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

lacustrine fan deltaic sedimentation in a proterozoic rift basin the sopa brumadinho tectonosequence southeastern brazil abstract the sopa brumadinho tectonosequence 100 to 200 m thick is the fourth unit in ascending order of the up to 2000 m thick mesoproterozoic espinhaco supergroup representing the depositional products of the third and main phase of the rift stage of the espinhaco basin the sopa brumadinho tectonosequence in the study area consists of diamond bearing lacustrine fan delta deposits bounded by prominent angular and erosional unconformities detailed lithofacies studies were carried out in the central part of the southern serra do espinhatco southeastern brazil to characterize the paleogeography and basin fill architecture of the sopa brumadinho tectonosequence thirteen lithofacies are present massive clast supported conglomerates lithofacies ug cs inversely graded clastsupported conglomerates lithofacies ig cs normally graded clast supported conglomerates lithofacies ng cs massive to crudely stratified clast supported conglomerates lithofacies cs cs sandy matrix supported conglomerates lithofacies s ms muddy matrix supported conglomerates lithofacies m ms talus breccia clast supported conglomerates lithofacies tb cs massive sandstones lithofacies sm horizontal stratified sandstones lithofacies sh trough cross stratified sandstones lithofacies st planar cross stratified sandstones lithofacies sp graded stratified sandstones lithofacies sg and pelites lithofacies p they represent the products of several types of subaerial and subaqueous sediment gravity flows ranging from turbidity currents to cohesive debris flows and ephemeral braided streams the deposits are usually arranged in coarsening to fining upward tectono depositional intervals each tectono depositional interval represents a progradational lobe which starts at the base with lacustrine pelites and evolves with time from distal subaqueous to proximal subaerial characteristics the fining upward part represents the abandonment phase of the depositional lobes the origin characteristics distribution and spatial arrangement of the various lithofacies the interbedding of gravityflow and stream flow deposits the predominance of debris flow conglomerates over aqueous current formed ones the semi radial fan like dispersion pattern of the paleocurrents and the recognition of associated subaerial and subaqueous depositional settings are all indicative of a lacustrine alluvial fan fan delta environment or a fan delta system an interplay between several intrabasinal and extrabasinal controls probably determined the fan evolution the sedimentation of the lacustrine fan delta systems of the sopa brumadinho tectonosequence probably took place in a n s elongated continental rift basin compartmentalized by n s trending normal faults and w e trending transfer faults under a tropical semi arid climate the basin fill architecture was probably determined by episodic subsidence clockwise block tilting and asymmetric graben evolution as well as by inherited characteristics of the source area additionally a new descriptive scheme for classification of conglomerate lithofacies is here proposed

seismic energy distribution in latitude and a possible tidal stress explanation abstract this paper utilizes a statistical technique to investigate the global seismic energy distribution in latitude the energy distribution in latitude has two peaks one in each of the northern and southern hemispheres with an axis of symmetry at about 10 n the two peaks for shallow earthquakes have an interval of 90 while those for intermediate and deep ones concentrate in low latitudes the twin peak distribution in energy of intermediate and deep earthquakes becomes more apparent with increasing depth almost no energy is released in the north and south pole areas the energy released in the northern hemisphere is about 30 greater than that in the southern hemisphere except for the focal depths from 100 to 150 km through a study of the shear stress component caused by the corresponding long period lunisolar potential it is found that the shear stress distribution due to lunisolar constant flattering wave m0s0 coincides with some of the above phenomena we conclude that the long period tidal shear stress may be one of the possible causes for the seismic energy release or a triggering effect

long term seismic behavior of the focal and adjacent regions of great earthquakes during the time between two successive shocks we analyze the spatial temporal energy distribution of shallow depth h 70 km seismicity surface wave magnitude ms 7 occurring in the focal and adjacent regions of very great shallow earthquakes rupture lengths of the order of hundreds of kilometers in the circum pacific seismic belt for as many decades as possible before and after the occurrence of the main shock for this purpose we have revised the catalog of data for the world instrumental seismicity 1900 1995 by removing a series of heterogeneities in the earthquake reporting and magnitude determination this revised catalog is fairly complete for earthquakes with m 7 since early in the century our findings indicate that once a main shock aftershock sequence occurs the focal region enters a period of relative quiescence for large ms 7 earthquakes significant seismic activity ms 7 occurs during many decades prior to the next main shock this activity is fairly continuous or random in time and lasts until the onset of the main event but clusters in space around the ends of the forthcoming rupture and or in the vicinity of the principal epicenter except in the case of rare bilateral breaks the main epicenter is located at one of these ends thus major portions of the rupture zone experience no events with ms 7 during the seismic cycle larger aftershocks also cluster near the edges of the rupture and near the principal epicenter preshock activity minutes to weeks before the main shock if any occurs in general near the main epicenter we also find that the nucleation and ends of the rupture often coincide in space with recognizable geometrical and or geological inhomogeneities barriers existing in the lithosphere it appears that while strain energy accumulates high stress concentrations often occur at the ends of the future rupture zone which results in the long term foreshock activity and in the subsequent initiation of the main rupture from within those regions we suggest a simple mechanical model that explains the observed pattern of earthquake occurrence for both unilateral and bilateral ruptures in all cases of great earthquakes that have occurred this century for which a long and complete to a level of 2 to 3 orders of magnitude smaller than the moment of the main shock catalog of prior seismicity exists we can not recognize any statistically significant quiescent or doughnut patterns in the preceding seismicity at the ms 7 level

comparison of seismic moment release rates along different types of plate boundaries summary this is a global survey of seismic moment release rates scalar moment length time along five categories of plate boundaries for shallow earthquakes we evaluate divergent transcurrent and convergent boundaries for deep earthquakes we consider separately boundaries where the deepest seismicity is intermediate 300 km or deep focus 500 600 km the objective is to evaluate the typical range of rates observed and present the results in a form where it is straightforward to compare factors that affect rates in the different environments for earthquakes occurring 1977 2005 the data are scalar moments from the global centroid moment tensor catalogue for earthquakes 1900 1976 we use a standard formula to obtain moment

crustal deformation at the southernmost part of the ryukyu subduction east taiwan as revealed by new marine seismic experiments abstract the southernmost part of the ryukyu subduction where the philippine sea plate is subducting under the eurasian plate is known to be a very seismically active region of transition from a north dipping subduction along the ryukyu subduction to an se nw collision along the taiwanese orogenic wedge in this paper we will focus on the ryukyu forearc area close to taiwan where the deformation is paroxysmal in order to decipher the nature of the seismic deformation in this region a three month passive experiment combining 22 ocean bottom seismometers and 51 onland stations has been led starting from an a priori heterogeneous model we have obtained 801 well located earthquake hypocenters a precise p wave tomography model and 14 focal mechanisms the seismicity along the ryukyu forearc is mainly located not only in the vicinity of the interplate seismogenic zone isz but also within both the subducting psp and the overriding plate seismicity within the upper plate is essentially localized east of nanao basin where nw se extension occurs and northwest of the hoping basin where strike slip dominates as revealed by both the p wave velocity structure and the newly derived seismicity we argue that a sub vertical step offsetting the subducting psp around 10 km may support the presence of a trench parallel tear the psp also undergoes extension in its upper part that is probably caused by buckling and slab pull the p wave velocity structure reveals three other major features 1 a continuity between the central range and the ryukyu arc with a shallower moho 30 km depth between 122 3 n and 122 5 n along the ryukyu arc 2 high p wave velocities along the eastern side of the central range and 3 two bodies with similar high crustal velocities 6 5 7 0 km s at 12 18 km depths embedded within the ryukyu arc basement just north of hoping basin and north of the nanao basin

