intermediate term predictions of earthquakes in italy algorithm m8 large earthquakes in italy are preceded by a specific seismic activation which could be diagnosed by a reproducible intermediate term earthquake prediction method a modification for lower seismic rate areas of the algorithm known as m8 keilis borok and kossobokov 1990 use has been made of the pfg ing catalog of earthquakes compiled on a regular basis to determine areas and times of increased probability for occurrences of m 6 earthquakes in retroactive simulation of forward prediction for the period 1972 1995 both the 1976 friuli m 6 1 and the 1980 irpinia m 6 5 earthquakes are predicted in the experiment where priority magnitude scale is used the times of increased probability for a strong earthquake to occur tips occupy less than a quarter of the total magnitude space time domain and are rather stable with respect to positioning of circles of investiga tion successful stability tests have been made considering a recently compiled catalog cci97 peresan et al 1997 in combination with the cn algorithm results costa et al 1996 the spatio temporal uncertainty of the prediction could be reduced to 5 the use of m8 for the forward prediction requires the computations to be repeated each half year using the updated catalog

estimation of seismic and aseismic deformation in mexicali valley baja california mexico in the 2006 2009 period using precise leveling dinsar geotechnical instruments data and modeling ground deformation and seismicity in mexicali valley baja california mexico the southern part of the mexicali imperial valley are influenced by active tectonics and human activity in this study data from two successive leveling surveys in 2006 and 2009 2010 are used to estimate the total deformation occurred in mexicali valley during 2006 2009 the leveling data span more than 3 5 years and include deformation from several natural and anthropogenic sources that acted at different temporal and spatial scales during the analyzed period because of its large magnitude the aseismic anthropogenic deformation caused by fluid extraction in the cerro prieto geothermal field obscures the deformation caused by other mechanisms and sources the method of differential interferograms stacking was used to estimate the aseismic interseismic tectonic and anthropogenic components of the observed displacement using sar images taken in 2007 during a period when no significant seismicity occurred in the study area after removing the estimated aseismic signal from the leveling data residual vertical displacement remained and to identify possible sources and mechanisms of this displacement a detailed analysis of records from tiltmeters and creepmeters was performed the results of this analysis suggest that the residual displacement is mainly caused by moderate sized seismicity in the area of study modeling of the vertical ground deformation caused by the coseismic slip on source fault primary mechanism of the two most important earthquakes may 24 2006 mw 5 4 and december 30 2009 mw 5 8 was performed the modeling results together with the analysis of geotechnical instruments data suggests that this moderate sized seismicity influences the deformation in the study area by coseismic slip on the source fault triggered slip on secondary faults and soft sediments deformation

geologic interpretation of geothermal fluid movement in cerro prieto field baja california mexico a geologic model of the liquid dominated cerro prieto geothermal field was developed on the basis of geophysical and lithologic well logs the direction of subsurface geothermal fluid flow before exploitation and the geologic features controlling this movement were determined by integrating well completion and downhole temperature data with the geologic model the data show that fluid possibly heated by intrusive dikes found in wells drilled in the eastern area of the field enters the system from the east at depths 10 000 ft 3 050 m the fluid moves westward through sandstone beds and rises to shallow depths through fault zones and permeable sandy gaps in the overlying shale layers the shale layers provide local cap rocks some of the hot fluid reaches the surface west of the field in an area characterized by numerous geothermal manifestations the rest of the fluid mixes with colder ground waters west of the geothermal resource

seismic reflection and magnetotelluric profiles across the luobusa ophiolite evidence for the deep structure of the yarlung zangbo suture zone southern tibet abstract the luobusa chromite mine in tibet the largest chromite deposit discovered in china to date is hosted in the luobusa ophiolite in the eastern section of the yarlung zangbo suture zone a combined seismic reflection and magnetotelluric survey was carried out on the mantle peridotites in which the chromitite deposits occur in order to investigate their origin and to prospect for other deposits in the area the survey indicates that the luobusa chromitite bearing ultramafic block is a tectonic slice thrust onto the southern margin of the gangdese batholith by multiple south dipping faults the maximum thickness of the ultramafic rock mass is 4 km and it is underlain by the upper crust of the indian plate low resistivity bodies in the upper crust of the luobusa area lie at a depth of up to 5 km and strata at a depth of 7 km cross the yarlung zangbo suture zone at a relatively small angle between depths of 20 50 km there are a number of oval low resistivity bodies the lower parts of which might have been close to the moho at a depth of approximately 65 km near the yarlung zangbo river it is inferred that such low resistivity bodies arise from partially molten bodies in the middle and lower crust and are related to deep tectonic activity and mantle material upwelling in the yarlung zangbo suture zone

