late cretaceous through cenozoic strike slip tectonics of southwestern alaska abstract new geologic mapping and geochronology show that margin parallel strike slip faults on the western limb of the southern alaska orocline have experienced multiple episodes of dextral motion since 100 ma these faults are on the upper plate of a subduction zone 350 450 km inboard of the paleotrench in southwestern alaska dextral displacement is 134 km on the denali fault at least 88 94 km on the iditarod nixon fork fault and perhaps tens of kilometers on the dishna river fault the strike slip regime coincided with late cretaceous sedimentation and then folding in the kuskokwim basin and with episodes of magmatism and mineralization at 70 60 and 30 ma no single driving mechanism can explain all of the 95 million year history of strike slip faulting since 40 ma the observed dextral sense of strike slip has run contrary to the sense of subduction obliquity this may be explained by northward motion of the pacific plate driving continental margin slivers into and or around the oroclin

earthquake ground motion estimation using strong motion records a review of equations for the estimation of peak ground acceleration and response spectral ordinates abstract engineering seismology is the link between earth sciences and engineering the main input of engineering seismology in engineering design are loading conditions which must satisfy certain conditions regarding their level and frequency of occurrence during the lifetime of a structure one method for estimating these loading conditions is through equations based on strong ground motion recorded during previous earthquakes these equations have a handful of independent parameters such as magnitude and source to site distance and a dependent parameter such as peak ground acceleration pga or spectral acceleration and the coefficients in the equation are usually found by regression analysis this review examines such equations in terms of data selection accelerogram processing techniques of the strong motion records used to construct the equations the characterisation of earthquake source travel path and local site used and regression techniques employed to find the final equations it is found that little agreement has been reached in the past 30 years of ground motion estimation relation studies workers have chosen their techniques based on the available data which varies greatly with geographical region also it is noted that there is a need to include more independent parameters into ground motion estimation equations if the large uncertainties associated with such equations are to be significantly reduced the data required to do this is unfortunately scarce

slip rates on the chelungpu and chushiang thrust faults inferred from a deformed strath terrace along the dungpuna river west central taiwan the chelungpu fault produced the september 1999 m w 7 6 chi chi earthquake central taiwan the shortening rate accommodated by this structure integrated over several seismic cycles and its contribution to crustal shortening across the taiwanese range have remained unresolved to address the issues we focus our study on the chelungpu and chushiang thrust faults within the southernmost portion of the chi chi rupture area structural measurements and available seismic profiles are used to infer the subsurface geometry of structures the chushiang and chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the chelungpu surface trace we survey a deformed strath terrace along the dungpuna river buried under a 11 540 309 years old fill deposit given this age the dip angles of the faults and the vertical throw determined from the offset of the strath terrace across the surface fault traces we estimate slip rates of 12 9 4 8 and 2 9 1 6 mm yr on the chelungpu and chushiang faults respectively these yield a total shortening rate of 15 8 5 1 mm yr to be absorbed on their common decollement at depth this total value is an upper bound for the slip rate on the chelungpu fault further north where the chushiang fault disappears and transfers shortening to adjacent faults combining these results with the recently constrained shortening rate on the changhua blind thrust reveals that all these frontal faults presently absorb most of the long term horizontal shortening across the taiwanese range they thus stand as the major sources of seismic hazards in this heavily populated area the return period of earthquakes similar to the chi chi event over a 80 km long stretch of the western foothills is estimated to be 64 years this value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening

earthquake size as a function of fault slip rate abstract estimates of the potential size of earthquakes on mapped active faults are generally based on regressions of earthquake magnitude m w versus length l of fault rupture for historical earthqukes the fault slip rate s has been ignored in formal prediction equations but more accurate predictions of future earthquake magnitudes on mapped faults may be obtained when it is included a least squares regression for a data set of 43 earthquakes occurring on faults for which slip rates are reported shows m w 5 12 1 16 log l 0 20 log s where l is in units of km and s is in units of mm yr the result indicates that the largest earthquakes will occur on the slowest slipping faults if the rupture length is held constant

sea99 a revised ground motion prediction relation for use in extensional tectonic regimes we present sea99 a revised predictive relation for geometric mean horizontal peak ground acceleration and 5 damped pseudovelocity response spec trum appropriate for estimating earthquake ground motions in extensional tectonic regimes which we demonstrate to have lower ground motions than other tectonic regimes sea99 replaces sea96 a relation originally derived by spudich et al 1996 1997 the data set used to develop sea99 is larger than that for sea96 and minor errors in the sea96 data set have been corrected in addition a one step regression method described by joyner and boore 1993 1994 was used rather than the two step method of joyner and boore 1981 sea99 has motions that are as much as 20 higher than those of sea96 at short distances 5 30 km and sea99 s motions are about 20 lower than sea96 at longer periods 1 0 2 0 sec and larger distance 40 100 km sea99 dispersions are significantly less than those of sea96 sea99 rock motions are on the average 20 lower than motions predicted by boore et al 1994 except for short distances at periods around 1 0 sec where sea99 motions exceed those predicted by boore et al 1994 by as much as 10 com parison of ground motions from normal faulting and strike slip events in our data set indicates that normal faulting horizontal ground motions are not significantly different from extensional regime strike slip ground motions

dependency of near field ground motions on the structural maturity of the ruptured faults little work has been undertaken to examine the role of specific long term fault properties on earthquake ground motions here we empirically examine the influence of the structural maturity of faults on the strong ground motions generated by the rupture of these faults and we compare the influence of fault maturity to that of other source properties slip mode and blind versus surface rupturing we analyze the near field ground motions recorded at rock sites for 28 large mw 5 6 7 8 crustal earthquakes of various slip modes the structural maturity of the faults broken by those earthquakes is classified into three classes mature intermediate and immature based on the combined knowledge of the age slip rate cumulative slip and length of the faults we compare the recorded ground motions to the empirical prediction equation of boore et al 1997 at all frequencies earthquakes on immature faults produce ground motions 1 5 times larger than those generated by earthquakes on mature faults the fault maturity appears to be associated with larger differences in ground motion amplitude than the style of faulting factor of 1 35 between reverse and strike slip earthquakes and the surface rupture occurrence factor of 1 2 between blind and surface rupturing earthquakes however the slip mode and the fault maturity are dependent parameters and we suggest that the effect of slip mode may only be apparent actually resulting from the maturity control we conclude that the structural maturity of faults is an important parameter that should be considered in seismic hazard assessment

deformation rates across the placerita northridge mw 6 7 aftershock zone and hopper canyon segments of the western transverse ranges deformation belt abstract aftershocks of the 1994 northridge m w 6 7 earthquake provide insights into the geometry of the seismic source faults in the san fernando valley and the east ventura basin and allow the calculation of deformation rates for the region the northridge thrust and santa susana faults dip in opposite directions with the northridge thrust entirely beneath the santa susana fault these opposing reverse faults interact resulting in a folded active santa susana fault and uplift in the footwall block of that reverse fault two balanced cross sections suggest thick skinned deformation of the western transverse ranges the western section across the modelo lobe segment of the north dipping san cayetano fault and the easternmost surface trace of the south dipping oak ridge fault is west of any aftershocks of the northridge earthquake and has been termed the hopper canyon segment of the deformation belt structural modeling predicts a dip of 46 s on the oak ridge fault at seismogenic depths horizontal shortening rates are calculated by adding the products of the dip slip displacements and the cosines of the dips of both faults the eastern cross section shows the northridge mainshock with a 45 south dipping nodal plane at a depth of 18 km aftershocks reach a depth of 20 km in a thin skinned paradigm a hinge should occur at the surface near the santa monica mountains due to rocks moving from a decollement at the brittle plastic transition and changing dip as they move up the ramp no hinge of that magnitude occurs there calculation of horizontal short ening rates across this part of the western transverse ranges must take into account the displacement on both the northridge thrust eastern extension of the oak ridge fault and the santa susana fault placerita segment horizontal shortening rates are 8 2 2 4 mm yr across the modelo lobe segment of the san cayetano fault and the oak ridge fault and 5 7 2 5 mm yr across the northridge thrust and the santa susana fault these rates are consistent with those based on tectonic geodesy using gps dip slip displacement rates on the faults are 1 7 mm yr for the northridge thrust since 2 3 ma 4 1 0 4 mm yr for the oak ridge fault since 500 ka 5 9 3 9 3 8 mm yr for the santa susana fault since 600 to 2300 ka and 7 4 3 0 mm yr for the modelo lobe segment of the san cayetano fault since 500 ka this indicates that the slip rates on the north dipping the eastern san cayetano and the santa susana faults are comparable but the slip rate on the south dipping faults decreases eastward the slip rate on the oak ridge fault in the ventura basin is more than double that of the northridge thrust

