an intensity survey of households affected by the northridge california earthquake of 17 january 1994 following the northridge california earthquake of 17 january 1994 the humboldt earthquake education center heec conducted a telephone survey of approximately 6000 adults from within the felt region to study the earthquake s effects on individual households we tabulate human responses to the earthquake and observations of the earthquake s effects on inanimate objects from the heec survey as a function of independently assigned u s geological survey modified mercalli usgs mm intensity for the same communities human responses and subjective judgments about the severity of shaking when averaged over a large number of samples are useful discriminants of the levels of strong ground motion up to those associated with usgs mm intensity vii notwithstanding that individual human responses and subjective judgments are notoriously unreliable a threshold of strong ground motion corresponds to usgs mm intensity of about vii above which over 40 of respondents described the earthquake as violent and most people reported difficulty standing furniture displaced and some damage to their homes even at intensities viii and ix however relatively few people about 15 described their reaction as panic and only about 12 reported major damage to their homes the heec phone survey data show that in communities of low to moderate shaking usgs mm intensities estimated from a single postal questionnaire are quite robust at usgs mm intensity of v and below 88 of usgs mm intensities determined from postal questionnaires are within one intensity unit of intensities determined from the more numerous heec telephone survey data for the same community we introduce the concept of a community decimal intensity scale cdi based on telephone survey data and calibrated to agree on average with the usgs mm intensities the cdis are more regularly distributed than the usgs mm intensities and show much less scatter when plotted as a function of epicentral distance cdis show promise as a tool for comparing regional attenuation for delineating variations in shaking strength within areas mapped as a single mm zone and for rapid preliminary intensity estimates utilizing electronic media

seismic and aseismic deformation associated with the 1952 kern county california earthquake and relationship to the quaternary history of the white wolf fault synthesis of geodetic geologic and seismic data from the white wolf fault california indicates that the fault separates an area of late quaternary and continuing rapid uplift in the tehachapi mountains and transverse ranges from even more rapid subsidence in the southern san joaquin valley on july 21 1952 rupture of the white wolf fault produced the ml 7 2 kern county earthquake we used the aftershock zone to delimit the size of the faulted slip surface and applied constraints imposed by the known 1952 1953 horizontal shear strains to model the measured coseismic vertical displacements with an elastic dislocation model a curved fault trace with decreasing fault depth 27 to 10 km from the surface vertically to the base slip 3 to 1 m and dip 75 to 20 from the 1952 epicenter at the southwest end of the fault toward the northeast provides the fit most consistent with the geodetic record the measured seismic moment the fault plane solution and the pattern of surface rupture two short releveled lines near the 1952 epicenter tilted 4 and 17 rad down to the north from 5 10 years before the earthquake the preseismic tilts differ significantly from ten other surveys of these lines left lateral fault crossing shear strain from 0 2 20 years before the quake was two times greater than both preseismic off fault strains and the post seismic fault crossing strains during the first seven years after the earthquake aseismic deformation was negligible from 1959 to 1972 uplift reached 160 mm over an area larger than the aftershock zone rising first in the epicentral region and then at the northeast end of the fault this was unaccompanied by any surface fault slip reconstruction of the vertical separation on the white wolf fault from late quaternary and late miocene stratigraphic marker beds shows that the rate of reverse fault slip increased forty fold from 0 1 0 2 mm yr to 3 9 mm yr between the past 10 15 m y and the most recent 0 6 1 2 m y we estimate a 170 to 450 yr average recurrence interval for earthquakes on the white wolf fault with slip equivalent to that in 1952 the 1952 earthquake appears to be characteristic of the quaternary record of fault displacement in the increase in white wolf slip toward the san andreas fault the ratio of reverse to lateral slip 1 3 1 and the ratio of vertical fault slip to emergence of the hanging wall block 3 1 the 8500 m deep sedimentary basin on the down thrown block cannot be explained by repeated slip of the white wolf fault in an elastic medium

