record of late holocene debris avalanches and lahars at iliamna volcano alaska abstract iliamna volcano is a 3053 meter high glaciated stratovolcano in the southern cook inlet region of alaska and is one of seven volcanoes in this region that have erupted multiple times during the past 10 000 yr prior to our studies of iliamna volcano little was known about the frequency magnitude and character of holocene volcanic activity here we present geologic evidence of the most recent eruptive activity of the volcano and provide the first outline of late holocene debris avalanche and lahar formation iliamna has had no documented historical eruptions but our recent field investigations indicate that the volcano has erupted at least twice in the last 300 yr clay rich lahar deposits dated by radiocarbon to 1300 and 90 yr bp are present in two major valleys that head on the volcano these deposits indicate that at least two large possibly deep seated flank failures of the volcanic edifice have occurred in the last 1300 yr noncohesive lahar deposits likely associated with explosive pyroclastic eruptions date to 2400 1300 1500 300 and debris avalanche deposits from recent and historical small volume slope failures of the hydrothermally altered volcanic edifice cover most of the major glaciers on the volcano although these deposits consist almost entirely of hydrothermally altered rock debris and snow and ice none of the recently generated debris avalanches evolved to lahars a clay rich lahar deposit that formed

reservoir fluid substitution effects on seismic profile interpretation a physical modeling experiment p wave seismic surveys are performed on realistic physical models of a reservoir formed of interbedded sand and shale layers and filled with gas water and oil they show characteristic behaviour which can be used to distinguish between fluids with significant implications for the interpretation of time lapse experiments discontinuous reflections originate in gas filled reservoirs with widely varying amplitude compared to oil or water filled reservoirs anomalous changes in seismic amplitude difference attributes for reflections within the reservoir are seen for gas oil substitution oil water substitution results in only weak variations of reservoir elastic properties thus amplitude difference attributes may be unsuitable for monitoring changes in oil water saturation however direct differences between the time traces are strong on time lapse sections strong amplitude difference anomalies do not necessarily correspond to the region where the fluid variations occur this is significant for monitoring oil field development by water injection

business and technology challenges for 4d seismic reservoir monitoring 4d seismic reservoir monitoring is a relatively new technology that consists of repeating 3d seismic surveys in order to make time lapse images of the fluid and pressure fronts as they move in a subsurface reservoir during hydrocarbon production when successful 4d seismic can locate areas of bypassed oil for new drilling opportunities map out water flooded areas to avoid the costly mistake of drilling new wells into swept zones and identify the geometry and nature of reservoir flow compartments that are key to optimizing hydrocarbon recovery 4d seismic has evolved during the past decade from a series of geophysical field experiments to a practical reservoir monitoring tool that can add significant value to the reservoir management process however it has not yet become a mainstream technology in this article i will discuss some of the business and technology challenges that need to be addressed before 4d seismic can become as widely utilized in the petroleum industry as 3d seismic is today figure 1 shows the geographical areas of the world where most of the industry s 4d seismic activity is located today figure 2 shows the cumulative 4d seismic expenditures to contractor and service companies for the four years 2000 2003 inclusive of a total us 500 million cumulative 4d service expenditures about 400 million 80 has been spent in the north sea 35 million 7 in west africa 30 million 6 in north america 20 million 4 in the far east and 15 million 3 elsewhere this estimate of expenditures is for 4d seismic acquisition processing and interpretation analysis services as determined by a recent study we participated in at the french institute of petroleum figure 1 geographical distribution of current 4d seismic activity figure 2 cumulative expenditures on 4d seismic services to contractor and service companies for 2000 2003 of 500 million cumulative 4d service expenditures about 400

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

shallow earthquake inhibits unrest near chiles cerro negro volcanoes ecuador colombian border magma movement or reservoir pressurisation can drive swarms of low magnitude volcano tectonic earthquakes as well as occasional larger earthquakes m5 on local tectonic faults earthquakes m5 near volcanoes are challenging to interpret in terms of evolving volcanic hazard but are often associated with eruptions and in some cases enhance the ascent of magma we present geodetic observations from the first episode of unrest known to have occurred near chiles and cerro negro de mayasquer volcanoes on the ecuador colombian border a swarm of volcano tectonic seismicity in october 2014 culminated in a mw 5 6 earthquake south of the volcanoes satellite radar data spanning this earthquake detect displacements that are consistent with dextral oblique slip on a reverse fault at depths of 1 4 3 4 km within a ssw nne trending fault zone that last ruptured in 1886 gps station measurements capture 20 days of uplift before the earthquake probably originating from a pressure source 10 15 km south of volcan chiles at depths exceeding 13 km after the mw 5 6 earthquake uplift ceased and the rate of seismicity began to decrease potential mechanisms for this decline in activity include a decrease in the rate of movement of magma into the shallow crust possibly caused by the restriction of fluid pathways our observations demonstrate that an earthquake triggered during volcanic unrest can inhibit magmatic processes and have implications for the hazard interpretation of the interactions between earthquakes and volcanoes

