discordant paleomagnetic data for middle cretaceous intrusive rocks from northern baja california latitude displacement tilt or vertical axis rotation 1 paleomagnetic results and u pb zircon dating from the san marcos dike swarm and the el testerazo pluton in the cretaceous peninsular ranges batholith of northern baja california are used to evaluate alternative pre neogene paleogeographic reconstructions of the baja california peninsula the san marcos dike swarm is a dense northwest striking regional dike swarm that is exposed over an 100 km long segment of the batholith and has yielded a u pb zircon crystallization age of 120 1 ma dike attitudes from the swarm suggest a regionally consistent average 320 e strike and 79 ne dip the el testerazo pluton is a younger tonalite intrusion that truncates the northern end of the dike swarm all but one of 36 sites sampled in this study show remanence of normal polarity paleopoles for the san marcos dike swarm and el testerazo pluton are indistinguishable and were combined into a paleopole at 248 1 e 86 6 n a95 4 8 which is displaced with respect to the 122 ma reference pole for stable north america at 198 2 e 72 3 n a95 3 3 the displacement may be described by an apparent clockwise rotation of 18 6 and an apparent northward shift of 8 5 restoring a northward shift of about 3 related to the separation of baja california from north america since 10 ma only a marginal northward displacement of 5 5 is left the clockwise rotation may be the result of crustal block rotations within the right lateral shear systems in northern baja california although there is no geological evidence that supports this possibility alternatively the difference between paleopole and reference pole may be due to tilting of the study area restoring a northeastward tilt of 11 based on the mean dip measured for the san marcos dike swarm in the study area yields a paleopole at 187 6 e 70 8 n a95 5 6 which is indistinguishable from the 122 ma north american reference pole the tilting hypothesis suggested previously as a potential explanation for low inclination of paleomagnetic data from baja california therefore seems to be viable for the discordant paleopoles from this segment of the batholith data obtained previously about 150 km further south and along the western edge of the batholith defined a concordant paleopole without any tilt correction indicating that regional tilting may not be valid for all of baja california

directional properties of van s ses and ulf mt signals at ioannina greece abstract in order to examine the validity of the earthquake prediction technique developed in greece by van varotsos alexopoulos and nomicos and elucidate the underlying physical processes we performed a magnetotelluric mt recording of the ulf band 3 200 s in the vicinity of van s sensitive station ioannina ioa by comparing mt electric field of ionospheric or magnetospheric origin electric field of lightning origin and van s seismic electric signals ses the following facts were revealed 1 the mt electric field always varies in the ene wsw direction indicating existence of significant electrical conductivity contrast near the site 2 the lightning electric field orientation is somewhat more scattered but still holds the same preferred direction as that of the mt electric field the scatter is larger for larger lightning field probably due to closer location of lightning stroke to the station and or due to no linear saturation of the recording signals 3 the ses electric field orientation is even more scattered than that of the lightning origin these observations suggest that the sources of the ses are in the neighborhood of the station it is still unclear how the ses associated with distant earthquakes are emitted from the sources near the ioa station

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

large earthquakes at the ibero maghrebian region basis for an eews large earthquakes mw 6 imax viii occur at the ibero maghrebian region extending from a point 12ow southwest of cape st vincent to tunisia with different characteristics depending on their location which cause considerable damage and casualties seismic activity at this region is associated with the boundary between the lithospheric plates of eurasia and africa which extends from the azores islands to tunisia the boundary at cape st vincent which has a clear oceanic nature in the westernmost part experiences a transition from an oceanic to a continental boundary with the interaction of the southern border of the iberian peninsula the northern border of africa and the alboran basin between them corresponding to a wide area of deformation further to the east the plate boundary recovers its oceanic nature following the northern coast of algeria and tunisia the region has been divided into four zones with different seismic characteristics from west to east large earthquake occurrence focal depth total seismic moment tensor and average seismic slip velocities for each zone along the region show the differences in seismic release of deformation this must be taken into account in developing an eews for the region

