earthquake generated tsunamis in the mediterranean sea scenarios of potential threats to southern italy italian civil defense project development of new technologies for the protection of the italian territory from natural hazards funded by the italian ministry of university and research

nonlinear elastic effects on permanent deformation due to large earthquakes abstract large earthquakes generate significant deformations near fault zones and it is known that under such conditions rocks do not behave linearly this nonlinearity is generally assumed to be due to ductile processes however some nonlinear elastic behavior is possible as well and this should have an effect on the ground deformation near fault zones which might be observable seismically or geodetically we calculate the difference of the permanent displacement field due to an earthquake when we consider hooke s law and a general nonlinear law under the simplified assumption that the nonlinear part of the constitutive law has a small effect we use a perturbation approach and keep only the first term this first term depends on m o r 3 implying that for large moments m o and small distances r the seismic moment as obtained far away from the source and within the linear regime will always be greater than the geodetic moment obtained within the nonlinear regime this result is in principle against our intuition since seismic moments relate to the rupture process of the main event which normally takes place during minutes while geodetic moments relate to the rupture process of the main event plus foreshocks if any aftershocks and other slow afterslip processes which normally occur during hours and days aftershocks normally share the same mechanism as the main event increasing thus the total moment of the sequence therefore geodetic moment should intuitively be greater than the seismic moment interestingly this reasoning yields the opposite effect than what is observed for large earthquakes as the cases of the chile 1960 m w 9 5 alaska 1964 m w 9 2 and some evidence for the sumatra 2005 m w 9 3 as well as other smaller earthquakes if the difference of geodetic and seismic moments is a real phenomenon it could be due to several factors we suggest here that one of these factors could be due to a nonlinear elastic effect

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

the 2003 boumerdes algeria earthquake regional moment tensor analysis 1 we used regional broadband seismograms to determine seismic moment tensors for the destructive may 21 2003 boumerdes algeria mw 7 0 earthquake and its larger aftershocks fully automatic inversions using near real time data provided solutions for seven mw 4 7 events within 90 minutes after event occurrence after adding off line data we manually obtained 30 solutions mw 3 8 from may 2003 to january 2004 all have shallow source depths 6 21 km the median p axis orientation 338 of 24 thrust and four strike slip events is consistent with africa eurasia plate motion 330 the main shock hypocenter at 8 10 km depth at the coastline and its shallow southward dip 25 5 puts the fault surface trace 15 20 km offshore consistent with documented seafloor deformation at the base of the continental slope a main shock rupture length of about 50 km is deduced from first day aftershocks and location of strike slip events the strike slip events probably define the western rupture end and indicate a left step of main convergence fault strike variability of thrust events suggests fault orientation changes and possibly fault segmentation

slip distribution of the 2003 boumerdes zemmouri earthquake algeria from teleseismic gps and coastal uplift data 1 using a joint inversion of seismological waveforms and ground displacement observations we estimate several parameters of the fault geometry and rupture process of the mw 6 9 may 21 2003 boumerdes zemmouri earthquake the relocated epicenter is considered as a known parameter total rupture length rupture duration and maximum slip are 55 km from 3 4 e to 4 0 e 12 s and 3 m the modeled south dipping reverse fault oriented ene wsw outcrops a few km offshore which is consistent with the absence of observed surface rupture inland two shallow and relatively localized slip zones are found on both sides of the hypocenter to the sw between boumerdes and zemmouri slip is concentrated between 11 and 2 km depth to the ne between zemmouri and dellys slip is concentrated between 6 km depth and the sea floor various resolution tests indicate that our model is well constrained by the available data and help understanding which data constrains each parameter of the model

seismic tomography of crustal p and s across eurasia summary in this paper we present inversion results for regional pg and sg phases for the eurasian continent to explore its use for understanding upper crustal velocity structure tomographic inversion of traveltimes from first arriving compressional and shear waves for velocity structure has been applied with great success at all length scales ranging from the laboratory benchtop to the entire earth while inversion of later arriving phases has been much more limited our inversion is performed using a damped smoothed lsqr implementation that solves for site and event terms as well as for velocity along great circle paths between the source and receiver results are broadly consistent with published upper crustal velocities for eurasia with predominantly high velocities in cratonic regions generally but not always lower velocities are observed in orogenic and extensional areas and in deep sedimentary basins a spotcomparison of vp vs from local and regional studies compares well with the ratio of observed pg to sg velocities from our study where resolution is high resolution is determined through the use of checkerboard tests and these suggest that in regions where data density is high we can resolve features down to at least 2 with 4 possible over broader areas rms residual reductions are on the order of 25 per cent for sg and 30 per cent for pg

rupture parameters of the 2003 zemmouri mw 6 8 algeria earthquake from joint inversion of interferometric synthetic aperture radar coastal uplift and gps 1 we study the surface deformation associated with the 21 may 2003 mw 6 8 zemmouri algeria earthquake the strongest seismic event felt in the algiers region since 1716 the thrust earthquake mechanism and related surface deformation revealed an average 0 50 m coastal uplift along 55 km long coastline we obtain coseismic interferograms using envisat advanced synthetic aperture radar asar is2 and radarsat standard beam st4 data from both the ascending and descending orbits of envisat satellite whereas the radarsat data proved useful only in the descending mode while the two radarsat interferograms cover the earthquake area envisat data cover only the western half of the rupture zone although the interferometric synthetic aperture radar insar coherence in the epicenter area is poor deformation fringes are observed along the coast in different patches in the boumerdes area the maximum coseismic deformation is indicated by the high gradient of fringes visible in all interferograms in agreement with field measurements tape differential gps leveling and gps to constrain the earthquake rupture parameters we model the interferograms and uplift measurements using elastic dislocations on triangular fault patches in an elastic and homogeneous half space we invert the coseismic slip using first a planar surface and second a curved fault both constructed from triangular elements using poly3dinv program that uses a damped least square minimization the best fit of insar coastal uplift and gps data corresponds to a 65 km long fault rupture dipping 40 to 50 se located at 8 to 13 km offshore with a change in strike west of boumerdes from n60 65 to n95 105 the inferred rupture geometry at depth correlates well with the seismological results and may have critical implications for the seismic hazard assessment of the algiers region

turbidite chronostratigraphy off algiers central algerian margin a key for reconstructing holocene paleo earthquake cycles northern algeria is threatened by moderate to large magnitude earthquakes resulting from the slow convergence between the african and european plates main active faults are located offshore along the algerian coast as exemplified by the 2003 mw 6 8 boumerdes earthquake this event triggered numerous and widespread turbidity currents over 150 km along strike in the algerian basin reaching 2800 m of water depth and demonstrates the multi source and multi path characteristics of earthquake triggered turbidity flows along this margin segment we rely on the sedimentological analysis of five cores located at the toe of the algiers margin close to the 2003 cable break sites to explore the potential for holocene turbidite paleoseismology radiocarbon measurements provide age models for hemipelagic sediments based on sedimentary facies identification analysis of depositional sequences stacking pattern and a stratigraphic framework established by age models a first correlation of turbidites between the 5 cores is attempted the number of turbidites is constant at the base of the continental slope and decreases seawards over 80 km away from the coast from turbidite correlations 36 synchronous events are identified along the algiers margin segment over the last 9 kyr and are tentatively interpreted as seismically triggered providing a 250 yr mean recurrence interval the main historical earthquakes in the algiers area 2003 1716 and 1365 ce reasonably correlate with three out of the four last turbidites strengthening the hypothesis that turbidites are suitable markers for holocene paleoseismology recurrence intervals of turbidites range between 50 and 900 yr defining quiescence periods exceeding 450 yr three quiescence periods lasting about 800 1400 and 500 yr 7 6 2 ka bp 5 4 4 ka bp and 1 5 1 ka bp respectively support irregular earthquake cycling earthquake triggered turbidites are more frequent in the study area than in the western adjacent margin segment offshore el asnam this higher frequency could arise from the close location of the seismogenic faults beneath the continental slope whereas they are located several tenths of kilometers onland in the el asnam area implying less instabilities of the submarine slope