monitoring and modeling land subsidence at the cerro prieto geothermal field baja california mexico using sar interferometry images derived from repeat pass spaceborne interferometric synthetic aperture radar insar systems offer the possibility of mapping surface deformation of small spatial extent and monitoring its spatio temporal evolution a slow local subsidence has been detected at the cerro prieto geothermal field from images acquired by the european space agency remote sensing satellites ers 1 2 between 1993 and 1997 although agricultural activity in the area limited the investigation interferometric monitoring revealed that the ground deformation is associated with the withdrawal of geothermal fluid and agreed with the leveling data modeling of the subsidence was carried out assuming elastic deformation in a half space from simple point sources of which five were necessary to reproduce the fringe patterns observed on the interferograms the depths and locations of three of the sources are compatible with the location of the known reservoir the study improves prior knowledge of the displacement field and of the mecanisms involved in the subsidence phenomenon

seismic anisotropy observations in the mexicali valley baja california mexico a study of seismic anisotropy was performed using data from earthquakes of the mexicali valley the investigated region encompasses the cerro prieto geothermal field cpgf one of the most important fields in the world the results showed that at most of our stations the average polarization directions of the fast s waves range from n14 w to n17 e a n s polarization direction was obtained for the whole area by averaging the polarization directions from all stations used in terms of the eda hypothesis this average trend agrees with the postulated state of stress for southern california and with fault plane solutions for events of the mexicali valley notorious deviations from the n s global trend were found southeast of the cpgf with polarization trends between n25 e and n67 e and in the geothermal field with polarization directions between n7 w and n14 w the polarization results for these zones indicated stress conditions that are different from the more regional stress pattern the delay times that were measured between the fast and slow shear waves reached values of up to 0 6 sec with a mean value of 0 35 sec consistent with our polarization results the larger delay times 0 2 0 6 sec were found in the cpgf smaller or null values were observed at the periphery of the study area no temporal trends in the delay times were apparent as shown by data from the two stations that recorded the larger number of events overall we conclude that the splitting effects of this study result from a shallow anisotropy volume the splitting results are thus interpreted as caused by the preferred orientation of vertical fluid filled microcracks aligned in a direction that is parallel to the regional stress field the stronger splitting effects that were observed in the area of the cpgf were found consistent with the geothermal reservoir that is embedded in the sedimentary cover of the zone at depths of 1 to 4 5 km from the surface we thus believe that such marked splitting effects have a direct relation with the reservoir of the cpgf

subsidence and stress change in the cerro prieto geothermal field b c mexico previous works have shown that ground deformation and seismicity in the cerro prieto geothermal field cpgf are due to both tectonics and field exploitation here we use information about current tectonics and data from precision leveling surveys to model tectonic and anthropogenic subsidence our results show that tectonic subsidence constitutes only 4 of the measured subsidence anthropogenic subsidence was evaluated using a model of rectangular tensional cracks based on the hydrological model of the field together with the coulomb 2 0 program from the resulting values of the fissure parameters and from extraction and injection data we calculate that the volume changes caused by closure of the geothermal and cold water reservoirs account for only 3 and 7 respectively of the volume change which should occur due to extraction since 18 of the extracted fluids are reinjected external recharge must compensate for about 72 of the expected volume reduction an analysis of the changes in coulomb stress caused by exploitation of the geothermal field suggest that even though the anthropogenic stresses account for only a fraction of tectonic stresses they are large enough to trigger seismicity

two mw 4 8 cerro prieto baja california mexico earthquakes on 1 june and 10 september 1999 strong motion observations we analyzed the strong motion records of two m w 4 8 normal fault earthquakes that occurred in june and september 1999 in the sedimentary environment of the mexicali valley peak ground accelerations of up to 0 452 g were recorded for these events at distances between 2 and 37 km we found that peak amplitudes recorded at the shorter distances tend to match the attenuation functions for southern california however as the distance from the epicenter increases the cerro prieto peak amplitudes decay at a significantly higher rate we also show that acceleration data from other small to moderate size earthquakes of the area decay with the same attenuation pattern thus as the sediments of the mexicali valley rapidly attenuate the intensity of the ground motion the potential of the earthquakes to cause damage at distance is reduced too although the higher accelerations were recorded at the station geo located in the yard of the cerro prieto geothermal plant the damage caused to the plant was minimal in this study we also explored the possibility of nonlinear behavior of the sediments beneath the station geo in the cerro prieto earthquakes for this a set of geo acceleration records from smaller magnitude earthquakes of the area was studied first to gain an understanding of the response of sediments to less intense ground motions horizontal to vertical component ratios of shear wave spectra indicated very similar ground amplifications for 17 earthquakes with magnitudes between 2 2 and 4 0 this result suggested that the sediments at geo behave linearly during earthquakes in this range of magnitude the mean site amplification from the smaller magnitude earthquakes was then compared to the ground amplifications from the two stronger events relative to this weak motion amplification only a light nonlinear response of the sediments for the june event was inferred for the september event however the comparison showed a clear reduction in the site amplification such deamplification of motion suggests nonlinear behavior of the sediments during the more intense ground shaking of this event furthermore a well defined peak of resonance in the weak motion amplification was clearly absent in the response of the two stronger events as has been reported in other studies of nonlinear response of sediments

