Earthquake Hazard Assessment Practice and Velocity Models and Reference Events in the Mediterranean Region

Santa Susanna, Spain

20-25 May 2001

With a Short Course on:

Understanding and Applying Probabilistic

Seismic Hazard Analysis

United Nations Educational, Scientific and Cultural Organization

Paris, France

Contact: Dr. Soren T. Malling

Telephone: 33 1 45 68 41 22

s.malling@unesco.org

Executive Summary

The Mediterranean region, because of its geological structure, seismicity, topography and climate, has been frequently subjected to natural disasters resulting in great losses of life and property. Field studies and investigations of disasters indicate that large portions of the land surface, population, infrastructure, and industry of the region have been subjected to earthquakes in the past or will be subjected to earthquakes in the future.

In recent years, there were several major, damaging earthquakes in the Mediterranean region. Therefore, in the interest of reducing earthquake risk in the Mediterranean region, UNESCO and the Instituto de Ciencias de la Tierra 'Jaume Almera' – CSIC convened a workshop in Santa Susanna, Spain, 20-25 May 2001, on Earthquake Hazard Assessment Practice and Velocity Models and Reference Events in the Mediterranean Region. Contributed papers on seismology and engineering were invited. More than 50 participants from the following countries attended the workshop: Algeria, Belgium, Cyprus, Denmark, Ecuador, Egypt, France, Greece, Israel, Italy, Iran, Jordan, Lebanon, Libya, Morocco, Netherlands, Saudi Arabia, Solvenia, Syria, the Palestinian Authority, Spain, Turkey, United States, and Yemen.

This workshop continued efforts addressed in similar RELEMR workshops in Amman, Jordan, 4-7 May 1998, in Istanbul, Turkey, 14‑17 October 1998, Nicosia, Cyprus, 3-7 May 1999, and in Istanbul, Turkey, 29 May – 2 June 2000; the goals of those workshops were to foster data exchange among countries in the region and to conduct joint activities and experiments that would improve the quality of seismic data in the EMR. In Amman, working groups were formed on 1) seismic calibration and 2) the development of a RELEMR seismic hazard map. The 1998 workshop in Istanbul was organized along these themes. The Cyprus-1999 workshop added sessions on the role of auxiliary station operators and their responsibilities and the interaction with their earthquake-reporting activities. The Istanbul-2000 workshop was dedicated to seismic calibration using the Dead Sea explosions and selected natural events.

In addition to the workshop, Dr. Robert T. Sewell (USA) presented a one-day training course on: Understanding and Applying Probabilistic Seismic Hazard Analysis and panel discussions were held on Earthquake Hazard Assessment in the Mediterranean Region and on Velocity Models and Reference Events in the Mediterranean Region.

Maria-Jose Jimenez presented the Keynote Address on The Unified Seismic Hazard Map of Europe and the Mediterranean.

Thirty contributed papers were presented that discussed various aspects of earthquake hazard assessment and velocity models and reference events in the Mediterranean region.

Participants were taken on a one-day field trip to the ‘La Garrotxa’ volcanic field, the Volcano Museum of Olot, and the area affected by the XVth century damaging earthquake series.

Introduction

In the EMR, these earthquakes are associated with the northward movement of the Arabian plate. The 1,000 km long western boundary of the Arabian plate is a complex plate boundary, extending from zones of sea‑floor spreading in the Red Sea to zones of plate convergence in Turkey, and lies along the line of the Gulf of Aqaba, the Dead Sea rift, and the Ghab depression. The sense of motion along the Dead Sea transform fault system is left lateral, with the eastern side moving northward relative to the western side. Total displacement is estimated at about 107 km since Oligocene time, with an annual rate of about 0.5 cm. over the last 7 to 10 million years.

On 22 November 1995, a Mw 7.2 earthquake occurred in the central Gulf of Aqaba region causing damage in nearby communities in Jordan, Egypt, Israel, and Saudi Arabia and was felt for more than 700 km. An aftershock sequence lasted for more than one year with numerous shocks exceeding Ms 5.0. The size of the main shock and some of the aftershocks demonstrates the threat that earthquakes pose to the EMR. These events occurred during RELEMR’s (Reduction of Earthquake Losses in the Eastern Mediterranean Region) second Joint Seismic Observing Period (JSOP‑II) and therefore we have the ability to accurately locate the earthquake sequence by integrating data from all the national networks in the region. This permits greatly improved accuracy in epicenter and magnitude determinations. In October 1997, a workshop was hosted by the Cyprus Geological Survey Department to locate the main shock and approximately ten aftershocks.

In the western Mediterranean region, which includes portions of Greece, Italy, Spain and northern Africa, seismicity is widely distributed and seismic hazards are high. Modern interpretations of this seismicity suggest the existence of seven micro-plates, with seismic activity concentrated at the micro-plate boundaries, which coincide with the Alps, Appenines, and Hellenic arc. Among the most notable recent (1996) seismic events was the M=6.8 earthquake in the historic city of Assisi in the Italian Appenines which destroyed numerous cultural artifacts, including important frescoes.

Since 1993, the U.S. Geological Survey (USGS) and UNESCO have been cooperating with EMR earth science organizations under the RELEMR program. Countries from the western Mediterranean region have also participated. The European-Mediterranean Seismological Center (EMSC) has coordinated the exchange of data among EMR countries and, since 1996, LLNL has also been cooperating in the program.

The Spain-2001 Workshop

Background