pinecone/core-2020-05-10-deduplication huggingface dataset:
Gravity changes due to overpressure sources in 3D heterogeneous media: application to Campi Flegrei caldera, Italy

Employing 3D finite element method, we develop an algorithm to calculate gravity changes
due to pressurized sources of any shape in elastic and inelastic heterogeneous media. We
consider different source models, such as sphere, spheroid and sill, dilating in elastic media
(homogeneous and heterogeneous) and in elasto-plastic media. The models are oriented to
reproduce the gravity changes and the surface deformation observed at Campi Flegrei caldera
(Italy), during the 1982-84 unrest episode. The source shape and the characteristics of the
medium have great influence in the calculated gravity changes, leading to very different values
for the source densities. Indeed, the gravity residual strongly depends upon the shape of the
source. Non negligible contributions also come from density and rigidity heterogeneities within
the medium. Furthermore, if the caldera is elasto-plastic, the resulting gravity changes exhibit
a pattern similar to that provided by a low effective rigidity. Even if the variation of the source volumes is quite similar for most of the models considered, the density inferred for the
source ranges from ∼ 400 kg/m3 (supercritical water) to ∼ 3300 kg/m3 (higher than trachytic
basalts), with drastically different implications for risk assessment
Modelling gravitational instabilities: slab break-off and Rayleigh-Taylor diapirism

A non-standard new code to solve multiphase viscous thermo–mechanical problems applied to geophysics is presented. Two numerical methodologies employed in the code are described: A level set technique to track the position of the materials and an enrichment of the solution to allow the strain rate to be discontinuous across the interface. These techniques have low computational cost and can be used in standard desktop PCs. Examples of phase tracking with level set are presented in two and three dimensions to study slab detachment in subduction processes and Rayleigh–Taylor instabilities, respectively. The modelling of slab detachment processes includes realistic rheology with viscosity depending on temperature, pressure and strain rate; shear and adiabatic heating mechanisms; density including mineral phase changes and varying thermal conductivity. Detachment models show a first prolonged period of thermal diffusion until a fast necking of the subducting slab results in the break–off. The influence of several numerical and physical parameters on the detachment process is analyzed: The shear heating exerts a major influence accelerating the detachment process, reducing the onset time to one half and lubricating the sinking of the detached slab. The adiabatic heating term acts as a thermal stabilizer. If the mantle temperature follows an adiabatic gradient, neglecting this heating term must be included, otherwise all temperature contrasts are overestimated. As expected, the phase change at 410 km depth (olivine–spinel transition) facilitates the detachment process due to the increase in negative buoyancy. Finally, simple plume simulations are used to show how the presented numerical methodologies can be extended to three dimensions.Peer ReviewedPostprint (author’s final draft
Dynamical system analysis and forecasting of deformation produced by an
  earthquake fault

We present a method of constructing low-dimensional nonlinear models
describing the main dynamical features of a discrete 2D cellular fault zone,
with many degrees of freedom, embedded in a 3D elastic solid. A given fault
system is characterized by a set of parameters that describe the dynamics,
rheology, property disorder, and fault geometry. Depending on the location in
the system parameter space we show that the coarse dynamics of the fault can be
confined to an attractor whose dimension is significantly smaller than the
space in which the dynamics takes place. Our strategy of system reduction is to
search for a few coherent structures that dominate the dynamics and to capture
the interaction between these coherent structures. The identification of the
basic interacting structures is obtained by applying the Proper Orthogonal
Decomposition (POD) to the surface deformations fields that accompany
strike-slip faulting accumulated over equal time intervals. We use a
feed-forward artificial neural network (ANN) architecture for the
identification of the system dynamics projected onto the subspace (model space)
spanned by the most energetic coherent structures. The ANN is trained using a
standard back-propagation algorithm to predict (map) the values of the observed
model state at a future time given the observed model state at the present
time. This ANN provides an approximate, large scale, dynamical model for the
fault.Comment: 30 pages, 12 figure
Characteristics of stable flows over Southern Greenland

