shallow magma transport for the 2002 3 mt etna eruption inferred from thermal infrared surveys abstract the 26 october 2002 28 january 2003 eruption of mt etna volcano was characterised by lava effusion and by an uncommon explosivity along a 1 km long eruptive fissure on the southern upper flank of the volcano the intense activity promoted rapid growth of cinder cones and several effusive vents analysis of thermal images recorded throughout the eruption allowed investigation of the distribution of vents along the eruptive fissure and of the nature of explosive activity the spatial and temporal distribution of active vents revealed phases of dike intrusion expansion geometric stabilization and drainage these phases were characterised by different styles of explosive activity with a gradual transition from fire fountaining through transitional phases to mild strombolian activity and ending with non explosive lava effusion here we interpret the mechanisms of the dike emplacement and the eruptive dynamics according to changes in the eruptive style vent morphology and apparent temperature variations at vents detected through thermal imaging this is the first time that dike emplacement and eruptive activity have been tracked using a handheld thermal camera and we believe that its use was crucial to gain a detailed understanding of the eruptive event

is the quiescence of major earthquakes m 7 5 since 1952 in the himalaya and northeast india real the earthquake catalog for the himalaya and the northeast india regions latitude 20 n to 38 n and longitude 75 e to 100 e comprising of portions of the himalaya and arakan yoma fold belt for the period 1897 to may 1995 shows that there have been 14 major earthquakes m 7 5 during the period 1897 to 1952 and no major earthquakes after 1952 to investigate the possibility that this quiescence is an artifact of nonuniform magnitude scales over the period of study we examined three global catalogs and found that there is indeed an absence of major earthquakes after 1952

seismic moment catalog of large shallow earthquakes 1900 to 1989 we compile a worldwide catalog of shallow depth 70 km and large ms 7 earthquakes recorded between 1900 and 1989 the catalog is shown to be complete and uniform at the 20 sec surface wave magnitude ms 7 0 we base our catalog on those of abe 1981 1984 and abe and noguchi 1983a b for events with ms 7 0 those catalogs however are not homogeneous in seismicity rates for the entire 90 year period we assume that global rates of seismicity are constant on a time scale of decades and most inhomogeneities arise from changes in instrumentation and or reporting we correct the magnitudes to produce a homogeneous catalog the catalog is accompanied by a reference list for all the events with seismic moment determined at periods longer than 20 sec using these seismic moments for great and giant earthquakes and a moment magnitude relationship for smaller events we produce a seismic moment catalog for large earthquakes from 1900 to 1989 the catalog is used to study the distribution of moment released worldwide although we assumed a constant rate of seismicity on a global basis the rate of moment release has not been constant for the 90 year period because the latter is dominated by the few largest earthquakes we find that the seismic moment released at subduction zones during this century constitutes 90 of all the moment released by large shallow earthquakes on a global basis the seismic moment released in the largest event that occurred during this century the 1960 southern chile earthquake represents about 30 to 45 of the total moment released from 1900 through 1989 a frequency size distribution of earthquakes with seismic moment yields an average slope b value that changes from 1 04 for magnitudes between 7 0 and 7 5 to b 1 51 for magnitudes between 7 6 and 8 0 this change in the b value is attributed to different scaling relationships between bounded large and unbounded small earthquakes thus the earthquake process does have a characteristic length scale that is set by the downdip width over which rupture in earthquakes can occur that width is typically greater for thrust events at subduction zones than for earthquakes along transform faults and other tectonic environments

the 2010 ash emissions at the summit craters of mt etna relationship with seismo acoustic signals 1 mt etna volcano italy typically generates lava fountains and strombolian eruptions from the summit craters producing significant emissions of tephra which may cause moderate to high impact both in the atmosphere and on the ground however we have also witnessed a number of minor ash emissions that although far less powerful may pose considerable volcanic hazards in this paper we deal with three ash emissions occurring in 2010 8 april at southeast crater 25 august at bocca nuova and 14 15 november at northeast crater correlating their volcanological features with the associated seismo acoustic signals we provide details regarding the chronology eruption column dispersal of the deposit and texture grain size componentry and morphology of the emitted ash each eruptive episode has also been characterized by means of seismo acoustic analyses evaluating the volcanic acoustic seismic ratio vasr furthermore the source of volcanic tremor recorded from march to december 2010 was localized the joint volcanological and seismo acoustic analyses allowed distinguishing two main kinds of ash emissions types a 8 april and 25 august and b 14 15 november regarding the former the accumulation of gas below a dense cap rock obstructing the conduit vent giving rise with the uncorking to impulsive explosivity was hypothesized the latter type instead is characterized by a longer lasting and less explosivity likely due to the existence of open conduit conditions therefore type b ash emissions are less hazardous than type a this simple model regarding minor explosive activity may constitute a starting point to assess the volcanic risk from unexpected explosions

dissolution kinetics of plagioclase in the melt of the system diopside albite anorthite and origin of dusty plagioclase in andesites the textures and kinetics of reaction between plagioclase and melts have been investigated experimentally and origin of dusty plagioclase in andesites has been discussed in the experiments plagioclase of different compositions an96 an61 an54 an23 and an22 surrounded by glasses of six different compositions in the system diopside albite anorthite was heated at temperatures ranging from 1 200 to 1 410 c for 30 min to 88 h textures were closely related to temperature and chemical compositions a crystal became smaller and rounded above the plagioclase liquidus temperature of the starting melt glass and remained its original euhedral shape below the liquidus whatever the temperature the crystal melt interface became rough and often more complicated sieve like texture composed of plagioclase melt mixture in the scale of a few m was developed from the surface of the crystal inward formation of mantled plagioclase if the crystal is less calcic than the plagioclase in equilibrium with the surrounding melt and the interface remained smooth if the crystal is more calcic than the equilibrium plagioclase from these results the following two types of dissolution have been recognized 1 a crystal simply dissolves in the melt which is undersaturated with respect to the phase simple dissolution and a crystal is partially dissolved to form mantled plagioclase by reaction between sodic plagioclase and calcic melt partial dissolution the amount of a crystal dissolved and reacted increased proportional to the square root of time this suggests that these processes are controlled by diffusion probably in the crystal mantled plagioclase produced in the experiments were very similar both texturally and chemically to some of the so called resorbed plagioclase in igneous rocks chemical compositions and textures of plagioclase phenocrysts in island arc andesites of magma mixing origin have been examined cores of clear and dusty plagioclase were clacic about an90 and sodic about an50 respectively this result indicates that dusty plagioclases were formed by the partial melting due to reaction between sodic plagioclase already precipitated in a dacitic magma and a melt of intermediate composition in a mixed magma during the magma mixing

consistency of teleseismic reporting since 1963 abstract changes in the rate of occurrence of smaller events have been recognized in the rupture zones of upcoming large earthquakes in several postearthquake and one preearthquake study a data set in which a constant portion of the events in any magnitude band are consistently reported through time is crucial for the recognition of seismicity rate changes which are real related to some process change in the earth such a data set is termed a homogeneous data set the consistency of reporting of earthquakes in the noaa hypocenter data file hdf since 1963 is evaluated by examining the cumulative number of events reported as a function of time for the entire world in eight magnitude bands it is assumed that the rate of occurrence of events in the entire world is roughly constant on the time scale examined here because of the great size of the worldwide earthquake production system the rate of reporting of events with magnitudes above m b 4 5 has been constant or increasing since 1963 significant decreases in the number of events reported per month in the magnitude bands below m b 4 4 occurred during 1968 and 1976 these decreases are interpreted as indications of decreases in detection of events for two reasons first they occur at times of constant rates of occurrence and reporting of larger events second the decrease during the late 19609s has also been recognized in the teleseismic data reported by the international seismological centre isc this suggests that the decrease in the number of small events reported was related to facets of the earthquake reporting system which the isc and noaa share the most obvious candidate is the detection system during 1968 detection decreased in the united states central and south america and portions of the south pacific this decrease is probably due to the closure of the vela arrays bmo tfo cpo ubo and wmo during 1976 detection decreased in most of the seismically active regions of the western hemisphere as well as in the region between kamchatka and guam the cause of this detection decrease is unclear these detection decreases seriously affect the amount of homogeneous background period available for the study of teleseismic seismicity rate changes if events below the minimum magnitude of homogeneity are eliminated from the teleseismic data sets the resulting small numbers of events render many regions unsuitable for study many authors have reported seismicity rate decreases as possible precursors to great earthquakes few of these authors have considered detection decreases as possible explanations for their results this analysis indicates that such considerations cannot be avoided in studies of teleseismic data

high resolution quantitative imaging of plagioclase composition using accumulated backscattered electron images new constraints on oscillatory zoning oscillatory zoning in plagioclase is investigated at small scale 10 m using accumulated backscattered electron bse images as high resolution imaging method combined with electron microprobe quantitative analysis gray value profiles across these images can be calibrated for an content with a resolution of 0 5 mol an applied to oscillatory zoned crystals this new application of bse imaging allows better characterization of zoning patterns along a profile and quantification of wavelength amplitude and shape of the oscillations we also obtain high resolution information on the morphology of growth zones boundaries this approach allows us to better classify the different types of oscillations and concentric zoning dissolution is more frequent than usually recognized major resorption surfaces crosscut several growth zones irregular 5 10 m saw tooth zones are delimited by faint wavy dissolution surfaces and must be distinguished from small scale oscillations 1 3 m with straight boundaries this suggests at least two mechanisms for the formation of these zoning patterns faint oscillations are probably caused by local kinetic control whereas wavy dissolution surfaces involve magma chamber dynamics

