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

the transition from strike slip to oblique subduction in southeastern alaska from seismological studies abstract body waveform modeling of 11 moderate to large earthquakes within southeastern alaska has been incorporated with earthquake relocations and the results of previous seismicity studies to examine the transition from strike slip to oblique subduction in southeastern alaska in the sitka region of extreme southeastern alaska earthquakes indicate seismic slip is parallel to the direction of motion between north america and the pacific plate as the plate margin begins to bend to the west near cross sound and encounters the southeastern edge of the yakutat block partitioning of seismic slip is evident both onshore and offshore although the largest earthquakes magnitude 6 0 in this region have slip parallel to plate motion most moderate sized events have slip vectors rotated clockwise from plate motion offshore the 1973 cross sound sequence indicates that the southern end of the transition zone is seismogenic with the pacific plate being thrust beneath the yakutat block while onshore strike slip faulting has occurred along the fairweather border ranges and denali faults in the st elias region thrust faulting is occurring along and above the plate interface moderate sized events in the st elias show a mix of slip vector orientations in the pamplona zone slip vectors of offshore earthquakes and deformation directions determined onshore from gps studies show a counter clockwise rotation relative to plate motion suggesting that a change in strain field occurs just west of the st elias region

seismic activity of the san francisco bay region moment magnitude m with objective confidence level uncertainties are estimated for felt san francisco bay region earthquakes using bakun and went worth s 1997 analysis strategy for seismic intensity observations the frequency magnitude distribution is well described for m 5 5 events since 1850 by a gutenberg richter relation with a b value of 0 90 the seismic moment rate m yr since 1836 is 2 68 1018 n m yr 95 confidence range 1 29 1018 n m yr to 4 07 1018 n m yr the seismic moment rate since 1850 is nearly the same m yr in the 56 years before 1906 is about 10 times that in the 70 years after 1906 in contrast m yr since 1977 is about equal that in the 56 years before 1906 80 1 14 of the plate motion moment accumulation rate is available for release in earthquakes the historical m yr and the portion of the plate motion moment accumulation rate available for release in earthquakes are used in a seismic cycle model to estimate the rate of seismic activity in the twenty first century high and low rates of future seismic activity are both permissible given the range of possible seismic cycle recurrence times t and the uncertainties in the historical m and in the percentage of plate motion available for release in earthquakes if the historical seismic moment rate is not greater than the estimated 2 68 1018 n m yr and the percentage of the plate motion moment accumulation available for release in earthquakes is not less than the estimated 80 then for all t the rate of seismic moment release from now until the next 1906 sized shock will be comparable to the rate from 1836 to 1905 when m 6 1 2 shocks occurred every 15 to 20 years

rupture process of the 1964 prince william sound alaska earthquake from the combined inversion of seismic tsunami and geodetic data 1 four great earthquakes 1952 1960 1964 and 2004 have occurred since seismic monitoring began and only two since the installation of a global seismic network a reexamination of the 1964 m 9 2 prince william sound pws alaska earthquake is timely due to the 2004 sumatra earthquake because it adds constraints to the potential range of source parameters for these types of infrequent events and aids in the ability to predict the ground motions for other subduction zone including cascadia we first measured the durations of high frequency energy radiation from teleseismic p wave codas recorded by short period world wide standardized seismographic network wwssn sp instruments to put constraints on the earthquake rupture length the durations ranged between 250 and 600 s and are shorter in time between azimuths of 190 and 260 the fault length is estimated to range from 540 to 740 km rupturing at average speeds of 1 4 2 km s in a 220 238 direction we developed a multiple time window kinematic rupture model for the pws earthquake from the least squares inversion of teleseismic p waves tsunami tide gauge records and geodetic leveling survey observations based on the green s function technique we assume three major fault segments for the subduction zone dipping 6 12 based on geologic data the subfault size on the megathrust was set to 50 50 km the patton bay fault pbf imbricate thrust was assigned a 60 dip with a subfault size of 20 20 km we estimated a seismic moment of 5 52 1022 n m mw9 12 we identified three areas of major moment release on the pws segment near montague and middleton islands extending out to the trench beneath the portlock anticline on the cook segment between 58 n fracture zone and the kodiak bowie seamount chain and finally on the katmai segment off the coast of kodiak island extending to the trench our preferred rupture model has a peak slip of 14 9 m along the megathrust and 17 4 m along the pbf the addition of the pbf resulted in an 8 improvement in residuals and also had a significant effect on the overall slip distribution moment release occurred as deep as 50 km depth slab contour near the 350 c isotherm and mantle fore arc wedge which is about 10 20 km deeper than previous coupling depths

