The Banda Arc in eastern Indonesia is one of the few present-day examples of incipient collision between two continents. As such, it teaches us about tectonic processes that build mountains and generate natural hazards including large earthquakes and volcanoes. Yet, for all of its scientific potential and societal relevance, the Banda Arc is also one of the more geologically complex regions. Understanding this complexity is important in order to develop better models for the evolution of Earth over time, and to better understand natural hazard along the boundaries between tectonic plates. The goal of this research project has been to add key pieces needed to solve that puzzle.

Along the length of the Indonesia archipelago, the Australian and Eurasian tectonic plates are converging. In the Sunda Arc in central Indonesia, this convergence takes place via subduction, with Indian Ocean crust descending underneath the Eurasian continent. This process generates the volcanic arc islands of central Indonesia, including Java and Sumatra. To the east, in the Banda Arc, convergence transitions from subduction to arc-continent collision, as the islands associated with prior subduction collide with the Australian continent. The progression of collision in time can today be studied in space from west to east along the length of the Banda Arc. Since this process unfolds over millions of years, this "space-for-time" substitution in the Banda Arc offers a unique experiment. This project brought together a number of approaches, seeking to take advantage of this experiment.

A primary focus of this research was installation of 30 broadband seismometers across eastern Indonesia and in Timor Leste. These instruments record seismic waves that carry information about the structure of the Earth?s interior, which can be linked to its geological history. The stations installed with support of this award recorded for nearly four years, vastly increasing the available data volume from this region (see Figure 1). Data from these stations were retrieved every 6 months and archived at the IRIS Data Management Center. These data can be used for a wide range of seismic imaging, and are already providing new structural models of the subsurface structure that help to understand the how arc-continent collision is unfolding. The data (which are all publicly available) will be fertile ground for scientists for years to come.

The new seismic observations of geological structures at depth within the Earth have been complemented by analysis of the topography at the surface of the Earth in the same region. Existing data collected from coral terraces along shorelines were compiled and used to guide the interpretation of the shape of rivers draining the islands along the Banda Arc, specifically looking at the topographic profile along rivers from their headwaters towards downstream. Calculations based on these river profiles have provided new estimates of the history of uplift of the Banda Arc islands, that is, how quickly the surface of these islands was rising up above sea level at different times in the past (see Figure 2). This uplift is directly related to the arc-continent collision, so new information on how the rate of uplift has changed over time provides important clues about how collision has evolved. 

The third piece of this project involved geodynamic modeling of arc-continent collision, aiming to tie together the new insights from the seismic observations of geological structures at depth and topographic interpretations of changes in uplift rate over time. This numerical modeling focused on studying subduction underneath a continent (similar to the configuration in the Sunda Arc), followed by the arrival and collision of a continent (similar to the configuration in the Banda Arc). These models show how different configurations (including material properties) affect the surface and subsurface expression of collision (see Figure 3), providing general insights on global processes, building on the regional observations made as part of this research.

This project supported several researchers, including two PhD students who graduated from the University of Southern California (USC) with doctoral theses that developed out of this work. Three postdoctoral scholars were supported, helping them to launch independent careers (one as a faculty member internationally, one as a field technician, and the other in an academic research position). In addition, this project supported three principle investigators, two of whom secured tenure during the project. More generally, the project facilitated new international collaboration, including with the Institute of Technology in Bandung, Indonesia, and with the Institute of Petroleum and Geology in Timor-Leste. The latter collaboration led to additional supplemental support for developing the first long-term seismological infrastructure in the country.

Last Modified: 10/10/2019
Modified by: A Joshua West