Numerical Modeling of Seismic Wave Fields in Media Modified by an Underground Nuclear Explosions and Identification of Cavity

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

Nuclear explosions are banned by the Comprehensive Nuclear-Test-Ban Treaty (CTBT). Obviously, the CTBT needs reliable verification tools to make sure that no nuclear explosion goes undetected. In addition to the global monitoring systems it is necessary to have reliable tools for on-site inspections (OSI) and investigations. Among other candidate methods, possibility of detecting and interpreting of the so-called resonance seismic phenomena has to be comprehensively investigated and potentially elaborated for practical use.

Numerical modelling of seismic wave fields makes it possible to investigate resonance phenomena and their signatures in free-surface records. In collaboration with the CTBT Organization and based on extensive review of the available literature we have developed 3D realistic models of the underground structure after an UNE. The most general model consists of cavity, chimney with apical void, crushed zone, fractured zone, environment and free surface. The models include a) 2 yields of the UNE (1 kt and 10 kt), b) 4 different types of the pre-shot geological environment (tuff, alluvium, granite, rock salt) characterized by P- and S-wave speeds and quality factors, and density, c) vacuum or fluid in cavity, d) 2 depths of burial (minimal and 2-times minimal).

We performed extensive parametric numerical modelling of seismic wave fields due to plane-wave excitation (representing regional and distant events), near point double-couple sources (representing aftershocks) and seismic ambient noise. We then comprehensively analyzed the simulated wave fields in the time, frequency and time-frequency domains.

In a seismic wave field due to a distant source it is possible to identify resonant motion and locate cavity. A seismic wave field generated by an aftershock is much more difficult to interpret in terms of the cavity presence due to strong effects of a radiation pattern. Analysis of seismic noise makes it possible to identify cavity at least for relatively shallow cavities.

Presenting Author: Miriam Kristekova

Authors