compositionally zoned crystals and real time degassing data reveal changes in magma transfer dynamics during the 2006 summit eruptive episodes of mt etna one of the major objectives of volcanology remains relating variations in surface monitoring signals to the magmatic processes at depth that cause these variations we present a method that enables compositional and temporal information stored in zoning of minerals olivine in this case to be linked to observations of real time degassing data the integrated record may reveal details of the dynamics of gradual evolution of a plumbing system during eruption we illustrate our approach using the 2006 summit eruptive episodes of mt etna we find that the history tracked by olivine crystals and hence most likely the magma pathways within the shallow plumbing system of mt etna differed considerably between the july and october eruptions the compositional and temporal record preserved in the olivine zoning patterns reveal two mafic recharge events within months of each other june and september 2006 and each of these magma supplies may have triggered the initiation of different eruptive cycles july 14 24 and august 31 december 14 correlation of these observations with gas monitoring data shows that the systematic rise of the co2 so2 gas values is associated with the gradual pre and syn eruptive supply of batches of gas rich mafic magma into segments of etna s shallow plumbing system where mixing with pre existing and more evolved magma occurred

recent seismicity and tomographic modeling of the mount etna plumbing system the monitoring of seismic activity in eastern sicily southern italy has been recently improved in the framework of the poseidon project to investigate both tectonics and volcanic processes of mount etna this effort has produced a homogeneous and complete data set which we use to image the deep structure of the volcano and to define the space and time distribution of the recent seismicity encompassing the 1995 eruption diffuse eruptions between 1995 and 1997 a further magma intrusion started in 1997 and an increase of volcanic activity in july 1998 we inverted p wave arrival times from 307 selected local earthquakes to obtain a three dimensional velocity model of the volcano with a simultaneous inversion for hypocenters and velocity parameters the new tomographic images permit us to define the structure beneath the volcano from the surface down to 18 km depth the main structural feature revealed by our inversion is a high velocity body located beneath the central craters whose lateral extent increases from 6 km between 18 and 9 km depth to 12 km between 9 and 3 km depth near the surface the fast anomaly branches in two separate high vp regions which are located below the summit craters and the eastern flank valle del bove respectively the high velocity features are interpreted as high density cumulates of solidified magma that intruded the shallow crust we hypothesize that magma ascends the crust within the relatively small high velocity conduit below 9 km depth and is stored at depth shallower than 9 km within the broad high velocity region as also suggested by petrological data a sharp increase of seismicity in 1997 with earthquakes occurring at the border of the high velocity body suggests that mount etna sustained recent episodes of intrusions which possibly herald future eruptions no large low velocity anomaly interpretable as a melted magma chamber is imaged in the upper 18 km of the crust while a broad low velocity anomaly in the uppermost mantle revealed by regional seismic data possibly indicates the magma source region at depth earthquake occurrence from the deep source to the shallow intrusive area helps to trace the magma migration and the feeding of the volcanic system

revisiting the earthquake sources in the himalaya perspectives on past seismicity abstract the 2500 km long himalaya plate boundary experienced three great earthquakes during the past century but none of them generated any surface rupture the segments between the 1905 1934 and the 1897 1950 sources known as the central and assam seismic gaps respectively have long been considered holding potential for future great earthquakes this paper addresses two issues concerning earthquakes along the himalaya plate boundary one the absence of surface rupture associated with the great earthquakes vis a vis the purported large slip observed from paleoseismological investigations and two the current understanding of the status of the seismic gaps in the central himalaya and assam in view of the paleoseismological and historical data being gathered we suggest that the ruptures of earthquakes nucleating on the basal detachment are likely to be restricted by the crustal ramps and thus generate no surface ruptures whereas those originating on the faults within the wedges promote upward propagation of rupture and displacement as observed during the 2005 kashmir earthquake that showed a peak offset of 7 m the occasional reactivation of these thrust systems within the duplex zone may also be responsible for the observed temporal and spatial clustering of earthquakes in the himalaya observations presented in this paper suggest that the last major earthquake in the central himalaya occurred during ad 1119 1292 rather than in 1505 as suggested in some previous studies and thus the gap in the plate boundary events is real as for the northwestern himalaya seismically generated sedimentary features identified in the 1950 source region are generally younger than ad 1400 and evidence for older events is sketchy the 1897 shillong earthquake is not a decollement event and its predecessor is probably 1000 years old compared to the central himalaya the assam gap is a corridor of low seismicity between two tectonically independent seismogenic source zones that cannot be considered as a seismic gap in the conventional sense

observations of plagioclase zoning using interference imaging abstract interference imaging techniques laser interference microscopy in transmitted light and nomarski differential interference contrast in reflected light have been used to study different types of zoning in magmatic plagioclase crystals samples studied come from a wide range of rock types and geological environments analysis of zoning profiles for individual unit zones shows that a saw tooth pattern in which an initially high an decreases as growth proceeds is the most common type of zoning configuration we recognize 2 major types of zoning type 1 small zones usually less than 10 microns thick with compositional amplitudes up to 10 an and type 2 zones up to50 microns thick with large compositional amplitudes of up to 35 an detailed analysis of zoning patterns shows that oscillatory zoning is not actually oscillatory in the sense of a sine wave it is discontinuous unit zones are characteristically bounded by discontinuities this common pattern is consistent with alternating periods of growth and periods of dissolution reaction and lack of growth or possibly very slow growth our observations firmly establish that dissolution and magmatic reaction involving both growth and dissolution are common during growth of the magmatic plagioclase which we have studied type 1 zonation appears consistent with perturbations of local conditions in a diffusion controlled boundary layer around the growing crystal type 2 zoning is probably due to large scale conditions faceted planar growth surfaces appear to be the rule in magmatic crystallization although in some instances rounded or irregular convolute zonation can occur the repetitive nature of many of the features we have observed is consistent with and suggestive of some form of self organization

how a complex basaltic volcanic system works constraints from integrating seismic geodetic and petrological data at mount etna volcano during the july august 2014 eruption the petrological part of this study was supported by the fir 2014 research grant to marco viccaro from the university of catania italy grant number 2f119b title of the project dynamics of evolution ascent and emplacement of basic magmas case studies from eruptive manifestations of eastern sicily

oblique plate convergence in the indo burma myanmar subduction region the indo burma myanmar subduction boundary is highly oblique to the direction of relative velocity of the indian tectonic plate with respect to the eurasian plate the area includes features of active subduction zones such as a wadati benioff zone of earthquakes a magmatic arc thrust and fold belts it also has features of oblique subduction such as an arc parallel strike slip fault sagaing fault that takes up a large fraction of the northward component of motion and a buttress the mishmi block that resists the motion of the fore arc sliver

location of tremor sources and estimation of lava output using tremor source amplitude on the piton de la fournaise volcano 2 estimation of lava output abstract we propose several relations for estimating the amounts of lava emitted during eruptions of the piton de la fournaise volcano based on the use of tremor source amplitude sources for eruption tremor are located in several frequency bands with a location method based on the use of seismic amplitudes corrected for recording site effects sources are usually found at shallow depth and close to the eruptive vents suggesting that tremor is directly generated by the eruptive activity simultaneously with the location of the tremor sources our program gives the source amplitude of the phenomenon we assume a linear or a quadratic relation between the lava output and the tremor source amplitude both relations are calibrated using data for the march 1998 eruption and tested using the volumes emitted during the july and september 1999 and february 2000 eruptions we found that the 5 10 hz frequency band gives lava output much higher than for lower frequencies suggesting that for that band the tremor generation depends on the eruption site in addition to the lava output or that tremor at those frequencies is not directly caused by the outflow of lava but maybe rather by gas the best estimations are obtained using the quadratic relation for frequencies below 5 hz with an agreement better than 15 with the field observations for the july and september 1999 eruptions and 30 for the february 2000 eruption our results show that the cumulative amplitude of tremor recorded during eruptions of the piton de la fournaise is directly related to the amounts of lava erupted

the continuing story of etna s new southeast crater 2012 2014 evolution and volume calculations based on field surveys and aerophotogrammetry abstract during the years 2013 2014 the new southeast crater nsec at the summit of mount etna produced frequent episodes of lava fountaining paroxysms and its cone continued to grow at unprecedented rates many of the episodes were of rather brief duration and violently explosive producing mostly pyroclastic material and minor volumes of lava other episodes especially those since mid december 2013 were characterized by violent strombolian activity without producing sustained lava fountains and significant amounts of tephra but emitting more voluminous lava flows one episode of intense strombolian and effusive activity that was possibly fed from the nsec conduit occurred from vents located approximately 1 km north of the crater on the east flank of the northeast crater in july august 2014 the evolution of the nsec cone between 2012 and 2014 was documented by repeated gps surveys carried out both from a distance and on the cone itself by the acquisition of comparison photographs and by two aerophotogrammetric surveys from these surveys the highest point of the nsec results to have grown from 190 m may 2012 to 215 m october 2014 above the pre cone surface reaching an elevation of 3290 m and its volume more than doubled to 50 0 6 5 10 6 m 3 representing the 40 of the total bulk volume of the volcanic products including pyroclastic fallout erupted in 2011 2014 which is 147 2 10 6 m 3 101 3 10 6 m 3 dense rock equivalent the whole of the 2011 2014 nsec activity marks an unusually high frequency of rather explosive tephra rich eruptive episodes compared to etna s activity in past decades and centuries although the average magma production rate in this interval is close to the supposed long term output rate of the volcano the latest eruptive episodes show a tendency of the nsec coalescing with the old southeast crater cone which therefore represents a miniature example of a growing compound volcano at the summit of etna

