most and least likely locations of large to great earthquakes along the pacific coast of mexico estimated from local recurrence times based on b values we mapped t l and p l local recurrence time and local probability density respectively for m max 7 2 earthquakes along the plate margin of the pacific coast of mexico in order to test two hypotheses the first is that the minima in t l or maxima in p l extracted probabilistically from the frequency magnitude distribution map asperities the second hypothesis is that recurrence times for characteristic events are estimated more correctly by local recurrence times than by the overall recurrence times of the zone comparing these results to the observed recurrence times for events of m 7 0 we find good agreement the coast of guerrero between longitude west 100 5 and 101 5 and the segment off the coast of southern chiapas show the shortest t l estimated as about 20 yr the location at longitude 98 5 near the boundary of guerrero with oaxaca the ometepec segment follows with estimates of about 30 yr as the next shortest t l along the coast of guerrero between 99 and 100 5 longitude t l is estimated as about 40 yr and finally in the segments off the oaxacan coast near 95 7 and 97 7 longitude t l ranges from 40 to 60 yr these volumes we define as asperities long local recurrence times are observed for the areas offshore from the isthmus of tehuantepec on the pacific plate off the coast of guerrero on land along the coast of most of oaxaca and along the northernmost 40 km of the guerrero coast if our ideas are correct then major moment release should emanate from the volumes we defined as asperities and relatively minor moment release should emanate from the volumes identified by the relatively long local recurrence times

hydrothermal alteration as a trigger mechanism for earthquake swarms the vogtland nw bohemia region as a case study summary earthquake swarms occur mostly in regions with co2 enriched pore fluids it is generally accepted that both geodynamic stress accumulation and critical pore fluid pressures act as a triggering mechanism for most seismic events the new thesis presented here is that hydrothermal alteration processes in fault zones help facilitate the shear failure propagation due to mechanical weakening and dissolution of the wall rock in addition to the normal shear stress and fluid overpressure the basic idea that stress corrosion cracking results from chemical weakening and comminution has been discussed for many years however it has not yet been applied to explain the earthquake swarm phenomenon studies of extensive alteration as well as the latest investigations of co2 sequestration give evidence that these high dissolution rates of wall rock in contact with an acid fluid phase exist in seismogenic fault zones several indications support the assumption that in the vogtland nw bohemia region the weakening of stressed fault zones by hydrothermal alteration could take place at seismogenic depths and could generate earthquake swarms investigations of quartz samples from the fracture zones by means of cathodoluminescence as well as spatiotemporal analysis of seismicity and numerical modelling of alteration induced earthquake swarms support this hypothesis

earthquake scaling laws for creeping and non creeping faults the dependence of the summed moment release on the fault dimension differs between non creeping faults and creeping faults or volcanic regions this can be attributed to different earthquake scaling laws the number n of events with fault length l scales for non creeping faults as n l l 2 and for creeping faults as n l l 3 this difference offers a means for mapping the distribution of creep in the seismogenic crust

frequency magnitude distribution of microearthquakes beneath the 9 50 n region of the east pacific rise october 2003 through april 2004 1 relocated hypocentral data from a 7 month deployment october 2003 to april 2004 of ocean bottom seismometers provide an opportunity to map microearthquake frequency magnitude distributions fmds along the 9 49 52 n region on the east pacific rise these analyses which incorporate more than 9000 earthquakes represent the first investigation of the 3 d spatial and temporal patterns of fmds along any mid ocean ridge spreading center the data are described well by a gutenberg richter model indicating a power law or fractal relationship between earthquake size and frequency the scaling exponent or b value shows significant spatial variability exceeding a value of 2 0 at the shallowest depths on axis and dropping below 1 0 away from the axial trough this spatial pattern is consistent with an inverse relationship between b value and ambient stress conditions with the lowest stress levels at shallow depths and relatively high stress levels or low pore pressures observed away from the axial zone intermediate b values are observed on axis above the ridge system s melt lens however within this region there also exists significant spatial variability this indicates that stress conditions and or structural heterogeneity may vary at subkilometer scales within the hydrothermal circulation cell although the observational period is characterized by increasing seismicity rates building toward an eruptive episode in january 2006 the first order spatial pattern of b values is sustained with no overall temporal trend as a byproduct of this b value analysis the detection capabilities of the array are assessed empirically

mount hood earthquake activity volcanic or tectonic origins on 29 june 2002 a m d 4 5 earthquake occurred 4 6 km south of mount hood oregon more than 200 small aftershocks m d 3 8 occurred between 29 june and 15 august 2002 by which time seismicity returned to background levels we analyze well constrained earthquakes from the summer 2002 sequence near mount hood recorded by the pacific northwest seismic network pnsn and well constrained small earthquakes m d 3 5 recorded by the pnsn between 1986 and 2002 we apply waveform cross correlation to selected events establish a one dimensional p wave velocity model and relocate the entire catalog by using the double difference algorithm of waldhauser and ellsworth 2000 we find that earthquakes before 2002 occur in four distinct clusters a a well defined linear feature striking n15e about 5 km south of the summit b a linear feature trending northwest southeast a few kilometers south of group a c a few tight clusters located about 9 km south southwest of the summit and d a small cluster beneath the summit earthquakes in group d do not appear to lie on a fault and may relate to volcanic activity however almost all earthquakes in the 2002 swarm occur in group a south of the summit at depths similar to earthquakes from previous swarms first motion fault plane solutions from the mainshock and largest aftershocks have normal mechanisms and solutions from well constrained aftershocks have normal to oblique normal mechanisms this is consistent with the apparent strike of the feature south of mount hood s summit and is similar to focal mechanisms of older earthquakes in group a b and p values for the summer 2002 earthquakes resemble a tectonic mainshock aftershock sequence we interpret these earthquakes as the northernmost example of basin and range seismicity yet recorded and conclude that the mount hood earthquakes do not yet suggest potential for volcanic unrest

change in the probability for earthquakes in southern california due to the landers magnitude 7 3 earthquake the landers earthquake in june 1992 redistributed stress in southern california shutting off the production of small earthquakes in some regions while increasing the seismicity in neighboring regions up to the present this earthquake also changed the ratio of small to large events in favor of more small earthquakes within about 100 kilometers of the epicenter this implies that the probabilistic estimate for future earthquakes in southern california changed because of the landers earthquake the location of the strongest increase in probability for large earthquakes in southern california was the volume that subsequently produced the largest slip in the magnitude 7 1 hector mine earthquake of october 1999

self organized fractal seismicity and b value of aftershocks of the 2001 bhuj earthquake in kutch india the devastating intraplate earthquake of m w 7 7 of 26 january 2001 took place along the south dipping reverse fault in the lower crust 23 km of kutch gujarat india obliterating some 14 000 people the aftershock activity has ensued for three years we analyzed 997 aftershocks of m 3 0 to study the b value and fractal correlation dimensions in time and space the b value is found to be 0 8 0 03 from the gutenberg richter relation and 0 76 0 02 from the maximum likelihood suggesting a typical value for the intraplate region the spatial correlation is 1 71 0 02 indicating that events are approaching a two dimensional region further the temporal correlation dimension is estimated to be 0 78 0 02 confirming the structure is mono fractal in time domain the depth section of b value shows a peak at 15 35 km depth range coinciding with the maximum occurrence of aftershocks 47 which is inferred as a fluid filled highly fractured rock matrix with fractures of high density it will be important to note that tomographic results also suggest a low vp low vs and a large poisson s ratio for the same depth range further confirming this inference additionally we have studied the variation of d2 s and b value with time during the first two months of aftershock activity the results show a marked negative correlation between spatial correlation dimension d2 large and b value low indicating the predominance of large events associated with weak clustering the negative correlation means the stress release along faults of a larger surface area after two months the fractal dimension d2 s and b value suggests a positive correlation implying more numerous smaller shocks with stress release along faults of a smaller surface area this would indicate a reduced probability of large magnitude earthquakes due to fragmentation of the fault zone