moment tensor inversion for iberia maghreb earthquakes 2005 2008 abstract we present and discuss a set of 77 moment tensor solutions for earthquakes in the iberia maghreb region from mid 2005 to the end of 2008 with moment magnitudes ranging from 3 2 to 6 0 inversion is based upon full three component intermediate period waveforms recorded at regional seismic broadband stations following the recent densification of permanent broadband networks and large scale temporary deployments at present more than 150 stations are recording in spain portugal and morocco this unprecedented station density allows analysis of small events from available short distance recordings and in general leads to more reliable source estimates due to data redundancies that permit elimination of waveforms affected by noise or complicated propagation effects the solutions for 2005 2008 constitute an important upgrade of the iberia maghreb moment tensor inventory to 225 solutions to date enhancing the image of seismotectonics at the compressive n algerian margin in the betic alboran shear zone and at the transpressive sw iberian margin as well as providing valuable constraints on seismic deformation in the western betics and the iberian foreland where little information has been previously available new solutions for the foreland and three recent seismic series in the western betics show strike slip and reverse faulting style contrasting with the dominance of normal faulting in the adjacent areas towards east in these areas as well as at the sw iberian margin faulting orientations are heterogeneous including solutions with opposite kinematics this indicates control by local stress conditions and points to fault interaction along the n algerian margin a counterclockwise rotation of slip vectors of thrust events from east to west becomes apparent several solutions for the area offshore cape st vincent are located at sub moho depths between 40 and 60 km supporting a large brittle layer thickness in the oceanic lithosphere

amplitude spectra moment tensor inversion of shallow earthquakes in spain summary the study of focal mechanisms for shallow earthquakes of low to moderate magnitude at regional distances requires a proper inversion technique one of the major problems is the correct separation of path effects from source effects the method used should take into account problems arising from errors in the definition of crustal structure and inclusion of the high frequency content of the waveforms in this study a method of frequency domain moment tensor inversion to determine deviatoric moment tensor solutions from body wave amplitude spectra is described the method has been tested with synthetic data to define instabilities that are due to mismodelling of several parameters the inversion technique is applied to broadband seismic data of shallow 10 km depth earthquakes in spain solutions are obtained for a range of depths and compared with solutions obtained with different methods such as first motion polarities and moment tensor inversion in the time domain a combined fit of amplitude spectra first motion polarities and double couple component is introduced as a method which resolves better the non uniqueness of solution the proposed method can be implemented in fast moment tensor inversion when a green functions database has been created in advance for the studied area

theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake crustal deformation processes occur with relative rapidity when short term precursors appear at the final preparatory stage of a tectonic earthquake this paper contains calculations of crustal bulk strain before an earthquake based on the model of a rigid inclusion the data give initial conditions for the problem of fluid percolation in a two phase medium accompanied by electrokinetic effects the solution provides a description of systems of currents arising in the vicinity of the source region an analysis of this theoretical evidence yields information on the behaviour of short term precursors in telluric currents and the geomagnetic field

simulations of strong ground motion in sw iberia for the 1969 february 28 ms 8 0 and the 1755 november 1 m 8 5 earthquakes i velocity model summary this is the first paper of a series of two concerning strong ground motion in sw iberia due to earthquakes originating from the adjacent atlantic area the aim of this paper is to build and calibrate a velocity model that will be used in the companion paper for seismic intensity modelling of the 1969 m s 8 0 and 1755 m 8 5 8 7 earthquakes taking into account the geological evolution of the region since the palaeozoic we build a 3 d velocity model down to the moho discontinuity substantially different from a simple 1 d layered model the velocity model presented in this paper is built a priori using information originating from a variety of geological and geophysical studies its resolution is sufficient to simulate realistically seismic wave propagation in the low frequency f 0 5 hz range which is the most significant for the study of the destructive effects of large earthquakes at a regional scale to validate the model we compute synthetic seismograms for three recent earthquakes of moderate magnitudes 4 6 m w 5 3 located offshore in the most seismically active area in the region synthetics are generated using a wave propagation code based on the finite difference method which was chosen for its simplicity and accuracy in the frequency range considered in this study 0 1 0 5 hz we compare simulated waveforms with threecomponent seismograms for 9 different stations traveltimes of the direct p waves and the amplitude of ground motion are accurately reproduced at all stations the frequency content of the seismograms fits the observations especially for the lowest frequencies investigated 0 1 0 3 hz for each earthquake the estimated seismic moment is in good agreement with values obtained by other authors using different methods we conclude that the velocity model provides encouraging results for the computation of low frequency seismograms in the region and can be used for the study of larger earthquakes for which the radiated wavefield has a predominant low frequency spectrum

