Joint Travel-time Inversion of Streamer and OBS Seismic Data for Improved Velocity Models and Interplate Boundary Geometry in Subduction Zone

Abstract:

We combine wide-angle (WAS) seismic and multichannel seismic reflection (MCS) data acquired in the northern Chile subduction zone during the CINCA'95 survey into a common inversion scheme to obtain high-resolution image of upper plate and inter-plate boundary, and to characterize seismic velocity (Vp) as well as tectonic structure across ~300 km long, E-W profile, 21.30°S. To illustrate the advantages of a common inversion approach we have compared the modeling results using two different travel-time inversion strategies:

First, we have produced seismic velocity and inter-plate boundary geometry using the WAS data, recorded on 19 OBH (Ocean Bottom Hydrophones) and 6 land stations following a typical joint refraction and reflection travel-time tomography strategy. In particular, the WAS model is obtained using tomo2d tomographic inversion code (Korenaga et al, 2000) and applying layer-stripping method.

Second, to compare structure, physical properties and rupture characteristics we jointly invert two types of seismic data sets, integrating multichannel seismic (MCS) data collected with a 3 km long streamer with the OBS wide-angle seismic (WAS) data described above into a common inversion scheme. To do so, we have adapted tomo2d to deal with streamer data. The scheme results in a joint travel time tomographic inversion based on integrated travel time information from refracted and reflected from WAS data and reflected phases from the top of the basement and the inter-plate boundaries identified in the MCS shot gathers. Our first results of the joint inversion indicate a 5 – 10 times smaller ray travel-time misfit in the deeper parts of the model around the interplate boundary, compared to models obtained inverting with just wide-angle seismic data.

Interpretation of the joint WAS-MCS velocity model, and MCS images provide improved models of physical properties of the upper plate and around inter-plate boundary. In turn this will help to better understand characteristics of the earthquake rupture propagation in the seismogenic zone based on the variations of the inter-plate geometry and upper plate physical properties.