shaking intensity from injection induced versus tectonic earthquakes in the central eastern united states abstract although instrumental recordings of earthquakes in the central and eastern united states ceus remain sparse the u s geological survey s did you feel it dyfi system now provides excellent characterization of shaking intensities caused by induced and tectonic earthquakes seventeen ceus events are considered between 2013 and 2015 it is shown that for 15 events observed intensities at epicentral distances greater than 10 km are lower than expected given a published intensity prediction equation for the region using simple published relations among intensity magnitude and stress drop the results suggest that 15 of the 17 events have low stress drop for those 15 events intensities within 10 km epicentral distance are closer to predicted values which can be explained as a consequence of relatively shallow source depths the results suggest that those 15 events most of which occurred in areas where induced earthquakes have occurred previously were likely induced although modera

source parameters of microearthquakes on an interplate asperity off kamaishi ne japan over two earthquake cycles summary we have estimated the source parameters of interplate earthquakes in an earthquake cluster off kamaishi ne japan over two cycles of m 4 9 repeating earthquakes the m 4 9 earthquake sequence is composed of nine events that occurred since 1957 which have a strong periodicity 5 5 0 7 yr and constant size m4 9 0 2 probably due to stable sliding around the source area asperity using p and s wave traveltime differentials estimated from waveform cross spectra three m 4 9 main shocks and 50 accompanying microearthquakes m1 5 3 6 from 1995 to 2008 were precisely relocated the source sizes stress drops and slip amounts for earthquakes of m2 4 or larger were also estimated from corner frequencies and seismic moments using simultaneous inversion of stacked spectral ratios relocation using the double difference method shows that the slip area of the 2008 m 4 9 main shock is co located with those of the 1995 and 2001 m 4 9 main shocks four groups of microearthquake clusters are located in and around the mainshock slip areas of these two clusters are located at the deeper and shallower edge of the slip areas and most of these microearthquakes occurred repeatedly in the interseismic period two other clusters located near the centre of the mainshock source areas are not as active as the clusters near the edge the occurrence of these earthquakes is limited to the latter half of the earthquake cycles of the m 4 9 main shock similar spatial and temporal features of microearthquake occurrence were seen for two other cycles before the 1995 m5 0 and 1990 m5 0 main shocks based on group identification by waveform similarities stress drops of microearthquakes are 3 11 mpa and are relatively constant within each group during the two earthquake cycles the 2001 and 2008 m 4 9 earthquakes have larger stress drops of 41 and 27 mpa respectively these results show that the stress drop is probably determined by the fault properties and does not change much for earthquakes rupturing in the same area the occurrence of microearthquakes in the interseismic period suggests the intrusion of aseismic slip causing a loading of these patches we also found that some earthquakes near the centre of the mainshock source area occurred just after the earthquakes at the deeper edge of the mainshock source area these seismic activities probably indicate episodic aseismic slip migrating from the deeper regions in the mainshock asperity to its centre during interseismic periods comparison of the source parameters for the 2001 and 2008 main shocks shows that the seismic moments 1 04 1016 nm and 1 12 1016 nm for the 2008 and 2001 earthquakes respectively and source sizes radius 570 m and 540 m for the 2008 and 2001 earthquakes respectively are comparable based on careful phase identification and hypocentre relocation by constraining the hypocentres of other small earthquakes to their precisely located centroids we found that the hypocentres of the 2001 and 2008 m 4 9 events are located in the southeastern part of the mainshock source area this location does not correspond to either episodic slip area or hypocentres of small earthquakes that occurred during the earthquake cycle

stress drop estimates of potentially induced earthquakes in the guy greenbrier sequence we calculate corner frequencies and stress drops for 25 potentially induced earthquakes mw 2 17 2 57 in the guy greenbrier sequence in the central arkansas we use the spectral ratio method employing highly similar earthquakes as empirical green s functions egfs we show that multiple egfs give consistent corner frequency estimates for the same earthquake and find a range of stress drops of 1 02 mpa to 42 50 mpa with a median of 10 57 mpa by using the brune spectral model and the source parameters given by sato and hirasawa 1973 we also analyze stress drop dependence on the assumed spectral models and source parameters and use a bootstrapping analysis to calculate the uncertainty in corner frequency and stress drop estimates the boatwright spectral model leads to lower stress drop estimates than the brune spectral model due to the limited bandwidth and fixed fall off rates we find that the uncertainty in the stress drop of each earthquake is generally much smaller than the range of stress drop estimates the value and range of these stress drops of the potentially induced earthquakes are similar to tectonic earthquakes in california reported by other spectral ratio studies our results highlight the value of spectral ratio analyses of earthquakes in the central united states

landslide tsunami vulnerability in the ligurian sea case study of the 1979 october 16 nice international airport submarine landslide and of identified geological mass failures summary the ligurian sea at the france italy boarder of the mediterranean sea has experienced in the past numerous submarine landslides within its very near continental slope the continental shelf being very narrow the most recent occurred on the 1979 october 16 near nice international airport and generated tsunami waves of order 3 m of amplitude in some specific locations more ancient landslides are also easily identified through bathymetric surveys of the seafloor for the 1979 event we propose two distinct tsunamigenic landslides based on identified scars observable on the seafloor the first one corresponds to the volume vol1 that slid at the airport in shallow water while the second one corresponds to the more substantial volume vol2 that has been localized at the slope former studies indicate that only the combination of the two slides may explain the event we complement these studies by asserting that when the two slides are taken separately they already explain a significant although not a total part of the event vol1 explains partly the tsunami observations in the vicinity of the airport while vol2 contributes to explain the ones away from the area in particular at antibes where the highest wave has been observed the modelling effort is then extended to evaluate the tsunamigenesis of selected but representative former landslides having a clear scar signature the vulnerability of the area to landslide triggered tsunami is then proposed to discussion along with possible mechanisms that can be responsible for local wave amplification

stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 mw 6 9 zemmouri algeria earthquake stress transfer among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake 1 the essential features of stress interaction among earthquakes on en echelon thrusts and tear faults were investigated first through idealized examples and then by study of thrust faulting in algeria we calculated coseismic stress changes caused by the 2003 m w 6 9 zemmouri earthquake finding that a large majority of the zemmouri afterslip sites were brought several bars closer to coulomb failure by the coseismic stresses while the majority of aftershock nodal planes were brought closer to failure by an average of 2 bars further we calculated that the shallow portions of the adjacent thenia tear fault which sustained 0 25 m slip were brought 2 bars closer to failure we calculated that the coulomb stress increased by 1 5 bars on the deeper portions of the adjacent boumerdes thrust which lies just 10 20 km from the city of algiers both the boumerdes and thenia faults were illuminated by aftershocks over the next 6 years the entire south dipping thrust system extending 80 km to the southwest experienced an increased rate of seismicity the stress also increased by 0 4 bar on the east sahel thrust fault west of the zemmouri rupture algiers suffered large damaging earthquakes in a d 1365 and 1716 and is today home to 3 million people if these shocks occurred on the east sahel fault and if it has a 2 mm yr tectonic loading rate then enough loading has accumulated to produce a m w 6 6 6 9 shock today thus these potentially lethal faults need better understanding of their slip rate and earthquake history among en echelon and opposing thrusts and tear faults triggering caused by the 2003 m w 6 9 zemmouri algeria earthquake

