non parametric seismic hazard in mines seismic hazard analysis methods in mines are reviewed for the purpose of selecting the best technique to achieve this goal the most often used hazard analysis procedure which is based on the classical frequency magnitude gutenberg richter relation as well as alternative procedures are investigated since the maximum regional seismic event magnitude m max is of paramount importance in seismic hazard analysis this work provides a generic formula for the evaluation of this important parameter the formula is capable of generating solutions in different forms depending on the assumptions of the model of the magnitude distribution and or the available information regarding past seismicity it includes the cases i in which seismic event magnitudes are distributed according to the truncated frequency magnitude gutenberg richter relation and ii in which no specific model of the magnitude distribution is assumed both synthetic monte carlo simulated seismic event catalogues and actual data from the copper mine in poland and gold mine in south africa are used to demonstrate the discussed hazard analysis techniques our studies show that the non parametric technique which is independent of the assumed model of the distribution of magnitude provides an appropriate tool for seismic hazard assessment in mines where the magnitude distribution can be very complex

evaluation of paleomagnetism as a correlation criterion for mogollon datil ignimbrites southwestern new mexico paleomagnetic and rock magnetic data show that 36 24 ma ignimbrite outflow sheets in the mogollon datil volcanic field carry thermoremanent magnetizations trms that provide useful reliable correlation criteria over 90 of 404 ignimbrite sites exhibit well grouped 95 500 m intracaldera ignimbrite sequences agree in polarity with associated outflow sheets but show less consistent trm directions probably reflecting syncooling secular variation and discrepancies between eutaxitic foliations and the syncooling paleohorizontal mean virtual geomagnetic pole positions vgps of normal and reverse polarity ignimbrites are nearly antipodal 175 6 apart showing no evidence of long term differences in the zonal harmonics of the normal and reverse polarity states less antipodal mean vgps 161 2 apart from normal and reverse polarity lavas are interpreted as defects in the data set probably including incompletely removed normal polarity viscous overprints the mean paleomagnetic pole position for mogollon datil ignimbrites n 68 independent unit mean vgps is located at 78 8 n 166 6 e k 19 8 a95 4 0 18 2

subsurface imaging of the garlock fault cantil valley california imaging of the garlock fault from seismic reflection data tests tectonic models for the mojave desert region of southern california models developed from geologic and geodetic evidence of fault movement rates disagree on whether the garlock fault should dip north or south such models are further at odds with focal mechanism and dislocation analyses consistent with a vertical strike slip fault our analysis demonstrates a nonvertical southward dip for the garlock fault consortium for continental reflection profiling mojave line 5 collected seismic reflection data across the garlock in cantil valley where the 3 km deep cantil pull apart basin has developed between the southwest and east branches of the fault we analyze the reflection data for evidence of the fault s structure to 5 km depths garlock fault plane reflections on unprocessed shot gathers merge with the first arrival as the source progresses to the surface trace of the east branch explicitly tracing the garlock fault as a seismic reflector from depth to the mapped contemporary fault trace the apparent velocity of these reflections gives a 37 10 south dip for the east branch of the fault a prestack kirchhoff sum migration images the east branch reflector with a 45 south dip our migration process fully accounts for the bending of seismic rays through the strong lateral velocity variations in cantil basin the south dip of the garlock s east branch together with basement steps that decrease to the south suggest that cantil basin developed from a 0 4 1 mm yr component of extension normal to the fault development of the basin by detachment provides a mechanism to widen it as left lateral motion lengthens it allowing the pull apart to maintain the globally constant length to width ratio of 3 detachment by the garlock at cantil valley similarly requires 0 4 1 mm yr of dextral strike slip on a northwest striking fault such as the helendale that cuts the mojave between the garlock and pinto mountain faults such motion is consistent with regional tectonic models

the mechanics of continental transforms an alternative approach with applications to the san andreas system and the tectonics of california article i nfo displacement on intracontinental transforms is commonly distributed over a zone several hundred km wide and may incorporate large regions of transtensional and transpressional strain but no consensus exists on what controls the distribution and style of this deformation we model the transform boundary as a weak shear zone of finite length that exerts shear stress on the deformable continental lithosphere on either side strain rate decreases away from the shear zone on a scale related to its length force balance in this system requires lateral gradients in shear strain rate to be balanced by longitudinal gradients in stretching rates which create zones of lithospheric thickening and thinning distributed anti symmetrically about the shear zone simple analytical estimates two dimensional 2d spectral models and 2d 3d numerical models are employed to study the spatial scales and magnitudes of the zones of uplift and subsidence using reasonable parameter values the models yield geologically relevant rates strain rate components inferred from the gps determined 2 d velocity field and analysis of seismicity using kostrov s method taken together with the geological data on the distribution of active faults uplift and subsidence suggest that the distribution and rates of active deformation in california are consistent with our predictions this validates the assumptions of the continuum approach and provides a tool for predicting and explaining the tectonics of california and of other intracontinental transform systems

temporal variation of seismic b values beneath northeastern japan island arc 1 analysis of a high quality seismic catalog reveals that the average of seismic b values in the crust beneath most part of northeastern japan island arc decreased from 0 86 between 1984 and 1990 to 0 73 between 1991 and 1995 the two areas with the largest decrease are found to be in the same areas where the coupling between the north american and the pacific plates is the highest as suggested by a recent geodetic study in the same time period the annual seismic moment release increased by 10 times in addition there seems to be a corresponding increase in volcanic activities in the same area one of the most likely interpretations for the observations is an increase in the subduction rate starting from 1991 the timing of this possible increase in subduction rate is consistent with an apparent increase in global seismic activity

paleomagnetism and neogene clockwise rotation of the northern cady mountains mojave desert of southern california the early to middle miocene hector formation of the northern cady mountains consists of about 400 m of syntectonic alluvial fan and volcaniclastic sediments deposited in the central mojave desert paleomagnetic samples were collected from 60 sites throughout this unit samples from each site were treated using both alternating field and thermal demagnetization these studies and isothermal remanent magnetization experiments indicate that the natural remanent magnetization nrm is complex and that characteristic directions can be carried in either high coercivity or continuous unblocking temperature spectra depending upon the sample a positive reversals test and concordant directions of the alternating field af and low and high temperature components suggest a stable magnetization although a unique magnetostratigraphic correlation to the time scale is difficult the section studied may represent chrons c6b to c5c after screening of individual components and calculation of site means using fisher statistics 48 of the original 60 sites were used to calculate an overall formation mean direction i e declination 18 6 inclination 45 4 95 6 0 using a 20 m y paleomagnetic pole for north america irving and irving 1982 the hector formation has undergone 20 6 7 6 r r of clockwise rotation around a vertical axis this amount of rotation is considerably less than reported for some early miocene rocks elsewhere in the mojave block least squares regression of the 48 site mean declinations versus stratigraphic position indicates no trend throughout the section suggesting that there was no syndepositional rotation of this unit the late cenozoic structural history of the mojave block is considerably more complex than was originally believed and currently available paleomagnetic data indicate that many blocks within this region have experienced different degrees of rotation there were at least two phases of tectonic rotation in this region 1 early miocene about 25 ma probably related to the initiation of extension within the mojave rift and 2 post middle miocene pliocene between about 16 ma to the present possibly related to movement along principal structural features such as the san andreas fault zone the exact timing of the younger phase of tectonic activity cannot be better constrained until paleomagnetic data become available for late cenozoic rocks within the mojave block

paleomagnetism of middle miocene volcanic rocks in the mojave sonora desert region of western arizona and southeastern california paleomagnetic directions have been obtained from 190 early to middle miocene 12 20 ma mafic volcanic flows in 16 mountain ranges in the mojave sonora desert region of western arizona and southeastern california these flows generally postdate early miocene tectonic deformation accommodated by low angle normal faults but predate high angle normal faulting in the region after detailed demagnetization experiments 179 flows yielded characteristic directions interpreted as original thermal remanent magnetizations trm because of the episodic nature of basaltic volcanism in this region the 179 flows yielded only 65 time distinct virtual geomagnetic poles vgps the angular dispersion of the 65 vgps is consistent with the angular dispersion expected for a data set that has adequately averaged geomagnetic secular variation the paleomagnetic pole calculated from the 65 cooling unit vgps is located at 85 5 n 108 9 within a 4 4 circle of 95 confidence this pole is statistically indistinguishable at 95 confidence from reference poles calculated from rocks of similar age in stable north america and from a paleomagnetic pole calculated from rocks of similar age in baja california the coincidence of paleomagnetic poles from the mojave sonora desert region with reference poles from the stable continental interior indicates that 1 significant vertical axis net tectonic rotations have not accompanied post middle miocene high angle normal faulting in this region 2 there has been no detectable post middle miocene latitudinal transport of the region and 3 long term nondipole components of the middle miocene geomagnetic field probably were no larger than those of the recent 0 5 ma geomagnetic field in contrast paleomagnetic data indicate vertical axis rotations of similar age rocks in the transverse ranges the eastern transverse ranges and the mojave block we speculate that a major structural discontinuity in the vicinity of the southeastward projection of the death valley fault zone separates western areas affected by vertical axis rotations from eastern areas that have not experienced such rotations

seismicity on tidally active solid surface worlds tidal interactions between planets or stars and the bodies that orbit them dissipate energy in their interiors the dissipated energy heats the interior and a fraction of that energy will be released as seismic energy here we formalize a model to describe the tidally driven seismic activity on planetary bodies based on tidal dissipation to constrain the parameters of our model we use the seismic activity of the moon driven by tidal dissipation from the earth moon interactions we then apply this model to predict the amount of seismic energy release and largest seismic events on other moons in our solar system and exoplanetary bodies we find that many moons in the solar system should be more seismically active than the earth s moon and many exoplanets should exhibit more seismic activity than the earth finally we examine how temporal spatial variations in tidal dissipation manifest as variations in the locations and timing of seismic events on these bodies

