regional bias in estimates of earthquake ms due to surface wave path effects continental earthquakes have long been known to have anomalously high surface wave magnitudes relative to their seismic moments a recent global study of shallow earthquakes by ekstrom and dziewonski 1988 confirmed this and found other regional systematic anomalies in the ms m relationship it is important to determine the source of these anomalies in order to understand the controls on earthquake source radiation and to obtain accurate estimates of historical seismic strain rates in this study the magnitudes of 82 earthquakes from eight different tectonic regions are recalculated using a simple surface wave path correction to determine whether path effects are responsible for the observed anomalies the magnitudes of continental earthquakes are reduced by an average of 0 2 magnitude units an improvement in fit to the global average significant at the 98 level surface wave path effects are clearly responsible for the high ms observed in continental areas there is a small decrease in scatter in the other areas but lateral refraction of the surface waves at plate boundaries prevents the simple correction from having a significant effect there is no evidence in the observed anomalies however for any dependence of earthquake source type on tectonic setting it is clear that to obtain reliable unbiased estimates of regional seismic strain rate and hazard a local moment magnitude relationship should be preferred to a global one

the makran earthquake of 1983 april 18 a possible analogue to the puget sound earthquake of 1965 summary on 1983 april 18 a large earthquake mb 6 5 m0 1 2x1019 nm occurred in the makran region near the pakistan iran border this earthquake is the only event of mb 6 2 in the entire makran region since the occurrence of the great makran earthquake m 8 0 8 3 in 1945 we determined the source parameters of the 1983 event by formally inverting its p and sh waves recorded by the world wide standard seismograph network wwssn and the canadian seismograph network csn at teleseismic distances the best fitting centroidal solution shows predominantly normal faulting at a depth of about 65 5 km these results provide an additional constraint on the configuration of the down going slab previously inferred from the occurrence of three small to moderate sized events located 100 300 km to the west of the event reported here we also discuss the possibility of drawing an analogy between the occurrence of the 1983 makran event and that of the puget sound earthquake of 1965 m0 1 4x1019nm mb 6 5 and between the seismotectonic settings of the two regions if the very large m 8 0 8 3 earthquake off the makran coast in 1945 is a low angle thrust due to slip along the plate interface its occurrence calls for the possibility of similar seismic risk in the puget sound region however in contrast to inferences made from geological observations in the field about a dozen p wave first motions read from historical seismograms and those reported by the international seismological summary suggest that the 1945 makran earthquake has a large component of normal faulting which can be attributed to the relatively old age of the subducted lithosphere

teleseismic detection of a slow precursor to the great 1989 macquarie ridge earthquake low frequency spectra for the 1989 macquarie ridge earthquake magnitude 8 2 show an amplitude increase and a phase delay decrease below 6 millihertz that require a short term slow precursor this earthquake can be modeled as a compound event in which a fast rupturing ordinary earthquake was initiated by an episode of slow smooth deformation that began more than 100 seconds before the main shock the moment released in the slow precursor was large about 3 x 10 20 newton meters equivalent to an event of magnitude 7 6 the data are consistent with the precursor being generated in a region of the oceanic upper mantle below the main rupture

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

systematic analysis of deep seismicity 200 centroid moment tensor solutions for earthquakes between 1977 and 1980 summary a systematic study of deep seismicity is performed using waveform data from the gdsn between 1977 and 1980 and the centroid moment tensor method of dziewonski et al two hundred new cmt solutions are found for events deeper than 100km their moments obtained using the same algorithm range between 7 x and 1 4 x lo2 dyne cm a factor of 20 000 a statistical analysis of the cmt parameters provides important conclusions among these the shift in origin time for deep events is found to be almost independent of the seismic moment providing an indication of the complexity of deep earthquakes the deviation from the double couple model appears to be correlated to the state of stress of the subducting slabs mechanisms showing down dip compression are generally dominated by the eigenvalue corresponding to the compression axis and down dip tension correlates with the predominance of the tensional eigenvalue comparison with moment tensors obtained by other authors using different waveform data shows good agreement between different methods comparison with published focal plane mechanisms confirms the precision and reliability of the cmt method examples of cmt solutions used to identify patterns of seismicity associated with deep fault planes are shown

on the geometric complexity of earthquake focal zone and fault systems a statistical study we discuss various methods used to investigate the geometric complexity of earthquakes and earthquake faults based both on a point source representation and the study of interrelations between earthquake focal mechanisms we briefly review the seismic moment tensor formalism and discuss in some detail the representation of double couple dc earthquake sources by normalized quaternions non dc earthquake sources like the clvd focal mechanism are also considered we obtain the characterization of the earthquake complex source caused by summation of disoriented dc sources we show that commonly defined geometrical fault barriers correspond to sources without any clvd component we analyze the cmt global earthquake catalog to examine whether the focal mechanism distribution suggests that the clvd component is likely to be zero in tectonic earthquakes although some indications support this conjecture we need more extensive and significantly more accurate data to answer this question fully

the great tumaco colombia earthquake of 12 december 1979 southwestern colombia and northern ecuador were shaken by a shal low focus earthquake on 12 december 1979 the magnitude 8 shock located near tumaco colombia was the largest in northwestern south america since 1942 and had been forecast to fill a seismic gap thrust faulting occurred on a 280 by 130 kilometer rectangular patch of a subduction zone that dips east beneath the pacific coast of colombia a 200 kilometer stretch of the coast tectonically subsided as much as 1 6 meters uplift occurred offshore on the continental slope a tsunami swept inland immediately after the earthquake ground shaking intensity vi to ix caused many buildings to collapse and generated liquefaction in sand fills and in holocene beach lagoonal and fluvial deposits

dominant fault plane orientations of intermediate depth earthquakes beneath south america the south american subduction zone exhibits considerable variation the subduction angle alternates between flat and steep the subducting plate has complex structures and arc volcanism in the overlying plate has gaps i investigate the effect of these differences in incoming plate structure and slab geometry on intermediate depth earthquakes specifically their fault orientations and rupture characteristics and find that slab geometry has the largest impact on fault orientation i use rupture directivity to estimate rupture direction and rupture velocity and to distinguish the fault plane from the auxiliary plane of the focal mechanism from analysis of 163 large mw 5 7 intermediate depth 60 360 km depth earthquakes from along the length of south america estimated rupture azimuths and plunges show no trends appearing to be randomly distributed on the determined population of fault plane orientations and a majority of earthquakes are made up of multiple subevents as seen in other subduction zones subduction segments descending at normal angles have predominantly subhorizontal faults flat slab segments also have a dominant fault orientation but those earthquakes slip along the conjugate nodal plane of the focal mechanism in strongly curved slab segments such as at the downdip edge of flat segments where the slab resubducts earthquakes may slip along either nodal plane orientation while both fault orientations could be consistent with the reactivation of fossil outer rise faults the fault orientations are also consistent with expectations for newly created faults in agreement with the ambient stress field fault reactivation alone does not explain why different fault orientations are active in segments with different geometries so the preferred explanation for having regionally consistent fault orientations is that they minimize the total work of the system the previously observed predominance of subhorizontal faults appears to be a consequence of slab geometry

double seismic zone in tonga the clear evidence of a double seismic zone beneath japan1 2 has led seismologists to search for other such zones elsewhere because they have been found in few other areas3 6 double seismic zones are thought to be rare and to depend strongly on a peculiar combination of external conditions such as age of the descending slab and the convergence rate 7 we report here a new double seismic zone which has been found beneath the tonga arc8 where the stress state in the subducting slab has been described as strongly down dip compressional7 9 10 this discovery suggests that the double seismic zone is a general feature of subducting slabs and may be found in many other subduction zones

large intermediate depth earthquakes and the subduction process this study provides an overview of intermediate depth earthquake phenomena placing emphasis on the larger tectonically significant events and exploring the relation of intermediate depth earthquakes to shallower seismicity especially we examine whether intermediate depth events reflect the state of interplate coupling at subduction zones and whether this activity exhibits temporal changes associated with the occurrence of large underthrusting earthquakes historic record of large intraplate earthquakes m b 7 0 in this century shows that the new hebrides and tonga subduction zones have the largest number of large intraplate events regions associated with bends in the subducted lithosphere also have many large events e g altiplano and new ireland we compiled a catalog of focal mechanisms for events that occurred between 1960 and 1984 with m 6 and depth between 40 and 200 km the final catalog includes 335 events with 47 new focal mechanisms and is probably complete for earthquakes with m b 6 5 for events with m 6 5 nearly 48 of the events had no aftershocks and only 15 of the events had more than five aftershocks within one week of the mainshock events with more than ten aftershocks are located in regions associated with bends in the subducted slab focal mechanism solutions for intermediate depth earthquakes with m 6 8 can be grouped into four categories 1 normal fault events 44 and 2 reverse fault events 33 both with a strike nearly parallel to the trench axis 3 normal or reverse fault events with a strike significantly oblique to the trench axis 10 and 4 tear faulting events 13 the focal mechanisms of type 1 events occur mainly along strongly or moderately coupled subduction zones where a down dip extensional stress prevails in a gently dipping plate in contrast along decoupled subduction zones great normal fault earthquakes occur at shallow depths e g the 1977 sumbawa earthquake in indonesia type 2 events with strike subparallel to the subduction zone and most of them with a near vertical tension axis occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity is deeper than 300 km the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may be responsible for the near vertical tensional stress at intermediate depth and consequently the change in focal mechanism from type 1 to type 2 events events of type 3 occur where the trench axis bends sharply causing horizontal parallel to the trench strike extensional or compressional intraplate stress type 4 are hinge faulting events for strongly coupled zones we observed temporal changes of intermediate depth earthquake activity associated with the occurrence of a large underthrusting event after the occurrence of a large underthrusting event the stress axis orientation of intermediate depth earthquakes changes from down dip tensional to down dip compressional e g 1960 chile 1974 peru 1982 tonga and 1952 kamchatka earthquakes or the number of large intermediate events decreases for a few years e g 1964 alaska and 1985 valparaiso earthquakes we conclude that even though the stress changes induced by slab pull and slab distortion control the general pattern of intermediate depth seismicity spatial and temporal variations of the intraplate stress associated with interplate coupling are important in controlling the global occurrence of large intermediate depth events

