stuck in the mud earthquake nucleation and propagation through accretionary forearcs 1 subduction zone earthquakes can propagate to the surface causing large seafloor displacements resulting in tsunamis this requires the earthquake to rupture through clay rich sediments of the accretionary wedge which are largely aseismic as found previously the frictional properties of a range of wet clays at low slip velocity are velocity strengthening thus inhibiting earthquake nucleation however at high slip velocity the same materials weaken almost immediately resulting in a negligible critical slip weakening distance and fracture energy we interpret this behaviour as rapid thermal pressurization of the pore fluid within the clay gouge the lack of fracture energy can explain how a large rupture propagating from depth might not be arrested by clay rich velocity strengthening sediments as is commonly seen the results suggest that generally earthquakes may be difficult to nucleate on mature faults dominated by clay but the propagation of earthquakes through these zones is energetically very favourable

the tindouf basin a marine refuge during the serpukhovian carboniferous mass extinction in the northwestern gondwana platform abstract several macrofaunas and microfossils of the carboniferous saharan basins have longer stratigraphic ranges than those of other basins in the western palaeotethys realm particularly in the tindouf basin morocco algeria foraminifers are particularly abundant and diverse in the serpukhovian and basal bashkirian compared to coeval basins and some taxa have longer ranges than in the neighbouring reggan and bechar basins although this effect is more marked compared to the western palaeotethyan assemblages in europe several rugose coral species are recorded from the early bashkirian that previously were considered to have disappeared in the serpukhovian the tindouf basin as one of the most western saharan basins in north africa shows the greatest stratigraphic ranges of taxa which diminish eastwards evidence for a mass extinction event during the serpukhovian in the tindouf basin has not been clearly recognized although a possible influence of glaciation is observed in the faunal diversity eustatic sea level changes were experienced in tindouf with the cyclic pattern of sedimentation but warm water ocean currents from the palaeoequator were able to maintain tropical conditions on the platform tectonics in the area led to emerging land masses and barriers and created a partly isolated basin in this sector of the western part of the sahara platform in northern gondwana the combination of those factors controlled the environmental conditions in the area allowing the persistence of the fauna for longer stratigraphic ranges than its equivalent counterparts in the western palaeotethys

fracture roughness and gouge distribution of a granite shear band 1 localization of deformation during fracture mechanical tests leads to the development of shear bands we performed triaxial tests using sidobre granite at four different confining pressures from 20 to 80 mpa we compared two sets of tests one set was stopped immediately after the formation of the shear band a second one included additional shear deformation from the analysis of thin sections of these laboratory samples we characterize the typical microstructures in the shear band mode i and ii cracks riedel cracks cataclastic flow statistical properties of rupture surface roughness and gouge grain size reveals scaling invariance using a mechanical profiler the fracture roughness is measured along parallel profiles and shown to be correctly described over up to 3 orders of magnitude by self affine geometry with a roughness exponent close to 0 80 this property is very similar to tensile crack even if local processes are different the influence of the slip is observed fracture surfaces are rougher along the slip direction 0 74 than perpendicular to it 0 80 the confining pressure is shown to have a weak effect on the fracture roughness it smoothes the surface slight increase of the roughness exponent gouge particles extracted from the shear band present a power law distribution with an exponent ranging from 1 44 to 1 91 this exponent appears to increase with the shearing displacement and the confining pressure when a significant shear of the band is combined with a high confining pressure i e impeded dilation of the band the hallmark of fragmentation is observed for the particle distribution and related to a smoothing of the band boundary

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

an exhumed palaeozoic underwater scenery the visean mud mounds of the eastern anti atlas morocco about one hundred carbonate mud mounds covering an area of 440 km 2 in the eastern anti atlas of morocco constitute one of the largest mound agglomerations known so far from lower carboniferous settings they occur within a 4000 m thick succession of shales with intercalated bedded limestones sandstones and siltstones according to conodont and goniatite biostratigraphy mound formation started in the early gnathodus texanus zone and terminated during the g bilineatus zone of the visean stage individual mounds are a few metres to 30 m high have base diameters of up to 300 m and are concentrated in several parallel wnw ese running belts from their lithology and facies relationships four types of mounds can be distinguished 1 massive crinoidal wacke or packstones without stromatactis 2 massive crinoidal wacke or packstones with rare stromatactis 3 similar to 2 but allochthonous and 4 biodetrital skeletal grainstone mounds while carbonate deposition in types 1 to 3 was probably triggered by microbial precipitation type 4 is the result of a predominantly mechanical accumulation of skeletal debris biota in the four types comprise a great variety of invertebrates among which crinoids sponges and bryozoans are most common diagenesis of the mound carbonates was dominated by recrystallization of micritic matrix and organic remains and late burial cementation oxygen and carbon isotope data of brachiopod and crinoid ossicles matrix and early marine cements plot in a large field and do not allow definite conclusions about the composition of the ambient seawater microbial activity and the absence or scarcity of green algae colonial corals and coralline sponges suggest deposition of the mounds in moderate water depth close to the lower limit of the photic zone d 2001 elsevier science b v all rights reserved

crystallographic controls on the frictional behavior of dry and water saturated sheet structure minerals 1 we compare the frictional strengths of 17 sheet structure mineral powders measured under dry and water saturated conditions to identify the factors that cause many of them to be relatively weak the dry coefficient of friction ranges upward from 0 2 for graphite leveling off at 0 8 for margarite clintonite gibbsite kaolinite and lizardite the values of dry correlate directly with calculated 001 interlayer bond strengths of the minerals this correlation occurs because shear becomes localized along boundary and riedel shears and the platy minerals in them rotate into alignment with the shear planes for those gouges with dry 0 8 shear occurs by breaking the interlayer bonds to form new cleavage surfaces where dry 0 8 consistent with byerlee s law the interlayer bonds are sufficiently strong that other frictional processes dominate the transition in dry friction mechanisms corresponds to calculated surface energies of 2 3 j m2 adding water causes to decrease for every mineral tested except graphite if the minerals are separated into groups with similar crystal structures wet increases with increasing interlayer bond strength within each group this relationship also holds for the swelling clay montmorillonite whose water saturated strength is consistent with the strengths of nonswelling clays of similar crystal structure water in the saturated gouges forms thin structured films between the plate surfaces the polar water molecules are bonded to the plate surfaces in proportion to the mineral s surface energy and wet reflects the stresses required to shear through the water films

development of the palaeogeography of pangaea from late carboniferous to early permian abstract old and new well and poorly known lithofacies data of moscovian and artinskian age in the area limited by the arctic sea and central africa the atlantic ocean and the ural mountains have been plotted on present day maps the facies mapped and related environments allow the recognition of a series of different palaeogeographic palaeotectonic units including the late carboniferous to early permian deep sea to palaeo tethyan ocean west siberia kazakhstan continent and uralian kazakhstan tienshan arc uralian foredeep up to the closing arms of the uralian ocean precaspian basin russian platform donets rift basin caucasian moesian dobrogean polish oslo basinal belt syn tectonic hercynian foreland basin intramontane post hercynian basins iran anatolian hellenic dinaric carnic basin branching into the hungarian seaway apennine basin branching into the cantabrian and south portuguese basins oman iraq levantine sicily deep basin and inferred oceanic sea way south peri tethyan platform basins east arabian cratonic basin and north african intracratonic basins the subsidence sedimentation trends of these units were correlated and compared through lithostratigraphic logs bathymetric curves and uncorrected cumulative stratigraphic curves the sets of original and processed data were used to test two different palaeodynamic models a pangaea a model static from late carboniferous to triassic and a mobile pangaea b model with different dextral displacements between laurussia and gondwanaland in the same time interval the best fit for our data requires a strike slip offset of about 800 km from moscovian to artinskian time this model implies a first quasi pangaea or pangaea b assembly at the carboniferous permian transition an ephemeral pangaea b break up driven by an early permian oblique rift across the mediterranean to caribbean areas and a final pangaea a assembly in the mid to late permian the two palinspastic maps describing the model have been cross checked by comparison with an independent set of biogeographic features of late carboniferous and early permian overall floral reptile and marine benthic organism distribution is consistent with the early permian trans pangaea seaway inferred from facies and palaeodynamic analyses