unusual magma storage conditions at mt etna southern italy as evidenced by plagioclase megacryst bearing lavas implications for the plumbing system geometry and summit caldera collapse at mt etna volcano the emission of plagioclase megacryst bearing lavas known locally as cicirara has occurred rarely and generally in association with unusual volcanological phenomena in this work we interpret the magma chamber processes and the structural features of the plumbing system that led to the production of these peculiar volcanic rocks based on a detailed study of plagioclase megacrysts including their oscillatory zoning sieve textures and fluid inclusions patchy zoning suggests limited ascent in the deep levels of the plumbing system based on the plagioclase nucleation threshold and the volatile saturation depth at intermediate water undersaturated levels of the plumbing system ascent is faster as indicated by crystals with coarse sieve textures storage at shallow water saturated levels less than 6 km deep is associated with oscillatory zoning with very small changes in an slightly larger an variations coupled with different wavelengths provide evidence of convection of crystals across distinct zones of the chamber stripes of melt inclusions formed at steps of magma ascent and volatile loss whereas layers of fluid inclusions may be related to episodes of volatile flushing into the magma chamber in contrast strongly sieve textured envelopes with an increase and constant feo may be related to mixing with more volatile rich magmas of similar composition we interpret the repeated occurrence of cicirara lavas as evidence that the shallow portion of the plumbing system underwent a progressive coalescence of a complex network of dykes and sills in response to increasing rates of magma supply from depth major magma withdrawals from this larger reservoir may be linked to episodes of summit instability associated with major caldera collapses

revision of magnitudes of large shallow earthquakes 1897 1912 abstract in previous research trace amplitudes of surface wave maxima recorded by undamped milne seismographs were used to determine the surface wave magnitudes ms of large shallow earthquakes which occurred prior to 1912 for this purpose the effective gain of these instruments was calibrated by using the surface wave magnitudes ms gr which were calculated from the unpublished worksheets for seismicity of the earth of gutenberg and richter in this paper the real quality of ms gr is critically re evaluated by using independent sets of data it is found that ms gr for the period 1904 1909 is considerably overestimated the average excess from the real ms is 0 5 units for 1904 1906 0 4 for 1907 0 3 for 1908 1909 and 0 0 for 1910 1912 this overestimation is so systematic and large that the previous results are all redetermined the average effective gain of milne instruments is revised to be 21 9 previously the gain depended on ms this revision results in systematic reduction in the previously assigned magnitudes the revised values of ms for 264 shallow earthquakes with ms 6 8 and over in the period 1897 1912 inclusive are listed the present revision is large enough to preclude the possibility of the high activity of large shallow earthquakes around the turn of the century the present results have a direct effect on all the magnitude catalogues of shallow earthquakes which occurred prior to 1909

detailed attenuation study of shear waves in the kumaon himalaya india using the inversion of strong motion data abstract the frequency dependent shear wave quality factor q f of the seismically active kumaon himalaya was calculated using strong motion data recorded between 2006 and 2012 the inversion algorithm of strong motion data developed here simultaneously gives the shear wave quality factor and the site effect for each earthquake the site effects obtained from the present inversion are within the standard limit of error and agree with those obtained through the h v technique h v being the ratio of the fourier spectra of the horizontal and vertical components of the record the q f values in which q is shear wave quality factor and f is frequency at different stations were computed using both the north south and east west components of acceleration records the q f values obtained from both components at 16 stations in the kumaon himalaya were used to compute a regional q f relationship having the form q f 28 2 0 f 1 2 0 07 this q f relationship suggests a low q 0 value n value 0 8 for tectonically and seismically active regions

the july august 2001 eruption of mt etna sicily the july august 2001 eruption of mt etna stimulated widespread public and media interest caused significant damage to tourist facilities and for several days threatened the town of nicolosi on the s flank of the volcano seven eruptive fissures were active five on the s flank between 3 050 and 2 100 m altitude and two on the ne flank between 3 080 and 2 600 m elevation all produced lava flows over various periods during the eruption the most voluminous of which reached a length of 6 9 km mineralogically the 2001 lavas fall into two distinct groups indicating that magma was supplied through two different and largely independent pathways one extending laterally from the central conduit system through radial fissures the other being a vertically ascending eccentric dike furthermore one of the eccentric vents at 2 570 m elevation was the site of vigorous phreatomagmatic activity as the dike cut through a shallow aquifer during both the initial and closing stages of the eruption for 6 days the magma column feeding this vent was more or less effectively sealed from the aquifer permitting powerful explosive and effusive magmatic activity while the eruption was characterized by a highly dynamic evolution complex interactions between some of the eruptive fissures and changing eruptive styles its total volume 25 106 m3 of lava and 5 10 106 m3 of pyroclastics was relatively small in comparison with other recent eruptions of etna effusion rates were calculated on a daily basis and reached peaks of 14 16 m3 s 1 while the average effusion rate at all fissures was about 11 m3 s 1 which is not exceptionally high the eruption showed a number of peculiar features but none of these except the contemporaneous lateral and eccentric activity represented a significant deviation from etna s eruptive behavior in the long term however the 2001 eruption could be but the first in a series of flank eruptions some of which might be more voluminous and hazardous placed in a long term context the eruption confirms a distinct trend initiated during the past 50 years toward higher production rates and more frequent eruptions which might bring etna back to similar levels of activity as during the early to mid seventeenth century

verification of magnitudes of himalayan region earthquakes of 1903 1985 from gottingen observatory abstract from the microfilms of gottingen observatory seismograms magnitudes are verified for thirty seven major and great earthquakes magnitude 7 in the himalayan region for the period 1903 1985 duda 1992 had earlier determined magnitudes of these earthquakes from gottingen records there were three other major earthquakes for which magnitudes could not be determined as their records from gottingen were not found the magnitude values were determined using p s and surface waves from long and medium period instruments the magnitudes from short period p and s waves were not redetermined to avoid uncertainties of such measurements from the microfilms as compared to duda 1992 the present values of the surface wave magnitudes corresponding to 20 3 s period from horizontal components are found to be higher for nine earthquakes by 0 2 0 5 units the body wave magnitudes are similarly changed these changes bring the magnitudes closer to the values given in earlier catalogs the relative quiescence after 1950 is striking the seismogram portions of earthquakes magnitude 7 5 are reproduced

evidence of a large triggered event in the nepal himalaya following the gorkha earthquake implications toward enhanced seismic hazard a dc double couple constrained multiple point source moment tensor inversion is performed on the band passed 0 008 0 10 hz displacement data of the 25 april mw 7 8 2015 nepal mainshock from 17 broadband stations in india our results reveal that the 25 april event strike 324 dip 14 rake 88 ruptured the north dipping main himalayan thrust mht at 16 km depth we modeled the coulomb failure stress changes cfs produced by the slip on the fault plane of the 25 april nepal mainshock a strong correlation with occurrences of aftershocks and regions of increased positive cfs is obtained below the aftershock zone of the 2015 nepal mainshock we notice that predicted cfs at 16 km depth show a positive coulomb stress of 0 06 mpa at the location of the 12 may 2015 event these small modeled stress changes can lead to trigger events if the crust is already near to failure but these small stresses can also advance the occurrence of future earthquakes the main finding of our cfs modeling implies that the 25 april event increased the coulomb stress changes by 0 06 mpa at 16 km depth below the site of the 12 may event and thus this event can be termed as triggered we propose that the seismic hazard in the himalaya is not only caused by the mainshock slip on the mht rather the occurrence of large triggered event on the mht can also enhance our understanding of the seismic hazard in the nepal himalaya

spherical and ellipsoidal volcanic sources at long valley caldera california using a genetic algorithm inversion technique abstract we model the second inflation period at long valley caldera california using a genetic algorithm technique and high quality geodetic measurements of elevation changes and baseline extensions we compare two source inversions for both spherical mogi point sources and the finite prolate ellipsoid of yang and davis a sensitivity analysis for the genetic algorithm is performed based upon synthetic data set inversions on similar sources in order to better constrain the areal location orientation and volume of the potential sources the spherical sources are well constrained the larger located at 9 9 km beneath the resurgent dome with a volume of 0 036 km 3 while the second at only 0 008 km 3 is located at a depth of 7 3 km beneath the south moat the depths to the ellipsoidal sources are switched with the larger source at a depth of 9 6 km and the smaller at 11 8 km with volumes of 0 037 and 0 002 km 3 respectively