seismic moment distribution revisited i statistical results summary an accumulation of seismic moment data gathered over the previous decade justifies a new attempt at a comprehensive statistical analysis of these data herein more rigourous statistical techniques are introduced their properties investigated and these methods are employed for analysis of large modern data sets several theoretical distributions of earthquake size seismic moment frequency relations are described and compared we discuss the requirements for such distributions and introduce an upper bound or a corner moment for a distribution to have a finite energy or moment flux we derive expressions for probability density functions and statistical moments of the distributions we also describe parameter evaluation in particular how to estimate the seismic moment distribution for the largest earthquakes simulating earthquake size distributions allows for a more rigourous evaluation of distribution parameters and points to the limitations of the classical statistical analysis of earthquake data simulations suggest that several earthquakes approaching or exceeding the corner magnitude mc limit need to be registered to evaluate mc with reasonable accuracy using the harvard catalogue data we compare moment distribution parameters for various temporal spans of the catalogue for different tectonic provinces and depth ranges and for earthquakes with various focal mechanisms the statistical analysis suggests that the exponent b is universal b 0 60 0 65 for all moderate earthquakes the corner moment mc value determined by the maximum likelihood method both in subduction zones and globally is about 10 21 n m corresponding to the corner moment magnitude mc 8 0 for midoceanic earthquakes mc is apparently smaller for spreading ridges it is about 5 8 and for strike slip earthquakes on transform faults it decreases from 7 2 to 6 5 as the relative slip velocity of faults increases we investigate the seismic moment errors both random and systematic and their dependence on earthquake size the relative errors seem to decrease for larger events the influence of moment uncertainties on the parameter estimates is studied whereas the b values do not appear to be significantly influenced by the errors for the corner moment large errors can lead to substantially biased estimates we compare the harvard catalogue results with the earthquake data from instrumental catalogues in the first three quarters of the 20th century several very large earthquakes mi9 occurred around the middle of the century their magnitude values cannot be fitted by a modified gutenberg richter law with mc 8 0 8 5 among other factors this discrepancy can be explained by either substantially higher errors in the earlier magnitude values or by mc being higher for some subduction zones it is unlikely that data available presently or soon will be sufficient to determine the corner magnitude of 9 and above with reasonable precision using purely statistical methods

cooperative joint inversion of 3d seismic and magnetotelluric data with application in a mineral province abstractthe integration of different geophysical data has the potential to provide more accurate estimate of subsurface rock properties several methodologies and attempts have been developed over the years with the objective of reducing exploration risk we have developed a cooperative joint inversion approach intended to facilitate recovery of acoustic impedance ai using seismic and magnetotelluric mt data in this approach the mt data provided a pathway for iteratively building large scale low frequency information content not directly recoverable from the seismic data themselves the mt data provided complementary information to seismic especially in seismically complex terrains such as overthrust belts subbasalt and subsalt carbonate reefs or for targets below deep cover containing limestone concretionary layers or basalt on the other hand the seismic data provided structural information necessary to derive accurate resistivity models from mt inversion and small scale features during seis

advances in velocity model building technology for subsalt imaging seismic imaging of hydrocarbon accumulations below salt is a formidable challenge because complexly shaped salt bodies severely distort wavefronts or scatter seismic energy we have highlighted some recent advances in building a velocity model for subsalt imaging there are three main stages suprasalt velocity determination salt model definition and subsalt velocity update volumetric high resolution tomography that incorporates high velocity contrast boundaries is used to derive a good sediment velocity model before building a salt model to facilitate integration of interpretation and depth processing beam based interactive imaging is used to refine the salt geometry for subsalt velocity update either subsalt tomography or subsalt scan based techniques can be used depending on the quality of subsalt reflections there are concepts and techniques for attaining subsalt images suitable for hydrocarbon exploration beneath complexly shaped salt bodies

on the probability of detecting picoseismicity estimation of the recording completeness of seismic catalogs recorded with small networks in a heterogeneous observation volume for example in mines is difficult local heterogeneities have a strong influence on the wave path and attenuation and must be taken into account in order to analyze the spatially varying completeness of such catalogs in three dimensions we present a new approach based on the probability based magnitude of completeness pmc method of schorlemmer and woessner 2008 we demonstrate that the traditional approach of schorlemmer and woessner 2008 is insufficient in very complex and heterogeneous settings to account for this problem we extend the pmc method taking into account the direction of incoming seismic waves this allows us to analyze the influence of small heterogeneities on the recording completeness in high resolution we compare the results with results obtained by a traditional gutenberg richter frequency magnitude analysis for the jaguars catalog the japanese german underground acoustic emission research in south africa jaguars project recorded approximately 500 000 seismic events with magnitudes 5 m w 1 in the mponeng gold mine carletonville south africa at 3 5 km depth the network is surrounded by several cavities and is located partly in the pink green dike a local geological feature we estimate that the completeness of the jaguars catalog varies significantly in space in the center of the network we estimate a magnitude of completeness of m p 4 8 whereas at stope level approximately 100 m from the network the magnitude of completeness is only m p 3 1 variations due to the influence of local heterogeneities for example tunnels are clearly resolvable

bayesian estimation of the spatially varying completeness magnitude of earthquake catalogs assessing the completeness magnitude mc of earthquake catalogs is an essential prerequisite for any seismicity analysis we employ a simple model to com putemc inspacebasedontheproximitytoseismicstationsinanetwork weshowthata relationship of the form m predd ad bc with d the distance to the kth nearest seismic station fits the observations well k depending on the minimum number of stations being required to trigger an event declaration in a catalog we then propose anewmc mappingapproach thebayesianmagnitude ofcompleteness bmc method based on a two step procedure 1 a spatial resolution optimization to minimize spatial heterogeneities and uncertainties in mc estimates and 2 a bayesian approach that merges prior information about mc based on the proximity to seismic stations with locally observed values weighted by their respective uncertainties contrary to the cur rentmc mappingprocedures theradiusthatdefineswhichearthquakestoincludeinthe local magnitude distribution is chosen according to an objective criterion and there are no gaps in the spatial estimation of mc the method solely requires the coordinates of seismic stations here we investigate the taiwan central weather bureau cwb seismic network and earthquake catalog over the period 1994 2010

integrating basin modeling with seismic technology and rock physics we explore the link between basin modelling and seismic inversion by applying different rock physics models this study uses the e dragon ii data in the gulf of mexico to investigate the impact of different rock physics models on the link between basin modelling and seismic inversion we first model relationships between seismic velocities and both 1 porosity and 2 effective stress for well log data using published rock physics models then we build 1d basin models to predict seismic velocities derived from basin modelling with different rock physics models in a comparison with average sonic velocities measured in the wells finally we examine how basin modelling outputs can be used to aid seismic inversion by providing constraints for the background low frequency model for this we run different scenarios of inverting near angle partial stack seismic data into elastic impedances to test the impact of the background model on the quality of the inversion results the results of the study suggest that the link between basin modelling and seismic technology is a two way interaction in terms of potential applications and the key to refine it is establishing a rock physics models that properly describes changes in seismic signatures reflecting changes in rock properties

the nature of the landers mojave earthquake line the landers california earthquake of 28 june 1992 magnitude 7 3 is the latest of six significant earthquakes in the past 60 years whose epicenters and slip directions define a 100 kilometer alignment running approximately n15 w across the central mojave region this pattern may indicate a geologically young throughgoing fault that replaces numerous older strike slip faults by obliquely cutting across them these older faults and perhaps also the bend in the san andreas fault may be losing their ability to accommodate upper crustal deformation because they have become unfavorably oriented with respect to the regional stress field

a new method for the estimation of the completeness magnitude abstract the estimation of the magnitude of completeness m c have strong consequences in any statistical analysis of seismic catalogue and in the evaluation of the seismic hazard here a new method for its estimation is presented the goodness of the method has been tested using 10 4 simulated catalogues then the method has been applied to five experimental seismic catalogues greece italy japan northern california and southern california

improving the estimation of detection probability and magnitude of completeness in strongly heterogeneous media an application to acoustic emission ae summary reliable estimations of magnitude of completeness mc are essential for a correct interpretation of seismic catalogues the spatial distribution of mc may be strongly variable and difficult to assess in mining environments owing to the presence of galleries cavities fractured regions porous media and different mineralogical bodies as well as in consequence of inhomogeneous spatial distribution of the seismicity we apply a 3 d modification of the probabilistic magnitude of completeness pmc method which relies on the analysis of network detection capabilities in our approach the probability to detect an event depends on its magnitude source receiver euclidian distance and source receiver direction the suggested method is proposed for study of the spatial distribution of the magnitude of completeness in a mining environment and here is applied to a 2 months acoustic emission ae data set recorded at the morsleben salt mine germany the dense seismic network and the large data set which includes more than one million events enable a detailed testing of the method this method is proposed specifically for strongly heterogeneous media besides it can also be used for specific network installations with sensors with a sensitivity dependent on the direction of the incoming wave e g some piezoelectric sensors in absence of strong heterogeneities the standards pmc approach should be used we show that the pmc estimations in mines strongly depend on the source receiver direction and cannot be correctly accounted using a standard pmc approach however results can be improved when adopting the proposed 3 d modification of the pmc method our analysis of one central horizontal and vertical section yields a magnitude of completeness of about mc 1 ae magnitude at the centre of the network which increases up to mc 4 at further distances outside the network the best detection performance is estimated for a nne sse elongated region which corresponds to the strike direction of the low attenuating salt body our approach provides us with small scale details about the capability of sensors to detect an earthquake which can be linked to the presence of heterogeneities in specific directions reduced detection performance in presence of strong structural heterogeneities cavities is confirmed by synthetic waveform modelling in heterogeneous media

cenozoic crustal rotations in the mojave desert from paleomagnetic studies around barstow california paleomagnetic data from the mojave desert around barstow california suggest 55 to 75 of clockwise rotation of this area in earliest miocene time followed by 23 of counterclockwise rotation in the early miocene and no rotation after 18 ma earliest miocene clockwise rotation of the barstow area is suggested by data from nine sites in the oligocene miocene lane mountain quartz latite and jackhammer formation and may be related to oroclinal bending of the southern sierra nevada batholith data from 13 sites in the early miocene pickhandle formation indicate counterclockwise rotation which coincides with early miocene e ne w sw extension and detachment faulting in the mojave desert other parts of the mojave desert experienced variable senses and amounts of rotation at this time which may be related to drag along transfer zones within the upper plate while the lower plate was not rotated these results suggest that miocene extension in the mojave desert is related to similarly oriented extension in the colorado river extensional corridor early miocene to pliocene rocks of the andesite and dacite of the calico mountains barstow formation andesite of murphy s well and black mountain basalt show no evidence for significant rotation of the barstow area after 18 ma most other paleomagnetic data from elsewhere in the mojave are consistent with a lack of significant post 18 ma rotations suggesting that post 10 ma right lateral faulting there has produced relatively little crustal rotation the exception to this generalization is the northeast corner of the mojave desert which underwent substantial post 18 ma clockwise rotation paleomagnetic flattening data also indicate that post oligocene n s translation of crustal blocks in the mojave desert has been insignificant

