source parameters and scaling relations for small earthquakes in the matsushiro region southwest honshu japan abstract using near field broadband data from a suite of crustal earthquakes which occurred in a small homogeneous source region we examine the scaling relationships among source parameters for earthquakes in the critical 1 5 to 4 5 magnitude range we take special precautions to insure that our conclusions are not biased by local structure seismic moment fault radius and stress drop relations were determined for 32 small shallow strike slip earthquakes 1 6 m l 4 3 in the matsushiro region of southwest honshu japan spectral and cepstral analyses of short period arrivals exhibit structure interpreted as resulting from reverberations within thin low velocity surface layers below the recording site furthermore calculated crustal transfer functions for sh predict a peak over the range of 2 to 4 hz this type of site response can bias estimates of spectral parameters particularly corner or characteristic frequencies for simple sources such a bias can be reduced by filtering in the cepstral domain the effect of cepstral filtering on corner frequency determinations is generally less than 20 per cent and tends to decrease them particularly for larger events where the structurally induced spectral enhancement is at frequencies above the source related corner frequencies estimates of the seismic moment brune stress drop and fault radius for each event were calculated from sh displacement amplitude spectra the seismic moments range from 10 18 to 10 22 dyne cm the stress drops range from 0 008 to 16 bars the relationship between log stress drop and log moment is approximately linear with a slope of 1 up to a moment of 2 10 21 dyne cm but for higher moments the slope is not significantly different from zero fault radii range from 0 3 to 1 2 km there is a physical scatter in radius for any given moment up to a factor of 1 5 for moments less than 2 10 21 dyne cm there is no significant trend in the radius as a function of moment but for higher moments the radius increases with moment the main conclusion is that the stress drop is the dominant scaling factor for moments less than 10 21 dyne cm for higher moment the source dimension becomes the controlling factor

the origin of deep buried channels of elsterian age in northwest germany buried channels cut to a depth of over 100m into the underlying substratum of north germany are almost exclusively of elsterian age evaluation of geophysical well logs in the hamburg area for the first time allows the construction of detailed longitudinal and transverse profiles it can be shown that an apparently chaotic infill known from borehole records in some cases is actually a regular sedimentary sequence fining from proximal to distal channel formation seems to have been the result of catastrophic meltwater release in the marginal parts of the ice sheet the channel infill reflects these episodic outbursts of meltwater during deglaciation the channel remnants became infilled with fine sediments the channels ceased to exist as morphologically detectable forms at the end of the holsteinian stage

relations among subduction parameters clues to the dynamics of the subduction process are found in the many measurable parameters of modern subduction zones based on a critical appraisal of the geophysical and geological literature 26 parameters are estimated for each of 39 modern subduction zones to isolate causal relationships among these parameters multivariate analysis is applied to this data set this analysis yields empirical quantitative relations that predict strain regime and strike slip faulting in the overriding plate maximum earthquake magnitude benioff zone length slab dip arc trench gap and maximum trench depth excellent correlation is found between length of the benioff zone and the product of convergence rate and age of the downgoing slab this relationship is consistent with the conductive heating model of molnar et al 1979 if the model is modified in one respect the rate of heating of the slab is not constant it is substantially slower during passage of the slab beneath the accretionary prism and overriding plate the structural style in the overriding plate is determined by its stress state though the stress state of overriding plates cannot be quantified one can classify each individual subduction zone into one of seven semiquantitative strain classes that form a continuum from strongly extensional class 1 back arc spreading to strongly compressional class 7 active folding and thrusting this analysis indicates that strain class is probably determined by a linear combination of convergence rate slab age and shallow slab dip interplate coupling controlled by convergence rate and slab age is an important control on strain regime and the primary control on earthquake magnitude arc parallel strike slip faulting is a common feature of convergent margins forming a forearc sliver between the strike slip fault and trench optimum conditions for the development of forearc slivers are oblique convergence a compressional environment and a continental overriding plate the primary factor controlling presence of strike slip faulting is coupling strongly oblique convergence is not required the rate of strike slip faulting is affected by both convergence obliquity and convergence rate maximum trench depth is a response to flexure of the underthrusting plate the amount of flexural deflection at the trench depends on the vertical component of slab pull force which is very sensitive to slab age and shallow slab dip shallow slab dip conforms to the cross sectional shape of the overriding plate which is controlled by width of the accretionary prism and duration of subduction deep slab dip is affected by the mantle trajectory established at shallow depth but may be modified by mantle flow much of the structural complexity of convergent margins is probably attributable to terrane juxtaposition associated with temporal changes in both forearc strike slip faulting and strain regime empirical equations relating subduction parameters can provide both a focus for future theoretical studies and a conceptual and kinematic link between plate tectonics and the geology of subduction zones