new empirical relationships among magnitude rupture length rupture width rupture area and surface displacement source parameters for historical earthquakes worldwide are compiled to develop a series of empirical relationships among moment magnitude m surface rupture length subsurface rupture length downdip rupture width rupture area and maximum and average displacement per event the resulting data base is a significant update of previous compilations and includes the additional source parameters of seismic moment moment magnitude subsurface rupture length downdip rupture width and average surface displacement each source parameter is classified as reliable or unreliable based on our evaluation of the accuracy of individual values only the reliable source parameters are used in the final analyses in comparing source parameters we note the following trends 1 generally the length of rupture at the surface is equal to 75 of the subsurface rupture length however the ratio of surface rupture length to subsurface rupture length increases with magnitude 2 the average surface displacement per event is about one half the maximum surface displacement per event and 3 the average subsurface displacement on the fault plane is less than the maximum surface displacement but more than the average surface displacement thus for most earthquakes in this data base slip on the fault plane at seismogenic depths is manifested by similar displacements at the surface log linear regressions between earthquake magnitude and surface rupture length subsurface rupture length and rupture area are especially well correlated showing standard deviations of 0 25 to 0 35 magnitude units most relationships are not statistically different at a 95 significance level as a function of the style of faulting thus we consider the regressions for all slip types to be appropriate for most applications regressions between magnitude and displacement magnitude and rupture width and between displacement and rupture length are less well correlated and have larger standard deviation than regressions between magnitude and length or area the large number of data points in most of these regressions and their statistical stability suggest that they are unlikely to change significantly in response to additional data separating the data according to extensional and compressional tectonic environments neither provides statistically different results nor improves the statistical significance of the regressions regressions for cases in which earthquake magnitude is either the independent or the dependent parameter can be used to estimate maximum earthquake magnitudes both for surface faults and for subsurface seismic sources such as blind faults and to estimate the expected surface displacement along a fault for a given size earthquake

fluid induced earthquakes with variable stress drop the static stress drop of an earthquake which quantifies the ratio of seismic slip to the size of the rupture is almost constant over several orders of magnitudes although variations are often observed it is difficult however to attribute these variations either to a well defined phenomenon or simply to measurement uncertainty in this study we analyze the static stress drop of earthquakes that occurred during a water circulation test in the soultz sous forets france geothermal reservoir in 2010 during this circulation test 411 earthquakes were recorded the largest event having a magnitude md2 3 we show that several earthquakes in the reservoir can be combined into groups of closely located similar repeating waveforms we infer that the amplitudes and hence magnitudes vary between the repeaters although the waveforms and spectra are both similar in shape we measure similar corner frequencies for these events despite their different magnitudes suggesting a similar rupture size our results imply that events at the same location may exhibit stress drop variations by as much as a factor of 300 we interpret that this variation in stress drop is caused by fluid pressure at the interface reducing the normal stress we also hypothesize that the observed variations reflect a transition from stable to unstable slip on the imaged asperities

geodetic measurements of crustal deformation in the western mediterranean and europe geodetic measurements of crustal deformation over large areas deforming at slow rates 5 mm yr over more than 1000 km such as the western mediterranean and western europe are still a challenge because 1 these rates are close to the current resolution of the geodetic techniques 2 inaccuracies in the reference frame implementation may be on the same order as the tectonic velocities we present a new velocity field for western europe and the western mediterranean derived from a rigorous combination of 1 a selection of sites from the itrf2000 solution 2 a subset of sites from the european permanent gps network solution 3 a solution of the french national geodetic permanent gps network rgp and 4 a solution of a permanent gps network in the western alps regal the resulting velocity field describes horizontal crustal motion at 64 sites in western europe with an accuracy on the order of 1 mm yr or better its analysis shows that central europe behaves rigidly at a 0 4 mm yr level and can therefore be used to define a stable europe reference frame in that reference frame we find that most of europe including areas west of the rhine graben the iberian peninsula the ligurian basin and the corsica sardinian block behaves rigidly at a 0 5 mm yr level in a second step we map recently published geodetic results in the reference frame previously defined geodetic data confirm a counterclockwise rotation of the adriatic microplate with respect to stable europe that appears to control the strain pattern along its boundaries active deformation in the alps apennines and dinarides is probably driven by the independent motion of the adriatic plate rather than by the africa eurasia convergence the analysis of a global gps solution and recently published new estimates for the african plate kinematics indicate that the africa eurasia plate motion may be significantly different from the nuvel1a values in particular geodetic solutions show that the convergence rate between africa and stable europe may be 30 60 slower than the nuvelia prediction and rotated 10 30 counterclockwise in the mediterranean

earthquake source scaling relationships from 1 to 5 ml using seismograms recorded at 2 5 km depth the scaling relationships of earthquake sources less than about magnitude 3 have been the subject of considerable controversy over the last two decades studies of such events have shown a tendency for the constant stress drop self similarity of larger earthquakes to breakdown at small magnitudes and an apparent minimum source dimension of about 100 m has been observed other studies showed that this apparent breakdown in scaling could be an artifact of severe near surface attenuation limiting the spatial resolution of surface data in this study source parameters are determined for over 100 nearby tectonic earthquakes from recordings at a depth of 2 5 km in granite in the cajon pass scientific drill hole southern california comparison of the seismograms recorded at this depth with those at the wellhead clearly demonstrates the effect of the severe attenuation in the upper kilometers of the earth s crust source parameters are calculated by spectral modeling of three component p and s waves assuming four source models based on the brune 2 n 2 model in model l n 2 is fixed and q of p and s waves is determined to be 912 581 1433 and 1078 879 1323 respectively the numbers in parentheses are 1 standard deviation in model 2 qp qs 1000 is assumed and n is allowed to vary the 2 model is a good average for the data set but there is some real scatter supported by the data in model 3 qp qs 1000 is also assumed and 2 is constrained and in model 4 attenuation is ignored and n is allowed to vary source dimensions of less than 10m are observed for all four models 10 times smaller than the proposed minimum no breakdown in constant stress drop scaling is seen in the downhole data approximately ml 1 to 5 5 m0 109 1016 nm the ratio between radiated seismic energy estimated by integrating the velocity squared spectra with adequate signal bandwidth and seismic moment appears to decrease gradually with decreasing moment in the magnitude range 1 to 7 this is not incompatible with a constant stress drop but could result from errors in calculating energy the ratio of the s wave energy to that radiated by the p waves is about 14 after correction for attenuation this low value is consistent with the corner frequency shift of about 1 3 this corner frequency shift is observed for all four source models and therefore is interpreted as being source controlled

rate change observed at jplm after the northridge earthquake geodetic time series determined with the global positioning system indicate that the geodetic rate of a permanent site in pasadena california jplm changed significantly after the 17 january 1994 northridge california earthquake subtracting the pre quake rate and co seismic offset leaves 30 4 mm of integrated eastward excess motion observed in the three years following the earthquake north and vertical components show excess motion of 11 plusmn 3 mm and 25 11 mm respectively local surveys to three additional points near jplm changed by no more than 6 mm e 3 mm n and 15 mm v during the two years after the earthquake ruling out the possibility of a local effect at the jplm monument the direction and size of the post seismic displacements at jplm are not consistent with additional slip on the fault which ruptured the most rapid accumulation of excess motion occurs immediately after the earthquake suggesting a relationship between the two events

variability of seismic source spectra estimated stress drop and radiated energy derived from cohesive zone models of symmetrical and asymmetrical circular and elliptical ruptures large variability of earthquake stress drops and scaled energy has been commonly reported in the literature but it is difficult to assess how much of this variability is caused by underlying physical source processes rather than simply observational uncertainties here we examine a variety of dynamically realistic rupture scenarios for circular and elliptical faults and investigate to what extent the variability in seismically estimated stress drops and scaled energy comes from differences in source geometry rupture directivity and rupture speeds we numerically simulate earthquake source scenarios using a cohesive zone model with the small scale yielding limit where the solution approaches a singular crack model with spontaneous healing of slip compared to symmetrical circular source models asymmetrical models result in larger variability of estimated corner frequencies and scaled energy over the focal sphere the general behavior of the spherical averages of corner frequencies and scaled energy in the subshear regime extends to the supershear regime although shear mach waves generated by the propagation of supershear rupture lead to much higher corner frequency and scaled energy estimates locally our results suggest that at least a factor of 2 difference in the spherical average of corner frequencies is expected in observational studies simply from variability in source characteristics almost independent of the actual stress drops translating into a factor of 8 difference in estimated stress drops furthermore radiation efficiency estimates derived from observed seismic spectra should not be directly interpreted as describing rupture properties unless there are independent constraints on rupture speed and geometry

fault location and source process of the boumerdes algeria earthquake inferred from geodetic and strong motion data the boumerdes earthquake occurred on a fault whose precise location offshore the algerian coast was unknown geodetic data are used to determine the absolute position of the fault the fault might emerge at about 15 km offshore accelerograms are used to infer the space time history of the rupture using a two step inversion in the spectral domain the observed strong motion records agree with the synthetics for the fault location inferred from geodetic data the fault plane ruptured for about 18 seconds the slip distribution on the fault indicates one asperity northwest of the hypocenter with maximum slip amplitude about 3 m this asperity is probably responsible for most of the damage another asperity with slightly smaller slip amplitude is located southeast of the hypocenter the rupture stops its westward propagation close to the thenia fault a structure almost perpendicular to the main fault