near field response to transpression along the southern san andreas fault based on exhumation of the northern san gabriel mountains southern california 1 near field mountain building is common along transpressive faults but how vertical deformation relates to oblique plate motion versus local structural complexity has not been universally established we have investigated the mechanisms of exhumation along the southern san andreas fault in the northern san gabriel mountains to examine the effects of pure shear dominated transpression obliquity 20 although rugged topography suggests near field uplift low temperature thermochronometry indicates minimal exhumation apatite u th he ages are 10 ma along narrow ridges within the fault zone implying near field rock uplift is not pervasive along this oblique plate boundary ages farther from the fault are younger 5 ma and suggest a deformation event occurred during the transition of activity from the san gabriel fault to the modern san andreas strand these results reveal a heterogeneous crustal response to transpression and imply that secondary structures or geometrical complexities play a primary role in near field bedrock uplift along transpressive faults

seismicity in deep gold mines of south africa implications for tectonic earthquakes we have studied induced seismicity associated with five deep gold mines located in the far west rand district republic of south africa focusing on the digital data recorded from january 1994 until february 2000 by in mine arrays of three component geophones the observed seismicity which exceeds 1 000 events per day can be divided into two kinds of events designated as types a and b type a events are tightly clustered in time and space and generally occur within 100 m of an active mining face or development tunnel their spectra are comparatively enriched in high frequencies and they have an upper moment magnitude cutoff at mmax 1 we associate these events with the fracture dominated rupture of com petent rock induced by dynamic stresses during blasting and quasi static stress per turbations from the excavation and closure of individual stopes in contrast type b events are temporally and spatially distributed throughout the active mining region they represent friction dominated slip in existing shear zones such as faults or dikes and have source scaling properties that agree well with extrapolations from tectonic earthquakes in the far west rand region type b events can have large magnitudes m 3 but they show a distinct lower magnitude cutoff at mmin 0 we interpret this cutoff in terms of a critical patch size for nucleation of shear failure and we show that the data are consistent with a rate and state dependent friction model in which the critical slip distance d c 10 4 m both the spectral predictions of this model and accelerograms of type b events agree that f max 200 hz

rapid acceleration leads to rapid weakening in earthquake like laboratory experiments after nucleation a large earthquake propagates as an expanding rupture front along a fault this front activates countless fault patches that slip by consuming energy stored in earth s crust we simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel the spontaneous evolution of strength acceleration and velocity indicates that our experiments are proxies of fault patch behavior during earthquakes of moment magnitude mw 4 to 8 we show that seismically determined earthquake parameters e g displacement velocity magnitude or fracture energy can be used to estimate the intensity of the energy release during an earthquake our experiments further indicate that high acceleration imposed by the earthquake s rupture front quickens dynamic weakening by intense wear of the fault zone

introduction to this special section low frequency seismic geophysicists in the seismic exploration industry have long recognized the potential benefits of extending the bandwidth of seismic measurements to well below 10 hz low frequencies generated by a seismic shot travel much farther through the subsurface than do higher frequencies just as the low frequencies in thunder travel farther in the atmosphere thus the amount of power available in the low end of the seismic spectrum is especially important for deep exploration targets such as subsalt and sub basalt plays and for deep crustal studies in many areas of the world higher frequencies are often too attenuated scattered and dispersed to provide useful signal for probing such objectives also low frequencies play a critical role in the inversion process by which seismic data are converted into acoustic impedance sections and ultimately into reservoir properties surface seismic data usually lack low frequencies necessary for accurate inversion so they are commonly augmented by data from well log me

analysis of temporal and spatial heterogeneity of magnitude frequency distribution inferred from earthquake catalogues summary statistical models are introduced for the simultaneous estimation of the changes of the b value and detection rate of earthquakes in a catalogue which develops in time or varies in space the three characteristic parameters including b for the magnitude frequency distribution of detected earthquakes are represented by respective three b spline functions of time or location in a space an objective bayesian method is adopted for the optimal estimate of such functions with many unknown coefficients the present procedure is applied to earthquake catalogues for japanese seismic activity

theoretical limits on detection and analysis of small earthquakes we investigate theoretical limits on detection and reliable estimates of source characteristics of small earthquakes using synthetic seismograms for shear tensile dislocations on kinematic circular ruptures and observed seismic noise and properties of several acquisition systems instrument response sampling rate simulated source time functions for shear tensile dislocation events with different magnitudes static stress drops and rupture velocities provide estimates for the amplitude and frequency content of p and s phases at various observation angles the source time functions are convolved with a green s function for a homogenous solid assuming given p s wave velocities and attenuation coefficients and a given instrument response the synthetic waveforms are superposed with average levels of the observed ambient seismic noise up to 1 khz the combined seismograms are used to calculate signal to noise ratios and expected frequency content of p and s phases at various locations the synthetic simulations of signal to noise ratio reproduce observed ratios extracted from several well recorded data sets the results provide guidelines on detection of small events in various geological environments along with information relevant to reliable analyses of earthquake source properties

moment tensors of ten witwatersrand mine tremors ground motions recorded both underground and on the surface in two of the south african gold mining districts were inverted to determine complete moment tensors for 10 mining induced tremors in the magnitude range 1 9 to 3 3 the resulting moment tensors fall into two separate categories seven of the events involve substantial coseismic volumetric reduction v together with normal faulting entailing shear deformation ad where the summation is over fault planes of areaa and average slipd for these events the ratio v ad ranges from 0 58 to 0 92 with an average value of 0 71 for the remaining three events v is not significantly different from zero these events are largely double couple sources involving normal faulting surprisingly the two types of source mechanism appear to be very distinct in that there is not a continuous distribution of the source mix from v 0 to v ad presumably the coseismic closure indicates substantial interaction between a mine stope and adjacent shear failure in the surrounding rock under the influence of an ambient stress for which the maximum principal stress is oriented vertically

paleomagnetic evidence that the central block of salinia california is not a far traveled terrane new paleomagnetic results from late cretaceous 75 85 m y red beds on the central block of salinia indicate that salinia was located within 6 in latitude of its current cratonal north american position during the late cretaceous after correction for neogene san andreas fault transport the red beds formed as alluvial fan overbank deposits with hematite cement deposited directly on salinian granites in the la panza range paleomagnetic analysis shows two components of magnetization in the red beds a low blocking temperature present day overprint residing in goethite and a high blocking temperature 600 component residing in hematite the hematite magnetization is a chemical remanent magnetization which formed soon after deposition during pedogenesis the bedding corrected hematite remanence contains a magnetic polarity stratigraphy with antipodal normal and reversed directions twenty three class i sites 95 20 have an average hematite direction with inclination 54 4 and declination 18 2 95 6 1 after structural correction these paleomagnetic data suggest that salinia resided at about 35 n latitude during the late cretaceous within 6 of its current location adjacent to cratonal north america by contrast a summary of paleomagnetic data from the peninsular ranges terrane and the sur obispo terrane which are currently outboard of salinia shows northward transport of these terranes of 12 to 22 relative to their current locations in north america since the cretaceous the offsets increase systematically away from the craton with the most outboard sur obispo terrane which is composed of accretionary prism and distal forearc material showing the largest degree of northward translation

the use of pseudorandom sweeps for vibroseis surveys pseudorandom vibroseis sweeps have long been suggested as an alternative to standard linear sweeps due to their potential for having superior orthogonality a lower likelihood for infrastructure damage and increased low frequency content in the past they were also attractive as they have a better autocorrelation shape although that is less important today their use has been limited but the increasing popularity of simultaneous acquisition techniques has rekindled interest as they offer the ability to reduce interference noise a wide variety of methods for generating pseudorandom sweeps have been developed over the last 45 years this paper gives an overview of the motivations for their use before classifying and describing the different sweep types finally the sweeps will be compared in terms of their major attributes including their suitability for simultaneous surveys

geogas transport in fractured hard rock correlations with mining seismicity at 3 54 km depth tautona gold mine south africa abstract an on site gas monitoring study has been conducted in the framework of an earthquake laboratory the international nelsam dafgas projects at the tautona gold mine south africa five boreholes up to 60 m long were drilled at 3 54 km depth into the highly fractured pretorius fault zone and instruments for chemical and seismic monitoring installed therein over the span of 4 years sensitive gas monitoring devices were continuously improved to enable the direct observation of geogas concentration variations in the dafgas borehole the major gas concentrations are constant and air like with about 78 n 2 21 o 2 1 ar the geogas components co 2 ch 4 he and h 2 show the most interesting trends and variations on the minute by minute basis and significantly correlate with seismic data while the 222 rn activity remains constant time series and cross correlation analysis allow the identification of different gas components geogas and tunnel air and the identification of two processes influencing the borehole gas composition 1 pumping induced tunnel air breakthrough through networks of initially water saturated fault fractures and 2 seismicity induced permeability enhancement of fault fractures to above 5 10 10 m 2 the current set up of the gas monitoring system is sensitive enough to quantify the resulting geogas transport during periods of intense blasting activities including recorded blasts with seismic moment 1 10 9 nm located within 1000 m of the cubby and it is suggested also during induced earthquakes a final goal of the project