the devastating muzaffarabad earthquake of 8 october 2005 new insights into himalayan seismicity and tectonics abstract the recent earthquake of 8 october 2005 in the muzaffarabad region in western himalaya destroyed several parts of pakistan and the north indian state of jammu and kashmir the earthquake of magnitude 7 6 claimed more than 80 000 lives clearly exposing the poor standards of building construction a major challenge facing the highly populated earthquake prone third world nations today in this paper we examine variations in the stress field seismicity patterns seismic source character tectonic setting plate motion velocities gps results and the geodynamic factors relating to the geometry of the underlying subsurface structure and its role in generation of very large earthquakes focal mechanism solutions of the muzaffarabad earthquake and its aftershocks are found to have steep dip angles comparable to the indian intra plate shield earthquakes rather than the typical himalayan earthquakes that are characterized by shallow angle northward dips a low p value of 0 9 is obtained for this earthquake from the decay pattern of 110 aftershocks which is comparable to that of the 1993 latur earthquake in the indian shield the deadliest stable continental region scr earthquake till date inversion of focal mechanisms of the harvard cmt catalogue indicates distinct stress patterns in the muzaffarabad region seemingly governed by an overturned himalayan thrust belt configuration that envelops this region adjoined by the pamir and hindukush regions recent developments in application of seismological tools like the receiver function technique have enabled accurate mapping of the dipping trends of the moho and lithosphere asthenosphere boundary lab of indian lithosphere beneath southern tibet these have significantly improved our understanding of the collision process the mechanism of himalayan orogeny and uplift of the tibetan plateau besides providing vital constraints on the seismic hazard threat posed by the himalaya new ideas have also emerged through gps macroseismic investigations paleoseismology and numerical modeling approaches while many researchers suggest that the himalayan front is already overdue for several 8 0 magnitude earthquakes some opine that most of the front may not really be capable of sustaining the stress accumulation required for generation of great earthquakes we propose that the occurrence of great earthquakes like those of 1897 in shillong and 1950 in assam have a strong correlation with their proximity to multiple plate junctions conducive for enormous stress build up like the eastern himalayan syntaxis comprising the junction of the india eurasia plates and the burma sunda micro plates

an accurate and efficient method for including the effects of topography in three dimensional elastic models of ground deformation with applications to radar interferometry topography has a large effect on the results predicted by elastic surface deformation models in regions of significant relief in some cases topography may have more influence on the predicted deformation field than do model source parameters we have developed an approximate analytical technique for including topographic effects that retains most of the computational simplicity of elastic half space models while providing an accurate representation of topographic effects we use a series expansion of the elastic half space solution with a small slope approximation yielding a set of higher order corrections the integrated effect of these corrections is evaluated using fourier methods we investigate the effectiveness of our method by comparing predicted results for a tilted triaxial ellipsoid with those predicted by finite element models the resulting displacements and displacement gradients are in good agreement with finite element results both for relatively smooth topography synthetically generated and for the greater relief in the vicinity of mount etna volcano we then compare the results of our method with those predicted by traditional elastic half space models using different reference elevations and with a previously proposed method of estimating topographic effects our new method provides a significantly better fit to the finite element results than do the other methods our method is able to accurately portray both the number and the horizontal pattern of fringes in a synthetic interferogram when compared with finite element results in particular the method accurately represents the broadening of fringes that is observed in regions of high relief as well as reproducing the location of the fringe center and the topographically induced deviation of the fringes from a regular pattern elastic half space models typically show a fringe center that is displaced with respect to the finite element results indicating that parameter inversions based on such a model would provide incorrect estimates of the horizontal source position the lack of topographically generated fringe distortions in elastic half space results would also likely lead to inaccuracies in the predicted magnitude and orientation of proposed deformation sources our new technique over comes these limitations and should be useful when evaluating either traditional geodetic results or the greater areal coverage provided by interferometric observations

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

reassessment of earthquakes 1900 1999 in the eastern mediterranean and the middle east summary we have reappraised locations and surface wave magnitudes of earthquakes this century in the eastern mediterranean and the middle east between 10 and 44 n and 18 and 70 e the results are presented in an improved parametric catalogue of shallow earthquakes h 40 km large enough ms 6 0 to be of interest in seismotectonics and earthquake engineering a considerable number of early events of 6 ms 7 2 not included in other catalogues have been identified and their magnitudes assessed we find that iss isc locations are systematically shifted by 10 30 km to the north or northeast of their macroseismic epicentres also we derived a regional average relationship between log m0 and ms we show that the correlation of magnitude with epicentral intensity is very weak as is expected and a source of error in frequency relations

multiparametric study of the february april 2013 paroxysmal phase of mt etna new south east crater european fp7 med suv mediterranean supersite volcanoes grant number 308665 european research council european fp7 fp 2007 2013 erc grant number 279802 sigma sistema integrato di sensori in ambiente cloud per la gestione multirischio avanzata

variable regimes in magma systems documented in plagioclase zoning patterns el misti stratovolcano and andahua monogenetic cones abstract magmas may experience closed or open system evolution during their ascent and evolution in the upper crust chemically closed system processes can involve heat transfer from underplating mafic magmas or decompression due to magma ascent on the other hand newly injected magmas can mix with the residing magma and hybridize plagioclase zonation patterns and electron microprobe major and trace element analysis constrain these contrasting scenarios for andesites from the 80 km3 el misti stratovolcano 5822 m and a field of relatively small monogenetic andahua scoria cones both in southern peru in particular fe concentration in plagioclase reveals valuable information within a magmatic system to explore the dominance of closed vs open system processes large and correlated anorthite fe contrasts at resorption zones identify compositional mixing related to recharge subhorizontal an fe variations record thermal or water induced effects el misti volcano a large but still relatively youthful stratovolcano is dominated during most of its approx 120 ka history by closed system effects during its evolution recharge and mixing mostly occurred cryptically as it is not recorded in drastic compositional changes in magmas or their phenocrysts a small volume erupted at el misti however is affected by strong open system behaviour as reflected in strongly correlated variations in an and fe contents of plagioclase compositions its crystal population is texturally and chemically very similar to lavas of the monogenetic cinder cones of the andahua volcanic field for the el misti magma reservoir resorption events caused by thermal effects or magma ascent are more frequent in comparison to the actual eruption frequencies many cycles of closed system evolution heat transfer and decompression therefore occurred without resulting in an eruption plagioclase zonations from lavas of the monogenetic andahua field indicate that any mafic batch that intruded the much smaller reservoirs immediately triggered an eruption by contrast a large magma system that feeds el misti volcano can easily accommodate a new batch without causing eruption

subduction in the indo burma region is it still active the indo burma region which includes longitude 92 96 e latitude 20 26 n is a subduction zone where the indian plate underthrusts the south eastern asian plate but the nature of subduction is complex i examine here the distribution of the p t and b axes of 37 earthquakes the time period 1977 1995 depths 0 153 km and magnitudes mb 4 8 6 8 with respect to the geometry of the wadati benioif zone the analysis shows that the t axes are clustered close to the down dip direction of the subducting slab implying a predominant down dip tensional stress regime within the slab which is typical of intermediate depth seismicity of active subduction zones these results suggest that the subduction in the indo burma region is possibly active

great earthquakes seismicity gaps and potential for earthquake disaster along the himalaya plate boundary abstract analysis of the space time patterns of seismicity in the himalaya plate boundary has established the existence of three seismic gaps 1 1 the kashmir gap lying west of the 1905 kangra earthquake 2 2 the central gap situated between the 1905 kangra and the 1934 bihar earthquakes 3 3 the assam gap between the 1897 and 1950 assam earthquakes this study has shown that the above great earthquakes were preceded as well as followed by long periods 19 years of decreased levels of seismic activity in the epicentral regions remarkable decrease in the seismicity following the year 1970 has been observed in the western half of the central gap as well as in the assam gap local seismic investigation in the assam gap confirms this feature and the seismicity suggests the existence there of an asperity the local seismic investigations in garhwal himalaya have shown that the small earthquakes are confined to the upper 6 8 km of the crust and may have strike slip motions these earthquakes occur in a region where teleseismically recorded events were few

the status of central seismic gap a perspective based on the spatial and temporal aspects of the large himalayan earthquakes abstract the central himalaya considered as a prominent seismic gap is generally believed to be the most vulnerable segment due for a great plate boundary earthquake m 8 two significant historical earthquakes are known to have occurred in this region in ad 1505 and 1803 interpreted by some workers as great earthquakes occurrences of these events question the validity of central himalaya being a seismic gap here we analyze the macroseismal data from the central himalaya and the gangetic plains and suggest that neither of these earthquakes can be qualified as a plate boundary type event and the size of at least the 1803 does not exceed mw 7 7 our studies further indicate that the central himalayan frontal thrusts may be undergoing a quiescence of 1000 years in terms of generation of great earthquakes assuming a steady elastic strain accumulation due to plate convergence and its simple translation as periodic great earthquakes such long quiescence may appear intriguing we suggest that the long term quiescence and the spatial and temporal clustering that characterize the distribution of large earthquakes in the himalaya is a manifestation of the tectonic deformation associated with a highly evolved fold and thrust belt our analyses also indicate that the large moderate earthquakes are mostly concentrated on higher level thrusts these structures probably accommodate most of the seismogenic slip in the himalaya and the rest of the strain could possibly be expended on passive folding consequently great earthquakes m 8 are relatively infrequent as in the case of central himalaya apparently leading to long periods of quiescence

prototype wireless sensors for monitoring subsurface processes in snow and firn the detection and monitoring of meltwater within firn presents a significant monitoring challenge we explore the potential of small wireless sensors etracer et to measure temperature pressure electrical conductivity and thus the presence or absence of meltwater within firn through tests in the dry snow zone at the east greenland ice core project site the tested sensor platforms are small robust and low cost and communicate data via a vhf radio link to surface receivers the sensors were deployed in low temperature firn at the centre and shear margins of an ice stream for 4 weeks and a bucket experiment was used to test the detection of water within otherwise dry firn the tests showed the et could log subsurface temperatures and transmit the recorded data through up to 150 m dry firn two vhf receivers were tested an autonomous phase sensitive radio echo sounder apres and a winradio the apres can combine high resolution imaging of the firn layers by radio echo sounding with in situ measurements from the sensors to build up a high spatial and temporal resolution picture of the subsurface these results indicate that wireless sensors have great potential for long term monitoring of firn processes

