sediment transport resuspension and accumulation rates in the northeastern skagerrak results of watercolumn light transmission measurements in the skagerrak and of 210pb excess and 137cs determinations in boxcore sediments of the eastern skagerrak are combined to study regional sediment transport resuspension and sedimentation patterns and rates in the upper water layer a 20 m thick surface nepheloid layer formed by concentration of particles at the thermocline and pycnocline is best developed in the eastern skagerrak and less well in the southwestern skagerrak off the danish coast bottom nepheloid layers are extensively developed in the southeastern skagerrak and indicate additional sediment input via resuspension in shallow water areas and near bottom sediment transport in suspension following the prevailing current regime locally the transmission in the bnl is reduced by more than 50 compared to clear water transmission values between 85 and 90 210pb and 137cs derived sedimentation rates are highest in the eastern and northeastern skagerrak and least in the central deep basin there is generally a good agreement between 137cs and 210pb data indicating that sediment accumulation on the short 30 year and longer 100 year time scale is of comparable magnitude

gravity changes and deformation due to a magmatic intrusion in a two layered crustal model we develop and extend theoretical and computational methods for the calculation of the deformation gravity and potential change due to a point source of magma injection into a multilayered elastic gravitational earth model in our calculations which are based upon the method outlined by rundle two distinct layers overlying a half space may be incorporated the source can be located in either of the layers or the half space the method is quite general and can be readily adapted to calculations in which stresses in either the layers or the half space relax by viscoelastic flow the results obtained indicate that the use of homogeneous half space to represent the earth may in some cases be too simple a model and that variations in elastic moduli have a more significant effect than variation in reference density on both the surface displacements and gravity changes as an example we calculate the displacement and gravity changes due to a subsurface mass injection in a crust mantle model appropriate to the volcanic island of lanzarote which is presently the subject of numerous geophysical experiments both historical and recent data indicate that lanzarote may be subject to some risk of volcanic eruption in the future thus our calculations may be useful in interpreting observations of preemption phenomena the results are discussed in terms of prediction versus measurement capabilities

elongated depressions associated with pockmarks in the western slope of the norwegian trench abstract terraces or elongated depressions have been surveyed in the western slope of the norwegian trench in origin the depressions seem to be closely related to the formation of pockmarks in the norwegian trench a study area d has been selected in the western slope for the description of the elongated depressions and their associated features an area of similar size e has also been selected in the norwegian trench in order to compare the recent geology of the two areas it is found that the elongated depressions probably are caused by a combination of shallow gas seepage the geometry of subsurface bedding and the action of bottom currents furthermore examples of faulting within soft silty unconsolidated clay is documented by use of deep towed boomer data the existence of such faults could explain how gas migrates through the upper layers

new results at mayon philippines from a joint inversion of gravity and deformation measurements in this paper we detail the combination of the genetic algorithm ga inversion technique with the elastic gravitational model originally developed by rundle and subsequently refined by fernandez and others a sensitivity analysis is performed for the joint inversion of deformation and gravity to each of the model parameters illustrating the importance of proper identification of both the strengths and limitations of any source model inversion and this technique in particular there is a practical comparison of the theoretical results with the inversion of geodetic data observed at the mayon volcano in the philippines where there are gravity changes without significant deformation after the 1993 eruption

phanerozoic continental drift abstract an account is given of phanerozoic continental drift a series of paleocontinental maps is presented for ten intervals from 600 to 25 my ago post triassic maps were reconstructed using the plate tectonic model based mainly on ocean floor spreading evidence continental edge fits and apparent polar wander apw paths the middle carboniferous triassic maps are less certain lacking ocean floor spreading evidence but continental positions are constrained by the assumptions of minimum relative continental motions the pre carboniferous maps are based on poorly defined apw paths and minimum motions and can only indicate probable configurations during that period the main theme is that the late precambrian pan african pangea has been progressively fragmented during the phanerozoic pieces broken off in the paleozoic have now collided with one another forming the present northern continents which have grown at the expense of pangea except for india fragments broken off in the mesozoic and cenozoic are still unattached and form the present southern continents