evolution of the rheic ocean the rheic ocean which separated laurussia from gondwana following the closure of iapetus is arguably the most important ocean of the palaeozoic its suture extends from mexico to turkey and its closure produced the climactic variscan alleghanian ouachita orogeny that assembled the supercontinent pangaea following protracted cambrian rifting that represented a continuum from neoproterozoic orogenic processes the rheic ocean opened in the early ordovician with the separation of several neoproterozoic arc terranes from the continental margin of northern gondwana separation occurred along the line of a former neoproterozoic suture following the onset of subduction in the outboard iapetus ocean the timing of rift drift transition and drive for subsequent spreading was likely governed by slab pull accounting for the rapid rate 8 10 cm yr at which the rheic ocean widened during the ordovician the ocean broadened at the expense of iapetus and attained its greatest width 4000 km in the silurian by which time baltica had sutured to laurentia and the neoproterozoic arc terranes had accreted to laurussia closing iapetus in the process closure of the rheic ocean began in the devonian and was facilitated by northward subduction beneath southern baltica and southward subduction beneath northwest gondwana closure was largely complete by the mississippian as gondwana and laurussia sutured to build pangaea north africa colliding with southern europe to create the variscan orogen in the devonian carboniferous and west africa and south america suturing to north america to form the alleghanian and ouachita orogens respectively during the carboniferous permian the rheic ocean consequently plays a dominant role in the basement geology of southern europe in the appalachian ouachita orogeny of north america and in the palaeozoic sedimentary structural and tectonothermal record from middle america to the middle east with its closure the ocean brought about the assembly of pangaea and brought the palaeozoic era to an end

an example of slip instability resulting from displacement varying strength a rock cylinder containing a clay filled sawcut making an angle of 30 to the sample axis was deformed at constant confining and pore pressures and constant remote shortening rate the sawcut surfaces contained a series of regularly spaced ridges and grooves oriented perpendicular to the direction of shear the interaction of these grooved surfaces resulted in a sliding strength which varied periodically with displacement by varying the effective machine stiffness through the use of an electronic feedback circuit a range of stable and unstable slip behavior was achieved in this way we examined fault slip behavior which was dominated by displacement dependent strength

under the hood of the earthquake machine toward predictive modeling of the seismic cycle advances in observational laboratory and modeling techniques open the way to the development of physical models of the seismic cycle with potentially predictive power to explore that possibility we developed an integrative and fully dynamic model of the parkfield segment of the san andreas fault the model succeeds in reproducing a realistic earthquake sequence of irregular moment magnitude m w 6 0 main shocks including events similar to the ones in 1966 and 2004 and provides an excellent match for the detailed interseismic coseismic and postseismic observations collected along this fault during the most recent earthquake cycle such calibrated physical models provide new ways to assess seismic hazards and forecast seismicity response to perturbations of natural or anthropogenic origins

aftershock slip behavior of the 1989 loma prieta california earthquake an analysis of 745 aftershocks of the m7 1 loma prieta earthquake of 17 october 1989 reveals a wide variety of focal mechanisms at the northwestern end of the aftershock zone earthquakes that apparently occurred off the main rupture plane exhibit mechanisms with predominantly reverse slip on planes nearly parallel to the san andreas fault at the southeastern end the mechanisms exhibit right lateral motion on near vertical planes suggesting that these aftershocks involve slip on the san andreas fault few of the aftershock mechanisms in the central zone resemble the main shock mechanism strike n130 degree e dip 70 degree sw rake 104 degree but instead exhibit reverse right lateral left lateral and normal motion on planes subparallel to the main shock rupture plane the dip of the aftershock zone is parallel to the main shock slip plane and includes the main shock hypocenter however the lack of agreement between the main shock and the aftershock mechanisms suggests that few of the aftershocks occurred on the main shock slip plane this behavior is consistent with observations of aftershock sequences for other dip slip events and also with studies indicating that main shock rupture zones are at all other times mostly aseismic if the stress drop for the main shock relievedmore most of the tectonic stress the mechanisms could reflect the heterogeneity of the near field stress redistribution alternatively the variety of the aftershock mechanisms may reflect deformation by block motion within a narrow zone adjacent to the main shock rupture plane less

palaeobiogeographic context in the development of shallow water late visean early bashkirian benthic foraminifers and calcareous algae in the cantabrian mountains spain abstract the late visean to early bashkirian shallow water carbonate valdediezma platform in the picos de europa province of the cantabrian zone has been subdivided into eight microbiotic intervals by means of similarity clusters using the morisita coefficient the most complete visean bashkirian interval is represented in the valdediezma valley jitu l escarandi road to tresviso where only the steshevian to lower part of the protvian middle serpukhovian is missing this interval is better represented in the pompedrei bridge to la hermida composite section and also in the deeper water section at vegas de sotres these intervals contain a succession from the mikhailovian upper visean up to the krasnopolyanian lower bashkirian the assemblages of the valdediezma limestone show comparatively low similarity indices with the neighbouring basins in the collisional front in the western extremity of the palaeotethys during the progression of the variscan orogeny in this mobile belt two domains are recognized a western domain composed of outcrops in south western spain and in the moroccan meseta and an eastern domain comprising basins located in southern france some basins such as the betic cordillera initially had more influence from the western domain but later during the late serpukhovian it is considered as being part of the eastern domain the valdediezma platform foraminiferal and algal content is coincident with its location as an isolated platform surrounded by deep water seas and with higher similarities with the eastern domain regional tectonic events are recognized from the late visean onward and they are mostly masked by the overprint of latest pennsylvanian events facies changes are commonly observed particularly at the base of the intervals suggesting that facies control is the most important factor controlling the assemblages it is considered that eustatic sea level changes exerted a certain control on the assemblages

upper visean coral biostrome in a volcanic sedimentary setting from the eastern tianshan northwest china abstract for the first time a mississippian coral biostrome is described from the eastern tianshan xinjiang province northwest china rugose corals and foraminifers show that the biostrome developed during the late visean in one of the rare carbonate levels in the mainly volcanic siliciclastic succession of the yamansu formation a single fasciculate coral siphonodendron irregulare dominates 80 this biostrome of the 22 coral genera found in the yamansu formation 5 colonial and 6 solitary dissepimented corals are recorded in the biostrome the biostrome can be divided vertically into two parts in the main thick part dominate large patches of in situ siphonodendron irregulare colonies in the thinner uppermost part siphonodendron irregulare and lithostrotion formed locally isolated small patches in a capping bed the initial growth of the coral patches was related to slight topographic irregularities in the underlying volcano sedimentary rocks siphonodendron irregulare appears to have been the best adapted species to the environmental pressures in the unstable tectono sedimentary environment of the yamansu formation it flourished and outnumbered the other corals when volcanic activity ceased and carbonate production became active for a short time the development of the siphonodendron biostrome ceased due to increases in sea level and volcanic activity compared to siphonodendron biostromes in the western and eastern paleotethys the siphonodendron biostrome in yamansu is unique for having developed in an island arc setting to date the yamansu biostrome is the only documented coral bioconstruction at similar latitudes in the central asian orogenic belt caob formation of this coral biostrome was controlled by extrinsic factors such as changes in global climate and ocean currents and intrinsic factors such as the pioneering nature of the fast growing siphonodendron irregulare both sets of factors are responsible for the expansion of the tropical reef belt into previously more temperate environments

identifying fault heterogeneity through mapping spatial anomalies in acoustic emission statistics 1 seismicity clusters within fault zones can be connected to the structure geometric complexity and size of asperities which perturb and intensify the stress field in their periphery to gain further insight into fault mechanical processes we study stick slip sequences in an analog laboratory setting analysis of small scale fracture processes expressed by acoustic emissions aes provide the possibility to investigate how microseismicity is linked to fault heterogeneities and the occurrence of dynamic slip events the present work connects x ray computer tomography ct scans of faulted rock samples with spatial maps of b values slope of the frequency magnitude distribution seismic moments and event densities our current experimental setup facilitates the creation of a series of stick slips on one fault plane thus allowing us to document how individual stick slips can change the characteristics of ae event populations in connection to the evolution of the fault structure we found that geometric asperities identified in ct scan images were connected to regions of low b values increased event densities and moment release over multiple stick slip cycles our experiments underline several parallels between laboratory findings and studies of crustal seismicity for example that asperity regions in lab and field are connected to spatial b value anomalies these regions appear to play an important role in controlling the nucleation spots of dynamic slip events and crustal earthquakes

