thrusting of the central california margin over the edge of the pacific plate during the transform regime wide angle seismic reflection and refraction data mapped geologic structures and marine magnetic anomalies provide evidence that oceanic crust underlies the coastal margin of california from morro bay northward beyond san francisco we interpret the presence of this oceanic slab to be at least partly the result of thrusting of north america over the pacific plate during pliocene to quaternary time well after the principal subduction regime ended likely causes of this thrusting are the change in plate motions at about 3 5 ma and extension in the basin and range province

detailed observations of california foreshock sequences implications for the earthquake initiation process we find that foreshocks provide clear evidence for an extended nucleation process before some earthquakes in this study we examine in detail the evolution of six california foreshock sequences the 1986 mount lewis ml 5 5 the 1986 chalfant ml 6 4 the 1986 stone canyon ml 4 7 the 1990 upland ml 5 2 the 1992 joshua tree mw 6 1 and the 1992 landers mw 7 3 sequence typically uncertainties in hypocentral parameters are too large to establish the geometry of foreshock sequences and hence to understand their evolution however the similarity of location and focal mechanisms for the events in these sequences leads to similar foreshock waveforms that we cross correlate to obtain extremely accurate relative locations we use these results to identify small scale fault zone structures that could influence nucleation and to determine the stress evolution leading up to the mainshock in general these foreshock sequences are not compatible with a cascading failure nucleation model in which the foreshocks all occur on a single fault plane and trigger the mainshock by static stress transfer instead the foreshocks seem to concentrate near structural discontinuities in the fault and may themselves be a product of an aseismic nucleation process fault zone heterogeneity may also be important in controlling the number of foreshocks i e the stronger the heterogeneity the greater the number of foreshocks the size of the nucleation region as measured by the extent of the foreshock sequence appears to scale with mainshock moment in the same manner as determined independently by measurements of the seismic nucleation phase we also find evidence for slip localization as predicted by some models of earthquake nucleation

seismically active fold and thrust belt in the san joaquin valley central california structural analysis of late cenozoic folds along the western and southern margins of the san joaquin basin suggests that the folds are related to development of a fold and thrust belt rather than to wrench tectonics the folds have formed by the processes of fault bend folding and fault propagation folding which commonly occur in fold and thrust belts our structural interpretation attributes the seismically active coalinga and kettleman hills north dome anticlines to fault bend folding above a thrust fault s that steps up from a detachment within the franciscan assemblage to a detachment at the base of the great valley group this thrust does not reach the surface blind thrust and its slip is consumed in backthrusting and formation of subsurface folds under the san joaquin valley movement on the postulated thrust s would explain the cause of the may 2 1983 coalinga earthquake and the august 15 1985 avenal earthquake and would account for the lack of significant surface rupture or shallow subsurface faulting during both earthquakes well documented examples of fault bend and fault propagation folding also occur at wheeler ridge in the san emigdio mountains and at kettleman hills south dome deformation associated with fold and thrust belts can be extremely complicated considerable fault movement can occur without accompanying surface rupture or shallow level faulting conversely surface rupture can occur that has no direct relationship to fault slip at depth an example would be flexural slip folding wherein the slip planes reach the surface but do not root into any significant faults at depth consequently traditional geologic approaches to seismic risk evaluation which rely largely on surface data are subject to numerous pitfalls when applied to fold and thrust belts our interpretation of the structural style that developed in central california during the late cenozoic requires that the strain associated with the transpressive motion between the pacific and north american plates be resolved into normal and tangential components thrust faulting and folding normal to the plate boundary and strike slip faulting parallel to the plate boundary san andreas fault the thrust faults root in a deecollement at the brittle ductile transition zone above which shortening is associated with folding and thrust faulting and beneath which shortening in the lower crust is accommodated by ductile processes of tectonic thickening or incipient subduction

the mw 5 8 mineral virginia earthquake of august 2011 and aftershock sequence constraints on earthquake source parameters and fault geometry the mw 5 8 earthquake of 23 august 2011 17 51 04 utc moment m0 5 7 10 17 n m occurred near mineral virginia within the central virginia seis mic zone and was felt by more people than any other earthquake in united states history the u s geological survey usgs received 148 638 felt reports from 31 states and 4 canadian provinces the usgs pager system estimates as many as 120 000 people were exposed to shaking intensity levels of iv and greater with approximately 10 000 exposed to shaking as high as intensity viii both regional and teleseismic moment tensor solutions characterize the earthquake as a northeast striking reverse fault that nucleated at a depth of approximately 7 2 km the distri bution of reported macroseismic intensities is roughly ten times the area of a similarly sized earthquake in the western united states horton and williams 2012 near source and far field damage reports which extend as far away as washington d c 135 km away and baltimore maryland 200 km away are consistent with an earthquake of this size and depth in the eastern united states eus within the first few days following the earthquake several government and aca demic institutions installed 36 portable seismograph stations in the epicentral region making this among the best recorded aftershock sequences in the eus based on modeling of these data we provide a detailed description of the source parameters of the mainshock and analysis of the subsequent aftershock sequence for defining the fault geometry area of rupture and observations of the aftershock sequence mag nitude frequency and temporal distribution the observed slope of the magnitude frequency curve or b value for the aftershock sequence is consistent with previous eus studies b 0 75 suggesting that most of the accumulated strain was released by the mainshock the aftershocks define a rupture that extends between approxi mately 2 8 km in depth and 8 10 km along the strike of the fault plane best fit modeling of the geometry of the aftershock sequence defines a rupture plane that strikes n36 e and dips to the east southeast at 49 5 moment tensor solutions of the mainshock and larger aftershocks are consistent with the distribution of aftershock locations both indicating reverse slip along a northeast southwest striking southeast dipping fault plane

improving local earthquake locations using the l1 norm and waveform cross correlation application to the whittier narrows california aftershock sequence experiments with different earthquake location methods applied to aftershocks of the october 1 1987 whittier narrows earthquake in california ml 5 9 suggest that local event locations can be greatly improved through the use of the l1 norm station corrections and waveform cross correlation the whittier narrows sequence is a compact cluster of over 500 events at 12 to 18 km depth located within the dense station coverage of the southern california seismic network scsn a telemetered network of several hundred short period seismographs scsn travel time picks and waveforms obtained through the southern california earthquake center are examined for 589 earthquakes between 1981 and 1994 in the vicinity of the mainshock using a smoothed version of the standard southern california velocity model and the existing travel time picks improved location accuracy is obtained through use of the l1 norm rather than the conventional least squares l2 norm approach presumably due to the more robust response of the former to outliers in the data a large additional improvement results from the use of station terms to account for three dimensional velocity structure outside of the event cluster to achieve greater location accuracy waveforms for these events are resampled and low pass filtered and the p and s wave cross correlation functions are computed at each station for every event pair for those events with similar waveforms differential times may be obtained from the cross correlation functions these times are then combined with the travel time picks to invert for an adjusted set of picks that are more consistent than the original picks and include seismograms that were originally unpicked locations obtained from the adjusted picks show a further improvement in accuracy location uncertainties are estimated using a bootstrap technique in which events are relocated many times for sets of picks in which the travel time residuals at the best fitting location are used to randomly perturb each pick improvements in location accuracy are indicated by the reduced scatter in the residuals smaller estimated location errors and the increased tendency of the locations to cluster along well defined fault planes median standard errors for the final inversion are 150 m in horizontal location and 230 m in vertical location although the relative locations within localized clusters of similar events are better constrained seismicity cross sections resolve the shallow dipping fault plane associated with the mainshock and a steeply dipping fault plane associated with a ml 5 3 aftershock these fault planes appear to cross and activity began on the secondary fault plane prior to the large aftershock

