a large refined catalog of earthquake relocations and focal mechanisms for the island of hawai i and its seismotectonic implications we present high quality focal mechanisms based on a refined earthquake location catalog for the island of hawai i focusing on mauna loa and k lauea volcanoes the relocation catalog is based on first arrival times and waveform data of both compressional and shear waves for about 180 000 events on and near the island of hawai i between 1986 and 2009 recorded by the seismic stations at the hawaiian volcano observatory we relocate all the earthquakes by applying ray tracing through an existing three dimensional velocity model similar event cluster analysis and a differential time relocation method the resulting location catalog represents an expansion of previous relocation studies covering a longer time period and consisting of more events with well constrained absolute locations the focal mechanisms are obtained based on the compressional wave first motion polarities and compressional to shear wave amplitude ratios by applying the hash program to the waveform cross correlation relocated earthquakes overall the good quality defined by the hash parameters focal solutions are dominated by normal faulting in our study area especially in the active ka iki and h lea seismic zones k lauea caldera is characterized by a mixture of approximately equal numbers of normal strike slip and reverse faults whereas its south flank has slightly fewer strike slip events our relocation and focal mechanism results will be useful for mapping the seismic stress and strain fields and for understanding the seismic volcanic tectonic relationships within the magmatic systems

deep magma body beneath the summit and rift zones of kilauea volcano hawaii a magnitude 7 2 earthquake in 1975 caused the south flank of kilauea volcano hawaii to move seaward in response to slippage along a deep fault since then a large part of the volcano s edifice has been adjusting to this perturbation the summit of kilauea extended at a rate of 0 26 meter per year until 1983 the south flank uplifted more than 0 5 meter and the axes of both the volcano s rift zones extended and subsided the summit continues to subside these ground surface motions have been remarkably steady and much more widespread than those caused by either recurrent inflation and deflation of the summit magma chamber or the episodic propagation of dikes into the rift zones kilauea s magmatic system is therefore probably deeper and more extensive than previously thought the summit and both rift zones may be underlain by a thick near vertical dike like magma system at a depth of 3 to 9 kilometers

focal mechanisms of earthquakes related to the 29 november 1975 kalapana hawaii earthquake the effect of structure models initial focal mechanism determinations for the 29 november 1975 kalapana hawaii earthquake indicated discrepancy between the mechanism determined from teleseismic data by ando and the mechanism determined using data from the local u s geological survey network surrounding the epicenter region the resolution of this difference is crucial to correctly understand this earthquake as well as to understand the tectonics of the south flank of kilauea volcano when a model with a low velocity layer at the base of the crust is used for projection back to the focal sphere for the local network mechanisms the discrepancy vanishes to further investigate this result focal mechanisms were determined using several contrasting models for a set of well recorded earthquakes a large number of these earthquakes have mechanisms identical to the main shock when the low velocity layer model is used dispersion of p and t axes is also minimized by use of this model a low angle slip direction favored for the main shock and typical of most other solutions exhibits remarkable stability normal to the east rift zone of kilauea our results suggest a tectonic model similar in nature to that proposed by ando in which the south flank of kilauea consists of a mobile block of crust which is relatively free to move laterally on a low strength zone at about 10 km depth forceful injection of magma along the rift zones provides the loading stress which is released by catastrophic failure in the weak horizontal layer in a cycle of perhaps 100 yr

