimensional moho topography in italy new constraints from receiver functions and controlled source seismology in complex tectonics regions seismological geophysical and geodynamic modeling require accurate definition of the moho geometry various active and passive seismic experiments performed in the central mediterranean region revealed local information on the moho depth in some cases used to produce interpolated maps in this paper we present a new and original map of the 3 d moho geometry obtained by integrating selected high quality controlled source seismic and teleseismic receiver function data the very small cell size makes the retrieved model suitable for detailed regional studies crustal corrections in teleseismic tomography advanced 3 d ray tracing in regional earthquake location and local earthquake tomography our results show the geometry of three different moho interfaces the european adriatic ionian and tyrrhenian the three distinct moho are fashioned following the alpine and apennines subduction collision and back arc spreading and show medium to high frequency topographic undulations reflecting the complexity of the geodynamic evolution

three dimensional modeling of the 1983 1984 eruption at piton de la fournaise volcano reunion island displacement vectors on 125 points over a 6 km 2 area were calculated zlotnicki et al 1990 for piton de la fournaise volcano reunion island from photogrammetric surveys conducted in september 1981 and again in september 1984 an eruptive crisis with two episodes occurred during the 3 years between the surveys we modeled the displacements from the photogrammetric surveys using a three dimensional mixed boundary element method the model shows that both eruptive episodes were fed by a single dike oriented 165 from north as the dike approached the ground surface it divided into segments that rotated into an en echelon pattern the model that best fits all observations suggests that the stress state within the volcano is quasi isotropic such that horizontal stresses equal the overburden these high horizontal stresses are incompatible with an elastic edifice loaded merely by gravitational forces however they may be attributed to the cumulative effect of repeated dike intrusions

seismically damaged regolith as self organized fragile geological feature 1 the s wave velocity in the shallow subsurface within seismically active regions self organizes so that typical strong dynamic shear stresses marginally exceed the coulomb elastic limit the dynamic velocity from major strike slip faults yields simple dimensional relations the near field velocity pulse is essentially a love wave the dynamic shear strain is the ratio of the measured particle velocity over the deep s wave velocity the shallow dynamic shear stress is this quantity times the local shear modulus the dynamic shear traction on fault parallel vertical planes is finite at the free surface coulomb failure occurs on favorably oriented fractures and internally in intact rock i obtain the equilibrium shear modulus by starting a sequence of earthquakes with intact stiff rock extending all the way to the surface the imposed dynamic shear strain in stiff rock causes coulomb failure at shallow depths and leaves cracks in it wake cracked rock is more compliant than the original intact rock cracked rock is also weaker in friction but shear modulus changes have a larger effect each subsequent event causes additional shallow cracking until the rock becomes compliant enough that it just reaches coulomb failure over a shallow depth range of tens to hundreds of meters further events maintain the material at the shear modulus as a function where it just fails the formalism provided in the paper yields reasonable representation of the s wave velocity in exhumed sediments near cajon pass and the san fernando valley of california a general conclusion is that shallow rocks in seismically active areas just become nonlinear during typical shaking this process causes transient changes in s wave velocity but not strong nonlinear attenuation of seismic waves wave amplitudes significantly larger than typical ones would strongly attenuate and strongly damage the rock

rock pulverization at high strain rate near the san andreas fault rocks near the san andreas fault are pervasively crushed at distances of up to 400 m from its core laboratory experiments and calculations suggest that the rocks were pulverized at high strain rates 150 s 1 associated with a supershear rupture a rupture propagating at a velocity equal to greater than that of seismic shear waves

