retrospective on the accelerating seismic release asr hypothesis controversy and new horizons abstract the hypothesis that large earthquakes may be preceded by a period of accelerating seismicity or accelerating seismic release asr was proposed about twenty years ago a compilation of almost one hundred peer reviewed publications on this topic since the late 1980s to the present day shows that the rate of asr studies increased gradually until 2004 but decreased afterwards this negative trend is amplified by a recent increase in the number of negative results and criticisms of the asr hypothesis the author suggests that much of the recent negativity regarding this topic is due to the formulation of this hypothesis as a power law fit to cumulative seismicity series this approach is intrinsically linked to the consensus for criticality evident from an overview of the asr literature to explain the emergence of power laws in earthquake populations the holistic view of the earth s crust as a complex system restricts seismicity pattern analyses to the study of main features such as power laws while a reductionist view would allow for more refined ones such a paradigm shift or sea change might be under way in the asr literature where in 2007 a new approach was proposed to explain the asr power law from combined concepts of elastic rebound and geometry reductionism versus holism is a fundamental problem that not only applies to the study of asr but also to the broader field of earthquake physics and earthquake predictability science

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

uniform slip rate along the kunlun fault implications for seismic behaviour and large scale tectonics a long term slip rate is derived from concordant 10 be 26 al and 14 c dating of cumulativeoffse ts along much of the length of the kunlun fault values at 6 sites indi cateuniform slip 11 5 2 0 mm yr since 40 kyr bp this relatively high slip rate corresponds to a first order discon tinuity in the asian crustal velocity field m 8a nd m 7 5 earthquakes on 2 segments of the fault recur with charac teristic slip 10 2ma nd 4 4 0 4m ev e ry 850 and 420 yrs respectively

intermediate term earthquake prediction using the modified time to failure method in southern california abstract based on retrospective modeling of earthquakes from the southern california earthquake catalog along with previously published evaluations from the new madrid seismic zone the modified time to failure method may be used as an intermediate term earthquake prediction technique for locating and predicting the size and time of a future mainshock modeling previous mainshocks for hypothesis development indicates that the method predicts the actual magnitude of the mainshock to within approximately 0 5 magnitude units the error associated with the time of failure is approximately 1 1 years assuming the last precursory event is known when the last event in the precursory sequence is not known the predicted magnitude remains similar but the predicted time will require refinement as additional events are added with time to the sequence the mainshock location can also be identified within a circular region with a radius on the order of tens of kilometers criteria are provided for defining acceleration sequences and mainshock locations the criteria reduce the number of false predictions but also eliminate some mainshocks from our evaluation mainshocks as small as magnitude 5 5 occurring between 1980 and 1995 were evaluated from the southern california earthquake catalog scc the results were used in association with previous studies to develop a method that can be used for practical future prediction applications the modified time to failure method was used to search the scc for future mainshocks occurring after 17 august 1998 one region satisfied all the criteria and may be modeled by the modified time to failure method the region likely to have a mainshock is a 65 km radius area centered at 31 43 n 115 47 w northern baja california mexico the predicted magnitude is 6 36 0 55 and the predicted time of failure is 1998 565 7 25 98 1 127 years the addition of future precursory events will allow refinement of the predicted values

a palaeomagnetic and mineral magnetic study of the loess sequence at liujiapo xian china employing an average vertical sampling interval of 20 cm oriented samples were collected from 26 m of the loess section at liujiapo near xian china in order to refine the existing magnetostratigraphic record palaeomagnetic results reveal two short reversed polarity subzones within a profile of predominantly normally magnetised sediments an interpretation that is at variance with previous results from this section and from other studies of chinese loess investigation of sediment mineral magnetic properties indicates a close correspondence between down section variations in intensity of magnetisation susceptibility and saturation isothermal journal of quaternary science remanence sirm and lithology the ratios irm 100mt sirm and sirm susceptibility appear to be particularly sensitive indicators of the degree of soil development and hence of palaeoclimate