a very broad band inversion method for the recovery of earthquake source parameters abstract waveform studies of the earthquake source have traditionally been performed in narrow bands of the seismic spectrum waveform matching of p and sh waves emphasizes frequencies near and above the corner frequency normal mode and surface wave analyses on the other hand are performed on data which contain information only below the corner frequency a new method is presented which formally includes the result of a long period centroid moment tensor analysis in an inversion of broad band body wave phases a parametrized source model is used which allows for the recovery of a detailed source time function as well as the direction and magnitude of rupture propagation the technical details and the performance of the method are demonstrated in an analysis of the october 28 1983 borah peak idaho earthquake in particular it is shown how the combination of the long period and broad band data sets in the inversion improves the resolution of both the focal mechanism and the scalar moment the very broad band method is applied in an analysis of the september 19 1985 michoacan m w 8 0 earthquake two concentrations of moment release are identified in the source time function separated by 25 30 s in time the spatial distribution of moment is well explained both by a model of unilateral rupture towards the east with a propagation velocity of 2 4 km s 1 and by two point sources separated by 95 km it is shown that the p wave data are largely insensitive to the scalar moment and that source time functions obtained without consideration of the total moment release exaggerate the heterogeneity of slip on the fault plane source time functions which do contain the total moment show that a large fraction of the moment was released smoothly over the whole duration 80 s of the event the results suggest that the fault plane was characterized by two regions of high stress drop but that a large portion of slip occurred on surrounding weak portions of the plane

a seismological reassessment of the source of the 1946 aleutian tsunami earthquake summary we present a re evaluation of the seismological properties of the aleutian tsunami earthquake of 1946 april 1 characterized by a deceptively low conventional magnitude 7 4 in view of its catastrophic tsunami both in the near and far fields relocation of 40 aftershocks show that the fault zone extends a minimum of 181 km along the aleutian trench in a geometry requiring a bilateral rupture from the original nucleation at the epicentre their spatial and temporal distribution are typical of the aftershock patterns of a large earthquake and rule out the model of a landslide source exclusive of a dislocation the analysis of the spectra of mantle waves favours the model of a large seismic source with a static moment of 8 5 10 28 dyn cm making the event one of the ten largest earthquakes ever recorded hence the destructive tsunami in the far field and of a slow bilateral rupture at an average velocity of only 1 12 km s 1 hence the destructive interference in all azimuths for all but the longest mantle waves the exceptionally slow character of the earthquake is confirmed by a deficiency in radiated seismic energy expressed by the lowest value measured to date of the energy tomoment ratio the earthquake appears as an end member in the family of tsunami earthquakes resulting from the combination of anomalous but not unprecedented parameters such as low stress drop and rupture velocity

disentangling the control of tectonics eustasy trophic conditions and climate on shallow marine carbonate production during the aalenian oxfordian interval from the western france platform to the western tethyan domain the objective of this work is to improve our understanding of the processes controlling changes in the architecture and facies of intracontinental carbonate platforms we examined the facies and sequence stratigraphy of aalenian to oxfordian limestones of western france seventy seven outcrop sections were studied and thirty one sedimentary facies identified in five depositional environments ranging from lower offshore to backshore platform evolution was reconstructed along a 500 km cross section twenty two depositional sequences were identified on the entire western france platform and correlated with european third order sequences at the biozone level demonstrating that eustasy was the major factor controlling the cyclic trend of accommodation the tectonic subsidence rate was computed from accommodation measurements from the aalenian to the oxfordian in key localities tectonism controlled the sedimentation rate and platform architecture at a longer time scale tectonic subsidence triggered the demise of carbonate production at the bathonian callovian boundary while the uplift made possible the recovery of carbonate platform from caen to le mans during the mid oxfordian topography of the paleozoic basement mainly controlled lateral variations of paleodepth within the western france platform until the mid bathonian a synthesis of carbonate production in the western tethyan domain at that time was conducted stages of high carbonate production during the bajocian bathonian and the middle to late oxfordian are synchronous with low 13c high eccentricity intervals and rather dry climate promoting 1 evaporation and carbonate supersaturation and 2 oligotrophic conditions periods of low carbonate production during the aalenian and from the middle callovian to early oxfordian correlate with high 13c and low eccentricity intervals characterized by wet climate and less oligotrophic conditions such conditions tend to diminish growth potential of carbonate platforms this work highlights the importance of climate control on carbonate growth and demise at large scale in western tethyan epicontinental seas

slab pull and the seismotectonics of subducting lithosphere this synthesis links many seismic and tectonic processes at subduction zones including great subduction earthquakes to the sinking of subducted plate earthquake data and tectonic modeling for subduction zones indicate that the slab pull force is much larger than the ridge push force interactions between the forces that drive and resist plate motions cause spatially and temporally localized stresses that lead to characteristic earthquake activity providing details on how subduction occurs compression is localized across a locked interface thrust zone because both the ridge push and the slab pull forces are resisted there the slab pull force increases with increasing plate age thus because the slab pull force tends to bend subducted plate downward and decrease the force acting normal to the interface thrust zone the characteristic maximum earthquake at a given interface thrust zone is inversely related to the age of the subducted plate the 1960 chile earthquake mw 9 5 the largest earthquake to occur in historic times began its rupture at an interface bounding oceanic plate 30 m y old however this rupture initiation was associated with the locally oldest subducting lithosphere weakest coupling the rupture propagated southward along an interface bounding progressively younger oceanic lithosphere terminating near the subducting chile rise prior to a great subduction earthquake the sinking subducted slab will cause increased tension at depths of 50 200 km with greatest tension near the shallow zone resisting plate subduction plate sinking not only leads to compressional stresses at a locked interface thrust zone but may load compressional stresses at plate depths of 260 350 km provided that the shallow sinking occurs faster than the relaxation time of the deeper mantle this explains k mogi s observations of m 7 thrust earthquakes at depths of 260 350 km immediately downdip and within 3 years prior to five great shallow earthquakes of northern japan the slab pull model explains the lower layer of double seismic zones as due to tension from the deeper sinking plate and the upper layer as due to localized in plate compression as plate motion is resisted by the bounding mantle just downdip of the interface thrust zone there occurs an aseismic 20 50 dip increase of subducted plate this slab bend reflects the summed slab pull force of deeper plate and probably is at the crustal basalt to eclogite phase change resistance to subduction provided by a continually developing slab bend may be an important factor in the size of slab pull force delivered to an interface thrust zone

low frequency source characteristics of the great 1960 chilean earthquake the low frequency nature of the great 1960 chilean earthquake the earth s largest recorded event is characterized and a source model composed of three events with a combined seismic moment of 5 5 1023 n m and a duration of 1500 s is presented the results show conclusively that large scale slip which is only observed at low frequencies preceded the main shock complex amplitude measurements of normal mode data in the band 1 0 5 0 mhz recorded at eight vertical component stations comprise the data set in this band the earthquake source is assumed to be described by a line source propagating at a constant rupture velocity the data set is the basis for a sequence of least squares inversions to determine the seismic moment rupture velocity spatial slip distribution and the temporal slip function the data are best explained by a source model that begins 1150 s before the main shock with an event of moment 1 9 1023 n m and rise time of 300 s a main shock with moment of 3 2 1023 n m and for which most of the low frequency energy was released beginning about 50 s after the short period origin time and an event 350 s later with moment of 0 4 1023 n m the uncertainty in the moment estimate of the great 1960 chilean earthquake is about 50 and is due primarily to the probable range of fault plane dip which is not well constrained at this time

the november 29 1978 oaxaca mexico earthquake a large simple event the recent oaxaca mexico earthquake november 29 1978 mw 7 6 ms 7 8 seismic moment m0 3 2 1027 dyne cm is of special interest because of its location within a predetermined seismic gap the event excited long period 100 200 s multiple rayleigh and love waves which were well recorded by the wwssn these data along with p wave first motion data and p waveforms were used to constrain the source mechanism the results indicate an oblique thrust mechanism consistent with subduction of the cocos plate to the northeast beneath mexico dip 14 strike n90 w rake 54 hence this event is indeed of the type anticipated by ohtake et al 1977 a local network of stations installed in a joint university of mexico california institute of technology program began operation 20 days prior to the mainshock gonzalez 1979 mcnally et al 1979 mcnally 1981 ponce et al 1980 the 43 foreshocks of magnitude m 2 8 were recorded by the network in a period of 20 days prior to the mainshock these events show an interesting spatial and temporal pattern which culminates in the last 1 8 days of the sequence with an apparent migration of activity toward the epicenter of the impending earthquake this pattern can be interpreted as a buildup of stress or migration of stress toward a fault zone asperity with supplemental stations the network continued operation until december 12 1978 singh et al 1980 and provided good hypocentral control for the more than 169 aftershocks of magnitude m 2 8 the area of the aftershock zone determined from these events is 5525 km2 85 km by 65 km in spite of the large size of the event p waves for the oaxaca event indicate an extremely simple source at the period range of the wwssn long period seismographs this simplicity suggests that the p waves were generated by a limited portion of the rupture surface perhaps by the breaking of a fault zone asperity this result may be further supported by the discrepancy between the larger surface wave moment compared with that determined from body waves such simplicity also appears to be the case for the 1965 and 1968 mexican earthquakes on the adjacent eastern and western ends of the oaxaca aftershock zone respectively chael et al 1980 this type of body wave simplicity for a large subduction zone earthquake is an important characteristic of the mode of strain release along some subducting plate boundaries

fault plane orientations of intermediate depth earthquakes in the middle america trench 1 intermediate depth earthquakes are often attributed to dehydration embrittlement reactivating preexisting weak zones the orientation of presubduction faults is particularly well known offshore of middle america where seismic reflection profiles show outer rise faults dipping toward the trench and extending 20 km into the lithosphere if water is transported along these faults and incorporated into hydrous minerals the faults may be reactivated later when the minerals dehydrate in this case the fault plane orientations should be the same in the outer rise and at depth after accounting for the angle of subduction to test this hypothesis we analyze the directivity of 54 large mw 5 7 earthquakes between 35 and 220 km depth in the middle america trench for 12 of these earthquakes the directivity vector allows us to identify the fault plane of the focal mechanism between 35 and 85 km depth we observe both subhorizontal and subvertical fault planes the subvertical fault planes are consistent with the reactivation of outer rise faults whereas the subhorizontal fault planes suggest the formation of new faults deeper than 85 km we only observe subhorizontal faults indicating that the outer rise faults are no longer being reactivated the similarity with previous results from the colder tonga kermadec subduction zone suggests that the mechanism generating these earthquakes and controlling fault plane orientations depends on pressure rather than temperature or other tectonic parameters and that the observed rupture characteristics constitute a basic feature of intermediate depth seismicity exclusively subhorizontal faults may result from isobaric rupture propagation or the hindrance of seismic slip on preexisting weak subvertical planes