geomorphic analysis of late quaternary faulting on hilton creek round valley and coyote warp faults east central sierra nevada california usa abstract geomorphic analysis of fault scarps and faulted surficial deposits allows for interpretation of late quaternary faulting on the hilton creek and round valley faults two major range front faults in the sierra nevada frontal fault system as well as three faults on the north flank of the coyote warp a structure that separates the round valley fault from range front faults to the south repeated movement on the two frontal faults during the last 15 000 25 000 years is evident from fault scarps on tioga oxygen isotope stage 2 surfaces the scarp data indicate that vertical slip on the round valley fault may have been generally consistent along strike during this time period and may have been characterized by 1 6 1 8 m of slip per faulting event if so 4 events may have occurred in either the last 7900 15 000 years or the last 13 000 15 000 years 5 7 events may have occurred in the last 15 000 20 000 years and 7 9 events may have occurred in the last 20 000 25 000 years which suggests possible repeat times for faulting of 2000 to 4000 years for the round valley fault bevels in scarp slopes and displacement of probable holocene age surfaces support holocene movement on the fault on the hilton creek fault scarps indicate that vertical slip increases northward along strike reaching a maximum on the north side of mcgee n creek based on the size of scarps individual displacements at mcgee n creek must have been either larger or more frequent than individual displacements on the round valley fault the size of single event displacements at mcgee n creek is unconstrained however if they have been on the order of 3 4 m per event a size well within limits associated with normal faulting then 7 9 faulting events could have occurred during the last 20 000 25 000 years as proposed for the round valley fault leaving open the possibility raised by other workers that the two faults may fail together holocene movement on the hilton creek fault is supported by morphology of the fault scarps and data from a trench at mcgee n creek that suggest a major surface faulting event has occurred there within the last 3800 cal yr b p estimating displacement on tahoe oxygen isotope stages 4 6 and pre tahoe probably oxygen isotope stage 6 moraines from crest height relations reveals that slip rates have been higher perhaps twice as high on the hilton creek fault at mcgee n creek than on the round valley fault throughout the late quaternary in contrast to the range front faults coyote warp faults in the study area show no signs of holocene movement the lack of scarps on tioga moraines and the degraded morphology of scarps on adjacent tahoe and pre tahoe moraines indicate that these faults have not ruptured in at least the last 15 000 25 000 years

site amplifications for generic rock sites seismic shear wave velocity as a function of depth for generic rock sites has been estimated from borehole data and studies of crustal velocities and these velocities have been used to compute frequency dependent amplifications for zero attenuation for use in simulations of strong ground motion we define a genetic rock site as one whose velocity at shallow depths equals the average of those from the rock sites sampled by the borehole data most of the boreholes are in populated areas for that reason the rock sites sampled are of particular engineering significance we consider two genetic rock sites rock corresponding to the bulk of the borehole data and very hard rock such as is found in glaciated regions in large areas of eastern north america or in portions of western north america the amplifications on rock sites can be in excess of 3 5 at high frequencies in contrast to the amplifications of less than 1 2 on very hard rock sites the consideration of unattenuated amplification alone is computationally convenient but what matters for ground motion estimation is the combined effect of amplification and attenuation for reasonable values of the attenuation parameter k 0 the combined effect of attenuation and amplification for rock sites peaks between about 2 and 5 hz with a maximum level of less than 1 8 the combined effect is about a factor of 1 5 at 1 hz and is less than unity for frequencies in the range of 10 to 20 hz depending on t using these amplifications we find provisional values of about ao 70 bars and k 0 0 035 sec for rock sites in western north america by fitting our empirically determined response spectra for an m 6 5 event to simulated values the borehole data yield shear velocities 033o of 618 and 306 rrdsec for rock and soil sites respectively when averaged over the upper 30 m from this we recommend that v30 equals 620 and 310 m sec for applications requiring the average velocity for rock and soil sites in western north america by combining the amplifications for rock sites and the site factors obtained from our analysis of strong motion data we derive amplifications for sites with 17 3o 520 m sec nehrp class c corresponding to a mix of rock and soil sites and v3o 310 and 255 m sec average soil and nehrp class d sites respectively for the average soil site the combined effect of amplification and attenuation exceeds a factor of 2 0 for frequencies between 0 4 and about 4 hz with a peak site effect of 2 4 the peak of the nehrp class d site effect is 2 7

the groundwater discharge in the mediterranean karst coastal zones and freshwater tapping set problems and adopted solutions case studies in the karstic regions of the mediterranean coastal zones the groundwater discharge and its outcrops the coastal and submarine springs represent the most typical natural phenomena of littoral karst the economic potential of which is significant the case studies discussed in this paper concern the problems of freshwater tapping in karst coastal zones along the mediterranean littoral owing to the geological and hydrogeological approach the set problems and adopted solutions involve two most important tasks 1 the regulation of groundwater flow in the tapping facilities and 2 the control system of saltwater encroachment in a larger protection zone between the coast and the site of tapping facilities

denali fault slip rates and holocene late pleistocene kinematics of central alaska the denali fault is the principal intracontinental strike slip fault accommodating deformation of interior alaska associated with the yakutat plate convergence we obtained the first quantitative late pleistocene holocene slip rates on the denali fault system from dating offset geomorphic features analysis of cosmogenic 10be concentrations in boulders n 27 and sediment n 13 collected at seven sites offset 25 170 m by the denali and totschunda faults gives average ages that range from 2 4 0 3 ka to 17 0 1 8 ka these offsets and ages yield late pleistocene holocene average slip rates of 9 4 1 6 12 1 1 7 and 8 4 2 2 mm yr 1 along the western central and eastern denali fault respectively and 6 0 1 2 mm yr 1 along the totschunda fault our results suggest a westward decrease in the mean pleistocene holocene slip rate this westward decrease likely results from partitioning of slip from the denali fault system to thrust faults to the north and west

rupture history and seismotectonics of the 1991 uttarkashi himalaya earthquake abstract the 19 october 1991 uttarkashi india earthquake occurred in the main thrust zone of the himalaya with a moment magnitude of 6 8 this event is characteristic of the present day motion on the thrust fault system we examine this earthquake using different sets of data in order to understand better the faulting process of a major earthquake in the himalayan region firstly the modeling of the teleseismic records indicates that the mechanism is similar to the published cmt and indicates a shallow between 10 and 15 km depth low angle thrust event in the vicinity of the source the earthquake was recorded by a network of accelerometers run by the university of roorkee six three component accelerometers were triggered within a radius of 60 km two of them were very close to the surface projection of the fault forward modeling of those records shows that the rupture propagated toward the west this forward modeling gives us the possibility to confirm the epicenter location and to evaluate the timing of the accelerograms the accelerogram records are inverted to obtain the distribution of slip on the fault plane the results show a complex rupture process the slip maxima 1 5 m occurred 10 km west and 15 km southwest of the hypocenter the slip source function obtained with near field data is similar to the function obtained from teleseismic records and shows a low moment release at the beginning of the rupture and a maximum rate of moment release 4 seconds after the relation between the slip distribution obtained by inversion isoseimals mapped faults and the aftershocks location is then discussed and we finally propose a seismotectonic interpretation of this earthquake the uttarkashi earthquake probably occurred along the detachment surface which coincides with the upper surface of the subducting indian lithosphere this detachment surface is gently dipping under the lesser himalaya and south of the vaikrita thrust the vaikrita thrust marks the line separating the very shallow dipping detachment along which big earthquakes like the uttarkashi earthquake could occur from the steeper dipping aseismic basement thrust this observation is important for correctly estimating the seismic hazard in the uttarkashi region