electric field polarization around ioannina van station greece inferred from a resistivity mapping abstract in the summer of 1997 we made a bipole dipole mapping survey around ioannina station of van varotsos alexopoulos and nomicos where detection of the pre seismic electric signal ses has been repeatedly reported since we had found the characteristic directional properties of the electric field in the previous study the present study was aimed to examine it by investigating the shallow electric structure around the station the apparent resistivity tensor was derived from two sets of measured voltages at each receiver position from a rough sketch of the resistivity tensor distribution we found that the electric field was enhanced along the direction parallel to the trend of the basin at receivers located in the conductive basin and perpendicular to it at receivers in the resistive mountainside conductance distribution models with thin plates were constructed by using the measured voltages the results showed that the van station is located on the resistive portion near the contact between the conductive and the resistive part furthermore we simulated the apparent resistivity tensor near the van station on the inferred conductance distribution model although the directional property similar to those of magnetotelluric mt and lightning electric field was not reproduced there we found that the electric field polarization is affected by heterogeneous structure not only around receivers but also around the source

the earthquakes of 29 july 2003 12 february 2007 and 17 december 2009 in the region of cape saint vincent sw iberia and their relation with the 1755 lisbon earthquake abstract the cape saint vincent region is of major seismological interest for its tectonic complexity and for the occurrence of the great 1755 lisbon earthquake no structure capable of generating such a large earthquake has yet been convincingly identified but all authors agree that there is a possibility of a similar earthquake occurring offshore of the cape sometime in the future to shed some light on the region s dynamics we here examine the mechanism of the three largest earthquakes to have occurred in the last 40 years west of the cape 29 july 2003 m w 5 3 12 february 2007 m w 6 1 and 17 december 2009 m w 5 5 by inversion of the body waves and the kinematic slip distribution we estimated the three earthquakes to have had similar characteristics dimensions maximum slip stress drop source time function focal depth and rupture velocity although there were differences in the geometry of the rupture that reflect the great seismotectonic complexity of the zone the focal mechanisms of the 2003 and 2007 earthquakes were similar corresponding to thrusting motion but the 2009 earthquake had a dip slip motion in a vertical plane as deduced from the slip distributions the three shocks show ne sw rupture planes with the energy released propagating to the ne compatible with the regional nw se horizontal compression produced by the convergence of the eurasian and african plates applied to the generation of the 1755 lisbon earthquake this direction of faulting would correspond to a complex rupture along ne sw trending thrust faults at the gorringe bank the horseshoe scarp and the marquis de pombal fault with the rupture propagating to the ne towards the portuguese coast such a model could explain that unusually large and tsunami generating earthquake

physical properties of the variations of the electric field of the earth preceding earthquakes ii determination of epicenter and magnitude abstract as reported in the preceding paper a transient change of the electric field of the earth seismic electric signal hereafter called ses appears many hours before an earthquake eq by measuring this change in a given direction and dividing it with a suitable relative effective resistivity one obtains a quantity that reflects the current density in this direction measurements in two directions e w and n s give the relative signal intensity jrel at the station under consideration by measuring jrel at a number of stations and considering that it attenuates according to a 1 r law the epicenter can be determined with an accuracy usually around 100 km once the epicenter has been determined the product jrel r can be evaluated so that the magnitude m can be estimated by resorting to an empirical log jrel r versus m plot the uncertainty of m is around 0 5 units following sobolev 1975 and for the statistics to be beyond any doubt predictions were officially documented before the eq occurrence for 23 earthquakes with a magnitude equal or greater than ms 5 0 two events were missed the present method is compared to other electrical methods used in china japan and soviet union a number of problems concerning the origin of the effect its directivity and the attenuation with distance remain open for further studies

latest aspects of earthquake prediction in greece based on seismic electric signals ii abstract since 1983 continuous monitoring of the electrotelluric field has been carried out using an array of measuring stations located at various sites in greece the basic physical properties of the transient changes seismic electric signals ses in the electrotelluric field that are forerunners of earthquakes were first described six years ago since then a large body of data has been collected resulting in new insight into various aspects of the method the present paper reviews the latest developments in ses based earthquake prediction and describes the current procedures used to predict the epicenter and magnitude of an impending earthquake a detailed list of the predictions officially issued in greece during the past 3 years january 1 1987 november 30 1989 is also given public warnings were issued well before the most destructive seismic activity

