waveforms and spectra of preshocks and aftershocks of the 1979 imperial valley california earthquake evidence for fault heterogeneity we have compared digitally recorded waveforms of m l 2 0 2 8 earthquakes that occurred in two small areas along the imperial fault before and after it broke in the ml 6 6 imperial valley earthquake on october 15 1979 eight preshocks 1977 1979 from a 4 by 1 km area centered 4 km se of the mainshock epicenter have strikingly similar waveforms over the entire record length 30 s with an average peak cross correlation between seismograms of 0 74 the seismograms are well correlated at frequencies up to at least 4 hz this implies similar source mechanisms and hypocenters within of the 4 hz wavelengths i e 200 400 m five aftershocks from the same area show an average peak cross correlation between seismograms of only 0 23 any associated changes in mechanism must be small because they are not reflected in the first motion data analysis of frequency content of these events using bandpass filtering techniques showed no systematic temporal changes in spectral shape ten preshocks and 24 aftershocks from a 1 by 2 km source area centered along the fault 16 km nw of the mainshock epicenter were also studied first motion data suggest that all of the aftershocks and a swarm of six preshocks on december 7 9 1978 were associated with the main fault but that four earlier preshocks were not the six preshocks on december 7 9 1978 were tightly clustered as evidenced by the strong similarity of the waveforms most peak cross correlations 0 6 during this swarm the 8 to 16 hz spectral amplitude increased relative to the 1 to 2 hz spectral amplitude over the whole record length by about a factor of 3 suggesting a systematic increase in stress drop groups of like events are also present among the aftershocks in this data set the average peak correlation for pairs of aftershocks 0 43 is almost the same as that for pairs of preshocks 0 45 if all 10 preshocks are included however several sources appear to have been active simultaneously during the aftershock period so that no more than two to three consecutive aftershocks have maximum cross correlations 0 6 the highly localized sources characterized by waveform similarity may represent fault asperities or clusters of asperities our observations are consistent with a decrease in the number of these asperities as the weaker ones fail under increasing stress during the intervals between large earthquakes

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

stress tensor analysis of the 1998 1999 tectonic swarm of northern quito related to the volcanic swarm of guagua pichincha volcano ecuador the phreatic activity and the subsequent dacitic dome growth in 1998 1999 at guagua pichincha volcano ecuador were associated with two seismic swarms one located in the northern part of quito population 1 500 000 and another one just below the active volcano about 15 20 km sw from the first one quito swarm tectonic events have high frequencies from 1 to 10 15 hz we registered more than 3200 events among which 2354 events of 1 4 m l 4 2 between june 1998 and december 1999 at the 2 and 17 km depth the volcanic events below the guagua pichincha caldera have high from 1 to 10 15 hz and low less than 3 hz frequencies approximately 130 000 events were registered between september 1998 and december 1999 at the 2 4 and 3 5 km depth here we study the stress tensors of these two swarms deduced from the polarities of p first motions and compare them to the regional stress tensor deduced from cmt harvard focal mechanisms the quito swarm stress tensor is relatively close to the regional stress tensor the 1 axis was oriented n117 e close to the n102 e direction of the plate motion found by the gps measurement and 3 is nearly vertical the difference may be due to the action of the closely active guagua pichincha volcano the guagua pichincha stress tensor is very different from the regional tectonic one the 1 axis of the volcano is oriented n214 e almost perpendicular to the 1 of the swarm of quito and 3 is almost horizontal even if these two tensors are different they can be explained in a more general tectonic scheme the almost horizontal direction of 3 just below the volcano is compatible with an extensional horizontal direction that may be expected in the shallow extrados part of a compressional region and consistent with an opening of the top of the guagua pichincha volcano the movement of the fluids magma gas and or groundwater produced by the closely active guagua pichincha volcano seems to have an influence in the acceleration of the generation of seismic events

