Analysis of fault patters based on erarthquake data on the land of Sumatera island

Geodynamics of Sumatra is interesting to study because of the unique geological setting Geodynamics of Sumatra is interesting to study because of the unique geological setting and high seismicity. This high seismicity is caused by the many faults found on land and in the surrounding waters. This paper presents the results of research that aims to determine fault patterns both on land and in the waters around Sumatra based on earthquake data from 1960-2000. The area under study is at the coordinates of 6°N - 6°S and 95°E - 109°E at an epicenter depth of <60 km with a magnitude between 4-10. The area is divided into two zones, namely the front arc and the Barisan arc. Data were obtained from ISC and Global CMT. By using the Focal Mechanism Method, the results show that the fault pattern in the Sumatran forearc Basin zone is dominated by an Reverse Fault located in the accretion zone while on the mainland of Sumatra it is dominated by Strike Slip along the Sumatran Fault System. By knowing the position and pattern of the fault, especially on the mainland of the island of Sumatra, it can be used as a reference for spatial planning. In addition, further studies will also be able to learn about the dangers or disasters caused by the fault pattern.

Fault Pattern and Seismotectonic Style of the Campania – Lucania 1980 Earthquake (Mw 6.9, Southern Italy): New Multidisciplinary Constraints

New fault trace mapping and structural survey of the active faults outcropping within the epicentral area of the Campania-Lucania 1980 normal fault earthquake (Mw 6.9) are integrated with a revision of pre-existing earthquake data and with an updated interpretation of the CROP-04 near-vertical seismic profile to reconstruct the surface and depth geometry, the kinematics and stress tensor of the seismogenic fault pattern. Three main fault alignments, organized in high-angle en-echelon segments of several kilometers in length, are identified and characterized. The inner and intermediate ones, i.e. Inner Irpinia (InIF) and Irpinia Faults (IF), dip eastward; the outer Antithetic Fault (AFA) dips westward. Both the InIF and the IF strike NW-SE along the northern and central segments and rotate to W-E along the southern segments for at least 16 km. We provide evidence of surface coseismic faulting (up to 1 m) not recognized before along the E-W segments and document coseismic ruptures with maximum vertical displacement up to ∼1 m where already surveyed from other investigators 40 years ago. Fault/slip data from surface data and a new compilation of focal mechanisms (1980 – 2018) were used for strain and stress analyses to show a coherent NNE-directed least principal stress over time and at different crustal depths, with a crustal-scale deviation from the classic SW-NE tensional direction across the Apennines of Italy. The continuation at depth of the outcropping faults is analyzed along the trace of the CROP-04 profile and with available hypocentral distributions. Integrating all information, a 3D seismotectonic model, extrapolated to the base of the seismogenic layer, is built. It outlines a graben-like structure with a southern E-W bend developed at depth shallower than 10–12 km, at the hanging wall of an extensional NE- to E-dipping extensional basal detachment. In our interpretation, such a configuration implies a control in the stress transfer during the 1980 earthquake ruptures and provides a new interpretation of the second sub-event, occurred at 20 s. Our reconstruction suggests that the latter ruptured a hanging wall NNE-dipping splay of the E-W striking main fault segment and possibly also an antithetic SSW-dipping splay, in two in-sequence episodes.