The continuous convergence between the Indian and Eurasian plates caused massive lithospheric deformation in the Tibetan Plateau and led to excessive crustal material escaping through its southeastern margin. However, the mechanisms that accommodate the escaping materials and whether they intrude into the Indochina Peninsula are continually under debate. Seismic Lg waves mostly propagate within the crust waveguide with an amplitude decay that is sensitive to crustal material properties, such as temperature, partial melting, and fracture. Therefore, Lg attenuation can be a useful indicator of potential crustal material escape. In this study, we developed a high‐resolution broadband Lg attenuation model in this region between 0.05 and 10.0 Hz, with the resolution reaching 1° in regions with dense raypath coverage. Prominent low‐Q anomalies beneath the southeastern margin of the Tibetan Plateau, correlating with previously observed low velocity, high conductivity and high Poisson’s ratio, may indicate possible high temperature and/or partial melting within a relatively weak crust, and suggest a north‐south interconnected corridor for gravity‐driven material flow. Through our results and other geological and geophysical observations, a dynamic model is suggested here by combining shallow rigid block extrusion and deep viscous crustal flow to explain crustal material escape in the southeastern margin of the Tibetan Plateau. Additionally, neither shallow extrusion nor deep material flow enter the Indochina Peninsula based on the relatively high Q values, which indicate a stronger crust there.

We report on a broad-band high-resolution attenuation model for the North China Craton and surrounding regions based on regional Lg-wave data. Vertical broad-band waveforms recorded at 39 stations from 176 crustal earthquakes are collected to extract the Lg-wave amplitude spectra between 0.05 and 10.0 Hz. We use the dual-station method to generate a preliminary Q_Lg model and use it as the initial model. Then, we combine the dual- and single-station data together to jointly invert the Q_Lg distribution and Lg source excitation functions. These inversions are conducted independently at individual frequencies without using any a priori assumption about the frequency dependences in Q_Lg and source terms. The maximum spatial resolution is approximately 1° × 1° in well-covered areas for frequencies between 0.05 and 2.0 Hz. The Q_Lg image is then used to determine the relationship between the attenuation and different geological structures. Results show an average Q₀ (1 Hz Q_Lg) of 374 for the entire North China Craton with an increasing trend from east to west. Average Q₀ values are 337, 361 and 421 for the east, central and west blocks, respectively. For the surrounding regions, the Eastern Tibetan plateau has a very low Q₀ of 188, while the Northeast China Plate and the Tianshan–Xingmeng fold belts are characterized by high Q₀ values of 506 and 424, respectively. We also investigate regional variations of the Lg attenuation in low-frequency band between 0.2 and 1.0 Hz.

Seismology plays an important role in characterizing potential underground nuclear tests. Using broadband digital seismic data from Northeast China, South Korea and Japan, we investigated the properties of the recent seismic event occurred in North Korea on January 6, 2016. Using a relative location method and choosing the previous 2006 explosion as the master event, the 2016 event was located within the North Korean nuclear test site, with its epicenter at latitude 41.3003°N and longitude 129.0678°E, approximately 900 meters north and 500 meters west of the previous event on February 12, 2013. Based on the error ellipse, the relocation uncertainty was approximately 70 m. Using the P/S spectral ratios, including Pg/Lg, Pn/Lg and Pn/Sn, as the discriminants, we identify the 2016 event as an explosion rather than an earthquake. The body-wave magnitude calculated from regional wave Lg is m_b(Lg) equal to 4.7 ± 0.2. Adopting an empirical magnitude-yield relation, and assuming that the explosion is fully coupled and detonated at a normally scaled depth, we find that the seismic yield is about 4 kt, with the uncertainties allowing a range from 2 to 8 kt.

Using Lg-wave Q tomography, we construct a broadband crustal attenuation model for the Middle East. The QLg images reveal a relationship between attenuation and geological structures. Strong attenuation is found in the continental collision orogenic belt that extends from the Turkish and Iranian plateau to the Pamir plateau. We investigate the frequency dependence of QLg in different geologic formations. The results illustrate that QLg values generally increase with increasing frequency but exhibit complex relationships both with frequency and between regions. An average QLg value between 0.2 and 2.0Hz, QLg (0.2–2.0Hz), may be a critical index for crustal attenuation and is used to infer the regional geology. Low-QLg anomalies are present in the eastern Turkish plateau and correlate well with low Pn-velocities and Cenozoic volcanic activity, thus indicating possible partial melting within the crust in this region. Very strong attenuation is also observed in central Iran, the Afghanistan block, and the southern Caspian Sea. This in line with the previously observed high crustal temperature, high-conductivity layers, and thick marine sediments in these areas, suggests the high Lg attenuation is caused by abnormally high tectonic and thermal activities

We characterize the seismic events that occurred in North Korea on 9 September 2016 and South Korea on 12 September 2016. The 9 September 2016 event was identified as an explosion, and the two 12 September 2016 events were identified as natural earthquakes using the P/S (P‐ and S‐wave) spectral ratios, Pg/Lg, Pn/Lg, and Pn/Sn as discriminants. The explosive event was relocated within the North Korean nuclear test site using a relative location method and the 2006 North Korea underground nuclear test as the master event, and the epicenter was identified at 41.2976° N latitude and 129.0804° E longitude. From the regional Lg and Rayleigh waves, the body‐ and surface‐wave magnitudes for the 9 September 2016 event were calculated as $mb(Lg)=4.8±0.2$ and $Ms=4.2±0.1$. By adopting an empirical magnitude–yield relation for the body‐wave magnitude, and assuming that the explosion was fully coupled and detonated at a normally scaled depth, we estimated that the seismic yield was $∼6kt$, and the uncertainty range was between 3 and 11 kt. If an overburied depth range between 780 and 1200 m was applied, then the yield would be increased to 16–22 kt.