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

accurate fault mechanism determinations for a 1984 earthquake swarm at campi flegrei caldera italy during an unrest episode implications for volcanological research we have analyzed 42 microearthquakes 1 ml 3 that occurred at campi flegrei volcanic area during an intense swarm like activity more than 500 events in half a day in the last period of strong ground uplift 1982 1984 focal mechanisms of these earthquakes have been computed by a probability method which uses p wave polarity and s wave polarization data composite focal mechanisms for different groups of earthquakes have also been computed by the same technique results show a well defined fault plane in agreement with the elongation of the epicentral pattern the orientation and dip of this fault plane together with other observations about hypocenter locations and focal mechanisms of the whole seismicity accompanying the ground uplift episode suggest the presence of an elliptical fracture system at the caldera center this fracture system dipping toward the center of the caldera should represent the limit of the most recent caldera collapse which is also indicated by a negative bouguer gravity anomaly moreover an important differential feature among various groups of earthquakes has been shown namely a rotation up to about 30 of the strike of the compressive stress axis between the easternmost and the westernmost events the resulting pattern indicates that the axis is always oriented towards the town of pozzuoli which roughly represents the very center of the caldera and also the center of symmetry of the ground deformation these observations strongly suggest that earthquakes are generated by the variation of the stress field associated with the deformation along prefractured zones because of their greater weakeness this study provides then the first direct evidence that both seismicity and ground deformations have a common origin

merging active and passive data sets in traveltime tomography the case study of campi flegrei caldera southern italy we propose a strategy for merging both active and passive data sets in linearized tomographic inversion we illustrate this in the reconstruction of 3d images of a complex volcanic structure the campi flegrei caldera located in the vicinity of the city of naples southern italy the caldera is occasionally the site of significant unrests characterized by large ground uplifts and seismicity the p and s velocity models of the caldera structure are obtained by a tomographic inversion based on travel times recorded during two distinct experiments the first data set is composed of 606 earthquakes recorded in 1984 and the second set is composed of recordings for 1528 shots produced during the serapis experiment in 2001 the tomographic inversion is performed using an improved method based on an accurate finite difference traveltime computation and a simultaneous inversion of both velocity models and earthquake locations in order to determine the adequate inversion parameters and relative data weighting factors we perform massive synthetic simulations allowing one to merge the two types of data optimally the proper merging provides high resolution velocity models which allow one to reliably retrieve velocity anomalies over a large part of the tomography area the obtained images confirm the presence of a high p velocity ring in the southern part of the bay of pozzuoli and extends its trace inland as compared to previous results this annular anomaly represents the buried trace of the rim of the campi flegrei caldera its shape at 1 5 km depth is in good agreement with the location of hydrothermalized lava inferred by gravimetric data modelling the vp vs model confirms the presence of two characteristic features at about 1 km depth a very high vp vs anomaly is observed below the town of pozzuoli and is interpreted as due to the presence of rocks that contain fluids in the liquid phase a low vp vs body extending at about 3 4 km depth below a large part of the caldera is interpreted as the top of formations that are enriched in gas under supercritical conditions

a model for earthquake generation during unrest episodes at campi flegrei and rabaul calderas we have analysed the seismicity that occurred at campi flegrei caldera italy in the period 1982 1984 during an unrest episode earthquake locations describe a system of inward dipping ring faults focal mechanisms of such events show a normal dip component which is not in agreement with the differential uplift of the inner caldera as defined by static ground deformations we have performed a simulation of the stress field generated by overpressure in a magma chamber in presence of lateral discontinuities using a boundary element method lateral discontinuities simulate the ring fault system marking the border of the inner caldera collapse results allow us to hypothesize that reverse fault slip on the ring fault is mainly aseismic and such aseismic movement is able to focus normal fault shear stress along the lateral discontinuities aseismic slip on the ring fault in response to static deformation is also supported by the low seismic moment released m0 1015 nm about two orders of magnitude lower than expected from the shear slip on the discontinuities needed to accomplish the total static surface deformation 1 8 m such results have been compared with observations at rabaul caldera during a similar unrest episode in this area the seismic moment release is in good agreement with shear slip produced on a system of outward dipping ring faults and seismicity is much more focused on the fault structures such a different behaviour can be interpreted in the framework of our model as due to the different sign of the stress normal to the ring faults for inward and outward dip the comparison between the two areas shed new light about the dynamics of earthquakes in calderas in terms of the role played by ring fault systems