large pockmarks gas charged sediments and possible clay diapirs in the skagerrak abstract extensive patches of shallow gas charged sediments have previously been documented in the eastern skagerrak the strait between norway and denmark recently obtained high resolution side scan sonar and sub bottom profiler data presented here document several surface and sub surface features at the border and inside zones of such gas charged shallow sediments four examples are presented and discussed 1 a low profile 3 m deep pockmark and gas charged sediments 2 a low profile 6 m deep pockmark associated with a rugged sub surface reflector 3 large up to 24 m deep and 500 m wide pockmarks and 4 patches of exposed material from the rugged sub surface reflector from similarities with previously described features and also with features found in the kattegat further south it is concluded that the pockmarks are formed by gas eruption and seepage and that the rugged sub surface reflector could possibly represent the upper surface of a diapirically deformed unit of gas charged plastic clays

coseismic three dimensional displacements determined using sar data theory and an application test we present a methodology to construct three dimensional deformation maps using different parameters that can be extracted using sar data we apply the methodology using envisat sar data before and after the december 26 th 2003 mw 6 6 bam earthquake in iran to determine spatial quasi continuous three dimensional coseismic deformation maps two near vertical deformation offset components are computed using envisat asar differential interferometry dinsar while two horizontal deformation offset components are measured using sub pixel correlation techniques applied to asar amplitude images using the presented methodology we combine four unevenly precise independent projections of surface coseismic deformation to obtain the full three dimensional coseismic deformation field caused by an earthquake the full 3 d coseismic displacement vector is modeled using elastic deformation models constraining details of the fault geometry and slip distribution at depth results from the inversion are interpreted in the framework of the iranian present day tectonism full exploitation of dense 3 d coseismic surface deformation using sar data even for moderate earthquakes should facilitate distinguishing between different interpretations of the mechanical properties of seismically active areas and within the inherent ambiguity of the geophysical inversion solutions

hazard assessment during caldera unrest at the campi flegrei italy a contribution from gravity height gradients hazard assessment and risk mitigation at restless calderas is only possible with adequate geophysical monitoring we show here how detailed long term micro gravity and deformation surveys may contribute to hazard assessment at the campi flegrei caldera cfc in italy by evaluating gravity height change g h gradients obtained during ground inflation and deflation between 1981 and 2001 such gradients provide a framework from which to assess the likelihood and type of volcanic eruptions our new analysis of unrest at the cfc allows us to separate noise during the gravity survey from the signal of deep seated magmatic processes this facilitates identification of the dynamics within the magma reservoir beneath the cfc we found that magma replenishment during rapid uplift between 1982 and 1984 was insufficient probably by one to two orders of magnitude to trigger an eruption similar to the 1538 monte nuovo eruption the most recent volcanic eruption within the cfc furthermore our interpretation of g h gradients for the ongoing period of deflation since 1984 suggests that eruptive volcanic activity is not imminent short periods of minor inflation associated with large gravity changes since 1981 are interpreted to reflect noise which to some degree is probably due to sub surface mass density changes within shallow hydrothermal systems beneath the cfc indicating no risk of eruptive volcanic activity we propose that monitoring g h gradients at restless calderas is essential as a caldera develops from a state of unrest to a state where volcanic eruptions have to be anticipated adoption of this method for the several tens of restless calderas world wide will provide early warning of changes in or increase of activity at these supervolcanoes

