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

high precision location of pre eruption seismicity at mount pinatubo philippines 30 may 3 june 1991 abstract we applied waveform cross correlation wcc to a selected set of 153 volcano tectonic vt earthquakes that occurred at mount pinatubo from 30 may through 3 june 1991 to determine improved relative p wave arrival times and locations simultaneous inversion for hypocenters and velocity model parameters using the refined arrival times resulted in extremely low arrival time misfits and well constrained relative earthquake locations pre eruption earthquakes from this time period occurred in two groups a shallow group located almost directly below the mount pinatubo summit at depths of 2 4 km and a deeper group located 3 5 km northwest nw of the summit at depths of 3 7 km we found that most off summit earthquakes in this time period occurred along a plane dipping approximately 60 and striking approximately 60 e of north this feature may have been a fault reactivated by mount pinatubo s magmatic activity the previously diffuse summit cluster collapsed from a cloud to a narrow roughly linear feature accompanied by a separate shallower group of events these features were not visible in previous studies of mount pinatubo seismicity indicating the importance of high precision arrival time picks for interpreting volcano seismicity

the accommodation of the south flank s motion by the koa e fault system kīlauea hawai i insights from the june 2012 earthquake sequence

source process of very long period events accompanying long period signals at cotopaxi volcano ecuador abstract renewed seismic activity of cotopaxi ecuador began in january 2001 with the increased number of long period lp events followed by a swarm of volcano tectonic vt earthquakes in november 2001 in late june 2002 the activity of very long period vlp 2 s events accompanying lp 0 5 1 s signals began beneath the volcano the vlp waveform was characterized by an impulsive signature which was accompanied by the lp signal showing non harmonic oscillations we observed temporal changes of both the vlp and lp signals from the beginning until september 2003 the vlp signal gradually disappeared and the lp signal characterized by decaying harmonic oscillations became dominant assuming possible source geometries we applied a waveform inversion method to the observed waveforms of the largest vlp event our inversion and particle motion analyses point to volumetric changes of a sub vertical crack as the vlp source which is located at a depth of 2 3 km beneath the northeastern flank the spectral analysis of the decaying harmonic oscillations of lp events shows frequencies between 2 0 and 3 5 hz with quality factors significantly above 100 the increased vt activity and deformation data suggest an intrusion of magma beneath the volcano a release of gases with small magma particles may have repetitively occurred due to the pressurization which was caused by sustained bubble growth at the magma ceiling the released particle laden gases opened a crack above the magma system and triggered the resonance of the crack we interpret the vlp and lp events as the gas release process and the resonance of the crack respectively

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

mount hood earthquake activity volcanic or tectonic origins on 29 june 2002 a m d 4 5 earthquake occurred 4 6 km south of mount hood oregon more than 200 small aftershocks m d 3 8 occurred between 29 june and 15 august 2002 by which time seismicity returned to background levels we analyze well constrained earthquakes from the summer 2002 sequence near mount hood recorded by the pacific northwest seismic network pnsn and well constrained small earthquakes m d 3 5 recorded by the pnsn between 1986 and 2002 we apply waveform cross correlation to selected events establish a one dimensional p wave velocity model and relocate the entire catalog by using the double difference algorithm of waldhauser and ellsworth 2000 we find that earthquakes before 2002 occur in four distinct clusters a a well defined linear feature striking n15e about 5 km south of the summit b a linear feature trending northwest southeast a few kilometers south of group a c a few tight clusters located about 9 km south southwest of the summit and d a small cluster beneath the summit earthquakes in group d do not appear to lie on a fault and may relate to volcanic activity however almost all earthquakes in the 2002 swarm occur in group a south of the summit at depths similar to earthquakes from previous swarms first motion fault plane solutions from the mainshock and largest aftershocks have normal mechanisms and solutions from well constrained aftershocks have normal to oblique normal mechanisms this is consistent with the apparent strike of the feature south of mount hood s summit and is similar to focal mechanisms of older earthquakes in group a b and p values for the summer 2002 earthquakes resemble a tectonic mainshock aftershock sequence we interpret these earthquakes as the northernmost example of basin and range seismicity yet recorded and conclude that the mount hood earthquakes do not yet suggest potential for volcanic unrest

constraining spatiotemporal characteristics of magma migration at piton de la fournaise volcano from pre eruptive seismicity volcano tectonic seismicity has been recorded for decades on various volcanoes and is linked with the magma transport and reservoir pressurization yet earthquakes often appear broadly distributed such that magma movement is difficult to infer from its analysis we explore the seismicity that occurred before eruptions at piton de la fournaise in the last 5 years using template matching and relocation techniques we produce a refined image of the summit seismicity demonstrating that most earthquakes are located on a ring structure however only a portion of this structure is activated before each eruption which provides an indication as to the direction of the future eruptive site furthermore we show that the delay between the pre eruptive swarm and the eruption onset is proportional to the distance of the eruptive fissures relative to the summit cone this reveals that the beginning of the intrusion already bears information regarding the future eruption location

deformation of kilauea volcano during 1982 and 1983 a transition period a major transition in the style of deformation of kilauea volcano occurred during the period january 1982 through november 1983 prior to 1983 the deformation was dominated by magma intrusions rapid extension of the summit and seaward movement of the south flank the pattern of activity changed to magma eruption and slowed deformation of the volcanic edifice in january 1983 an earthquake swarm in the southwest rift zone in june 1982 and an intrusion of a large dike in the east rift zone in january 1983 prepared the volcano for the eruptive sequences that continue today we estimate the sources of surface displacements associated with these events using a least squares nonlinear inversion technique and planar dislocations the models are constrained with measurements of line length changes and of surface height changes from tide gauges water wells and spirit level tilt data deformation associated with the 1982 earthquake swarm is best modeled as the emplacement of a steeply dipping dike in the upper and middle southwest rift zone extending from 2 3 km to 10 11 km depth with a width of 1 2 m tilt measurements gathered at the time of the earthquake swarm record a small deflation of kilauea s summit however trilateration data indicate the summit was rapidly extending in 1982 the extension and our models are consistent with seaward slip of the south flank on a low angle basal thrust fault dislocation models of the january 1983 dike intrusion yield a 14 to l5 km long dike along the zone of observed ground rupture the dike extends from just below the surface to the region of the most intense rift zone seismicity at 4 5 km depth a strong nonlinear relationship among height dip and width results in a suite of models that explain the data equally well tests of parameter sensitivity indicate that the dike width and height are the least constrained parameters the best fit average width ranges from 1 7 to 2 8 m our models also include a source of contraction at 5 km depth that produces 40 cm of ground subsidence near makaopuhi the point of initiation of the intrusion this location is consistent with geochemical and seismic evidence that indicate magma is stored in the rift zone residual errors for all models indicate that substantial line length changes are unexplained seaward motions of the south flank during 1982 and 1983 are not well modeled by simple dikes and summit deflations however attempts to constrain low angle faults in the south flank were only partly successful due to the limited extent of the geodetic networks

a reinterpretation of seismicity associated with the january 1983 dike intrusion at kilauea volcano hawaii in january 1983 a dike intrusion fissure eruption generated a swarm of 375 magnitude 1 to 3 earthquakes along a 16 km segment of kilauea s middle east rift zone we searched the hawaiian volcano observatory catalog for multiplets of similar events from this region from 1980 through 1985 and obtained precise relative locations by waveform cross correlation over 150 of the intrusion earthquakes could be grouped into 14 multiplets of five or more events with sufficient similarity for accurate relocation some multiplets were active for only a few minutes during the downrift migration phase of the seismic swarm consistent with generation near the propagating dike tip while others were active for several days the two multiplets nearest the origin of the seismic swarm include events from the preceding days and months most multiplets span only 50 to 100 m following relocation are located at about 3 to 4 km depth and appear to deepen downrift the catalog depths of those earthquakes in multiplets and those not in multiplets are similar suggesting that most of the recorded seismicity may have come from a very limited depth interval despite the fact that the dike breached the surface by analogy with a mechanical model used to explain a similar clustering of background seismicity in the upper east rift in 1991 we infer that the earthquakes are generated in regions of high stress concentration immediately above kilauea s deforming deep rift body this conclusion is consistent with the depth of the top of the deep rift body inferred from geodetic data and with numerical calculations suggesting that a significant ambient differential stress is required for dikes to produce earthquakes larger than magnitude 1