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

refined age and geological context of two of australia s most important jurassic vertebrate taxa rhoetosaurus brownei and siderops kehli queensland abstract australia s jurassic vertebrate fossil record remains extremely sparse with only two dinosaur taxa and two temnospondyl amphibians identified to date of these the spectacular and extremely well preserved giant amphibian siderops kehli and the only known pre cretaceous sauropod in australia rhoetosaurus brownei are perhaps the most important the age of both specimens and the stratigraphic context of rhoetosaurus brownei are weakly constrained and imprecisely defined limiting our understanding of their evolutionary relationships within a broader gondwanan context to clarify and contextualise the evolutionary relationships and ages of these two iconic jurassic taxa we used u pb detrital zircon geochronology to date the sandstone matrix from around the bones of the historic museum specimens the robust maximum depositional age for siderops was calculated at 176 6 ma 2 ma indicating that it is no older than late toarcian which refines existing biostratigraphic estimates the rhoetosaurus maximum depositional age was determined to be 162 6 1 1 ma no older than early oxfordian demonstrating that the fossils are younger than expected and definitely recovered from the walloon coal measures

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

devonian shallow water sequences from the north gondwana coastal margin central and eastern taurides turkey sedimentology facies and global events abstract turkey is an integral part of the alpine himalayan orogenic belt with a number of tectonostratigraphic units striking in an e w direction these belts consist of terranes of different tectonic settings ranging from oceanic basins to active and passive continental margins the age of incorporated units of continental margin origin ranges from the cambrian to the cenozoic and includes unmetamorphosed to low grade devonian rocks in the pontides taurides and on the arabian plate this paper describes the detailed sedimentology facies and biostratigraphy of three 900 to 1200 m thick devonian successions in the central and eastern taurides eceli halevikdere and kocadere during the devonian the central and eastern taurides were situated at the northern margin of gondwana the sediments described were deposited on this margin in coastal to shelf environments despite similar large scale trends regional differences in the sedimentary sequences can be distinguished especially for the lower part of the devonian for the first time sufficient biostratigraphical data have been recovered to allow the successions to be subdivided at a stage scale permitting their approximate correlation and comparison with the regional lithostratigraphy the temporal development of sedimentary processes facies changes and hinterland signatures recorded in the individual sections have been reconstructed allowing their correspondence to global events to be recognized and discussed for the first time the palaeobiogeographic distribution of various organisms within these succession suggests a comparatively narrow sea rheic ocean between laurasia and gondwana peri gondwana during the devonian

ultrasonic velocities acoustic emission characteristics and crack damage of basalt and granite acoustic emissions ae compressional p shear s wave velocities and volumetric strain of etna basalt and aue granite were measured simultaneously during triaxial compression tests deformation induced ae activity and velocity changes were monitored using twelve p wave sensors and eight orthogonally polarized s wave piezoelectric sensors volumetric strain was measured using two pairs of orthogonal strain gages glued directly to the rock surface p wave velocity in basalt is about 3 km s at atmospheric pressure but increases by 50 when the hydrostatic pressure is increased to 120 mpa in granite samples initial p wave velocity is 5 km s and increases with pressure by 20 the pressure induced changes of elastic wave speed indicate dominantly compliant low aspect ratio pores in both materials in addition etna basalt also contains high aspect ratio voids in triaxial loading stress induced anisotropy of p wave velocities was significantly higher for basalt than for granite with vertical velocity components being faster than horizontal velocities however with increasing axial load horizontal velocities show a small increase for basalt but a significant decrease for granite using first motion polarity we determined ae source types generated during triaxial loading of the samples with increasing differential stress ae activity in granite and basalt increased with a significant contribution of tensile events close to failure the relative contribution of tensile events and horizontal wave velocities decreased significantly a concomitant increase of double couple events indicating shear suggests shear cracks linking previously formed tensile cracks

fractal dimension and b value on creeping and locked patches of the san andreas fault near parkfield california we tested the hypotheses 1 that the fractal dimension d of hypocenters are different in a locked and a creeping segment of the san andreas fault and 2 that the relationship d 2b holds approximately where b is the slope of the frequency magnitude relationship the test area was the 30 to 50 km fault segment north of park eld for which two earthquake catalogs exist the borehole high resolution seismic network data and the u s geological survey data which have a minimum magnitude of completeness of mc 0 4 and mc 1 0 1 2 respectively the relative location errors in the two catalogs are estimated as 0 25 km and less than 1 km respectively the periods of high quality data available extend from 1987 to 1998 5 and 1981 to 2000 2 respectively furnishing 2609 and 3775 events for analysis in the two catalogs in the locked part 0 5 b 0 7 and 0 96 d 1 14 whereas in the creeping segment 1 1 b 1 6 and 1 45 d 1 72 however the spatial distribution of the hypocenters in the creeping segment is not well approximated by a fractal distribution we conclude 1 that the frequency magnitude distribution as described by b as well as the fractal dimension d are different in the locked and creeping segments near park eld 2 that the spatial distribution in the creeping segment is not well approximated by a fractal distribution and 3 that the relationship d 2b holds in the locked segment where both parameters can be measured accurately thus we propose that the heterogeneity of seismogenic volumes lead to differences in d and b and that these differences where established by high quality data may furnish clues concerning properties of fault zones

the 1997 kagoshima japan earthquake doublet a quantitative analysis of aftershock rate changes we quantitatively map relative rate changes for the aftershock sequence following the second mainshock of the 1997 earthquake doublet m w 6 1 m w 6 0 in the kagoshima province japan using the spatial distribution of the modified omori law parameters for aftershocks that occurred during the 47 8 days between the two mainshocks we forecast the aftershock activity in the next 50 days and compare it to the actually observed rates the relative rate change map reveals four regions with statistically significant relative rate changes three negative and one positive our analysis suggests that the coseismic rate changes for off fault aftershocks could be explained by changes in static stress however to explain the activation and deactivation of on fault seismicity other mechanism such as unusual crustal properties and the presence of abundant crustal fluids are required

earth science microseismicity data forecast rupture area on 28 september 2004 there was an earthquake of magnitude 6 0 at parkfield california here we show that the size distribution of the micro earthquakes recorded in the decades before the main shock occurred allowed an accurate forecast of its eventual rupture area applying this approach to other well monitored faults should improve earthquake hazard assessment in future

