source constraints of tungurahua volcano explosion events the most recent eruptive cycle of tungurahua volcano began in may 2004 and reached its highest level of activity in july 2004 this activity cycle is the last one of a series of four cycles that followed the reawakening and major eruption of tungurahua in 1999 between june 30 and august 12 2004 three temporary seismic and infrasonic stations were installed on the flanks of the volcano and recorded over 2 000 degassing events the events are classified by waveform character and include explosion events the vast majority spanning three orders of pressure amplitudes at 3 5 km from the vent 0 1 180 pa jetting events and sequences of repetitive infrasonic pulses called chugging events travel time analysis of seismic first arrivals and infrasonic waves indicates that explosions start with a seismic event at a shallow depth 200 m followed 1 s later by an out flux of gas ash and solid material through the vent cluster analysis of infrasonic signals from explosion events was used to isolate four groups of similar waveforms without apparent correlation to event size location or time the clustering is thus associated with source mechanism and probably spatial distribution explosion clusters do not exhibit temporal dependence

spatial and temporal distribution of slip for the 1999 chi chi taiwan earthquake we investigated the rupture process of the 1999 chi chi taiwan earth quake using high quality near source strong motion records broadband teleseismic displacement waveforms and well distributed global positioning system gps data the near source strong motion displacement waveforms recorded significant static offsets of up to 8 m the teleseismic displacement records show a significant pulse with duration of about 18 to 20 sec taking into account the surface displacements observed along the chelungpu fault we considered two fault geometries a single planar fault and a two segment fault with a northeast striking section near the north ern end using the finite fault model with variable slip vectors we derived two models of the temporal and spatial slip distribution of the earthquake the gps data provided good surface displacement constraints for the slip distribution determina tion the spatial slip distribution is generally consistent with field observations the results for the simple fault model show a large asperity located in the region about 25 to 55 km north of the hypocenter with maximum slip of about 15 m when we use the two segment model the asperity further extends to the region where the fault bends toward the northeast with a maximum slip of up to 20 m a large amount of right lateral slip beneath station tcu068 is necessary to explain its observed large west movement it implies a local converging slip at the corner where the fault bends to the northeast the slip amplitude near the hypocenter is about 3 to 6 m the seismic moments determined from the various data sets are within the range of 2 to 4 10 27 dyne cm most of the slip concentrated at shallow depths less than 10 km the total rupture duration is about 28 sec and the rupture velocity is 75 to 80 of the shear wave velocity the slip vector shows a clockwise rotation during the fault rupture the static stress drop of the large asperity region is comparable with the dynamic stress drop as observed directly from the slip velocity at the station near the large slip region

pyroclastic density currents pdc of the 16 17 august 2006 eruptions of tungurahua volcano ecuador geophysical registry and characteristics abstract tungurahua located in the eastern cordillera of the ecuadorian andes is a 5023 m high active volcano notable for its extreme relief 3200 m steep sides and frequent eruptive cycles from 1999 until 2006 tungurahua experienced short periods of low to moderate strombolian activity characterized by fire fountaining explosions frequent ash falls and debris flows and no pdc events without warning tungurahua initiated pdc activity on 15 16 july 2006 which became more intense on the night of 16 17 august 2006 which is the focus of this study continuous monitoring of tungurahua has employed seismic both short period and broadband bb instruments so 2 gas emission cospec and doas and geodetic methods edm tilt meters and gps in addition to thermal imagery airborne and ground based acoustic flow monitors afm installed to monitor lahar activity were important for detecting pdc events acoustic signals were monitored at riobamba 40 km to the sw as well as by infrasound sensors at tungurahua s bb seismic stations based on geophysical parameters visual observations and pdc deposit characteristics four phases of distinct eruptive activity are recognized during the 16 17 august episode phase i 08h37 to 21h13 of 16 aug local time experienced low to moderate strombolian activity with occasional high energy impulsive bursts and small pdc phase ii 21h13 16 aug to 00h12 17 aug was characterized by a number of discrete events with high amplitude seismo acoustic signals followed by the generation of larger pdc that overran monitoring stations and had velocities of 30 33 m s after midnight phase iii 00h12 to 01h14 saw an intense period of unrelenting eruptive activity corresponding to the episode s greatest energy release it was characterized by subplinian activity accompanied by a series of high energy outbursts and constant low frequency jetting that together formed a continuous plume it was during this phase that the largest pdc were produced reaching the surrounding river valleys phase iv after 01h14 followed the cessation of the paroxysmal eruption but witnessed many granular pdc generated by degassed lava spill outs from the crater that developed lobe and channel morphology on the cone s lower flanks hours later a blocky lava flow issued from the crater during these episodes more than 30 pdc events were detected the majority being small flows that remained high on the cone the two largest pdc occurred after midnight probably generated by fountain collapse their descent down the cone s upper steep flanks 28 and 2 4 km in length favored air entrainment resulting in pdc with greater fluidity these flows had volumes of 9 to 17 10 6 m 3 and produced widespread but relatively thin 1 2 m thick normally graded deposits at their distal ends the character and evolution of the pdc activity apparently reflect decreasing volatile contents of the magma and a diminishing magma supply

