novel retrieval of volcanic so2 abundance from ultraviolet spectra projects i firb miur simulazione dei flussi lavici con gli automi cellulari n rbau01rmz4 002 ii sviluppo di sistemi di monitoraggio funded by dipartimento di protezione civile della regione sicilia ingv istituto nazionale di geofisica e vulcanologia sezione di catania italy iii eu funded sixth framework programme project 18354 novac iv leverhulme trust fellowship

centennial to millennial scale hard rock erosion rates deduced from luminescence depth profiles abstract the measurement of erosion and weathering rates in different geomorphic settings and over diverse temporal and spatial scales is fundamental to the quantification of rates and patterns of earth surface processes a knowledge of the rates of these surface processes helps one to decipher their relative contribution to landscape evolution information that is crucial to understanding the interaction between climate tectonics and landscape consequently a wide range of techniques has been developed to determine short 10 2 a and long term 10 4 a erosion rates however no method is available to quantify hard rock erosion rates at centennial to millennial timescales here we propose a novel technique based on the solar bleaching of luminescence signals with depth into rock surfaces to bridge this analytical gap we apply our technique to glacial and landslide boulders in the eastern pamirs china the calculated erosion rates from the smooth varnished surfaces of 7 out of the 8 boulders sampled in this study vary between 0 038 0 002 and 1 72 0 04 mm ka 1 the eighth boulder gave an anomalously high erosion rate possibly due to a recent chipping cracking loss of surface given this preferential sampling of smooth surfaces assumed to arise from grain by grain surface loss we consider these rates as minimum estimates of rock surface denudation rates in the eastern pamirs china

rock weathering rates as functions of time the scarcity of documented numerical relations between rock weathering and time has led to a common assumption that rates of weathering are linear this assumption has been strengthened by studies that have calculated long term average rates however little theoretical or empirical evidence exists to support linear rates for most chemical weathering processes with the exception of congruent dissolution processes the few previous studies of rock weathering rates that contain quantitative documentation of the relation between chemical weathering and time suggest that the rates of most weathering processes decrease with time recent studies of weathering rinds on basaltic and andesitic stones in glacial deposits in the western united states also clearly demonstrate that rock weathering processes slow with time some weathering processes appear to conform to exponential functions of time such as the square root time function for hydration of volcanic glass which conforms to the theoretical predictions of diffusion kinetics however weathering of mineralogically heterogeneous rocks involves complex physical and chemical processes that generally can be expressed only empirically commonly by way of logarithmic time functions incongruent dissolution and other weathering processes produce residues which are commonly used as measures of weathering these residues appear to slow movement of water to unaltered material and impede chemical transport away from it if weathering residues impede weathering processes then rates of weathering and rates of residue production are inversely proportional to some function of the residue thickness this results in simple mathematical analogs for weathering that imply nonlinear time functions the rate of weathering becomes constant only when an equilibrium thickness of the residue is reached because weathering residues are relatively stable chemically and because physical removal of residues below the ground surface is slight many weathering features require considerable time to reach constant rates of change for weathering rinds on volcanic stones in the western united states this time is at least 0 5 my

effects of the 1989 fracture system in the dynamics of the upper se flank of etna revealed by volcanic tremor data the missing link 1 fracture reactivation is a widespread process in nature even though evidence of magma induced reactivation is less documented here we provide evidence of the reactivation of a fracture system on the upper flank of the mt etna volcano and consider its possible implications in understanding the recent volcanic and tectonic activity a nnw sse trending fracture partly accompanied by magma emplacement in the form of a laterally propagating dike formed in 1989 on the upper se flank of etna lava effusions in 1991 1993 2001 and 2006 were associated with volcano tectonic vt seismicity and ground deformations on the upper part of the volcano which document the seismogenetic involvement of the 1989 fractures although without eruptive phenomena along the discontinuity in addition to the aforementioned episodes of vt seismicity differences in the characteristics of the background seismic radiation volcanic tremor were measured at stations close to these fractures during the eruptive activity on 24 november 2006 for which more detailed volcanological and seismological time histories are available moving on from these findings we analyze volcanic tremor data recorded close to the summit and along the s flank of the volcano to highlight the interactions between seismic radiation and the 1989 fracture system centroid location of volcanic tremor and wave field characteristics at stations of the permanent local seismic network of etna highlight the guidance role played by the 1989 fractures during the eruptive activity on 24 november 2006 in addition the collected data shed light on hitherto unknown structural features which appear to connect the volcano summit to the lower se slope and also play an important role in controlling the instability of the e flank more generally this study shows how 1 using an integrated approach it is possible to link apparently different features to a common structure showing uniform and distinct dynamics relevant at the volcano scale and 2 fracture reactivation can also occur by means of magma intrusion playing an important role in the transfer of magma within a volcanic edifice

cosmic ray labeling of erosion surfaces in situ nuclide production rates and erosion models a number of in situ cosmogenic radionuclides and stable nuclides have been measured in natural exposed rock surfaces with a view to study their in situ production and rock erosion rates 1 the in situ radionuclides can be used for a high resolution tomography of the erosional history of an exposed surface two stable nuclides 3he 21ne and five radionuclides 10be 26al 36cl 14c 39ar having half lives in the range of 300 1 5 106 yr half life are measurable in many rock types a prerequisite for the application of the in situ nuclides for the study of erosional histories of surfaces is a knowledge of their production rates under different irradiation conditions altitude latitude irradiation geometry and shielding relative nuclide production rates can be determined fairly accurately using the extensive available data on cosmic ray neutrons 2 absolute nuclide production rates cannot generally be predicted with any accuracy because of lack of data on excitation functions of nuclides unless some normalization is possible as was done in the case of several cosmic ray produced isotopes in the atmosphere 3 based on a recent natural calibration experiment in which erosion free surfaces exposed to cosmic radiation for 11 000 yrs were sampled the absolute production rates of 10be and 26al in quartz have been accurately estimated for mountain altitudes in sierra nevada 4 the absolute production rates of 10be and 26al in quartz can therefore be estimated fairly accurately for any given latitude and altitude some measurements of 14c in rocks of low erosion rate 5 similarly allow an estimate of its production rate attempts made to measure the in situ production rates of 3he in rocks have not yet led to a convergent production rate in view of the importance of knowing the production rates of isotopes of he ne and ar i present here theoretical estimates of their production rates based on available cross section data i discuss the information that can be extracted from the study of the in situ nuclides in rocks useful parameters characterizing the exposure history of a rock surface are 1 the effective surface exposure age and 2 the time averaged erosion rate the implications of these parameters for single and multiple nuclide studies are discussed in terms of the erosion models considered

erosion by an alpine glacier assessing the impact of glaciation on earth s surface requires understanding glacial erosion processes developing erosion theories is challenging because of the complex nature of the erosion processes and the difficulty of examining the ice bedrock interface of contemporary glaciers we demonstrate that the glacial erosion rate is proportional to the ice sliding velocity squared by quantifying spatial variations in ice sliding velocity and the erosion rate of a fast flowing alpine glacier the nonlinear behavior implies a high erosion sensitivity to small variations in topographic slope and precipitation a nonlinear rate law suggests that abrasion may dominate over other erosion processes in fast flowing glaciers it may also explain the wide range of observed glacial erosion rates and in part the impact of glaciation on mountainous landscapes during the past few million years

valley formation by fluvial and glacial erosion cross valley profiles from the west slope of the olympic peninsula washington are used to investigate the relative effects of fluvial and glacial erosion on valley formation unlike most ranges where glaciers and rivers sequentially occupied the same valleys neighboring valleys in the olympic mountains developed in similar lithologies but were subject to different degrees of glaciation allowing comparison of the net effect of glacial and fluvial processes integrated over many glacial cycles upslope drainage area was used to normalize comparisons of valley width ridge crest to valley bottom relief and valley cross sectional area as measures of net differences in the mass of rock excavated from below ridgelines for 131 valley spanning transects valley width relief and cross sectional areas are similar for glaciated partly glaciated and unglaciated fluvial valleys with drainage areas of 10 km 2 but diverge downslope glaciated valleys draining 50 km 2 reach two to four times the cross sectional area and have to 500 m greater relief than comparable fluvial valleys partly glaciated valleys have intermediate dimensions at distances of 5 km from valley heads the cumulative upstream volume of rock removed to form valleys is two to four times greater in glacially incised valleys than in fluvial valleys the finding of strong differences in the net result of valley excavation by fluvial and glacial erosion supports the interpretation that alpine glaciers are more effective erosional agents than are rivers and implies that large alpine valleys deepened and enlarged in response to pleistocene glaciation

real and apparent changes in sediment deposition rates through time 1 field measurements show that estimated sediment deposition rate decreases as a power law function of the measurement interval this apparent decrease in sediment deposition has been attributed to completeness of the sedimentary record the effect arises because of incorporation of longer hiatuses in deposition as averaging time is increased we demonstrate that a heavy tailed distribution of periods of nondeposition hiatuses produces this phenomenon and that observed accumulation rate decreases as t 1 over multiple orders of magnitude where 0 1 is the parameter describing the tail of the distribution of quiescent period length by using continuous time random walks and limit theory we can estimate the actual average deposition rate from observations of the surface location over time if geologic and geometric constraints place an upper limit on the length of hiatuses then average accumulation rates approach a constant value at very long times our model suggests an alternative explanation for the apparent increase in global sediment accumulation rates over the last 5 million years

the relative efficacy of fluvial and glacial erosion over modern to orogenic timescales it has been debated whether rivers or glaciers are more effective agents of erosion a global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift since the late nineteenth century it has been debated whether rivers or glaciers are more effective agents of erosion1 the dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers and recent studies have documented the topographic signature of an ice controlled limit of mountain height known as the glacial buzz saw 2 3 here we present a new global compilation of erosion rates which questions the conventional view of glaciers and erosion in regions of rapid tectonic uplift erosion rates from rivers and glaciers both range from 1 to over 10 mm yr 1 indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift moreover a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles whereas fluvial erosion rates show no apparent dependence on time we conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion 10 mm yr 1 generally result from a transient response to disturbance by volcanic eruptions climate change and modern agriculture