seismicity of the wrangell and aleutian wadati benioff zones and the north american plate along the trans alaska crustal transect chugach mountains and copper river basin southern alaska the configuration of the aleutian and wrangell wadati benioff zones in southern alaska between longitudes 142 w and 148 w is determined from regionally recorded earthquakes from 1971 to 1986 the earthquakes are located with a simple velocity model calibrated with seismic refraction measurements conducted for the trans alaska crustal transect tact west of the transect meridian approximately 145 20 w and beneath the chugach mountains shocks in the depth range 25 60 km compose the shallow part of the northwest to north dipping aleutian zone this zone can be traced updip and seaward beneath prince william sound east of the transect meridian and north of 61 n latitude the weakly active north northeast dipping wrangell zone extends to a depth of at least 100 km beneath the wrangell volcanoes and along strike for at least 150 km the two zones appear to be continuous at least in the depth range 20 45 km and may define adjacent limbs of a buckle in the subducted oceanic lithosphere north of 61 n focal mechanisms in the shallow aleutian zone are compatible with a uniform stress field characterized by in plane least compressive stress directed toward the steeply dipping deeper part of the aleutian zone north of cook inlet stress orientation in the wrangell zone is unresolved because of the low level of seismicity no focal mechanisms corresponding to slip on a gently northward dipping megathrust have been observed along the transect meridian a change of focal mechanism with depth near the top of the dipping seismic zone is inferred to reflect the interplate boundary beneath the chugach mountains this boundary coincides with a band of strong reflectors imaged by tact vertical seismic profiling the overriding plate appears to be aseismic beneath the northern chugach mountains but minor shallow seismicity occurs beneath the copper river basin first motion patterns for these shallow shocks suggest the most compressive stress within the overriding plate is oriented subhorizontally and approximately north south

evidence of nonlinear elasticity of the crust from the mw7 6 manyi tibet earthquake satellite synthetic aperture radar sar interferometry shows that the magnitude 7 6 manyi earthquake of 8 november 1997 produced a 170 kilometer long surface break with up to 7 meters of left lateral slip reactivating a n76 e quaternary fault in western tibet the radar interferometric map reveals asymmetric along strike displacement profiles between the two sides of the surface rupture a pattern that cannot be explained with linear elastic theory this observation suggests that the elastic moduli of the crust in tension and in compression are different because of the presence of cracks in the crust at shallow depth a model indicates that a ratio of 2 between compressive and tensile elastic moduli can account for the observed asymmetry a ratio that is consistent with laboratory and borehole measurements

the chinese loess in xifeng i the primary study on magnetostratigraphy of a loess profile in xifeng area gansu province summary 1848 specimens were collected systematically from about 900 horizons in the loess profile of xifeng gansu province china the magnetostratigraphy is established on the basis of the palaeomagnetic results after thermal cleaning usually at 300 c this result has been found to be generally consistent with previous work in luochuan the susceptibility varies regularly with the appearance of loess and palaeosol in the profile and thus could be used as a criterion to classify the loess and palaeosol sequence

volcanic stratigraphy of a high altitude mammuthus columbi tlacotenco sierra chichinautzin central mexico the discovery of a near complete skeleton of mammuthus columbi in a cornfield located on the northern slopes of the sierra chichinautzin volcanic field south of mexico city sparked the interest of the scientific and public community although remains of this species of mammoth are frequently discovered in central mexico this new find is at the southernmost and highest ca 2770 m asl location yet within the mexico basin in addition the bones were found embedded in dark volcanic ash raising the possibility of a relationship between the death of the animal and explosive activity at a neighboring scoria cone as the site is located 10 km from several young volcanoes stratigraphic sedimentological geochemical and geochronological studies were conducted at the discovery site and within a 5 km radius to determine the tephra stratigraphy in the area and constrain the source of the mammoth ash and the age and taphonomy of the fossil remains results show that the mammoth was buried after death by stream flows dilute lahars that were triggered by torrential rain that remobilized loose scoriaceous ash ejected by the san miguel cone some time after its eruption ca 17 000 bp

