determination of earthquake energy release and ml using terrascope we estimated the energy radiated by earthquakes in southern california using on scale very broadband recordings from terrascope the method we used involves time integration of the squared ground motion velocity and empirical determination of the distance attenuation function and the station corrections the time integral is typically taken over a duration of 2 min after the p wave arrival the attenuation curve for the energy integral we obtained is given by q r cr n exp kr r 2 2 h ref 2 with c 0 49710 n 1 0322 k 0 0035 km 1 and h ref 8 km where is the epicentral distance a similar method was used to determine m l using terrascope data the station corrections for m l are determined such that the m l values determined from terrascope agree with those from the traditional optical wood anderson seismographs for 1 5 6 5 m l saturates the ratio e s m 0 m 0 seismic moment a measure of the average stress drop for six earthquakes the 1989 montebello earthquake m l 4 6 the 1989 pasadena earthquake m l 4 9 the 1990 upland earthquake m l 5 2 the 1991 sierra madre earthquake m l 5 8 the 1992 joshua tree earthquake m l 6 1 and the 1992 landers earthquake m w 7 3 are about 10 times larger than those of the others that include the aftershocks of the 1987 whittier narrows earthquake the sierra madre earthquake the joshua tree earthquake and the two earthquakes on the san jacinto fault the difference in the stress drop between the mainshock and their large aftershocks may be similar to that between earthquakes on a fault with long and short repeat times the aftershocks which occurred on the fault plane where the mainshock slippage occurred had a very short time to heal hence a low stress drop the repeat time of the major earthquakes on the frontal fault systems in the transverse ranges in southern california is believed to be very long a few thousand years hence the events in the transverse ranges may have higher stress drops than those of the events occurring on faults with shorter repeat times such as the san andreas fault and the san jacinto fault the observation that very high stress drop events occur in the transverse ranges and the los angeles basin has important implications for the regional seismic potential the occurrence of these high stress drop events near the bottom of the seismogenic zone strongly suggests that these fault systems are capable of supporting high stress that will eventually be released in major seismic events characterization of earthquakes in terms of the e s m 0 ratio using broadband data will help delineate the spatial distribution of seismogenic stresses in the los angeles basin and the transverse ranges

seismological and geodetic constraints on the 2011 mw5 3 trinidad colorado earthquake and induced deformation in the raton basin the raton basin of southern colorado and northern new mexico is an actively produced hydrocarbon basin that has experienced increased seismicity since 2001 including the august 2011 mw5 3 trinidad normal faulting event following the 2011 earthquake regional seismic observations were used to relocate 21 events including the 2011 main shock two foreshocks and 13 aftershocks additionally interferometric synthetic aperture radar insar observations of both the 2011 event and preevent basin deformation place constraint on the spatial kinematics of the 2011 event and localized basin subsidence due to ground water or gas withdrawal we find that the 2011 earthquake ruptured an 8 10 km long segment of a normal fault at depths of 1 5 6 0 km within the crystalline precambrian basement underlying the raton basin sedimentary rocks the earthquake also nucleated within the crystalline basement in the vicinity of an active wastewater disposal site the ensuing aftershock sequence demonstrated statistical properties expected for intraplate earthquakes though the length of the 2011 earthquake is unexpectedly long for an mw5 3 event suggesting that wastewater disposal may have triggered a low stress drop otherwise natural earthquake additionally preevent and postevent seismicity in the raton basin spatially correlates to regions of subsidence observed in insar time series analysis while these observations cannot discern a causal link between hydrocarbon production and seismicity they constrain spatial relationships between active basin deformation and geological and anthropogenic features furthermore the insar observations highlight the utility of space based geodetic observations for monitoring and assessing anthropogenically induced and triggered deformation