gas emissions from failed and actual eruptions from cook inlet volcanoes alaska 1989 2006 cook inlet volcanoes that experienced an eruption between 1989 and 2006 had mean gas emission rates that were roughly an order of magnitude higher than at volcanoes where unrest stalled for the six events studied mean emission rates for eruptions were 13 000 t d co2 and 5200 t d so2 but only 1200 t d co2 and 500 t d so2 for non eruptive events failed eruptions statistical analysis suggests degassing thresholds for eruption on the order of 1500 and 1000 t d for co2 and so2 respectively emission rates greater than 4000 and 2000 t d for co2 and so2 respectively almost exclusively resulted during eruptive events the only exception being two measurements at fourpeaked while this analysis could suggest that unerupted magmas have lower pre eruptive volatile contents we favor the explanations that either the amount of magma feeding actual eruptions is larger than that driving failed eruptions or that magmas from failed eruptions experience less decompression such that the majority of h2o remains dissolved and thus insufficient permeability is produced to release the trapped volatile phase or both in the majority of unrest and eruption sequences increases in co2 emission relative to so2 emission were observed early in the sequence with time all events converged to a common molar value of c s between 0 5 and 2 these geochemical trends argue for roughly similar decompression histories until shallow levels are reached beneath the edifice i e from 20 35 to 4 6 km and perhaps roughly similar initial volatile contents in all cases early elevated co2 levels that we find at these high latitude andesitic arc volcanoes have also been observed at mid latitude relatively snow free basaltic volcanoes such as stromboli and etna typically such patterns are attributed to injection and decompression of deep co2 rich magma into a shallower chamber and open system degassing prior to eruption here we argue that the c s trends probably represent tapping of vapor saturated regions with high c s and then gradual degassing of remaining dissolved volatiles as the magma progresses toward the surface at these volcanoes however c s is often accentuated due to early preferential scrubbing of sulfur gases the range of equilibrium degassing is consistent with the bulk degassing of a magma with initial co2 and s of 0 6 and 0 2 wt respectively similar to what has been suggested for primitive redoubt magmas

crustal earthquake bursts in california and japan their patterns and relation to volcanoes 1 we analyze 153 bursts of earthquakes in southern california and japan the burst patterns are similar in southern california and japan they fill a spectrum between swarm like sequences without obvious mainshocks and mainshocks with omori law abiding aftershocks in agreement with our previous work the swarm like sequences in japan have more events are more voluminous and tend to expand with time when compared to mainshock aftershock type sequences in both regions we find that the sequences starting with their largest events tend to be much shorter in duration bursts within 50 km of volcanoes are similar in character to those elsewhere except they tend to have longer duration we hypothesize that swarminess is a proxy for fluid pressure redistribution and or aseismic slip driving the seismicity bursts and conversely the mainshock aftershock style sequences have end member behavior that results solely from a cascade of elastic failures the complexity of the spatial seismicity distribution does not correlate with the style of swarm observed indicating that fluid conditions and composition are likely more influential than geometry in determining the patterns we observe

volcano tectonic seismicity at unzen volcano japan 1985 1999 abstract the eruption of unzen volcano in southwestern japan began on november 17 1990 and an extrusion of a dacite lava dome lasted from may 20 1991 until early february 1995 the seismic network operated by the shimabara earthquake and volcano observatory of kyushu university sevo located about 4000 volcano tectonic earthquakes during the period from 1985 to 1999 the seismicity was greatest in the period between one year before the eruption and the start of the lava dome extrusion the hypocenters were mostly distributed within a 12 20 km area on the western side of the volcano an inclined seismic aseismic boundary shallows eastward to the summit probably reflecting the thermal structure beneath the volcano within 4 km west from the summit however the seismicity is very low it was suggested that the high temperature ductile and low q bodies exist there we obtained focal mechanism solutions for about 90 earthquakes among them orientations of p axes for the earthquakes occurring on the upper side of the inclined seismic aseismic boundary suggest a pressure source located below this boundary although most of the focal mechanisms have t axes nearly horizontal in the n s direction consistent with the n s extensional tectonic stress several earthquakes whose focal mechanisms are inconsistent with the tectonic stress were observed within a horizontal distance of 5 km from the summit this is because the pressurization of volcanic gas or magma beneath the summit produced a strong local stress in the summit surroundings

using repeating volcano tectonic earthquakes to track post eruptive activity in the conduit system at redoubt volcano alaska in the year following the end of the 2009 eruption of redoubt volcano alaska four signifi cant swarms of low frequency lowmagnitude m l 0 1 earthquakes occurred at shallow depths beneath the summit because swarms of low frequency lf earthquakes preceded eruptions in 1989 and 2009 the posteruption swarms caused considerable concern and prompted the alaska volcano observatory to raise the monitoring levels on three occasions none of these swarms led to eruptions however and most observers including us initially concluded that the swarms had been caused by minor stress adjustments in the new lava dome or in the surrounding summit glaciers new observations reveal that the shallow lf swarms were accompanied by 2 families of repeating earthquakes at depths between 3 km and 6 km below sea level where the magma storage region is thought to be these mid crustal volcano tectonic vt type earthquakes were identical to earthquakes recorded during the 2009 redoubt eruption more than 6 months earlier focal mechanisms demonstrate that these earthquakes have thrust mechanisms inconsistent with the strike slip nature of regional faulting based on these observations we conclude that they are generated through processes occurring within the magma storage region the concurrence of the repeating vt earthquakes with the shallow lf swarms indicates that the shallow lf earthquakes were also magmatically driven our results emphasize that even brief episodes of low amplitude earthquake activity such as the lf swarms observed at redoubt following the 2009 eruption can be indicative of magmatic activity perhaps more signifi cant however is the demonstration that the conduit system at redoubt remained active intact and capable of transporting heat and fl uids to the surface months after the eruption was considered over

