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Seismic Tomography and Surface Deformation in Krfsuvik, SW Iceland by Jing Liu B.S

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Seismic Tomography and Surface Deformation in Krfsuvik, SW Iceland by Jing Liu B.S Seismic Tomography and Surface Deformation in Krfsuvik, SW Iceland by Jing Liu B.S. Geophysics, China University of Geosciences (Wuhan), 2008 Submitted to the Department of Earth, Atmospheric, and Planetary Sciences in Partial Fulfillment of the Requirements for the Degree ACHUES of INS1W Master of Science in Geophysics MSSACHUSMOF TECHNOLOGY at the MAR 0 3 2014 Massachusetts Institute of Technology LIBRARIES February 2014 C 2014 Massachusetts Institute of Technology. All rights reserved. Signature of Author ................... ............................................... Department of Earth, Atmospheric, and Planetary Sciences November. 21, 2013 C ertified by ........ ............................................ Michael C. Fehler Senior Research Scientist-Earth Resources Laboratory Thesis Supervisor /7 J & Certified by. ................................................. Bradford H. Hager Cecil & Ida Green Pro r, Director of Earth Resources Laboratory Thesis Co-Supervisor 7 Accepted by Y Rob Van der Hilst Schlumberger Professor Head, Department of Earth, Atmospheric and Planetary Sciences Seismic Tomography and Surface Deformation in Krfsuvik, SW Iceland by Jing Liu Submitted to the Department of Earth, Atmospheric, and Planetary Sciences On November 21, 2013, in partial fulfillment of the requirements for the Degree of Master of Science in Geophysics Abstract The Krfsuvik region of southwestern Iceland is a region of high potential for geothermal energy that is currently experiencing seismic swarm activity and active surface deformation. Understanding the subsurface structure of the area is of great scientific and practical significance. Using permanent and temporary seismic stations deployed in the region, we captured an earthquake swarm from Nov. 2010 to Feb. 2011 clustered around the center of the Krfsuvik volcanic system. We studied the seismicity and Vp, Vs and Vp/Vs ratio in this region by applying double difference tomography. Our tomography result indicates a low velocity zone at a depth of about 6 kin, directly beneath the earthquake swarm. At the same time, our relocation result delineates strike-slip and dip- slip faults above and around this low velocity zone. Brittle-ductile transition is delineated based on the distribution of the earthquakes in this area. In order to understand the relation between the subsurface structure and the surface deformation, we modeled surface deformation using the input parameters constrained from our tomography results. We found that the main deformation is well captured by a pressure source yielding a volume expansion of about 30x 106 m 3 at the depth of about 6 km, centered on the low velocity zone detected in tomography. And the secondary deformation could be explained by the normal and the right-lateral slip faults, whose patterns are delineated by the earthquake relocations. The combination of the local stress caused by the expanding source and regional stress that yields a combination of left-lateral shear and extension might have triggered the earthquakes. Based on the low Vp, Vs and possibly high Vp/Vs ratio at depth of ~6 km and its expanding property, the possibilities of supercritical water, H2 0-rich partial melting with magma intrusion are discussed. The results of this thesis provide new insights to understand the seismicity and surface deformation in volcanic zones as well as provided important reference in exploration of new geothermal areas. Thesis Supervisors: Michael C. Fehler . Title: Senior Research Scientisph- EarthResouycpe Laboratory Bradford H. Hager Title: Cecil & Ida Green Professor, birector of Earth Resources Laboratory 2 Acknowledgements I would like to thank the people for their help towards the completion of this thesis during my two years of studying in the Earth Resource Laboratory at MIT. First of all, I would like to thank my advisor, Dr. Michael Fehler for his support and guidance throughout my study at MIT. I always feel lucky to meet and work with such a reputable scientist as Dr. Fehler who offered me the chance to enter MIT as well as the field of geophysics. I would also like to thank Prof. Brad Hager for his fruitful and patient suggestions regarding my current as well as future work. I would like to acknowledge the people in Earth Resource Laboratory (Micheal Fehler, Bradford Hager, Maria Zuber, Robert van der Hilst, Alison Malcolm, Anna Shaughnessy, Haijiang Zhang, Yingcai Zheng, Xingding Fang, Qin Cao, Hui Huang, Xuefeng Shang, Chunquan Yu, Di Yang, Haoyue Wang, Lucas Willemsen, Alan Richardson) for many helpful comments and exposure to different aspects of the seismology and geodynamics problems in my work. I would also like to thank my husband, Rong, for his support during difficult times. This work was funded by US DOE, Iceland GEORG Program, Iceland & Swedish National Science Foundations. 3 Contents Chapter 1................................................................................................................................. 8 Introduction.............................................................................................................................. 9 1.1 Plate Boundary of Iceland .......................................................................................... 9 1.2 Reykjanes Peninsula, SW Iceland .................................................................................. 10 1.3 Previous Study of Seismicity, Deformation and Structure in Krfsuvik........12 1.4 Surface Manifestations of Krysuvik Geotherm al Field ....................................... 15 1.5 Our Study of the Krf'suvik Geotherm al Field ............................... ...................... 16 Chapter 2 .................................................. ......................................................................... 19 Seism ic Event Relocation and Tom ography............................................................. 19 2.1 Seism ic Data and Stations ............................................................................................. 19 2.2 Theory of Event Relocation and Tom ography...................................................... 21 2.3 Results of Event Relocation and Tom ography...................................................... 22 2.3.1 Travel times used in this study.......................................................................................... 22 2.3.2 Event Relocation Results ........................................................................................................... 23 2.3.3 Checkerboard Test ....................................................................................................................... 26 2.3.4 Tom ography Results.................................................................................................................... 31 Chapter 3 .................................... ................................. ...... ............................. 36 Surface Deform ation Observation and M odeling................................................... 36 3.1 Geodetic Observation ..................................................................................................... 36 3.2 Surface Deform ation Modeling................................................................................... 40 Chapter 4 ............................................................................................................................... 45 Discussion..... ............................................ ........ .................. ..................... 45 4.1 Brittle-ductile Transition ................... ............................. ..................................... 45 4.2 Possibilities of the low velocity zone..................................................................... 48 Chapter 5 . ........................ ... ............................................. ............................. 54 Conclusion .......................................... ............... ........................................................... 54 Appendix A .......................... ................................................................................ 56 Geotherm al M anifestation in Krysuvik..................................................................... 56 Appendix B ..................................................................... ..................................................... 57 GPS m easurem ents in Krysuvik ................................................................................... 57 References ......................... .... ................... ... ............ ..... ........................... 59 4 List of Figures Figure 1-1: Iceland plate boundary. (Hjaltadottir, 2010). Fissure swarms are shown as grey areas and central volcanoes enclosed with grey, thin circles. The black dotted lines are the transform zones. HM: Hreppar micro-plate................. 10 Figure 1-2: Tectonic map of Reykjanes Peninsula and its location in SW Iceland (inset). The blue lines are the plate boundary (solid-axial rifts, long dashed line-propagating rift, dotted line-fracture zones). The hatched areas indicate the high-temperature geothermal fields. Fissure swarms are shown as grey areas in the inset, along the NE-SW direction. RR, Reykjanes Ridge; H, Hengill volcano zone; WVZ, west Volcanic Zone; SISZ, South Iceland Seismic Zone. M odified after Keiding et al., (2009) ................................................ 12 Figure 1-3: Historical earthquakes in Krfsuvik from 1997 to 2006 (Keiding et al., 2009). The two stars indicated the
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