glacial rebound and plate spreading results from the first countrywide gps observations in iceland iceland is one of the few places on earth where a divergent plate boundary can be observed on land direct observations of crustal deformation for the whole country are available for the first t

fault kinematics at the hengill triple junction sw iceland derived from surface fracture pattern abstract the hengill triple junction in iceland is formed by the intersection of the western volcanic zone wvz reykjanes peninsula oblique rift rpor and a transform zone the south iceland seismic zone sisz the 19 13 km2 study area thus contains extensional structures related to volcanic systems of the two rift zones hengill and hromundartindur as well as strike slip structures characteristic of the transform zones high definition aerial photographs satellite images and digital elevation models are used supported by field studies to accurately map and classify tectonic features in an effort to separate n s trending strike slip faults from the fissure swarms of the volcanic systems a portion of the southern hengill fissure swarm lies within the area it trends ne sw and exhibits extensional features characteristic of spreading ridges i e normal faults open fractures and eruptive fissures it is clearly delineated by surface fractures and is traced a length of 28 km southwest from the central volcano terminating before reaching the coastline the fissure swarm is 2 3 5 km wide in the study area widening southwards elevation profiles across the fissure swarm suggest a spreading rate comparable to the southern wvz which spreads at 4 5 mm year a portion of the nesjahraun eruptive fissure is anomalously smooth and may represent secondary rifting east west shearing in the rpor and sisz is accomplished by many smaller and less conspicuous northerly oriented strike slip faults in a bookshelf faulting manner these parallel faults are overprinted on the volcano tectonic structures of the rpor evidence of 11 northerly striking strike slip faults is found within the study area the zone of bookshelf faulting is thus shown to be continuous across the triple junction area from the sisz to the rpor finally several structures eruptive fissures exposed dikes and faults strike near perpendicular to the fissure swarm and may be the result of changes in the direction of maximum stress caused by rifting events however their tectonic significance remains uncertain

seismicity of the reykjanes peninsula 1971 1976 abstract the reykjanes peninsula oblique rift a segment of the mid atlantic plate boundary connects the reykjanes ridge to the rift zones of iceland the axis of the deformation zone of the plate boundary can be traced as a rather narrow epicentral zone of earthquakes that is highly oblique to the spreading direction of the north america plate with respect to the eurasia plate the seismicity of the area is episodic active periods with a duration of about a decade are separated by more quiet periods of one to two decades our observation period spans a good part of an episode that began in 1967 and ended in 1975 nine earthquake swarms illuminate a 50 km long segment of the plate boundary the epicentral zone cuts obliquely across the fissure swarms of the volcanic systems of the peninsula geothermal areas are preferentially located at the intersection of the fissure swarms with the seismic zone outside the intersections with the seismic zone the fissure swarms show very low seismicity the tectonic characteristics gradually change along the plate boundary segment from being similar to those of a spreading segment in the western part to being more like a transform zone in the eastern part this is seen in the type of earthquake sequences maximum magnitude and type of faulting

coseismic stress changes and crustal deformation on the reykjanes peninsula due to triggered earthquakes on 17 june 2000 1 a large mw 6 5 earthquake struck the south iceland seismic zone sisz on 17 june 2000 the 17 june main shock triggered increased seismicity over a large area and significant slip on at least three distinct faults on the reykjanes peninsula up to 87 km to the west of the event a second large mw 6 4 earthquake in the sisz occurred on 21 june 2000 about 17 km west of the 17 june main shock this event does not appear to have triggered as much activity on the reykjanes peninsula as the 17 june main shock although the epicenter was closer crustal deformation signals due to the june 2000 earthquakes on the reykjanes peninsula were observed with campaign and continuous gps and synthetic aperture radar interferometry with the largest coseismic deformation signal near lake kleifarvatn we model the faults using three uniform slip rectangular dislocations in an elastic half space best fit uniform slip models consistent with seismic and geodetic data indicate that all three faults trend n s and the motion on them was primarily right lateral strike slip our study suggests that the event near kleifarvatn had a significantly larger moment than seismic estimates indicating a component of aseismic slip on the fault lasting no more than several hours static coulomb failure stress change calculations indicate that the event at kleifarvatn increased the coulomb stress at the hypocenter of the nupshlidarhals event by 0 1 0 2 mpa as well as loading the hvalhnukur fault

volcano geodesy and magma dynamics in iceland abstract here we review the achievements of volcano geodesy in iceland during the last 15 years extensive measurements of crustal deformation have been conducted using a variety of geodetic techniques including leveling electronic distance measurements campaign and continuous global positioning system gps geodesy and interferometric analysis of synthetic aperture radar images insar results from these measurements provide a comprehensive view of the behavior of icelandic volcanoes between inflation intrusion and eruption episodes volcanoes are likely to deflate or show no sign of seismic activity subsidence rates are often in the range of a few millimeters to a few centimeters a year reducing progressively with time since the last eruption or intrusion at the volcano subsidence can be caused by cooling and contraction of magma outflow of magma it can be related to plate spreading volcano subsidence or lack of deformation is often interrupted by episodic magma flow towards near surface locations such magma recharge has been observed geodetically at hengill hekla eyjafjallajokull katla grimsvotn and krafla volcanoes with inflow inferred to last from a few months up to two decades in the last 15 years five volcanic eruptions three intrusive events and two m6 earthquakes have occurred in recent years the grimsvotn and katla volcanoes have exhibited continuous inflation of a few centimeters per year which at grimsvotn culminated in an eruption on 1 november 2004 hekla and torfajokull volcanoes have inflated at rates an order of magnitude less subsidence is occurring presently at the askja and krafla volcanoes within the period of geodetic measurement signals consistent with no deformation are typical for most of the 35 active volcanoes in iceland

seismically induced changes of the fluid signature detected by a multi isotope approach he co2 ch4 n2 at the wettinquelle bad brambach central europe 1 we present a study considering the systematics of gas and isotope compositions 3 he 4 he 13 c co2 13 c ch4 15 n of a permanent magmatic co 2 flux in the hydrothermal system of the spring wettinquelle in bad brambach and their relation to the seismic activity beneath the western eger rift the gas and isotope compositions were monitored for more than 3 years the time series includes periods before during and after a 4 month long seismically active period from the end of august to the end of december 2000 shifts due to admixture of crustal components were found for all monitored isotope ratios during and after the seismically active period in case of helium and nitrogen isotopic anomalies occurred already about 6 weeks before the beginning of the seismically active period contemporaneous with a water level anomaly of the well vl4 near the wettinquelle on the one hand preseismic deformations may be responsible for the observed isotope anomalies on the other hand coseismic fracturing processes in the surroundings of the hypocenters may play a role both effects produce greater permeability and result in the release of crustal fluids the migration and admixture of these crustal components to the permanent upper mantle derived fluid flux result in geochemical anomalies that persist for more than 2 years the results of the detailed isotope monitoring have proven to be an important contribution to understand the geodynamic processes that may presently be going on in the region vogtland nw bohemia