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

hot faults iridescent slip surfaces with metallic luster document high temperature ancient seismicity in the wasatch fault zone utah usa and localized iridescence in the footwall dam age zone of the wasatch fault utah usa and document elevated temperatures on these faults we propose that the formation of these iridescent slip surfaces requires frictional heat generated at geometric asperities at seismic slip rates wasatch fault zone abstract we document new geological indicators of ancient seismicity in the form of highly reflec tive iridescent hematite coated fault surfaces small faults that cut the paleoproterozoic farmington canyon complex in the footwall damage zone of the brigham city segment of the wasatch fault utah usa are smooth to striated surfaces tens of square centimeters to 30 m 2 in area the dull rusty to high metallic luster and moderate to high gloss surfaces exhibit multicolored elliptical iridescent patches 0 5 3 cm across preexisting hematite crystals were deformed during slip on 1 200 mm thick slip surfaces textural observations x ray diffraction x ray photoelectron spectroscopy electron backscattered diffraction analysis surface metrology and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high temperature 300 c reduction of iron fe 3 to fe 2 and associated conversion of hematite to magnetite we pro pose that the iridescent slip surfaces in the wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults the thousands of these sur faces represent coseismic or aftershock deformation down to magnitude 3 in the exhumed footwall damage zone of the wasatch fault

magnitude frequency relation for small earthquakes a clue to the origin of ƒmax of large earthquakes in order to test the hyothesis that the max of large earthquakes is due to the source effect and is causally related to the corner frequency of small earthquakes when it becomes constant below magnitude about 3 we constructed the frequency magnitude relation for earthquakes with magnitude range from 1 3 to 4 recorded at a borehole seismograph station operated by the university of southern california at baldwin hills in the middle of the newport inglewood fault a procedure was developed for an accurate estimation of moment magnitude from the measurement of coda amplitude as a function of lapse time the cumulative number of earthquakes per unit time period and area was estimated by finding the detection limit for ts p for each magnitude we found a clear depature of the observed log frequency magnitude relation for m 3 the observed frequency of earthquakes with m 0 5 is almost 10 times less than that expected from the extrapolation of empirical relation for earthquakes with magnitudes larger than 3 we conclude that the observed frequency magnitude relation departs from self similarity for earthquakes with magnitude smaller than about 3 this departure coincides with the widely observed departure of the moment corner frequency relation from self similarity these observations are consistent with the interpretation of max of large earthquakes in terms of the slip weakening instability model in which the critical slip may be a few tenths of a meter to a few meters and the cohesive zone size may be a few hundred meters to a few kilometers

quasi static fault growth and cracking in homogeneous brittle rock under triaxial compression using acoustic emission monitoring this paper describes the localization of deformation acceleration in the period prior to dynamic failure in hornblende schist rock under triaxial compression using acoustic emission ae monitoring rather than stabilize the failure process by controlling axial stress to maintain a constant rate of ae for monitoring ae hypocenters as in previous works e g lockner et al 1991 we have instead developed a rapid multichannel data collection system this enables us to elucidate the dynamics of fault nucleation under condition of constant stress creep loading which is a better approximation to low strain rate condition in the earth and allows both quasi static and dynamic crack growth to occur the waveforms of more than 8000 ae events which occurred mainly during a 15 s period were recorded on 32 channels with a sampling rate of 50 ns and mask time of 200 s hypocentral locations of ae sources revealed that the fault initiated at one end of the core and then propagated into the unfaulted rock with a process zone fault front of intense cracking we found that there were two different processes operating during the quasi static nucleation of a shear fault namely a process zone in front of the fault tip and a wake of damage zone following the process zone the process zone had the following features 1 major tensile cracking 2 low b value and fewer larger events and 3 strong self excitation the mechanism of crack interaction and fault growth was therefore a mutual enhancement on dilatation due to tensile cracking on the other hand the damage zone was characterized by 1 major shear cracking 2 low b value and more larger events and 3 weak self excitation indicating that in the damage zone following the development of a shear fault linkage between cracks became the major mechanism of crack interaction and fault development the mutual changes of b value and self exciting strength observed in our experiments seem to occur as a result of the hierarchy of fault growth which was not observed under slowed down loading conditions therefore our experimental results under a realistic approximation of the dynamic condition of the earth are meaningful for the problems of earthquakes as well as rock bursts

detachment and rotation of a metamorphic core complex during extensional deformation palaeomagnetic study of the catalina rincon core complex basin and range province arizona abstract the catalina rincon complex exposes a metamorphic core of mid crustal rocks exhumed by extensional tectonism along a major detachment exposed along the southeast side of the catalina rincon mountains near tucson arizona the juxtaposition of core complexes against high level crust segmented into rotated and tilted fault blocks is an important component to models for crustal extension and key questions surround the way s that cores are exhumed we report palaeomagnetic results from rocks beneath the detachment in the catalina rincon core and additional data from lavas and tuffs in adjoining hanging wall rocks immediately above the detachment magnetic remanence in the metamorphic core is carried predominantly by magnetite with a dominant wnw ese dual polarity direction a1 d i 288 50 n 59 components r 55 60 95 4 6 this remanence is interpreted to have been acquired through a broadened blocking temperature spectrum during protracted exhumation and cooling in oligocene times since the magnetic inclination accords with the mid cenozoic field it is difficult to explain this magnetization in terms of large later tilting and it appears to be the record of near vertical axis ccw rotation of 63 5 relative to cratonic north america although magnetic inclination identifies no significant horizontal axis rotation this could be fortuitous and hide the influence of magnetic anisotropy and resultant inclination shallowing to assess this contribution both anisotropy of magnetic remanence amr and anisotropy of magnetic susceptibility ams have been investigated ams resolves only weak fabrics comparable with the top ne mylonite deformational fabric near the detachment which probably dates from a mid eocene high temperature event amr shows that deflections of magnetic remanence of up to several tens of degrees into the foliation may be anticipated although weak alignment of the magnetite is likely to reduce this effect the full importance of horizontal axis tilting remains unresolved although a possible relict component in the core a2 d i 269 9 n 24 components r 22 91 95 6 6 is rotated 20 more ccw than a1 and also of presumed mid cenozoic cooling related origin it suggests that segments of middle crust comprising the exposed core might have been rotated by large amounts into their present position highly faulted early oligocene pantano formation volcanic rocks in the hanging wall immediately above the detachment zone appear to have rotated by a much smaller amount ccw on the south west side d i 161 45 6 sites and by larger variable amounts on the northeast side movements of the upper plate immediately above the detachment are difficult to resolve with precision due to complex fault block rotations although the underlying core complex has clearly undergone large differential slip relative to these cover rocks the magnitude of inferred vertical axis rotation of the catalina rincon core implies that it is not rooted into adjoining crust as proposed in classical simple shear models instead the core exposed below the detachment may be part of a fault carapace that has decoupled and rotated over a ductile lower crust

fine scale partitioning of contemporary strain in the southern walker lane implications for accommodating divergent strike slip motion treating the crust as a micropolar continuum and inverse modeling a high quality catalog of earthquake focal mechanisms reveals that km scale heterogeneous strain is partitioned at km scales into pairs of plane strains with sub perpendicular principal axes these earthquakes occurred in a shallow crustal volume centered on the western indian wells valley of eastern california the site of divergent right lateral strike slip motion along the boundary between the sierran microplate and the southern basin and range province the seismic events defining the plane strains occur in a diffuse seismic source zone and cannot be additionally subdivided on the basis of the type of strain they accommodate the results indicate that seismic moment release for background earthquakes is partitioned into events associated with either fault zone perpendicular extension by normal faults or horizontal shearing by conjugate strike slip faults the spatial scales over which this partitioning occurs suggest that outcrop scale brittle faults may in some cases record nearly perpendicular plane strains related to a single continuous deformation

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling

constraints on the size of the smallest triggering earthquake from the epidemic type aftershock sequence model bath s law and observed aftershock sequences 1 the physics of earthquake triggering together with simple assumptions of self similarity imply the existence of a minimum magnitude m0 below which earthquakes do not trigger other earthquakes noting that the magnitude md of completeness of a seismic catalog is not in general the same as the magnitude m0 of the smallest triggering earthquake we compare observed aftershock sequence parameters with the predictions made by the epidemic type aftershock sequence model to constrain the value of m0 in particular we use quantitative fits to observed aftershock sequences from three previous studies as well as bath s law to obtain four estimates of m0 we show that the branching ratio n average number of triggered earthquakes per earthquake also equal to the fraction of aftershocks in a seismic catalog is the key parameter controlling the estimate of the minimum triggering magnitude m0 conversely physical upper bounds for m0 estimated from rate and state friction indicate that at the very least 55 of all earthquakes are aftershocks

evolution of the southern san joaquin basin and mid tertiary transitional tectonics central california a cenozoic tectonic and sedimentary history is proposed for the southern san joaquin basin ssjb and tehachapi mountains that evolved adjacent to the plate margin off central california seismic reflection borehole field biostratigraphic and paleomagnetic data are integrated into geologic and fault structure maps cross sections and geohistory plots and are analyzed with previous work in the region to develop a model relating the sequence timing and distribution of complex tectonically linked events the largely buried structures and strata in the ssjb preserve an unusually complete record of the mid tertiary transition from convergent to transform plate boundary as well as the regional transition to contraction during the pliocene significant structural relief existing across both extensional and contractile features is preserved in the subsurface and an active fold thrust belt propagates basinward along the margin of the u shaped tejon embayment the cenozoic evolution of the ssjb reflects the regional deformation of central california as different tectonic events followed each other along the adjacent north american plate margin five oligocene miocene basin phases are identified in the ssjb 1 late oligocene early miocene extensional subsidence with high and low angle normal faulting accompanied by volcanism and deposition of coarse syntectonic conglomerates 2 middle miocene uplift 3 later mid miocene transtensional subsidence to lower bathyal depths 4 alternating subsidence and uplift until the late miocene and 5 flexural subsidence due to pliocene to recent contraction reconstructions of mid tertiary california place the southern san joaquin tehachapi extensional terrane as a paleotectonic block located between the western mojave terrane then to the east and the western california terrane then to the south and west regional extension occurred during a long transition period between convergent and transform boundaries along the north american plate margin significant slip along the san andreas transform postdates this extensional event its origin apparently coincided with a regional middle miocene uplift event indicating that the san andreas fault is younger than previously supposed the tertiary ssjb has subsided due to extension transtension crustal tilting and thrust related loading the maricopa subbasin floor is likely composed of ensimatic and mafic rocks like those along the west side of the sierra nevada and locally has subsided beyond 12 km in contrast the relatively stable tejon embayment underlain by sierran crystalline crust achieved its maximum subsidence in the miocene since pliocene time the ssjb has filled and continued to deepen after the basin was tectonically shut off from the pacific ocean

