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Mario A. Aurelio
Mines and Geosciences Bureau, Philippines






Results of five sets of GPS measurements from 1994 to 1998 in Mindanao Island in the southern Philippines show that velocity vectors in stations close to major structures such as those in Surigao or Zamboanga are characterized by significant magnitude and direction variations within separate time intervals. The station in Surigao exhibits a strong easterly component after the first and third round of measurements, suggesting extensional tectonics along the Lake Mainit segment of the Philippine Fault. This tectonic deformation, occurring in between measurements, implies that activity on the fault during this period has been characterized by strike-slip faulting coupled with normal faulting (transtension). Western Mindanao on the other hand, has been characterized by an essentially compressive tectonic regime. This interplay of transtensional and compressional tectonics in eastem and western Mindanao respectively appears to be a consequence of the simultaneous activity along major tectonic boundaries including the Philippine Fault, the Cotabato Fault and the Cotabato Trench.




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