estimating locations and magnitudes of earthquakes in southern california from modified mercalli intensities modified mercalli intensity mmi assignments instrumental moment magnitudes m and epicenter locations of thirteen 5 6 m 7 1 training set events in southern california were used to obtain the attenuation relation mmi 1 64 1 41 m 0 00526 h 2 63 log h where h is the hypocentral distance in kilometers and m is moment magnitude intensity magnitudes m i and locations for five 5 9 m 7 3 independent test events were consistent with the instrumental source parameters fourteen historical earthquakes between 1890 and 1927 were then analyzed of particular interest are the m i 7 2 9 february 1890 and m i 6 6 28 may 1892 earthquakes which were previously assumed to have occurred near the southern san jacinto fault a more likely location is in the eastern california shear zone ecsz these events and the 1992 m 7 3 landers and 1999 m 7 1 hector mine events suggest that the ecsz has been seismically active since at least the end of the nineteenth century the earthquake catalog completeness level in the ecsz is m 6 5 at least until the early twentieth century online material figures and table of empirical mmi site corrections

earthquake monitoring in southern california for seventy seven years 1932 2008 the southern california seismic network scsn has produced the scsn earthquake catalog from 1932 to the present a period of more than 77 yrs this catalog consists of phase picks hypocenters and magnitudes we present the history of the scsn and the evolution of the catalog to facilitate user understanding of its limitations and strengths hypocenters and magnitudes have improved in quality with time as the number of stations has increased gradually from 7 to 400 and the data acquisition and measuring procedures have become more sophisticated the magnitude of completeness m c of the network has improved from m c 3 25 in the early years to m c 1 8 at present or better in the most densely instrumented areas mainshock aftershock and swarm sequences and scattered individual background earthquakes characterize the seismicity of more than 470 000 events the earthquake frequency size distribution has an average b value of 1 0 with m 6 0 events occurring approximately every 3 yrs the three largest earthquakes recorded were 1952 m w 7 5 kern county 1992 m w 7 3 landers and 1999 m w 7 1 hector mine sequences and the three most damaging earthquakes were the 1933 m w 6 4 long beach 1971 m w 6 7 san fernando and 1994 m w 6 7 northridge earthquakes all of these events ruptured slow slipping faults located away from the main plate boundary fault the san andreas fault their aftershock sequences constitute about a third of the events in the catalog the fast slipping southern san andreas fault is relatively quiet at the microseismic level and has not had an m 6 earthquake since 1932 in contrast the slower san jacinto fault has the highest level of seismicity including several m 6 events thus the spatial and temporal seismicity patterns exhibit a complex relationship with the plate tectonic crustal deformation

an example of identifying karst groundwater flow hydrogeological investigations for the purpose of regulating the karst aquifer were carried out in the mountain massif of kucaj in the carpatho balkan range of eastern serbia different geophysical methods were applied in order to identify the position of karstified zones with active circulation of karst underground streams especially good results were obtained by using the spontaneous potential method for the exploration and construction of boreholes and wells in the valleys of crni timok and radovanska reka the measurements have been carried out upstream along the whole width of the alluvium to the limestone periphery a number of positive and negative anomalies have been recorded in the centres of positive anomalies several boreholes were located hg 19 centre of anomaly 30 mv total length of the biggest cavern is 9 m hg 1 20 mv cavern of 2 m hg 15 max 114 mv effective cavernousness is 17

reservoir prediction of deep water turbidite sandstones with seismic lithofacies control a case study in the c block of lower congo basin abstract currently conventional forecasting methods of well to seismic integration are unable to identify turbidite channel sandstones due to scarcity of well data in deepwater areas small geophysical differences between sandstones and mudstones of turbidite channels and strong sandstones heterogeneity the reservoir prediction of deep water turbidite channels is still a difficult issue in deep water research on the basis of previous studies we propose a new technology named reservoir prediction of deep water turbidite sandstones with seismic lithofacies control in view of the characteristics of deep water turbidite sandstones this new technology improves the reservoir prediction of complex sedimentary systems after classifying seismic lithofacies and connecting lithofacies with rock physics furthermore it can accomplish the genetic classification statistics of rock physics improve conversion accuracy of seismic elastic parameters reservoir parameters and achieve the quantitative reservoir prediction under the double control of seismic geomorphology and seismic lithofacies the c block of lower congo basin is characterized by few well data complex lithology but high resolution seismic we use the technology to predict the reservoirs of this area and have achieved excellent results this has great significance for the later exploration