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

evidences for strong directional resonances in intensely deformed zones of the pernicana fault mount etna italy 1 in this paper we investigate ground motion properties in the western part of the pernicana fault this is the major fault of mount etna and drives the dynamic evolution of the area in a previous work rigano et al 2008 showed that a significant horizontal polarization characterizes ground motion in fault zones of mount etna both during earthquakes and ambient vibrations we have performed denser microtremor measurements in the ne rift segment and in intensely deformed zones of the pernicana fault at piano pernicana this study includes mapping of azimuth dependent horizontal to vertical spectral ratios along and across the fault frequency wave number techniques applied to array data to investigate the nature of ambient vibrations and polarization analysis through the conventional covariance matrix method our results indicate that microtremors are likely composed of volcanic tremor spectral ratios show strong directional resonances of horizontal components around 1 hz when measurements enter the most damaged part of the fault zone their polarization directions show an abrupt change by 20 to 40 at close measurements between the northern and southern part of the fault zone recordings of local earthquakes at one site in the fault zone confirm the occurrence of polarization with the same angle found using volcanic tremor we have also found that the directional effect is not time dependent at least at a seasonal scale this observation and the similar behavior of volcanic tremors and earthquake induced ground motions suggest that horizontal polarization is the effect of local fault properties however the 1 hz resonant frequency cannot be reproduced using the 1 d vertically varying model inferred from the array data analysis suggesting a role of lateral variations of the fault zone although the actual cause of polarization is unknown a role of stress induced anisotropy and microfracture orientation in the near surface lavas of the pernicana fault can be hypothesized consistently with the sharp rotation of the polarization angle within the damaged fault zone

dynamics of a lava fountain revealed by geophysical geochemical and thermal satellite measurements the case of the 10 april 2011 mt etna eruption 1 geophysical tilt seismic tremor and gravity signals geochemical crater so2flux and infrared satellite measurements are presented and discussed to track the temporal evolution of the lava fountain episode occurring at mt etna volcano on 10 april 2011 the multi disciplinary approach provides insight into a gas rich magma source trapped in a shallow storage zone inside the volcano edifice this generated the fast ascending gas magma dispersed flow feeding the lava fountain and causing the depressurization of a deeper magma storage satellite thermal data allowed estimation of the amount of erupted lava which summed to the tephra volume yielded a total volume of erupted products of about 1 106 m3 thanks to the daylight occurrence of this eruptive episode the so2 emission rate was also estimated showing a degassing cycle reaching a peak of 15 000 mg d 1 with a mean daily value of 5 700 mg d 1 the so2 data from the previous fountain episode on 17 18 february to 10 april 2011 yielded a cumulative degassed magma volume of about 10 5 106 m3 indicating a ratio of roughly 10 1 between degassed and erupted volumes this volumetric balance differently from those previously estimated during different styles of volcanic activities with long term years recharging periods and middle term weeks to months effusive eruptions points toward the predominant role played by the gas phase in generating and driving this lava fountain episode

extensive boulder erosion resulting from a range fire on the type pinedale moraines fremont lake wyoming abstract in july 1988 the flatfish range fire burned over the type pinedale moraines at fremont lake wyoming and caused extensive exfoliation of exposed boulder surfaces the mass of exfoliated material from 130 of 1030 boulders investigated was measured and recorded with information concerning factors that could influence the extent of fire induced exfoliation the range in thickness of material removed from 98 randomly selected boulders within the burn area averaged over the entire exposed boulder surface area is 6 1 to

climatic limits to headwall retreat in the khumbu himalaya eastern nepal ice free bedrock headwalls are widespread landforms of many glacial landscapes but their formation and evolution are not well understood here i present observations from the khumbu himalaya eastern nepal of a distinct elevation zone that aligns the base of many steep headwalls with the highest predicted frost cracking intensity fci below this zone median ice free hillslope angles are 40 and similar to those of other areas in the himalaya where threshold hillslopes that are close to the critical angle of stability have been inferred at higher elevations ice free hillslopes of different rock types have median slope angles of 50 55 suggesting threshold hillslopes with higher rock mass strength possibly related to the presence of deep reaching permafrost high altitude meteorological data combined with fci models support frost cracking as a mechanism for headwall retreat by undercutting of threshold headwalls while glacial transport inhibits the accumulation of scree deposits at their base this mechanism could account for continued headwall retreat as long as climatic conditions enable frost cracking near the base of headwalls that are high enough to sustain glaciers at their base even if subglacial erosion is minor

future fluctuations of mer de glace french alps assessed using a parameterized model calibrated with past thickness changes simulations of glacier evolution are needed to assess future changes in the runoff regime of mountain catchments a simplified parameterized model is applied here to simulate future thickness changes and glacier retreat of mer de glace french alps a normalized thickness change function describing the spatial distribution of surface elevation changes as a function of elevation has been determined the model reveals that under present climatic conditions mer de glace will continue to shrink dramatically in the coming decades retreating by 1200 m between now and 2040 the method has certain limitations related to the uncertainties of the normalized function based on thickness change data an error of 10 in the normalized function leads to uncertainties of 46 30 and 18 in mer de glace front surface area and glacier wide mass balance changes respectively in 2040 because the difference of the normalized function largely exceeds 10 from one glacier to another even within a given glacier size class and elevation range it would be very risky to extrapolate the normalized function to unmeasured glaciers consequently the method is applicable only on glaciers where past surface elevation changes are well constrained

petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites abstract ji s salisbury m h and hanmer s 1993 petrofabric p wave anisotropy and seismic reflectivity of high grade tectonites tectonophysics 222 195 226 in order to understand seismic anisotropy and its influence on the reflectivity of lower crustal fault zones we have undertaken experimental measurements of p wave velocities up to 600 mpa for 20 granulite and upper amphibolite facies mylonites from the snowbird tectonic zone canada the rocks whose composition ranges from ultramafic to felsic have experienced extremely large ductile strain it is found that the amphibolitic mylonites exhibit significant vp anisotropy 6 13 at 600 mpa whereas the pyroxene bearing granulite facies mylonites and the quartz or feldspathic tonalitic granitic and diatexitic mylonites are quasi isotropic in order to constrain interpretation of the measured vp properties microstructural analyses have been systematically performed in the samples studied it is shown that the interaction between feldspar and quartz or pyroxene and the absence of amphibole cause anisotropy in the granulite facies mylonites to be low the amphibolitic mylonites are strongly anisotropic because of a large volume fraction of hornblende with strong lpo 001 lineation and 100 foliation the anisotropy pattern in the amphibolitic mylonites is consistently orthorhombic vp x vp y vp z where x is parallel to stretching lineation y is normal to the lineation in the foliation plane and z is normal to the foliation plane but the anisotropy pattern in the mica rich mylonites is transversely isotropic vp x vp y vp z if sufficiently large volumes of the crust display such patterns this difference may be an important indicator for kinematic analysis in the middle to lower crust using modern seismic techniques the study demonstrates that while seismic reflectivity is strongly lithology controlled fabric induced anisotropy can both enhance and decrease seismic reflectivity hence the discontinuity of seismic reflections along ductile shear zones in the lower crust is not necessarily indicative of the discontinuity of the shear zones but may indicate changes in composition or metamorphic grade

geological interpretation of dekorp 2 s a deep seismic reflection profile across the saxothuringian and possible implications for the late variscan structural evolution of central europe abstract a 250 km long deep seismic section the first of its kind in west germany s dekorp project is interpreted in terms of late variscan collisional tectonics the structural model used is based on the intracontinental thrust tectonics concept of modern collision orogens the crustal profile across the saxothuringian zone seems to indicate north facing ramps antiformal stacks and culminations within the crystalline basement of the internal mid european variscides that have been only partially overprinted by permo mesozoic crustal stretching

rock control on microweathering of bedrock surfaces in a periglacial environment abstract microweathering of ice smoothed bedrock surfaces was investigated in the roldal area of hardanger plateau 60 southern norway postglacial rates of weathering were determined from surface lowering using quartz veins as reference surfaces weathering processes are inferred from assessment of weathering rind formation surface hardness and the preservation of small scale glacial erosional features surface lowering rates for a range of metamorphic rocks vary from 0 05 to 2 20 mm ka 1 and are broadly comparable with those obtained from crystalline rocks in other periglacial environments the mean rate of surface lowering at 0 55 mm ka 1 is low and demonstrates the relatively small impact of microweathering on postglacial landscape evolution variations in bedrock microweathering can be explained by lithological variation amphibolite and mica rich bedrock surfaces experience greater denudation and weakening least weathering rind formation and abundant preservation of glacial striae despite greater surface lowering conversely quartz rich bedrock surfaces are most resistant to denudation and weakening but have greater weathering rind formation and fewer preserved striae postglacial microweathering is achieved primarily through granular disintegration involving detachment and removal of mineral grains and weakening from increased porosity granular decomposition is manifest in the formation of weathering rinds analysis of interactions between weathering indices indicates that rind accumulation is limited by microerosion a conceptual model is proposed that illustrates the temporal interrelationships between in situ and erosional facets of microweathering in two contrasting mineral assemblages the model proposes that cyclic processes of in situ disintegration decomposition and erosion are at work the relative balance between these processes varies with lithology so that in more resistant quartz rich rocks the net effect is minimal surface lowering and accumulation of weathering rind in weaker amphibolitic and micaceous rocks the net effect is greater surface lowering and minimal accumulation of weathering rind the results of the research demonstrate the important influence of rock properties notably mineral composition in postglacial microweathering of crystalline bedrock in a periglacial environment