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

calibration of the hglp seismograph network and centroid moment tensor analysis of significant earthquakes of 1976 abstract a methodology is developed for determining accurate instrument response functions for seismographs of the high gain long period hglp network recordings of daily transient calibration pulses provide a detailed history of the time varying responses of the hglp stations when the instrument displacement transfer function is available knowledge of the seismometer mass calibration coil constant and calibration current allows for the prediction of the shape and amplitude of the calibration signal by simple integration of the transfer function in theory the inverse of this statement is also true but in practice noise in the recordings contaminates the instrument response function recovered through direct differentiation of the calibration pulse the unknown transfer function of the seismograph system is instead first described by the product of the nominal responses of its mechanical and electromagnetic components specific values of the characteristic parameters for each seismograph component are subsequently determined by iterative least squares minimization of the misfit between observed and model transient calibration pulses by application of this method to daily calibration pulses recorded on the ten stations of the hglp network refined instrument response functions for 1976 and part of 1975 are determined the results agree well with single frequency amplitude calibration data recovered from station maintenance records and produce synthetic waveforms which are consistent with data from other well calibrated stations we use the recalibrated hglp data together with long period data from early international deployment of accelerometers ida and seismic research observatory sro digital stations to determine 108 centroid moment tensor cmt solutions for moderate and large earthquakes of 1976 the new cmt results for several major earthquakes including the tangshan guatemala and friuli events are compared with those of previous studies

centroid single force inversion of seismic waves generated by landslides the centroid moment tensor cmt waveform inversion method of dziewonski et al 1981 is modified to analyze long period seismic waves generated by single force events such as the gigantic landslides associated with the 1980 eruption of mount st helens we refer to the method as centroid single force csf inversion as the result of the inversion we obtain the spatio temporal centroid and three components of a vector we call the csf vector which is the seismic point source representation of a landslide and whose direction is the opposite of the direction of sliding the sealer magnitude of the csf vector measures the overall size of the landslide and is given by mcsf md where m is the mass of the sliding object and d is the sliding distance we apply csf inversion to the long period surface waves generated by the 1980 mount st helens event the 1975 kalapana earthquake and the 1974 mantaro landslide using seismograms from the gdsn ida and hglp networks the csf solution for the st helens event is remarkably consistent with the actual geological observations and proves the efficacy of csf inversion the csf solution for the kalapana event does not fit the overall waveforms better than the cmt solution does however because the cmt solution does not explain the observed love wave radiation pattern it may be necessary to invoke a combination of both types of mechanism for this event although the geometry of the csf solution the direction of the force for the mantaro event is consistent with the actual landslide mcsf is about 5 times smaller than that expected from the mass and travel distance of the landslide estimated by geological observations this discrepancy may suggest either the relatively aseismic nature of this landslide or that the total volume of the slide was overestimated by analogy to single station cmt inversion single station csf inversion also appears to be stable and useful

analysis of long period seismic waves excited by the may 18 1980 eruption of mount st helens a terrestrial monopole long period 100 to 260 s love and rayleigh waves excited by the eruption of mount st helens on may 18 1980 and recorded by ida sro and asro stations were analyzed to determine the mechanism of the eruption the amplitude radiation patterns of both rayleigh and love waves are two lobed with a nodal direction in e5 s for rayleigh waves and in n5 e for love waves these radiation patterns preclude any double couple mechanism the radiation pattern the initial phase the relatively large amplitude ratio of love to rayleigh waves and the existence of clear nodes in the radiation patterns of fundamental mode and higher mode rayleigh waves suggest that the source is represented by an almost horizontal less than 15 from the horizontal single force pointed toward s5 w the surface wave spectra fall off very rapidly at periods shorter than 75 s suggesting a very slow source process although the details of the source time history could not be determined a smooth bell shaped time function f o s t 1 2 f o l cos t for 0 t 2 and f o s t 0 for t 2 with 75 s is considered appropriate on the basis of comparison between synthetic and observed seismograms and of the shape of the source spectrum the peak value of the force f 0 is about 10 18 dynes the tailing end of the source time function could not be resolved and some overshoot may be added the magnitude and the time history of the force can be explained by a northward landslide followed by a lateral blast observed at the time of the eruption two distinct events about 110 s apart can be identified on body wave and short period surface wave records the first event may correspond to the earthquake which triggered the landslide and the lateral blast the second event appears to correspond to a second large earthquake and explosion which took place about 2 minutes after the first earthquake