source parameters for the 1952 kern county earthquake california a joint inversion of leveling and triangulation observations coseismic leveling and triangulation observations are used to determine the faulting geometry and slip distribution of the july 21 1952 mw 7 3 kern county earthquake on the white wolf fault a singular value decomposition inversion is used to assess the ability of the geodetic network to resolve slip along a multisegment fault and shows that the network is sufficient to resolve slip along the surface rupture to a depth of 10 km below 10 km the network can only resolve dip slip near the fault ends the preferred source model is a two segment right stepping fault with a strike of 51 and a dip of 75 sw the epicentral patch has deep 6 27 km left lateral oblique slip while the northeastern patch has shallow 1 12 5 km reverse slip there is nearly uniform reverse slip epicentral 1 6 m northeast 1 9 m with 3 6 m of left lateral strike slip limited to the epicentral patch the seismic moment is m0 9 2 0 5 1019 n m mw 7 2 the signal to noise ratio of the leveling and triangulation data is reduced by 96 and 49 respectively the slip distribution from the preferred model matches regional geomorphic features and may provide a driving mechanism for regional shortening across the comanche thrust and structural continuity with the scodie seismic lineament to the northeast

contourite porosity grain size and reservoir characteristics abstract contourites are now recognised as having a significant potential as hydrocarbon reservoirs in the subsurface and several fields have been interpreted as comprising bottom current reworked turbidite sands however very little has been published on the porosity characteristics of contourites this study documents porosity data from iodp expedition 339 sites in the gulf of cadiz we use grain size analyses porosity depth plots and exponential models to yield a better understanding of grain size characteristics and facies porosity characteristics and the reservoir potential of contourites in the subsurface new grain size data for over 350 samples from the cadiz contourites is presented building on earlier work these data confirm the distinctive trends in textural properties linked to depositional processes under the action of bottom currents the finest muddy contourites porosity depth relationships from four cadiz sites show a moderately high initial porosity for both sand and mud facies 50 60 and a systematic decrease with depth to around 35 40 near 500 m burial depth according to the exponential models of porosity with depth contourite porosity should exceed 10 at 2500 m burial depth we compare the data from the gulf of cadiz contourite depositional system with those of the eirik drift newfoundland drift gardar drift and canterbury slope drifts similar depth trends are observed and all show anomalies linked to interbedded sandy and muddy facies composition carbonate vs siliciclastic and the presence of hiatuses in the sediment record these data provide good insight into the likely reservoir characteristics of contourites for both conventional and unconventional reservoirs they are comparable with those of existing contourite fields most of which are mixed turbidite contourite systems

worlwide deepwater exploration and production past present and future approximately 58 billion barrels of oil equivalent have been discovered in deepwater defined as waters of at least 500 m from 18 basins on 6 continents figure 1 this consists of 39 million barrels of oil and condensate and approximately 112 trillion ft3 of gas more than half has been discovered since 1995 however only about 25 of the discoveries are developed or under development and less than 5 have been produced indicating that large expenditures remain to be made most resources have been found in the gulf of mexico brazil and west africa see map in pettingill and weimer 2001

leakage below dam sites in limestone terrains by enhanced karstification a modeling approach unnaturally high hydraulic gradients below dam sites enhance dissolutional widening of fractures in limestone a model is presented which suggests that under unfavorable conditions leakage rates could become unbearably high during the lifetime of the dam at the beginning when water is impounded leakage rates are low and increase slowly a positive feedback loop however causes a sudden dramatic increase of leakage within a few years deep grouting becomes necessary to prevent such failures inefficiencies in grouting may leave some open fractures in the grouting curtain these fractures widen faster than pathways below the grouting curtain and reduce the effect of the grouted region located below therefore open fractures act in a similar way as reduction of the grouting depth