stress drops and radiated seismic energies of microearthquakes in a south african gold mine 1 we estimate stress drops and radiated seismic energies of 20 microearthquakes 0 0 mw 1 3 in a south african gold mine to investigate their rupture characteristics and scaling relationships to large earthquakes we analyze seismograms of borehole accelerometers recorded with high sampling rate 15 khz within 200 m of the hypocenters at the depth of 2650 m the waveform data have very high signal to noise ratio and no significant later phases are observed at all stations corner frequencies and quality factors of the anelastic attenuation q are estimated from spectra of velocity seismograms by assuming the omega squared model of boatwright 1978 we also investigate moment tensors for double couple solutions and volumetric components from the waveform inversion static stress drops of the 20 earthquakes calculated from the model of madariaga 1976 are from 3 2 to 88 mpa and scaled energies er mo the ratio of the radiated energy er to the seismic moment mo are from 4 2 10 6 to 1 1 10 4 we find that both the static stress drops and the scaled energies of the analyzed earthquakes are comparable to those values of larger earthquakes our results indicate that the dynamic rupture processes of these microearthquakes are similar to those of larger earthquakes

the mojave extensional belt of southern california it is proposed that the regional pattern of early miocene low and high angle normal faulting and dike swarm emplacement in the western and central mojave desert is the result of regional extension developed within a roughly east trending zone named here the mojave extensional belt this zone of extension although now disrupted by late cenozoic right slip faulting can be traced from the intersection of the san andreas and garlock faults to the eastern mojave desert near bristol lake and the granite mountains fault restoration of post oligocene movement along the san andreas fault system places the now buried western part of the mojave extensional belt opposite a similar age extended area of west central california surface mapping and limited subsurface data suggest that the dominant tectonic process responsible for development of the mojave extensional belt was low angle normal sense simple shear detachment faulting strain within the mojave extensional belt is partitioned between four domains edwards waterman daggett and bullion terranes that each consist of one or more half grabens each half graben is composed of tilted normal fault bounded blocks that lie above a rooted low angle brittle ductile normal sense shear zone tilting and extension of the upper plate resulted from the superposition of several generations of originally steeply dipping 80 planar to slightly curviplanar normal faults at least one generation of high angle faults postdates the formation of the detachments differential extension between the domains was accommodated by strike slip faults transfer zones similarly the lack of early miocene extensional elements north of the western segment of the garlock fault suggests that the garlock may have been active in the early miocene and served as the northern transfer boundary of the mojave extensional belt the mojave extensional belt initially began to open about 22 m y ago with the major phase of extension occurring between 22 and 20 ma local high angle normal faults cut older detachments and were active between 20 and 17 ma kinematic indicators suggest that the western part of the mojave extensional belt opened in a ne sw direction whereas the eastern portion extended in an ene wsw direction present day reference frame rotation of the region about vertical axes as revealed by paleomagnetic studies suggests that the direction of extension within the mojave extensional belt was originally oriented n s and was rotated as much as 50 clockwise between 20 and 18 ma early miocene

fault structure frictional properties and mixed mode fault slip behavior abstract recent high resolution gps and seismological data reveal that tectonic faults exhibit complex multi mode slip behavior including earthquakes creep events slow and silent earthquakes low frequency events and earthquake afterslip the physical processes responsible for this range of behavior and the mechanisms that dictate fault slip rate or rupture propagation velocity are poorly understood one avenue for improving knowledge of these mechanisms involves coupling direct observations of ancient faults exhumed at the earth s surface with laboratory experiments on the frictional properties of the fault rocks here we show that fault zone structure has an important influence on mixed mode fault slip behavior our field studies depict a complex fault zone structure where foliated horizons surround meter to decameter sized lenses of competent material the foliated rocks are composed of weak mineral phases possess low frictional strength and exhibit inherently stable velocity strengthening frictional behavior in contrast the competent lenses are made of strong minerals possess high frictional strength and exhibit potentially unstable velocity weakening frictional behavior tectonic loading of this heterogeneous fault zone may initially result in fault creep along the weak and frictionally stable foliated horizons with continued deformation fault creep will concentrate stress within and around the strong and potentially unstable competent lenses which may lead to earthquake nucleation our studies provide field and mechanical constraints for complex mixed mode fault slip behavior ranging from repeating earthquakes to transient slip episodic slow slip and creep events

direct measurement of asperity contact growth in quartz at hydrothermal conditions earthquake recurrence requires interseismic fault restrengthening which results from solid state deformation in room temperature friction and indentation experiments in contrast exhumed fault zones show solution transport processes such as pressure solution and contact overgrowths influence fault zone properties in the absence of fluid flow overgrowths are driven by gradients in surface curvature where material is dissolved diffuses and precipitates at the contact without convergence normal to the contact to determine the rate of overgrowth for quartz we conducted single contact experiments in an externally heated pressure vessel convergence was continuously monitored using reflected light interferometry through a long working distance microscope contact normal force was constant with an initial effective normal stress of 1 7 mpa temperature was between 350 and 530 c and water pressure was constant at 150 mpa two control experiments were conducted one dry at 425 c and one bimaterial sapphire at 425 c and 150 mpa water pressure no contact growth or convergence was observed in the controls for wet single phase contacts growth was initially rapid and then decreased with time no convergence was observed fluid inclusions indicate that the contact is not uniformly wetted the contact is bounded by small regions of high aperture reflecting local free face dissolution as the source for the overgrowth the apparent activation energy is 125 kj mol extrapolation predicts rates of contact area increase orders of magnitude faster than in dry room temperature and hydrothermal friction experiments suggesting that natural strength recovery near the base of the seismogenic zone could be dominated by contact overgrowth

frequency size distribution of competent lenses in a block in matrix melange imposed length scales of brittle deformation 1 this study explores the frequency size distribution of competent lenses phacoids in the chrystalls beach complex a melange shear zone within the otago schist accretion collision assemblage new zealand the distribution of phacoids within a cleaved pelitic matrix follows a power law distribution with exponent 1 18 d 2 37 2 d at outcrop scale whereas distributions at thin section scale have higher d than the outcrop they were sampled from d relates to volume fraction and distribution of competent material where high d correlates with small aspect ratio phacoids and high matrix volume fraction in outcrops which experienced mixed continuous discontinuous deformation d 1 4 0 2 it is suggested that d 1 4 indicates dominant continuous deformation whereas d 1 4 is indicative of localized deformation on shear discontinuities in this melange d therefore appears a function of dominant deformation style actively deforming melange shear zones likely exhibit a range of seismic styles and earthquake magnitudes at length scales limited by lithological layering and shear zone thickness a hypothesis is suggested where strongly coupled shear zone segments may be distinguished by a high volume fraction of competent material low d while aseismically creeping regions are characterized by a high proportion of incompetent rock high d as the b value in the gutenberg richter frequency magnitude relationship also tends to be high in coupled and low in creeping fault segments it may be that d is analogous to b and the b value is also related to the ratio of incompetent competent material and dominant fault zone deformation style

spatiotemporal variations in the b value of earthquake magnitude frequency distributions classification and causes abstract interpretation of the b value of earthquake frequency magnitude distributions has received considerable attention in recent decades this paper provides a comprehensive review of previous investigations of spatial and temporal variations in b value including their classification and possible causes based on least squares regression of seismicity data compiled from the neic iris and isc catalogs we find an average value of 1 02 0 03 for the whole earth and its two hemispheres consistent with the general view that in seismically active regions the long term average value is close to unity nevertheless wide ranging b variations 0 3 b 2 5 have been reported in the literature this variability has been interpreted to arise from one or more of the following factors prevailing stress state crustal heterogeneity focal depth pore pressure geothermal gradient tectonic setting petrological environmental geophysical characteristics clustering of events incomplete catalog data and or method of calculation excluding the latter all of these factors appear to be linked directly or indirectly with the effective state of stress although time dependent changes in b value are well documented conflicting observations reveal either a precursory increase or decrease in b value before major earthquakes our compilation of published analyses suggests that statistically significant b variations occur globally on various timescales including annual monthly and perhaps diurnal taken together our review suggests that b variations are most plausibly linked with changes in effective stress

frequency magnitude distribution of 3 7 mw 1 mining induced earthquakes around a mining front and b value invariance with post blast time we investigated frequency magnitude distribution fmd of acoustic emissions ae occurring near an active mining front in a south african gold mine using a catalog developed from an ae network which is capable of detecting aes down to m w 5 when records of blasts were removed fmds of aes obeyed a gutenberg richter law with similar b values not depending on post blasting time from the initial 1 min interval through more than 30 h this result denies a suggestion in a previous study richardson and jordan bull seismol soc am 92 1766 1782 2002 that new fractures generated by blasting disturb the size distribution of background events which they interpreted as slip events on existing weak planes our ae catalog showed that the gr law with b 1 2 was valid between m w 3 7 and 0 for aes around the mining front further using the mine s seismic catalog which covers a longer time period of the same area we could extend the validity range of the gr law with the same b value up to m w 1

minimum size of earthquakes and minimum value of dynamic rupture velocity abstract the very small aftershocks of the 1984 western nagano prefecture japan earthquake mjma 6 8 were studied in order to investigate the faulting processes of small earthquakes earthquakes with m the fault length l of the smallest event is estimated to be 1 5 m by using relationships between seismic moment and fault length which are derived from aftershock areas the rupture velocity of the smallest event is calculated to be 50 250 m s from the fault length and the pulse width of the source time function these values are much smaller than those of large earthquakes 2 3 km s it was deduced by iio 1986a that smaller earthquakes with m0

extension of gutenberg richter distribution to mw 1 3 no lower limit in sight 1 with twelve years of seismic data from tautona gold mine south africa we show that mining induced earthquakes follow the gutenberg richter relation with no scale break down to the completeness level of the catalog at moment magnitude mw 1 3 events recorded during relatively quiet hours in 2006 indicate that catalog detection limitations not earthquake source physics controlled the previously reported minimum magnitude in this mine within the natural earthquake laboratory in south african mines nelsam experiment s dense seismic array earthquakes that exhibit shear failure at magnitudes as small as mw 3 9 are observed but we find no evidence that mw 3 9 represents the minimum magnitude in contrast to previous work our results imply small nucleation zones and that earthquake processes in the mine can readily be scaled to those in either laboratory experiments or natural faults