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

variability in earthquake stress drop and apparent stress 1 we apply empirical green s function coda based analysis to four earthquake sequences in japan that span a magnitude range of 1 8 to 6 9 to measure radiated energy corner frequency and stress drop we find no systematic dependence of apparent stress or stress drop on seismic moment for these sequences and find they both are log normally distributed however we identify several anomalous events both energetic and enervated that show sharply different spectral signatures from the rest of the population these events indicate that much of the variation in apparent stress and stress drop is statistically significant which may have important implications for seismic hazard analysis

the 2016 mihoub north central algeria earthquake sequence seismological and tectonic aspects abstract on 28 may 2016 at 23 54 utc an mw5 4 earthquake occurred in mihoub village algeria 60 km southeast of algiers this earthquake was the largest event in a sequence recorded from 10 april to 15 july 2016 in addition to the permanent national network a temporary network was installed in the epicentral region after this shock recorded event locations allow us to give a general overview of the sequence and reveal the existence of two main fault segments the first segment on which the first event in the sequence was located is near vertical and trends e w the second fault plane on which the largest event of the sequence was located dips to the southeast and strikes ne sw a total of 46 well constrained focal mechanisms were calculated the events located on the e w striking fault segment show mainly right lateral strike slip strike n70 e dip 77 to the sse rake 150 the events located on the ne sw striking segment show mainly reverse faulting strike n60 e dip 70 to the se rake 130 we calculated the static stress change caused by the first event md4 9 of the sequence the result shows that the fault plane of the largest event in the sequence mw5 4 and most of the aftershocks occurred within an area of increased coulomb stress moreover using the focal mechanisms calculated in this work we estimated the orientations of the main axes of the local stress tensor ellipsoid the results confirm previous findings that the general stress field in this area shows orientations aligned nnw sse to nw se the 2016 mihoub earthquake sequence study thus improves our understanding of seismic hazard in north central algeria

stress drop heterogeneity within tectonically complex regions a case study of san gorgonio pass southern california in general seismic slip along faults reduces the average shear stress within earthquake source regions but stress drops of specific earthquakes are observed to vary widely in size to advance our understanding of variations in stress drop we analysed source parameters of small magnitude events in the greater san gorgonio area southern california in san gorgonio the regional tectonics are controlled by a restraining bend of the san andreas fault system which results in distributed crustal deformation and heterogeneous slip along numerous strike slip and thrust faults stress drops were estimated by fitting a brune type spectral model to source spectra obtained by iteratively stacking the observed amplitude spectra the estimates have large scatter among individual events but the median of event populations shows systematic statistically significant variations we identified several crustal and faulting parameters that may contribute to local variations in stress drop including the style of faulting changes in average tectonic slip rates mineralogical composition of the host rocks as well as the hypocentral depths of seismic events we observed anomalously high stress drops 20 mpa in a small region between the traces of the san gorgonio and mission creek segments of the san andreas fault furthermore the estimated stress drops are higher below depths of 10 km and along the san gorgonio fault segment but are lower both to the north and south away from san gorgonio pass showing an approximate negative correlation with geologic slip rates documenting controlling parameters of stress drop heterogeneity is important to advance regional hazard assessment and our understanding of earthquake rupture processes

source pulse enhancement by deconvolution of an empirical green s function observations of the earthquake source time function are enhanced if path recording site and instrument complexities can be removed from seismograms assuming that a small earthquake has a simple source its seismogram can be treated as an empirical green s function and deconvolved from the seismogram of a larger and or more complex earthquake by spectral division when the deconvolution is well posed the quotient spectrum represents the apparent source time function of the larger event this study shows that with high quality locally recorded earthquake data it is feasible to fourier transform the quotient and obtain a useful result in the time domain in practice the deconvolution can be stabilized by one of several simple techniques in this paper the method is implemented and tested on high quality digital recordings of aftershocks of the jan 9 1982 miramichi new brunswick earthquake in particular seismograms from a jan 17 aftershock 017 13 33 gmt local mag 3 5 exhibit path or site effects which complicate the determination of source parameters after deconvolution the apparent far field source of this event is a simple pulse in displacement with duration 0 07 second for both p and s

apparent break in earthquake scaling due to path and site effects on deep borehole recordings 1 we reexamine the scaling of stress drop and apparent stress rigidity times the ratio between seismically radiated energy to seismic moment with earthquake size for a set of microearthquakes recorded in a deep borehole in long valley california in the first set of calculations we assume a constant q and solve for the corner frequency and seismic moment in the second set of calculations we model the spectral ratio of nearby events to determine the same quantities we find that the spectral ratio technique which can account for path and site effects or nonconstant q yields higher stress drops particularly for the smaller events in the data set the measurements determined from spectral ratios indicate no departure from constant stress drop scaling down to the smallest events in our data set mw 0 8 our results indicate that propagation effects can contaminate measurements of source parameters even in the relatively clean recording environment of a deep borehole just as they do at the earth s surface the scaling of source properties of microearthquakes made from deep borehole recordings may need to be reevaluated

seismotectonics of the lower cheliff basin structural background of the el asnam algeria earthquake the 1980 el asnam earthquake should be understood within its tectonic environment a seismotectonic map of the lower cheliff basin scale 1 500 000 has been synthesized from known geologic tectonic and seismological work on the region and from satellite photos the data set was integrated by a computer in order to handle different scales and projections several important tectonic features divide the region into 5 domains active faults and recent folds are consistent with a nnw sse direction of compression the cheliff basin is limited to the south by the relizane fault the basin is also crossed by three broken folds the eastern one being the one associated with the el asnam fault historical and instrumental seisinicity seems to be located at both ends of relizane fault it is suggested that the sites corresponding to folds and reverse faulting crossing the basin are relevant to seismic risk a simple tectonic model is proposed