precession and glacial cycle controls of monsoon precipitation isotope changes over east asia during the pleistocene abstract precipitation isotope reconstructions derived from speleothems and plant waxes are important archives for understanding hydroclimate dynamics their climatic significance in east asia however remains controversial here we present terrestrial plant wax stable hydrogen isotope dwax records over periods covering the last four interglacials and glacial terminations from sediment cores recovered from the northern south china sea scs as an archive of regionally integrated precipitation isotope changes in southeast china combined with previous precipitation isotope reconstructions from china we find that the scs dwax and southwest central china stalagmite 18 o records show relatively enriched and depleted isotopic values respectively during interglacial peaks but relatively similar isotopic variations during most sub interglacials and glacial periods over the past 430 thousand years during interglacial peaks strong summer insolation should have intensified the convection intensity the isotopic fractionation along moisture trajectories and the seasonality which are all in favor of causing isotopically depleted rainfall over the east asian monsoon regime these effects in combination with a relatively high proportion of indian ocean versus pacific sourced moisture influx should have resulted in strongly depleted precipitation isotopes stalagmite 18 o over most parts of china however southeast china should have been affected by a relatively low ratio of indian ocean versus pacific sourced moisture influx which dominated over effects yielding depleted precipitation isotopes and led to enriched precipitation isotopes dwax it is thus concluded that glacial boundary conditions and insolation forcing are the two most important factors for causing regional differences in precipitation isotope compositions over subtropical east asia on orbital timescales

influence of pore pressure on the event size distribution of induced earthquakes 1 during an enhanced geothermal system egs experiment fluid is injected at high pressure into crystalline rock to enhance its permeability and thus create a reservoir from which geothermal heat can be extracted the fracturing of the basement caused by these high pore pressures is associated with microseismicity however the relationship between the magnitudes of these induced seismic events and the applied fluid injection rates and thus pore pressure is unknown here we show how pore pressure can be linked to the seismic frequency magnitude distribution described by its slope theb value we evaluate the dataset of an egs in basel switzerland and compare the observed event size distribution with the outcome of a minimalistic model of pore pressure evolution that relates event sizes to the differential stress d we observe that the decrease of b values with increasing distance of the injection point is likely caused by a decrease in pore pressure this leads to an increase of the probability of a large magnitude event with distance and time

gas injection may have triggered earthquakes in the cogdell oil field texas between 1957 and 1982 water flooding was conducted to improve petroleum production in the cogdell oil field north of snyder tx and a contemporary analysis concluded this induced earthquakes that occurred between 1975 and 1982 the national earthquake information center detected no further activity between 1983 and 2005 but between 2006 and 2011 reported 18 earthquakes having magnitudes 3 and greater to investigate these earthquakes we analyzed data recorded by six temporary seismograph stations deployed by the usarray program and identified 93 well recorded earthquakes occurring between march 2009 and december 2010 relocation with a double difference method shows that most earthquakes occurred within several northeast southwest trending linear clusters with trends corresponding to nodal planes of regional focal mechanisms possibly indicating the presence of previously unidentified faults we have evaluated data concerning injection and extraction of oil water and gas in the cogdell field water injection cannot explain the 2006 2011 earthquakes especially as net volumes injection minus extraction are significantly less than in the 1957 1982 period however since 2004 significant volumes of gases including supercritical co2 have been injected into the cogdell field the timing of gas injection suggests it may have contributed to triggering the recent seismic activity if so this represents an instance where gas injection has triggered earthquakes having magnitudes 3 and larger further modeling studies may help evaluate recent assertions suggesting significant risks accompany large scale carbon capture and storage as a strategy for managing climate change

temporal and three dimensional spatial analyses of the frequency magnitude distribution near long valley caldera california summary the 3 d distribution of the b value of the frequency magnitude distribution is analysed in the seismically active parts of the crust near long valley caldera california the seismicity is sampled in spherical volumes containing n 150 earthquakes and centred at nodes of a grid separated by 0 3 km significant variations in the b value are detected with b ranging from b 0 6 to b 2 0 high b value volumes are located near the resurgent dome and at depths below 5 km at mammoth mountain b values are found to be much lower south of the long valley caldera we interpret this to indicate that an active magma body has advanced from depths below 8 km to depths of 4 to 5 km beneath mammoth mountain in 1989 and that anomalous crust either highly fractured or containing unusually high pore pressure such as is the case in the vicinity of active magma bodies exists north of the seismically active area beneath the resurgent dome at all depths we also investigate the spatial distribution of temporal variations of the frequency magnitude distribution by introducing diverential b value maps b values increased from b 0 8 to b 1 5 underneath mammoth mountain at the onset of the 1989 earthquake swarm and remained high thereafter this suggests that an intrusion permanently altered the average distribution of cracks at 5 10 km depth or that the pore pressure permanently increased we propose that high b values are a necessary but not suycient condition near a magmatic body and therefore spatial b value mapping can be used to aid in the identification of active magma bodies

