An example of regional seismicity recovery on June 22, 2020, using waveform cross-correlation

June 22nd, 2020 was an important day for nuclear test monitoring. The US undersecretary, Thomas DiNanno, made an official claim that a secret nuclear test was conducted at the Lop Nor testing site on that day. However, the Provisional Technical Secretariat (PTS) of the Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) reported that there were no seismic events consistent with a nuclear explosion on that date. This means that the event was either hidden under the threshold of the international monitoring system (IMS), or it was missed by the international data center (IDC). Alternatively, no event occurred. All scenarios are of interest to the scientific community. The routine processing of seismic data by the IDC is well documented in open sources. The threshold for detection is not uniform across the globe, especially in continental areas. Additionally, it is not low enough to detect weapon-sized explosions using the cavity decoupling method. There are methods to lower this threshold using waveform cross-correlation (WCC) techniques. On June 22th, 2020, the IDC ran a preliminary pipeline for processing seismic data from the IMS. This was done in a testing mode. Since 2020, the development of WCC methods has allowed for revisiting cases and obtaining high-quality reports on events that were not reported five years ago.