{"title":"日本伊豆半岛东侧火山活跃地区的地震变化","authors":"K. Z. Nanjo, Y. Yukutake, T. Kumazawa","doi":"arxiv-2407.19648","DOIUrl":null,"url":null,"abstract":"The Izu-Tobu region, on the eastern side of Izu Peninsula, in Japan, is\nvolcanically and seismically active. In this region, earthquake swarms of\nordinary earthquakes frequently occur at shallow depths, which is considered to\nbe associated with magma intrusion. Beneath ordinary earthquakes, low-frequency\nearthquakes (LFEs) are infrequently observed. We conducted a timeseries\nanalysis of both types of earthquakes during the time period 2005-2020, using a\nvariant of the Epidemic-Type Aftershock Sequence model. For this analysis, we\nused the Japan Meteorological Agency catalog of ordinary earthquakes and the\ncatalog of LFEs produced using the matched filter method. The observed result,\nwhich was common to both types of earthquakes, showed a significant change in\nseismicity, which became quiet, with the inflection point falling sometime\nbetween late 2009 and mid-2013, during which two out of three pronounced\nearthquake swarms occurred. We associated this seismic quiescence with changes\nin background rate to be low, where background rate, by removing the triggering\neffect of aftershocks, was interpreted as having been caused directly by the\nmagma source, which can vary with time. We used surface displacement data\nobtained from the Geospatial Information Authority of Japan, and observed that\nthe uplift due to magma intrusion was significant during the 1970s-1990s\nwhereas it was in abatement or unobservable during the studied period\n(2005-2020). We also found that the seismic quiescence occurred without\nsignificant crustal movement during the studied period. Our implication from\nthis finding is that magma source, which caused magma intrusion into the\nIzu-Tobu region, is in a transition phase, becoming less active, compared with\nthe magma source during the 1970s-1990s.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"78 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Changes in seismicity in a volcanically active region, on the eastern side of Izu Peninsula, Japan\",\"authors\":\"K. Z. Nanjo, Y. Yukutake, T. Kumazawa\",\"doi\":\"arxiv-2407.19648\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The Izu-Tobu region, on the eastern side of Izu Peninsula, in Japan, is\\nvolcanically and seismically active. In this region, earthquake swarms of\\nordinary earthquakes frequently occur at shallow depths, which is considered to\\nbe associated with magma intrusion. Beneath ordinary earthquakes, low-frequency\\nearthquakes (LFEs) are infrequently observed. We conducted a timeseries\\nanalysis of both types of earthquakes during the time period 2005-2020, using a\\nvariant of the Epidemic-Type Aftershock Sequence model. For this analysis, we\\nused the Japan Meteorological Agency catalog of ordinary earthquakes and the\\ncatalog of LFEs produced using the matched filter method. The observed result,\\nwhich was common to both types of earthquakes, showed a significant change in\\nseismicity, which became quiet, with the inflection point falling sometime\\nbetween late 2009 and mid-2013, during which two out of three pronounced\\nearthquake swarms occurred. We associated this seismic quiescence with changes\\nin background rate to be low, where background rate, by removing the triggering\\neffect of aftershocks, was interpreted as having been caused directly by the\\nmagma source, which can vary with time. We used surface displacement data\\nobtained from the Geospatial Information Authority of Japan, and observed that\\nthe uplift due to magma intrusion was significant during the 1970s-1990s\\nwhereas it was in abatement or unobservable during the studied period\\n(2005-2020). We also found that the seismic quiescence occurred without\\nsignificant crustal movement during the studied period. Our implication from\\nthis finding is that magma source, which caused magma intrusion into the\\nIzu-Tobu region, is in a transition phase, becoming less active, compared with\\nthe magma source during the 1970s-1990s.\",\"PeriodicalId\":501270,\"journal\":{\"name\":\"arXiv - PHYS - Geophysics\",\"volume\":\"78 1\",\"pages\":\"\"},\"PeriodicalIF\":0.0000,\"publicationDate\":\"2024-07-29\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"\",\"citationCount\":\"0\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"arXiv - PHYS - Geophysics\",\"FirstCategoryId\":\"1085\",\"ListUrlMain\":\"https://doi.org/arxiv-2407.19648\",\"RegionNum\":0,\"RegionCategory\":null,\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"\",\"JCRName\":\"\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Geophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2407.19648","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
Changes in seismicity in a volcanically active region, on the eastern side of Izu Peninsula, Japan
The Izu-Tobu region, on the eastern side of Izu Peninsula, in Japan, is
volcanically and seismically active. In this region, earthquake swarms of
ordinary earthquakes frequently occur at shallow depths, which is considered to
be associated with magma intrusion. Beneath ordinary earthquakes, low-frequency
earthquakes (LFEs) are infrequently observed. We conducted a timeseries
analysis of both types of earthquakes during the time period 2005-2020, using a
variant of the Epidemic-Type Aftershock Sequence model. For this analysis, we
used the Japan Meteorological Agency catalog of ordinary earthquakes and the
catalog of LFEs produced using the matched filter method. The observed result,
which was common to both types of earthquakes, showed a significant change in
seismicity, which became quiet, with the inflection point falling sometime
between late 2009 and mid-2013, during which two out of three pronounced
earthquake swarms occurred. We associated this seismic quiescence with changes
in background rate to be low, where background rate, by removing the triggering
effect of aftershocks, was interpreted as having been caused directly by the
magma source, which can vary with time. We used surface displacement data
obtained from the Geospatial Information Authority of Japan, and observed that
the uplift due to magma intrusion was significant during the 1970s-1990s
whereas it was in abatement or unobservable during the studied period
(2005-2020). We also found that the seismic quiescence occurred without
significant crustal movement during the studied period. Our implication from
this finding is that magma source, which caused magma intrusion into the
Izu-Tobu region, is in a transition phase, becoming less active, compared with
the magma source during the 1970s-1990s.