resolving fault plane ambiguity for small earthquakes summary we have developed an automated procedure to resolve fault plane ambiguity for small to medium sized earthquakes 2 5 ml 5 using synthetic green s tensors computed in a 3 d earth structure model and applied this procedure to 35 earthquakes in the los angeles area for 69 per cent of the events we resolved fault plane ambiguity of our cmt solutions at 70 per cent or higher probability for some earthquakes the fault planes selected by our automated procedure were confirmed by the distributions of relocated aftershock hypocentres in regions where there are no precisely relocated aftershocks or for earthquakes with few aftershocks we expect our method to provide the most convenient means for resolving fault plane ambiguity our procedure does not rely on detecting directivity effects therefore it is applicable to any types of earthquakes

seismotectonics of the central segment of the indonesian arc abstract in this paper a revision of seismicity affecting the central segment of the indonesian island arc ranging between 110 and 126 e is presented using the areal and in depth distribution of seismic activity strain release maps and focal mechanisms lateral changes in the wadati benioff zone have been analyzed to determine possible boundaries between portions of lithosphere with different subduction geometries the seismicity pattern indicates that the sumbawa flores wetar sector shows different forms of behaviour with respect to the adjacent sectors these include driving mechanism inclination and continuity of the subducting slab and subduction features this area therefore seems to be isolated from the sunda and banda arcs by two principal boundaries these having a nearly n s trend in the bali region and with a nearly e w trend in the region ranging between wetar northern timor and tanibar the first boundary characterized by an absolute minimum of seismic activity at all ranges of depth has been interpreted in terms of subduction of the roo rise aseismic bathymetric ridge for the second boundary dividing a northwardly steeply dipping slab from an e w subducting slab dipping with an angle of 30 40 a tear in the upper part depth less than 300 km and a hinge fault system in the deepest part of the lithosphere have been proposed from the analysis of focal mechanisms of shallow earthquakes it was inferred that the central part of the indonesian arc is subject to a vortex shaped stress field centred on the savu basin in this model the compressive axes appear to rotate counterclockwise from sw to nne in the sumba sumbawa western flores region and clockwise from w to nnw in the timor eastern flores zone to interpret these features on the basis of seismological evidence a lateral discontinuity in the arc trench system close to sumba a collision between sumba and sumbawa and a rotation towards the north northeast of sumba have been suggested the proposed structural discontinuity trending nw se may represent a major transcurrent fault zone through which the australian continental lithosphere comes into contact with the indian oceanic lithosphere

assessing the scalar moment of moderate earthquake and the effect of lateral heterogeneity on normal modes an example from the 2013 04 20 lushan earthquake sichuan china medium frequency normal modes in the frequency range of 2 0 6 0 mhz excited by moderate earthquakes 6 0 mw 7 0 are weak seismic signals and seldom concerned in academic study we show that the validity of predicted m0 scalar seismic moment for a complex moderate earthquake can be effectively assessed by a systematic comparison of observed and synthetic medium frequency spheroidal modes and the effect of lateral heterogeneity on normal mode amplitudes can also be well assessed in the comparison for a complex moderate earthquake the differences between predicted m0 derived from different inversion methods are significant in some cases as large as factors of 1 56 3 18 in this study we focus on the lushan earthquake a moderate thrust event on 20 april 2013 in the western sichuan china five reported m0 for the earthquake differ significantly from 0 4 1019 to 1 06 1019 n m up to about 2 5 times difference to assess the validity of reported m0 we compare observed with synthetic modes corresponding to five centroid moment tensor solutions at 17 stations which located within epicental distances of 5 30 and distributed in a wide range of source receiver azimuths synthetic modes corresponding to moment tensor solutions derived from long period waveforms show good agreement to observations however synthetics corresponding to moment tensor solutions derived from body waves display significant deviations of amplitudes from observations we show underestimate of m0 is the main cause for such a large deviation another important result obtained from the comparison is that lateral heterogeneity has very little effects on the amplitudes of spherical modes at frequencies below 6 0 mhz this observational result is inconsistent with previous theoretical result of lateral structure perturbations to normal modes

earthquake mechanics and deformation in the tonga kermadec subduction zone from fault plane orientations of intermediate and deep focus earthquakes 1 we make use of rupture directivity to analyze 82 deep earthquakes 100 km depth in the tonga kermadec subduction zone identifying the fault planes for 25 of them we are able to place new constraints on both the physical mechanism of intermediate and deep focus earthquakes and deformation within the subducting slab we find that half of deep earthquakes with mw 6 have detectable directivity we compare the obtained fault orientations with those expected for the reactivation of outer rise normal faults and with those expected for the creation of new faults in response to the ambient stress field earthquakes 300 km depth match the patterns expected for the creation of a new system of faults we observe both subhorizontal and subvertical fault planes consistent with a downdip compressional stress field slip along these faults causes the slab to thicken rupture propagation shows no systematic directional pattern in contrast at intermediate depths 100 300 km all ruptures propagate subhorizontally and all identified fault planes whether in the upper or lower region of the double seismic zone are subhorizontal rupture propagation tends to be directed away from the top surface of the slab after accounting for the angle of subduction the subhorizontal fault plane orientation is inconsistent with the orientation of outer rise normal faults allowing us to rule out mechanisms that require the reactivation of these large surface faults subhorizontal faults are consistent with only one of the two failure planes expected from the slab stress field suggesting that isobaric rupture processes or preexisting slab structures may also influence the fault plane orientation if all deformation takes place on these subhorizontal faults it would cause the slab to thin assuming the slab is incompressible this implies that the slab is also lengthening and suggests that slab pull rather than unbending is the primary force controlling slab seismicity at intermediate depths

teleseismic estimates of the energy radiated by shallow earthquakes the energy flux contained in the p wave groups p pp sp or the s wave groups s ps ss radiated by a shallow earthquake is modeled assuming that the energy flux in the direct and depth phases adds incoherently by defining generalized radiation patterns which incorporate this neutral interference the wave groups are analyzed as though they were comprised of a single phase measurements of the energy flux in the wave groups are corrected in the frequency domain for both the body wave attenuation and the frequency band of the recording the corrected measurements are then used to estimate the seismic energy radiated by the earthquake this analysis is applied to digital recordings of the teleseismic wave groups radiated by the may 2 1983 coalinga california earthquake and the october 28 1983 borah peak idaho earthquake for the coalinga earthquake an estimate of es 1 6 0 4 1021 dyn cm was determined from six p wave groups while the sh wave group recorded at station col returned an estimate of es 1 2 1021 dyn cm for the borah peak earthquake an estimate ofes 3 2 0 5 1021 dyn cm was determined from seven p wave groups the distribution of the isoseismals for the borah peak earthquake indicate that the energy radiated by this event was focussed to the northwest in the direction of rupture propagation correcting the teleseismic estimate for this focussing gives es 3 6 0 5 1021 dyn cm combining these estimates of the radiated energy with broad band estimates of the seismic moment yields estimates of the apparent stress of 17 and 7 bars for the coalinga and the borah peak earthquakes respectively

downdip tensional earthquakes beneath the tonga arc a double seismic zone characteristics of seismicity at intermediate depth beneath the tonga arc are studied special attention is paid to newly identified downdip tensional events because the dominance of downdip compression has been known in this area we reexamine the relatively shallow 70 km downdip tensional events reported in the harvard centroid moment tensor solutions by modeling bodywave waveforms of world wide standard seismograph network seismograms and conclude that they are in fact intraplate downdip tensional events furthermore these downdip tensional events are consistently located below and seaward of downdip compressional events and appear to constitute a double seismic zone the result of a relative relocation technique applied to these earthquakes also supports this observation which was originally based on routinely determined epicenters the subducting slab beneath the tonga arc has been considered as a prototype of a compressionally loaded slab the existence of a double seismic zone in tonga therefore would suggest that double seismic zones located at intermediate depth in subducting slabs are more common than previously thought

source process of the great 1977 sumba earthquake in order to investigate the applicability of the asperity model to intraplate earthquakes we have studied the rupture process of the great 1977 sumba normal faulting earthquake mw 8 2 8 3 one of the largest earthquakes since 1963 this event has been variously interpreted as a plate detachment event i e rupture through the entire lithosphere or a shallow plate bending event we have analyzed long period body waves in order to determine the spatiotemporal rupture characteristics including the depth extent of the rupture area visible depth phases in the initial stage of weak radiation beginning about 15 s before the main pulse suggest that the earthquake nucleated near 29 km depth which corresponds to the maximum depth of the aftershock sequence the excitation of a strong tsunami implies that rupture extends to the surface while deconvolutions of long period p waves suggest a relatively shallow 50 km maximum depth extent however the existence of slip below this depth cannot be ruled out particularly if it preferentially radiates frequencies below the passband of the body waves used 0 02 hz for undiffracted phases the source time function of the principal rupture which initiated 30 km west of the epicenter of the precursor comprises a dominant initial short duration 24 s triangular pulse followed by several smaller pulses however slightly diffracted phases indicate a simple basic underlying character for the rupture consisting of the initial 24 s triangle superimposed on a longer duration 42 44 s trapezoid the absence of observable directivity in the deconvolved source time functions suggests a bilateral rupture mode although the body waves do not require a fault length greater than 80 km the aftershock area and surface wave results of zhang and kanamori 1988 imply a total length of at least 200 km the body wave source functions are well modeled by a 200 km long fault extending to 30 50 km depth on which slip nucleates at the center of the fault and has variable displacement along strike the peak moment release of the deconvolved source functions indicates higher displacement in the hypocentral area than in other areas of the fault the spatial relationship of the precursor and the main pulse is suggestive of rupture initiating at and propagating along the edge of an asperity prior to the rupture of the asperity itself the large size of the event may be due to an unusual stress environment arising from strong lateral gradients in seismic interplate coupling along the java timor arc

estimating finite source properties of small earthquake ruptures many of the most fundamental questions in earthquake science are currently limited by a lack of knowledge about small earthquake ruptures small earthquakes are difficult to study owing to the poor constraints placed on many of the interesting physical parameters by bandlimited far field seismic data traditionally dynamic models such as an expanding circular crack have been utilized to bridge the gap between the easily measurable quantities for small earthquakes and more interesting physical parameters such as stress drop and rupture velocity here i present a method for estimating the basic finite source properties of a rupture that is independent of any a priori model and utilizes the description of a finite source the second moments that far field waves are inherently sensitive to application to two magnitude 5 events in southern california demonstrates the ability of an empirical green9s function approach to estimating the second moments to resolve the fault plane ambiguity rupture length and overall directivity additional results are presented for two example m 2 7 events from the creeping section of the san andreas fault to examine the likely lower bound on event size that can be studied with surface seismometers the creeping section earthquakes have very similar rupture areas but would be improperly interpreted as significantly different using the traditional methodology one of these events presents a relatively clear interpretation of the velocity of rupture front propagation which is about 0 8 of the rayleigh speed suggesting little difference in rupture velocity between it and typical large earthquakes