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

scaling law and its applications to earthquake statistical relations abstract the spectra of the far field body wave displacement for earthquakes of various magnitudes have been obtained using a two dimensional faulting model on a rectangular fault there are three corner frequencies f c 1 f c 2 and f c 3 in the displacement spectra f c 1 and f c 2 relate to faulting times for the long and wide directions on the rectangular fault respectively and f c 3 corresponds to the rise time of the source time function according to these three corner frequency values four spectral regions are defined u u 0 f 0 f f c 1 in the first region u 1 f f c 1 f f c 2 in the second region u 1 f 2 f c 2 f f c 3 in the third region and u 1 f 3 f f c 3 in the fourth region this results in different source parameter relations for different magnitude ranges i e different seismic moment ranges because the attenuation rates depend on frequency it is supposed that earthquake faulting is satisfied by three conditions of geometrical similarity stress environment and dynamic similarity therefore seismic moment faulting time along the length and width of the fault and rise time can all be scaled with fault length the constants in the scaling relations can be determined from seismic moment data for about 800 earthquakes that occurred during 1981 1983 and are given by dziewonski and woodhouse 1983 and m s and m b data from the isc bulletin thus the source parameter relations between m s and m b m s and m l m b and m l log m o and log s fault area log s and m s log l fault length and m s and log d average dislocation and m s can be deduced from the scaling law rather than from pure statistical relations these relations are statistically consistent with the observed data the average rupture velocity of the fault can also be estimated from the scaling law it is 2 65 km s the total time of rupture is 0 35 s km l km which is close to that estimated by kanamori 1981 and the dislocation slip rate is 287 1143 cm s

earthquake history of the sumatran fault indonesia since 1892 derived from relocation of large earthquakes abstract we map the fault planes of m 7 0 earthquakes along the sumatran fault in sumatra western indonesia for the period since 1892 to obtain precise hypocenter locations of large earthquakes and identify fault planes of m 7 0 earthquakes we relocated 27 m 6 0 earthquakes from 1921 to 2012 using the modified joint hypocenter determination method we found that six m 7 0 events appear to have occurred on segments of the sumatran fault as follows kumering for the 1933 m s 7 5 event the northwestern and southeastern parts of tripa for the 1935 m s 7 0 and 1936 m s 7 2 events respectively the southeastern half of sunda for the april 1943 m s 7 1 event ketaun for the first m s 7 3 event of the june 1943 doublet and suliti and sumani for the second m s 7 6 event of the june 1943 doublet we also identified the faults of four m 7 0 earthquakes between 1892 and 1920 by using information on crustal deformation and damage distributions from the results of earthquake locations between 1892 and 2012 and the corresponding fault lengths of m 7 0 earthquakes we have interpreted the large m 7 0 earthquake history of the sumatran fault for the past 120 years possible seismic gaps for m 7 0 earthquakes along the sumatran fault are the northern half of the sunda segment and the semangko dikit sianok barumun toru renun aceh and seulimeum segments

source investigation and comparison of the 1939 1946 1949 and 1965 earthquakes cascadia subduction zone western washington over the past 65 years intraslab earthquakes have caused the most significant damage in the western washington region this study examines regional and teleseismic seismograms for four historic suspected intraslab events of m 5 5 occurring within the cascadia subduction zone in 1939 south seattle 1946 puget sound 1949 olympia and 1965 sea tac to better determine the source locations mechanisms and rupture histories of these events our study is aided by digital seismograms of post 1990 intraslab events with well determined focal depths and focal mechanisms that were recorded in the same locations as the historic events thus the recent events were used as empirical greens functions to study the historic events our results suggest that the 1946 earthquake is not an intraslab event that the 1939 event closely resembles the 1965 event and that the 1949 event is similar to the 2001 nisqually earthquake although the 1949 event appears to have ruptured toward the south causing significantly more damage than the nisqually event these results suggest that earthquakes periodically rupture along the same or similarly oriented faults within the subducting slab

long term earthquake prediction in the circum pacific convergent belt investigation of the time dependent seismicity in 274 seismogenic regions of the entire continental fracture system indicates that strong shallow earthquakes in each region exhibit short as well as intermediate term time clustering duration extending to several years which follow a power law time distribution mainshocks however interevent times of the order of decades show a quasiperiodic behaviour and follow the regional time and magnitude predictable seismicity model this model is expressed by the following formulas begin gathered log t t 0 19 m min 0 33 m p 0 39 log m 0 q hfill m f 0 73 m min 0 28 m p 0 40 log m 0 m hfill end gathered which relate the interevent time tt in years and the surface wave magnitude mf of the following mainshock with the magnitude mmin of the smallest mainshock considered the magnitude mp of the preceded mainshock and the moment rate m0 in dyn cm yr 1 in a seismogenic region the values of the parametersq andm vary from area to area the basic properties of this model are described and problems related to its physical significance are discussed

an alternative view of the bayesian probabilistic prediction of strong shocks in the hellenic arc abstract a bayesian discrete distribution as developed by ferraes 1985 is applied to predict the inter arrival times for strong shocks in the hellenic arc on the basis of nine samples of shocks with seismotectonic locations very different from those used by ferraes the results suggest an alternative view of the bayesian probabilistic prediction of strong earthquakes in the hellenic arc and can be summed up as follows 1 a maximum final bayesian probabilities of various inter arrival times in a given seismotectonic segment are very dependent on the data set used and particularly on its time length 2 b when using this method to determine the time intervals during which large shocks are to be expected in the western and eastern hellenic arcs it is very difficult to estimate intervals of less than a decade the determination of the occurrence time even in the long term sense remains the major problem in the prediction of these shocks 3 c bayesian probabilities in conjunction with seismicity observations indicate that large intermediate depth earthquakes in the hellenic arc are long overdue shocks of this sort can be expected to occur in the next few years it is also pointed out that although bayesian type predictions may be useful for engineering purposes they are not a suitable basis for making specific predictions or taking special precautions

the earthquake and tsunami of 1865 november 17 evidence for far field tsunami hazard from tonga summary historical reports of an earthquake in tonga in 1865 november identify it as the only event from that subduction zone which generated a far field tsunami observable without instruments run up heights reached 2 m in rarotonga and 80 cm in the marquesas islands hydrodynamic simulations require a moment of 4 1028 dyn cm a value significantly larger than previous estimates of the maximum size of earthquake to be expected at the tonga subduction zone this warrants an upwards re evaluation of the tsunami risk from tonga to the cook islands and the various polynesian chains which had hitherto been regarded as minor

re evaluation of the surface ruptures of the november 1951 earthquake series in eastern taiwan and its neotectonic implications the earthquakes of november 1951 constitute the most destructive seismic episode in the recorded history of the longitudinal valley eastern taiwan however information about their source parameters is sparse to understand the relationship between the 1951 ruptures and new interpretations of the regional neotectonic architecture of the longitudinal valley we re evaluated the november 1951 ruptures by analyzing old documents reports and photographs and by interviewing local residents who experienced the earthquake as a result we have revised significantly the rupture map previously published we divide the surface ruptures from south to north into the chihshang yuli and rueisuei sections the first shock of the 1951 series probably resulted from the chihshang rupture and the second shock probably resulted from the yuli and rueisuei ruptures the lengths of these ruptures indicate that the two shocks had similar magnitudes the chihshang and rueisuei ruptures are along segments of the longitudinal valley fault a left lateral oblique fault along which the coastal range thrusts westward over the longitudinal valley the yuli rupture on the other hand appears to be part of a separate left lateral strike slip yuli fault which traverses the middle of the longitudinal valley the complex behavior of these structures and interaction between them are important in understanding the future seismic hazard of the area

quantification of major earthquake tsunamis of the japan sea abstract the size of major tsunamigenic earthquakes which occurred in the japan sea is quantified on the basis of seismic and tsunamigenic source parameters the tsunami magnitude mt is determined from the instrumental tsunami wave amplitudes the mt values thus obtained are on average 0 2 units larger than the values of moment magnitude mw though the mt scale has originally been adjusted to agree with mw moreover the volume of displaced water at the source is on average 2 3 times as large as that for the pacific events with a comparable mw nevertheless the observed height of the sea level disturbance at the source is found consistent with the amount of crustal deformation computed for the seismic fault models these results indicate that the tsunami source potential itself is large for mw in comparison with the pacific events the large source potential is explained in terms of the effective difference both in the rigidity of the source medium and in the geometry of the fault motion for the japan sea events the mt scale still provides the physical measure of the tsunami potential and mt minus 0 2 corresponds to mw this predicts that the maximum amplitude of tsunami waves from japan sea earthquakes is at least two times as large as that from pacific earthquakes with a comparable mw

progradational sequences in miocene shoreline deposits southeastern caliente range california abstract an exceptionally well exposed marine nonmarine transition in middle miocene strata exists in the southeastern caliente range california about 50 individual progradational sequences form a succession that ranges in thickness from approximately 1000 m where predominantly nonmarine to more than 2500 m where predominantly marine paleogeographic evidence in basalt flows near the top of the succession and in overlying fluvial deposits indicates that these middle miocene strata were deposited across a north northwest trending shoreline a complete progradational sequence typically is several meters to a few tens of meters thick and includes strata that represent three intertonguing stratigraphic units individual sequences generally rest on a thin gravel deposit interpreted as a transgressive lag on an erosional surface the gravel is overlain by structureless siltstone or fine grained sandstone deposited at water depths where the rate of faunal mixing exceeded that of production of structures by physical processes these rocks grade upward into bedded fine sandstone deposited closer to shore where physical processes exceeded bioturbation crossbedded lenses of coarse sand or fine gravel in the upper part of this facies suggest the presence of fairly long period surface waves the bedded fine sandstone is sharply ove lain by a cross bedded coarse sandstone facies that is interpreted as a combined offshore bar rip channel surf zone assemblage cross strata dip dominantly offshore suggesting substantial deposition from rip currents a secondary shoreparallel mode of cross strata direction suggests longshore currents produced by surface waves from the northwest the crossbedded coarse grained sandstone grades upward into planar bedded medium grained sandstone that is interpreted as a beach foreshore this facies grades upward through structureless medium grained sandstone into nonmarine or lagoonal red and green mudstone of the caliente formation the middle miocene succession was deposited in a subsiding basin that was otherwise remarkably stable tectonically the position of the strand line differed no more than a few kilometers through a period of 1 to 3 m y the average duration of the transgressive regressive cycles a few tens of thousands of years together with their distribution in groups of three or four in the lower two thirds of the succession is consistent with the pattern of long term climatic cycles produced by periodicity of the earth s solar orbit and may be related to eustatic sea level changes attendant to the development of the antarctic ice cap changes in the pattern of progradation in the upper part of the succession and nearby basaltic eruptions may have been precursors to the onset of movement along th san andreas fault in this area 12 14 m y ago

