Seismic Monitoring for the United Arab Emirates

Seismic Monitoring for the United Arab Emirates

Postby salsinawi » Sat Mar 03, 2007 2:02 am

http://www.llnl.gov/tid/lof/documents/pdf/318857.pdf

Seismic Monitoring for the United Arab Emirates

Arthur Rodgers and Keith Nakanishi
Earth Sciences Division
Lawrence Livermore National Laboratory,
Livermore, CA 94551
April 11, 2005

Disclaimer

This document was prepared as an account of work sponsored by an agency of the United States
Government. Neither the United States Government nor the University of California nor any of their
employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for
the accuracy, completeness, or usefulness of any information, apparatus, product, or process
disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any
specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise,
does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United
States Government or the University of California. The views and opinions of authors expressed herein
do not necessarily state or reflect those of the United States Government or the University of California,
and shall not be used for advertising or product endorsement purposes.
This work was performed under the auspices of the U.S. Department of Energy by University of
California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48

Seismic Monitoring for the United Arab Emirates

Arthur Rodgers and Keith Nakanishi

Earth Sciences Division
Lawrence Livermore National Laboratory,
Livermore, CA 94551
April 11, 2005

Executive Summary

There is potential for earthquakes in the United Arab Emirates and in the Zagros
mountains to cause structural damage and pose a threat to safety of people. Damagingeffects from earthquakes can be mitigated by knowledge of the location and size ofearthquakes, effects on construction, and monitoring these effects over time. Although ageneral idea of seismicity in the UAE may be determined with data from global seismicnetworks, these global networks do not have the sensitivity to record smaller seismicevents and do not have the necessary accuracy to locate the events. A National Seismic
Monitoring Observatory is needed for the UAE that consists of a modern seismic networkand a multidisciplinary staff that can analyze and interpret the data from the network. Aseismic network is essential to locate earthquakes, determine event magnitudes, identifyactive faults and measure ground motions from earthquakes. Such a network can providethe data necessary for a reliable seismic hazard assessment in the UAE. The NationalSeismic Monitoring Observatory would ideally be situated at a university that wouldprovide access to the wide range of disciplines needed in operating the network andproviding expertise in analysis and interpretation.

Introduction

The motion of tectonic plates on the earth’s surface is marked most dramatically byearthquakes that occur along the plate boundaries. The UAE is situated in the Arabiantectonic plate (Figure 1). Near the UAE, earthquakes occur along the collision of theArabian and Eurasian Plates that forms the Zagros Mountains of Iran, one of the mostseismically active regions in the world. Large (greater than magnitude 5.0) earthquakesin the Zagros are common and larger events (say, magnitude 6.5 can be expected). Theseearthquakes can occur within 100 km of the UAE and pose a potential hazard to propertyand lives.Earthquakes can also strike in the UAE as evidenced by the damaging earthquakes nearMasafi in early 2002. The largest event in this series was a magnitude 5.1 that occurredon March 11, 2002 and was detected and located by global seismic networks, such as theUnited States Geologic Survey (USGS) National Earthquake Information Center (NEIC)and the International Seismological Centre (ISC). Another smaller event (magnitude 4.0)occurred in January. Several smaller events were felt during the months before andafter the main event. In October 2004, another earthquake struck near Dibba.Only relatively large earthquakes can be detected and located by seismic stations atdistances greater than several hundred kilometers from the event, because seismic energyweakens with distance from the source. Furthermore, the precise location of seismicevents cannot be known with distant observations unless one has exceptionally accuratemodels of the seismic wave speed structure of the earth. While seismologists haveapproximate models of sub-surface earth structure, detailed accurate structure is not known. Because of these factors, the only way to have reliable knowledge of all earthquake activity in the UAE is to deploy a network of seismic stations that can
continuously measure ground motions, including motions from very small earthquakes.Monitoring small earthquakes is essential because frequent small earthquakes can indicate the likelihood of larger earthquakes. Also, the locations of smaller earthquakesindicate which faults are active and are likely to have larger earthquakes. In order to
obtain an accurate and comprehensive evaluation of seismic activity in the UAE, anetwork of stations located in the UAE is needed.

Figure 1. Map of earthquakes (red circles) in and around the Arabian Peninsula.Northeastward motion of the Arabian Plate leads to the seismic activity along the ZagrosMountains near the UAE.