qp structure of mount etna constraints for the physics of the plumbing system 1 in this study we present the three dimensional qp structure of the mount etna volcano italy obtained by using local earthquake data the attenuation along ray paths t computed from the high frequency decay of velocity spectra is used to reconstruct the deep structure of the volcano down to 15 km depth the tomographic images reveal two broad low qp anomalies at 0 and 3 km depth located to the south and southwest of the summit area and extending at depth to the west of a central high qp anomaly located between 6 and 15 km depth the joint analysis of p wave attenuation and velocity allows us to better constrain the physics of the plumbing system the shallow low qp anomalies are associated with high vp anomalies beneath the top of the volcano and normal low vp toward its western borders we interpret the regions of low qp and normal low vp as shallow volumes where magmatic fluids are stored conversely the low qp high vp region may indicate intensely fractured rock volumes filled by fluids surrounding the magma branches at depth the low qp anomaly defines the path of the magma ascent to the west of an extremely high qp high vp volume located beneath the southeastern side of the summit area the high qp high vp body is interpreted to be the compact solidified high density intrusive body formed by nonerupted material during past volcano activity

location of long period events below kilauea volcano using seismic amplitudes and accurate relative relocation 1 we present methods for improving the location of long period lp events deep and shallow recorded below kilauea volcano by the permanent seismic network lp events might be of particular interest to understanding eruptive processes as their source mechanism is assumed to directly involve fluid transport however it is usually difficult or impossible to locate their source using traditional arrival time methods because of emergent wave arrivals at kilauea similar lp waveform signatures suggest the existence of lp multiplets the waveform similarity suggests spatially close sources while catalog solutions using arrival time estimates are widely scattered beneath kilauea s summit caldera in order to improve estimates of absolute lp location we use the distribution of seismic amplitudes corrected for station site effects the decay of the amplitude as a function of hypocentral distance is used for inferring lp location in a second stage we use the similarity of the events to calculate their relative positions the analysis of the entire lp seismicity recorded between january 1997 and december 1999 suggests that a very large part of the lp event population both deep and shallow is generated by a small number of compact sources deep events are systematically composed of a weak high frequency onset followed by a low frequency wave train aligning the low frequency wave trains does not lead to aligning the onsets indicating the two parts of the signal are dissociated this observation favors an interpretation in terms of triggering and resonance of a magmatic conduit instead of defining fault planes the precise relocation of similar lp events based on the alignment of the high energy low frequency wave trains defines limited size volumes

spatio temporal changes in glacier wide mass balance quantified by optical remote sensing on 30 glaciers in the french alps for the period 1983 2014 remote sensing is a powerful method to reconstruct annual mass balance series over past decades by exploiting archives of available images as well as to study glaciers in inaccessible regions we present the application of a methodological framework based only on optical satellite images to retrieve glacier wide annual mass balances for 30 glaciers in the french alps the glacier wide annual mass balance for the period 1983 2014 was reconstructed by combining changes in glacier volumes computed from remote sensing derived dems with annual measurements of the snow line altitude on satellite images data from direct observations on two of the glaciers confirmed the accuracy of the annual mass balances quantified by remote sensing with an average difference of 0 3 m w e within the uncertainty range of the methods our results confirm the significant increase in mass loss since the early 2000s with a difference 1 m w e a 1 between the periods 1983 2002 and 2003 14 the region wide mass balance for the french alps over the period 1979 2011 was 0 66 0 27 m w e a 1 close to that of the european alps we also show that changes in glacier surface area or length are not representative of changes in mass balance at the scale of a few decades

glacial effects limiting mountain height the height of mountain ranges reflects the balance between tectonic rock uplift crustal strength and surface denudation tectonic deformation and surface denudation are interdependent however and feedback mechanisms in particular the potential link to climate are subjects of intense debate spatial variations in fluvial denudation rate caused by precipitation gradients are known to provide first order controls on mountain range width crustal deformation rates and rock uplift moreover limits to crustal strength are thought to constrain the maximum elevation of large continental plateaus such as those in tibet and the central andes there are indications that the general height of mountain ranges is also directly influenced by the extent of glaciation through an efficient denudation mechanism known as the glacial buzzsaw here we use a global analysis of topography and show that variations in maximum mountain height correlate closely with climate controlled gradients in snowline altitude for many high mountain ranges across orogenic ages and tectonic styles with the aid of a numerical model we further demonstrate how a combination of erosional destruction of topography above the snowline by glacier sliding and commensurate isostatic landscape uplift caused by erosional unloading can explain observations of maximum mountain height by driving elevations towards an altitude window just below the snowline the model thereby self consistently produces the hypsometric signature of the glacial buzzsaw and suggests that differences in the height of mountain ranges mainly reflect variations in local climate rather than tectonic forces

physical properties of crustal and upper mantle rocks with regards to lithosphere dynamics and high pressure mineralogy this paper focusses on the physical properties of rocks and property changes occurring during geodynamic processes it addresses a number of outstanding petrophysical problems in the framework of crustal and mantle deformation the major themes to be discussed will be the seismic signature of crustal and mantle shear zones the nature of crustal and mantle anisotropy and the contribution of anisotropic rocks to seismic reflectivity in particular seismic shear waves traversing anisotropic strata can reveal important information on the spatial orientation of deformed structures because the measured seismic anisotropy has a structural origin emphasis will be placed on the relations between shear wave splitting and fabric anisotropy fabric anisotropy and strain and strain and geologic tectonic processes the second part of this paper discusses the effect that metamorphic phase transitions in crustal and mantle rocks may have on rock physical properties velocity density specifically the possible role that the gabbro eclogite transition could have in crustal delamination and recycling of material into the mantle will be considered

p wave velocity across a noncoaxial ductile shear zone and its associated strain gradient consequences for upper crustal reflectivity in order to simulate a normal incidence reflection profile across a noncoaxial ductile shear zone we determined p wave velocities of samples cut parallel and normal to mylonite foliation along a closely spaced profile 27 cm long through a transition zone and its associated strain gradient the ductile shear zone developed within an aplitic leucogranite was sampled from a kilometer wide ductile transcurrent fault in the northern french massif central strain analysis indicates that the sample experienced heterogeneous and progressive simple shear deformation shear strain systematically increases from zero in the undeformed protolith to 30 in the mylonite the transition zone thickness t is about 30 cm and the mylonite thickness m is about 10 cm the amount of quartz and mica increases relative to feldspar toward the mylonite indicating that a mineralogical composition change accompanied mylonitization mica and quartz developed a strong crystallographic preferred orientation cpo in the least strained domain seismic anisotropy is low and mean vp is 6 km s at 600 mpa anisotropy increases up to 10 and vp decreases up to 5 35 km s for propagation normal to the mylonite foliation through the transition zone this systematic velocity change correlates with the increasing through the transition zone and can be directly related to the cpo of mica and the increase in volume percent mica within the mylonite zone these results indicate that velocity and anisotropy gradients may in some cases be associated with ductile shear zones and that mylonite boundaries may not represent first order discontinuities the reflectivity of a ductile shear zone depends on the thickness of the transition zone relative to the seismic wavelength and on the t m ratio synthetic seismograms show that for a given seismic wavelength the reflectivity decreases when the transition zone thickness increases and when the ratio t m increases we show that layers with second order boundaries velocity gradients in transition zones are only seismically detectable within a narrow thickness range extrapolation to thicker shear zones is based on the assumption that the strain gradient thickness relative to shear zone thickness is to a first approximation scale independent in granitic domains ductile shear zones with similar geometrical and petrophysical features to the example studied here will be detected on deep seismic profiles only if their width is between 20 and 400 m development of ductile shear zones with strain gradients of the appropriate thickness to enhance reflectivity is favored under low temperature conditions in the granitic upper crust indeed low temperature strain gradient may explain the high seismic reflectivity of the upper crust in the scandinavian caledonides whereas high temperature strain gradient may explain in part the relative transparency of the european variscan upper crust

seismic monitoring and modeling of an active volcano for prediction we describe seismic monitoring and modeling of an active volcano for the purpose of predicting the magma transport process in real time we selected the piton de la fournaise which has been monitored by an observatory since the early 1980s and is active with 28 eruptions from 1980 until august 1992 it erupted on march 9 1998 after an unusually long quiet period the eruption lasted until september 21 1998 before the march eruption we completed the initial construction of a model of a magma system based primarily on long period lp events and coda localization we found that lp events are associated with the lateral movement of magma to the rift zone and not with the vertical movement to the summit we also found that the source of 2 hz lp events is located below that of 1 hz lp events the coda localization is a newly discovered phenomenon that helped to locate a magma body this model was used for interpreting the incoming information from the precursory seismic crisis and the eruption tremor during the 6 months of the eruption the simultaneous monitoring and modeling of an active volcano led us to a quantitative simulation of the eruption process computing excess pressure and flow rate in a system of reservoirs connected by channels