inversion of temporal gravity changes by the method of local corrections a case study from mayon volcano philippines abstract the 3d inversion method based on local corrections has been introduced by prutkin to invert potential field data it has been applied to gravity data inversion on local regional and global scales here we introduce the application of this method to invert temporal gravity changes the inversion procedure is demonstrated by a case study on gravity changes observed at the mayon stratovolcano between campaigns spanning a period of 1992 1996 residual gravity changes are compiled from the observed ones no significant surface deformation was observed within the accuracy of the campaign gps measurements during the considered period residual gravity changes were first inverted in terms of sources represented by 3d line segments the line segment approximation facilitates the second step of the iterative non linear inversion based on local corrections in the second step the residual gravity changes were inverted in terms of 3d star convex homogenous bodies representing sources of subsurface mass density changes published geological evidence indicates a shallow magma system at mayon the absence of significant deformation accompanying the gravity changes indicates that this system was nearly open during 1992 1996 we hypothesize that the sources of the gravity signal represent mass transport namely injection of magma into voids of the shallow system inversion results for campaign differences 3 1 and 4 1 are presented for both epochs the inversion results in a source located at a depth of about 4 4 km 0 3 km below sea level the mass of injected magma was estimated at 0 35 0 10 mu and 0 12 0 04 mu for the two epochs respectively we also compare our results with previous interpretations of the same data

volcanic eruption prediction magma chamber physics from gravity and deformation measurements one of the greatest remaining problems in modern volcanology is the process by which volcanic eruptions are triggered it is generally accepted that eruptions are preceded by magma intrusion sigurdsson and sparks 1978 the degree of interaction between previously ponded magma in a chamber and newly intruded magma determines the nature and rate of eruption and also the chemistry of erupted lavas and shallow dykes here we investigate the physics of this interaction volcano monitoring at its most effective is a synergy between basic science and risk assessment while hazard mitigation depends on reliable interpretation of eruption precursors the simple and much used mogi model relates ground deformation h to changes in magma chamber volume gravity changes g combined with ground deformation provide information on magma chamber mass changes our new models predict how the g h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity thus by simultaneous measurement of deformation and gravity at a few key stations magma chamber processes can be identified prior to the onset of conventional eruption precursors

deformation gravity and potential changes due to volcanic loading of the crust a method for calculating deformation gravity and potential changes induced by volcanic loads imposed within and on the earth s crust is presented the method involves application of techniques developed for earthquake loading problems in elastic gravitational earth models by considering the elastic gravitational equilibrium of the layered system the gravitational and displacement response due to intruding masses and to pressurized magma chambers can be computed for applications involving seamount loading variations in the height of sea level can be calculated by requiring that seawater lie along an equipotential in continental loading problems the change in potential can be used to calculate the orthometric height cahnge as distinct from the geometric height change for some plausible loading geometries the difference between these two qunatities can be significant results for various loads and earth structures are shown and discussed in particular a magmatic mass intruding into an elastic gravitational lithosphere overlying a compressible gravitating asthenosphere produces distinct gravity anomalies which depend on the depth of intrusion applications of this result can be made to problems of isostatic compensation the intrusion of a magmatic mass together with the associated pressurization of the magma chamber produces distinctive surface gravity and deformation in the near field gravity gradients more defined as surface gravity divided by uplift vary with distance from the source moreover orthometric elevations can be significantly 25 less than geometric elevations these results have clear application to data from events such as the posteruption deflation of kilauea volcano less

inflation or deflation new results for mayon volcano applying elastic gravitational modeling volcanic activity produces deformation and gravity changes that many times can be used as precursors of future eruptions applying geodetic techniques to monitoring activity involves interpretation using deformation models usually the observed changes of the deformation and gravity fields are interpreted seperately not in a joint inversion it can be difficult if not impossible to interpret the data coherently or correctly in terms of the characteristics of the intrusion or the deflation derived from the gravity changes with purely elastic models as in the case of mayon volcano phillipines we show that elastic gravitational models can be used to interpret these cases simultaneously leading to a result that is more plausible on the basis of the available information thus we may need to change the philosophy normally used to interpret geodetic observations interpretation as proposed in this work can significantly improve the possibility of predicting future eruptions