the effects of attenuation and site response on the spectra of microearthquakes in the northeastern caribbean abstract the spectra of microearthquakes recorded by a seismic network in the northeastern caribbean were analyzed to determine the effects of attenuation and site response on these spectra the ratios of the spectral amplitudes at 5 and 20 hz were measured for several earthquakes at different distances from a fixed receiver to estimate q for p and s waves in the crust and upper mantle the average q p determined from three stations was 380 for epicentral distances between 40 and 200 km the average q s determined from two stations was estimated at 400 spectra of earthquakes closer than 40 km to one station indicate that a high q path q 800 exists for these short distances in the island arc platform the near equivalence of q p and q s observed in this study of the upper lithosphere contrasts with estimates of anderson et al 1965 that q p 9 4 q s in the asthenosphere this finding that q p is approximately equal to q s suggests that the attenuation mechanism in the upper lithosphere differs from that in the asthenosphere the spectra of nearby microearthquakes unaffected by crustal attenuation display corner frequencies which are uniform despite large differences in the seismic moments of the events the corner frequencies of these spectra appear to be characteristic of the receiver site and insensitive to the location and moment of the earthquakes at one station the s wave corner frequency of a nearby blast was identical to the corner frequency of a magnitude 4 8 earthquake derived from the record of a strong motion accelerograph at the same site

relative motion of the nazca farallon and south american plates since late cretaceous time by combining reconstructions of the south american and african plates the african and antarctic plates the antarctic and pacific plates and the pacific and nazca plates we calculated the relative positions and history of convergence of the nazca and south american plates despite variations in convergence rates along the andes periods of rapid convergence averaging more than 100 mm a between the times of anomalies 21 49 5 ma and 18 42 ma and since anomaly 7 26 ma coincide with two phases of relatively intense tectonic activity in the peruvian andes known as the late eocene incaic and mio pliocene quechua phases the periods of relatively slow convergence 50 to 55 30 mm a at the latitude of peru and less farther south between the times of anomalies 30 31 68 5 ma and 21 and between those of anomalies 13 36 ma and 7 correlate with periods during which tectonic activity was relatively quiescent thus these reconstructions provide quantitative evidence for a correlation of the intensity of tectonic activity in the overriding plate at subduction zones with variations in the convergence rate

mining induced microseismicity monitoring and applications of imaging and source mechanism techniques the study of microseismicity in mines provides an ideal method for remote volumetric sampling of rock masses the nature and uniqueness of microseismic monitoring is outlined in the context of acquisition hardware and software requirements several topics are used to highlight the potential for novel applications of microseismicity and to outline areas where further study is required these topics reflect some of the current interest areas in seismology namelyb values and source parameters fault plane solutions modes of failure and moment tensor inversion imaging and seismicityvelocity correlations these studies suggest potential correlations between zones of high seismic velocity high microseismic activity and maximal stress drops which can be interpreted spatially to be the locations of highly stressed ground with a potential for rock bursting fault plane solutions are shown to be useful in determining the slip potential of various joint sets in a rock mass source parameter studies and moment tensor analysis clearly show the importance of non shear components of failure andb values for microseismicity appear to be magnitude limited and related to spatial rather than temporal variations in effective stress levels

influence of source region properties on scaling relations for m 0 events excavation induced seismic events with moment magnitudesm 0 are examined in an attempt to determine the role geology excavation geometry and stress have on scaling relations correlations are established based on accurate measurements of excavation geometry and methodology stress regime rock mass structure local tectonics and seismic locations scaling relations incorporated seismic moments and source radii obtained by spectral analysis accounting for source propagation and site effects and using madariaga s dynamic circular fault model observations suggest that the interaction of stresses with pre existing fractures fracture complexity and depth of events are the main factors influencing source characteristics and scaling behaviour self similar relationships were found for events at similar depths or for weakly structured rock masses with reduced clamping stresses whereas a non similar behaviour was found for events with increasing depth or for heavily fractured zones under stress confinement additionally the scaling behaviour for combined data sets tended to mask the non similar trends overall depth and fracture complexity initially thought as second order effects appear to significantly influence source characteristics of seismic events withm 0 and consequently favour a non similar earthquake generation process

