Seismicity Reveals Clear Segmentation and Differences in Coupling along the Costa Rica Subduction Zone Marino Protti and Víctor González Observatorio Vulcanológico y Sismológico de.
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Seismicity Reveals Clear Segmentation and Differences in Coupling along the Costa Rica Subduction Zone Marino Protti and Víctor González Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA) Susan Schwartz University of California, Santa Cruz Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Other Lords of this International Cartel: Daniel Sampson, University of California, Santa Cruz Timothy Dixon and Kim Psencik, University of Miami Teruyuki Kato, Tokyo University Yoshiyuki Kaneda, IFREE-JAMSTEC Geoff Abers, Columbia University Karen Fisher, Brown University Andy Newman, Georgia Tech. Gerry Simila. California State University at Nortridge Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Agenda Tectonic setting of Central America Geometry of the Wadati-Benioff Zone Characteristics of the subducting plate Segmentation of the subduction zone in Costa Rica The Nicoya network Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Tectonic setting of Central America Tectonic Setting of Costa Rica Nicaragua 1992 .. 11o Hess Escarpment Nicaragua-Papagayo segment Costa Caribbean Rica Sea 1916 1900 1853 10 o Nicoya segment 9o Limon 1939 1950 Panama Thrust Belt 1990 1991 ODP Leg 170 Pacific Ocean 1916 Cobano-Herradura segment Middle American Trench North American Plate 1916 Quepos-Sierpe segment 1941 1904 Panama Osa-Burica1983 segment 8o Caribbean Plate Cocos Plate Panama Block 87 o Cocos Ridge ? Nazca Plate 86 o Panama Fracture Zone 100 km 85 o 84 o 83 o 82o Seismicity and sections across Costa Rica Nicaragua vs S Costa Rica Subduction of the Cocos Ridge Age of the Oceanic Cocos Plate From Barckhausen Tectonic Setting of Costa Rica Nicaragua 1992 .. 11o Hess Escarpment Nicaragua-Papagayo segment Costa Caribbean Rica Sea 1916 1900 1853 10 o Nicoya segment 9o Limon 1939 1950 Panama Thrust Belt 1990 1991 ODP Leg 170 Pacific Ocean 1916 Cobano-Herradura segment Middle American Trench North American Plate 1916 Quepos-Sierpe segment 1941 1904 Panama Osa-Burica1983 segment 8o Caribbean Plate Cocos Plate Panama Block 87 o Cocos Ridge ? Nazca Plate 86 o Panama Fracture Zone 100 km 85 o 84 o 83 o 82o NICARAGUA-PAPAGAYO SEGMENT Low degree of coupling. Earthquakes on this segment are very frequent and of moderate size (several events per year with Mw ≥ 5.2); large events here have slow rupture velocities. Relatively old and smooth subducting plate. Steep angle of Wadati-Benioff zone Earthquakes of different sizes in 1750, 1840, 1844, 1863, 1881, 1889, 1901, 1916, 1921, 1956 and 1992. NICOYA SEGMENT Relatively old and smooth subducting plate. Steep angle of Wadati-Benioff zone. The Nicoya peninsula in this segment applies an important lithostatic load on the plate interface increasing the normal stress and therefore the coupling between the plates. Large earthquakes and low background seismicity level during the interseismic periods. Large earthquakes have occurred here in 1826, 1853, 1900 and 1950. CÓBANO-HERRADURA AND QUEPOS-SIERPE SEGMENTS Young and rough plate with small seamounts. When subducting, seamounts reduce the coupling area to small asperities that rupture frequently with moderate size events. The Cóbano-Herradura segment produced earthquakes of Mw~7 in 1882, 1939 and 1990. The Quepos-Sierpe is the weakest and generates only earthquakes with Mw<7; some of these occurred in 1940, 1941, 1952, 1974, 1982, 1990, 1996 and 1999. These two segments fail every time the neighboring segments of Nicoya to the NE and Osa-Burica to the SE, break with earthquakes of Mw>7; These segments tend to break with duplets, like the August September, 1996 and the August, 1999, pairs. OSA SEGMENT Very young and thick subducting lithosphere (the Cocos ridge). The buoyant effect of both, young lithosphere and the Cocos ridge, increases the coupling along the plate interface; the lithostatic weight of the Osa peninsula also helps increase this coupling. For these reasons this segment is capable to generate large (Mw>7) earthquakes: 1867, 1904, 1941 and 1983. The Nicoya Seismic Gap Nicaragua 1992 .. 