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Influence of Buried Geometries on Ground Response Analysis: The Case of the Pescara Paleovalley System

Description: 

Detailed ground response analyses (GRAs) require a deep understanding of the geophysical properties and geometry of sediment bodies; however, GRAs have focused traditionally on vertical characterization, underestimating the importance of depositional architecture and the lateral variability of buried geometries. In this context, late Quaternary paleovalley systems represent a complex geological environment and a potential threat due to their unconsolidated infill, sharp contrast with adjacent substrates, and complex lenticular geometries, which have often been oversimplified in the attempt to model site-specific seismic effects. In this study, we employed a dense stratigraphic framework comprising continuous core stratigraphic descriptions, an extensive network of microtremor measurements, Down-Hole tests, and undisturbed samples for the estimation of shear modulus decay (G/G₀) and damping ratio (D%) to get robust, local data to perform GRA of the Pescara paleovalley system. Through the correlation of high-resolution stratigraphic data and microtremor measurements, we mapped resonance frequencies, highlighting rapid changes in the frequency range of interaction with common building types, and built the 3D geophysical depth model. The facies architecture was reconstructed through a cross-section transversal to the paleovalley axis and implemented into a 2D finite element model. GRA revealed higher seismic amplification (reaching a factor of 4) compared to simpler geological contexts, strongly linked to the buried paleovalley geometry, and peaked at frequencies between 0.9 and 1.3 Hz in the paleovalley center and up to 5 Hz towards the flanks. We computed the response spectra and compared them with those proposed by the Eurocode 8 guideline (EC8), which relies on soil category and Vs30. Remarkably, the strong amplifications observed show a significant underestimation of spectral accelerations compared to EC8. In this work, we modeled the seismic amplification due to the buried paleovalley body, highlighting the importance of integrating geophysical and subsurface geological data to achieve high-resolution GRA.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? [Poster Session]

Type: Poster

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Andrea

Student Presenter: No

Invited Presentation: 

Authors