complex geometry and segmentation of the surface rupture associated with the 14 november 2001 great kunlun earthquake northern tibet china abstract the 14 november 2001 kunlun china earthquake with a moment magnitude m w 7 8 occurred along the kusai lake kunlun pass fault of the kunlun fault system we document the spatial distribution and geometry of surface rupture zone produced by this earthquake based on high resolution satellite landsat etm aster spot and ikonos images combined with field measurements our results show that the surface rupture zone can be divided into five segments according to the geometry of surface rupture including the sun lake buka daban hongshui river kusai lake hubei peak and kunlun pass segments from west to east these segments each 55 to 130 km long are separated by step overs the sun lake segment extends about 65 km with a strike of n45 75 w between 90 05 e 90 50 e along the previously unrecognized west sun lake fault a gap of about 30 km long exists between the sun lake and buka daban peak where no obvious surface ruptures can be observed either from the satellite images or field observations the buka daban hongshui river kusai lake hubei peak and kunlun pass segments run about 365 km striking n75 85 w along the southern slope of the kunlun mountains between 91 07 e 94 58 e this segmentation of the surface rupture is well correlated with the pattern of slip distribution measured in the field detailed mapping suggest that these five first order segments can be further separated into over 20 second order segments with a length of 10 30 km linked by smaller scale step overs or bends our result also shows that the total coseismic surface rupture length produced by the 2001 kunlun earthquake is about 430 km excluding the 30 km long gap which is the longest coseismic surface rupture for an intracontinental earthquake ever recorded finally we suggest a multiple bilateral rupture propagation model that shows the rupture process of the 2001 m w 7 8 earthquake is complex it consists of westward and eastward rupture propagations and interaction of these bilateral rupture processes

present day crustal deformation in china constrained by global positioning system measurements global positioning system gps measurements in china indicate that crustal shortening accommodates most of india s penetration into eurasia deformation within the tibetan plateau and its margins the himalaya the altyn tagh and the qilian shan absorbs more than 90 of the relative motion between the indian and eurasian plates internal shortening of the tibetan plateau itself accounts for more than one third of the total convergence however the tibetan plateau south of the kunlun and ganzi mani faults is moving eastward relative to both india and eurasia this movement is accommodated through rotation of material around the eastern syntaxis the north china and south china blocks east of the tibetan plateau move coherently east southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year respectively with respect to the stable eurasia

pleistocene climates in china dated by magnetic susceptibility the magnetic susceptibility of loess and interbedded soils in central china varies with the degree of pedogenesis and serves as a proxy measure of climate the concentration of magnetic minerals in the sediment is inversely proportional to sedimentation rates throughout the brunhes epoch susceptibility measurements combined with the reversal stratigraphy provide a time scale that is independent of astronomic chronology on this scale the susceptibility record closely parallels the oxygen isotope fluctuations in deep sea sediments suggesting a close interdependence of the chinese dust falls the volume of land based ice and global climate

stress distribution along the fairweather queen charlotte transform fault system tectonic loading and coulomb stress transfer are modeled along the right lateral fairweather queen charlotte transform fault system using a three dimensional boundary element program the loading model includes slip below 12 km along the transform as well as motion of the pacific plate and it is consistent with most available global positioning system gps displacement rate data coulomb stress transfer is shown to have been a weak contributing factor in the failure of the southeastern sitka segment of the fairweather fault in 1972 hastening the occurrence of the earthquake by only about 8 months failure of the sitka segment was enhanced by a combination of cumulative loading from below 95 by slip of about 5 cm yr since 1848 by stress transfer about 1 from major earthquakes on straddling segments of the queen charlotte fault m 8 1 in 1949 and the fairweather fault m 7 8 in 1958 and by viscoelastic relaxation about 4 following the great 1964 alaska earthquake modeled by pollitz et al 1998 cumulative stress increases in excess of 7 mpa at a depth of 8 km are projected prior to the m 7 6 earthquake coulomb stress transferred by the rupture of the great m 9 2 alaska earthquake in 1964 bufe 2004a also hastened the occurrence of the 1972 event but only by a month or two continued tectonic loading over the last half century and stress transfer from the m 7 6 sitka event has resulted in restressing of the adjacent segments by about 3 mpa at 8 km depth the occurrence of a m 6 8 earthquake on the northwestern part of the queen charlotte fault on 28 june 2004 the largest since 1949 also suggests increased stress the cape st james segment of the fault immediately southeast of the 1949 queen charlotte rupture has accumulated about 6 mpa at 8 km through loading since 1900 and stress transfer in 1949 a continued rise in earthquake hazard is indicated for the alaska panhandle and queen charlotte islands region in the decades ahead as the potential for damaging earthquakes increases