revision of magnitudes of large shallow earthquakes 1897 1912 abstract in previous research trace amplitudes of surface wave maxima recorded by undamped milne seismographs were used to determine the surface wave magnitudes ms of large shallow earthquakes which occurred prior to 1912 for this purpose the effective gain of these instruments was calibrated by using the surface wave magnitudes ms gr which were calculated from the unpublished worksheets for seismicity of the earth of gutenberg and richter in this paper the real quality of ms gr is critically re evaluated by using independent sets of data it is found that ms gr for the period 1904 1909 is considerably overestimated the average excess from the real ms is 0 5 units for 1904 1906 0 4 for 1907 0 3 for 1908 1909 and 0 0 for 1910 1912 this overestimation is so systematic and large that the previous results are all redetermined the average effective gain of milne instruments is revised to be 21 9 previously the gain depended on ms this revision results in systematic reduction in the previously assigned magnitudes the revised values of ms for 264 shallow earthquakes with ms 6 8 and over in the period 1897 1912 inclusive are listed the present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century the present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909

3 d viscoelastic anisotropic modeling of data from a multicomponent multiazimuth seismic experiment in northeast texas three component seismic data were acquired along six azimuths at a site in northeast texas sources were inclined impacts combined to produce equivalent vertical and crossline horizontal components the data were analyzed by iterative modeling using a new 3 d staggered grid finite differencing scheme the 3 d model is defined in terms of spatially variable anisotropic viscoelastic parameters p velocity s velocity density qp and qs and converted to elastic tensor components and relaxation times for computation simultaneous fitting of amplitudes of near surface reverberations surface waves converted waves and deeper reflections gives an anisotropic viscoelastic model that provides constraints on earth properties the assumption of transverse isotropy in previous experiments is supported by the results of this experiment the final model consists of a stack of flat layers each of which has isotropic p velocity qp and qs the wills point and kincaid shales are strongly transversely isotropic

rupture of a seismic gap in southeastern alaska the 1972 sitka earthquake ms 7 6 abstract the sitka alaska earthquake of july 30 1972 m s 7 6 is one of the largest strike slip events since 1963 this earthquake is thought to have ruptured the pacific north america plate boundary segment between the large strike slip events in 1949 and 1958 and the sitka earthquake was heralded as one of the first successful forecasts of an earthquake based on the seismic gap hypothesis another motivation to study this event is the availability of a strong ground motion recording 50 km from the epicenter which is near the middle of the 180 km long plate boundary segment the teleseismically located aftershocks occur only in the southern half of this segment we have analyzed rayleigh waves and p waves recorded by wwssn long period vertical instruments a total of 25 very long period rayleigh phases r2 r5 define a symmetric four lobed radiation pattern from which we can infer a nearly pure right lateral strike slip fault striking 340 n20 w and a bilateral rupture comparison of synthetic and observed rayleigh waves yields a seismic moment of 3 10 27 dyn cm m w 7 6 the p waves are characterized by a dominant complex pulse in the first 40 s and a succession of smaller pulses after that the source time functions are deconvolved from 32 p waves with good azimuthal distribution to obtain the moment depth extent and rupture history the mean moment of the source time functions is 5 0 2 4 10 27 dyn cm and the depth extent is 0 10 km tomographic inversion of the source time functions produces an image of the earthquake rupture process this procedure maps the moment release of the complex pulse into two high displacement regions i e asperities 1 the epicentral area to 40 km north and 2 between 60 and 90 km south of the epicenter the main asperity just north of the epicenter coincides with a quiescent zone of microaftershocks while the overall average seismic displacement is 6 m the displacement at the main asperity is 7 m the same value as the tectonic displacement accumulated since the previous earthquake in 1848 the fault averaged stress drop is 100 bars while the asperity stress drop is 130 bars tomographic imaging of the source time functions thus resolves several features of the rupture process notably the bilateral propagation and rupture initiation at the largest asperity this is in contrast to the large 1976 guatemala strike slip earthquake where the largest displacements occurred away from rupture initiation

