aftershock tectonics of the 1978 tabas e golshan iran earthquake sequence a documented active thin and thick skinned tectonic case summary in this study a locally recorded aftershock sequence of the 1978 tabas e golshan earthquake m 7 4 was accurately located out of 1560 located events 329 best located aftershocks passed a strict quality criterion these well located aftershocks which have uncertainties in epicentre and in focal depth of about 1 and 2km respectively together with the wellconstrained focal mechanisms provided a detailed picture of active continental deformation during an aftershock sequence almost all aftershocks follow very closely the pattern of the earthquake faults at the surface and lie in the hanging wall block of the active fault the hypocentres occurred mainly at depths less than 23 km with a high concentration of seismic activity between 8 14 km depth the aftershocks clearly demonstrate an active imbricate listric thrust system with fault planes flattening into a basement decollement zone and the reactivation of different basement reverse faults in response to a considerable amount of shortening of the top sedimentary cover the sense of motion was almost universally thrusting and the aftershocks shared the same tectonic causes as the main shock the study indicates that the development of the young fold thrust mountain belts necessarily involves basement shortening thin and thick skinned tectonics and that the frontal reverse faults in young active fold thrust mountain belts are the most seismically active faults geological and seismic data propose that the active frontal reverse fault systems are possibly reactivated old normal faults and may add support to the contention of reversal of fault motion during rethickening of continental crust the active thinand thick skinned tectonics documented in this study may prevail in other young and active fold thrust mountain belts which are characterized by a thick sequence of telescoped top sedimentary cover over a decollement detachment zone

sediment transfer by shallow landsliding in the queen charlotte islands british columbia despite the importance of landsliding in routing sediment through mountainous drainage basins few studies have documented landsliding rates over extended time and space scales we have investigated landsliding in surficial material in the queen charlotte islands using a large inventory of events derived from aerial photography covering an area of 166 7 km 2 the mean erosion rate for shallow landsliding is 0 10 mm a 1 which is at the upper end of shallow landsliding rates observed in the pacific northwest and coastal british columbia but several orders of magnitude lower than rock based landsliding rates reported in the literature probability distributions for landslide area and volume are somewhat convex in form flattening of the curve found at low magnitudes may be due to sampling bias or physical mechanisms inhibiting failure and the steepening for high values may exist because the sampling period is not long enough to adequately represent large events landslides generally initiate on hillslope gradients greater than 0 50 0 60 the largest numbers of landslides occur on south to southwest facing slopes and east to northeast facing slopes most events occur on concave and straight hillslopes in upper slope positions landsliding rates were found not to be af fected by rock type hillslopes in the queen charlotte islands are often mantled by weathered quaternary deposits and hence landsliding events are not directly controlled by weathering of bedrock about 31 of landslides identified in this study deposited material in stream reaches with about 83 of these landslides deposited in reaches with gradients between 3 and 10 resume malgre la grande contribution des glissements de terrain a acheminer des sediments a travers des bassins de drainage montagneux peu d etudes ont documente les taux de glissements de terrain sur une longue periode de temps et sur de grandes superficies nous avons fait des recherches sur des glissements de materiaux de surface dans les iles de la reine charlotte en utilisant un grand inventaire d evenements tires de photographies aeriennes couvrant une re

estimates of stress drop of the chi chi taiwan earthquake of 20 september 1999 from near field seismograms the apparent stress and stress drop of the chi chi taiwan earthquake are estimated from near field seismograms the estimated apparent stress and stress drop for the southern part of the fault are about 100 bars lower than those for the northern part the estimated ratio e s m also suggests that there is a higher dynamic stress drop in the northern part than in the southern one this indicates the transformation of a higher percentage of strain energy into the seismic wave energy in the northern part than in the southern part based on a parameter proposed by ramon zuniga 1993 we propose that the stress model of frictional overshoot can interpret the rupture of the chelungpu fault on which the chi chi taiwan earthquake occurred manuscript received 31 july 2000