three dimensional numerical modeling of eustatic control on continental margin sand distribution abstract eustasy constitutes a key control on continental shelf accommodation along with tectonism the combined effect of these processes influences relative sea level which is thought to regulate the location of facies stratigraphic architecture and distribution of sediment to basin margins here we used a nonlinear diffusion based numerical stratigraphic forward model to investigate the impact of the eustatic curve we ran two models one using a eustatic curve derived from the new jersey margin u s a and the other a base case with no eustatic variation but which were otherwise identical we conclude that changing the eustatic curve resulted in a 0 9 difference in cumulative deep water 200 m sand volumes between models this is because the no eustatic variation model resulted in deep water sand delivery events with magnitudes similar to those observed in the eustatic model which were due to the delta becoming fixed at the shelf edge and the subsequent temporary suspension of avulsive processes in the eustatic model maximum deep water sand accumulation occurred during short term sea level falls but peak sand delivery was not well related to the amplitude of the sea level fall itself further examination of the relationship between rates of relative sea level and deep water sand delivery show a poor correlation r 2

construction of grout curtain in karstic environment case study salman farsi dam salman farsi is an arch gravity dam it is 125 m high and located on the ghareh agaj river in fars province south of iran from the geological and hydrogeological point of view this dam is one of the most complicated sites in iran existence of 40 springs at the river level including hot springs and many faults and crushed zones are part of these complications the dam site is famous for its numerous big caverns main characteristics of the rock mass are 1 low permeable limestone of moderate to high strength 2 high karstification generally localized around intersection of faults or discontinuities the main purpose of grout curtains is to change the hydrogeological characteristics reducing the permeability of the rock mass constructing a grout curtain in a karstic environment with a high random distribution of karst features contains some uncertainties and surprises cannot be excluded

the distribution of modified mercalli intensity in the 18 april 1906 san francisco earthquake we analyze boatwright and bundock s 2005 modified mercalli intensity mmi map for the 18 april 1906 san francisco earthquake reviewing their interpretation of the mmi scale and testing their correlation of 1906 cemetery damage with mmi intensity we consider in detail four areas of the intensity map where boatwright and bundock 2005 added significantly to the intensity descriptions compiled by lawson 1908 we show that the distribution of off fault damage in sonoma county suggests that the rupture velocity approached the p wave velocity along tomales bay in contrast the falloff of intensity with distance from the fault appears approximately constant throughout mendocino county the intensity in humboldt county appears somewhat higher than the intensity in mendocino county suggesting that the rupture process at the northern end of the rupture was relatively energetic and that there was directivity consistent with a subsonic rupture velocity on the section of the fault south of shelter cove finally we show that the intensity sites added in santa cruz county change the intensity distribution so that it decreases gradually along the southeastern section of rupture from corralitos to san juan bautista and implies that the stress release on this section of rupture was relatively low

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

slope fan depositional architecture from high resolution forward stratigraphic models abstract submarine fans in tectonically active continental slope basins are targets of petroleum exploration and production these slope fans commonly comprise compensationally stacked sandy and muddy architectural elements including mass transport deposits weakly confined to distributary channel and lobe deposits and leveed channel deposits the lateral continuity and vertical connectivity of these architectural elements are important uncertainties in reservoir characterization that influence fluid flow behavior during hydrocarbon production here we use a simple forward stratigraphic model to simulate the stratigraphic patterns and illuminate the likely distribution of fine scale sub seismic heterogeneity in a slope fan we used published seismic reflection horizons from the tectonically active columbus basin offshore trinidad to define the top and base of a pleistocene submarine fan we then simulated the stratigraphic evolution of the slope fan with a series of dionisosflow forward stratigraphic models all variables were kept constant during the simulations in order to test the hypothesis that the autogenic evolution of the surface topography alone as a result of erosion and deposition can produce compensational stacking patterns common in submarine fans a reference case model is similar to the thickness trend of published isochron maps of the trinidad slope fan the reference case model also produced patterns of compensational stacking varying the time step impacts the heterogeneity of the model shorter time steps are characterized by less sediment accumulation which results in less sediment diversion during the subsequent time step more gradual migration of channel deposits shorter offset distances of depocenters and shorter length scale heterogeneity compared to longer time steps thus a key characteristic of slope fan deposits is autogenic compensational stacking without any external forcing which governs heterogeneity in these reservoirs furthermore our results suggest that relatively simple diffusion based models can produce realistic compensation patterns and future work will be focused on higher resolution model calibration to seismic reflection data and the influence of input variables on heterogeneity of channel and lobe deposits of slope fans