The main characteristic features of stable atmospheric flows over a large mountain plateau are summarised and then compared with mesoscale and synoptic scale numerical simulation, meteorological analysis, satellite imagery, and surface observations for the cases of flows over Southern Greenland for four wind directions. The detailed features are identified using the concepts and scaling of stably stratified flow over large mountains with variations in surface roughness, elevation, and heating. For westerly and easterly winds detached jets form at the southern tip, where coastal jets converge, which propagate large distances across the ocean. Near coasts katabatic winds can combine with barrier jets and wake flows generated by synoptic winds. Note how the approach flow rises/falls over southern Greenland for easterly/westerly winds, leading in both cases to more cloud on the western side. Some conclusions are drawn about the large-scale influences of these flows; detached jets in the atmosphere; air-sea interaction; formation of low pressure systems. For accurate simulations of these flows, mesoscale models are necessary with resolutions of order of 20 km or less. Â© BirkhÃ¤user Verlag, Basel, 2005
Volcanic tremor at Mt. Etna, Italy, preceding and accompanying the eruption of July-August, 2001

The July 17 – August 9, 2001 flank eruption of Mt. Etna was preceded and accompanied
by remarkable changes in volcanic tremor. Based on the records of stations belonging to the permanent
seismic network deployed on the volcano, we analyze amplitude and frequency content of the seismic
signal. We find considerable changes in the volcanic tremor which mark the transition to different styles of
eruptive activity, e.g., lava fountains, phreatomagmatic activity, Strombolian explosions. In particular, the
frequency content of the signal decreases from 5 Hz to 3 Hz at our reference station ETF during episodes
of lava fountains, and further decreases at about 2 Hz throughout phases of intense lava emission. The
frequency content and the ratios of the signal amplitude allow us to distinguish three seismic sources, i.e.,
the peripheral dike which fed the eruption, the reservoir which fed the lava fountains, and the central
conduit. Based on the analysis of the amplitude decay of the signal, we highlight the migration of the dike
from a depth of ca. 5 km to about 1 km between July 10 and 12. After the onset of the effusive phase, the
distribution of the amplitude decay at our stations can be interpreted as the overall result of sources
located within the first half kilometer from the surface. Although on a qualitative basis, our findings shed
some light on the complex feeding system of Mt. Etna, and integrate other volcanological and geophysical
studies which tackle the problem of magma replenishment for the July–August, 2001 flank eruption. We
conclude that volcanic tremor is fundamental in monitoring Mt. Etna, not only as a marker of the different
sources which act within the volcano edifice, but also of the diverse styles of eruptive activity
Fault-controlled soil CO2 degassing and shallow magma bodies: summit and lower east rift of Kilauea volcano (Hawai’i)

Soil CO2 flux measurements were carried out along traverses across mapped faults and
eruptive fissures on the summit and the lower East Rift Zone of Kilauea volcano. Anomalous levels of soil
degassing were found for 44 of the tectonic structures and 47 of the eruptive fissures intercepted by
the surveyed profiles. This result contrasts with what was recently observed on Mt. Etna, where most of the
surveyed faults were associated with anomalous soil degassing. The difference is probably related to the
differences in the state of activity at the time when soil gas measurements were made: Kilauea was erupting,
whereas Mt. Etna was quiescent although in a pre-eruptive stage. Unlike Mt. Etna, flank degassing on
Kilauea is restricted to the tectonic and volcanic structures directly connected to the magma reservoir
feeding the ongoing East Rift eruption or in areas of the Lower East Rift where other shallow, likely
independent reservoirs are postulated. Anomalous soil degassing was also found in areas without surface
evidence of faults, thus suggesting the possibility of previously unknown structures
Steric sea-level variations inferred from combined Topex/Poseidon altimetry and GRACE gravimetry