energy release and heat generation during the 1999 ms7 6 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan integrating observed and inversed results of source parameters the fracture energy eg and frictional energy ef on the fault and its northern and southern segments are estimated together with given values of strain energy e and seismic radiation energy es the seismic efficiency i e es e and the radiation efficiency i e r es es eg are evaluated the average fracture energy per unit area g is also calculated from eg the frictional heat caused by dynamic frictional stress is calculated from ef results show a marked difference in source properties between the two segments the average frictional and ambient stress levels on the two segments are estimated the total energy budget of and heat generated by the earthquake are elucidated based on a two dimensional faulting model with frictional heat both observed and calculated results suggest the possible existence of fluids which produced suprahydrostatic gradients on the fault during faulting lubrication and thermal fluid pressurization might play a significant role on rupture

factors controlling prolific gas production from low permeability sandstone reservoirs implications for resource assessment prospect development and risk analysis low permeability reservoirs from the greater green river basin of southwest wyoming are not part of a continuous type gas accumulation or a basin center gas system in which productivity is dependent on the development of enigmatic sweet spots instead gas fields in this basin occur in low permeability poor quality reservoir rocks in conventional traps we examined all significant gas fields in the greater green river basin and conclude that they all occur in conventional structural stratigraphic or combination traps we illustrate this by examining several large gas fields in the greater green river basin and suggest that observations derived from the greater green river basin provide insight to low permeability gas charged sandstones in other basins we present evidence that the basin is neither regionally gas saturated nor is it near irreducible water saturation water production is both common and widespread low permeability reservoirs have unique petrophysical properties and failure to fully understand these attributes has led to a misunderstanding of fluid distributions in the subsurface an understanding of multiphase effective permeability to gas as a function of both varying water saturation and overburden stress is required to fully appreciate the controls on gas field distribution as well as the controls on individual well and reservoir performance low permeability gas systems such as those found in the greater green river basin do not require a paradigm shift in terms of hydrocarbon systems as some have advocated we conclude that low permeability gas systems similar to those found in the greater green river basin should be evaluated in a manner similar to and consistent with conventional hydrocarbon systems to date resource assessments in the greater green river basin have assumed a widespread continuous type resource distribution failure to recognize some of the fundamental elements of low permeability reservoirs has led to an underappreciation of the risks associated with exploration and development investment decisions in these settings and likely a significant overestimation of available resource levels