earthquake swarms and dike intrusions off the east coast of izu peninsula central japan abstract relationships between earthquake swarms and dike intrusions are investigated in the monogenetic volcano region off the east coast of the izu peninsula central japan hypocentral distribution of an earthquake swarm associated with the 1989 ito oki submarine eruption and those of eight major earthquake swarms for 7 years before the eruption in the same region are precisely relocated comparison of the hypocentral distribution with a dike model obtained from crustal movement measurements by okada and yamamoto 1991 ensures that hypocentral areas of the earthquake swarms can be used as reliable indicators of intruded dikes the epicentral area of each earthquake swarm shows an elliptic shape with a 3 5 km long axis and a 2 4 km short axis the long axis trending from a nw se to wnw ese direction the total hypocentral distribution of the nine swarms forms a seismic zone of about 20 km long and about 5 km wide with each of the swarm areas overlapping focal migrations from deep 10 km to shallow 3 km depths are found in the two largest events in 1988 and 1989 indicating that dikes propagated from deep to shallow areas in the upper crust these features of the hypocentral distributions suggest that the seismic swarms were induced by dike intrusions which ascended from a deep seated magma reservoir with dike like geometry located beneath the seismic zone solidification time of a dike with thickness comparable to that of the dike model of okada and yamamoto 1 45 m at the bottom of the dike is several days indicating that the dikes inducing the earthquake swarms solidified almost during the swarm period the physical mechanisms of the dike induced earthquake swarms are investigated for the izu region the focal depth migration and fault type of the earthquake swarm suggest that stress change in the region surrounding the dike due to dike emplacement is the most important factor for the cause of the earthquakes

dike induced faulting in rift zones of iceland and afar geodetic data and field observations demonstrate that the emplacement of dikes in volcanic rift zones frequently generates normal faulting and graben subsidence at the earth9s surface elastic modeling of the vertical ground surface displacements above dikes and faults indicates that the extent of graben subsidence can be achieved only if fault slip extends virtually to or beyond the dike plane at depth a mechanical model that includes dikes and frictional faults shows that dike opening tends to compress and lock faults located to either side of the dike therefore slip extending into or beyond the dike cavity must occur either 1 on faults that intersect the dike near its top above the zone of dike induced compression or 2 on faults that slip ahead of the dike as it propagates laterally data from iceland indicate that slip occurred on deep faults that presumably slipped in advance of the laterally propagating dike

carbonate rocks and petroleum reservoirs a geological perspective from the industry abstract carbonate oil reservoirs are sometimes regarded with apprehension in the petroleum industry since it can be difficult to predict the quality of and ensure high recovery factors from this rock family particular problems are the complex and heterogeneous nature of porosity in carbonate rocks often leading to large ranges in permeability for any given porosity and the organization of carbonate successions most commonly as vertically heterogeneous but laterally persistent layers important issues that arise time and again in carbonate reservoir description include a predicting reservoir quality at inter well scales and in uncored wells b recognizing problematic high permeability layers c determining the permeability component to allocate to fractures and connected vug systems and d populating reservoir models with representative physical parameters because porosity in carbonate rocks generally presents as diverse and heterogeneous conventional core plugs are seldom representative of large rock volumes and significant issues remain in terms of the scale compatibility of the various datasets for measured physical parameters that are used in carbonate reservoir description many of the world9s largest carbonate reservoirs were discovered and developed shortly after the second world war and are now showing signs of maturity expressed variously as poor pressure support water or gas breakthrough and stranded resources the proportion of the world9s conventional petroleum that is reservoired in carbonate rocks is commonly estimated at around 50 60 and many large carbonate reservoirs are likely to have a production lifetime beyond 50 years it is no coincidence then that the petroleum industry has been the primary source of funding of and promotion of research into carbonate rocks and depositional systems often with impacts extending well beyond oil and gas exploitation

temporal and spatial variation of local stress fields before and after the 1992 eruptions of crater peak vent mount spurr volcano alaska we searched for changes in local stress field orientation at mount spurr volcano alaska between august 1991 and december 2001 this study focuses on the stress field orientation beneath crater peak vent the site of three eruptions in 1992 and beneath the summit of mount spurr local stress tensors were calculated by inverting subsets of 140 fault plane solutions for earthquakes beneath crater peak and 96 fault plane solutions for earthquakes beneath mount spurr we also calculated an upper crustal regional stress tensor by inverting fault plane solutions for 66 intraplate earthquakes located near mount spurr during 1991 2001 prior to the 1992 eruptions and for 11 months beginning with a posteruption seismic swarm the axis of maximum compressive stress beneath crater peak was subhorizontal and oriented n67 76 e approximately perpendicular to the regional axis of maximum compressive stress n43 w the strong temporal correlation between this horizontal stress field rotation change in position of the 1 3 axes relative to regional stress and magmatic activity indicates that the rotation was related to magmatic activity and we suggest that the crater peak stress field rotation resulted from pressurization of a network of dikes during the entire study period the stress field beneath the summit of mount spurr also differed from the regional stress tensor and was characterized by a vertical axis of maximum compressive stress we suggest that slip beneath mount spurr s summit occurs primarily on a major normal fault in response to a combination of gravitational loading hydrothermal circulation and magmatic processes beneath crater peak online material regional and local fault plane solutions

calendar time interpolation of amplitude maps from 4d seismic data a calendar time interpolation method for 2d seismic amplitude maps done in two steps is presented the contour interpolation part is formulated as a quadratic programming problem whereas the amplitude value interpolation is based on a conditional probability formulation the method is applied on field data from the sleipner co2 storage project the output is a continuous image movie of the co2 plume besides visualization the output can be used to better couple 4d seismic to other types of data acquired the interpolation uncertainty increases with the time gap between consecutive seismic surveys and is estimated by leaving a survey out blind test errors from such tests can be used to identify problems in understanding the flow and possibly improve the interpolation scheme for a given case field life cost of various acquisition systems and repeat frequencies are linked to the time lapse interpolation errors the error in interpolated amplitudes increased by 3 4 per year of interpolation gap for the sleipner case interpolation can never fully replace measurements