seismic activity at the cerro prieto geothermal area mexico from august 1994 to december 1995 and its relationship with tectonics and fluid exploitation a continuous monitoring of the cerro prieto geothermal field was carried out from august 1994 to december 1995 to investigate the seismicity of tectonic origin and the seismicity triggered by exploitation activities hypocenters for 148 events were located mainly around the northern end of the cerro prieto fault and within the geothermal zone the estimated focal depths range mostly from 1 to 6 km for earthquakes with magnitudes from 0 5 to 4 6 it was difficult to distinguish between natural and triggered seismicity we observed a single case of an earthquake for which a correlation in time and space seems plausible with a sharp increase of fluid injection in a well located at less than 1 km from the epicenter fault plane solutions of 26 events with magnitudes between 2 8 and 4 6 indicate right lateral strike slip motion for earthquakes that occur near the cerro prieto and imperial faults inside the geothermal zone events with normal components of motion were recorded as expected from the extensional stress regime of the pull apart basin laying between both faults

times of increased probability of strong earthquakes m 7 5 diagnosed by algorithm m8 in japan and adjacent territories this paper continues to explore the possibility of identifying the times of increased probability tips of occurrence of a strong earthquake by premonitory intermediate term seismic activation in lower magnitude range as defined in the algorithm m8 a tip refers to a 5 year period and an area whose linear size is several times larger than that of an incipient earthquake in the course of the global test of the algorithm we applied it retrospectively to the data from the national earthquake information center worldwide earthquake catalog since the regional japan meteorological agency catalog was unavailable to authors related to the segment of circum pacific belt between latitudes 20 n and 48 n from the south of kuril arc to the taiwan and izu bonin arc the worldwide catalog allows us to diagnose tips for earthquakes above magnitude 7 5 from 1975 on five out of six earthquakes with m 7 5 occurred within the tips diagnosed by the algorithm m8 with a priori fixed parameters the missed earthquake occurred at the final stage of formation of the corresponding tip altogether the tips occupy less than 20 and times of expectation occupy about 8 of the total space time domain considered there are also current tips covering about half of the territory application of the additional algorithm of localization named mendocino scenario indicates that the southern part of the japan trench is an area deserving particular attention the results obtained here by no means constitute the definitive earthquake prediction but merely outline the territories for more detailed and comprehensive analysis if confirmed by regional data the results may be used for implementation of some safety measures and evaluation of other precursors including short term ones

testing earthquake prediction algorithms statistically significant advance prediction of the largest earthquakes in the circum pacific 1992 1997 abstract algorithms m8 and msc i e the mendocino scenario were used in a real time intermediate term research prediction of the strongest earthquakes in the circum pacific seismic belt predictions are made by m8 first then the areas of alarm are reduced by msc at the cost that some earthquakes are missed in the second approximation of prediction in 1992 1997 five earthquakes of magnitude 8 and above occurred in the test area all of them were predicted by m8 and msc identified correctly the locations of four of them the space time volume of the alarms is 36 and 18 correspondingly when estimated with a normalized product measure of empirical distribution of epicenters and uniform time the statistical significance of the achieved results is beyond 99 both for m8 and msc for magnitude 7 5 10 out of 19 earthquakes were predicted by m8 in 40 and five were predicted by m8 msc in 13 of the total volume considered this implies a significance level of 81 for m8 and 92 for m8 msc the lower significance levels might result from a global change in seismic regime in 1993 1996 when the rate of the largest events has doubled and all of them become exclusively normal or reversed faults the predictions are fully reproducible the algorithms m8 and msc in complete formal definitions were published before we started our experiment keilis borok v i kossobokov v g 1990 premonitory activation of seismic flow algorithm m8 phys earth and planet inter 61 73 83 kossobokov v g keilis borok v i smith s w 1990 localization of intermediate term earthquake prediction j geophys res 95 19763 19772 healy j h kossobokov v g dewey j w 1992 a test to evaluate the earthquake prediction algorithm m8 u s geol surv ofr 92 401 m8 is available from the iaspei software library healy j h keilis borok v i lee w h k eds 1997 algorithms for earthquake statistics and prediction vol 6 iaspei software library