tsunami earthquakes the quest for a regional signal using the technique developed by newman and okal j geophys res 103 1998 26885 a dataset of digital records from 84 earthquakes is analyzed to investigate their source slowness in the quest for a possible regional signal in three subduction zones which experienced recent tsunami earthquakes nicaragua 1992 java 1994 peru 1996 the dataset is augmented by analog seismograms from historical events including major tsunamigenic earthquakes of the past 65 years we fail to detect a regional trend for slowness which suggests that the latter may be controlled on a more local scale by morphological structures of the subducting plate no correlation is found between slowness and either depth focal mechanism or seismic moment in nicaragua we document two slow historical earthquakes located on the slab down dip from the 1992 shock the most interesting results are in peru where a local area of slowness is tentatively defined around the source of the 1960 tsunami earthquake and where both the 1996 and 1960 tsunami earthquakes occur at the intersection of the trench with major topographic features on the nazca plate the mendana fracture zone and the trujillo trough respectively 2001 elsevier science b v all rights reserved

time variations in the earth s gravity field detectable with geopotential research mission intersatellite tracking the geopotential research mission grm is a proposed system of two artificial satellites in tandem drag free polar orbits of low altitude 160 km designed for a detailed global mapping of the earth s gravitational and magnetic fields the mission should provide a large amount of new information about the gravity field particularly over continents resolving spatial variations in the gravity field as short as 100 km half wavelength however grm should also perform a much more difficult task the detection of time variations in the gravity field among the effects which produce changes in the field that are large enough to be detected by the intersatellite millimeter wavelength 1 s precision grm sensor are the following 1 rebound from ancient deglaciation 2 very large dip slip earthquakes 3 detailed ocean tides and 4 the seasonal growth and decline of continental glacial fields in particular many nonzonal as well as zonal components affected by postglacial rebound should be detected in a 6 month grm mission repeat passes over the fault zones of earthquakes similar to alaska 1964 chile 1960 or sumbawa 1977 should reveal signal changes due to their earth movements the effect of ocean tides on the grm signal should be readily detectable over a broad band of frequencies even if all but 10 of the tides are correctly modeled continued geophysical interest in these now largely unobserved phenomena warrants extension of the grm mission to somewhat higher altitudes

body wave deconvolution for variable source parameters application to the 1978 december 6 kuriles earthquake summary a method to determine the depth and mechanism of subevents in earthquakes with complex rupture is developed complex body waves are deconvolved using a damped lanczos inversion to retrieve the source time function some constraints on the mechanism and depth of the first subevent are assumed though not required the data set is deconvolved using the green s function for the first subevent to obtain a best fitting source time function this source time function is then windowed in time around the first pulse and the corresponding synthetic seismogram is subtracted from the data this process is repeated on residual data to determine mechanisms and depths of subsequent subevents this method is applied to the 1978 december 6 kuril islands earthquake a complex event which ruptured vertically from 100 to 220km in depth and represents tearing of the pacific plate as it subducts beneath the kuril and honshu arcs using long period wwssn data we found three main subevents with the mechanism o 150 80 and 20 at depths of 120 165 and 210km in this particular case one nodal plane is very well constrained and there is some a priori evidence for significant vertical rupture

late wisconsinan helmeted muskoxen bootherium bombifrons from southwestern alberta canada the first known occurrence of helmeted muskox in the late wisconsinan ca 16 000 11 000 radiocarbon years bp of alberta is recorded and described 14c dating places the specimen at 10 980 80 ra

slab decoupling in the tonga arc the june 22 1977 earthquake the june 22 1977 earthquake in the southern tonga arc is a large normal faulting event with downdip rupture propagation on a steeply dipping fault plane we use a standard least squares inversion of p and sh waves for the source time function to determine a source consisting of two subevents located at depths of 40 55 and 105 125 km and a total time duration of 50 s the ratios of the spectral amplitudes of the radial modes 0s0 1s0 and 2s0 independently require a centroid depth of at least 100 km at their lower frequencies the body wave analysis suggests a moment of 1 04 1028 and the 0s0 spectral amplitude suggests a value of 1 8 2 0 1028 dyn cm the emerging picture is that of a complete rupture of the sinking lithospheric slab starting from 40 km depth and propagating down to 125 km this indicates that the decoupling of the overriding lithosphere from the slab in this area of the tonga arc takes place by gravitational pull

variable rupture mode of the subduction zone along the ecuador colombia coast three large earthquakes occurred within the rupture zone of the 1906 colombia ecuador earthquake m w 8 8 in 1942 m s 7 9 1958 ms 7 8 and 1979 m s 7 7 we compared the size and mechanism of these earthquakes by using long period surface waves tsunami data and macroseismic data the 1979 event is a thrust event with a seismic moment of 2 9 10 28 dyne cm and represents subduction of the nazca plate beneath south america the rupture length and direction are 230 km and n40 e respectively examination of old seismograms indicates that the 1906 event is also a thrust event which ruptured in the northeast direction the seismic moment estimated from the tsunami data and the size of the rupture zone is 2 10 29 dyne cm the 1942 and 1958 events are much smaller about 1 5 to 1 10 of the 1979 event in the seismic moment than the 1979 event we conclude that the sum of the seismic moments of the 1942 1958 and 1979 events is only formula of that of the 1906 event despite the fact that the sequence of the 1942 1958 and 1979 events ruptured approximately the same segment as the 1906 event this difference could be explained by an asperity model in which the fault zone is held by a discrete distribution of asperities with weak zones in between the weak zone normally behaves aseismically but slips abruptly only when it is driven by failure of the asperities a small earthquake represents failure of one asperity and the rupture zone is pinned at both ends by adjacent asperities so that the effective width and the amount of slip are relatively small a great earthquake represents failure of more than one asperity and consequently involves much larger width and slip

spatial patterns of aftershocks of deep focus earthquakes this paper presents precise relative relocations for aftershocks of 59 intermediate and deep earthquakes using p pp and pkp arrival times read by us or reported in the literature these aftershocks included 36 rupture subevents occurring within 1 min of the initial event and 71 true aftershocks occurring later and identified statistically as being related to the initial event we compare the relative locations with the orientations of the wadati benioff zones and with the available focal mechanisms using statistical methods not previously applied to earthquake data surprisingly neither true aftershocks nor rupture subevents cluster along the nodal planes of intermediate or deep earthquake focal mechanisms aftershocks more than 20 km from the initial events occur preferentially in the plane of the wadati benioff zone while those lying closer have isotropically distributed directions rupture subevents occur after the travel time of the s wave from the initial event larger magnitude earthquakes generally possess rupture subevents lying farther from the initial event whereas true aftershocks can occur 50 km or more from initial events having magnitudes as small as 5 3 except following a few unusually large earthquakes with focal depths of about 100 km we find no rupture subevents or true aftershocks more than about 80 km from the initial hypocenter the existence of many aftershocks far from nodal planes does not favor models in which deep earthquake failure is simply slip along a planar fault rather the aftershocks may occur in response to a general redistribution of stress caused either by the occurrence of the initial event or possibly by nearby continuing phase transitions alternatively the failure zones of deep earthquakes may be surfaces which are frequently curved by 40 or more from the orientation of the initial nodal plane perhaps due to inhomogeneous stress distributions

co seismic geomorphic and geologic fold growth associated with the 1978 tabas e golshan earthquake fault in eastern iran we describe the seismicity and late cenozoic deformation associated with a blind thrust fault at tabas e golshan hereafter referred to as tabas eastern iran which generated a devastating mw 7 3 earthquake on the 16th september 1978 measurements from a structural transect through the sardar anticline segment indicate fault propagation folding above a gently 20 eastward dipping blind thrust fault the thrust flattens into a horizontal detachment at a depth of only 2 km tightening of the fold forelimb is accommodated by flexural slip along numerous bedding planes with many of the slip surfaces showing fresh striations with a large component of right lateral strike slip a steeply dipping fault zone showing almost pure strike slip is also developed within the forelimb of the fold our field observations are consistent with the source parameters of the 1978 tabas earthquake and additional events in 1979 and 1980 which all involved slip on a shallowly dipping thrust with a significant component of right lateral slip the surface of an alluvial fan which is likely to have been abandoned at 8 10 ka has been folded as it crosses the sardar anticline the age constraints combined with topographic profiles along the deformed fan surface and constraints on the dip of the fault at depth provide an approximate rate of horizontal shortening of 1 5 mm yr shortening at tabas appears to result from transpressional bending at the north end of the nayband strike slip fault a northward continuation of the nayband fault which may be slipping at rates of 2 mm yr is identified along the base of the shotori mountains 10 20 km east of the tabas thrust the range front fault did not move in 1978 and constitutes an additional threat to local populations

duration and depth of faulting of the 22 june 1977 tonga earthquake the 22 june 1977 mw 8 2 tonga earthquake has the longest rupture duration ever reported for a normal fault event the 150 km depth range spanned by aftershocks of the earthquake is also unusually large there has been substantial controversy over both the depth and duration of faulting for this great event obscuring its tectonic significance we study the source process of the tonga event using long period rayleigh waves recorded by the global digital seismograph network gdsn and international deployment of accelerometers ida networks for a standard assumption of a haskell source a total duration of 84 4 sec is obtained using a least squares inversion method we introduce the use of the spectral amplitude as a weighting factor in measuring the misfit between the data and a given source finiteness model which reduces the scatter and improves the resolution of source duration determined from data ranging in period from 150 to 300 sec using a more realistic shape for the source time function in the inversion drawing upon results from body wave analysis reveals a much longer 165 sec process time component of the source process of the tonga earthquake the fundamental mode rayleigh waves do not resolve any horizontal source directivity however the centroid depth of the earthquake is well resolved as 96 km with 90 per cent confidence range 93 104 km the estimated error in the depth determination due to the uncertainties in the source finiteness and earth models is only a few kilometers the results indicate that the rupture of the earthquake excited long period seismic waves at depths somewhat greater than the 70 to 80 km depth range where the primary bodywave radiation occurred favoring rupture on the steeply dipping plane of the focal mechanism the fundamental mode rayleigh waves with periods longer than 150 sec cannot resolve vertical extent of the faulting however additional information from body wave and free oscillation analyses indicates a vertical fault extent of about 50 km with a frequency dependent variation in seismic radiation with depth