migration of seismic activity during the 1998 volcanic unrest at iwate volcano northeastern japan with reference to p and s wave velocity anomaly and crustal deformation abstract we describe the seismicity at iwate volcano northeastern japan during the volcanic unrest of 1998 with reference to a three dimensional p and s wave velocity model from tomographic analysis the abnormal seismic activity beneath iwate volcano started under the caldera in february 1998 and migrated westward in the period february to august 1998 previous geodetic modeling sato and hamaguchi chikyu monthly 21 1999 312 317 suggested the growth of a dike in the time of the seismic activity comparing the seismicity and dike extension with the tomographic images of the p and s wave velocity structure we find that the trace of the growing dike coincides with the region of the high vp and high vp vs ratio beneath the volcano the seismic and geodetic data are consistent with an intrusion of magma or other fluid under the caldera in 1998 another pressure source causing the predominant crustal deformation at iwate volcano was detected from geodetic data which was located in the region with high vp vs ratio under the western end of the volcano through the period from february to august it is suggested that the activation of the point pressure source probably associated with the inflation of a hot fluid reservoir relate to a geothermal region adjacent to the western edge of the volcano

stress triggering in thrust and subduction earthquakes and stress interaction between the southern san andreas and nearby thrust and strike slip faults 1 we argue that key features of thrust earthquake triggering inhibition and clustering can be explained by coulomb stress changes which we illustrate by a suite of representative models and by detailed examples whereas slip on surface cutting thrust faults drops the stress in most of the adjacent crust slip on blind thrust faults increases the stress on some nearby zones particularly above the source fault blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults we calculate that during a progressive thrust sequence in central california the 1983 mw 6 7 coalinga earthquake brought the subsequent 1983 mw 6 0 nunez and 1985 mw 6 0 kettleman hills ruptures 10 bars and 1 bar closer to coulomb failure the idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events in agreement with findings of prior investigations subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust faulting events on the periphery of the seismic rupture and its downdip extension these features are evident in aftershocks of the 1957 mw 9 1 aleutian and other large subduction earthquakes we further examine stress changes on the rupture surface imparted by the 1960 mw 9 5 and 1995 mw 8 1 chile earthquakes for which detailed slip models are available calculated coulomb stress increases of 2 20 bars correspond closely to sites of aftershocks and postseismic slip whereas aftershocks are absent where the stress drops by more than 10 bars we also argue that slip on major strike slip systems modulates the stress acting on nearby thrust and strike slip faults we calculate that the 1857 mw 7 9 fort tejon earthquake on the san andreas fault and subsequent interseismic slip brought the coalinga fault 1 bar closer to failure but inhibited failure elsewhere on the coast ranges thrust faults the 1857 earthquake also promoted failure on the white wolf reverse fault by 8 bars which ruptured in the 1952 mw 7 3 kern county shock but inhibited slip on the left lateral garlock fault which has not ruptured since 1857 we thus contend that stress transfer exerts a control on the seismicity of thrust faults across a broad spectrum of spatial and temporal scales

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

conditions for the arrest of a vertical propagating dyke magma ascent towards the earth s surface occurs through dyke propagation in the vast majority of cases we investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation so that no eruption occurs the first is that the input of magma from the source is not maintained continuously such that a fixed volume of magma is released laboratory experiments show that in this case the dyke stops at a finite distance from the source this behaviour is specific to the fracturing process in 3 d we derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth when large magma volumes are available eruption may also be prevented by a thick low density layer in the upper crust numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement magma overpressure is largest at this interface and increases with increasing penetration into the upper layer it may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill which prevents eruption this requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock if the magma volume is smaller than a threshold value neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade shaped dyke straddling the interface scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 2 coeruptive deflation july august 2008 1 a hydrovolcanic eruption near cone d on the floor of okmok caldera alaska began on 12 july 2008 and continued until late august 2008 the eruption was preceded by inflation of a magma reservoir located beneath the center of the caldera and 3 km below sea level bsl which began immediately after okmok s previous eruption in 1997 in this paper we use data from several radar satellites and advanced interferometric synthetic aperture radar insar techniques to produce a suite of 2008 coeruption deformation maps most of the surface deformation that occurred during the eruption is explained by deflation of a mogi type source located beneath the center of the caldera and 2 3 km bsl i e essentially the same source that inflated prior to the eruption during the eruption the reservoir deflated at a rate that decreased exponentially with time with a 1 e time constant of 13 days we envision a sponge like network of interconnected fractures and melt bodies that in aggregate constitute a complex magma storage zone beneath okmok caldera the rate at which the reservoir deflates during an eruption may be controlled by the diminishing pressure difference between the reservoir and surface a similar mechanism might explain the tendency for reservoir inflation to slow as an eruption approaches until the pressure difference between a deep magma production zone and the reservoir is great enough to drive an intrusion or eruption along the caldera ring fracture system

temporal changes in stress preceding the 2004 2008 eruption of mount st helens washington abstract the 2004 2008 eruption of mount st helens msh washington was preceded by a swarm of shallow volcano tectonic earthquakes vts that began on september 23 2004 we calculated locations and fault plane solutions fps for shallow vts recorded during a background period january 1999 to july 2004 and during the early vent clearing phase september 23 to 29 2004 of the 2004 2008 eruption fps show normal and strike slip faulting during the background period and on september 23 strike slip and reverse faulting on september 24 and a mixture of strike slip reverse and normal faulting on september 25 29 the orientation of 1 beneath msh as estimated from stress tensor inversions was found to be sub horizontal for all periods and oriented ne sw during the background period nw se on september 24 and ne sw on september 25 29 we suggest that the ephemeral 90 change in 1 orientation was due to intrusion and inflation of a ne sw oriented dike in the shallow crust prior to the eruption onset