violations of gutenberg richter relation in anthropogenic seismicity anthropogenic seismicity as is the undesired dynamic rockmass response to technological processes as environments are shallow hence their heterogeneities have important impact on as moreover as is controlled by complex and changeable technological factors this complicated origin of as explains why models used in tectonic seismicity may be not suitable for as we study here four cases of as testing statistically whether the magnitudes follow the gutenberg richter relation or not the considered cases include the data from mponeng gold mine in south africa the data observed during stimulation of geothermal well basel 1 in switzerland the data from acu water reservoir region in brazil and the data from song tranh 2 hydropower plant region in vietnam the cases differ in inducing technologies in the duration of periods in which they were recorded and in the ranges of magnitudes in all four cases the observed frequency magnitude distributions statistically significantly differ from the gutenberg richter relation although in all cases the gutenberg richter b value changed in time this factor turns out to be not responsible for the discovered deviations from the gutenberg richter born exponential distribution model though the deviations from gutenberg richter law are not big they substantially diminish the accuracy of assessment of seismic hazard parameters it is demonstrated that the use of non parametric kernel estimators of magnitude distribution functions improves significantly the accuracy of hazard estimates and therefore these estimators are recommended to be used in probabilistic analyses of seismic hazard caused by as

in situ monitoring of rock fracturing using shear wave splitting analysis an example from a mining setting summary changing stress conditions are well known to cause rupturing of rock this is well constrained on a small scale from laboratory experiments and inferred on a much larger scale from tectonic earthquakes here we present a study of rock fracturing induced by changes in stress state during block caving operations in an australian mine this intermediate scale study provides further evidence of the scalability of processes involved in rock fracturing and thus helps to link laboratory and seismological observations we analyse the temporal evolution of rock fracturing during a production cycle using the analysis of fracture induced anisotropy fracturingoftherockmassismonitoredusingevidenceofseismicanisotropyfromestimates of shear wave splitting and their subsequent inversion for fracture parameters the data set consists of more than 40 000 three component seismograms recorded by an array of sensors which provides excellent ray coverage we applied a novel automatic quality assessment technique to handle this large data set and find that anisotropy and thus fracturing correlates strongly with the excavation process we then perform a grid search over a series of synthetic models based on rock physics to invert the splitting parameters for fracture orientation and density finally by applying a sliding window on our results we are able to identify production related fracture evolution during production the fracture density increases with horizontal fracture density being stronger than the vertical fracture density this can be explained by the removal of the supporting rock during caving during short intervals of reduced production the horizontal fracture density decreases whereas vertical fracture density increases we relate this to change in stress regime with reducing overburden mass during cavity collapse this scenario is similar to a collapsing caldera or the inverse of an inflating magma chamber

earthquake rupture at focal depth part ii mechanics of the 2004 m2 2 earthquake along the pretorius fault tautona mine south africa we analyze here the rupture mechanics of the 2004 m2 2 earthquake based on our observations and measurements at focal depth part i this event ruptured the archean pretorius fault that has been inactive for at least 2 ga and was reactivated due to mining operations down to a depth of 3 6 km depth thus it was expected that the pretorius fault zone will fail similarly to an intact rock body independently of its ancient healed structure our analysis reveals a few puzzling features of the m2 2 rupture zone 1 the earthquake ruptured four non parallel cataclasite bearing segments of the ancient pretorius fault zone 2 slip occurred almost exclusively along the cataclasite host rock contacts of the slipping segments 3 the local in situ stress field is not favorable to slip along any of these four segments and 4 the archean cataclasite is pervasively sintered and cemented to become brittle and strong to resolve these observations we conducted rock mechanics experiments on the fault rocks and host rocks and found a strong mechanical contrast between the quartzitic cataclasite zones with elastic brittle rheology and the host quartzites with damage elastic plastic rheology the finite element modeling of a heterogeneous fault zone with the measured mechanical contrast indicates that the slip is likely to reactivate the ancient cataclasite bearing segments as observed due to the strong mechanical contrast between the cataclasite and the host quartzitic rock

modeling of neogene crustal block rotation case study of southeastern california numerical modeling using a two dimensional distinct element method dem was performed to give an additional understanding of the mechanism of crustal block rotation in a highly active portion of the pacific north america transform plate boundary paleomagnetic and structural investigations have shown that large 30 50 horizontal rotations of crustal blocks occurred in the eastern transverse zone and the northeast mojave block southeastern california since the end of early miocene the main aspect of the modeling was to investigate whether an anisotropic horizontal stress state can be responsible for the rotation of crustal blocks with a length of 100 km or not the simulations were performed using different stress boundary conditions and different parameters of the fault strength applying an assumed ratio of 2 for the horizontal stress components as boundary condition block rotations in the order of 40 only occur if 1 the major horizontal stress sh is oriented n20 e with a maximal deviation of 15 to the east or west and 2 the fault strength described by the friction coefficient is smaller than 0 12 or 14 only of the value 0 85 for intact rocks byerlee s law for a weakening model of the fault strength an initial friction coefficient of 0 85 allows also rotations of about 40 if the friction coefficient decreases rapidly due to an increasing shear displacement to a basic friction coefficient of 0 12 or smaller for the same amount of rotation 40 a decreasing stress ratio requires a lowering of the friction coefficient used whereas an increase of the ratio allows a higher friction coefficient the simulation also show that the modeling with elastic blocks can adequately describe the observed main features of the crustal deformation especially the cumulative slip values discrepancies in the observations and modeling results for the western parts of the mojave desert are the result of a neglect of the three dimensional deformation in our two dimensional modeling

clockwise rotation of the western mojave desert paleomagnetic results from miocene volcanic rocks in the western mojave desert suggest about 25 of clockwise rotation for this region twelve sites 110 oriented cores were collected from the 20 ma saddleback basalt and seven sites 56 oriented cores from the red buttes quartz basalt around boron california structural corrections were made from the attitude of the basalt or the tropico group sedimentary rocks in which the sampled basalts are interbedded paleomagnetic directions are coincident for the two basalts and show both normal and reversed polarity after demagnetization to 40 or 60 mt application of structural corrections and inversion of reversed sites the data yield an average direction of i 51 6 and d 15 6 k 19 95 8 2 comparison with the expected direction for miocene rocks for stable north america shows a clockwise rotation of 23 8 11 3 and a flattening of 2 1 7 4 clockwise rotation of the western mojave agrees in direction with oroclinal bending of the southern sierra nevada due to right lateral shear along the western margin of north america most of this rotation is constrained by other paleomagnetic and structural information to have occurred soon after the sampled basalts were deposited about 20 ma and before about 16 ma these clockwise declination anomalies also indicate that any subsequent counterclockwise rotation of the mojave is small and or compensated by previous clockwise rotation

faults in the mojave desert california as revealed on enhanced landsat images previously unknown strike slip and normal faults in the central and eastern mojave desert have been revealed on landsat thematic mapper images enhanced by four component processing this method provides color images on which lithologies are discriminated by their contrasting absorption and reflection primarily at infrared wavelengths and particularly with regard to their ferric iron ferrous iron and hydroxyl contents while retaining landform depiction these discriminants represent a new type of geophysical display for geologic mapping in regions of well exposed bedrock faults are revealed on the images by abrupt spectral and textural contrasts that coincide with aligned topographic features the newly discovered faults form part of an extensive regional network of right shear that connects faults in the death valley region with the san andreas fault system they support a heterogeneous strain model for late cenozoic tectonic evolution of the region regional structural relations indicate a westward migration of the locus of strain through time some of the newly identified faults bound blocks that have experienced contrasting rotational histories since early miocene time

cenozoic evolution of the mojave block of southern california the recorded cenozoic history of the mojave desert region of southern california began in the latest oligocene when intense volcanism and tectonism interrupted a long early tertiary silence volcanism commenced across the region in an east west band ca 24 22 ma northwest of barstow volcanism was accompanied by intense crustal extension and development of a metamorphic core complex outside of this relatively restricted area extension was minor or absent after extension ceased ca 18 ma volcanism shifted to small volume eruptions of basalt post extensional deformation has largely been by strike slip faulting along northwest striking dextral faults and west striking sinistral faults and total dextral slip across the mojave desert region since the early miocene is 45 60 km strike slip deformation has been overprinted locally by intense north south contraction that is the dominant style of deformation in the western mojave block paleomagnetic data indicate that parts of the mojave block were rotated clockwise although the magnitude and timing of this rotation are poorly determined the best evidence for large 45 rotation comes from the area east of barstow where large clockwise declination anomalies and mesozoic and cenozoic dikes with anomalous strikes may reflect early miocene clockwise deflection along the mojave river fault volcanism and tectonism in the mojave block resulted from interactions among the north american pacific and various oceanic plates patterns of volcanism and tectonism do not correlate with growth of slab windows beneath the continent but do correlate with the position of the subducted mendocino fracture zone plate circuit reconstructions suggest that the driving force for extension was divergence between the pacific and north american plates along the transform margin that separated the two this hypothesis accounts for the direction magnitude and rate of extension in the mojave block

earthquake size distribution power law with exponent beta 1 2 we propose that the widely observed and universal gutenberg richter relation is a mathematical consequence of the critical branching nature of earthquake process in a brittle fracture environment these arguments though preliminary are confirmed by recent investigations of the seismic moment distribution in global earthquake catalogs and by the results on the distribution in crystals of dislocation avalanche sizes we consider possible systematic and random errors in determining earthquake size especially its seismic moment these effects increase the estimate of the parameter beta of the power law distribution of earthquake sizes in particular we find that estimated beta values may be inflated by 1 3 because relative moment uncertainties decrease with increasing earthquake size moreover earthquake clustering greatly influences the beta parameter if clusters aftershock sequences are taken as the entity to be studied then the exponent value for their size distribution would decrease by 5 10 the complexity of any earthquake source also inflates the estimated beta value by at least 3 7 the centroid depth distribution also should influence the beta value an approximate calculation suggests that the exponent value may be increased by 2 6 taking all these effects into account we propose that the recently obtained beta value of 0 63 could be reduced to about 0 52 0 56 near the universal constant value 1 2 predicted by theoretical arguments we also consider possible consequences of the universal beta value and its relevance for theoretical and practical understanding of earthquake occurrence in various tectonic and earth structure environments using comparative crystal deformation results may help us understand the generation of seismic tremors and slow earthquakes and illuminate the transition from brittle fracture to plastic flow

impact of magnitude uncertainties on seismic catalogue properties catalogue based studies are of central importance in seismological research to investigate the temporal spatial and size distribution of earthquakes in specified study areas methods for estimati