intermediate term earthquake prediction an earthquake of magnitude m and linear source dimension l m is preceded within a few years by certain patterns of seismicity in the magnitude range down to about m 3 in an area of linear dimension about 5l 10l prediction algorithms based on such patterns may allow one to predict approximately 80 of strong earthquakes with alarms occupying altogether 20 30 of the time space considered an area of alarm can be narrowed down to 2l 3l when observations include lower magnitudes down to about m 4 in spite of their limited accuracy such predictions open a possibility to prevent considerable damage the following findings may provide for further development of prediction methods i long range correlations in fault system dynamics and accordingly large size of the areas over which different observed fields could be averaged and analyzed jointly ii specific symptoms of an approaching strong earthquake iii the partial similarity of these symptoms worldwide iv the fact that some of them are not earth specific we probably encountered in seismicity the symptoms of instability common for a wide class of nonlinear systems

intermediate term earthquake prediction in the area of greece application of the algorithm m8 the 3 strongest earthquakes m 7 0 which have occurred since 1973 in the area of greece were preceded by a specific increase of the earthquake activity in the lower magnitude range this activation is depicted by algorithm m8 this algorithm of intermediate term earthquake prediction was originally designed for diagnosis by times of increased probability tips of the strongest earthquake m 8 0 worldwide keilis borok andkossobokov 1984 at present the algorithm is retrospectively tested for smaller magnitudes in different seismic regions keilis borok andkossobokov 1986 1988 a tip refers to a time period of 5 years and an area whose linear size is proportional and several times larger than that of the incipient earthquake source altogether the tips diagnosed by the algorithm m8 in the area of greece occupy less than 20 and the times of expectation tes about 10 of the total space time domain considered also there is a current tip for the southeastern aegean sea and 1988 1992 it may specify the long term prediction given inwyss andbaer 1981a b

stress heterogeneity in the cerro prieto geothermal field baja california mexico we studied the background seismic activity in the cerro prieto geothermal field cpgf earthquakes were located below the exploitation area of the cpgf between 3 and 12 km deep this activity is located on a horstlike structure below the geothermal field and coincides with the zone of maximum subsidence in the cpgf two earthquake swarms occurred one in november 2000 and the second in february 2001 along the southeast northwest strike of the cerro prieto fault and in the neighborhood of the cerro prieto volcano magnitudes of the located microevents range from 0 3 to 3 5 a v p v s ratio of 1 91 for the region below the volcano suggests a water saturated medium and or a partial melt medium seventy six focal mechanisms of individual microearthquakes reveal significant variation in the orientation of the p and t axes focal mechanism inversions using the gephart 1990 code also reveal significant lateral stress variation of the best fit stresses below the cpgf the orientation of the best fit maximum intermediate and minimum stresses are plunge azimuth 1 66 72 2 6 328 and 3 24 235 for the november 2000 earthquake swarm the best fit principal stress orientations are 1 12 117 2 11 25 and 3 74 253 whereas for the february 2001 earthquake swarm they are 1 36 235 2 24 127 and 3 45 11 the 1 orientations are considerably different from the orientation of the maximum compressive regional stress that lies approximately north south on 1 june and 10 september 1999 two earthquakes of m w 5 2 and 5 3 occurred in the basement at depths of 7 4 and 3 8 km below the cpgf waveform modeling resulted in fault plane geometries given by strike 236 dip 60 slip 58 normal and strike 10 dip 90 slip 159 right lateral strike slip respectively an observed triangular source time function of 0 7 sec and a double source with a total duration of 1 9 sec were used to calculate the synthetics seismograms for these two events static stress drops and seismic moments for the june and september events are 82 5 mpa m 7 65 1016 n m and 31 3 mpa and m 1 27 1017 n m these stress drops are typical of continental events rather than of events originating in spreading centers we concluded from the focal mechanism inversions of the background seismicity and the june and september 1999 events that complex stress heterogeneity exits in the cpgf as a result of the continual thinning of the crust in the cerro prieto basin

