Probabilistic Earthquake Disaster Scenario for San José, Costa Rica
Total Page：16
File Type：pdf, Size：1020Kb
PROBABILISTIC EARTHQUAKE DISASTER SCENARIO FOR SAN JOSÉ, COSTA RICA San José, Costa Rica - December 2016 Acknowledgement This report forms part of the USAID/OFDA funded Preparing Rescue and Emergency Personnel to Ameliorate the Response to Earthquakes (USAID/OFDA PREPARE program). It was originally published under the title: Phase 1: Assessment of Earthquake Risks. The USAID/OFDA PREPARE program has been made possible thanks to the support and generosity of the American people through the United States Agency for International Development (USAID) and its Office of Foreign Disaster Assistance (OFDA). Miyamoto International, Inc. administers and executes the resources of USAID and manages the implementation of the program in conjunction with the governments of Pasto, Colombia; Costa Rica; El Salvador and Mexico. The goal of the program is to strengthen risk management policy and practice of national and municipal Disaster Risk Reduction/Management (DRR/DRM) institutions for a reduction in internally displaced people (IDPs), lives lost, less people injured and less economic disruption in the selected PREPARE cities: Pasto, Colombia; San José, Costa Rica; San Salvador, El Salvador and Guadalajara, Mexico. This report is the result of a multi-stakeholder engagement and consultation process which involved authorities from the national and municipal level governments, academic institutions, and private sector partners. We hereby acknowledge the contributions of, and thank the agencies, institutions and partners, for their valuable time, guidance and support. December 2016 Submitted by Miyamoto International, Inc. www.miyamotointernational.com © 2016 Miyamoto International, Inc. All rights reserved. This report or any part thereof must not be reproduced in any form without the written permission of Miyamoto International, Inc. DISCLAIMER: This publication is made possible by the support of the American People through the United States Agency for International Development (USAID). The opinions, findings and conclusions stated herein are those of the authors and do not necessarily reflect the views of USAID or the United States Government. EXECUTIVE SUMMARY Probabilistic seismic risk assessment for the canton of San José in Costa Rica was undertaken as part of Phase I of the Preparing Rescue and Emergency Personnel to Ameliorate the Response to Earthquakes (PREPARE) program. The objectives of the project were to assess the expected values of the building damage, fatalities (for both daytime and nighttime scenarios), and debris volume that would result from a potential earthquake. The findings can then be used to prepare policies or plans of action to lessen the human and socioeconomic impact that would be caused by future earthquakes in San José. The current research data and available maps were used to develop the design-level (475-year return period) seismic hazard and the site conditions that were used as the probabilistic seismic input for risk analysis. As part of the risk assessment program, satellite imagery was examined and field surveys were conducted to collect data for a pool of representative buildings. The exposure data for the area of study is presented in Table 1. The collected data was used to divide buildings into various groups of similar construction. This approach formed the basis for the exposure model. For each building typology, fragility functions were then developed. The consequence (structural damage, fatality, and de- bris) functions that correspond to each damage state (DS) for a given building type formed the last piece of input. The input files were then used to run Monte Carlo simulations with the OpenQuake risk engine. The earthquake risk analysis was conducted for all building assets of the exposure model, and the risk results of each building asset were accumulated with respect to 196 barrios individually and for the canton of San José as a whole. The distribution for individual barrios is beneficial for government and city officials in allocating resources for risk preparation and mitigation. Table 1. Exposure data No. of Built area, Occupants Occupants buildings km2 (daytime) (nighttime) 85,800 26.9 472,000 352,000 Table 2 summarizes the estimated earthquake risks of the entire canton of San José. Analysis showed that: • The number of buildings that are expected to be yellow-tagged (moderately damaged) or red-tagged (severely damaged or collapsed) is estimated at about 51,000 structures, or approximately 60% of the building stock. • Depending on the time of the event, approximately 3,000 fatalities (for an estimated rate of 0.7%) is antic- ipated. • The generated debris volume of 4,940,000 m3 is significant and must be accounted for. Table 2. Expected values of earthquake risk for the canton of San José Structural Fatalities Fatalities Yellow-tagged Red-tagged Debris damage daytime nighttime buildings buildings volume % Area, km2 % No. % No. % No. % No. (106) m3 42% 11.35 0.64% 3,000 0.76% 2,700 33% 28,000 26% 22,500 4.94 SJ Phase 1 Report_2016-11-15 3 © 2016 Miyamoto International, Inc. Figure 1. Spatial distribution of red-tagged buildings The spatial distribution of the 22,500 red-tagged buildings is presented in Figure 1. As shown in the figure, a large concentration of red-tagged buildings is in a few barrios. The high physical damage and fatality rates from an earthquake that are computed in this report are not unex- pected, and they highlight the need for development of a risk mitigation program. As part of such a program, it is recommended that the following strategies be implemented: • Provide a seismic strengthening program for key structures that are identified as exhibiting the most risk because of their inherent structural vulnerability, density of occupants, and importance. • Establish a post-earthquake damage assessment program. It is critical to train and certify engineers and to establish logistics. Such a program will improve response and recovery efforts after major earthquakes. • Establish communication and public outreach programs. It is critical to communicate results and the abovementioned recommendations. Communities should be informed about earthquake risk and risk reduction methods. • Optimize allocation of emergency response and recovery resources by identifying the most vulnerable regions. The results, findings, and conclusions that are presented in this report are based on a seismic risk analysis derived from internationally recognized references and state-of-the-art analytical techniques. However, as with any engineering project, the underlying methods and analysis are based on certain assumptions and engineering judgment. Addi- tionally, the findings are based on a given design-level scenario earthquake intensity and correspond to the expected values or means. That is, the results present the expected outcome for an average event from a sample of a large pool of events with similar intensities. As such, the findings in this report include a certain level of uncertainty (inherent in risk assessment) and should not be extrapolated directly to a future seismic event. Accordingly, these assumptions and variations should be accounted for when interpreting the findings and applying the results for future planning. SJ Phase 1 Report_2016-11-15 4 © 2016 Miyamoto International, Inc. CONTENTS Executive Summary ............................................................................................................................... 3 1. Introduction ........................................................................................................................................ 8 1.1 Project background ............................................................................................................. 8 1.2 Phase I description .............................................................................................................. 8 2. Earthquake Hazard for San José .................................................................................................... 12 2.1 Overview ............................................................................................................................ 12 2.2 Bedrock acceleration ........................................................................................................ 12 2.3 Site class ............................................................................................................................ 12 2.4 Seismic design parameters ............................................................................................... 14 3. Exposure Model ............................................................................................................................... 15 3.1 Over view ............................................................................................................................ 15 3.2 Canton of San José building asset and occupancy distribution ..................................... 15 3.3 Zones for surveyed buildings ............................................................................................ 18 3.4 Building typology .............................................................................................................. 18 3.4.1 Overview ............................................................................................................................ 18 3.4.2 Building exposure inventory ............................................................................................. 19 4. Fragility and Damage Functions