shallow seismicity of the anchorage alaska region 1964 1999 we have relocated over 4200 shallow 40 km earthquakes occurring in the anchorage region for 35 years following the 1964 great m w 9 2 alaska earthquake the shallowest 20 km earthquakes delineate several faults within the crust including one associated with mapped folds located north of upper cook inlet inversion of first motion data for the stress field orientation in upper cook inlet indicates east west oriented horizontal 1 and near vertical 3 a condition favoring reverse faulting along north south striking faults with trends similar to the orientation of mapped faults and fault cored anticlines within the inlet 1 is rotated 60 to 90 counterclockwise from the direction of plate convergence in agreement with global positioning system gps geodesy studies that indicate the western portion of the kenai peninsula and upper cook inlet do not appear to be moving in the direction of plate motion due to a change in coupling across the plate interface the stress regime north of the castle mountain fault is conducive to strike slip or normal faulting along faults striking east northeast or north northwest similar to previous studies we observed a persistent aseismic zone in the upper crust that appears to be located above and immediately downdip of the portion of the plate interface that slipped 20 25 m in the 1964 mainshock deeper 20 40 km earthquakes indicate intense deformation and a rapidly changing stress field near the boundary between the kenai and mckinley segments of the subducted slab the 1943 m w 7 0 susitna lowlands earthquake may have been associated with this region of complex deformation

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

efficient 3 d viscoelastic modeling with application to near surface land seismic data three dimensional viscoelastic modeling is implemented by reparameterizing the viscoelastic wave equation for a standard linear solid the formulation uses weighting factors corresponding to relaxation frequencies and composite memory variables this novel 3 d formulation requires less computer memory than the traditional relaxation time formulation because one set of relaxation frequencies can be used for all mechanisms for all parts of a model and only three sets of composite memory variables are needed rather than the seven used in the standard implementation giving a net reduction of 40 in the total required memory computational time is also reduced approximately 25 because of reduced input output i o the algorithm is applied to 3 d modeling of the viscoelastic response of the near surface structure beneath a 3 d reflection survey in the ouachita frontal thrust zone of southeast oklahoma comparison of the 3 d field data with both viscoelastic and elastic response clearly demonstrates the importance of inclusion of viscoelasticity when accurate amplitude fitting is desired observed amplitude and traveltime variations can be explained by shallow velocity and q distributions obtained independently by 3 d tomography

mmi attenuation and historical earthquakes in the basin and range province of western north america earthquakes in central nevada 1932 1959 were used to develop a modified mercalli intensity mmi attenuation model for estimating moment mag nitude m for earthquakes in the basin and range province of interior western north america m is 7 4 7 5 for the 26 march 1872 owens valley california earthquake in agreement with beanland and clark s 1994 m 7 6 that was estimated from geologic field observations m is 7 5 for the 3 may 1887 sonora mexico earthquake in agreement with natali and sbar s 1982 m 7 4 and suter s 2006 m 7 5 both estimated from geologic field observations mmi at sites in california for earthquakes in the nevada basin and range appar ently are not much affected by the sierra nevada except at sites near the sierra nevada where mmi is reduced this reduction in mmi is consistent with a shadow zone produced by the root of the sierra nevada in contrast mmi assignments for earthquakes located in the eastern sierra nevada near the west margin of the basin and range are greater than predicted at sites in california these higher mmi values may result from critical reflections due to layering near the base of the sierra nevada

numerical viscoelastic modelling by the spectral laguerre method seismic wave propagation in a viscoelastic media can be described by a system of integro differential equations the solution of such equations requires special methods when using finite difference techniques in the time domain in the frequency domain the integral terms are represented by complex elastic parameters this paper presents an efficient algorithm for viscoelastic modelling based on the integral laguerre transform for the approximation of temporal derivatives and for the calculation of convolution integrals for the calculation of spatial derivatives it is possible to use various methods finite difference and finite element techniques spectral and pseudo spectral methods we then obtain a system of algebraic equations with a matrix independent of the parameter m i e the degree of the laguerre polynomials in this case only the right hand side of the system has recurrent dependence on the parameter m which is an analogue of the temporal frequency in the frequency domain the obtained system with a large number of right hand sides can be solved using fast methods where the matrix is transformed only once as opposed to the frequency domain approach when the matrix is transformed for each temporal frequency

estimating magnitude and location of alaskan earthquakes using intensity data abstract i have developed relationships describing the attenuation of modified mercalli intensity mmi with distance for three regions of alaska south central interior and southeast the sparse intensity data precluded development of site specific corrections similar to those determined in other regions of the united states i tested the intensity attenuation relationships on sets of calibration events events with well determined locations and instrumentally determined magnitudes for south central and interior alaska sufficient events were not available for the southeast region my comparisons indicate the attenuation relationships gave event intensity centers within 50 to 60 km of event epicenters and magnitude estimates within 0 35 to 0 44 magnitude units of instrumentally determined magnitude i then used these attenuation relationships to analyze historic earthquakes occurring between 1899 and 1965 in the three regions that had poorly determined epicenters and or magnitudes including eight events with no previously determined magnitude values most intensity centers for earthquakes with poorly known epicenters lay within their estimated epicentral error ellipses for historic earthquakes with known instrumental magnitudes magnitude estimated from intensity differed by an average of 0 5 south central 1 0 interior and 0 05 southeast magnitude units these results indicate that although intensity data in alaska are sparse they can be used to estimate earthquake locations and magnitudes as additional intensity data become available the three broad regions of alaska can be further subdivided to reflect areas of similar geology and stress orientation and new attenuation relationships can be developed i also anticipate that additional intensity data will allow the development of site specific corrections to further improve epicentral and magnitude estimates from mmi data