seismological and sar signature of unrest at nisyros caldera greece abstract nisyros island a quaternary volcanic center located at the se of the aegean volcanic arc has been in the past characterized by periods of intense seismic activity accompanied sometimes by hydrothermal explosions the last one being in 1887 the recent long lasting episode of unrest 1995 1998 in the area is the first instrumentally documented providing information on the behavior of the volcano evidence from seismicity and sar interferometry suggests that the presently active part of the kos nisyros volcano tectonic complex is located at the nw coast of nisyros island defining an area much smaller than the whole volcano tectonic area seismicity patterns vary both temporally and spatially consistently with different rates of vertical ground deformation inferred from sar interferometry these observations help us to discuss the different elements controlling the behavior of the volcanic system such as the existence location and timing of magma chamber inflation the occurrence of tensile failure at the boundaries of the chamber and the possibility of magmatic fluids being expelled to form a shallow magmatic intrusion the seismic failure and migration of hypocenters indicating shallow magma transport

seismic imaging of the 2001 bhuj mw7 7 earthquake source zone b value fractal dimension and seismic velocity tomography studies abstract we use precisely located aftershocks of the 2001 mw7 7 bhuj earthquake 2001 2009 to explore the structure of the kachchh seismic zone by mapping the 3 d distributions of b value fractal dimension d and seismic velocities from frequency magnitude analysis we find that the catalog is complete above mw 3 0 thus we analyze 2159 aftershocks with mw 3 0 to estimate the 3 d distribution of b value and fractal dimensions using maximum likelihood and spatial correlation dimension approaches respectively our results show an area of high b d and vp vs ratio values at 15 35 km depth in the main rupture zone mrz while relatively low b and d values characterize the surrounding rigid regions and gedi fault gf zone we propose that higher material heterogeneities in the vicinity of the mrz and or circulation of deep aqueous fluid volatile co2 is the main cause of the increased b d and vp vs ratio values at 15 35 km depth seismic velocity images also show some low velocity zones continuing in to the deep lower crust supporting the existence of circulation of deep aqueous fluid volatile co2 in the region probably released from the eclogitasation of olivine rich lower crustal rocks the presence of number of high and low velocity patches further reveals the heterogeneous and fractured nature of the mrz interestingly we observe that aki 1981 s relation d 2b is not valid for the spatial b d correlation of the events in the gf d2 1 2b zone however the events in the mrz d2 1 7b show a fair agreement with the d 2b relationship while the earthquakes associated with the remaining parts of the aftershock zone d2 1 95b show a strong correlation with the aki 1981 s relationship thus we infer that the remaining parts of the aftershock zone are probably behaving like locked un ruptured zones where larger stresses accumulate we also propose that deep fluid involvement may play a key role in generating seismic activity in the mrz therefore a similar episode of deep fluid inflow could play a crucial role in causing the next strong earthquakes in the surrounding blocks of nwf

duration magnitude uncertainty due to seismic noise inferences on the temporal pattern of g r b value at mt vesuvius italy we analyze the statistical properties of seismic noise amplitude at seismic station ovo in the mt vesuvius volcano southern italy monitoring network the root mean square of seismic noise amplitude has a lognormal distribution using the mean and standard deviation of this distribution we evaluate the uncertainties in the estimate of duration magnitude m d for the volcano tectonic seismic events at mt vesuvius we develop a method based on knowledge of the coda envelope pattern of local events and find an empirical formula for determining the standard deviation of m d we then recalculate the b value time pattern for mt vesuvius from 1972 to the present using a weighted least squares approach where the inversion weights are given by the magnitude errors and the number of events included in each magnitude bin results are compared to a suite of synthetic catalogs with the same number of events the same magnitude errors and the same completeness threshold as the true mt vesuvius catalog our results indicate that the method presented in this note has a lower bias than the maximum likelihood approach previously used for calculating b values at vesuvius propagation of uncertainties in m d measurements into the estimate of b value indicates that previously determined time changes in b values at mt vesuvius are not statistically significant manuscript received 5 november 2002

near lithostatic pore pressure at seismogenic depths a thermoporoelastic model summary a model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure this configuration is thought to be pertinent to the south iceland seismic zone sisz and to other tectonically active regions of recent volcanism where volatiles are continuously released by ascending magma below the brittle ductile transition poroelastic parameters are computed for basaltic rock the model is 1 d the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium environment conditions are considered pertinent to basalt saturated with water at shallow depth case i and at mid crustal depth case ii if the intrinsic permeability of the rock is high no significant effects are observed in the pressure field but advective heat transfer shifts the brittle ductile transition to shallower depths if the intrinsic permeability is low the pressure dependent permeability can propagate near lithostatic pore pressures throughout most of the transition layer while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition geometrical parameters characterizing the fracture distribution are important in determining the effective permeability in particular if an interconnected system of fractures develops within the transition layer the effective permeability may increase by several orders of magnitude and near lithostatic pore pressure propagates upwards these modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the sisz in connection with the two 2000 june m 6 5 earthquakes including i fluid pressure pulses in deep wells ii low resistivity at the base of the seismogenic layer iii low vp vs ratio and time dependent seismic tomography iv heterogeneity of focal mechanisms v shear wave splitting vi high b value of deep foreshocks vii triggered seismicity and viii radon anomalies

seismic response of the fractured and faulted granite of soultz sous forets france to 5 km deep massive water injections summary the european enhanced geothermal system egs formerly hot dry rock hdr programme of soultz sous foris organized around three wells drilled to a depth of about 5000 m hydraulic stimulations were performed in the wells in 2000 gpk2 well 2003 gpk3 well and 2004 and 2005 gpk4 well the stimulation of gpk2 induced more than 700 seismic events with a magnitude greater than 1 0 the seismicity depicts a dense homogeneous cloud without any apparent structure medium size earthquakes represent more than 80 per cent of the cumulative seismic moment the b value of the gutenberg and richter law is larger than 1 2 the injectivity has been increased by a factor 20 these characteristics indicate that the stimulation reactivated a 3 d dense network of fractures the stimulation of gpk3 induced only about 250 events with a magnitude greater than 1 0 but with a greater proportion of large events up to 2 9 the hypocentres form clear structures identified as large faults the b value is about 0 9 and the large events m 2 0 account for the greater part of the cumulative seismic moment the injectivity of the well which was already high before the stimulation remained unchanged the stimulation of gpk4 was achieved in two stages this stimulation produced even less induced events making the interpretation difficult the differences between the seismic response of gpk2 and gpk3 are due to the presence of large faults cut by gpk3 or in its close vicinity and reached by the injected water once a seismic event occurs on a fault a sequence of earthquakes is triggered and the seismicity behaves for a large part independent of the injected flow rate the stimulations also show some evidence that creeping could be a major source of deformation if not the main one the future egs programme will have to drill wells in zones free of large faults to avoid poor hydraulic performance and inconvenience to the population