structure and evolution of the hengill grensdalur volcanic complex iceland geology geophysics and seismic tomography recent geological and geophysical research indicates the presence of three volcanic systems in the hengill grensdalur area and progressive westerly migration of the accretionary plate boundary the hengill system comprises the active hengill central volcano and a nne trending fissure swarm that is the present locus of crustal accretion in the area extinct volcanic systems are identified with the mountain hromundartindur and the grensdalur area and associated nne trending zones the grensdalur system was formerly the locus of accretion in the area a widespread geothermal area encompasses the whole area and is fueled by at least three distinct heat sources associated with the three volcanic systems a tomographic study of the upper 5 km of crust using local earthquakes imaged three bodies with velocities up to 15 higher than the average background velocities and volumes of several tens of cubic kilometers one of these underlies the grensdalur volcano and a second underlies the olkelduhals area within the hromundartindur system these are interpreted as intrusions that are the solidified magma reservoirs of their respective volcanic systems and the heat sources of those parts of the geothermal area above them the third high velocity body underlies the extinct basalt shield husmuli which is not associated with geothermal resources that body is interpreted as a cold intrusion that is the frozen magma conduit that fed the surface eruptive site a low velocity body with a volume of a few cubic kilometers was imaged in the depth range 2 4 km beneath the northern part of the presently active hengill central volcano this volume may contain partial melt and represent the heat source or part of the heat source fueling the hengill field heat balance calculations show that subsurface magmatism continued in the extinct grensdalur volcano long after volcanic activity and crustal accretion migrated from it to the hengill system

the hengill geothermal area iceland variation of temperature gradients deduced from the maximum depth of seismogenesis abstract given a uniform lithology and strain rate and a full seismic data set the maximum depth of earthquakes may be viewed to a first order as an isotherm these conditions are approached at the hengill geothermal area s iceland a dominantly basaltic area the likely strain rate calculated from thermal and tectonic considerations is 10 15 s 1 and temperature measurements from four drill sites within the area indicate average near surface geothermal gradients of up to 150 c km 1 throughout the upper 2 km the temperature at which seismic failure ceases for the strain rates likely at the hengill geothermal area is determined by analogy with oceanic crust and is about 650 50 c the topographies of the top and bottom of the seismogenic layer were mapped using 617 earthquakes located highly accurately by performing a simultaneous inversion for three dimensional structure and hypocentral parameters the thickness of the seismogenic layer is roughly constant and about 3 km a shallow aseismic low velocity volume within the spreading plate boundary that crosses the area occurs above the top of the seismogenic layer and is interpreted as an isolated body of partial melt the base of the seismogenic layer has a maximum depth of about 6 5 km beneath the spreading axis and deepens to about 7 km beneath a transform zone in the south of the area beneath the high temperature part of the geothermal area the maximum depth of earthquakes may be as shallow as 4 km the geothermal gradient below drilling depths in various parts of the area ranges from 84 9 ckm 1 within the low temperature geothermal area of the transform zone to 138 15 ckm 1 below the centre of the high temperature geothermal area shallow maximum depths of earthquakes and therefore high average geothermal gradients tend to correlate with the intensity of the geothermal area and not with the location of the currently active spreading axis

plate boundary deformation and man made subsidence around geothermal fields on the reykjanes peninsula iceland abstract we present interferometric synthetic aperture radar insar data from 1992 1999 and 2003 2008 as well as gps data from 2000 2009 for the active plate boundary on the reykjanes peninsula southwest iceland the geodetic data reveal deformation mainly due to plate spreading anthropogenic subsidence caused by geothermal fluid extraction and possibly increasing pressure in a geothermal system subsidence of around 10 cm is observed during the first 2 years of production at the reykjanes geothermal power plant which started operating in may 2006 we model the surface subsidence around the new power plant using point and ellipsoidal pressure sources in an elastic halfspace short lived swarms of micro earthquakes as well as aseismic fault movement are observed near the geothermal field following the start of production possibly triggered by the stresses induced by geothermal fluid extraction

gas emissions and crustal deformation from the krýsuvik high temperature geothermal system iceland abstract the kr suvik volcanic system is located on the oblique spreading reykjanes peninsula sw iceland since early 2009 the region has been undergoing episodes of localized ground uplift and subsidence from april november 2013 we operated near real time monitoring of gas emissions in kr suvik using a multi component gas analyzer system multi gas collecting data on gas composition from a fumarole h2o co2 so2 h2s the dataset in this study comprises a near continuous gas composition time series the quantification of diffuse co2 gas flux analytical results for direct samples of dry gas seismic records and gps data gas emissions from the kr suvik geothermal system were examined and compared with crustal deformation and seismicity the gas emissions from the kr suvik system are h2o dominated with co2 as the most abundant dry gas species followed by smaller concentrations of h2s the average subsurface equilibrium temperature was calculated as 278 c this is consistent with previous observations made through sporadic spot sampling campaigns in addition the semi continuous multi gas dataset reveals higher variations in gas composition than previously reported by spot sampling the diffuse soil co2 flux is found to be variable between the three studied degassing areas in kr suvik ranging from 10 9 70 9 t day with the highest flux in hveradalir where the multi gas station is located the total flux is estimated as 101 t day comparison between multi gas and geophysical data shows that peaks of h2o rich emissions appears to follow crustal movements coinciding with the h2o rich peaks so2 is detected in minor amounts 0 6 ppmv allowing for calculations of h2o so2 co2 so2 and h2s so2 ratios this is the first time so2 has been detected in the kr suvik area the large variations in h2o co2 and h2o h2s ratios are considered to reflect variable degassing activity in the fumarole the activity of the fumarole appears less intense during intervals of low or no recorded seismic events the h2o co2 and h2o h2s ratios are lower presumably due to h2o condensation affecting the steam jet before reaching the multi gas inlet tube