physical size of tsunamigenic earthquakes of the northwestern pacific abstract the new scale m t of tsunami magnitude is a reliable measure of the seismic moment of a tsunamigenic earthquake as well as the overall strength of a tsunami source this m t scale was originally defined by abe 1979 in terms of maximum tsunami amplitudes at large distances from the source a method is developed whereby it is possible to determine m t at small distances on the basis of the regional tsunami data obtained at 30 tide stations in japan the relation between log h maximum amplitude m and log a distance of not less than 100 km away from the source km is found to be linear with a slope close to 1 0 using three tsunamigenic earthquakes with known moment magnitudes m w for calibration the relation m t log h log d is obtained where d is 5 80 for single amplitude crest or trough data and 5 55 for double amplitude crest to trough data using a number of tsunami amplitude data m t is assigned to 80 tsunamigenic earthquakes that occurred in the northwestern pacific mostly in japan during the period from 1894 to 1981 the m t values are found to be essentially equivalent to m w for 25 events with known m w the 1952 kamchatka earthquake has the largest m t 9 0 of all the 80 events listed at least seven unusual earthquakes which generated disproportionately large tsunamis for their surface wave magnitude m s are identified from the relation from the viewpoint of tsunami hazard reduction the present results provide a quantitative basis for predicting maximum tsunami amplitudes at a particular site

a simple discrete element model for large multiplet earthquakes adjacent segments of the plate boundary may fail separately as earthquakes that occur very close in time when the time between events is a small fraction of the recurrence interval then the sequence is referred to as doublets or multiplets in the first part of this paper we determine the frequency of occurrence of large multiplet earthquakes we count the number of multiplet earthquakes present in the abe catalogue with aftershocks removed ms 7 1 using a series of space time and magnitude filters we compare this number to the number of multiplet earthquakes present in the abe catalogue where origin times of earthquakes are randomized and epicentral locations and magnitudes are kept constant the difference between the observed and random number of multiplets gives us the percentage of multiplets that do not occur randomly we find that this percentage ranges from 2 to 7 of all large earthquakes based on the best choice of space time and magnitude filters in the second part of this paper we model multiplet earthquakes using three simple frictional slider models the models consist of slider blocks resting on a frictional conveyer belt and interconnected by springs the seismogenic portion of the plate interface is represented by blocks that exhibit stick slip behavior asperities aseismic creep within the seismogenic zone is represented by creepers the creepers are blocks that obey a simple linear creep law the three models differ in that the positions of the creeping blocks within the system of asperities and creepers are different we find that model 3 produces a complex sequence of events consisting of single double and multiplet earthquakes these synthetic sequences of events are comparable to the earthquake cycle observed along nankai trough model 3 produces a high percentage of multiplet earthquakes when the creeper is allowed to relax within a small fraction of the maximum recurrence time of the event sequence this implies that the details of the frictional law invoked for the creeper blocks does not influence the model results significantly the time evolution of model 3 is compared to the postseismic phase of the loading cycle at muroto point japan we suggest that the rapid postseismic deformation that occurs immediately after the nankaido earthquake is due to a rapid creeping zone that is in this region

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

the 16 april 2016 mw 7 8 ms 7 5 ecuador earthquake a quasi repeat of the 1942 ms 7 5 earthquake and partial re rupture of the 1906 ms 8 6 colombia ecuador earthquake the 2016 ecuador m w 7 8 earthquake ruptured the subduction zone boundary between the nazca and south american plates joint modeling of seismic and tsunami observations indicates an 120 km long rupture area beneath the coastline north of the 1998 m w 7 2 rupture the slip distribution reveals two discrete asperities near the hypocenter and around the equator their locations and the patchy pattern are consistent with the prior interseismic geodetic strain which showed highly locked patches also beneath the coastline aftershocks cluster along two streaks one aligned nearly parallel to the plate convergence direction up dip of the main slip patches and the other on a trench perpendicular lineation south of the 1958 rupture zone comparisons of seismic waveforms and magnitudes show that the 2016 event and 1942 earthquakes have similar surface wave magnitude m s 7 5 overlapping rupture areas and similar main pulses of moment rate the same area ruptured as the southernmost portion of the larger earthquake of 1906 m w 8 6 m s 8 6 the seismic behavior reflects persistent heterogeneous frictional properties of the colombia ecuador megathrust

isc gem global instrumental earthquake catalogue 1900 2009 i data collection from early instrumental seismological bulletins abstract in order to produce a new global reference earthquake catalogue based on instrumental data covering the last 100 years of global earthquakes we collected digitized and processed an unprecedented amount of printed early instrumental seismological bulletins with fundamental parametric data for relocating and reassessing the magnitude of earthquakes that occurred in the period between 1904 and 1970 this effort was necessary in order to produce an earthquake catalogue with locations and magnitudes as homogeneous as possible the parametric data obtained and processed during this work fills a large gap in electronic bulletin data availability this new dataset complements the data publicly available in the international seismological centre isc bulletin starting in 1964 with respect to the amplitude period data necessary to re compute magnitude we searched through the global collection of printed bulletins stored at the isc and entered relevant station parametric data into the database as a result over 110 000 surface and body wave amplitude period pairs for re computing standard magnitudes m s and m b were added to the isc database to facilitate earthquake relocation different sources have been used to retrieve body wave arrival times these were entered into the database using optical character recognition methods international seismological summary 1918 1959 or manually e g british association for the advancement of science 1913 1917 in total 1 000 000 phase arrival times were added to the isc database for large earthquakes that occurred in the time interval 1904 1970 the selection of earthquakes for which data was added depends on time period and magnitude for the early years of last century until 1917 only very large earthquakes were selected for processing m 7 5 whereas in the periods 1918 1959 and 1960 2009 the magnitude thresholds are 6 25 and 5 5 respectively such a selection was mainly dictated by limitations in time and funding although the newly available parametric data is only a subset of the station data available in the printed bulletins its electronic availability will be important for any future study of earthquakes that occurred during the early instrumental period

nonlinear characteristics of paleoseismicity in china detailed studies of historical seismicity and paleoseismological data for major late quaternary faults in china reveal spatial and temporal patterns in paleoseismic activity associated with these faults analysis of space time distributions of late quaternary faults and consideration of new models for deformation of the asian continent provide a basis for proposing a division of china and surrounding areas into five active tectonic provinces slip rates for active faults are highest in the himalayan collision zone between the indian and eurasian plates and gradually decrease away from the collision zone into the adjacent active tectonic provinces paleoearthquake recurrence intervals in the active tectonic provinces of china reflect seismogenic properties that are closely related to the position of these provinces relative to the converging indian and eurasian plates average recurrence intervals are 2000 years to as little as 310 900 years for active faults in the qinghai tibetan active tectonic province whereas recurrence intervals are 2000 4500 years in the xinjiang active tectonic province and longer than 2000 years to as much as 7250 years in the north china active tectonic province although average recurrence intervals are closely related to the slip rates of late quaternary faults no simple linear relationship exists between recurrence interval and slip rate further analysis of paleoseismicity on major active faults shows that there are temporal variations in recurrence intervals the case studies also indicate that for some provinces faults or fault segments there are three paleoseismic patterns linear logarithmic and stepped in the logarithmic and stepped patterns the earthquake temporal sequence is characterized by active periods earthquake clusters with relatively short recurrence intervals and quiet periods lack of clustering and relatively long recurrence intervals

maximum magnitude mmax in the central and eastern united states for the 2014 u s geological survey hazard model probabilistic seismic hazard assessment psha requires an estimate of m max the moment magnitude m of the largest earthquake that could occur within a specified area sparse seismicity hinders m max estimation in the central and eastern united states ceus and tectonically similar regions worldwide stable continental regions scrs a new global catalog of moderate to large scr earthquakes is analyzed with minimal assumptions about enigmatic geologic controls on scr m max an earlier observation that scr earthquakes of m 7 0 and larger occur in young 250 23 ma passive continental margins and associated rifts but not in cratons is not strongly supported by the new catalog scr earthquakes of m 7 5 and larger are slightly more numerous and reach slightly higher m in young passive margins and rifts than in cratons however overall histograms of m from young margins and rifts and from cratons are statistically indistinguishable this conclusion is robust under uncertainties in m the locations of scr boundaries and which of two available global scr catalogs is used the conclusion stems largely from recent findings that 1 large southeast asian earthquakes once thought to be scr were in actively deforming crust and 2 long escarpments in cratonic australia were formed by prehistoric faulting the 2014 seismic hazard model of the u s geological survey represents ceus m max as four point probability distributions the distributions have weighted averages of m 7 0 in cratons and m 7 4 in passive margins and rifts these weighted averages are consistent with m max estimates of other scr pshas of the ceus southeastern canada australia and india