diagnosis of time of increased probability tip for volcanic earthquakes at mt vesuvius the possibility of intermediate term earthquake prediction at mt vesuvius by means of the cn algorithm is explored cn was originally designed to identify the times of increased probability tips for the occurrence of strong tectonic earthquakes with magnitude m m0 within a region a priori delimited here the cn algorithm is applied for the first time to the analysis of volcanic seismicity the earthquakes recorded at mt vesuvius during the period from february 1972 to june 2004 are considered and the magnitude threshold m0 selecting the events to be predicted is varied within the range 3 0 3 3 satisfactory prediction results are obtained by retrospective analysis when a time scaling is introduced in particular when the length of the time windows is reduced by a factor 2 5 3 with respect to the standard version of cn algorithm more than 90 of the events with m m0 occur within the tip intervals with tips occupying about 30 of the total time considered the control experiment seismic history demonstrates the stability of the obtained results and indicates that the cn algorithm can be applied to monitor the preparation of impending earthquakes with m 3 0 at mt vesuvius

mapping the b value anomaly at 100 km depth in the alaska and new zealand subduction zones a positive anomaly in the frequency magnitude distribution b value is detected at approximately 90 100 km depth in two subduction zones the b value in this anomalous zone is 40 higher than in adjacent volumes we use regional catalogs with a magnitude of completeness of 2 6 central alaska and cook inlet 2 0 shumagin islands and 3 5 new zealand to resolve the b value as a function of space in more detail we project all earthquakes onto planes perpendicular to the strike of the slab these cross section views of the b value distribution locate the high b value anomalies at a depth of 90 100 km on the upper surface of the wadati benioff zone at these depths slab dehydration may increase pore pressure thus lowering the effective stress and increasing the b value increased pore pressure would also lower the liquidus in the overlying asthenosphere giving rise to the volcanism that occurs directly above this zone

variations in the frequency magnitude distribution with depth in two volcanic areas mount st helens washington and mt spurr alaska the frequency magnitude distribution of earthquakes characterized using the b value is examined as a function of space beneath mount st helens 1988 1996 and mt spurr 1991 1995 at mount st helens two volumes of anomalously high b b 1 3 can be observed at depths of 2 6 3 6 km below the crater floor and below 6 4 km these anomalies coincide with 1 the depth of vesiculation of ascending magma and 2 the suggested location of a magma chamber at mount st helens study of mt spurr reveals an area of high b value b 1 3 at a depth of about 2 3 4 5 km below the crater floor of the active vent crater peak we propose that the higher material heterogeneity in the vicinity of a magma chamber or conduit due to vesiculation of the ascending magma is the main cause of the increased b value at shallow depths alternatively interaction of magma with groundwater may have increased pore pressure and lowered the effective stress the deeper anomaly at mount st helens is likely caused by high thermal stress gradients in the vicinity of the magma chamber our results indicate that detailed mapping of the frequency magnitude distribution can be used as a tool to trace vesiculation and locate active magma chambers

seismic b value anomalies in the sumatran region seismotectonic implications abstract the spatial variations in the seismic b value seismic moment bouguer gravity change and fault plane solution are estimated in the sumatran region based on homogeneous seismicity data from june 2005 to march 2012 to investigate the seismotectonic characteristics and tectonic activity between the 2004 sumatran earthquake and the 2012 east indian ocean earthquakes based on changes in the seismicity rate this time period is divided into five intervals with different earthquake distributions and faulting styles the seismic b values faulting mechanisms and seismic moment release values are mapped throughout the sumatran region and the gravity change every two years between the 2004 event and the 2012 events are determined from satellite grace gravity data the b values vary from 0 45 to 1 59 and an inverse correlation is observed between the b values and convergence rates low b values are located at depths between 20 km and 40 km in the subduction zone and between 20 km and 35 km in the oceanic plate the lowest b values are located at a depth of approximately 28 km in both regions which indicates a homogeneous fault system between them the areas with low b values are associated with megathrust and strike slip mechanisms while the area with the lowest b values is dominated by a megathrust mechanism seismically active regions have low b values associated with a high stress accumulation and high seismic moment release low b value areas are located mainly along the andaman sunda trench and andaman nicobar sumatra forearc temporal variations in the seismicity distribution and faulting style are recognized with temporal variations in the b values in each period relationships exist between the epicenter of the 2004 event and the location of the maximum bouguer gravity change in 2012 and between the epicenters of the 2012 events and the location of the maximum bouguer gravity change in 2004 furthermore a zone of continuous 2 year positive gravity change is located near the nicobar islands the 2004 event boost the 2012 events and intraplate seismicity via stress transfer the seismicity distributions in individual periods within the studied timeframe highlight the active and locked portions of the fault systems

results from local earthquake velocity tomography implications toward the source process involved in generating the 2001 bhuj earthquake in the lower crust beneath kachchh india to comprehend the source processes of the 26 january 2001 bhuj earthquake sequence of m w 7 7 and its influence on the seismic hazard of the kachchh we estimate various seismological parameters using reliable and accurate aftershock data the estimated parameters led to several important findings including the delineation of an east west trending south dipping 45 fault north wagad fault nwf which touches the surface about 25 km north of kachchh mainland fault kmf the aftershock zone is confined to a 60 km long and 40 km wide region lying between the kmf to the south and nwf to the north extending from 10 to 45 km depth focal mechanism solutions of the mainshock and 25 significant aftershocks of m w 3 0 obtained from waveform inversion of broadband data and local earthquake moment tensor inversion suggest that the region between the kmf and nwf is mainly characterized by reverse faults with east west trend and southerly dip matching with the geological faults in the region the tomographic inversion technique is used to invert 5516 p wave travel times and 4061 s p travel time differences from 600 aftershocks recorded at 8 18 stations tomographic results suggest a regional high velocity body characterized by high v p 7 0 8 5 km sec high v s 4 0 4 8 km sec and low 0 24 0 26 with a head extending 60 km in north south and 40 km in east west at 10 40 km depths this high velocity anomaly is inferred to be a mafic pluton rift pillow which might have intruded during the rifting time 135 ma this crustal mafic pluton must be contributing significantly in accumulating large crustal stresses resulting in the generation of large earthquakes in this intraplate area another important result of our study is the detection of a low velocity zone low v p 6 5 7 0 km sec low v s 3 6 4 0 km sec large 0 26 0 265 within the mafic body at the hypocentral depth of the mainshock 18 25 km which is inferred to be a fluid filled trapped aqueous fluid resulting from metamorphism fractured rock mass the analysis of depth distribution of b values suggests a high b value zone between 15 and 25 km depths which further supports this contention hence the presence of fluids at the hypocenter might have facilitated the occurrence of the 2001 bhuj earthquake within the inferred mafic body in the lower crust

megathrust asperities and clusters of slab dehydration identified by spatiotemporal characterization of seismicity below the andean margin summary the space time size distributions of seismicity during the last four decades 1973 2010 are used to identify megathrust asperities the degree of plate coupling hence potential future large earthquakes and slab dehydration below the andean margin 15 48 s this seismicity displays globally a typical magnitude distribution with a b value of 1 04 0 024 for a magnitude of completeness of 4 5 and without considering aftershock sequences however this unitary b value of the entire catalogue masks large variations 0 6 1 7 in space and time interpreted as related to different tectonics contexts or different states of the seismic cycle the study has been performed for different regions upper continental plate upper and lower parts of the subducting oceanic plate with respect to a 3 d slab geometry model all along the andean margin low b values 0 6 0 8 are observed in areas that were ruptured by large mw 7 5 megathrust earthquakes a temporal analysis of these features show that b values where low before these earthquakes and remain low after the relaxation of the aftershock phase suggesting that they are related to time persistent asperities within the seismogenic zone of the megathrust interestingly a persistently low b value was observed from 2001 to the end 2009 within the southern limit of the maule mw 8 8 earthquake 2010 february 27 our results also identify other low b asperities below the chilean margin that have not ruptured during the last 40 yr and are places of potentially large megathrust earthquakes in the future in contrast large b values 1 1 1 7 are observed at seismicity clusters occurring inside the subducted slab beneath the central volcanic zone cvz of the andes and below the forearc near the subduction point of aseismic ridges and fracture zones clusters below the cvz are spatially related to relative large intermediate depth earthquakes like the mw 7 8 tarapaca 2005 earthquake and may reveal extensive thermally driven dehydration of the oceanic lithosphere that favours wet mantle melting and therefore magmagenesis feeding the volcanic chain