platform subsidence behind an active subduction zone numerical models of viscous mantle flow indicate that a broad subsidence should occur above subduction zones1 4 this platform subsidence is predicted to cause an asymmetrical depression 500 1 000 km wide with a maximum depth of 2 km if filled with water direct evidence linking platform subsidence to mantle flow has remained elusive however here we offer evidence from western new zealand for a complete link in both space and time between subduction initiation and platform subsidence because of the broad wavelength 200 km of the observed 1 500 m subsidence it is unlikely that the subsidence is due to a flexural foredeep the observed subsidence does however match in both wavelength and amplitude that predicted by a model of subduction induced mantle flow the occurrence of platform subsidence has implications not only for understanding mantle convection but also for explaining geoid anomalies over active margins5 and patterns of continental submergence6 and sedimentation7 that could otherwise be interpreted as a eustatic sea level change8

andean tectonics as a consequence of sea floor spreading abstract the evolution of sea floor spreading directions and rates in the southeast pacific shows a close relationship with the andean structural directions and the plutonic episodicity as well as the succession of short compressive orogenic phases alternating with relatively longer periods of extension the orogenic periods coincided with the beginning of periods of relatively higher rates of plate convergence immediately after periods of relative quiescence with the following periodicity 110 85 76 70 63 60 49 45 35 33 16 13 7 m y the presence of oceanic structures as aseismic ridges or fracture zones produces weak benioff zones shallow and poorly defined without a corresponding active volcanism on the other hand ancient continental structures such as the precambrian paleozoic orogenic belts have active volcanism and neat deep and well developed benioff zones

effects of rupture complexity and stress regime on scaling relations of induced microseismic events source parameter scaling relations are examined for microseismic events 2 4 m 0 3 occurring within highly and moderately stressed and fractured rock masses at strathcona mine sudbury canada insight into scaling is provided by waveform complexities calculated rupture velocities and maximum shear stresses based on in situ and numerical modelling data the importance of normal stress on the failure process is also considered our results show that a strong dependence exists between stress release and seismic moment an observed positive scaling in excess stress release 2 a is consistent with the concept of overshoot rupture velocities ranging from 0 2 to 0 5 and waveform complexities less than 1 5 suggested that overshoot was related to healing behind a slowly advancing rupture front scaling in seismic efficiency paralleled that in apparent stress implying that seismic stress release estimates arc quasi independent of the maximum shear stress high levels of normal stress further supported the importance of high resisting stress in the observed overshoot behaviour and its role in the failure process

can small events m 0 it is becoming evident that under different circumstances such as injection rates and geologic conditions it might be possible to generate larger magnitude m 0 events during hydraulic fracture stimulations by utilizing fully integrated passive seismic monitoring programs we can examine the relationship between the occurrence of small magnitude events m 0 and the fracture and stress conditions that may lead to larger events in our investigations we identify that over all scales of observation the events follow a self similar behavior however the small magnitude events are generally lower in stress release than observed for the larger events these differences can be explained by the observed failure mechanisms where smaller events tend to be driven by shear tensile failures of pre existing discrete fractures joints whereas the larger events appear to be dominated by shear driven failure processes associated with pre existing faults these observations suggest that there can be sufficient

plate boundary forces at subduction zones and trench arc compression abstract viscoelastic finite element modelling has been used to study the state of stress in the overriding and subducting plates meeting at a subduction zone the subduction fault is included using the dual node technique it is demonstrated that substantial horizontal deviatoric compressive stress occurs in the trench arc region as a result of the downpull of the dense slab and the associated surface depression including the trench and other downflexing of the plates this may be masked at the trench by bending stress it is the lack of significant shearing stress along an unlocked subduction fault in the presence of this compressive stress that gives rise to the slab pull and trench suction plate boundary forces slab pull and trench suction were found to be of comparable magnitude within the range 1 0 to 4 0 10 12 n m in models studied with vertical subduction and there are indications that this may also apply when the slab dips at 45 as a result of viscous flow induced by rollback when the slab dips beneath the arc backarc region it is shown that horizontal deviatoric compression can occur in this region contemporaneous with plate interior tension produced by trench suction this suggests that backarc tension associated with marianas type trench arch systems may be related to the nearly vertical slab whereas backarc compression in the chilean type may result from the low dip and small downpull of the slab it is also shown that successive locking and unlocking of the subduction fault may give rise to large variations of stress in plate interiors