winter monsoon convection in the vicinity of north borneo part i structure and time variation of the clouds and precipitation abstract radar and satellite observations in the vicinity of northern borneo obtained during the international winter monsoon experiment wmonex showed that the convection in that region underwent an extremely regular diurnal cycle over the sea to the north of borneo the general level of convective activity was increased during monsoon surges and during the passages of westward propagating near equatorial disturbances convective activity was decreased during monsoon lulls the diurnal cycle was well defined regardless of whether the general level of convective activity was enhanced or suppressed by synoptic scale events the cycle of convection over the sea was especially well documented it was typically initiated at about midnight when an offshore low level wind began where this wind met the monsoonal northeasterly flow usually just off the coast convective cells formed after midnight the convection continued to develop and by 0800 lst it had evolved into an organized mesoscale system with a

seismicity and geometry of a 110 km long blind thrust fault 1 the 1985 kettleman hills california earthquake the august 4 1985 kettleman hills earthquake was the third in a sequence of moderate shocks to occur beneath the northern half of a 110 km long fold chain bounding the eastern california coast ranges the 1982 mw 5 4 new idria 1983 mw 6 5 coalinga and 1985 mw 6 1 kettleman hills events define a southward progression of seismic activity beneath the fold we use teleseismic waveforms geodetic modeling hypocenters relocated in a three dimensional velocity model and subsurface structural data to investigate the kettleman hills earthquake the main shock results from motion on a shallowly dipping thrust fault buried at 10 km depth aftershocks and coseismic fault slip extend 20 km along the fold axis nearly the full extent of the kettleman hills north dome anticline aftershocks occur primarily several kilometers in front of the fault tip and in the core of the anticline the main shock and several foreshocks occurred at a 2 km right step in the quaternary fold axis which also corresponds to the southern end of the 1983 coalinga and northern end of the 1985 kettleman hills aftershock zones from this we infer that the step in the fold is caused by an offset or tear in the underlying fault the scalar seismic moment is 1 6 1018 n m consistent with the geodetic deformation and the duration of rupture is 16 s 3 4 times greater than for the average earthquake with this scalar moment the slow rate of moment release provides an explanation for the low level of ground shaking and low local magnitude reported for the event the peak of the geodetic uplift is located 5 km perpendicular to the quaternary fold axis we argue that the fault is propagating northeast into the undeformed san joaquin valley sediments and that the overlying fold is growing at about 0 5 mm yr

crustal rheology from focal depths in the north china basin abstract in order to investigate earthquakes in the lower crust of north china basin ncb we develop a new method of resolving very accurately the focal depth for local earthquakes in the sedimentary regions by using p and s to p converted wave sp at the sedimentary interface theoretical analysis shows clearly that the travel time difference between the sp and p wave almost linearly correlates with the focal depth this finding provides tight constraints on the depth with this method we obtain well constrained depths of 44 events in the ncb with uncertainties in the depth of about 2 km such a fine resolution can have great potential in asking questions regarding the crustal rheology the depth distribution shows abundance of earthquakes in depth interval of 20 km with some events in the lower crust but also reveals the absence of seismicity deeper than 25 km we find a good fit between the depth frequency distribution in this region and the yield strength envelope yse in the baikal rift systems brs we infer that the seismogenic thickness is 25 km in the ncb and the main deformation mechanism is brittle fracture we further hypothesize that 1 the rheological layering of dominant rheology in the ncb is similar to that of the brs which can be explained with a quartz rheology at 0 10 km depth and a diabase rheology at 10 35 km depth 2 the temperature is moderate in the seismogenic zone of crust we emphasize that many accurately resolved earthquake locations can shed light on the local nature of the crustal rheology and this strategic method can be employed in other sedimentary regions which are seismically active

automated procedure for point and kinematic source inversion at regional distances 1 the development of fast automatic routines for the retrieval of point source parameters of medium to large earthquakes was convincingly established in the last years and decades providing an increasing number of focal mechanism solutions original applications at teleseismic distances have been successively accompanied by specific routines for regional data sets the majority of these methods are based on the fit of low passed time traces we present here a new technique for the automatic retrieval of point source parameters and highly parameterized kinematic rupture models at regional distances assuming the recently proposed eikonal model to describe the extended source in our approach we use a larger set of information to better constrain the source parameters including the fit of amplitude spectra and displacements at different phases and frequency ranges the time consumption of the inversion process is significantly improved thanks to the implementation of green s functions databases we adopt a multistep inversion approach finally providing the focal mechanism magnitude and centroid location of the point source for events with magnitude higher than a threshold of mw 5 5 source geometry rupture extension and average slip may be additionally retrieved we discuss the methodology and the inversion stability showing applications to significant earthquakes in two case areas we focus on germany and greece and their neighboring areas considering major shallow earthquakes in the last 5 years the proposed method is currently implemented for automatic data processing at the seismological observatory of the federal institute for geosciences and natural resources in germany

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

global compilation of interferometric synthetic aperture radar earthquake source models 1 comparisons with seismic catalogs 1 while many earthquakes have now been studied using interferometric synthetic aperture radar insar data a full assessment of the quality and additional value of insar source parameters compared to seismological techniques is still lacking we compile a catalog of source models obtained using insar and estimate the corresponding centroid moment tensor cmt parameters we refer to this compilation as the icmt archive we compare source parameters from over 70 insar studies of 57 global earthquakes with those in the global cmt gcmt international seismological centre isc and engdahl hilst buland ehb seismic catalogs we find an overall good agreement between fault strike dip and rake values in the gcmt and icmt archives likewise the differences in seismic moment between these two archives are relatively small and we do not find support for previously suggested trends of insar leading to larger moments than seismic data however epicentral locations show substantial discrepancies which are larger for the gcmt median differences of 21 km than for the ehb and isc catalogs median differences of 10 km since insar data have a high spatial resolution and thus should map epicentral locations accurately this allows us to obtain a first independent estimate of epicentral location errors in the seismic catalogs earthquake depths from insar are systematically shallower than those in the ehb catalog with a median of differences of 5 km while this trend may be partly due to unmodeled crustal complexity it is also compatible with the observation that the rupture of crustal earthquakes tends to propagate upward in the seismogenic layer

interaction of potential vorticity anomalies in extratropical cyclogenesis part ii sensitivity to initial perturbations in part i of this series of papers the static potential vorticity pv inversion diagnostics are performed to examine the lateral and vertical interactions between two upper level northern and southern troughs and their possible influences on the development of the march 1993 superstorm this study continues the investigation of the relative importance of two pv anomalies associated with the short wave troughs and their interaction in the surface cyclogenesis by considering their individual roles as an initial value problem the piecewise pv inversion technique is first used to isolate the upper level disturbances with a balanced vortex for each the vortex is then either removed or its intensity doubled by subtracting the balanced vortex from or adding to the control initial conditions with the modified initial conditions a mesoscale model is integrated for 36 h to examine how each of the upper level disturbances contributes to the surface development it is found that the northern and southern troughs play different roles in the surface cyclogenesis without the northern trough the eastward propagation of the southern trough slows down and the surface development is severely impeded more rapid cyclogenesis occurs when the northern trough s intensity is doubled on the other hand the deepening rate increases considerably when the southern trough is removed doubling the southern trough intensity slows the eastward progression of the northern trough and leads to a reduced deepening rate in conclusion the northern trough is crucial for the rapid development of the superstorm whereas the southern trough is important only during the incipient stage of the cyclone in particular a much stronger surface cyclone could be spawned in the absence of the southern trough this finding appears to contradict the previous work on the roles of trough mergers in extratropical cyclogenesis