observations of long period earthquakes accompanying hydraulic fracturing waveforms of most seismic events accompanying hydraulic fracturing have been reported to contain clear p and s waves and have fault plane solutions consistent with shear displacement across a fault this observation is surprising since classical hydraulic fracturing theory predicts the creation of a tensile opening of a cavity in response to fluid pressure very small long period events similar to long period earthquakes observed at volcanoes were found to occur during four hydraulic fracturing experiments carried out at fenton hill new mexico since the long period earthquakes occur in the same region as the shear type events it is concluded that the unusual character of the long period earthquake waveforms is due to a source effect and not a path effect the occurrence of long period earthquakes during hydraulic fracturing could indicate tensile fracturing many waveforms of these events are identical which implies that these events represent repeated activation of a given source a proposed source for these long period events is the sudden opening of a channel that connects two cracks filled with fluid at different pressures the sizes of the two cracks differ which causes two or more peaks to appear in the spectra each peak beingmore associated with one physical dimension of each crack from the frequencies at which spectral peaks occur crack lengths are estimated to be between 3 and 20m less

a linear gradient crustal model for south hawaii a new crustal model with linear velocity gradients within layers does as good a job of locating earthquakes on south hawaii as any model yet published incorporating linear gradients means the model can be simpler and free of artificial velocity discontinuities using travel time residuals from local earthquakes and consistency of focal mechanism solutions as tests it is seen that a low velocity zone at the base of the crust is not required

monitoring velocity variations in the crust using earthquake doublets an application to the calaveras fault california we present a technique that greatly improves the precision in measuring temporal variations of crustal velocities using an earthquake doublet or pair of microearthquakes that have nearly identical waveforms and the same hypocenter and magnitude but occur on different dates we compute differences in arrival times between seismograms recorded at the same station in the freqency domain by cross correlation of short windows of signal a moving window analysis of the entire seismograms including the coda gives t the difference in arrival times versus running time along the seismogram the time resolution of the method is an order of magnitude better than the digitization interval the t technique is illustrated with a pair of microearthquakes m 1 7 and 2 0 that occurred before and after the coyote lake california earthquake m 5 9 of august 6 1979 and on the same segment of the calaveras fault that ruptured during the earthquake the coda wave arrivals for some stations are progressively delayed for the second earthquake in the doublet so that its seismogram appears as a stretched version of the earlier event we interpret this systematic variation in t along the coda as a change in the average s velocity in the upper crust in the time interval between the two doublets s wave velocities appear to have decreased by 0 2 in an oblong region 5 10 km in radius at the south end of the aftershock zone

deep fault plane geometry inferred from multiplet relative relocation beneath the south flank of kilauea dense microearthquake swarms occur in the upper south flank of kilauea providing multiplets composed of hundreds of events the similarity of their waveforms and the quality of the data have been sufficient to provide accurate relative relocations of their hypocenters a simple and efficient method has been developed which allowed the relative relocation of more than 250 events with an average precision of about 50 m horizontally and 75 m vertically relocation of these events greatly improves the definition of the seismic image of the fault that generates them indeed relative relocations define a plane dipping about 6 northward although corresponding absolute locations are widely dispersed in the swarm a composite focal mechanism built from events providing a correct spatial sampling of the multiplet also gives a well constrained northward dip of about 5 to the near horizontal plane this technique thus collapses the clouds of hypocenters of single event locations to a plane coinciding with the slip plane revealed by previous focal mechanism studies we cannot conclude that all south flank earthquakes collapse to a single plane there may locally be several planes perhaps with different dips and depths throughout the south flank volume the 6 northward dipping plane we found is too steep to represent the overall flexure of the oceanic crust under the load of the island of hawaii this plane is probably an important feature that characterizes the basal slip layer below the upper south flank of kilauea volcano differences in seismicity rate and surface deformations between the upper and lower south flank could be related to the geometry of this deep fault plane the present work illustrates how high precision relative relocations of similar events in dense swarms combined with the analysis of geodetic measurements can help to describe deep fault plane geometry systematic selection and extensive relative relocation of similar earthquakes could be attempted in other well instrumented highly seismic areas to provide reliable basic information especially useful for understanding of earthquake generation processes

seismic activity at cadamosto seamount near fogo island cape verdes formation of a new ocean island summary in global catalogues only a handful of earthquakes occurred at or near the cape verde islands the two most recent events occurring in 1998 and 2004 were observed in the southwest of the cape verde archipelago away from aerial volcanic centres event relocation suggests that both earthquakes may occur at the cadamosto seamount a 3 km tall submarine volcanic edifice to the southwest of the active volcanic islands of fogo swath mapping efforts revealed numerous small volcanic cones between the volcanic island of brava and the seamount and between fogo and brava the distribution of volcanic vents may support two plumbing systems one feeding fogo and volcanic cones between fogo and brava and another system feeding cadamosto seamount using ocean bottom seismic stations of opportunity deployed roughly a month after a mb 4 3 earthquake occurred in 2004 august near or at the cadamosto seamount we were able to locate local seismic activity clustering at the seamount we propose that these events reflect brittle rock failure due to magma redistribution in or near a central magma reservoir or more likely dyke intrusion the observations reported here suggest that cadamosto seamount is the seismically most active feature in the archipelago it might be reasonable to hypothesis that ongoing activity causes the cadamosto seamount to grow forming a new oceanic island in the future

time dependent dike propagation from joint inversion of seismicity and deformation data dike intrusions both deform earth s surface and induce propagating earthquake swarms we develop methods to utilize both deformation and seismicity from brittle volcano tectonic earthquakes to image time dependent dike propagation dieterich s 1994 seismicity rate theory is used to relate dike induced stress changes to seismicity rate and is combined with elastic green s functions relating dike opening to deformation different space time patterns of seismicity develop if earthquakes occur at the same depth as the dike compared to above below the dike in the former seismicity initiates near the dike s leading edges but shuts off as the dike tips pass and seismogenic volumes fall into stress shadows in the latter seismicity continues at a decaying rate after the tips pass we focus on lateral propagation and develop a nonlinear inversion method that estimates dike length and pressure as a function of time the method is applied to the 2007 father s day intrusion in kilauea volcano seismicity is concentrated at 3 km depth comparable to geodetic estimates of dike depth and decays rapidly in time with lateral propagation only and a vertical dike tip line it is difficult to fit both gps data and the rapid down rift jump in seismicity suggesting significant vertical propagation for the events to have occurred below the dike requires a very short aftershock decay time hence unreasonably high background stressing rate the rapid decay is better explained if the dike extends somewhat below the seismicity we suggest that joint inversion is useful for studying the diking process and may allow for improved short term eruption forecasts

capturing magma intrusion and faulting processes during continental rupture seismicity of the dabbahu afar rift continental rupture models emphasize the role of faults in extensional strain accommodation extension by dyke intrusion is commonly overlooked a major rifting episode that began in 2005 september in the afar depression of ethiopia provides an opportunity to examine strain accommodation in a zone of incipient plate rupture earthquakes recorded on a temporary seismic array 2005 october to 2006 april direct observation of fault patterns and geodetic data document ongoing strain and continued dyke intrusion along the 60 km long dabbahu rift segment defined in earlier remote sensing studies epicentral locations lie along a 3 km wide 50 km long swath that curves into the se flank of dabbahu volcano a second strand continues to the north toward gab ho volcano considering the 8 m of opening in the september crisis we interpret the depth distribution of microseismicity as the dyke intrusion zone the dykes rise from 10 km to the near surface along the 60 km long length of the tectono magmatic segment focal mechanisms indicate slip along nnw striking normal faults perpendicular to the arabia nubia plate opening vector the seismicity insar continuous gps and structural patterns all suggest that magma injection from lower or subcrustal magma reservoirs continued at least 3 months after the main episode persistent earthquake swarms at two sites on dabbahu volcano coincide with areas of deformation identified in the insar data 1 an elliptical northwestward dipping zone of seismicity and subsidence interpreted as a magma conduit and 2 a more diffuse 8 km radius zone of shallow seismicity 2 km above a shadow zone interpreted as a magma chamber between 2 5 and 6 km subsurface insar and continuous gps data show uplift above a shallow source in zone 2 and uplift above the largely aseismic gab ho volcano the patterns of seismicity provide a 3 d perspective of magma feeding systems maintaining the along axis segmentation of this incipient seafloor spreading segment

