Gok, R.

Harris, D.

Herzog, S.

Mellors, R.

Nakanishi, K.

Pasyanos, M.

Rodgers, A.

Vergino, E.

UNT Digital Library

LLNL-CONF-563571LITHOSPHERIC MODELS OF THEMIDDLE EAST TO IMPROVE SEISMICSOURCE PARAMETERDETERMINATION/EVENT LOCATIONACCURACYR. Gok, S. Herzog, K. Nakanishi, M. Pasyanos, R.Mellors, A. Rodgers, D. Harris, E. VerginoJuly 6, 2012Monitoring Research ReviewAlbuquerque, NM, United StatesSeptember 18, 2012 through September 20, 2012Disclaimer  This document was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor Lawrence Livermore National Security, LLC, nor any of their employees makes any warranty, expressed 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 Lawrence Livermore National Security, LLC. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or Lawrence Livermore National Security, LLC, and shall not be used for advertising or product endorsement purposes.  LITHOSPHERIC MODELS OF THE MIDDLE EAST TO IMPROVE SEISMIC SOURCE PARAMETER DETERMINATION/EVENT LOCATION ACCURACYRengin Gök1, Stephen Herzog2, Keith Nakanishi1, Michael E. Pasyanos1, Rob J. Mellors1, Arthur J. Rodgers1, David B. Harris1, and Eileen Vergino1Lawrence Livermore National Laboratory1 and National Nuclear Security Administration2Sponsored by the National Nuclear Security Administration and the U.S. Department of StateAward No. DE-AC52-07NA27344/24.2.3.2 and DOS_SIAA-11-AVCABSTRACTThe Middle East is a tectonically complex and seismically active region. The ability to accurately locate earthquakes and other seismic events in this region is complicated by tectonics, the uneven distribution of natural earthquakes, and the fact that countries run separate national seismic networks without well-developed data-sharing agreements. We report here on a variety of scientific efforts to enhance knowledge of the velocity structure in the Middle East, making use of data from national networks in Saudi Arabia, Oman, and Kuwait to improve seismic location accuracy for events throughout the region.Collaborative seismology engagements with research institutes in the Middle East have produced several important findings. Studies of regional seismic structure revealed that the Arabian Shield and the Arabian Platform have fundamental differences in velocity structure. The earth’s crust is relatively thicker than average in Kuwait and Iraq as a result of the Mesopotamian Foredeep, characterized by 8-10 km thick sediments. Ophiolites dominate the southeastern margin of the Arabian Peninsula where the crust is thicker and seismic velocities are faster. In Kuwait, seismic activity is intensified near oil fields, and seismic source parameters show that this activity comes from tectonic events.  This work is informed by continuous or event-based regional seismic data obtained from 68 seismic stations from national networks, and this number is expected to grow in the future. A current effort is focused on developing better and more accurate seismic magnitude scales based on coda for stations in these national networks. Data and derived measurements from stations are integrated into lithospheric velocity and attenuation models to increase resolution, to improve event location accuracy and source parameter determination, as well as to advance tectonic understanding of the region.OBJECTIVESThe Middle East is part of the Alpine-Himalayan system, where the Iranian and Turkish Plateaus meet at the Arabian Plate, and the divergent plate boundary is at the Red Sea and the convergent plate boundary is at the Zagros Mountains. Despite this geophysical complexity, seismological studies of the region typically suffer from a lack of available data. Data availability issues result from an uneven distribution of seismic stations due to logistical, financial, and even political reasons. Consequently, seismic event data distribution is highly uneven, strongly sampling from some parts of the region, while minimally sampling from others. Seismicity is also unevenly scattered throughout the region, with the highest concentration near the eastern Zagros Mountains. Location accuracies and lithospheric models are greatly influenced by these factors. Specifically, small event detection and identification for seismic hazard mitigation and Comprehensive Nuclear-Test-Ban Treaty (CTBT) monitoring poses a significant challenge in the region due to the complicated tectonic regime and uneven distribution of both seismic sources and seismic stations. Seismic source, attenuation, and 3-D velocity models can be improved by incorporating national networks data from the greater Middle East region. Openly available data through the CTBT International Monitoring System (IMS) and other sources like the Global Seismographic Network (GSN), operated by Incorporated Research Institutions for Seismology (IRIS), is fairly limited (Figure 1a).  