late neogene relative motions of the pacific and north america plates in this paper a new set of finite rotations describing the relative motion of the pacific and north america plates during the last 10 m y incorporating recently published studies of the pacific antarctic antarctic africa and africa north america plate boundaries is presented these finite rotations show that changes have occurred in pacific western north america motion at 2 48 ma and between 3 40 and 3 9 ma resulting in increased compression along the pacific north america plate boundary the most significant change in relative motion was of the latter age during this change the predicted motion of the pacific plate along the california coast changes from transform to transpressive due to a clockwise rotation of the relative convergence vector by 12 this timing of the onset of transpression agrees well with a variety of geologic data along the california plate boundary including the onset of compressive deformation in onshore and offshore sedimentary basins formation of reverse faults and anticlines which are parallel to strike slip faults of the previous more westerly directed azimuth of relative motion a change in the orientation of the san andreas fault and formation of a set of new more northerly trending strike slip faults in this model this change in relative motion is caused by a change in the absolute motion of the pacific plate due to the detachment of a slab beneath the fiji basin between 3 4 and 3 9 ma the detachment of this slab and the resultant change in overall pacific plate torque resulted in a noncollisional orogeny along the california plate boundary this study shows that minor adjustments in the motion of large oceanic plates such as the pacific plate can have profound consequences on the preserved geologic record copyright 1991 by the american geophysical union

winds in the strait of gibraltar summary automated meteorological observations were made from october 1985 to september 1986 in the narrows of the strait of gibraltar additional surface and upper air measurements were made in the strait from may to july 1986 the main wind events in summer were mostly mesoscale levanters winds from the east through the strait and a lesser number of synoptic scale levanters and westerlies during mesoscale levanters the wind speed increased and the pressure decreased from gibraltar downstream through the narrows as far as tangier a mesoscale low and the highest winds were found over the axis of the strait north of tangier high velocity 20 m s winds occurred only under 1 km height the air temperature profile became progressively warmer moving from gibraltar towards tangier a weak air temperature inversion decreased in height to the west of the narrows venturi flow as an explanation for the downstream increase of the low level winds during a levanter is inconsistent with observations a new model is proposed to explain the wind field associated with levanter winds in the strait that includes some orographic blocking and low level convergence into the narrows some west side divergence due to drag over water and leeside heating that generates a leeside mesoscale low pressure the surface low accelerates the surface winds to their maximum strength well downstream of the narrows a similar flow regime has been observed recently in the sea level channel between hawaii and maui

a windstorm in the lee of a gap in a coastal mountain barrier abstract this paper describes a localized windstorm that struck some areas of northwest washington state on 28 december 1990 with winds exceeding 45 m s 1 resulting in extensive property damage treefalls and power outages arctic air originating within the interior of british columbia descended into a mesoscale gap in the coast cascade mountains and then accelerated ageostrophically to the west this gap acceleration is explained quantitatively by a three way balance among the pressure gradient force friction and inertia the flow maintained its integrity as a narrow current of high speed air as it exited the gap and subsequently accelerated over water troughing in the lee of the cascade mountains enhanced the horizontal pressure gradient over northwest washington this pressure gradient approximately balanced frictional drag resulting in only minimal acceleration farther south the flow decelerated as the current spread out horizontally

an application of potential vorticity inversion to improving the numerical prediction of the march 1993 superstorm in this study a methodology is proposed to improve the model initial conditions based on available surface temperature observations from ships buoys and drifters it is tested with the numerical prediction of the 12 14 march 1993 superstorm that is initialized at its incipient stage over the gulf of mexico in this methodology the authors make use of the piecewise potential vorticity pv inversion technique and treat the temperature errors at the lowest level as a surrogate pv anomaly after inverting the wind and mass perturbations from the surface thermal anomaly and its pertinent interior pv anomaly a three dimensional dynamically consistent set of errors are obtained and added to the model initial conditions to improve the representation of the lower troposphere over the data sparse ocean it is found that the numerical model prediction initialized with the modified initial conditions exhibits significant improvements in the early rapid deepening and the track of the superstorm over ocean the development of a prefrontal squall line and the central sea level pressure traces during the life cycle of the cyclone as verified against observations these results show that the methodology proposed is promising in improving the representation of lower tropospheric meteorological variables in the model initial conditions based on available surface observations over data sparse regions

resolving focal depth in sparse network with local depth phase spl a case study for the 2011 mineral virginia earthquake sequenceresolving focal depth in sparse network with local depth phase spl

on an improved method to obtain the moment tensor and depth of earthquakes from the amplitude spectrum of rayleigh waves abstract a new method is presented to invert for the moment tensor and depth using the amplitude spectra of vertical component rayleigh waves in the period range 20 to 100 sec the technique follows a similar approach to that suggested by romanowicz 1982a to invert for the moment tensor from the complex spectra of rayleigh waves and presents some distinct advantages to the method proposed originally by mendiguren 1977 it eliminates some biases and errors in the data arising for example from inaccurate propagation corrections furthermore it is substantially faster computationally and permits us to study independently the variance reduction as a function of depth of each of the momenttensor elements resulting in better focal depth resolution the method is applied to three earthquakes in the tien shan mountains of central asia the eastern cordillera of peru and the gibbs transform fault in the north atlantic in all three cases the results of the moment tensor inversion agree with those determined using long period body wave modeling

an updated stress map of the continental united states reveals heterogeneous intraplate stress knowledge of the state of stress in earth s crust is key to understanding the forces and processes responsible for earthquakes historically low rates of natural seismicity in the central and eastern united states have complicated efforts to understand intraplate stress but recent improvements in seismic networks and the spread of human induced seismicity have greatly improved data coverage here we compile a nationwide stress map based on formal inversions of focal mechanisms that challenges the idea that deformation in continental interiors is driven primarily by broad uniform stress fields derived from distant plate boundaries despite plate boundary compression extension dominates roughly half of the continent and second order forces related to lithospheric structure appear to control extension directions we also show that the states of stress in several active eastern united states seismic zones differ significantly from those of surrounding areas and that these anomalies cannot be explained by transient processes suggesting that earthquakes are focused by persistent locally derived sources of stress such spatially variable intraplate stress appears to justify the current spatially variable estimates of seismic hazard future work to quantify sources of stress stressing rate magnitudes and their relationship with strain and earthquake rates could allow prospective mapping of intraplate hazard

evolution of the northern santa cruz mountains by advection of crust past a san andreas fault bend the late quaternary marine terraces near santa cruz california reflect uplift associated with the nearby restraining bend on the san andreas fault excellent correspondence of the coseismic vertical displacement field caused by the 17 october 1989 magnitude 7 1 loma prieta earthquake and the present elevations of these terraces allows calculation of maximum long term uplift rates 1 to 2 kilometers west of the san andreas fault of 0 8 millimeters per year over several million years this uplift in concert with the right lateral translation of the resulting topography and with continual attack by geomorphic processes can account for the general topography of the northern santa cruz mountains

a diagnostic analysis of the superstorm of march 1993 abstract in this study the synoptic evolution of the march 1993 superstorm is documented using conventional observations and the predictability and deepening mechanisms of the storm are investigated using a newly implemented mesoscale version of the canadian regional finite element rfe mode it is found that although the rfe model can predict well the large scale background flow associated with the storm it fails to predict various important mesoscale elements when it is initialized with fields that contain weak signals of the low level circulations however when the storm is located close to the data rich region the model has considerable skill in predicting those mesoscale elements such as a prefrontal squall line upper and low level jets as well as the quantitative aspects of their associated precipitation observational analysis reveals that the storm developed in a convectively unstable prestorm environment with ample moisture content it first experienced an antecedent surface vorticity g