role of olivine cumulates in destabilizing the flanks of hawaiian volcanoes the south flank of kilauea volcano is unstable and has the structure of a huge landslide it is one of at least 17 enormous catastrophic landslides shed from the hawaiian islands mechanisms previously proposed for movement of the south flank invoke slip of the volcanic pile over seafloor sediments slip on a low friction decollement alone cannot explain why the thickest and widest sector of the flank moves more rapidly than the rest or why this section contains a 300 km3 aseismic volume above the seismically defined decollement it is proposed that this aseismic volume adjacent to the caldera in the direction of flank slip consists of olivine cumulates that creep outward pushing the south flank seawards average primary kilauea tholeiitic magma contains about 16 5 wt mgo compared with an average 10 wt mgo for erupted subaerial and submarine basalts this difference requires fractionation of 17 wt 14 vol olivine phenocrysts that accumulate near the base of the magma reservoir where they form cumulates submarine erupted kilauea lavas contain abundant deformed olivine xenocrysts derived from these cumulates deformed dunite formed during the tholeiitic shield stage is also erupted as xenoliths in subsequent alkalic lavas the deformation structures in olivine xenocrysts suggest that the cumulus olivine was densely packed probably with as little as 5 10 vol intercumulus liquid before entrainment of the xenocrysts the olivine cumulates were at magmatic temperatures 1100 c when the xenocrysts were entrained olivine at 1100 c has a rheology similar to ice and the olivine cumulates should flow down and away from the summit of the volcano flow of the olivine cumulates places constant pressure on the unbuttressed seaward flank leading to an extensional region that localizes deep intrusions behind the flank these intrusions add to the seaward push this mechanism ties the source of gravitational instability to the caldera complex and deep rift systems and therefore limits catastrophic sector failure of hawaiian volcanoes to their active growth phase when the core of olivine cumulates is still hot enough to flow

mechanical response of the south flank of kilauea volcano hawaii to intrusive events along the rift systems abstract increased earthquake activity and compression of the south flank of kilauea volcano hawaii have been recognized by previous investigators to accompany rift intrusions we further detail the temporal and spatial changes in earthquake rates and ground strain along the south flank induced by six major rift intrusions which occurred between december 1971 and january 1981 the seismic response of the south flank to individual rift intrusions is immediate the increased rate of earthquake activity lasts from 1 to 4 weeks horizontal strain measurements indicate that compression of the south flank usually accompanies rift intrusions and eruptions emplacement of an intrusion at a depth greater than about 4 km such as the june 1982 southwest rift intrusion however results in a slight extension of the subaerial portion of the south flank horizontal strain measurements along the south flank are used to locate the january 1983 east rift intrusion which resulted in eruptive activity the intrusion is modeled as a vertical rectangular sheet with constant displacement perpendicular to the plane of the sheet this model suggests that the intrusive body that compressed the south flank in january 1983 extended from the surface to about 2 4 km depth and was aligned along a strike of n66 e the intrusion is approximately 11 km in length extended beyond the january 1983 eruptive fissures which are 8 km in length and is contained within the 14 km long region of shallow rift earthquakes

new and revised 14c dates for hawaiian surface lava flows paleomagnetic and geomagnetic implications radiocarbon dates have been obtained for 30 charcoal samples corresponding to 27 surface lava flows from the mauna loa and kilauea volcanoes on the island of hawaii the submitted charcoal was a mixture of fresh and archived material preparation and analysis was undertaken at the nerc radiocarbon laboratory in glasgow scotland and the associated suerc accelerator mass spectrometry facility the resulting dates range from 390 years b p to 12 910 years b p with corresponding error bars an order of magnitude smaller than previously obtained using the gas counting method the new and revised 14c data set can aid hazard and risk assessment on the island the data presented here also have implications for geomagnetic modelling which at present is limited by large dating errors

mechanical models for dikes a third school of thought abstract geological and geophysical data from continental volcanic centers and giant radial swarms and from oceanic shield volcanoes and rift zones indicate that dikes propagate laterally for distances that can be 10 to over 100 times their height what traps dikes within the shallow lithosphere and promotes these highly eccentric shapes gravity induced stress gradients in the surrounding rock and pressure gradients in the magma are the primary loading mechanisms pressure gradients due to magma flow are secondary to insignificant because the flow direction is dominantly horizontal this configuration of vertical blade shaped dikes with horizontal dike propagation and magma flow is fundamentally different from the two dike model configurations described in a recent review paper as two schools of thought for mechanical models of dikes in school i a dike is disconnected from its source and ascends under the influence of buoyancy in school ii a dike is connected to a magma reservoir and is driven upward by magma flux from the source we review the geological and geophysical data supporting the vertical dike horizontal flow propagation configuration and suggest the abundance and veracity of these data in many different geological settings and the modeling results that address this physical process warrant adding this as a third school of thought a new analytical solution for the boundary value problem of a homogeneous isotropic and linear elastic solid with a vertical fluid filled crack is used to investigate the effects of gravitationally induced stress and pressure gradients on the aperture distribution dike tip stress intensity and stable height model results indicate that in a homogeneous crust dikes can achieve stable heights greater than a kilometer only if the host rock fracture toughness k ic 100 mpa m 1 2 however density stratification of the crust is an effective mechanism for trapping kilometer scale dikes even if the host rock is very weak k ic 0 this analysis may explain why vertical dikes propagate laterally for great distances but reside within a narrow range of depths in the crust

investigating the p wave velocity structure beneath harrat lunayyir northwestern saudi arabia using double difference tomography and earthquakes from the 2009 seismic swarm 1 in 2009 a swarm of more than 30 000 earthquakes occurred beneath the harrat lunayyir lava field in northwest saudi arabia this event was just one of several seismic swarms to occur in this region over the past decade surface deformation associated with the seismicity modeled in previous studies using interferometric synthetic aperture radar insar data is best attributed to the intrusion of a 10 km long dyke however little is known about the velocity structure beneath harrat lunayyir making assessment of future seismic and volcanic hazards difficult in this study we use local double difference tomography to generate a p wave velocity model beneath harrat lunayyir and to more precisely locate earthquakes from the 2009 seismic swarm a pronounced fast velocity anomaly centered at 15 km depth with a shallower extension to the n nw is interpreted as an area of repeated magmatic intrusion the crust surrounding the fast intrusion is slower than that suggested by broader scale models for the arabian shield the largest magnitude events occurred early in the swarm concentrated at shallow depths 2 8 km beneath northern harrat lunayyir and these events are associated with the dyke intrusion later deep earthquakes 15 km beneath the southern end of the study region as well as a group of intermediate depth events connecting the shallow and deep regions of seismicity occurred these later events likely represent responses to the local stress conditions following the intrusion our results are unique since harrat magma systems are rarely imaged and our observations coupled with the seismic history in this region suggest that future volcanic intrusions beneath harrat lunayyir are likely

rapid deformation of the south flank of kilauea volcano hawaii the south flank of kilauea volcano has experienced two large magnitude m 7 2 and m 6 1 earthquakes in the past two decades global positioning system measurements conducted between 1990 and 1993 reveal seaward displacements of kilauea9s central south flank at rates of up to about 10 centimeters per year in contrast the northern side of the volcano and the distal ends of the south flank did not displace significantly the observations can be explained by slip on a low angle fault beneath the south flank combined with dilation deep within kilauea9s rift system both at rates of at least 15 centimeters per year

the cookie cutter a method for obtaining a quantitative 3d description of glacial bedforms recording the position and attributes of subglacial bedforms particularly drumlins is paramount in determining the extent and dynamics of former ice sheets this paper presents a method of deriving 3d properties of glacier bedforms drumlins in this case in order to quantify bedform dimensions and acquire information necessary for further investigations such as calculating amounts of sediment moved subglacially and hence interactions between a glacier and a deformable bed the method developed here is a semi automated technique called cookie cutter after the baking implement process this method is applied to 5 m spatial resolution dem data and is based on manual geomorphological mapping of the dem images which forms the judgmental part of the process the mapped bedforms are then processed individually using an automated technique which is described in detail with worked examples from western central scotland which was last glaciated during the last glacial maximum and the younger dryas the advantages and potential sources of error are discussed and results from the sample area are used to compare the volumes of drumlins in an area of lgm glaciation with those in an area glaciated during the younger dryas

the fracturing in volcanic edifice before an eruption the june july 1998 high frequency earthquake swarm at volcan de colima mexico the recent eruption of volcan de colima mexico began in november 1998 and was preceded by a 12 month period of seismic activity which consisted from a few swarms of numerous microeathquakes we study the source characteristics of earthquakes that occurred during june july 1998 swarm within the edifice of volcan de colima which consists of the dormant nevado de colima and active volcan de fuego a three component digital seismic station added to the one component seismic network of five stations during this period allowed us to analyze s wave spectra for our study thirty two microearthquakes with hypocentral distances up to 7 km and magnitudes mw between 0 5 and 1 8 were analyzed in the frame of brune s model these events were characterized by high frequency radiation with corner frequencies from 3 9 to 9 0 hz their seismic moments varied from 0 9 1010 to and stress drops were obtained in the range between 0 05 and 13 bars we found three groups of events with different corner frequencies that may reflect the presence of three fracture zones with distinct characteristic lengths of fissures formed by the subsurface dike intrusion before the eruption the first stage from june 16 to july 3 of swarm development was characterized by simultaneous fracturing within two fracture zones the first zone was represented by a system of fractures with length of about 80 90 m and was situated below nevada de colima the second zone was represented by a system of fractures with length of about 130 150 m and was situated below the crater zone of volcan de fuego the second stage from july 4 to 6 of swarm development was characterized by simultaneous fracturing within three fracture zones a third zone was added to the first two zones with the fracture length of intermediate size about 110 m the majority of foci that occurred from june 16 to july 3 were situated along the se slope of nevado de colima the events of july 4 to 6 occurred mainly below the crater zone of volcan de fuego the fracturing in the volcanic edifice occurred within a system of fractures of ene direction tracing by epicenters and coinciding with the general trend of tamazula regional fault that intersects the volcanic structure we suggested that this development of the earthquake swarm reflects either 1 the migration of dike to the active crater of volcan de colima or 2 the growth of branches of the dike swarm tree within the volcanic edifice