times of increased probability of earthquakes of ml 5 5 in greece diagnosed by algorithm m8 an attempt is made to explore the possibility of identifying the times of increased probability tips of occurrence of earthquakes with ml 5 5 by premonitory intermediate term seismic activation in lower magnitude ranges as defined in the algorithm m8 a tip refers to a 5 year period and an area whose length is several times greater than that of an incipient earthquake this algorithm has been already tested retrospectively for the strongest earthquakes of magnitude greater than or equal to 7 0 which have occurred in greece since 1973 in the present study the same algorithm is also applied retrospectively by considering smaller earthquakes of local magnitude ml greater than or equal to 5 5 the obtained results show that ten out of eleven events with m 5 5 which took place in greece and surrounding region from january 1 1977 till december 31 1990 occurred within the tips diagnosed by the algorithm m8 retrospectively only the thessaloniki earthquake of june 20 1978 did not occur within tip the m8 algorithm failed in four cases namely those that occurred in regions for which our catalogue was not complete altogether the tips occupy less than 25 and times expectation about 8 of the total space time considered there is also a current tip started at the end of 1986 or at the beginning of 1987 for the south southwestern part of thehellenic arc indicating that this area deserves particular attention if the algorithm m8 works reliably then this tip will be filled by the end of 1992 this result by no means constitute the definitive earthquake prediction but merely outline a territory for more detailed and comprehensive analysis

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

an optimization of using the m8 algorithm for prediction of major m7 0 earthquakes in the iranian plateau the casualties and financial losses caused by large earthquakes have led to an awareness of prediction importance of such earthquakes the earthquake prediction is divided into four categories long term intermediate term short term and immediate the m8 algorithm is one of the intermediate term middle range prediction algorithms primarily used to predict earthquake of magnitude 8 or more and is applied later for smaller magnitudes the iranian plateau is less exposed to earthquake with magnitude 8 or more and it is observed that the seismicity rate in this region is generally low thus the original m8 is not suitable for applying in this region the objective of this study is to modify the m8 algorithm for prediction of major m7 0 earthquakes in the iranian plateau the major earthquake of magnitude 7 or more in the iranian plateau from 1975 to 2018 is considered as the target earthquakes the hit rate times 1 minus alarm rate is defined as objective function and the particles swarm optimization meta heuristic algorithm is used to maximize it the optimum m8 could predict 14 out of 17 large earthquakes in the iranian plateau while occupying 31 7 of the spatio temporal space as the alarm the results show that by employing an optimization algorithm we can modify the m8 algorithm for efficient prediction of the target magnitudes less than 8 in the regions with low seismicity rate

testing an earthquake prediction algorithm the 2016 new zealand and chile earthquakes the 13 november 2016 m7 8 54 km nne of amberley new zealand and the 25 december 2016 m7 6 42 km sw of puerto quellon chile earthquakes happened outside the area of the on going real time global testing of the intermediate term middle range earthquake prediction algorithm m8 accepted in 1992 for the m7 5 range naturally over the past two decades the level of registration of earthquakes worldwide has grown significantly and by now is sufficient for diagnosis of times of increased probability tips by the m8 algorithm on the entire territory of new zealand and southern chile as far as below 40 s the mid 2016 update of the m8 predictions determines tips in the additional circles of investigation cis where the two earthquakes have happened thus after 50 semiannual updates in the real time prediction mode we 1 confirm statistically approved high confidence of the m8 msc predictions and 2 conclude a possibility of expanding the territory of the global test of the algorithms m8 and msc in an apparently necessary revision of the 1992 settings

near fault strong ground motions recorded during the morelia normal fault earthquakes of may 2006 in mexicali valley b c mexico by the end of may 2006 a series of earthquakes had occurred in the mexicali valley baja california mexico this activity which included an m w 5 4 event developed in the vicinity of the cerro prieto geothermal field the earthquakes occurred on the morelia fault one of the east dipping normal faults in the mexicali valley cracks and fissures visible on the ground after the stronger earthquake defined two parallel fault segments of 4 and 2 km length the shorter segment being 1 km to the east of the other one down dip displacements of up to 25 30 cm were measured at some places along this surface break zone the ten larger events of the series were recorded by strong motion stations that operate in the epicenter area so that accurate hypocenter locations were obtained on the basis of p wave arrival times from the strong motion recordings the estimated shallow depths combined with the earthquake magnitude explain the strong shaking felt by residents and some damage observed on the cerro prieto geothermal plant the m w 5 4 event produced peak ground accelerations that go from 0 002 g at cuc on rock to 0 5 g at geo on sediments at 13 and 1 7 km from the epicenter respectively the station geo recorded closer to the epicenters and on the hanging wall side of the fault static ground displacements and a predominance of the strike normal over the strike parallel velocity components were determined from the acceleration records of this station these and other ground motion characteristics are also seen on pseudovelocity and absolute acceleration response spectra calculated from data of the larger event altogether the observed ground motion characteristics provide useful insights into the levels of ground shaking that near fault structures in the mexicali valley should be designed to withstand