Dr. Jeff Marshall
Undergraduate Research Advising



Fookgiin (Jonathan) Khaw

Research Project:

Active tectonics and Quaternary marine terraces along a convergent margin coastline, Northern Nicoya Peninsula, Costa Rica


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Jonathan Khaw and Julie Parra walking on the beach near an uplifted carbonate-cemented beachrock horizon dated at 1610 ybp (radiocarbon). The uplifted Pleistocene Iguanazul marine terrace (12 m above MSL) is visible in the background, Playa Negra (Pochotes), Nicoya Peninsula, Costa Rica (March 2003)

Jonathan Khaw presenting a research poster on coastal tectonics of Costa Rica’s Nicoya Peninsula, Southern California Conference on Undergraduate Research (SCCUR), University of California, Irvine  (November 2003).


Images:  Project photos and illustrations


Project Overview:

Jonathan’s research investigated uplifted Quaternary marine terraces along the northern Pacific coast of Costa Rica. In March 2003, he traveled to Costa Rica with Dr. Marshall, and fellow students Julie Parra and Lauren Annis, for 10 days of fieldwork on the Nicoya Peninsula, an emergent segment of the Middle America fore arc. The goal of this fieldwork was to investigate uplifted Quaternary marine terraces located along the northern Nicoya Peninsula coastline, between Playa Tamarindo and Playa Junquillal. Three Pleistocene marine terraces were identified within a 3-4 km wide, low-relief coastal surface (Iguanazul surface). Terrace treads were mapped and surveyed in the field using topographic maps, aerial photographs, hand-held GPS, and differential barometric altimetry. Topographic profiles were generated for the terrace flights, and uplift rates were determined using standard sea-level curve correlations. In addition, we mapped and sampled uplifted Holocene beachrock horizons (carbonate-cemented beach sand deposits) along the seaward edge of the Pleistocene terraces. Radiocarbon ages for these deposits yielded short-term constraints on Holocene uplift rates.

Tectonic uplift of the Nicoya Peninsula occurs in response to rapid subduction of the Cocos oceanic plate at the Middle America Trench (9 cm/yr). 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) occurred on October 5, 1950 causing 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.

Jonathan presented preliminary research results in co-written abstracts and posters at the 2003 Geological Society of America Annual Meeting in Seattle, Washington, at the 2003 Southern California Conference on Undergraduate Research at U.C. Irvine, and at the 2004 Geological Society of America Cordilleran Section Meeting in Boise, Idaho.


Research Abstracts:

2004 GSA Cordilleran Meeting Abstract: Geological Society of America Cordilleran Section Meeting, Boise, Idaho, 2004

2003 SCCUR Abstract: 11th Annual Southern California Conference on Undergraduate Research, University of California, Irvine, 2003

2003 GSA Annual Meeting Abstract: Geological Society of America Annual Meeting, Seattle, Washington, 2003


Senior Thesis:

Khaw, F., in progress, Active Tectonics and Quaternary marine terraces along a convergent margin coastline, northern Nicoya Peninsula, Costa Rica: [B.S. Thesis] Cal Poly Pomona University, Pomona, California.


Honors and Awards:

·       Margaret Van Buskirk Scholarship (2004): Geological Sciences Department, Cal Poly Pomona University