Fidest – Agenzia giornalistica/press agency

Quotidiano di informazione – Anno 33 n° 244

Posts Tagged ‘earthquakes’

The epicentral fingerprint of earthquakes marks the coseismically activated crustal volume”

Posted by fidest press agency su venerdì, 21 maggio 2021

InSAR images allow to detect the coseismic deformation, delimiting the epicentral area where the larger displacement has been concentrated. By inspecting the InSAR fringe patterns it is commonly recognized that, for dip-slip faults, the most deformed area is elliptical, or quadrilobated for strike-slip faults. This area coincides with the surface projection of the volume coseismically mobilized in the hanging wall of thrusts and normal faults, or the crustal walls adjacent to strike-slip faults. In the present work we analyzed a dataset of 32 seismic events, aiming to compare the deformation fields in terms of shape, spatial extents, and amount of deformed rock volumes, and the corresponding earthquake type and magnitudes. The dimension of the deformed area detected by InSAR scales with the magnitude of the earthquake, and we found that for M ≥ 6 is always larger than 100 km2, increasing to more than 550 km2 for M ≈ 6.5. Moreover, the comparison between InSAR and Peak Ground Accelerations documents the larger shaking within the areas suffering higher vertical deformation. As well established, the seismic epicenter rarely coincides with the area of larger shaking. Instead, the higher macroseismic intensity often corresponds to the area of larger vertical displacement (either downward or upward), apart local site amplification effects. Outside this area, the vertical displacement is drastically lower, determining the strong attenuation of seismic waves and the decrease of the peak ground acceleration in the surrounding far-field area. Indeed, the segment of the activated fault constrains the area where the vertical oscillations are larger, allowing the contemporaneous maximum freedom degree of the crustal volume affected by horizontal maximum shaking, i.e., the near-field or epicentral area; therefore, the epicentral area and volume are active, i.e., they coseismically move and are contemporaneously crossed by seismic waves (active volume and surface active domain) where trapped waves and constructive interference are expected, whereas the surrounding far-field area is mainly fixed and passively crossed by seismic waves (passive volume and surface passive domain). All these considerations point out that InSAR images of areas affected by earthquakes are a powerful tool representing the fingerprint of the epicentral area where the largest shaking has taken place during an earthquake. Seismic hazard assessments should primarily rely on the expected future active domains. Patrizio Petricca, Christian Bignami, Carlo Doglioni (2021). Earth Science Reviews. doi: https://doi.org/10.1016/j.earscirev.2021.103667

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The fingerprint of earthquakes identified with satellite interferometry

Posted by fidest press agency su venerdì, 21 maggio 2021

From the analysis of satellite images, the areas with the greatest seismic intensity of an earthquake are recognized. Through the images obtained by means of satellite interferometry technique, a team of researchers from the Sapienza University of Rome and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) analyzed the “fingerprint” of earthquakes through the recognition of the ground deformation that accompanies a seismic event. Scientists, in fact, have been able to estimate its dimensions and recognize the area where the most violent shaking accompanying earthquakes are concentrated. The study “The epicentral fingerprint of earthquakes marks the coseismically activated crustal volume” has just been published in ‘Earth Science Reviews’. The InSAR (Interferometric Synthetic Aperture Radar) data allow to detect the coseismic deformation (that is, the instantaneous and permanent deformation caused by the earthquake) delimiting the epicentral area where the greatest displacement is concentrated, through the analysis of the deformation of the ground around the fault activated during an earthquake. “Since 1993, with the images given by InSAR, a long list of seismic events has been analyzed; this list is always growing thanks to the increase in the number of satellites and to the improvement of the quality of SAR sensors and InSAR techniques in continental areas”, the researchers Patrizio Petricca (Sapienza University) and Christian Bignami (INGV) state. “With them it is possible to detect the coseismic deformation, delimiting the epicentral area where most of the displacement is concentrated. Outside this area, apart from phenomena of local amplification, the ground displacement decreases, resulting in the attenuation of the seismic shaking”. “Knowing these Earth manifestations helps to focus more specifically on seismic prevention in future epicentral areas, helping to calibrate the assessment of seismic hazard in which vertical movement plays a relevant role in increasing greater horizontal shaking and therefore greater damage. Earthquakes will return: on average, in Italy about 20 destructive earthquakes are generated per century”, concludes President Carlo Doglioni. font: The epicentral fingerprint of earthquakes marks the coseismically activated crustal volume” Patrizio Petricca, Christian Bignami, Carlo Doglioni (2021). Earth Science Reviews. doi: https://doi.org/10.1016/j.earscirev.2021.103667

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