the december 28 1908 messina straits southern italy earthquake waveform modeling of regional seismograms the 1908 messina straits earthquake is one of the most catastrophic events in history there were 60 000 to more than 100 000 deaths and the cities of messina and reggio calabria on the opposite sides of the straits were almost completely destroyed during the last decades only low magnitude events occurred in the area the 1908 earthquake is then crucial for understanding the mode of stress release in the area we collected and digitized several regional seismograms of this event recorded in central europe with the aim of studying the source characteristics in order to separate the path effects we analyzed recent events with simple and known sources owing to the small azimuth range spanned by the available stations we could not determine a fault plane solution for the messina straits event nor discriminate between the published focal mechanisms however the normal fault character of the rupture is confirmed by inverting the historical p waveforms we derived source time functions and obtained a seismic moment of 5 38 2 16 1019 n m mw 7 1 this is in good agreement with the results obtained by several authors from the inversion of the historical leveling data this value is confirmed by the sh wave modeling which also allowed the assessment of the unilateral northward character of the rupture propagation along an 43 km fault finally we applied a simple rupture model in order to derive the slip distribution along the fault the resulting function is in good correspondence with the geodetic inversions performed by boschi et al 1989 and de natale and pingue 1991 in particular a maximum slip of 4 m is located in proximity of the center of the slipped area the high dislocation patch beneath the messina harbor as depicted by de natale and pingue is not confirmed by our analysis and is probably connected to surface collapse of some of the bench marks

seismic hazard evaluation for specific seismic regions of the world tsapanos t m and burton p w 1991 seismic hazard evaluation for specific seismic regions of the world tectonophysics 194 153 169 seismic hazard is estimated for fifty of the most seismically active countries of the world using the technique of gumbel s third asymptotic distribution of extreme values and hazard maps are produced for this purpose a catalogue of 9700 earthquakes with magnitudes m 2 5 5 has been compiled and earthquakes in the time period 1898 1985 are examined here an equal area grid point mesh of about 5 o latitude x 5 o longitude is chosen to represent the local seismicity this cell size corresponds approximately to the area of romania which is the smallest country examined the results estimate the most probable maximum magnitude for a time period of 85 years which exceeds magnitude 7 for all fifty of the cellular seismic regions and the contour maps and tables show its spatial variation and rank the countries in terms of overall relative seismic hazard the maps effectively produce a brief seismic hazard atlas

sedimentology of proterozoic cratonic sheet sandstones of the eastern canadian shield sims formation labrador canada abstract the upper lower proterozoic to middle proterozoic sims formation rests unconformably on lower proterozoic strata of the knob lake group of the labrador trough sequence the 700 m thick sims formation consists of basal fluvial arkoses and conglomerates about 100 m and an upper sheet like sand body about 600 m thick composed of quartz arenites and minor quartz clast conglomerates this upper unit is interpreted as beach shoreface tidal and shallow shelf deposits the lowest 70 m of the quartz arenite unit appear to be of fluvial origin but probably were formed by reworking of quartzose sands produced in coastal environments during a period of elevated sea level the lower sims formation probably represents molasse shed from either the hudson or labrador orogens rivers flowed northwest away from these upland areas the upper part of the sims formation records deposition during a period of slow steady sea level rise in an ocean that deepened to the west the sims formation outliers are remarkably similar to outliers of the sakami formation of northern quebec a unit that has a poorly constrained early to middle proterozoic age if these units are correlative a hypothesis supported mainly by identical facies and facies sequences then the transgressive quartz arenites would originally have covered an area of at least 200 000 km2

study of the properties of seismicity in the mexico region summary new statistics of seismic properties are investigated in space and time for the mexico region they are main events seismicity number of earthquakes with aftershocks excluded swarming property average magnitude another way to study the slope of the recurrence time law maximum magnitude average focal depth and comparative efficiency of earthquakes in surface and body waves generation known as creepex quite a number of anomalies of the spatial distributions of the statistics were found some of them have evident geophysical meaning the explanation of others is rather controversial and some others have no interpretation as yet the most interesting phenomena are as follows 1 the average focal depth distribution indicates a different trend for the benioff zone west of approximately 96ow longitude due north which fits the position of the neovolcanic belt 2 creepex clearly distinguishes different tectonic areas i e subduction zones with low values transform faults medium and ridges high 3 high swarming is related to places with young sedimentary geology the time pattern of those properties in places of strong earthquakes is quite consistent and includes a phase of concentration of stress indicated by quiescence in average and maximum magnitude and main events seismicity and also more efficient body wave generation and anomalous swarming this phase is followed by an apparent weakening of the material indicated by a higher efficiency in surface wave generation

an application of the time and magnitude predictable model for the long term prediction of strong shallow earthquakes in the japan area the country of japan and its surrounding area has been divided into 12 seismogenic sources on the basis of certain seismotectonic and geomorphological criteria in each of these sources interevent times between successive mainshocks with magnitudes equal to or larger than certain cutoff magnitudes were considered these interevent times as well as the magnitudes of the mainshocks have been used to determine the following relations log t t 0 30 m min 0 19 m p 0 18 log m 0 2 41 m f 0 88 m min 0 25 m p 0 46 log m 0 9 06 where tt is the interevent time measured in years m min is the surface wave magnitude of the smallest mainshock considered mp is the magnitude of the preceding mainshock mf is the magnitude of the following mainshock and m is the yearly released seismic moment in each source on the basis of these two relations and taking into account the time of occurrence and the magnitude of the last mainshock in each source time dependent conditional probabilities for the occurrence of the next large ms 7 5 shallow mainshocks in the 12 seismogenic sources during the next 10 yrs 1993 to 2002 and the magnitudes of the expected mainshocks are determined for seismogenic sources 5 fukushima 9 western honshu 7 southern hokkaido 1 ryukyu islands and 12 okushiri island relatively high probabilities p 10 0 5 were assigned it is of interest to note that in seismogenic source 12 okushiri for which an expected magnitude of 7 5 was calculated an earthquake with a magnitude of 7 6 national earthquake information center occurred on 12 july 1993

the october 1980 earthquake sequence near the new hebrides four large earthquakes occurred in 1980 in a seismic gap near the loyalty islands in the new hebrides at 3 25 ut on october 24 an event with m s 6 7 initiated the sequence three events m s 6 7 7 2 and 6 5 followed on the next day we investigated this sequence by using the seismicity first motion and waveform data and long period surface waves the first motion data constrain one of each pair of nodal planes with this constraint inversion of rayleigh and love wave spectra at 256 seconds determines the other nodal plane the mechanisms of all four events are almost pure thrust on a plane dipping about 20 degrees east and striking parallel to the local strike of the new hebrides trench the first day aftershocks indicate an initial rupture zone of about 2 000 km which is consistent with the estimated seismic moment of 3 10 27 dyne cm during the next two days the aftershock activity expanded to an area of 10 000 to 20 000 km in the directions both along and perpendicular to the trench within 5 hours after the third and largest event the initial rupture zone had become mostly quiescent modeling of waveforms suggests a body wave moment of between 0 5 and 1 0 10 27 dyne cm and a source process time of 11 seconds this pattern suggests that the initial rupture zone represents a zone of increased strength i e an asperity and the stress change due to failure of this asperity subsequently migrated outward during the two year period before the main event seismicity in the initial rupture zone was very low except near the point where the first mainshock initiated a very tight clustering of activity occurred there this pattern indicates gradual stress concentration near the asperity which finally failed during the mainshock sequence

