UTIG RESEARCH PROJECTS ARCHIVE

Field Reports from the cruise

Funding agency: National Science Foundation MARGINS Program (Award# OCE-9905355)

Research Cruise to Costa Rica Aboard the R/V Ewing.
Check out the processed seismic data!

Foreign Collaborators:

Ernst Flueh	GEOMAR, Kiel, Germany
Christian Walther	GEOMAR, Kiel, Germany
Cesar Ranero	GEOMAR, Kiel, Germany
Roland von Huene	GEOMAR, Kiel, Germany
Wilfried Strauch	INETER, Managua, Nicaragua
Stephan Husen	ETH Zurich, Switzerland

The participant list on the R/V Ewing is:

Kirk McIntosh	UTIG
Kevin Johnson	UTIG
Imtiaz Ahmed	UTIG
Junru Jiao	UTIG
Timothy (Tip) Meckel	UTIG
Eli Silver	UCSC
Tony Ramirez	UCSC
Barrie Taylor	Landmark
Christian Walther	GEOMAR
Cesar Ranero	GEOMAR
Arnim Berhors	GEOMAR
Carlos Guzmán	INETER
Robyn Kelly	WHOI

In addition, Jim Dolan (UTIG) will operate 8 instruments onshore during part of the shooting. He will work with Wilfried Strauch (INETER) on this and will be joined by Stephan Husen (ETH Zurich) with 8 additional instruments.

Project Summary:
Around the world there is tremendous variation in seismogenic character of convergent margins and in the geochemical character of the associated volcanic arcs. This may be expected due to the wide range of upper and lower plate composition and thickness and variation of subduction parameters such as slab age and convergence rate. Because arc geochemistry and seismogenic patterns associated with the subduction system of Nicaragua and Costa Rica show along-strike variations comparable to those worldwide, we propose to investigate the nature of this variability along this margin with a single subducting plate and gradually changing subduction parameters (Figure 1). The Costa Rica segment of the margin has been well studied by seismic reflection and refraction techniques, swath bathymetry, and ODP drilling on Leg 170, but in contrast, the Nicaragua margin is poorly studied. Only one MCS profile is present on the Nicaraguan trench slope and a single block of swath bathymetry has been collected (Figure 2). The sparse data we presently have suggest that structural and stratigraphic differences are a significant reason why these two margins develop such different subduction processes. For example, fault block rotation on the subducting plate may lead to particularly efficient sediment subduction and may also enhance the tsunamigenic potential of the Nicaraguan margin segment (Figure 3). However the extent of this type of basement structure, as well as the importance other factors, is unknown due to lack of data. Thus, we plan to acquire, process, and interpret an extensive MCS survey supplemented with three selected refraction profiles and additional Hydrosweep swath bathymetry. We will use these data to document variations in the subducting Cocos plate structure and stratigraphy and the effects of these variations on the upper (Caribbean) plate. Ultimately these data will help identify how factors, such as Cocos plate fault block rotation, fault throw, and stratigraphy affect structural deformation styles in the upper plate that control sediment accretion, subduction, or erosion, processes which are critical to gradients in arc geochemistry (Figure 4) and seismogenic characteristics.

This project will directly support many goals of the Subduction Factory Initiative of the MARGINS program in Central America. In particular, we will document sediment fluxes into the system, we have a good chance to identify accretionary or erosional processes at shallow depths, and we hope to identify factors influencing the efficiency of sediment subduction. Similarly, our investigation of the Cocos Plate, its interaction with the upper plate (especially the plate boundary fault zone), and determination of margin velocity structure will directly benefit the SEIZE Initiative (Seismogenic Zone Experiment). The science plans of both these initiatives picked Costa Rica/Nicaragua as a highest priority area and call for extensive seismic reflection and refraction surveying to provide the critical framework for subsequent interdisciplinary investigations.

This project will involve international collaboration with scientists from Nicaragua and Germany and it will build on ongoing programs in the area. A German research vessel, R/V Sonne, was in this area in fall 1999 to investigate crustal thickness variations of the Cocos plate along the Costa Rica segment and crustal structure of the Nicaraguan forearc near the coast. Kirk McIntosh participated in that project and is working with a portion of the refraction data acquired. The work we propose here is complementary to this ongoing work, and, with the planned MCS and OBH data, provides the key elements for further interdisciplinary research.