INVESTIGATION OF THE MAULE, CHILE RUPTURE ZONE USING SEISMIC ATTENUATION TOMOGRAPHY AND SHEAR WAVE SPLITTING METHODS By MEGAN ELIZABETH TORPEY A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2016 © 2016 Megan Elizabeth Torpey To my family, for always being there for me and supporting me throughout this journey ACKNOWLEDGMENTS I would first like to express my appreciation to my advisor, Raymond Russo, who provided me with amazing opportunities throughout my graduate career. I am also thankful for his guidance and motivation in my research projects, without which it would not have been possible for me to succeed. I would like to thank my committee members Mark Panning, David Foster, Liz Screaton, James Channell, Tim Olson, and Jean Larson, who all helped me to better understand my research projects. Additionally, I would like to thank Sebastien Chevrot for hosting me at the Observatoire Midi-Pyrenees in Toulouse, France and guiding my research as part of the Chateaubriand Fellowship. I would also like to thank my fellow “seismo” group members, Christian Stanciu, Paul Bremner, Sutatcha Hongsresawat, Stephanie James, Matt Farrell, and Emily Rodriguez who were always willing to lend a helping hand, whether it was during fieldwork or in the office. I would like to especially thank the office staff of the UF Department of Geological Sciences, Pamela Haines, Nita Fahm, and Carrie Williams who made it possible for me to remain on track with academic paperwork. And lastly, I would like to thank the National Science Foundation for funding this grant (EAR-1045609). 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 7 LIST OF FIGURES .......................................................................................................... 8 LIST OF ABBREVIATIONS ........................................................................................... 11 ABSTRACT ................................................................................................................... 12 CHAPTER 1 INTRODUCTION .................................................................................................... 14 1.1 Motivation for the Project .................................................................................. 14 1.2 2010 Mw 8.8 Maule, Chile Earthquake .............................................................. 16 1.3 Tectonic Setting ................................................................................................ 18 1.3.1 Tectonic Overview ................................................................................... 18 1.3.2 Convergence Rate and Nazca Age ......................................................... 20 1.3.3 Subduction Dip ........................................................................................ 20 1.3.4 Bathymetric Features .............................................................................. 22 1.3.5 Crustal Shortening ................................................................................... 23 1.3.6 Maule Rupture Zone ................................................................................ 23 2 SEISMIC ATTENUATION WITHIN THE MAULE, CHILE RUPTURE ZONE .......... 32 2.1 Introduction ....................................................................................................... 32 2.2 Seismic Attenuation Background ...................................................................... 36 2.3 Data and Methods............................................................................................. 38 2.4 Results .............................................................................................................. 44 2.5 Model Resolution .............................................................................................. 45 2.6 Discussion ........................................................................................................ 46 2.6.1 Large-Scale Subduction Structures ......................................................... 46 2.6.2 High-Qs Bodies at the Surface ................................................................. 47 2.6.3 Cobquecura Anomaly .............................................................................. 48 2.7 Conclusion ........................................................................................................ 51 3 SHEAR WAVE SPLITTING OF TELESEISMIC EVENTS ....................................... 81 3.1 Background ....................................................................................................... 81 3.2 Previous Teleseismic Shear Wave Splitting Studies in South America............. 81 3.3 Data and Methods............................................................................................. 84 3.4 Results .............................................................................................................. 88 3.5 Discussion ........................................................................................................ 88 5 3.5.1 Time Delay .............................................................................................. 88 3.5.2 Contributions from Crustal Anisotropy ..................................................... 89 3.5.3 Fossilized Lithospheric Fabrics ............................................................... 89 3.5.4 Trench Parallel Splitting and Sub-Slab Mantle Flow ................................ 90 3.5.5 Alignment with Nazca Slab Depth Contours ............................................ 91 3.6 Conclusion ........................................................................................................ 92 4 SHEAR WAVE SPLITTING OF MAULE AFTERSHOCKS ................................... 104 4.1 Background ..................................................................................................... 104 4.2 Data and Methods........................................................................................... 104 4.3 Results ............................................................................................................ 106 4.4 Discussion ...................................................................................................... 106 4.4.1 Supra-slab Entrained Mantle Flow ........................................................ 107 4.4.2 Contributions from Crustal Anisotropy ................................................... 107 4.4.3 Lateral Mantle Flow in the Forearc ........................................................ 110 4.4.4 Robustness of Multichannel Analysis Method for Local Datasets ......... 110 4.4.5 Comparison to Teleseismic Dataset ...................................................... 111 4.6 Conclusion ...................................................................................................... 112 5 SUMMARY AND CONCLUSIONS ........................................................................ 122 APPENDIX A SEISMIC ATTENUATION THEORY ..................................................................... 127 A.1 Sources of Attenuation ................................................................................... 127 A.2 Quantifying Attenuation .................................................................................. 127 B ANISOTROPY AND SHEAR WAVE SPLITTING THEORY .................................. 130 LIST OF REFERENCES ............................................................................................. 134 BIOGRAPHICAL SKETCH .......................................................................................... 151 6 LIST OF TABLES Table page 3-1 Teleseismic event locations ................................................................................ 94 3-2 Teleseismic splitting measurements ................................................................... 95 4-1 Local event locations ........................................................................................ 113 4-2 Local splitting measurements ........................................................................... 116 7 LIST OF FIGURES Figure page 1-1 Historic earthquakes from Hayes et al. (2013).................................................... 26 1-2 IRIS CHAMP temporary broadband seismic network. ........................................ 27 1-3 CHAMP stations with alphanumeric labels ......................................................... 28 1-4 From Kroner and Stern (2005), map of Gondwana at the end of the Neoproterozoic (~540 Ma) showing the arrangement of Pan-African belts.. ...... 29 1-5 Modified from Ramos (1988), terranes accreted to Southern South America and South American cratonic regions. ................................................................ 30 1-6 Modified from Hicks et al. (2014), the large-scale geologic units of the Maule rupture zone (33°S-38°S). .................................................................................. 31 2-1 Main morphostructural units in study area. ......................................................... 53 2-2 The P, S, and pre-signal noise windows are shown to demonstrate the evolving time window method for the April 5, 2010 seismic recording ................ 54 2-3 Illustration of the evolving time window method.