rift transform kinematics in south iceland deformation from global positioning system measurements 1986 to 1992 crustal deformation in the plate boundary regions in south iceland is estimated from repeated global positioning system gps geodetic measurements in the period 1986 1992 we compare coordinate solutions for the 1986 and 1989 surveys with the results from the most recent survey in 1992 horizontal position uncertainty is about 2 cm for the 1986 and 1989 coordinates and about 4 mm for the 1992 coordinates little internal deformation is observed in the area west of the western volcanic zone within the north american plate and at the southern tip of the eastern volcanic zone within the eurasian plate the observed relative velocity of these two areas is 2 1 0 4 cm yr in direction n117 11 e 1 uncertainties compatible with the 1 94 cm yr widening in direction n 104 e across south iceland predicted from the nuvel 1 global plate motion model left lateral shear strain is developing across the intervening transform zone the e w trending south iceland seismic zone sisz strain is concentrated within a 20 to 30 km wide zone that correlates with seismic activity in the sisz about 85 15 of the relative plate motion is accommodated by this zone in such a way that the area south of the sisz is moving toward the east with the eurasian plate and the area north of the sisz is moving toward the west with the north american plate accordingly north of the sisz the western rift zone can accommodate a maximum of 15 15 of the relative plate motion within the sisz the shear strain results in an anticlockwise rotation of lineaments oriented north south at a rate of 0 5 1 rad yr the shear strain accumulation can be accommodated by bookshelf faulting on mapped recent north south faults in the sisz if the deformation is accommodated by an array of n s faults spaced 1 5 km apart an average slip rate of about 0 5 5 mm yr is required on each fault the rate of geometric moment release due to earthquakes averaged over centuries m 0 expected from such an array is about the same as expected from a simple transform fault 2vad where 2v is the relative plate motion a is the total length of the seismic zone and d is the thickness of the brittle crust if 2v 0 85 0 15 1 94 cm yr d 10 15 km ana a 75 85 km then m 0 1 0 2 5 107 m3 yr comparable to the rate of geometric moment release in large historical earthquakes in the sisz for the last several centuries we conclude that historical seismicity in the sisz can be attributed to left lateral shear accumulation across the seismic zone at a similar rate throughout historical times as during the years 1986 1992

monitoring of helium and carbon isotopes in the western eger rift area czech republic relationships with the 2014 seismic activity and indications for recent 2000 2016 magmatic unrest abstract we report new data of the regional distribution pattern of total gas compositions as well as he and co2 isotopic compositions from 25 gas exhalations in the western eger rift and its surroundings additionally the first time series data from gas exhalations in a clay pit within the cheb basin cb are given at 21 degassing locations the first data were obtained 20 years ago from 7 locations within the degassing center cb and from 3 degassing sites belonging to the marianske lazn ml degassing center neon and argon isotope compositions were determined also co2 is the major component at all degassing sites the 13c values display a small range 1 7 to 5 1 and the 3he 4he ratios vary from 1 9 to 5 9 ra the highest 3he 4he ratios are found at locations along the pocatky plesna fault zone followed by the degassing site in the clay pit on the nova ves fault and the locations on the ml fault at the edge of the cb although gas flow and co2 concentrations in all degassing centers are very high the fractions of mantle derived helium are different with presently up to 94 in relation to the sclm 3he 4he of 6 32 ra in the cb up to 73 in the ml and up to 35 in the karlovy vary degassing center at the locations in the eastern part of the cb a clear progressive increase of the 3he 4he ratio has been observed since the first sampling campaigns there in 1993 and 1994 whereas at the other degassing sites the helium isotope ratio remained essentially the same the progressive increase of the 3he 4he ratio in the eastern part of the cb together with further short time increases up to 6 3 ra at one location bublak before both the 2000 and 2008 earthquake swarms indicate an ongoing magmatic process beneath this area which seems to be associated with the occurrence of seismicity the cb is located close to the nov kostel focal zone where since the beginning of our investigations four strong periods of seismicity with magnitudes 3 occurred the latest gas data confirm our earlier findings time series studies showed that in relation with seismic events decreased 3he 4he ratios were repeatedly observed due to admixed seismically released crustal helium presently the eastern part of the cb is the most active non volcanic region in the european cenozoic rift system with gas signatures similar to those found in free mantle derived gases from the east african rift system

electron microscopy of a muscovite biotite interface an intergrowth of muscovite and biotite from mitchell creek mine upson county georgia was studied with a high resolution transmission electron microscope atomic arrangements of the interface between muscovite and biotite have been derived revealing far more complexity for the interface structure than that proposed previously based on optical and x ray analysis gresens and stensrud 1971 it was found that the muscovite has an almost perfectly ordered 2m 1 structure while the biotite is highly disordered despite such disorder in biotite both octahedral layers and k ion interlayers of the two minerals are connected perfectly at the interface while about 60 of the tetrahedral sheets are discontinued across the interface occasional occurrences of coherent intergrowths of chlorite like structure in biotite were recognized in the vicinity of the interface journal abstract

fissure swarms and fracture systems within the western volcanic zone iceland effects of spreading rates abstract the western volcanic zone wvz in iceland is 120 km long and 40 km wide it offers an opportunity to study rift zones in a local ultra slow spreading area close to a hotspot fractures were mapped from aerial photographs and digital elevation models most surface fractures are located in the southern part of the wvz the majority of the fractures have a north northeasterly orientation some deviations occur from this especially in the north part of the wvz fracture orientations are therefore quite uniform in the southern faster spreading part of the wvz but more irregular in the slower spreading northern part this suggests different stress fields in the north part which could be due to the influence of the hreppar microplate and possibly also due to stress fields induced by crustal deformation because of changes in glacial load in the area such glacially induced stress fields may have similar or even more influence than crustal spreading in the slower spreading northern part of the wvz lower fracture density towards the north within the wvz suggests lower frequency of rifting events in the north part in accordance with less spreading in the north as measured by gps geodetic measurements

monthly monitoring of gas and isotope compositions in the free gas phase at degassing locations close to the nový kostel focal zone in the western eger rift czech republic abstract we report new data on gas and isotope compositions of mantle derived exhalations from five locations in the vogtland germany nw bohemia czech republic area close to the nov kostel focal zone recorded by monthly sampling of gases over a three year period this region is the locus typicus for the term earthquake swarm since 1985 86 the largest numbers of earthquake swarms in the vogtland nw bohemia have occurred in the nov kostel focal zone mantle derived degassing has been studied at four locations within the cheb basin degassing centre and at the wettinquelle spring to the north on the edge of the cheb basin the bublak and u mostku locations are on the pocatky plesna fault zone ppz while the kopanina and dolni castkov locations are on the marianske lazn fault mlf the mantle derived helium content at locations along the ppz covers the range of the sub continental lithospheric mantle sclm along the mlf the 3 he 4 he ratios are with up to 5 4 ra a little bit lower as at the ppz locations the co 2 3 he ratios point to a predominantly magmatic source depending on the magnitude of gas flux the monthly sampling results indicated various major influences on the fluid signatures at the monitored locations due to seasonal cycles based on the different strong influence of co 2 water interaction micro seismicity occurred repeatedly during the monitoring period and seismically triggered geochemical anomalies were repeatedly observed at the locations close to the focal zone the 3 he 4 he ratios drop from 5 9 ra mean up to 5 6 ra at bublak and from 5 6 ra up to 5 3 ra at u mostku a decrease in 3 he 4 he ratios was observed prior to seismic events due to stress accumulation before rupturing and also after the events due to the release of crustal derived components within the area of the focal zone due to the higher helium baseline content of the kopanina gas the 3 he 4 he ratios decreased there only from 4 6 to 4 5 ra at the wettinquelle the most distant from the focal zone the 3 he 4 he ratios ranged between 2 3 and 2 5 ra altogether superimposed to the seismically induced anomalies a clear three month lasting increase of mantle derived helium was observed at the locations on the ppz the 3 he 4 he ratios increased to 6 3 ra at bublak and to 6 0 ra at u mostku an increase in the 3 he 4 he ratios was also noted at kopanina to 4 7 ra and dolni castkov to 5 4 ra interpreted as indicating an ascent of less degassed magma dyke intrusions from the deeper lithospheric mantle reservoir superimposed geochemical effects initiated by the temporal and spatial evolution of a hidden magmatic driven geodynamic process have therefore been observed in a continental rift system for the first time