an examination of the continuous wavelet transform for volcano seismic spectral analysis abstract volcanoes produce widely varying seismic signals due to the presence of complex and non linear physical processes the temporal distribution of seismicity at volcanoes ranges from individual transients to swarms of many small events and protracted volcanic tremor the spectral range of volcanic signals is unequivocally broadband with coincident high 20 hz and very low down to periods of hundreds of seconds frequency signals frequently observed at many volcanic systems as such interpretations of volcano seismic source and process require suitable characterisation in the time frequency t f domain the adoption of automated approaches to routine seismic processing at volcanoes also creates the need to evaluate how we suitably extract discriminatory features of interest from such diverse volcano seismic signals here we assess the performance of the continuous wavelet transform cwt for spectral representations of volcano seismic signals the localisation property of wavelet transforms gives the cwt a distinct advantage over commonly used moving window fourier transforms enabling it to capture sharp changes in signal and represent signals over a wide range of timescales examination of seismic data for typical volcano seismic phenomena such as volcano tectonic earthquakes vts shows that cwt scalograms have better t f resolution across broader frequency ranges than fourier transform spectrograms which suffer from greater spectral smearing in the time domain at higher frequencies the inherent log scale representation of cwt scalograms is also better suited for detection and representation of very long period vlp signals and for distinguishing volcanic signals from ambient microseismic noise when applied to seismic data from santiaguito volcano in guatemala cwt analysis reveals pre and syn eruptive signals across a wide range of frequency bands ranging from 600 s to 50 hz with ultra long period signals ulps 30 to 600 s detected on instruments up to 1 9 km from the active vent which is beyond the range of previously detected ulps at this volcanic system the cwt scalogram conveniently represents these simultaneous syn eruptive spectral features in a single plot which can aid exploratory analysis and inform source models furthermore the edge detection capabilities of the cwt accurately identify sharp changes in the raw signal over the vlp ulp frequency range 5 to 600 s thought to represent sudden deflation associated with eruption providing a useful tool for picking explosive eruptions the addition of an average wavelet energy distribution to cwt scalograms which reveals the average energy across the whole signal at each wavelet scale is also useful for characterising spectral content and identifying spectral peaks as its smooth appearance is easier to interpret than fft spectral amplitude plots we conclude that wavelet transform methods are underutilised in volcano seismology where their t f localisation properties would be particularly well suited and suggest potential applications in terms of automated event detection and classification

ground surface deformation patterns magma supply and magma storage at okmok volcano alaska from insar analysis 1 intereruption deformation 1997 2008 eruption magma storage had increased by 3 7 5 2 1 0 7 m 3 or 85 100 of the 1997 eruption volume we propose that the supply rate decreased in response to the diminishing pressure gradient between the shallow storage zone and a deeper magma source region eventuallytheeffectsofcontinuingmagmasupplyandvesiculationofstoredmagmacaused acriticalpressurethresholdtobeexceeded triggeringthe2008eruption asimilarpatternof initially rapid inflation followed by oscillatory but generally slowing inflation was observed prior to the 1997 eruption in both cases withdrawal of magma during the eruptions depressurized the shallow storage zone causing significant volcano wide subsidence and initiating a new intereruption deformation cycle

high precision relocation of earthquakes at iliamna volcano alaska abstract in august 1996 a period of elevated seismicity commenced beneath iliamna volcano alaska this activity lasted until early 1997 consisted of over 3000 earthquakes and was accompanied by elevated emissions of volcanic gases no eruption occurred and seismicity returned to background levels where it has remained since we use waveform alignment with bispectrum verified cross correlation and double difference methods to relocate over 2000 earthquakes from 1996 to 2005 with high precision 100 m the results of this analysis greatly clarify the distribution of seismic activity revealing distinct features previously hidden by location scatter a set of linear earthquake clusters diverges upward and southward from the main group of earthquakes the events in these linear clusters show a clear southward migration with time we suggest that these earthquakes represent either a response to degassing of the magma body circulation of fluids due to exsolution from magma or heating of ground water or possibly the intrusion of new dikes beneath iliamna s southern flank in addition we speculate that the deeper somewhat diffuse cluster of seismicity near and south of iliamna s summit indicates the presence of an underlying magma body between about 2 and 4 km depth below sea level based on similar features found previously at several other alaskan volcanoes

mechanism of the 1996 97 non eruptive volcano tectonic earthquake swarm at iliamna volcano alaska a significant number of volcano tectonic vt earthquake swarms some of which are accompanied by ground deformation and or volcanic gas emissions do not culminate in an eruption these swarms are often thought to represent stalled intrusions of magma into the mid or shallow level crust real time assessment of the likelihood that a vt swarm will culminate in an eruption is one of the key challenges of volcano monitoring and retrospective analysis of non eruptive swarms provides an important framework for future assessments here we explore models for a non eruptive vt earthquake swarm located beneath iliamna volcano alaska in may 1996 june 1997 through calculation and inversion of fault plane solutions for swarm and background periods and through coulomb stress modeling of faulting types and hypocenter locations observed during the swarm through a comparison of models of deep and shallow intrusions to swarm observations we aim to test the hypothesis that the 1996 97 swarm represented a shallow intrusion or failed eruption observations of the 1996 97 swarm are found to be consistent with several scenarios including both shallow and deep intrusion most likely involving a relatively small volume of intruded magma and or a low degree of magma pressurization corresponding to a relatively low likelihood of eruption