A National Seismic Monitoring Observatory

Damage from earthquakes can cause loss of life, injuries and severe damage to buildingsand industrial facilities. A National Seismic Monitoring Observatory would combineexpertise and data and provide the government with information on earthquakemonitoring and research. This Observatory can provide the government with thenecessary technical consultations for monitoring earthquakes and providing technicalinput on seismic hazards and building codes. Furthermore, such an observatory canprovide the government and public with earthquake alerts and educational materials topromote earthquake awareness.

Operational Organization

Earthquake science is a dynamic and multidisciplinary enterprise, and requires expertisefrom seismologists, geologists, engineers, computer programmers and public policymakers. The operation of a seismic network involves research and development and themultidisciplinary technical skills including electronics engineers, who must maintaincommunications equipment, computer programmers and system administrators who mustmaintain computer hardware and software, and of course seismologists who mustperform routine data processing to determine locations and magnitudes of events.

Earthquake hazard assessment requires evaluation by civil engineers and discussions withpublic policy makers to implement the results.
Most seismic observatories are operated with funding from the national governmenthowever are closely aligned with universities or research institutions to take advantage ofthe multidisciplinary research required. The research staff members are university facultywith the operations part having responsibilities for reporting earthquake activity to thegovernment. This is the model of most observatories in the United States which areoperated by universities such as the University of California at Berkeley, CaliforniaInstitute of Technology, Columbia University and Saint Louis University. Results aretransmitted to the national earthquake authority at the United States Geological Survey,
however the primary operations and research responsibility lies with the university.Oman has a similar model, with the Earthquake Monitoring Center (EMC) at SultanQaboos University. The EMC supports research activities done by university faculty,graduate students and visiting scholars and receives funding directly from thegovernment and has a responsibility to report earthquake activity directly to thegovernment.

A National Seismic Network

Key to the seismic observatory is a national seismic network consisting of severalcomponents. There is the seismic recording, communications and processing equipment(hardware). There is computer software that can automate many of the routineprocessing of the data. Lastly, but most importantly, there are the personnel tomake allthe hardware and software function properly and perform the research to understand andreport the earthquakes and groundsection we outline specific plans for a national network, including potential stationlocations. Because we do not expect large earthquakes to occur frequently in the UAE, aweak motion network is needed in order to define active faults within the UAE and builda catalog of earthquake data for seismic hazard assessment. This would provide valuableinformation for future investigations. A small network of strong motion instruments canbe placed in cities near critical structures such as tall buildings, power plants, dams, andbridges to provide data for design and construction practices.

Site Selection Issues

Weak motion stations should be distributed to broadly cover the expected earthquakefaults and seismogenic zones. The reliability of event locations depends on how well theevent is surrounded by stations of the network, so it is important that stations bedistributed as broadly as possible. Unfortunately the desired distribution of stations canbe prohibited by geography, such as coastlines, unfavorable geology (such as sand),
impenetrable mountains and/or national boundaries.The selection of site locations for seismic stations involves the consideration of several
factors. These factors often involve trade-offs between the logistical convenience andtechnical performance of the network. Weak motion stations should be deployed awayfrom cities, roads and coastlines in order to minimize noise levels. The instrumentsshould be emplaced below the surface in order to shield them from variations intemperature and minimize wind noise. The desire to locate stations away from citiesresults in logistical challenges to communications systems. It is imperative that reliablecommunications exist between remote stations and the central data center. Modernremote communications systems rely on line-of-sight radio telemetry or VSAT satellitecommunications. Mobile phone communication is reliable, but prohibitively expensive.

Proposed Site Locations

Considering the known geology of the UAE and the constraints imposed by the geology,a plan could be developed for stations locations in a national seismic network. Mainly,the sedimentary (sand) deposits of the eastern majority of the country (Abu DhabiEmirate) offer few good locations for stations. Fortunately this difficult could be offsetby the likelihood that this region is seismically less active than the mountainous northernand western emirates.Based on our studies of population density and geology, we would propose a seismic network of weak and string motion stations configure as shown in Figure 2


Figure 2. Notional configuration of a seismic network in the United Arab Emirates. Thenetwork would consist of weak motion (yellow triangles) and strong motion (red squares)sites.
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