interpretation of 1992 1994 gravity changes around mayon volcano philippines using point sources significant gravity changes observed around the mayon volcano philippines between 1992 and 1994 at 26 stations are interpreted in terms of an increase of mass and pressure changes at several point sources modelled using a fast inversion process this inversion approach attempts to fit gravity and elevation changes by combining a random search for the positions of the sources and a linear least squares fit for the incremental mass pressure and possible common regional values for gravity or elevation changes some stabilizer terms are included in the misfit function models with one and two sources were tested against the observed changes at mayon models with only one source give a best fit for a shallow source with a positive mass increment horizontally displaced far from the summit the study using two sources gives a best fit that is similar to the one source model but in addition indicates anomalous behavior at stations in the sw neglecting the stations located southward from a local fracture the best fitting model suggests one central positive mass change source which is likely to be an intrusion of about 0 5 mu with a depth of about 5 km beneath the volcano standard deviation for the residuals ranges from 7 8 gal for one source models to 6 7 gal for models with two sources both of the cases are below the error value of 9 4 gal estimated for the gravity data so that it is not possible to discriminate between both possible interpretations without additional information

constraints in 3d gravity inversion a three dimensional 3d inversion program is developed to interpret gravity data using a selection of constraints this selection includes minimum distance flatness smoothness and compactness constraints which can be combined using a lagrangian formulation a multigrid technique is also implemented to resolve separately large and short gravity wavelengths the subsurface in the survey area is divided into rectangular prismatic blocks and the problem is solved by calculating the model parameters i e the densities of each block weights are given to each block depending on depth a priori information on density and the density range allowed for the region under investigation the present computer code is tested on modelled data for a dipping dike and multiple bodies results combining different constraints and a weight depending on depth are shown for the dipping dike the advantages and behaviour of each method are compared in the 3d reconstruction recovery of geometry depth size and density distribution of the original model is dependent on the set of constraints used from experimentation the best combination of constraints for multiple bodies seems to be flatness and a minimum volume for the multiple bodies the inversion method is tested on real gravity data from the rouyn noranda quebec mining camp the 3d inversion model for the first 10 km is in agreement with the known major lithological contacts at the surface it enables the determination of the geometry of plutons and intrusive rocks at depth

biostratigraphic and sedimentological evidence of hydrographic changes in the kattegat during the later part of the holocene abstract detailed sedimentological and micropaleontological investigations complemented with 14 c analyses were made in a large number of cores from the kattegat in general the holocene in the kattegat is represented by sediments deposited since 4000 yrs b p resting directly upon glacial sediments sediments formed between the younger dryas and 4000 yrs b p are found in restricted areas near the coast at present day water depths of less than 20 25 m the cores yield evidence of one pronounced hydrographic shift at 4000 yrs b p and two minor changes at 2000 and at about 300 yrs b p these three hydrographic shifts are in addition to sedimentological changes also characterized by the following biostratigraphic markers 1 at 4000 yrs b p the benthic foraminifers nonion labradoricum a different variety of ammonia batavus and a benthic microforaminiferal fauna became established 2 at 2000 yrs b p a pronounced appearance of an algal cyst occurred called here varia type a and 3 at about 300 yrs b p varia type a peaked and subsequently vanished the hydrographic shifts are attributed to changes in the inflow outflow regime between the north sea and the skagerrak kattegat baltic and tentatively to changes in the large scale circulation patterns of the north atlantic

imaging the complex geometry of a magma reservoir using fem based linear inverse modeling of insar data application to rabaul caldera papua new guinea we test an innovative inversion scheme using green s functions from an array of pressure sources embedded in finite element method fem models to image without assuming an a priori geometry the

detecting volcanic eruption precursors a new method using gravity and deformation measurements abstract one of the fundamental questions in modern volcanology is the manner in which a volcanic eruption is triggered the intrusion of fresh magma into a reservoir is thought to be a key component the amount by which previously ponded reservoir magma interacts with a newly intruded magma will determine the nature and rate of eruption as well as the chemistry of erupted lavas and shallow dykes the physics of this interaction can be investigated through a conventional monitoring procedure that incorporates the simple and much used mogi model relating ground deformation most simply represented by h to changes in volume of a magma reservoir gravity changes g combined with ground deformation provide information on magma reservoir mass changes our models predict how during inflation the observed g h gradient will evolve as a volcano develops from a state of dormancy through unrest into a state of explosive activity calderas in a state of unrest and large composite volcanoes are the targets for the methods proposed here and are exemplified by campi flegrei rabaul krafla and long valley we show here how the simultaneous measurement of deformation and gravity at only a few key stations can identify important precursory processes within a magma reservoir prior to the onset of more conventional eruption precursors