evolution of a lateral dike intrusion revealed by relatively relocated dike induced earthquakes the 2014 15 barðarbunga holuhraun rifting event iceland abstract understanding dikes is vital as they serve both as bodies that build the crust and as conduits that feed eruptions and must be monitored to evaluate volcanic hazard during the 2014 15 bar arbunga rifting event iceland intense seismicity accompanied the intrusion of a 50 km lateral dike which culminated in a 6 month long eruption we here present relocations of earthquakes induced by the lateral dike intrusion using cross correlated sub sample relative travel times the 100 m spatial resolution achieved reveals the complexity of the dike propagation pathway and dynamics jerky segmented and allows us to address the precise relationship between the dike and seismicity with direct implications for hazard monitoring the spatio temporal characteristics of the induced seismicity can be directly linked in the first instance to propagation of the tip and opening of the dike and following this after dike opening indicate a relationship with magma pressure changes i e dike inflation deflation followed by a general post opening decay seismicity occurs only at the base of the dike where dike imposed stresses combined with the background tectonic stress from regional extension over 200 yr since last rifting are sufficient to induce failure of pre existing weaknesses in the crust while the greatest opening is at shallower depths emplacement oblique to the spreading ridge resulted in left lateral shear motion along the distal dike section studied here and a prevalence of left lateral shear failure fault plane strikes are predominately independent of the orientation of lineations delineated by the hypocenters indicating that they are controlled by the underlying host rock fabric this high resolution study provides unprecedented opportunity for comparison with both geodetic and field frozen dike observations and development and consolidation of analytical and analogue models with implications for rifting processes and real time monitoring of magma intrusion

double difference tomography the method and its application to the hayward fault california we have developed a double difference dd seismic tomography method that makes use of both absolute and relative arrival times by reducing systematic errors using the more accurate relative arrival times the method produces an improved velocity model simultaneously it yields event locations of a quality equivalent to those of the dd location method while avoiding simplifying assumptions of that method we test this method on a synthetic dataset and find that it produces a more accurate velocity model and event locations than standard tomography we also test this method on a hayward fault california earthquake dataset spanning 1984 1998 the earthquakes relocated by this method collapse to a thin line along the fault trace consistent with previous results the dd velocity model has sharper velocity contrasts near the source region than the standard tomography model

modeling the three dimensional structure of macroscopic magma transport systems application to kilauea volcano hawaii we report the results of modeling the three dimensional internal structure of kilauea s magmatic passageways the approach uses a clear plexiglass model containing equally spaced levels upon which well located seismic hypocenters are plotted application of constraining geologic and geophysical criteria to this distributed volume of earthquakes permits the interpretation of seismic structures produced by fracturing in response to locally high fluid pressures four magma transport and storage structures have been identified within and beneath kilauea 1 primary conduit the conduit transporting magma into kilauea s summit storage reservoir rises from the model base 14 6 km to the 6 5 km depth level it is a zone of intense fracturing and inferred intrusion whose horizontal sections are elliptical in planform over its height the average major axis of the component horizontal sections is 3 3 km with an average minor axis of 1 7 km this yields an aspect ratio of 0 52 at the 14 6 km level the strike of the major axis is n67 e during passage from the upper mantle through the oceanic crust this axis rotates in a right handed sense until the strike is n41 w at the 6 5 km level 2 magma chamber complex floor the interval from 6 5 to 5 7 km immediately over the primary conduit is aseismic this suggests differentially high fluid to rock ratios and relatively weak pathways for further vertical transport into higher levels of the storage complex as well as lateral leakage eastward into the mauna ulu staging area for later vertical ascent beneath the upper east rift zone seismicity within the immediately subjacent rocks that form the top of the primary conduit at 6 5 km suggests that this inferred magma rich horizon forms the effective floor of the summit storage complex 3 magma chamber crown intense seismicity over the 1 1 1 9 km depth interval defines an elliptical region in plan view the top of this region has a broad apex with an average major axis of 1 5 km and an average minor axis of 1 1 km producing an aspect ratio of 0 73 this region coincides with the epicentral position of summit vertical displacement maxima during inflationary deformation and is interpreted as a region of intense diking crowning the summit storage complex 4 upper east rift zone pipe from a depth of 5 7 km a cylindrical region of seismicity rises beneath the upper east rift zone to the 1 9 km level where it merges with the subhorizontal upper east rift zone duct this pipe like zone has a mean diameter of 1 4 km and a vertical axis that pierces the surface of the volcano at the intersection of the koae fracture system and the upper east rift zone we suggest this pipe forms a principal connection between the base of the summit storage reservoir and near surface storage compartments and ducts in the upper east rift zone in this role the pipe is suggested to have contributed heavily to mauna ulu s magma supply during 1969 1974 the model of magma transport and storage thus constructed provides a context in which other types of data e g ground deformation and electrical conductivity may be interpreted as well as a means of refining petrological inferences based on lava chemistry

observations of volcanic tremor at mount st helens volcano digital recordings of ground motion during tremor episodes accompanying eruptions at mount st helens volcano in the state of washington on august 7 and october 16 18 1980 are studied the spectra of the vertical component waveforms contain at least two dominant peaks at 1 0 and 1 3 hz for all events recorded during both eruptions that were studied spectra of horizontal ground motion show peaks at 0 9 and 1 1 hz the relative amplitude of the two peaks changes between tremor episodes and during single tremor episodes and shows no consistent relation to amplitude of ground motion spectra of long period earthquakes are very similar to those of tremor events suggesting that tremor is composed of many long period earthquakes that occur over a period of time the unique waveform of tremor events observed at mount st helens must be due to a source effect since the relative amplitude of the two dominant peaks changes during tremor episodes the path effect on tremor waveforms is small since there are no peaks in the spectra of waveforms recorded during tectonic earthquakes occurring in the vicinity of mount st helens the consistency of the location of the spectral peaks for the wide range of tremor amplitudes means that there must be a physical length at the source that is constant independent of the amplitude of motion at the source variations in amplitude of motion generated during tremor events must be due to variations in the force driving the tremor amplitudes of ground motion varies between 0 11 and 4 7 m seismic moment rates during the two eruptions are calculated using the model of aki et al 1977 and found to vary between 6 1018 and 1 1020 dynes cm s 1 which are larger than values found by aki et al 1977 who studied amplitudes of shallow tremor events recorded during the october 1963 eruption of kilauea volcano in hawaii study of tremor amplitudes recorded at corvallis oregon leads to the conclusion that tremor accompanying the cataclysmic may 18 1980 eruption was at least one order of magnitude larger in amplitude than tremor during august and october

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

seismogenic magma intrusion before the 2010 eruption of eyjafjallajokull volcano iceland we present relatively relocated earthquake hypocentres for 1000 microearthquakes ml 3 that occurred during the 2 weeks immediately prior to the 2010 march 20 fissure eruption at fimmvor uhals on the flank of eyjafjallajokull volcano in iceland our hypocentre locations lie predominantly in horizontally separated clusters spread over an area of 10 km2 and approximately 4 km below sea level 5 km below the surface seismic activity in the final 4 d preceding the eruption extended to shallower levels 2 km below sea level and propagated to the surface at the fimmvor uhals eruption site on the day the eruption started we demonstrate using synthetic data that the observed apparent 1 km vertical elongation of seismic clusters is predominantly an artefact caused by only small errors 0 01 0 02 s in arrival time data where the signal to noise ratio was sufficiently good to make subsample arrival time picks by cross correlation of both p and s wave arrivals the mean depth of 103 events in an individual cluster were constrained to 3 84 0 06 km epicentral locations are significantly less vulnerable to arrival time errors than are depths for the seismic monitoring network we used within clusters of typically 100 recorded earthquakes most of the arrivals exhibit similar waveforms and identical patterns of p wave first motion polarities across the entire monitoring network the clusters of similar events comprise repetitive sources in the same location with the same orientations of failure probably on the same rupture plane the epicentral clustering and similarity of source mechanisms suggest that much of the seismicity was generated at approximately static constrictions to magma flow in an inflating sill complex these constrictions may act as a form of valve in the country rock which ruptures when the melt pressure exceeds a critical level then reseals after a pulse of melt has passed through this would generate recurring similar source mechanisms on the same weak fault plane as the connection between segments of the sill system is repeatedly refractured in the same location we infer that the magmatic intrusion causing most of the seismicity was likely to be a laterally inflating complex of sills at about 4 km depth with seismogenic pinch points occurring between aseismic compartments of the sills or between adjacent magma lobes as they inflated during the final 4 d preceding the eruption onset between 22 30 and 23 30 utc on 2010 march 20 the seismicity suggests that melt progressed upwards to a depth of 2 km this seismicity was probably caused by fracturing of the country rock at the margins of the propagating dyke subsequently on the morning of the eruption a dyke propagated eastward from the region of precursory seismic activity to the fimmvor uhals eruption site