In this study, we propose to estimate the steric sea-level variations over a < 2-year period (April 2002 through December 2003) by combining global mean sea level (GMSL) based on Topex/ Poseidon (T/P) altimetry with time-variable geoid averaged over the oceans, as observed by the GRACE (Gravity Recovery and Climate Experiment) satellite. In effect, altimetry-derived GMSL changes results from two contributions: Steric (thermal plus salinity) effects due to sea water density change and ocean mass change due to water exchange with atmosphere and continents. On the other hand, GRACE data over the oceans provide the ocean mass change component only. The paper first discusses the corrections to apply to the GRACE data. Then the steric contribution to the GMSL is estimated using GRACE and T/P data. Comparison with available thermal expansion based on in situ hydrographic data is performed
Tidal gravity observations at Mt. Etna and Stromboli: results concerning the modeled and observed tidal factors

Continuous gravity observations performed in the last few years, both at Mt. Etna and Stromboli, have prompted
the need to improve the tidal analysis in order to acquire the best corrected data for the detection of volcano
related signals. On Mt. Etna, the sites are very close to each other and the expected tidal factor differences are
negligible. It is thus useful to unify the tidal analysis results of the different data sets in a unique tidal model.
This tidal model, which can be independently confirmed by a modeling of the tidal parameters based on the elastic
response of the Earth to tidal forces and the computation of the ocean tides effects on gravity, is very useful
for the precise tidal gravity prediction required by absolute or relative discrete gravity measurements. The
change in time of the gravimeters’ sensitivity is also an important issue to be checked since it affects not only
the results of tidal analysis but also the accuracy of the observed gravity changes. Conversely, if a good tidal
model is available, the sensitivity variations can be accurately reconstructed so as to retune observed tidal
records with the synthetic tide, since the tidal parameters are assumed to be constant at a given location
Vertical crustal motion along the Mediterranean and Black Sea coast derived from ocean altimetry and tide gauge data

Tide gauge (TG) data along the northern Mediterranean and Black Sea coasts are compared to the sea-surface height (SSH) anomaly obtained from ocean altimetry (TOPEX/Poseidon and ERS-1/2) for a period of nine years (1993–2001). The TG measures the SSH relative to the ground whereas the altimetry does so with respect to the geocentric reference frame; therefore their difference would be in principle a vertical ground motion of the TG sites, though there are different error sources for this estimate as is discussed in the paper. In this study we estimate such vertical ground motion, for each TG site, from the slope of the SSH time series of the (non-seasonal) difference between the TG record and the altimetry measurement at a point closest to the TG. Where possible, these estimates are further compared with those derived from nearby continuous Global Positioning System (GPS) data series. These results on vertical ground motion along the Mediterranean and Black Sea coasts provide useful source data for studying, contrasting, and constraining tectonic models of the region. For example, in the eastern coast of the Adriatic Sea and in the western coast of Greece, a general subsidence is observed which may be related to the Adriatic lithosphere subducting beneath the Eurasian plate along the Dinarides fault.This work is supported by the Spanish Science and Technology Ministery (Project ESP2001-4533-PE, Project ESP2005-02212), and NASA’s Physical Oceanography Program
Source of the 6 February 2013 Mw 8.0 Santa Cruz Islands Tsunami

On 6 February 2013 an Mw 8.0 subduction earthquake occurred close to Santa Cruz Islands
at the transition between the Solomon and the New Hebrides Trench. The ensuing tsunami
caused significant inundation on the closest Nendo Island. The seismic source was studied
with teleseismic broadband P waves inversion optimized with tsunami forward modeling at
DART buoys (Lay et al., 2013), and with inversion of teleseismic body and surface waves
(Hayes et al., 2014). The two studies also use different hypocenters and different planar fault
models, and found quite different slip models. In particular, Hayes et al. (2014) argued for
an aseismic slip patch SE from the hypocenter. We here develop a 3D model of the fault
surface from seismicity analysis and retrieve the tsunami source by inverting DART and tide-gauge data. Our tsunami source model features a main slip patch (peak value of ~11 m)
SE of the hypocentre, and reaching the trench. The rake direction is consistent with the
progressively more oblique plate convergence towards the Solomon trench. The tsunami
source partially overlaps the hypothesized aseismic slip area, which then might have slipped
coseismically
Management of post-mining large-scale ground failures : blast swarms field experiment for calibration of permanent microseismic early-warning systems

