Institute of Computational Mathematics and Mathematical Geophysics SB RAS

International Conference on Mathematical Methods in Geophysics «MMG-2008»

Akademgorodok, Novosibirsk, Russia, October 13-15, 2008

Abstracts

Mathematical Simulation in Geophysical Problems. Seismic Methods, Problems of Geomonitoring and Geodynamics

Searching for realistic structure of the Earth interior based on joint forward modeling and tomographic inversion

Koulakov I.

Institute of Petrol Geology and Geopysics SB RAS (Novosibirsk)

Seismic tomography is one of the most effective tools for investigating the deep structure of the Earth. At the same time, this method has some fundamental limitations which bias the reconstruction results with respect to “true” velocity distribution. In particular, there is uncertainty of damping level determination that leads to ambiguity of amplitudes of the retrieved anomalies. Furthermore, the tomographic inversion provides continuous velocity distributions; while in the real Earth, the most important changes often occur on sharp interfaces. In order to overcome these and other problems, we propose a method for joint applying the forward modeling and tomographic inversion which helps to reconstruct the most probable velocity distribution in the real Earth.

The algorithm consists in the following steps. Denote the unknown velocity distribution in the real Earth as A. When the real seismic rays pass trough this model, they produce the dataset with real travel times. We apply the inversion tomographic operator to these data and obtain a velocity model B. Due to aforesaid reason, this model can be significantly different of the “true” distribution A. Construction of the realistic model, C, is performed by trial and error method. In each trial, we compute the synthetic travel times using an algorithm of forward modeling (e.g. 3D ray tracing). These synthetic data are then processed by the same inversion operator, as was used for the real data inversion. The result of synthetic reconstruction is denoted as D. In a case if we achieve the resemblance of models B and D, we can claim that the synthetic model C is similar to the unknown velocity distribution A in the real Earth.

This approach has been applied in practice for different observation schemes. For example, based on deep seismic sounding profiling data, we have reconstructed the complex structure of the accretion wedge in the subduction zone in Central Andes. Furthermore, the similar scheme was used to investigate the interior structure of underwater volcanoes in Pacific. The joint forward-inverse modeling scheme has been used in studies based on unknown sources, earthquakes on local and regional scales. In this study we present examples of such modeling for the data in Toba caldera (Sumatra) and Central Java. The regional modeling is represented by European and Pamir-Hindukush regions.

Note. Abstracts are published in author's edition

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