chasing the garlock a study of tectonic response to vertical axis rotation vertical axis clockwise block rotations in the northeast mojave block are well documented by numerous authors however the effects of these rotations on the crust to the north of the northeast mojave block have remained unexplored in this paper we present a model that results from mapping and geochronology conducted in the north and central owlshead mountains the model suggests that some or all of the transtension and rotation observed in the owlshead mountains results from tectonic response to a combination of clockwise block rotation in the northeast mojave block and basin and range extension the owlshead mountains are effectively an accommodation zone that buffers differential extension between the northeast mojave block and the basin and range in addition our model explores the complex interactions that occur between faults and fault blocks at the junction of the garlock brown mountain and owl lake faults we hypothesize that the bending of the garlock fault by rotation of the northeast mojave block resulted in a misorientation of the garlock that forced the owl lake fault to break in order to accommodate slip on the western garlock fault subsequent sinistral slip on the owl lake fault offset the garlock creating the now possibly inactive mule springs strand of the garlock fault dextral slip on the brown mountain fault then locked the owl lake fault forcing the active leach lake strand of the garlock fault to break

significance of seismic reflections beneath a tilted exposure of deep continental crust tehachapi mountains california the focus of this article is a process whereby lower crustal crystalline and schistose rocks can rise to the surface with the tehachapi mountains in california being the case in point as a prime example of the lower crust these mountains expose cretaceous gneisses that formed 25 30 km down in the sierra nevada batholith and appear to be underlain by the ensimatic rand schist integrated geophysical and geological studies by the calcrust program have produced a cross section through this post mid cretaceous structure and suggest a general model for its development seismic reflection and refraction profiles show that the batholithic rocks dip northward as a tilted slab and extend beneath the southern end of the san joaquin basin s tejon embayment two south dipping reverse faults on the rim of the tejon embayment were discovered in the reflection data and verified in the field the faults have a combined separation of several kilometers and cut through an upper crustal reflection zone that projects to the surface outcrop of the rand schist the upper and lower crusts are separated by a zone of laterally discontinuous reflectors reflections from the lower crust form a wedge the base of which is a nearly flat moho at 33 km regional geological relations and gravity models both suggest that the reflective zone corresponds to the rand schist and the newly recognized faults account for its neogene exposure alternatively the reflective zone maybe part of the gneiss complex suggesting that the schist either lies deeper or is not present under the gneisses if the rand schist underlies the tehachapi mountains and mojave region to their south a model for their evolution can be constructed from regional geological relations it seems that during late cretaceous laramide subduction the protolith of the schist was thrust eastward beneath the mojave along this portion of the cordilleran batholithic belt the subduction was evidently at very low angles the bottom of the batholith was removed and replaced by a thick section of schist fluids from which weakened the overlying batholith this thickened crust collapsed by horizontal flow in the schist and faulting of the upper crust into flat lying slabs when emplacement of the schist ended in latest cretaceous earliest paleocene the underlying mantle rose compensating for the extension and providing material for magmatic underplating in the neogene transpression and rotation of the upper crust along the san andreas and garlock faults resulted in the exposure of the schist

discriminating characteristics of tectonic and human induced seismicity we analyze statistical features of background and clustered subpopulations of earthquakes in different regions in an effort to distinguish between human induced and natural seismicity analysis of end member areas known to be dominated by human induced earthquakes the geyser geothermal field in northern california and tautona gold mine in south africa and regular tectonic activity the san jacinto fault zone in southern california and the coso region excluding the coso geothermal field in eastern central california reveals several distinguishing characteristics induced seismicity is shown to have 1 higher rate of background events both absolute and relative to the total rate 2 faster temporal offspring decay 3 higher rate of repeating events 4 larger proportion of small clusters and 5 larger spatial separation between parent and offspring compared to regular tectonic activity these differences also successfully discriminate seismicity within the coso and salton sea geothermal fields in california before and after the expansion of geothermal production during the 1980s online material figures of examined regions earthquake epicenters and joint distributions of the time and space components of the nearest neighbor distance

extension tectonics the neogene opening of the north south trending basins of central thailand paleomagnetic samples were collected from late neogene basalt flows from thailand all of these flows are horizontal and are relatively unaltered in thin section these rocks possess a stable magnetization which is believed to be primary samples from 48 lava flows were collected from sites located within the khorat plateau the chao phraya phitsanulok basin and the mountainous terrane west of the chao phraya phitsanulok basin these data were combined with previously reported late neogene data from five flows from western thailand although the average inclination from the 53 sites is indistiguishable from the expected dipole inclination the average declination has a net clockwise rotation of 13 5 5 8 from the geocentric dipole field furthermore the mean declination values from the 29 flows from the khorat plateau are indistinguishable from the present dipole field direction dm 4 3 7 5 and indistinguishable from the mean declination from 28 late neogene volcanic flows from vietnam in contrast the mean declinations from 24 flows collected from central and western thailand are deflected significantly clockwise dm 24 4 7 7 from the geocentric dipole field direction the differential rotation between western and central thailand versus the khorat plateau suggests that indochina is composed of at least two structural blocks which underwent a different rotational history these observations when combined with geologic and geophysical data from the chao phraya phitsanulok basin gulf of thailand and the intermontane basins of western thailand suggest that the rotations are recording a late neogene phase of e w extension of these basins we suggest that the formation of these basins and the related basaltic volcanism developed in reponse to subduction of the indian plate under western burma we envision the tectonics of this region is similar in style to the basin and range region of the western united states last we have observed field relationships from some of the rhyolites located in the central basin although these rhyolites are reported to be mesozoic or paleozoic in age our field observations and a k ar age date show that at least some of these rhyolites are younger than the basalts we suggest that the rhyolites form a bimodal suite with the basaltic rocks which were erupted in the later stages of the extension

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

predictability of repeating earthquakes near parkfield california summary we analyse sequences of repeating microearthquakes that were identified by applying waveform coherency methods to data from the parkfield high resolution seismic network because by definition all events in a sequence have similar magnitudes and locations the temporal behaviour of these sequences is naturally isolated which coupled with the high occurrence rates of small events makes these data ideal for studying interevent time distributions to characterize the temporal predictability of these sequences we perform retrospective forecast experiments using hundreds of earthquakes we apply three variants of a simple algorithm that produces sequence specific time varying hazard functions and we find that the sequences are predictable we discuss limitations of these data and more generally challenges in identifying repeating events and we outline the potential implications of our results for understanding the occurrence of large earthquakes

foreshocks during the nucleation of stick slip instability 1 we report on laboratory experiments which investigate interactions between aseismic slip stress changes and seismicity on a critically stressed fault during the nucleation of stick slip instability we monitor quasi static and dynamic changes in local shear stress and fault slip with arrays of gages deployed along a simulated strike slip fault 2 m long and 0 4 m deep in a saw cut sample of sierra white granite with 14 piezoelectric sensors we simultaneously monitor seismic signals produced during the nucleation phase and subsequent dynamic rupture we observe localized aseismic fault slip in an approximately meter sized zone in the center of the fault while the ends of the fault remain locked clusters of high frequency foreshocks mw 6 5 to 5 0 can occur in this slowly slipping zone 5 50 ms prior to the initiation of dynamic rupture their occurrence appears to be dependent on the rate at which local shear stress is applied to the fault the meter sized nucleation zone is generally consistent with theoretical estimates but source radii of the foreshocks 2 to 70 mm are 1 to 2 orders of magnitude smaller than the theoretical minimum length scale over which earthquake nucleation can occur we propose that frictional stability and the transition between seismic and aseismic slip are modulated by local stressing rate and that fault sections which would typically slip aseismically may radiate seismic waves if they are rapidly stressed fault behavior of this type may provide physical insight into the mechanics of foreshocks tremor repeating earthquake sequences and a minimum earthquake source dimension

synthetic aperture controlled source electromagnetics controlled source electromagnetics csem has been used as a de risking tool in the hydrocarbon exploration industry although there have been successful applications of csem this technique is still not widely used in the industry because the limited types of hydrocarbon reservoirs csem can detect in this paper we apply the concept of synthetic aperture to csem data synthetic aperture allows us to design sources with specific radiation patterns for different purposes the ability to detect reservoirs is dramatically increased after forming an appropriate synthetic aperture antenna consequently the types of hydrocarbon reservoirs that csem can detect are significantly extended because synthetic apertures are constructed as a data processing step there is no additional cost for the csem acquisition synthetic aperture has potential for simplifying and reducing the cost of csem acquisition we show a data example that illustrates the increased sensitivity obtained by applying synthetic aperture csem source

shear heating induced thermal pressurization during earthquake nucleation 1 we model earthquake nucleation in 2d on narrow faults with coupled rate state friction and shear heating induced thermal pressurization including diffusive transport of heat and pore pressure thermal pressurization increases pore pressure p decreasing frictional resistance observed fault core permeability is generally too low to mitigate thermal pressurization at subseismic slip speeds under drained isothermal conditions nucleation with the aging law is crack like with the interior of the slip zone always near maximum slip speed when thermal pressurization is included it can dominate weakening at speeds of 0 02 20 mm s for hydraulic diffusivities chyd from 10 8 to 10 3 m2 s and nominal material parameters well before seismic radiation occurs dramatic along strike localization of slip occurs due to feedback in which the area of maximum slip experiences the greatest weakening which in turn favors more slip with the slip law however nucleation is pulse like with slip speed decaying behind the pulse tip thermal pressurization is diminished relative to the aging law case since most weakening occurs in locations with limited slip yet we find that it can overwhelm frictional weakening at slip speeds in the range of 1 100 mm s for chyd from 10 8 to 3 10 5 m2 s at higher slip speeds the finite thickness of the shear zone becomes significant reducing thermal pressurization even if not the dominant weakening mechanism thermal pressurization is likely to be significant at or before the onset of seismic radiation

active tectonic studies in the united states 1987 1990 the techniques and instrumentation used in active tectonic studies are discussed and recent results are reviewed it is suggested that a critical mass of data on several particular regions has been accumulated making possible critical debates and attempts to assess earthquake hazards particular attention is given to studies of the pacific northwest region basin and range deformation studies and distributed deformation and hidden earthquake sources also included is a comprehensive bibliography for the period