how sensitive are fault slip rates in the los angeles basin to tectonic boundary conditions geodetic studies have produced different interpretations of the relative vertical thickening versus escape tectonics occurring within the los angeles basin based on calculated horizontal strain rates ranging from 56 10 9 yr contraction at n36 et o 85 10 9 yr north south contraction and 60 10 9 yr east west extension three dimensional forward mechanical models of faults in the los an geles basin are used to compare modeled slip rates and slip styles represented as the rakes of average net slip vectors under four representative horizontal strain condi tions with geologically determined late quaternary slip rates and observed slip styles the comparisons strive to identify the most mechanically viable tectonic boundary conditions for the los angeles basin the three dimensional fault surfaces used within the mechanical models have been defined by southern california earthquake center scec workers based on surface geology and subsurface data the model results suggest that northeast southwest principal contraction is inappropriate for the los angeles basin because this tectonic boundary condition produces left lateral slip along the whittier and san gabriel faults in contrast with abundant geologic evidence of right lateral slip of the four tectonic boundary conditions evaluated north south contraction accompanied by either zero or slow east west contraction gives the low est mismatch of modeled and observed fault slip style these results suggest that vertical thickening may be more predominant than escape tectonics in this region

morphology displacement and slip rates along the north anatolian fault turkey 1 geological and geomorphological offsets at different scales are used to constrain the localization of deformation total displacement and slip rates over various timescales along the central and eastern north anatolian fault naf in turkey the naf total displacement is reevaluated using large rivers valleys 80 15 km and structural markers pontide suture 85 25 km tosya vezirkopru basins 80 10 km these suggest a neogene slip rate of 6 5 mm yr over 13 myr the river network morphology shows offsets at a range of scales 20 m to 14 km across the main fault trace and is also used to estimate the degree to which deformation is localized at a smaller scale the morphology associated with small rivers is offset by 200 m along the naf the age of these features can be correlated with the holocene deglaciation and a slip rate of 18 3 5 mm yr is determined this is consistent with a rate of 18 5 mm yr deduced independently from the 14c dating of stream terrace offsets over the short term gps data gives a similar rate of 22 3 mm yr all our results tend to show that most of the deformation between the anatolian and eurasian lithospheric plates has been accommodated along or very close to the active trace of the naf the difference between the neogene and the holocene slip rate may be due to the recent establishment of the current plate geometry after the creation of the naf

seismicity and geometry of a 110 km long blind thrust fault 2 synthesis of the 1982 1985 california earthquake sequence during 1982 1985 three 5 4 mw 6 5 earthquakes migrated 65 km along the north half of a string of quaternary folds at the east front of the california coast ranges there is no surface fault associated with these earthquakes but the fold chain oriented parallel to the san andreas fault 30 km to the west takes up contraction normal to the san andreas fault identification of active blind thrust faults is hindered by the absence of a fault trace but may be revealed by the presence of growing folds at the surface and by earthquakes at depth because of excellent seismic geodetic and geologic data this earthquake sequence illuminates the geometry of the blind faults and enables us to probe their mechanics we relocate seismicity and compute focal mechanisms in a three dimensional velocity space and model the vertical deformation associated with the 1983 m 6 5 coalinga earthquake the aftershock zones abut at echelon offsets in the fold axes and the mainshocks display reverse slip perpendicular to the axes suggesting that the folds conceal a contiguous segmented thrust fault background seismicity concentrates at bends and breaks in the fold chain sites that may correspond to tears and ramps in the thrust fault at depth seismic reflection profiles reveal thrust and reverse faults dipping toward the san andreas fault at depths of 5 10 km with several kilometers of cumulative slip and high angle reverse faults in the anticlines with several hundred meters cumulative slip coseismic fold uplift accompanied the coalinga and kettleman hills north dome earthquakes suggesting that fold growth is episodic and coupled closely to repeated earthquakes on the underlying thrusts the north half of the fold chain has been the site of several 6 m 6 5 earthquakes since 1885 thus kettleman hills middle dome the next fold segment to the south has an elevated seismic potential the aftershock zones of the three main shocks are diffuse and occupy a region much larger than the site of seismic slip aftershocks occur 5 7 km from the fault regions where on the basis of a boundary element model the shear strain increase caused by the fault slip exceeds 20 ppm equivalent to about 0 7 mpa we argue that the broad aftershock zone is a product of high sustained off fault stress caused by repeated displacement on faults that do not cut the earth s surface the fault tip stresses lead to the formation of secondary faults which can become sites of aftershocks and postseismic creep

paleoseismological evidence from lake sediments for recent movement on the denali and other faults yukon territory canada abstract most of the pacific north america plate motion in northwestern canada and southeastern alaska occurs along coastal faults that are the inland extension of the queen charlotte dextral transform fault more ancient faults farther east such as the denali and duke river faults exhibit moderate earthquake activity and may be accommodating part of the pacific plate motion paleoseismological results based on seismic resuspension of lake sediments covering a period of up to 3000 years show that the seismicity on the denali duke river fault system is remarkably recent spanning just the last three to five centuries there is a northerly trending zone of seismicity from the active fairweather contact fault system on the coast across to the part of the denali fault that is currently as well as prehistorically active this partial transfer eastward of pacific plate motion may be analogous to a similar proposed transfer of motion northward to the denali fault from the same fairweather contact fault system farther west in alaska

structural geology of a classic thrust belt earthquake the 1999 chi chi earthquake taiwan mw 7 6 abstract we document the structural context of the 1999 chi chi earthquake m w 7 6 in western taiwan which is one of the best instrumented thrust belt earthquakes the main surface break and large slip 3 10 m is on two segments of the shallow otherwise aseismic bedding parallel chelungpu sanyi thrust system which shows nearly classic ramp flat geometry with shallow detachments 1 6 km in the pliocene chinshui shale and mio pliocene kueichulin tungkeng formations however rupture is complex involving at least six faults including a previously unknown deeper thrust 8 10 km on which the rupture began we compare the coseismic displacements with a new 3d map of the chelungpu sanyi system the displacements are spatially and temporally heterogeneous and well correlated with discrete geometric segments of the 3d shape of the fault system geodetic displacement vectors are statistically parallel to the nearest adjacent fault segment and are parallel to large scale oblique fault corrugations the displacement magnitudes are heterogeneous at several scales which requires in the long term other non chi chi events or significant aseismic deformation the chelungpu thrust has a total displacement of 14 km but the area of largest chi chi slip 10 m is on a newly propagated north chelungpu chinshui detachment 0 3 km total slip which shows abnormally smooth rupture dynamics

