source parameters of the 1992 melilla spain mw 4 8 1994 alhoceima morocco mw 5 8 and 1994 mascara algeria mw 5 7 earthquakes and seismotectonic implications source mechanisms of the melilla alhoceima and mascara earthquakes including fault plane solutions waveform modeling and spectral analysis are presented strike slip solutions have been obtained for the melilla and alhoceima earthquakes and reverse faulting for mascara teleseismic p wave inversion using broadband data show a complex mechanism for the alhoceima earthquake formed by two subevents at very shallow depth 7 and 8 km and scalar seismic moments of 1 1 10e 17 n m and 4 8 10e 17 n m the mascara earthquake was a single event with a shallow depth 4 5 km and a scalar seismic moment of 3 3 10e 17 n m results of the alhoceima melilla and mascara earthquakes together with 53 focal mechanisms in the region show a regional stress regime that corresponds to horizontal compression in a nw se direction associated with the convergence between eurasia and africa a change of the stress regime in the plate boundary of the ibero maghrebian region has been found

reactivated faulting near cushing oklahoma increased potential for a triggered earthquake in an area of united states strategic infrastructure in october 2014 two moderate sized earthquakes mw 4 0 and 4 3 struck south of cushing oklahoma below the largest crude oil storage facility in the world combined analysis of the spatial distribution of earthquakes and regional moment tensor focal mechanisms indicate reactivation of a subsurface unnamed and unmapped left lateral strike slip fault coulomb failure stress change calculations using the relocated seismicity and slip distribution determined from regional moment tensors allow for the possibility that the wilzetta whitetail fault zone south of cushing oklahoma could produce a large damaging earthquake comparable to the 2011 prague event resultant very strong shaking levels mmi vii in the epicentral region present the possibility of this potential earthquake causing moderate to heavy damage to national strategic infrastructure and local communities

an integrated geophysical investigation of recent seismicity in the al hoceima region of north morocco abstract data produced by the moroccan national seismological network and marine seismic reflection profiles are used to investigate the most seismically active region in morocco located on the mediterranean coast at the intersection of the rif mountain belt and the submarine alboran ridge this region in the vicinity of the city of al hoceima marks an east west transition in the marine and land deformation styles of the distributed plate boundary between africa and iberia and was the site of an m w 6 0 earthquake on 26 may 1994 the epicenter of the al hoceima earthquake is relocated onshore refining the initial submarine location close to the alboran ridge the spatial distribution of foreshocks and aftershocks shows a ne sw trend that continues partly offshore and is subparallel to the earlier yet still prominent miocene geologic structural trend the predominantly strike slip focal mechanism for the al hoceima event is characteristic of earthquakes in the region marine seismic reflection profiles that intersect the offshore region of seismicity image active high angle faults with possible strike slip components the seismicity trend is not directly related to the submarine alboran ridge or the geomorphologically prominent nekor fault deformation appears to be occurring on a number of subsidiary strike slip faults that together compose a ne sw zone of distributed shear the distributed strike slip and documented normal faulting taking place in the eastern rif mountains although characteristic of the rif region are in contrast to the thrusting style of deformation that occurs farther to the east in the algerian tell atlas this may be related to the reported lateral variations and evolution of the convergent plate boundary in these regions during the neogene and quaternary times

models of the complex source of the el asnam earthquake abstract the el asnam earthquake of 10 october 1980 was originated by a thrust across a sw ne oriented fault 36 km long and 15 km wide it is a complex event with a rupture propagating from the sw to the ne fault mapping hypocenter distribution and b factor studies indicate fault branching to the ne a dislocation model is used to explain the branch with normal faulting at beni rached as a consequence of the thrust across a main fault that changes orientation the mechanism of the 1954 earthquake must be similar even though only normal faulting was observed at the surface

effective pressure or what is the effect of pressure using time lapse seismics as a reservoir monitoring tool geophysics can help distinguish different reservoir production scenarios for example eiken et al 2000 successfully detected fluid saturation changes after co2 injection using time lapse seismics at sleipner field over the cycle of a reservoir life oil saturation usually decreases reservoir pressure declines and gas breakout may occur these changes cause rock property changes that are detectible in time lapse seismics therefore it is important to understand the effects of pressure and saturation changes on rock properties while the effects of saturation changes are often well described by gassmann 1951 brown and korringa 1975 and mavko 1975 the effects of pressure changes are less understood here we focus on understanding the effects of fluid pressure on velocities