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

seismicity and aseismic slip along the eltanin fracture zone table al is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 006 2 50 payment must accompany order the seismic history of the eltanin fracture zone on the pacific antarctic ridge for the years 1920 1981 shows that the seismic slip accumulated during this recording interval accounts for only a small fraction less than 10 of the amount of slip predicted by kinematic models of plate motion we propose that the remainder of the plate motion along the transform faults making up the eltanin system occurs as aseismic creep this property singles out the eltanin among transform systems where previous studies have found good agreement between seismic slip and predicted rates of motion the absence of record of any gigantic earthquakes and the geometry of the fault area reduce the likelihood of the eltanin rupturing along its entire length we interpret the eltanin fracture zone in the light of an asperity model involving small well separated asperities its segmented nature and creeplike behavior may be due to the presence of excess magma and possibly local upwelling which could also be involved in the mechanism of generation of the louisville ridge

microstructure changes of red clay during its loss and leakage in the karst rocky desertification area karst rocky desertification is a unique type of desertification caused by unreasonable human activities in a vulnerable ecological environment it has severely restrained the sustainable development of southwest china chenqi village which is the studied area in this paper has suffered karst rocky desertification for decades red clay samples were collected from different sites around this village and analyzed through mercury intrusion porosimetry mip and scanning electron microscope sem tests then the microstructure changes of soil during its loss and leakage were observed to study the impact of rainfall erosion and the mechanism of soil loss and leakage the results demonstrate that the land use patterns can change the distribution of micro small pores in soil the shrub grass land which is least exploited by human activities has the largest volume of micro small pores meanwhile soil leakage can change the distribution of medium large pores the soil from surface 0 15 cm which is deposited at the beginning of soil leakage has the largest volume of medium large pores pore surface fractural dimension is negatively correlated with human activity impact and positively correlated with the distribution of micro and small pores the microstructure can well represent different phases of soil loss and leakage as well as the soil breakage level

origin of thick first cycle quartz arenite successions evidence from the 1 7 ga ortega group northern new mexico abstract the 1700 ma old ortega group in northern new mexico represents a 1000 m thick succession of metamorphosed quartz arenites and subordinate pelites published ages of detrital zircon grains from the ortega group indicate that the sediments were derived mainly from 1760 1700 ma old volcano plutonic basement rocks and not from the archean wyoming province to the north evidence for recycling within the ortega group also is lacking consequently the ortega group quartz arenites are considered to be first cycle sediments the compositional and textural maturity of these sandstones is attributed to intense chemical and mechanical weathering abnormally high al contents of pelites within the ortega group imply intense chemical weathering in the provenance similar to present day low relief tropical regions quartz arenites in the ortega group were deposited exclusively within a shallow marine shelf environment influenced by tide storm and wave processes prolonged sediment transport especially on the tide dominated inner shelf in conjunction with inferred gradual subsidence optimized mechanical destruction of labile grains and rounding of quartz grains although the maturity of sediments in the ortega group can be accounted for the mode of origin of 850 m of quartz arenites remains enigmatic thick quartz arenite sequences of global distribution in the phanerozoic coincide with first order eustatic sea level rises world wide occurrences of 1700 ma old thick quartz arenite shelf successions suggest that the ortega group may have accumulated in response to a similar major eustatic sea level rise

assessment of the size of large and great historical earthquakes in peru a critical reappraisal of great historical earthquakes in peru is made in order to obtain quantitative estimates of rupture length seismic moment tsunami magnitude mt and moment magnitude mw newly collected information concerning several historical earthquakes permits the evaluation of macroseismic zones and from the size of these zones the estimation of length of rupture seismic moment and magnitude mw it is found that local tsunami data provide good quantitative estimates of mt and therefore an independent way of verifying macroseismic estimates of rupture length and seismic moment a space time diagram of great historical earthquakes shows the existence of three zones roughly corresponding to the segmentation of the nazca plate hasegawa and sacks 1981 subducting under peru the northern zone looks aseismic the central one is very complex it breaks either completely or in smaller segments and it may go through long quiescence periods the recurrence time for the southern segment the more regular one is of the order of one century

source process of the 1911 m8 0 chon kemin earthquake investigation results by analogue seismic records several destructive earthquakes have occurred in tien shan region at the beginning of 20th century however the detailed seismological characteristics especially source parameters of those earthquakes are still poorly investigated the chon kemin earthquake is the strongest instrumentally recorded earthquake in the tien shan region this earthquake has produced an approximately 200 km long system of surface ruptures along kemin chilik fault zone and killed about similar to 400 people several studies presented the different information on the earthquake epicentre location and magnitude and two different focal mechanisms were also published the reason for the limited knowledge of the source parameters for the chon kemin earthquake is the complexity of old analogue records processing digitization and analysis in this study the data from 23 seismic stations worldwide were collected and digitized the earthquake epicentre was relocated to 42 996na degrees and 77 367ea degrees the hypocentre depth is estimated between 10 and 20 km the magnitude was recalculated to m b 8 05 m s 7 94 and m w 8 02 the focal mechanism determined from amplitude ratios comparison of the observed and synthetic seismograms was str 264a degrees dip 52a degrees rake 98a degrees the apparent source time duration was between similar to 45 and similar to 70 s the maximum slip occurred 25 s after the beginning of the rupture two subevents were clearly detected from the waveforms with the scalar moment ratio between them of about 1 3 the third subevent was also detected with less certainty taking into account surface rupture information the fault geometry model with three patches was proposed based on scaling relations we conclude that the total rupture length was between similar to 260 and 300 km and a maximum rupture width could reach similar to 70 km

constraints on macquarie ridge tectonics provided by harvard focal mechanisms and teleseismic earthquake locations in this study we evaluate teleseismically determined focal mechanisms and epicenters for earthquakes along the macquarie ridge complex mrc from 45os to 61 os and 155oe to 168oe a region characterized by some previous investigators as undergoing subduction initiation from 65 centroid moment tensors reported by harvard we develop statistical guidelines for choosing 26 which represent better determined more reliable focal mechanisms for tectonic analysis although thrust mechanisms occur in the north near fiordland elsewhere along the mrc the better determined mechanisms virtually all indicate that present day motion along most of the mrc is strike slip this is consistent with sidescan sonar and multichannel reflection data collected between 50os and 57os on 1994 and 1996 cruises the active plate boundar3 zone appears to be quite narrow 5 km wide and no active compressional features can be observed on the seafloor if we determine a rotation pole for plate boundary motion using only slip vectors from better determined harvard mechanisms along the mrc the best fitting instantaneous pole is at 57 4os 179 4oe about 2 5 o north of the nuvel i australian pacific pole which averages motion over the last 3 0 my if the mrc pole was formerly farther south than at present this could explain the existence of relict features associated with crustal shortening such as bathymetric highs and troughs yet the absence of active features such as thrust faults etc suggests ongoing compression or subduction initiation we also carefully read arrival times for p phases for 53 earthquakes at 16 teleseismic stations selected to represent a range of azimuths surrounding the earthquakes we relocated these earthquakes using standard joint epicentral determination jed methods while most of the better quality relocations lie on or very close to the australia pacific boundar3 as determined on the 1994 cruise a few epicenters occur well away from the boundar3 apparently on cenozoic fracture zones thus on the macquarie ridge complex and other major strike slip boundaries e g in california it appears that the very largest earthquakes occur on the principal plate boundar3 fault but that other earthquakes some quite large may occur away from the boundary along zones of preexisting weakness

paleoseismology of the 1912 acambay earthquake and the acambay tixmadeje fault trans mexican volcanic belt the acambay graben is a major intra arc basin of the trans mexican volcanic belt trenching studies at four sites along the acambay tixmadeje fault reveal evidence for the 1912 acambay earthquake and at least four late pleistocene and holocene ground rupturing earthquakes with similar displacements to the 1912 event evidence for multiple events was recognized by a combination of upward terminating faults fissure fills erosionally truncated fissures colluvial wedge fills and downward increasing separation of stratigraphic units sites along the central part of the ese wnw trending rangefront fault indicates large dip slip separations across a multi event scarp in holocene colluvium with a penultimate event that occurred since 5230 calibrated years before present cal yr b p on the huapango plain near the eastern end of the 1912 rupture where slip was oblique the penultimate earthquake occurred after 4700 cal yr b p and there is evidence for at least four more earthquakes in the last 34 000 cal yr b p three dimensional excavation of lacustrine and channel deposits at las lomas yields a left normal slip vector of s40 5 e with 105 10 cm of slip for the last three events there this slip vector is consistent with nne oriented extension across the graben the amount and style of slip documented for prehistoric ruptures are also consistent with the 1912 rupture with a mean of 60 cm event of dip slip on the rangefront and a mean of 35 cm event of oblique slip on the n48 w trending huapango plain assuming these values represent a characteristic behavior yields an average recurrence interval of 3600 years for the last four large earthquakes since 11 570 cal yr b p and a slip rate of 0 17 mm yr across the rangefront empirical earthquake parameters calculated from our paleoseismic data support instrumental measures indicating that the 1912 acambay earthquake was of m 6 8 7 0 the 1912 event is representative of ground rupturing earthquakes on the acambay tixmadeje fault and demonstrates that large seismic events m 7 can be generated by faults in the trans mexican volcanic belt and in other intra arc settings

probabilistic models for earthquakes with large return periods in himalaya region determination of the frequency of large earthquakes is of paramount importance for seismic risk assessment as large events contribute to significant fraction of the total deformation and these long return period events with low probability of occurrence are not easily captured by classical distributions generally with a small catalogue these larger events follow different distribution function from the smaller and intermediate events it is thus of special importance to use statistical methods that analyse as closely as possible the range of its extreme values or the tail of the distributions in addition to the main distributions the generalised pareto distribution family is widely used for modelling the events which are crossing a specified threshold value the pareto truncated pareto and tapered pareto are the special cases of the generalised pareto family in this work the probability of earthquake occurrence has been estimated using the pareto truncated pareto and tapered pareto distributions as a case study the himalayas whose orogeny lies in generation of large earthquakes and which is one of the most active zones of the world has been considered the whole himalayan region has been divided into five seismic source zones according to seismotectonic and clustering of events estimated probabilities of occurrence of earthquakes have also been compared with the modified gutenberg richter distribution and the characteristics recurrence distribution the statistical analysis reveals that the tapered pareto distribution better describes seismicity for the seismic source zones in comparison to other distributions considered in the present study

