G021-0014
Mid-Holocene sea-level and paleoseismic histories in Badoc, Ilocos Norte, Philippines

Wednesday, 16 December 2020
Poster
Xinnan Li1, Joanne TY Lim1, Anandh Gopal1, Andrew Paul Mitchell1, Gina Muthia Sarkawi1,2, Aron J Meltzner1,2, Loraine Faye Sarmiento3, Junki Komori4, Kathrine Valdez Maxwell1, Jennifer Weil-Accardo1, Tsai-Luen Yu5, Hsun-Ming Hu6, Chuan-Chou Shen6, Shou-Yeh Gong7, Ke Lin1, Yanbin LU1, Xianfeng Wang1,2 and Noelynna Tuazon Ramos3, (1)Nanyang Technological University, Earth Observatory of Singapore, Singapore, Singapore, (2)Nanyang Technological University, Asian School of the Environment, Singapore, Singapore, (3)National Institute of Geological Sciences, University of the Philippines, Quezon City, Philippines, (4)The University of Tokyo, Tokyo, Japan, (5)National Taiwan University, High-precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geoscience, Taipei, Taiwan, (6)National Taiwan University, High‐precision Mass Spectrometry and Environment Change Laboratory (HISPEC), Department of Geoscience, Taipei, Taiwan, (7)National Museum of Natural Science, Geology, Taichung, Taiwan
Abstract:
Holocene land level and relative sea level are affected by a multitude of processes along the west coast of Luzon Island in the Philippines. Melting of higher-latitude continental ice sheets from last glacial maximum through the mid-Holocene led to eustatic sea-level rise, and the redistribution of ice and meltwater loads resulted in glacial isostatic adjustment (GIA) processes that are ongoing today, even in low latitudes. Off the west coast of Luzon, the South China Sea plate subducts under the Philippine Mobile Belt at the Manila Trench, inducing elastic deformation over the megathrust seismic cycle that has a maximum amplitude somewhere between the coastline and the trench but which may still be appreciable onshore. Yet some relative plate motion is taken up onshore, as evidenced by uplifted inferred Pleistocene terraces tens of meters above present mean sea level.

We have dated, slabbed, and analyzed a set of Holocene coral microatolls at the Pagsanahan site in Badoc municipality, Ilocos Norte province, on Luzon. Coral microatolls precisely track relative sea level (RSL), allowing the reconstruction of both the position of RSL and rates of RSL change. Preliminary analysis reveals the complicated interplay of multiple drivers of RSL: RSL rose rapidly until ~7500 cal yr BP, before dropping abruptly by ~1 m. We surmise these reconstructions capture rapid RSL rise toward a regional mid-Holocene highstand due to meltwater input and GIA, interrupted by ~1 m of coseismic uplift locally. We are working to elucidate details and identify potential causative faults.

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