origin of reflections from the brevard fault zone the brevard fault zone is a belt of mylonitic metamorphic rocks that extends northeast over 700 km from alabama into virginia seismic reflection studies show that the fault zone produces excellent reflections which dip gently to the southeast and sole at depth the origin of these reflections has been investigated by measuring compressional wave velocities to 800 mpa confining pressure in 127 samples obtained from drill core which continuously sampled the fault zone to a depth of over 300 m densities are reported as well as chemical analyses at selected depths anisotropy at elevated pressures ranges within the fault zone from less than 5 to over 26 similarly the fault zone rocks show significant chemical variability with sio2 ranging from 58 0 to 70 4 by weight synthetic seismograms generated from the velocity and density measurements show that the reflections originate within the brevard fault zone from the complex interaction of compositional variations and seismic anisotropy resulting from ductile strain essential to this study has been the continuous coring of a major section of the brevard fault zone which has provided the necessary stratigraphic control as well as unweathered samples for laboratory studies

seismic anisotropy in mylonites an example from the mannin thrust zone southwest connemara ireland abstract mylonites associated with the mannin thrust zone of southwesternmost connemara formed when the high grade metamorphic rocks typical of most of the connemara massif were thrust to the southeast over low metamorphic grade low greenschist facies acid volcanics and volcaniclastic sediments while being metamorphosed in the epidote amphibolite facies triaxial and biaxial ultrasonic velocity measurements of mylonite specimens from a 240 m borehole have established that there is significant seismic anisotropy up to about 11 when comparing velocities perpendicular and parallel to the foliation this would ultimately lead to a reflection coefficient of about 0 02 when comparing the mean isotropic seismic velocity with that perpendicular to the foliation the finely striped discontinunous mineral lithons that define mylonitic foliation but which form no real and continuous surfaces could interact with seismic energy to produce reflections that do not relate to lithological contacts within the rocks but to a tectonically induced orientated acoustic impedance however the results support the work of others in suggesting that on its own the fabric would not produce the high amplitude reflections observed on deep seismic lines and other mechanisms need to be investigated

etna 2004 2005 an archetype for geodynamically controlled effusive eruptions 1 the 2004 05 eruption of etna was characterised by outpouring of degassed lava from two vents within valle del bove after three months of eruption lava volumes were estimated to be between 18 5 and 32 106 m3 with eruption rate between 2 3 and 4 1 m3 s petrological analyses show that magma is resident in the shallow plumbing system emplaced during the last south east crater activity so2 flux data show no increase at the onset of the eruption and so2 hcl ratios in gas emitted from the eruptive fissure are consistent with a degassed magma no seismic activity was recorded prior to eruption unlike eruptions observed since the 1980 s the purely effusive nature of this eruption fed by a degassed resident magma and the fracture dynamics suggest that magmatic overpressure played a limited role in this eruption rather lateral spreading of etna s eastern flank combined with general inflation of the edifice triggered a geodynamically controlled eruption

reflection characteristics of a mylonite zone based on compressional wave velocities of rock samples summary a combined field and laboratory study of the seismic reflection response and seismic properties of the mylonite zone capping the kettle dome metamorphic core complex provides important constraints on reflectivity of mylonites because of its structural and petrologic characteristics this mylonite zone can be regarded as a model for mid to deep crustal mylonite zones cdp reflection profiling revealed that the mylonite zone is reflective laboratory measurements of compressional wave velocities v at high confining pressures in samples collected directly up dip from the cdp reflection line revealed a wide variation of v in common mid crustal lithologies mafic and carbonate rock mean v values range from 6 67 to 7 31 km s at 600 mpa and quartzite and quartzo feldspathic values range from 6 16 to 6 52 km s seismic anisotropy at low pressures can be related to open microcracks and preferred mineral orientation whereas the latter effect controls anisotropy at high pressures the laboratory data provide the basis for a seismic model which indicates that the kettle dome mylonite zone can generate reflections from zones where high and low velocity lithologies are interlayered these reflections correlate with those observed on the cdp data thus demonstrating that the reflectivity of the mylonite zone is a direct result of its lithologic diversity and layered nature in this case it is not necessary to explain the reflections by the effects of anisotropy retrogression high pore pressure or constructive interference

crustal structure of northwestern svalbard and the adjacent yermak plateau evidence for oligocene detachment tectonics and non volcanic breakup summary in 1999 new seismic refraction data were collected off northwestern svalbard and the adjacent yermak plateau a 260 km long profile provides detailed velocity information for the northeastern edge of the eurasian continent and the adjacent yermak plateau north of forlandsundet graben the depth of the moho varies between 23 and 28 km and remains at this depth to the northern edge of the profile at 81 n the crustal lithology off western svalbard can be related to the basement province west of the raudfjorden fault zone off the northern shoreline of svalbard the structure of the tertiary danskoya basin is mapped below this a late silurian early devonian basin with seismic velocities between 5 1 and 5 8 km s 1 and a thickness of up to 8 km is present a palaeozoic sequence of up to 6 km thickness is expected below the tertiary cover north of the danskoya basin an earlier suggestion that oligocene rift processes affected the southern yermak plateau is confirmed a detachment structure is situated below the palaeozoic basin below danskoya basin which is probably a consequence of simple shear tectonics the middle crust exhibits low seismic velocities above the detachment fault the lowermost crust beneath is slightly contaminated by mantle derived melts which is deduced by the slightly elevated velocities of the lowermost crust these melts can be attributed to decompressive melting caused by modest uplift of the moho during stretching the velocity depth model provides no evidence for large magmatic activity which implies a non volcanic rifted margin history this leads to the assumption that the proposed yermak hotspot during the breakup of svalbard from northern greenland did not exist

bedrock incision rock uplift and threshold hillslopes in the northwestern himalayas the topography of tectonically active mountain ranges reflects a poorly understood competition between bedrock uplift and erosion dating of abandoned river cut surfaces in the northwestern himalayas reveals that the indus river incises through the bedrock at extremely high rates 2 12 mm yr 1 in the surrounding mountains the average angles of hillslopes are steep and essentially independent of erosion rate suggesting control by a common threshold process in this rapidly deforming region an equilibrium is maintained between bedrock uplift and river incision with landsliding allowing hillslopes to adjust efficiently to rapid river down cutting

comment on complex magma dynamics at mount etna revealed by seismic thermal and volcanological data by b behncke s falsaperla and e pecora

plio pleistocene increase of erosion rates in mountain belts in response to climate change here we review an ensemble of observations that point towards a global increase of erosion rates in regions of elevated mountain belts or otherwise high relief since the onset of northern hemisphere glaciation about 2 3 ma during that period of earth s history atmospheric co2 concentrations may have dropped and global climate cooled and evolved towards high amplitude oscillating conditions that are associated with the waxing and waning of continental ice sheets in the northern hemisphere we argue for a correlation between climate change and increased erosion rates and relief production which we attribute to some combination of the observed cooling onset of glaciation and climatic oscillation at orbital timescales in our view glacial erosion played a major role and is driven by the global cooling furthermore analyses of the sedimentary fluxes of many mountain belts show peaks of erosion during the transitions between glacial and inter glacial periods suggesting that the variable climatic conditions have also played a role

observations of volcanic tremor at mount st helens in april and may 1980 abstract high amplitude nearly monochromatic volcanic tremor was observed before during and after the 18 may 1980 eruption of mount st helens the tremor often remained stationary for periods of several minutes or more for the period before and immediately following the main eruption spectra calculated from three component seismograms contained a nearly constant dominant frequency of 1 1 to 1 5 hz this contrasts with a dominant frequency of 1 7 to 2 1 hz calculated for the tremor associated with the 25 may eruption amplitude decay with distance obeys the form a r n where a is the tremor amplitude and r is the observation distance from the source the exponent n was determined in a least squares sense to be 1 5 0 4 1 5 0 3 and 1 7 0 3 before and shortly after the main eruption on 18 may 1980 and 24 may 1980 respectively the exponent for low frequency volcanic earthquakes before the main eruption was 1 6 0 3 a value similar to that of the volcanic tremor and suggests that the source of the volcanic tremor is shallow as is the source of the low frequency earthquakes the spectra of the tremor periods are very similar to those of the low frequency volcanic earthquakes there are cases where volcanic tremor appears as a continuation of a low frequency earthquake these observations suggest that the volcanic tremor and the low frequency volcanic earthquakes are strongly interconnected and indeed may well share a common source mechanism based on both signal stationarity and spectral amplitude decay consistency we suggest in common with others that the monochromatic nature of volcanic tremor is mainly due to a source effect while the path and station effects are relatively minor the tremor amplitude changes as a result of variations in the source driving force the frequency shift for the 24 may 1980 tremor may be due to a source dimension change