large earthquakes in the tonga region associated with subduction of the louisville ridge subduction of the louisville ridge influences both interplate and intraplate seismicity in the southern tonga region 22 s 26 s five earthquakes with diverse mechanisms and seismic moments greater than 1 1027 dyn cm have occurred in this region since 1975 these include two outer rise one underthrusting and two intermediate depth events all of which occurred in close proximity to the subducting ridge in order to understand better the nature of these events and to determine the role played by the louisville ridge in the subduction process detailed rupture models have been determined for each earthquake by body and surface wave analysis three events occurred at shallow depths near the oblique intersection of the louisville ridge and the tonga are these are the compressional thrust outer rise event of october 11 1975 mw 7 4 the tensional normal outer rise event of october 10 1977 mw 7 4 and the subsequent underthrusting event on december 19 1982 mw 7 5 the latter being the largest documented interplate event in tonga the intermediate depth events of june 22 1977 d 70 km mw 8 1 and april 13 1980 d 160 km mw 7 6 both have normal fault mechanisms however the 1977 event has a downdip tension axis whereas the 1980 event has a downdip compression axis the 1977 event is unusual due to its large size and the fact that most intermediate depth activity in tonga involves downdip compression the body wave radiation for the 1977 event indicates concentrated rupture in the depth range 70 90 km near the downdip projection of the louisville ridge it appears that the louisville ridge perturbs the regional stress regime at both intermediate and shallow depths in the slab the ridge appears to be a buoyant feature that produces locally strong interplate coupling to the north of its junction with the tonga trench which accounts for the 1982 thrust event and the preceding 1975 compressional outer rise event located seaward of the thrust rupture zone south of the ridge intersection the plate interface appears to be less strongly coupled tensional stresses due to slab pull are communicated to shallow depths resulting in the october 10 1977 mw 7 4 tensional outer rise event the locally enhanced interplate coupling along with a downdip stress barrier to the intraplate compressional stresses that arise from deep resistance to the slab subduction are two effects of the ridge that appear to explain the accumulation of in plate tension in the region of the june 22 1977 event the april 13 1980 downdip compressional event reflects a return to in plate compression following the great 1977 rupture which relaxed the tensional stress the unusual stress regime of the subducting ridge and its oblique trajectory down the plate are thus responsible for the diversity of large earthquake occurrence in the southern tonga arc

the source rupture process of the great banda sea earthquake of november 4 1963 abstract the banda sea earthquake of november 4 1963 is one of the largest m w 8 3 intraplate events it involved oblique thrusting at an intermediate depth within the subducted lithosphere near the abrupt bend in the southeastern banda arc 6 86 s 129 58 e to better understand the tectonic significance of this earthquake the detailed source process of the banda sea event was determined by body wave analysis the rupture history was established by deconvolving source time functions from long period p wave seismograms using both individual station and multi station time domain deconvolution methods the seismic moment release occurred within the first 50 s of rupture initiating at a depth near 120 km and expanding laterally and downdip over a vertical extent of about 50 km slip and moment release were concentrated in one main region near the hypocenter at depths between 110 and 130 km the along strike rupture length was only about 100 km so it is difficult to resolve any horizontal directivity the compressional stress orientation inferred from the focal mechanism parallels the strike of the slab and reflects the importance of contortion of the lithosphere in this region the banda sea event may be part of a major detachment at the leading edge of the subducted australian continental shelf

predominance of unilateral rupture for a global catalog of large earthquakes the manner in which an earthquake rupture propagates across a fault reflects both the initial properties of the fault and the dynamical stresses produced by the rupture we quantify the propagation of an earthquake rupture using the second moments of the earthquake space time distribution in particular the second moments provide a simple way to differentiate between approximately bilateral and predominantly unilateral ruptures we determined the second moments for a catalog of m w 7 earthquakes that have occurred since 1994 the results show that approximately 80 of large shallow ruptures are predominantly unilateral our result agrees well with strong motion inversions from previous studies on moderate and large earthquakes the predominance of unilateral propagation in large earthquakes is explained by a simple characteristic earthquake model in which large events rupture an entire structurally defined fault segment and nucleation points are uniformly distributed along the fault the predominance of unilateral rupture may also be enhanced by the dynamic stress field produced by contrasts in the elastic properties between the two sides of plate boundary faults manuscript received 16 november 2001

centroid moment tensor solutions for 113 large earthquakes in 1977 1980 abstract the centroid moment tensor technique is applied to 113 large earthquakes of the period 1977 1980 including all the shallow events with magnitude mb ms or ml 6 5 we use digital data recorded by the global digital seismograph network gdsn and international deployment of accelerometers ida networks solutions are determined for three sequences of events close in time by inverting mantle wave data simultaneously for multiple sources

an experiment in the retrieval of depth and source mechanism of large earthquakes using very long period rayleigh wave data abstract the possibility of obtaining an estimate of depth for large earthquakes from low frequency mantle wave data alone is investigated using moment tensor formalism after illustrating the sensitivity to depth of the eigenfunctions in the period range of 160 to 350 sec we give several examples of application of the two step inversion procedure proposed earlier for shorter period rayleigh wave data romanowicz 1982 we find that for earthquakes below a depth of about 50 km we are able to resolve depth even when a spherically symmetric average earth model is used for propagation corrections this is particularly interesting in the case of large subduction zone earthquakes for which an estimate of the vertical extent of faulting can thus be obtained independently of aftershock studies in a very fast and simple manner which does not involve any synthetic seismogram calculations or lateral heterogeneity modeling for shallower earthquakes especially those with one steeply dipping nodal plane the resolution of depth is less precise taking lateral heterogeneity into account by using available regionalized phase velocities improves the results marginally we anticipate that accounting more accurately for the low order harmonics in the worldwide phase velocity distribution should prove most helpful since these interfere the most with the theoretical radiation patterns of earthquakes the determination of depth depends more critically on the source process time which has to be accounted for especially for horizontally propagating faults

tectonic model of the pacific north american plate boundary in the gulf of alaska from broadband analysis of the 1979 st elias alaska earthquake and its aftershocks the st elias alaska earthquake of 28 february 1979 ms 7 2 is reanalyzed using broadband teleseismic body waves and long period surface waves because of unresolved questions about its depth focal mechanism seismic moment and location in a seismic gap teleseismic waveforms are simultaneously inverted to determine the source mechanism seismic moment rupture history and centroid depth these data are well modeled with a point source propagating in the ese direction with an average kinematic rupture velocity of 2 5 km s the best fitting source mechanism indicates underthrusting on a ne dipping plane the mainshock depth of 24 km and the depth of aftershocks determined from inversions are consistent with locations on the gently dipping main thrust of the pacific north american plate boundary these depths are substantially different from those of earlier body wave studies and regional seismic network aftershock depth determinations but are in accord with the harvard centroid moment tensor and international seismological centre determinations the seismic moment determined from body waves is 9 4 1019 n m mw 7 3 the spatial and temporal distribution of moment release indicates that the st elias earthquake was a complex rupture consisting of two distinct subevents within 38 s of the initial onset followed by low moment release during the next 34 s earlier studies indicated an unusual amount of surface wave energy at very long periods 200 s that led some workers to suggest that st elias was a slow earthquake our broadband modeling does not require more than 34 s of additional moment release after the first two subevents moreover we are able to match the phase and amplitude of 200 s love and rayleigh waves with a thrust fault point source of moment 1 3 1020 n m mw 7 4 located at the body wave centroid the moment difference is not discernible with body waves for moment evenly distributed over 72 s thus the st elias earthquake is not slow with respect to 200 s surface waves but is complex with regard to the broadband body waves upper plate structure apparently controlled the gross characteristics of rupture the rupture direction parallels mapped upper plate faults rupture propagated unilaterally to the ese with little initial moment release as a shallow north dipping thrust that later changed to more steeply ne dipping with a large right lateral strike slip component the locations and source mechanisms of these subevents and locations of aftershocks define a shallow dipping surface at the eastern edge of the pacific plate moreover the component of strike slip motion increases with time in the mainshock implying that the transition to strike slip faulting occurs along the plate interface the estimated nucleation point of the second subevent coincides with a large concentration of aftershocks interpreted as representing a barrier to continuous rupture associated with the northern most boundary of the yakutat terrane joint relocation of aftershocks suggests that the main plate boundary may be offset vertically by 5 10 km as a result of this structure the southern part of the aftershock zone while containing many aftershocks appears not to have ruptured coseismically but may have failed later by aseismic creep as seen in geodetic measurements faults associated with the malaspina fault system the onshore extension of the aleutian trench appear to be the surface expression of the underthrusting plate boundary however upper plate deformation is widespread because of the collision of the yakutat terrane the convergence direction may explain the lack of a highly active wadati benioff zone downdip of the st elias zone the neotectonic deformation of the chugach st elias mountains is probably related to collision and subduction of the yakutat terrane a terrane in the process of accreting and subducting will cause considerable upper plate deformation over a wide zone once subduction of a terrane has begun deformation may then become localized

average seismic source parameter relations for plate margin earthquakes abstract empirical mb ms and mo data are used to develop an average spectral scaling relation for plate margin earthquakes using equations based upon a rectangular bilateral dislocation model with uniform rupture velocity the spectra give values of fault rupture length and width static stress drop and average fault displacement as a function of mb ms and mo compared to mid plate earthquakes of the same seismic moment the large average plate margin earthquake has a bigger rupture length rupture area and average fault displacement and a smaller rupture width and static stress drop

active tectonics of the alpine himalayan belt between western turkey and pakistan summary over 80 new fault plane solutions combined with satellite imagery as well as both modern and historical observations of earthquake faulting are used to investigate the active tectonics of the middle east between western turkey and pakistan the deformation of the western part of this region is dominated by the movement of continental material laterally away from the lake van region in eastern turkey this movement helps to avoid crustal thickening in the van region and allows some of the shortening between arabia and eurasia to be taken up by the thrusting of continental material over oceanic type basement in the southern caspian mediterranean makran and black sea thus central turkey bounded by the north and east anatolian strike slip faults is moving west from the van region and overrides the eastern mediterranean at two intermediate depth seismic zones one extending between antalya bay and southern cyprus and the other further west in the hellenic trench the motion of northern iran eastwards from the van region is achieved mainly by a conjugate system of strike slip faults and leads to the low angle thrusting of iran over the southern caspian sea the seismicity of the caucasus shows predominantly shortening perpendicular to the regional strike but there is also some minor elongation along the strike of the belt as the causcasus overrides the caspian and black seas the deformation of the eastern part of this region is dominated by the shortening of iran against the stable borders of turkmenistan and afghanistan the north east direction of compression seen in zagros is also seen in north east iran and the kopet dag where the shortening is taken up by a combination of strike slip and thrust faulting large structural as well as palaeomagnetic rotations are likely to have occurred in ne iran as a result of this style of deformation north south strike slip faults in southern iran allow some movement of material away from the collision zone in ne iran towards the makran subduction zone where genuinely intermediate depth seismicity is seen within this broad deforming belt large areas such as central turkey nw iran azerbaijan central iran and the southern caspian appear to be almost aseismic and therefore to behave as relatively rigid blocks surrounded by active belts 200 300 km wide the motion of these blocks can usefully be described by poles of rotation the poles presented in this paper predict motions consistent with those observed and also predict the opening of the gulf of iskenderun ne of cyprus the change within the zagros mountains from strike slip faulting in the nw to intense thrusting in the se and the relatively feeble seismicity in se iran baluchistan this description also explains why the north south structures along the iran afghanistan border do not cut the east west ranges of the makran within the active belts surrounding the relatively aseismic blocks a continuum approach is needed for a description of the deformation even though motions at the surface may be concentrated on faults the evolution of fault systems within the active zones is controlled by geometric constraints such as the requirement that simultaneously active faults do not in general intersect many of the active processes discussed in this paper particularly large scale rotations and lateral movement along the regional strike are likely to have caused substantial complexities in older mountain belts and should be accounted for in any reconstructions of them