inversion for sources of crustal deformation and gravity change at the yellowstone caldera the 3100 km2 yellowstone caldera yellowstone national park was formed in the latest of three explosive eruptions of rhyolites and ash flow tuffs totalling 3700 km3 at 2 1 2 and 0 6 m y before present its youthful volcanic history widespread hydrothermal activity intense seismicity and extremely high heat flow in excess of 30 times the continental average marks the yellowstone volcanic system as a giant caldera at unrest orthometric height increases of the caldera of up to 76 cm measured from precise leveling surveys from 1923 to 1975 1977 were inverted to determine volume expansion source models for the caldera wide deformation for the 1923 to 1977 uplift episode two regions of expansion were found 1 in the northern part of the caldera near the sour creek resurgent dome of 0 37 km3 and 2 in the southern part of the caldera near the mallard lake resurgent dome of 0 41 km3 both bodies occur in the upper crust from near surface depths to 6 0 km but the largest volume expansions were found in the 3 0 6 0 tan depth range the southern caldera source volume near the mallard lake dome may extend down to 9 0 km the data are however unable to resolve if these two resurgent domes separated laterally by 40 km are connected prom 1976 to 1987 nearly simultaneous measurements of elevation and gravity changes were made on a profile across the northern caldera during a period of net uplift models of the temporal gravity variation infer that the volume increase for the northern caldera source must lie above 9 0 km and involved a density perturbation greater than 0 002 g cm3 the modeled volumetric sources are in the same general locations as bodies of low p wave velocities high seismic attenuation and large negative bouguer gravity anomalies in view of the intense quaternary volcanism the anomalously high heat flow and the correlation of the source volumes with the regional geophysical anomalies it is likely that the modeled volumetric increases were caused by migration of magmas and or the introduction of large volumes of hydrothermal fluids into the upper crust

earthquake swarms to the west of mt ruapehu preceding its 1995 eruption abstract some months prior to the 1995 eruption of mt ruapehu new zealand a series of shallow earthquake swarms occurred about 15 20 km west of the summit of ruapehu several earthquakes in these swarms were felt and the largest event was m l 4 8 crustal earthquakes of m l 3 0 within 20 km of the summit of ruapehu have been rather uncommon in recent years furthermore the two periods of strongest activity were both just before times when the temperature of crater lake showed rapid increases the second of these rapid heating phases was immediately followed by increases in the mg 2 ion concentration in crater lake indicating that chemical interactions were occurring between fresh magmatic material and the lake water the coincidence between seismicity and lake changes suggested a link with the following eruption a 1 d simultaneous inversion to locate the earthquakes more accurately showed that most of the earthquakes fell into three spatial clusters each cluster having a small horizontal cross section the predominant depth was about 10 16 km the b value of this swarm was 0 74 quite compatible with ordinary tectonic earthquakes each cluster of earthquakes lies close to the normal raurimu fault which runs predominantly north south to the west of ruapehu with an east trending branch splaying off near its northern end see fig 1 b composite focal mechanisms of events in the two more southern clusters are oblique normal while the other cluster to the north has an oblique reverse mechanism the two oblique normal mechanisms suggest that extension has occurred on part of the fault this stress pattern was also observed in the focal mechanism solutions of events that occurred after the eruption when a denser network of portable seismographs covered the region although we cannot definitely connect the occurrence of these swarms to the eruptions later in 1995 there is a strong suggestion that the seismicity was connected to the process of magma movement which temperature and chemical changes in crater lake suggest was occurring during the first half of 1995

seismically triggered anomalies in the isotope signatures of mantle derived gases detected at degassing sites along two neighboring faults in nw bohemia central europe the vogtland and nw bohemia region is known for its earthquake swarms the most intensive swarm since 1985 86 occurred in october 2008 to find further indications for the interaction of ascending mantle derived fluids and the occurrence of earthquake swarms detailed fortnightly studies of gas compositions co2 n2 ar he h2 and ch4 and isotope ratios 13c 15n and 3he 4he were carried out between october 2008 and april 2011 at four locations close to the nov kostel focal zone and at the wettinquelle spring bad brambach from the start of the 2008 earthquake swarm seismically induced isotope geochemical anomalies were recorded at locations along the pocatky plesna fault zone ppz and were for the first time also found at degassing locations on the marianske lazn fault zone mlf variations were observed in both the temporal and spatial distributions of the anomalies as well in anomaly strengths probably due to the positions of these fault zones relative to the focal zone and to differences in fluid migration pathways prior to both the 2000 and 2008 swarms 3he 4he ratios 6 ra were recorded at the bublak mofette these anomalous pre seismic 3he 4he ratios suggest that both the 2000 and 2008 swarms may have been associated with the supply of fresh magma from a less degassed reservoir in the lithospheric mantle the temporal 13cco2 pattern from detailed studies at bublak between 2005 and 2011 indicates progressive magma degassing as well as seismically induced variations in the 13c providing additional support to the interpretation derived from the 3he 4he ratios

strain accumulation along an oblique plate boundary the reykjanes peninsula southwest iceland strain accumulation along an oblique plate boundary the reykjanes peninsula southwest iceland

coulomb stress changes in the south iceland seismic zone due to two large earthquakes in june 2000 1 the south iceland seismic zone experienced the largest earthquakes for 88 years in june 2000 with a ms 6 6 event on june 17 followed by another ms 6 6 earthquake on june 21 these events occurred on two parallel n s striking right lateral strike slip faults separated by about 17 km we calculate the static coulomb stress change for the june 17 and 21 earthquakes using a distributed slip model derived from joint inversion of insar and gps data we find that the static stress change caused by the june 17 event is about 0 1 mpa at the location of the june 21 hypocenter promoting failure on the second fault locations of aftershocks agree well with areas of increased coulomb failure stress our calculations indicate that positive stress changes due to the two earthquakes make the area west of the june 21 rupture the most likely site of the next large earthquake in south iceland