global review of human induced earthquakes the human induced earthquake database hiquake is a comprehensive record of earthquake sequences postulated to be induced by anthropogenic activity it contains over 700 cases spanning the period 1868 2016 activities that have been proposed to induce earthquakes include the impoundment of water reservoirs erecting tall buildings coastal engineering quarrying extraction of groundwater coal minerals gas oil and geothermal fluids excavation of tunnels and adding material to the subsurface by allowing abandoned mines to flood and injecting fluid for waste disposal enhanced oil recovery hydrofracturing gas storage and carbon sequestration nuclear explosions induce earthquakes but evidence for chemical explosions doing so is weak because it is currently impossible to determine with 100 certainty which earthquakes are induced and which not hiquake includes all earthquake sequences proposed on scientific grounds to have been human induced regardless of credibility challenges to constructing hiquake include under reporting which is 30 of m 4 events 60 of m 3 events and 90 of m 2 events the amount of stress released in an induced earthquake is not necessarily the same as the anthropogenic stress added because pre existing tectonic stress may also be released thus earthquakes disproportionately large compared with the associated industrial activity may be induced knowledge of the magnitude of the largest earthquake that might be induced by a project mmax is important for hazard reduction observed mmax correlates positively with the scale of associated industrial projects fluid injection pressure and rate and the yield of nuclear devices it correlates negatively with calculated inducing stress change likely because the latter correlates inversely with project scale the largest earthquake reported to date to be induced by fluid injection is the 2016 m 5 8 pawnee oklahoma earthquake by water reservoir impoundment the 2008 m 8 wenchuan people s republic of china earthquake and by mass removal the 1976 m 7 3 gazli uzbekistan earthquake the minimum amount of anthropogenic stress needed to induce an earthquake is an unsound concept since earthquakes occur in the absence of industrial activity the minimum amount of stress observed to modulate earthquake activity is a few hundredths of a megapascal and possibly as little as a few thousandths equivalent to a few tens of centimeters of water table depth faults near to failure are pervasive in the continental crust and induced earthquakes may thus occur essentially anywhere in intraplate regions neither infrastructure nor populations may be prepared for earthquakes human induced earthquakes that cause nuisance are rare but in some cases may be a significant problem e g in the hydrocarbon producing areas of oklahoma usa as the size of projects and density of populations increase the potential nuisance of induced earthquakes is also increasing and effective management strategies are needed

escape tectonics in the los angeles metropolitan region and implications for seismic risk recent damaging earthquakes in california including the 1971 san fernando1 1983 coalinga2 1987 whittier narrows3 and 1994 northridge4 events have drawn attention to thrust faults as both potentially hazardous seismic sources and as a mechanism for accommodating shortening in many regions of southern california consequently many geological studies5 6 have concluded that thrust faults in southern california pose the greatest seismic hazard and also account for most of the estimated 5 7 mm yr 1 of contraction across the greater los angeles metropolitan area7 8 indicated by global positioning system geodetic measurements9 our study demonstrates however that less than 50 of the geodetically observed contraction is accommodated on the principal thrust systems across the los angeles region we integrate the most recent geological geodetic and seismological data to assess the spatial distribution of strain across the los angeles metropolitan region we then demonstrate that a significant component of seismic moment release and shortening in this region is accommodated by east west crustal escape extrusion along known strike slip and oblique slip faults

how do ghost transients from past earthquakes affect gps slip rate estimates on southern california faults 1 in this study we investigate the extent to which viscoelastic velocity perturbations or ghost transients from individual fault segments can affect elastic block model based inferences of fault slip rates from gps velocity fields we focus on the southern california gps velocity field exploring the effects of known large earthquakes for two end member rheological structures our approach is to compute at each gps site the velocity perturbation relative to a cycle average for earthquake cycles on particular fault segments we then correct the scec cmm4 0 velocity field for this perturbation and invert the corrected field for fault slip rates we find that if asthenosphere viscosities are low 3 1018 pa s the current gps velocity field is significantly perturbed by viscoelastic earthquake cycle effects associated with the san andreas fault segment that last ruptured in 1857 mw 7 9 correcting the gps velocity field for this perturbation or ghost transient adds about 5 mm a to the saf slip rate along the mojave and san bernardino segments the gps velocity perturbations due to large earthquakes on the garlock fault most recently events in the early 1600s and the white wolf fault most recently the mw 7 3 1952 kern county earthquake are smaller and do not influence block model inverted fault slip rates this suggests that either the large discrepancy between geodetic and geologic slip rates for the garlock fault is not due to a ghost transient or that un modeled transients from recent mojave earthquakes may influence the gps velocity field