tectonic setting of the 1971 sylmar and 1994 northridge earthquakes in the san fernando valley california the san fernando valley lies above the north dipping 1971 sylmar and south dipping 1994 northridge earthquake faults to understand the tectonic setting of these two earthquakes we mapped subsurface geology of the san fernando valley down to a depth of 3 km using industry oil well and seismic data the 1994 northridge earthquake did not rupture the surface and the south dipping aftershock zone terminated against the north dipping 1971 aftershock zone at a depth of 5 8 km however the blind northridge fault has a near surface geologic expression fault propagation folding related to the northridge fault has preserved a thick forelimb sequence of plio pleistocene saugus formation in the sylmar basin and merrick syncline which are located on the hanging wall side of north dipping reverse faults the north dipping mission hills verdugo and northridge hills reverse faults are interpreted to be potential seismic sources because fault propagation folds above these faults have tectonic geomorphic expression these north dipping reverse faults were initiated during the deposition of the saugus formation between 2 3 and 0 5 ma and have minimum dip slip rates of 0 35 to 1 1 mm yr based on the oldest possible age of the initiation of faulting the northridge hills and mission hills faults are interpreted to merge at depth and are located at the updip extension of the 1971 aftershock zone even though these faults did not rupture during the 1971 earthquake surface breaks appeared north of these faults mostly along north dipping bedding planes and are interpreted as secondary features related to flexural slip folding rather than a direct extension of the 1971 seismogenic fault surface and subsurface geology together with seismological data of the 1971 and 1994 earthquakes suggests that the north and south dipping deformation zones in the san fernando valley are divided into multiple segments separated by northeast trending structural discontinuities

fault slip rates and earthquake histories for active faults in southern california abstract within the context of the historical record of seismicity we review the geological data bearing on the quaternary slip rates and paleoearthquake histories of active faults in southern california

present day kinematics of the middle east and eastern mediterranean the middle east and eastern mediterranean regions contain three major strike slip fault zones the dead sea fault zone dsfz and the north and east anatolian fault zones nafz and eafz these accommodate northward motion of the african and arabian plates relative to eurasia and westward motion of the small turkish plate this study deduces an internally consistent solution for the present day kinematics of these plates which is accurate to better than 20 and applicable throughout time since 5 ma by constraining the slip senses and rates on these strike slip fault zones the 7 0 5 mm yr 1 left lateral slip rate on the dsfz is associated with counterclockwise rotation of arabia relative to africa at 0 33 m y 1 around an eulcr pole near 33 n 23 e the nafz takes up counterclockwise rotation of the turkish plate relative to eurasia at 0 83 m y 1 13 around a pole at 31 n 35 5 e with right lateral slip rate 15 mm yr 1 the resulting prediction for the eafz involves 14 mm yr 1 left lateral motion and 2 mm yr 1 of shortening between arabia and turkey the triple junction of africa arabia and turkey is near the city of kahramanmaras this locality contains a narrow promontory bounded by ssw trending left lateral faults at the edges of the arabian and turkish plates which is loosely attached to the african plate moving westward relative to its interior at 4 mm yr 1

high resolution image of calaveras fault seismicity 1 by measuring relative earthquake arrival times using waveform cross correlation and locating earthquakes using the double difference technique we are able to reduce hypocentral errors by 1 to 2 orders of magnitude over routine locations for nearly 8000 events along a 35 km section of the calaveras fault this represents 92 of all seismicity since 1984 and includes the rupture zone of the m 6 2 1984 morgan hill california earthquake the relocated seismicity forms highly organized structures that were previously obscured by location errors there are abundant repeating earthquake sequences as well as linear clusters of earthquakes large voids in seismicity appear with dimensions of kilometers that have been aseismic over the 30 year time interval suggesting that these portions of the fault are either locked or creeping the area of greatest slip in the morgan hill main shock coincides with the most prominent of these voids suggesting that this part of the fault may be locked between large earthquakes we find that the calaveras fault at depth is extremely thin with an average upper bound on fault zone width of 75 m given the location error however this width is not resolvably different from zero the relocations reveal active secondary faults which we use to solve for the stress field in the immediate vicinity of the calaveras fault we find that the maximum compressive stress is at a high angle only 13 from the fault normal supporting previous interpretations that this fault is weak

seismic behavior of the southern san andreas fault zone in the northern coachella valley california comparison of the 1948 and 1986 earthquake sequences moderate earthquakes in 1948 and 1986 that occurred along the southern san andreas fault zone are examined to help understand the subsurface geometry and seismic behavior of active fault segments in the northern coachella valley the 1986 north palm springs earthquake occurred between the banning and mission creek traces of the san andreas fault zone based on data from both portable and permanent stations aftershocks of the 1986 event define a nearly planar surface that strikes about n60 to 70 w is about 15 km long and dips northeast from near the banning surface trace at about 45 to 50 relocation of the mainshock using revised station corrections and a local velocity model inverted from the aftershock arrival times indicates a location at 34 n00 26 116 w36 34 and a focal depth of 10 4 km the first motion focal mechanism for the mainshock indicates pure right slip on a plane dipping northeast at 40 to 45 with a strike of n60 w previous moment tensor solutions e g hartzell 1989 exhibit significant oblique reverse slip on a plane with a more westerly strike and a seismic moment of 1 4 to 1 7 1018 n m mw 6 1 actual and synthetic wood anderson recordings indicate a local magnitude of ml 6 0 the 1948 desert hot springs earthquake produced waveforms similar to 1986 although amplitudes for 1948 are typically 20 to 30 larger the 1948 mainshock is relocated at 33 n55 2 116 w28 9 with a focal depth of 12 km a revised magnitude of ml 6 3 and an estimated seismic moment of 2 to 3 1018 n m based on arrival time information from close 20 km portable stations deployed in 1948 to 1949 the 1948 aftershock distribution is about 15 km long 8 to 10 km wide and abuts the 1986 aftershock sequence to the southeast along the banning fault the 1948 aftershock zone is consistent with a focal mechanism that exhibits predominantly right slip motion rake 169 on a plane that strikes n55 w and dips more steeply northeast at 60 to 70 in 1986 the horizontal extent of the rupture may have been controlled by secondary cross faults and possible changes in fault geometry while the down dip extent may have been controlled by the presence at depth of a regional detachment in 1948 the rupture likely had a steeper dip than in 1986 and extended southeast as far as the northern indio hills where the surface trace of the banning fault undergoes an approximate 7 change in strike these results indicate that the banning fault is nonvertical is likely segmented according to fault dip as well as fault strike and has been the primary locus of recent moderate sized earthquake activity in the northern coachella valley

characterization of fault zones there are currently three major competing views on the essential geometrical mechanical and mathematical nature of faults the standard view is that faults are possibly segmented and heterogeneous euclidean zones in a continuum solid the continuum euclidean view is supported by seismic gravity and electromagnetic imaging studies by successful modeling of observed seismic radiation geodetic data and changes in seismicity patterns by detailed field studies of earthquake rupture zones and exhumed faults and by recent high resolution hypocenter distributions along several faults the second view focuses on granular aspects of fault structures and deformation fields the granular view is supported by observations of rock particles in fault zone gouge by studies of block rotations and the mosaic structure of the lithosphere which includes the overall geometry of plate tectonics by concentration of deformation signals along block boundaries by correlation of seismicity patterns on scales several times larger than those compatible with a continuum framework and by strongly heterogeneous wave propagation effects on the earth s surface the third view is that faults are fractal objects with rough surfaces and branching geometry the fractal view is supported by some statistical analysis of regional hypocenter locations by long range correlation of various measurements in geophysical boreholes by the fact that observed power law statistics of earthquakes are compatible with an underlying scale invariant geometrical structure by geometrical analysis of fault traces at the earth s surface and by measurements of joint and fault surfaces topography

a balanced cross section of the 1994 northridge earthquake southern california the northridge earthquake of 17 january 19941 was the latest in a series of very damaging thrust fault generated earthquakes to strike california following the san fernando2 1971 coalinga3 1983 and whittier narrows4 5 1987 events like the last two of these the northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic hazard methods6 7 balanced cross sections8 9 which flatten and remove the crustal deformation can be used to identify and quantify the seismic hazard posed by thrust faults here we present a balanced cross section through the northridge portion of the transverse ranges fold and thrust belt10 which shows that the earthquake occurred on what we call the pico thrust a cross section of this sort constructed before the earthquake would have revealed the fault although it would not have predicted the earthquake cross sectional modelling of the pico thrust yields an average slip rate of 1 4 1 7 mm yr 1 and a recurrence interval of northridge sized mw 6 7 earthquakes every 1 500 1 800 years we show that the pico thrust is the back thrust to the 170 km elysian park thrust3 4 which underlies some of the most densely urbanized portions of the los angeles basin