slip rates on the chelungpu and chushiang thrust faults inferred from a deformed strath terrace along the dungpuna river west central taiwan the chelungpu fault produced the september 1999 m w 7 6 chi chi earthquake central taiwan the shortening rate accommodated by this structure integrated over several seismic cycles and its contribution to crustal shortening across the taiwanese range have remained unresolved to address the issues we focus our study on the chelungpu and chushiang thrust faults within the southernmost portion of the chi chi rupture area structural measurements and available seismic profiles are used to infer the subsurface geometry of structures the chushiang and chelungpu faults appear as two splay faults branching onto a common ramp that further north connects only to the chelungpu surface trace we survey a deformed strath terrace along the dungpuna river buried under a 11 540 309 years old fill deposit given this age the dip angles of the faults and the vertical throw determined from the offset of the strath terrace across the surface fault traces we estimate slip rates of 12 9 4 8 and 2 9 1 6 mm yr on the chelungpu and chushiang faults respectively these yield a total shortening rate of 15 8 5 1 mm yr to be absorbed on their common decollement at depth this total value is an upper bound for the slip rate on the chelungpu fault further north where the chushiang fault disappears and transfers shortening to adjacent faults combining these results with the recently constrained shortening rate on the changhua blind thrust reveals that all these frontal faults presently absorb most of the long term horizontal shortening across the taiwanese range they thus stand as the major sources of seismic hazards in this heavily populated area the return period of earthquakes similar to the chi chi event over a 80 km long stretch of the western foothills is estimated to be 64 years this value is an underestimate because it assumes that all the faults locked during the interseismic period slip only during such large events comparison with historical seismicity suggests that episodic aseismic deformation might also play a major role in accommodating shortening

the hydrocarbon trap distribution patterns of the simple dip area of a continental basin a case study from the western slope of the songliao basin china simple dip areas of continental sedimentary basins feature stratal overlap gentle changes in slope uniform dip angles and minimal fault development locating hydrocarbon traps in these environments therefore presents a difficult challenge this paper analyzes reservoir sand body and hydrocarbon trap development and their distributions within the gently dipping western area of the songliao basin and discusses the determinants influencing the distribution of reservoir sand bodies and oil and gas bearing zones sand bodies within the simple east dipping western basin margin exhibit thin singular layering extensive planar distribution and frequent interbedding with mudstone layers in the homoclinal slope areas that lack significant fault development sand bodies served as important hydrocarbon migration pathways spatial shifts in the paleosedimentary system caused by basin subsidence and late stage tectonism can help constrain the search for hydrocarbon traps the spatial patterns of the depositional system influenced the distribution of different types of traps southerly prograding delta lobes were subsequently tilted to the east creating sand bodies that form up dip wedge out lithologic stratigraphic traps along their western edge some of the delta lobes are folded or cut by faults along their peripheral edges making structural traps and combination traps the primary types in this region the delta lobes in the western provenance system however dip in a direction parallel to that of sediment supply most subaqueous distributary channel sand bodies are continuous into the western source area and lack seal conditions lenticular lithologic traps are therefore found only along the outer edges of delta lobes and the adjacent shallow lacustrine environments

a viscoelastic earthquake cycle model for taiwan 1 while recent geophysical measurements including global positioning system gps surveys have clarified the mechanisms of active mountain building in the taiwan arc continent collision the geometry of faults beneath the island remains unclear in this paper we use gps data collected before the 1999 chi chi earthquake to image the geometry of active faults under taiwan and estimate slip rates on these faults we invert the data using kinematic and mechanical earthquake cycle models consisting of faulting in an elastic lithosphere overlying a viscoelastic asthenosphere in the kinematic model uniform slip is prescribed on the faults at a constant rate while in the mechanical model the faults slip in response to shear stresses in the lithosphere these models explain the essential features of both the horizontal and vertical gps velocity fields we find a 27 39 km thick elastic lithosphere overlying a viscoelastic asthenosphere with maxwell relaxation time of 15 80 years or viscosity of 0 5 4 1019 pa s the models produce a combined slip rate of 30 50 mm yr on the frontal thrusts in western taiwan and 60 80 mm yr of slip on the longitudinal valley fault inversion of the data using both models indicates a decollement dipping 10 under western taiwan and increasing in dip by no more than 10 under the central ranges and eastern taiwan

ecuadorian andes volcanism a review of late pliocene to present activity abstract this article provides background information about ecuador s general volcanic setting as an introduction to the numerous articles in this special issue of the journal dealing with the many facets of ecuadorian volcanism it also provides a brief description of ecuador s physiography as well as its geodynamic setting a comprehensive bibliography is included as a guide to further reading the ecuadorian andes contain at least 20 volcanoes active during the holocene several reach altitudes of 5000 to 6000 m and are glacier clad eleven have erupted in pre columbian and historic times and have greatly affected local populations and caused fatalities