morphological evolution of a well constrained subaerial subaqueous source to sink system wabush lake since 1964 the iron ore company of canada has deposited iron tailings resulting from mining operations into wabush lake western labrador canada this activity has resulted in a continuous hyperpycnal flow flowing over the lake floor bathymetric surveys were carried out between 1999 and 2008 as part of the overall environmental iron ore company of canada plans to maintain safe disposal strategies of tailings into the lake here this dataset is used to study the evolution of different channels present in wabush lake and their link with knickpoints found at the head of most of these channels the channels show notable evolution from one survey to the next some knickpoints and channels may be followed throughout more than one survey the evolution of these knickpoints is the process responsible for the creation of erosional channels the context in which they appear as well as the evolution of some of the subaqueous channels is analysed cyclic steps and sediment waves are also found in the lake these rhythmic bedforms also created by the passage of turbidity currents are analysed sediment waves found in wabush lake show values for both wavelength and wave height that are approximately one order of magnitude smaller than most of those found in the marine environment

toward a consistent model for strain accrual and release for the new madrid seismic zone central united states 1 at the heart of the conundrum of seismogenesis in the new madrid seismic zone is the apparently substantial discrepancy between low strain rate and high recent seismic moment release in this study we revisit the magnitudes of the four principal 1811 1812 earthquakes using intensity values determined from individual assessments from four experts using these values and the grid search method of bakun and wentworth 1997 we estimate magnitudes around 7 0 for all four events values that are significantly lower than previously published magnitude estimates based on macroseismic intensities we further show that the strain rate predicted from postglacial rebound is sufficient to produce a sequence with the moment release of one mmax6 8 every 500 years a rate that is much lower than previous estimates of late holocene moment release however mw6 8 is at the low end of the uncertainty range inferred from analysis of intensities for the largest 1811 1812 event we show that mw6 8 is also a reasonable value for the largest main shock given a plausible rupture scenario one can also construct a range of consistent models that permit a somewhat higher mmax with a longer average recurrence rate it is thus possible to reconcile predicted strain and seismic moment release rates with alternative models one in which 1811 1812 sequences occur every 500 years with the largest events being mmax 6 8 or one in which sequences occur on average less frequently with mmax of 7 0 both models predict that the late holocene rate of activity will continue for the next few to 10 thousand years

post spreading transpressive faults in the south china sea basin the south china sea was formed by seafloor spreading during the late oligocene to the mid miocene after the cessation of spreading compression due to the northwestward moving taiwan luzon are and strike slip motion have been occurring on the south china sea s eastern and west margins respectively however due to limited survey coverage little is known about the tectonics in the oceanic basin of the south china sea satellite altimetry derived bathymetric data in a 2 x 2 grid shows not only a young seamount chain along the e w trending spreading axis of the south china sea basin but also three previously unmapped nw to nnw trending segmented linear features these features are topographic highs rising 300 600 m above the surrounding sea floor 10 30 km wide and 300 500 km long bathymetric and seismic reflection data reveal that they are strike slip fault zones in which folds of various amplitude and patterns have developed these basin wide transpressive fault zones and the young volcanism may be the result of ongoing nnw convergence of the taiwan luzon arc following the cessation of seafloor spreading in the south china sea the nnw trending strike slip fault at longitude 116 degrees e is considered to be the boundary between the eastern subbasin and the sw subbasin c 2008 elsevier b v all rights reserved