structural analysis of an accretionary prism in a continental collisional setting the late paleozoic pulo do lobo zone southern iberia abstract models concerning the tectonic evolution of accretionary complexes typically relate outcrop scale to plate scale multiphase deformation as a smooth variation of strain on all scales however at oblique convergent margins regional scale brittle faults in the shallow crust are commonly parallel to the main orogenic grain these faults impose a strong structural anisotropy and can subsequently control deformation at subordinate scales as a result finite strain in each domain may not record local kinematics consistent with the overall orogenic scale motion implying that structural data must be analyzed selectively from a large area in order to relate outcrop scale kinematics to global plate scale dynamics field mapping and preliminary structural analysis of the late devonian pulo do lobo pdl formation and suspect exotic south portuguese zone spz in southern iberia indicate tectonic juxtaposition of diverse deposits such as foreland basin flysch sedimentary and tectonic melange and passive margin sediments showing an overall geometry consistent with an accretionary wedge setting variations in finite strain lithology and regional structure were used as proxies for defining tectonic domains for structural analysis numerous local kinematic indicators within the pdl suggest a complex regional deformation with several enigmatic features that can be explained by sequential compartmentalization of strain during the development of the imbricate stack followed by late stage bulk strain imposed across the entire complex structural data produced by local strain partitioning reveals kinematic indicators which contradict the overall regional structural style e g spatial juxtaposition of sinistral and dextral fabrics when viewed at larger scales i e regional scale however these data indicate that significant sinistral strike slip movement occurred in conjunction with both an extension and shortening outcrop scale deformation in polydeformed domains is controlled by local conditions resulting from brittle deformation coeval with orogenic scale bulk strain the entire pulo do lobo zone is dominated by a pervasive late stage vertical to sub vertical e w cleavage axial planar to chevron folds which overprint earlier deformation in the older passive margin units this overprinting suggests that in the late stages of the evolution of the accretionary complex bulk strain was imposed over the entire complex as a result of internal locking of the accretionary complex and reduced strain rates during the waning stages of collision between gondwana and laurussia stereographic analysis of fabric elements from each distinct tectonic domain together with regional geological constraints support this hypothesis and are indicative of progressive deformation imposed on the pdl during the variscan orogeny

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

spatial variability of seismicity parameters in aftershock zones the spatial variability of the b value of the frequency magnitude relationship and the decay rate of aftershocks as described by the p value of the modified omori law is investigated by using dense spatial grids we map out the distribution of b and p values within the landers northridge morgan hill and kobe aftershock sequences considerable spatial variability is found with b values of independent subvolumes ranging from 0 6 to 1 4 and p values ranging from 0 6 to 1 8 these systematic and statistically highly significant differences argue that it is an oversimplification to assign one single p and b value to an aftershock sequence that extends up to 100 km the spatial distribution of these two parameters is compared with the slip distribution during the mainshock suggesting that the areas of largest slip release correlate with high b value regions we hypothesize that the frictional heat created during the event may influence the p value distribution within an aftershock zone while applied shear stress crack density and pore pressure govern the frequency magnitude distribution by investigating the frequency magnitude distribution separately for preseismic and postseismic periods for the morgan hill mainshock we find that only the volume in the vicinity of the highest slip release shows a significant increase in the b value which decays to premainshock values within a year surrounding areas of the aftershock zone show an approximately constant b value with time because the aftershock hazard after a mainshock depends strongly on both the b and p value we propose that aftershock hazard assessment can be improved by taking into account the spatial distribution of the parameters

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

earthquake hazard after a mainshock in california after a strong earthquake the possibility of the occurrence of either significant aftershocks or an even stronger mainshock is a continuing hazard that threatens the resumption of critical services and reoccupation of essential but partially damaged structures a stochastic parametric model allows determination of probabilities for aftershocks and larger mainshocks during intervals following the mainshock the probabilities depend strongly on the model parameters which are estimated with bayesian statistics from both the ongoing aftershock sequence and from a suite of historic california aftershock sequences probabilities for damaging aftershocks and greater mainshocks are typically well constrained after the first day of the sequence with accuracy increasing with time

talc bearing serpentinite and the creeping section of the san andreas fault the section of the san andreas fault located between cholame valley and san juan bautista in central california creeps at a rate as high as 28 mm yr 1 ref 1 and it is also the segment that yields the best evidence for being a weak fault embedded in a strong crust serpentinized ultramafic rocks have been associated with creeping faults in central and northern california and serpentinite is commonly invoked as the cause of the creep and the low strength of this section of the san andreas fault however the frictional strengths of serpentine minerals are too high to satisfy the limitations on fault strength and these minerals also have the potential for unstable slip under some conditions here we report the discovery of talc in cuttings of serpentinite collected from the probable active trace of the san andreas fault that was intersected during drilling of the san andreas fault observatory at depth safod main hole in 2005 we infer that the talc is forming as a result of the reaction of serpentine minerals with silica saturated hydrothermal fluids that migrate up the fault zone and the talc commonly occurs in sheared serpentinite this discovery is significant as the frictional strength of talc at elevated temperatures is sufficiently low to meet the constraints on the shear strength of the fault and its inherently stable sliding behaviour is consistent with fault creep talc may therefore provide the connection between serpentinite and creep in the san andreas fault if shear at depth can become localized along a talc rich principal slip surface within serpentinite entrained in the fault zone

clustering and periodic recurrence of microearthquakes on the san andreas fault at parkfield california the san andreas fault at parkfield california apparently late in an interval between repeating magnitude 6 earthquakes is yielding to tectonic loading partly by seismic slip concentrated in a relatively sparse distribution of small clusters 20 meter radius of microearthquakes within these clusters which account for 63 of the earthquakes in a 1987 92 study interval virtually identical small earthquakes occurred with a regularity that can be described by the statistical model used previously in forecasting large characteristic earthquakes sympathetic occurrence of microearthquakes in nearby clusters was observed within a range of about 200 meters at communication speeds of 10 to 100 centimeters per second the rate of earthquake occurrence particularly at depth increased significantly during the study period but the fraction of earthquakes that were cluster members decreased

asperity generating upper crustal sources revealed by b value and isostatic residual anomaly grids in the area of antofagasta chile in our study we show that the locations of largest coseismic slip asperities on the fault plane of the m w 8 0 1995 antofagasta earthquake in northern chile can be mapped by the spatial distribution of the seismic b value obtained from the aftershock sequence of the megathrust earthquake these areas of high seismic moment release and concurrent high b values are congruent with anomalies of the gravity isostatic residual ir field in the antofagasta region they are superimposed on the seismogenic part of the north chilean subduction zone where the strongest coupling of the upper and lower plate is expected the ir anomalies are interpreted to be caused by large jurassic early cretaceous batholiths which intruded into the upper crust the observed positive correlations between high seismic b values ir anomalies and geologic structures enable us to propose a mechanical model for the generation of the asperities in the antofagasta region we suggest that the batholiths in conjunction with buoyant forces acting on the subducted slab of the nazca plate are responsible for locking the interface where the asperities are located this implies long term conditions for the existence of the asperity generating tectonic situation concequently the asperities around antofagasta could be stationary features at least for several seismic cycles hence we propose that the ir anomalies along the north chilean convergent margin can be used as an indicator for high moment release and slip in future large earthquakes

distribution of seismicity across strike slip faults in california 1 the distribution of seismicity about strike slip faults provides measurements of fault roughness and damage zone width in california seismicity decays with distance from strike slip faults according to a power law 1 x2 d2 2 this scaling relation holds out to a fault normal distance x of 3 6 km and is compatible with a rough fault loading model in which the inner scale d measures the half width of a volumetric damage zone and the roll off rate is governed by stress variations due to fault roughness according to dieterich and smith s 2 d simulations approximates the fractal dimension of along strike roughness near fault seismicity is more localized on faults in northern california nocal d 60 20 m 1 65 05 than in southern california socal d 220 40 m 1 16 05 the parkfield region has a damage zone half width d 120 30 m consistent with the safod drilling estimate its high roll off rate 2 30 25 indicates a relatively flat roughness spectrum k 1 versus k 2 for nocal k 3 for socal our damage zone widths the first direct estimates averaged over the seismogenic layer can be interpreted in terms of an across strike fault core multiplicity that is 1 in nocal 2 at parkfield and 3 in socal the localization of seismicity near individual faults correlates with cumulative offset seismic productivity and aseismic slip consistent with a model in which faults originate as branched networks with broad multicore damage zones and evolve toward more localized lineated features with low fault core multiplicity thinner damage zones and less seismic coupling our results suggest how earthquake triggering statistics might be modified by the presence of faults