long period source characteristics of the 1975 kalapana hawaii earthquake the 1975 kalapana hawaii earthquake occurred under the highly mobile south flank of kilauea volcano it has been interpreted variously as a normal faulting earthquake a thrust faulting earthquake and a landslide primary evidence for the landslide model has been the failure of previous faulting models to explain the observed love wave radiation pattern and the tsunami amplitudes generated by the kalapana event here we present a reanalysis of the long period digital seismic data for this event centroid moment tensor analysis shows that the seismic radiation pattern can be explained well by thrust faulting on a plane dipping shallowly landward the seismic moment of 3 8 10 20 n m m w 7 7 that we determine is approximately twice as large as earlier estimates the geometry and seismic moment of the focal mechanism determined here are consistent with the observed tsunami amplitudes inversion of long period body wave waveforms shows that the earthquake source duration 72 sec is unusually long for an earthquake of this size

rapid deformation of kilauea volcano global positioning system measurements between 1990 and 1996 campaign global positioning system gps measurements from 1990 to 1996 are used to calculate surface displacement rates on kilauea volcano hawaii the gps data show that the south flank of the volcano which has generated several large earthquakes in the past 3 decades is displacing at up to 8 cm yr to the south southeast the summit and rift zones are subsiding with maximum subsidence rates of 8 cm yr observed a few kilometers south of the summit caldera elastic dislocation modeling of the gps data suggests that the active sources of deformation include deep rift opening along the upper east and east rift zone fault slip along a subhorizontal fault near the base of the volcano and deflation near the summit caldera a nonlinear optimization algorithm was used to explore the parameter space and to find the best fitting source geometry there is a broad range of model geometries that fit the data reasonably well however certain models can be ruled out including those that have shallow rift opening or shallow fault slip some offshore aseismic slip on a fault plane that dips between 258 north northwest and 88 south southeast is required best fitting slip and rift opening rates are 23 28 cm yr although rates as low as 10 cm yr are permitted by the data

earthquake source parameters and stress distribution in the adak island region of the central aleutian islands alaska source parameters have been systematically determined for all earthquakes with mw 5 that occurred between 172 w and 179 w longitude in the adak island region of the central aleutian islands during 1977 march 1987 we relocate the events using a plate velocity model developed for the region and use two alternative methods of depth determination the first method uses arrival times of direct and prominent reflected phases primarily pwp the second method uses broadband p wave displacement seismograms in an inversion for source depth the analysis of these events provides a well constrained data set for the study of stress release along an active subduction zone three earthquakes which occurred seaward of the trench axis are located just below the crust mantle interface and show extension nearly perpendicular to the trench axis seven events occurred in the wadati benioff zone sixty four events are located in the main thrust zone and except for five unusual events are characterized by thrust mechanisms with one nodal plane dipping north at a shallow angle in cross section the thrust zone appears as a thin 10 15 km thickness interplate region which extends from 15 to 50 km depth a 10 15 average discrepancy between observed slip vector azimuths and the predicted relative motion direction between the pacific and north american plates exists for these events the observed slip vectors are oriented more normal to the trench than is predicted by plate motions five earthquakes which occurred as aftershocks to the may 7 1986 earthquake mw 8 0 in the crust of the overriding plate have strike slip mechanisms consistent with right lateral motion on arc parallel fault planes observations of slip vectors along the whole aleutian arc show a similar trend to that observed in the adak island region the largest differences 30 between observed and predicted slip azimuths occur around 175 e we propose a model of plate interaction in which a portion of the along arc motion occurs along a weak strike slip shear zone in the upper plate near the volcanic line the slip azimuths in the main thrust zone fit this model well if the amount of transcurrent slip occurring in the upper plate is 60 of the arc parallel relative plate motion a consequence of the model is along arc extension of the overriding plate between the accretionary wedge and the volcanic line especially in the western part of the aleutian arc calculations based on a tectonic model by geist et al 1988 for the formation of arc summit basins through block rotation and translation suggest that along arc extension has been significant since late miocene or early pliocene