the accommodation of large strains in the upper lithosphere of the earth and other solids by self similar fault systems the geometrical origin of b value plate tectonics has provided a method of visualizing the geometry of the deformation of the earth s lithosphere on a large scale the description is so concise that for many purposes it provides an explanation of geological processes that overshadows the need to understand the driving processes the mechanics of the zones between the plates are less well understood particularly in continental regions where large areas are subject to deformation both continuous and discontinuous models have been tried but both have obvious drawbacks

potential of ambient seismic noise techniques to monitor the st gallen geothermal site switzerland the failures of two recent deep geothermal energy projects in switzerland basel 2006 st gallen 2013 have again highlighted that one of the key challenges for the successful development and operation of deep underground heat exchangers is to control the risk of inducing potentially hazardous seismic events in st gallen after an injection test and two acid injections that were accompanied by a small number of micro earthquakes ml 0 2 operators were surprised by an uncontrolled gas release from the formation gas kick the killing procedures that had to be initiated following standard drilling procedures led to a ml3 5 earthquake with ambient seismic noise cross correlations from nine stations we observe a significant loss of waveform coherence that we can horizontally and vertically constrain to the injection location of the fluid the loss of waveform coherence starts with the onset of the fluid injections 4 days prior to the gas kick we interpret the loss of coherence as a local perturbation of the medium we show how ambient seismic noise analysis can be used to assess the aseismic response of the subsurface to geomechanical well operations and how this method could have helped to recognize the unexpected reservoir dynamics at an earlier stage than the microseismic response alone allowed

magnitudes of induced earthquakes and geometric scales of fluid stimulated rock volumes sometimes rock stimulations by fluid injections into geothermal boreholes are able to trigger perceptible or even potentially damaging earthquakes this does not seem to be the case for hydraulic fracturing of hydrocarbon reservoirs reasons for such a difference and factors defining magnitudes of induced earthquakes triggered tectonicly as well as induced artificially remain unclear we analyzed microseismic data obtained by fluid stimulations at different geothermal and hydrocarbon sites this analysis indicates that a rupture corresponding to a fluid induced earthquake seems to be only probable along a surface located mainly inside a stimulated rock volume we approximated the stimulated volume by an ellipsoid and compared the statistics of induced events with the statistics of randomly distributed thin flat disks modeling rupture surfaces we found that one of the main factors limiting the probability to induce a large magnitude event is the minimum principal axis of a fluid stimulated rock volume

decay rate of fluid induced seismicity after termination of reservoir stimulations we present a model describing the seismicity rate of fluid injection induced seismicity we put the focus on seismicity induced after termination of fluid injections here our primary objective is the identification of parameters controlling the decay rate of seismicity the particular importance of a theoretical model for postinjection seismicity is underlined by observations after stimulations of geothermal reservoirs at different locations for instance the postinjection phase is relevant for a seismic risk which up to now has been difficult to control because processes leading to postinjection events are not well understood based on the assumption of pore pressure diffusion as the governing mechanism leading to the triggering of seismic events we develop a method to calculate the seismicity rate during and after fluid injections we find that the decay rate of seismicity after termination of injection is very similar to the omori law which describes the decay rate of aftershock activity after t