cretaceous to early paleogene tectonic evolution of the northern central andes 0 18 s and its relations to geodynamics the tectonic phases subsidence patterns and location of the magmatic arc along the peruvian margin during late cretaceous and paleogene times are compared with the main geodynamic parameters absolute plate motion convergence velocity and direction age of the subducted slab and accretional events for the same periods during the late cretaceous long termed compression seems to be controlled by the absolute trenchward motion of the overriding plate and to a minor extent by the young age of the subducted lithosphere short lived contractional or extensional phases are mainly linked to the acceleration or deceleration of the convergence between the oceanic and continental plates and probably to changes in the convergence direction periods of high and low convergence rates coincide with increased and decreased subsidence rates along the margin respectively and seem to be independent of compressional tensional regimes during the paleogene in addition to the mentioned processes the eastward shift of the magmatic belt and subsidence in the forearc zone are interpreted as the result of the subduction erosion of the margin this process seems to be related to the decrease of the dip of the benioff zone expressed by the drastic widening of the magmatic arc

sedimentary evolution of an active margin during middle and upper cretaceous times the north peruvian margin from late aptian up to senonian the sedimentary evolution of the north peruvian margin during upper cretaceous can be summarized as follows

controls of subduction geometry location of magmatic arcs and tectonics of arc and back arc regions most variation in geometry and angle of inclination of subducted oceanic lithosphere is caused by four interdependent factors combinations of 1 rapid absolute upper plate motion toward the trench and active overriding of the subducted plate 2 rapid relative plate convergence and 3 subduction of intraplate island seamount chains aseismic ridges and oceanic plateaus anomalously low density oceanic lithosphere cause low angle subduction under conditions of low angle subduction the upper surface of the subducted plate is in contact with the base of the overlying plate the wedge of low density asthenosphere is replaced by subducted lithosphere and the width of the arc trench gap either is significantly increased or a magmatic arc is not developed within the overlying plate the fourth factor is age of the subducting lithosphere subduction of young lithosphere produces two opposing tendencies 1 low angle subduction and increased arc trench distance owing to its low density and 2 decreased arc trench distance owing to its higher temperature two factors of secondary importance contribute to variation in subduction zone geometry and arc trench distance accretion of sediment in trenches depresses the upper portion of the subducting oceanic plate and causes the trench axis to migrate seaward prolonged subduction thickens the upper plate depresses the isotherms in the subducted plate and may create a broader arc both factors increase the arc trench gap the four primary factors also control development of other tectonic elements such as regional subsidence for example the amazon basin and a portion of the cretaceous interior seaway of western united states intra arc extension for example the basin and range province foreland fold and thrust belts and laramide style tectonics

stresses and plate boundary forces associated with subduction plate margins primary tectonic stress in the lithosphere is predominantly caused by lateral density variations within the earth and associated topographical loading when such a stress system caused by major sublithospheric density anomalies is intersected by a weak zone which cuts across the lithosphere plate boundary forces develop and modify the plate interior stresses in this paper unite element analysis is used to model the stresses and plate boundary forces associated with subduction plate boundaries with dipping and vertical slabs extending to about 270 and 400 km depths having the subduction fault both locked and unlocked in such regions several types of horizontal deviatoric stress may occur including 1 local compression in the trench arc region caused by the dense sinking slab and the associated surface downflexure 2 plate interior tension which occurs when this compression is intersected by a weak subduction fault 3 local tension associated with thickening of the crust at the arc and elsewhere 4 local tension in the back arc region produced by the underlying low density upper mantle and 5 downbending stresses in the subducting slab thermal stresses and transmitted ridge push which are not included in the modelling here a gradient from compression in the forearc to tension in the back arc can be modelled in terms of these stresses when the fault is partially locked it is however the intersection of the local compression 1 by an unlocked or partially locked subduction fault that modifies the plate interior stresses and gives rise to the slab pull and trench suction plate boundary forces the state of stress in the interior of the overriding plate is also crucially influenced by back arc spreading where this occurs plate boundary forces have been evaluated for each of the models it is shown that slab pull and trench suction may be of comparable magnitude