the deliberate search for the stratigraphic trap twenty four years have elapsed since the publication of halbouty s aapg memoir of 1982 the deliberate search for the subtle trap since then the technologies employed in hydrocarbon exploration have become extraordinarily sophisticated yet current exploration for stratigraphic traps is to some extent restricted to areas where seismic data simplifies exploration by allowing direct inference of fluid fill and reservoir development this special publication draws upon contributions that examine current industry perceptions of stratigraphic trap exploration and the technologies tools and philosophies employed in such exploration given the changing industry environment this book contains a collection of papers examining a number of themes related to exploration for stratigraphic traps ranging from play and risk assessment through regional assessments of stratigraphic trapping potential specific exploration programmes targeted at stratigraphic traps to specific working traps and plays where stratigraphic trapping is prevalent

horizontal coseismic deformation of the 1999 chi chi earthquake measured from spot satellite images implications for the seismic cycle along the western foothills of central taiwan 1 the 1999 chi chi earthquake mw 7 6 broke a major thrust fault along the western foothills of the central range of taiwan we have measured the horizontal coseismic displacement field by correlating optical satellite images acquired before and after the earthquake these data reveal the fault trace and a clockwise rotation of surface displacements toward the north with much larger displacements and strain in the hanging wall at the surface coseismic slip increases from 5 6 m near the epicenter to 10 11 m to the north in the epicentral area we observe a left lateral strike slip zone trending n125 e and farther north a fault zone trending n s with a right lateral component the data were modeled using elastic dislocations the fault geometry consists of a shallow

a dynamic study of frictional and viscous effects on earthquake rupture a case study of the 1999 chi chi taiwan earthquake friction is commonly considered an important factor in controlling earthquake rupture in this work it is assumed that viscosity is also a significant factor a strike slip type two body spring slider model in the presence of both friction and viscosity is applied to approximate the rupture processes of an earthquake along the fault striking direction results show that in addition to friction viscosity is also an important factor in controlling rupture the m s 7 6 chi chi earthquake which struck central taiwan on 20 september 1999 ruptured a 100 km long east dipping transpressive fault the chelungpu fault measured and inferred results show that there are differences in physical properties between the northern and southern segments of the fault simulation results from a two body model can explain the differences in displacement velocity acceleration and predominant period between the two fault segments

san francisco bay area earthquake simulations a step toward a standard physical earthquake model earthquakes in california s san francisco bay area are likely to be more strongly affected by stress interaction than earthquakes in any other place in the world because of the region s closely spaced subparallel distribution of faults i believe therefore that meaningful quantification of earthquake probability and hazard in the bay area can be made only with the guidance provided by physically based and regionwide earthquake models that account for this interaction this article represents a first step in developing a standard physical earthquake model for the san francisco bay area through realistic 3000 year simulations of earthquakes on all of the area s major faults these simulations demonstrate that a standard physical earthquake model is entirely feasible they illustrate its application and they blueprint its construction a standard physical earthquake model provides the mechanism to integrate fully the diverse disciplines within the earthquake research community as a platform for data utilization and verification a physical earthquake model can employ directly any earthquake property that is measurable in the field or in the laboratory to tune and test its seismicity products as a platform for probability forecasts a physical earthquake model can supply rational estimates of every imaginable earthquake statistic while simultaneously satisfying all slip and earthquake rate constraints as a platform for hazard analysis a physical earthquake model can compute earthquake shaking intensity from first principles by convolving a full suite of rupture scenarios with site specific dislocation green s functions physical earthquake models have advanced greatly in the last decade simulations of earthquake generation and recurrence are now sufficiently credible that such calculations can begin to take substantial roles in scientific studies of earthquake probability and hazard manuscript received 9 march 1999