ubiquitous weakening of faults due to thermal pressurization faults weaken during earthquakes analysis of the amount of energy released during earthquakes globally suggests that heat induced pressurization of pore fluids can weaken faults during earthquakes of all sizes laboratory simulations of earthquakes show that at high slip rates faults can weaken significantly aiding rupture1 2 3 various mechanisms such as thermal pressurization and flash heating have been proposed to cause this weakening during laboratory experiments1 4 5 6 yet the processes that aid fault slip in nature remain unknown measurements of seismic radiation during an earthquake can be used to estimate the frictional work associated with fault weakening known as an event s fracture energy7 8 9 here we compile new and existing8 9 measurements of fracture energy for earthquakes globally that vary in size from borehole microseismicity to great earthquakes we observe a distinct transition in how fracture energy scales with event size which implies that faults weaken differently during small and large earthquakes and earthquakes are not self similar we use an elastodynamic numerical model of earthquake rupture to explore possible mechanisms we find that thermal pressurization of pore fluid by the rapid shear heating of fault gouge can account for the observed scaling of fracture energy in small and large earthquakes over seven orders of fault slip magnitude we conclude that thermal pressurization is a widespread and prominent process for fault weakening

high stress drop events in the victoria baja california earthquake swarm of 1978 march summary the victoria earthquake swarm of 1978 march with magnitudes up to ml 4 8 occurred near the northern end of the cerro prieto fault in northern baja california mexico accurate epicentre locations of a number of earthquakes in the swarm reveal that the activity concentrated in a zone of about 6 km radius projected on the horizontal with earthquakes occuring mostly at depths of around 12 km a composite fault plane solution prepared with data from the larger earthquakes of the swarm indicates right lateral strike slip motion along a vertical plane extending parallel to the cerro prieto fault seismic moment source radius and stress drop are calculated from strong motion records and digital seismograph records obtained at short epicentral distances in most cases less than 10 km from calculated displacement spectra and brune s model stress drops between 1 bar and 1 kbar were estimated for earthquakes with seismic moments in the range 1 4 1019 2 9 1023 dyne cm eighteen events of 44 studied here had stress drops higher than 90 bar a result in striking contrast to lower stress drop results from previous distant station studies of earthquakes in the region results of comparing near source and large distance spectral shapes for two earthquakes in the victoria swarm region indicate that scattering and attenuation are a likely cause of the severe reduction of high frequency energy clearly shown by the larger distance spectra and thus of the resulting lower stress drop determinations at large distances if these events are characteristic of other large events in the region then the low stress drop determinations of thatcher and thatcher hanks for this region may be in doubt very high peak horizontal ground accelerations up to 0 6 g were measured from the near source records which were characterized by short duration bursts of high frequency energy it is suggested here that these high peak accelerations resulted from a combined effect of high stress drop and sediment amplification using a crustal model derived from mcmechan mooney a sedimentary amplification factor of 3 4 is estimated and used as a correction in calculation of the earthquake source parameters four other high stress drop up to 2 5 kbar earthquakes in this area were also analysed the high stress drop values obtained from seismic spectra are corroborated by using the rms root mean square acceleration formulation introduced by hanks

long period surface waves of four western united states earthquakes recorded by the pasadena strainmeter long period surface waves recorded on the north south pasadena strainmeter are used to determine the seismic moments and fault parameters of the 19 may 1940 imperial valley california the 16 december 1954 dixie valley and fairview peak nevada and the 18 august 1959 hebgen lake montana earthquakes synthetic strain seismograms are matched with the observed strainmeter seismograms source parameters from the strainmeter modeling are more consistent with source parameters estimated from geodetic and geologic information than parameters estimated from short period 15 sec body wave data long period surface wave moment estimates agree well with geodetic estimates of moment but are 1 5 to 5 times greater than moments obtained from modeling of teleseismic body waves or geologic information the imperial valley earthquake is best modeled as consisting of 5 point sources along a fault 87 5 km in length with a strike rake and dip of 326 180 and 90 the moment for the earthquake was 4 8 10 19 n m the synthetic seismogram that best models the fairview peak and dixie valley earthquakes assumes that the fairview peak earthquake was twice the size of the dixie valley event moments of 5 9 to 13 10 19 and 3 to 6 5 10 19 n m are obtained for these events a moment of 1 5 10 20 n m is obtained for the hebgen lake earthquake love waves of this earthquake are best modeled by a fault striking 102 although surface faulting produced during the earthquake strikes 130

