Dmitry Bobrov

Towards global seismic monitoring of underground nuclear explosions using waveform cross correlation. Part I: Grand master events

We propose to use waveform cross correlation techniques for seismic monitoring of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) by proving the ability to build the Global Grid (GG) of master events using high-quality waveform templates at stations of the International Monitoring System. In seismically active regions, the choice of the highest quality and most representative signals from earthquakes as templates for master events is straightforward and one can reduce the current amplitude detection threshold at the International Data Centre (IDC) by a factor of 2 to 3. This gain practically doubles the number of built events, and thus, is crucial for seismic monitoring under the CTBT. However, the coverage by real masters is confined to areas with natural seismicity. Here, we investigate the possibility to populate the GG with real and synthetic master events as a two part study. In Part I, we estimate the effectiveness of cross correlation based on a regular grid filled with grand-master events with replicated high-quality waveform templates.In Part II, we develop and estimate efficiency of synthetic waveform templates for aseismic zones. Both approaches are quantitatively tested using the aftershock sequence of the April 11, 2012 Sumatera earthquake. The cross correlation bulletin previously built using sixteen real master events is a natural benchmark to evaluate the performance of the replicated masters and synthetic waveforms. In Part I, we prove that the replicated grand masters demonstrate the performance at the level of real masters. The Primary IMS Seismic Network includes many array stations, which provide a higher resolution monitoring based on cross correlation.

Remote detection of aftershock activity as a new method of seismic monitoring

A weak seismic event with body wave magnitude 2.1 was detected near the epicenter of an underground explosion conducted by the Democratic People’s Republic of Korea (DPRK) on September 9, 2016. The event occurred approximately two days after the test. Using the method of waveform cross-correlation, two array stations of the International Monitoring System (IMS), USRK and KSRS, recorded the arrival of Pn waves. At the same time, this event was not recorded during the standard automatic processing at the International Data Center. The location and other characteristics of this weak event indicate that it is likely to have been an aftershock of the preceding explosion. Based on the successful automatic detection and construction of the event, we conducted an extended investigation, which consisted in searching for secondary seismic phases at the nearest stations that do not belong to the International Monitoring System. The final solution, which is based on waveform cross-correlation, includes stations MDJ (China) and SEHB (Republic of Korea), the aftershock epicenter is located at ~2 km northwest of the epicenter of the DPRK test.

The Chelyabinsk Meteorite as a multiple source of acoustic and seismic waves

Shock waves and impact of the Chelyabinsk Meteorite fragments on the ground initiated various waves in the atmosphere and the earth. Three different sources of seismic and infrasound waves were found by arrival time and azimuth of seismic and infrasound waves recorded by the International Monitoring System.