equivalent strike slip earthquake cycles in half space and lithosphere asthenosphere earth models by virtue of the images used in the dislocation solution the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike slip fault in an earth model consisting of an elastic plate lithosphere overlying a viscoelastic half space asthenosphere can be duplicated by prescribed slip on a vertical fault embedded in an elastic half space for the case in which each earthquake ruptures the entire lithosphere thickness h the half space equivalent slip rate is as follows depth interval 0 h slip identical to that in lithosphere asthenosphere model i e abrupt coseismic slip and no subsequent slip depth interval 2n 1 h to 2n 1 h n 1 2 slip rate uniform in space and dependent upon time as fn t exp t a where fn is a n 1 degree polynomial in t a is twice the asthenosphere relaxation time and t is measured from the instant after the preceding earthquake the slip rate averaged over the seismic cycle in each depth interval equals the secular rate of relative plate motion for reasonable values of a slip rates below 5h do not vary much from that mean value and can be treated as constant thus the surface deformation due to the earthquake cycle in the lithosphere asthenosphere model can be calculated very simply from the half space model with time dependent slip in the two depth intervals h 3h and 3h 5h and uniform slip at a rate equal to the secular relative plate velocity below depth 5h inversion of 1973 1988 geodetic measurements of deformation across the segment of the san andreas fault in the transverse ranges north of los angeles for the half space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm yr below 30 km one equivalent lithosphere asthenosphere model would have a 30 km thick lithosphere and an asthenosphere relaxation time greater than 33 years but other models are possible

the aftershock sequence of the 2011 mineral virginia earthquake temporal and spatial distribution focal mechanisms regional stress and the role of coulomb stress transfer abstract the aftershocks of the 23 august 2011 m w 5 7 mineral virginia earthquake were recorded by 36 temporary stations installed by several institutions we located 3960 aftershocks from 25 august 2011 through 31 december 2011 a subset of 1666 aftershocks resolves details of the hypocenter distribution we determined 393 focal mechanism solutions aftershocks near the mainshock define a previously recognized tabular cluster with orientation similar to a mainshock nodal plane other aftershocks occurred 10 20 km to the northeast a large percentage of the aftershocks occurred in regions of positive coulomb static stress change and 80 of the focal mechanism nodal planes were brought closer to failure however the aftershock distribution near the mainshock appears to have been influenced strongly by rupture directivity aftershocks at depths less than 4 km exhibit reverse mechanisms with north northwest trending nodal planes most focal mechanisms at depths greater than 6 km are similar to the mainshock with north northeast trending nodal planes a concentration of aftershocks in the 4 6 km depth range near the mainshock are mostly of reverse type but display a 90 range of nodal plane trend those events appear to outline the periphery of mainshock rupture where positive coulomb stress transfer is largest the focal mechanisms of aftershocks at depths less than 4 km and those greater than 6 km along with the mainshock point to the possibility of a depth dependent stress field prior to the occurrence of the mainshock analysis of earthquake occurrence using a new magnitude scale indicates a gutenberg richer law b value of 0 864 and an omori law p value of 1 085 indicative of a typical aftershock sequence online material catalogs of aftershock location magnitude and focal mechanisms

analysis of similar event clusters in aftershocks of the 1994 northridge california earthquake 1 we perform waveform cross correlation on over 14 000 aftershocks of the 1994 northridge mw 6 7 earthquake in southern california as recorded by short period stations of the southern california seismic network scsn approximately 10 30 of the events belong to similar event clusters depending upon the similarity criteria that are applied we relocate events within 218 of these clusters to a relative location accuracy of about 30 m using the differential times obtained from the cross correlation these relocated event clusters often show planar features suggestive of faults at depth and we apply principal parameter analysis to characterize the shape of each cluster and to compute best fitting planes in several cases these planes are parallel to the main shock fault plane however more generally the seismicity planes exhibit a wide range of orientations suggesting complexity in the aftershock faulting composite focal mechanisms can be obtained for each cluster by combining the p polarity data from individual events a comparison of polarity measurement differences within similar event clusters provides constraints on the error rate in the individual focal mechanisms for some clusters we are able to resolve the primary versus auxiliary fault plane ambiguity by comparing the computed focal mechanisms with the best fitting seismicity planes individual event focal mechanisms are in general agreement with the composite focal mechanisms for the similar event clusters events occurring along the main shock rupture plane are mainly thrust whereas events in the hanging wall are predominately strike slip

joint inversion for earthquake depths using local waveforms and amplitude spectra of rayleigh waves reliable earthquake depth is fundamental to many seismological problems in this paper we present a method to jointly invert for centroid depths with local distance 5 seismic waveforms and regional distance of 5 15 rayleigh wave amplitude spectra on sparse networks we use earthquake focal mechanisms and magnitudes retrieved with the cut and paste cap method to compute synthetic amplitude spectra of fundamental mode rayleigh wave for a range of depths then we grid search to find the optimal depth that minimizes the joint misfit of amplitude spectra and local waveforms as case studies we apply this method to the 2008 wells nevada mw6 0 earthquake and a mw5 6 outer rise earthquake to the east of japan trench in 2013 uncertainties estimated with a bootstrap re sampling approach show that this joint inversion approach constrains centroid depths well which are also verified by independent teleseismic depth phase data

doppler radar observation of a land breeze cold front abstract during the early morning hours of ii january 1981 a very narrow intense band of snow which had formed along the leading edge of a land breeze cold front was viewed by cp 4 radar near muskegon michigan the front formed well inland and moved through the area from the northeast shortly after dawn the driving force for the land breeze was the large temperature contrast that existed between radiationally cooled air over the northern highlands of lower michigan and the relatively warm lake modified air near the shore of lake michigan the possibility that the observed snowband was associated with a mesoscale feature other than the land breeze is investigated an analysis of minimum temperatures in the great lakes region for 11 january 1981 shows that a strong temperature gradient existed over western lower michigan this gradient reached a maximum value well inland rather than at the lake shore radar observations show the band to be over 80 km long and only 4 km wide oriented roughly parallel t

observations and modeling of a mesoscale cold surge during wispit a transient feature marked primarily by a sudden increase in wind speed and brief period of heavy snow was observed over northeastern colorado on 11 12 march 1993 little if any abrupt changes in surface pressure or temperature were noted such as might accompany a gravity current gradual temperature falls and pressure rises were observed behind the velocity surge however there was no cyclonic wind shift nor did the feature last for more than a few hours suggesting that it was not likely a classical front data indicate that the surge originated near the peak of the cheyenne ridge a 400 m east west elongated hill near the border between colorado and wyoming simulations using an idealized two dimensional isentropic model show that a transient resembling observed surge results from impulsively started flow over heated terrain heating creates convergence that is in phase with the velocity surge at the leading edge of the topographic wave the result is a coherent disturbance in velocity which moves downstream at nearly the mean flow speed simulations with the pennsylvania state university national center for atmospheric research nonhydrostatic model mm5 using a horizontal resolution of 6 7 km capture the evolution of the observed surge these simulations support the identification of the surge as a topographic wave modified by heating but they also indicate an important role played by latent heating in the updraft at the leading edge of the surge because the latent heating occurs mainly downstream from the cheyenne ridge the formation of the topographic wave is unaltered by it however the updraft at the leading edge of the surge it greatly intensified leading to a narrow propagating band of heavy snow