new insights into kilauea s volcano dynamics brought by large scale relative relocation of microearthquakes 1 we investigated the microseismicity recorded in an active volcano to infer information concerning the volcano structure and long term dynamics by using relative relocations and focal mechanisms of microearthquakes there were 32 000 earthquakes of the mauna loa and kilauea volcanoes recorded by more than eight stations of the hawaiian volcano observatory seismic network between 1988 and 1999 we studied 17 000 of these events and relocated more than 70 with an accuracy ranging from 10 to 500 m about 75 of these relocated events are located in the vicinity of subhorizontal decollement planes at a depth of 8 11 km however the striking features revealed by these relocation results are steep southeast dipping fault planes working as reverse faults clearly located below the decollement plane and which intersect it if this decollement plane coincides with the pre mauna loa seafloor as hypothesized by numerous authors such reverse faults rupture the pre mauna loa oceanic crust the weight of the volcano and pressure in the magma storage system are possible causes of these ruptures fully compatible with the local stress tensor computed by gillard et al 1996 reverse faults are suspected of producing scarps revealed by kilometer long horizontal slip perpendicular lineations along the decollement surface and therefore large scale roughness asperities and normal stress variations these are capable of generating stick slip large magnitude earthquakes the spatial microseismic pattern observed in the south flank of kilauea volcano and hilina type instabilities rupture intersecting the decollement surface causing its large scale roughness may be an important parameter controlling the growth of hawaiian volcanoes

the july august 2000 seismic swarms at campi flegrei volcanic complex italy two swarms of microearthquakes ml 2 2 occurred on july 2 7 and august 22 2000 at campi flegrei accompained by a ground uplift episode 4 cm which interrupted on early march 2000 the descending trend started on 1985 spectral analysis indicates a direct involvement of magmatic hydrothermal fluids in the source process of the july swarm while the august events are typical of shear failure similar to most of the earthquakes that occurred during the last 1982 1984 bradyseismic crisis precise 3 d relative location applied to similar earthquakes allows for the recognition of two parallel alignments trending ne sw at depths of 1 7 and 3 2 km this trend is consistent with the direction of the main focal plane obtained from fault plane solutions and evidences tensile failure in close proximity to the zone of maximum uplift as depicted by geodetic measurements a fault weakening mechanism triggered by increasing pore pressure is invoked as the cause of these earthquakes

history of earthquakes and vertical ground movement in campi flegrei caldera southern italy comparison of precursory events to the a d 1538 eruption of monte nuovo and of activity since 1968 abstract the record of felt earthquakes around naples bay in southern italy is probably complete since the mid 15th century according to this record intense earthquake swarms originating beneath campi flegrei an explosive caldera located along the north coast of naples bay have occurred only twice 1 before the only historical eruption in campi flegrei in 1538 and 2 from mid 1983 to december 1984 earthquake activity during the earlier period which began at least a few years and possibly as many as 30 years before the 1538 eruption damaged many buildings in the city of pozzuoli located near the center of campi flegrei minor seismic activity which consisted of only a few felt earthquakes occurred from 1970 to 1971 the second period of intense earthquake swarms lasted from mid 1983 to 1984 again damaging many buildings in pozzuoli two periods of uplift along the shoreline within campi flegrei have also been noted since the mid 15th century 1 during the few decades before the 1538 eruption and 2 as two distinct episodes since 1968 uplift of a few meters probably occurred a few decades before the 1538 eruption uplift of as much as 3 0 m has occurred in pozzuoli since 1968 these similarities strongly suggest that for the first time in 440 years the same process that caused intense local earthquake swarms and uplift in the early 1500 s and led to an eruption in 1538 has again occurred beneath campi flegrei though no major seismicity or uplift has occurred since december 1984 because of the large amount of extensional strain accumulated during the past two decades if a third episode of seismicity and rapid uplift occurs it may lead to an eruption within several months after the resumption of activity