magmatic residence times of zoned phenocrysts introduction and application of the binary element diffusion modelling bedm technique this paper describes a general technique binary element diffusion modelling bedm for determining single crystal residence times in magmas that relies on modelling the diffusion of two or more elements in the crystal bedm has the advantage over other diffusion based models in that it does not need a precisely defined initial compositional profile for the crystal at zero time and instead requires that the concentrations of the two elements are correlated during crystallisation any differences subsequently observed between the two elements are caused by intracrystalline diffusion during residence in hot magma these differences are removed by artificially ageing the slower diffusing of the two elements and the amount of time taken to undo the difference between the elements is simply related to the crystal residence time decoupling time at high temperatures the bedm principle is demonstrated using artificial data and is then applied to literature data for sr and ba in a zoned sanidine crystal from the bishop tuff anderson et al in j petrol 41 3 449 473 2000 for this crystal the method gives a residence time estimate of 114 ka at 800 c which is then compared with estimates from other methods in theory the method can be further expanded for use as a geothermometer as well as geochronometer however this is not easily possible with the diffusivity data currently available

plagioclase residence times at two island arc volcanoes kameni islands santorini and soufriere st vincent determined by sr diffusion systematics the diffusive relaxation of trace element profiles in plagioclase phenocrysts may provide important constraints on magma residence times in crustal magma chambers initial trace element profiles in plagioclase phenocrysts are governed by variations in the concentration of a trace element in the melt and by the plagioclase melt partition coefficient trace element diffusion will subsequently act to modify this initial profile and given enough time produce a profile that is in equilibrium with the anorthite variations within the crystal we argue that the trace element partition coefficient da b between two parts a and b of a plagioclase crystal of variable anorthite content is equal to the ratio of their crystal liquid partition coefficients and that the equilibrium profile of the crystal can be calculated the time required to establish diffusive equilibrium is dependent on the wavelength and amplitude of the initial trace element concentration range and on the diffusivity of the trace element in plagioclase strontium plagioclase melt partition coefficients and diffusivities are calculated for a range of magmatic temperatures and plagioclase compositions a one dimensional diffusion model is developed that describes the diffusive destruction of oscillatory trace element zoning with time and allows the calculation of upper limits for plagioclase crystal residence times in a magma reservoir the model is tested using major and trace element concentrations measured along crystal traverses of plagioclase phenocrysts from the kameni island dacites santorini and from the 1979 soufriere andesite st vincent three out of eight plagioclase phenocrysts have sr concentration profiles that are not in diffusive equilibrium for these the diffusion model is employed to calculate maximum crystal residence times from incomplete diffusive equilibration of trace element zoning in plagioclase maximum crystal residence times range from 100 to 450 years this is in good agreement with estimates from crystal size distribution and from ra th disequilibrium studies for the kameni islands for soufriere however such short residence times are incompatible with u th mineral errorchron data that suggest residence times of 40 ka in a thermally buffered magma reservoir to reconcile these apparently different ages we invoke a more complicated magmatic history for soufriere where an initially buffered magma reservoir is disturbed by magma mixing and suffers limited additional crystal fractionation prior to eruption

earthquakes and associated deformation in northern baluchistan 1892 2001 we examine a century of seismicity and earthquake related deformation on the western margin of the indian plate in the pakistan region of northern baluchistan several catalogs of earthquakes for this region currently exist but early catalogs in particular suffer from errors incompleteness inhomogeneity and location bias we form a new catalog of more than 1000 earthquakes using original sources to confirm macroseismic locations and assign m s magnitudes to earthquakes since 1892 in doing so we reveal a systematic east northeast bias in locations caused largely by the uneven global distribution of seismic stations used in their determination an appendix provides narrative accounts and historical references to 34 significant earthquakes in the region the pattern of seismicity in the past century shows activity over a 700 km long 200 km wide segment of the plate boundary with predominantly strike slip faulting to the west and thrust faulting to the east at its narrowest near 29 n transpression of the plate boundary is partitioned into reverse and strike slip components separated by approximately 100 km the m 7 3 1931 mach earthquake slip 1 1 m on a 40 east southeast dipping reverse fault released fault normal stresses that may have unclamped the subsequent m 7 7 left lateral quetta earthquake 4 years later the northern chaman fault system in the past century has been largely inactive suggesting that this time period is not representative of long term activity in the region and that up to 4 m of potential slip is currently available to drive one or more future m 7 earthquakes despite triangulation installed in the late nineteenth and early twentieth centuries no recent geodetic data are available to permit plate boundary velocities to be measured directly

mapping seismic quiescence in california the decrease of microearthquake activity is a controversial possible precursor for mainshock prediction the calculation of seismic quiescence is a convenient tool to quantify this decrease however the actual size of an anomaly significantly depends on the calculation parameters the necessary averaging over space and time acts as 3d lowpass filter the sliding statistics windows introduce highpass behavior and the magnitude threshold shall ensure catalog completeness but also biases the data selection to argue on any claimed anomaly the only conclusive solution would be an exhaustive search over all parameters over an area significantly larger than just the epicenter region and against a test of the null hypothesis qmap is a new mapping approach to process full catalogs that is some twenty years of data for areas of one million km 2 with one fixed set of parameters it utilizes fractil statistics to avoid errors otherwise induced by clusters of aftershock series qmap features two different scaling modes one to display absolute decrease and a second for weighted anomalies by erosion filtering applied to california one can recognize quiescence anomalies of regional scale prior to the coalinga and loma prieta earthquakes but there are more and greater anomalies distributed all along the san andreas fault system without further criteria to understand these patterns the additional anomalies degrade seismic quiescence to an observation with high false alarm rate for earthquake prediction

dynamic plumbing system beneath volcanoes revealed by kinetic modeling and the connection to monitoring data an example from mt etna abstract our ability to monitor volcanoes using seismic signals ground deformation gas fluxes or other ground and satellite based observations as well as our understanding of melt reservoirs that feed eruptions have evolved tremendously in recent years the complex plumbing systems that are thought to feed eruptions are however difficult to relate to the monitoring signals here we show that the record preserved in compositional zoning of erupted minerals may be used to reconstruct sections of the plumbing system kinetic modeling of such zoning can yield information on the residence time of magma in different segments of the plumbing systems this allows a more nuanced evaluation of the link between observed monitoring signals or eruption styles and the magmatic processes and movement of batches of melts at depth the approach is illustrated through a study of the compositional zoning recorded in olivine crystals from the 1991 1993 se flank eruption products of mt etna sicily the zoning patterns in crystals reveal that the plumbing system of the volcano consisted of at least three different magmatic environments between which magma was transported and mixed in the year or two preceding the start of eruption quantification of this history indicates that two main pathways of melt migration and three timescales dominated the dynamics of the system combination of this information with the timing of observation of various monitoring signals allows a reconstruction of the dynamic evolution of this section of the plumbing system during the early stages of the 1991 1993 eruption it is seen for example how the migration of melt through the same sections of the plumbing system can cause pre eruptive triggering enhance strombolian activity and through the ensuing eruption cleanse and flush the plumbing system different kinds of mixing occur simultaneously at different sections of the plumbing system on different timescales a few days up to two years

monitoring seismo volcanic and infrasonic signals at volcanoes mt etna case study volcanoes generate a broad range of seismo volcanic and infrasonic signals whose features and variations are often closely related to volcanic activity the study of these signals is hence very useful in the monitoring and investigation of volcano dynamics the analysis of seismo volcanic and infrasonic signals requires specifically developed techniques due to their unique characteristics which are generally quite distinct compared with tectonic and volcano tectonic earthquakes in this work we describe analysis methods used to detect and locate seismo volcanic and infrasonic signals at mt etna volcanic tremor sources are located using a method based on spatial seismic amplitude distribution assuming propagation in a homogeneous medium the tremor source is found by calculating the goodness of the linear regression fit r 2 of the log linearized equation of the seismic amplitude decay with distance the location method for long period events is based on the joint computation of semblance and r 2 values and the location method of very long period events is based on the application of radial semblance infrasonic events and tremor are located by semblance brightness and semblance based methods respectively the techniques described here can also be applied to other volcanoes and do not require particular network geometries such as arrays but rather simple sparse networks using the source locations of all the considered signals we were able to reconstruct the shallow plumbing system above sea level during 2011