dynamic driving of small shallow events during strong motion abstract high pass filtering 20 hz of acceleration records from the 1999 chi chi taiwan and 2004 parkfield california earthquakes reveals a series of bursts that occur only during strong shaking initially interpreted as originating from asperity failure on the chelungpu fault bursts observed during the chi chi earthquake were subsequently determined to be a local effect within about 1 km of the seismic stations similar bursts were observed at the u s geological survey parkfield seismic array during the parkfield earthquake and were constrained to originate less than 20 m from the instruments such small shallow events cannot result from the triggered release of stored elastic energy because rate and state friction rules out stick slip instability on such small shallow patches our hypothesis is that the bursts are not triggered but are driven by simultaneous shear and tensile stresses near the surface during the strong motion at 2 hz sv to p wave mode conversion at the free surface produces tensile stresses to depths of 70 m where standard triggering releases stored elastic energy and adds to the incident wave field this new driving mechanism takes energy out of the 2 hz strong motion and reradiates it at high frequencies it is thus an attenuation mechanism that we estimate can contribute 3 to the net attenuation in the very shallow crust

shallow sedimentary rock as a fragile geological feature effects of clay content and hydrology on frictional strength strong long period 3 s seismic waves impose dynamic strains on the shallow subsurface the dynamic strain is the dynamic velocity divided by the phase velocity of the waves the dynamic stress is the strain times the shear modulus a testable hypothesis is that the shear modulus of the rock self organizes so that the rock barely fails in friction with typical imposed dynamic strains the predicted value of stiffness divided by depth is then independent of depth for constant rock density and constant coefficient of friction with the water table at the surface predicted stiffness divided depth deviates from constancy for finite water table depth prior laboratory studies indicate that the coefficient of friction is lower in clay rich rocks than in clay free rocks these effects provide appraisal of the concept in which hydrology and lithology are constrained four boreholes near parkfield california qualitatively exhibit the predicted effects there is some indication of the predicted effect of water table depth within accumulating sediments penetrated by borehole mcglincy mgcy in the santa clara valley of california but the effect of clay is not well resolved due to a dearth of clay rich beds

band of precariously balanced rocks between the elsinore and san jacinto california fault zones constraints on ground motion for large earthquakes a spectacular band of precariously and semiprecariously bal anced rocks extends from riverside to near borrego valley cali fornia about halfway between the elsinore and san jacinto fault zones the rocks are distributed in a band a few kilometers wide midway between the san jacinto and elsinore fault zones an in dication that the distribution is caused by attenuation of strong ground motion from numerous large events along these two fault zones these rocks have apparently been in place for thousands of years and thus place important constraints on ground motions from earthquakes on the basis of field tests and photographic analysis the estimated quasi static toppling accelerations for the precariously balanced rocks are 0 32 6 0 10 g g 5 gravitational acceleration the dynamic toppling accelerations are within this range for earthquakes with waveforms similar to those recorded during the izmit and denali earthquakes these constraints are roughly consistent with the median predicted value of ground mo tion for m7 earthquakes but somewhat lower than 11s ground motion curves and much lower than the values from the 2 in 50 yr hazard maps the evidence from these rocks has importance for some of the assumptions that go into calculating probabilistic seismic hazard assessment including median and standard devia tion of ground motion attenuation curves especially for hard rock for which few instrumental data are available the possible exis tence of random background earthquakes and the smoothing dis tance for historical seismicity

nonlinear behavior of strong surface waves trapped in sedimentary basins abstract numerical calculations and observations indicate that surface waves reverberate within sedimentary basins a site response approach is inapplicable to the nonlinear attenuation of these waves as the energy passes repeatedly through the shallow subsurface computed dynamic stresses obtained by using published shakeout calculations graves et al 2008 indicate that nonlinear attenuation is modest but not negligible in the los angeles california basin for large earthquakes on the san andreas fault the dominant surface waves have velocity amplitudes of 1 5 m sec 1 and periods 3 5 sec around 20 of the total elastic strain energy resides above dynamic lithostatic stress ratios of 0 2 for both rayleigh and love waves where prestressed rock is highly likely to fail somewhat in friction

