Dr. Jeff Marshall
Undergraduate Research Advising

 

Student:

Eli LaFromboise

Research Project:

Variations in subduction related coastal uplift along the Nicoya Peninsula seismic gap, Costa Rica

 

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Eli LaFromboise and John Utick collecting beach sand samples, Playa Negra, Nicoya Peninsula, Costa Rica (March 2005)

Eli LaFromboise examining uplifted Quaternary alluvial fan deposits, Morote Valley, Nicoya Peninsula, Costa Rica (January 2007).

Eli LaFromboise presenting a research poster on coastal tectonics of Costa Rica’s Nicoya Peninsula, Council on Undergraduate Research (CUR) poster session, Geological Society of America Cordilleran Section Meeting, Anchorage, Alaska  (May 2006).

 

Images:  Project photos and illustrations

 

Project Overview:

Eli’s research examines differences in tectonic uplift rates for Quaternary marine terraces along two coastal segments of Costa Rica’s Nicoya Peninsula. Tectonic uplift of this fore arc peninsula occurs in response to rapid subduction of the Cocos oceanic plate at the Middle America Trench (9 cm/yr), 60 km offshore. The Nicoya Peninsula is recognized as a high-potential seismic gap with an estimated 50-year recurrence interval for large earthquakes (>M 7.5). The last major event (M 7.7) on October 5, 1950 caused widespread damage, liquefaction, landslides, and a local tsunami. This earthquake also generated 1-2 m of coseismic uplift along the peninsula’s central coastline. Much of this coseismic uplift has been recovered by subsequent interseismic subsidence, yet emergent marine terraces along the peninsula’s coastline attest to long-term net uplift.

In March 2005, Eli traveled to Costa Rica with Dr. Marshall and fellow student John Utick, for 10 days of fieldwork on the Nicoya Peninsula. The students worked together on two distinct, but related research projects: 1) Eli’s research on marine terrace uplift, and 2) John’s study of beach morphology and sedimentology.

Eli’s fieldwork focused on two different flights of Quaternary marine terraces: 1) the low-relief Iguanazul terrace sequence between Tamarindo and Nosara on the northern Nicoya coast, and 2) the high-relief Cobano terrace sequence near Cabo Blanco at the peninsula’s southern tip. The goal of this project was to investigate differences in coastal uplift patterns between these two areas, and to evaluate how these differences might relate to contrasts in subducting plate morphology and the geometry of the underlying seismogenic zone. Marine terrace surfaces were mapped and surveyed in the field using topographic maps, aerial photographs, hand-held GPS, and differential barometric altimetry. Age constraints were established based on prior radiometric dating of terrace deposits (radiocarbon and OSL). Topographic profiles were generated for the terrace flights, and uplift rates were determined using standard sea-level curve correlations. The results were evaluated with respect to known variations in subduction zone characteristics along the Nicoya Peninsula seismic gap.

Eli and John presented preliminary research results in co-written abstracts and posters at the 2005 Geological Society of America Annual Meeting in Salt Lake City, Utah, and at the 2006 Geological Society of America Cordilleran Section Meeting in Anchorage, Alaska.

 

Research Abstracts:

2006 GSA Cordilleran Meeting Abstract: Geological Society of America Cordilleran Section Meeting, Anchorage, Alaska, 2006

2005 GSA Annual Meeting Abstract: Geological Society of America Annual Meeting, Salt Lake City, Utah, 2005

 

Senior Thesis:

LaFromboise, E., 2006, Variations in subduction related coastal uplift along the Nicoya Peninsula seismic gap, Costa Rica: [B.S. Thesis] Cal Poly Pomona University, Pomona, California.

 

Honors and Awards:

·       Ernest Prete Jr. Scholarship (2005): Geological Sciences Department, Cal Poly Pomona University