seismicity associated with the 2004 2006 renewed ground uplift at campi flegrei caldera italy abstract following the significant ground uplift 1 8 m of the 1982 1984 bradyseismic crisis the recent history of campi flegrei volcanic complex italy has been dominated by a subsidence phase recent geodetic data demonstrate that the subsidence has terminated and that positive ground deformation renewed in november 2004 at a low but accelerating rate leading to about 4 cm of uplift by the end of october 2006 as in previous episodes ground uplift has been accompanied by swarms of micro earthquakes m 1 4 in three distinct episodes october 2005 october 2006 and december 2006 hypocenters of these earthquakes are mainly located beneath the solfatara volcano at depths ranging between 0 5 and 4 km inversion of s wave spectra indicates source radius and stress drop on the order of 30 60 m and 104 9 105 pa respectively fault plane solutions indicate predominantly normal mechanisms accompanying the october 2006 swarm we detected intense long period lp activity for about 1 week these signals consist of weak monochromatic oscillations whose spectra exhibit a main peak at frequency 0 8 hz this peak is common to all the stations of the network and not present in the noise spectra suggesting that it is a source effect about 75 of the detected lps cluster into three groups of mutually similar events adjustment of waveforms using cross correlation allows for precise alignment and stacking which enhances signal onsets and permits accurate absolute arrival picks and thus better absolute as well as relative locations locations associated with the three different clusters are very similar and appear to delineate the se rim of the solfatara volcano at a depth of about 500 m the most likely source process for the lp events involves the resonance of a fluid filled buried cavity quality factors of the resonator cluster in a narrow interval around 4 which is consistent with the vibration of a buried cavity filled with a water vapour mixture at poor gas volume fractions we propose a conceptual model to interpret the temporal and spatial patterns of the observed seismicity

recent ground movement and seismic activity in campi flegrei southern italy episodic growth of a resurgent dome leveling surveys in campi flegrei an active volcanic caldera in southern italy show that this caldera has undergone both subsidence and uplift of a few meters during the past 85 years a single source located at a depth of about 3 km beneath the center of the caldera can account for almost all elevation changes recorded in campi flegrei since the first leveling survey conducted in 1905 1907 this includes leveling surveys that span periods of subsidence such as between 1905 1907 and 1919 and between january 1985 and october 1986 and periods of rapid uplift between march 1970 and october 1971 and between january 1981 and december 1984 a possible geometry for the source of uplift and subsidence beneath campi flegrei is a rectangular horizontal sheet located at a depth of about 3 km and centered a few hundred meters east of the city of pozzuoli the horizontal dimensions of this sheet are about 1 5 km by 3 0 km the long axis is oriented n70 w this sheet lies adjacent to the most intense area of seismicity that occurred from mid 1983 to december 1984 during an uplift episode this sheet may represent the top of a magma body undergoing internal pressure changes possibly by intrusion of additional magma subsidence is caused by groundwater removal from the water saturated deposits that fill this caldera to a depth of a few kilometers a temporary increase in subsidence rate after an uplift episode is caused by increased rate of groundwater removal from newly fractured regions that lie immediately above the magma body the close proximity of this water saturated region and the magma body makes it impossible to separate the depth to these two sources from the results of leveling surveys two observations indicate that uplift has occurred in the center of campi flegrei for at least the past several thousand years first marine deposits in the center of campi flegrei were uplifted at least 40 m between 4000 and 8000 years ago second continuous seismic profiles of the undersea portion of campi flegrei have identified only one region where rocks are fractured and faulted adjacent to the uplifted marine deposits that surround the point of maximum uplift indicated by recent leveling surveys on the basis of these observations and the historical record of activity we suggest that campi flegrei caldera is in a stage of growing a resurgent dome the present diameter of the resurgent dome is about 4 km and the maximum amount of vertical uplift during the past 10 000 years has probably not exceeded 100 m the episodes of rapid uplift and shallow earthquake swarms during the past 20 years are probably related to the growth of this resurgent dome

a physical appraisal of a new aspect of bradyseism the miniuplifts 1 the campi flegrei caldera is characterized by well known episodes of fast uplift called bradyseism the last of which produced 1 8 m of maximum vertical displacement in the period 1982 1984 less known is a particular aspect of campi flegrei unrests detected only in the last 20 years namely the occurrence of miniuplift episodes characterized by relatively small positive vertical displacements in the range 0 03 0 11 m miniuplift episodes occurred in 1989 1994 and 2000 and probably one or two times in the period 1972 1982 these small ground uplifts were also accompanied by moderate seismicity each of them was followed by a short phase of relatively quick subsidence after which the previous rate of subsidence of the period was resumed an order of magnitude analysis of the forces energy and power that can cause the onset and determine the evolution of these events is derived on the basis of a thermal fluid dynamical approach it allows the quantitative correlation of the power input from the energy source with the rate of energy dissipation in the geologic system during the miniuplifts in order to assess the likelihood of our fluid dynamical model for these episodes theoretical ground displacements have been computed these displacements result from the changes in pressure as a function of depth predicted by the fluid dynamical model for reasonable perturbations of the geothermal system described as changes of the peclet number theoretical results agree extremely well with the observed amounts of the miniuplifts