characteristics of deep 13 km hawaiian earthquakes and hawaiian earthquakes west of 155 55 w 1 high precision relocation of earthquakes recorded by the hawaiian volcano observatory hvo seismic network provides new information on the characteristics of seismic faulting at this oceanic hot spot using waveform cross correlation we have measured correlation coefficients and travel time differences for a set of 14 605 deep 13 km earthquakes recorded from 1988 to 1998 we find that about half of the analyzed earthquakes are in similar event clusters that delineate fault zones in the lower crust and upper mantle we suggest that much of this deep seismicity reflects rupture in the brittle lithosphere away from the magma pathways although at kilauea the stresses from magma movement may additionally help trigger mantle earthquakes on preexisting faults in regions with high differential ambient stresses focal mechanisms of similar event clusters throughout hawaii display characteristic patterns and appear consistent with the hypothesis that deep earthquakes on preexisting faults reflect the stresses due to volcano loading and flexure we also present the results of applying cross correlation analyses and relocation to 7000 earthquakes at all depths located west of 155 55 w and recorded from 1988 to 1998 the pattern of relocated earthquakes at the kealakekua fault zone is consistent with the presence of a low angle detachment on the west flank of mauna loa

focal mechanisms and locations of earthquakes in the vicinity of the 1975 kalapana earthquake aftershock zone 1970 1979 implications for tectonics of the south flank of kilauea volcano island of hawaii the november 29 1975 kalapana earthquake of magnitude 7 1 on the south flank of kilauea volcano hawaii represents a major rift tectonic event it is generally understood that the earthquake resulted from movement on a nearly horizontal fault plane with the crustal block south of kilauea s east rift zone moving south southeastward up to several meters well recorded earthquakes on the south flank of kilauea from 1970 to 1979 were analyzed and focal mechanisms determined to obtain a better understanding of the details of south flank tectonics included are a large number of earthquakes from the aftershock sequence of the 1975 earthquake hypocenters are distributed in a subplanar zone that dips 2 to 3 to the west at a depth of about 8 9 km depth we interpret this pattern to coincide with a portion of the slip plane of the kalapana earthquake and to be consistent with the notion of the slip plane occurring in a weak layer at the top of the old oceanic crust focal mechanisms are remarkably constant throughout this time period both before and after the 1975 event and closely agree with the mainshock mechanism p axis azimuths and slip vectors for the low angle fault planes are normal to the middle and lower east rift zones of kilauea there is suggestion of a change in the orientation of p axes from shallower to steeper plunge at the time of the kalapana earthquake such a change is consistent with a general reduction in the horizontal compressional stress normal to the rift zone at the time of the large earthquake no other evidence of precursory reorientation of the stress field was found and the precise predictability of this event remains in doubt however a general model of the tectonics of the volcanic rift system is now available that satisfies a number of geological and geophysical observations

comment on a single force model for the 1975 kalapana hawaii earthquake by holly k eissler and hiroo kanamori

comparison of a complex rupture model with the precursor asperities of the 1975 hawaii m s 7 2 earthquake a simplified multiple source model was constructed for the 1975 hawaiims 7 2 earthquake by matching synthetic signals with three component accelerograms at two stations located approximately 45 km from the epicenter six major subevents were identified and located approximately the signals of these are larger by factors of 1 4 to 3 2 than that of theml 5 9 foreshock which occurred 70 minutes before the main rupture and also triggered the sam 1 recorders at the two stations dividing the rupture length 40 km by the duration of strong ground shaking 50 sec an average rupture velocity of 0 8 km sec about 25 of s velocity is obtained thus it is likely that the rupture stopped between subevents the approximate epicenters of the 6 major subevents and of the foreshock support the hypothesis that they were located in high stress asperities which rupture during the main shock except for the last events which is interpreted as a stopping phase generated at a barrier these asperities have been previously defined on the basis of differences in the precursor pattern before the mainshock thus it appears that both the details of the precursors and of the main rupture depended critically on the heterogeneous tress distribution in the source volume this suggests that main rupture initiation points and locations of high rupture accelerations may be identified before the mainshock occurs based on precursor anomaly patterns a satisfactory match of synthetic signals with the observations could be obtained only if the aximuth of the fault plane of subevents was rotated from n60 e to n90 e and back to n30 e these orientations are approximately parallel to the nearest kilauea rift segments hence the slip directions and greatest principal stresses were oriented perpendicular to the rifts everywhere from this analysis and other work it is concluded that this fault surface consisted of three types of segments with different strength hard asperities radius 5 km soft but brittle segments between the asperities radius 5 km and a viscous half 10 40 km which slipped during the mainshock but where microearthquakes and aftershocks are not common

