Assessing Seismic Damage Through Stochastic Simulation of Ground Shaking: The Case of the 1998 Faial Earthquake (Azores Islands)

Abstract

In July 1998, an M w = 6.2 earthquake struck the islands of Faial, Pico and San Jorge (in the Azores Archipelago), registering VIII on the Modified Mercalli Intensity scale and causing major destruction in the northeastern part of Faial. The main shock was located offshore, 8 km North East of the island, and it triggered a seismic sequence that lasted for several weeks. The existing data for this earthquake include both the general tectonic environment of the region and the teleseismic information. This is accompanied by one strong-motion record obtained 15 km from the epicentre, the epicentre location of aftershocks, and a large collection of the damage inflicted to the building stock (as poor rubble masonry, of 2-3 storeys). The present study was carried out in two steps: first, with a finite-fault stochastic simulation method of ground motion at sites throughout the affected islands, for two possible locations of the rupturing fault and for a large number of combinations of rupture mechanisms (as a parametric analysis); secondly, the damage to buildings was modelled using a well-known macroseismic method that considers the building typologies and their associated vulnerabilities. The main intent was to integrate different data (geological, seismological and building features) to produce a scenario model to reproduce and justify the level of damage generated during the Faial earthquake. Finally, through validation of the results provided by these different approaches, we obtained a complete procedure for the parameters of a first model for the production of seismic damage scenarios for the Azores Islands region.

Seismic vulnerability assessment and characterisation of the buildings on Faial Island, Azores

“…The fact that the islands of the Azores were affected by seismic events over the last decades, has resulted in the reconstruction, strengthening and modification of the traditional building stock, contributing to a variety of building types. Building a database of construction features allows the reproduction of more realistic models in order to obtain seismic damage scenarios (Zonno et al 2009). Table 1 shows the catalogued construction types: traditional construction (TC), altered traditional building (ATC), current construction (CC) and mixed construction (MC).…”

The concept of a disruption index: application to the overall impact of the July 9, 1998 Faial earthquake (Azores islands)

“…However, the main shock relocation based on a one-dimensional velocity model suggested an epicentre about 8 km North East, offshore of Faial Island" (Zonno et al 2010).…”

The use of Artificial Neural Networks to estimate seismic damage and derive vulnerability functions for traditional masonry

“…Even though the authors were allowed to access the full database, a complementary field work was conducted to understand the evolution and the diachronic process resulting from rehabilitation interventions implemented since 1998 [21]. Zonno et al [22] presented a proposal of a macroseismic intensity distribution map for the Faial island, which was constructed on the basis of the post-earthquake field survey and observation campaigns that followed the earthquake of July 9, 1998.…”