the north anatolian fault a new look dedicated to the memory of three pioneers ihsan ketin sirri erinc and melih tokay and a recent student aykut barka who burnt himself out in pursuit of the mysteries of the north anatolian fault abstract the north anatolian fault naf is a 1200 km long dextral strike slip fault zone that formed by progressive strain localization in a generally westerly widening right lateral keirogen in northern turkey mostly along an interface juxtaposing subduction accretion material to its south and older and stiffer continental basements to its north the naf formed approximately 13 to 11 ma ago in the east and propagated westward it reached the sea of marmara no earlier than 200 ka ago although shear related deformation in a broad zone there had already commenced in the late miocene the fault zone has a very distinct morphological expression and is seismically active since the seventeenth century it has shown cyclical seismic behavior with century long cycles beginning in the east and progressing westwa

surface rupture of 1999 chi chi earthquake yields insights on active tectonics of central taiwan the 1999 chi chi earthquake was caused by rupture of the chelungpu fault one of the most prominent active thrust faults of taiwan this largest of taiwan s historical fault ruptures broke the surface for over 90 km at the western base of the rugged mountain range a short right lateral tear extended southwestward from the southern end of the chelungpu fault and a complex assemblage of shallow folds and faults ran northeastward from the northern end vertical offsets averaged about 2 m along the southern half of the chelungpu fault and about 4 m along the northern half and offsets of 5 to 7 m were typical along the northern part of the major thrust the sinuous nature of the surface trace is consistent with seismographic data that indicate a dip of about 30 the 1999 rupture draws attention to the fact that this active fault system is highly segmented and that this segmentation influences the characteristics of seismic ruptures active faults to the south north and west of the chelungpu fault have distinctly different characteristics faults to the south and north broke the surface during earthquakes in 1906 and 1935 the active changhua fault to the west a blind thrust similar in length to the chelungpu has not ruptured in the historical period and should be considered a prime candidate for generating a future earthquake manuscript received 4 october 2000

magnitude scaling of the near fault rupture directivity pulse abstract current ground motion models all assume monotonically increasing spectral amplitude at all periods with increasing magnitude however near fault recordings from recent earthquakes confirm that the near fault fault normal forward rupture directivity velocity pulse is a narrow band pulse whose period increases with magnitude this magnitude dependence of the period of the near fault pulse is expected from theory because the period of the pulse is related to source parameters such as the rise time duration of slip at a point on the fault and the fault dimensions which generally increase with magnitude this magnitude dependence of the pulse period causes the response spectrum to have a peak whose period increases with magnitude such that the near fault ground motions from smaller earthquakes may exceed those of larger earthquakes at intermediate periods around 1 s this paper presents preliminary equations relating the period of the fault normal component of the forward rupture directivity velocity pulse to the earthquake magnitude and a preliminary model for the acceleration response spectra of near fault fault normal ground motions that includes the magnitude dependence of the period of the response spectral peak

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

source parameters of the 1980 mammoth lakes california earthquake sequence from the more than 1500 mammoth lakes earthquakes recorded on three component digital seismographs spudich et al 1981 150 were used in an analysis of the locations mechanism and source parameters a composite fault plane solution of nine earthquakes 3 9 m 5 1 defines a right lateral strike slip mechanism on a steeply dipping nearly east west plane striking s75 e or left lateral strike slip on a nearly north south plane striking n10 e vertical cross sections of well located aftershocks indicate possibly three east west planes that coincide with the locations of the four largest earthquakes with ml 6 0 using the spectral analysis of s waves brune 1970 source parameters for 67 earthquakes were determined forty eight had magnitudes greater than or equal to 3 0 seismic moments ranged from 9 20 1018 dyn cm to 2 33 1024 dyn cm earthquakes with seismic moment greater than about 1 0 1021 dyn cm had nearly constant stress drops 50 bars earthquakes with seismic moment less than about 1 0 1021 dyn cm had stress drops that apparently decrease as seismic moment decreases

an analysis of the 1985 nahanni earthquakes abstract two large magnitude earthquakes occurred in 1985 near the north nahanni river in the northeast cordillera northwest territories canada on 5 october m s 6 6 and 23 december m s 6 9 these events were unprecedented for this region of the cordillera and the december event is the largest earthquake ever known in the eastern part of the canadian cordillera this report presents detailed studies of the nahanni earthquakes their source parameters macroseismic effects aftershock sequences triggered rock avalanches their relationship to the geology of the epicentral area and their seismic hazard implications parameters calculated here for these two major events are parentheses indicate other studies the earthquakes occurred within a small relatively undeformed plateau the mackenzie plain in the foreland fold belt created along the northeastern cordillera during the columbian or laramide orogeny that fold belt is now subjected to northeast southwest horizontal compressive stresses possibly very similar to the original laramide stress regime and the fault plane implied by the seismic mechanisms is very similar to the laramide faults in the area however no surface fault break has been found and none of the mapped laramide faults in the epicentral area appears to be involved in the aftershock activity it is thus believed that the nahanni earthquakes occurred on a blind laramide thrust fault under the mackenzie plain the large magnitudes of the nahanni earthquakes show that the present seismic zoning for building code purposes in the eastern cordillera north of 60 n needs reassessment and suggest that the zoning in the eastern cordillera in british columbia and alberta may also need revision the felt areas of the earthquakes show that regional anelastic attenuation in the eastern canadian cordillera is significantly anisotropic and much lower along strike than across strike the felt areas also appear to scale with seismic moment rather than m b magnitude the thrust mechanisms regional stress regime shallow focal depth and high velocity sedimentary rocks in the focal region suggest that the nahanni earthquakes and particularly the near field strong ground motion recorded for the second event are ideal engineering design data for critical facilities in eastern north america

earthquake scaling fault segmentation and structural maturity abstract slip and length measurements on earthquakes suggest large stress drop variability we analyze an extended set of slip length measurements for large earthquakes m 6 to seek for the possible origin s of this apparent variability we propose that such variability arises from earthquakes breaking a variable number of major fault segments that number depends on the strength of the inter segment zones which itself depends on the structural maturity of the faults we propose new d max l parameterizations based on that idea of multiple segment ruptures in such parameterizations each broken segment roughly scales as a crack while the total multi segment rupture does not stress drop on individual segments is roughly constant only varying between 3 5 to 9 mpa the slight variation that is still observed depends on fault structural maturity more mature faults have lower stress drops than immature ones the new d max l functions that we propose reduce uncertainties with respect to available relationships they thus provide a more solid basis to estimate seismic hazard by integrating fault properties revealed by geological studies

apparent stress fault maturity and seismic hazard for normal fault earthquakes at subduction zones summary the behavior of apparent stress for normal fault earthquakes at subduction zones is derived by examining the apparent stress a es m 0 w here es is radiated energy and m 0 is seismic moment of all globally distributed shallow depth h 1m pa are also generally intraslab but occur where the lithosphere has just begun subduction beneath the overriding plate they usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis or where there are local contortions or geometrical complexities of the plate boundary lower a 1m pa i sassociated with events occurring at the outer rise or complex between the or and the trench axis as well as with intracrustal events occurring just landward of the trench the average apparent stress of intraslab normal fault earthquakes is considerably higher than the average apparent stress of interplate thrust fault earthquakes in turn the average a of strike slip earthquakes in intraoceanic environments is considerably higher than that of intraslab normal fault earthquakes the variation of average a with focal mechanism and tectonic regime suggests that the level of a is related to fault maturity lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements from hundreds to thousands of kilometres in contrast immature faults such as those on which intraslab normal fault earthquakes generally occur are found in cold and intact lithosphere in which total fault displacement has been much less from hundreds of metres to a few kilometres also faults on which high a oceanic strike slip earthquakes occur are predominantly intraplate or at evolving ends of transforms at subduction zones earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than earthquakes occurring on mature faults we have identified earthquake pairs in which an interplate thrust and an intraslab normal earthquake occurred remarkably close in space and time the intraslab normal member of each pair radiated anomalously high amounts of energy compared to its thrust fault counterpart these intraslab earthquakes probably ruptured intact slab mantle and are dramatic examples in which me an energy magnitude is shown to be a far better estimate of the potential for earthquake damage than mw this discovery may help explain why loss of life as a result of intraslab earthquakes was greater in the 20th century in latin america than the fatalities associated with interplate thrust events that represented much higher total moment release