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

sedimentology stratigraphy and tectonic implications of a paleo proterozoic continental extensional basin the el sherana edith river groups northern territory australia the ca 1 83 ga el sherana edith river basin of northern territory australia contains terrestrial sedimentary and volcanic rocks deposited during continental extension or transtension braid pl

the large andaman islands earthquake of 26 june 1941 why no significant tsunami we present a modern seismological study of the earthquake of 26 june 1941 in the andaman islands the largest pre 2004 event along that section of the india burma plate boundary despite a large conventional magnitude m text pas 8 1 it generated at best a mediocre tsunami for which no definitive quantitative reports are available we show that the 1941 earthquake took place under the andaman accretionary prism and consisted of a composite event whose nucleating phase had a strike slip mechanism incompatible with a data set of spectral amplitudes of mantle rayleigh and love waves combining this initial phase with a larger normal faulting mechanism can reconcile them with p wave first motions reports of subsidence on the eastern coast of the andaman islands and the small amplitudes of any putative tsunami the small tsunami results from a combination of that mechanism and of a source located under the islands themselves and in shallow water implying a reduction in amplitude under green s law when transitioning to a deeper basin

40ar 39ar incremental release age of biotite from a gabbro of the shabogamo intrusive suite southwestern labrador biotite from a gabbro sill of the shabogamo intrusive suite in southwestern labrador records a well defined 40ar 39ar plateau age of 1353 17 ma this is similar to the 1375 60 ma dates recorded by sm nd and rb sr whole rock isotopic systems of the suite together recent radiometric results suggest that members of the suite were emplaced at approximately 1375 ma and cooled quickly at shallow crustal levels

geology and geochronology of helikian magmatism western labrador the shabogamo intrusive suite a predominantly gabbroic magma series intrusive into a variety of archean aphebian and helikian units in the churchill and grenville provinces of western labrador

crestal overtop and washover sedimentation on a fringing sandy gravel barrier coast carnsore point southeast ireland abstract storm sedimentation on a fringing sandy gravel barrier system in southeast ireland is examined recent wave overtopping and overwashing during severe onshore storms have resulted in a distinctive pattern of crest and backbarrier sedimentation this is not easily matched with available models of washover sedimentation drawn from the barrier islands of the eastern united states beach crest overtopping occurs at heights up to 6 m mhws and is related to the development of upper beach swash ramps that are plastered against storm wave eroded dune scarps located at the barrier crest ramp sediments comprise coarse basal beach gravels overlain by coarsening upward units and finally topped by distinctive seawarddipping fine grit coarse sand couplets in places where ramps reach the dune cre t overtopping swash has deposited a fine marine gravel veneer

systematic relocation of early instrumental seismicity earthquakes in the international seismological summary for 1960 1963 abstract we have relocated 2556 events that were reported in the bulletins of the international seismological summary iss during the period 1960 1963 using the phase arrival time data listed in the bulletins parts of the data were already available in digital form and the rest we obtained by scanning the printed bulletins and applying an optical character recognition procedure earthquakes were then relocated with a teleseismic location method that uses an improved 1d global travel time earth model depth phases and corrections for ellipticity bounce point bathymetry topography and station elevation the aspherical velocity structure below stations was partially taken into account through the use of teleseismic station patch corrections the quality of the newly obtained locations and the improvements in data fit are similar to relocations of earthquakes in the early bulletins of the international seismological centre isc the most significant improvement of the new locations is in focal depth and a significant number of blatant mislocations such as earthquakes deeper than 100 km below midocean ridges have also been corrected the relocations presented here extend by 10 the time period for which homogeneous and reliable hypocenters are available on a global basis this is the first of a series of studies addressed towards relocating using the same methodology all the instrumentally recorded earthquakes listed in the bulletins of the iss 1918 1963

the mid proterozoic mporokoso basin northern zambia sequence stratigraphy tectonic setting and potential for gold and uranium mineralisation abstract the mporokoso basin was formed on a dying silicic magmatic arc between 1800 and 1100 ma the basin consists of up to 5000 m of fluvial and shallow marine siliciclastic sediments the stratigraphy and tectonic setting resembles that of mid proterozoic cratonic basins elsewhere the mporokoso basin is the result of crustal extension rather than compression the gravitational collapse of crust thickened by tectonic and magmatic processes may have caused the extension and subsidence in this and other mid proterozoic basins fluvial sediments in the lower part of the basin fill are known to contain traces of gold analysis has shown up to 1 3 ppm gold in conglomerates gold concentrations are most likely to occur along subtle unconformities which form the boundaries of depositional sequences these sequence boundaries can be identified through sedimentary facies relationships the underlying silicic igneous rocks are unlikely to have been the source of the gold the lupa goldfields of tanzania lie to the east of the mporokoso basin and are the nearest probable source however only the lowermost sequence in the basin was derived from the east the basement and sediments of the mporokoso basin are enriched in uranium the critical factor missing for an uranium deposit of the unconformity type is a reducing lithology the only known possible reductants are carbonaceous mudstone within the basin and graphite in the basement 200 km away

cratonic sedimentation during the proterozoic an anorogenic connection in wisconsin and the upper midwest certain proterozoic quartzites including baraboo barron and sioux and associated metasedimentary rocks in the upper midwest represent a distinct epicontinental depositional environment new data indicate that argillite chert iron formation micaceous conglomerate and rhyolite are much more abundant and significant in this sequence than previously reported the entire group of rocks was deposited during one period in a series of tectonic episodes magmatism and uplift related to epeirogeny none of these episodes included overt rifting sedimentation began on subsiding continental crust during the waning stages of anorogenic magmatism 1760 m y ago following deposition a regional event 1630 m y ago is interpreted as a time of uplift and mild deformation with no magmatic expression in the region epeirogenic tectonism was culminated in the widespread intrusion of 1500 m y old alkalic plutonism which metamorphosed and further deformed the sedimentary rocks and surroundings

changes in frequency size relationship from small to large earthquakes the constant b value observed in frequency magnitude distributions of earthquakes has been taken as an indication of self similarity at all magnitudes hence earthquake properties should scale uniformly in the same way from small to large earthquakes it has often been observed however that the seismic moment released in small earthquakes scales differently with rupture length than it does for large events1 2 where the crossover between small and large events is defined at a rupture dimension equal to the down dip width of the seismogenic zone a possible explanation for this contradiction is that frequency size distributions are biased by small earthquakes small events dominate most global earthquake catalogues because of the short time period covered another source of bias in size distributions is the saturation of earthquake magnitudes for large events here we correct biases in calculations of b values and present evidence for a change in b value in frequency size distributions we find that a break in self similarity from small to large earthquakes occurs at a point where the dimension of the event equals the down dip width of the seismogenic layer

magnitude scale for the central american tsunamis based on the tsunami data in the central american region the regional characteristic of tsunami magnitude scales is discussed in relation to earthquake magnitudes during the period from 1900 to 1993 tsunami magnitudes on the imamura iida scale of the 1985 mexico and 1992 nicaragua tsunamis are determined to be m 2 5 judging from the tsunami height distance diagram the magnitude values of the central american tsunamis are relatively small compared to earthquakes with similar size in other regions however there are a few large tsunamis generated by low frequency earthquakes such as the 1992 nicaragua earthquake inundation heights of these unusual tsunamis are about 10 times higher than those of normal tsunamis for the same earthquake magnitude m s 6 9 7 2 the central american tsunamis having magnitude m 1 have been observed by the japanese tide stations but the effect of directivity toward japan is very small compared to that of the south american tsunamis

paleoseismology of deep sea faults based on marine surveys of northern okushiri ridge in the japan sea 1 the eastern margin of the japan sea is an incipient convergent margin characterized by distributed active faults and large scale earthquakes to evaluate the earthquake potential of the northern margin the source area of the 1940 shakotan hanto oki earthquake m7 5 was reexamined and the earthquake recurrence interval was estimated by combining bathymetric seismic and dive survey data with a tsunami simulation seismic profiling clarified that five anticlines have formed in and around this source area during the last 1 8 million years the balanced cross section of one anticline supports that thrust faults extend to the base of the upper brittle crust at about 11 km depth and total slip is about 850 m dive surveys identified fresh collapses along the forelimbs of two anticlines inversion of observed tsunami waveforms to estimate the slip distribution suggests that these two anticlines were the sources of the 1940 earthquake the other three anticlines may be seismic gaps the dive surveys collected debris layers possible records of paleoearthquakes in muddy sediments from the rate of muddy sediment deposition around the anticlines the minimum recurrence interval of earthquakes was estimated to be about 1100 years from structural modeling the average interval was about 6400 years assuming that fault slip started 1 8 million years ago and 3 m of slip occurred during each earthquake taking into account the above results and the instantaneous plate convergent rate between the okhotsk and amurian plates the recurrence interval was inferred to be 1100 to a few thousand years