earthquake early warning for southern iberia a p wave threshold based approach 1 the south of the iberian peninsula is a region in which large damaging earthquakes occur separated by long time intervals an example was the great 1755 lisbon earthquake intensity imax x which occurred sw of san vicente cape sw iberian peninsula due to this risk of damaging earthquakes the implementation of earthquake early warning system eews technologies is of considerable interest with the aim of investigating the feasibility of an eews in this region of the iberian peninsula empirical scaling relationships have been derived between the early warning parameters and the earthquake size and or its potential damaging effects for this region an appropriate and suitable strategy is proposed for an eews in the sw iberian peninsula which takes into account the limitations of the existing seismological networks

magnetotelluric evidence for crustal suture zones bounding the southern great valley california a geoelectric section inferred from a regional magnetotelluric study across the coast ranges the great valley and the sierra nevada reveals significant variations in electrical resistivity zones of lower resistivity interpreted at depths from 10 km to at least 30 km lie near mapped geologic boundaries between the coast ranges and the great valley and beneath the eastern side of the great valley the former boundary is inferred by others to separate the subduction complex of the coast ranges from the mafic basement of the great valley the lower resistivities are most likely associated with metasediments trapped between the coast ranges ophiolite and the former oceanic crust beneath the great valley the latter boundary is problematic but may be evidence for a deep metasedimentary section trapped between the ophiolites beneath the great valley and the granitic rocks of the sierra nevada the lack of change in the magnetotelluric phase across the great valley indicates that a suture zone marked by lower resistivities is unlikely to be present beneath the valley however this does not preclude the existence of a resistive suture zone

seismic electric signals from displacement of charged dislocations abstract one possible mechanism for the generation of seismic electric signals is the displacement of segments of charged dislocations responding to changes in the applied stress using information available from the study of simpler ionic crystals a crude estimate is made of the voltage that could be generated from large blocks of the earth s crust during a pre earthquake stress adjustment within the many uncertainties of critical parameters the results are consistent with the magnitudes of precursor signals that have been observed in greece

seismic sources on the iberia african plate boundary and their tectonic implications the plate boundary between iberia and africa has been studied using data on seismicity and focal mechanisms the region has been divided into three areas a the gulf of cadiz b the betics alboran sea and northern morocco and c algeria seismicity shows a complex behavior large shallow earthquakes h 30 km occur in areas a and c and moderate shocks in area b intermediate depth activity 30 h 150 km is located in area b the depth earthquakes h 650 km are located to the south of granada moment rate slip velocity andhvalues have been estimated for shallow shocks and show similar characteristics for the gulf of cadiz and algeria and quite different ones for the central region focal mechanisms of 80 selected shallow earthquakes 8 mb 4 show thrust faulting in the gulf of cadiz and algeria with horizontal nnw sse compression and normal faulting in the alboran sea with e w extension focal mechanisms of 26 intermediate depth earthquakes in the alboran sea display vertical motions with a predominant plane trending e w solutions for very deep shocks correspond to vertical dip slip along n s trends frohlich diagrams and seismic moment tensors show different behavior in the gulf of cadiz betic alboran sea and northern morocco and northern algeria for shallow events the stress pattern of intermediate depth and very deep earthquakes has different directions vertical extension in the nw se direction for intermediate depth earthquakes and tension and pressure axes dipping about 45 o for very deep earthquakes regional stress pattern may result from the collision between the african plate and iberia with extension and subduction of lithospheric material in the alboran sea at intermediate depth the very deep seismicity may be correlated with older subduction processes

determination of earthquake early warning parameters τ c and pd for southern california summary we explore a practical approach to earthquake early warning in southern california by determining a ground motion period parameter c and a high pass filtered displacement amplitude parameter pd from the initial 3 s of the p waveforms recorded at the southern california seismic network stations for earthquakes with m 4 0 at a given site we estimate the magnitude of an event from c and the peak ground motion velocity pgv from pd the incoming threecomponent signals are recursively converted to ground acceleration velocity and displacement the displacements are recursively filtered with a one way butterworth high pass filter with a cut off frequency of 0 075 hz and a p wave trigger is constantly monitored when a trigger occurs c and pd are computed we found the relationship between c and magnitude m for southern california and between pd and pgv for both southern california and taiwan these two relationships can be used to detect the occurrence of a major earthquake and provide onsite warning in the area around the station where onset of strong ground motion is expected within seconds after the arrival of the p wave when the station density is high the methods can be applied to multistation data to increase the robustness of onsite early warning and to add the regional warning approach in an ideal situation such warnings would be available within 10 s of the origin time of a large earthquake whose subsequent ground motion may last for tens of seconds