fracture process zone in granite a microstructural analysis shear fracture propagation in rock is accompanied by localized microcracking in a process zone surrounding the fracture tip we investigated the crack microstructures along experimentally formed shear fractures from four granite samples uniaxial compression tests five transects across a macroscopic fracture were inspected optically in transmitted light five hundred thirty two photomicrographs were taken from seven study areas along each transect we determined length width density and orientation of open cracks and their assignment to intra transgranular or grain boundary cracks crack density decreases with increasing distance to the macroscopic shear fracture and toward the fracture tip the highest crack densities correlate with the maximum number of acoustic emissions most cracks enclose a small angle 0 20 with the macroscopic shear fracture intragranular cracks are more abundant than transgranular and grain boundary cracks the number of transgranular cracks increases towards the macroscopic shear fracture but the number of grain boundary cracks decreases the decrease in crack density with increasing distance to the fault is accompanied by a change from strongly preferred crack orientation in the fault core to a random crack distribution away from the fault fracture process zone widths range from 2 1 0 8 mm ag51r to 5 6 1 9 mm ag18r the ratio of process zone width to fault length is approximately 0 04 0 07 this observation agrees with observations from natural fault zones the fracture surface energy ranges from 0 2 to 1 2 j this corresponds to 10 of the total strain energy

early carboniferous basins of the atlas meseta domain morocco sedimentary model and geodynamic evolution in the atlas meseta basins of morocco early carboniferous clastics comprise wave dominated shelf sediments turbidites and mass flow deposits crustal extension controlled the formation of troughs continental uplift and general marine subsidence sedimentation passed from turbidites into storm deposits the moroccan meseta formed a complex marine basin composed of deep troughs shallow shelves and islands the late visean marine transgression advanced from the north and reached as far south in the high atlas domain as the tizi n test fault zone the variscan compressive phase ended the early carboniferous sedimentation

spatial correlation of aftershock locations and on fault main shock properties 1 we quantify the correlation between spatial patterns of aftershock hypocenter locations and the distribution of coseismic slip and stress drop on a main shock fault plane using two nonstandard statistical tests test t1 evaluates if aftershock hypocenters are located in low slip regions hypothesis h1 test t2 evaluates if aftershock hypocenters occur in regions of increased shear stress hypothesis h2 in the tests we seek to reject the null hypotheses h0 aftershock hypocenters are not correlated with 1 low slip regions or 2 regions of increased shear stress respectively we tested the hypotheses on four strike slip events for which multiple earthquake catalogs and multiple finite fault source models of varying accuracy exist because we want to retain earthquake clustering as the fundamental feature of aftershock seismicity we generate slip distributions using a random spatial field model and derive the stress drop distributions instead of generating seismicity catalogs we account for uncertainties in the aftershock locations by simulating them within their location error bounds our findings imply that aftershocks are preferentially located in regions of low slip u umax and of increased shear stress 0 in particular the correlation is more significant for relocated than for general network aftershock catalogs however the results show that stress drop patterns provide less information content on aftershock locations this implies that static shear stress change of the main shock may not be the governing process for aftershock genesis

nucleation points of recent mainshocks in southern iceland mapped by b values the earthquake catalog in southern iceland between 20 25 w and 21 3 w is complete down to approximately mw 0 and shows no evidence for mag nitude shifts as a function of time since 1991 this means that 6902 earthquakes m 0 1 depth 20 km are available for studies of seismicity patterns preceding the two ms 6 6 mainshocks in 2000 in their source volumes and vicinity 20 25 w and 20 9 w the power law of the frequency magnitude relationship holds down to m0 detailed mapping including 3d mapping of the b value of the frequency magnitude distribution shows that variations from b 0 6 to 1 4 exist over distances of about 2 km this suggests that the tectonic fabric in southern iceland is hetero geneous on a small scale the hypocenters of the two ms 6 6 mainshocks and one additional m 4 5 mainshock are associated with low b values 0 6 0 8 statistically significantly different from volumes in their vicinity therefore one can expect future mainshocks in southern iceland to also emanate from volumes characterized by low b values however the small dimensions of these asperities may render it difficult to identify them before the mainshocks occur low values of estimated local recur rence times 500 2000 years map the two fault zones that ruptured in 2000 against a background of local recurrence times longer than 5000 years the first of the two m 6 6 mainshocks emanated from a volume of short estimated local recurrence time this supports the hypothesis that asperities with short local recurrence times control locations of major ruptures mapping of b values in cross sections shows anomalies of high b at the bottom of the seismogenic crust correlating with the change of its thickness in the middle of the study area these high b value anomalies and other pockets of such anomalies at shallower depths are best interpreted as caused by high pore pressure because evidence of fluids under high pressure is ubiquitous in this area

stable creeping fault segments can become destructive as a result of dynamic weakening faults in earth s crust accommodate slow relative motion between tectonic plates through either similarly slow slip or fast seismic wave producing rupture events perceived as earthquakes these types of behaviour are often assumed to be separated in space and to occur on two different types of fault segment one with stable rate strengthening friction and the other with rate weakening friction that leads to stick slip the 2011 tohoku oki earthquake with moment magnitude m w 9 0 challenged such assumptions by accumulating its largest seismic slip in the area that had been assumed to be creeping here we propose a model in which stable rate strengthening behaviour at low slip rates is combined with coseismic weakening due to rapid shear heating of pore fluids allowing unstable slip to occur in segments that can creep between events the model parameters are based on laboratory measurements on samples from the fault of the m w 7 6 1999 chi chi earthquake the long term slip behaviour of the model which we examine using a unique numerical approach that includes all wave effects reproduces and explains a number of both long term and coseismic observations some of them seemingly contradictory about the faults at which the tohoku oki and chi chi earthquakes occurred including there being more high frequency radiation from areas of lower slip the largest seismic slip in the tohoku oki earthquake having occurred in a potentially creeping segment the overall pattern of previous events in the area and the complexity of the tohoku oki rupture the implication that earthquake rupture may break through large portions of creeping segments which are at present considered to be barriers requires a re evaluation of seismic hazard in many areas

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

a generalized omori s law for earthquake aftershock decay 1 earthquake aftershock sequences have been found to approximately satisfy three empirical scaling relations i the gutenberg richter frequency magnitude scaling ii bath s law for the difference in the magnitude of a mainshock and its largest aftershock and iii the modified omori s law for the temporal decay of aftershock rates the three laws are incorporated to give a generalized omori s law for aftershock decay rates that depend on several parameters specific for each given seismogenic region it is shown that the characteristic time c first introduced in the modified omori s law is no longer a constant but scales with a lower magnitude cutoff and a mainshock magnitude the generalized omori s law is tested against earthquake catalogs for the aftershock sequences of the landers northridge hector mine and san simeon earthquakes

observations of premonitory acoustic emission and slip nucleation during a stick slip experiment in smooth faulted westerly granite 1 to investigate laboratory earthquakes stick slip events were induced on a saw cut westerly granite sample by triaxial loading at 150 mpa confining pressure acoustic emissions ae were monitored using an innovative continuous waveform recorder the first motion of each stick slip was recorded as a large amplitude ae signal these events source locate onto the saw cut fault plane implying that they represent the nucleation sites of the dynamic failure stick slip events the precise location of nucleation varied between events and was probably controlled by heterogeneity of stress or surface conditions on the fault the initial nucleation diameter of each dynamic instability was inferred to be less than 3 mm a small number of ae were recorded prior to each macro slip event for the second and third slip events premonitory ae source mechanisms mimic the large scale fault plane geometry

