Thus, InSAR could not be utilized to describe the deformation nearby the test site 34. The biggest explosion inevitably caused complex and steep surface deformation which exceeds the phase difference of 2 π between adjacent pixels 1, 8, 36– 38. In order to measure large collapses in North Korea’s test site, three main issues need to be considered.įirst, InSAR measurements near the test site was too decorrelated to map the deformation 1, 2, 8, 35– 37. ![]() However, there have been no deformation analysis about large surface collapses induced by the 2017 North Korea Nuclear test. (2018) observed the deformation from the 2017 North Korea nuclear test using SAR measurements and suggested a reasonable deformation scenario 1. Since InSAR was firstly applied to Nevada nuclear test site to measure the surface deformation, several studies have been reported about observing the nuclear test sites using InSAR 8, 32– 34. monitored land subsidence on the subway and water pump tunnels 31. introuduced surface deformation rate variation according to mining and rail tunnel excavation progression 30. For example, risk assesments of underground voids(mines, tunnels) were performed via multiple-temporal InSAR. ![]() Among them, land subsidence is especially successful and traditional application of SAR deformation measurement 27– 31. A lot of geological events have been measured by using SAR Interferometry (InSAR) or offset tracking (OT) methods such as volcano 14– 16, earthquakes 14, 17, 18, landslides 19, 20, land subsidence 21, 22 and glaciers 23– 26. Synthetic aperture radar (SAR) is a unique method that can generate deformation map with milimeter to centimeter precision 10– 13. However, there have been no valid measurements about the collapse or ground subsidence in the North Korea Nuclear test site because of a paucity of information about the North Korea nuclear test 8, 9. Measuring surface subsidence could be used to estimate the ground stablility 6, 7. The infrastructures in seismically active area usually experience irrecoverable damages and ground subsidence 4– 6. Many research groups including USGS have considered the source of second earthquake as a large collapse, which also raised up questions on the stability of the infrastructures of the test site under the Mt. ![]() After 8 min 32 s from the sixth test, the second earthquake of smaller magnitude occured 1, 2. Due to North Korea’s sixth underground nuclear tests, large and complex deformations occurred, which also caused landslides around the test site 1– 3. The magnitude of the sixth test was mb 6.1, which is the biggest one among the six tests. The seismic magnitudes estimated from the North Korean’s nuclear tests has been increased since it’s first test. Mantap, Pungyeri, North Korea since 2006. North Korea has conducted six nuclear tests at Mt. On the basis of our results including the shapes, locations and volume changes of the large collapse, evidently a new vital piece of information was obtained so that it could be used to interprete the sixth nuclear test more accurately. Moreover, the severe collapse was observed westside from the epicenter of the sixth nuclear test, and it has a depth of about 68.6 cm on the area of 0.3765 km 2. The collapse may seem to occur along the underground tunnels and at the test site’s epicenter as well. The horizontal deformation clearly showed a radial pattern because it was mainly caused by the explosions and landslides, while the vertical deformation displayed a rugged pattern because it was affected by the explosions, compaction and collapse. ![]() The maximum horizontal deformation was approximately 515 cm. The measured maximum deformation was about − 491, − 343 and 166 cm with the measurement uncertainty of about 3.3, 4.1 and 2.7 cm in the east, north and up directions, respectively. Since the precise vertical deformation measurement is very important to estimate the stability of the nuclear test facility, we retrieved a precise 3D surface deformation field and then decomposed the vertical deformation pattern from the 3D deformation. The surface deformation was composed of expansion of explosions, collapse, compaction and landslides. It was reported that a large and complex surface deformation was caused by the event. Mantap, North Korea on September 3, 2017. The artificial earthquake of mb 6.1 related to the North Korea’s sixth nuclear test occured at Mt.
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