the coupling between very long period seismic events volcanic tremor and degassing rates at mount etna volcano 1 from december 2005 to january 2006 an anomalous degassing episode was observed at mount etna well correlated with an increase in volcanic tremor and in the almost complete absence of eruptive activity in the same period more than 10 000 very long period vlp events were detected through moment tensor inversion analyses of the vlp pulses we obtained quantitative estimates of the volumetric variations associated with these events this allowed a quantitative investigation of the relationship between vlp seismic activity volcanic tremor and gas emission rate at mount etna we found a statistically significant positive correlation between so2 gas flux and volcanic tremor suggesting that tremor amplitude can be used as a first order proxy for the background degassing activity of the volcano vlp volumetric changes and so2 gas flux are correlated only for the last part of our observations following a slight change in the vlp source depth we calculate that the gas associated with vlp signal genesis contributed less than 5 of the total gas emission the existence of a linear correlation between vlp and degassing activities indicates a general relationship between these two processes the effectiveness of such coupling appears to depend upon the particular location of the vlp source suggesting that conduit geometry might play a significant role in the vlp generating process these results are the first report on mount etna of a quantitative relationship between the amounts of gas emissions directly estimated through instrumental flux measurements and the quantities of gas mass inferred in the vlp source inversion

continuous tracking of volcanic tremor at mount etna italy summary using data from two dense array of short period seismometers we analyse the kinematic properties of volcanic tremor preceding and accompanying the 2004 2005 eruption of etna volcano italy results from slowness analyses indicate the action of at least two distinct sources the first dominates the pre eruptive period and is likely associated with the main plumbing system feeding the summit and southeast craters following the onset of the eruption secondary directions of wave arrival encompass the eruptive fissures located on the lower eastern flank of the southeast crater nonetheless significant energy radiation from this latter source was also occurring prior to the onset of the lava effusion likely suggesting the presence of a resident magma batch in agreement with independent petrologic and geochemical data

petrology of lavas from the 2004 2005 flank eruption of mt etna italy inferences on the dynamics of magma in the shallow plumbing system following the 2001 and 2002 2003 flank eruptions activity resumed at mt etna on 7 september 2004 and lasted for about 6 months this paper presents new petrographic major and trace element and sr nd isotope data from sequential samples collected during the entire 2004 2005 eruption the progressive change of lava composition allowed defining three phases that correspond to different processes controlling magma dynamics inside the central volcano conduits the compositional variability of products erupted up to 24 september is well reproduced by a fractional crystallization model that involves magma already stored at shallow depth since the 2002 2003 eruption the progressive mixing of this magma with a distinct new one rising within the central conduits is clearly revealed by the composition of the products erupted from 24 september to 15 october after 15 october the contribution from the new magma gradually becomes predominant and the efficiency of the mixing process ensures the emission of homogeneous products up to the end of the eruption our results give insights into the complex conditions of magma storage and evolution in the shallow plumbing system of mt etna during a flank eruption furthermore they confirm that the 2004 2005 activity at etna was triggered by regional movements of the eastern flank of the volcano they caused the opening of a complex fracture zone extending ese which drained a magma stored at shallow depth since the 2002 2003 eruption this process favored the ascent of a different magma in the central conduits which began to be erupted on 24 september without any significant change in eruptive style deformation and seismicity until the end of eruption

space time evolution of magma storage and transfer at mt etna volcano italy the 2015 2016 reawakening of voragine crater programma nazionale ricerche grant number pnra14 00011 university of catania fir 2014 grant numbers 2f119b pra 2016 18 22722132120

detecting imminent eruptive activity at mt etna italy in 2007 2008 through pattern classification of volcanic tremor data abstract volcano monitoring aims at the recognition of changes in instrumentally observable parameters before hazardous activity in order to alert governmental authorities among these parameters seismic data in general and volcanic tremor in particular play a key role recent major explosive eruptions such as okmok aleutians and chaiten chile in 2008 and numerous smaller events at mt etna italy have shown that the period of premonitory seismic activity can be short only a few hours which entails the necessity of effective automatic data processing near on line here we present a synoptic pattern classification analysis based on self organizing maps and fuzzy cluster analysis which is applied to volcanic tremor data recorded during a series of paroxysmal eruptive episodes and a flank eruption at etna in 2007 2008 in total eight episodes were analyzed in six of these significant changes in the dynamic regime of the volcano were detected up to 9 h prior to the onset of eruptive activity and long before changes in volcanic tremor amplitude and spectral content became evident in classical analysis in two cases the state transition was

complex magma dynamics at mount etna revealed by seismic thermal and volcanological data 1 three eruptive episodes during the 2006 summit eruptions of mount etna were exceptionally well documented by visual seismic and thermal monitoring the first 16 november was strongly explosive with vigorous strombolian activity and ash emission from multiple vents lava emission and phreatomagmatic explosions generating pyroclastic density currents pdcs the second episode 19 november had a rather weakly explosive component with mild strombolian activity but more voluminous lava emission the third 24 november was a moderately explosive paroxysm with intermittent lava fountaining and generation of a tephra column as well as lava emission and pdcs data recorded by a thermal monitoring camera clearly document the different phases of each paroxysm weather clouds occasionally hampering thermal monitoring the images show a rapid onset of the volcanic activity which during each of the paroxysms reached a peak in eruptive and thermal intensity and then decreased gradually the stronger phreatomagmatic explosions and pdcs on 16 and 24 november did not yield any seismic signature linked to the opening of new vents nor were they associated with peculiar characteristics of the seismic signal nevertheless eruptive styles strombolian activity lava emission and different levels in the intensity of explosive activity were generally well reflected in the amplitude and frequency content of the seismic signal and in the source location of the volcanic tremor centroid throughout the three eruptive episodes this multidisciplinary study therefore not only provides a key to distinguish between endogenous and exogenous origins of the phenomena observed but also documents the complex magma dynamics within the volcano

cosmogenic nuclide derived rates of diffusive and episodic erosion in the glacially sculpted upper rhone valley swiss alps denudation rates of small tributary valleys in the upper rhone valley of the swiss central alps vary by more than an order of magnitude within a very small distance tens of kilometers morphometric data indicate two distinct erosion processes operate in these steep mountain valleys we determined the rates of these processes using cosmogenic beryllium 10 10be in pooled soil and stream sediment samples denudation in deep glacially scoured valleys is characterized by rapid non uniform processes such as debris flows and rock falls in these steep valleys denudation rates are 760 2100 mm kyr 1 in those basins which show minimal previous glacial modification denudation rates are low with 60 560 mm kyr 1 the denudation rate in each basin represents a binary mixture between the rapid non uniform processes and soil creep the soil production rate measured with cosmogenic 10be in soil samples averages at 60 mm kyr 1 mixing calculations suggest that the debris flows and rock falls are occurring at rates up to 3000 7000 mm kyr 1 these very high rates occur in the absence of baselevel lowering since the tributaries drain into the rhone trunk stream up stream of a knickzone the flux weighted spatial average of denudation rates for the upper rhone valley is 1400 mm kyr 1 which is similar to rock uplift rates determined in this area from leveling the pace and location of erosion processes are determined by the oscillation between a glacial and a non glacial state preventing the landscape from reaching equilibrium copyright 2010 john wiley sons ltd

influence of a glacial buzzsaw on the height and morphology of the cascade range in central washington state usa abstract analysis of climatic and topographic evidence from the cascade range of washington state indicates that glacial erosion limits the height and controls the morphology of this range glacial erosion linked to long term spatial gradients in the ela created a tilted planar zone of 373 cirques across the central part of the range peaks and ridges now rise 600 m above this zone hypsometric analysis of the region shows that the proportion of land area above the cirques drops sharply and mean slopes 30 indicate that the areas above the cirques may be at or near threshold steepness the mean plus 1 relief of individual cirque basins 570 m corresponds to the 600 m envelope above which peaks rarely rise the summit altitudes are set by a combination of higher rates of glacial and paraglacial erosion above the ela and enhanced hillslope processes due to the creation of steep topography on the high precipitation western flank of the cascades the dominance of glacial and hillslope erosion at altitudes at and above the ela may explain the lack of a correspondence between stream power erosion models and measured exhumation rates from apatite u th he thermochronometry

magnitude of crustal extension in the southern great basin strike slip faults in the southern great basin separate areas of cenozoic upper crustal extension from relatively stable tectonic blocks linear geologic features offset along the garlock fault las vegas valley shear zone and lake mead fault system allow reconstruction of the southern great basin to a pre extension configuration the sierra nevada mojave desert spring mountains and colorado plateau are treated as stable unextended blocks that have moved relative to each other in response to crustal extension with the spring mountains held fixed to the mojave block our reconstruction indicates a minimum of 65 extension 140 km between the southern sierra nevada and colorado plateau

dating the onset of lgm ice surface lowering in the high alps abstract the general chronological outline of the last glacial maximum lgm in the alps is well known after more than two centuries of ice age research in europe current studies focus on resolving the details of the deglaciation process after the lgm particularly few data in this context are available from the high alps here we report chronological constraints on the onset of deglaciation in two different study areas from the western and eastern alps the mont blanc italy and zillertal alps austria we sampled 32 bedrock and boulder surfaces from high elevation ridges beneath the glacial trimline the oldest 10 be exposure ages of 18 5 ka correspond to the initiation of lowering of the lgm ice surface identical ages from both study areas suggest synchronous decay of the lgm glaciers in the accumulation zones of the western and eastern alps thus the high alpine ice surface lowered roughly synchronously to the downwasting of the glacier tongues in the forelands that was completed 19 18 ka in both study areas ages of numerous samples that are consistently 2 3 ka younger than 18 5 ka suggest the persistance of remnant ice patches at high elevations in the lateglacial accumulation zones approximately until the bolling allerod interstadial