11o Hess Escarpment Nicaragua-Papagayo segment Costa Caribbean Rica Sea 1916 1900 1853 10 o Nicoya segment 9o Limon 1939 1950 Panama Thrust Belt 1990 1991 ODP Leg 170 Pacific Ocean 1916 Cobano-Herradura segment Middle American Trench North American Plate 1916 Quepos-Sierpe segment 1941 1904 Panama Osa-Burica1983 segment 8o Caribbean Plate Cocos Plate Panama Block 87 o Cocos Ridge ? Nazca Plate 86 o Panama Fracture Zone 100 km 85 o 84 o 83 o 82o Kona, Hawaii, junio 1997 La Jolla, California, junio 1998 Nicoya Costa Rica-Nicaragua Nankai Izu-Bonín-Marianas NICOYA and NANKAI Why so much interest in the Nicoya Peninsula? It is the seismogenic region that generates the largest earthquakes in Costa Rica. It has been 58 years since its last rupture (1853, 1900 and 1950). The peninsula is sitting right over the seismogenic zone. It has been studied for many years with different techniques (high resolution marine seismics, refraction profiles, scan mapping, an ALVIN cruise, ODP legs, broadband off-shore and on shore seismic networks, GPS, electronic tiltmeters). The recorded deformation rates are very high. It is part of the target region of both, the Seismogenic Zone Experiment (SEIZE) and the Subduction Factory (SUBFAC) initiatives of MARGINS. Sámara, May 2008 benchmark seawall ¿Drainage? Almond trees FUTURE CGPS NETWORK 50 km Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Education and Social impact (just a few examples) Talks in towns and local government. Keep the media informed (documentaries). Science text books for junior-high schools in Costa Rica have a section on the MARGINS-SEIZE initiative. All of the above retrofit the project by having people interested in having a monitoring site on their property. Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Nicoya is not just an effort to monitor a seismic gap (nobody will buy it for funding!) It is a geographical and temporal opportunity to record data in the near field for the understanding of subduction processes (i.e. location and factors that control the upper and lower limits of the seismogenic zone, record and study pre-seismic deformation, quantify the elastic locking, observe slow slip motion and address other fundamental questions we still have from subduction zones). There is still something missing in Nicoya: Drilling for monitoring the updip portion of the seismogenic zone Why Nicoya? IT GENERATES LARGE EARTHQUAKES SHORT RECURRENCE TIMES CLOSE TO FAILURE FAST DEFORMATION RATES POLITICALLY EASY LOTS OF DATA AVAILABLE SLOW EARTHQUAKES AND TREMOR LAND CLOSE BY FOR LOGISTICS AND DATA LINKS THE SEISMOGENIC ZONE IS REACHABLE BY DRILLING TWO WAYS AND TIMES YOU CAN DO IT: Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA NOW AND CHEAP NON-RISER HOLES WITH IN SITU RECORDING SYSTEMS Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA LATER AND WITH MORE RESOURCES CHIKIU AND DRILLING UNDERWATER CABLE NETWORKS Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA CONCLUSIONS Subduction, under Nicaragua and Costa Rica, of Cocos plate lithosphere with different genesis and geomorphic features produces important changes along the plate interface. We have divided the subduction zone in southern Central America in five segments, based on features on the subducting plate and on differences in seismicity patterns both, historical as well as instrumental. Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA ONE MORE CONCLUSION The Nicoya monitoring network is the result of a successful collaboration effort between Costa Rica, the US and Japan. It is a network for science: earthquake locations, tectonic tremor, receiver functions, focal mechanisms, seismic tomography and hopefully to capture the rupture history and post-seismic deformation of the next Nicoya earthquake. Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA Tectonic Setting of Costa Rica Nicaragua 1992 .. 11o Hess Escarpment Nicaragua-Papagayo segment Costa Caribbean Rica Sea 1916 1900 1853 10 o Nicoya segment 9o Limon 1939 1950 Panama Thrust Belt 1990 1991 ODP Leg 170 Pacific Ocean 1916 Cobano-Herradura segment Middle American Trench North American Plate 1916 Quepos-Sierpe segment 1941 1904 Panama Osa-Burica1983 segment 8o Caribbean Plate Cocos Plate Panama Block 87 o Cocos Ridge ? Nazca Plate 86 o Panama Fracture Zone 100 km 85 o 84 o 83 o 82o What is next? (at least for me) Post-seismic deformation in Nicoya once it ruptures. Move down to Osa peninsula (1904, 1941, 1983, 2021-4?) (I will not retire until 2025!) Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA MUCHAS GRACIAS PAZ SOBRE LA TIERRA Observatorio Vulcanológico y Sismológico de Costa Rica - OVSICORI-UNA