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

high precision relative locations of earthquakes at mount st helens washington several earthquake sequences have occurred at mount st helens as clusters of shallow events with nearly identical waveforms multiplets we present a technique that allows the relative relocation of events within a multiplet to at least an order of magnitude higher precision than is typically possible with traditional techniques a multiplet is studied in pairs of events called doublets each doublet is made up of a reference event and one other event from the multiplet the cross spectrum of a short window beginning just before the p arrival is used to compute differences in arrival times between seismograms from the same station for each doublet these time differences computed with a precision of 1 2 ms are then used to locate each earthquake relative to the reference event engineering explosions with well known locations are used to test the relocation technique explosions can be relocated with accuracy better than 20 m for events within 250 m of the reference explosion the relocation technique is applied to earthquakes preceding the september 10 1984 and the may june 1985 dome building eruptions of mount st helens forty events that occurred during a 12 hour period in september 1984 are located in a volume approximately 30 m in diameter beneath the lava dome the earthquakes following the extrusion do not occur in multiplets and appear to be distributed over a much larger volume in the may june 1985 eruption we recognize three multiplet sets that took place successively in time the multiplets are interpreted as repeated failure or slip within a relatively small volume due to high strain rates around the magma supply conduit

seismological significance of the 1977 1978 eruptions and the magma intrusion process of usu volcano hokkaido abstract an earthquake swarm and the major pumice eruptions in august 1977 which followed marked the start of the dacitic doming activity of usu volcano in southwestern hokkaido japan the sequence of magma intrusion processes was investigated in detail by means of seismological and other geophysical data the distribution of the abundant hypocenters shows clearly an earthquake free zone beneath the summit crater the hypocenters migrated in a manner consistent with the development of the observed asymmetrical surface deformations considered due to magma intrusion into this earthquake free zone the earthquake mechanism solutions are mostly of dip slip type and are interpreted in terms of the doming deformations the existence of earthquake families earthquakes with similar waveforms is the main cause of the peculiar occurrence of earthquakes in space time and magnitude the concept of scattered barriers of different sizes and strengths can explain well the distinct characteristics of the occurrence of the swarm and the observed episodic deformations

experimental study of caldera formation scaled experiments have been carried out on caldera collapse mechanisms using silicone as analogue magma and dry sand as analogue rock experiments were carried out in two and three dimensions using a range of roof aspect ratios thickness width 0 2 to 4 5 appropriate for caldera collapse they reveal a general mechanism of collapse only weakly dependent on the shape of the reservoir for low roof aspect ratios 1 subsidence starts by flexure of the roof and the formation of outward dipping reverse ring faults which in turn trigger formation of peripheral inward dipping normal ring faults the subsidence always occurs asymmetrically in cross section the reverse faults delimit a coherent piston bounded on each side by an annular zone of inwardly tilted strata located between the reverse and normal ring fault sets the surface depression consists of a nondeformed area piston surrounded by an annular extensional zone tilted strata for high aspect ratios 1 multiple reverse faults break up the roof into large pieces and subsidence occurred as a series of nested wedges 2 d or cones 3 d the extensional zone dominates the surface depression in the case where preexisting regional faults do not play a major role the collapse mechanics of calderas probably depends strongly on the roof aspect ratio calderas with low roof aspect ratios are predicted to collapse as coherent pistons along reverse faults the annular extensional zone might be the source of the large landslides that generate intracaldera megabreccias collapse into magma reservoirs with high roof aspect ratios may be the origin of some funnel calderas where explosive reaming is not dominant

climatic signals of the antarctic ocean a preliminary examination of the winds and sea surface temperatures in the 120 year record of ocean climate produced by the historical sea surface temperature project has provided evidence of two distinct ocean wide modes of variability one of these has a typical time scale of a few years and is closely related to the ei nino phenomenon the other has a time scale of the order of 30 100 years and has exhibited sharp changes in higher southern latitudes however the uneven distribution of the marine observations in space and time is a potential source of spurious anomaly changes a comparison of average ship winds for different sized areas with winds derived for the same areas from weather charts is presented to illustrate the limited significance that can be attached to the local anomalies this points up a need for the joint interpretation of anomaly changes over wider areas as resulting from changes in the characteristic behavior of synoptic pressure systems a tentative explanation of the nearly simultaneous changes in the winds and sea surface temperatures of the latitude belt 40 s to 50 s is derived from wyrtki s 1960 1961 circulation model for the southern ocean that region apparently plays a leading role in the long term fluctuations of ocean climate through the antarctic intermediate water and sub antarctic mode water these water masses acquire their characteristics from the surface energy balance and sea ice processes in high southern latitudes and occupy a deep layer extending up to just below the thermocline in the tropical ocean it is suggested that they could be a pathway for climatic signals from the antarctic ocean to the rest of the globe