moment tensor inversion of induced microseisnmic events evidence of non shear failures in the 4 m 2 moment magnitude range to assess objectively the source mechanism of mining induced seismic events we developed an algorithm to invert for the moment tensor components from this inversion the ratio of isotropic deviatoric component in the source is obtained we are applying this method to microseismic events 4 m 2 recorded at the underground research laboratory url in pinawa manitoba where a tunnel is being excavated at 420 m depth to monitor the seismic activity induced by this opening an array of 16 triaxial accelerometers was installed around the planned tunnel results from the moment tensor inversion on a fist data set provide evidence of non shear failure mechanisms furthermore the location of events displaying a tensile component corresponds to a breakout observed underground in the roof of the tunnel

scaling of ground motion parameters state of stress and focal depth the ground motion parametersrv and ra where r is hypocentral distance v is peak velocity is density and a is peak acceleration are found observationally to be strong functions of stress state and linearly related to focal depth z if the stress state and focal depth are properly taken into account then the ground motion parameters depend on the seismic moment m0 as expected from basic scaling principles that is rv m01 3 and ra is independent of earthquake size regression lines fitted to observations covering broad ranges in seismic moment and focal depth indicate that for extensional and compressional tectonic regimes corresponding to normal and thrust or reverse faulting earthquakes respectively peak acceleration is given by ra 1 08 mpa 3 06 mpa km z normal and ra 5 65 mpa 8 76 mpa km z thrust and for peak velocity rv m01 3 10 4 m2 s n m 1 3 3 00 0 69 km 1 z normal and rv m01 3 10 4 m2 s n m 1 3 4 63 1 82 km 1 z thrust for strike slip earthquakes the data currently are insufficient to define regression fits but such lines would definitely lie between those for the normal and thrust stress regimes these equations are appropriate for ground motion at small hypocentral distance as recorded in a whole space it follows that for comparable hypocentral depth peak acceleration in a compressional tectonic regime for example much of the eastern united states is a factor of about 3 greater than in an extensional regime such as nevada and for peak velocity a similar comparison yields a factor of 2 difference the similarity in behavior of the peak acceleration parameter to crustal strength estimated from byerlee s law of friction with respect to depth and stress state indicates that crustal strength is probably the factor governing the seismic source processes that give rise to the high frequency peak ground motion analysis of the peak acceleration data in the context of crustal strength suggests bounds on this ground motion parameter as recorded at a typical surface site that depend on stress state specifically a normal 0 5 g and a thrust 1 9 g thus the state of stress as well as the focal depth clearly is an important factor to be taken into account in the prediction of seismic ground motion

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

asperities barriers characteristic earthquakes and strong motion prediction recent results from paleoseismology suggest that earthquakes recurrent on a given fault may often have the same characteristic length and amount of slip stable asperities and barriers which survive many earthquakes can explain these results the activity of volcano usu japan since 1977 which produced a dacite dome with a total upheaval of 180 m offered a great opportunity to study the recurrence behavior of a fault seismologists at hokkaido university revealed a family of repeated earthquakes with nearly the same amount of slip generated from the same fault plane on the crater wall along which the dome moved upward this family can be explained by the existence of a stable asperity on the crater wall and is called the asperity type family they found however another type of family of earthquakes which share the same fault plane but show a great range of variation in the amount of slip the behavior of the latter family can be explained by the presence of weak barriers over a fault plane defined by strong stable barriers and this family is referred to as the barrier type family this type of earthquake model has been used successfully in the interpretation of observed strong motion acceleration spectra from california and the results reveal the stability of local stress drop among different earthquakes the agreement found between local stress drops estimated from strong motion data and those inferred from geological observation supports the possibility for predicting earthquake strong motion directly from geological observation of the causative fault

space time variations in source parameters of mining induced seismic events with m 0 space time variations in source parameters and fault plane solutions are related to structural mapping data and local regional stress field measurements in an attempt to characterize the behavior of a rock mass in the vicinity of an excavation in a mine source parameters i e total seismic energy p and s wave energy seismic moment static stress drop and apparent stress were analyzed for 85 events with moment magnitudes between 2 2 m 0 3 within a 90 m microseismic envelope ahead of an excavation these data allowed three types of failure mechanisms to be postulated a zone of flat lying extensional failures next to the excavation a zone of subvertical shear failures at the microseismic envelope boundary and a transition zone between these two where both shear and shear extensional failures occur two spatially distinct event clusters occurred at distance from the excavation for early and late stages of the excavation and next to the excavation during intermediate stages worth noting was an apparent change in p axis orientation with excavation where the average p axes before and following ore extraction were compatible with the local maximum principal stress and the p axes during intermediate excavation stages were compatible with the regional maximum principal stress or local intermediate principal stress distinct from these trends was the general increase in the values of each of the above source parameters over the duration of the excavation suggesting that stress levels were increasing as a result of the excavation geometry and procedure this was considered to be significant as rockbursts mn 1 8 to 2 7 occurred above the study area 6 months following the completion of the excavation