source characteristics of earthquakes in the michoacan seismic gap in mexico we investigated the source characteristics of large earthquakes which occurred in the michoacan mexico seismic gap during the period from 1981 to 1986 in relation to historical seismicity in the region the rupture pattern of the michoacan gap during this period can be characterized by a sequential failure of five distinct asperities before 1981 the michoacan gap had not experienced a large earthquake since 1911 when an m s 7 8 earthquake occurred the recent sequence started in october 1981 with the playa azul earthquake which broke the central part of the gap body wave modeling indicates that the playa azul earthquake is 27 km deep with a seismic moment of 7 2 10 27 dyne cm it is slightly deeper than the recent michoacan earthquakes and its stress drop is higher suggesting a higher stress level at depths in the michoacan gap the seismic moment of the 19 september 1985 m w 8 1 earthquake was released in two distinct events with the rupture starting in the northern portion of the seismic gap and propagating to the southeast with low moment release through the area already broken by the 1981 playa azul earthquake the rupture propagated further southeast with an m w 7 5 event on 21 september 1985 another aftershock occurred on 30 april 1986 to the northwest of the 19 september main shock body wave modeling indicates that this event has a simple source 10 sec long at 21 km depth and fault parameters consistent with subduction of the cocos plate 280 12 and 70 and m 0 2 0 to 3 1 10 26 dyne cm m w 6 8 to 6 9 although this distribution of asperities is considered characteristic of the michoacan gap whether the temporal sequence exhibited by the 1981 to 1986 sequence is also characteristic of this gap or not is unclear it is probable that depending on the state of stress in each asperity the entire gap may fail in either a single large event with a complex time history or a sequence of moderate to large events spread over a few years the seismic moment and the time since the last earthquake in michoacan in 1911 fit an empirical relation between moment and recurrence time found for the guerrero oaxaca region of the mexico subduction zone

recent large earthquakes along the middle american trench and their implications for the subduction process several large shallow earthquakes ms 7 0 have occurred along the middle american trench since the installation of the wwssn network included are the 1965 1968 and 1978 oaxaca events the 1970 chiapas event the 1973 colima event and the 1979 petatlan event these earthquakes have been studied in an attempt to identify similarities and differences between them that may lead to a better understanding of fracture and subduction processes the events have seismic moments ranging from 1 0 1027 dyne cm for the 1968 event to 3 2 1027 dyne cm for the 1978 event all events are of predominantly thrust type consistent with subduction to the northeast of the cocos plate body waves for the 1965 1968 1978 and 1979 events along the trench indicate rather simple faulting processes these events all had focal depths of 15 to 20 km and stress drops of the order of 10 bars the 1970 and 1973 events the easternmost and westernmost respectively of the events studied here are located close to triple junctions for the cocos north america caribbean plates 1970 and the cocos north america rivera plates 1973 these two events generated more complex body waves than the oaxaca and petatlan quakes this source complexity may have been related to the more complicated tectonics near the 1970 and 1973 epicenters this may offer a new perspective to viewing source complexity in relation to subduction zones

the matter of size on the moment magnitude of microseismic events abstractwe investigated the method of estimating seismic moment and moment magnitude for microseismic events we determined that the m0t defined by bowers and hudson is the proper scalar moment to be used in microseismic studies for characterizing the size of an event and calculating its moment magnitude for non double couple sources the proportional relationship between body wave amplitude and seismic moment in the brune model breaks down so under such situations the brune model is not an appropriate way to estimate the seismic moment and magnitude moreover the s wave alone is not sufficient for determining the total seismic moment instead the p wave must be analyzed an example barnett shale data set was studied and the results concluded that the magnitudes estimated with the brune model could be off by as much as 1 92 with an absolute average of 0 35 the moment magnitudes based on the scalar moment m0t also gave a significantly different event size distribution and b value estimation finall

characteristics of well determined non double couple earthquakes in the harvard cmt catalog abstract this paper evaluates earthquakes in the harvard centroid moment tensor cmt catalog which possess well determined deviatoric non double couple mechanisms i e mechanisms with significantly large compensated linear vector dipole clvd components for a cmt m we measure the strength of the non double couple component with the statistic norm 2 6det m m 3 which is 0 0 for a pure double couple and 1 0 for a pure clvd for each cmt we measure whether norm is well determined by allowing individual elements of m to vary within their range of uncertainties as reported in the harvard catalog then determining the range of variation of norm as m varies the most well determined 11 of the catalog has a range for norm of 0 2 or less of these earthquakes about one quarter have predominantly clvd mechanisms with norm of 0 4 or greater these 283 mechanisms make up the principal data for this study these clvd earthquakes occur commonly in almost all tectonic environments along mid ocean ridges and transforms in shallow subduction zones within wadati benioff zones and in the interiors of plates in both oceanic and continental regions along ridge transforms the majority have horizontal t axes in shallow subduction zones the majority have horizontal p axes which are approximately perpendicular to the trench these observations are consistent with a schematic model which explains clvd mechanisms as the sum of two or more elementary double couple subevents with orientation fixed by the type and geometry of the plate boundary within ridge transforms subduction zones and wadati benioff zones where the plate motion lithospheric structure etc is sufficiently uniform about 75 of the clvd mechanisms conform to this model

study of the montenegro earthquake sequence march july 1979 abstract data from more than 80 european seismic stations concerning foreshocks the main shock and aftershocks of the earthquake which occurred near the coast of montenegro on 15 april 1979 have been collected and analyzed the data have allowed the focal mechanism of the two strongest shocks to be estimated the hypocentral coordinates of more than 180 aftershocks and some foreshocks have been also computed giving the time space distribution of the sequence the shocks are mostly contained in an area about 100 km long and 30 km wide almost corresponding to the adriatic coast line of the yugoslavia albania border region the hypocentral depths although determined approximately appear to be in the order of 15 to 20 km the results have been compared with previous knowledge of the tectonics of the zone

source retrieval for mantle earthquakes by iterative deconvolution of long period p waves abstract long period p waves of eighteen deep and intermediate depth earthquakes in a moment range 1 10 26 3 10 28 dyn cm are analysed by the method of kikuchi and fukao this issue to iteratively derive point dislocations on a plane the fault plane is defined as the plane of point dislocations that gives the best fit between the synthetic and observed waveforms for dip slip type earthquakes the fault plane is found to dip more steeply than the auxiliary plane in general point dislocations tend to cluster into one or a few subevents we characterize the largest subevent by its maximum moment rate m 0 m and its half duration from which the associated stress drop can be roughly estimated for earthquakes shallower than 400 km half duration is approximately constant 5 s so that stress drop increases from 1000 bar as m 0 m increases the value of for the great banda sea earthquake of 1963 h 100 km is exceptionally large 10 s for which 700 bar for earthquakes deeper than 400 km increases from 3 s to 9 s as m 0 m increases so that is approximately constant 700 bar stress drop so obtained approximates to an overall stress drop with a possible exception of the several largest earthquakes the distribution of point dislocations and the moment rate function indicate that rupture most often expands in a fan shaped fault area and that a large part of the rupture front ceases propagation in a coherent manner a sharp contrast in stress drop behavior across a depth of 400 km may be related to the olivine spinel transition within the downgoing slab of lithosphere

finite moment tensor of the 3 september 2002 yorba linda earthquake we have developed procedures for inverting broadband waveforms for the finite moment tensors fmts of regional earthquakes the fmt is defined in terms of second order polynomial moments of the source space time function it removes the fault plane ambiguity of the centroid moment tensor cmt and yields several additional parameters of seismological interest the characteristic length lc width wc and duration tc of the faulting as well as the directivity vector v d of the fault slip following mcguire et al 2001 we represent the observed waveform relative to the synthetic in terms of two frequency dependent differential times a phase delay p and an amplitude reduction time q which we measure using the generalized seismological data functional gsdf method gee and jordan 1992 we numerically calculate the fmt partial derivatives which allows us to use synthetics computed by using any forward modeling tools we have tested our methodology on southern california seismic network scsn recordings of the 03 september 2002 yorba linda earthquake m w 4 3 using 1d synthetic green s functions we determined the cmt and resolved fault plane ambiguity to resolve the details of source finiteness we employed a joint inversion technique that recovers the cmt parameters of the aftershocks and the cmt and fmt parameters of the mainshock the joint system of equations relating the data to the source parameters of the mainshock aftershock cluster is denuisanced for path anomalies in both observables this projection operation effectively corrects the mainshock data for path related anomalies in a way similar to but more flexible than empirical green s function egf techniques our results indicate that the yorba linda rupture occurred as left lateral slip on a fault patch conjugate to the nearby right lateral whittier fault we obtained source dimensions of lc 0 7 0 1 km wc 0 4 0 1 km and tc 0 2 0 05 sec implying a stress drop of about 3 2 mpa and we found a directivity of 0 8 0 2 oriented up and to the northeast the inferred fault plane is consistent with the mainshock aftershock distribution relocated by hauksson et al 2002