on the physical background of the van earthquake prediction method abstract seismic electric signals ses have been used as precursors of earthquakes for the van method of earthquake prediction in greece its generation is theoretically expected from the thermodynamics of point defects in rock forming minerals this paper reviews the theoretical and observational basis of the van method and points out several unsolved problems in its physical background the problems can be classified into three source energetics signal generation mechanism and signal transmission further investigations on the geological and geoelectrical structure laboratory experiments and theoretical aspects are recommended to solve these problems and to establish a better understanding of the physics of the focal process

subtraction of the telluric inductive component from van measurements abstract in order to understand the role of electrical properties in the vicinity of van stations that have already been found to be appropriate for the collection of seismic electric signals ses a magnetotelluric mt investigation was carried out over of the entire van network we present preliminary mt results for two stations of the van telemetric network in continental greece a procedure was developed by which a real time subtraction of the telluric inductive component from the electric measurements can be made the resulting real time recording of the residual electric field allows a better identification of the ses such an example is presented for an ses that preceded a 5 5 magnitude earthquake in western greece

a threshold based earthquake early warning using dense accelerometer networks most earthquake early warning systems eews developed so far are conceived as either regional network based or on site stand alone systems the recent implementation of nationwide high dynamic range dense accelerometer arrays makes now available potentially in real time unsaturated waveforms of moderate to large magnitude earthquakes recorded at very short epicentral distances 10 20 km this would allow for a drastic increase of the early warning lead time for example the time between the alert notification and the arrival time of potentially destructive waves at a given target site by analysing strong motion data from modern accelerograph networks in japan taiwan and italy we propose an integrated regional on site early warning method which can be used in the very first seconds after a moderate to large earthquake to map the most probable damaged zones the method is based on the real time measurement of the period c and peak displacement pd parameters at stations located at increasing distances from the earthquake epicentre the recorded values of early warning parameters are compared to threshold values which are set for a minimum magnitude 6 and instrumental intensity vii according to the empirical regression analyses of strong motion data at each recording site the alert level is assigned based on a decisional table with four alert levels defined upon critical values of the parameters pd and c which are set according to the error bounds estimated on the derived prediction equations given a real time evolutionary estimation of earthquake location from first p arrivals the method furnishes an estimation of the extent of potential damage zone as inferred from continuously updated averages of the period parameter and from mapping of the alert levels determined at the near source accelerometer stations the off line application of the method to strong motion records of the m w 6 3 2009 central italy earthquake shows a very consistent match between the rapidly predicted within a few seconds from the first recorded p wave and observed damage zone the latter being mapped from detailed macroseismic surveys a few days after the event the proposed approach is suitable for italy where during the last two decades a dense network of wide dynamic range accelerometer arrays has been deployed by the department of civil protection dpc the istituto nazionale di geofisica e vulcanologia ingv and other regional research agencies

magnitude estimation using the first three seconds p wave amplitude in earthquake early warning 1 pd is the peak amplitude of displacement in the first three seconds after the arrival of the p wave we investigated the attenuation of pd with the hypocentral distance r in southern california as a function of magnitude m and obtained the following relationship log pd 3 463 0 729 m 1 374 log r 0 305 given an earthquake location determined by the p wave arrival times at stations close to the epicenter this relationship can be used to define a so called pd magnitude of earthquakes our result shows that for earthquakes in southern california the pd magnitudes agree with the catalog magnitudes with a standard deviation of 0 18 for events less than magnitude 6 5 therefore pd is a robust measurement for estimating the magnitudes of earthquakes and has practical application in earthquake early warning systems citation wu y m and l zhao 2006 magnitude estimation using the first three seconds p wave amplitude in earthquake early warning geophys res lett 33 l16312 doi 10 1029 2006gl026871