fluid controlled faulting process in the asal rift djibouti from 8 yr of radar interferometry observations the deformation in the asal rift djibouti is characterized by magmatic inflation diking distributed extension fissure opening and normal faulting an 8 yr time line of surface displacement maps covering the rift constructed using radar interferometry data acquired by the canadian satellite radarsat between 1997 and 2005 reveals the aseismic behavior of faults and its relation with bursts of microseismicity the observed ground movements show the asymmetric subsidence of the inner floor of the rift with respect to the bordering shoulders accommodated by slip on three of the main active faults fault slip occurs both as steady creep and during sudden slip events accompanied by an increase in the seismicity rate around the slipping fault and the fieale volcanic center slip distribution along fault strike shows triangular sections a pattern not explained by simple elastic dislocation theory these observations suggest that the asal rift faults are in a critical failure state and respond instantly to small pressure changes in fluid filled fractures connected to the faults reducing the effective normal stress on their locked section at depth

geodetic gps measurements in south iceland strain accumulation and partitioning in a propagating ridge system 1 gps observations in south iceland between 1994 and 2003 are compared with two dimensional elastic half space and viscoelastic coupling models for two parallel rift zones representing the western and eastern volcanic zones wvz evz gps data from the hreppar block between the wvz and evz fit a rigid block model within uncertainties spreading rates across the wvz increase from 2 6 0 9 mm yr in the northeast to 7 0 0 4 mm yr in the southwest conversely spreading rates in the evz decrease from 19 0 2 0 mm yr in the northeast to 11 0 0 8 mm yr in the southwest the direction of ridge propagation summed extension rates across the two rift zones are approximately constant and equal to the total plate rate 18 20 mm yr consistent with a simple propagating ridge model whereby the wvz is deactivating in the direction of evz propagation the coupling model confirms results from the simple elastic half space model including relatively shallow locking depths 5 km beneath the rift zones and allows for an estimate of mean viscosity 1019 1020 pa s beneath the elastic layer the location of maximum surface velocity gradient in the evz presumably the locus of subsurface magma accumulation and future rifting does not coincide with the 1783 1784 lakagigar fissure eruption but is 20 km to the west on the bar abunga veidivotn fissure swarm this had a small volume eruption in 1862 1864 but a major eruption in 1477 a d

evidence for ascending upper mantle derived melt beneath the cheb basin central europe 1 we present new 3he 4he data of co2 rich gas exhalations of three presently nonvolcanic areas in europe the 3he 4he ratios from the cheb basin czech republic are clearly higher than data obtained ten years ago whereas the 3he 4he ratios from the other areas laacher see germany and marianske lazn cr have remained nearly constant no other locality showing such high 3he 4he ratios in free gases supplied by continental mantle degassing is known in the european cenozoic rift system at the northeastern edge of the cheb basin swarm earthquakes repeatedly occur in the context of contemporaneous periods of seismicity the increased 3he 4he ratios are interpreted as the first geochemical evidence for ascending mantle derived melt beneath the cheb basin which is related to the triggering of earthquake swarms

strain accumulation 1986 1992 across the reykjanes peninsula plate boundary iceland determined from gps measurements gps geodetic observations 1986 1992 spanning the oblique plate boundary on the reykjanes peninsula sw iceland show that left lateral shear strain is accumulating in the area the principal strain rates are 1 0 255 0 055 strain yr extension at n121 6 e and 2 0 190 0 053 strain yr contraction at n31 6 e the principal axis of extension is perpendicular to the strike of fractures within volcanic systems on the peninsula the direction of maximum left lateral shear strain is n76 6 e the same as the trend of the seismic zone on the peninsula tensor shear strain in this direction is 0 222 0 054 strain yr continuous aseismic slip of the north american eurasian plates below a 5 11 km locking depth on the peninsula can explain the observed depth of earthquakes the width of the deformation zone determined from recent fissuring and faulting and the gps measurements of strain

evolution of stress fields and faulting in seismic zones measurements indicate that stress magnitudes in the crust are normally limited by the frictional equilibrium on pre existing optimally oriented faults fault zones where these limitations are frequently reached are referred to as seismic zones fault zones in the crust concentrate stresses because their material properties are different from those of the host rock most fault zones are spatially relatively stable structures however the associated seismicity in these zones is quite variable in space and time here we propose that this variability is attributable to stress concentration zones that migrate and expand through the fault zone we suggest that following a large earthquake and the associated stress relaxation shear stresses of a magnitude sufficient to produce earthquakes occur only in those small parts of the seismic zone that because of material properties and boundary conditions encourage concentration of shear stress during the earthquake cycle the conditions for seismogenic fault slip migrate from these stress concentration regions throughout the entire seismic zone thus while the stress concentration regions continue to produce small slips and small earthquakes throughout the seismic cycle the conditions for slip and earthquakes are gradually reached in larger parts of and eventually the whole seismogenic layer of the seismic zone prior to the propagation of an earthquake fracture that gives rise to a large earthquake the stress conditions in the zone along the whole potential rupture plane must be essentially similar this follows because if they were not then on entering crustal parts where the state of stress was unfavourable to this type of faulting the fault propagation would be arrested the proposed necessary homogenisation of the stress field in a seismic zone as a precursor to large earthquakes implies that by monitoring the state of stress in a seismic zone its large earthquakes may possibly be forecasted we test the model on data from iceland and demonstrate that it broadly explains the historical as well as the current patterns of seismogenic faulting in the south iceland seismic zone

seismicity of the hengill area sw iceland details revealed by catalog relocation and collapsing seismicity of the hengill area sw iceland details revealed by catalog relocation and collapsing

temporal stress changes associated with the 2008 may 29 mw 6 earthquake doublet in the western south iceland seismic zone on 2008 may 29 two magnitude m w similar to 6 earthquakes occurred on two adjacent n s faults in the western south iceland seismic zone the first main shock was followed approximately 3 s later by the rupture on a parallel fault about 5 km to the west an intense aftershock sequence was mostly confined to the western fault and an e w aligned zone extending west of the main shock region into the reykjanes oblique rift in this study a total of 325 well constrained focal mechanisms were obtained using data from the permanent icelandic sil seismic network and a temporary network promptly installed in the source region following the main shocks which allowed a high resolution stress inversion in short time intervals during the aftershock period more than 800 additional focal mechanisms for the time period 2001 2009 obtained from the permanent sil network were analysed to study stress changes associated with the main shocks results reveal a coseismic counter clockwise rotation of the maximum horizontal stress of 11 10 degrees 95 per cent confidence level in the main rupture region from previous fault models obtained by inversion of geodetic data we estimate a stress drop of about half of the background shear stress on the western fault with a stress drop of 8 10 mpa the pre event shear stress is estimated to 16 20 mpa the apparent weakness of the western fault may be caused by fault properties pore fluid pressure and the vicinity of the fault to the western rift zone but may also be due to the dynamic stress increase on the western fault by the rupture on the eastern fault further a coseismic change of the stress regime from normal faulting to strike slip faulting was observed at the northern end of the western fault this change could be caused by stress heterogeneities but may also be due to a southward shift in the location of the aftershocks as compared to prior events

