ROTATION OF THE CHORTIS BLOCK CAUSES DEXTRAL SLIP ON THE GUAYAPE FAULT

The Chortis block is undergoing deformation as a direct result of larg e-magnitude sinistral strike-slip faulting on the North America-Caribb ean plate boundary. We have studied the Chortis block using geologic m apping, remote imagery, and earthquake seismology to evaluate the effe ct that large-magnitude strike-slip faulting has on an adjacent microc ontinental block. In the eastern part of the Chortis block, recent geo logic mapping has shown that the northeast striking Guayape fault is d extral instead of sinistral as previously assumed. Because this is a m ajor fault that cuts most of the Central America isthmus, the new evid ence for dextral slip necessitates a reinterpretation of the active te ctonics of the Chortis block. The presence of several north trending r ifts in the western part of the Chortis block has led previous workers to propose that the Chortis block is divided into smaller, independen tly rotating blocks. We use earthquake seismology and remote imagery d ata to extend this interpretation to the central portion of the Chorti s block. However, we have modified their model to account for dextral slip on the Guayape fault. We believe that rotation of the Chortis blo ck causes dextral slip on the Guayape fault even though Central Americ a is undergoing large sinistral displacement with respect to North Ame rica.