the propagation effects of lightning electromagnetic fields over mountainous terrain in the earth ionosphere waveguide in this paper a full wave two dimensional finite difference time domain model is developed to evaluate the propagation effects of lightning electromagnetic fields over mountainous terrain in the earth ionosphere waveguide in the model we investigate the effect of the earth ionosphere waveguide structure and medium parameters including the effect of the ionospheric cold plasma characteristics the effect of the earth curvature and the propagation effects over mountainous terrain for the first time the obtained results are validated against simultaneous experimental data consisting of lightning currents measured at the santis tower and electric fields measured in neudorf austria located at 380 km distance from the tower it is shown that both the time delays and amplitudes of the lightning electromagnetic fields at 380 km distance can be strongly affected by the ionospheric electron density profile the mountainous terrain and the earth curvature after taking into account the effect of the irregular terrain between the santis tower and the field measurement station the vertical electric fields calculated by using our model are found to be in good agreement with the corresponding measured cases occurred in both daytime and nighttime the ideal approximation used in either the classical solutions or the simplified models might lead to inaccuracies in the estimated reflection height furthermore we discuss the sensitivity of our results by considering different return stroke models as well as different typical values of the return stroke speed and of the ground conductivity

inadvertent changes in magnitude reported in earthquake catalogs their evaluation through b value estimates a simple procedure is presented for analyzing magnitudes and seismicity rates reported in earthquake catalogs in order to discriminate between inadvertently introduced changes in magnitude and real seismicity changes we assume that the rate and the frequency magnitude relation of the independent background seismicity do not change with time observed differences in the frequency magnitude relation a and b values between data from two periods are modeled as due to a transformation of the magnitude scale the transformation equation is found by a least squares fitting process based on the seismicity data for earthquakes large enough to be reported completely and by comparing the linear relation of one period to the other for smaller events an additional factor accounting for increased decreased detection is allowed this fitting technique is tested on a data set from parkfield for which two types of magnitudes amplitude and duration were computed for each earthquake we found that the b value fitting technique yielded virtually the same result as a linear regression assuming the same errors in the two magnitudes the technique is also applied to interpret the nature of reporting rate changes in a local guerrero mexico and a regional italy earthquake catalog in guerrero a magnitude change in 1991 37 can be modeled about equally well by m new m old 0 5 or by m new 1 02 m old 0 38 but residuals with the latter transformation are smaller in italy a magnitude change in 1980 21 cannot be modeled satisfactorily by a simple magnitude shift but is well described by a compression of the magnitude scale given by m new 0 67 m old 1 03 the proposed b slope fitting method provides a means to interpret quantitatively and in some cases correct for artificial reporting rate changes in earthquake catalogs

two year survey of earthquakes and injection production wells in the eagle ford shale texas prior to the mw4 8 20 october 2011 earthquake abstract between november 2009 and september 2011 the earthscope usarray program deployed 25 temporary seismograph stations on a 70 km grid in south central texas between 27 n 31 n and 96 w 101 w this area includes the eagle ford shale for decades this geographic region has produced gas and oil from other strata using conventional methods but recent developments in hydrofracturing technology has allowed extensive development of natural gas resources from within the eagle ford our study surveys small magnitude seismic events and evaluates their correlation with fluid extraction and injection in the eagle ford identifying and locating 62 probable earthquakes including 58 not reported by the u s geological survey the 62 probable earthquakes occur singly or in clusters at 14 foci of these foci two were situated near wells injecting recently increased volumes of water eight were situated near wells extracting recently increased volumes of oil and or water and four were not situated near wells reporting significant injection extraction increases thus in this region while the majority of small earthquakes may be triggered induced by human activity they are more often associated with fluid extraction than with injection we also investigated the m w 4 8 20 october 2011 fashing earthquake the largest historically reported earthquake in south central texas that occurred two weeks after the removal of the temporary usarray stations a field study indicated that the highest intensity mmi vi region was about 10 km south of 2010 2011 foreshock activity and that there were no high volume injection wells within 20 km of the mmi v vi region or the foreshocks however the 20 october 2011 earthquake did coincide with a significant increase in oil water extraction volumes at wells within the mmi v vi region and this was also true for previous earthquakes felt at fashing in 1973 and 1983 in contrast our study found significant increases in injection prior to an mblg3 6 20 july 1991 earthquake near falls city texas thus the eagle ford geographic region with seismic activity associated both with extraction and injection appears to be more complex than the barnett shale of northeast texas where a similar survey found possible correlations only with fluid injection