postseismic deformation following the june 2000 earthquake sequence in the south iceland seismic zone 1 we observe postseismic deformation on two spatiotemporal scales following mw 6 5 earthquakes in the south iceland seismic zone on 17 and 21 june 2000 we see a rapidly decaying deformation transient lasting no more than 2 months and extending about 5 km away from the two main shock ruptures this local month scale transient is captured by several radar interferograms and is also observed at a few campaign gps sites located near the faults a slower transient with a characteristic timescale of about a year is detected only by gps measurements the month scale deformation pattern has been explained by poroelastic rebound due to postearthquake pore pressure changes in contrast the year scale deformation can be explained by either afterslip at 8 14 km depth or viscoelastic relaxation of the lower crust and upper mantle in response to the coseismic stress changes the optimal viscoelastic models have lower crustal viscosities of 0 5 1 1019 pa s and upper mantle viscosity of 3 1018 pa s because of the limitations of our gps campaign data we consider both afterslip and viscoelastic relaxation as plausible mechanisms explaining the deformation field both types of postseismic deformation models suggest that the areas of large coseismic stress increase east of the 17 june and west of the 21 june ruptures continue to be loaded by the postseismic deformation

possible role of fluids in the process of earthquake swarm generation in the west bohemia vogtland seismoactive region abstract the west bohemia vogtland region in the western part of the bohemian massif known for periodic occurrence of earthquake swarms is also characterised by 0 2 0 5 ma old quaternary volcanoes rich co2 emissions anomalies of mantle derived he mineral springs and moffets the detailed analysis of the time space pattern of seismicity during the january 1997 swarm demonstrates the gradual and ordered migration of micro seismic activity suggesting the step by step penetration of fluids into a small fractured volume this scenario is supported by the similarity of the source mechanisms of the natural events of the january 1997 swarm with artificial injection induced micro earthquakes during the german deep drilling project ktb in neighbouring ne bavaria also the comparison of the west bohemia vogtland earthquake swarm region with other intraplate earthquake swarm regions and with earthquake swarms induced by current volcanic processes indicates a role of intrusions of magma and related fluids in generation process of earthquake swarms

surface effects of faulting and deformation resulting from magma accumulation at the hengill triple junction sw iceland 1994 1998 the hengill triple junction sw iceland is subjected to both tectonic extension and shear causing seismicity related to strike slip and normal faulting between 1994 and 1998 the area experienced episodic swarms of enhanced seismicity culminating in a ml 5 1 earthquake on june 4 1998 and a ml 5 earthquake on november 13 1998 geodetic measurements using global positioning system gps leveling and synthetic aperture radar interferometry insar detected maximum uplift of 2 cm yr and expansion between the hromundartindur and grensdalur volcanic systems a number of faults in the area generated meter scale surface breaks geographic information system gis software has been used to integrate structural field and geophysical data to determine how the crust failed and to evaluate how much of the recent activity focused on zones of pre existing weaknesses in the crust field data show that most surface effects can be attributed to the june 4 1998 earthquake and have occurred along or adjacent to old faults surface effects consist of open gashes in soil shattering of lava flows rockfall along scarps and within old fractures loosened push up structures and landslides seismicity in 1994 1998 was distributed asymmetrically about the center of uplift with larger events migrating toward the main fault of the june 4 1998 earthquake surface effects are most extensive in the area of greatest structural complexity where n and e trending structures related to the transform boundary intersect ne trending structures related to the rift zone insar gps and field observations have been used in an attempt to constrain slip along the trace of the fault that failed on june 4 1998 geophysical and field data are consistent with an interpretation of distributed slip along a segmented right lateral strike slip fault with slip decreasing southward along the fault plane we suggest a right step or right bend between fault segments to explain local deformation near the fault b 2002 elsevier science b v all rights reserved

temporal development of the 1999 intrusive episode in the eyjafjallajokull volcano iceland derived from insar images eyjafjallajokull volcano located in southern iceland is characterized by its quiet nature only about a handful of earthquakes associated with the volcanic system had been detected prior to the 1990s earthquake swarms did however occur in 1994 and 1999 here we investigate the spatio temporal evolution of a magmatic intrusion associated with the 1999 earthquake swarm via analysis of produced surface deformation a series of interferometric synthetic aperture radar insar images spanning various periods of the intrusion show that in 1999 surface deformation occurred mainly on the southern flanks of the volcano the deformation amounts to more than 20 cm of range change inverse modeling resolves the deformation source to be a sill intrusion at 6 3 km depth sill opening was up to 1 m and the total intruded volume amounts to 0 03 km3 the insar data display a migration of the center of deformation through time enabling us to create time dependant sill opening models furthermore we investigate the spatio temporal distribution of earthquakes and find that the distribution supports the insar derived model and additionally provides indications for a possible site of a feeder channel magmatic flow rate estimates indicate an initial intrusion rate of 4 6 m3 s declining over a few weeks

absolute and relative locations of similar events with application to microearthquakes in southern iceland it is well known that similar earthquakes i e earthquakes having almost identical waveforms allow extremely accurate relative timing of the seismic arrivals this has traditionally been used for

the 1994 1995 seismicity and deformation at the hengill triple junction iceland triggering of earthquakes by minor magma injection in a zone of horizontal shear stress since july 1994 an unusually persistent swarm of earthquakes m 4 0 has been in progress at the hengill triple junction sw iceland activity is clustered around the center of the hromundartindur volcanic system geodetic measurements indicate a few centimeters uplift and expansion of the area consistent with a pressure source at 6 5 3 km depth beneath the center of the volcanic system the system is within the stress field of the south iceland transform zone and the majority of the recorded earthquakes represent strike slip faulting on subvertical planes we show that the secondary effects of a pressure source modeled as a point source in an elastic half space include horizontal shear that perturbs the regional stress near the surface shear stress is enhanced in quadrants around the direction of maximum regional horizontal stress and diminished in quadrants around the direction of minimum regional stress the recorded earthquakes show spatial correlation with areas of enhanced shear the maximum amount of shear near the surface caused by the expanding pressure source exceeds 1 strain sufficient to trigger earthquakes if the crust in the area was previously close to failure