three dimensional seismic velocity structure of mauna loa and kilauea volcanoes in hawaii from local seismic tomography we present a new three dimensional seismic velocity model of the crustal and upper mantle structure for mauna loa and kilauea volcanoes in hawaii our model is derived from the first arrival times of the compressional and shear waves from about 53 000 events on and near the island of hawaii between 1992 and 2009 recorded by the hawaiian volcano observatory stations the vp model generally agrees with previous studies showing high velocity anomalies near the calderas and rift zones and low velocity anomalies in the fault systems the most significant difference from previous models is in v p vs structure the high vp and high v p vs anomalies below mauna loa caldera are interpreted as mafic magmatic cumulates the observed low vp and high v p vs bodies in the kaoiki seismic zone between 5 and 15 km depth are attributed to the underlying volcaniclastic sediments the high vp and moderate to low vp vs anomalies beneath kilauea caldera can be explained by a combination of different mafic compositions likely to be olivine rich gabbro and dunite the systematically low vp and low vp vs bodies in the southeast flank of kilauea may be caused by the presence of volatiles another difference between this study and previous ones is the improved vp model resolution in deeper layers owing to the inclusion of events with large epicentral distances the new velocity model is used to relocate the seismicity of mauna loa and kilauea for improved absolute locations and ultimately to develop a high precision earthquake catalog using waveform cross correlation data 2014 american geophysical union all rights reserved

joint analysis of geodetic and earthquake fault plane solution data to constrain magmatic sources a case study from kīlauea volcano abstract a joint analysis of geodetic and seismic datasets from k lauea volcano during a period of magmatic unrest in 2006 demonstrates the effectiveness of this combination for testing and constraining models of magma dynamics for a complex multi source system at the end of 2003 k lauea s summit began a four year long period of inflation due to a surge in magma supply to the volcano in 2006 for the first time since 1982 k lauea s southwest rift zone swrz also experienced inflation to investigate the characteristics of active magma sources and the nature of their interactions with faults in the swrz during 2006 we integrate through coulomb stress modeling contemporary geodetic data from insar and gps with a new catalogue of double couple fault plane solutions for volcano tectonic earthquakes we define two periods of inflation during 2006 based on the rate of deformation measured in daily gps data spanning february to 15 march 2006 period 1 and 16 march to 30 september 2006 period 2 insar data for these two periods are inverted to determine the position change in size and shape of inflation sources in each period our new models are consistent with microseismic activity from each period they suggest that during period 1 deformation in the swrz can be explained by pressurization of magma in a spherical reservoir beneath the south caldera and that during period 2 magma was also aseismically intruded farther to the southwest into the swrz along a sub horizontal plane our coulomb stress analysis shows that the microseismicity recorded in the swrz is induced by overpressurization of the south caldera reservoir and not by magma intrusion into the swrz this study highlights the importance of a joint analysis of independent geophysical datasets to fully constrain the nature of magma accumulation

analysis of the microseismicity induced by a fluid injection in a granitic rock mass the microseismicity induced by a fluid injection at a depth of 443 m in a granitic rock mass has been monitored with a 16 station network the location of the five events observed on the near totality of the network suggests that flow away from the well occurred along a preexisting fracture nearly parallel to the maximum horizontal principal stress direction and not along the fractures observed at the wellbore focal mechanisms of these events are coherent with shear motions along fissures which intersect the main flow path a difficulty has been encountered in the determination of source parameters from spectral analysis of signals because of attenuation effects indeed for uncorrected spectra the corner frequency was found to decrease as the source to station distance increased this demonstrates the effect of attenuation on the signals and therefore the necessity of correcting spectra for attenuation effects before estimating source parameters

comparison of dike intrusions in an incipient seafloor spreading segment in afar ethiopia seismicity perspectives 1 oceanic crust is accreted through the emplacement of dikes at spreading ridges but the role of dike intrusion in plate boundary deformation during continental rupture remains poorly understood between 2005 and 2009 the 70 km long dabbahu manda hararo rift segment in ethiopia has experienced 14 large volume dike intrusions 9 of which were recorded on temporary seismic arrays a detailed comparison of the seismic characteristics of the seismically monitored dikes is presented with implications for dike intrusion processes and magmatic plumbing systems all of the migrating swarms of earthquakes started from a 80 of energy is released during the propagation phase with minimal seismic energy release after the dike propagation ceases we interpret that faulting and graben formation above the dikes occurs hours after the passage of the dike tip coincident with the onset of low frequency earthquakes dike lengths show no systematic reduction in length with time suggesting that topographic loading and stress barriers influence dike length as well as changes in tectonic stress the propagation velocities of all the dikes follow a decaying exponential northward propagating dikes had faster average velocities than those that propagated southward suggesting preconditioning by the 2005 megadike or ongoing heating from a subcrustal magma source north of the midsegment

volcano deformation and eruption forecasting recent advances in global positioning system gps tilt and interferometric synthetic aperture radar insar have greatly increased the availability of volcano deformation data these measurements combined with appropriate source models can be used to estimate magma chamber depth and to provide information on chamber shape and volume change however kinematic models cannot constrain magma chamber volume and provide no predictive

episodicity of seismicity accompanying melt intrusion into the crust 1 microseismicity from a dike intruding the mid crust of iceland occurs episodically on fractures orientated parallel to the dike plane we interpret it as caused by fragments of chilled magma being broken and pushed along the conduit by melt flow laboratory experiments on basalt samples under shear strains of 10 4show that the shear strength of a sample cooled through the glass transition initially increases to a maximum at 0 7 homologous temperature but subsequently decreases until failure at 0 58 homologous temperature we interpret the failure as due to the connection of microcracks episodicity in microseismicity on timescales of hours to days can arise from a cycle in which magma in 0 1 0 5 meter thick dikes first cools and becomes stronger but then weakens along the dike margins with continued cooling against the country rock continued pressure of magma from below may then cause failure along dike parallel fractures

rates of similar micro earthquakes comparison between campi flegrei southern italy and other volcanic areas abstract the precise relocation of micro earthquakes using waveform cross correlation is an efficient tool for defining the spatial characteristics of seismogenic structures in volcanic areas to be applied and to provide meaningful results the technique requires however the presence of sufficient amounts of similar events we examined about 870 earthquakes recorded at the campi flegrei cf caldera by a temporary digital network during the end of the 1982 1984 bradiseismic crisis the classification of these earthquakes indicates a surprising low amount of similar events especially according to the clustered aspect of the seismicity the relocation technique allows only to identify 3 elongated patterns that may be interpreted as small faults which are dipping inward toward the center of the caldera to determine up to which point this low similarity rate is unusual we examined the rates for several data sets coming from various volcanic areas hawaii mount pinatubo philippines and piton de la fournaise la reunion island the results show for all areas percentages of similar events significantly higher than for cf and indicate that the low rate observed there is not just a matter of low detection threshold or network characteristics at cf most of the seismicity appears to be diffused and generated along small fractures rather than along well defined fault structures the low similarity rate is in good agreement with a seismicity generated in a fractured medium by overpressure in the hydrothermal system and low deviatoric local stress

a constant influx model for dike propagation implications for magma reservoir dynamics 1 most observations of seismicity rate during dike propagation on basaltic volcanoes show 1 rate stationarity despite possible variations of the dike tip velocity 2 frequent lack of clear and monotonic hypocenter migration following dike propagation and 3 event occurrences located backward with respect to the dike tip position on these bases the origin of the seismicity contemporary to dike intrusion within basaltic volcanoes cannot be solely related to the crack tip propagation seismicity rather appears to be the response of the edifice itself to the volumetric deformation induced by the magma intruding the solid matrix the volume change induced into the volcano edifice over time by the intruding magma is equal to the magma flux injected into the dike from the reservoir the consequence of this is that the stationary seismicity rate observed during the intrusion is a proxy for the magma flux withdrawn from the reservoir we consider a two phase dike propagation model including a first vertical propagation followed by a lateral migration along a lithological discontinuity we explore 1 under which geophysical conditions the vertical dike is fed at constant flow rate of magma and 2 dike propagation patterns implications entailed by constant volumetric flux on the piton de la fournaise volcano case study suggest a minimum size for the magma reservoir of about 1 km3 and a maximum value for the initial magma reservoir overpressure of about 2 2 mpa considering similar magma inflow rates during vertical and lateral dike propagation phases we reproduce independent estimates of propagation velocities rise times and injected volumes when applying the model to the august 2003 piton de la fournaise eruption