intermediate and deep earthquakes in spain recent improvements in the seismological networks on the ibero maghrebian region have permitted estimation of hypocentral location and focal mechanisms for earthquakes which occurred at south spain alboran sea and northern morocco of deep and intermediate depth with magnitudes between 3 5 and 4 5 intermediate depth shocks range from 60 to 100 km with greater concentration located between granada and malaga fault plane solutions of 5 intermediate shocks have been determined they present a vertical plane in ne sw or e w direction seismic moments of about 1015 nm and dimensions of about 1 km have been determined from digital records of spanish stations p wave forms are complex this may be explained by the crustal structure near the station discontinuities in the upper mantle and inhomogeneities near the source deep activity at about 650 km has only 3 shocks since 1954 1954 1973 1990 shocks are located at a very small region fault plane solutions show a consistent direction of the pressure axis dipping 45 in e direction for the 1990 shock seismic moment is 1016 nm and dimensions 2 6 km thep waves are of simpler form with a single pulse the intermediate and deep activities are not connected and no activity has been detected between 100 and 650 km the intermediate shocks may be explained in terms of a recent subduction from africa under iberia in se direction the very deep activity must be related to a sunk detached block of lithospheric material still sufficiently cold and rigid to generate earthquakes

flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments flow rate dictates permeability enhancement during fluid pressure oscillations in laboratory experiments thibault candela 1 2 emily e brodsky 2 chris marone 1 derek elsworth 1 1 dept geosciences penn state univ university park pa united states 2 dept earth sciences uc santa cruz santa cruz ca united states

high rate injection is associated with the increase in u s mid continent seismicity an unprecedented increase in earthquakes in the u s mid continent began in 2009 many of these earthquakes have been documented as induced by wastewater injection we examine the relationship between wastewater injection and u s mid continent seismicity using a newly assembled injection well database for the central and eastern united states we find that the entire increase in earthquake rate is associated with fluid injection wells high rate injection wells 300 000 barrels per month are much more likely to be associated with earthquakes than lower rate wells at the scale of our study a well s cumulative injected volume monthly wellhead pressure depth and proximity to crystalline basement do not strongly correlate with earthquake association managing injection rates may be a useful tool to minimize the likelihood of induced earthquakes

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

neogene extensional collapse in the western mediterranean betic rif alpine orogenic belt implications for the genesis of the gilbraltar arc and magmatic activity the betic rif orogenic belt crops out in the western mediterranean and constitutes the westernmost part of the alpine edifice the building up of this belt by compressional nappe tectonics occured during a series of alpine deformational episodes subsequent neogene extension resulted from the collapse of the previous compressional edifice through major extensional detachment systems this episode was accompanied by cafe alkaline to shoshonitic and lamproitic volcanism tectonic denudation of metamorphic core complexes and emplacement of peridotite bodies as a final consequence of the evolution of detachment systems furthermore we relate the generation of the gibraltar arc and the opening of the alboran sea to this major extensional event finally two main stages of tectonic denudation of these detachment systems are defined 1 nevado filabride stage with ex humation of metamorphic core complexes and 2 ronda beni boussera stage with a more advanced degree of denudation leading to the exhumation of upper mantle peridotites which may be tentatively termed mantle core complexes

stress and palaeostress in the betic rif cordilleras miocene to the present palaeostress orientation in the betic rif cordilleras can be determined for the miocene to the quaternary by analysis of brittle microstructures faults joints striated pebbles and stylolites in the central and northern south iberian domain 1 was subhorizontal and trended nw se from the early miocene to the present in the northern alboran domain from the burdigalian to the serravallian palaeostress ellipsoids were oblate with 3 subhorizontal and trending ene wsw in the southern part of the south iberian domain and in the northern part of the alboran domain betic cordillera from the tortonian to the quaternary palaeostress ellipsoids were variable in the granada region they were prolate with 1 subvertical but in the almeria region they were triaxial with 2 subvertical and 3 subhorizontal and trending ne sw to e w in the rif the alboran and african maghrebian domains were affected by palaeostresses with 1 subhorizontal varying from ne sw in tortonian times to n s in the plio quaternary a study of earthquake focal mechanisms by the right dihedra method indicates that the present day general stress field around the betic rif cordilleras is compressional with 1 subhorizontal and trending nw se in the betic rif cordilleras this general stress field is modified and the present day orientations of 1 2 and 3 are nearly the same as those of the palaeostresses in the pliocene and quaternary the distribution and evolution of stresses in the betic rif cordilleras from the miocene to the present can be correlated with the main neogene deformations extensional structures in the central and northern alboran domain and the southern part of the south iberian domain and compressional structures in the south iberian and african maghrebian domains and in the southern part of the alboran domain