mechanical models of the 1975 kalapana hawaii earthquake and tsunami abstract our objective is to produce a mechanically realistic model for the 1975 kalapana event that explains the overall deformation and geological evolution of the south flank of kilauea and reproduces most known earthquake and tsunami observations to do this we present a new structural interpretation of geological data from kilauea along with modeling of the tsunami using recent seismic analyses in so doing we hypothesize an offshore north facing normal fault that we call the kalapana fault because of its limited onshore expression near kalapana we argue that several different interpretations of seismic data are simultaneously true each coinciding with a specific geological structure we perform a direct numerical simulation of the 1975 kalapana tsunami and we report results for the near field and the far field simultaneously our interpretation of geological structures provides sufficient constraints to derive three tsunami sources the kalapana fault a slump and a thrust fault these three tsunami sources are mechanically coupled according to our model of kilauea evolution although their contributions to tsunami generation remain relatively distinct slump displacement predicts a small shear stress beneath kilauea volcano we find that our geological interpretation and tsunami sources are sufficiently robust to reproduce almost all tsunami observations repeated earthquakes like the 1975 kalapana event will produce extension and subsidence in the upper flank of kilauea as well as compression and uplift of the toe region accompanied by limited slump movement these deformations appear to stabilize kilauea and make catastrophic failure of the volcano flank less likely at this time

overthrusting and sediment accretion along kilauea s mobile south flank hawaii evidence for volcanic spreading from marine seismic reflection data a large intermittently active submarine landslide known as the hilina slump has been interpreted along the south flank of kilauea volcano seaward dipping faults on land mark its headwall and an offshore bench may define its uplifted toe geodetic data show that the entire south flank is also moving seaward by a process referred to as volcanic spreading this provides an alternative explanation for the bench i e overthrusting along the edge of the sliding flank the latter interpretation is consistent with new seismic reflection data across the submarine flank a prominent reflection near the top of the oceanic plate suggests the decollement upon which the mobile flank slides landward dipping reflections rise from this horizon and bound packages of bedded strata faulted and imbricated within the bench the absence of correlative seaward dipping faults and rotated strata on the upper flank suggests that the bench is not coupled to a slump moreover kinematic reconstructions of the bench indicate that it has accommodated 15 24 km of displacement this value is consistent with estimates for rift zone extension but too high for shortening at the toe of a slump we interpret the bench to result from overthrusting and accretion of volcaniclastic sediments to the edge of the mobile flank and suggest that morphologic benches develop preferentially where landslide debris has accumulated near the base of the volcano and can be accreted to its sliding edifice