effect of flow rules and elastic strains on pressuremeter test results in dense sand simple numerical methods that allow to obtain stress and strain paths in sand during self boring pressuremeter tests are presented in this paper the material is considered to undergo deformation in drained and plane strain conditions the flow rules of rowe cambridge type cam clay and nova model and the sawtooth model are used in the analysis elastic strains are also considered in relation with the flow rule of rowe the proposed approach has been evaluated using a reference pressuremeter test performed on ticino sand in a calibration chamber the results indicate that the stress strain volume change responses of the sand predicted by the various models are quite similar with and without consideration of the elastic strain components

the restless resurgent campi flegrei nested caldera italy constraints on its evolution and configuration abstract we have collected new stratigraphic data in the campi flegrei caldera through surface geological mapping and study of cores drilled to various depths we integrate these data with geological geochronological and geophysical constraints available in the literature to reconstruct the volcanic and deformational history of the caldera the caldera is a resurgent nested structure resulting from two main collapses related to the campanian ignimbrite 37 ka and the neapolitan yellow tuff 12 ka eruptions while the structure is affected by a broad subsidence ongoing local resurgence and unrest occur inside the younger nested caldera structure although most of the caldera floor consists of multiple structural blocks due to long term deformations magmas were able to erupt only in one sector of the resurgent part the caldera has shown signs of unrest during the past 25 years with short term deformations that have generated a net uplift of 3 5 m the short term deformations are related to the neapolitan yellow tuff caldera resurgence and interpreted as the net result of brittle and ductile components the long term deformations likely represent the sum of the permanent brittle component of each short term deformational event

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

fracture mapping in the soultz sous forets geothermal field using microearthquake locations 1 in 2003 a massive hydraulic fracturing experiment was carried out at the european geothermal hot dry rock site at soultz sous forets france the 2 week injection of water generated a high level of microseismic activity triggering about 90 000 microearthquakes during and after the fluid injection of these 21 000 events detected at all stations were located individually with a grid search algorithm to characterize the extent of the seismic zones and ultimately of the fracture network the accuracy of these initial locations was around 70 m not sufficient to map detailed fracture patterns a precise relocation effort was undertaken to reduce the location uncertainties using three different techniques joint hypocenter determination jhd collapsing and multiplet analysis the collapsing method was added to the jhd results to further consolidate the hypocenters on the other hand a multiplet analysis was performed on the initial data set for identifying microearthquakes with similar waveforms and hence relocating relatively the correlated events the delays in traveltime were computed by wavelet analysis and the events were relocated using a grid search algorithm we found 7463 events whose seismograms correlated with a correlation coefficient of 0 8 or higher most of which were doublets multiplets are horizontal tube like structures with lengths from a hundred to several hundred meters striking along the direction of the maximum compressive horizontal stress we interpret these structures as the preferential paths where fluid flow is largely confined this hypothesis is reinforced by the good correlation in depth between the events and the fluid outflows observed in the well therefore we believe that these relocated events highlight the zones where the permeability of the reservoir is increased

modelling gravity variations consistent with ground deformation in the campi flegrei caldera italy abstract in recent years 1970 72 and 1982 84 two inflation episodes took place in the campi flegrei caldera italy characterized by significant ground uplift and gravity variations an elastic half space model with vertical density stratification is employed to compute the displacement field and the gravity variations produced by the deformation of buried layers following the inflation of a spherically symmetric deformation source contributions to gravity variations are produced by dilation contraction of the medium by the displacements of density interfaces the free surface and subsurface layers and of source boundaries and possibly by new mass input from remote distances into the source volume three cases were examined in detail in case i the magma chamber is identified as the deformation source and volume and pressure increase in the magma chamber is due to input of new magma from remote distances in case ii deformation is due to magma differentiation within the magma chamber deformation source with constant mass in case iii the geothermal system is identified as the deformation source and a pressure increase possibly driven by the exsolution of high temperature and high pressure volatiles in the magma chamber is assumed to play a dominant role from the comparison between measured and computed gravity residuals free air corrected gravity variations we can assess that in case i an inflation source with constant density would predict gravity residuals compatible with observations whereas an expansion at constant mass case ii would predict gravity residuals much lower than observed the resolving power of gravity data however prevents accurate assessment of the density of the emplaced material in case iii the pervasive density increase of the geothermal fluids induced by pressure increase is assumed to be the main source of gravity variations the average porosity value required for this model to match both the ground deformation and the gravity residuals is found to be 10 a value which is compatible with measured porosity values at campi flegrei in deep wells the subsidence phases following both inflation episodes and the gravity residuals during subsidence lead us to consider case iii as more plausible even if a suitable combination of cases i and iii cannot be discarded