macroseismic study of shallow earthquakes in the central and eastern parts of the trans mexican volcanic belt mexico we present isoseismal maps for eight shallow earthquakes 1887 pinal de amoles 1912 acambay 1920 jalapa 1950 ixmiquilpan 1976 cardonal 1979 maravatio 1987 actopan and 1989 landa 4 1 mb 6 9 that occurred in the central and eastern parts of the trans mexican volcanic belt based on their intensity distributions we can relate several of these earthquakes to east west striking quaternary normal faults known from geological observations furthermore we derive for these events by empirical curve fitting linear relations between the magnitude calculated from the instrumental record the intensity distribution and the maximum intensity the comparison of these relations with equations from the literature suggests that the area shaken with a certain intensity by an earthquake in the trans mexican volcanic belt is approximately 10 times smaller than the area shaken by a shallow earthquake of the same magnitude in the intracratonic part of north america moreover we use the derived relationships between magnitude isoseismal area and maximum intensity to estimate the intensity magnitude mi of the 1887 pinal de amoles earthquake as 5 3 0 5

heterogeneities of the instrumental seismicity catalog 1904 1980 for strong shallow earthquakes we analyze the world wide consistency of teleseismic reporting completeness of the seismicity record and homogeneity of magnitude determination for strong shallow earthquakes magnitude m 6 depth h 70 km in the period 1904 to 1980 for earthquakes with magnitude m 7 we used the catalog given by abe 1981 which lists the surface wave magnitude ms of every reported large event that occurred between 1904 and 1980 according to the original formulation of gutenberg 1945 under the postulate that the rate of earthquake occurrence for the entire world as a whole is consistent on a time scale of decades and that since the installation of the world wide standardized seismograph network in the early 1960s the earthquake catalog for strong m 6 shocks is complete and the seismicity rates are typical of all periods in the century we find that for instrumental related reasons the ms of large events prior to 1908 have been systemically overestimated by at least 0 5 magnitude unit and the ms of events in the period 1908 to 1948 have been consistently overestimated by 0 2 unit relative to the ms assigned to shocks occurring after 1948 when these corrections are taken into account the catalog of events with ms 7 0 is shown to be largely complete i e nearly all the large shallow shocks which occurred in the earth are listed for most of the world since early in the century for earthquakes as the magnitude 6 level we used the international seismological center isc tape and regional catalogues of earthquakes this file compiles the earthquake data given by gutenberg and richter 1954 for the first half of the century and data from various international agencies after 1945 we find a highly incomplete seismicity catalog at this magnitude level for the first half of the century mainly due to numerous increases and decreased in the earthquake detection and reporting capabilities a more complete but extremely inhomogeneous catalog for the period 1950 to 1963 due to the use of different formulations and criteria to calculate and report the parameter magnitude by the various seismological agencies and a largely complete and homogeneous in ms record since 1964

new constraints on the 1922 atacama chile earthquake from historical seismograms we recently found the original omori seismograms recorded at hongo tokyo of the 1922 atacama chile earthquake m s 8 3 in the historical seismogram archive of the earthquake research institute eri of the university of tokyo these recordings enable a quantitative investigation of long period seismic radiation from the 1922 earthquake we document and provide interpretation of these seismograms together with a few other seismograms from mizusawa japan uppsala sweden strasbourg france zi ka wei china and de bilt netherlands the 1922 event is of significant historical interest concerning the cause of tsunami discovery of g wave and study of various seismic phase and first motion data also because of its spatial proximity to the 1943 1995 and 2015 great earthquakes in chile the 1922 event provides useful information on similarity and variability of great earthquakes on a subduction zone boundary the 1922 source region having previously ruptured in 1796 and 1819 is considered to have significant seismic hazard the focus of this paper is to document the 1922 seismograms so that they can be used for further seismological studies on global subduction zones since the instrument constants of the omori seismographs were only incompletely documented we estimate them using the waveforms of the observed records a calibration pulse recorded on the seismogram and the waveforms of better calibrated uppsala wiechert seismograms comparison of the hongo omori seismograms with those of the 1995 antofagasta chile earthquake m w 8 0 and the 2015 illapel chile earthquake m w 8 3 suggests that the 1922 event is similar to the 1995 and 2015 events in mechanism i e on the plate boundary megathrust and rupture characteristics i e not a tsunami earthquake with m w 8 6 0 25 however the initial fine scale rupture process varies significantly from event to event the g1 and g2 and r1 and r2 of the 1922 event are comparable in amplitude suggesting a bilateral rupture which is uncommon for large megathrust earthquakes

complements to magnitudes of large shallow earthquakes from 1904 to 1980 abstract in the previous paper magnitudes of large earthquakes of the world were determined on a very uniform basis and catalogued in order to arrive at a more homogeneous catalogue for a study of global seismicity some complements are presented the major complements are as follows 1 the m s values for the period 1904 1909 in the previous paper were overestimated in the extreme case by 0 5 magnitude units 2 the m b values for the period 1904 1908 in the previous paper were also overestimated 3 the magnitudes of deep and intermediate shocks which are listed in seismicity of the earth by gutenberg and richter are found to be approximated by m b m b 7 4 4 the catalogues of m b for shallow intermediate and deep shocks are continued for the period up to 1980

subduction and back arc activity at the hikurangi convergent margin new zealand the hikurangi margin is a region of oblique subduction with northwest dipping intermediate depth seismicity extending southwest from the kermadec system to about 42 s the current episode of subduction is at least 16 20 ma old the plate convergence rate varies along the margin from about 60 mm a at the south end of the kermadec trench to about 45 mm a at 42 s the age of the pacific lithosphere adjacent to the hikurangi trench is not known

velocity field for crustal deformation in china derived from seismic moment tensor summation of earthquakes the intraplate motion is studied in the territory of china where about 150 polygonal seismic sources are considered and grouped on the basis of the available fault plane solutions large known faults and level of seismic activity every polygon is divided into several triangles and velocities at the triangle vertices are determined from the available moment rate tensors by assuming a linear continuity of the velocity field within each triangle the estimation of the moment rate tensor is partitioned in the unit scaled moment tensor obtained by the available fault plane solutions of large event mz5 0 after 1900 which define the type of deformation and the scalar annual moment rate obtained by the complete seismicity catalogue which defines the rate of seismic deformation the results show that the convergence between india and eurasia is about 50 mm year with eurasia fixed while the eastern part of china moves eastwards at about 8 10 mm year the motion direction changes gradually from northeastward around the himalayan region to southeastward around the red river fault and to southwestward around eastern himalayan syntaxis which partially compensates the penetration of the indian plate a sharp change of the velocity gradient was found near the southeastern part of tibet plateau the qilianshan region and fuyun fault where large strain rates are released due to strong earthquakes there the results are supported by recent horizontal gps motion model and other independent evidence the motion pattern between the altun qilianshan longmenshan faults and the himalayan fault in qinghai tibet region strongly suggests that this area exhibits a more or less continuous deformation pattern rather than a rigid block behavior d 2002 published by elsevier science b v

paleomagnetism and time stratigraphic correlation of proterozoic redbeds of the labrador trough and outliers of northern quebec one hundred and forty two oriented cores were collected from redbeds of the sakami formation near lg 4 85 dieter 19 cambrian 18 and snow ball 4 lakes all in quebec and from two outliers in labrador evening lake 6 and sims lake 10 a further 73 oriented drill cores were collected from the strongly folded chakonipau formation redbeds 44 in the labrador trough and undeformed redbeds near lac imbault 29 on the western edge of the trough thermal demagnetization of the trough redbeds yielded 52 core directions each of which showed good specimen end points and sufficient homogeneity of magnetization and 101 such core directions were obtained for the outlier redbeds in most of these samples there are no indications that the stable remanence is multi component and the fold test yields for lg 4 sakami formation and the chakonipau formation a significant 95 probability improvement of the dispersion parameter k thus the chakonipau formation remanence is probably pre hudsonian and th

time dependent seismicity in china precise zonation of the territory of china has been performed based on the active known faults type of faulting and seismicity level one hundred and forty seven seismogenic regions were defined forming 10 larger seismic areas and the seismotectonic characteristics in each one of them were investigated in detail after checking for data accuracy and completeness of the shallow earthquakes h 60 km the regional time and magnitude predictable model was applied and the model parameters were estimated based on the model applicability in the studied area probabilities for the occurrence of strong m 6 0 earthquakes during the next 10 years were calculated for each seismogenic region statistical tests have been used proving the superiority of the model in comparison with the time independent one as well as in comparison with the actual earthquake occurrence q 2001 elsevier science ltd all rights reserved