the andean orogenic period and its major structures in central and northern peru the andean orogenic period began in the albian and consisted of at least 6 discrete compressional phases which are albian to late miocene in age deformation migrated progressively toward the amazonian foredeep the major andean structures in central and northern peru are related to the eocene incaic early miocene quechua 1 and late miocene quechua 3 phases the maranon thrust and fold belt mtfb which bounds the western cordillera to the ne rose in the eocene it was reactivated partly by the quechua 1 phase which also folded the altiplano farther e and possibly part of the eastern cordillera the sub andean thrust and fold belt stfb is related to the quechua 3 phase in both mtfb and stfb the imbricate thrusts merge at depth in large decollement faults gravity sliding does not play a dominant role for these faults have to be rooted westward in the pre andean basement the corresponding crustal shortening played a significant part in the creation of the sialic root of the andes

source parameters of seismic events at heinrich robert mine ruhr basin federal republic of germany evidence for nondouble couple events abstract a three component digital seismic station is in operation at heinrich robert coal mine in the ruhr basin at a depth of 890 m a cluster of seismic events occurred at the beginning of 1987 at a distance of about 5 km from the station and continued in 1988 source parameters of 46 tremors selected from the cluster with local magnitude from 1 2 to 2 3 are studied the ratio of p wave to s wave corner frequency is variable implying its dependence on the angle of observation and in turn the variability of focal mechanism with time the scaling relations indicate that characteristic tremors with a fault length of about 200 m are possibly generated in the area but the evidence is not conclusive the seismic energy for a given seismic moment can vary by a factor of 20 and the ratio of s wave to p wave energy ranges from 1 5 to 30 stress release estimates show low values not exceeding a few bars typical for tremors induced by mining a comparison of the apparent stress with the static stress drop divides the selected tremors into high and low apparent stress events the latter events are characterized by high p wave energy and almost constant and large ratio of p wave to s wave corner frequency which differs from the lower ratios of other events implying similar focal mechanism these high p wave energy tremors are the most likely candidates for nondouble couple events

how geology can influence scaling relations abstract this study presents an attempt to determine the influence of the environment through lithology and mechanical properties on source parameters and subsequently scaling relations this aim is pursued using data collected from a gas field during a 3 year long period the induced seismicity is recorded by a local permanent network allowing the precise location of 149 earthquakes with local magnitudes ranging from 1 0 to 4 2 moreover geology of the site is defined by 70 bore holes up to 5 km deep such information allows a geological correlation of seismic events then a spectral analysis is performed to compute the source parameters of earthquakes using a dynamic circular fault model seismic moments source radii and post rupture stress drops are evaluated taking into account source propagation and site effects however it is shown from our results that relative uncertainties remain especially for seismic moments and stress drops the diagram of seismic moment versus source radius for the whole data set indicates relatively constant stress drops around 10 bar confirming the self similarity assumption even for microearthquakes in contradiction with this result scaling relations in each geological unit do not verify self similarity this feature implies that second order factors as the mechanical properties of the rock influence source characteristics and bring new complications in scaling relations however even in this case of a very differentiated medium these parameters cannot explain a global breakdown in scaling laws

topography effect at the critical sv wave incidence possible explanation of damage pattern by the whittier narrows california earthquake of 1 october 1987 abstract buildings damaged by the whittier narrows california earthquake of 1 october 1987 were concentrated in several areas most of which were located 8 to 10 km from the epicenter corresponding to the critical incidence for sv waves and were near topographic irregularities such as the northern part of whittier just south of puente hills the purpose of this study is to show the possibility that this anomalous damage pattern is due to the amplification by the topographic irregularity when sv waves are near critical incidence first we examined the accelerograms obtained at the usgs station 7215 bright ave nearest to downtown whittier and conclude that the dominantly eastwest motion observed at the station is due to the influence of the building in which accelerograms were recorded we next demonstrate that strong ground motions recorded by 12 stations in the epicentral area show a polarization direction pattern that is primarily sv type which is consistent with a simple thrust fault located at the hypocenter then we calculated the response of a two dimensional hill with the height 0 3 km and the width 2 4 km to 1 a plane sv wave with a nearly critical angle of incidence 2 a horizontal line force 3 a haskell type 2d dislocation source and 4 a bouchon type 2d multiple crack source the results show that the amplification due to the hill relative to the flat surface is more than 1 5 for all the source models since this amplification is nearly independent of the source type and spectrum we conclude that the combined effect of the topographic irregularity and critically incident sv waves might be responsible for the concentration of damage observed during the whittier narrows earthquake