new magnetostratigraphic dates of lantian homo erectus skeletal remains of homo erectus found in pleistocene loess at two sites near lantian in central china are of greatly different geologic age the cranium found in the fossil bearing strata at gongwangling is about 1 15 myr old whereas the remains found at the chenjiawo locality in middle pleistocene loess are about 0 65 myr old the dating is based on new paleomagnetic polarity determinations and on the lithostratigraphic position of the fossils in the loess paleosol sequence our results confirm that both localities are older than the first occupation of zhoukoudian new dates palaeoenvironmental settings and morphological features of the hominids from lantian localities have significant bearing on the understanding of adaptive radiations of the middle and late hominids in asia

role of oblique convergence in the active deformation of the himalayas and southern tibet plateau noting similarities with subduction along curved oceanic trenches and using a simple block model we show that radial vergence evident in earthquake slip vectors along the himalayan deformation front east west extension on north trending normal faults in the himalayas and southern tibet and right lateral strike slip on the karakorum jiali fault zone can all result from basal shear caused by the indian plate sliding obliquely beneath tibet along a gently dipping arcuate plate boundary within the framework of this mechanism the normal faults in the himalayas and southern tibet are not proxies for the uplift history of tibet the distribution and style of the faults in the himalayas and southern tibet suggest that the basal drag from the underthrusting indian lithosphere extends northward beneath most of southern tibet

postseismic motion after the 2001 mw 7 8 kokoxili earthquake in tibet observed by insar time series 1 on november 14th 2001 a mw 7 8 earthquake occurred in the kokoxili region of northern tibet the earthquake ruptured more than 400 km along the western part of the kunlun fault with a maximum of 8 m left lateral slip in this paper we use a multitemporal interferometric sar insar time series technique to map the postseismic motion following the large kokoxili event sar data from envisat descending orbits along five adjacent tracks covering almost the entire ruptured fault length are used to calculate the displacement time series for a period between 2 and 6 years after the earthquake a peak to trough signal of 8 cm in the radar line of sight is observed during the period between 2003 and 2008 two different mechanisms are employed to explain the observed surface displacements namely afterslip and viscoelastic relaxation the observations inverted for afterslip on and below the coseismic rupture plane shows that the maximum slip in the afterslip model is 0 6 m the position of the maximum postseismic slip is located in the middle of two relatively high coseismic slip patches which suggests that afterslip is a plausible mechanism models of viscoelastic stress relaxation in a maxwell half space give a best fitting viscosity for the mid to lower crust of 2 5 1019 pa s and the principal postseismic relaxation process is due to viscous flow in the lower crust to upper mantle however the insar observations are incapable of distinguishing between localized afterslip and distributed viscoelastic relaxation deformation and the lowest misfits are produced by mixed models of viscoelastic relaxation in the mantle below 70 km and afterslip in the crust modeling of viscoelastic relaxation in a maxwell half space and also a mixed mechanism model enables us to place an effective viscosity of 2 1019 pa s on the lower crust to mantle of northern tibet

rupture segmentation and process of the 2001 mw 7 8 central kunlun china earthquake field investigations allow us to constrain the coseismic surface rupture zone of 400 km with a strike slip up to 16 3 m associated with the 2001 m w 7 8 central kunlun earthquake that occurred along one of the western segments of the kunlun fault northern tibet the rupture zone may be divided into four segments based on the geological structures tectonic landform features spatial displacement distributions obtained from field observations and analysis of teleseismic waveforms the deformational characteristics of the surface ruptures and focal mechanism solutions reveal that the earthquake had a nearly pure strike slip mechanism the inversion results from seismic data show that the rupture started from the west near the epicentral area bilaterally and rapidly extended to the east in an unilateral manner for 380 km and that the largest slip region was limited in the subsegment 150 280 km east of the epicenter consistent with field observations the average stress drop is estimated to be 7 mpa in the area where the largest displacements occurred a value typical of intraplate earthquakes the geologic evidence and the inversion results from seismic data clearly show that temporal and spatial displacement distributions and the rupture process are restricted by the pre existing geological structures of the kunlun fault