the 1993 superstorm cold surge frontal structure gap flow and tropical impact in the wake of the eastern united states cyclone of 12 14 march 1993 a cold surge originating over alaska and western canada brought northerlies exceeding 20 m s21 and temperature decreases up to 158c over 24 h into mexico and central america this paper addresses the multiscale aspects of the surge from the planetary scale to the mesoscale focusing on 1 the structure and evolution of the leading edge of the cold surge 2 the reasons for its extraordinary intensity and equatorward extent and 3 the impact of the surge on the tropics specifically on the strength of the trade winds and on the sea surface temperature in the eastern pacific the cold surge was initiated as a developing cyclone over the gulf of mexico and an upstream anticyclone east of the rockies caused an along barrier pressure gradient to form forcing topographically channeled northerlies along the rocky and sierra madre mountains to transport cold air equatorward on the mesoscale the leading edge of the cold surge possessed nonclassical frontal structure for example as the cold surge entered mexico the coldest air and the strongest wind arrived at about 900 hpa before affecting the surface suggestive of a tipped forward leading edge to the surge also satellite imagery and surface observations indicate that the leading edge appeared to be successively regenerated in the warm presurge air the cold surge had characteristics reminiscent of a kelvin wave a tipped forward cold front a pressure jump line a bore and a gravity current but none of these conceptual dynamical models was fully applicable associated with the cold surge gap winds up to 25 m s21 were observed in the gulfs of tehuantepec a tehuantepecer fonseca papagayo and panama owing to the strong cross mountain pressure gradient in the case of the tehuantepecer a rope cloud emanated from the isthmus of tehuantepec and turned anticyclonically consistent with an inertial oscillation on the synoptic and planetary scales the extraordinary equatorward extent of the cold surge was aided by topographic channeling similar to cold air damming by a low latitude upper tropospheric trough and by the lower branch of the secondary circulation associated with a confluent jet entrance region aloft the cold surge also impacted the tropical atmosphere and ocean by contributing to the strengthening of the northeast trade winds over the eastern pacific ocean and by inducing local cooling of the sea surface temperature in the gulfs of tehuantepec and papagayo by about 48 88c

a family of frontal cyclones over the western atlantic ocean part i a 60 h simulation despite marked improvements in the predictability of rapidly deepening extratropical cyclones many operational models still have great difficulties in predicting frontal cyclogenesis that often begins as a mesoscale vortex embedded in a large scale parent cyclone system in this paper a 60 h simulation and analysis of a family of frontal cyclones that were generated over the western atlantic ocean during 13 15 march 1992 are performed using the pennsylvania state university national center for atmospheric research mesoscale model with a fine mesh grid size of 30 km although it is initialized with conventional observations the model reproduces well the genesis track and intensity of the frontal cyclones their associated thermal structure and precipitation pattern as well as their surface circulations as verified against the canadian meteorological centre analysis and other available observations it is shown that each frontal cyclone is initiated successively to the southwest of its predecessor in the cold sector first appearing as a pressure trough superposed on a baroclinically unstable basic state in the lowest 150 300 hpa then it derives kinetic energy from the low level available potential energy as it moves over an underlying warm ocean surface with weak static stability toward a leading large scale frontal zone and deepens rapidly by release of latent heat occurring in its own circulations one of the frontal cyclones originating in the cold air mass deepens 44 hpa in 42 h and overwhelms the parent cyclone after passing over the warm gulf stream water into the leading frontal zone these cyclones have diameters ranging from 500 to 1100 km as denoted by the last closed isobar and are spaced 1000 1400 km apart between their circulation centers during the mature stage they begin to establish their own cold warm frontal circulations once their first closed isobars appear thus distorting the leading large scale frontal structures and altering the distribution and type convective versus stratiform of precipitation it is found that the frontal cyclones accelerate and experience their central pressure drops as they move from high to low pressure regions toward the parent cyclone center and then they decelerate and fill as they travel away from the parent cyclone their spatial and temporal scales vertical structures as well as deepening mechanisms are shown to differ significantly from those typical extratropical cyclones as previously studied

current sierra nevada north america motion from very long baseline interferometry implications for the kinematics of the western united states we use geodetic measurements from very long baseline interferometry to estimate the motion of the sierra nevadan microplate which is composed of the sierra nevada and the great valley the motion of the sierra nevadan microplate relative to the north american plate is described by a right handed rotation of 0 61 m y about lat 32 n long 128 w this euler pole lies only 10 southwest of the sierra nevadan microplate and predicts a significant counterclockwise rotation about a local vertical axis it further predicts a velocity of the eastern edge of the sierra nevada at 38 0 n 119 3 w relative to stable north america of 11 1 mm yr toward n36 3 w quoted uncertainties are plus or minus one standard error which accounts for about one fourth of the velocity between the pacific and north american plates and is 25 clockwise of many prior estimates the velocity nearly parallels the boundary between the sierra nevada and the great basin which implies that current motion within the great basin results in a rotational noncoaxial deformation we use this velocity to estimate how motion is distributed across the broad deforming zone taking up pacific north america plate motion we find that the vector sum of strike slip along the san andreas fault and motion of the sierra nevada relative to stable north america taken up by deformation within the great basin differs little from the pacific north america plate velocity the difference can be described at 36 n along the san andreas fault by a vector of 6 mm yr directed toward n20 w this vector resolves into components of 5 mm yr parallel to the fault and 2 mm yr perpendicular to the fault with 95 confidence intervals of 0 to 10 mm yr and 1 to 5 mm yr respectively the component perpendicular to the fault is several times smaller than found in prior studies and places a small upper bound on fault perpendicular shortening we conclude that motion previously inferred to be taken up by deformation other than strike slip along the san andreas fault or deformation within the great basin is much smaller than previously thought

near source geometrical spreading in the central virginia seismic zone determined from the aftershocks of the 2011 mineral virginia earthquake we used aftershocks of the 2011 mineral virginia earthquake to study geometrical spreading at hypocentral distances less than 60 km in the central virginia seismic zone sixty nine aftershocks occurring from 25 august 2011 through 24 december 2011 provided the data we used the coda normalization method to estimate the attenuation coefficient associated with geometrical spreading we filtered the time domain signals in several octave wide frequency bands and examined attenuation of peak s wave amplitude in the 1 0 30 0 hz frequency range amplitude was assumed to decrease as a function of hypocenter distance r according to r the coefficient of attenuation was examined for the three component s wave amplitudes with corrections for sh and sv radiation patterns we observed no systematic frequency dependence of the coefficient of attenuation for the radial and transverse components assuming infinite quality factor q derived as a weighted mean over the entire range of frequencies 1 30 hz are both 1 51 0 05 the weighted mean value of the attenuation coefficient on the vertical component over the same range of frequencies is 1 45 0 05 slightly less than for the horizontal components we corrected the data assuming three q models the estimated geometrical spreading coefficients are in the 1 30 1 46 range depending on the assumed q model and component which is only slightly less than the estimates of determined assuming infinite q the estimated attenuation coefficients differ significantly from the value of 1 0 expected for a whole space the results for the horizontal components are in agreement with previous full wavefield modeling however the observed vertical component attenuation is substantially less than that predicted by the synthetics the depths of the earthquakes are less than 8 km so these results may not be representative of geometrical spreading in parts of eastern north america where earthquakes occur at greater depths online material table of earthquake hypocenters and focal mechanisms

the influence of mesoscale features of the sea surface temperature distribution on marine boundary layer winds off the scotian shelf during the superstorm of march 1993 abstract this paper studies the mesoscale wind field during the blizzard of march 1993 off the east coast of north america and examines the influence of the sea surface temperature distribution on surface winds can the gulf stream and its meanders by its strong influence on the marine boundary layer generate mesoscale features in the wind field numerical simulations of the storm are carried out using the mc2 a fully elastic nonhydrostatic model simulations are conducted at different resolutions 50 25 10 5 and 2 km with both detailed and smoothed sst fields so as to examine the influence of these parameters on the marine boundary layer winds results from these numerical simulations are compared with surface observations from buoys the study reveals some mesoscale features in the wind field caused by the gulf stream s meanders and the warm eddies of the sst field in a stable boundary layer the meanders shaped a 50 55 kt 26 28 m s 1 band of winds in a general 40 45 kt 21 23 m s 1 wind fi