However, national seismic networks run by governments, universities, and non-governmental organizations and research institutes enhance the quality of data and increase the number of seismic stations in the region (Figure 1b).These stations are used for various purposes such as seismic hazard mitigation, tsunami warning systems, andstudies of oil field-related seismicity. Incorporating data from these stations—which is usually absent from but essential for higher quality lithospheric models—will greatly improve scientific knowledge of locations and source characteristics in the Middle East.To improve lithospheric models of the Middle East and build regional seismological capacity, in 1996, the U.S. Department of Energy (DOE) began sponsoring Lawrence Livermore National Laboratory (LLNL) cooperation with research institutes in the Middle East. Since 2006, this work has been pursued by the National Nuclear Security Administration’s (NNSA) Confidence-Building Measures (CBM) Program and includes seismic data-sharing, joint data analysis, technical training, and seismic station installation (Figure 1).  In 1998, LLNL seismological cooperation in the Middle East began with the engagement of the Jordan Seismological Observatory (JSO), which involved the deployment of two broadband seismometers, exchange visits of seismologists, and joint research projects. And in 1999, with LLNL technical support, DOE initiated seismic cooperation with King Saud University (KSU) in Riyadh, Saudi Arabia. The LLNL-KSU relationship has resulted in temporary deployments of seismic stations, as well as ongoing technical cooperation in seismological research. This scope of work continued through relationships with the Kuwait Institute for Scientific Research (KISR) and the Earthquake Monitoring Center (EMC) at Sultan Qaboos University (SQU) in Muscat, Oman. Further, CBM worked with the University of Sharjah in the United Arab Emirates (UAE) to begin a regional seismology meeting called the Gulf Seismic Forum (GSF), which completed its seventh iteration in Jeddah, Saudi Arabia in January 2012. CBM also provides assistance to the Reducing Earthquake Losses in the Extended Mediterranean Region (RELEMR) workshops run by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) and the U.S. Geological Survey (USGS). This series of mutually beneficial bilateral and multilateral arrangements in the Middle East provides important data coverage and improved location accuracy for lithospheric velocity and attenuation models in the region that can be used for earthquake hazard mitigation, tsunami warning systems, and CTBT monitoring. Research conducted through these relationships enhances scientific knowledge of seismic wave propagation patterns in the greater Middle East region.Figure 1. (1a) Operational International Monitoring System (IMS) Seismic Stations and Global Seismographic Network (GSN) (1b) Stations of national networks in Middle East Locations of IMS Seismic Stations and Kingdom ofSaudi ArabiaYemenUAEArabian/PersianGulfEgyptCyprusSudanRedSeaIsraelOmanIraqJordanTurkeyIranSyriaKuwaitQatarBahrainYemenKingdom of SaudiArabiaAzerbaijanGeorgiaEgyptSyria20 20 30 30 40 40 50 50 60 60 10 10 20 20 30 30 40 40 stations collaboratively operated by Lawrence Livermore National Laboratory with the Kuwait Institute for Scientific Research and King Saud UniversityRESEARCH ACCOMPLISHEDWe perform data analysis that increases scientific understanding of regional seismicity in the Middle East. In doing so, we use several techniques for estimating the velocity models in the crust and upper mantle. One key technique that we use is to jointly invert receiver functions with surface waves (Gök et al., 2006; Tkalčić et al., 2006), which is a technique that has wide applicability in various parts of the world. The new velocity models from our data analysis are used for improving seismic network location accuracy and/or informing seismic hazard studies. Seismic waveform modeling studies for source parameter estimates also benefit from these new velocity models that help to calculate Green’s function.Joint work in Saudi Arabia includes data analysis and collaboration that has resulted in number of papers in leading, peer-reviewed seismological journals (e.g. Rodgers et al., 2003; Tkalčić et al., 2006; Hansen et al., 2007). Data analyzed through these efforts samples various tectonic environments on the Arabian Peninsula, including both active continental rifting and more stable environments. The resultant velocity models confirm rapid crustal thinning of the Arabian Shield toward the Red Sea (Tkalčić et al., 2006). Lithospheric thickness on the Arabian Peninsula varies