the el asnam algeria earthquake of 10 october 1980 multiple source mechanism determined from long period records we present a study of the el asnam algeria earthquake of 10 october 1980 from a large collection of long period surface and body wave records the focal mechanism of the main shock is well constrained by the p wave first motions at teleseismic distances and field observations it was a thrust event on a plane striking n45 e and a dip angle of 54 to the north it had a small component of left lateral motion 83 ouyed et al 1981 gaudemer et al 1981 this earthquake was very well recorded on wwssn stations and on gdsn and ida digital stations with a good azimuthal distribution from these records we confirm the focal solution and obtain a seismic moment m o 5 1026 dyne cm the p wave seismograms indicate a complex source we show that it is not sufficient to model the source by a multiple event but it is also necessary to include a propagation effect in order to explain accurately the waveform with assumptions based on field observation of the surface breaks we model the p waves including two discontinuities of the propagation along the fault plane and obtain a good agreement of the waveform

ground motion hazard values for northern algeria this study examines distinctive features of ground motion parameters in northern algeria an initial computation of seismic hazard in terms of horizontal peak ground acceleration pga and spectral acceleration sa at different periods damped at 5 is carried out for three different types of soils rock stiff soils and soft soils for return periods of 100 and 475 years in addition uniform hazard spectra uhs are computed for these two return periods at several locations in the region then the uhs computed for different soil types are proposed as a starting point to define elastic design spectra for building code purposes we have used the well known newmark hall approach as proposed in the most recent international building codes the sa 0 2 s value is used to establish the spectral region for lower periods region controlled by acceleration whereas the sa 1 0 s value is used to establish the spectral region for intermediate periods region controlled by velocity we also obtained important relations dependent on site condition between sa 0 2 s sa 1 0 s or samax values and the pga for both return periods of 100 and 475 years other relationships between pga or samax values have also been derived for return periods of 100 and 475 years in this case independent of site condition

postseismic deformation at el asnam algeria in the seismotectonic context of northwestern algeria summary we use a combination of seismicity tectonic features focal mechanisms seismic strain and postseismic movement to study the western part of north algeria the el asnam region and its surrounding area in particular a seismotectonic map of this part of algeria delimited by the mediterranean sea in the north and the tellian mountains in the south was built from available geological and seismological data an examination of this map shows that the most significant earthquakes are concentrated along tectonic features and quaternary basins elongated in an east west direction suggesting nnw sse compressional movements during the large el asnam earthquake of 1980 october 10 m 7 1 vertical movement was measured along a 40 km northeastsouthwest thrust fault these movements were determined geodetically in 198 1 with reference to a basic network previously measured in 1976 in order to control postseismic movement and to ensure the monitoring of the seismic area a dense geodetic network has been regularly measured since 1986 both in planemetry and altimetry the results of the altimetric remeasurements show significant vertical movements the elevation changes of the benchmarks have been deduced from precise levelling measurements a remarkable uplift 5 1 5 1 9 mm yr of the northwestern block during the 1986 91 period has been observed whereas the southeastern block is seen to be relatively stable the sar el maiirouf anticline situated along the central segment of the el asnam surface breaks appears to be growing with a maximum postseismic slip rate of 9 6 1 4 mm yr i the mean uplift rates computed for the northwestern block support the view that the 1954 earthquake did not occur on the same reverse fault as the 1980 event

the 1954 and 1980 algerian earthquakes implications for the characteristic displacement model of fault behavior joint epicenter determination of earthquakes that occurred in northern algeria near ech cheliff named orleansville in 1954 and el asnam in 1980 shows that the earthquake of 9 september 1954 m 6 5 occurred at nearly the same location as the earthquake of 10 october 1980 m 7 3 the 1954 main shock and earliest aftershocks were concentrated close to the boundaries of segment b nomenclature of deschamps et al 1982 king and yielding 1984 of the 1980 fault system which was to experience approximately 8 m of slip in the 1980 earthquake later aftershocks of the 1954 earthquake were spread over a broad area notably in a region north of the 1980 fault system that also experienced many aftershocks to the 1980 earthquake the closeness of the 1954 main shock and earliest aftershocks to the 1980 segment b implies that the 1954 earthquake involved either 1 rupture of segment b proper or 2 rupture of a distinct fault in the hanging wall or footwall block of segment b the first interpretation cannot be accommodated in the characteristic displacement model of fault behavior but instead requires a model such as the time predictable model which would permit slip in 1954 to have released only a fraction of the elastic strain that was stored on segment b and which would later be released in 1980 the second interpretation specifically with rupture in the hanging wall block of segment b accounts more directly than the first interpretation for differences in the focal mechanisms and ground deformations associated with the two main shocks this interpretation is therefore preferred the second interpretation is consistent with a characteristic displacement model of the 1980 fault system no matter how it is modeled the algerian episode provides an example of an earthquake 1954 that was large enough to perhaps be judged the culminating event of the seismic cycle in a regionally important fault zone but that was followed instead by an even larger shock 1980 the space time characteristics of the episode are unusual enough that they cannot represent the most likely mode of strain release on reverse fault systems in general but the episode should be viewed as one possible scenario for the evolution of seismicity on other such fault systems