precarious rock and overturned transformer evidence for ground shaking in the ms 7 7 kern county earthquake an analog for disastrous shaking from a major thrust fault in the los angeles basin precariously balanced rocks and overturned transformers in the vicinity of the white wolf fault provide constraints on ground motion during the 1952 m s 7 7 kern county earthquake a possible analog for an anticipated large earthquake in the los angeles basin shaw et al 2002 dolan et al 2003 on the northeast part of the fault preliminary estimates of ground motion on the footwall give peak accelerations considerably lower than predicted by standard regression curves on the other hand on the hanging wall there is evidence of intense ground shattering and lack of precarious rocks consistent with the intense hanging wall accelerations suggested by foam rubber modeling numerical modeling and observations from previous thrust fault earthquakes there is clear evidence of the effects of rupture directivity in ground motions on the hanging wall side of the fault from both precarious rocks and numerical simulations on the southwest part of the fault which is covered by sediments the thrust fault did not reach the surface blind thrust overturned and damaged transformers indicate significant transfer of energy from the hanging wall to the footwall an effect that may not be as effective when the rupture reaches the surface is not blind transformers near the up dip projection of the fault tip have been damaged or overturned on both the hanging wall and footwall sides of the fault the transfer of energy is confirmed in a numerical lattice model and could play an important role in a similar situation in los angeles we suggest that the results of this study can provide important information for estimating the effects of a large thrust fault rupture in the los angeles basin specially given the fact that there is so little instrumental data from large thrust fault earthquakes

the 1952 kern county california earthquake a case study of issues in the analysis of historical intensity data for estimation of source parameters abstract seismic intensity data based on first hand accounts of shaking give valuable insight into historical and early instrumental earthquakes comparing an observed intensity distribution to intensity prediction models based on modern calibration events allows the magnitude to be estimated for many historic earthquakes magnitude estimates can also potentially be refined for earthquakes for which limited instrumental data are available however the complicated nature of macroseismic data and the methods used to collect and interpret the data introduce significant uncertainties in this paper we illustrate these challenges and possible solutions using the 1952 kern county california earthquake as a case study published estimates of its magnitude vary from mw 7 2 7 5 making it possibly the second largest in california during the 20th century we considered over 1100 first hand reports of shaking supplemented with other data and inferred the magnitude in several ways using intensity prediction equations yielding a preferred intensity magnitude mi 7 2 0 2 where the uncertainty reflects our judgement the revised intensity distribution reveals stronger shaking on the hanging wall south of the surface expression of the white wolf fault than on the footwall characterizing the magnitude and shaking distribution of this early instrumental earthquake can help improve estimation of the seismic hazard of the region such reinterpreted intensities for historic earthquakes combined with u s geological survey usgs did you feel it data for more recent events can be used to produce a uniform shaking dataset with which earthquake hazard map performance can be assessed

revisiting the 23 february 1892 laguna salada earthquake according to some compilations the laguna salada baja california earthquake of 23 february 1892 ranks among the largest earthquakes in california and baja california in historic times although surface rupture was not documented at the time of the earthquake recent geologic investigations have identified and mapped a rupture on the laguna salada fault that can be associated with high probability with the 1892 event mueller and rockwell 1995 the only intensity based magnitude estimate for the earthquake m 7 8 was made by strand 1980 based on an interpretation of macroseismic effects and a comparison of isoseismal areas with those from instrumentally recorded earthquakes in this study we reinterpret original accounts of the laguna salada earthquake we assign modified mercalli intensity mmi values in keeping with current practice focusing on objective descriptions of damage rather than subjective human response and not assigning mmi values to effects that are now known to be poor indicators of shaking level such as liquefaction and rockfalls the reinterpreted isoseismal contours and the estimated magnitude are both significantly smaller than those obtained earlier using the method of bakun and wentworth 1997 we obtain a magnitude estimate of m 7 2 and an optimal epicenter less than 15 km from the center of the mapped laguna salada rupture the isoseismal contours are elongated toward the northwest which is qualitatively consistent with a directivity effect assuming that the fault ruptured from southeast to northwest we suggest that the elongation may also thus reflect wave propagation effects with more efficient propagation of crustal surface lg waves in the direction of the overall regional tectonic fabric

