After each strong earthquake, maps known as macroseismic intensity maps (or shakemaps) are automatically produced in quasi-real-time to describe the severity of the seismic shaking in impacted cities. These maps utilize various scientific information, including seismic recordings from stations deployed across the territory (in France, stations from the public networks RAP and RLBP), and citizens testimonies regarding their perception and potential damage (in France, testimonies collected on the website franceseisme.fr). They also incorporate seismic shaking models called GMM in the specialists terminology. Shakemaps are utilized by a wide range of operators : state services, local authorities, public or private organizations, emergency operators, as well as the general public for scientific information.

Shakemaps were initially designed for high-magnitude earthquakes (greater than 7), where the intensity of the shaking is primarily controlled by fault rupture. However, their relevance for moderate earthquakes (magnitude less than 7, but which can still cause significant damage) remains questionable, as other physical processes become predominant, such as local shaking amplification due to the presence of loose sedimentary soils. These local phenomena are only partially considered in shakemaps or are addressed in a basic way. Consequently, shakemaps do not always accurately reflect the actual impact of a moderate earthquake, as pertinent scientific information is lacking at the local scales of cities or buildings.

The scientific project SASHA ("Satellite Imagery Strategies for Earthquake Strong-Motion Prediction and Shakemap Generation"), funded by the French National Research Agency (ANR), aims to enhance the reliability of shakemaps and damage maps within cities located in sedimentary valleys susceptible to seismic amplification effects. Our objective is to better predict the impact of an earthquake anywhere, including in complex geological environments and in the absence of seismic recordings. We aim to provide relevant information on a fine scale, in the order of a point every few meters, to feed shakemaps with high-resolution seismic information. To achieve this, we leverage satellite imagery in France to develop an innovative method for estimating sediment thickness and its effect on seismic shaking, utilizing InSAR measurements of subsidence rates in alluvial and urbanized valleys. This satellite-derived information becomes available in high spatial resolution.

The combination of high-resolution shakemaps with an innovative damage prediction model will provide building-scale damage maps for any earthquake scenario.

SASHA ANR : https://anr.fr/Projet-ANR-22-CE04-0013

Updated on 28 novembre 2023