dike induced deformation and martian graben systems abstract the tharsis region of mars is characterized by large volcanic and tectonic centers with distinct sets of graben systems many of the radially oriented grabens have been inferred to form in response to intrusion of magmatic dikes this interpretation is based primarily upon early physical and numerical boundary element models that were developed originally to understand surface deformation associated with dike emplacement on earth in this study we constructed and analyzed two dimensional discrete element models to test the hypothesis of shallow dike emplacement and widening as a primary mechanism for the production of grabens on mars in particular our models are designed to explore the extent to which a widening subsurface dike in the absence of regional extension or pre existing faults will induce near surface graben formation the use of discrete element models allows for the permanent deformation and material heterogeneity to be captured as opposed to boundary element models that are limited by an assumption of homogeneous elastic behavior our analyses consider both homogeneous materials as well as mechanical stratification the results indicate that forcible widening of a dike alone is unlikely to produce grabens at the surface furthermore estimates of subsurface dike widths and emplacement depths based solely on measurements of surface graben widths may significantly over or underestimate actual parameters finally the model results suggest that the ability to distinguish between fault induced or dike induced graben formation mechanisms may not be possible unless the subsurface mechanical stratigraphy can be well characterized

dynamics and rapid migration of the energetic 2008 2009 yellowstone lake earthquake swarm 1 yellowstone national park experienced an unusual earthquake swarm in december january 2008 2009 that included rapid northward migration of the activity at 1 km per day and shallowing of the maximum focal depths from 12 to 2 km beneath northern yellowstone lake the swarm consisted of 811 earthquakes 0 5 mw 4 1 aligned on a n s 12 km long vertical plane of hypocenters the largest earthquake of the swarm had a 50 tensile crack opening source determined by a full waveform inversion that we interpret as a magmatic expansion component in addition gps data revealed e w crustal extension coincident with the swarm modeling of gps and seismic data is consistent with e w opening of 10 cm on a n s striking vertical dike our interpretation is that the swarm was induced by magmatic fluid migration or propagation of a poroelastic stress pulse along a pre existing fracture zone

temporal change of upper crustal vp vs ratios with volcanic evolution in redoubt volcano abstract volcanic activities accompany changes in the physical and chemical properties of the medium the ratio between p and s wave velocities v p v s is sensitive to the medium property changes we investigate temporal variations of the v p v s ratios in the upper crust around redoubt volcano in the 1989 2014 time period using the traveltimes of local earthquakes the v p v s ratios reached 2 0 immediately prior to the 1989 1990 and 2009 eruptions these high v p v s ratios may be associated with partial melts in the edifice the v p v s ratios rapidly decreased to 1 7 during the 1989 1990 and 2009 eruptions due to decreasing temperatures fluids and pore pressures and increasing effective stresses after melt eruptions and gas emission the change rates of the v p v s ratios showed evident spatial distributions the v p v s ratios increased at a rate of 0 025 0 003 yr 1 below the 2009 vent during the inter eruption period between the 1989 1990 and 2009 eruptions due to an increase in the temperature which may be associated with the recharge of the magma in the lower crust the increase rate of the v p v s ratios was as low as 0 005 0 001 yr 1 in the regions located away from the eruption site the v p v s ratios appear to have increased consistently at a rate of 0 017 0 004 yr 1 since the 2009 eruption

mechanism diversity of the loma prieta aftershocks and the mechanics of mainshock aftershock interaction the diverse aftershock sequence of the 1989 loma prieta earthquake is inconsistent with conventional models of mainshock aftershock interaction because the aftershocks do not accommodate mainshock induced stress changes instead the sense of slip of the aftershocks is consistent with failure in response to a nearly uniaxial stress field in which the maximum principal stress acts almost normal to the mainshock fault plane this orientation implies that i stress drop in the mainshock was nearly complete ii mainshock induced decreases of fault strength helped were important in controlling the occurrence of after shocks and iii mainshock rupture was limited to those sections of the fault with preexisting shear stress available to drive fault slip

precursory swarms of long period events at redoubt volcano 1989 1990 alaska their origin and use as a forecasting tool abstract during the eruption of redoubt volcano from december 1989 through april 1990 the alaska volcano observatory issued advance warnings of several tephra eruptions based on changes in seismic activity related to the occurrence of precursory swarms of long period lp seismic events dominant period of about 0 5 s the initial eruption on december 14 occurred after 23 years of quiescence and was heralded by a 23 hour swarm of lp events that ended abruptly with the eruption after a series of vent clearing explosions over the next few days dome growth began on december 21 another swarm with lp events similar to those of the first began on the 26th and ended in a major tephra eruption on january 2 eruptions continued over the next two weeks and then ceased until february 15 when a large eruption initiated a long phase of repetitive dome building and dome destroying episodes that continued into april warnings were issued before the major events on december 14 and january 2 but as the eruptive sequence continued after january 2 the energy of the swarms decreased and forecasting became more difficult a significant but less intense swarm preceded the february 15 eruption which was not forecast this eruption destroyed the only seismograph on the volcanic edifice and stymied forecasting until march 4 when the first of three new stations was installed within 3 km of the active vent from march 4 to the end of the sequence on april 21 there were eight eruptions six of which were preceded by detectable swarms of lp events although weak these swarms provided the basis for warnings issued before the eruptions on march 23 and april 6 the initial swarm on december 13 had the following features 1 short duration 23 hours 2 a rapidly accelerating rate of seismic energy release over the first 18 hours of the swarm followed by a decline of activity during the 5 hours preceding the eruption 3 a magnitude range from 0 4 to 1 6 4 nearly identical lp signatures with a dominant period near 0 5 s 5 dilatational first motions everywhere and 6 a stationary source location at a depth of 1 4 km beneath the crater this occurrence of long period events suggests a model involving the interaction of magma with groundwater in which magmatic gases steam and water drive a fixed conduit at a stationary point throughout the swarm the initiation of that sequence of events is analogous to the failure of a pressure relief valve connecting a lower supercharged magma dominated reservoir to a shallow hydrothermal system a three dimensional model of a vibrating fluid filled crack recently developed by chouet is found to be compatible with the seismic data and yields the following parameters for the lp source crack length 280 380 m crack width 140 190 m crack thickness 0 05 0 20 m crack stiffness 100 200 sound speed of fluid 0 8 1 3 km s compressional wave speed of rock 5 1 km s density ratio of fluid to rock 0 4 and ratio of bulk modulus of fluid to rigidity of rock 0 03 0 07 the fluid filled crack is excited intermittently by an impulsive pressure drop that varies in magnitude within the range of 0 4 to 40 bar such disturbance appears to be consistent with a triggering mechanism associated with choked flow conditions in the crack

precise relocation of earthquakes following the 15 june 1991 eruption of mount pinatubo philippines 1 the 15 june 1991 climactic eruption of mount pinatubo philippines was followed by intense seismicity that remained at a high level for several months we located 10 839 events recorded between 1 july and mid december 1991 in contrast to the preeruptive seismicity which was focused in two groups below the summit area posteruptive events were widely distributed below and around the volcano the classification of the events indicates the presence of several large multiplets and the application of relative relocation techniques to the similar events by calculating high precision delays between traces outlines a number of clear seismogenic structures we used different methods to confirm the validity of our results these tests indicate that reliable features can be detected with a small monitoring network while the main cluster of activity can be attributed to an intrusive process starting from below the 15 june crater the volcanic origin of the seismic activity in the other areas is more difficult to establish away from the summit relocations define streaks or planes which are oriented predominantly southwest northeast with in several cases the presence of northwest southeast conjugate structures most of the composite focal mechanisms that we could determine indicate predominantly strike slip right lateral faulting our results indicate that most of the seismicity that occurred after the 15 june eruption is related to the east west regional compressional stress field related to the subduction we suggest that the regional stress field induces seismicity along new or preexisting faults in the medium surrounding the volcano where the stress field was locally disturbed by the volcanic eruption