implications of post thrusting extension and underplating for p t t paths in granulite terranes a grenville example mineral zoning studies in several granulite terranes have yielded nearly isobaric retrograde pressure temperature p t paths with significant path dispersion explanations include magmatic underplating incomplete isostatic rebound following thrusting and cooling after tectonic denudation associated with crustal extension one dimensional thermal models help to interpret the p t t time paths generated by such processes basaltic underplating yields p t paths in good agreement with data for the grenville province of ontario but yields t t paths that disagree strongly with thermochronometry in addition seismic heat flow and gravity data from the grenville province are not consistent with a mafic lower crust calculations based on simple thrust models agree with the t t data but yield isothermal rather than isobaric initial p t paths and consistently underestimate the pressure at which peak temperature is achieved the only model we found that fits both the p t and t t data incorporates a post thrusting episode of tectonic denudation near the peak of metamorphism this model also suggests that the temperature dependence of diffusion in garnet may explain the difference between measured isobaric and isothermal paths in granulites and amphibolites

an improved method for determining the regional stress tensor using earthquake focal mechanism data application to the san fernando earthquake sequence the orientations of fault planes and slip directions indicated by a population of earthquake focal mechanisms can be used to determine best fit regional principal stress directions and r 2 1 3 1 a measure of relative stress magnitudes under the assumption of uniform stress in the source region this analysis allows for the possibility that failure occurs on preexisting zones of weakness of any orientation in the inversion we perform a grid search of stress models to find the one which requires the smallest total rotation of all the fault planes that is needed to match the observed and predicted slip directions the method allows for errors in orientations of both the fault planes and slip directions we have an objective means for identifying the more likely of the two possible fault planes from each focal mechanism relative to a given stress model thus we do not face the problem of ambiguity of nodal planes which plagues other analyses of this kind by using a grid search of stress models rather than a linearization scheme we are able to perform a realistic error analysis and thus establish confidence limits for the preferred regional stresses the method can be used to investigate possible stress inhomogeneities during earthquake sequences by analyzing subsets of the data population the technique has been applied to 76 events from the san fernando earthquake sequence for which we have found best fit stresses plunge and azimuth 1 7 187 2 27 281 3 62 84 and r 0 65 the average misfit between this stress model and all the data is about 8 and all but eight of the aftershocks have misfits of less than 20 these values are considerably less than the uncertainty of the focal mechanism determinations therefore significant stress inhomogeneities are not required by the data our analysis does not support the suggestion of a change in stresses during the aftershock sequence as proposed by others on the basis of an apparent change in focal mechanisms

mineral zoning p t x m phase relations and metamorphic evolution of some adirondack granulites new york detailed petrologic analysis of ten meta anorthosites and related introduction rocks from the adirondack highlands new york has been used to the adirondack highlands of new york are one of constrain the p t history of the region metamorphic orthopyroxene the best studied granulite facies terranes of the world and clinopyroxene occur in aggregates of 1 mm diameter grains e g bohlen et al 1985 valley et al 1990 and that are zoned concentrically with decreasing al and fe fe mg references therein based on this considerable volume and increasing ca towards the rim moreover zoning is not related of work the peak metamorphic conditions in the to the presence of garnet zoning is interpreted to have been produced adirondack highlands have been fairly well constrained during growth by the reaction igneous pyroxene plagioclase at pressures of 7 8 kbar crustal depths of 25 30 metamorphic opx metamorphic cpx along a cooling path with a km and temperatures that range from 775 c in slope of 6 bars c starting at 850 c and 6 5 8 kbar garnet the central highlands to t 675 c in the southern occurs as isolated clusters of 5 25 grains of 1 mm diameter adirondacks e g bohlen et al 1985 p t paths have crystals and as necklaces of 1 mm diameter crystals surrounding been shown to follow nearly isobaric cooling trajectories metamorphic pyroxenes or oxides plagioclase quartz typically e g bohlen 1987 because of this wealth of inseparates garnet from pyroxene but locally garnet embays metaformation some fundamental questions about the origin morphic pyroxene suggesting that garnet grew at the expense of of the adirondack granulite facies terrane have emerged pyroxene garnet clusters have slightly lower fe fe mg than e g bohlen et al 1985 how did the crust achieve garnet in necklaces fe fe mg 0 73 and 0 75 0 78 rethe relatively high temperature conditions necessary to spectively and slightly higher grossular xgrs 0 20 vs 0 19 produce granulite facies rocks at depths of 25 30 km neither is zoned in mn and zoning towards increasing fe and what is the relative importance of magmatic fe mg is restricted to contacts with biotite and locally clinoheating vs continental burial in this process pyroxene biotite adjacent to garnet is zoned towards decreasing this study will present new data on mineral comfe fe mg production of garnet in necklaces is interpreted position and element zoning in garnet pyroxene to be the result of the continuous fe mg reaction opx pl biotite amphibole and plagioclase from adirondack grt cpx qtz p t x m modeling of this reaction reveals a meta anorthosite and related rocks with the goal of p t path with a slope of 6 bars c no evidence for early prefurther constraining the metamorphic evolution of this metamorphic peak garnet is observed which rules out any possibility terrane mineral compositions will be used to construct of early higher pressure metamorphism the p t path is therefore phase diagrams in an attempt to evaluate approach to inferred to be counterclockwise with loading to 6 5 8 kbar at a chemical equilibrium theoretical analysis will be used maximum temperature of 850 c occurring during or immediately to construct p t x m phase diagrams depicting how following an influx of heat presumably from early orogenic plutons mineral composition and modes change with p and t this theoretical analysis will then be applied to the mineral zoning to constrain the p t path and the results will be discussed in the context of a tectonic

