Indonesian Institute of Sciences

About: Indonesian Institute of Sciences is a facility organization based out in Jakarta, Indonesia. It is known for research contribution in the topics: Population & Biology. The organization has 4795 authors who have published 10544 publications receiving 76990 citations. The organization is also known as: Indonesian Institute of Sciences Cibinong, Indonesia.

Seismic anisotropy in the Sumatra subduction zone

Abstract: An important tool for understanding deformation occurring within a subduction zone is the measurement of seismic anisotropy through observations of shear wave splitting (SWS). In Sumatra, two temporary seismic networks were deployed between December 2007 and February 2009, covering the fore arc between the fore-arc islands to the back arc. We use SKS and local SWS measurements to determine the type, amount, and location of anisotropy. Local SWS measurements from the fore-arc islands exhibit trench-parallel fast directions which can be attributed to shape preferred orientation of cracks/fractures in the overriding sediments. In the Sumatran Fault region, the predominant fast direction is fault/trench parallel, while in the back-arc region it is trench perpendicular. The trench-perpendicular measurements exhibit a positive correlation between delay time and raypath length in the mantle wedge, while the fault-parallel measurements are similar to the fault-parallel fast directions observed for two crustal events at the Sumatran Fault. This suggests that there are two layers of anisotropy: one due to entrained flow within the mantle wedge and a second layer within the overriding crust due to the shear strain caused by the Sumatran Fault. SKS splitting results show a NNW-SSE fast direction with delay times of 0.8–3.0 s. The fast directions are approximately parallel to the absolute plate motion of the subducting Indo-Australian Plate. The small delay times exhibited by the local SWS (0.05–0.45 s), in combination with the large SKS delay times, suggest that the anisotropy generating the teleseismic SWS is dominated by entrained flow in the asthenosphere below the slab.

Monsoonal differences in phytoplankton biomass and production in the Indonesian seas: Tracing vertical mixing using temperature

Abstract: Measurements made in the Indonesian Seas during the 1994 northwest monsoon (January–February) and the 1993 southeast monsoon (August–September) show up to an order of magnitude increase in average surface chlorophyll a from 0.25 mg mṫ during the northwest monsoon to over 2.5 mg m−3 during the southeast with a strong east-west gradient. Carbon assimilation was similar for both seasons in the eastern seas (Banda, Flores and Seram), 1.2 g C m−2 day−1 but dropped by half in the western seas (Sulawesi and Makassar Strait) in February, from 1.2 to 0.5 g C m−2 day−1. Areal chi a decreased in the western seas from 20.2 to 5.5 mg m−2 from the northwest to southeast monsoons. The eastern seas showed an opposite trend, with areal chi a increasing from 20.8 to 55.8 mg m−2 between seasons. The increase in surface and integral euphotic zone phytoplankton biomass in the eastern seas is correlated with cooler sea surface temperatures, suggesting that phytoplankton biomass is proportional to the strength of upwelling and vertical mixing.

The structure of the Sumatran Fault revealed by local seismicity

Abstract: The combination of the Sunda megathrust and the (strike-slip) Sumatran Fault (SF) represents a type example of slip-partitioning. However, superimposed on the SF are geometrical irregularities that disrupt the local strain field. The largest such feature is in central Sumatra where the SF splits into two fault strands up to 35 km apart. A dense local network was installed along a 350 km section around this bifurcation, registering 1016 crustal events between April 2008 and February 2009. 528 of these events, with magnitudes between 1.1 and 6.0, were located using the double-difference relative location method. These relative hypocentre locations reveal several new features about the crustal structure of the SF. Northwest and southeast of the bifurcation, where the SF has only one fault strand, seismicity is strongly focused below the surface trace, indicating a vertical fault that is seismogenic to ∼15 km depth. By contrast intense seismicity is observed within the bifurcation, displaying streaks in plan and cross-section that indicate a complex system of faults bisecting the bifurcation. In combination with analysis of topography and focal mechanisms, we propose that the bifurcation is a strike-slip duplex system with complex faulting between the two main fault branches.