seismic hazard in northern algeria using spatially smoothed seismicity results for peak ground acceleration seismic hazard in terms of peak ground acceleration pga has been evaluated in northern algeria using spatially smoothed seismicity data we present here a preliminary seismic zoning in northern algeria as derived from the obtained results initially we have compiled an earthquake catalog of the region taking data from several agencies afterwards we have delimited seismic areas where the b and mmax parameters are different finally by applying the methodology proposed by frankel seismol res lett 66 1995 8 and using four complete and poissonian seismicity models we are able to compute the seismic hazard maps in terms of pga with 39 3 and 10 probability of exceedance in 50 years a significant result of this work is the observation of mean pgavalues of the order of 0 20 and 0 45 g for return periods of 100 and 475 years respectively in the central area of the tell atlas d 2003 elsevier b v all rights reserved

seismic evidence for rock damage and healing on the san andreas fault associated with the 2004 m 6 0 parkfield earthquake we deployed a dense linear array of 45 seismometers across and along the san andreas fault near parkfield a week after the m 6 0 parkfield earthquake on 28 september 2004 to record fault zone seismic waves generated by aftershocks and explosions seismic stations and explosions were co sited with our previous exper iment conducted in 2002 the data from repeated shots detonated in the fall of 2002 and 3 months after the 2004 m 6 0 mainshock show 1 0 1 5 decreases in seismic wave velocity within an 200 m wide zone along the fault strike and smaller changes 0 2 0 5 beyond this zone most likely due to the coseismic damage of rocks during dynamic rupture in the 2004 m 6 0 earthquake the width of the damage zone characterized by larger velocity changes is consistent with the low velocity waveguide model on the san andreas fault near parkfield that we derived from fault zone trapped waves li et al 2004 the damage zone is not symmetric but extends farther on the southwest side of the main fault trace waveform cross correlations for repeated aftershocks in 21 clusters with a total of 130 events located at different depths and distances from the array site show 0 7 1 1 increases in s wave velocity within the fault zone in 3 months starting a week after the earthquake the velocity recovery indicates that the damaged rock has been healing and regaining the strength through rigidity recovery with time most likely due to the closure of cracks opened during the mainshock we estimate that the net decrease in seismic velocities within the fault zone was at least 2 5 caused by the 2004 m 6 0 parkfield earthquake the healing rate was largest in the earlier stage of the postmainshock healing process the magnitude of fault healing varies along the rupture zone being slightly larger for the healing beneath middle mountain correlating well with an area of large mapped slip the fault healing is most promi nent at depths above 7 km

influence of pore pressure on velocity in low porosity sandstone implications for time lapse feasibility and pore pressure study as seismic data quality improves time lapse seismic data is increasingly being called upon to interpret and predict changes during reservoir development and production since pressure change is a major component of reservoir change during production a thorough understanding of the influence of pore pressure on seismic velocity is critical laboratory measurements show that differential pressure overburden minus fluid pressure does not adequately determine the actual reservoir conditions changes in fluid pressure are found to have an additional effect on the physical properties of rocks the effective stress coefficient n is used to quantify the effect of pore pressure compared to confining pressure on rock properties however the current practice in time lapse feasibility studies reservoir pressure inversion and pore pressure prediction is to assume that n 1 laboratory measurements reported in both this and previous research show that n can be significantly less than unity for low porosity rocks and that it varies with porosity rock texture and wave type we report the results of ultrasonic experiments to estimate n for low porosity sandstones with and without microcracks our results show that for p waves n is as low as 0 4 at a differential pressure of 20 mpa about 3000 psi for a low porosity sandstone thus in pore pressure inversion an assumption of n 1 would lead to a 150 underestimation of the pore pressure comparison of the effective stress coefficient for fractured and unfractured samples suggests that the presence of microfractures increases the sensitivity of p wave velocity to pore pressure and therefore the effective stress coefficient our results show that the effective stress coefficient decreases with the differential pressure with a higher differential pressure resulting in a lower effective stress coefficient while the effective stress coefficient for p wave velocity can be significantly less than unity it is close to one for s waves

