Fabrics and mechanics for forearc deformation at the Costa Rica erosive convergent margin and implications for seismogenic fault zone behavior - Follow-up of IODP expedition 334 (Costa Rica Seismogenesis Project, CRISP)
ACRONYM
FAME
Title
Fabrics and mechanics for forearc deformation at the Costa Rica erosive convergent margin and implications for seismogenic fault zone behavior - Follow-up of IODP expedition 334 (Costa Rica Seismogenesis Project, CRISP)
General information
Subduction zones at active continental margins at which 90% of the worldwide earthquakes occur are either accretionary or erosive. At accretionary margins, material from the downgoing oceanic plate, mostly marine sediments, is tectonically detached during subduction and accreted to the upper continental plate. At erosive margins, material from the overriding continental plate, mostly continental basement and slope sediments, is tectonically eroded and attached to the lower plate. Although these two different types of subduction have approximately the same worldwide frequency of occurrence, the Megathrust earthquakes with a magnitude > 8.5 have so far almost exclusively been recorded at accretionary margins (e.g., 8.8 Maule, Chile, 2010; 9.0 Sumatra, Indonesia, 2004; 9.5 Valdivia, Chile, 1960). To better understand the related earthquake mechanisms two major projects of the International Ocean Drilling Program (IODP) endeavor to drill for the first time into the seismogenic zone of an accretionary (Nankai trench, Japan; project NanTroSEIZE) and an erosive margin (Costa Rica; project CRISP) at approximately 5000 – 6000 meters below sea floor. The subduction channel between the continental upper and the oceanic lower plate where plate tectonics’ deformation concentrates is mainly filled with upper plate material at the erosive margin and lower plate material at the accretionary margin. The properties of this infill is one of the most important factors controlling the deformation behavior. If deformation is distributed it is usually continuous, whereas if deformation localizes it can be discontinuous. At major thrust faults characteristic of localized deformation high friction and asperities might lock the fault preventing continuous sliding and strain energy release. When a critical threshold in stress build-up is reached friction and asperities are overcome and earthquakes nucleate. However, it is assumed that only if the fault material is prone to velocity weakening, i.e. it becomes weaker with faster sliding rate, large and very large earthquakes can develop. The erosive subduction channel material is lithologically rather variable and characterized by a long history of compaction and deformation in the continental fore arc wedge whereas the accretionary subduction channel material mainly consists of more homogeneous pelagic and trench fill deposits which is continuously transported down into the seismogenic zone. In our study we will investigate this input material from the fore arc wedge offshore Costa Rica and from the Nankai trench and incoming plate offshore Japan by microstructural analysis and rock mechanial testing. By this approach we want to find out if these differences in material input are significant and if they could be crucial for differences in deformation, earthquake nucleation and propagation.
Start
November, 2012
End
October, 2014
Funding (total)
-
Funding (GEOMAR)
131000
Funding body / Programme
-
DFG
/ Priority Programme (ODP)
Coordination
null
Contact