mechanism of the 1975 kalapana hawaii earthquake inferred from tsunami data we investigated the source mechanism of the 1975 kalapana hawaii earthquake m s 7 2 by modeling the tsunamis observed at three tide gauge stations hilo kahului and honolulu we computed synthetic tsunamis for various fault models the arrival times and the amplitudes of the synthetic tsunamis computed for ando s fault model fault length 40 km fault width 20 km strike n70 e dip 20 se rake 90 fault depth 10 km and slip 5 6 m are 10 min earlier and 5 times smaller than those of the observed respectively we tested fault models with different dip angles and depths models with a northwest dip direction yield larger tsunami amplitudes than those with a southeast dip direction models with shallower fault depths produce later first arrivals than deeper models we also considered the effects of the hilina fault system but its contribution to tsunami excitation is insignificant this suggests that another mechanism is required to explain the tsunamis one plausible model is a propagating slump model with a 1 m subsidence along the coast and a l m uplift offshore this model can explain the arrival times and the amplitudes of the observed tsunamis satisfactorily an alternative model is a wider fault model that dips 10 nw with its fault plane extending 25 km offshore well beyond the aftershock area of the kalapana earthquake these two models produce a similar uplift pattern offshore and kinematically are indistinguishable as far as tsunami excitation is concerned the total volume of displaced water is estimated to be 2 5 km 3 from the comparison of slump model and the single force model suggested earlier from seismological data we prefer a combination of faulting and large scale slumping on the south flank of kilauea volcano as the most appropriate model for the 1975 kalapana earthquake two basic mechanisms have been presented for explaining the deformation of the south flank of kilauea 1 pressure and density variation along the rift zone caused by magma injection and 2 gravitational instability due to the steep topography of the south flank of kilauea in either mechanism large displacements on the south flank are involved that are responsible for the observed large tsunamis

acoustic and physical property relationships in marine sediment in situ sediment acoustic impedance measured from a ship underway is being used to infer the physical properties of the sea bed these inferences rely on published regression relationships developed to estimate impedance from sediment density or porosity thus the equations must be rearranged to yield the desired parameter when impedance is known rearranging or inverting regression equations is not a valid technique it is justified only when properly derived equations are unavailable herein are regressions of sediment density porosity and mean grain size on impedance to complement relationships already in the literature presented also are data and methods to place confidence limits on the predictions

the 1992 nicaragua earthquake a slow tsunami earthquake associated with subducted sediments the 1992 nicaragua earthquake was a tsunami earthquake that is it generated tsunamis disproportionately large for its surface wave magnitude m s the moment magnitude m w determined from long period 250 s surface waves was 7 6 significantly larger than the 20 s m s of 7 this m s m w disparity is also characteristic of tsunami earthquakes the nicaragua earthquake is the first tsunami earthquake to be captured by modern broadband seismic networks allowing us to present here seismograms of sufficiently high quality to make inferences about the rupture mechanisms we conclude that the nicaragua earthquake was a slow thrust earthquake which occurred on the subduction interface between the cocos and north american plates and because of the absence of sediments on the trench floor offshore of nicaragua the slip propagated up dip all the way to the ocean bottom exciting large tsunamis the occurrence of slip on a plate interface filled with soft subducted sediments caused the rupture process to be slower than in ordinary subduction zone thrust earthquakes our results reinforce the idea that tsunami warning systems using long period 100 s waves are necessary to reduce the hazard from this type of earthquake

moderate magnitude earthquakes induced by magma reservoir inflation at kīlauea volcano hawai i 1 although volcano tectonic vt earthquakes often occur in response to magma intrusion it is rare for them to have magnitudes larger than m4 on 24 may 2007 two shallow m4 earthquakes occurred beneath the upper part of the east rift zone of k lauea volcano hawai i an integrated analysis of geodetic seismic and field data together with coulomb stress modeling demonstrates that the earthquakes occurred due to strike slip motion on pre existing faults that bound k lauea caldera to the southeast and that the pressurization of k lauea s summit magma system may have been sufficient to promote faulting for the first time we infer a plausible origin to generate rare moderate magnitude vts at k lauea by reactivation of suitably oriented pre existing caldera bounding faults rare moderate to large magnitude vts at k lauea and other volcanoes can therefore result from reactivation of existing fault planes due to stresses induced by magmatic processes