monitoring the earthquake source process in north america with the implementation of the usgs national earthquake information center prompt assessment of global earthquakes for response system pager rapid determination of earthquake moment magnitude is essential especially for earthquakes that are felt within the contiguous united states we report an implementation of moment tensor processing for application to broad seismically active areas of north america this effort focuses on the selection of regional crustal velocity models codification of data quality tests and the development of procedures for rapid computation of the seismic moment tensor we systematically apply these techniques to earthquakes with reported magnitude greater than 3 5 in continental north america that are not associated with a tectonic plate boundary using the 0 02 0 10 hz passband we can usually determine with few exceptions moment tensor solutions for earthquakes with m w as small as 3 7 the threshold is significantly influenced by the density of stations the location of the earthquake relative to the seismic stations and of course the signal to noise ratio with the existing permanent broadband stations in north america operated for rapid earthquake response the seismic moment tensor of most earthquakes that are m w 4 or larger can be routinely computed as expected the nonuniform spatial pattern of these solutions reflects the seismicity pattern however the orientation of the direction of maximum compressive stress and the predominant style of faulting is spatially coherent across large regions of the continent

depth of faulting during the 1968 meckering australia earthquake sequence determined from waveform analysis of local seismograms waveforms for 11 foreshocks and 48 aftershocks of the ms 6 8 meckering earthquake recorded at the world wide standard seismograph network station mundaring are analyzed to determine the depth distribtion of faulting during this unusual intraplate earthquake sequence clear depth phases including sp and rg are seen in the local seismograms at distances of 60 95 km and are studied using synthetic seismograms computed using generalized ray theory and wave number integration techniques large rg s ratios seen on the vertical component short period data for many events imply source depths less than 2 km the short period p waveform contains the best depth estimator in the form of sp so that depth can be estimated to within an uncertainty of about 1 km for most events the foreshocks cluster at less than 2 km depth and most aftershocks occur within 1 km of the surface a few aftershocks occur as deep as 7 km these results are consistent with a previous teleseismic waveform study in which faulting was inferred to start near the surface at 1 5 km depth with rupture proceeding downward and not exceeding 6 km depth these results coupled with previous stress studies in the australian shield and models of crustal strength show that faulting in a cold shield area is a near surface phenomenon and implies that most of the crust is too strong to be fractured

the ohio valley wave merger cyclogenesis event of 25 26 january 1978 part i multiscale case study abstract the long standing observational view of cyclogenesis involves an interaction between tropopause and surface based finite amplitude disturbances there are however instances where more than one upper level disturbance contributes to low level development a subset of these events involves wave or trough merger which has been defined as the amalgamation of two or more distinct 500 hpa vorticity maxima an example of this phenomenon involving a case of very intense continental cyclogenesis 25 26 january 1978 over the eastern united states is selected to elucidate the origin and evolution of precursor disturbances from the planetary scale to the mesoscale the analysis of this event reveals that the two well defined tropopause based disturbances that contribute to cyclogenesis have distinctly different origins and are brought together by confluent planetary scale flow one of these disturbances originates over the western north pacific ocean 10 days prior to cyclogenesis and tracks eastward

mantle viscosity and ice age ice sheet topography ice age paleotopography and mantle viscosity can both be inferred from observations of earth s response to the most recent deglaciation event of the current ice age this procedure requires iterative application of a theoretical model of the global process of glacial isostatic adjustment results demonstrate that the iterative inversion procedure converges to a paleotopography that is extremely close to that from the ice 4g model the accompanying mantle viscosity profile is furthermore shown to reconcile the requirements of aspherical geoid anomalies related to the mantle convection process thus resolving a fundamental issue concerning mantle rheology the combined model also explains postglacial sea level histories for the east coast of the united states

source mechanism and rupture directivity of the 18 may 2009 mw 4 6 inglewood california earthquake on 18 may 2009 an m w 4 6 earthquake occurred beneath inglewood california and was widely felt though source mechanism and its location suggest that the newport inglewood fault nif may be involved in generating the earthquake rupture directivity must be modeled to establish the connection between the fault and the earthquake we first invert for the event s source mechanism and depth with the cut and paste method in the long period band 5 s because of the low velocity shallow sediments in the los angeles la basin we use two velocity models in the inversion for stations inside and outside the la basin however little difference is observed in the resolved source mechanism m w 4 6 strike 246 145 dip 50 77 rake 17 138 and depth 7 to 9 km compared to an inversion using the standard southern calfornia model with the resolved source parameters we calibrate the amplitude anomaly of the short period 0 5 2 hz p waves with amplitude adjustment factors aaf these aafs are used as corrections when retrieving source mechanisms of the smaller aftershocks using short period p waves alone most of the aftershocks show similar source mechanisms as that of the mainshock providing ideal empirical green s functions egfs for studying its rupture process we use a forward modeling approach to retrieve rupture directivity of the mainshock consistent with movement on the nif with rupture toward the southeast although we focus on p waves for analyzing rupture directivity the resolved unilateral pattern is also confirmed with the azimuthal variation of the duration of sh waves observed in the basin the high rupture velocity near the shear velocity and relatively low stress drop are consistent with the hypothesis of rupture on a mature fault

three dimensional models of deformation near strike slip faults we use three dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike slip faults deformation of the brittle upper crust in the vicinity of strike slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle the driving motion is represented by displacement that is spectied on the bottom of a 15km thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults which we term the shear zone stress free basal boundary conditions are specified within the shear zone the basal driving displacement is either pure strike slip or strike slip with a small oblique component and the geometry of the fault system includes a single fault several parallel faults and overlapping en echelon faults we examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults in models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude i c1 j l c i rl l b blhi aill i srizcxi ld 3 rr ij i n flail 3il i dilitiiiat df ti ijtluii clicili c i i zor tz a j t s ii acmes strong fault lnnlds havs lnore luc tlixd dxz a ac tip of tne faults and the deformation is partly distributed outside the fault zone the dimensions of large basins along strike slip faults such as the rukwa and dead sea basins and the absence of uplift around pull apart basins fit models with weak faults better than models with strong faults our models also suggest that the length to width ratio of pull apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested we show that pure strike slip motion can produce tectonic features such as elongate half grabens along a single fault rotated blocks at the ends of parallel faults or extension perpendicular to overlapping en echelon faults which can be misinterprete d to indicate a regional component of extension zones of subsidence or uplift can become wider than expected for transform plate boundaries when a minor component of oblique motion is added to a system of parallel strike slip faults

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

a technique for diagnosing three dimensional ageostrophic circulations in baroclinic disturbances on limited area domains abstract the methodology developed by keyser et al for representing and diagnosing three dimensional vertical circulations in baroclinic disturbances using a two dimensional vector streamfunction referred to as the psi vector is restricted to f plane channel model geometry the vertical circulation described by the psi vector consists of the irrotational or divergent part of the ageostrophic wind and the vertical velocity a key property of the psi vector is that its projections onto arbitrarily oriented orthogonal vertical planes yield independent vertical circulations allowing separation of a three dimensional vertical circulation into two two dimensional components and thus objective assessment of the extent to which a three dimensional vertical circulation is oriented in a preferred direction here the methodology for determining the psi vector is modified to be suitable for real data applications the modifications consists of reformulating the diagnostic equations to apply to conformal map pr

focal depths for small to moderate earthquakes mn 2 8 in western quebec southern ontario and northern new york regional depth phase modeling is a useful technique to constrain earthquake focal depths for events within sparse networks we demonstrate how regional depth phases can be used to obtain focal depths for hundreds of earthquakes with m n 2 8 that occurred from 1980 to 2004 in southern ontario western quebec and northern new york state we discuss the development of regional depth phases with distance their use in focal depth determinations by matching waveforms to synthetics and possible sources of error in general focal depths can be determined to within about 3 km when there is at least one record at regional distances with clearly identifiable depth phases such as spmp or spg in southwestern ontario and northern new york focal depths range from 2 to 15 km in areas of western quebec and along the ottawa river valley in ontario focal depths range from 2 to 25 km more than half of the earthquakes in a cluster of activity near maniwaki in western quebec are deeper than 20 km all earthquakes deeper than 20 km occurred north of about 45 3 n there is an intriguing tendency for earthquake depths to cluster near 8 km 12 km 15 km and 22 km another interesting observation is that there are several earthquake pairs or small groups with very similar epicenters but quite different depths the most active regions in western quebec and along the ottawa river valley tend to exhibit a relatively wide range of focal depths along broad zones that trend roughly northwest suggesting that seismicity is occurring along diffuse northwest trending faults throughout the crust the wide range of focal depths may indicate the potential for a larger maximum scale of fault rupture and serve as a contemporary marker of locations where large events have occurred in the recent geologic past