collapse of southwestern north america and the evolution of early miocene detachment faults metamorphic core complexes the sierra nevada orocline and the san andreas fault system plate reconstructions indicate that early miocene pacific north american relative motion was not parallel to the transform but was instead oblique and transtensional we propose that the western edge of the north american plate east of the transform gravitationally collapsed to the southwest in response to this divergence the northern and eastern edges of the collapsed region underwent extension between 24 and 20 ma whereas extension in southeastern california and southern arizona during this interval was coaxial with the overall s50 60 w collapse direction the extension direction along the northern oundary mojave extensional belt was north south and the result of the combined effects of the southwestward collapse and the independent northwestward translation of the region to the north collapse continued between 20 and 16 ma and extension persisted in southeastern california and southern arizona extension along the northern boundary waned owing to the apparent cessation of motion of the region to the north thus the kinematics of the northern boundary changed to dextral shear and extension along what is here named the trans mojave sierran shear zone this east west zone of mainly right shear oroclinally folded the southern tail of the sierra nevada and the central mojave desert rocks within this 83 110 km wide zone were rotated approx 40 60 clockwise about vertical axes finally as collapse moved the north american plate progressively west across the locus of transform shear its western edge became increasingly subject to the motion of the pacific plate over time the edge of north america was truncated by faults of the san andreas system and transferred to the pacific plate

seismic moment frequency relation for shallow earthquakes regional comparison we determine the parameter values for the seismic moment frequency relation using flinn engdahl s regionalization of global seismicity and the harvard centroid moment tensor data the earthquake size distribution is approximated by the gamma law a version of the gutenberg richter distribution with an exponential taper at the maximum moment there is no statistically significant variation of the fj value the analog of the b value for all seismic regions except for the midocean ridge systems for the latter regions fj 0 93 whereas for all other zones fj 0 63 the maximum moment mxg can be statistically evaluated only for subduction zones treated as a whole mxg 10 21 2 x 10 22 newton m which corresponds to the worldwide mxg value for other regions as well as for single subduction zones mxg is determined by comparing the number of events in each zone with the seismic moment rate calculated on the basis of the nuvel 1 model of plate motion for subduction zones we obtain the estimate of mxg which agrees with the statistical value giving evidence that most tectonic deformation is released by earthquakes we test the hypothesis that no statistically significant variation in mxg occurs in subduction and continent collision zones the hypothesis cannot be rejected with available data for the midocean ridges the mxg estimate cannot be unambiguously determined it is quite possible that the estimate is significantly biased because only a small part of tectonic deformation at the ridges is released by earthquakes these results have importance in evaluating seismic risk and may also lead to developing a physical theory for earthquake generation

frequency magnitude characteristics down to magnitude 4 4 for induced seismicity recorded at mponeng gold mine south africa this article aims to investigate the frequency magnitude characteristics and lower magnitude limits of the microseismic catalog recorded with a seismic network sensitive to high frequencies at mponeng mine south africa the network composed of one three component accelerometer and eight acoustic emission sensors is located at a depth of 3 5 km below the surface and covers the limited volume of approximately 300 300 300 m the three component accelerometer was used to estimate the moment magnitude for the limited number of 135 events m w ranged from 4 1 to 0 3 well recorded by the network we use the relation between the moment magnitude estimated from accelerometer data and radiated energy moment magnitude estimated from acoustic emission sensors to extend the catalog to lower magnitudes the magnitude of completeness of selected spatiotemporal subsets of the catalog was estimated for 1 an aftershock sequence of an m w 1 9 event that occurred approximately 30 m from the network and 2 postblasting activity during working days located more than 80 m from the network the data follow the gutenberg richter gr frequency magnitude relationship with no visible deviation from self similar behavior of seismicity between m w 4 4 and 1 9 for the aftershock sequence and between 3 5 and 1 5 for the postblasting dataset we estimated the magnitude of completeness of selected subset as low as 4 3 b 1 26 for the aftershock sequence and 3 4 b 1 17 for the postblasting activity differences in magnitude of completeness are attributed to location of recorded activity and site effects

likelihood analysis of earthquake catalogues summary we apply several classes of stochastic multidimensional models to statistical analysis of earthquake catalogues using likelihood methods we investigate the importance of including different earthquake parameters in the model epicentral coordinates hypocentral depth time limits for interearthquake interaction and especially spatial distribution of earthquakes as well as spatial aftershock patterns results of this study combined with other investigations suggest that most distributions controlling earthquake interaction have a fractal or scale invariant form developed models are used for statistical analysis of several earthquake catalogues to evaluate parameters of earthquake occurrence these parameters are shown to be similar for shallow earthquakes of different magnitude ranges and seismogenic regions confirming self similarity of the earthquake process whereas intermediate earthquakes seem to emulate the pattern of shallow earthquake occurrence albeit at a much smaller aftershock rate deep earthquakes differ significantly in their properties predictability of standard shallow earthquake catalogues has been analysed we present evidence that for the best availabfe catalogues the predictability is close to 10 bits per earthquake several synthetic earthquake catalogues have been created and processed through the likelihood inversion scheme the results from likelihood analysis of these catalogues confirm our approach

clockwise rotation and implications for northward drift of the western transverse ranges from paleomagnetism of the piuma member sespe formation near malibu california 1 new paleomagnetic results from mid tertiary sedimentary beds in the santa monica mountains reinforce the evidence for large scale rotation of the western transverse ranges and anisotropy measurements indicate that compaction induced inclination flattening may resolve a long standing controversy regarding the original paleolatitude of the rotated block previously published paleomagnetic data indicate that post oligocene rotation amounts to 70 110 clockwise affecting the channel islands santa monica mountains and santa ynez mountains the sespe formation near malibu consists of a lower member dominated by nonmarine sandstone and conglomerate and an upper section the piuma member which consists of gray red sandstone and mudstone interbedded with minor tuff and limestone beds the piuma member has a paleomagnetic pole at 36 6 n 326 7 e a95min 5 0 a95max 9 6 obtained by thermal demagnetization of 34 oriented cores from oligocene and early miocene beds after correcting for plunge of the geologic structure the data are consistent with significant clockwise rotation 77 7 of the region relative to stable north america rotation of the western transverse ranges is generally viewed as a consequence of pacific north american plate interactions after 28 ma when east west subduction gave way to northwest transform motion in southern california inclinations from the piuma study indicate a paleolatitude anomaly of 11 7 and are consistent with a mean northward drift that exceeds generally accepted san andreas fault displacement by a factor of 3 however sedimentary inclination error may accentuate the anomaly anisotropy of isothermal remanent magnetization indicates inclination flattening of approximately 8 and correction for the effect reduces the paleolatitude anomaly to 5 3 5 8 compaction may explain the inclination flattening in these sedimentary rocks but the process does not adequately explain lower than expected inclinations found in previous studies of miocene volcanic rocks of the western transverse ranges

a preliminary neogene paleomagnetic data set from leyte and its relation to motion on the philippine fault abstract leyte island is bisected by the left lateral philippine fault paleomagnetic samples were collected from nineteen lava flows in leyte and nearby islands to the north the data collected from these sites were combined with previously reported results from northeastern mindanao the paleomagnetic data from neogene rocks within or very near the philippine fault zone on leyte mindanao biliran maripipi and genuruan islands fall into two populations seventeen late neogene sites fourteen normal polarity and three reversed polarity yield a mean direction d 358 9 i 20 1 95 6 6 k 30 1 and a paleomagnetic pole 88 9 n 12 5 e a95 4 8 k 56 1 eight early neogene sites three normal polarity and five reversed polarity give a mean direction d 23 2 i 13 9 95 9 3 k 36 2 and a paleomagnetic pole 66 5 n 220 5 e a95 7 1 k 62 0 the late neogene pole is indistinguishable from plio pleistocene poles from the philippines taiwan and vietnam and the late miocene pole of the central philippines suggesting there have been no significant rotations or translations of this region with respect to other southeast asian regions during the past 5 m y the early neogene paleomagnetic pole is statistically indistinguishable from the middle to early miocene pole of the central philippines the early neogene pole is statistically distinguishable from early miocene pole of marinduque island philippines as well as the late miocene pole of the central philippines and the plio pleistocene pole of the entire philippines this preliminary paleomagnetic data set suggests that leyte and adjacent islands to the north have been a portion of the same tectonic block as northeastern mindanao cebu and western panay since early neogene there are also no paleomagnetically detectable fault related rotations associated with the philippine fault given the resolution of this data set no consensus exists as to the amount of offset or the age of inception of the philippine fault the 110 km offset between ophiolitic basement in northeast leyte and that in southwest leyte suggests this amount of left lateral displacement has occurred along the philippine fault since the middle tertiary in contrast to data from continental regions no shear related rotations are found associated with the philippine fault this observation suggests that the hot immature transitional island arc continental crust of the philippine region deforms differently in response to shear than well developed continental crust

estimation of earthquake hazard parameters from incomplete data files part iii incorporation of uncertainty of earthquake occurrence model most probabilistic seismic hazard analysis procedures require that at least three seismic source parameters be known namely the mean seismic activity rate the gutenberg richter b value and the area characteristic seismogenic source maximum possible earthquake magnitude m max in almost all currently used seismic hazard assessment procedures that utilize these three parameters it is explicitly assumed that all three remain constant over time and space however closer examination of most earthquake catalogs has indicated that significant spatial and temporal variations existed in the seismic activity rate as well as in the gutenberg richter b value in this study the maximum likelihood estimation of these earthquake hazard parameters considers the incompleteness of the catalogs the uncertainty in the earthquake magnitude determination as well as the uncertainty associated with the applied earthquake occurrence models the uncertainty in the earthquake occurrence models is introduced by assuming that both the mean seismic activity rate and the gutenberg richter b value are random variables each described by the gamma distribution this approach results in the extension of the classic frequency magnitude gutenberg richter relation and the poisson distribution of the number of earthquakes with their compounded counterparts benjamin 1968 campbell 1982 1983 the proposed procedure was applied in the estimation of the seismicity parameters in an area that had experienced the strongest and most devastating earthquake in contemporary south african history namely the 29 september 1969 m w 6 3 ceres tulbagh event in this example it was shown that the introduction of uncertainty in the earthquake occurrence model reduced the mean return periods leading to an increase of the estimated seismic hazard additionally this study confirmed that accounting for magnitude uncertainties had the opposite effect that is it brought about increases in the return periods or equivalently a reduction of the estimated seismic hazard