tsunami mapping related to local earthquakes on the french italian riviera western mediterranean the ligurian coast located at the french italian border is densely populated as well as a touristic area it is also a location where earthquakes and underwater landslides are recurrent the nature of the local tsunamigenesis is therefore a legitimate question because no tsunami warning system can resolve tsunami arrival times of a few minutes which is the case for the area as far as the seismicity of the area is concerned the frequent recurrent earthquakes are generally of moderate magnitude most of them are lower than mw 5 however the relatively large mw 6 9 earthquake larroque et al in geophys j int 2012 doi 10 1111 j 1365 246x 2012 05498 x that occurred on the february 23 1887 offshore of imperia italian riviera is quite emblematic this unusual event for the region merits a complete study the quantification of its rupture mechanism is essential 1 to understand the regional active deformation but also 2 to evaluate its tsunamigenesis potential by deriving relevant rupture scenarios obtained from our knowledge of the event for that purpose the event is extensively described here the first point has been the subject of quite a few studies based on the seismotectonics of the area the last documented approach has been completed by larroque et al geophys j int 2012 doi 10 1111 j 1365 246x 2012 05498 x who proposed a rupture scenario involving a reverse faulting along a north dipping fault and favoring a mw 6 9 magnitude in the present paper 1 we study the accuracy of their solutions in relation to the computational grid spacing and the dispersive nondispersive parameterization 2 based on an uncertainty on the recorded wave amplitude of the genoa tide gauge they used we propose a mw 6 7 earthquake magnitude solution for the event the kinematics is unchanged co existing with the mw 6 9 3 we evaluate the tsunami coastal impact of the 1887 event and 4 we test a range of possible ruptures that local faults may undergo in order to propose a synoptic mapping of the tsunami threat in the area the spatial distribution of the maximum wave height mwh is provided with a tentative identification of the processes that are responsible for it this latter issue is imperative in order to make our mapping as generic as possible in the framework of our deterministic approach based on realistic scenarios and not on ensemble statistics the predictions suggest that the wave impact is mostly local considering the relatively moderate size of the rupture planes although the present day seismicity in this region is moderate stronger earthquakes m 6 5 have occurred in the past the studied scenarios show that for such events specific localities along the french italian riviera may experience very significant mwh related to the shallow focal depth tested for such scenarios we may reasonably conclude that the tsunami threat is relatively significant and uniform at the italian side of the riviera from ventimiglia to imperia while it is more localized sporadic at the french side from antibes to menton with however higher local level of inundation e g nice city center

the rupture process and location of the 2003 zemmouri boumerdes earthquake mw 6 8 inferred from seismic and geodetic data this work is a study of the earthquake mw 6 8 that occurred on may 21 2003 in zemmouri boumerdes algeria using methodology based on teleseismic data uplift measurements and synthetic aperture radar data as a starting point we fix the two source fault models obtained in this work solution 1 strike 64 dip 50 and rake 97 solution 2 strike 256 dip 40 and rake 91 with a length of 60 km and width of 20 km to calculate the slip distribution that best explains the seismic and geodetic observations the interferometric fringes revealed a strong displacement in the satellite direction 53 cm along the coast of algeria between the cities of boumerdes and zemmouri the inversion of teleseismic body waves for the two focal solution types one plane dipping to the se and the second plane dipping to the nw showed distinct ruptures however both bilateral ruptures included two asperities one near the hypocentre and the other at a shallower location the maximum slip solution 1 3 8 m and solution 2 4 0 m occurred near the hypocentre in both seismic source models the surface displacement model was obtained with okada s equations using the edcmp algorithm the three components of the displacements calculated were projected regarding the satellite direction los line of sight for comparison with the interferogram the geographic location of the fault plane was determined by comparing the uplift measurements with the vertical displacement models calculated with the source at several locations the surface displacements calculated from these source models indicate that the model based on the se plane and the epicentre location at 36 846 n and 3 660 e produces results closer to the interferogram and the uplift measurements

the tsunami induced by the 2003 zemmouri earthquake mw 6 9 algeria modelling and results summary a strong tsunami with sea disturbances observed along the algerian coast but with significant damage mainly in the balearic islands spain harbours affected the western mediterranean following the 2003 zemmouri earthquake m w 6 9 algeria an average regional uplift of 0 55 m was measured along the shoreline in the epicentral area field observations main shock and aftershocks characteristics are consistent with thrust along a 55 km long rupture trending ne sw dipping se the seismotectonic parameters indicate a hypocentre 7 8 km deep and a possible fault break between 5 and 15 km offshore several tide gauges located in the western mediterranean coast indicated an average of 0 4 m of sea level change with a maximum of 2 m in the balearic islands we generated high resolution bathymetry grids from the algerian coasts to the balearic islands coasts in order to test different seismic sources with different fault rupture location strike and dip and model the tsunami initiation and propagation for the modelling we employed the crank nicolson numerical schema with a finite difference method and the okada elastic dislocation theory for the fault rupture we also highlight the different factors responsible for waves amplification around the balearic coast the best fit between synthetic and real data tide gauges gps levelling and coastal uplift as compared to run up values are obtained for a thrust rupture comparable with the earthquake fault inferred from seismotectonic studies and located within 15 km offshore an analysis of t waves reinforces the earthquake rupture origin for the tsunami this study presents the results and modelling of a major tsunami recorded in the western mediterranean sea

the tadjena earthquake mw 5 0 of december 16 2006 in the cheliff region northern algeria waveform modelling regional stresses and relation with the boukadir fault the cheliff region has experienced some significant earthquakes in the last century 1937 1954 and 1980 the most destructive one is that of el asnam on october 10 1980 ms 7 3 io ix which destroyed the chlef city formerly el asnam and its surrounding villages on december 16 2006 a moderate earthquake mw 5 0 hit the cheliff region the maximum observed intensity io v msk scale was observed at abou el hassen benaria bouzghaia and tadjena no damages or human losses were recorded nevertheless minor cracks on walls of the old school at tadjena were observed the point source focal mechanism of the event was determined by inverting the waveforms of three regional broadband stations of the adsn algerian digital seismic network it corresponds to thrust reverse faulting with a strike slip component the stress tensor obtained by the inversion of the 15 focal mechanisms available in the cheliff region exhibits a well constrained compression axis 1 horizontal and trending n145 the nw dipping nodal plane indicating a ne sw thrust fault with a right lateral component strike dip rake 249 38 137 is more compatible with the regional stress tensor than the steep dipping nne ssw nodal plane showing reverse faulting with a left lateral component strike dip rake 15 65 60 accordingly the tadjena moderate size earthquake can be related to the boukadir active fault bordering the lower cheliff basin to the north a situation similar to that of the el asnam fault bordering the middle cheliff basin to the north

investigating uncertainties in empirical green s function analysis of earthquake source parameters i use a well recorded earthquake sequence to investigate the uncertainties of earthquake stress drops calculated using an empirical green s function egf approach the earthquakes in the largest m 2 1 repeating sequence targeted by the san andreas observatory at depth safod parkfield california are recorded by multiple borehole stations and have simple sources well constrained stress drops and abundant smaller earthquakes to use as egfs i perform three tests to estimate quantitatively the likely uncertainties to arise in less optimal settings i use egf earthquakes with a range of cross correlation values and separation distances from the main earthquakes the stress drop measurements decrease by a factor of 3 as the quality of the egf assumption decreases a good egf must be located within approximately one source dimension of the large earthquake with high cross correlation i subsample the large number of measurements for the main earthquakes to investigate the expected stress drop uncertainties in studies where fewer stations or egfs are available if only one measurement is available the uncertainties are likely to be at least 50 the uncertainties decrease to 20 with five or more measurements using multiple egfs is a good alternative to multiple stations to investigate the effects of limited frequency bandwidth i recalculate the corner frequencies after progressively decimating the sample rate decreasing the high frequency limit of the bandwidth decreases the estimate of the corner frequency and stress drop the corner frequency may be underestimated if it is within a factor of 3 of the maximum frequency of the signal

coastal amplification laws for the french tsunami warning center numerical modeling and fast estimate of tsunami wave heights along the french riviera tsunami modeling tools in the french tsunami warning center operational context provide rapidly derived warning levels with a dimensionless variable at basin scale a new forecast method based on coastal amplification laws has been tested to estimate the tsunami onshore height with a focus on the french riviera test site nice area this fast prediction tool provides a coastal tsunami height distribution calculated from the numerical simulation of the deep ocean tsunami amplitude and using a transfer function derived from the green s law due to a lack of tsunami observations in the western mediterranean basin coastal amplification parameters are here defined regarding high resolution nested grids simulations the preliminary results for the nice test site on the basis of nine historical and synthetic sources show a good agreement with the time consuming high resolution modeling the linear approximation is obtained within 1 min in general and provides estimates within a factor of two in amplitude although the resonance effects in harbors and bays are not reproduced in nice harbor especially variation in tsunami amplitude is something that cannot be really assessed because of the magnitude range and maximum energy azimuth of possible events to account for however this method is well suited for a fast first estimate of the coastal tsunami threat forecast