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

variations in earthquake size distribution across different stress regimes the earthquake size distribution follows in most instances a power law1 2 with the slope of this power law the b value commonly used to describe the relative occurrence of large and small events a high b value indicates a larger proportion of small earthquakes and vice versa statistically significant variations of b values have been measured in laboratory experiments mines and various tectonic regimes such as subducting slabs near magma chambers along fault zones and in aftershock zones3 however it has remained uncertain whether these differences are due to differing stress regimes as it was questionable that samples in small volumes such as in laboratory specimens mines and the shallow earth s crust are representative of earthquakes in general given the lack of physical understanding of these differences the observation that b values approach the constant 1 if large volumes are sampled4 was interpreted to indicate that b 1 is a universal constant for earthquakes in general5 here we show that the b value varies systematically for different styles of faulting we find that normal faulting events have the highest b values thrust events the lowest and strike slip events intermediate values given that thrust faults tend to be under higher stress than normal faults we infer that the b value acts as a stress meter that depends inversely on differential stress

statistical evidence of transitioning open vent activity towards a paroxysmal period at volcan santiaguito guatemala during 2014 2018 abstract long term eruptive activity at the santiaguito lava dome complex guatemala is characterised by the regular occurrence of small to moderate size explosions from the active caliente dome between november 2014 and december 2018 we deployed a seismo acoustic network at the volcano which recorded several changes in the style of eruption including a period of elevated explosive activity in 2016 here we use a new catalogue of explosions to characterise changes in the eruptive regime during the study period we identify four different phases of activity based on changes in the frequency and magnitude of explosions at the two ends of the spectrum of repose times we find pairs of explosions with near identical seismic and acoustic waveforms recorded within 1 10 min of one another and larger explosions with recurrence times on the order of days to weeks the magnitude frequency relationship for explosions at santiaguito is well described by a power law we show that changes in b value between eruptive regimes reflect temporal and spatial changes in rupture mechanisms likely controlled by variable magma properties we also demonstrate that the distribution of inter explosion repose times between and within phases is well represented by a poissonian process the poissonian distribution describing repose times changes between and within phases as the source dynamics evolve we find that changes in source properties restrict the extrapolation of explosive behaviour to within a given eruptive phase limiting the potential for long term assessments of anticipated eruptive behaviour at santiaguito

optimizing multi station earthquake template matching through re examination of the youngstown ohio sequence abstract a series of earthquakes in 2011 near youngstown oh has been a focal point for discussions of seismicity induced by a nearby wastewater disposal well utilizing an efficient waveform template matching procedure the optimal correlation template to study the youngstown sequence was identified by varying parameters such as the stations utilized frequency passband and seismogram length a catalog composed of 566 events was identified between january 2011 and february 2014 double difference relocation refines seismicity to a 800 m linear streak from the northstar 1 injection well to the wsw along the same strike as the fault plane of the largest event calculated gutenberg richter b values are consistent with trends observed in other regions with seismicity induced by fluid injection

minimum magnitude of completeness in earthquake catalogs examples from alaska the western united states and japan we mapped the minimum magnitude of complete reporting m c for alaska the western united states and for the junec earthquake catalog of japan mc was estimated based on its departure from the linear frequency magnitude relation of the 250 closest earthquakes to grid nodes spaced 10 km apart in all catalogs studied mc was strongly heterogeneous in offshore areas the mc was typically one unit of magnitude higher than onshore on land also mc can vary by one order of magnitude over distance less than 50 km we recommend that seismicity studies that depend on complete sets of small earthquakes should be limited to areas with similar mc or the minimum magnitude for the analysis has to be raised to the highest com mon value of mc we believe that the data quality as reflected by the mc level should be used to define the spatial extent of seismicity studies where mc plays a role the method we use calculates the goodness of fit between a power law fit to the data and the observed frequency magnitude distribution as a function of a lower cutoff of the magnitude data mc is defined as the magnitude at which 90 of the data can be modeled by a power law fit mc in the 1990s is approximately 1 2 0 4 in most parts of california 1 8 0 4 in most of alaska aleutians and panhandle excluded and at a higher level in the junec catalog for japan various sources such as ex plosions and earthquake families beneath volcanoes can lead to distributions that cannot be fit well by power laws for the hokkaido region we demonstrate how neglecting the spatial variability of m c can lead to erroneous assumptions about deviations from self similarity of earthquake scaling