detailed fracture system of the soultz sous forets hdr field evaluated using microseismic multiplet analysis the reservoir structure of the soultz hdr field has been investigated by examining induced microearthquake multiplets microseismic events with similar waveforms have been selected from microseismic data obtained during a 1993 hydraulic fracturing experiment precise relative arrival times and source locations have been determined by cross spectrum analysis the cross spectrum analysis decreased the residual from 0 75 ms to 0 1 ms the estimated orientations of the multiplet planes are consistent with fracture orientations detected in soultz boreholes a comparison between the stress field and the orientation of structural planes suggests that the structural planes were under a critical condition of frictional slip

spatiotemporal variations of crustal anisotropy from similar events in aftershocks of the 1999 m7 4 izmit and m7 1 duzce turkey earthquake sequences summary we analyse spatiotemporal variations of crustal anisotropy along the karadere duzce branch of the north anatolian fault from similar earthquakes in the aftershock regions of the 1999 mw7 4izmit and mw7 1 duzce earthquakes the similar earthquake clusters are identified by performing cross correlation on waveforms generated by 18 000 earthquakes depending on the applied similarity criterion about 4 60 per cent of the events belong to similar event clusters splitting parameters averaged within each cluster show significant variations for slightly different ray paths indicating strong spatial variations of crustal anisotropy in this area we also find clear changes in the spatiotemporal seismicity patterns following the duzce main shock large apparent co seismic changes up to 30 per cent of shear wave splitting delay times are observed across the time of the duzce main shock at stations near the epicentral region however the changes can be mostly explained by the spatial variations of ray paths due to the changing seismicity rather than changes in the properties of the anisotropic medium splitting parameters measured within similar earthquake clusters indicate at most 2 per cent changes in delay times associated with the occurrence of the duzce main shock the results do not show systematic precursory changes before the duzce main shock

genesis and evolution of unrest episodes at campi flegrei caldera the role of thermal fluid dynamical processes in the geothermal system we develop a model for describing water flow in a porous medium under the effect of thermal and pressure gradients the model simulates geothermal systems in calderas given the boundary conditions and the fluid dynamical properties of the medium the model allows computation in fluid dynamical stationary states of parameters characterizing the flow such as flow velocity and temperature and pressure distributions at depth the model is applied to investigate the effects of the local geothermal system on the unrest episodes at campi flegrei caldera using experimentally determined fluid dynamical parameters for the caldera rocks we show that changes of water flow in shallow aquifers under the effect of pressure and or temperature variations within the geothermal system can be very important in the genesis and evolution of unrest crises in particular they can strongly amplify the effect of pressure increase in the magma chamber on ground uplift they can also explain the timescales of evolution of ground movements in terms of transit times of the water front and of the connected temperature fronts due to advective transport on such grounds an integrated mechanic thermal fluid dynamical model was built allowing us to give a semiquantitative global explanation to the genesis and evolution of unrest phenomena results obtained here can be generalized to other similar calderas

a preliminary study of stress pattern at phlegraean fields as inferred from focal mechanisms thirty seven selected earthquakes which occurred in phlegraean fields from april to december 1983 are investigated from the focal mechanism point of view in order to attempt a preliminary representation of the stress pattern in the area from 37 earthquakes 15 reliable solutions were obtained ten mechanisms for events located around the solfatara crater are of tensional type 2 located in the gulf of pozzuoli seem to be compressive no predominant orientation ofp andt axes seem to occur evidently a more accurate analysis with a greater number of data in particular for compressive events is necessary in order to resolve a detailed map of stress pattern