recent uplift of the alban hills volcano italy evidence for magmatic inflation first order leveling surveyed in 1951 and 1994 along a line across the alban hills volcano reveals maximum vertical uplift of 30 cm average of 7 mm yr in the region of geologically recent 0 020 0 030 ma explosive activity the uplifted region corresponds to an area where seismic activity is concentrated at depths of 3 6 km uplift exceeding 10 cm is observed over a 14 km wide zone in the center of a 40 km long line with the deformation tapering to zero at both ends of the line data from a few sparse older benchmarks measured in 1891 and 1927 suggest that the deformation in the first half of this century was very small compared to the period 1951 1994 the observed uplift together with increased seismic activity suggest that recent magma injection has occurred in the upper crust beneath the alban hills volcano

hydrothermal alteration of plagioclase and growth of secondary feldspar in the hengill volcanic centre sw iceland dissolution of igneous feldspar and the formation and occurrence of secondary feldspar in tholeiitic basalts from the hengill volcanic centre in sw iceland was studied by microprobe analysis of cuttings from two ca 2000 m deep geothermal wells well ng 7 in nesjavellir represents a geothermal system in a rift zone where the intensity of young insignificantly altered intrusions increases with depth well khg 1 in kolvioarholl represents the margin of a rift zone where the intensity of intrusives is lower and the intensity of alteration higher this marginal well represents altered basaltic crust in an early retrograde state the secondary plagioclase in both wells is mainly oligoclase occurring in association with k feldspar and chlorite actinolite the texture of this assemblage depends on the lithology and intensity of alteration in nesjavellir ng 7 the composition of secondary albite oligoclase is correlated with the host rock composition this connection is not apparent in more intensely altered samples from kolvioarholl khg 1 the influence of temperature on composition of secondary na feldspar is unclear in both wells although ca is expected to increase with temperature any temperature dependence may be suppressed by the influence of rock composition in nesjavellir and by retrograde conditions at kolvioarhall the absence of clear compositional gradients between igneous plagioclase and secondary feldspar and between na feldspar and k feldspar suggests that secondary feldspars formed by dissolution precipitation reactions c 2002 elsevier science b v all rights reserved less

injection induced surface deformation and seismicity at the hellisheidi geothermal field iceland abstract induced seismicity is often associated with fluid injection but only rarely linked to surface deformation at the hellisheidi geothermal power plant in south west iceland we observe up to 2 cm of surface displacements during 2011 2012 indicating expansion of the crust the displacements occurred at the same time as a strong increase in seismicity was detected and coincide with the initial phase of geothermal wastewater reinjection at hellisheidi reinjection started on september 1 2011 with a flow rate of around 500 kg s micro seismicity increased immediately in the area north of the injection sites with the largest seismic events in the sequence being two m4 earthquakes on october 15 2011 semi continuous gps sites installed on october 15 and 17 and on november 2 2011 reveal a transient signal which indicates that most of the deformation occurred in the first months after the start of the injection the surface deformation is evident in ascending terrasar x data covering june 2011 to may 2012 as well we use an inverse modeling approach and simulate both the insar and gps data to find the most plausible cause of the deformation signal investigating how surface deformation seismicity and fluid injection may be connected to each other we argue that fluid injection caused an increase in pore pressure which resulted in increased seismicity and fault slip both pore pressure increase and fault slip contribute to the surface deformation

three dimensional υp and υp υs structure of the hengill triple junction and geothermal area iceland and the repeatability of tomographic inversion we investigate the crustal structure of the hengill triple junction in southwestern iceland applying tomographic methods to local earthquake data recorded in two field experiments with different network geometries and instrumentation data from the two experiments enable us to derive three dimensional models of the compressional wave speed p and the wave speed ratio p s well resolved high p bodies correlate with sites of gabbroic intrusions a small reduction in p s associated with the high temperature part of the geothermal area is probably due to mineral alteration or supercritical fluids the rms difference between the two p models about 0 26 km s 1 indicates the approximate repeatability that may be expected of good tomographic inversions

magma intrusion mechanisms and redistribution of seismogenic stress at mt etna volcano 1997 1998 terra nova 23 339 348 2011 abstract several volcanoes worldwide have shown changes in their stress state as a consequence of the deformation produced by the pressurization of a magmatic body this study investigated seismic swarms occurring on the western flank of mt etna in january 1997 january 1998 integrating seismic observations and geodetic data we constrained the seismogenic fault system and on the basis of stress tensor inversion and shmax analyses we inferred an inflating pressure source located at 5 5 km b s l beneath the west portion of summit area evaluation of coulomb failure stress related to the proposed model showed how a large part of the seismogenic fault underwent a significant coulomb failure stress increase 500 kpa we inferred the presence of a sub vertical faulted region potentially weak n50 e oriented beneath the western sector of mt etna this structure could be brought closer to failure thereby generating seismic swarms as the effect of elastic stress transfer induced by movement and or overpressure of magmatic masses within the upper crust under the volcano

natural laboratory nw bohemia comprehensive fluid studies between 1992 and 2005 used to trace geodynamic processes comprehensive studies of co2 rich fluids close to the swarm earthquake region nov kostel at the czech german border have been started 15 years ago and have in particular included two extended chemical and isotope monitoring studies lasting for several years each the regional surface distribution patterns of the fluid signatures including the identification of the origin of fluid components are the focus of the detailed studies three degassing centers cheb basin marianske lazn and karlovy vary with high co2 flux and the same level of 13c values but different levels of 3he 4he ratios have been identified the studies have located the co2 source and have investigated seismically induced changes in fluid characteristics on the basis of unique weekly sampling campaigns at selected locations a seismically triggered release of crustal helium was confirmed by both monitoring campaigns finally indications for a presently active magmatic process beneath the cheb basin have been found in contrast to volcanically active regions magma accumulation in the study area takes place at the crust mantle boundary and is not yet accompanied by heat transfer to the surface likewise reactive magma derived components are absent in the degassing fluids the area of investigation has the potential to be a natural laboratory for fundamental studies of active geodynamic processes the results of our fluid monitoring including the stunning observation of mantle derived free fluids marked by 3he 4he ratios within the subcontinental mantle range are supported by geophysical findings from seismic studies and geologic indications

crustal deformation at the oblique spreading reykjanes peninsula sw iceland gps measurements from 1993 to 1998 in 1993 and 1998 a 38 point gps network was surveyed on the reykjanes peninsula sw iceland according to the nuvel 1a plate motion model the spreading rate of the north american and eurasian plates in sw iceland is 18 9 0 5 mm yr toward n102 7 1 1 e highly oblique to the plate boundary instead of oblique spreading the measurements indicate left lateral shear strain accumulation parallel to the reykjanes peninsula seismic zone n76 e at the rate of about eyx 0 2 strain yr tensor shear strain subsidence is generally observed toward the seismic zone a local maximum subsidence of 60 mm was measured in the svartsengi geothermal area subsidence in this area has previously been detected with geodetic measurements and is considered a result of geothermal usage expansion was observed in the area of the hengill triple junction this is probably a result of magma accumulation beneath mount hromundartindur as previous seismic and geodetic measurements have indicated using a simple screw dislocation model we fit the majority of the data assuming a left lateral shear zone at depth along the seismic zone we estimate locking depth of 6 5 km and deep slip rate of 16 5 mm yr the maximum left lateral displacement predicted by the screw dislocation model 11 85 0 06 mm yr is consistent with the observed value of 11 9 0 5 mm yr if the hengill area is excluded little extension is observed across the peninsula the discrepancy between the nuvel 1a oblique spreading and the observed transcurrent motion is thought to be caused by lack of magma intrusion into the crust during this time period