International audienceIn France, decades of coal and iron-ore mining have left extensive underground cavities beneath or in the vicinity of urban areas. This poses an environmental challenge for society. To ensure post-mining risk management and public safety, wherever remediation is not possible, numerous real-time microseismic monitoring systems are being installed. The objective is to detect remote rock mass fracturing processes, precursory events and acceleration phases for appropriate and timely action. Although no consistent collapse has occurred in any of the monitored areas yet, single 3-D probes record many microseismic events of very low amplitude which create difficulties in the quantitative data analysis. The development of specific quantitative processing has therefore become a major issue in our research work. For that purpose, a field experiment was carried out on six of the instrumented sites. It consisted of sequences of small blasts in mine pillars which were accurately controlled in terms of the location, orientation and energy of the explosive source. The data analysis was used to calibrate parameters (velocity model, 3-D sensor orientation, etc.) for reliable 3-D localization and to develop an empirical law to estimate the source energy from the sensor energy. This work now enables us to analyze real microseismic events with a considerably better level of accuracy and to obtain enough information and confidence to discuss these data in terms of site stability
Equivalent Monopole Source of the Geomagnetic South Atlantic Anomaly

The South Atlantic magnetic Anomaly (SAA) is an important feature of the present geomagnetic field. In this paper we model the space–time evolution of this anomaly over the past 400 years in terms of the resultant between a decrease of a global axial dipole and an increase of a virtual local monopole source. Certain characteristics of this evolution are investigated and some considerations
are made in the light of a possible special state of the global geomagnetic field dynamical regime. Among the possible
speculations, one is made regarding the topography of the coremantle boundary (CMB) and its possible aspect beneath the SAA
region in terms of simple sinusoidal undulations met by the monopole source during its centennial motion
HAZGRIDX: earthquake forecasting model for ML ≥ 5.0 earthquakes in Italy based on spatially smoothed seismicity

We present a five-year, time-independent, earthquake-forecast model for earthquake magnitudes of 5.0 and greater in Italy using spatially smoothed seismicity data. The model is called HAZGRIDX, and it was developed based on the assumption that future earthquakes will occur near locations of historical earthquakes; it does not take into account any information from tectonic, geological, or geodetic data. Thus HAZGRIDX is based on observed earthquake occurrence from seismicity data, without considering any physical model. In the present study, we calculate earthquake rates on a spatial grid platform using two declustered catalogs: 1) the Parametric catalog of Italian earthquakes (Catalogo Parametrico dei Terremoti Italiani, CPTI04) that contains the larger earthquakes from MW 7.0 since 1100; and 2) the Italian seismicity catalogue (Catalogo della Sismicità Italiana, CSI 1.1) that contains the small earthquakes down to ML 1.0, with a maximum of ML 5.9, over the past 22 years (1981-2003). The model assumes that earthquake magnitudes follow the Gutenberg-Richter law, with a uniform b-value. The forecast rates are presented in terms of the expected numbers of ML>5.0 events per year for each grid cell of about 10 km × 10 km. The final map is derived by averaging the earthquake potentials that come from these two different catalogs: CPTI04 and CSI 1.1. We also describe the earthquake occurrences in terms of probabilities of occurrence of one event within a specified magnitude bin, DM0.1, in a five year time period. HAZGRIDX is one of several forecasting models, scaled to five and ten years, that have been submitted to the Collaboratory for the Study of Earthquake Probability (CSEP) forecasting center in ETH, Zurich, to be tested for Italy
Space- and time- dependent probabilities for earthquake fault systems from numerical simulations: feasibility study and first results

In weather forecasting, current and past observational data are routinely assimilated into numerical simulations to produce ensemble forecasts of future events in a process termed “model steering”. Here we describe a similar approach that is motivated by analyses of previous forecasts of the Working Group on California Earthquake Probabilities (WGCEP). Our approach is adapted to the problem of earthquake forecasting using topologically realistic numerical simulations for the strike-slip fault system in California. By systematically comparing simulation data to observed paleoseismic data, a series of spatial probability density functions (PDFs) can be computed that describe the probable locations of future large earthquakes. We develop this approach and show examples of PDFs associated with magnitude M > 6.5 and M > 7.0 earthquakes in California.Peer reviewe
Imaging the Seismic Crustal Structure of the Western Mexican Margin between 19ºN and 21ºN