coseismic thrusting and folding in the 1999 mw 7 6 chi chi earthquake a high resolution approach by aerial photos taken from tsaotun central taiwan we used aerial photos taken before and after the 21 september 1999 m w 7 6 chi chi earthquake in central taiwan to measure the near field ground deformation a total of 12 pairs of images were processed with co registration of optically sensed images and correlation to produce a horizontal displacement map of a 10 km 10 km area near tsaotun using pairs of images with different viewing angles both the horizontal and vertical slip across the fault zone can be measured our measurements when resampled into lower resolution are consistent with lower resolution measurements of horizontal displacements obtained from spot images as well as with vertical displacements obtained from repeated leveling measurements and field observations horizontal strain is strongly localized along the chelungpu fault clpf and along a secondary scarp that runs parallel to the clpf about 2 km to the east the ailiao fold scarp alf this pattern closely matches the surface ruptures mapped in the field horizontal strain across clpf correlates remarkably well with the topographic features produced by long term deformation the cumulative horizontal shortening across the clpf and alf amounts to 4 9 0 4 and 6 1 0 6 m respectively and fault parallel displacement is 3 4 0 4 m the pattern of surface strain is consistent with the interpretation of the alf as a fold scarp formed over an active axial hinge zone this study shows that even in this compressional setting most surface deformation is localized within narrow fault zones or active axial hinges

local infrasound observations of large ash explosions at augustine volcano alaska during january 11 28 2006 1 we present and interpret acoustic waveforms associated with a sequence of large explosion events that occurred during the initial stages of the 2006 eruption of augustine volcano alaska during january 11 28 2006 13 large explosion events created ash rich plumes that reached up to 14 km a s l and generated atmospheric pressure waves that were recorded on scale by a microphone located at a distance of 3 2 km from the active vent the variety of recorded waveforms included sharp n shaped waves with durations of a few seconds impulsive signals followed by complex codas and extended signals with emergent character and durations up to minutes peak amplitudes varied between 14 and 105 pa inferred acoustic energies ranged between 2 108 and 4 109 j a simple n shaped short duration signal recorded on january 11 2006 was associated with the vent opening blast that marked the beginning of the explosive eruption sequence during the following days waveforms with impulsive onsets and extended codas accompanied the eruptive activity which was characterized by explosion events that generated large ash clouds and pyroclastic flows along the flanks of the volcano continuous acoustic waveforms that lacked a clear onset were more common during this period on january 28 2006 the occurrence of four large explosion events marked the end of this explosive eruption phase at augustine volcano after a transitional period of about two days characterized by many small discrete bursts the eruption changed into a stage of more sustained and less explosive activity accompanied by the renewed growth of a summit lava dome

bullwinkle a unique 3 d experiment in the spring of 1988 shell offshore inc acquired two orthogonal three dimensional 3 d surveys at prospect bullwinkle located in the green canyon area of the gulf of mexico to aid the development program which began later that year two surveys were acquired because of the complexity of the salt structures in the vicinity of the prospect the independent acquisition and processing of two surveys shot perpendicular to each other provided a unique data set for checking the quality and accuracy of standard 3 d techniques the high development cost of this deep water 410 m turbidite field supported the acquisition of two 3 d data sets to provide a valuable redundancy for stratigraphic interpretation this large scale 3 d experiment has been analyzed in terms of interpretive impact detailed comparisons of the seismic images away from the salt complex show good agreement between the two surveys and verify the relative accuracy and repeatability of the acquisition processing and interpretation techniq

recurrence models and parkfield california earthquakes main shocks of the earthquake sequences that occurred on the parkfield section of the san andreas fault in central california in 1922 1934 and 1966 are characterized by southeast rupture expansion over the same 20 to 30 km long section of the fault whereas the seismic moments for the 1922 and 1934 events are identical to within a precision of 10 the seismic moment for 1966 is 20 greater than for the earlier events to within a precision of 20 the parkfield area seismicity in general seems well described by a recurring moderate size characteristic earthquake repeating the same epicenter magnitude seismic moment rupture area and southeast direction of rupture expansion an unexplained 10 year advance of the 1934 event is the only discrepancy in the hypothesis that the parkfield earthquakes in 1857 1881 1901 1922 1934 and 1966 represent a strictly periodic process assuming the strictly periodic model and the absence since 1966 of the perturbations hypothesized for the 1922 to 1934 period the next characteristic parkfield earthquake should occur between 1983 and 1993