expulsion of shallow gas in the skagerrak evidence from sub bottom profiling seismic hydroacoustical and geochemical data a combined high resolution seismic sub bottom profiling and multi beam echo sounding survey in the skagerrak danish sector of the north sea together with gas analyses at a station along the profile exhibit the expulsion of gas mainly methane and the presence of gas charged sediments at shallow depth the echo soundings yield detailed insight into the distribution and shape of typical sea floor features associated with gas seepage such as pockmarks the pockmarks reach dimensions of 800 m in length 300 m in width and 15 m in depth with the long axis running parallel to the slope of the norwegian trench processing of the multi channel high resolution seismic data and the digitally recorded sub bottom profiler signals indicate an internal compressional velocity of about 1050 m s 1 within the gas charged sediments reaching from the sea floor to a sub bottom depth of about 23 m using the lateral distribution and thickness of the gas charged sediments in conjunction with a mean concentration of gas of 3000 ppb the present amount of trapped gas is estimated to be 6 45 1011 g ch4 the flux of methane through the sea bed into the water column appears to be 7 2 1010 g ch4 per year to explain the small difference in size between the methane pool in near surface sediments and the annual flux through the sea bed a constantly high supply of methane from leaking hydrocarbon reservoirs at greater depths has to be active

sandwaves and other large scale bedforms as indicators of non tidal surge currents in the skagerrak off northern denmark abstract results from side scan sonar surveys made at two sites in the skagerrak off hanstholm and hirtshals show that transverse and longitudinal current induced bedforms are widespread in both areas down to a water depth of 70 m a maximum sandwave height of 7 m is found off hanstholm comet marks have a maximum length of near 50 m off hanstholm wave action markedly affects the seabed at depths of less than 25 m this can cause significant deformation of current induced bedforms the bedforms are not relict structures they demonstrate that maximum bottom flow velocities associated with the jutland current can locally reach a magnitude of at least 70 100 cm s bedform configuration and sediment distribution off hansholm indicate continuation of the jutland current bottom flow axis in a northeast direction diverging from the coastline this may favour sand transport in greater water depths than is usually found elsewhere in the area as an exception at one occasion at the site off hirtshals megaripples were found to have southwest facing leeside slopes and small comet marks were also directed towards the southwest this must have resulted from exceptional outflow conditions with bottom current speed in excess of 60 cm s

mayon volcano philippines change of monitoring strategy after microgravity and gps measurements from 1992 to 1996 abstract mayon volcano is part of the bicol volcanic chain on the island luzon philippines during this century there were ten activity periods distributed almost regularly because of the density of population about one million people living in the vicinity of the volcano three seismological observatories are in operation measurements of gravity changes started in 1992 just before the eruption of february march 1993 two profiles at the slope were established connected to a regional network around the volcano in order to enable the determination of mass changes between the campaigns the height control was provided by parallel gps measurements in all the network consists of 26 points which were remeasured with three gravimetres at least three times within one campaign during five campaigns within 4 years the differential gps gives no significant changes of the elevation within 4 cm nevertheless the gravity increased significantly by up to 1500 nm s2 equivalent to 150 gal as no significant change of elevation is observed gps no extended shallow magma chamber system below the volcano can be proved this is in accordance with geochemical results indicating a rather undifferentiated magma the youngest lava which is of interest for the eruption dynamics belongs to the medium k basaltic andesite field of the k2o vs sio2 diagram a rather qualitative check of groundwater level changes reveals that these cannot be the sources for the observed gravity changes thus the increase of gravity after the eruption of february 1993 can be explained by a mass redistribution in the volcanic vent from above the level of the gravity points to below practical conclusions of these results lead to changes in the monitoring strategy deformation measurements did not reveal any volcanic activities at least for the eruption of 1993 no significant deformation was observed gravity could be an indicator for long term changes thus repeated gravity measurements gps at selected points could be used in parallel to seismic monitoring to detect slow mass movements prior to changes in seismicity