mapping active magma chambers by b values beneath the off ito volcano japan the b value of the frequency magnitude relation and thus the mean magnitude in the off ito volcanic area is not uniform based on detailed b value tomography using about 10 000 events in an area of 10 km radius and in the upper 15 km of the crust a high b value anomaly b 15 below 7 km depth and with a radius of about 2 km located below the coast southeast of ito contrasts with lower values of typically b 0 7 north of it and at shallower depths on the basis of surface deformations a tensile crack dislocation source was located above 7 km depth thus we surmise that the magma chamber in the off ito area was located below 7 km depth the correlation of a high b value anomaly with this model supports our hypothesis that active magma chambers may be mapped by high b value anomalies the magma body may be described as consisting of two parts a lower well established chamber below 11 km depth and a shallower part 11 7 km depth the b value in the volume surrounding the magma chamber increased from 0 7 during the 1980s to 1 5 during the earthquake swarms of the 1990s this may reflect a trend of increasing crack density due to the intrusion activity

hydrologic response of catchments to precipitation quantification of mechanical carriers and origins of water 1 precipitation induced overland and groundwater flow and mixing processes are quantified to analyze the temporal event and pre event water and spatial groundwater discharge and overland runoff origins of water entering a stream using a distributed parameter control volume finite element simulator that can simultaneously solve the fully coupled partial differential equations describing 2 d manning and 3 d darcian flow and advective dispersive transport mechanical flow driven by hydraulic potential and tracer based hydrograph separation driven by dispersive mixing as well as mechanical flow are simulated in response to precipitation events in two cross sections oriented parallel and perpendicular to a stream the results indicate that as precipitation becomes more intense the subsurface mechanical flow contributions tend to become less significant relative to the total pre event stream discharge hydrodynamic mixing can play an important role in enhancing pre event tracer signals in the stream this implies that temporally tagged chemical signals introduced into surface subsurface flow systems from precipitation may not be strong enough to detect the changes in the subsurface flow system it is concluded that diffusive dispersive mixing capillary fringe groundwater ridging and macropore flow can influence the temporal sources of water in the stream but any sole mechanism may not fully explain the strong pre event water discharge further investigations of the influence of heterogeneity residence time geomorphology and root zone processes are required to confirm the conclusions of this study

the 1980 pressure response and flank failure of mount st helens usa inferred from seismic scaling exponents the cataclysmic 18 may 1980 eruption at mount st helens was preceded by intense seismic activity marking the mechanical response of the volcanic edifice to interior pressurisation this seismicity is analysed to yield the temporal change in the seismic scaling exponent d inferred from the seismic b value that in turn is related to the seismic moment of an earthquake time evolution of d preceding the eruption onset reveals 1 a major decrease in d occurring over only a few days at the end of march 2 a steady but stepped decrease in d steps 5 10 days occurring from the end of march to early may 3 a sharp decrease in d in early may and 4 steady low values of d occurring 2 3 days before the eruption onset this response is interpreted as major ruptures formed at the end of march arresting and participating in but not triggering the ultimate failure of the flank rather the rate of interior fracturing slowed in the 2 months preceding the 18 may 1980 major blast and the triggering of failure is consistent with interior gas overpressurisation the occurrence of two swarms of low frequency seismic events and the high values of the harmonic tremor indicate the action of interior pressurisation on a cycle of 20 25 days solutions are applied to represent the harmonic interior pressurisation of the edifice by gas exsolving from the volcano core the transient radial migration of overpressured gas may reduce the apparent strength of the edifice and ultimately trigger failure of the flank importantly this mechanism is capable of triggering flank failure both after multiple core pressurisation cycles have been sustained and as core pressures are low and diminishing and may be a minimum these twin attributes are both apparent in the seismic record for mount st helens used as a proxy for the unrecorded timing and magnitude of gas pressurisation at the volcano core d 2004 elsevier b v all rights reserved

faults strengthening and seismicity induced by geothermal exploitation on a spreading volcano mt amiata italia abstract seismogenic structures such as faults play a primary role in geothermal system generation recharge and output they are also the most susceptible to release seismic energy over fluid injection extraction operations during anthropic exploitation we describe the microseismic activity recorded in 2000 2001 in the piancastagnaio geothermal field on the se flank of mt amiata volcano southern tuscany italy from our field observations we find that a relatively high percentage i e about 5 of the recorded events are of hydro fracturing origin and have a distinct waveform seismic signature when compared to the recorded events of tectonic shear fracturing origin while hydrofracturing events are mostly concentrated around the geothermal fields the spatial distribution of hypocenters shows a deepening and a density increase of the micro seismic activity from the volcanic axis toward the exploited geothermal reservoir suggesting that volcanic spreading at amiata is still active the study of different data sets from different time periods together with the knowledge from terzaghi s law that production of large quantity of pore fluid with the associated fluid pressure reduction could augment the stress normal to faults surfaces and thus their resistance to slip make us argue that the process of volcanic spreading affecting the edifice of amiata may allow augmented accumulation of stresses on faults eventually leading to the release of higher stress drops once ruptures occur the gutenberg richter magnitude frequency distribution shows that the strongest events on record have a local magnitude in the 5 5 5 m l range for 100 year recurrence time in conclusions we infer that geothermal exploitation at mt amiata should be closely monitored in order to understand how fluid injection production is responsible for the hydrofracturing seismic activity and affects stress accumulation on and rupture of faults within and in the neighborhood of the geothermal fields this understanding may allow a geothermal field management that will hopefully reduce the risk for inducing larger seismic events in the area

precursory seismicity of the 1994 eruption of popocatepetl volcano central mexico popocatepetl volcano is located in the central mexican volcanic belt within a densely populated region inhabited by over 20 million people the eruptive history of this volcano indicates that it is capable of producing a wide range of eruptions including plinian events after nearly 70 years of quiescence popocatepetl reawakened in december 21 1994 the eruptive activity has continued up until the date of this submission and has been characterized by a succession of lava dome growth and destruction episodes similar to events that have apparently been typical for popocatepetl since the fourteenth century in this regime the episodes of effusive and moderately explosive activity alternate with long periods of almost total quiescence in this paper we analyze five years of volcano tectonic seismicity preceding the initial eruption of the current episode the evolution of the v t seismicity shows four distinct stages which we interpret in terms of the internal processes which precede an eruption after a long period of quiescence the thermal effects of a magma intrusion at depth the fracturing related to the slow development of magma related fluid pathways the concentration of stress causing a protracted acceleration of this process and a final relaxation or redistribution of the stress shortly before the initial eruption are reflected in the rates of v t seismic energy release a hindsight analysis of this activity shows that the acceleration of the seismicity in the third stage asymptotically forecast the time of the eruption the total seismic energy release needed to produce an eruption after a long period of quiescence is related to the volume of rock that must be fractured so imposing a characteristic threshold limit for polygenetic volcanoes limit that was reached by popocatepetl before the eruption

