Earthquake Frequency-Magnitude Distribution and Interface Locking at the Middle America Subduction Zone near Nicoya Peninsula, Costa Rica

dc.contributor.advisor Newman, Andrew V.
dc.contributor.author Ghosh, Abhijit en_US
dc.contributor.committeeMember Dominic Assimaki
dc.contributor.committeeMember Peng, Zhigang
dc.contributor.department Earth and Atmospheric Sciences en_US
dc.date.accessioned 2007-08-16T17:58:10Z
dc.date.available 2007-08-16T17:58:10Z
dc.date.issued 2007-06-21 en_US
dc.description.abstract Subduction zone megathrusts produce the majority of the world's largest earthquakes. To understand the processes that control seismicity here, it is important to improve our knowledge on the subduction interface characteristics and its spatial variations. Nicoya Peninsula, Costa Rica, extends the continental landmass ~50 km towards the trench, making it a very suitable place to study interface activity from right on the top of the seismogenic zone of the Middle America Subduction Zone (MASZ). We contribute to and utilize an earthquake catalog of 8765 analyst-picked events to determine the spatial variability in the earthquake frequency-magnitude distribution (FMD) in this region. After initial detection, magnitude determination and location, the events are precisely relocated using a locally derived 3-D seismic compressional and shear wave velocity model (DeShon et al., 2006). After restricting the dataset to events nearest the interface and with low formal error (horizontal location error < 5 km), we retain a subset of 3226 events that best resolves interface activity. Beneath Nicoya, we determine the spatial variability and mean FMD of the interface, and focus on the relative relationship of small-to-large earthquakes, termed b-value. Across the region, the overall b-value (1.18 ± 0.04) is higher than the global average (b~1), and much larger than the global subduction zone average (b~0.6). Significant variation in b-value is observed along the active plate interface. A well resolved zone of lower b is observed at and offshore central Nicoya coast, in a previously determined locked patch using deformation observed from Global Positioning System (GPS). Conversely, high b-values prevail over the subducted portion of the Fisher ridge, which likely ruptured in the 1990 Gulf of Nicoya Mw 7.0 earthquake. Observed regions of low b-value approximately corresponds to more strongly-locked segments of the subduction interface resulting in higher differential stress, which may be released in the next large interface earthquake in this part of the MASZ. Across the region the b-value is found to vary inversely with the degree of interface locking. Thus, it is proposed that if sufficient data exist, spatial b-value mapping can be used as a proxy to determine interface locking. This method is especially useful along the subduction megathrust, which is generally offshore making geodetic measurements difficult. en_US
dc.description.degree M.S. en_US
dc.identifier.uri http://hdl.handle.net/1853/16288
dc.publisher Georgia Institute of Technology en_US
dc.subject Middle America Subduction Zone en_US
dc.subject Middle America Trench en_US
dc.subject Nicoya en_US
dc.subject Earthquake en_US
dc.subject Frequency-magnitude distribution en_US
dc.subject B-value en_US
dc.subject Interface locking en_US
dc.title Earthquake Frequency-Magnitude Distribution and Interface Locking at the Middle America Subduction Zone near Nicoya Peninsula, Costa Rica en_US
dc.type Text
dc.type.genre Thesis
dspace.entity.type Publication
local.contributor.advisor Newman, Andrew V.
local.contributor.corporatename School of Earth and Atmospheric Sciences
local.contributor.corporatename College of Sciences
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relation.isOrgUnitOfPublication 85042be6-2d68-4e07-b384-e1f908fae48a
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