structure of the mobile south flank of kilauea volcano hawaii how do huge landslides occur in hawaii we can begin to address this question by examining an incipient landslide structure on the mobile south flank of kilauea volcano between 1970 and 1989 this part of the south flank moved in a southeast direction seaward by 4 m on its eastern end and by 10 m on its western end parallel to the western boundary of a large oifshore topographic bench we show that abrupt decreases in cumulative flank movement correspond to abrupt decreases in hypocenter concentration most of the earthquakes occur in a 7 to 10 km deep band beneath the south flank and relative relocation of a subset of these events shows that they are derived from a single horizontal plane which appears to be a decollement focal mechanisms for this deep seismicity are dominated by thrust fault mechanisms with the overlying block moving seaward a comparison of south flank bathymetry with decollement structures on other volcanoes suggests that the distal end of this decollement coincides with the distal end of the offshore topographic bench 30 50 km from shore and 5 km below sea level the fault system forming the hilina pali is connected with this decollement so that slip on the hilina pali s normal faults coincides with slip of the decollement and with reverse faulting of the distal end of the bench this interpretation is supported by studies of the events associated with the m7 2 kalapana earthquake in 1975 when the hilina pali is connected to the outer bench with a decollement inferred from seismicity a wedge 8 km thick adjacent to kilauea s magma system and 1 2 km thick along the edge of the outer bench an area over 3000 km2 is defined the thickness adjacent to the magma system decreases eastward along kilauea s east rift zone and southwestward from kilauea caldera whereas the thickness of the lip of the outer bench decreases only eastward geologic observations and geophysical studies of the subaerial flank reveal an extensive magma system beneath the koae fault system as well as beneath kilauea caldera and its east rift zone we infer that the boundary of the proximal end of the mobile flank is the southern boundary of this magma system and that this boundary coincides with the southern boundaries of both the koae fault system and kilauea s east rift zone

a single force model for the 1975 kalapana hawaii earthquake a single force mechanism is investigated as the source of long period seismic radiation from the 1975 kalapana hawaii earthquake m s 7 1 the observed love wave radiation pattern determined from the spectra of world wide standard seismograph network and high gain long period records at 100 s is two lobed with azimuth consistent with a near horizontal single force acting opposite strike 330 to the observed displacement direction of the earthquake this pattern is inconsistent with the expected double couple pattern assuming a form of the force time history of a one cycle sinusoid the total duration of the event estimated from rayleigh waves at two international deployment of accelerometers stations is approximately 180 s the peak amplitude f o of the time function is 1 10 15 n from amplitudes of love and rayleigh waves the interpretation is that the bulk of the seismic radiation was produced by large scale slumping of a large area of the south flank of kilauea volcano the single force is a crude representation of the effect on the earth of the motion of a partially decoupled large slide mass using the mass estimated from the tsunami generation area 10 15 10 16 kg the peak acceleration of the slide block 0 1 1 m s 2 inferred from the seismic force is comparable with the acceleration due to gravity on a gently inclined plane the slump model for the kalapana earthquake is also more qualitatively consistent with the large horizontal deformation 8 m on land and tsunami associated with the earthquake which are difficult to explain with the conventional double couple source model the single force source has been used previously to model the long period seismic waves from the landslide accompanying the eruption of mount st helens volcano and may explain other anomalous seismic events as being due to massive slumping of sediments or unconsolidated material and not to elastic dislocation

an increment of volcano collapse kinematics of the 1975 kalapana hawaii earthquake abstract earthquakes on kilauea volcano can be even more hazardous than volcanic eruptions the most recent large earthquake was the 1975 kalapana quake which generated a locally damaging tsunami over 8 m of horizontal surface displacement and 3 m of subsidence at the coast the seismic magnitude estimates for this earthquake range from ms 7 2 to mw 7 7 the complexity of the seismic data is matched by the complex surface deformation that was observed with a combination of leveling tilt and electronic distance measurements edm the geodetic data shows evidence of collapse of the caldera due to magma withdrawal localized subsidence over the rift zone normal faulting associated with shallow slumping along the hilina pali and displacement on the basal detachment fault we model the summit caldera rift zones and basal detachment fault as dislocations in an elastic half space to better quantify the sources of deformation related to this devastating event using inversion techniques that allow us to let the data constrain the geometry and magnitude of these sources we find 0 04 km3 of magma withdrawal at the summit between 3 5 m of opening along the rift zone and 7 1 m of slip along the basal detachment at 8 3 km depth models that allow for finer spatial resolution of slip on the detachment show that the largest slip occurred west of the seismically recorded earthquake hypocenter along the region of the fault below the coast and that the majority of the fault slip occurred south of the region of microseismicity our best fitting model has a geodetic moment of 4 1 1020 nm mw 7 7 which is consistent with tsunami models and recent analysis of long period seismic data the residual displacements of sites located in the hanging wall of the hilina pali slump system which were not used in the inversion of the other sources suggest that triggered shallow slumping contributed several meters of horizontal displacement to the coseismic displacement at these sites