spatio temporal evolution of frequency magnitude distribution and seismogenic index during initiation of induced seismicity at guy greenbrier arkansas abstract in this study we carry out detailed analyses of the spatio temporal variations of seismic b value during the onset of the potentially induced earthquake sequence between guy and greenbrier arkansas to investigate correlations with pore pressure change the range of b values suggests that the seismicity in the guy greenbrier area is mostly a result of the activation of pre existing faults the spatial distribution of b value correlates with modeled pore pressure changes in the northern segment of the fault b value increases with depth due to large pore pressure changes and opening of new fractures in the deeper part and stress relaxation in the shallower parts whereas in the southern segment the shallower part shows higher b values due to higher pore pressure fluctuations but the deeper part in the crystalline basement has low b value due to higher confining stress the correlation between the temporal variation of b value and hypocentral depth explains a previously observed temporal drop of b value this suggests that temporal variations should be interpreted along with the spatial variations estimation of the seismogenic indices for the guy greenbrier fault is provided our analysis suggests that monitoring changes in b value and seismogenic indices during an injection period might be used to avoid the occurrence of significant events if injection volume is reduced at critical times

does maximum earthquake size depend on focal depth abstract while the gutenberg richter law gr with b value of 1 0 is an inexact description of the earthquake frequency magnitude distribution it does provide a convenient statistical basis for identifying when the largest earthquakes in a catalog are either anomalously large or anomalously small when the largest earthquakes are as predicted by the gr distribution it is inappropriate to infer that the largest historically known earthquake is the largest possible only when the largest observed earthquakes are significantly smaller than predicted can we infer that the largest possible earthquakes have occurred analysis of the global historical catalog demonstrates that at nearly all depths the largest deep and intermediate earthquakes have sizes close to those predicted by a gr distribution with b of 1 0 only between about 300 to 450 km and beneath 600 km are the largest known earthquakes somewhat larger than predicted however when geographically isolatable subgroups within catalogs are considered separately largest earthquakes that are either anomalously large or small are quite common often this is because individual regions have b values much different than 1 0 alternatively sometimes there appear to be physical constraints limiting the size of the largest possible earthquake as examples illustrating these assertions this article evaluates two subgroups deep focus earthquakes occurring beneath spain and intermediate depth earthquakes in the bucaramanga colombia nest

transport of mantle volatiles through the crust traced by seismically released fluids a natural experiment in the earthquake swarm area vogtland nw bohemia central europe abstract vogtland which is located on the czech german border near the crossing of the eger rift and the marianske lazn fault zone is characterised by co 2 rich mineral springs fed by a magmatic source and swarm earthquake activity the free gas of the eisenquelle mineral spring was studied weekly from april 1994 to june 1996 a period which included a quake swarm on december 4 and 5 1994 comprising approximately 500 individual events m local 2 2 co seismic shifts in he content after about a month as well as in the 13 c of co 2 and 3 he 4 he after about 220 days were resolved from seasonal background variations the he concentration shift is assumed to originate near the discharge whereas the isotopic shifts are probably caused by the addition of crustal fluids released by crushing rocks within the hypocentre from the distance of 14 km between the hypocentre to the mineral spring the transport velocity of the released crustal fluids was determined to be at least 50 m day such a high speed indicates gaseous fluid transport along channel like conduits rather than being predominantly controlled by dissolution in water using a simple mass balance it is shown that the amount of crustal fluids potentially released by seismic activity strongly exceeds that required for the observed shifts in 3 he 4 he and 13 c this fact along with the coincidence of both shifts supports the hypothesis that magmatic fluids occurring in mineral waters of the eisenquelle environs flush the hypocentral crustal block by means of advectional transport

constraints on the dynamics and spatio temporal evolution of the 2011 oichalia seismic swarm sw peloponnesus greece abstract in this paper we present a detailed study of a shallow seismic swarm which took place in the area of oichalia sw peloponnesus between august and december 2011 the seismic crisis started on 14 8 2011 with an mw 4 8 earthquake and was followed by more than 1600 events several of which having magnitude over 4 0 the activity was recorded by local temporary and regional permanent seismic stations thousands of records were collected and routinely analyzed p and s wave arrival times were manually picked and incorporated in the hypoinverse algorithm together with a new optimum local velocity model hypocentral solutions were improved by applying a double difference method focal mechanisms show that the activated fault zone is dominated by dip slip normal faulting trending nnw sse with the average t axes orientation being n70 e consistent with regional tectonics we have investigated towards stress triggering and fluid diffusion by employing coulomb stress transfer spatio temporal and frequency magnitude distribution fmd analyses the negligible coulomb stress transfer and seismicity rate changes that were calculated imply for a stress deficit in the broader study area hence an external triggering mechanism is required to justify the observed pattern the b values increase towards the sse compatible with the similarly directed migration of seismicity showed that the oichalia swarm could possibly be adapted to an epidemic type aftershock sequence model etas fluid diffusion is reflected in the spatio temporal hypocenter migration clustering analysis combined with the temporal distribution of b values has shown that the swarm evolved in three major phases the first two being initiated by major events which were probably triggered externally due to fluid injection that brought the seismogenic volume into a critical state likely followed by afterslip the last phase signified a relaxation period with dispersed seismicity throughout the area and the b values gently diminishing towards unity

earthquake statistics at parkfield 1 stationarity of b values 1 in this paper paper 1 we quantitatively show that the heterogeneous pattern of b values of the gutenberg richter relation in the parkfield segment of the san andreas fault is to a high degree stationary for the past 35 years this prepares the grounds for paper 2 where we test the hypothesis that our model of spatially varying b values forecasts future seismicity more accurately than the approach in which one assumes a constant b value equal to the average regional value the method we develop to measure stationarity in the presence of spatial heterogeneity consists of the following steps 1 determine the optimal dimensions of the sampling volume by mapping b values with a wide range of radii and selecting the largest radius that gives the most detailed resolution of the b value heterogeneity along the selected fault segment the high data density permits the definition of the dominant dimensions of the seismotectonic fabric which is about 8 10 km 2 map the difference in b value between two periods selecting numerous possible catalog divisions 3 identify significant changes of b values by the utsu test utsu 1992 along the studied fault segment of 110 km length only one patch of radius 5 km showed a significant increase in b from below average to above as a function of time this change in b initiates around 1993 and thus correlates in space and time with a well documented episode of creep at depth using the derived spatial variable b value distributions we find that the highest probability for earthquakes with magnitude m 6 is in the middle mountain asperity where the 1966 parkfield earthquake nucleated and where all m 4 5 events in the data set occurred in contrast if only the regional average b value of 0 92 is used to predict future seismicity the creeping segment north of parkfield should produce major earthquakes most frequently a conclusion that contradicts the observations

a correlation between the b value and the fractal dimension from the aftershock sequence of the 1999 chi chi taiwan earthquake summary we analyse large number of aftershock events from the 1999 chi chi taiwan earthquake m l 7 3 recorded around the epicentre area of the main shock in central taiwan where events can be precisely located due to dense coverage of modern seismometers the seismicity is characterized by the b value of the gutenberg richter relation and the fractal correlation dimension d of earthquake hypocenters calculated from sliding windows containing more than 100 events over a span of 6 months after the main shock we find a positive correlation between b and d from the aftershock sequence our result thus suggests that aki s relation d 3b c could be possibly applied to one single fracturing process and its related aftermath