tsunami earthquakes slow thrust faulting events in the accretionary wedge the november 20 1960 peru october 20 1963 kurile and june 10 1975 kurile earthquakes are classified as tsunami earthquakes based on anomalously large tsunami excitation relative to earthquake magnitude long period surface wave analysis indicates double couple faulting mechanisms for all three events rather than single force mechanisms indicative of submarine landslides the earthquakes have shallow depths 15 km and are located near the trench axis and seaward of most other thrust zone events beneath the accretionary prism body waveform inversion indicates very shallowly dipping thrust faulting mechanisms for the three events with dip angles of 6 8 surface wave spectral amplitudes and deconvolution of sh waveforms suggests anomalously long source durations and large seismic moments relative to ms specifically the 1963 kurile event ms 7 2 shows a duration of 85 s and a moment of 6 0 1027 dyn cm mw 7 8 the 1975 kurile event ms 7 0 shows a duration of 60 s and a moment of 2 0 1027 dyn cm mw 7 5 and the 1960 peru event ms 6 75 shows a time function consisting of four subevents with a total duration of 110 130 s and a seismic moment of 3 4 1027 dyn cm mw 7 6 estimated rupture velocities are about 1 km s or less but there is no evidence of unusually low stress drops the august 1 1968 philippines event previously classified as a tsunami earthquake shows none of the anomalous source properties and teleseismic tsunami height measurements are sparse we do not consider this event a tsunami earthquake most of the anomalous tsunami excitation results from underestimation of earthquake size by ms due to the long source duration the tsunami heights are not significantly anomalous relative to seismic moment the slow nature of these events may result from rupture through the sedimentary rock along the basal decollement of the accretionary prism standard scaling laws when adjusted for the slow seismic velocity in the source region show an mw ms relationship similar to that observed for the tsunami earthquakes and predict ms saturation at about 7 3 rather than 8 0 for typical events

the 1977 sumba earthquake series evidence for slab pull force acting at a subduction zone the great 1977 sumba earthquake occurred at the eastern sunda trench just west of the collision of australian continental lithosphere with the island arc the length of the aftershock zone of this normal faulting earthquake is about 200 km aftershocks are concentrated 65 115 km east of the main shock epicenter with very few aftershocks in a 50 km long segment that spans the main shock epicenter relocated hypocenters and focal mechanism data are consistent with normal faulting throughout the upper 28 km of the oceanic lithosphere there is no evidence for thrust faulting of the deeper aftershocks these data imply that the neutral bending surface must be at least 35 40 km deep a second aftershock zone about 180 km northwest of the main shock became active immediately following the main shock but events were concentrated during days 50 52 this zone is a 70 km long lineation that trends toward the main shock epicenter and reflects right lateral strike slip faulting within the subducted oceanic plate seismicity exists to a depth of about 650 km in the very old plate beneath the sunda banda arc and that plate s negative buoyancy causes very large slab pull forces great interface thrust earthquakes are absent at the sumba region and slab pull forces are inferred to have partially decoupled the subducted plate from the overriding plate this decoupling permits slab pull stresses to be guided updip to the region of the sumba main shock such shallow acting slab pull provides a bending moment at the trench and explains the deformation and timing observed for the entire sumba earthquake series in this model slab pull forces stretch the subducted plate until the increasing stresses at the shallow subduction zone lead to a subduction zone earthquake postseismically the released oceanic plate undergoes a pulse of downdip strain returning the plate to a less extended state the moment of this downdip plate motion could exceed the seismic moment of the main shock

stopping phases in seismograms and the spatiotemporal extent of earthquakes on the basis of long period wwssn and some broadband seismograms from grafenberg we investigate the following earthquakes view this table p wave seismograms or true ground displacements show clearly the directivity effect of rupture propagation and the multiple event nature of these earthquakes fault plane solutions of individual source shocks and their relative localization by the master event technique yield fixpoints of rupture history the most striking feature is a strong stopping phase which is interpreted kinematically by abrupt termination of rupture expansion at the end of the fault we use the stopping phase to determine total source extent in space and time as well as the mean rupture velocity the results of this first stage of investigation are subsequently used for modeling the rupture according to the dislocation theory of shear faulting wave propagation through the earth s mantle is treated by ray theory this forward modeling approach yields seismic moment source dimensions mean dislocation and stress drop source complexities are related to unbroken fault gaps bending of the fault plane acceleration of rupture propagation in asperities and most impressive in its radiation effect to the sudden termination of rupture in front of a barrier source complexities are also discussed with respect to tectonic implications

a new method for determining the long period component of the source time function of large earthquakes inversions of seismic body waves indicate that most large earthquakes involve spatial and temporal heterogeneity of the moment release but seismic body waves usually lack sufficient bandwidth to constrain the long period component of the radiation analysis of long period surface waves and free oscillations can constrain the overall source duration and moment however most procedures assume simple trapezoidal or boxcar source time histories inconsistent with the body wave complexity the authors find that source time function complexity can affect long period surface waves sufficiently to impact estimates of the source moment tensor rupture duration and centroid depth they present a procedure to objectively determine the long period component of complex source time functions in which they directly utilize results from body wave analysis the method is applied to two great normal fault events of june 22 1977 tonga m sub w 8 2 and august 19 1977 indonesia m sub w 8 5 standard long period analysis procedures underestimate the total slip duration in both cases the overall source process times of both earthquakes are longer than 120 s

seismic moment assessment of earthquakes in stable continental regions ii historical seismicity summary this part i study in conjunction with part 11 develops a method to determine within specified uncertainty bounds the seismic moment and thus moment magnitude of all earthquakes of stable continental regions scr for which instrumental or intensity data exist its basis is polynomial regression analysis using a database of scr earthquakes with direct seismic moment determination the independent variables include modern teleseismic magnitudes and regional magnitudes part i and isoseismal areas or number of recording stations part 11 part i11 is an application of the methodology of parts i and i1 to several major historical earthquakes all data used in the regressions are assigned individual uncertainties estimated from the literature or from experience formal confidence limits 68 per cent or 95 per cent on both the regression formulas and the predicted seismic moment values are then possible via error propagation analysis the most complete development is for the teleseismic magnitudes m and mb for both the final regression for log m is a quadratic formula that closely emulates the relationship between amplitude magnitudes and log m expected from dislocation theory and source scaling arguments regressions are also derived for the regional magnitudes mlg and m because there are many scr events mainly pre 1964 that have no teleseismic magnitudes prediction uncertainties from teleseismic magnitudes in moment magnitude units are in the ao 18 0 28 range and from regional magnitudes in the ko 23 0 38 range over a wide magnitude band finally the methodology developed here is generic even though the database is specific application to plate boundary oceanic intraplate or active continental intraplate regions should be straightforward

focal depths and moment tensor representations of shallow earthquakes associated with the great sumba earthquake focal depths in the range 8 to 24 km below the seafloor were determined for seven of the larger shocks associated with the great sumba earthquake of august 19 1977 depth control was achieved by modeling digitized long period p waves recorded by the world wide standard seismic network if the base of the rupture at the time of the mainshock were no greater than the depth of the deepest aftershock the stress drop would be nearly 500 bars amplitude and first motion data from the p waves were inverted for point source moment tensors the inversion of rayleigh and love wave spectra computed from digital seismograms recorded by the seismic research observatories sro and the abbreviated seismic research observatories asro broadened the source study to include earthquakes with moments as small as 1024 dyn cm too small for either traditional first motion solutions or p wave modeling the inversion procedure was applied to data in the passband from 30 to 120 s the propagation phase for the love and the rayleigh waves was calibrated with signals from two earthquakes for which the source phase was inferred from the p wave solutions agreement with the corresponding p wave solutions is nearly the same whether or not the smaller eigenvalues of the inner product matrix are retained in the inversions the double couple components generally account for more than two thirds of the total moment normal faulting along an east to northeasterly strike characterizes the mechanisms in the principal zone of aftershock activity strike slip mechanisms consistent with horizontal compression normal to the arc prevail in the delayed aftershock zone located 200 km northwest of the mainshock of the earthquakes subjected to this surface wave analysis the foreshock stood out as having felt a significantly higher apparent stress perhaps as much as one half an order of magnitude higher than the others these results suggest that accurate source parameters for moderate to small magnitude earthquakes can be determined from surface waves recorded by the sro and asro in particular the mechanisms of small magnitude foreshocks could be obtained in this way

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 procedure for the systematic interpretation of body wave seismograms i application to moho depth and crustal properties summary teleseismic body waves represent a natural tool for the investigation of earth structure but most studies have used only a very small part of the available information we present a general procedure for the interpretation of body wave seismograms which allows us to incorporate information from the entire set of body wave arrivals and which is based on a new method for the calculation of synthetic seismograms these complete ordered ray expansion core seismograms are both complete in the sense of incorporating all significant energy contributions and interpretable in the sense that we can identify all such contributions explicitly we show how our procedure can form the basis for a waveform inversion scheme exploiting the natural division of body wave arrivals into main phases associated with smooth structure and families of interaction phases associated with discontinuities we present the results of applying this technique to the moho beneath various rstn and dwwssn stations showing that it is possible to obtain very consistent values of crustal thickness from single deep focus events using phases associated with both the p and s arrivals by incorporating such arrivals in a linearized waveform inversion we also obtain estimates of a mean poisson s ratio for the crust

source parameters of 1978 tabas and 1979 qainat iran earthquakes from long period surface waves the teleseismic records of three strong earthquakes which inflicted heavy damage and loss of many thousands of lives in northeastern iran during 1978 and 1979 are analyzed the observed r 2 and r 3 phases of the 16 september 1978 tabas earthquake across the ida network are inverted to derive the gross source parameters of the main shock the synthetic seismograms computed for the inferred source model are compared with observations the agreement is generally good at most of the stations however unexpected asymmetrical observations at esk cmo kip and pfo stations cannot be explained by directivity alone possible factors responsible for these observations may include regional heterogeneities or the departure of fault plane from simple planar geometry the resulting focal mechanism agrees with nearly pure reverse mechanism with a nw se strike the seismic moment estimate for this earthquake is about 1 5 10 27 dyne cm m w 7 4 the seismic moment of the same earthquake obtained from long period p wave observations at six wwssn stations is smaller than the above estimate by a factor of 2 starting with the geologic field data of the qainat earthquakes of 14 and 27 november 1979 the r 2 and g 2 phases on the ultra long period instruments at pasadena and berkeley are analyzed to estimate their seismic source moments the estimated values are 1 0 10 26 dyne cm for the 14 november and 8 0 10 26 dyne cm for the 27 november 1979 events their corresponding moment magnitudes are 6 6 and 7 2 respectively