influence of macro fractures and micro fractures on permeability and elastic wave velocities in basalt at elevated pressure fractures are ubiquitous on all scales in crustal rocks the investigation of fractures and their influence on physical and transport properties of rocks is therefore essential for understanding of many key problems in seismology volcanology and rock engineering in crystalline rocks pore water is primarily stored in and migrates through networks of cracks and fractures at all scales it is therefore essential to know how fluid flow in such fracture networks responds to the elevated pressures found at depth here we report results from an investigation of changes in fluid permeability and associated changes in p wave and s wave velocities at elevated effective pressure for intact macro fractured and micro fractured samples of seljadur basalt in all cases permeability decreases and both wave velocities increase with increasing effective pressure permeability decreases were smallest in the intact material from approximately 10 19 m 2 to 3 x 10 20 m 2 intermediate in the micro fractured material from approximately 5 x 10 17 m 2 to 1 x 10 17 m 2 and largest in the macro fractured material from approximately 3 x 10 15 m 2 to 9 x 10 19 m 2 for a material containing both micro fractures and macro fractures the closure of macro fractures dominated the permeability reduction at low pressure with the closure of micro fractures exerting an increasing influence at higher pressure c 2010 elsevier b v all rights reserved

discussion of origins of hinterland basins to the rif betic cordillera and carpathians abstract the hinterland basins of the rif betic cordillera western alboran sea and the carpathians pannonian basin are in part composed of a thick in excess of 3 4 km thermal sag basin sequence the underlying crust has been thinned to 25 km in parts of the pannonian basin and to 15 km in parts of the alboran sea modern tectonic models for these areas envision tectonic collision and thickening of the crust followed by crustal thinning either by gravitational collapse back arc extension or a combination of the two contemporaneous with thrusting basin and range type extension has been envisioned for parts of these extensional collapse systems extensional features are common and they interact in a complex way with strike slip systems flexural cantilever modelling agrees with earlier mckenzie type pure shear modelling of the extensional systems in suggesting that extension alone cannot generate sufficient thermal decay to explain the great thickness of the sag basins associated with the alboran sea and pannonian basin consequently it is suggested that uplift of the asthenosphere accompanying subduction roll back is an important factor in the evolution of these basins roll back of the mantle lithosphere permits hot asthenospheric mantle to upwell and lie close to the base of the crust initially uplift and erosion of the crust overlying the asthenosphere occurs as the thermal perturbation cools the crust thermally subsides to produce a large sag basin

estimating rock porosity and fluid saturation using only seismic velocities evaluation of the fluid content in deep earth reservoirs or fluid contaminants in shallow earth environments has required the use of geophysical imaging methods such as seismic reflection prospecting interpretation of seismic velocities and amplitudes is based on theories of fluid saturated and partially saturated rocks that have been available since the 1950s here we present a new synthesis of the same physical concepts that uses compressional wave velocities together with shear wave velocities in a scheme that is much simpler to understand and apply yet yields detailed information about porosity and fluid saturation magnitudes and spatial distribution the key idea revolves around the fact that the density and the lame elastic parameter are the only two parameters determining seismic velocities that also contain information about fluid saturation at low enough frequencies gassmann s well known equations show that the shear modulus is independent of the fluid saturation level we use these facts to

role of strike slip faults in the betic rifian orogeny abstract a new model for the betic rifian orogeny of the western mediterranean spain and north africa is proposed in which four strike slip faults play an important role the faults are not of the same age two faults the left lateral jebha fault to the south in morocco and principally in the mediterranean sea and the right lateral north betic fault southern spain to the north define the boundaries of the alboran block betic and rifian internal zones final movement along these faults was during the burdigalian time two other faults the left lateral nekor fault north africa to the south of the jebha fault and the right lateral crevillente fault somewhat to the north of the north betic fault define a larger alboran block including part of the betic and rifian external zones that was present during the tortonian the following sequence of events is proposed 1 a during the eocene and oligocene the african and european plates converged in a n s sense causing the breakup and overthrusting of the betic rifian and kabyle internal zones and then the movement towards the wsw of the alboran block by slip along the jebha and north betic faults 2 b by the end of burdigalian time movement along the jebha and north betic faults ceased 3 c with continued n s convergence the nekor and crevillente faults which bound a larger alboran block were formed during the mid and late miocene the arc of gibraltar the zone lying between the four major faults seems to be a result of wsw motion of a crustal block being thrust over external zones the model proposed adds to the earlier idea that tectogenesis proceeds from the interior to the exterior of an erogenic belt in the betic rifian orogeny major strike slip fracture zones shifted to the exterior of the orogenic belt as the orogeny progressed in order to relieve the stress caused by locking of the more internal faults