seismic stratigraphy and quaternary sedimentation in the skagerrak northeastern north sea abstract ice movement sea level fluctuations and currents are the controlling factors of the late pleistocene and holocene sedimentation processes in the skagerrak the erosional truncation at the top of a mesozoic depositional sequence defines the extent of the norwegian channel and functions as the initial depositional surface for quaternary sedimentation on this surface in shallow waters off the danish coast weichselian glacial sediments are deposited an end morain ridge marks a temporary stillstand of the retreating ice front at the beginning of ice free conditions some 15 000 yrs ago when the sea was about 70 m below the present level the skagerrak was a fjord like forebasin of the northern atlantic and constituted a favorable outlet for rivers draining the subaerial glacial deposits of the southern skagerrak and the present southern north sea fluvial erosion released large amounts of detrital material which was laid down in the form of a progradational delta prodelta complex slumping and mass flow processes led to high sedimentation rates and a rapid infilling of the norwegian channel in front of the delta complex with the rapid transgression of the southern north sea at the beginning of the holocene a dramatic change in the depoenvironment of the skagerrak took place the modern current pattern became established whereby sediment transport and redeposition became the rule along the danish coast sandwaves and megaripples with an apparent northeasterly migration direction were formed as a result of the wind forced jutland current fine suspended particles bypass the coastal zones to settle out in the deep norwegian channel

a hybrid model for the summit region of merapi volcano java indonesia derived from gravity changes and deformation measured between 2000 and 2002 three dimensional displacements and gravity changes were measured at 20 points between 2000 and 2002 at merapi volcano java indonesia former models focused on the modeling of a single magmatic source located in the summit region of the volcano such models do not fit to our measurements between 2000 and 2002 a new hybrid model approach is developed consisting of an elastic gravitational source described by a mass and energy term as well as a combined dip slip strike slip fault zone in the summit region both nonlinear optimization problems given by the common inversion of three dimensional displacements and gravity changes are solved by applying a genetic algorithm the hybrid model fits the measurements accurately tested by fisher test statistics furthermore our model for merapi volcano confirms previous structural models for this region so that the new model is statistically proven as well as physically reliable

residual gravity changes and eruption magnitudes abstract research during the last four decades has demonstrated that systematic temporal gravity changes are associated with eruptive activity these gravity changes are caused by the free air effect of elevation changes induced by magma bodies and by mass redistributions where gravity change data are accompanied by concurrent elevation control observed gravity changes can be corrected for the free air effect giving residual gravity changes residual gravity changes reflect only mass redistributions at most volcanoes residual gravity changes can be accounted for by the addition of mass during pre eruption time and by the removal or addition of mass during post eruption time at explosive volcanoes however the data show mass must be removed from near surface magma systems during preeruptive time the only reasonable mechanism acounting for these negative pre eruption mass redistributions is displacing dense country rock or magma with gas bubbles in vesiculated magma application of gauss theorem to areal residual gravity changes and an assumed density for the displaced material give an estimate of the volume of exsolved gas contained within the magma body the kinetic energy released in explosive magmatic eruptions to a first approximation is caused by the explosive expansion of exsolved and dissolved gases contained within magma if the density and temperature of magma and if the amount pressure and composition of volatiles contained in magma bodies are known or assumed then the kinetic energy released by explosive gas decompression can be computed or estimated using simple thermodynamic relationships kinetic energy estimates for explosive magmatic eruptions computed from muzzle velocities and computed for isothermal and adiabatic gas decompression using assumed volatile contents pressures and temperatures give similar results minimum pre eruption exsolved volatile contents estimated from negative pre eruption mass deficits and assumed magma densities temperatures and pressures were used to compute predicted kinetic energies for five eruption gravity change sequences at pacaya mihara usu and mt st helens volcanoes although the data are too few to be conclusive they do indicate the possibility of forecasting eruption magnitudes at some volcanoes using precursory gravity changes