interaction of potential vorticity anomalies in extratropical cyclogenesis part i static piecewise inversion the relative importance of various potential vorticity pv perturbations and their mutual interactions associated with the superstorm of 12 14 march 1993 are investigated by applying a piecewise pv inversion diagnostic system to a 36 h simulation of the storm it is shown that the contributions from all pv anomalies to the surface development increase with time although their relative significance varies during the rapid deepening stage in general the upper level dry pv anomalies contribute the most to the rapid deepening of the storm followed in order by the lower level thermal anomaly and latent heat release comparing the pv anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper and lower level anomalies that allows lower and upper level mutual interactions in which the circulations associated with the upper level pv anomalies enhance the lower level anomalies and vice versa in addition to the vertical interactions lateral interactions are also present among the upper level pv anomalies and the background flow it is also found that the background flow advection dominates the vortex vortex and vortex background flow interactions in the deepening of the storm the vortex vortex interactions of the two upper level positive pv anomalies cause the negative tilt of the main upper level trough during the rapid deepening period

the structure and evolution of gap outflow over the gulf of tehuantepec mexico abstract mesoscale model simulations are used to examine the structure and dynamics of a gap outflow event over the gulf of tehuantepec mexico that was associated with a surge of cold air along the eastern slopes of the sierra madre the simulated gap outflow winds emerged from chivela pass reached a maximum speed of 25 m s 1 and turned anticyclonically as they fanned out over the gulf northerly winds were also able to ascend the mountains east and to a lesser extent west of chivela pass indicating that the movement of cold air across the sierra madre was not confined to the pass a mesoscale pressure ridge was aligned along the axis of the gap outflow jet which was flanked to the west by an anticyclonic eddy and to the east by a weaker cyclonic eddy a model derived trajectory along the axis of the outflow jet traced an inertial path with anticyclonic curvature produced primarily by the coriolis acceleration the cross flow pressure gradient acceleration along this trajectory was negligible be

testing fault models with numerical simulation example from central california abstract stress distribution in faulted areas is often calculated and used to assess the potential of regional seismic hazard yet the result of the calculation may strongly depend on the modeled fault configuration thus it is important to assess the accuracy of the assumed fault configuration for a specific faulted area two distinct tectonic models have been proposed for central california in one model a master detachment is assumed to be present below the seismogenic layer which connects the san andreas fault and the other faults in the system in another no basal detachment is assumed how significant are the different models in predicting seismic hazards in california to what extent are geodetic data useful in distinguishing these models in this paper we report the results from a 3d finite element analysis of stress and deformation in a crust containing a straight transform fault bordered by two thrust faults which is intended to simulate a segment of the san andreas fault system in central california significant results are 1 the different models predict notably different states of stresses thus notably different seismic potentials and 2 the differences in the predicted surface deformation between the two models are smaller than the current gps resolution

rupture model of the 2011 mineral virginia earthquake from teleseismic and regional waveforms 1 we independently invert teleseismic p waveforms and regional crustal phases to examine the finite fault slip model for the 2011 mw 5 8 mineral virginia earthquake theoretical and empirical green s functions are used for the teleseismic and regional models respectively both solutions show two distinct sources each about 2 km across and separated by 2 5 km the source at the hypocenter is more localized in the regional model leading to a higher peak slip of 130 cm and higher average stress drop of 250 bars compared with 86 cm and 150 bars for the same source in the teleseismic model both sources are centered at approximately 8 km depth in the regional model largely below the aftershock distribution in the teleseismic model the sources extend updip to approximately 6 km depth into the depth range of the aftershocks the rupture velocity is not well resolved but appears to be near 2 7 km s

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

meteorological tower measurements of a surface cold front abstract measurements from the boulder atmospheric observatory meteorological research tower are used to describe the structure and physical processes of a strong surface cold front analysis reveals that the horizontal gradients in temperature and wind velocity at the front are concentrated within a 200 m distance and measured vertical velocities exceed 5 m s 1 at the leading edge of the front calculations with the miller frontogenesis equation show the magnitude and relative importance of cross frontal confluence versus differential vertical motion tilting in forcing frontogenesis

focal depth determination for moderate and small earthquakes by modeling regional depth phases spg spmp and spn there are three usable regional depth phases spg spmp and spn and their corresponding reference phases pg pmp and pn the differential time between each depth phase and its reference phase can be used to estimate earthquake focal depth we have developed a method to determine focal depth for moderate and small earthquakes by using a regional depth phase modeling rdpm method we used a default focal mechanism to generate the differential times for all earthquakes to estimate the reliability of the modeled focal depths we compared our solutions with those obtained by other methods and found the consistency is good because the focal depths estimated by rdpm are model dependent we tested the extent of the dependency and found that a 10 error in the crustal model may generate a 10 15 error in the modeled depth the absolute error is determined by the error in the crustal model and the focal depth itself we found that earthquake location errors have only a small effect on the modeled focal depths by analyzing synthetic and observed waveforms we found a distance window within which spmp and pmp are well developed and within the window the p portion of the waveform is relatively simple and spmp and pmp are easy to identify we also demonstrated that the assumptions of spmp and pmp are correct that regional depth phases are not developed or not discernible in some regions and that regional depth phases have special features that can be used to identify those phases

earthquake source mechanism and rupture directivity of the 12 september 2016 mw 5 5 gyeongju south korea earthquakeshort note

neogene transpressive evolution of the california coast ranges the san andreas fault has long been viewed as a vertical structure that extends from the ground surface to the base of the lithosphere and separates the pacific plate from the north american plate along a transform plate boundary analysis of neogene structures in the central coast ranges indicates however that crustal blocks defined by strands of the san andreas fault system have undergone pervasive compressive deformation that has shifted these blocks and their boundary faults east relative to north america this suggests that the blocks and their boundary structures are bounded below by an active decollement that appears to coincide with the midcrustal brittle to ductile transition at the base of the seismogenic zone these compressive structures may be related to a currently seismically active fold and thrust belt that characterizes the eastern front of the coast ranges seismic profiles from the central valley east of the range front show that tectonic wedges blind thrusts developed within stratified rocks are present throughout this zone of deformation and that crystalline basement that underlies these stratified rocks is not involved in the deformation crystalline basement may underlie most of the coast ranges as indicated by the presence of metamorphic rocks of possible sierran affinity preserved in neogene thrust sheets as far west as loma prieta and by seismic velocities in the lower crust appropriate for mafic to intermediate granitoid rocks on the basis of these relations we suggest that the san andreas fault system is confined to the brittle crust above the decollement and does not penetrate to the base of the lithosphere thus the san andreas fault should not be considered as a plate boundary instead the functional plate boundary within the coast ranges appears to be the inferred subhorizontal midcrustal decollement this decollement corresponds approximately to the 350 c isotherm the temperature at which quartz becomes ductile if our hypothesis is proven to be correct by geologic and geophysical investigations currently underway then extensive revisions in popular plate tectonic models applied to the coast ranges will be required in addition assessment of seismic hazards will be rendered more difficult but more realistic owing to realization of the greater likelihood for occurrence of thrust faulting on blind or buried faults or on faults currently deemed inactive