estimating earthquake location and magnitude from seismic intensity data analysis of modified mercalli intensity mmi observations for a training set of 22 california earthquakes suggests a strategy for bounding the epicentral region and moment magnitude m from mmi observations only we define an intensity magnitude m i that is calibrated to be equal in the mean to m m i mean m i where m i mmi i 3 29 0 0206 i 1 68 and i is the epicentral distance km of observation mmi i the epicentral region is bounded by contours of rms m i rms m i m i rms m i m i where rms is the root mean square rms m i m i is the minimum rms over a grid of assumed epicenters and empirical site corrections and a distance weighting function are used empirical contour values for bounding the epicenter location and empirical bounds for m estimated from m i appropriate for different levels of confidence and different quantities of intensity observations are tabulated the epicentral region bounds and m i obtained for an independent test set of western california earthquakes are consistent with the instrumental epicenters and moment magnitudes of these earthquakes the analysis strategy is particularly appropriate for the evaluation of pre 1900 earthquakes for which the only available data are a sparse set of intensity observations

foreshocks and aftershocks of the great 1857 california earthquake the san andreas fault is the longest fault in california and one of the longest strike slip faults anywhere in the world yet we know little about many aspects of its behavior before during and after large earthquakes we conducted a study to locate and to estimate magnitudes for the largest foreshocks and aftershocks of the 1857 m 7 9 fort tejon earthquake on the central and southern segments of the fault we began by searching archived first hand accounts from 1857 through 1862 by grouping felt reports temporally and by assigning modified mercalli intensities to each site we then used a modified form of the grid search algorithm of bakun and wentworth derived from empirical analysis of modern earthquakes to find the location and magnitude most consistent with the assigned intensities for each of the largest events the result confirms a conclusion of sieh that at least two foreshocks dawn and sunrise located on or near the parkfield segment of the san andreas fault preceded the mainshock we estimate their magnitudes to be m 6 1 and m 5 6 respectively the aftershock rate was below average but within one standard deviation of the number of aftershocks expected based on statistics of modern southern california mainshock aftershock sequences the aftershocks included two significant events during the first eight days of the sequence with magnitudes m 6 25 and m 6 7 near the southern half of the rupture later aftershocks included a m 6 event near san bernardino in december 1858 and a m 6 3 event near the parkfield segment in april 1860 from earthquake logs at fort tejon we conclude that the aftershock sequence lasted a minimum of 3 75 years

near field ground motions and shaking from the 2019 mw 7 1 ridgecrest california mainshock insights from instrumental macroseismic intensity and remote sensing data

water losses risk assessment an example from carpathian karst the multipurpose dam and reservoir bogovina in the crni timok valley is one of several projects that have been initiated to improve water availability in serbia the site and height of the dam were initially proposed without consideration of risk factors such as water leakage or stability of the banks later complex hydrogeological and speleological surveys and tests identified the potential of significant water losses from the reservoir area connected mainly to the karstic aquifer and the nearby bogovina cave system the analyses show that once the reservoir is filled up groundwater flow currently oriented towards the future reservoir would saturate the upper part of the karstified rocks reactivate currently unsaturated pathways and form a reverse discharge outside of the reservoir area in response to these findings the dam design and technical details have been adapted accordingly the dam height has been reduced by 9 m and it is proposed that grouting and consolidation work be conducted both at the foundation of the dam and extensively on the embankments it was concluded that although the proposed remedial measures cannot guarantee reservoir tightness they can reduce the risk of large scale leaking

geodetic measurements of horizontal strain near the white wolf fault kern county california 1926 1993 the white wolf fault located north of the big bend segment of the san andreas fault is the ne sw trending left lateral oblique reverse fault responsible for the ms 7 8 1952 kern county earthquake we combined global positioning system gps measurements with historical triangulation and trilateration data to determine changes in the strain rate over 7 decades 1926 1993 we reanalyzed the historical geodetic data and calculated an elevated preseismic 1926 1952 maximum shear strain rate of 0 62 0 16 strain yr across the white wolf fault the maximum shear strain rate decreased with distance toward the garlock fault to 0 09 0 08 strain yr in the decade following the earthquake 1952 1963 the near fault was high 0 85 0 23 strain yr and decreased to 0 23 0 13 strain yr across the garlock fault in 1993 we resurveyed many of the same monuments with gps receivers to estimate fault crossing and off fault strain rates for the preceding 30 years across the white wolf fault the maximum shear strain rate dropped to 0 19 0 07 strain yr the azimuths of the maximum principal strain rates for the 1963 1993 epoch rotate from a fault normal orientation 57 15 across the white wolf fault to 11 3 e across the garlock fault