decadal time gaps between mafic intrusion and silicic eruption obtained from chemical zoning patterns in olivine abstract intrusion of mafic magma in a silicic crustal reservoir has been reported in numerous studies of subduction related volcanoes and is considered a main process for triggering explosive eruptions and for transferring geochemical signatures from the mantle to the crust here we determine the timescales between mafic silicic encounters and eruption by exploiting the fact that during such interactions magmas exchange crystals and their mineral compositions will strive to equilibrate to the new environmental conditions specifically we model the fe mg zoning patterns of olivine found in the dacites andesite and quenched mafic inclusions of the holocene zoned eruption of volcan san pedro 36 s chilean andes the san pedro eruption is an example where mixing between silicic and mafic magmas produced intermediate compositions e g andesite at depth in the magma reservoir for modeling the compositional profiles we took into account the anisotropy of fe mg diffusion in olivine and also the effects of diffusion in multiple dimensions aspects that have been largely neglected in previous works the retrieved timescales for olivine melt equilibration by diffusion display an array ranging from 1 year for the most silica rich dacite to 50 years for the andesite this array of timescales rather than a single value provides new insight into the details of mafic silicic mixing at depth they reveal processes that occur on a longer timescale than the days to weeks time gap for cases where the mafic intrusion triggered the eruption and they might be associated with the instances where seismic activity or significant inflation of the volcanic edifice was not immediately followed by eruption on the other hand the year to decade timescales that we report for producing magmas of intermediate composition e g andesites are much shorter than the 10 3 10 5 years inferred from u series disequilibria data for igneous differentiation by closed system fractionation to produce similar magma compositions at subduction zones

paleoliquefaction evidence and periodicity of large prehistoric earthquakes in shillong plateau india abstract the tectonic setting and the occurrence of the great assam earthquake m 8 7 of 1897 in the shillong plateau succeeded by three great earthquakes 1905 1934 and 1950 in the adjoining himalayan frontal arc indicates the vulnerability of the shillong plateau to large earthquakes the lack of seismicity records of the region earlier than 100 years and data on the recurrence of damaging earthquakes led us to investigate the paleoseismicity of the shillong plateau our paleoseismic investigations in the meizoseismal area of the 1897 earthquake revealed well preserved liquefaction and deformed syndepositional features at 10 selected sites in the alluvial deposits along two north flowing tributaries of the brahmaputra river these features are 14c dated using associated organic samples as the liquefaction of sediments was an important feature of the 1897 earthquake we identified this seismic event and other large major prehistoric earthquakes through paleoliquefaction and other coseismic structural deformation at the investigated sites in addition to the 1897 event we provide geological evidence for at least three large seismic events two of them occurred during 1450 1650 and 700 1050 ad the third predates 600 ad the analysis of the 14c data suggests a return period of about 400 600 yr for the large earthquakes in the shillong plateau this finding is the first of its kind from the himalaya and adjoining region

determination of magnitude for large shallow earthquakes 1898 1917 abstract in order to arrive at a uniform basis for a study of the global seismicity the surface wave magnitude ms of shallow earthquakes for 1898 1917 is newly determined by using maximum amplitudes of surface waves recorded by undamped milne and omori seismographs the effective gain of these instruments needs to be calibrated with great care because of the lack of a damping device the calibration of milne instruments is based on a comparison of amplitudes measured by milne instruments with those by more modern damped instruments the effective gain varies from 7 to 20 in the range of ms from 6 to 8 5 the reported amplitudes for the years 1910 1912 are twice as large as the standard and need to be corrected by applying these results to a wealth of the milne data ms is determined for a large number of earthquakes between 1898 and 1912 to supplement the data for 1913 1917 records of undamped omori seismographs are used for the entire period from 1898 to 1917 308 shallow earthquakes with m s 7 0 are listed here both this list and the previous catalogue of abe 1981 for 1918 1980 provide a catalogue of large shallow earthquakes much more uniform than any previously established between 1899 and 1910 the annual frequency of shocks with m s 7 0 is 20 which is twice as large as the annual average of 10 during 1911 and 1980

volcanic tremor location during the 2004 mount etna lava effusion 1 a lava emission started at mt etna italy on 7 september 2004 neither earthquake seismicity heralded or accompanied the opening of the fracture field from which the lava poured out nor volcanic tremor changed in amplitude and frequency content at the onset of the effusive activity to highlight long term changes we propose a method for the location of the tremor source based on a 3d grid search using the amplitude decay of the seismic signal from january to november 2004 we find the centroid of the tremor source within a zone close to and partially overlapped with the summit craters pre effusive phase which extended up to 2 km south of them effusive phase the depths are of between 1698 and 2387 m a s l we hypothesize the lava effusion stemmed from a degassed magma body although we find evidence of temporary magma overpressure conditions such as those documented on 25 september

unravelling the processes controlling gas emissions from the central and northeast craters of mt etna abstract we measured volcanic gas emissions from the northeast crater nec and central crater cc of mount etna on 21st july 2008 and 3rd and 31st august 2009 using a novel lightweight open path fourier transform infrared spectrometry op ftir in active mode with a portable infrared lamp contemporaneously we measured the so2 flux of the total gas emission released by the combined summit craters 14 km downwind and the so2 flux emitted by the nec measured at the summit combining these data we determined the flux of the major volcanic components h2o co2 so2 hcl and hf emitted individually from cc and nec craters the results reveal similar so2 hcl ratios but distinct co2 so2 ratios 1 3 and 10 9 for nec and cc respectively and an order of magnitude greater co2 flux from the cc compared with the nec a simple model in which the nec branches from a central feeding conduit at a depth of 2 km can reproduce these observations we highlight that in such a system short term variations in co2 so2 ratios at each crater can occur due to minor variations in the magma gas flux entering each conduit at the branch without an overall change in magma supply co2 so2 variations measured at individual craters may therefore be unrepresentative of the volcanic system and require cautious interpretation monitoring of the total co2 and so2 fluxes emitted from each crater is on the contrary an optimal monitoring strategy and can be achieved using a combination of co2 so2 instruments and so2 imaging cameras

instrumental magnitudes of historical earthquakes 1892 to 1898 in the 1890s of the dawn of instrumental seismology a variety of primitive but sophisticated seismographs were erected in europe the quality varies greatly from instrument to instrument in use of those records the instrument magnification needs to be calibrated with extreme caution because of the lack of damping from comparison of the trace amplitudes measured by such instruments with those by reliable instruments the effective gain for surface wave maxima of distant shocks is determined here for each of the vertical or horizontal pendulums that were operated at catania rocca di papa ischia roma padua nicolajew charkow strassburg and shide the effective gain is found to be greatly different from the static magnification the period of surface wave maxima is on average 17 sec the results are applied to reported amplitudes for determining the surface wave magnitude of 53 major earthquakes recorded from 1892 to 1898 the magnitude of the destructive tsunami earthquake that occurred off northeastern honshu japan on 15 june 1896 is determined to be 7 2 the great assam india earthquake of 12 june 1897 has a magnitude of 8 0 the present study demonstrates that despite various difficulties historical records if properly interpreted provide invaluable information

heterogeneities of the instrumental seismicity catalog 1904 1980 for strong shallow earthquakes we analyze the world wide consistency of teleseismic reporting completeness of the seismicity record and homogeneity of magnitude determination for strong shallow earthquakes magnitude m 6 depth h 70 km in the period 1904 to 1980 for earthquakes with magnitude m 7 we used the catalog given by abe 1981 which lists the surface wave magnitude ms of every reported large event that occurred between 1904 and 1980 according to the original formulation of gutenberg 1945 under the postulate that the rate of earthquake occurrence for the entire world as a whole is consistent on a time scale of decades and that since the installation of the world wide standardized seismograph network in the early 1960s the earthquake catalog for strong m 6 shocks is complete and the seismicity rates are typical of all periods in the century we find that for instrumental related reasons the ms of large events prior to 1908 have been systemically overestimated by at least 0 5 magnitude unit and the ms of events in the period 1908 to 1948 have been consistently overestimated by 0 2 unit relative to the ms assigned to shocks occurring after 1948 when these corrections are taken into account the catalog of events with ms 7 0 is shown to be largely complete i e nearly all the large shallow shocks which occurred in the earth are listed for most of the world since early in the century for earthquakes as the magnitude 6 level we used the international seismological center isc tape and regional catalogues of earthquakes this file compiles the earthquake data given by gutenberg and richter 1954 for the first half of the century and data from various international agencies after 1945 we find a highly incomplete seismicity catalog at this magnitude level for the first half of the century mainly due to numerous increases and decreased in the earthquake detection and reporting capabilities a more complete but extremely inhomogeneous catalog for the period 1950 to 1963 due to the use of different formulations and criteria to calculate and report the parameter magnitude by the various seismological agencies and a largely complete and homogeneous in ms record since 1964

complements to magnitudes of large shallow earthquakes from 1904 to 1980 abstract in the previous paper magnitudes of large earthquakes of the world were determined on a very uniform basis and catalogued in order to arrive at a more homogeneous catalogue for a study of global seismicity some complements are presented the major complements are as follows 1 the m s values for the period 1904 1909 in the previous paper were overestimated in the extreme case by 0 5 magnitude units 2 the m b values for the period 1904 1908 in the previous paper were also overestimated 3 the magnitudes of deep and intermediate shocks which are listed in seismicity of the earth by gutenberg and richter are found to be approximated by m b m b 7 4 4 the catalogues of m b for shallow intermediate and deep shocks are continued for the period up to 1980

pressurization and depressurization phases inside the plumbing system of mount etna volcano evidence from a multiparametric approach during 2013 mount etna volcano experienced intense eruptive activity at the summit craters foremost at the new southeast crater and to a minor degree at the voragine and bocca nuova bn which took place in two cycles february april and september december in this work we mainly focus on the period between these cycles applying a multiparametric approach the period from the end of april to 5 september showed a gradual increase in the amplitude of long period lp events and volcanic tremor a slight inflation testified by both tilt and gps data and a co2 flux increase such variations were interpreted as due to a gradual pressurization of the plumbing system from the shallowest part where lp and volcanic tremor are located down to about 3 9 km below sea level pressure source depths obtained by both geodetic and co2 data on 5 september at the same time as a large explosion at bn we observed an instantaneous variation of the aforementioned signals decrease in amplitude of lp events and volcanic tremor slight deflation and co2 flux decrease and the activation of a new infrasonic source located at bn in the light of it the bn explosion probably caused the instantaneous end of the pressurization and the opening of a new vent at bn that has become a new steady source of infrasonic events this apparently slight change in the plumbing system also led to the gradual resumption of activity at the new southeast crater culminating with the second lava fountain cycle of 2013