three dimensional p wave velocity structure and precise earthquake relocation at great sitkin volcano alaska abstract waveform cross correlation with bispectrum verification is combined with double difference tomography to increase the precision of earthquake locations and constrain regional 3d p wave velocity heterogeneity at great sitkin volcano alaska from 1999 through 2005 the alaska volcano observatory avo recorded 1700 earthquakes in the vicinity of great sitkin including two m l 4 3 earthquakes that are among the largest events in the avo catalog the majority of earthquakes occurred during 2002 and formed two temporally and spatially separate event sequences the first sequence began on 17 march 2002 and was centered 20 km west of the volcano the second sequence occurred on the southeast flank of great sitkin and began 28 may 2002 it was preceded by two episodes of volcanic tremor earthquake relocations of this activity on the southeast flank define a vertical planar feature oriented radially from the summit and in the direction of the assumed regional maximum compressive stress due to convergence along the alaska subduction zone this swarm may have been caused or accompanied by the emplacement of a dike relocations of the mainshock aftershock sequence occurring west of great sitkin are consistent with rupture on a strike slip fault tomographic images support the presence of a vertically dipping fault striking parallel to the direction of convergence in this region the remaining catalog hypocenters relocate along discrete features beneath the volcano summit here low p wave velocities possibly indicate the presence of magma beneath the volcano

strike slip faulting during the 2014 barðarbunga holuhraun dike intrusion central iceland over a 13 day period magma propagated laterally from the subglacial bar arbunga volcano in the northern rift zone iceland it created 30 000 earthquakes at 5 7 km depth along a 48 km path before erupting on 29 august 2014 the seismicity which tracked the dike propagation advanced in short bursts at 0 3 4 7 km h separated by pauses of up to 81 h during each surge forward seismicity behind the dike tip dropped moment tensor solutions from the leading edge show exclusively left lateral strike slip faulting subparallel to the advancing dike tip releasing accumulated strain deficit in the brittle layer of the rift zone behind the leading edge both left and right lateral strike slip earthquakes are observed the lack of non double couple earthquakes implies that the dike opening was aseismic

aftershocks of an m 4 2 earthquake in hawaii and comparison with long term studies of the same volume abstract study of the aftershocks recorded in a 3 hr period after a 4 2 magnitude event on the east rift zone of kilauea volcano hawaii on 12 april 1982 shows that the aftershocks occurred on different planes than the main shock probably as a result of stress redistribution the aftershock locations are probably controlled by preexisting structures this study also suggests that these relatively small aftershocks occurred in the same seismicity patterns as larger events recorded in the same volume over a period of 10 yr slips on most of the aftershocks and the main shock are in the same direction perpendicular to the east rift zone as has been found in studies of other larger earthquakes however fault plane solutions varied more as did the tensional axes and several of the smaller events showed movement in the opposite direction from the main shock and the rest of the aftershocks suggesting some rebound was occurring near the edges of the aftershock zone because ten times as much energy was released in the aftershocks in a narrow linear region as elsewhere and since the main shock epicenter was oceanward of all the aftershocks we suggest that rupture began at the main shock hypocenter and propagated landward implying an almost one dimensional fault for the aftershocks the relationship between moment and magnitude was log m 0 1 18 0 17 m l 17 3 0 17 differences in amplification lead to site differences of up to 0 8 units in local magnitude and 1 5 orders of magnitude in energy release these correlated somewhat with station time corrections in that the stations with the longest delay times also had greatest amplification

motion of kilauea volcano during sustained eruption from the puu oo and kupaianaha vents 1983 1991 kilauea erupted almost continuously from january 1983 through 1991 although the summit began subsiding during the rift zone dike intrusion that initiated this eruption remarkably steady ground surface motions began in late 1983 after a magnitude 6 6 earthquake beneath the slopes of nearby mauna loa volcano and continued until the onset of brief upper east rift zone earthquake swarms in late 1990 during these 7 years the summit and upper rift zones subsided up to 10 11 and 4 8 cm yr 1 respectively and summit baselines contracted up to 6 cm yr 1 baselines directed northward from the summit to stations on mauna loa extended at rates up to 7 cm yr 1 and a baseline from south of the summit to mauna loa extended 4 cm yr 1 much of this extension is inconsistent with deformation caused solely by summit magma reservoir collapse and more likely reflects rifting as the south flank of the volcano moved seaward from the summit and rift zones farther from the summit baselines crossing the south flank extended up to 2 cm yr 1 and a south flank tide gauge rose 2 cm yr 1 the lower east rift zone 40 50 km from the summit subsided about 2 cm yr 1 motion on kilauea then is broadly consistent with slip along low angle south flank faults generating subsidence that is focused at the summit and along the rift system behind the faulting and uplift along the coastal south flank ahead of it dislocation models that combine these elements show that much of kilauea s edifice migrated seaward producing ground surface motions along the south flank of up to about 6 cm yr 1 the magnitude 6 1 earthquake of 1989 punctuated these motions along the eastern south flank producing more than 25 cm of seaward displacement and 15 km east of the epicenter up to 24 cm of subsidence south of the lower east rift zone unlike the magnitude 7 2 south flank earthquake of 1975 the 1989 event was preceded neither by summit magma reservoir inflation nor by rift zone dike intrusions and accompanying compression of the south flank deformation was probably caused by the weight of the volcanic overburden and by ongoing dilation and slip within the rift system

the relationship between earthquake swarms and magma transport kilauea volcano hawaii a detailed investigation of earthquake locations and focal mechanisms for swarms associated with intrusive events at kilauea volcano hawaii further illuminates the relationships among stress state faulting and magma transport we determine the earthquake locations and mechanisms using a three dimensional crustal model to improve their accuracy and consistency swarms in kilauea s upper east and southwest rift zones from the years 1980 through 1982 provide clear evidence for the propagation and or dilation of dikes focal mechanisms are predominantly strike slip and the faulting and inferred dike orientations can be interpreted quite consistently in terms of the model ofhill 1977 stresses induced by the summit magma reservoir system strongly control faulting and magma transport in the rift zones close to the summit

seismicity and deformation induced by magma accumulation at three basaltic volcanoes we analyzed the evolution of volcano tectonic vt seismicity and deformation at three basaltic volcanoes kilauea mauna loa piton de la fournaise during phases of magma accumulation we observed that the vt earthquake activity displays an accelerating evolution at the three studied volcanoes during the time of magma accumulation at the same times deformation rates recorded at the summit of kilauea and mauna loa volcanoes were not accelerating but rather tend to decay to interpret these observations we propose a physical model describing the evolution of pressure produced by the accumulation of magma into a reservoir this variation of pressure is then used to force a simple model of damage where damage episodes are equivalent to earthquakes this model leads to an exponential increase of the vt activity and to an exponential decay of the deformation rate during accumulation phases seismicity and deformation data are well fitted by such an exponential model the time constant deduced from the exponential increase of the seismicity is in agreement with the time constant predicted by the model of magma accumulation this vt activity can thus be a direct indication of the accumulation of magma at depth and therefore can be seen as a long term precursory phenomenon at least for the three studied basaltic volcanoes unfortunately it does not allow the prediction of the onset of future eruptions as no diverging point i e critical time is present in the model

a quantitative approach to the dike intrusion process inferred from a joint analysis of geodetic and seismological data for the 1998 earthquake swarm off the east coast of izu peninsula central japan 1 a series of earthquake swarms off the east coast of izu peninsula central japan is typically associated with dike intrusion around active volcanoes numerous studies in this region have documented the seismic activity and ground deformations without fully resolving the process of dike intrusion this study involves a joint analysis of geodetic and seismic data from the most recent major activity in this region occurring in 1998 to reveal the process of dike intrusion quantitatively we combine data from a dense gps array including 10 temporary stations with seismic analysis published previously we estimate the location of the dikes from seismic data and the volume of intruded magma from geodetic data combined analysis of both data sets enables us to reveal the kinematic process of dike intrusion associated with the 1998 earthquake swarm the process of dike intrusion is quantitatively modeled using the time evolution of recorded dike volume and the use of seismic hypocenters as an indicator of the site of instantaneous dike intrusion on the basis of these observations we propose the following process of the dike intrusion the magma rose upward through a pathway aligned vertically and created a dike when it lost buoyancy we also evaluate the dike intrusion process quantitatively using a model of a circular dike that grows under a continuous magma supply from a deep magma reservoir from the observational data we infer the time evolution in the dike shape pressure distribution and magma viscosity in the dike the acquired viscosity increases over time and it may be reasonable because magma cools gradually however its value is too large compared to typical basaltic magma expected in this region it may represent magma within the dike that is nearly solidified otherwise the magma is supplied intermittently and the dike growth is mainly controlled by the magma supply rate from a deep reservoir the quantitative description of the dike intrusion process in nature described in this study is very rare and our results provide constraints on several parameters that have not been solved in many previous theoretical studies on the dike intrusion process

