TAO, Vol.6, No.2, 233-250, Jue 1995 A Regional Gravity Map for the Subduction-Collision Zone Near Taiwan HOANG-YUAN YEN1' WEN-TZONG LIANG1'2' BAN-YUAN Kuo1, YIH-HSIUNG YEH1, CHAR-SHUAN Ltu2, DONALD REE 0 3 , NEIL LUNDBERG4• FU-CHEN su5 and HOU-SHENG CHUNG5 (Manuscript received 30 Decemoer, 1994,.in final form 2 Februar 1995) ABSTRACT To delineate the tectonic character of the subucton-collision zone in te marine ara near Taiwan, we have con5tructed a rgional gravity map by rconciling the shipboard data of 15 cruises that have surveyed the rgion of 20-26°N and 119-124°E over the past· 20 y�rs. Among te 15 cruise, thre have known, reliable base-tie information. The absolut level for te other 12's cruises a r adjusted in such a way tat their crssover errors with rpect to the other: thre ar minimized. T he rot-mean-squar difernce of the totlly 865 crossovers in the fnal data set i 6.0 mgal, rp1sentng an acceptable quality considering the multi-agency natur of the source and the rugged seafor. The distribution of the ship tracks is uneven, with the better rsolution around Taiwan but a prgrsive undersampling toward the east and nortwest. To make a rgonal map, we interpolate both the marine data . and te 6 fre-air �nomaly· measurement on Taiwan and it ofshor is- • lands into S minute spaced grids using a minim1m curvatur technique. The SEASAT altmetry derive gravity value ar placed on part of te map's boundar as an additonal constraint in the minimum curvature calculation. On the map, the fre-air anomaly range frm -250 to 350 mgal, primar ily rfecting the topography, with te maximum and minimum at te high mountains of Taiwan and the Ryukyu Tnch-Tiwan interection, rc tvely. T he Lutao-Lanyu volcanic arc is manifeted as a prominent, contin uous high from the southern border of the map, mergng northerly wi t the Coastal Range in eastern Taiwan. The Hengchun Ridge show$ a much more 1 Institute of Earh Sciences, Academia Sinica, P.O. Box 1-55, Nankang, Taiwan, R.O.C. 2 Institute of Oeanography, National Taiwan Univerity, Taipei, Taiwan, R.O.C. 3 Deparment of Geology, San Jose State University, San Jose, California, U.S.A. 4 Deparment of Geology, Florida State University, Tallahassee, Florida, U.S.A. 5 Chinese P etroleum Corporation, Taipei, Taiwan, R.O.C. 233