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

the initial phases of the 2008 2009 mount etna eruption a multidisciplinary approach for hazard assessment accepted for publication in journal of geophysical research copyright 2010 american geophysical union

seismoacoustic investigations of paroxysmal activity at mt etna volcano new insights into the 16 november 2006 eruption 1 on 16 november 2006 a 1 day long paroxysmal eruption occurred at the summit craters of mt etna volcano a multiparametric approach consisting of analyzing infrasonic seismic and video camera recordings was carried out to follow its evolution volcanological and geophysical observations identified three eruptive phases in the first phase infrasonic and seismic characteristics reflected the highly explosive nature of the activity waveform characterization of infrasound events confirmed the activity of the several explosive vents at the summit of southeast crater sec during the second phase results highlighted the decoupling between seismic and infrasonic sources which was due to the decrease in explosive activity and the reactivation of effusive vents located south of bocca nuova and on the saddle between bocca nuova and sec the third phase was the most intense and was characterized by various volcanic phenomena pyroclastic flows jets of dark ash and white steam the very high radiated infrasonic energy together with infrasound event features led us to infer a gas enrichment of the shallow magma column preceding by a few minutes and likely related to the pyroclastic flows in the sec area after the eruption at sec variations in infrasound events related to the activity of northeast crater nec were found the observed spectral changes and the source mechanism modeling of the nec infrasound events suggest the existence of a link in the plumbing system feeding the two craters

time variation of spectral and wavefield features of volcanic tremor at mt etna january june 1999 abstract we have studied the volcanic tremor recorded at mt etna during january june 1999 by using three component seismic stations this time period was characterised by both explosive and effusive eruptions occurring at the summit craters we found significant time variations in the trend of the overall spectral amplitude of tremor as well as in the dominant spectral peaks moreover the tremor wavefield features polarization particle motion and ratios between the amplitude of the three components of the ground velocity have been studied too confirming significant time variations this leads us to suggest the existence of at least two tremor sources a shallow one mainly characterised by relatively high frequencies 3 5 7 hz is linked to the upper portions of the active conduits and directly related to the observed eruptive activity the latter deeper source was active for only a few weeks and characterised by frequencies lower than about 2 5 hz it had no relationship with the observed eruptive activity and was speculatively related to the gas exsolution from fresh magma refilling a small batch

do periglacial landscapes evolve under periglacial conditions polar and alpine periglacial areas are traditionally regarded as necessarily submitted to very efficient frost driven processes that control the holocene and ongoing geomorphic activity during the last decade the validity of this academic view has been increasingly questioned among the international scientific community the search for the real past and present processes responsible for landform evolution in cold nonglaciated areas is based mainly on more and more refined monitoring protocols relying upon sophisticated equipment to assess the representativeness and significance of monitoring data collected in restricted sites it appears necessary however to widen the perspective by adopting a twofold multiscale approach as proposed in the present paper 1 in space by integrating various scales from the general slope system to the bioclimatic nanoenvironment and 2 in time by taking into account the landscape history from tertiary inherited features to recent process changes induced by the contemporary warming reintegrating the historical approach should help both to place the ongoing processes within a succession and or combination of interoperating processes and to avoid misinterpretations of features considered wrongly as emblematic of frost action overall both the historical and monitoring approaches tend to reduce the geomorphic efficiency of frost derived processes instead the role of noncold related processes such as chemical thermal biogenic and rainfall induced ones is being emphasized of special interest would be an interdisciplinary discussion between geomorphologists and various disciplines of biological sciences including biochemistry and ecology studying processes of primary successions

a multiparameter approach to volcano monitoring based on 4d analyses of seismo volcanic and acoustic signals the 2008 mt etna eruption 1 volcanic tremor and low frequency events together with infrasound signals can represent important precursory phenomena of eruptive activity because of their strict relationship with eruptive mechanisms and with fluid flows through the volcano s feeding system important variations of these seismo volcanic and infrasound signals recorded at mt etna volcano occurred both in the medium and short term before the eruption that took place on 13 may 2008 the most significant changes were observed in the frequency content and location of lp events as well as in volcanic tremor location that allowed us to track the magma pathway feeding the 2008 eruptive activity the infrasound showed three different families of events linked to the activity of the three active vents north east crater south east crater and the eruptive fissure the seismic and infrasonic variations reported corroborated by ground deformations variations help to develop a quantitative prediction and early warning system for effusive and or explosive eruptions

seismic reflectivity of the whipple mountain shear zone in southern california the whipple mountains shear zone of southeastern california comprises part of the whipple mountains metamorphic core complex of the north american cordillera the 3 9 km thick shear zone displays excellent exposures of ductilely deformed mid tertiary mylonitic gneisses as well as kinematically related but younger cataclasites which underlie a major low angle normal fault the whipple detachment fault prominent crustal reflections beginning at 3 4 s were recorded on calcrust seismic profiles southwest of the whipple mountains in order to interpret these seismic reflections and to understand why detachment faults are imaged on some profiles but not on others we collected oriented rock specimens from all major structural units in the whipple mountains and determined p wave velocities for these samples parallel to three principal fabric directions under laboratory induced confining pressures up to 500 mpa using a geologic section through the mylonitic gneisses from a previous investigation we then constructed a detailed acoustic impedance section for the whipple mountain shear zone based upon laboratory results this section was in turn used to compose two dimensional synthetic reflection seismograms for comparison with the calcrust records significant impedance contrasts are enhanced by the opposing fabric orientations between the interlayered but structurally isolated relict domains of nonmylonitized rocks and the surrounding mylonitic gneisses the finite thickness and lateral extent of these rock units cause constructive interference in seismic modeling to create the seismic fabric of strong laterally discontinuous but subparallel reflections as seen in the calcrust profiles southwest of the whipple mountains chloritic breccias beneath the whipple detachment fault wdf have much lower seismic impedance than that of rocks occurring both structurally above and below however the significant thinning of the chloritic breccia zone to the southwest of the whipple mountains may have caused the poor image of the wdf on the calcrust profiles the absence of a detachment reflection is thus not necessarily indicative of the absence of a subsurface fault zone

erosion rates of alpine bedrock summit surfaces deduced from in situ 10be and 26al we have measured the concentration of in situ produced cosmogenic 10be and 26al from bare bedrock surfaces on summit flats in four western u s mountain ranges the maximum mean bare bedrock erosion rate from these alpine environments is 7 6 3 9 m my 1 individual measurements vary between 2 and 19 m my 1 these erosion rates are similar to previous cosmogenic radionuclide crn erosion rates measured in other environments except for those from extremely arid regions this indicates that bare bedrock is not weathered into transportable material more rapidly in alpine environments than in other environments even though frost weathering should be intense in these areas our crn deduced point measurements of bedrock erosion are slower than typical basin averaged denudation rates 50 m my 1 if our measured crn erosion rates are accurate indicators of the rate at which summit flats are lowered by erosion then relief in the mountain ranges examined here is probably increasing we develop a model of outcrop erosion to investigate the magnitude of errors associated with applying the steady state erosion model to episodically eroding outcrops our simulations show that interpreting measurements with the steady state erosion model can yield erosion rates which are either greater or less than the actual long term mean erosion rate while errors resulting from episodic erosion are potentially greater than both measurement and production rate errors for single samples the mean value of many steady state erosion rate measurements provides a much better estimate of the long term erosion rate

permanent tremor of masaya volcano nicaragua wave field analysis and source location the masaya volcano nicaragua is a basaltic caldera in a subduction zone the permanent source of the volcanic tremor was located inside santiago crater at the lava lake s position and 400 m below the ne rim and therefore corresponds to superficial magma activity we used two tripartite arrays 90 m side one semicircular array r 120 m in 1992 and two semicircular arrays r 60 m and a 2500 m long linear array radiating out from the source and on the flank of the crater in 1993 we used both a cross spectrum method and a correlation method to determine the wave delay time between the reference station and the other stations of an array and to quantify the wave field using the delays therefore by intersecting the back azimuth wave directions from the arrays we could pinpoint the source additionally the correlation coefficients obtained as functions of frequency for the three components of motion confirm the inferred position of the source of tremor the tremor s wave field is composed of comparable quantities of dispersed rayleigh and love surface waves whose phase velocities lie in the ranges 730 1240 m s at 2 hz and 330 550 m s at 6 hz the dispersive phase velocities were inverted to obtain crustal structures with a minimal number of layers the resulting velocity models are similar for the northern and southern parts of the volcano after geometrical spreading corrections q2hz 14 and q3hz 31 were determined along the northern linear array the typical low velocities and low q corresponding to the cone structure and are similar to those of other basaltic volcanoes like puu oo hawaii and klyuchevskoy kamchatka

linking danube river activity to alpine ice sheet fluctuations during the last glacial ca 33 17 ka bp insights into the continental signature of heinrich stadials abstract offshore archives retrieved from marine lacustrine environments receiving sediment from large river systems are valuable quaternary continental records in the present study we reconstruct the danube river activity at the end of the last glacial period based on sedimentological mineralogical and geochemical analyses performed on long piston cores from the north west black sea margin our data suggest that the danube river produced hyperpycnal floods throughout the ca 33 17 ka period four main periods of enhanced danube flood frequency each of 1 5 3 kyr duration are recorded at ca 32 5 30 5 ka equivalent to the first part of heinrich stadial hs 3 at ca 29 27 5 ka equivalent to greenland stadial 4 at ca 25 3 23 8 ka equivalent to hs 2 and at ca 22 3 19 ka based on mineralogical and geochemical data we relate these events to enhanced surface melting of the alpine ice sheet ais that covered 50 000 km2 of the danube watershed at the last glacial maximum lgm our results suggest that i the ais growth from the inner alps to its lgm position in the northern alpine foreland started from ca 30 5 ka ended no later than ca 25 3 ka and was interrupted by a melting episode ca 29 27 5 ka ii the ais volume drastically decreased from ca 22 3 to 19 ka as soon as summer insolation energy at the ais latitude increased and iii hss strongly impacted the ais mass balance through enhanced summer surface melt this together with evidence of severely cool winters and the rapid expansion of sea ice in the north atlantic implies strong seasonality in continental europe during stadials