bath s law and its relation to the tectonic environment a case study for earthquakes in mexico abstract we studied 66 mainshocks and their largest aftershocks in the mexican subduction zone and in the gulf of california with magnitudes in the range of 5 2 m w

the energy release in earthquakes energy calculations are generally made through an empirical application of the familiar gutenberg richter energy magnitude relationships the precise physical significance of these relationships is somewhat uncertain we make use here of the recent improvements in knowledge about the earthquake source to place energy measurements on a sounder physical basis for a simple trapezoidal far field displacement source time function with a ratio x of rise time to total duration t 0 the seismic energy e is proportional to 1 x 1 x 2 m 0 2 t 0 3 where m 0 is seismic moment as long as x is greater than 0 1 or so the effect of rise time is not important the dynamic energies thus calculated for shallow events are in reasonable agreement with the estimate e 5 10 5 m 0 based on elastostatic considerations deep events despite their possibly different seismological character yield dynamic energies which are compatible with a static prediction similar to that for shallow events studies of strong motion velocity traces obtained near the sources of the 1971 san fernando 1966 parkfield and 1979 imperial valley earthquakes suggest that even in the distance range of 1 to 5 km most of the radiated energy is below 1 to 2 hz in frequency far field energy determinations using long period wwssn instruments are probably not in gross error despite their band limited nature the strong motion record for the intermediate depth bucharest earthquake of 1977 also suggests little teleseismic energy outside the pass band of a long period wwssn instrument

strong ground motion from the michoacan mexico earthquake the network of strong motion accelerographs in mexico includes instruments that were installed under an international cooperative research program in sites selected for the high potenial of a large earthquake the 19 september 1985 earthquake magnitude 8 1 occurred in a seismic gap where an earthquake was expected as a result there is an excellent descripton of the ground motions that caused the disaster

the seismic spectrum radiated energy and the savage and wood inequality for complex earthquakes abstract we have integrated velocity squared spectra in order to determine the seismic energy radiated during fault rupture the high frequency spectral fall off and the shape of the spectrum at the corner frequency are critical to the energy calculation high frequency spectral fall offs of 2 beyond the corner frequency in a brune 1970 source model return radiated energies approximately equal to that of an orowan 1960 type fault failure where the final stress level is equal to the dynamic frictional stress any spectra with an extended intermediate slope of 1 would therefore result in higher radiated energies savage and wood 1971 proposed a model in which the final stress level was less than the dynamic stress level and that this was the result of overshoot they based their model on the observation that the ratio of twice the apparent stress to the stress drop was typically around 0 3 we show that for such a ratio to exist high frequency spectral fall offs of 3 would be required composite spectra have been constructed for several moderate to large earthquakes these spectra have been compared to that predicted by the haskell 1966 model and velocity squared spectra have been integrated to determine the radiated energy in all cases this ratio twice the apparent stress to the stress drop is greater than or equal to one violating the savage and wood 1971 inequality and provides evidence against overshoot as a source model

an alternative method for a reliable estimation of seismicity with an application in greece and the surrounding area abstract an alternative method is proposed for the robust estimation of a and b values of the gutenberg richter relation the main hypothesis is that b values depend on material properties and the seismotectonic setting and therefore should vary relatively smoothly in space as far as the a values are concerned more sharp variations are allowed because these values determine the seismicity level once the b value is fixed the study area is organized into a grid and the a and b values are simultaneously determined for the whole grid by solving an appropriate linear system smooth b variations are imposed by introducing additional linear constraints similar to the occam9s inversion used in tomography studies the method is applied to greece and the surrounding area which is a high seismicity area the results are in very good agreement with previous studies and further enhance our knowledge for the study area moreover additional seismicity measures return periods probabilities etc are estimated robustly because they depend on the a and b values obtained for this area