surface traces and related deformation structures of the southern sanyi fault taiwan as deduced from field mapping electrical resistivity tomography and shallow drilling abstract the southern sanyi fault extends across a highly urbanized area in central west taiwan it is within 1 2 km from and generally parallels the northern chelungpu fault which last ruptured in 1999 mw 7 6 chi chi earthquake and caused about 2400 fatalities several questions thus arise is the sanyi fault likewise active what is its geometry and extent and should it be zoned or otherwise designated to mitigate risk through restrictions on development or engineering design we address these questions by mapping river exposed outcrops by interpreting nine near surface geophysical surveys electrical resistivity tomography ert and by compiling and assessing existing shallow borehole data outcrops in the dajia river show that the sanyi fault is mainly a low angle thrust that juxtaposes poorly lithified sandstone over alluvial gravels fault branches are common both in the hanging wall and footwall to the south the fault is not marked by a break in topography and its trace has not been clearly mapped within the alluvial plain in part motivating the current effort here the ert surveys identify the hanging wall sandstone by a relatively low resistivity of

earthquakes rupturing the chelungpu fault in taiwan are time predictable 1 on september 20 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan the time predictable model is able to describe earthquakes rupturing the fault during the past 1900 years the average recurrence periods and total slip rates are 1900 years and 3 8 mm yr for the northern segment of the fault and 630 years and 5 8 mm yr for the southern one about 30 strains caused by tectonic loading are released during failures of the fault

thermal and pore fluid pressure history on the chelungpu fault at a depth of 1111 m during the 1999 chi chi taiwan earthquake 1 on 20 september 1999 the ms7 6 chi chi earthquake ruptured the chelungpu fault in central taiwan in 2005 the taiwan chelungpu fault drilling project was launched to drill two deep holes holes a and b cutting across the fault plane the heat strength 7 0 c m within a heated layer of 5 mm on the fault at hole a due to frictional faulting is evaluated from the values of shear stress and thermal and mechanical parameters measured from the core samples based on a 1 d heat conduction equation and 2 d faulting model with the values of thermal diffusivity evaluated within a representative temperature range the thermal and pore fluid pressure history at depths 1110 37 1111 34 m in hole a is constructed results show that the peak temperature at the center of the heated layer could have been higher than 1100 c during faulting and temperature rise decreased with increasing distance and time the possible relationships between the temperatures and chemical reactions of clay minerals are discussed in detail in the heated layer pseudotachylites have been formed and quartz plasticity might also have been operative during faulting outside this slip zone the temperature rise was low and thus clay minerals were stable during faulting the evaluated pore fluid pressure is 22 5 mpa this suggests the existence of a suprahydrostatic state in the fault zone during the earthquake indirect evidence of the existence of fluids in the fault zone during faulting is described additionally rock physics is applied to interpret the observations

bomb rich basaltic pyroclastic flow deposit from nakadake aso volcano southwestern japan abstract a bomb rich basaltic pyroclastic flow deposit the izumikawa pyroclastic flow deposit occurs at the northeastern foot of nakadake volcano which is the only active central cone of aso caldera southwestern japan the pyroclastic flow deposit covers a fan shaped area of about 1 9 km2 and the bulk volume is estimated at 9 4 106 m3 the deposit is poorly sorted and consists of subangular faceted clasts and spherical cauliflower bombs set in a sandy non cohesive matrix the deposit forms two different facies a black reversely graded lower unit and a reddish gray reversely graded upper unit the cauliflower bombs which have slightly vesiculated crusts 1 0 1 5 cm thick and denser interiors are more abundant in the lower unit than in the upper unit the presence of cauliflower bombs suggests that the izumikawa pyroclastic flow was generated by an explosion at the source lava lake or conduit which was filled with mixture of solidified and molten lavas we propose the term bomb and ash flow deposit to describe this type of deposit the age of the izumikawa pyroclastic flow deposit was estimated at ca 19 cal ka based on a 14c age obtained from charred wood fragments in the deposit although all recent activity of nakadake has been ash eruptions strombolian eruptions and phreatomagmatic explosions the izumikawa pyroclastic flow deposit underscores the hazard of bomb rich pyroclastic flows that rush down the flanks of the volcano