multifractal dimension and b value analysis of the 1998 1999 quito swarm related to guagua pichincha volcano activity ecuador 1 temporal variations of spatial multifractal dimensions of quito swarm seismicity ecuador are related to the august 1998 to december 1999 guagua pichincha volcanic activity multifractal dimensions decrease a few days before the five main seismic energy peaks and increase again before or just after these peaks this behavior reveals a self organization of earthquakes that precedes main seismic energy peaks the quito swarm is also characterized by a bimodal gutenberg richter law with two b values b1 0 95 0 15 and b2 1 48 0 15 this bimodality may reveal the superposition of two different processes one related to a classical elastic rupture and the other related to hydraulic fracture leading to high b values resulting from magma and overpressurized groundwater movements groundwater expulsion may be driven by heat released from deeper upgoing magma and manifested on the surface by the occurrence of phreatic explosions beginning 7 august 1998 and by the formation of eight dacitic lava domes beginning 25 september 1999

are volcanic seismic b values high and if so when abstract the gutenberg richter exponent b is a measure of the relative proportion of large and small earthquakes it is commonly used to infer material properties such as heterogeneity or mechanical properties such as the state of stress from earthquake populations it is well known that the b value tends to be high or very high for volcanic earthquake populations relative to b 1 for those of tectonic earthquakes and that b varies significantly with time during periods of unrest we first review the supporting evidence from 34 case studies and identify weaknesses in this argument due predominantly to small sample size the narrow bandwidth of magnitude scales available variability in the methods used to assess the minimum or cutoff magnitude m c and to infer b informed by this we use synthetic realisations to quantify the effect of choice of the cutoff magnitude on maximum likelihood estimates of b and suggest a new work flow for this choice we present the first quantitative estimate of the error in b introduced by uncertainties in estimating m c as a function of the number of events and the b value itself this error can significantly exceed the commonly quoted statistical error in the estimated b value especially for the case that the underlying b value is high we apply the new methods to data sets from recent periods of unrest in el hierro and mount etna for el hierro we confirm significantly high b values of 1 5 2 5 prior to the 10 october 2011 eruption for mount etna the b values are indistinguishable from b 1 within error except during the flank eruptions at mount etna in 2001 2003 when 1 5 b b 1 our results confirm that these volcano tectonic earthquake populations can have systematically high b values especially when associated with eruptions at other times they can be indistinguishable from those of tectonic earthquakes within the total error the results have significant implications for operational forecasting informed by b value variability in particular in assessing the significance of b value variations identified by sample sizes with fewer than 200 events above the completeness threshold

spatial variation of seismic b values beneath makushin volcano unalaska island alaska abstract the frequency magnitude distribution was spatially mapped beneath makushin volcano unalaska island alaska using an earthquake catalog of 491 events that occurred between july 2001 and april 2005 an area of high seismic b values 2 0 is found 4 km east of makushin s main vent at a depth between 4 and 7 km the anomaly is statistically significant based on utsu s p test t utsu on seismicity in report of the joint research institute for statistical mathematics tokyo 1992 139 157 and is not data processing method or parameter dependent interestingly a recent insar interferometric study z lu j a power v s mcconnell c wicks jr d dzurism preeruptive inflation and surface interferometric coherence characteristics by satellite radar interferometry at makushin volcano alaska 1993 2000 j geophys res 107 2002 2266 doi 10 1029 2001jb000970 inferred a surface uplift of about 7 cm during the two year period prior to october 1995 centered approximately in the area with the observed anomalous b values the uplift was caused by the volume increase of an inferred magma chamber at a depth of about 7 km the close correspondence of the seismic and insar observations suggests that the heterogeneous area associated with the observed high b values is most likely the result of increased crack density associated with the magma chamber this study demonstrates the effectiveness of combining insar and seismological observations in locating magma chambers and areas of high heterogeneity in the crust

correlating variations of b values and crustal deformations during the 1990s may have pinpointed the rupture initiation of the mw 7 4 izmit earthquake of 1999 august 17 summary the b value increases from 1 1 along straight segments to 1 7 along a releasing bend of the north anatolian fault system between 30 1 e and 30 8 e the tensional nature of the bend is corroborated by extension rates of 0 3 strain yr 1 as obtained from global positioning system gps data fault plane solutions in this area change from abundant right lateral strike slip to oblique slip with normal components in the central part of the bend compatible with the formation of a pull apart basin we suggest that this crustal volume is highly fractured corresponding to a short mean crack length due to the superposition of horizontal and normal faulting as a consequence of low normal stress on the existing cracks frictional sliding is assumed to be the predominant mechanism for the generation of seismic events resulting in high b values the lowest b values b 0 8 in the area investigated are found at the junction between the fault bend and the adjoining segment which runs through the epicentre of the 1999 izmit earthquake at the junction a localized stress concentration is expected from numerical models of seismicity along geometrical barriers thus the site of lowest b has been considered to be the most likely place for a major earthquake a conclusion that is confirmed by the izmit earthquake with epicentre located about 13 km from the anticipated site in early 1992 the spatially averaged b value started to increase along the central and northwestern parts of the fault bend and there was a corresponding period of intensified horizontal extension since no large earthquake was recorded in 1992 it is assumed that the anomalous extension and the associated change in stress have been caused by aseismic fault creep in view of the available seismotectonic information surface displacements due to a slow dislocation at depth were calculated the gps data are reasonably explained by a source of normal fault type at a depth of 10 km and equivalent magnitude mw 5 9 stress changes at seismogenic depths are calculated under the assumption that an increase in b is most likely to be observed along those segments where both deviatoric and mean stress are reduced while the coulomb stress change is positive that is the fault is brought closer to failure for right lateral strike slip the stress condition is fulfilled at the sites of the largest b value increase the surface rupture of the izmit earthquake is associated with known fault traces only in the west and in the east of the study area along the fault bend it detaches itself from mapped fault traces and runs through the regions of positive coulomb stress change caused by the inferred 1992 slow event maximum surface slip 5 m is observed in the immediate vicinity of sites of maximum coulomb stress change 3 bar indicating that the 1992 event could have partially unclamped the rupture plane of the subsequent izmit earthquake we propose that the strong differences in b observed along the complex fault bend can be used to characterize different states of tectonic deformation in space and time

assessment of pre crisis and syn crisis seismic hazard at campi flegrei and mt vesuvius volcanoes campania southern italy in this study we address the issue of short term to medium term probabilistic seismic hazard analysis for two volcanic areas campi flegrei caldera and mt vesuvius in the campania region of southern italy two different phases of the volcanic activity are considered the first which we term the pre crisis phase concerns the present quiescent state of the volcanoes that is characterized by low to moderate seismicity the second phase syn crisis concerns the unrest phase that can potentially lead to eruption for the campi flegrei case study we analyzed the pattern of seismicity during the 1982 1984 ground uplift episode bradyseism for mt vesuvius two different time evolutionary models for seismicity were adopted corresponding to different ways in which the volcano might erupt we performed a site specific analysis linked with the hazard map to investigate the effects of input parameters in terms of source geometry mean activity rate periods of data collection and return periods for the syn crisis phase the analysis in the present study of the pre crisis phase allowed a comparison of the results of probabilistic seismic hazard analysis for the two study areas with those provided in the italian national hazard map for the mt vesuvius area in particular the results show that the hazard can be greater than that reported in the national hazard map when information at a local scale is used for the syn crisis phase the main result is that the data recorded during the early months of the unrest phase are substantially representative of the seismic hazard during the whole duration of the crisis