gas induced erosion features in the north sea pockmarks are prominent features on the seafloor at two main regions of the north sea the south fladen area and the norwegian trench the pockmarks vary in size from 5 m across to about 150 m and in depth from 1 m to about 20 m some of the features consist of several very small unit pockmarks these are probably gas induced erosion features and found only in soft finegrained marine and glaciomarine sediments they are probably caused by shallow or deep seated gas or fluid release through the seabed whereby the finest particles are thrown into suspension and redistributed by nearbottom currents on the north sea plateau a small pockmarked area has recently been found a close relationship exists here between mobile gas in the upper sediments faulting in the soft sediments and the morphology of the seabed other morphological features in the north sea such as coast parallel depressions and elongated depressions or terraces are also interpreted here as gas induced erosion products this applies yet again to the mottled seabed features which appear as patches of high reflectivity on side scan sonar records from the north sea plateau they correspond to shallow seabed depressions on the deep towed boomer records judging from reported observations from several shallow seas world wide volatile transport through the seabed is probably quite common and several morphological features are undoubtably induced by this process several erosion features of similar origin are probably common also in deep ocean basins

deformation and stress states along the central segmentof the philippine fault implications to wrench fault tectonics abstract this paper discusses the space time evolution of deformation and states of stress along the central segment of the left lateral philippine fault from bondoc peninsula to leyte island this segment is characterized by deformations and stress states which do not always conform to predictions of classical wrench tectonics directions of the maximum principal stress axis 1 are in some cases oriented perpendicular to the fault trace contradicting the classical fault strike 1 angle of 30 45 in other cases it is the minimum axis 3 that orients perpendicular to the fault or in other cases parallel to it rotations of 1 directions as functions of time and space are observed all along the fault more complex stress regimes are observed in areas where the philippine fault intersects with two other major left lateral strike slip faults namely the legaspi lineament in the ragay gulf area and the sibuyan sea fault in masbate these observations strongly underline the urgence of prudence and precaution in applying wrench fault tectonic principles in natural examples

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

multiple pleistocene ice advances into the skagerrak a detailed seismic stratigraphy from high resolution seismic profiles abstract a detailed pleistocene seismic stratigraphy is proposed for the skagerrak an over 700 m deep elongated depression in the northeastern north sea by comparing our high resolution seismic results with those from glacial environments of canada alaska and antarctica we conclude that at least during the weichselian if not also during the saalian a glacier grounded in the eastern skagerrak and advanced well into its western part as indicated by a thick layer of basal till the surging glacier truncated the basinal flank of a ridge like delta moraine that was presumably deposited under uniform glacial conditions in an ice distal environment the deposition of the hirtshals moraine in shallow waters of hirtshals might originate from a glacier that advanced from sweden into north jutland soon after the ice withdrawal from the skagerrak a layer of well stratified glaciomarine sediments was deposited over the basal till suggesting floating ice conditions in a fjord like environment due to the rising sea level in the late pleistocene fluvioglacial and shallow marine deposits soon dominated over the glaciomarine sediments indicating an end of glacial conditions in this region these post glacial sediments were first deposited in the western skagerrak but as the transgression came to an end in the mid holocene the depocenter shifted to the east today the highest sedimentation rates are found in this eastern part