seismogenic zone survey by algerian telemetered seismological network case study of rouina earthquake 19 january 1992 abstract a new telemetered seismological network has been recently installed in northern algeria at present this new seismic network includes 30 stations with a final goal of 32 stations connected by radio and dedicated telephone lines to a centre located at the craag headquarters in alger bouzare ah the algerian telemetered seismological network atsn stations are all equipped with short period seismometers monitoring by this network will allow a more precise knowledge of the seismicity in algeria and southern europe as an example the sequence of the rouina earthquake m 5 2 of 19 january 1992 recorded by the atsn is described

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

mapping pressurized volcanic fluids from induced crustal seismic velocity drops volcanic eruptions are caused by the release of pressure that has accumulated due to hot volcanic fluids at depth here we show that the extent of the regions affected by pressurized fluids can be imaged through the measurement of their response to transient stress perturbations we used records of seismic noise from the japanese hi net seismic network to measure the crustal seismic velocity changes below volcanic regions caused by the 2011 moment magnitude m w 9 0 tohoku oki earthquake we interpret coseismic crustal seismic velocity reductions as related to the mechanical weakening of the pressurized crust by the dynamic stress associated with the seismic waves we suggest therefore that mapping seismic velocity susceptibility to dynamic stress perturbations can be used for the imaging and characterization of volcanic systems

seismotectonics of the ibero maghrebian region abstract a study of the seismotectonics of the ibero maghrebian region is presented as deduced from main geological features seismicity and focal mechanism data the hypocentral distribution of shallow intermediate depth and deep earthquakes is analyzed the direction of the stress distribution is inferred from the focal mechanism of 24 selected events a seismotectonic framework summarizing these results together with the main geological features shows that a nw se general direction of horizontal compressive stresses is present in the region with a localized zone of horizontal tensions in the betics and the alboran sea the presence of intermediate depth and deep earthquakes is tentatively explained as caused by two consecutive processes of subduction

modern tectonic stress field in the mediterranean region evidence for variation in stress directions at different scales summary a compilation of more than one thousand stress indicators which include in situ stress measurements focal mechanisms microtectonic and other geological data allowed us to reconstruct the modern stress field in the mediterranean region and the surrounding area average stress directions at different scales have been reconstructed by means of a linear interpolation method this method takes into account the distribution scale and quality of stress data the results of the interpolation at plate scale allow us to recognize slightly deformed regions such as the northwestern european platform where average maximum horizontal stress direction is oriented roughly nnw sse subparallel to absolute and relative plate velocity directions other regions such as the caucasus alps and pyrenees where recent tectonic deformation and seismicity are present display important variations of stress directions the reconstruction of the average stress directions at different scales within the french alps pointed out that the average stress field pattern may vary from one scale to another nevertheless variations of stress directions at a given scale are consistent with the kinematics of faults of the same scale

palaeomagnetic rotations and fault kinematics in the rif arc of morocco palaeomagnetic and structural investigations in the rif arc of morocco indicate that there have been large rotations associated with a pattern of outwardly directed thrusting rock magnetic experiments in conjunction with thermal and alternating field demagnetization demonstrate that eight sites in jurassic and cretaceous limestones along the internal external boundary have a stable remanent magnetization this is in most cases rotated anticlockwise by as much as 100 from the expected mesozoic declination but in the tetuan area there are large clockwise rotations kinematic indicators from fault surfaces indicate the following 1 in the eastern rif there has been predominantly south directed thrusting partly overprinted by extensional and sinistral strike slip faults 2 at the eastern end of the n 70 e striking jebha fault zone there is a pattern of dominant sinistral ne trending and subsidiary dextral se trending strike slip faults overprinted by normal faults while at the western end deformation consists largely of south directed thrusting 3 in the northern section of the chain where the structural trends are dominantly n s thrusting is directed w to nw it is suggested that the data are best explained by differential motion and rotation of thrust sheets during outwardly directed thrusting around the arc