shear wave anisotropy beneath the tibetan plateau eleven broadband digital seismic stations were deployed across the central tibetan plateau in the first extensive passive source experiment attempted within the tibetan plateau one year of recording resulted in 186 event station pairs which we analyze to determine the characteristics of shear wave splitting in the upper mantle beneath the array measurements of the fast polarization direction and delay time t for sks and direct s arrivals reveal systematic variations along the north south oriented array in the north central region of the plateau very large delay times are observed at three stations the largest of which is budo with of t 2 4 s however at tunl which is off the northern edge of the plateau and 110 km from budo and at sites in the south central plateau t decreases by nearly a factor of 3 we also observe systematic rotation of from about 45 ne to 90 e w from south to north along the array a previously identified zone of inefficient sn propagation correlates well with our region of large t observations the large delay times suggest that a relateively high number of anisotropic crystals are preferentially alligned within the mantle lid beneath the north central portion of the tibetan plateau in most cases fast polarization directions appear to be parallel to surface geologic features suggesting as much as 200 km of the upper mantle has been involved in the collisional deformation that has produced the tibetan plateau

loess stratigraphy in central china abstract the loess deposits in central china record world wide climate changes of the last 2 5 ma numerous climatic oscillations are marked by alternating loess and soil units with continuous coverage of the matuyama and brunhes epochs magnetic susceptibility of the deposits correlates closely with the oxygen isotope record of the deep sea sediments and provides an independent measure of climate and time the key marker bed of the chinese loess sequence is the paleosol s5 the time equivalent of the mid brunhes oxygen isotope stages 13 14 and 15 it marks a prolonged interval of warm humid climate lasting from approximately 615 to 470 thousand years ago several episodes of river downcutting coincide with deposition of the exceptionally thick loess units l1 oceanic oxygen isotope stages 2 to 4 l2 stage 6 l5 stage 12 l6 stage 16 l9 stage 22 l15 stage 38 about 1 15 ma and ws4 about 2 3 ma these erosional events are interpreted as a result of episodic uplift of the loess plateau the deposition of the earliest loess layers between 2 5 and 2 3 ma ago marks a first order shift from warm and humid environments toward harsh continental steppes comparable to those of the middle and late pleistocene little if any lithologic or paleontologic changes were noted within or above the olduvai magnetozone so that the proposed plio pleistocene boundary at approximately 1 65 ma has no lithostratigraphic and biostratigraphic representation in the chinese loess series comparison with the deep sea drilling program core 552a in the north atlantic and with the santerno river section near bologna shows that the occurrence of the earliest loess in china coincides with the timing of the first significant ice rafting in the north atlantic and with the appearance of cold water foraminifers in the marine deposits of northern italy an extension of the stage system of the oxygen isotope signal extended back to the gauss matuyama boundary is proposed

co seismic strike slip and rupture length produced by the 2001 ms 8 1 central kunlun earthquake field investigations show that the surface wave magnitude ms 8 1 central kunlun earthquake tibetan plateau of 14 november 2001 produced a nearly 400 kilometer long surface rupture zone with as much as 16 3 meters of left lateral strike slip along the active kunlun fault in northern tibet the rupture length and maximum displacement are the largest among the co seismic surface rupture zones reported on so far the strike slip motion and the large rupture length generated by the earthquake indicate that the kunlun fault partitions its deformation into an eastward extrusion of tibet to accommodate the continuing penetration of the indian plate into the eurasian plate

holocene left slip rate determined by cosmogenic surface dating on the xidatan segment of the kunlun fault qinghai china cosmogenic dating using in situ sup 26 al and sup 10 be in quartz pebbles from alluvial terrace surfaces constrains the late holocene slip rate on the xidatan segment of the kunlun fault in northeastern tibet two terrace risers offset by 24 3 and 33 4 m having respective ages of 1799 388 and 2914 471 yr imply a slip rate of 12 1 2 6 mm yr the full range of ages obtained le 22 8 k y most of them between 6 7 and 1 4 k y confirm that terrace deposition and incision hence landform evolution are modulated by post glacial climate change coupled with minimum offsets of 9 12 m this slip rate implies that great earthquakes m approximately 8 with a recurrence time of 800 1000 yr rupture the kunlun fault near 94 e