forecasting the evolution of seismicity in southern california animations built on earthquake stress transfer 1 we develop a forecast model to reproduce the distribution of main shocks aftershocks and surrounding seismicity observed during 1986 2003 in a 300 310 km area centered on the 1992 m 7 3 landers earthquake to parse the catalog into frames with equal numbers of aftershocks we animate seismicity in log time increments that lengthen after each main shock this reveals aftershock zone migration expansion and densification we implement a rate state algorithm that incorporates the static stress transferred by each m 6 shock and then evolves coulomb stress changes amplify the background seismicity so small stress changes produce large changes in seismicity rate in areas of high background seismicity similarly seismicity rate declines in the stress shadows are evident only in areas with previously high seismicity rates thus a key constituent of the model is the background seismicity rate which we smooth from 1981 to 1986 seismicity the mean correlation coefficient between observed and predicted m 1 4 shocks the minimum magnitude of completeness is 0 52 for 1986 2003 and 0 63 for 1992 2003 a control standard aftershock model yields 0 54 and 0 52 for the same periods four m 6 0 shocks struck during the test period three are located at sites where the expected seismicity rate falls above the 92 percentile and one is located above the 75 percentile the model thus reproduces much but certainly not all of the observed spatial and temporal seismicity from which we infer that the decaying effect of stress transferred by successive main shocks influences seismicity for decades finally we offer a m 5 earthquake forecast for 2005 2015 assigning probabilities to 324 10 10 km cells

seismicity at the volcanoes of katmai national park alaska july 1995 december 1997 abstract upper crustal seismicity located within katmai national park occurs mainly within four distinct clusters originating near martin mageik mm subnet volcanoes trident volcano katmai caldera and snowy volcano analyses of earthquake frequency magnitude distributions reveal high b values beneath mm subnet 1 5 normal b values at trident volcano 1 0 and intermediate b values at katmai caldera 1 3 for all seismicity occurring between july 1995 and december 1997 detailed analyses of subsets of b values and hypocenter locations at mm subnet reveal a temporal increase in b value associated with an increase in the maximum depth of seismicity the changes occurred during a shallow earthquake swarm beneath mageik volcano between october 16 and 25 1996 and again in november december 1997 before the swarm the weighted least squares b value was 1 01 at mm subnet increased to 1 59 during the swarm and remained anomalously high until april 1997 the corresponding maximum depth of seismicity is generally less than 5 km for well located earthquakes occurring after september 18 1996 but shifted to 10 km during both the october 1996 swarm and the november december 1997 period the november december 1997 event is not associated with an increase in the rate of seismicity or the b value the october 1996 swarm had a cumulative moment release of 5 0 10 20 dyn cm and decayed from a peak rate of 110 events per day with a modified omori law p value of 1 06 0 11 modelling by the flow law with a 10 km depth limit for seismicity suggests that temperature gradients are on the order of 20 40 c km 1 in agreement with the p value estimate we infer that a simple pressurizing intrusion was not associated with the october swarm because higher stresses should increase seismicity and lower the b value the opposite of what we observed alternatively an actively degassing intrusion would reduce the effective stress and increase the b value at shallow depths while the increased stress would induce seismicity at depth surface temperature measurements taken at the mageik crater lake in july 1995 and again in july 1997 revealed an increase of about 10 c in the lake water temperature consistent with a degassing intrusive event

evidence for dike emplacement beneath iliamna volcano alaska in 1996 two earthquake swarms comprising 88 and 2833 locatable events occurred beneath iliamna volcano alaska in may and august of 1996 swarm earthquakes ranged in magnitude from 0 9 to 3 3 increases in so2 and co2 emissions detected during the fall of 1996 were coincident with the second swarm no other physical changes were observed in or around the volcano during this time period no eruption occurred and seismicity and measured gas emissions have remained at background levels since mid 1997 earthquake hypocenters recorded during the swarms form a cluster in a previously aseismic volume of crust located to the south of iliamna s summit at a depth of 1 to 4 km below sea level this cluster is elongated to the nnw sse parallel to the trend of the summit and southern vents at iliamna and to the regional axis of maximum compressive stress determined through inversion of fault plane solutions for regional earthquakes fault plane solutions calculated for 24 swarm earthquakes located at the top of the new cluster suggest a heterogeneous stress field acting during the second swarm characterized by normal faulting and strike slip faulting with p axes parallel to the axis of regional maximum compressive stress the increase in earthquake rates the appearance of a new seismic volume and the elevated gas emissions at iliamna volcano indicate that new magma intruded beneath the volcano in 1996 the elongation of the 1996 1997 earthquake cluster parallel to the direction of regional maximum compressive stress and the accelerated occurrence of both normal and strike slip faulting in a small volume of crust at the top of the new seismic volume may be explained by the emplacement and inflation of a subvertical planar dike beneath the summit of iliamna and its southern satellite vents

preeruptive inflation and surface interferometric coherence characteristics revealed by satellite radar interferometry at makushin volcano alaska 1993 2000 1 pilot reports in january 1995 and geologic field observations from the summer of 1996 indicate that a relatively small explosive eruption of makushin one of the more frequently active volcanoes in the aleutian arc of alaska occurred on 30 january 1995 several independent radar interferograms that each span the time period from october 1993 to september 1995 show evidence of 7 cm of uplift centered on the volcano s east flank which we interpret as preeruptive inflation of a 7 km deep magma source v 0 022 km3 subsequent interferograms for 1995 2000 a period that included no reported eruptive activity show no evidence of additional ground deformation interferometric coherence at c band is found to persist for 3 years or more on lava flow and other rocky surfaces covered with short grass and sparsely distributed tall grass and for at least 1 year on most pyroclastic deposits on lava flow and rocky surfaces with dense tall grass and on alluvium coherence lasts for a few months snow and ice surfaces lose coherence within a few days this extended timeframe of coherence over a variety of surface materials makes c band radar interferometry an effective tool for studying volcano deformation in alaska and other similar high latitude regions