analysis of peak ground motion in terms of a model of inhomogeneous faulting measurements of peak ground velocity v and acceleration a for earthquakes and mine tremors with local magnitudes ranging from 0 8 to 6 4 have been analyzed in terms of a model of inhomogeneous faulting the fault model involves the failure of a circular asperity of radius ri surrounded by a previously faulted annular region of outer radius r0 the failure of the asperity results in seismic radiation with a characteristic frequency proportional to 1 ri followed by lower frequency radiation proportional to 1 r0 as static equilibrium is regained over the larger region for r0 ri 1 both v and a are associated primarily with the failure of the asperity but also depend on the large scale source parameters specifically v r0 r 0 10 r0 ri 0 15 and a r 0 30 r0 ri 2 0 45 where is the shear wave velocity is the overall stress drop is the modulus of rigidity and is density the terms involving r0 ri correspond to the high frequency radiation associated with the failure of the asperity and the other terms indicate the peak parameters due to the broad scale readjustment observations of peak ground motion for events with seismic moments ranging from 5 1016 to 1026 dyn cm indicate that r0 ri is normally in the range of 1 10 and appears to be independent of earthquake size the inhomogeneous fault model also yields convenient expressions for the small scale displacement and stress drop of the asperity failure as well as for the level of regional stress available to cause slip

aftershocks of the coyote lake california earthquake of august 6 1979 a detailed study aftershock hypocenters and focal mechanism solutions for the coyote lake california earthquake reveal a geometrically complex fault structure consisting of multiple slip surfaces the faulting surface principally consists of two right stepping en echelon northwest trending partially overlapping nearly vertical sheets and is similar in geometry to a slip surface inferred for the 1966 parkfield california earthquake the overlap occurs near a prominent bend in the surface trace of the calaveras fault at san felipe lake slip during the main rupture as inferred from the distribution of early aftershocks appears to have been confined to a 14 km portion of the northeastern sheet between 4 and 10 km depth focal mechanisms and the hypocentral distribution of aftershocks suggest that the main rupture surface itself is geometrically complex with left stepping imbricate structure seismic shear displacement on the southwestern slip surface commenced some 5 hours after the mainshock aftershocks in this zone define a single vertical plane 8 km long between 3 and 7 km depth within the overlap zone between the two main slip surfaces the average strike of aftershock nodal planes is significantly rotated clockwise relative to the strike of the fault zone in close agreement with the stress perturbations predicted by crack interaction models aftershock activity in the overlap zone is not associated with a simple dislocation surface space and time clustering within the entire aftershock set suggest an alternation of seismic displacement between the component parts of the fault zone this alternation is consistent with local stress perturbations predicted by crack interaction models we conclude that the fault structure is geometrically complex and that the displacements that occur on its component surfaces during the aftershock process dynamically interact by generating perturbations in the local stress field which in turn control the displacements table 5 is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document j82 006 1 00 payment must accompany order

on the scaling of slip with rupture length for shallow strike slip earthquakes quasi static models and dynamic rupture propagation we explore whether observations of average surface rupture properties among strike slip earthquakes reflect the underlying mechanics we compare the observed relationship between average slip and rupture length for 27 surface ruptures 18 plate boundary earthquakes and 9 away from transform plate boundaries with predictions from two families of uniform stress drop models purely elastic models with a rupture limiting locking depth predict a nonlinear relationship while a quasidynamic model with no locking depth predicts a linear relationship we explore whether observations of fault slip at the earth s surface distinguish which if either of these two families of models may be favored we find that the data provide insufficient constraints to rule out either a linear or a nonlinear relationship this might arise from uncertainties in the observations or from reasonable but unrecoverable variations in locking depths and uniform stress drops among earthquakes we advance an alternative interpretation that the complexity among the observations is consistent with dynamic rupture models featuring spatially varying stress drops

source mechanism of the september 19 1985 michoacan earthquake and its implications moment tensor inversion of low frequency teleseismic data for the september 19 1985 michoacan mexico earthquake gave an average strike 298 slip 268 and seismic moment 10 3 1027 dyne cm low frequency body waves clearly show the complex nature of this event cross correlation of the september 19 p wave with that of the smaller and colocated october 25 1981 playa azul earthquake show that the michoacan earthquake consisted of two subevents separated in time by 25 s and located approximately 30 km northwest and 40 km southeast respectively of the playa azul epicenter body wave inversion of the first subevent gave strike 298 slip 266 and seismic moment 3 0 1027 dyne cm the second subevent had a comparable seismic moment the cumulative moment for large earthquakes occurring along the michoacan northwest guerrero coast indicate that seismic displacement along this segment of the mexican subduction zone is similar to that occurring on other portions indicating that the former michoacan gap was not anomalously aseismic