seismicity at the volcanoes of katmai national park alaska july 1995 december 1997 abstract upper crustal seismicity located within katmai national park occurs mainly within four distinct clusters originating near martin mageik mm subnet volcanoes trident volcano katmai caldera and snowy volcano analyses of earthquake frequency magnitude distributions reveal high b values beneath mm subnet 1 5 normal b values at trident volcano 1 0 and intermediate b values at katmai caldera 1 3 for all seismicity occurring between july 1995 and december 1997 detailed analyses of subsets of b values and hypocenter locations at mm subnet reveal a temporal increase in b value associated with an increase in the maximum depth of seismicity the changes occurred during a shallow earthquake swarm beneath mageik volcano between october 16 and 25 1996 and again in november december 1997 before the swarm the weighted least squares b value was 1 01 at mm subnet increased to 1 59 during the swarm and remained anomalously high until april 1997 the corresponding maximum depth of seismicity is generally less than 5 km for well located earthquakes occurring after september 18 1996 but shifted to 10 km during both the october 1996 swarm and the november december 1997 period the november december 1997 event is not associated with an increase in the rate of seismicity or the b value the october 1996 swarm had a cumulative moment release of 5 0 10 20 dyn cm and decayed from a peak rate of 110 events per day with a modified omori law p value of 1 06 0 11 modelling by the flow law with a 10 km depth limit for seismicity suggests that temperature gradients are on the order of 20 40 c km 1 in agreement with the p value estimate we infer that a simple pressurizing intrusion was not associated with the october swarm because higher stresses should increase seismicity and lower the b value the opposite of what we observed alternatively an actively degassing intrusion would reduce the effective stress and increase the b value at shallow depths while the increased stress would induce seismicity at depth surface temperature measurements taken at the mageik crater lake in july 1995 and again in july 1997 revealed an increase of about 10 c in the lake water temperature consistent with a degassing intrusive event

characterization of the causative fault system for the 2001 bhuj earthquake of mw 7 7 abstract precise hypocenters erh m w 2 0 5 3 delineate a east west trending blind thrust dipping 45 towards south named as north wagad fault nwf about 25 km north of kachchh main land fault kmf as the causative fault for the 2001 bhuj earthquake of m w 7 7 the aftershock zone involves a crustal volume of 60 40 35 km 3 lying between kmf and nwf the waveform inversion of 45 aftershocks of m 3 0 5 3 suggest that the e w trending south dipping reverse faulting mainly characterizes the aftershock zone however some reverse faulting along nw se as well as ne sw planes and some strike slip faulting along nw se trending vertical plane are also noticed the estimated p axes point on an average towards n s while t axes orient in e w agreeing well with the prevailing regional plate tectonic stress directions the estimated velocity model from one dimensional inversion of 8000 p and 5000 s travel times from 600 aftershocks deciphers a detailed crustal structure of the region upper 0 6 km on an average suggests a low velocity zone characterizing the jurassic and younger sediments the depth range 6 42 km is characterized on an average by larger values of v p 6 31 to 6 98 km s with an average of 6 71 km s v s 3 64 to 4 05 km s with an average of 3 85 km s and v p v s 1 69 to 1 81 with an average of 1 75 the high crustal velocities can be attributed to the existence of a high velocity mafic intrusive rift pillow structure beneath the region probably emplaced during the rifting time this brittle competent high velocity zone beneath the epicentral area in response to the compression due to the northward movement of the indian plate could induce sufficient local stress perturbation for generating large intraplate earthquakes of m w 7 5 in the lower crust further within the overall higher velocity depth range a layer characterized by large values of v p 6 98 km s v s 3 854 km s and v p v s 1 81 is found in the depth range of 20 5 30 km which is inferred to be fractured and saturated high crack density and probably fluid filled presence of numerous fractures in this layer is confirmed by a high b value 0 75 1 1 in this layer this layer might have facilitated the nucleation process of the 2001 bhuj earthquake the major rupture and 47 of the aftershocks have occurred within this layer

mapping of the b value anomalies beneath mt etna italy during july august 2001 lateral eruption 1 the pattern of b value of the frequency magnitude relation or mean magnitude has been analyzed as function of space beneath mt etna during the intense lateral eruption of july august 2001 the data used august 1999 august 2001 subdivided in the pre eruptive and eruption period show significant space variations in the b value for each of the two periods a volume of anomalously high b value can be observed in the southeastern flank of the volcano the anomalies located at 3 1 km b 1 84 0 20 and at about 1 1 km b 2 11 0 29 depth are interpreted as two different steps of a magma migration process ended with the july august 2001 eruption all the available geophysical evidences such as geodetic deformation measurements focal mechanism and tomographic studies support this interpretation

mapping the frequency magnitude distribution in asperities an improved technique to calculate recurrence times we hypothesize that highly stressed asperities may be defined by mapping anomalously low b values along the san andreas fault near parkfield the asperity under middle mountain with its b 0 46 can be distinguished from all other parts of the fault surface likewise along the calaveras fault the northern asperity of the morgan hill 1984 m6 2 rupture can be identified by its low b of 0 5 as a high stress patch along the fault we add further evidence to the observations that the b value of the frequency magnitude relationship of earthquakes is inversely proportional to stress by showing that it decreases with depth in the parkfield segment of the san andreas and along the calaveras fault in both of these areas b values above and below 5 km depth are 1 2 and 0 8 respectively we propose that probabilistic recurrence times tr based on the seismicity parameters a and b should be calculated from their values within asperities only instead of from the values of the entire rupture area of the maximum expected earthquake the strong patches on faults control the time of rupture because they are capable of accumulating larger stresses than the rest of the fault zone which slips along passively when an asperity breaks therefore no information on tr is contained in the passive fault segments only in the asperities at parkfield the probabilistic estimates of tr derived from the data in the whole rupture and in the asperity only are 72 18 24 and 23 12 18 years respectively compared to the historically observed repeat time of 22 years at morgan hill the tr estimates are 122 46 76 and 78 47 110 years respectively compared to the observed repeat time of 72 years

spatial mapping of the b value at mount etna italy using earthquake data recorded from 1999 to 2005 1 the spatial pattern of the b value of the frequency magnitude relation has been analyzed using gridding techniques beneath mount etna italy a regional data set of 2900 events with md duration magnitude 1 5 up to 15 km depth occurring between august 1999 and december 2005 has been used two regions with an abnormally high b value have been found one centered beneath the southern part of the valle del bove above the 6 km below sea level bsl deep basement and the other beneath the summit region 2 km bsl east of the central craters we can infer that these high b value anomalies are regions of increased crack density and or high pore pressure related to the presence of nearby magma storage this interpretation is supported by all the available geophysical evidence such as tomographic studies and geodetic deformation measurements the data set has also been subdivided into five periods corresponding to different phases of volcanic activity 2001 preeruption 2001 eruptive 2002 2003 preeruption 2002 2003 eruptive and 2002 2003 posteruption the minimum magnitude of completeness mc and the b value were computed for each period a volume of anomalously high b values can be observed in each of these periods except for the 2002 2003 preeruption interval this approach has allowed the detection of the transient presence of magmatic intrusions during the various periods evaluated

