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mHVSR-Based 3D Modeling of a Late Quaternary Paleovalley System From Italy: Influence of Internal Facies Architecture on Resonance Frequencies and Shear Wave Velocities

Description: 

Late Quaternary paleovalley systems are shallow subsurface incisions formed during the last episode of global sea-level fall and filled with sediment during the Holocene sea-level rise. They are typically buried beneath flat, modern coastal plains, with no geomorphic expression. Paleovalley systems are increasingly studied worldwide, as their occurrence is related to greater damage in case of earthquake, due to the soft and unconsolidated nature of their sedimentary fill. Previous work along the Adriatic Sea coastal plain of Italy reconstructed the 2D geometry of the buried valley beneath the city of Pescara, but complete seismic site characterization and 3D paleovalley modeling, including shear wave velocity and resonance frequencies, are lacking. In this context, we acquired 85 microtremor measurements in a 10 km² wide area and performed the microtremor-based horizontal-to-vertical spectral ratio (mHVSR). We used a pre-existing geological dataset as a framework to constrain the mHVSR curves to create a Frequency-Depth model and transform the mHVSR curves from the frequency to the spatial domain, thus reconstructing the paleovalley geometry. We obtained a 3D model of the paleovalley fill, which is about 40 m thick. The fundamental resonance frequency shows considerable variability over very short distances (700 m only), ranging from 4.5 Hz on the interfluves to 0.9 Hz in the depocenter. Through high-resolution stratigraphic cross-sections, we reconstructed the internal facies architecture, mapping in 3D the main sedimentary bodies and delineating facies changes within the paleovalley fill. Using Down-Hole data, we classified major sedimentary bodies into five classes, with distinct Vs; Coastal Sand Vs ≃ 260 m/s, Swamp clay Vs ≃ 170 m/s, Poorly Drained Floodplain clay Vs ≃ 220 m/s, Fluvial Gravel Vs ≃ 650 m/s, Substrate Vs ≃ 310 m/s, providing information about geometry, resonance frequency, and shear wave velocity that can be used for future seismic simulations.

Session: Site-specific Modeling of Seismic Ground Response: Are We Quantitative Enough to Predict? [Poster]

Type: Poster

Date: 4/19/2023

Presentation Time: 08:00 AM (local time)

Presenting Author: Andrea Di Martino

Student Presenter: No

Invited Presentation: 

Authors