preliminary results of a paleoseismological analysis along the sahel fault algeria new evidence for historical seismic events abstract the 60 km long sahel ridge west of algiers tell atlas north algeria is considered as an ene wsw fault propagation fold running along the mediterranean coast and associated with a north west dipping thrust its proximity with algiers makes this structure a potential source of destructive earthquakes that could hit the capital city as occurred in 1365 ad and 1716 ad the first paleoseismologic investigation on the sahel ridge was conducted in order to detect paleo ruptures related to active faulting and to date them from the first investigations in the area a first trench was excavated across bending moment normal faults induced by flexural slip folding in the hanging wall of the sahel anticline thrust ramp paleoseismological analyses recognize eight rupture events affecting colluvial deposits 14c dating indicates that these events are very young six of them being younger than 778 ad the first sedimentary record indicates two ruptures before 1211 ad i e older than the first historical earthquake documented in the region three events have age ranges compatible with the 1365 1673 and 1716 algiers earthquakes whereas three other ones depict very recent ages i e younger than 1700 ad potential of these secondary extrados faults for determining paleoseismic events and thrust behaviour is discussed

coseismic deformation of the may 21st 2003 mw 6 8 boumerdes earthquake algeria from gps measurements 1 on may 21st 2003 a mw 6 8 earthquake struck the central part of northern algeria causing extensive damage in the boumerdes area 40 km east of algiers it is among the largest events to occur in the western mediterranean over the past 25 years we present gps measurements of horizontal coseismic displacements that provide new constraints on the rupture geometry modeling the data with a uniform dislocation on a rectangular fault in an elastic half space we find that the rupture occurred on a reverse fault dipping 42 s with its upper edge 6 km offshore and lower edge 4 km inland the amplitude distribution of the coseismic displacements indicates that the rupture did not reach the surface at least in its western part and ended to the west around 3 4 e offshore faults like that of the boumerdes earthquake could account for part of the africa eurasia relative plate motion in the western mediterranean and represent a significant seismic threat for algeria

the 17 may 2012 m4 8 earthquake near timpson east texas an event possibly triggered by fluid injection this study summarizes our investigation of the 17 may 2012 mw rmt4 8 earthquake near timpson texas the largest earthquake recorded historically in eastern texas to identify preshocks and aftershocks of the 17 may event we examined the arrivals recorded at nacogdoches natx 30 km from the 17 may epicenter at nearby usarray transportable array stations and at eight temporary stations deployed between 26 may 2012 and mid 2013 at natx we identified seven preshocks the earliest occurring in april 2008 reliably located aftershocks recorded by the temporary stations lie along a 6 km long nw se linear trend corresponding to a previously mapped basement fault that extends across the highest intensity mmi vii region of the 17 may main shock earthquakes in this sequence are relatively shallow with focal depths ranging from 1 6 to 4 6 km evidence supporting these depths include hypocentral locations of exceptionally well recorded aftershocks s p intervals at the nearest stations and comparisons of synthetics and observed seismograms within 3 km of the linear trend of aftershock activity there are two class ii injection disposal wells injecting at 1 9 km depth beginning in august 2006 and february 2007 with injection rates averaging 42 750 m3 mo and 15 600 m3 mo respectively several observations support the hypothesis that fluid injection triggered the timpson sequence well located epicenters are situated near a mapped basement fault and near high volume injection wells focal depths are at or below the depths of injection and the earliest preshock april 2008 occurred after the onset of injection in 2006

comprehensive analysis of earthquake source spectra in southern california we compute and analyze p wave spectra from earthquakes in southern california between 1989 and 2001 using a method that isolates source receiver and path dependent terms we correct observed source spectra for attenuation using both fixed and spatially varying empirical green s function methods estimated brune type stress drops for over 60 000 m l 1 5 to 3 1 earthquakes range from 0 2 to 20 mpa with no dependence on moment or local b value median computed stress drop increases with depth in the upper crust from about 0 6 mpa at the surface to about 2 2 mpa at 8 km where it levels off and remains nearly constant in the midcrust down to about 20 km however the results at shallow depths could also be explained as reduced rupture velocities near the surface rather than a change in stress drop spatially coherent variations in median stress drop are observed with generally low values for the imperial valley and northridge aftershocks and higher values for the eastern transverse ranges and the north end of the san jacinto fault we find no correlation between observed stress drop and distance from the san andreas and other major faults significant along strike variations in stress drop exist for aftershocks of the 1992 landers earthquake which may correlate with differences in main shock slip

full aftershock sequence of the m w 6 9 2003 boumerdes earthquake algeria space time distribution local tomography and seismotectonic implications we present a detailed analysis of the aftershocks of the may 21 2003 boumerdes earthquake m w 6 9 recorded by 35 seismological stations and 2 obs deployed in the epicentral area this network recorded the aftershock activity for about 1 year and resulted in locating about 2500 events the five main aftershocks 4 7 m 5 8 display thrust faulting consistent with the main shock except for the second event m5 8 29 05 2003 which depicts a strike slip focal solution at the western tip of the rupture zone most aftershocks are clustered near the main rupture plane in the footwall or at the westernmost tip of the 2003 boumerdes rupture area many aftershocks last over the whole seismic crisis ahead north of the main rupture zone forming a diffuse low angle surface within the footwall where the coseismic static stress change is predicted to increase at the sw tip of the rupture short lived clusters locate at intersections of faults near the contact between the inner kabylia and outer tell zones the tomographic inversion depicts high velocity p and s wave anomalies coinciding with miocene magmatic intrusive bodies in the upper crust partially hidden by surrounding basins the area of the main shock is associated with a large low velocity body subdivided into sub domains including neogene basins on land and offshore our results support a rupture model strongly controlled by geological inhomogeneities and extending as ramp flat ramp systems upward favoring heterogeneous slip and segmentation in the fault plane with strong afterslip toward the surface the diffuse aftershock activity in the footwall evidences an inherited discontinuity at mid crustal depth that we interpret as the contact of kabylian and african tethyan continental crusts that were stacked during the upper miocene collision

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

testing the earthquake early warning parameter correlations in the southern iberian peninsula the south of the iberian peninsula is of especial interest for the application of earthquake early warning system eews technologies due to the past occurrence of damaging earthquakes such as the 1755 lisbon earthquake however there are several critical issues that need to be addressed in order to develop an eews in this area the first is the magnitude scale inhomogeneity of the available catalogues a second is that most of the available broad band seismograms for this area correspond to earthquakes with magnitudes less than 6 0 recorded at distances greater than 100 km and sometimes with a low signal to noise ratio and third the occurrence of large earthquakes in this area means that the standard eews time window normally used needs to be tested in order to check whether it is long enough our paper describes the results of homogenizing the catalogue magnitudes by using empirical relationships to obtain the moment magnitude mw a criterion based on a threshold value for the signal to noise ratio is applied in order to avoid noise contaminated seismogram data an important part of the study is a check of whether the correlations previously obtained for south iberia are valid for other neighbouring areas such as algeria and for larger earthquakes finally since recent studies have shown that the larger the earthquake the longer the time window needed to properly estimate the magnitude the window was increased progressively from 0 to 20 s in order to study the behaviour of the eews parameters for the largest earthquakes in the database

stress drops of repeating earthquakes on the san andreas fault at parkfield i calculate well resolved corner frequencies and stress drops for 25 earthquakes 1989 2006 in the three repeating sequences targeted by the san andreas fault observatory at depth using borehole data and multiple highly correlated empirical green s functions egfs the earthquakes in the largest magnitude m 2 1 cluster exhibit source spectra well fit by a circular source model the corner frequencies correlate with those from the regional study by allmann and shearer 2007 suggesting that the interevent variability is resolvable the earthquakes have stress drops between 25 and 65 mpa with a gradual increase before the 2004 m6 earthquake followed by an immediate decrease then a rapid return to previous levels the spectra of the cluster of m 1 9 earthquakes include high frequency energy not fit by simple source models and so stress drops are unreliable and probably underestimated 1 20 mpa there is no correlation with previous studies and interevent variation is not resolvable the earthquakes in the smallest magnitude cluster m 1 8 have the highest corner frequencies but similar stress drops 4 120 mpa the stress drops exhibit the same temporal variation as the first cluster but there is poor correlation with allmann and shearer 2007 probably because their frequency bandwidth is too limited

