15:30 〜 16:30
[S06-P-01] Seismic wave analysis of North Korean nuclear tests using seismographic networks in Japan
Seismic waves generated by a series of North Korean nuclear tests in the past decade have been observed in seismic networks deployed throughout the Japanese Islands. Seismic signals corresponding to Pn arrivals are observed clearly at seismic stations of Hi-net (High Sensitivity Seismograph Network) and F-net (Broadband Seismograph Network) deployed by NIED (National Research Institute for Earth Science and Disaster Resilience).
We analyzed the waveforms of the five nuclear tests recorded at Hi-net and F-net stations. Apparent path-average velocities of Pn waves and their maximum amplitudes are estimated from observed seismograms in the vertical component. We found significant regional variations of apparent path-average velocity and maximum amplitude along propagation paths, which are likely to reflect the structural variations in the crust and uppermost mantle beneath the Sea of Japan. For example, fast apparent Pn velocity and larger amplitude are observed in the paths across the Japan Basin in the northern part of the Sea of Japan, which is characterized by thinner curst (about 9 km), while slow velocity as well as relatively smaller amplitude are found in the paths to Kyushu, which traverse the eastern margin of the Korean Peninsula with thicker crust.
Such regional variability of Pn wave speeds and amplitudes makes it difficult to precisely estimate the source parameters and yield of explosion, by using only the Japanese seismographic network without any proper correction for 3-D structure in the curst and uppermost mantle beneath the Sea of Japan. Such Pn wave anomalies derived from the past explosions observed throughout Japan may be of help in empirical corrections for the rapid and precise determination of hypocenter and yield of explosive source.
We analyzed the waveforms of the five nuclear tests recorded at Hi-net and F-net stations. Apparent path-average velocities of Pn waves and their maximum amplitudes are estimated from observed seismograms in the vertical component. We found significant regional variations of apparent path-average velocity and maximum amplitude along propagation paths, which are likely to reflect the structural variations in the crust and uppermost mantle beneath the Sea of Japan. For example, fast apparent Pn velocity and larger amplitude are observed in the paths across the Japan Basin in the northern part of the Sea of Japan, which is characterized by thinner curst (about 9 km), while slow velocity as well as relatively smaller amplitude are found in the paths to Kyushu, which traverse the eastern margin of the Korean Peninsula with thicker crust.
Such regional variability of Pn wave speeds and amplitudes makes it difficult to precisely estimate the source parameters and yield of explosion, by using only the Japanese seismographic network without any proper correction for 3-D structure in the curst and uppermost mantle beneath the Sea of Japan. Such Pn wave anomalies derived from the past explosions observed throughout Japan may be of help in empirical corrections for the rapid and precise determination of hypocenter and yield of explosive source.