the anza array a high dynamic range broadband digitally radiotelemetered seismic array a small aperture seismic array has been deployed along a 30 km stretch of the san jacinto fault in the vicinity of the town of anza california the array was installed to study specifically the scaling laws of body wave spectra the character of high frequency ground motion the physical interpretation of seismic stress drops and the interaction of earthquakes this region was chosen for these studies due to its high rate of seismic activity in the 2 m 4 5 range the likelihood of a m 6 event in the next decade and the existence of the southern california batholith on either side of the fault reducing problems associated with attenuation and large scale anisotropy these studies employ an instrument package with a frequency response of 100 hz a dynamic range of 138 db a sampling rate of 250 times per second per component and a 16 bit a d converter the array consists of 10 three component stations telemetered via digital vhf radio to a nearby mountain peak and thence via a microwave link to la jolla california a minicomputer system monitors the array s performance detects events and records data upon demand initial results demonstrate the feasibility of digital transmission with an inherent increase in data quality over analog systems

simulations of strong ground motion for earthquakes in the mexicali imperial valley region summary in this paper computer modelling is used to test simple approximations for simulating strong ground motions for moderate and large earthquakes in the mexicali imperial valley region initially we represent an earthquake rupture process as a series of many independent small earthquakes distributed in a somewhat random manner in both space and time along the rupture surface by summing real seismograms for small earthquakes used as empirical green s functions strong ground motions at specific sites near a fault are calculated alternatively theoretical green s functions that include frequencies up to 20 hz are used in essentially similar simulations the model uses random numbers to emulate some of the non deterministic irregularities associated with real earthquakes due either to complexities in the rupture process itself and or strong variations in the material properties of the medium simulations of the 1980 june 9 victoria baja california earthquake ml 6 1 approximately agree with the duration of shaking the maximum ground acceleration and the frequency content of strong ground motion records obtained at distances of up to 35 km for this moderate earthquake in the initial stages of modelling we do not introduce any scaling of spectral shape with magnitude in order to see at what stage the data require it surprisingly such scaling is not critical in going from m 4 5 events to the m 6 1 victoria earthquake however it is clearly required by the el centro accelerogram for the imperial valley 1940 earthquake which had a much higher moment ms 7 we derive the spectral modification function for this event the resulting model for this magnitude 7 earthquake is then used to predict the ground motions at short distances from the fault predicted peak horizontal accelerations for the m 7 event are about 25 50 per cent higher than those observed for the m 6 1 victoria event

preseismic and coseismic deformation associated with the coyote lake california earthquake supplement is available with entire article on microfiche orderfrom american geophysical union 2000 florida avenue n w washington d c 20006 document j79 008 01 00 payment mustaccompany order the coyote lake earthquake ml 5 9 august 6 1979 epicenter about 100 km southeast of san francisco occurred on the calaveras fault within a geodetic network that had been surveyed annually since 1972 to monitor strain accumulation the rupture surface as defined by aftershocks is a vertical rectangle 20 km in length extending from a depth of 4 km to about 12 km the observed deformation of the geodetic network constrains the average slip to be about 0 33 0 05 m right lateral although the geodetic data furnished an exceptionally detailed picture of the preearthquake deformation no significant premonitory anomaly associated with the coyote lake earthquake can be identified

the seismic radiation from composite models of faulting abstract the failure of an asperity i e the dynamic rupture of a small fault area with finite stress drop surrounded by a broken or weak fault area which has no stress drop but which slips after the asperity fails is proposed as a model for the rupture process of a subevent in a composite earthquake the rupture area of the composite earthquake surrounding the subevent is modeled by the weak fault area surrounding the asperity in the subevent model the resulting seismic moment of the subevent is proportional to the stress drop and the rupture area of the subevent as well as the radius of the composite earthaquake by setting the stress drops of the asperity models equal to the dynamic stress drops of the subevents the composite earthquake can be modeled as the sum of a set of subevents which cover the rupture area of the composite earthquake the scaling of the high and low frequency radiation from composite earthquakes composed of asperities is commensurate with generally observed spectral scaling laws in contrast to composite earthquakes composed of cracks or smaller earthquakes a simple filtering strategy is proposed for filtering the waveforms radiated by cracks to approximate the waveforms radiated by asperities the p and s waves radiated by an m l 5 2 earthquake which occurred on 9 may 1983 at coalinga california are simulated using the p and s waves radiated by an m l 3 6 aftershock the aftershock waveforms are first filtered to approximate the radiation from asperities with the appropriate rupture areas and then the waveforms of 12 asperity subevents are summed together to simulate the waveforms and spectra of the composite earthquake