three dimensional compressional wavespeed model earthquake relocations and focal mechanisms for the parkfield california region we present a new three dimensional 3d compressional wavespeed v p model for the parkfield region taking advantage of the recent seismicity associated with the 2003 san simeon and 2004 parkfield earthquake sequences to provide increased model resolution compared to the work of eberhart phillips and michael 1993 epm93 taking the epm93 3d model as our starting model we invert the arrival time data from about 2100 earthquakes and 250 shots recorded on both permanent network and temporary stations in a region 130 km northeast southwest by 120 km northwest southeast we include catalog picks and cross correlation and catalog differential times in the inversion using the double difference tomography method of zhang and thurber 2003 the principal v p features reported by epm93 and michelini and mcevilly 1991 are recovered but with locally improved resolution along the san andreas fault saf and near the active source profiles we image the previously identified strong wavespeed contrast faster on the southwest side across most of the length of the saf and we also improve the image of a high v p body on the northeast side of the fault reported by epm93 this narrow body is at about 5 to 12 km depth and extends approximately from the locked section of the saf to the town of parkfield the footwall of the thrust fault responsible for the 1983 coalinga earthquake is imaged as a northeast dipping high wavespeed body in between relatively low wavespeeds 5 km sec extend to as much as 10 km depth we use this model to derive absolute locations for about 16 000 earthquakes from 1966 to 2005 and high precision double difference locations for 9 000 earthquakes from 1984 to 2005 and also to determine focal mechanisms for 446 earthquakes these earthquake locations and mechanisms show that the seismogenic fault is a simple planar structure the aftershock sequence of the 2004 mainshock concentrates into the same structures defined by the pre 2004 seismicity confirming earlier observations waldhauser et al 2004 that the seismicity pattern at parkfield is long lived and persists through multiple cycles of mainshocks online material 3d v p model and earthquake relocations

two severe freezes in brazil precursors and synoptic evolution abstract two freezes with repercussions on world coffee markets struck brazil in recent years one during fgge in 1979 the other in 1981 data from multiple sources including satellites and drifting buoys were analyzed for early warning signs and synoptic evolution of the freeze events two important precursors were found 1 a slowly moving long wave pattern in the central south pacific ocean amplified greatly one to two days before frontogenesis in south america and four to five days before the freezes in brazil 2 the long wave ridge when at maximum amplitude was located near the southern andes and the next long wave trough downstream was located in the south atlantic at the longitude of brazil this configuration channeled subantarctic air northward entirely over land into subtropical latitudes frontogenesis in low latitudes in the mid pacific was the first sign of wave amplification in the 1979 case subsequent frontogenesis in northern argentina was accelerated by the opportune approach of a s

earthquake hypocenters and focal mechanisms in central oklahoma reveal a complex system of reactivated subsurface strike slip faulting the sharp increase in seismicity over a broad region of central oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure since early 2010 numerous organizations have deployed temporary portable seismic stations in central oklahoma in order to record the evolving seismicity in this study we apply a multiple event relocation method to produce a catalog of 3639 central oklahoma earthquakes from late 2009 through 2014 regional moment tensor rmt source parameters were determined for 195 of the largest and best recorded earthquakes combining rmt results with relocated seismicity enabled us to determine the length depth and style of faulting occurring on reactivated subsurface fault systems results show that the majority of earthquakes occur on near vertical optimally oriented ne sw and nw se strike slip faults in the shallow crystalline basement these are necessary first order observations required to assess the potential hazards of individual faults in oklahoma

the black mountain asperity seismic hazard of the southern san francisco peninsula california black mountain a 860 m high wedge of franciscan formation mostly comprising basic ultrabasic rock sw of palo alto and just ne of the san andreas fault marks an abrupt bend in the fault at the northern end of a 100 km long segment of the fault that strikes 9 more e w than the fault to the north or south it also bounds a marked change in the physiographic setting of the fault which to the north follows a well developed linear fault valley and to the south follows a poorly defined topographic trace that traverses the rugged santa cruz mountains the bend at black mountain had a profound effect on the 1906 rupture the 75 km section to the se of this point slipped only 1 1 4 m as compared to the 2 5 4 m typical of the rupture on the san francisco peninsula to the nw this 75 km long slip deficit region from black mountain to san juan bautista if ruptured in its entirety would produce a ms 6 9 earthquake the conditional probability of this rupturing in the near future is the highest of any section of the san andreas fault except parkfield this earthquake would rupture 30 km farther northwest and be about 3 times larger than that previously proposed by others and this constitutes a greater risk to the southern san francisco peninsula than previously expected

improved location procedures at the international seismological centre summary the international seismological centre isc is a non governmental non profit organization with the primary mission of producing the definitive account of the earth s seismicity the isc bulletin covers some 50 yr 1960 2011 of seismicity the recent years have seen a dramatic increase both in the number of reported events and especially in the number of reported phases owing to the ever increasing number of stations worldwide similar ray paths will produce correlated traveltime prediction errors due to unmodelled heterogeneities in the earth resulting in underestimated location uncertainties and for unfavourable network geometries location bias hence the denser and more unbalanced the global seismic station coverage becomes the less defensible is the assumption that is the observations are independent which is made by most location algorithms to address this challenge we have developed a new location algorithm for the isc that accounts for correlated error structure and uses all iaspei standard phases with a valid ak135 traveltime prediction to obtain more accurate event locations in this paper we describe the new isc locator and present validation tests by relocating the ground truth events in the iaspei reference event list as well as by relocating the entire isc bulletin we show that the new isc location algorithm provides small but consistent location improvements considerable improvements in depth determination and significantly more accurate formal uncertainty estimates we demonstrate that the new algorithm through the use of later phases and testing for depth resolution considerably clusters event locations more tightly thus providing an improved view of the seismicity of the earth

three dimensional numerical experiments of strain partitioning at oblique plate boundaries implications for contrasting tectonic styles in the southern coast ranges california and central south island new zealand a three dimensional numerical model is used to investigate the nature and distribution of crustal scale deformation and strain partitioning across obliquely convergent transpressive plate boundaries a uniform elastic plastic crustal layer obeying murrell s extension to three dimensions of the griffith failure criterion was deformed under basal kinematic boundary conditions that correspond to the oblique convergence between two mantle lithospheres one of which detaches and subducts beneath the other the results show deformation concentrated in relatively narrow shear zones the character planar versus curved and dip of these shear zones or crustal scale faults depend on the relative amount of convergence versus transcurrent motion imposed across the plate boundary in models dominated by transcurrent boundary conditions two separate sets of coexisting structures develop 1 a pair of planar relatively shallow dipping thrust zones arranged in a v structure that accommodate convergent motion and 2 a set of curved near vertical strike slip zones arranged in a flower structure that accommodates the transcurrent motion in models dominated by convergence both contractional and transcurrent deformations are accommodated by oblique slip across a single pair of structures that have the same geometry as the thrust shear zones there is a gradational behavior between these end member partitioned and nonpartitioned modes for intermediate boundary conditions in all cases the dip of the shear zones predicted by the numerical model is in good agreement with the dip of ideal faults predicted by mohr s incipient faulting hypothesis the two basic modes are interpreted to underlie the contrasting tectonic styles of the southern coast ranges california and central south island new zealand factors other than obliquity of convergence which play a role in strain partitioning are discussed

atmospheric structure and momentum balance during a gap wind event in shelikof strait alaska abstract gap winds occur in topographically restricted channels when a component of the pressure gradient is parallel to the channel axis aircraft flight level data are used to examine atmospheric structure and momentum balance during an early spring gap wind event in shelikof strait alaska alongshore sea level pressure ridging was observed vertical cross sections show that across strait gradients of boundary layer temperature and depth accounted for the pressure distribution geostrophic adjustment of the mass field to the along strait wind component contributed to development of the observed pressure pattern boundary layer structure and force balance during this event was similar to that often observed along isolated barriers however the rossby radius was lager than the strait width and atmospheric structure in the strait exit region indicates transition of the flow to open coastline conditions two across strait momentum budgets show that the coriolis force and across strait pressure gradient w