teleseismic inversion for the second degree moments of earthquake space time distributions summary determining detailed descriptions of the space time distribution of an earthquake s rupture using only teleseismic data is often a difficult and non unique process however a description of an earthquake that goes beyond a point source is often needed for many seismotectonic problems we have developed a method that inverts measurements of the shifts in traveltime and amplitude of various seismic phases at global stations for the second degree polynomial moments of an event s space time distribution our values for the second moments of the 1995 mw 8 0 jalisco mexico thrust event correspond to a characteristic rupture length of 121t10 km along strike a characteristic rupture width of 76t11 km downdip a characteristic duration of 29t2 s and a direction of rupture propagation along the strike of the subduction zone to the nw for the 1995 mw 7 2 gulf of aqaba earthquake our estimates of the second moments correspond to a characteristic rupture length of 53t2 km a characteristic duration of 12t1 s and rupture propagation to the ne along the strike of the dead sea transform our estimates of the first and second moments agree well with values from local seismic and geodetic networks for both the jalisco and aqaba events we are able to resolve the fault plane ambiguity associated with the events moment tensors using our estimates of the second spatial moment

bibliographical search for reliable seismic moments of large earthquakes during 1900 1979 to compute mw in the isc gem global instrumental reference earthquake catalogue abstract moment magnitude m w determinations from the online gcmt catalogue of seismic moment tensor solutions gcmt catalog 2011 have provided the bulk of m w values in the isc gem global instrumental reference earthquake catalogue 1900 2009 for almost all moderate to large earthquakes occurring after 1975 this paper describes an effort to determine m w of large earthquakes that occurred prior to the start of the digital seismograph era based on credible assessments of thousands of seismic moment m 0 values published in the scientific literature by hundreds of individual authors m w computed from the published m 0 values for a time period more than twice that of the digital era are preferable to proxy m w values especially for earthquakes with m w greater than about 8 5 for which m s is known to be underestimated or saturated after examining 1 123 papers we compile a database of seismic moments and related information for 1 003 earthquakes with published m 0 values of which 967 were included in the isc gem catalogue the remaining 36 earthquakes were not included in the catalogue due to difficulties in their relocation because of inadequate arrival time information however 5 of these earthquakes with bibliographic m 0 and thus m w are included in the catalogue s appendix a search for reliable seismic moments was not successful for earthquakes prior to 1904 for each of the 967 earthquakes a preferred seismic moment value if there is more than one was selected and its uncertainty was estimated according to the data and method used we used the iaspei formula iaspei 2005 to compute direct moment magnitudes m w m 0 based on the seismic moments m 0 and assigned their errors based on the uncertainties of m 0 from 1900 to 1979 there are 129 great or near great earthquakes m w 7 75 the bibliographic search provided direct m w values for 86 of these events or 67 the gcmt catalog provided direct m w values for 8 events or 6 and the remaining 35 or 27 earthquakes have empirically determined proxy m w estimates an electronic supplementary file is included with this paper in order to provide our m 0 m w catalogue of earthquakes 1904 1978 from the published literature and a reference list of the 1 123 papers that we examined

global creepex distribution and its relation to earthquake source geometry and tectonic origin summary the ms mb ratio conventionally used for the discrimination of earthquakes and underground nuclear explosions has been studied for a pure earthquake catalogue in an attempt to classify earthquakes into two categories one related to extremely lowfrequency events of creep and the other to relatively high frequency explosions ms and mb measured at 20 s and 1 s respectively are considered as estimates of source spectra at two separate points thus allowing one to compare large samples of earthquakes from the spectral point of view creepex or the deviation of ms mfc points from the orthogonal regression of ms on mb is by definition a parameter independent of the size of seismic events it has been estimated from neic magnitudes and is studied in relation to parameters of central moment tensor solutions of the harvard group for this purpose the parameters of central moment tensors have been factorized to make classes of equivalence of events with the same dip and rake and arbitrary strike and size the resulting triangle representation of source mechanisms has been used to correct the global distribution of creepex for the type of source mechanism dip slip events have consistently lower creepex than strike slip ones however the global distribution of creepex either corrected or uncorrected for source mechanism has a clear tectonic pattern negative values in most of the subduction zones and positive ones in mid ocean ridges the dependence of creepex on focal depth is negligible according to empirical data for events shallower than 40 km limitation of the sample by considering only events in this depth range does not diminish considerably the amount of data and does not change the tectonic pattern of the creepex

self consistent retrieval of source parameters using mantle waves the large number of high quality stations from global networks e g iris geoscope allows for rapid and robust recovery of source parameters of large earthquakes we present a self consistent analysis of surface waves in terms of directivity parameters the boxcar is often used to recover source parameters but is rarely a faithful representation of an event s time function we demonstrate that more reliable estimates of directivity parameters can be obtained when we take into account the source time function stf of the event a low frequency stf is obtained from first r1 and second r2 orbit rayleigh waves in the range 2 to 15 mhz with a spectral synthesis and inversion method we measure the differential amplitudes between data and 3d synthetics we use the r1 r2 ratio of differential amplitudes to invert in a single narrow frequency band for the event s apparent rupture azimuth and velocity for the mw 8 1 chile 1995 event data are consistent with unilateral southward propagation with a velocity of about 2 4 km sec for the mw 7 9 mexico 1995 earthquake the rupture propagated toward the nw at about 2 0 km sec our low frequency estimates agree with broadband studies of both events and can be retrieved rapidly on a routine basis after a large earthquake

total moment spectra of fourteen large earthquakes total moment spectra mt m where m is the moment rate tensor are computed for 14 large earthquakes recorded by the international deployment of accelerometers ida network using the scalar moment retrieval method proposed by silver and jordan 1982 for each event we obtain estimates of mt averaged over the 10 disjunct 1 mhz intervals in the low frequency band 1 11 mhz typical ida record sets from events with mt 0 2 a 1 a 1027 dyne cm yield standard errors on the 1 mhz averages that are generally less than 20 our multiple band estimates of mt are usually consistent with comparable single band values found by other investigators from the total moment spectra we derive the zero frequency static moment mt 0 and the characteristic source duration c 2 var f t where f t is the time function of the moment rate tensor assumed to be the same for all components the parameter c formally depends on the second degree temporal spatial and mixed spatial temporal moments of an extended source but calculations with realistic source geometries indicate that the interpretation of tc strictly in terms of the second temporal moment leads to very little error a plot of c against shows considerable scatter some events lie significantly above the empirical scaling curve of kanamori and given 1981 slow earthquakes and some below fast earthquakes examples of the former include all three deep focus events analyzed here as well as the 1970 colombia and 1963 peru bolivia deep focus earthquakes whose total moment spectra are calculated from the moment tensor solutions of gilbert and dziewonski 1975 an example of the latter is the great sumbawa earthquake of august 9 1977 24 3 a which is inferred to have a relatively shallow spatial centroid 20 km and a nearly flat moment spectrum suggesting that the faulting was confined to the upper more brittle portion of the oceanic lithosphere three other large earthquakes tonga june 22 1977 23 2 a kuril islands december 6 1978 3 6 0 2 a and tumaco december 12 1979 25 2 a exhibit moment spectra which significantly decrease toward higher frequencies indicating larger values of c the aftershocks of both the tonga and kuril islands events are distributed over a considerable range of depths consistent with rupture into the lower more ductile portions of the oceanic lithosphere we speculate that the characteristic source duration may be causally related to the depth of coseismic rupturing within the lithosphere

multichannel deconvolution for earthquake apparent source time functions abstract previous studies of earthquake apparent source time functions astfs removed propagation effects through seismogram deconvolution with a smaller earthquake known as an empirical green s function egf we develop a multichannel deconvolution mcd algorithm for recovering astfs that does not require an egf but instead the availability of two or more earthquakes that share a common green s function under this condition astfs satisfy u i s j u j s i 0 in which u i and s i are the seismogram and astf for a given earthquake this system can be augmented with a scaling equation and written as ax b in which matrix a comprises the seismograms in a block toeplitz structure and x contains the target astfs we minimize an objective function for this linear system with a newton projection algorithm that honors positivity causality and duration constraints if the earthquakes have a suitable range in magnitude egf deconvolution may be used to estimate differences in the duration of the events and to obtain a starting model for the larger astf s we demonstrate the effectiveness of mcd using synthetic tests and apply it to seven m w 5 earthquakes from the kamaishi sequence japan related to the 2011 tohoku oki m w 9 event we demonstrate that mcd is an effective way to recover earthquake astfs and that the details of rupture revealed by mcd astfs will be useful in furthering our understanding of the earthquake source electronic supplement figures of seismograms and multichannel deconvolution mcd apparent source time functions astfs from the kamaishi earthquake sequence

rupture characteristics of the 1982 tonga and 1986 kermadec earthquakes source time functions are obtained for the december 19 1982 tonga and october 20 1986 kermadec earthquakes from deconvolution of p waves using a model including a significant dip of the ocean bottom in such a geometry the amplitudes of subsequent water multiples are large and irregular as a result we can model these two events as consisting of a single pulse of short duration 23 s in the case of the 1982 event and 19 s for the 1986 one despite complex teleseismic waveshapes this is in contrast to inversions using flat layered models which required very complex source time functions which were mutually inconsistent at different stations the anomalously large tsunami generated by the 1982 event is modeled as the result of propagation of the rupture into the sedimentary wedge at the trench rather than due to a long lived complex source time function the latter being also incompatible with the total lack of excitation of the earth s normal modes in the low frequency limit for the 1986 event we derive a source duration 19 s very short in relation to its moment 8 1027 dyn cm this earthquake a high stress drop rupture featuring a unique combination of strike slip and thrust motion on a plane dipping oceanwards of the trench is interpreted as expressing internal deformation of the subducting pacific slab at a depth of 40 km under the compressional stresses resulting from the collision

surface expression of thrust faulting in eastern iran source parameters and surface deformation of the 1978 tabas and 1968 ferdows earthquake sequences summary previously unrecognised thrust faults in eastern iran were responsible for a destructive earthquake at tabas 1978 september 16 which produced over 80 km of distributed and discontinuous surface ruptures above a series of low anticlinal hills to the west of a major range front analysis of long period body wave seismograms shows a simple rupture on a gently dipping 16 thrust with a slight right lateral component this is compatible with the locally recorded aftershock distribution body wave analysis of two later smaller events show similar source orientations several indicators of long term active folding at tabas can be recognised in the geomorphology and surface ruptures from 1978 are consistent with co seismic fold growth drainage incision also indicates uplift at depth on thrust faults dipping eastwards beneath the folds body wave seismograms for two earthquakes near ferdows 150 km east of tabas in september 1968 also show thrust faulting at depths of 10 km again the surface geomorphology indicates a region of folding above an eastward dipping thrust fault which is 10 km west of a fault bounded range front in both tabas and ferdows the active faulting appears to show quaternary migration away from the range front possibly in response to stresses produced by the elevated topography the identification of zones of active fault related folding is important for earthquake hazard assessment and also for an understanding of the local tectonics we conclude that the structures which gave rise to the 1968 and 1978 earthquakes could have been recognised beforehand from the clear signals in the geomorphology had we known what to look for at that time