electromagnetic precursors to earthquakes in the ulf band a review of observations and mechanisms despite over 2 decades of international and national monitoring of electrical signals with the hope of detecting precursors to earthquakes the scientific community is no closer to understanding why precursors are observed only in some cases laboratory measurements have demonstrated conclusively that self potentials develop owing to fluid flow and that both resistivity and magnetization change when rocks are stressed however field experiments have had much less success many purported observations of low frequency electrical precursors are much larger than expectations based on laboratory results in some cases no precursors occurred prior to earthquakes or precursory signals were reported with no corresponding coseismic signals nonetheless the field experiments are in approximate agreement with laboratory measurements maximum resistivity changes of a few percent have been observed prior to some earthquakes in china but the mechanism causing those changes is still unknown anomalous electric and magnetic fields associated with fluid flow prior to earthquakes may have been observed finally piezomagnetic signals associated with stress release in earthquakes have been documented in measurements of magnetic fields

earthquake predictions issued in greece by seismic electric signals since february 6 1990 abstract the present paper describes the results of all official predictions that were issued on the basis of seismic electric signals recorded in greece during the period feb 6 1990 may 31 1991 they amount to four cases of activities multiple events in two cases the predictions were also submitted for publication to tectonophysics before the beginning of the corresponding seismic activities while in a third case the prediction was announced during an international conference held in japan also before the occurrence of the earthquake after the submission of the manuscript a number of earthquakes occurred during the period up to may 31 1992 they are summarized along with their predictions in appendix 1

estimation of electric fields in the conducting earth s crust for oscillating electric current dipole sources and implications for anomalous electric fields associated with earthquakes abstract electromagnetic radiation possibly associated with earthquake occurrences in the earth s crust can be treated as a problem of electromagnetic induction within a conducting half space representing the crust we estimated the magnitude of the electric field near the earth s surface for oscillating electric current dipole sources located at various depths this shows that the electric field highly attenuates as expected and the source must be stronger than 10 5 a m even if it is located at a depth of several kilometers for practically detecting signals at frequencies in the ulf ultra low frequency range we also examined the electric field near the earth s surface for a box car type source in uniform and non uniform crust models we found that the wave form of the source is rather well preserved in both models but signal amplitudes are very small and unlikely to be drastically enhanced even in a non uniform crustal structure although this discussion is based only on a specific non uniform model

fault identification for buried strike slip earthquakes using insar the 1994 and 2004 al hoceima morocco earthquakes summary the 1994 m w 6 0 and 2004 m w 6 5 al hoceima earthquakes are the largest to have occurred in morocco for 100 yr and give valuable insight into the poorly understood tectonics of the area bodywave modelling indicates the earthquakes occurred on near vertical strike slip faults with the nodal planes oriented nw se and ne sw distinguishing between the primary fault plane and auxiliary planes using either geodetic or seismic data is difficult due to the spatial symmetry in deformation fields and radiation pattern of moderately sized buried strikeslip earthquakes preliminary studies using aftershock locations and surface observations have been unable to identify the orientation of the primary fault plane for either earthquake conclusively we use radar interferometry and aftershock relocation of the earthquake sequence to resolve the ambiguity for the 2004 earthquake inverting the interferograms for a uniform slip model based either of the two potential nodal planes results in similar misfits to the data however the ne sw best fit fault plane has an unrealistically high fault slip to length ratio and we conclude the nw se striking nodal plane is the primary fault plane and slip was right lateral we carry out tests on synthetic data for a buried strike slip earthquake in which the orientation of the fault plane is known a priori independent of geometry missing data and correlated noise models produced assuming the auxiliary plane to be the fault plane have very high fault slip to length ratios the 1994 earthquake had a smaller magnitude and comparisons of model misfits and slip to length ratios do not conclusively indicate which of the nodal planes is the primary fault plane nonetheless the insar data provides valuable information by improving the accuracy of the earthquake location by an order of magnitude we carry out a multiple event relocation of the entire earthquake sequence including aftershocks making use of the absolute locations for the 1994 and 2004 main shocks from our insar study the aftershock locations are consistent with a nw se orientated fault plane in 2004 and suggests that the 1994 earthquake occurred on a ne sw fault perpendicular to the fault which ruptured in 2004 previous tectonic models of the area proposed a bookshelf model of block rotation with nne ssw left lateral faults this model requires modification to accommodate the observation of right lateral slip on a nw se fault plane for the 2004 earthquake and we prefer to interpret the fault orientations as due to a zone of distributed shear with a right lateral fault striking at 115 and conjugate clockwise rotating left lateral faults striking at 25