faulting associated with large earthquakes and the average rate of deformation in central and eastern asia we determine approximate average rates of deformation in portions of eastern and central asia for the last 80 years these rates are based on estimates of source dimensions average displacements seismic moments and orientations of faults of all large earthquakes m 7 5 and as many other major earthquakes m 7 0 as possible in asia since 1900 a major part of this study is the compilation of these data for separate parts of asia we combine seismic moment tensors to estimate the average rotational strain or deformation tensors for these regions for the last 80 years we estimate that shortening across the tien shan has occurred at 11 mm yr between 5 and 19 mm yr left lateral shear on easterly trending planes in mongolia in northwestern tibet gansu and ningxia and on the xianshuihe fault in western sichuan has been very rapid more than 10 mm yr in each region and apparently as rapid as 40 mm yr in northwestern tibet gansu and ningxia slower rates of a few to 10 mm yr appear to characterize east west extension and conjugate north south shortening of tibet the earthquake history of the himalaya is consistent with rates of underthrusting of more than 10 mm yr but is probably less than the convergence rate of india with eurasia of about 50 mm yr the overall strain field is consistent with a large part of india s penetration into eurasia being absorbed by the extrusion of material out of india s way as a result southeast china moved at about 21 mm yr east southeast with respect to eurasia in the last 80 years with an uncertainty of about a factor of 2 in this estimated rate

comparing the november 2002 denali and november 2001 kunlun earthquakes major strike slip earthquakes recently occurred in alaska on the central denali fault m 7 9 on 3 november 2002 and in tibet on the central kunlun fault m 7 8 on 14 november 2001 both earthquakes generated large surface waves with m s u s geological survey usgs of 8 5 denali and 8 0 kunlun each event occurred on an east west trending strike slip fault situated near the northern boundary of an intense deformation zone that is characterized by lateral extrusion and rotation of crustal blocks each earthquake produced east directed nearly unilateral ruptures that propagated 300 to 400 km maximum lateral surface offsets and maximum moment release occurred well beyond 100 km from the rupture initiation with the events exhibiting by far the largest separations of usgs hypocenter and harvard moment tensor centroid cmt for strike slip earthquakes in the 27 year cmt catalog in each sequence the largest aftershock was more than two orders of magnitude smaller than the mainshock regional moment release had been accelerating prior to the main shocks the close proximity in space and time of the 1964 prince william sound and 2002 denali earthquakes relative to their rupture lengths and estimated return times suggests that these events may be part of a recurrent cluster in the vicinity of a complex plate boundary

predictive modeling of the seismic cycle of the greater san francisco bay region the seismic cycle for the san francisco bay region is synthesized by a model combining the pre and post 1906 seismic histories the long term acceleration of seismic release seismic moment benioff strain release or event count in the seismic cycle and the shorter term accelerations preceding the larger earthquakes within that cycle are modeled using an empirical predictive technique called time to failure analysis in which rate of seismic release is proportional to an inverse power of the remaining time to failure the exponent of time to failure in the accelerating sequences appears to be scale invariant and the length of the full cycle is estimated at 269 50 years the 1989 loma prieta earthquake which is the culmination of the first subcycle in the present long term seismic cycle should have been predictable with an uncertainty of 2 years in time and 0 5 in magnitude although the specific location at loma prieta was not predictable by this technique if our model is correct and if the loma prieta earthquake is the culmination of a subcycle the san francisco bay region should be entering a relatively long 20 50 years period of seismic quiescence above magnitude 6 a great earthquake such as the 1906 san francisco event would appear to be more than a century in the future

stress transfer to the denali and other regional faults from the m 9 2 alaska earthquake of 1964 stress transfer from the great 1964 prince william sound earthquake is modeled on the denali fault including the denali totschunda fault segments that ruptured in 2002 and on other regional fault systems where m 7 5 and larger earth quakes have occurred since 1900 the results indicate that analysis of coulomb stress transfer from the dominant earthquake in a region is a potentially powerful tool in assessing time varying earthquake hazard modeled coulomb stress increases on the northern denali and totschunda faults from the great 1964 earthquake coincide with zones that ruptured in the 2002 denali fault earthquake although stress on the susitna glacier thrust plane where the 2002 event initiated was decreased a southeasterly trending coulomb stress transect along the right lateral totschunda fairweather queen charlotte trend shows stress transfer from the 1964 event advancing slip on the totschunda fairweather and queen charlotte segments including the southern fairweather segment that ruptured in 1972 stress transfer retarding right lateral strike slip was observed from the southern part of the totschunda fault to the northern end of the fairweather fault 1958 rupture this region encompasses a gap with shallow thrust faulting but with little evidence of strike slip faulting connecting the segments to the northwest and southeast stress transfer toward failure was computed on the north south trending right lateral strike slip faults in the gulf of alaska that ruptured in 1987 and 1988 with inhibitory stress changes at the northern end of the northernmost 1987 rupture the northern denali and totschunda faults including the zones that ruptured in the 2002 earthquakes follow very closely within 3 for about 90 an arc of a circle of radius 375 km the center of this circle is within a few kilometers of the intersection at depth of the patton bay fault with the alaskan megathrust this inferred asperity edge may be the pole of counterclockwise rotation of the block south of the denali fault these observations suggest that the asperity and its recurrent rupture in great earthquakes as in 1964 may have influenced the tectonics of the region during the later stages of evolution of the denali strike slip fault system