seismic history and seismotectonics of the sunda arc historic records of the last 300 years reveal two great interplate earthquakes 1833 mw 8 1861 mw 8 8 which ruptured major segments of the sumatra fore arc in western indonesia a significant percentage of interplate slip along this portion of the plate boundary appears to occur seismically the ends of these rupture zones are coincident with clusters of large ms 7 and moderate 6 ms 7 shocks and with heterogeneities in the plate interface as inferred from geologic and geophysical data the northern extent of the 1833 rupture zone is coincident with a group of moderate and large earthquakes a structural arch in the fore arc and a fracture zone on the subducted plate the southern portion is coincident with a very prominent cluster and the along strike extension of a sediment filled trough on the subducted plate prior to this study sumatra was characterized as relatively aseismic as inferred from the lack of great earthquakes in the instrumental record of this century java and the lesser sunda islands had major ms 6 earthquakes in the historic record but none are of the same magnitude as the great events near sumatra there is no clear evidence that shocks in the java fore arc were interplate events yet geophysical data indicate recent uplift of the trench slope break and a change in strike of the trench axis where the northernmost flank of the roo rise a prominent bathymetrie high appears to be interacting with the fore arc this feature was formed at a ridge crest and is more buoyant and thus more difficult to subduct than the surrounding seafloor there is no increase in seismicity associated with this tectonism however that may indicate a lack of contact between the crystalline portions of the plates at this time we infer that a majority of slip on the plate interface near java occurs aseismically the variation in occurrence of great interplate earthquakes along the sunda arc may be interpreted in terms of a model that attributes variation in interplate coupling to the age of the subducted lithosphere great interplate earthquakes occur near sumatra where the age of the youngest crust is 46 ma the characteristics of the sunda arc and analogies with pacific arcs imply that the entire length of sumatra has the potential to produce great thrust earthquakes its seismic potential should be considered high as there has been no recurrence of the great events of 1833 and 1861 in contrast no such events have been reported off java and the lesser sunda islands where the oldest crust is 152 ma the plate interface near java and the lesser sunda islands should be considered to have low seismic potential

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

source characteristics of hypothetical subduction earthquakes in the northwestern united states historic earthquake sequences on subduction zones that are similar to the cascadia subduction zone are used to hypothesize the nature of shallow subduction earthquakes that might occur in the northwestern united states based on systematic comparisons of several physical characteristics including physiography and seismicity subduction zones that are deemed most similar to the cascadia subduction zone are those in southern chile southwestern japan and colombia these zones have all experienced very large earthquake sequences and if the cascadia subduction zone is also capable of storing elastic strain energy along its greater than 1000 km length then earthquakes of very large size m w 8 1 2 must be considered circumstantial evidence is presented that suggests but does not prove that large subduction earthquakes along the cascadia subduction zone may have an average repeat time of 400 to 500 yr

quartz arenites review and interpretation abstract quartz arenites orthoquartzites are exceptional sands pettijohn et al 1972 that in the past have formed extensive and commonly thick formations they are somewhat enigmatic in that they do not appear to be forming at the present time this paper examines the origin of quartz rich sands documents the range of environments in which they are found and suggests a model for their genesis quartz sand is most commonly formed by tropical weathering of coarse grained quartz bearing rocks such as granite it may be deposited as texturally immature fluvial sandstones generally under a humid climate with drying of the climate quartz rich bauxitic soils and sandy alluvium can be a substantial source of poorly rounded dune sands for major deserts quartz sand when transported into shallow marine environments becomes very well rounded through reworking by tidal currents such sand may spill into deep oceanic environments and by sedimentary or tectonic transport may come to rest in both stable and active tectonic settings quartz rich sandstones can also be formed by diagenetic destruction of labile framework grains of immature sandstones precambrian orthoquartzites are commonly thick and widespread when compared to younger examples the thinness of post silurian quartz arenites may be largely due to the trapping effect of land vegetation and solution of quartz by organic acids in weathering profiles there is an abundance of shallow marine and fluvial quartz arenites in the early paleozoic and the cretaceous this is due to widespread continental flooding and a humid world climate following the disintegration of supercontinents the shallow marine examples are commonly associated with bituminous sometimes phosphatic shale glauconite and possibly chamositic ironstone there is an abundance of eolian quartz arenites in the permo triassic this is related to a widespread dry continental climate during assembly of the pangean supercontinent

a catalog of shallow earthquakes of mexico from 1900 to 1981 a catalog of shallow earthquakes depth 65 km of mexico 15 to 20 n 94 5 to 105 5 w covering the period 1900 to 1981 is presented the catalog includes only those events whose magnitudes m ms or magnitude from pasadena are 5 9 it is most likely complete for shocks with ms 6 5 from july 1906 to december 1981 for many shocks ms has been determined from uppsala bulletins and or uppsala and gottingen wiechert seismograms the statistics of incremental frequency n ms shows a peak at ms 7 7 reinforcing a previous observation by singh et al 1981 in the range 6 4 ms 7 5 the observed n ms deviates significantly from an exponential distribution the catalog provides a basis for further statistical analysis of earthquakes in mexico

the regional time and magnitude predictable model and its application to the alpine himalayan belt abstract the regional time and magnitude predictable model has been introduced and has been shown to be appropriate to describe the behaviour in the occurrence of mainshocks the model implies that the magnitude of the preceding mainshock in a seismogenic region that is the largest earthquake during a seismic excitation governs the time of occurrence and the magnitude of the expected mainshock in this region this model has been applied in 149 seismogenic regions of the alpine himalayan seismic belt the model probability for the occurrence of the next very strong main shock ms 6 5 during the decade 1993 2002 as well as the magnitude of this shock in each of these regions have been calculated furthermore two tests have been performed to check the validity of this model these tests have shown the reliability of the model and its superiority compared to the classical time independent model

evaluation of precursory seismic quiescence in sixteen subduction zones using single link cluster analysis this paper describes a new method single link cluster analysis slc to evaluate percursory quiescence for shallow earthquakes in sixteen subduction zones using data from the isc catalog to define quiescent regions we divided the catalog into time intervals with a durationt overlapping byt 2 we considered all earthquakes having magnitudes larger than some magnitudemmin lying within a specified distance of a great circle which is approximately coincident with the trench near a subduction zone within each time interval we connected or linked all earthquakes lying within some cutoff distanced of one another we then projected all these links onto the great circle and defined a region to be quiescent if it was not covered by the projection of any links for this study t was two years mmin wasmb 4 9 and we variedd from 100 to 400 km we defined an earthquake as following quiescence if it occurred within two years following and within 75 km of a quiescent zone as defined above the primary conclusion of this study was that earthquakes with surface wave magnitudes 7 2 and greater were about 5 15 more likely to follow quiescence than were the smaller background earthquakes withmb 4 9 a chi squared analysis shows that this result is significant at the 99 level in contrast earthquakes with surface wave magnitude of 6 7 to 7 1 were no more likely to follow quiescence than were background earthquakes of sixteen individual regions central america japan and peru chile were the only regions where large earthquakes were more likely to occur following quiescence than were background earthquakes for a cutoff link length of 300 km only in central america was the difference between large earthquakes and background earthquakes significant at the 95 level of significance for a cutoff link length of 250 km the significance level exceeded 95 only in japan the slc method is an objective quantitative method for evaluating large data catalogs or for monitoring quiescence in regions where quiescence is conjectured to precede large earthquakes

large earthquake doublets and fault plane heterogeneity in the northern solomon islands subduction zone in the solomon islands and new britain subduction zones the largest earthquakes commonly occur as pairs with small separation in time space and magnitude this doublet behavior has been attributed to a pattern of fault plane heterogeneity consisting of closely spaced asperities such that the failure of one asperity triggers slip in adjacent asperities we analyzed body waves of the january 31 1974 m w 7 3 february 1 1974 m w 7 4 july 20 1975 14 37 m w 7 6 and july 20 1975 19 45 m w 7 3 doublet events using an iterative multiple station inversion technique to determine the spatio temporal distribution of seismic moment release associated with these events although the 1974 doublet has smaller body wave moments than the 1975 events their source histories are more complicated lasting over 40 seconds and consisting of several subevents located near the epicentral regions the second 1975 event is well modeled by a simple point source initiating at a depth of 15 km and rupturing an approximate 20 km region about the epicenter the source history of the first 1975 event reveals a westerly propagating rupture extending about 50 km from its hypocenter at a depth of 25 km the asperities of the 1975 events are of comparable size and do not overlap one another consistent with the asperity triggering hypothesis the relatively large source areas and small seismic moments of the 1974 doublet events indicate failure of weaker portions of the fault plane in their epicentral regions variations in the roughness of the bathymetry of the subducting plate accompanying subduction of the woodlark rise may be responsible for changes in the mechanical properties of the plate interface