shaking from injection induced earthquakes in the central and eastern united states abstract in this study i consider the ground motions generated by 11 moderate m w 4 0 5 6 earthquakes in the central and eastern united states that are thought or suspected to be induced by fluid injection using spatially rich intensity data from the u s geological survey did you feel it system i show the distance decay of intensities for all events is consistent with that observed for tectonic earthquakes in the region but for all of the events intensities are lower than the values predicted from an intensity prediction equation that successfully characterizes intensities for regional tectonic events i introduce an effective intensity magnitude m ie defined as the magnitude that on average would generate a given intensity distribution for all 11 events m ie is lower than the event magnitude by 0 4 1 3 magnitude units with an average difference of 0 82 units this suggests stress drops of injection induced earthquakes are systematically lower than tectonic earthquakes by an estimated factor of 2 10 however relatively limited data suggest intensities for epicentral distances less than 10 km are more commensurate with expectations for the event magnitude which can be reasonably explained by the shallow focal depth of the events the results suggest damage from injection induced earthquakes will be especially concentrated in the immediate epicentral region

the 21 may 2003 tsunami in the western mediterranean sea statistical and wavelet analyses we report the statistical and wavelet analyses of the 21 may 2003 tsunami produced by an mw 6 8 6 9 thrust earthquake in the western mediterranean sea using 19 tide gauge records the largest trough to crest wave height was 196 cm recorded at the sant antoni station in the lee of the incoming tsunami wave except at one station the first wave was not the largest wave at all the analyzed stations and the largest wave arrived several hours after the first arrival in addition the tsunami waves persisted for more than 1 day at most stations as the spectra of coastal tide gauge stations are strongly influenced by topographic features special care was taken here while interpreting the results of spectral and wavelet analysis our wavelet analysis shows that only a peak at around 23 min is persistent for long duration and other peaks at 14 30 45 and 60 min appeared at short durations the 23 min signal is possibly associated with the width of the source fault whereas the fault length contributed to the 45 min signal based on these dominant periods the tsunami source dimensions are estimated as 95 km 45 km the statistical and wavelet analyses performed here provide some new insights into the characteristics of the tsunami that was generated and propagated in the western mediterranean basin

stress drop variations of induced earthquakes at the basel geothermal site 1 we determine stress drops from p wave spectra of about 1000 earthquakes induced by hydraulic stimulation in crystalline rock for a deep heat mining project in basel switzerland we observe an increase in stress drop by about a factor of five with radial distance from 10 m to 300 m which suggests that stress drop correlates with pore pressure perturbations due to the injection we test this hypothesis by calculating the injection related pore pressure perturbation based on a simple linear pore pressure diffusion model and find a good correlation of the expected pore pressure perturbation with the estimated stress drops

spatial and temporal stress drop variations in small earthquakes near parkfield california 1 we estimate source parameters from spectra of 42367 earthquakes between 1984 and 2005 that occurred in the parkfield segment of the san andreas fault in central california we use a method that isolates the source term of the displacement spectra based on a convolutional model and correct the observed p wave source spectra with a spatially varying empirical green s function egf our brune type stress drop estimates vary from 0 1 to over 100 mpa with a median value of 6 75 mpa which is nearly constant with moment implying self similarity over the ml 0 5 to 3 0 range of our data the corner frequency decreases for earthquakes at shallower depths consistent with slower rupture velocities and reduced shear wave velocities in local velocity models the estimated median stress drops show significant lateral variations we find lower stress drops in the middle mountain asperity and along the creeping fault section and higher stress drops in the hypocentral region of the 2004 m6 0 parkfield earthquake the main shock did not alter the overall pattern of high and low stress drop regions however a statistical test reveals areas with significant changes in computed stress drops after the main shock which we compare to estimated absolute shear stress changes from a main shock slip model by calculating t from the spectral egf ratio we also identify areas with increased attenuation after the main shock and we are able to distinguish source effects and near source attenuation effects in the spectral analysis these results are confirmed independently from spectral ratios of repeating microearthquake clusters

evidence for a post 3 16 ma change in nubia eurasia north america plate motions we combine updated gps velocities from the nubian nu eurasian eu and north american na plates with 500 new 3 16 myr average seafloor spreading rates and nine transform fault azimuths from the northern atlantic and arctic basin seafloor spreading centers to estimate and test for changes in the relative motion between these plates the numerous new seafloor spreading rates and gps velocities improve our ability to detect recent changes in the relative motions of these plates the angular velocity vector that best fits the eu na gps velocities lies significantly north of the 3 ma average pole in accord with previously published geologic evidence that the eu na pole has migrated northward since v3 ma although we also find evidence for a significant post 3 ma change in nu na motion it is less compelling because the nubian plate gps velocity field is sparse and nu na seafloor spreading rates appear to have remained steady within the 1 mm yr 31 uncertainties if we systematically decrease the seafloor spreading rates to correct for outward displacement of seafloor spreading magnetic lineations the nu eu pole derived from gps site velocities lies more than 30 angular degrees south of the tightly constrained 3 ma average estimate and predicts significantly slower and more oblique present day nu eu convergence in the mediterranean both models for nu eu motion pass a key test for their accuracy namely they correctly predict strike slip motion along the well mapped gloria fault east of the azores the change to more oblique nu eu motion may reflect increasing difficulty in maintaining margin normal convergence within this continent continent collision zone 8 2003 published by elsevier b v

blind reverse faulting system associated with the mont chenoua tipaza earthquake of 29 october 1989 north central algeria a shallow and damaging earthquake struck the region of tipaza located on the coast 70 km to the west of algiers north central algeria the main shock was felt as far as 200 km from the epicentral area and particularly in the urbanized zone of algiers the main shock epicentre determined by craag is on mt chenoua close to the coastline coseismic surface breaks with 4 0 km of fault length and 7 0 cm of vertical displacement appeared on the southern side of mt chenoua they consist of cracks and fissures on vertical bedding planes that belong to a neogene flexure the aftershock activity was recorded for several weeks and comprised more than 100 seismic events per day with 1 m 5 aftershocks are distributed in a ene wsw to ne sw zone extending offshore a nw se cross section indicates that seismic events affect the crust to a maximum depth of 20 km showing a complex fault plane geometry dipping to the nw for the main shock the focal mechanism solution obtained from the readings of first motion polarities of seismograms yields an ene wsw reverse fault dipping to the nnw which is in good agreement with both field observations and the aftershock distribution at depth the occurrence of the mt chenoua tipaza moderate sized event in a previously identified active zone improves the seismotectonic characterization of this part of the tellan atlas mountains this thrust and fold geological domain also shows active folds capable of producing larger earthquakes since only a small portion of the sahel anticline ridge has been reactivated a serious seismic hazard must be urgently recognized in the algiers region

frequency dependent attenuation in the crust beneath central france from lg waves data analysis and numerical modeling abstract the quality factor of shear waves in the crust beneath central france is evaluated by the combined use of data analysis and theoretical modeling the measurement is made from lg wave records of 18 earthquakes at 22 short period vertical seismic stations of the french seismic network the geometrical attenuation of lg waves has been calculated through a numerical simulation in a perfectly elastic model the station responses including site effects have been evaluated from lg waves and from records of the seismic noise q has been calculated for a set of 11 frequencies between 0 5 and 10 hz and has been found to be in the form q 290 f 0 52 where f is the frequency the numerical simulation leads to the interpretation of q of lg waves as the mean value of q within the crust theoretical and experimental decay of energy with distance are in very good agreement the lg waves present a different sensitivity to a low q zone whether this zone is associated with the sediments or with scattering in the lower crust the lower crust beneath central france appears from our experimental results to be associated with high values of q

