Earthquake Frequency - Magnitude Distribution and Interface Locking at the Middle

ACKNOWLEDGEMENTS I would like to thank my primary advisor Dr. Andrew V. Newman for providing his excellent guidance and scientific insight throughout the study. I am thankful to Dr. for their thoughtful advice and suggestions. I am grateful to Dr. Tapas Bhattacharyya for the stimulating discussions and his support. I would also like to thank numerous prior and recent earthquake analysts, including Research Foundation supported this study. I would like to express my gratitude to my family members, including my fiancée Deblina Datta, for their continuing support. Figure 1: The oceanic Cocos plate subducting beneath the continental Caribbean plate along the MAT at a rate of ~85 mm/yr (DeMets, 2001) near Nicoya. Notice the rough bathymetry near Cocos Ridge off Nicoya Peninsula, Figure 2: Map of the Nicoya Peninsula, Costa Rica with low error (within 5 km horizontal error) earthquakes (solid squares) recorded between late-1999 to early-2001 as a part of the CRSEIZE project. Open diamonds indicates the location of the seismic stations. Saw-toothed curve represents the Middle America Trench. Dashed box is boundary of grid used for subsequent b-value results. [Inset] map of the region with present study area in smaller black box…………………………………………………. 4 Figure 3: Tectonic map of the study area and its surrounding region. Lines with numbers represent isochrones with ages derived from magnetic anomalies. Triangles are volcanoes. FS, Fisher Seamount; QSC, Quesada Sharp Contortion. (after Barckhausen et al., 2001)………………………………………….. 7 Figure 4: Frequency−magnitude distributions for pure normal (green) and pure thrust (blue) events of the SCSN and Harvard catalogues (Schorlemmer et al., 2005)…………………………………………. 12 Figure 5: The best fit model for locking along the subduction interface near Nicoya Peninsula using GPS data between 1994 and 2000 (Norabuena et al., 2004). Locking had been modeled as locked slip. Note the elliptical highly locked patch just offshore Nicoya. The near trench updip region which appears weakly locked is poorly constrained due to lack of data in that Figure 6: A screenshot of the Antelope program. 'dbpick' window is showing waveform and manually picked first P-and S-wave arrivals………………………………………………………………… 19 Figure 7: Magnitude comparison between ANSS catalog and Nicoya2000 catalog. Solid straight line is the best fit line (slope = 0.71) between magnitudes reported in two catalogs. v Figure 8: Vertical cross-section of low error CRSEIZE seismicity (open circles). Solid circles represent events defining subduction zone seismicity. Only these events are considered for the frequency-magnitude distribution in this study………………………………... 23 …