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

faulting parameters of the 1999 mula earthquake southeastern spain abstract the seismicity of southern spain is characterized by low to moderate earthquake activity magnitudes

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

study of the damaging earthquakes of 1911 1999 and 2002 in the murcia southeastern spain region seismotectonic and seismic risk implications a detailed study of four earthquakes that occurred in the murcia region southeastern spain in 1911 1999 and 2002 has been carried out new intensity maps have been plotted for the march and april 1911 shocks these show maximum values of vii viii ems we have found values of vi and v respectively for the 1999 and 2002 earthquakes surface wave magnitudes range from 5 2 for the bullas 2002 event to 5 7 for the march 1911 event focal mechanisms for the mula 1999 and bullas 2002 events indicate reverse and strike slip motions with scalar seismic moments of 5 9 10 16 n m and 8 6 10 15 n m respectively and focal dimensions of 4 0 and 1 5 km both earthquakes were recorded at epicentral distances greater than 21 km showing low values of peak ground acceleration pga 0 020 g these records involve a ground motion less than the ones expected in the region according to different hazard studies the seismic hazard map that we obtained for the murcia region for a return period of 475 years shows higher values than those given in the spanish building code ncse 02 2002 e g 0 24 g for pga in the city of murcia compared with 0 16 g in the code

early magnitude and potential damage zone estimates for the great mw 9 tohoku oki earthquake the mw 9 0 2011 tohoku oki earthquake has reopened the discussion among the scientific community about the effectiveness of earthquake early warning for large events a well known problem with real time procedures is the parameter saturation which may lead to magnitude underestimation for large earthquakes here we measure the initial peak ground displacement and the predominant period by progressively expanding the time window and distance range to provide consistent magnitude estimates m 8 4 and a rapid prediction of the potential damage area this information would have been available 35 s after the first p wave detection and could have been refined in the successive 20 s using data from more distant stations we show the suitability of the existing regression relationships between early warning parameters and magnitude provided that an appropriate p wave time window is used for parameter estimation we interpret the magnitude under estimation as a combined effect of high pass filtering and frequency dependence of the main radiating source during the rupture process

physical properties of the variations of the electric field of the earth preceding earthquakes i abstract in an earlier paper we described the physical properties of the preseismic transient variations in the electrotelluric field the present letter clarifies a few points that were not properly emphasized in our previous publications furthermore recent results like that of the destructive kalamata earthquake on september 13 1986 indicate that the duration of a preseismic electric signal may reach considerably high values lasting up to several hours

plausibility of long distance electrotelluric precursors to earthquakes a systematic analysis of the plausibility of different classes of models which could account for low frequency precursory electrotelluric signals observable at large distances from a large earthquake is carried out first we consider linear models for which either a stationary electrical field is generated by a current dipole in the source volume or a static deformation field results from a precursory strain in the source volume linearly inducing a streaming potential effect near the electrode in the former case only the conjunction of very favorable circumstances may lead to an electrical field larger than 10 mv km at more than 100 km with the constraint that no anomaly exceeds a few volts per kilometer in the source area it indeed requires a powerful electrical dipole current 104 a length 1 km which might be produced by a streaming potential effect associated with the connection of nonhydrostatic fluid reservoirs pore pressure difference up to 100 mpa a two dimensional channeling of the electrical currents from the source to the electrode area which would result from high conductivity horizontal layers and finally a local amplification factor of typically 100 near the electrodes which might be produced by a narrowing of the conductive channel for an elastic long distance interaction an electric field of 10 mv km at a distance 10 times the source length 100 km away from a m 6 earthquake requires a precursory deformation larger than the coseismic deformation if no strong local amplification is considered alternatively nonlinear models are proposed and discussed assuming that the crust is stuffed with small scale local instabilities fractures and nonhydrostatic fluid reservoirs among which a number are close to their instability threshold these instabilities may follow their own evolutionary process inducing sporadic fluid flow and hence streaming potential effect in the vicinity of the electrodes without any relation to a remote tectonic activity however these instabilities may be sensitive to very small changes in the stress field and hence be triggered by the elastic precursory deformation of a remote seismic source this requires that the precursory deformation near the instability is at least larger than the tidal strain 10 7 this necessary condition is met at a distance of up to 10 times the source dimension when the precursory strain source is only 10 of the coseismic deformation provided that the strain source is double the size of the seismic fault itself this model could account for the absence of self potential anomalies related to the earthquake itself as a large proportion of the available instabilities could have been swept away by the precursory strain furthermore with such a model a precursory strain in the source area could induce a detectable change in the background seismic activity over a vast area which may give a new interpretation of the times of increased probability observations for short distances the triggering of fluid instabilities by strain perturbation and the associated streaming potential effect may well be a promising model for explaining low frequency electric and magnetic precursors