an experiment in systematic study of global seismicity centroid moment tensor solutions for 201 moderate and large earthquakes of 1981 data from the global digital seismograph network were used to obtain centroid moment tensor solutions using the method of dziewonski et al 1981 results were obtained for 201 earthquakes ranging in seismic moment from 7 1023 to 3 1027 dyne cm the wide dynamic range of the sro asro stations allows us to investigate using the same algorithm series of events among which the smallest and the largest may differ in moment by a factor as large as 1000 among the events studied is a particularly interesting series in january 1981 off the island of honshu the main shock was preceded by three foreshocks and followed by four aftershocks all falling within the range of our analysis there is an indication that the source mechanism changes with the size of the event statistical analysis of the results for all earthquakes reveals that the half duration of shallow and intermediate events is approximated by 1 6 10 8 m01 3 the shifts in origin time for deep focus earthquakes are indicative of the general complexity of these events which depends only weakly on the seismic moment the extreme departures from a double couple mechanism seem to depend both on the moment and on the focal depth while for shallow earthquakes these departures decrease from a maximum at about 1025 dyne cm with increasing moment the reverse appears to be true with respect to deep focus earthquakes shallow earthquakes north of new guinea and along the solomon islands show systematic and substantial departures from the double couple mechanism

pressurized magma reservoir within the east rift zone of kīlauea volcano hawai i evidence for relaxed stress changes from the 1975 kalapana earthquake we use 2000 2012 insar data from multiple satellites to investigate magma storage in k lauea s east rift zone erz the study period includes a surge in magma supply rate and intrusion eruptions in 2007 and 2011 the kupaianaha area inflated by 5 cm prior to the 2007 intrusion and the n pau crater area by 10 cm following the 2011 intrusion for the n pau crater area elastic modeling suggests an inflation source at 5 2 km depth or more below sea level the reservoir is located in the deeper section of the rift zone for which secular magma intrusion was inferred for the period following the 1975 mw7 7 decollement earthquake reservoir pressurization suggests that in this section of the erz extensional stress changes due to the earthquake have largely been compensated for and that this section is approaching its pre 1975 state reservoir pressurization also puts the molten core model into question for this section of k lauea s rift zone

a preliminary study on the offshore stratigraphy in hong kong and its hydrogeological implications offshore groundwater reserves commonly sequestered in relict fluvial systems have been reported globally in hong kong submarine terrestrial sediments are the evidence of local fluvial systems during glacial periods and they probably sequester relatively fresh water this study aims to locate these sand deposits an offshore vibrocore in the southwestern waters of hong kong was analysed for its geophysical and elemental properties in order to deduce the palaeoenvironment also marine seismic profiling was adopted at two selected sites to depict the distribution of sand and gravel deposits and to estimate the average thickness of these aquifer materials a four unit sequence was noted with increasing marine influence since 8 ka bp this agrees with the hypothesis that the offshore groundwater reserves are the relics of flow systems during glacial periods the extensive sand deposits in the study areas are often shielded by sufficiently thick marine clay against vertical salinisation allowing fresh groundwater to be preserved the average thickness of these aquifer materials is about 11 m at the study sites if these sand deposits are recharged through onshore outcrops the reserves may be a sustainable water resource