considerably, with thin lithosphere centered on the rift axis, thickening toward the Arabian interior (Hansen et al., 1997). A nine-element seismic array is jointly sponsored by LLNL and KSU for small event detection and joint data analysis purposes. The array was originally installed at Ar-Rayn, Saudi Arabia in 2010 (Figure 2) but was moved to Al-Quwayiyah in 2012 to strengthen data collection efforts. Initial beam-forming results demonstrate that the array will provide improved estimates of P wave arrival times and waveforms for small events in the region. We currently have seismic attenuation and ambient-noise correlation data analysis projects with KSU to study the crust and upper mantle structure of Saudi Arabia through data collection from broadband stations. Figure 2. (2a) Map of Arabian Plate showing major tectonic elements of Arabian Shield and Arabian Platform and position of Ar-Rayn seismic array (triangle): earthquakes greater than magnitude 5 for period 2000-2010 and volcanic centers  (black circles and white diamonds, respectively) (2b) Array geometry: broadband sensor (STS-2) at center (triangle with circle), surrounded by two rings of short-period sensors (triangles)Collaboration with the Kuwait Institute for Scientific Research (KISR) began in 1999 when the Kuwait National Seismic Network (KNSN) had few stations and difficulties with network operations. Two jointly written, peer-reviewed papers were published on the seismic structure and the source characteristics of earthquakes in the Persian Gulf region (Pasyanos et al., 2007; Rodgers et al., 2006). Seismic source studies demonstrated that the location of earthquakes is predominantly confined to the upper crust and they show the features of tectonic events (Figure 4).Due to Kuwaiti concerns about seismicity and whether oil field activities were triggering earthquakes, a cooperative project between KISR and LLNL began in May 2010. Two broadband, three-component seismic stations were successfully deployed in the existing vaults for KNSN sites MIB (Mutribah) and UMR (Umm ar Rimam) (Figure 4).  The average crustal thickness is 43-45 km in average.Figure 3. Seismicity and station location in Kuwait: notice proximity of earthquakes to oil fieldsAdditionally, two temporary broadband stations were deployed in Bagdad (BHD) and Mosul (MSL) in early 2005.The stations were equipped with Guralp CMG-3ESPD digital broadband seismometers. Despite the fact that the sites were prone to background noise due to their location near major Iraqi cities, we were able to estimate the crustal thickness under stations BHD and MSL (Gök et al., 2007) (Figure 4). Our results indicated that crustal thicknesses increase toward the south correlated with increasing sedimentary thickness due to the Mesopotamian Foredeep.  Ignoring the sediments of the Mesopotamian Foredeep, crustal velocities and thicknesses are remarkable similar between northern and southern Iraq near Kuwait, suggesting that the crustal structure of the proto-Arabian Platform in northern Iraq was uniform before subsidence and deposition of the sediments in the Cenozoic.Figure 4. Crustal and sediment thickness in northwest Persian Gulf regionAnother fruitful collaboration was between LLNL and the Earthquake Monitoring Center (EMC) of Sultan Qaboos University (SQU) in Oman to study the lithospheric structure of the southeastern Arabian Peninsula by analyzing teleseismic P-receiver functions recorded at broadband and short-period seismic stations of the Oman Seismological Network. Lithospheric structure is obtained by jointly inverting receiver functions and Rayleigh wave group velocities derived from continental-scale surface tomography. We observed relatively thick crust (40-48 km) within the ophiolite-formed mountains in northern Oman. The crustal thickness is about 35 km within the passive continental margin of the southern Dhofar region (Figure 5). Uppermost (<5 km) crustal shear wave velocities are faster in the northern ophiolite regions compared to the southern Dhofar region, while shear velocities in the middle crust are faster in the Dhofar region compared to the ophiolite region. This observation coincides well with Cretaceous to Eocene marine platform sequences overlying the Precambrian to Cambrian basement of the southern region. Joint inversions analysis shows that the Moho depth within the southeastern Arabian Peninsula varies from 34 km in the southern region to 48 km in the northern part.  Currently, studies are underway to supplement this effort with ambient noise cross-correlation for Green’s functions and coda-magnitude calibration.  Our goal is to calibrate the magnitudes of smaller events in the country for their operational needs.  