elongate depressions on the southern slope of the norwegian trench skagerrak morphology and evolution abstract multibeam echosounder surveys conducted on the southern slope of the norwegian trench between norway and denmark show that elongate depressions interpreted as current modified pockmarks are widespread in water depths of 100 500 m in the holocene recent succession the long axes of the depressions are oriented at an angle of about 15 downslope relative to the depth contours the long axes appear to almost exactly parallel the effective bottom currents in this part of the skagerrak the present current directions were probably established about 4000 years ago following a major shift in the oceanographic circulation pattern the most characteristic feature of the depressions is their large size with maximum depths of 45 m widths of 400 m and lengths of 2 km strong bottom currents continuously transport particles thrown into suspension by the seepage process away from the pockmarks and prevent further deposition continuous seepage of shallow gas at fixed pockmark sites over long time periods combined with generally high sedimentation rates are thought to be responsible for the exceptional size of many depressions the shallow gas probably has a mixed biogenic thermogenic origin however the thermogenic component is considered to be most important for the formation of pockmarks seepage from permeable layers in the jurassic cretaceous bedrock is evidenced by linear rows of depressions above these horizons while pockmarks above sub surface faults indicate gas seeps also from there in shallow water areas the shape and size of pockmarks are locally dependent on their location with respect to giant sand waves which trend sub parallel to the depth contours and are interpreted to be of late weichselian to early holocene age in deeper water areas the pockmarks have been further modified by gravity slides caused by collapse of steep pockmark walls

pockmarks and the recent geology of the central section of the norwegian trench a small area of 3 1 km2 in the norwegian trench has been selected for a detailed analysis of possible relationships between the recent geology and the formation of pockmarks two sets of side scan sonar and deep towed boomer dts data were used for the analysis the most recent deposit is unit 1 consisting of finely layered soft silty clays unit 1 has been divided into three seismic subunits 1a 1b and 1c based upon the boomer records the underlying unit 2 is seismically homogeneous consisting of stiff silty sandy clay with fragments of chalk most of the irregularities in the surface of unit 2 are found to be furrows traversing the study area in a n s general direction the seabed is heavily pockmarked mean density 30 km2 and some of the pockmarks are asymmetric with steep ese walls the maximum pockmark depth within the study area is 5 8 m and the maximum wall angle is about 12 in addition to describing the recent geology and surface pockmarks the following features are described and their relationship with pockmark formation discussed 1 sloping reflectors found below some of the pockmarks 2 columnar disturbances seen under many of the buried pockmarks and 3 masked reflectors intermittent strong reflectors found within subunit 1a which are probably caused by a raised gas concentration in porous layers pockmarks and associated features are assumed to be caused by gas escaping through the seabed a possible gas migration mechanism through the interface between units 1 and 2 and through unit 1 is also discussed

structural setting of the bicol basin and kinematic analysis of fractures on mayon volcano philippines mayon volcano is located within the bicol basin in the southeastern region of luzon philippines the basin is contained within a releasing bend associated with the curvature of the central segment of the left lateral philippine fault a structural analysis of the faults that traverse the bicol basin was conducted through reviews of existing literature seismic data interpretation and remote sensing in particular those structures that may have influenced the growth and evolution of mayon dynamic analysis of the aforementioned structures reveals a regional transtensional stress regime for the bicol basin field investigation on mayon s slopes revealed the existence of fractures along its western and eastern flanks these structures on mayon have the same geometry as the dominant faults found within the bicol basin interpretation of these fractures indicates a tectonic control over their origin the identification of fractures on mayon s slopes is the first description of such features on its edifice these new data highlight the probable landslide hazards associated with an oversteepened volcano that may have been further destabilized by tectonic activity

gravity changes and internal processes some results obtained from observations at three volcanoes temporal gravity changes provide information about mass and or density variations within and below the volcano edifice three active volcanoes have been under investigation each of them related to a plate boundary mayon luzon philippines merapi java indonesia and galeras colombia the observed gravity changes are smaller than previously expected but significant for the three volcanoes under investigation and within the observation period mainly the increase of gravity is observed ranging from 1 000 nm 2 to 1 600 nms 2 unexpectedly the gravity increase is confined to a rather small area with radii of 5 to 8 km around the summit at mayon and merapi the parallel gps measurements yield no significant elevation changes this is crucial for the interpretation as the internal pressure variations do not lead to significant deformation at the surface thus the classical mogi model for a shallow extending magma reservoir cannot apply to confine the possible models the attraction due to changes of groundwater level or soil moisture is estimated along the slope of merapi exemplarily by 2 d modelling mass redistribution or density changes were evaluated within the vent as well as deeper fluid processes to explain the gravity variations the results are compared to the model incorporating the additional effect of elastic deformation