Publications

Paleostress terminologically consists of two words: paleo and stress. Paleo means of past time, and stress means forces worked in an area, thus paleostress means forces occured in geologic past times. In other words, paleostress is related to orientations of stress. The Grindulu Fault an active fault segment in Java that could potentially produce earthquakes. The lineament of the Grindulu Fault is from SW–NE across the Tegalombo Sub-district, Pacitan District, Province of East Java. Paleostress of the Grindulu Fault was conducted using stress inversion of fault slip data as the main data. The results of the stress inversion show five paleostress orientations defined from fault slip data: (1) ESE–WNW SHmax in the Cretaceous–Late Oligocene, (2) SE–NW SHmax in the Late Oligocene, (3) SSE–NNW SHmax in the Late Oligocene–early of Early Miocene, (4) S–N SHmax in the Early Miocene, (5) SSW–NNE SHmax in the Middle Miocene to present. The Grindulu Fault itself is a left-lateral strike-slip fault (sinistral) formed in the Early Miocene with S–N paleostress in a pure strike-slip stress regime condition and then changes to a transtensive stress regime condition at Middle Miocene until present with SSW–NNE stress direction. The final stress state (SSW–NNE) is in the direction of the India oceanic plate beneath south of Java Island. Today, the Grindulu Fault is normal left-lateral slip fault with transtensive stress regime (R’ 0.29–1.07). According to the 3D top basement modeling, it shows one of the lineaments is NE–SW, as an old pattern, the Complex of Meratus Mountain lineament. This pattern also has the same strike as the Grindulu Fault. Thus, the Grindulu Fault is formed from reactivation of preexisting NE–SW faults as an old pattern in its basement. Keywords: Paleostress, Tensor, Stress Inversion, Structure Geology, Tectonic, East Java Microplate.