coulomb stress transfer and tectonic loading preceding the 2002 denali fault earthquake pre 2002 tectonic loading and coulomb stress transfer are modeled along the rupture zone of the m 7 9 denali fault earthquake dfe and on adjacent segments of the right lateral denali totschunda fault system in central alaska using a three dimensional boundary element program the segments modeled closely follow for about 95 the arc of a circle of radius 375 km centered on an inferred asperity near the northeastern end of the intersection of the patton bay fault with the alaskan megathrust under prince william sound the loading model includes slip of 6 mm yr below 12 km along the fault system consistent with rotation of the wrangell block about the asperity at a rate of about 1 m y as well as slip of the pacific plate at 5 cm yr at depth along the fairweather queen charlotte transform fault system and on the alaska megathrust the model is consistent with most available pre 2002 global positioning system gps displacement rate data coulomb stresses induced on the denali totschunda fault system locked above 12 km by slip at depth and by transfer from the m 9 2 prince william sound earthquake of 1964 dominated the changing coulomb stress distribution along the fault the combination of loading 70 85 and coseismic stress transfer from the great 1964 earthquake 15 30 were the principal post 1900 stress factors building toward strike slip failure of the northern denali and totschunda segments in the m 7 9 earthquake of november 2002 postseismic stresses transferred from the 1964 earthquake may also have been a significant factor the m 7 2 7 4 delta river earthquake of 1912 carver et al 2004 may have delayed or advanced the timing of the dfe depending on the details and location of its rupture the initial subevent of the 2002 dfe earthquake was on the 40 km susitna glacier thrust fault at the western end of the denali fault rupture the coulomb stress transferred from the 1964 earthquake moved the susitna glacier thrust fault uniformly away from thrust failure by about 100 kpa the initiation of the denali fault earthquake was advanced by transfer of 30 50 kpa of positive coulomb stress to the susitna glacier fault anderson and ji 2003 by the nearby m 6 7 nenana mountain foreshock of 23 october 2002 the regional tectonic loading model used here suggests that the semidi alaska peninsula segment of the megathrust that ruptured in 1938 m 8 2 may be reloaded and approaching failure

frequency of occurrence of moderate to great earthquakes in intracontinental regions implications for changes in stress earthquake prediction and hazards assessments we investigate the departure of shallow intracontinental earthquakes from the frequency magnitude relationship log n m a bm we consider seven large continental regions but exclude subduction zones in each active and stable areas are differentiated within active areas we separately categorize earthquakes on faults with high slip rates we use data sets from 1978 1994 and 1900 1994 which are complete for moment magnitudes mw 5 3 and 7 0 to calculate changes in b value with mw for all active intracontinental regions combined except asia b changes at 98 confidence from 0 90 to 2 1 at a corner magnitude mc of 6 9 to 7 0 the distribution for stable regions indicates a similar change values of mc are associated with downdip widths of rupture of about 23 to 27 km which are smaller than those for subduction zones in each case mc marks a transition from unbounded to bounded earthquakes in asia events from 1958 to 1994 also delineate a similar change near mc 7 0 earthquakes in asia of 7 0 mw 8 1 from 1900 to 1957 however define a b value of 1 0 and a moment release rate 5 6 times higher than that from 1958 to 1994 those anomalous values indicate that a large region of asia was close to failure i e near a self organized critical state during the earlier period we associate those changes with the giant himalayan earthquake in 1950 of mw 8 6 regional variations in seismic strain release rates correlate with the types of processes at adjacent plate boundaries extrapolating rates of activity of the past 95 years to mw 8 0 indicates that such events should be very rare in stable areas