instability of deformation this chapter addresses the mechanisms by which instabilities can develop in rocks in the nominally ductile regime under conditions that the authors believe are relevant to earth we will not address brittle failure or frictional sliding processes in detail but much of our discussion will be couched in terms of knowledge gained in studies of these processes as a consequence we will begin by discussing why brittle failure and frictional sliding cannot be the mechanism by which rocks become unstable at depth despite the strong evidence that they are the underlying mechanism of earthquakes at shallow depths e g scholz 1990 2002 brittle shear failure in the normal sense is fundamentally a tensile process tensile microcracks must first nucleate and self organize via interaction of the stress concentrations at their tips as a consequence brittle failure and frictional sliding are strongly inhibited by pressure because work must be done against the pressure to open the mode i cracks the inhibition is so strong that the stress required to create a fault or initiate sliding on an existing fault becomes greater than the room temperature flow stress of many rocks at pressures equivalent to only a few tens of kilometers in earth increasing temperature has little effect on brittle processes but in contrast the ductile flow stress of rocks falls exponentially with temperature because both pressure and temperature increase with depth in earth earthquakes by unassisted brittle fracture mechanisms or frictional sliding can only occur at depths less than 30 50 km nevertheless earthquakes occur to depths of almost 700 km in earth and seismological evidence demonstrates unequivocally that they occur by displacement across a surface or narrow zone i e they occur by faulting this conundrum can be explained qualitatively by certain specific types of mineral reactions occurring under certain restricted conditions the

a comparison of seismicity characteristics and fault structure between stick slip experiments and nature fault zones contain structural complexity on all scales this complexity influences fault mechanics including the dynamics of large earthquakes as well as the spatial and temporal distribution of small seismic events incomplete earthquake records unknown stresses and unresolved fault structures within the crust complicate a quantitative assessment of the parameters that control factors affecting seismicity to better understand the relationship between fault structure and seismicity we examined dynamic faulting under controlled conditions in the laboratory by creating saw cut guided natural fractures in cylindrical granite samples the resulting rough surfaces were triaxially loaded to produce a sequence of stick slip events during these experiments we monitored stress strain and seismic activity after the experiments fault structures were imaged in thin sections and using computer tomography the laboratory fault zones showed many structural characteristics observed in upper crustal faults including zones of localized slip embedded in a layer of fault gouge laboratory faults also exhibited a several millimeter wide damage zone with decreasing micro crack density at larger distances from the fault axis in addition to the structural similarities we also observed many similarities between our observed distribution of acoustic emissions aes and natural seismicity the aes followed the gutenberg richter and omori utsu relationships commonly used to describe natural seismicity moreover we observed a connection between along strike fault heterogeneity and variations of the gutenberg richter b value as suggested by natural seismicity studies areas of low b value marked the nucleation points of large slip events and were located at large asperities within the fault zone that were revealed by post experimental tomography scans our results emphasize the importance of stick slip experiments for the study of fault mechanics the direct correlation of acoustic activity with fault zone structure is a unique characteristic of our laboratory studies that has been impossible to observe in nature

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

microearthquake imaging of the parkfield asperity microearthquake data from a downhole seismometer network on the san andreas fault appear to outline two aseismic asperities that may correspond to the locations of the foreshocks and main shocks of the parkfield characteristic earthquakes the source parameters of the microearthquakes show that a few of the earthquakes have significantly higher stress drops than most furthermore the magnitude frequency statistics suggest that at local magnitude 0 6 the cumulative number of small events begins to fall off the usual gutenberg richter b 1 relation in which the number of events increases exponentially with decreasing magnitude the downhole seismometer data establish a baseline from which the evolution of the earthquake process at parkfield can be monitored and suggest that different mechanical conditions than those that lead to the typical gutenberg richter relation may be operating for the smallest of parkfield microearthquakes

seismicity analysis through point process modeling a review the occurrence times of earthquakes can be considered to be a point process and suitable modeling of the conditional intensity function of a point process is useful for the investigation of various statistical features of seismic activity this manuscript summarizes likelihood based methods of analysis of point processes and reviews useful models for particular analyses of seismicity most of the analyses can be implemented by the computer programs published by the author and collaborators

waulsortian type bioherm development and response to sea level fluctuations upper visean of bechar basin western algeria abstract an exceptionally well developed and well preserved upper visean succession rich in sponge bryozoan crinoid mounds in the foreland carboniferous bechar basin northwestern algerian sahara is described and discussed the succession is composed of recurrent facies mosaics forming individual superposed members an ideal member is made up of two distinct fades assemblages the lower assemblage forms the actual mounds and is composed of sponge bafflestone wackestone at the base overlain by massive sponge fenestellid bafflestone wackestone and capped by massive crinoid wackestone with bedded flanks of lithoclastic wackestone in contrast to massiveness of the mounds the upper facies assemblage is composed of well bedded crinoid packstone grainstone and ooid grainstone with local rugose coral and algal foraminiferal banks on the basis of benthic assemblages and nature of substrate seven bathymetric zones are defined and indicate that each member of the bioherm rich formations is a shallowing upward parasequence controlled by an asymmetrical transgressive regressive cycle the local curve of relative sea level for the late visean shows 13 cycles interpreted as fourth order eustatic sea level changes each cycle averaging half a million years in duration third order cycles could not be identified the platform model proposed is a distally steepened ramp 15 20 km wide that developed in a rapidly subsiding foreland basin lateral distribution of facies on the ramp depended strongly on local tectonic setting whereas vertical development was controlled by sea level fluctuation the deep water mud rich sponge bryozoan crinoid mounds developed in 100 150 m water depths during phases of sea level highstand whereas deposition of shallow water facies occurred on top of the mounds in less than 70 80 m water depths during regressive phases the bechar mounds share similarities with the classical lower carboniferous waulsortian mounds but they differ in two aspects the abundance of large sponges which is unique and their vertical zonation wherein basal facies consist of sponge dominated assemblages the proposed model can serve as a tool in developing exploration strategies in the search for hydrocarbon reservoirs in the bechar basin because the peculiar architecture of the platform may provide suitable plumbing systems for fluid migration and the depositional signature of the mounds and associated facies is possibly recognizable on seismic profiles

trace elements and ree geochemistry of middle devonian carbonate mounds maider basin eastern anti atlas morocco implications for early diagenetic processes abstract trace and rare earth elements rees have proven their utility as tools for assessing the genesis and early diagenesis of widespread geological bodies such as carbonate mounds whose genetic processes are not yet fully understood carbonates from the middle devonian conical mud mounds of the maider basin eastern anti atlas morocco have been analysed for their ree and trace element distribution collectively the carbonates from the maider basin mud mounds appear to display coherent ree patterns three different geochemical patterns possibly related with three different diagenetic events include i dyke fills with a normal marine ree pattern probably precipitated in equilibrium with seawater ii mound micrite with a particular enrichment of overall ree contents and variable ce anomaly probably related to variation of ph increase of alkalinity or dissolution remineralization of organic matter during early diagenesis and iii haematite rich vein fills precipitated from venting fluids of probable hydrothermal origin our results reinforce the hypothesis that these mounds were probably affected by an early diagenesis induced by microbial activity and triggered by abundance of dispersed organic matter whilst venting may have affected the mounds during a later diagenetic phase

upper visean mississippian metazoan microbial reefs from guangxi south china insights regarding reef recovery after the end devonian extinction abstract the mississippian was an important interval for metazoan reef recovery after the collapse of stromatoporoid coral reef ecosystems during the late devonian mass extinctions based on field observation and quantitative studies of biotic composition in thin sections four different reef types were identified in the upper visean strata in the gandongzi section of guangxi province south china these are coral reef coral microbial microproblematica bryozoan reef coral microbial bryozoan reef and microbial bryozoan coral reef their positive topographic relief from one metre to ten metres is either directly observed in the section or by correlation to the coeval non reef facies in the adjacent longfeng section these reefs are constructed primarily of different proportion of colonial rugose corals diphyphyllum and siphonodendron tabulate corals multithecopora and syringopora cystoporate bryozoans fistulipora and calcimicrobes e g garwoodia and renalcis reef dwellers are rich and diversified including crinoids brachiopods bryozoans gastropods heterocorals calcispheres green algae foraminifers and ostracods their composition and abundance vary among the different reef types facies analysis reveals a variable composition including framestone and bindstone in reef facies and rudstone grainstone packstone dolomitic crinoidal packstone and dolostone in the strata intercalated with reefs the microbial reef facies is characterized by abundant spar filled cavities which can be classified as stromatactis and fenestral fabrics in the non reef facies geopetal structures are abundant relative sea level changes controlled the growth and demise of the gandongzi reefs they commonly grew during relative sea level rise and died during relative sea level fall as evident from increasing and decreasing abundance of micrite and decreasing and increasing abundance of cortoids green algae and sparry calcite in reefs and their overlying strata respectively however the final demise of the gandongzi reef succession was triggered by a dramatic relative sea level rise indicated by increased micrite abundance associated with articulated and convex down brachiopod shells overlying the uppermost reef the gandongzi reefs resemble coeval similar reef types on other palaeocontinents in terms of reef builder composition and internal structures the important role of corals in the framework building of the gandongzi reefs coincided with the late visean coral reef proliferation which is a major phase for re establishment of metazoan reef ecosystems after the end devonian mass extinction