the failed eruption of mt etna in december 2005 evidence from volcanic tremor analyses 1 strong changes in seismic radiation comparable to those preceding and or accompanying eruptive activity in recent years were recorded at mt etna volcano italy from november 2005 to january 2006 the amplitude of volcanic tremor peaked in mid december 2005 after a continuous slow increase from august 2005 onward during which neither effusive nor paroxysmal activity was observed by volcanologists and alpine guides during this time span the centroid locations of volcanic tremor moved toward the surface more and more clustered below the summit craters the application of pattern classification analysis based on self organizing maps and fuzzy clustering to volcanic tremor data highlighted variations in the frequency domain as well these changes were temporally associated with ground deformation variations as indicative of a mild inflation of the summit of the volcano and with a conspicuous increase in the so2 plume flux emission overall we interpret this evidence as the result of recharging of the volcanic feeder at depth 3 km below sea level during which magma did not reach the shallow plumbing system

the effects of out of plane seismic energy on reflections in crustal scale 2d seismic sections abstract crustal scale seismic surveys mostly collect data along single profiles and the data processing has an underlying assumption that the data have imaged two dimension 2d structure striking at right angles to the seismic profile however even small amounts of out of plane topography on a reflector can result in reflections that do not map the reflector shape accurately out of plane energy will migrate within the plane of the section to an apparent depth represented as two way time twt that is greater than the depth of the reflection point out of the plane of the section it will fall within the plane of the section at depths less than equal to or greater than the intersection of the reflector with the plane of the section depending on both the amount of out of plane topographic relief on the reflector and the offset of the topographic relief from the plane of the section reflectors that are a single surface can therefore be manifested in the seismic section as a band of several reflections rather than a single reflection more complex reflectors such as shear zones that have a finite thickness because they are made up of several to many anastomosing layers of altered and anisotropic rock embedded in protolith will appear as laterally short reflections within a laterally continuous reflection band other examples of such reflectors would be the moho in some places and rock with compositional layering with increasing out of plane topographic relief on the reflector the top of the reflection band for both single and multi layer reflectors will be a poor indicator of the top of the reflector in the earth the bottom of the reflection band will always be a poor indicator of the bottom of the reflector because out of plane energy can arrive at twts that are different from those of the reflector in the plane of the section out of plane energy has the potential to interfere constructively or destructively with the in plane energy in synthetic data calculated for a simple model assuming one layer and topographic relief of 250 m over wavelengths of 4 5 km similar to that imaged in a real sub horizontal detachment amplitudes ranged up to 2 6 times the expected amplitude for the layer a model with anastomosing layers built to resemble a thick shear zone rather than a discrete fault surface allowed tuning between layers the effects of out of plane energy when combined with the effects of tuning caused amplitudes up to 3 1 times those expected larger amplitudes could be achieved if a suitable model was contrived the results indicate that care must be taken when calculating impedance contrasts using real data the highest amplitude reflections are likely to yield overestimates of the true impedance contrast

subglacial extensional fracture development and implications for alpine valley evolution 1 bedrock stresses induced through exhumation and tectonic processes play a key role in the topographic evolution of alpine valleys using a finite difference model combining the effects of tectonics erosion and long term bedrock strength we assess the development of near surface in situ stresses and predict bedrock behavior in response to glacial erosion in an alpine valley the matter valley southern switzerland initial stresses are derived from the regional tectonic history which is characterized by ongoing transtensional or extensional strain throughout exhumation of the brittle crust we find that bedrock stresses beneath glacial ice in an initial v shaped topography are sufficient to induce localized extensional fracturing in a zone extending laterally 600 m from the valley axis the limit of this zone is reflected in the landscape today by a valley shoulder separating linear upper mountain slopes from the deep u shaped inner valley we propose that this extensional fracture development enhanced glacial quarrying between the valley shoulder and axis and identify a positive feedback where enhanced quarrying promoted valley incision which in turn increased in situ stress concentrations near the valley floor assisting erosion and further driving rapid u shaped valley development during interglacial periods these stresses were relieved through brittle strain or topographic modification and without significant erosion to reach more highly stressed bedrock subsequent glaciation caused a reduction in differential stress and suppressed extensional fracturing a combination of stress relief during interglacial periods and increased ice accumulation rates in highly incised valleys will reduce the likelihood of repeat enhanced erosion events

an experiment of muon radiography at mt etna italy interactions of conduit geometry with gas liquid flows control volcanic activity implying that the evaluation of volcanic hazards requires quantitative understanding of the inner structure of the volcano the more established geophysical imaging techniques suffer from inherent ambiguity may require spatially dense measurements in active areas and may not provide sufficient spatial resolution in the uppermost part of the conduit system it is thus desirable to develop new imaging techniques allowing a better spatial resolution of a volcano s upper feeding system with reduced ambiguity and a low level of risk for operators muon particles can be utilized to image the internal density distribution of volcanic structures the principle of muon radiography is essentially the same as x ray radiography except for substituting penetrating particles in place of photons muons are more attenuated by higher density parts inside the target and thus information about its inner structure are obtained from the differential muon absorption we report on a muon imaging experiment that was conducted at mt etna in 2010 the target structure was one of the summit craters of the volcano this experiment was performed using a muon telescope suitably designed to withstand the harsh conditions in the summit zone of a high volcano we found a marked difference between synthetic and observed attenuation of muons through the target this discrepancy is likely due to the bias on the observed flux arising from false muon tracks they are caused by low energy particles that by chance hit simultaneously the two matrixes of the telescope leading to detection of a false positive we separated the useful from the unwanted signal through a first order model of the background noise the resulting signal is compared with the corresponding synthetic flux eventually we found regions of higher and lower than expected muon flux that are possibly related to inner features of the target crater

constraining processes of landscape change with combined in situ cosmogenic 14c 10be analysis abstract reconstructing quaternary landscape evolution today frequently builds upon cosmogenic nuclide surface exposure dating however the study of complex surface exposure chronologies on the 102 104 years timescale remains challenging with the commonly used long lived radionuclides 10be 26al 36cl in glacial settings key points are the inheritance of nuclides accumulated in a rock surface during a previous exposure episode and partial shielding of a rock surface after the main deglaciation event e g during phases of glacier readvance combining the short lived in situ cosmogenic 14c isotope with 10be dating provides a valuable approach to resolve and quantify complex exposure histories and burial episodes within lateglacial and holocene timescales the first studies applying the in situ 14c 10be pair have demonstrated the great benefit from in situ 14c analysis for unravelling complex glacier chronologies in various glacial environments worldwide moreover emerging research on in situ 14c in sedimentary systems highlights the capacity of combined in situ 14c 10be analysis to quantify sediment transfer times in fluvial catchments or to constrain changes in surface erosion rates nevertheless further methodological advances are needed to obtain truly routine and widely available in situ 14c analysis future development in analytical techniques has to focus on improving the analytical reproducibility reducing the background level and determining more accurate muonic production rates these improvements should allow extending the field of applications for combined in situ 14c 10be analysis in earth surface sciences and open up a number of promising applications for dating young sedimentary deposits and the quantification of recent changes in surface erosion dynamics

climatic limits on landscape development in the northwestern himalaya the interaction between tectonism and erosion produces rugged landscapes in actively deforming regions in the northwestern himalaya the form of the landscape was found to be largely independent of exhumation rates but regional trends in mean and modal elevations hypsometry frequency distribution of altitude and slope distributions were correlated with the extent of glaciation these observations imply that in mountain belts that intersect the snowline glacial and periglacial processes place an upper limit on altitude relief and the development of topography irrespective of the rate of tectonic processes operating

climatic controls on frost cracking and implications for the evolution of bedrock landscapes 1 in mountainous landscapes the role of periglacial processes in producing sediment is poorly defined despite evidence of abundant talus slopes ice growth in rock has long been recognized as an efficient erosion mechanism but the effects have not been readily applied to landscape evolution in response to tectonic and climatic forcing here we quantify how and where ice driven mechanical erosion occurs in cold bedrock dominated landscapes using a simple one dimensional numerical heat flow model in our model ice grows by water migration to colder regions in shallow rock by the reduction in chemical potential associated with intermolecular forces between ice and mineral surfaces a process called segregation ice growth the depth and intensity of frost cracking is primarily dependent on mean annual temperature mat with positive mat sites characterized by intense cracking in the top meter of the rock mass and a maximum frost penetration of 4 m in contrast negative mat areas have less intense cracking that primarily occurs at depths between 50 and 800 cm we compare the depth and intensity of frost cracking predicted by our model with measures of the intensity of frost processes determined in three studies the first measured the timing of rockfall in the canadian rockies niagara escarpment and japanese alps the second analyzed scree deposits in the southern alps new zealand and the third documented rockfall frequency in utah these natural examples show that rockfalls tend to nucleate at elevations that coincide with zones of intense frost cracking predicted by our model as such climatic variations associated with interglacial glacial cycles may impart a significant influence on the denudation of mountainous landscapes