effect of regional tectonic setting on local fault response to episodes of volcanic activity 1 in this study we examine the interaction of tectonic and volcanically generated stress fields and their combined effect on patterns of volcanotectonic vt seismicity by calculating coulomb stress changes on local faults induced by a constant dike inflation event in a background stress field of systematically varying magnitude and orientation we find that patterns of vt seismicity earthquake locations and fault plane solutions resulting from dike inflation depend strongly on the relative strength and orientation of background tectonic stresses patterns of vt seismicity similar to those predicted by our coulomb stress models have been observed at several recently active volcanoes and appear to correspond to the relative strength of the regional stress field thus it is critical to consider the regional tectonic setting when interpreting patterns of vt seismicity in terms of magmatic processes

yardsticks for industrial tomography seismic tomography has been developed and applied for decades in seismological applications and for basic research purposes during the last decade large scale applications in the oil and gas industry became standard as tomostatics and velocity modelling for pre stack depth migration in this paper i take a snapshot of some current industrial applications quantifying practical aspects by yardsticks such as data and model size and i try to draw a road map for the current decade

exhumation of high pressure rocks a review of concepts and processes the exhumation of high pressure metamorphic rocks requires either the removal of the overburden that caused the high pressures or the transport of the metamorphic rocks through the overburden exhumation cannot be achieved simply by thrusting or strike slip faulting it may be caused by erosion of shortened and thickened crust but this is unlikely to be the only mechanism for exhuming rocks from depths greater than about 20 km one or more of the following additional mechanisms may be involved 1 corner flow of low viscosity material trapped between the upper and lower plates in a subduction zone can cause upward flow of deeply buried rock and may explain some occurrences of high pressure tectonic blocks in melange this process does not however appear to be adequate to explain the exhumation of regional high pressure terrains 2 buoyancy forces acting directly on metamorphic rock bodies may cause them to rise relative to more dense surroundings this is likely to be the most important mechanism of exhumation of crustal rocks subducted into the mantle but cannot explain the emplacement of coherent tracts of high density metamorphic rock into shallow crustal levels some high pressure blocks emplaced at shallow levels in accretionary terrains may have been entrained in diapiric intrusions of low density mud or serpentinite 3 extension driven by the forces associated with contrasts in surface elevation may explain the exhumation and structural setting of many high pressure terrains extension may occur in the upper part of an accretionary wedge thickened by underplating or it may affect the whole lithosphere in a region of intracontinental convergence if surface elevation has been increased by the removal of a lithospheric root in the second case extension may be accompanied by magmatism and an evolution towards higher temperature during decompression of the metamorphic terrain

ground deformation associated with the march 1996 earthquake swarm at akutan volcano alaska revealed by satellite radar interferometry in march 1996 an intense swarm of volcano tectonic earthquakes 3000 felt by local residents mmax 5 1 cumulative moment of 2 7 1018 n m beneath akutan island in the aleutian volcanic arc alaska produced extensive ground cracks but no eruption of akutan volcano synthetic aperture radar interferograms that span the time of the swarm reveal complex island wide deformation the western part of the island including akutan volcano moved upward while the eastern part moved downward the axis of the deformation approximately aligns with new ground cracks on the western part of the island and with holocene normal faults that were reactivated during the swarm on the eastern part of the island the axis is also roughly parallel to the direction of greatest compressional stress in the region no ground movements greater than 2 83 cm were observed outside the volcano s summit caldera for periods of 4 years before or 2 years after the swarm we modeled the deformation primarily as the emplacement of a shallow east west trending north dipping dike plus inflation of a deep mogi type magma body beneath the volcano the pattern of subsidence on the eastern part of the island is poorly constrained it might have been produced by extensional tectonic strain that both reactivated preexisting faults on the eastern part of the island and facilitated magma movement beneath the western part alternatively magma intrusion beneath the volcano might have been the cause of extension and subsidence in the eastern part of the island we attribute localized subsidence in an area of active fumaroles within the akutan caldera by as much as 10 cm during 1992 1993 and 1996 1998 to fluid withdrawal or depressurization of the shallow hydrothermal system

seismicity and stress in the vicinity of mount spurr volcano south central alaska focal mechanism solutions and hypocenters for earthquakes near mount spurr volcano in south central alaska reveal spatial perturbations in the regional stress field and in the maximum depth of seismicity at the volcano practically all the shocks during the dormant decade 1981 1991 have depths shallower than 5 km and are characterized by nearly pure normal slip in contrast earthquakes located outboard of the volcano mostly concentrate in the depth range 3 18 km and exhibit predominantly strike slip oblique reverse slip or reverse slip the regional stress field is characterized by subhorizontal maximum principal stress directed n30 w concordant with the direction of convergence between the north american and pacific plates whereas the maximum principal stress is probably more nearly vertical beneath the volcano we suggest that the shoaling of seismicity beneath the volcano reflects localized elevation of the depth to the midcrustal transition from brittle failure to plastic flow we attribute this localized elevation to relict magmatic heat associated with past volcanic eruptions the available data are not sufficient to determine the cause of the suggested rotation of the maximum principal stress axis beneath the volcano possible mechanisms include an increase in the vertical stress from the weight of the mount spurr massif and a decrease in the maximum horizontal stress associated with doming of the shallow crust from magmatic processes