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

common dependence on stress for the two fundamental laws of statistical seismology the gutenberg richter relation and the omori utsu law both power laws are two of the long standing relationships of statistical seismology here aftershock sequences are described according to the faulting style of their main shocks showing that the time delay before the onset of the power law aftershock decay rate is on average shorter for thrust main shocks than for normal fault earthquakes these similar dependences on the faulting style indicate that both the fundamental power laws are governed by the state of stress

mississippian coral assemblages from the khenifra area central morocco biostratigraphy biofacies palaeoecology and palaeobiogeography abstract analysis of mississippian coral assemblages from the khenifra region of central morocco together with data from foraminiferal algal microfossils has established new age dating of 5 localities within the azrou khenifra basin souk el had and sidi lamine where corals occur mainly in biostromes protected by oolitic shoals tabainout where corals have been recorded in different environments related to microbial mounds alhajra almatkouba where corals occur in biostromal reworked beds and tiouinine where corals occur in a well structured fringing reef this study demonstrates the presence of richer more diverse coral assemblages than previously recorded in a variety of environmental settings these coral assemblages strengthen correlations with the adarouch area in the ne part of the azrou khenifra basin it is emphasised that in the upper visean there are close similarities with rugose coral assemblages in other parts of the western palaeotethys including north africa sw spain and nw europe and that all belong to the same biogeographic province

the world s most spectacular carbonate mud mounds middle devonian algerian sahara abstract in the southern ahnet basin of algeria a unique middle devonian underwater scenery is revealed which consists of 191 mud mounds 15 mud ridges and 2 mud atolls distributed over nine discrete areas of a shallow pelagic carbonate shelf all the buildups are totally exhumed thus perfectly exhibiting their original morphologies slope angles elevations and the pattern of the onlapping strata as well as their relationship to the surrounding off buildup sequences types of buildups include 1 small mud mounds 1 5 m high 10 20 m diameter 2 large mud mounds up to 40 m high up to 200 m diameter 3 lens shaped mounds 1 30 m thick 10 15 slopes 4 mud ridges up to 100 m high 150 8500 m long and 5 semicircular mud atolls 2500 2800 m long 20 30 m high the buil ups were constructed during a short time span in the early givetian part of the lower varcus zone probably not exceeding a few hundred thousand years sedimentation rates in coeval off buildup areas were at least 3 10 times lower the lithology of the buildups is a massive boundstone with a high proportion of irregular spar filled cavities stromatactis but only very scattered potential frame builders the carbonate mud is considered to be an in situ cyanobacterial precipitate although evidence of such is poor organic components of the buildups are not significantly different from those of the off buildup lithologies and include numerous crinoid ossicles some tabulate and solitary rugose corals brachiopods mollusc debris trilobites and very rare sponge spicule and bryozoans the total absence of stromatoporoids large tabulate and colonial rugose corals green algae and micritic envelopes around grains suggests growth of the buildups in the lower part of the photic zone 100 200 m they are onlapped by a discontinuous sequence a few meters thick of skeletal packstones and grainstones and locally orthoceratid floatstones that were deposited later in the givetian a widespread rise of sea level in the early frasnian buried both buildups and adjacent areas under shales and siltstones postdepositional alteration of the mud buildups includes 1 formation of stromatactis cavities probably by dewatering and internal erosion 2 cementation of stromatactis cavities and interparticle pore spaces by early high mg calcite and late blocky low mg calcite 3 neomorphic transformation of mg calcitic mud and aragonitic skeletal debris 4 occasional formation of neptunian dikes 5 slight erosion of buildup surfaces 6 compaction and slumping of onlapping capping beds and 7 local dolomitization the formation and growth of the mud build ups is envisaged as a sequence of stages starting with patchy coral thickets evolving into small mud mounds that coalesced into larger mounds by continuous vertical and lateral growth closely spaced mounds amalgamated into mud ridges and mud atolls regular nw se and n s patterns of some mound rows and ridges show a relationship of buildup formation to rejuvenated late precambrian tectonic lineaments which reappear in the hercynian orogeny the isotopic signature of matrix and early ements of mound rocks however does not support the idea of fluid migration and hydrothermal co2 supply during buildup growth

fault slip rates at depth from recurrence intervals of repeating microearthquakes unique attributes in sequences of recurring similar microearthquakes at parkfield california provide a means for inferring slip rate at depth throughout the active fault surface from the time intervals between sequence events application of the method using an 11 year microseismicity record revealed systematic spatial and temporal changes in the slip rate that were synchronous with earthquake activity and other independent measures of fault zone slip if this phenomenon is found to be generally common behavior in active faults it forms the basis for a method to monitor the changing strain field throughout a seismogenic fault zone

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

fracture process zone in granite in uniaxial compression tests performed on aue granite cores diameter 50 mm length 100 mm a steel loading plate was used to induce the formation of a discrete shear fracture a zone of distributed microcracks surrounds the tip of the propagating fracture this process zone is imaged by locating acoustic emission events using 12 piezoceramic sensors attached to the samples propagation velocity of the process zone is varied by using the rate of acoustic emissions to control the applied axial force the resulting velocities range from 2 mm s in displacement controlled tests to 2 m s in tests controlled by acoustic emission rate wave velocities and amplitudes are monitored during fault formation p waves transmitted through the approaching process zone show a drop in amplitude of 26 db and ultrasonic velocities are reduced by 10 the width of the process zone is 9 times the grain diameter inferred from acoustic data but is only 2 times the grain size from optical crack inspection the process zone of fast propagating fractures is wider than for slow ones the density of microcracks and acoustic emissions increases approaching the main fracture shear displacement scales linearly with fracture length fault plane solutions from acoustic events show similar orientation of nodal planes on both sides of the shear fracture the ratio of the process zone width to the fault length in aue granite ranges from 0 01 to 0 1 inferred from crack data and acoustic emissions respectively the fracture surface energy is estimated from microstructure analysis to be 2 j a lower bound estimate for the energy dissipated by acoustic events is 0 1 j

implications for mechanical properties of brittle faults from observations of the punchbowl fault zone california field observations of the punchbowl fault zone an inactive trace of the san andreas are integrated with results from experimental deformation of naturally deformed punchbowl fault rocks for a qualitative description of the mechanical properties of the fault and additional information for conceptual models of crustal faulting the punchbowl fault zone consists of a single continuous gouge layer bounded by zones of extensively damaged host rock fault displacements were not only localized to the gouge layer but also to discrete shear surfaces within the gouge deformation in the exposure studied probably occurred at depths of 2 to 4 km and was dominated by cataclastic mechanisms textural data also suggest that significant amounts of pore fluids were present during faulting and that fluid assisted mechanisms such as dissolution diffusion and precipitation were operative the experimental data on specimens collected from the fault zone suggest that there is a gradual decrease in strength and elastic modulus and an increase in relative ductility and permeability toward the main gouge zone the gouge layer has fairly uniform mechanical properites and it has significantly lower strength elastic modulus and permeability than both the damaged and the undeformed host rock for the punchbowl fault and possibly other brittle faults the variations in loading of the gouge zone with time are primarily governed by the morphology of the fault and the mechanical properties of the damaged host rock in addition the damaged zone acts as the permeable unit of the fault zone and surrounding rock it appears that the gouge primarily governs whether displacements are localized and it therefore may have a significant influence on the mode of slip