assessing soil erosion in mediterranean karst landscapes of lebanon using remote sensing and gis abstract maps showing the potential for soil erosion at 1 100 000 scale are produced in a study area within lebanon that can be used for evaluating erosion of mediterranean karstic terrain with two different sets of impact factors built into an erosion model the first set of factors is soil erodibility morphology land cover use and rainfall erosivity the second is obtained by the first adding a fifth factor rock infiltration high infiltration can reflect high recharge therefore decreasing the potential of surface runoff and hence the quantity of transported materials infiltration is derived as a function of lithology lineament density karstification and drainage density all of which can be easily extracted from satellite imagery the influence of these factors is assessed by a weight rate approach sharing similarities between quantitative and qualitative methods and depending on pair wise comparison matrix the main outcome was the production of factorial maps and erosion susceptibility maps scale 1 100 000 spatial and attribute comparison of erosion maps indicates that the model that includes a measure of rock infiltration better represents erosion potential field investigation of rills and gullies shows 87 5 precision of the model with rock infiltration this is 17 5 greater than the precision of the model without rock infiltration these results indicate the necessity and importance of integrating information on infiltration of rock outcrops to assess soil erosion in mediterranean karst landscapes

microearthquake seismicity and fault plane solutions around the nekor strike slip fault morocco abstract three hundred and twenty eight earthquakes recorded in the course of 5 weeks in 1989 in the central rif of northern morocco provided no evidence for activity on the nekor fault the principal geological structure in the region itself most of the seismicity is located northwest of the nekor fault most of the 41 fault plane solutions show mainly strike slip motion left lateral on n s striking planes with p axes trending n145 this deformation is consistent with the n s trending normal faults caused by the e w quaternary extension and with the present relative nw se convergence between africa and europe the active deformation around the eastern rif is better represented by a distributed shear zone than by a strike slip fault

influence of shear and deviatoric stress on the evolution of permeability in fractured rock 1 the evolution of permeability in fractured rock as a function of effective normal stress shear displacement and damage remains a complex issue in this contribution we report on experiments in which rock surfaces were subject to direct shear under controlled pore pressure and true triaxial stress conditions while permeability was monitored continuously via flow parallel to the shear direction shear tests were performed in a pressure vessel under drained conditions on samples of novaculite arkansas and diorite coso geothermal field california the sample pairs were sheared to 18 mm of total displacement at 5 mm s at room temperature and at effective normal stresses on the shear plane ranging from 5 to 20 mpa permeability evolution was measured throughout shearing via flow of distilled water from an upstream reservoir discharging downstream of the sample at atmospheric pressure for diorite and novaculite initial preshear fracture permeability is 0 5 1 10 14 m 2 and largely independent of the applied effective normal stresses these permeabilities correspond to equivalent hydraulic apertures of 15 20 mm because of the progressive formation of gouge during shear the postshear permeability of the diorite fracture drops to a final steady value of 0 5 10 17 m 2 the behavior is similar in novaculite but the final permeability of 0 5 10 16 m 2 is obtained only at an effective normal stress of 20 mpa

hydraulic mechanical properties of microfaults in granitic rock using the punch through shear test abstract fault zones are key features in crystalline geothermal reservoirs or in other subsurface environments due to the fact that they act as main fluid pathways an adequate experimental description of the evolution of permeability of a realistic microscopic fault zone under in situ reservoir and fracture parallel flow conditions is required to address this topic we demonstrate a novel experimental set up punch through shear test that is able to generate a realistic shear zone microfault under in situ reservoir conditions while simultaneously measuring permeability and dilation three samples of intact granite from the odenwald upper rhine graben were placed into a mts 815 tri axial compression cell where a self designed piston assembly punched down the inner cylinder of the sample creating the desired microfault geometry with a given offset permeability was measured and fracture dilation was inferred from an lvdt extensometer chain as well as the balance of fluid volume flowing in and out of the sample after fracture generation the shear displacement was increased to 1 2 mm and pore pressure changes of 5 or 10 mpa were applied cyclically to simulate injection and production scenarios formation of a microfault increased the permeability of the granite rock by 2 to almost 3 orders of magnitude further shear displacement led to a small increase in permeability by a factor of 1 1 to 4 0 but permeability was reduced by a factor of 2 5 to 4 within 16 h due to compaction and fault healing effective pressure cycling led to reversible permeability changes ct images showed that the fracture network is rather complex but depicts all features commonly observed in larger scale fault zones

coping with earthquakes induced by fluid injection large areas of the united states long considered geologically stable with little or no detected seismicity have recently become seismically active the increase in earthquake activity began in the mid continent starting in 2001 1 and has continued to rise in 2014 the rate of occurrence of earthquakes with magnitudes m of 3 and greater in oklahoma exceeded that in california see the figure this elevated activity includes larger earthquakes several with m 5 that have caused significant damage 2 3 to a large extent the increasing rate of earthquakes in the mid continent is due to fluid injection activities used in modern energy production 1 4 5 we explore potential avenues for mitigating effects of induced seismicity although the united states is our focus here canada china the uk and others confront similar problems associated with oil and gas production whereas quakes induced by geothermal activities affect switzerland germany and others