state of the art of research in kinetic modelling of oil formation and expulsion abstract the last ten years have seen a rapid development in the understanding of petroleum generation and expulsion by a combined use of natural series and experimental simulation this knowledge is now used to develop mathematical models which reproduce the kinetics of petroleum generation and migration in the purpose of basin evaluation by a combination of observation of homogeneous geochemical series experimental simulation and mathematical modelling it has been now established that parameters governing the quantity and composition of petroleum are temperature type of organic matter time or heating rate catalysis by clay minerals which would produce important amounts of isoalkanes is not necessary to produce petroleum the role of minerals although still controversial is rather to retain the heavy fraction of petroleum pressure seems to have a limited influence within the range for effective source rocks kerogen is a tremendously complex macromolecule which is now insufficiently characterized to develop fundamental predictive models of thermal cracking i e involving intermediates such as radicals and olefins such models presently apply only to the cracking of simple molecules hexane hexadecane at limited degrees of cracking for this reason kinetic models are still empirically calibrated on pyrolysis experiments and or on natural maturation trends the most popular models involve a series or a continuous distribution of parallel reactions to describe primary cracking i e direct formation of mobile compounds from kerogen these are generally calibrated against open system pyrolysis with various temperature programs consideration of natural maturation trends i e decrease in petroleum potential may be used also for calibration but discrepancies of organic matter properties availability of deep samples and uncertainties on thermal history limit the effectiveness of such methods whatever the method main activation energies are found in the range 45 60 kcal mol secondary cracking which refers generally to cracking of mobile compounds cannot be modelled from open system pyrolysis nor from natural series unknown residence times but only from closed system pyrolysis although models of primary and secondary cracking still need experimental improvements and more realistic kinetic schemes their ability to predict quantities and composition of petroleum depends primarily on migration which is poorly known indeed migration controls the residence time of petroleum in hot zones of sedimentary basins and thus determines the extent of oil conversion into gas as reproduced by recent numerical models preliminary studies documenting the interactions between thermal cracking and expulsion are shown from haltenbanken area and paris basin in the last few years a kind of agreement has been reached that primary migration was most likely occuring in a separate phase from water and that a sufficient concentration of petroleum must be generated for expulsion to start indeed high expulsion efficiencies over 50 are systematically found for rich and mature source rocks a further understanding of primary migration requires observations of natural series petrophysical studies of source rocks porosities under 10 permeabilities in the nanodardy range thermodynamic investigation of unconventional multiphase organic systems kerogen liquid s gas and experimental simulation under stress this on going research should enable models to track correctly migration paths and thermal history of petroleum fluids as necessary to model their composition

depth dependence of earthquake frequency magnitude distributions in california implications for rupture initiation statistics of earthquakes in california show linear frequency magnitude relationships in the range of m2 0 to m5 5 for various data sets assuming gutenberg richter distributions there is a systematic decrease in b value with increasing depth of earthquakes we find consistent results for various data sets from northern and southern california that both include and exclude the larger aftershock sequences we suggest that at shallow depth 0 to 6 km conditions with more heterogeneous material properties and lower lithospheric stress prevail rupture initiations are more likely to stop before growing into large earthquakes producing relatively more smaller earthquakes and consequently higher b values these ideas help to explain the depth dependent observations of foreshocks in the western united states the higher occurrence rate of foreshocks preceding shallow earthquakes can be interpreted in terms of rupture initiations that are stopped before growing into the mainshock at greater depth 9 15 km any rupture initiation is more likely to continue growing into a larger event so there are fewer foreshocks if one assumes that frequency magnitude statistics can be used to estimate probabilities of a small rupture initiation growing into a larger earthquake then a small m2 rupture initiation at 9 to 12 km depth is 18 times more likely to grow into a m5 5 or larger event compared to the same small rupture initiation at 0 to 3 km

insights into the 2011 2012 submarine eruption off the coast of el hierro canary islands spain from statistical analyses of earthquake activity summary the purpose of this work is to gain insights into the 2011 2012 eruption of el hierro canary islands by mapping the evolution of the seismic b value the el hierro seismic sequence offers a rather unique opportunity to investigate the process of reawakening of an oceanic intraplate volcano after a long period of repose the 2011 2012 eruption is a submarine volcanic event that took place about 2 km off of the southern coast of el hierro the eruption was accompanied by an intense seismic swarm and surface manifestations of activity the earthquake catalogue during the period of unrest includes over 12 000 events the largest with magnitude 4 6 the seismic sequence can be grouped into three distinct phases which correspond to well separated spatial clusters and distinct earthquake regimes the estimated b value is of 1 18 0 03 and a magnitude of completeness of 1 3 for the entire catalogue b is very close to 1 0 which indicates completeness of the earthquake catalogue with only minor departures from the linearity of gutenberg richter frequency magnitude distribution the most straightforward interpretation of this result is that the seismic swarm reached its final stages and no additional large magnitude events should be anticipated similarly to what one would expect for non volcanic earthquake sequences the results dividing the activity in different phases illustrate remarkable differences in the estimate of b value during the early and late stages of the eruption the early pre eruptive activity was characterized by a b value of 2 25 in contrast the b value was 1 25 during the eruptive phase based on our analyses and the results of other studies we propose a scenario that may account for the observations reported in this work we infer that the earthquakes that occurred in the first phase reflect magma migration from the upper mantle to crustal depths the area where magma initially intruded into the crust because of its transitional nature is characterized by high fracturing thus favours anomalously high b values the larger magnitude earthquakes recorded in the second phase may reflect relaxation around the magma reservoir that had fed the eruption and thus lower b values

spatial variation in the frequency magnitude distribution of earthquakes under the tectonic framework in the middle east abstract spatial variations of seismic energy released and b value over the middle east region are investigated based on a seismicity catalog from 1995 to 2007 the goal is to use these seismic parameters and based on other geodetic and geophysical observations such as gps measurements strain rate model fault distribution focal mechanism crustal model q model and gravity measurements etc to uncover spatial patterns that seem anomalous areas of high energy released cumulative seem to correspond to the areas of relatively high b values areas of high energy released and high b values seem to correspond very well with the location of continental collision where earthquake activities are high the divergent boundary between arabia and african plates and subduction zone at makran seem to correspond to low to moderate energy release northern pamir azerbaijan caucasus the lower part of zagros mountains eastern turkey owen fracture zone strait of bob el mandeb and south of the sulaiman shear zone seem to correspond to high cumulative energy released high strain rate high b values and high fault density while the central and eastern iran southern zagros northern pakistan gulf of aden alborz southwest of the caspian sea western caucasus and kopeh dagh seem to correspond with lower b values the cross section map for hindu kush shows general decreasing of the b values with depth however a region of high b value is observed underneath pamir at depths from 170 to 230 km this anomaly region can be due to dehydration of pamir crustal slab at depth

a structural interpretation of the aftershock cloud of the 1992 mw 7 3 landers earthquake we analyze the spatial relationship of relocated aftershocks to the principal rupture planes of the m w 7 3 1992 landers mainshock from a structural point of view we find that the aftershocks constitute primarily a several kilometer wide damage zone centered on the mainshock rupture planes the intensity of damage decreases away from the principal faults less than half of the aftershocks occurred within 1 km of the mainshock planes and perhaps only 5 of the aftershocks are candidates for rerupture of the mainshock faults moreover it seems that aftershocks along the landers rupture have b values that correlate well with the complexity of the mainshock rupture low b values occur along segments that are simple whereas higher b values correlate with sections that are more complex thus structural complexity appears to correlate with a greater relative abundance of small earthquakes these observations imply that aftershock populations reflect fault populations in the medium surrounding the principal faults rather than the behavior of the mainshock planes themselves online material arcview information about the surface rupture of the landers mainshock

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