temporal variations in seismicity during quasi static and dynamic rock failure abstract a comprehensive model is presented which can explain temporal fluctuations in seismic b values in the period leading to mechanical failure in terms of the underlying physical processes of time varying applied stress and stress corrosion enhanced crack growth under conditions of constant strain rate the form of the b value anomaly in the period leading to failure depends on the form of the stress time relationship for the case where dynamic failure occurs at peak stress after a period of strain hardening the model predicts a single cusp like b value anomaly reaching a critically low value of 0 5 at failure for the physically most realistic case where dynamic failure is preceded by a period of precursory strain energy release during strain softening the model predicts two minima in the b value separated by a temporary maximum or inflection point these fluctuations in the b value are consistent with reported intermediate term and short term earthquake precursors separated by a period of seismic quiescence for the case of quasi static cataclastic flow the b value mirrors the stress and never falls to the critical value because there is no critical rupture new results from a series of controlled laboratory experiments are presented in which microseismic event rates and b value were monitored contemporaneously with stress time data for all variants of the stress time relationship recent field observations of temporal changes in seismicity rates and b value preceding major earthquakes are also reported both data sets exhibit b value anomalies which are consistent with the model predictions

brittle ductile transition and associated seismicity experimental and numerical studies and relationship with the b value the acoustic emission ae and the mechanical behavior of granite samples during triaxial compression tests have been analyzed the size of ae events displays power law distributions conforming to the gutenberg richter law observed for earthquakes which is characterized by the b value as the confining pressure increases the macroscopic behavior becomes more ductile for all different stages of the rock mechanical behavior linear nonlinear prepeak nonlinear postpeak shearing there is a systematic decrease of the b value with increasing confining pressure a numerical model based on progressive elastic damage and the finite element method allows simulations of the main experimental observations on ae and of a wide range of macroscopic behaviors from brittleness to ductility the model reproduces a decrease in the b value that appears to be related to the type of macroscopic behavior brittle ductile rather than to the confining pressure both experimental and numerical results suggest a relationship between the b value and the brittle ductile transition moreover these results are consistent with recent earthquake observations and give new insight into the behavior of the earth s crust

a mid tournaisian late visean carbonate ramp reconstructed from nappes and olistolites in the southern montagne noire france abstract the mainly calcareous succession from the mid tournaisian to the lower part of the upper visean in the southern montagne noire mont peyroux nappes and cabrieres slices is sedimentologically revised from the late visean the variscan orogeny affected the area and the studied mississippian part of the succession was considered as part together with the devonian of a period of tectonic quiescence later included as nappes and olistolites in a wildflysch this study presents the facies from pelagic limestones calciturbidites bioclastic limestones and microbial limestones and the relationship between platform and calciturbidites in the pre orogenic context of the montagne noire basin during the mississippian the differences in the lithostratigraphy is analyzed by means of four tectonostratigraphical units mont peyroux nappe roquessels band cabrieres area and la serre band previously defined by other authors that together with the deep water vieussan caragnas unit not studied here due to the poverty in chronostratigraphical data allow reconstructing the original carbonate platform the latter seems to correspond to a ramp for the latest tournaisian to early visean and a distally steppened ramp from the middle visean to the early late visean including basin plain to slope as the deepest water environments and middle ramp as the shallowest except for the uppermost part of the succession where the inner ramp is recognized during this period the shallowing tendency in the tectonostratigraphic units is well marked mont peyroux nappe roquessels band cabrieres area la serre band from deeper to shallower which differs from the shallowing trend defined by previous authors during the devonian strong similarities are observed with the preserved mississippian carbonates in the mouthoumet massif to the south which might represent the shallowest water deposits of the ramp not preversed in the cabrieres la serre areas

most likely locations of large earthquakes in the kanto and tokai areas japan based on the local recurrence times abstract we examined the hypothesis that minima in local recurrence time tl or equivalently maxima in local probability pl may map asperities in the kanto and tokai areas of japan where the earthquake catalog of the national research institute for earth science and disaster prevention nied is complete at the m 1 5 m1 5 level we mapped tl pl based on the a and b values of the nearest earthquakes within 20 km of every node of a grid spaced 0 01 for m7 target events only earthquakes within the top 33 km were used the b values increase strongly with depth in several areas therefore some of the tl pl anomalies are not revealed if data from the entire crustal seismogenic zone are mixed thus we mapped tl pl separately for the top 15 km and the rest of the depth range as well as for the entire seismogenic crust the resulting tl and pl maps show that approximately 12 of the total area shows anomalously short recurrence times out of six shallow target events with m 6 5 and which occurred since 1890 five are located within the anomalous areas with tl

the structure of an exhumed intraplate seismogenic fault in crystalline basement abstract the 600 m thick gole larghe fault zone glfz is hosted in jointed crystalline basement and exposed across glacier polished outcrops in the italian alps ancient seismicity is attested by the widespread occurrence of cataclasites associated with pseudotachylytes solidified frictional melts formed at 9 11 km depth and ambient temperatures of 250 300 c previous work focused on the southern part of the fault zone here we quantitatively document fault zone structure across the full width of the glfz and surrounding tonalite host rocks by using a combination of structural line transects and image analysis of samples collected across fault strike these new datasets indicate that the glfz has a broadly symmetric across strike damage structure and contains distinct southern central and northern zones distinguished by large variations in fracture density distribution of pseudotachylytes volume of fault rock materials and microfracture sealing characteristics the c 100 m wide central zone is bound by two thick 2 m and laterally continuous 1 km protocataclastic to ultracataclastic horizons within and immediately surrounding the central zone fracture density is relatively high due to cataclastic fault fracture networks that reworked earlier formed pseudotachylytes the fault fracture networks were associated with pervasive microcracking and fluid rock interaction resulting in the development of a c 200 m thick alteration zone delimited by lobate fluid infiltration fronts in the c 250 m thick southern and northern zones fracture densities are much lower and pseudotachylytes systematically overprint cataclastic faults that exploited pre existing magmatic cooling joints analysis of the structure of the glfz suggests that it shares certain characteristics with the seismogenic source responsible for the 2002 au sable forks intraplate earthquake sequence in the northeastern usa including seismicity distributed across a fault zone 500 1000 m thick and large 100 mpa static stress drops associated with frictional melting

temporal variations in seismic event rate and b values from stress corrosion constitutive laws abstract main i g meredith p g and sammonds p r 1992 temporal variations in seismic event rate and b values from stress corrosion constitutive laws in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 233 246 a model is developed to characterise the state of damage for a fractal population of cracks in terms of a mean energy release rate g which depends on the stress the event rate n and the seismic b value n is assumed to be proportional to the total number of potentially active cracks and b to be proportional to the exponent d of the crack length distribution g is then positively correlated with n and negatively correlated with b consistent with experimental observation based on stress intensity as a constitutive variable the model predicts that higher b values are associated either with lower stress intensity or greater material heterogeneity both experiment and theory predict intermediate term seismic quiescence of similar magnitude to that observed in the field 45 90 for only a small simultaneous reduction in stress and stress intensity 2 7 or the equivalent mean energy release rate the theoretical model predicts three different types of quiescence associated with increasing constant or decreasing b value the first two are associated with stable intermediate term quiescence due to a reduction in g and the third is associated with unstable short term quiescence associated with constant or increasing g the theory can be used to infer relative changes in g from acoustic emissions in the laboratory experiments to date show that quiescence of the order 10 can be seen in the laboratory at strain rates of 10 5 s 1 but that this has the characteristics of short term rather than intermediate term quiescence