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

coseismic and postseismic vertical movements associated with the 1940 m7 1 imperial valley california earthquake elevation changes derived from precise leveling surveys conducted by the national geodetic survey in 1931 1941 1972 and 1974 along two routes crossing the imperial fault in southern california represent the first documented examples of spatially coherent vertical movements associtated with strike slip faulting in the united states the leveling routes cross the northern section of the fault that broke at the time of the 1940 m7 1 imperial valley earthquake the observed vertical movements which extend approximately 25 km east and west of the fault are among the largest observed anywhere in the united states these movements are consistent with simple elastic models of coseismic and postseismic secondary vertical deformation due to right lateral strike slip movement along a finite length fault the spatial and temporal patterns of deformation suggest a simple scenario consisting of large coseismic slip on the southern part of the imperial fault which transferred stresses to the northern part of the imperial fault and the brawley fault en echelon fault northeast of imperial fault these stresses were subsequently released primarily by aseismic creep the estimates of coseismic faulting determined from the leveling observations are roughly consistent with field observations of horizontal surface offset made after the earthquake as well as with some estimates derived from triangulation measurements the postseismic fault offsets reported here suggest slip to shallower levels than previous estimates of postseismic slip determined from repeated triangulation measurements the overall shallow slip coseismic plus postseismic required by the leveling observations is larger on the southern part of the imperial fault than on the northern part of this fault or on the brawley fault the 1979 m6 6 imperial valley earthquake apparently eliminated some of this difference in overall shallow slip by causing surface offsets on the northern part of the imperial fault and the southern brawley fault even though the epicenter for the 1979 event was located on the southern imperial fault other geophysical observations in this part of the imperial valley fault creep seismicity seismic faulting suggest that stick slip on the southern part of the imperial fault and creep on the northern part of this fault and on the brawley fault may characterize the long term fault behavior in the imperial valley

simulation of ground accelerations for the may 1980 mammoth lakes california earthquakes abstract strong motion accelerograms from the may 1980 mammoth lakes earthquake sequence are used to support the technique of estimating near source ground motion by the summation of existing records an sma 1 record recovered 3 km from the epicenter of the first magnitude m l 6 earthquake in the mammoth lakes sequence 25 may 16 33 44 utc is simulated by the summation of records from later events the source time history on which this summation is based comes from a study of the teleseismic p waves the summation method has several distinct advantages it is easy to apply inexpensive costly wave propagation codes are not needed and source to receiver propagation effects are automatically included the method however requires a good data base from which to perform the summation

the 1978 tabas iran earthquake an interpretation of the strong motion records the 1978 tabas iran earthquake ms 7 4 was registered on 11 accelerograph stations with source distances ranging from 3 to 350 km and corresponding recorded peak accelerations ranging from 0 95 down to 0 01 g respectively at least four subevents are recognized at dayhook the station nearest the epicenter at the southern limit of the fault the rupture propagated to the northwest with a rupture velocity of 2 7 km sec the subevents occurred along the fault as the rupture proceeded curves which describe the distance dependence of peak values of acceleration velocity and band passed acceleration are constructed for this earthquake although attenuation of seismic waves is similar in iran and the western united states the prediction curves based on peak strong motion acceleration data from the western united states systematically underestimate the peak values of the tabas earthquake and the similar 1952 kern county earthquake prediction curves based on peak velocity in the western united states overestimate peak velocity for distances less than about 60 km site effects are recognized at some recording stations the various estimates for stress operating during the earthquake range from 25 to 90 bars the radiated energy of the main event estimated from accelerograms by two methods is about 2 3 1023 ergs larger than the energy calculated by gutenberg and richter energy formula with ms 7 4 each of the four subevents released approximately the same amount of energy corresponding to ms 7 teleseismic energy estimates for this earthquake are one to two orders of magnitude smaller indicating large systematic errors exist in one or both of the energy estimation procedures