current plate movements across the mid atlantic ridge determined from 5 years of continuous gps measurements in iceland 1 we analyze data spanning up to 5 years from 18 continuous gps stations in iceland computing daily positions of the stations with three different high level geodetic processing software packages we observe large scale crustal deformation due to plate spreading across iceland the observed plate divergence between the north american and the eurasian plates is in general agreement with existing models of plate motion spreading is taken up within a 100 150 km wide plate boundary zone that runs through the island of the two parallel branches of the plate boundary in south iceland the eastern volcanic zone is currently taking up the majority of the spreading and little is left for the western volcanic zone the plate boundary deformation field has been locally and temporarily affected in south iceland by two mw 6 5 earthquakes in june 2000 inflation at katla volcano during 2000 to 2004 and an eruption of hekla volcano in february 2000 all stations with significant vertical velocities are moving up relative to the reference station reyk with the highest velocity exceeding 20 mm yr in the center of the island

kinematic models of plate boundary deformation in southwest iceland derived from gps observations 1 we use data from gps campaign and continuous measurements from 1992 to 2004 in sw iceland to map the surface velocity field from the reykjanes peninsula to the eastern volcanic zone we divide the time series into preseismic july 1992 to june 2000 and postseismic june 2000 to may 2004 time intervals and we estimate gps station velocities for each interval as well as coseismic offsets due to the june 2000 earthquake sequence in the south iceland seismic zone sisz in addition to the plate spreading the preseismic velocity field shows the effects of inflation at hengill and hekla volcanoes whereas the postseismic velocities show deformation following the june 2000 earthquakes we consider several kinematic models to explain the preseismic velocities our preferred model includes several dislocations and point sources in an elastic half space with left lateral slip along the plate boundary on the reykjanes peninsula and below the sisz opening across the reykjanes peninsula and the western and eastern rift zones the optimal model has a locking depth of about 8 km in the central and eastern part of the reykjanes peninsula with a deep slip rate of about 17 mm yr and an opening of about 9 mm yr this locking depth is in agreement with the thickness of the seismogenic crust on the reykjanes peninsula which appears to vary between 7 and 9 km for the sisz we obtain a deep slip rate of about 19 mm yr below 16 km depth which is considerably deeper than the earthquake hypocenter depths in the area

geological roles of the siltstones in tight oil play abstract understanding the hydrocarbon accumulation pattern in unconventional tight reservoirs is crucial for hydrocarbon evaluation and oil gas extraction from such reservoirs previous studies on tight oil accumulation are mostly concerned with self generation or from source to reservoir rock over short distances however the lucaogou tight oil in jimusar sag of junggar basin shows transitional feature in between the lucaogou formation comprises fine grain sedimentary rocks characterized by thin laminations and frequently alternating beds the lucaogou tight silt fine sandstones are poorly sorted dissolved pores are the primary pore spaces with average porosity of 9 20 although the toc of most silt fine sandstones after soxhlet extraction is lower than that before extraction they show that the lucaogou siltstones in the area of study have fair to good hydrocarbon generation potential average toc of 1 19 average s2 of 4 33 mg g while fine sandstones are relatively weak in terms of hydrocarbon generation average toc of 0 4 average s2 of 0 78 mg g the hydrocarbon generation amount of siltstones which was calculated according to basin modeling transformation ratio combined with original toc based on source rock parameters occupies 16 72 of oil retention amount although siltstones cannot produce the entire oil reserve they certainly provide part of them grain size is negatively correlated with organic matter content in the lucaogou silt fine sandstones fine grain sediments are characterized by lower deposition rate stronger adsorption capacity and oxidation resistance which are favorable for formation of high quality source rocks low energy depositional environment is the primary reason for the formation of siltstones containing organic matter positive correlation between organic matter content and clay content in lucaogou siltstones supports this view point lucaogou siltstones appear to be effective reservoir rocks due to there relatively high porosity and also act as source rocks due to the fair to good hydrocarbon generation capability

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

kinematic model of the south icelandic tectonic system summary due to the hot spot ridge interaction the tectonical situation in the southern part of iceland is quite complex within this investigation it is shown that the western volcanic zone is in spite of missing recent volcanic activity still an active spreading zone its annual widening of 8 1 1 0 mm yr 1 represents more than 45 per cent of the spreading of the southern part of iceland the full spreading rate of the investigated region amounted to 17 1 3 0 mm yr 1 these are the results of a constrained linear multiepoch deformation analysis of six gps measurement campaigns which have been carried out between 1986 and 1999 in the southwest of iceland the presented solution combines the motion information of 79 stations to yield a linear velocity field which is a snapshot of the medium term motion the used gps measurement campaigns had changing network geometries with a lack of point identities

hengill triple junction sw iceland 1 tectonic structure and the spatial and temporal distribution of local earthquakes the hengill area is an unstable ridge ridge transform triple junction in sw iceland it contains the active central volcano hengill associated with the present accretionary zone and the extinct grensdalur central volcano associated with an accretionary zone that became inactive at about 0 7 m y when the locus of spreading migrated about 5 km w to the hengill zone the dominant tectonic trend of the area is n25 e parallel to the accretionary zones but transverse tectonic topographic features have also developed in the neighborhood of the two central volcanoes these result from local modification of the regional stress field associated with the spreading by radially symmetric stress fields associated with the volcanoes and the migration of volcanism a double high temperature geothermal system mirrors the double volcanic system the transform branch of the triple junction is represented by an ew striking zone of historic destructive earthquakes in the s of the area a seismological study was conducted with the aims of studying the tectonic structure and evaluating the passive seismic method as a geothermal prospecting tool the seismicity may be broadly divided into two groups first infrequent intense episodes of crustal movement occur that are associated with the release of tectonic stress along the plate boundary second continuous small magnitude activity occurs on a day to day basis this activity is mostly associated with the extinct grensdalur central volcano not the present plate boundary statistically significant temporal variations in b accompanied a swarm in the transform zone the continuous small magnitude activity may be geothermal in origin releasing thermal stress and not associated with plate boundary tectonics

three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland three dimensional imaging of the p and s wave velocity structure and earthquake locations beneath southwest iceland