morphodynamics of intermittently open closed coastal lagoon entrances new insights and a conceptual model abstract ocean entrances to coastal lakes and lagoons are a complex sensitive and important part of the coastal environment they provide estuarine water exchange between inland waterways and the open ocean and are increasingly the focus of intense urban and industrial development coastal lagoons that are only intermittently connected to the ocean are particularly sensitive during periods of closure water quality issues are exacerbated along with the increased risk of flooding mechanical clearance was undertaken in 2006 at the ocean entrance to narrabeen lagoon sydney australia historically this site has intermittently opened and closed both naturally and mechanically with the ingress of marine sand into the entrance restricting water exchange between the estuary and the ocean this instantaneous reset of the system provided a unique opportunity to monitor and quantify generic inlet sedimentation processes and mechanisms an intensive data collection campaign was undertaken for one entire year following the clearance this dataset includes current and water level measurements calculation of the alongshore sediment supply and regular highly detailed morphological surveys of the infilling lagoon entrance system this contribution utilises this unique dataset to quantify the sediment ingress volumes rates and pathways within the accreting flood tide delta of the lagoon entrance it was found that ingress of sand into the system proceeds via a rapid landward infilling process as opposed to backfilling toward the ocean with the evolution of the flood tide delta occurring in distinct phases the location of the divergence point of the flood tidal current the amount of available accommodation space within the entrance system and the influence of storm events were found to be key factors in the evolving morphodynamics of this intermittently open closed coastal lagoon

surface rupture on the denali fault interpreted from tree damage during the 1912 delta river mw 7 2 7 4 earthquake implications for the 2002 denali fault earthquake slip distribution during the 3 november 2002 denali fault earthquake surface rupture propagated through a small old growth forest in the delta river valley and damaged many trees growing on the fault damage was principally the result of fault offset of tree roots and tilting of trees some trees were split by surface faults that intersected the base of their trunks or large taproots a few trees appear to have been damaged by strong shaking many of the older trees damaged in 2002 were deformed and scarred some of these scarred trees exhibit past damage indicative of surface faulting and have abrupt changes in their annual ring patterns that coincide with the past damage annual ring counts from several of these older scarred trees indicate the damage was caused by surface rupture on the denali fault in 1912 the only earthquake of sufficient magnitude that fits the requirements for timing and general location as recorded by the damaged trees is a widely felt m s 7 2 7 4 earthquake on 6 july 1912 informally referred to as the 1912 delta river earthquake seismologic data and intensity distribution for the 1912 delta river earthquake indicate that its epicenter was within 60 90 km of the delta river and that rupture probably propagated toward the west inferred fault length displacement and rupture direction suggest the 1912 rupture was probably largely coincident with the western lower slip section of the 2002 rupture

regional intensity attenuation models for france and the estimation of magnitude and location of historical earthquakes summary intensity assignments for 33 calibration earthquakes were used to develop intensity attenuation models for the alps armorican provence pyrenees and rhine regions of france intensity decreases withmost rapidly in the french alps provence and pyrenees regions and least rapidly in the armorican and rhine regions the comparable armorican and rhine region attenuation models are aggregated into a french stable continental region model and the com parable provence and pyrenees region models are aggregated into a southern france model we analyse msk intensity assignments using the technique of bakun wentworth which provides an objective method for estimating epicentral location and intensity magnitude m i m i for the 1356 october 18 earthquake in the french stable continental region is 6 6 for a location near basle switzerland and moment magnitude m is 5 9 7 2 at the 95 per cent 2 confidence level m i for the 1909 june 11 trevaresse lambesc earthquake near marseilles in the southern france region is 5 5 and m is 4 9 6 0 at the 95 per cent confidence level bootstrap resampling techniques are used to calculate objective reproducible 67 per cent and 95 per cent confidence regions for the locations of historical earthquakes these confidence re gions for location provide an attractive alternative to the macroseismic epicentre and qualitative location uncertainties used heretofore