electromagnetic signals generated in the solid earth by digital transmission of radio waves as a plausible source for some so called seismic electric signals abstract claims by the van group varotsos p alexopoulos k 1984 physical properties of the variations of the electric field of the earth preceding earthquakes i tectonophysics 110 73 98 and later works to have developed a short term earthquake prediction technique in greece continue to arouse contentious debates claims of success in using geoelectrical precursors to predict earthquakes are criticized and defended 1998 letters phys today 51 6 15 100 great debates in seismology the van method of earthquake prediction 1998 eos 79 573 580 this is partly because of the unknown origin of the so called seismic electric signals ses precursors their particular characteristics are not those of the usual electromagnetic noise cultural noise or of the natural electromagnetic field magnetotelluric field in this paper we show that transient electric signals looking like ses can be generated by digital transmitters of the radio telecommunication network such signals have been observed in different regions of the world including greece and vietnam their characteristics have been analyzed in a broad band of frequencies 10 3 103 hz in the ioannina greece site which is considered as the most sensitive area of the van network it is concluded that some of the signals recorded at this site and identified as ses are probably of artificial origin and that the criteria used by the van group are not sufficient to guarantee that the so called ses are not man made without an extended and thorough study of the ambient electromagnetic noise in a broad band of frequencies and better information about the electrical properties of the deep structure beneath the monitoring station earthquake predictions issued on the basis of signals recorded by the van network are of dubious significance

waveform inversion of small to moderate earthquakes located offshore southwest iberia summary in this paper we apply the kinematic waveform inversion kiwi tools to the study of smallto moderate earthquakes in southwest sw iberia the earthquakes have magnitudes in the range ml 3 5 4 9 with the exception of one earthquake with magnitude ml 6 0 most events are located offshore are recorded with a large azimuthal gap and generate waves that travel throughastronglyheterogeneous crustalstructure weobtainnewestimatesofcentroid depth seismic moment strike dip and rake for 12 of the 29 studied events the earthquakes whose waveforms we cannot successfully model are 1 located too far from the stations 2 have small magnitude hence low signal to noise ratio or 3 are located within the cadiz basin which is a major sedimentary basin that affects wave propagation notably our results indicate that onshore earthquakes occur at shallow depths 15 km whereas offshore earthquakes occur deeper down to 46 km focal mechanisms indicate transpressive faulting

earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records 1 we show that the low pass filtered peak amplitudes of initial p and s wave seismic signals recorded in the vicinity of an occurring earthquake source correlates with the earthquake magnitude and may be used for real time estimation of the event size in seismic early warning applications the earthquake size can be therefore estimated using only a couple of seconds of signal from the p or s wave onsets i e while the rupture itself is still propagating and rupture dimension is far from complete we argue that dynamic stress release and or slip duration on the fault in the very early stage of seismic fracture scales both with the observed peak amplitude and with the elastic energy available for fracture propagation the probability that a fracture grows to a larger size should scale with the energy initially available citation zollo a m lancieri and s nielsen 2006 earthquake magnitude estimation from peak amplitudes of very early seismic signals on strong motion records geophys res lett 33 l23312 doi 10 1029 2006gl027795

a three year continuous sample of officially documented predictions issued in greece using the van method 1987 1989 abstract copies of all officially documented predictions issued in greece using the van method for the period 1987 1989 are presented a correlation between these predictions and earthquakes is attempted selectivity maps based on experimental data are drawn and the selectivity effect with relation to some earthquake source parameters is commented upon finally the quality of the predictions for large earthquakes is discussed