paleoseismology of the chelungpu fault during the past 1900 years abstract the 1999 earthquake brought about 80 km long surface ruptures along the shihkang chelungpu and tajienshan faults central taiwan several trenches have been excavated across the chelungpu fault of the middle segment the surface ruptures display clear scarps ranging from 0 2 to 4 m high showing a complex geomorphic pattern due to coseismic faulting and folding in the study measurement of the vertical offset or structural relief was taken with reference to the hanging wall beyond the trishear deformation zone therefore we suggest that for the measurement of offset we should disregard the trishear zone and that structural relief on the hanging wall should be represented as a real vertical offset the net slip is then calculated from the structural relief and dip angle of the thrust on a vertical plane along the slip direction through the excavation of a pineapple field across the chelungpu fault we are able to provide evidence of at least four earthquake events for the past about 1900 years including the 1999 earthquake furthermore based on the radiocarbon dates and historical record the timing of the penultimate event is bracketed to be between 430 and 150 years ago and the average recurrence interval is less than 700 years these data indicate that the average slip rate is about 8 7 mm yr for the past 1900 years

west of shetland revisited the search for stratigraphic traps the west of shetland area has scope for the stratigraphic entrapment of hydrocarbons at various jurassic to palaeogene stratigraphic levels mapping and identification of such traps requires a fundamental understanding of the regional geology the study of analogues and source kitchens and a thorough approach to trap validation since 1982 47 exploration wells have been positioned on paleocene prospects with a significant stratigraphic component but few have found hydrocarbons many failing as a result of poor trap definition and overconfidence in the predictive use of amplitude anomalies hydrocarbon sourcing of many of the failed prospects was also poorly constrained few amplitude related stratigraphic features could be tied with confidence to a viable source kitchen the presence of a regional seal is a prerequisite ingredient for a successful paleocene play many remaining undrilled subtle prospects rely on a stratigraphic trapping component and high quality 3d seismic data are seen as an essential search tool examples of undrilled prospects are presented from the paleocene of the northern faroe shetland basin and the mesozoic of the east solan basin and corona ridge

broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches 1 we systematically used two approaches to analyze broadband seismic signals for monitoring active volcanoes one is waveform inversion of very long period vlp signals assuming possible source mechanisms the other is a source location method of long period lp events and tremor using their amplitudes the deterministic approach of the waveform inversion is useful to constrain the source mechanism and location but is basically only applicable to vlp signals with periods longer than a few seconds the source location method assumes isotropic radiation of s waves and uses seismic amplitudes corrected for site amplifications this simple approach provides reasonable source locations for various seismic signals such as a vlp event accompanying lp signals an explosion event and tremor associated with lahars and pyroclastic flows observed at five or fewer stations our results indicate that a frequency band of about 5 12 hz and a q factor of about 60 are appropriate for the determination of the source locations in this frequency band the assumption of isotropic radiation may become valid because of the path effect caused by the scattering of seismic waves the source location method may be categorized as a stochastic approach based on the nature of scattering waves systematic use of these two approaches provides a way to better utilize broadband seismic signals observed at a limited number of stations for improved monitoring of active volcanoes

estimating rates of decompression from textures of erupted ash particles produced by 1999 2006 eruptions of tungurahua volcano ecuador persistent low to moderate level eruptive activity of andesitic volcanoes is difficult to monitor because small changes in magma supply rates may cause abrupt transitions in eruptive style as direct measurement of magma supply is not possible robust techniques for indirect measurements must be developed here we demonstrate that crystal textures of ash particles from 1999 to 2006 vulcanian and strombolian eruptions of tungurahua volcano ecuador provide quantitative information about the dynamics of magma ascent and eruption that is difficult to obtain from other monitoring approaches we show that the crystallinity of erupted ash particles is controlled by the magma supply rate msr ash erupted during periods of high magma supply is substantially less crystalline than during periods of low magma supply this correlation is most easily explained by efficient degassing at very low pressures 50 mpa and degassing driven crystallization controlled by the time available prior to eruption our data also suggest that the observed transition from intermittent vulcanian explosions at low msr to more continuous periods of strombolian eruptions and lava fountains at high msr can be explained by the rise of bubbles through strombolian or trapping of bubbles beneath vulcanian vent capping variably viscous and crystalline magma