17 pages, 9 figuresThree thousand kilometres of multichannel (MCS) and wide-angle seismic profiles, gravity and magnetic, multibeam bathymetry and backscatter data were recorded in the offshore area of the west coast of Mexico and the Gulf of California during the spring 1996 (CORTES survey). The seismic images obtained off Puerto Vallarta, Mexico, in the Jalisco subduction zone extend from the oceanic domain up to the continental shelf, and significantly improve the knowledge of the internal crustal structure of the subduction zone between the Rivera and North American (NA) Plates. Analyzing the crustal images, we differentiate: (1) An oceanic domain with an important variation in sediment thickness ranging from 2.5 to 1 km southwards; (2) an accretionary prism comprised of highly deformed sediments, extending for a maximum width of 15 km; (3) a deformed forearc basin domain which is 25 km wide in the northern section, and is not seen towards the south where the continental slope connects directly with the accretionary prism and trench, thus suggesting a different deformational process; and (4) a continental domain consisting of a continental slope and a mid slope terrace, with a bottom simulating reflector (BSR) identified in the first second of the MCS profiles. The existence of a developed accretionary prism suggests a subduction–accretion type tectonic regime. Detailed analysis of the seismic reflection data in the oceanic domain reveals high amplitude reflections at around 6 s [two way travel time (twtt)] that clearly define the subduction plane. At 2 s (twtt) depth we identify a strong reflection which we interpret as the Moho discontinuity. We have measured a mean dip angle of 7° ± 1° at the subduction zone where the Rivera Plate begins to subduct, with the dip angle gently increasing towards the south. The oceanic crust has a mean crustal thickness of 6.0–6.5 km. We also find evidence indicating that the Rivera Plate possibly subducts at very low angles beneath the Tres Marias Islands.Funding is from the Spanish National Research\ud
Project (ANT94-0182-C02-01/02). Additional funding comes from INSU-France, ORSTOM-IRD,\ud
France bilateral cooperation (HF1997-077), and CSIC/CONACYT 0894PT, the Secretaría de Marina of Mexico, CICESE project 644107 and by CIRIT (Project 1995SGR00438).R. Bartolome acknowledges the financial support of the Spanish Ministry of Science and Innovation (Ramon y Cajal program).Peer reviewe
Long-term variations of fumarole temperatures on Vulcano Island (Italy)

Fumarole temperatures are the ultimate results of many processes that
are encountered by deep fluids during their passage to the surface. Here,
the time variations of high-temperature fumaroles acquired by
continuous monitoring are presented, to show the effects of the forces that
act on the system. Data acquired by continuous monitoring of fumaroles
and the time relationships with the different parameters related to the
activity of the volcanic system are discussed. From 1998 to 2010, the
temperature and compositional changes of fumarolic gases were
monitored at the same time as variations in the number of volcanoseismic
events, which indicate frequent variations of energy release (heat
and mass flow, and seismic strain release). Geochemical modeling applied
to the volcanic system of Vulcano Island suggests that the overall
expansion of magmatic gas through the fractured system is an almost
iso-enthalpic process at depth, which shifts to an adiabatic process at
shallow depth, where the rock permeability increases. Thus, the time
variations of the fumarole temperatures reflect various physical
variations of the system that can either occur at depth or close to the
surface. The temperature monitoring performed in the fumarolic area of
La Fossa Cone showed short-term effects related to rain events, and
negligible effects related to other external agents (ambient temperature
and atmospheric pressure variations). At the same time, the long-term
monitoring highlighted some mean-term and long-term variations. These
last are the main characters observed in the time-series, and they both
appear to be related to endogenous forces that perturb the equilibrium of
this complex geochemical system