geologic and paleoseismic study of the lavic lake fault at lavic lake playa mojave desert southern california paleoseismic investigations of the lavic lake fault at lavic lake playa place constraints on the timing of a possible earlier earthquake along the 1999 hector mine rupture trace and reveal evidence of the timing of the penultimate earthquake on a strand of the lavic lake fault that did not rupture in 1999 three of our four trenches trenches a b and c were excavated across the 1999 hector mine rupture a fourth trench d was excavated across a vegetation lineament that had only minor slip at its southern end in 1999 trenches a c exposed strata that are broken only by the 1999 rupture trench d exposed horizontal bedding that is locally warped and offset by faults stratigraphic evidence for the timing of an earlier earthquake along the 1999 rupture across lavic lake playa was not exposed thus an earlier event if there was one along that rupture trace predates the lowest stratigraphic level exposed in our trenches radiocarbon dating of strata near the bottom of trenches constrains a possible earlier event to some time earlier than about 4950 b c buried faults revealed in trench d are below a vegetation lineament at the ground surface a depositional contact about 80 cm below the ground surface acts as the upward termination of fault breaks in trench d thus this contact may be the event horizon for a surface rupturing earthquake prior to 1999 the penultimate earthquake on the lavic lake fault radiocarbon ages of detrital charcoal samples from immediately below the event horizon indicate that the earthquake associated with the faulting occurred later than a d 260 an approximately 1300 year age difference between two samples at about the same stratigraphic level below the event horizon suggests the potential for a long residence time of detrital charcoal in the area coupled with a lack of bioturbation that could introduce young organic material into the stratigraphic section the charcoal ages provide only a maximum bounding age thus the recognized event may be younger there is abundant subtle evidence for pre 1999 activity of the lavic lake fault in the playa area even though the fault was not mapped near the playa prior to the hector mine earthquake the most notable indicators for long term presence of the fault are pronounced persistent vegetation lineaments and uplifted basalt exposures primary and secondary slip occurred in 1999 on two southern vegetation lineaments and minor slip locally formed on a northern lineament trench exposures across the northern vegetation lineament revealed the post a d 260 earthquake and a geomorphic trough extends northward into alluvial fan deposits in line with this lineament the presence of two basalt exposures in lavic lake playa indicates the presence of persistent compressional steps and uplift along the fault fault line scarps are additional geomorphic markers of repeated slip events in basalt exposures

fault trace complexity cumulative slip and the shape of the magnitude frequency distribution for strike slip faults a global survey summary we examine whether the shape of the magnitude frequency distribution for strike slip faults is described by the gutenburg richter relationship log n a bm or by the characteristic earthquake model by analysing a data set of faults from california mexico japan new zealand china and turkey for faults within regional seismic networks curves of the form log n yrpl a bm where n yr is the number of events per year equal to magnitude m are fit to the instrumental record of seismicity and geological data are used to estimate independently the size and recurrence rate of the largest expected earthquakes that would rupture the total length of the fault extrapolation of instrumentally derived curves to larger magnitudes agrees with geological estimates of the recurrence rate of the largest earthquakes for only four of the 22 faults if uncertainties in curve slope are considered and significantly underestimates the geological recurrence rates in the remaining cases also if we predict the seismicity of the faults as a function of fault length and slip rate and the predicted seismicity is distributed in accord with the gutenburg richter relationship we find the predicted recurrence rate to be greater than the observed recurrence rates of smaller earthquakes along most faults if individual fault zones satisfy the gutenburg richter relationship over the long term our observations imply that during the recurrence interval of the largest expected earthquakes the recurrence of lesser sized events is not steady but rather strongly clustered in time however if the instrumental records provide an estimate of the long term rate of small to moderate earthquakes along the faults our observations imply that the faults generally exhibit a magnitude frequency distribution consistent with the characteristic earthquake model also we observe that the geometrical complexity of strike slip faults is a decreasing function of cumulative strike slip offset the four faults we observe to be consistent with the gutenburgrichter relationship are among those characterized by the least amount of cumulative slip and greatest fault trace complexity we therefore suggest that the ratio of the recurrence rate of small to large earthquakes along a fault zone may decrease as slip accumulates and the fault becomes smoother

new moment magnitude scale evidence of stress drop magnitude scaling and stochastic ground motion model for the french west indies in this study we analyse records from the les saintes seismic sequence following the mw 6 3 earthquake of 2004 november 11 which occurred close to guadeloupe french west indies 485 earthquakes with magnitudes from 2 to 6 recorded at distances between 5 and 150 km are used s waves fourier spectra are analysed to simultaneously determine source path and site terms the results show that the duration magnitude routinely estimated for the events that occurred in the region underestimate moment magnitude by 0 5 magnitude units over the whole magnitude range from the inverted seismic moments and corner frequencies we compute brune s stress drops we show that stress drops increase with increasing magnitude the same pattern is observed on apparent stresses i e the seismic energy to moment ratio however the rate of increase diminishes at high magnitudes which is consistent with a constant stress drop model for large events using the results of the inversions we perform ground motion simulations for the entire data set using the smsim stochastic simulation tool the results show that a good fit 0 25 with observed data is achieved when the source is properly described by its moment magnitude and stress drop and when site effects are taken into account although the magnitude dependent stress drop model is giving better results than the constant stress drop model the interevent variability remains high which could suggest that stress drop depends on other parameters such as the depth of the hypocentre in any case the overall variability is of the same order of magnitude as usually observed in empirical ground motion prediction equations

paleoseismology of the johnson valley kickapoo and homestead valley faults clustering of earthquakes in the eastern california shear zone paleoseismic data from 11 trenches at seven sites excavated across the southern johnson valley kickapoo and homestead valley faults that ruptured in the 1992 landers earthquake as well as the northern johnson valley fault which did not fail in 1992 indicate that the return period for large surface rupturing events in this part of the eastern california shear zone is in the range of 5 15 ka the inferred slip rates based on their respective recurrence intervals are in the range of 0 2 0 6 mm yr for each of the faults studied a previous large earthquake ruptured the southern johnson valley and kickapoo faults about 5 ka b p the northern johnson valley fault also failed at about this time at 5 8 ka b p and may have been part of the same rupture in contrast the penultimate large earthquake that we identify on the homestead valley fault occurred about 15 ka b p much earlier than other faults involved in the 1992 rupture from these observations combined with paleoseismic work by others after the 1992 earth quake it appears that previous events along the southern johnson valley and kick apoo faults were different than those of 1992 and may have involved other fault segments it has been over 5 ka since the most recent rupture on the northern johnson valley fault therefore it is surprising that it did not fail in the 1992 rupture from our observations dextral shear appears to be distributed across the entire eastern california shear zone with individual faults taking only a small proportion of the overall slip release of this regional strain appears to occur in temporal clusters of large earthquakes with the 1992 event apparently the most recent of a sequence of late holocene 0 1 ka earthquakes that have ruptured the nine faults we have trenched in the southwestern mojave desert previous clusters of earthquake activity occurred in the early 8 9 ka and middle 5 6 ka holocene and possibly the latest pleistocene 15 ka