Figure 5. Moho depths color coded at each Oman Seismological Network StationCONCLUSIONS AND RECOMMENDATIONSResearch results show that as expected, tectonic and seismic complexity is observed in structural complexity.  Large variation in structural complexity is the major reason for source and location inaccuracies. Open source seismological data-sharing mechanisms are highly useful for scientists and other researchers interested in studying the lithospheric structure of the Middle East and regional seismic wave propagation patterns. However, both national investments in seismic instrumentation and formal data-sharing agreements between states in this region of high seismicity are limited. LLNL collaboration with research institutes in the Middle East has enhanced the ability of partner countries to operate national seismic networks and seismic expertise. These scientific and technical relationships have improved lithospheric velocity and attenuation models of the Middle East by revealing information about the complexity of crustal and upper mantle structure in the regionFurther scientific and technical cooperation in seismic monitoring with research institutes and universities in the Middle East can help to build upon these models, increasing station coverage and event data availability. In turn, new data and velocity models will increase our lithospheric knowledge of the Arabian Peninsula, enhancing seismic source parameter determination and event location accuracy. This will benefit geophysical studies, city planning and development efforts, civilian and military disaster responses, mining and oil drilling activities, and CTBT monitoring.ACKNOWLEDGEMENTSThe authors would like to thank several individuals for their programmatic contributions to this research.Preparatory Committee of the Comprehensive Nuclear-Test-Ban Treaty Organization: John Coyne, Belkacem Djermouni, and Lassina Zerbo.  King Saud University: Abdullah Al-Amri. Kuwait Institute for Scientific Research:Abdullah Al-Enezi, Lawrence Livermore National Laboratory: William Walter and Jay Zucca, National Nuclear Security Administration: Paula Alfonso, Leslie Casey, Michele Dash-Pauls, Tim Evans, Edward Fei, Wayne Mei, Mike Newman, Anne Phillips, and Anne Winterfield, Sultan Qaboos University: Issa El-Hussein,  United States Department of State: John Godfrey and Terrill RayREFERENCESAl-Hashmi, S., R. Gok, K. Al-Toubi, Y. Al-Shijbi, I. El-Hussain, and A. J. Rodgers (2011). Seismic velocity structure at the southeastern margin of the Arabian Peninsula, Geophys. J. Int. 186: 782-792.Al-Amri, A.M.S., D.B. Harris, M. Fnais, A.J. Rodgers, M. Hemaida (2011). A Regional Seismic Array of Three-Component Stations in Central Saudi Arabia, Seismo. Res. Lett. 83: 49-58.Al-Amri, A., A.J. Rodgers, and T.A. Al-khalifah (2008). Improving the level of seismic hazard parameters in Saudi Arabia using earthquake location, Arab J. Geosci. 1: 1-15.Aldamegh, K.S., Abou Elenaen, K.M., Hussein, H.M., and A. J. Rodgers (2009). Source mechanism of June 2004 Tabuk earthquake sequence, Eastern Red Sea margin, Kingdom of Saudi Arabia, J. Seismology. 13: 561-576.Gök, R., H. Mahdi, H. Al-Shukri, and A.J. Rodgers (2007). Crustal structure of Iraq from receiver functions and surface wave dispersion: implications for understanding the deformation history of the Arabian–Eurasian collision, Geophys J. Int. 172: 1179-1187.Hansen, S., J. Gaherty, S. Schwartz, A. Rodgers, and A. Al-Amri (2008). Seismic velocity structure and depth-dependence of anisotropy in the Red Sea and Arabian shield from surface wave analysis, J. Geophys. Res. 113.Park, Y., A. Nyblade, A. Rodgers, and A. Al-Amri (2007). Upper mantle structure beneath the Arabian Peninsula from regional body-wave tomography: Implications for the origin of Cenozoic uplift and volcanism in the Arabian Shield, Geophysics, Geochemistry and Geosystems. 8.Pasyanos, M. E., H. Tkalčić, R. Gök, A. Al-Enezi, and A. J. Rodgers (2007). Seismic structure of Kuwait, Geophys. J. Int. 170: 299-312.Rodgers, A., A.R. Fowler, A.M.S. Al-Amri, and A. Al-Enezi (2006). The March 11, 2002 Masafi, United Arab Emirates Earthquake: Insights into the Seismotectonics of the Northern Oman Mountains, Tectonophysics. 415: 57-64.Tkalčić, H., Pasyanos, M.E., Rodgers, A.J., Gök, R., Walter, W.R., Al-Amri, A. (2006). A multi-step approach in joint modeling of surface wave dispersion and teleseismic receiver functions: implications for lithospheric structure of the Arabian Peninsula, J. Geophys. Res. 111.

Lithospheric Models of the Middle East to Improve Seismic Source Parameter Determination/Event Location Accuracy

Lithospheric Models of the Middle East to Improve Seismic Source Parameter Determination/Event Location Accuracy

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