microseismic monitoring and stability evaluation for the large scale underground caverns at the houziyan hydropower station in southwest china abstract the stability of underground caverns and the excavatability of rock masses are important for geotechnical engineering practices during the design and construction stages the risks associated with underground caverns at the houziyan hydropower station in southwest china are growing due to excavation induced unloading to assess the instability of underground caverns and resolve the complex subsurface conditions of the highly fractured rock mass a high resolution microseismic monitoring system was established in deep underground caverns this system was used to determine the relationship between the measured microseismic activities and the excavation damage zones of the surrounding rock mass the excavation damage zones and potential risk regions in the underground caverns were identified by analyzing the tempo spatial distribution of microseismic activities in addition the correlation between microseismic activities and pre existing geological structures was determined and traditional monitoring results were analyzed to validate the correlation between seismicity and the excavation damaged zones of the underground caverns a numerical model was employed to further evaluate the deformation and stability of the surrounding rock mass the monitoring results demonstrate that microseismic events mainly occurred in high stress concentration regions corresponding with the results obtained from the numerical analysis therefore this comprehensive method which incorporates microseismic monitoring numerical analysis traditional monitoring and field observations is promising for predicting the deformation and instability of surrounding rock masses in the underground caverns subjected to excavation

on relating apparent stress to the stress causing earthquake fault slip apparent stress a is defined as where is the average shear stress loading the fault plane to cause slip and is the seismic efficiency defined as ea w where ea is the energy radiated seismically and w is the total energy released by the earthquake the results of a recent study in which apparent stresses of mining induced earthquakes were compared to those measured for laboratory stick slip friction events led to the hypothesis that this hypothesis is tested here against a substantially augmented data set of earthquakes for which can be estimated mostly from in situ stress measurements for comparison with a the expanded data set which includes earthquakes artificially triggered at a depth of 9 km in the german kontinentales tiefbohrprogramm der bundesrepublik deutschland ktb borehole and natural tectonic earthquakes covers a broad range of hypocentral depths rock types pore pressures and tectonic settings nonetheless over 14 orders of magnitude in seismic moment apparent stresses exhibit distinct upper bounds defined by a maximum seismic efficiency of 0 06 consistent with the hypothesis proposed before this behavior of a and can be expressed in terms of two parameters measured for stick slip friction events in the laboratory the ratio of the static to the dynamic coefficient of friction and the fault slip overshoot typical values for these two parameters yield seismic efficiencies of 0 06 in contrast to efficiencies for laboratory events for which is always near 0 06 those for earthquakes tend to be less than this bounding value because ea for earthquakes is usually underestimated due to factors such as band limited recording thus upper bounds on appear to be controlled by just a few fundamental aspects of frictional stick slip behavior that are common to shallow earthquakes everywhere estimates of from measurements of a for suites of earthquakes using are found to be comparable in magnitude to estimates of shear stress on the basis of extrapolating in situ stress data to seismogenic depths

scaling relations for seismic events induced by mining the values of seismic moment ands wave corner frequency from 1575 seismic events induced in south african canadian polish and german underground mines were collected to study their scaling relations the values ofp wave corner frequency from 649 events were also available seismic moments of these events range from 5 103 to 2 1015 n m moment magnitude is from 3 6 to 4 1 thes wave corner frequency ranges from 0 7 to 4438 hz and thep wave corner frequency is between 5 and 4010 hz the slope of a regression line between the logarithm ofs andp wave corner frequencies is equal to one and the corner frequencies ofp waves are higher than those ofs waves on the average by about 25 percent in studies of large and moderate earthquakes it has been found that stress drop is approximately independent of the seismic moment which means that seismic moment is inversely proportional to the third power of corner frequency such a behavior was confirmed for most of the data considered here a breakdown in the similarity betwen large and small events seems to occur for the events with moment magnitude below 2 5 the average values of seismic moment referred to the same range of corner frequency however are vastly different in various mining areas