magnitude and location of historical earthquakes in japan and implications for the 1855 ansei edo earthquake 1 japan meteorological agency jma intensity assignments ijma are used to derive intensity attenuation models suitable for estimating the location and an intensity magnitude mjma for historical earthquakes in japan the intensity for shallow crustal earthquakes on honshu is equal to 1 89 1 42mjma 0 00887 h 1 66log h where mjma is the jma magnitude h 2 h2 1 2 and and h are epicentral distance and focal depth km respectively four earthquakes located near the japan trench were used to develop a subducting plate intensity attenuation model where intensity is equal to 8 33 2 19mjma 0 00550 h 1 14 log h the ijma assignments for the mjma7 9 great 1923 kanto earthquake on the philippine sea eurasian plate interface are consistent with the subducting plate model using the subducting plate model and 226 ijma iv vi assignments the location of the intensity center is 25 km north of the epicenter mjma is 7 7 and mjma is 7 3 8 0 at the 1 confidence level intensity assignments and reported aftershock activity for the enigmatic 11 november 1855 ansei edo earthquake are consistent with an mjma 7 2 philippine sea eurasian interplate source or philippine sea intraslab source at about 30 km depth if the 1855 earthquake was a philippine sea eurasian interplate event the intensity center was adjacent to and downdip of the rupture area of the great 1923 kanto earthquake suggesting that the 1855 and 1923 events ruptured adjoining sections of the philippine sea eurasian plate interface

seismicity of the prince william sound region for over thirty years following the 1964 great alaskan earthquake in this paper we present results of body wave form modeling of 19 earthquakes generally m b 5 7 occurring from 1964 to 1983 in the vicinity and down dip of the large asperity within the prince william sound region that ruptured in 1964 these data are supplemented with source parameters from studies of more recent post 1980 events our results suggest that moderate earthquakes which occurred in the region between 1964 and 1984 were predominantly located in the vicinity of the prince william sound asperity and could be assigned to two groups the first group consists of events occurring above the plate interface within prince william sound along reverse faults or low angle thrusts the second group occurs at 35 to 60 km depth in the region north of prince william sound and represents normal to normal oblique faulting within the subducted pacific crust or upper mantle these earthquakes occur below the northern edge of the 1964 asperity in a region where the subducting plate undergoes a rapid change in strike and dip a third group of events occurs in cook inlet well down dip of the 1964 asperity and below the plate interface these events exhibit a variety of mechanisms and many at depths of 50 to 70 km may be associated with complexities in the shape of the downgoing slab most of the cook inlet events occurred after 1984 whereas a few events of similar magnitude have occurred in the vicinity of the prince william sound asperity since 1984

a determination of source properties of large intraplate earthquakes in alaska historically large and potentially hazardous earthquakes have occurred within the interior of alaska however most have not been adequately studied using modern methods of waveform modeling the 22 july 1937 16 october 1947 and 7 april 1958 earthquakes are three of the largest events known to have occurred within central alaska ms 7 3 ms 7 2 andms 7 3 respectively we analyzed teleseismic body waves to gain information about the focal parameters of these events in order to deconvolve the source time functions from teleseismic records we first attempted to improve upon the published focal mechanisms for each event synthetic seismograms were computed for different source parameters using the reflectivity method a search was completed which compared the hand digitized data with a suite of synthetic traces covering the complete parameter space of strike dip and slip direction in this way the focal mechanism showing the maximum correlation between the observed and calculated traces was found source time functions i e the moment release as a function of time were then deconvolved from teleseismic records for the three historical earthquakes using the focal mechanisms which best fit the data from these deconvolutions we also recovered the depth of the events and their seismic moments the earthquakes were all found to have a shallow foci with depths of less than 10 km

rampart seismic zone of central alaska abstract this paper describes the characteristics of the rampart seismic zone by means of the aftershock sequence of the rampart earthquake m l 6 8 which occurred in central alaska on 29 october 1968 the magnitudes of the aftershocks ranged from about 1 6 to 4 4 which yielded a b value of 0 96 0 09 the locations of the aftershocks outline a nne ssw trending aftershock zone about 50 km long which coincides with the offset of the kaltag fault from the victoria creek fault the rupture zone dips steeply 80 to the west and extends from the surface to a depth of about 10 km fault plane solutions for a group of selected aftershocks which occurred over a period of 22 days after the main shock show simultaneous occurrences of strike slip and normal faults a comparison of the trends in seismicity between the neighboring areas shows that the rampart seismic zone lies outside the area of underthrusting of the lithospheric plate in southcentral and central alaska the seismic zone outlined by the aftershock sequence appears to represent the formation of an intraplate fracture caused by regional northwest compression