shallow magma pathway geometry at mt etna volcano 1 a fundamental goal of volcano seismology is to understand the dynamics of active magmatic systems in order to assess eruptive behavior and the associated hazard imaging of magma conduits quantification of magma transport and investigation of long period seismic sources together with their temporal variations are crucial for the comprehension of eruption triggering mechanisms at mt etna volcano several intense episodes of tremor activity were recorded during 2007 in association with strombolian activity and or intense fire fountaining episodes occurring from the south east crater sec the locations of the tremor sources and of the long period seismic events are used here to constrain both the area and the depth range of magma degassing highlighting the geometry of the shallow conduits feeding sec the imaged conduits consist of two connected resonating dike like bodies nnw sse and nw se oriented extending from sea level to the surface in addition we show how tremor long period lp and very long period vlp event locations and signatures reflect pressure fluctuations in the plumbing system associated with the ascent discharge of gas rich magma linked to the lava fountains the evidence here reported also corroborated by ground deformation variations can help develop a better prediction and early warning system for those eruptions effusive or explosive that apparently manifest no clear precursors

medium term forecast of the 1988 north east india earthquake abstract northeast india is seismically one of the most active intra continental regions in the world it has been a site of 10 earthquakes of magnitude m 7 5 during the last 100 years gupta and singh j geol soc india 28 1986 367 406 systematically analysed the time series of earthquakes associated with several main shocks in an area bound by 20 n and 32 n latitude and 87 e and 100 e longitude and concluded 1 moderate magnitude to great earthquakes in the north east india region are found to be preceded generally by well defined earthquake swarms and quiescence periods 2 on the basis of an earthquake swarm and quiescence period an area bound by 21 n and 25 5 n latitude and 93 e and 96 e longitude is identified to be the site of a possible future earthquake of m 8 0 5 with a focal depth of 100 40 km this earthquake should occur any time from now onwards should it not occur till the end of 1990 this forecast could be considered as a false alarm this medium term earthquake forecast came true with the occurrence of the m 7 3 earthquake on august 6 1988 within the specified spatial and temporal parameters the forecast of this earthquake was based on the concept of precursory swarms and quiescence preceding main shocks it is worthwhile noting that in the entire region under study the august 6 1988 earthquake was the largest since the august 17 1952 earthquake of m 7 5 this lends support to the worldwide effort to study and identify spatial and temporal variation of seismicity and recognise patterns that precede major earthquakes

mt etna 2001 eruption new insights into the magmatic feeding system and the mechanical response of the western flank from a detailed geodetic dataset abstract in the last decades the increasing availability of comprehensive geodetic datasets has allowed for more detailed constraints on subsurface magma storage and conduits at several active volcanoes worldwide here by using a large dataset of geodetic measurements collected between early january 2001 and august 2001 we identified at least six different deformation stages that allow us to quantify the surface deformation patterns before during and after the 2001 mt etna volcanic eruption our results are largely in agreement with previous works e g the presence of a deep inflating source and a shallow dike located beneath the north western and upper southern flanks of the volcano respectively however we provide 1 finer resolution of the temporal activity of these magmatic sources leading to 2 new evidence related to the evolution of the magmatic system and the mechanical response of the western flank in particular during the pre eruptive phase results and analysis show a clear change in the ground deformation pattern of the volcano in response to the 20 24 april 2001 seismic swarm that occurred beneath the western flank evolving from a volcano wide inflation to a slight deflation of the summit area we suggest that the source responsible for the volcano wide inflation beginning in the fall of 2000 experienced a drastic reduction in the inflation rate in response to this seismic swarm moreover we provide evidence for the presence of a new inflating source located beneath the upper southern flank at a depth of 7 0 km bsl that triggered both the occurrence of the 20 24 april 2001 seismic swarm and led to the rapid ascent of magma upward to the surface after 12 july the lower vents system was fed by fresh magma rising from this source the presence of this inflating source is inferred by 1 seismological and volcanological observations coming from the 2001 eruption and 2 seismological constraints coming from a previous similar episode that occurred at etna during the 1993 1998 period furthermore both shallow deflations observed after the 20 24 april 2001 seismic swarm and during the first day of the eruption also could be due to the deflation of two adjacent portions of the same shallow 2 km bsl reservoir such reservoirs would feed the activity that occurred at the south east crater after january 2001 and the activity of the upper vents system during the july august eruption in agreement with petrochemical observations through an updated revision of the available data we shed some light on the relevance of pre eruptive activity patterns an important element for an effective volcano monitoring

partition coefficients for iron between plagioclase and basalt as a function of oxygen fugacity implications for archean and lunar anorthosites abstract experimental studies were undertaken to determine d for feot between plagioclase and melt as a function of oxygen fugacity for a basaltic composition that occurs as matrices for plagioclase megacrysts that are similar to those in calcic anorthosites at liquidus conditions the d for feot between calcic plagioclase and tholeiitic basalt changes very little from 0 030 to 0 044 between the very low o 2 of the iron wustite buffer and that of the quartz fayalite magnetite qfm buffer at fugacities above qfm the value for d increases rapidly to 0 14 at the magnetite hematite buffer and 0 36 in air the increase in d results from the fact that nearly all of the fe is in the fe2 state at o 2 below qfm and the fe 3 fe 2 ratio in the melt increases rapidly above qfm causing more fe to enter the plagioclase which accepts fe3 more readily than fe2 there is essentially no change in values of d over cooling rates that vary by two orders of magnitude the d for feot of 0 030 at iron wustite is in good agreement with earlier studies at low o2 terrestrial calcic plagioclase matrix pairs display ds of about 0 043 in excellent agreement with the experimental value of 0 044 at qfm which is the accepted fugacity for terrestrial tholeiitic basalts application of the ds for feot and other components to terrestrial calcic anorthosites indicates that the anorthosites were in equilibrium with nearby coeval tholeiitic basalts at qfm as was expected lunar anorthosites however have anomalously low contents of feot as well as mgo and would be in equilibrium with melts that are several times lower in these components than expected the low values of feot and mgo in the plagioclase of lunar anorthosites are a result of subsolidus reequilibration with pyroxene olivine and other fe mg bearing phases during high temperature metamorphism as is the case in terrestrial anorthosites that have undergone granulite grade metamorphism the ds for k2o mgo and tio2 were determined as 0 21 0 044 and 0 033 respectively and show no variation with o 2 the value for k2o is in good agreement with natural assemblages the values for mgo and tio2 however are lower in natural assemblages but the high degree of mobility of mg and the very low contents of tio2 in plagioclase makes the reliability of the natural values rather low also the d for tio2 may be affected by rate of cooling attempts to determine the d for cr2o3 as a function of o 2 were made difficult by the low levels of cr2o3 300 to 500 ppm in the melt when saturation with a cr spinel occurred because the cr concentrations in plagioclase are nearly 100 times less than those in the melt it was not possible to obtain reliable analyses for plagioclase these uncertainties constrain the d for cr to be less than 0 07 at the qfm buffer

teleseismic detection in the aleutian island arc recently it has become apparent that teleseismic detection has decreased substantially in many regions of the world the major decrease was related to the closure of the vela arrays in the united states during the late 1960 s this detection decrease has been recognized in south and central america mexico the kuriles the caribbean tonga and the new hebrides in this paper the effect of the closure of these arrays on the reporting of events in the aleutian island arc is examined in the aleutians the detection history is complicated by the short term installation of a local network on and near amchitka island during the early 1970 s the temporal coincidence of the installation of this network and the closure of the vela arrays delayed the detection decrease in the central aleutians until the amchitka network was closed in early 1973 reporting in the eastern aleutians was unaffected by the installation of the amchitka network in that region the detection decreased between 1968 and 1970 the time of the closure of the vela arrays new techniques have been developed which make it possible to determine the effect of station installation or closure on the reporting in some regions these techniques rely on plots which show the distribution of an observed seismicity rate change in the magnitude domain these plots make it possible to recognize probable detection changes and to determine quantitatively magnitude cutoffs which avoid these changes the magnitude level at which these cutoffs are made is termed the minimum magnitude of homogeneity mmin h the reporting of events with mb 4 6 in the aleutians decreased substantially during the mid 1970 s so mmin h in this region is 4 7 this is different from the magnitude of completeness mmin c which is mb 5 0 0 1 if one is interested in examining seismicity rates for changes which may be precursors to earthquakes then awareness of detection related changes and magnitude cutoffs which avoid these changes are essential for meaningful results