the 1991 sierra madre earthquake sequence in southern california seismological and tectonic analysis the m l 5 8 sierra madre earthquake of 28 june 1991 occurred at a depth of 12 km under the san gabriel mountains of the central transverse ranges since at least 1932 this region had been quiescent for m 3 the mainshock focal mechanism derived from first motion polarities exhibited almost pure thrust faulting with a rake of 82 on a plane striking n62 e and dipping 50 to the north the event appears to have occurred on the clamshell sawpit fault a splay of the sierra madre fault zone the aftershock sequence following the mainshock occurred at a depth of 9 to 14 km and was deficient in small earthquakes having a b value of 0 6 twenty nine single event focal mechanisms were determined for aftershocks of m 1 5 the 4 km long segment of the clamshell sawpit fault that may have ruptured in the mainshock is outlined by several thrust focal mechanisms with an east northeast striking fault plane dipping to the north to the west several thrust aftershocks with east striking nodal planes suggest some complexity in the aftershock faulting such as a curved rupture surface in addition several strike slip and normal faulting events occurred along the edges of the mainshock fault plane indicating secondary tear faulting the tectonic stress field driving the coexisting left lateral strike slip and thrust faults in the northern los angeles basin is north south horizontal compression with vertical intermediate or minimum principal stress axis

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

offset on the main recent fault of nw iran and implications for the late cenozoic tectonics of the arabia eurasia collision zone summary we use drainage patterns geological markers and geomorphological features to determine a right lateral offset of 50 km and possibly as much as 70 km on the main recent fault in nw iran this fault trends nw se and forms the ne border of the zagros mountains it accommodates the strike slip component of the n s convergence between arabia and eurasia with the ne sw shortening component being accommodated in the zagros fold belt its 50 km strike slip offset implies a shortening of 50 km in the fold belt and 70 km total n s convergence accommodated in the nw zagros this is a substantial fraction of the 85 140 km overall arabia eurasia convergence expected over the last 3 5 ma if the main recent fault initiated at that time as seems likely from geological arguments it has a horizontal slip rate of at least 10 17 mm yr 1 and should be the source of frequent earthquakes of ms 6 7 as has been seen in the 20th century and the earlier historical record the similarity of the offsets and probable ages of the north anatolian and main recent faults suggests that they have been active as an almost continuous zone of right lateral shear on the north edge of the arabian and anatolian plates since the early pliocene

a broadband study of the 13 august 1978 santa barbara earthquake the santa barbara earthquake of 13 august 1978 provides an opportunity to perform a broadband investigation of body waves for a well recorded moderate size m l 5 1 event the long and short period teleseismic body waves are modeled in the time domain to construct a source time function which is consistent in the period range of 1 to 20 sec the long period records indicate an overall duration of 6 sec while the short period records reveal the fine scale character of the slip history consisting of two sharp pulses separated by about 1 sec the source mechanism determined from this analysis is a moderately dipping 30 ne thrust with significant left lateral slip the moment was determined to be 1 1 10 25 dyne cm the earthquake was also reasonably well recorded on accelerographs in the near field the modeling of the strong motion displacements was a two step procedure 1 the displacements were modeled alone and 2 in an attempt to achieve consistency between the local and far field time functions the qualitative features of the teleseismic short period time function were used to predict the displacements if the two sources in the short period time function are allowed to have different mechanisms the displacements can be modeled quite well this suggests that the overall faulting process was rough and the multiple source character suggested at high frequencies is due to high stress drop asperities the two sources are modeled as asperities separated by 1 5 km the first source has a mechanism consistent with the teleseismic solution while the second source is more steeply dipping the total moment determined from the strong motion data is 3 5 10 24 dyne cm or one third the long period moment this is consistent with other recent studies which suggest that the high frequency strong ground motion is controlled by the distribution of asperities even though the sum of their moments may be small compared to the overall moment this study also shows the importance of teleseismic short periods in predicting the local displacements

strong ground motion from the uttarkashi himalaya india earthquake comparison of observations with synthetics using the composite source model the uttarkashi earthquake of 19 october 1991 ms 7 0 occurred in the greater himalayan region north of the main central thrust at an estimated depth of 12 km the fault plane solution indicates a low angle thrust mechanism striking northwest consistent with the tectonic pattern of thrusting in the region aftershocks define a belt parallel to and north of the surface trace of the main central thrust roughly 10 km wide and 30 km long the mainshock is located at the northeast edge of this zone the earthquake was recorded on 13 strong motion accelerographs at distances ranging from 25 to 150 km from the epicenter one station at bhatwari peak horizontal acceleration of 272 cm sec 2 is above the aftershock zone the maximum peak horizontal acceleration was about 313 cm sec 2 at uttarkashi at an epicentral distance of 36 km the amplitudes and frequency content of the strong ground motions are more or less consistent with expectations for an earthquake of this magnitude in california synthetics generated using the composite source model and synthetic green s functions zeng et al 1994a b are successful in producing acceleration velocity and displacement with a realistic appearance and the correct statistical properties of the two accelerograms recorded nearest the fault bhatwari and uttarkashi to produce these we introduced trial and error modifications of the layered medium velocity model within uncertainties at more distant stations we first used the velocity structure that worked for the two nearest stations differences emphasize the large potential role of unknown site and wave propagation effects for the station at tehri we explored different velocity models and found one there that was also quite successful we then used these two velocity models to predict strong ground motions at bhatwari and tehri from a potential magnitude 8 5 earthquake filling part of the seismic gap along the himalayan frontal faults the synthetics show peak accelerations that are only somewhat larger than those in the uttarkashi event but much longer durations and increased amplitudes of response spectra at long periods

an 8 month slow slip event triggers progressive nucleation of the 2014 chile megathrust the mechanisms leading to large earthquakes are poorly understood and documented here we characterize the long term precursory phase of the april 1st 2014 mw8 1 north chile megathrust we show that a group of coastal gps stations accelerated westward eight months before the mainshock corresponding to a mw6 5 slow slip event on the subduction interface 80 of which was aseismic concurrent interface foreshocks underwent a diminution of their radiation at high frequency as shown by the temporal evolution of fourier spectra and residuals with respect to ground motions predicted by recent subduction models such ground motions change suggests that in response to the slow sliding of the subduction interface seismic ruptures are progressively becoming smoother and or slower the gradual propagation of seismic ruptures beyond seismic asperities into surrounding metastable areas could explain these observations and might be the precursory mechanism eventually leading to the mainshock