preseismic deformation and coseismic displacements associated with the 1999 chi chi taiwan earthquake the destructive 1999 chi chi taiwan earthquake m w 7 5 produced an approximately 100 km long surface rupture mostly along the previously recognized north south trending chelungpu fault preseismic deformation in central taiwan is realized from annually repeated global positioning system gps data acquired during the 1992 1999 period the total wnw ese shortening rate in the vicinity of the epicentral region that is from the west coast to the western boundary of the central range is up to 25 mm yr the crustal deformation before the chi chi earthquake was essentially a uniaxial compressional strain of 0 36 strain yr in the direction of 114 the gps measurements taken 0 2 2 7 yr before and within 3 months after the mainshock were utilized to estimate the coseismic displacements horizontal movements of 1 1 9 1 m in the nw nnw directions are observed on the hanging wall eastern side of the fault there is a northward increasing trend in the magnitude of the displacement vectors and a dramatic change in the direction of about 50 toward the east along the fault strike in contrast much smaller se see movements of 0 1 1 5 m are found on the footwall western side of the fault the gps data show 2 4 10 1 m of total horizontal offsets across the chelungpu fault vertical offsets of 1 2 4 4 m with the eastern side up are also observed along the surface rupture the uplift on the hanging wall decreases rapidly toward the east it becomes subsidence at sun moon lake and in the puli wushe area the stations on the footwall show subsidence of 0 02 0 26 m the width of the uplift zone increases from about 10 km in the south to approximately 30 km in the north manuscript received 13 october 2000

infrasound from tungurahua volcano 2006 2008 strombolian to plinian eruptive activity abstract strombolian to plinian activity from tungurahua volcano ecuador has been recorded by the autonomous infrasound arrays of the acoustic surveillance for hazardous eruptions ashe project since early 2006 our studies suggest that acoustic energy release during large eruptions does appear to broadly scale with eruption intensity this manuscript provides a detailed chronology and characterization of tungurahua s eruptive activity between 2006 and 2008 and demonstrates the ability to constrain source parameters of significant eruptions such as onset duration and escalation at regional distances by combining infrasound and remote sensing techniques the ashe system in ecuador automatically detected over 20 000 volcanic explosions at an array 37 km from tungurahua and was successful at notifying the onset escalation and cessation of a hazardous february 2008 eruption with a latency of 5 min elevated infrasonic energy from sustained and intense tungurahua eruptions correlates well with ash column heights and their lateral extent during the study period the spectra of these sustained explosive eruptions appear to be recurrent readily recognizable and indicative of volcanic jetting and significant atmospheric ash injection the paroxysmal plinian phase of the august 2006 eruption produced an ash cloud that extended well into the stratosphere 24 km coinciding with a shift of the dominant jetting frequency from 0 25 hz to below 0 1 hz and radiation of over 5 107 w of acoustic power transient explosions were often marked by minor or no ash release and are presumed to be more gas rich a change in the acoustic spectrum of volcanic jetting was also detected in the transition from a sustained to collapsed eruption column at the end of the july 14 2006 eruption the jetting spectrum at tungurahua during a period of sustained pyroclastic density current production changes from a typical double peaked to a single peaked spectrum suggesting remote acoustic monitoring can help ascertain the stability and dynamics of an eruptive column

the deliberate search for the stratigraphic trap an introduction this special publication draws upon contributions to a similarly titled conference the deliberate search for the stratigraphic trap where are we now held at the geological society in london during 2004 observations in this introductory paper have been drawn from the authors experience talks given at the conference and papers within this volume specifically it is noted that by analogy to basins which are perceived to be mature for structural traps stratigraphic traps can have substantial remaining potential additionally current exploration for stratigraphic traps seems rather restricted to areas where seismic data allow the direct assessment of fluid fill and reservoir development it is argued that the industry is probably not doing enough to learn from established stratigraphic traps to guide future exploration for such traps looking forward it is suggested that the industry faces two key challenges firstly the use of all available data to assess fluid type and reservoir presence in areas of unfavourable rock physics and secondly the development of sufficiently sophisticated predictive models of stratigraphic trap development