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

earthquake classification location and error analysis in a volcanic environment implications for the magmatic system of the 1989 1990 eruptions at redoubt volcano alaska abstract determination of the precise locations of seismic events associated with the 1989 1990 eruptions of redoubt volcano posed a number of problems including poorly known crustal velocities a sparse station distribution and an abundance of events with emergent phase onsets in addition the high relief of the volcano could not be incorporated into the hypoellipse earthquake location algorithm this algorithm was modified to allow hypocenters to be located above the elevation of the seismic stations the velocity model was calibrated on the basis of a posteruptive seismic survey in which four chemical explosions were recorded by eight stations of the permanent network supplemented with 20 temporary seismographs deployed on and around the volcanic edifice the model consists of a stack of homogeneous horizontal layers setting the top of the model at the summit allows events to be located anywhere within the volcanic edifice detailed analysis of hypocentral errors shows that the long period lp events constituting the vigorous 23 hour swarm that preceded the initial eruption on december 14 could have originated from a point 1 4 km below the crater floor a similar analysis of lp events in the swarm preceding the major eruption on january 2 shows they also could have originated from a point the location of which is shifted 0 8 km northwest and 0 7 km deeper than the source of the initial swarm we suggest this shift in lp activity reflects a northward jump in the pathway for magmatic gases caused by the sealing of the initial pathway by magma extrusion during the last half of december volcano tectonic vt earthquakes did not occur until after the initial 23 hour long swarm they began slowly just below the lp source and their rate of occurrence increased after the eruption of 01 52 ast on december 15 when they shifted to depths of 6 to 10 km after january 2 the vt activity migrated gradually northward this migration suggests northward propagating withdrawal of magma from a plexus of dikes and or sills located in the 6 to 10 km depth range precise relocations of selected events prior to january 2 clearly resolve a narrow steeply dipping pencil shaped concentration of activity in the depth range of 1 7 km which illuminates the conduit along which magma was transported to the surface a third event type named hybrid which blends the characteristics of both vt and lp events originates just below the lp source and may reflect brittle failure along a zone intersecting a fluid filled crack the distribution of hybrid events is elongated 0 2 0 4 km in an east west direction this distribution may offer constraints on the orientation and size of the fluid filled crack inferred to be the source of the lp events

fracking in tight shales what is it what does it accomplish and what are its consequences fracking is a popular term referring to hydraulic fracturing when it is used to extract hydrocarbons we distinguish between low volume traditional fracking and the high volume modern fracking used to recover large volumes of hydrocarbons from shales shales are fine grained rocks with low granular permeabilities during the formation of oil and gas large fluid pressures are generated these pressures result in natural fracking and the resulting fracture permeability allows oil and gas to escape reducing the fluid pressures these fractures may subsequently be sealed by mineral deposition resulting in tight shale formations the objective of modern fracking is to reopen these fractures and or create new fractures on a wide range of scales modern fracking has had a major impact on the availability of oil and gas globally however there are serious environmental objections to modern fracking which should be weighed carefully against its benefits

high resolution locations of triggered earthquakes and tomographic imaging of kilauea volcano s south flank 1 the spatiotemporal patterns of seismicity beneath kilauea s south flank give insight to the structure and geometry of the decollement on which large tsunamigenic earthquakes have occurred and its relation to slow slip events sses which have been observed every 1 to 2 years since 1997 in order to record earthquakes triggered by a sse that was predicted to occur in march 2007 a temporary network of 20 seismometers was deployed on kilauea s south flank termed the seq network while the sse did not occur until 17 june 2007 theseq network recorded over 3000 earthquakes including those triggered by the sse we relocate hypocenters of volcano tectonic earthquakes and invert for p and s wave velocity structure using waveform cross correlation and double difference tomography using data from the seq network and the permanent hawaii volcano observatory network hvo data with additional data from other previous temporary arrays the best constrained hypocenters recorded by both the seq and hvo networks indicate the decollement as a subhorizontal layer of seismicity at 8 km depth less than 1 km thick in most areas with the western portion of the decollement dipping to the southeast the seismicity triggered by the june 2007 sse includes over 400 earthquakes overlapping with the southern edge of the decollement seismicity a shallower swarm of earthquakes also occurred between 2 and 7 km depth in april 2007 near apua point and may have been indirectly triggered by the mw 8 1 solomon islands earthquake at 6000 km distance which occurred 48 h prior to the beginning of the swarm

constructing the upper crust of the mid atlantic ridge a reinterpretation based on the puna ridge kilauea volcano the volcanic morphology of a number of segments of the slow spreading mid atlantic ridge mar have been reinterpreted based on our understanding of dike emplacement dike propagation and eruption at the east rift zone of kilauea volcano hawaii and its submarine extension the puna ridge the styles of volcanic eruption at the submarine puna ridge are remarkably similar to those of the axial volcanic ridges avrs constructed on the median valley floor of the mar we use this observation to relate volcanic processes occurring at kilauea volcano to the mar we now consider that volcanic features e g seamounts and lava terraces built on the flanks of the avrs are secondary features that are fed from lava tubes or channels not primary features fed directly from an underlying dike we examine simple models of pipe flow and conclude that lava tubes can transport lava down the flanks of submarine rifts to build all of the volcanic features observed there in addition deep water lava tubes are strong enough to withstand the pressures of a few megapascals that the building of a volcanic structure 150 m high at the end of the tube would generate the volumes of individual volcanic terraces and seamounts on the puna ridge and at the mar are large 0 1 1 km3 and similar to the volumes of lava flows that are broadly distributed at the subaerial east rift zone of kilauea this striking difference in the volcanic morphology on a scale of 1 2 km producing terraces and seamounts underwater and low relief flows on land must be related to the enhanced cooling and to the greater mechanical stability of tubes in the submarine environment we suggest that at the mar a crustal magma reservoir most likely located beneath shallow flat sections of the segment provides magma to the rift axis through dikes that propagate laterally tens of kilometers the zone of dike intrusion at least in the neighborhood of the magma body is likely narrower than the width resurfaced by flows yielding a crustal structure that has a rapid vertical transition from lavas to sheeted dikes at segment ends the zone of dike intrusion is likely to be wider giving a resulting structure with a more gradual transition from lavas to dikes

non double couple earthquake mechanisms at the hengill grensdalur volcanic complex southwest iceland the hengill grensdalur area in iceland generates frequent small non double couple earthquakes with explosive volumetric components we collected high quality three component digital recordings of 4 000 earthquakes on a purpose designed 32 station network in 1991 and determined focal mechanisms for 100 of the best recorded earthquakes by inverting amplitude ratios many of the mechanisms are consistent within the errors with simultaneous shear and tensile faulting with tensile faults parallel to the local spreading ridge and shear faulting similar to that in the south iceland transform fault zone some events cannot be explained by this model however and require other processes such as crack closing and partial compensation of tensile cracks by fluid flow

inversion for the composite moment tensor abstract the composite moment tensor is defined in analogy to the composite focal mechanism as the averaged representative seismic moment tensor characteristic for a focal area under study in contrast to the composite focal mechanism which provides information on shear faulting the composite moment tensor can provide additional information on nonshear rupture mode and on physical conditions along the fault the composite moment tensor is calculated by a joint inversion of multiple earthquakes associated with the same fault system and displaying a similar focal mechanism the method utilizes amplitudes of p and or s waves or full waveforms because the inversion is linear it is fast and applicable to datasets of many earthquakes the method is particularly suitable for the analysis of microseismicity earthquake swarms or aftershock sequences where observations of multiple earthquakes are available the composite moment tensor can be retrieved even when the station configuration or data quality prevent inversion for the full moment tensors of individual earthquakes

late cenozoic uplift of the eastern cordillera bolivian andes abstract this paper analyses late cenozoic uplift in the bolivian andes using the morphology of well preserved regional paleosurfaces in the eastern cordillera that define three axially draining braided river catchments that formed between 12 and 9 ma rock uplift since the formation of the paleodrainage systems which has been quantified using four different methods is 1705 695 m with a mean erosion of 230 90 m as a consequence of entrenchment of the drainage systems the lack of faulting or tilting in the regions immediately farther west strongly suggest that rock uplift of the paleodrainage systems also extends to the western margin of the eastern cordillera balanced structural cross sections require crustal deformation at depth beneath the eastern cordillera in order to accommodate underthrusting of the brazilian shield beneath the thin skinned fold and thrust belt on the eastern margin of the bolivian andes in this case the observed uplift of the eastern cordillera is easily explained by sliding up a ramp in the major decollement dipping in the range 4 16 w as a consequence of the observed 60 110 km of shortening farther east in the subandean zone contemporaneous uplift of the western margin of the eastern cordillera is easily explained in terms of crustal thickening as a result of ductile squeezing in the lower crust accommodating at depth the subandean shortening it remains unclear how this uplift relates to that of the regions farther west in the altiplano and volcanic arc except that uplift in the eastern cordillera coincides with a phase of intense shortening in the northern altiplano commencing at 9 5 ma and continuing to 2 7 ma and possibly younger