magma recharge contamination and residence times revealed by in situ laser ablation isotopic analysis of feldspar in volcanic rocks we illustrate a rapid and effective method for determining variations in 87sr 86sr across single plagioclase feldspar crystals using laser ablation interfaced to a multicollector inductively coupled plasma source mass spectrometer the speed of analysis proves to be a particular advantage permitting representative populations of crystals to be characterized or enabling reconnaissance analysis of rocks to test for mineral scale isotopic heterogeneity our results from magmatic crystals in lavas from el chichon volcano confirm trends previously obtained by the more time consuming microdrilling method for the first time with confidence the laser data allow us to associate abrupt changes in 87sr 86sr with distinct petrographic discontinuities such as dissolution surfaces in the crystal because the isotopic variations within crystals would be expected to equilibrate diffusively with time the width over which abrupt changes in 87sr 86sr occur can also be used to constrain timescales at which the crystal has been held at magmatic temperatures

seismicity in the kingdom of bhutan 1937 2003 evidence for crustal transcurrent deformation we investigate moderate sized historic to recent earthquakes in the bhutan himalaya spanning the years from 1937 to 2003 we find that few moderate sized earthquakes occurred in the region during this time period in order to better characterize the seismicity we relocate all earthquakes and estimate focal mechanisms for events for which we have adequate data we use first motion data for older events and waveform model digital seismograms for three earthquakes that occurred in 1980 m w 6 4 1995 m w 5 4 and 2003 m w 5 4 for the modern events we utilize three techniques for focal mechanism and depth determination regional full waveform time domain modeling of the two moderate m w 5 4 events and surface wave spectral method and body wave depth modeling approach for the m w 6 4 event we find that the first motion and digital data focal mechanisms are mostly strike slip with midcrustal to deep crustal depths although no recent great event has occurred along the main himalayan thrust the indian plate is undergoing significant midcrustal to deep crustal transcurrent deformation likely due to oblique convergence of the indian asian collision in this region unlike oceanic continent oblique subduction strike slip and thrust partitioning occurs throughout the crust not in distinct zones the geological and geophysical nature of the bhutan himalaya appears significantly different than other himalayan regions due to the strike slip nature of many of the events an out of sequence thrust fault and the implications of deformation in the shillong plateau

ascent driven crystallisation of dacite magmas at mount st helens 1980 1986 we introduce a novel scheme that enables natural silicic glasses to be projected into the synthetic system qz ab or h2o in order to relate variations in volcanic glass chemistry to changing pressure p and temperature t conditions in the sub volcanic magma system by this means an important distinction can be made between ascent driven and cooling driven crystallisation under water saturated or undersaturated conditions in samples containing feldspar and a silica phase quartz or tridymite quantitative p t estimates of the conditions of last equilibrium between crystals and melt can be made formation of highly silicic melts i e 77 wt sio2 is a simple consequence of the contraction of the silica phase volume with decreasing pressure such that high silica glasses can only form by crystallisation at low pressure resorption of quartz crystals appears to be a further diagnostic feature of decompression crystallisation groundmass and inclusion glasses in dacites from the 1980 1986 eruption of mount st helens volcano wa span a wide range in sio2 68 80 wt anhydrous the compositions of the least evolved sio2 poor inclusions in amphibole phenocrysts record entrapment of silicic liquids with 5 4 wt water corresponding to a water saturation pressure of 200 mpa at 900 c the compositions of more evolved higher sio2 plagioclase hosted inclusions and groundmass glasses are consistent with extensive ascent driven fractional crystallisation of plagioclase oxide and orthopyroxene phenocrysts and microlites to low pressures during this polybaric crystallisation plagioclase phenocrysts trapped melts with a wide range of dissolved water contents 3 5 5 7 wt magmas erupted during the plinian phase of the 18 may 1980 eruption were derived from a large reservoir at depths of 6 km subsequent magmas ascended to varying depths within the sub volcanic system prior to extraction from glass chemistry and groundmass texture two arrest levels have been identified at depths of 0 5 1 and 2 4 km a single dome sample from february 1983 contains groundmass plagioclase tridymite and quartz testifying to temperatures of at least 885 c at 11 mpa these shallow storage conditions are comparable to those in the cryptodome formed during spring 1980 the corresponding thermal gradient 0 2 c mpa 1 is consistent with near adiabatic magma ascent from 8 km we argue that the crystallisation history of mount st helens dacite magma was largely a consequence of decompression crystallisation of hot magma beyond the point of water saturation this challenges the conventional view that phenocryst crystallisation occurred by cooling in a large magma chamber prior to the 1980 1986 eruption because the crystallisation process is both polybaric and fractional it cannot be simulated directly using isobaric equilibrium crystallisation experiments however calculation of the phase proportions in water saturated 910 15 c experiments by rutherford et al 1985 over the pressure range 220 125 mpa reproduces the crystallisation sequence and phenocryst modes of mount st helens dacites from 18 may 1980 by allowing for the effects of fractional versus equilibrium crystallisation entrained residual source material and small temperature differences between nature and experiment phase compositions can also be matched to the natural samples we conclude that decompression of water saturated magma may be the dominant driving force for crystallisation at many other silicic volcanic centres

decadal to monthly timescales of magma transfer and reservoir growth at a caldera volcano caldera forming volcanic eruptions are low frequency highimpact events capable of discharging tens to thousands of cubic kilometres of magma explosively on timescales of hours to days with devastating effects on local and global scales1 because no such eruption has been monitored during its long build up phase the precursor phenomena are not well understood geophysical signals obtained during recent episodes of unrest at calderas such as yellowstone usa and campi flegrei italy are difficult to interpret and the conditions necessary for large eruptions are poorly constrained2 3 here we present a study of pre eruptive magmatic processes and their timescales using chemically zoned crystals from the minoan caldera formingeruption of santorini volcano greece4 which occurred in the late 1600s bc the results provide insights into how rapidly large silicic systems may pass from a quiescent state to one on the edge of eruption5 6 despite the large volume of erupted magma4 40 60 cubic kilometres and the 18 000 year gestation period between the minoan eruption and the previous major eruption most crystals in the minoan magma record processes that occurred less than about 100 years before the eruption recharge of the magma reservoir by large volumes of silicic magma and some mafic magma occurred during the century before eruption and mixing between different silicicmagmabatches was still taking place during the final months final assembly of large silicic magma reservoirs may occur on timescales that are geologically very short by comparison with the preceding repose period with major growth phases immediately before eruption these observations have implications for the monitoring of long dormant but potentially active caldera systems

insights into magma and fluid transfer at mount etna by a multiparametric approach a model of the events leading to the 2011 eruptive cycle 1 since the second half of the 1990s the eruptive activity of mount etna has provided evidence that both explosive and effusive eruptions display periodic variations in discharge and eruption style in this work a multiparametric approach consisting of comparing volcanological geophysical and geochemical data was applied to explore the volcano s dynamics during 2009 2011 in particular temporal and or spatial variations of seismicity volcano tectonic earthquakes volcanic tremor and long period and very long period events ground deformation gps and tiltmeter data and geochemistry so2 flux co2 flux co2 so2 ratio were studied to understand the volcanic activity as well as to investigate magma movement in both deep and shallow portions of the plumbing system feeding the 2011 eruptive period after the volcano deflation accompanying the onset of the 2008 2009 eruption a new recharging phase began in august 2008 this new volcanic cycle evolved from an initial recharge phase of the intermediate shallower plumbing system and inflation followed by i accelerated displacement in the volcano s eastern flank since april 2009 and ii renewal of summit volcanic activity during the second half of 2010 culminating in 2011 in a cyclic eruptive behavior with 18 lava fountains from new southeast crater nsec furthermore supported by the geochemical data the inversion of ground deformation gps data and the locations of the tremor sources are used here to constrain both the area and the depth range of magma degassing allowing reconstructing the intermediate and shallow storage zones feeding the 2011 cyclic fountaining nsec activity

volcanic tremor at mt etna inferences on magma dynamics during effusive and explosive activity abstract during 1999 the volcanic activity at mt etna was both explosive and effusive at the summit craters strombolian activity lava fountains and lava flows affected different areas of the volcano involving three of the four summit craters results from analysis of the 1999 volcanic tremor features are shown at two different time scales first the long term time variation of the features of the volcanic tremor including spectral and polarization parameters during the entire year was compared with the evolution of the eruptive activity this approach demonstrated the good agreement between tremor data and observed eruptive activity the activation of different tremor sources was suggested then a more refined analysis of the volcanic tremor recorded during 14 lava fountain eruptions was performed in particular a shift of the dominant frequencies towards lower values was noted which corresponds with increasing explosive activity similar behaviour in the frequency content has already been observed in other explosive eruptions at mt etna as well as on other volcanoes this behaviour has been explained in terms of either an increase in the tremor source dimension or a decrease in the sound speed in the magma within the conduit these results confirm that the volcanic tremor is a powerful tool for better understanding the physical processes controlling explosive eruptions at mt etna volcano

buoyancy controlled eruption of magmas at mt etna buoyancy controls the ability of magma to rise its ascent rate and the style of the eruptions geophysical geological and petrological data have been integrated to evaluate the buoyancy of magmas at mt etna the density difference between host rocks and magmas is mainly related to the amount of h2o dissolved in the magma and to the bubble liquid separation processes in the depth interval 22 2 km b s l highly hydrated h2o 3 basaltic magmas or mixtures of bubbles liquid have positive buoyancy and rise rapidly conversely bubble depleted liquids with an intermediate h2o content 1 5 having neutral buoyancy will spread out and form magmatic reservoirs at different depths until cooling crystallization further modify composition and density these different processes account for the magma compositions location of magmatic reservoirs as determined by geophysical methods and the complex eruptive cycles slow effusions fire fountains and plinian eruptions that have been observed in the history of the volcano