a cross section of the los angeles area seismically active fold and thrust belt the 1987 whittier narrows earthquake and earthquake hazard retrodeformable cross sections across the los angeles area interpret the pliocene to quaternary deformation to be a developing basement involved fold and thrust belt the fold and thrust belt is seismically active as evidenced by the 1987 whittier narrows earthquake ml 5 9 and the 1971 san fernando earthquake mw 6 6 the structural geology of the los angeles area is dominated by three major compressional uplift trends 1 the palos verdes anticlinorium and western shelf 2 the santa monica mountains anticlinorium and 3 the verdugo mountains san rafael hills and the san gabriel mountains these trends result from major thrust ramps off a detachment s at 10 15 km depth thrusts of the verdugo mountains san rafael hills and the san gabriel mountains reach the surface the other two uplifts are associated with blind thrusts compressional seismicity is concentrated along these thrust ramps the 1987 whittier narrows earthquake probably occurred on the elysian park thrust which underlies the santa monica mountains anticlinorium the thrust interpretation accounts for the geometry of the anticlinorium the seismological characteristics of the earthquake and the geometry of coseismic uplift the earthquake and aftershocks occurred within a structurally complex narrow zone of miocene and pliocene northwest trending faults that cross the anticlinorium at a high angle these northwest trending faults are interpreted to be reactivated faults now behaving as tears in the elysian park thrust and not the result of active right lateral deformation extending into the whittier narrows area our analysis suggests the whittier narrows earthquake sequence occurred within a structurally weakened zone along the elysian park thrust we also suggest that the whittier fault is not an important quaternary structure and may not be seismogenic the regional cross section is a nonunique solution and other possible solutions are considered multiple solutions arise from the presence of two intersecting compressional belts in the los angeles area the transverse ranges and the northern peninsular ranges the belts may be due to one or more regional detachments and the northern peninsular ranges may be northeast or southwest vergent the deformed top of the crystalline basement along the regional cross section requires a minimum of 15 0 km of north south convergence between the palos verdes hills and the san andreas fault regardless of the structural solution restoration of our cross section solution requires 21 4 km of north south convergence on top of the crystalline basement including 6 4 km of slip continuing offshore to make structures of the continental borderland and 29 7 km of convergence on the basal detachment geologic relationships suggest major shortening started between early and late pliocene time 2 2 4 0 ma which yields a minimum convergence rate of 3 8 6 8 mm yr between the palos verdes hills and the san andreas fault convergence rates for our solution range from 5 4 to 13 5 mm yr between the edge of the continental borderland and the san andreas fault slip rate estimates for the elysian park thrust along the eastern portion of the santa monica mountains anticlinorium are 2 5 5 2 mm yr if the 1987 whittier narrows earthquake is the characteristic earthquake along the 170 km long anticlinorium then recurrence intervals are estimated to be 5 6 12 1 years this recurrence is higher than the historic seismic record along the santa monica mountains anticlinorium and suggests that 1 our slip rates are too high 2 some crustal shortening is taken up aseismically and or 3 earthquakes larger than the 1987 whittier narrows earthquake will occur along the anticlinorium but less frequently

long dormancy low slip rate and similar slip per event for the emerson fault eastern california shear zone excavations in a playa along the 1992 rupture of the emerson fault reveal evidence of two paleoseismic events with only one large prehistoric rupture in the past 15 millennia accelerator mass spectrometer radiocarbon ages of charcoal from playa sediments and from fault scarp colluvium directly beneath the playa beds indicate that the last large prehistoric slip event occurred about 9000 ka trench wall exposures revealed clear evidence of at least one pre 9 ka rupture at the playa site the event horizon of this earthquake is between two pedogenic carbonate layers that have radiocarbon ages of 14 8 ka and 24 1 ka implying that the earthquake occurred about 20 000 years b p the actual bracketing ages for this rupture are likely a few thousand years older because of the mean residence time for the pedogenic carbonate and calibration of the 14c ages by 230th dating despite the large uncertainties a dormant period of at least 6 kyr to as much as 13 kyr separates the older event from the 9 ka event because the scarp formed by the penultimate event is similar in height to the scarp formed by the 1992 mw 7 3 landers earthquake the penultimate rupture was at least locally similar in size to the most recent rupture this similarity supports the concept of characteristic slip for the emerson fault preliminary results from paleoseismic studies at other sites on the 1992 rupture suggest that large ruptures occurred on other nearby faults within a few hundred years of this penultimate event on the emerson fault the interseismic period that preceded the 1992 earthquake on the emerson fault was about 40 times longer than the average interval between large events on the nearby san andreas fault therefore in comparison to events on the san andreas fault the 1992 landers earthquake was an exceedingly rare event

earthquake supercycles in central italy inferred from 36cl exposure dating we use 36cl surface exposure dating to determine the slip release pattern over the last 15 kyr for the velino magnola fault a major active normal fault in central italy we sampled the fault at five well separated sites along its length and modeled the 36cl concentrations measured in the 376 samples we find that the fault broke in at least 9 large earthquakes that occurred in two 5 6 ka long supercycles each cycle included a 4 5 ka long phase of relative quiescence followed by a cluster of at least 3 large earthquakes or earthquake sequences that released most of the accumulated strain in 1 ka all 9 identified events broke the entire fault and produced maximum surface slips of 2 3 m though the velino magnola fault seems presently in a stage of relative quiescence it may re enter a phase of paroxysmal seismic activity in a few hundred of years

complex faulting associated with the 22 december 2003 mw 6 5 san simeon california earthquake aftershocks and postseismic surface deformation we use data from two seismic networks and satellite interferometric synthetic aperture radar insar imagery to characterize the 22 december 2003 m w 6 5 san simeon earthquake sequence absolute locations for the mainshock and nearly 10 000 aftershocks were determined using a new three dimensional 3d seismic velocity model relative locations were obtained using double difference the mainshock location found using the 3d velocity model is 35 704 n 121 096 w at a depth of 9 7 0 7 km the aftershocks concentrate at the northwest and southeast parts of the aftershock zone between the mapped traces of the oceanic and nacimiento fault zones the northwest end of the mainshock rupture as defined by the aftershocks projects from the mainshock hypocenter to the surface a few kilometers west of the mapped trace of the oceanic fault near the santa lucia range front and the 5 mm postseismic insar imagery contour the oceanic fault in this area as mapped by hall 1991 is therefore probably a second order synthetic thrust or reverse fault that splays upward from the main seismogenic fault at depth the southeast end of the rupture projects closer to the mapped oceanic fault trace suggesting much of the slip was along this fault or at a minimum is accommodating much of the postseismic deformation insar imagery shows 72 mm of postseismic uplift in the vicinity of maximum coseismic slip in the central section of the rupture and 48 and 45 mm at the northwest and southeast end of the aftershock zone respectively from these observations we model a 30 km long northwest trending northeast dipping mainshock rupture surface called the mainthrust which is likely the oceanic fault at depth a 10 km long southwest dipping backthrust parallel to the mainthrust near the hypocenter several smaller southwest dipping structures in the southeast and perhaps additional northeast dipping or subvertical structures southeast of the mainshock plane discontinuous backthrust features opposite the mainthrust in the southeast part of the aftershock zone may offset the relic nacimiento fault zone at depth the insar data image surface deformation associated with both aseismic slip and aftershock production on the mainthrust and the backthrusts at the northwest and southeast ends of the aftershock zone the well defined mainthrust at the latitude of the epicenter and antithetic backthrust illuminated by the aftershock zone indicate uplift of the santa lucia range as a popup block aftershocks in the southeast part of the zone also indicate a popup block but it is less well defined the absence of backthrust features in the central part of the zone suggests range front uplift by fault propagation folding or backthrusts in the central part were not activated during the mainshock

the work budget of rough faults abstract faults in nature have measurable roughness at many scales and are not planar as generally idealized we utilize the boundary element method to model the geomechanical response of synthetic rough faults in an isotropic linear elastic continuum to external tectonic loading in terms of the work budget faults are generated with known fractal roughness parameters including the root mean square slope a measure of roughness amplitude and the hurst exponent h a measure of geometric self similarity energy within the fault models is partitioned into external work w ext internal elastic strain energy w int gravitational work w grav frictional work w fric and seismic energy w seis results confirm that w ext or work done on the external model boundaries is smallest for a perfectly planar fault and steadily increases with increasing this pattern is also observed in w int the energy expended in deforming the host rock the opposite is true for gravitational work or work done against gravity in uplifting host rock as well as with frictional work or energy dissipated with frictional slip on the fault and w seis or seismic energy released during slip events effects of variation in h are not as large as for but w grav w fric and w seis increase with increasing h with w int and w ext decreasing across the same range remarkably however for a narrow range of roughness amplitudes which are commonly observed along natural faults the total work of the system remains approximately constant while slightly larger than the total work of a planar fault faults evolve toward the most mechanically efficient configuration therefore we argue that this range of roughness amplitudes may represent an energy barrier preventing faults from removing asperities and evolving to smooth planar discontinuities a similar conclusion is drawn from simulations at relatively shallow depths with results showing that shallower faults have larger energy barriers and can be mechanically efficient at higher roughness amplitudes

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