active thrust faulting offshore boumerdes algeria and its relations to the 2003 mw 6 9 earthquake 1 we investigate the active seismogenic fault system in the area of the 2003 mw 6 9 boumerdes earthquake algeria from a high resolution swath bathymetry and seismic survey a series of 5 main fault propagation folds 20 35 km long leave prominent cumulative escarpments on the steep slope and in the deep basin fault activity creates plio quaternary growth strata within uplifted areas such as a rollover basin on the slope and piggyback basins in the deep ocean most thrusts turn to fault propagation folds at the sub surface and depict ramp flat trajectories we find that the two main slip patches of the 2003 mw 6 9 boumerdes earthquake are spatially correlated to two segmented cumulative scarps recognized on the slope and at the foot of the margin the overall geometry indicates the predominance of back thrusts implying underthrusting of the neogene oceanic crust

comment on zemmouri earthquake rupture zone mw 6 8 algeria aftershocks sequence relocation and 3d velocity model by a ayadi et al although often difficult to characterize the relationship between a seismic rupture its aftershock sequence and cumulative subsurface or surface faulting or folding is an important challenge to modern seismology and seismotectonics among other benefits it helps document fault length slip and magnitude relationships reconstruct the evolution of the rupture process through historical and prehistorical times and identify the complexity of the deformation in its path toward the surface this approach is a prerequisite to any seismic hazard assessment but is particularly difficult for faults whose surface trace projects offshore a specific effort to identify and quantify the source parameters of large earthquakes in coastal areas is therefore needed not only in subduction zones but also in areas of slow rate and or diffuse deformation

the northwestern maghreb boundary of the nubia africa plate abstract a study of the present compressional deformation of the northwestern maghreb nubia africa margin is derived from the analysis of more than 20 000 km of seismic profiles in the western part the compression is distributed in a large zone with on land compression in algeria mainly strike slip deformation on the algerian margin and folds and strike slip faulting in eastern spain in the middle of the algerian margin around algiers the evidences of compression become more obvious in this area a ridge trending n s that is interpreted as a middle to late miocene spreading center interacted with the transpressional margin that trends e w north of the location of the boumerdes zemmouri earthquake the oceanic crust is deformed by blind thrusts up to 60 km from the coast these thrusts are south dipping and with the northward dipping thrusts located onshore form a wedge that maybe a positive flower structure at a crustal scale related to the right lateral transpression of the margin in the eastern part of the northwestern maghreb nubia africa deformed belt off eastern algeria and tunisia the deformation is more intense but limited to the north by the continental slope large late miocene tortonian folds are cut by the messinian erosional surface but the present deformation is also evident it is suggested that the deformation with a double vergence may be followed up to the north of sicily after the docking 18 ma of the kabylies to the africa plate the crust has been thinned and the algerian basin opened during the middle late miocene with an e w direction from the late miocene to the present the margin has been rethickened by transpression and uplifted

empirical green s function analysis taking the next step an extension of the empirical green s function egf method is presented that involves determination of source parameters using standard egf deconvolution followed by inversion for a common attenuation parameter for a set of colocated events recordings of three or more colocated events can thus be used to constrain a single path attenuation estimate i apply this method to recordings from the 1995 1996 ridgecrest california earthquake sequence i analyze four clusters consisting of 13 total events with magnitudes between 2 6 and 4 9 i first obtain corner frequencies which are used to infer brune stress drop estimates i obtain stress drop values of 0 3 53 mpa with all but one between 0 3 and 11 mpa with no resolved increase of stress drop with moment with the corner frequencies constrained the inferred attenuation parameters are very consistent they imply an average shear wave quality factor of approximately 20 25 for alluvial sediments within the indian wells valley although the resultant spectral fitting using corner frequency and is good the residuals are consistent among the clusters analyzed their spectral shape is similar to the the theoretical one dimensional response of a layered low velocity structure in the valley an absolute site response cannot be determined by this method because of an ambiguity between absolute response and source spectral amplitudes i show that even this subtle site response can significantly bias estimates of corner frequency and if it is ignored in an inversion for only source and path effects the multiple egf method presented in this paper is analogous to a joint inversion for source path and site effects the use of colocated sets of earthquakes appears to offer significant advantages in improving resolution of all three estimates especially if data are from a single site or sites with similar site response

plio quaternary reactivation of the neogene margin off nw algiers algeria the khayr al din bank the algiers region northern algeria is known to be seismically active with recurrent large m 6 earthquakes because of the lack of high resolution bathymetry the offshore structures remained for a long time poorly known thanks to a new marine data base maradja 2003 cruise the offshore part of the margin is accurately mapped and new active and recent structures are described west of the bay of algiers the margin enlarges forming the khayr al din bank interpreted as a tilted block of the passive margin born during the opening of the algero provencal basin at the slope break a 80 km long fault tip quaternary fold namely the khayr al din fault extends at the foot of the margin off nw algiers and represents the largest active structure of the coastal area together with the sahel anticline we also map for the first time a set of overlapping en echelon active folds in the upper part of the khayr al din bank located off previously known active structures on land most of these faults represent actually a threat for the algiers region in terms of seismic hazard but also geological hazards such as tsunamis as most of them depicts significant dimensions and slip rates the highest long term horizontal shortening rate is found on the khayr al din fault and is estimated at 0 5 0 1 mm yr with a maximal magnitude of 7 3 which provides one of the highest seismogenic potential in the region a new tectonic framework for the algiers region is proposed in which the main south dipping offshore structure of opposite vergence relative to most thrusts on land appears to be nowadays the main driving fault system as also found further east in the boumerdes m 6 8 2003 rupture zone the overall apparent pop up structure of the recent and active faults may result from a progressive migration of the plate limit from the late miocene north dipping suture zone on land to the quaternary south dipping main khayr al din fault at sea suggesting a process of subduction inception

temporal variation in the magnitude frequency distribution during the guy greenbrier earthquake sequence the recent increase in earthquake activity in the central u s has led to concerns about the hazard posed by induced earthquakes understanding earthquake phenomena and monitoring in all settings can be improved by the detection of small events however the catalog of induced earthquakes is incomplete for small events due to the sparse instrumentation this is particularly true in settings of low background seismicity like the central u s we apply single station template matching to detect small earthquakes during the guy greenbrier sequence in central arkansas and find over 100 times more earthquakes than are registered in the advanced national seismic system catalog between july 2010 and october 2011 a complete catalog over nearly 4 units of magnitude enables us to analyze the magnitude frequency distribution of induced earthquakes we find that earthquakes deviated from the gutenberg richter statistics during the operation of nearby injection wells but returned to gutenberg richter statistics after the wells were shut in

shallow afterslip following the 2003 may 21 mw 6 9 boumerdes earthquake algeria summary we investigated post seismic deformation following the 2003 may 21 mw 6 9 boumerdes algeria earthquake using surface displacements from six continuous global positioning system sites that operated in the epicentral area for 2 5 yr following the event we find up to 4 cm of cumulative horizontal displacement during that time period with a time dependence well fit by a logarithmic decay post seismic deformation appears to continue at all sites after the 2 5 yr observation period with rates on the order of 1 cm yr 1 or less the data is consistent with shallow afterslip 0 5 km and shows no evidence for afterslip downdip of the coseismic rupture the data is poorly explained by viscoelastic relaxation in the lower crust or upper mantle or by poroelastic rebound the concentration of afterslip adjacent to and updip of the coseismic rupture at least in the western half of the fault suggests that afterslip is driven by coseismic stresses the correlation between the depth of afterslip and that of the sedimentary wedge along the algerian margin while coseismic slip occurs in deeper basement rocks suggests 1 that post seismic deformation may also involve folding and 2 that spatial variations in frictional properties along the fault correlate with the type of rocks involved