Search results for "seismic tomography"
showing 10 items of 19 documents
2018
The Yellowstone magmatic system is one of the largest magmatic systems on Earth, and thus an ideal location to study magmatic processes. Whereas previous seismic tomography results could only image...
The marine activities performed within the TOMO-ETNA experiment
2016
<p>The TOMO-ETNA experiment was planned in order to obtain a detailed geological and structural model of the continental and oceanic crust beneath Mt. Etna volcano and northeastern Sicily up to the Aeolian Islands (southern Italy), by integrating data from active and passive refraction and reflection seismic methodologies, magnetic and gravity surveys. This paper focuses on the marine activities performed within the experiment, which have been carried out in the Ionian and Tyrrhenian Seas, during three multidisciplinary oceanographic cruises, involving three research vessels (“Sarmiento de Gamboa”, “Galatea” and “Aegaeo”) belonging to different countries and institutions. During the o…
3-D attenuation image of fluid storage and tectonic interactions across the Pollino fault network
2021
SUMMARYThe Pollino range is a region of slow deformation where earthquakes generally nucleate on low-angle normal faults. Recent studies have mapped fault structures and identified fluid-related dynamics responsible for historical and recent seismicity in the area. Here, we apply the coda-normalization method at multiple frequencies and scales to image the 3-D P-wave attenuation (QP) properties of its slowly deforming fault network. The wide-scale average attenuation properties of the Pollino range are typical for a stable continental block, with a dependence of QP on frequency of $Q_\mathrm{ P}^{-1}=(0.0011\pm 0.0008) f^{(0.36\pm 0.32)}$. Using only waveforms comprised in the area of seism…
Study of Southern Tyrrhenian and Sicilian regions by a sequential procedure to integrate WAM seismic tomographies and Bouguer anomaly data
2009
A procedure to obtain 3D velocity-density models and earthquake relocation by integrated inversion of P and S wave traveltimes and Bouguer anomaly distribution was applied to a large dataset concerning the Southern Tyrrhenian and Sicilian areas. The seismic dataset was subdivided into two subsets for separate inversions, whose results were later on joined by the WAM (Weighted Average Model) technique. This is a post-processing technique proposed by Calò et al. (2009) by which preliminary tomographic models are unified in a common 3D grid. The first dataset concerns 28873 P and 9990 S arrival times of 1800 earthquakes located in the area 14°30′ E - 17°E, 37°N - 41°N while the second dataset …
Sequential techique for joint inversion of gravimetric and seismic data applied to the Sicilian area
2009
Method to find the Minimum 1D Linear Gradient Model for Seismic Tomography
2016
The changes in the state of a geophysical medium before a strong earthquake can be found by studying of 3D seismic velocity images constructed for consecutive time windows. A preliminary step is to see changes with time in a minimum 1D model. In this paper we develop a method that finds the parameters of the minimum linear gradient model by applying a two-dimensional Taylor series of the observed data for the seismic ray and by performing least-square minimization for all seismic rays. This allows us to obtain the mean value of the discrete observed variable, close to zero value.
Geodynamic inversion to constrain the non-linear rheology of the lithosphere
2015
A common method to determine the strength of the lithosphere is through estimating its effective elastic thickness from the coherence between gravity and topography. This method assumes a priori that the lithosphere is a thin elastic plate floating on a viscous mantle. Whereas this seems to work well with oceanic plates, it has given controversial results in continental collision zones. Usually, continental collisions zones are well-studied areas for which additional geophysical datasets such as receiver functions and seismic tomography exist that constrain the geometry of the lithosphere and often show that it is rather complex. Yet, lithospheric geometry by itself is insufficient to under…
Propagation of errors due to incorrect positions of sources and detectors in wave-field tomography
2004
Tomographic data processed by 2D inversion programs can produce fairly large distortions due to incorrect source and/or detector positions. This problem is very serious in high-frequency electromagnetic tomography (GPR), due to the dimensions of the transmitter and receiver antennae. The errors can even be larger when coupled antennae are used (receiver and transmitter inside the same box) whose positions are not clearly known. Similar errors can be involved in seismic tomography, for instance when the mechanical connection between transducers and sample is defective. In this paper the problem has been studied using synthetic data which were calculated for different acquisition geometries. …
Seismic investigation for the characterization of a gravity concrete dam
2016
Monitoring of large-scale infrastructures plays an important role for public safety and prevention. The control of the safety assessment of a dam is largely dependent on knowledge of the mechanical parameters of the actual construction, as well as its geological substratum. The application of geophysical methods can considerably contribute to the examination indicating the less consolidated material and the degradation of mechanical parameters. A seismic tomographic approach has been used in a typical gravity concrete dam without reinforcement to detect mechanical properties of the body of the dam and its geological setting. Three seismic travel time tomographies in the dam body as well as …
Understanding seismic path biases and magmatic activity at Mount St Helens volcano before its 2004 eruption
2020
SUMMARY In volcanoes, topography, shallow heterogeneity and even shallow morphology can substantially modify seismic coda signals. Coda waves are an essential tool to monitor eruption dynamics and model volcanic structures jointly and independently from velocity anomalies: it is thus fundamental to test their spatial sensitivity to seismic path effects. Here, we apply the Multiple Lapse Time Window Analysis (MLTWA) to measure the relative importance of scattering attenuation vs absorption at Mount St Helens volcano before its 2004 eruption. The results show the characteristic dominance of scattering attenuation in volcanoes at lower frequencies (3–6 Hz), while absorption is the primary atte…