patterns in the recent 2007 2008 activity of mount etna volcano investigated by integrated geophysical and geochemical observations 1 seismic deformation and volcanic gas observations offer independent and complementary information on the activity state and dynamics of quiescent and eruptive volcanoes and thus all contribute to volcanic risk assessment in spite of their wide use there have been only a few efforts to systematically integrate and compare the results of these different monitoring techniques here we combine seismic volcanic tremor and long period seismicity deformation gps and geochemical volcanic gas plume co2 so2 ratios measurements in an attempt to interpret trends in the recent 2007 2008 activity of etna volcano we show that each eruptive episode occurring at the southeast crater sec was preceded by a cyclic phase of increase decrease of plume co2 so2 ratios and by inflation of the volcano s summit captured by the gps network these observations are interpreted as reflecting the persistent supply of co2 rich gas bubbles and eventually more primitive magmas to a shallow depth of 1 2 8 km asl magma storage zone below the volcano s central craters ccs overpressuring of the resident magma stored in the upper ccs conduit triggers further magma ascent and finally eruption at sec a process which we capture as an abrupt increase in tremor amplitude an upward 2800 m asl and eastward migration of the source location of seismic tremor and a rapid contraction of the volcano s summit resumption of volcanic activity at sec was also systematically anticipated by declining plume co2 so2 ratios consistent with magma degassing being diverted from the central conduit area toward sec

surface exposure dating of non terrestrial bodies using optically stimulated luminescence a new method abstract we propose a new method for in situ surface exposure dating of non terrestrial geomorphological features using optically stimulated luminescence osl our approach is based on the progressive emptying of trapped charge with exposure to light at depth into a mineral surface a complete model of the resetting of osl with depth and time is presented for the first time this model includes the competing effects of both optical resetting and irradiation we consider two extreme conditions at the time the resetting is initiated a a negligibly small trapped charge population and b a saturated trapped charge population the potential dating applications for a include dust accumulation volcanic rocks and impact related sediments and for b fault scarps rock falls landslides and ice scoured bedrock using assumptions based on terrestrial observations we expect that this approach will be applicable over the last 100 ka the method is ideally suited to in situ measurement using existing technology developed for space applications and so offers for the first time the realistic possibility of direct determination of exposure ages of young non terrestrial surfaces

climatic reconstruction for the younger dryas early holocene transition and the little ice age based on paleo extents of argentiere glacier french alps abstract investigation of holocene extents of mountain glaciers along with the related naturally driven climate conditions helps improve our understanding of glacier sensitivity to ongoing climate change here we present the first holocene glacial chronology in the mont blanc massif argentiere glacier in the french alps based on 25 in situ produced cosmogenic 10be dates of moraines and glacial bedrocks the obtained ages from mapped sequences of moraines at three locations reveal that the glacier retreated from its lateglacial extent and oscillated several times between 11 7 ka and 10 4 ka i e during the younger dryas early holocene yd eh transition before substantially retreating at 10 4 ka climate conditions corresponding to the past extents of argentiere glacier during the yd eh transition 11 ka and the little ice age lia were modelled with two different approaches by determining summer temperature differences from reconstructed ela rises and by using a positive degree day pdd mass balance model the ela rise reconstructions yield a possible range of temperatures for the yd eh transition that were lower by between 3 0 and 4 8 c compared to the year 2008 depending on the choice of the ela sensitivity to temperature the results from the pdd model indicate temperatures lower by 3 6 5 5 c during the yd eh transition than during the 1979 2002 period for the lia our findings highlight the role of local precipitation changes superimposed on the dominant temperature signal in the detailed evolution of the glacier overall this study highlights the challenge that remains in accurately inferring paleoclimate conditions from past glacier extents

tertiary extension north of the las vegas valley shear zone sheep and desert ranges clark county nevada detailed mapping reveals the presence of high angle extensional faults and low angle gravity slides on the west side of the sheep range three major high angle faulting events each account for 20 of eastward rotation and accommodate extension between the las vegas range and the desert range low angle faults represent surficial slides in response to topography produced by extension on the high angle faults faulting took place during the miocene synchronously with deposition of the horse spring formation and with displacement on the las vegas valley shear zone the extension in the sheep range took place without volcanism intrusion or metamorphism of the paleozoic sedimentary rocks offset thrust faults suggest that the area west of the sheep range extended almost 100 during the miocene while the corresponding area south of the las vegas valley shear zone did not extend significantly the shear zone bounded the extending terrane on the south acting as a transform fault this extension west of the sheep range may in part balance that mapped by anderson 1971 in the eldorado mountains the las vegas valley shear zone and the lake mead fault system may have acted together to compensate for areas of localized extension between the colorado plateau and the vicinity of the specter range

the 2011 unrest at katla volcano characterization and interpretation of the tremor sources abstract a 23 hour tremor burst was recorded on july 8 9th 2011 at the katla subglacial volcano one of the most active and hazardous volcanoes in iceland this was associated with deepening of cauldrons on the ice cap and a glacial flood that caused damage to infrastructure increased earthquake activity within the caldera started a few days before and lasted for months afterwards and new seismic activity started on the southern flank no visible eruption broke the ice and the question arose as to whether this episode relates to a minor subglacial eruption with the tremor being generated by volcanic processes or by the flood the tremor signal consisted of bursts with varying amplitude and duration we have identified and described three different tremor phases based on amplitude and frequency features a tremor phase associated with the flood was recorded only at stations closest to the river that flooded correlating in time with rising water level observed at gauging stations using back projection of double cross correlations two other phases have been located near the active ice cauldrons and are interpreted to be caused by volcanic or hydrothermal processes the greatly increased seismicity and evidence of rapid melting of the glacier may be explained by a minor sub glacial eruption a less plausible interpretation is that the tremor was generated by hydrothermal boiling and or explosions with no magma involved this may have been induced by pressure drop triggered by the release of water when the glacial flood started all interpretations require an increase of heat released by the volcano

long period and very long period events at mt etna volcano characteristics variability and causality and implications for their sources abstract almost 50 000 long period lp events were recorded at mt etna from november 2003 to may 2006 we analysed these events as well as very long period vlp events which were associated with some of them during some intervals the spectral and wavefield features of lp events remained steady with significant changes occurring between the intervals based on the times of the changes we distinguish five different sub periods in particular during sub period iii june november 2005 the wavefield at the stations nearest to the summit area was composed of p waves locations for 150 lp events occurring in sub period iii determined using radial semblance changed at the same time as the events spectral features changed it was during this sub period that many of the lp events were associated with vlp events based on similarity of the waveforms we distinguished two families of vlp events with gradually evolving waveforms the two families are located in slightly different places but near the sources of the lp events the change between the families occurred at the same time as the spectra of the lp events changed finally the source of the vlp events was investigated by performing complete waveform moment tensor inversion of stacks of the two families synthetic green s functions for the full moment tensor were calculated for a homogeneous half space for both families the source region with the highest variance reduction lies approximately beneath the active craters at 500 m below the altitudes of the stations the solutions for both families are very similar with sources that are between 60 and 70 isotropic attempts to determine deviatoric moment tensors produced consistently poorer fits the remaining energy is poorly constrained and is likely to be noise in conclusion these results highlight changes in the lp and vlp events at mt etna over time and the causal relationship between them

three years of so2 flux measurements of mt etna using an automated uv scanner array comparison with conventional traverses and uncertainties in flux retrieval 1 sviluppo di sistemi di monitoraggio dipartimento di protezione civile della regione sicilia 2 ingv istituto nazionale di geofisica e vulcanologia sezione di catania italy 3 novac network for observation of volcanic and atmospheric change eu funded sixth framework programme project 18354 4 uk nerc national centre for earth observation via the dynamic earth and geo hazards

location of microseismic swarms induced by salt solution mining ground failures caving processes and collapses of large natural or man made underground cavities can produce significant socio economic damages and represent a serious risk envisaged by the mine managements and municipalities in order to improve our understanding of the mechanisms governing such a geohazard and to test the potential of geophysical methods to prevent them the development and collapse of a salt solution mining cavity was monitored in the lorraine basin in northeastern france during the experiment a huge microseismic data set similar to 50 000 event files was recorded by a local microseismic network 80 per cent of the data comprised unusual swarming sequences with complex clusters of superimposed microseismic events which could not be processed through standard automatic detection and location routines here we present two probabilistic methods which provide a powerful tool to assess the spatio temporal characteristics of these swarming sequences in an automatic manner both methods take advantage of strong attenuation effects and significantly polarized p wave energies at higher frequencies 100 hz the first location approach uses simple signal amplitude estimates for different frequency bands and an attenuation model to constrain the hypocentre locations the second approach was designed to identify significantly polarized p wave energies and the associated polarization angles which provide very valuable information on the hypocentre location both methods are applied to a microseismic data set recorded during an important step of the development of the cavity that is before its collapse from our results systematic spatio temporal epicentre migration trends are observed in the order of seconds to minutes and several tens of meters which are partially associated with cyclic behaviours in addition from spatio temporal distribution of epicentre clusters we observed similar epicentre migration in the order of hours and days all together we suggest that the recorded microseismicity mainly represents detachment and block breakage processes acting at the cavity s roof indicating a zone of critical state of stress and where partial fractures cause chain reaction failures as a result of stress redistribution processes