rate and state dependent friction of intact rock and gouge the shear traction during frictional sliding depends on the instantaneous sliding strain rate e and on a state variable which represents the previous history of the sample a formulation of rate and state friction covers the continuum between gouge and intact rock as well as the behavior at high and low normal tractions a traditional formula for the instantaneous coefficient of friction is retained 0 a in e e 0 b in 0 where 0 is the steady state coefficient of friction at the reference strain rate e 0 and a and b are small constants the normalizing 0 for isothermal conditions is p n p 0 n where ap is the effective normal traction p 0 is a reference normal traction and n is an exponent the coefficient of friction of intact rock is approximately close bn in p p close where the coefficient of friction is close at the normal traction p close where essentially all the pore space is closed during steady state sliding the formulation provides an acceptable fit to the observed coefficient of friction of westerly granite at normal tractions up to 1500 mpa including steady sliding and intact rock failure

erosion in the western alps dora baltea basin 1 quantifying sediment provenance abstract sourced in the m bianco the highest mountain of the alps the dora baltea river cuts across the arc of the western alps drains all major alpine tectonic units from the helvetic domain to the south alpine domain and finally joins the po river petrographic composition of clastic detritus carried by the dora baltea river and its tributaries faithfully mirrors the complex geology of the western alps high resolution modal analysis of dora baltea sands allowed us to distinguish seven end member metamorphoclastic provenances river sands from the m bianco external massif are dominated by quartz feldspars and hornblende detritus from basement and cover rocks of the brianconnais zone includes low grade metasedimentary lithic fragments epidote chloritoid and garnet sands from the internal penninic massifs include quartz and subordinate feldspars garnet and epidote abundant metabasite and serpentine schist lithic grains along with epidote actinolite and few pyroxenes characterize detritus from the calcschists and meta ophiolites of the oceanic piemonte zone sands from the austroalpine zone include quartz abundant metamorphic lithic fragments garnet and locally significant sillimanite dent blanche kinzigites the relative contribution of each end member to the dora baltea sediment flux was assessed with forward modelling of end member mixing our estimates calculated from the entire petrographic and mineralogical data set indicate that the main sources of bed load in the dora baltea mountain basin are the granitoid to gneissic rocks exposed in the m bianco massif and in the austroalpine zone in order to make allowance for the contribution of a particular bedrock constituent in a compound source area to the derivative sand the original concept of sand generation index sgi was modified to assess the relative contribution of the seven end member sources of detritus the highest total basin sgi indices are calculated for the m bianco massif sgi 16 4 and austroalpine domain sgi 1 4 the m bianco massif which represents only 3 of the whole catchment has the highest capacity of sand sized bed load production owing to its granitoid lithology and extreme relief this actualistic provenance study demonstrates that sediment composition can be markedly influenced by source rocks that occupy only a minor portion of the drainage area

real contacts and evolution laws for rate and state friction the well known formalism of rate and state dependent friction represents the transition between static and dynamic friction the instantaneous coefficient of friction is proportional to the logarithm of the sliding velocity v and the logarithm of a state variable whose inverse is a measure of the current amount of damage within a shearing gouge layer or on a sliding surface evolution equations that represent the change of the state variable with time include damage from sliding and healing the dieterich 1979 evolution law contains separate terms for the two effects the ruina 1983 law groups the two effects into one term proportional to v ln v in addition the state variable depends exponentially on porosity as exp f c where is the porosity at reference conditions and c is a dimensionless constant i obtain these relationships as well as relationships between friction law parameters and physical parameters by representing asperity contacts as rectangular deformable regions between two rigid sheets the creep rate within an asperity depends exponentially on the second invariant of the deviatoric stress in terms of asperity scale quantities the invariant includes normal traction and shear traction the derivations assume that contact stresses scale with macroscopic stresses this yields simple expressions analogous to those in rate and state friction the ruina 1983 evolution law in general and the decrease in compaction rate during a hold in a slider experiment in particular arise because a sudden decrease in sliding velocity implies that the shear traction and hence the invariant decrease the porosity state relationship arises when real stresses at contacts or the inverse real contact area depend linearly on the separation of the sheets and by analogy the porosity conversely the ruina 1983 evolution law is inapplicable when asperity scale stresses within a deforming material do not scale with macroscopic stresses