seismological evidence for a delamination process in the lithosphere under the alboran sea summary the continental collision between the african and eurasian plates in the iberian peninsula is solved with a nw se compression with an extensional basin the alboran sea to explain this paradox several models have been proposed including the subduction process of a lithospheric plate in this study a relocation of the seismicity of the area using a jhd algorithm for the period 1950 1995 has been performed which shows a specific hypocentre pattern that is not compatible with plate subduction in addition the direction of the stresses acting in the area has been determined through a comprehensive study of all existing focal mechanisms together with calculations for 19 new earthquakes with sufficient data to determine the focal solution after considering all these data the absence of intermediate shocks in the central part of the alboran basin and the predominantly thrusting mechanisms at the borders of the basin with pressure axes perpendicular to the front we consider a delamination process as a possible mechanism acting in the area

seismicity and focal mechanisms in south spain abstract recent improvements in regional seismological networks allow a better definition of the seismicity and the determination of focal mechanisms in south spain this region is part of the lithospheric plate boundary between africa and eurasia and shows a continuous seismic activity of moderate magnitude m h h 650 km earthquakes also occurring in the region eight fault plane solutions have been determined that can be related to the tectonics of the area the solutions for the shallow shocks are compatible with regional stresses with horizontal compressions in nw se direction and tensions in e w direction that produce normal faulting along the n30 to 60 w and n10 to 30 e systems of faults the mechanisms of the intermediate depth shocks can be explained in terms of a subduction zone from africa in a nw direction that is under compression

anthropogenic seismicity rates and operational parameters at the salton sea geothermal field geothermal power is a growing energy source however efforts to increase production are tempered by concern over induced earthquakes although increased seismicity commonly accompanies geothermal production induced earthquake rate cannot currently be forecast on the basis of fluid injection volumes or any other operational parameters we show that at the salton sea geothermal field the total volume of fluid extracted or injected tracks the long term evolution of seismicity after correcting for the aftershock rate the net fluid volume extracted injected provides the best correlation with seismicity in recent years we model the background earthquake rate with a linear combination of injection and net production rates that allows us to track the secular development of the field as the number of earthquakes per fluid volume injected decreases over time

induced seismic deformation in the cogdell oil field of west texas a sequence of induced earthquakes occurred at the cogdell oil field in west texas from about 1974 to 1982 the earthquakes occurred within an array of injecting wells which surrounded the perimeter of the field and which decreased in radius during the life of the injection project we examine this sequence of earthquakes in terms of two failure models in the first model seismic failure occurs when and where fluid pressures exceed some critical value in the second model earthquakes occur at the edges of low fluid pressure areas where stresses have been transferred as a result of aseismic deformation in adjacent high fluid pressure regions we calculate the history of fluid pressures in the cogdell field using the theis equation for fluid flow in an areally infinite aquifer the calculations show that the earthquakes occur in a region of relatively low pressure surrounded by regions of higher fluid pressure the cogdell earthquakes may occur on pre existing faults however fluid pressures are sufficiently high in surrounding portions of the field to also produce failure a long time delay between the start of injection and the onset of seismicity may correspond to the time required for fluid pressures on a pre existing fault to reach critical values or may be the result of an evolving injection pattern whereby the inward migration of injecting wells produces aseismic failure which loads stress onto stronger regions within the center of the field injection of fluids for secondary recovery occurs at over three thousand sites in the state of texas many of these sites are geographically near cogdell and many have higher injection pressures and volumes of injected fluid than cogdell however they do not exhibit any seismicity a failure model which incorporates stress loading suggests that the perimeter injection pattern is responsible for the onset of seismicity a consequence of this interpretation is that many other injection fields may be undergoing large amounts of aseismic deformation

present day state of stress in northern morocco from focal mechanism analysis abstract the use of focal mechanisms of micro earthquakes and moderate teleseisms in the al hoceima area northern morocco enables the determination of the state of stress in the southern part of the gibraltar arc two different states of stress were determined 1 a ene wsw extension in the imzouren area probably with similar magnitudes of 2 and 1 which may be controlled by pre existing structures and 2 a strike slip regime in beni boucetta tamassint and beni abdallah areas 1 nnw sse 3 ene wsw in the two first areas and 1 ne sw 3 nw se in the latter contrary to recently proposed ideas the mean state of stress determined with the help of moderate teleseisms corresponds to a strike slip regime with a nnw sse oriented main compressional axis and a ene wsw horizontal extension similar to the stress field determined from neotectonic studies and somewhat different from that determined from the el asnam aftershock sequence of 1980