Lessons from April 6, 2009 L’Aquila earthquake to enhance microzoning studies in near-field urban areas

Abstract

This study focuses on two weak points of the present procedure to carry out microzoning study in near-field areas: (1) the Ground Motion Prediction Equations (GMPEs), commonly used in the reference seismic hazard (RSH) assessment; (2) the ambient noise measurements to define the natural frequency of the near surface soils and the bedrock depth. The limitations of these approaches will be discussed throughout the paper based on the worldwide and Italian experiences performed after the 2009 L'Aquila earthquake and then confirmed by the most recent 2012 Emilia Romagna earthquake and the 2016-17 Central Italy seismic sequence. The critical issues faced are (A) the high variability of peak ground acceleration (PGA) values within the first 20-30 km far from the source which are not robustly interpolated by the GMPEs, (B) at the level 1 microzoning activity, the soil seismic response under strong motion shaking is characterized by microtremors' horizontal to vertical spectral ratios (HVSR) according to Nakamura's method. This latter technique is commonly applied not being fully compliant with the rules fixed by European scientists in 2004, after a 3-year project named Site EffectS assessment using AMbient Excitations (SESAME). Hereinafter, some "best practices" from recent Italian and International experiences of seismic hazard estimation and microzonation studies are reported in order to put forward two proposals: (a) to formulate site-specific GMPEs in near-field areas in terms of PGA and (b) to record microtremor measurements following accurately the SESAME advice in order to get robust and repeatable HVSR values and to limit their use to those geological contests that are actually horizontally layered.

2D FEM Numerical Prediction of Local Seismic Effects at San Salvador Municipality (El Salvador) Induced by 2001 Earthquakes

“…Numerical prediction of local seismic effects in urban areas is performed worldwide through 1D, 2D, and 3D simulations based on methods such as Finite Element (FE) [1][2][3][4][5][6], Finite Difference (FD) [7][8][9][10] and Spectral Element (SE) [11][12][13] and the references herein. This approach aims at modelling the complex geo-morphological and litho-technical subsoil characters to predict the effect at the surface of the seismic wave propagation, in terms of spectral acceleration, velocity and displacements, and amplification factors and functions [14] and to evaluate the influence of these effects on damage over large areas [15]. These studies are needed to draw maps of seismic shaking effects (in terms of amplitude, frequency content, and duration) throughout the urbanized areas, leading urban planning to improve the resilience of human communities [16].…”

A Microtremor Survey to Identify Seismic Vulnerability Around Banda Aceh Using HVSR Analysis

“…The results are used to find the seismic vulnerability index (K g ). With a seismic vulnerability index, infrastructure planning and development in an area can be carried out following soil conditions and implementing disaster mitigation (Vessia et al, 2020).…”