Event Size Distribution of Shallow Tectonic Tremor in the Nankai Trough. Issue 11 (14th June 2019)

• Record Type: Journal Article
• Authors: Nakano, Masaru; Yabe, Suguru; Sugioka, Hiroko; Shinohara, Masanao; Ide, Satoshi
• Is Part Of: Geophysical research letters. Volume 46:Issue 11(2019)
• Page Start: 5828
• Page End: 5836
• Publication Date: 2019-06-14
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2019GL083029
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Slow earthquake size distributions have been found to follow either a power law or an exponential law, depending on the data set. We investigated the size distribution of shallow tectonic tremor events along the Nankai trough, southwestern Japan, observed in 2009, 2015, 2016, and 2018 and estimated the seismic energy radiated during the events as a measure of event size. The obtained size distributions mostly followed a power law with a b value of about 1, but an exponential law also fits well the data of the largest events; this result indicates that the size distribution follows the Gutenberg‐Richter law with an exponential taper. If only the largest events were observed, an exponential size distribution would be obtained. This exponential taper could be attributed to a source fault limitation. Because the maximum event size differed among activity periods, the source fault size varied among them, although the source areas largely overlap. Plain Language Summary: The size distribution of ordinary earthquakes mostly follows a power law, in which number of earthquakes reduces to 1/10 when the earthquake magnitude increases in 1 (the Gutenberg‐Richter law), while that of volcanic tremor follows an exponential law, in which event number exponentially decreases as the event size increases. On the other hand, the size distribution of tectonic tremor has not been clarified yet. We investigated the size distribution of shallow tectonic tremor events along the Nankai trough, southwestern Japan. The obtained size distributions mostly followed a power law with a b value of about 1, similar to ordinary earthquakes, but an exponential law also fits well the data of the largest events. This result indicates that the size distribution follows the Gutenberg‐Richter law with an exponential taper. The tapered power law distribution of tremor events implies that the source fault of small events, which follow a power law size distribution, is self‐similar, whereas that of larger events, which follow an exponential law distribution, is limited by the size of the entire fault. Key Points: We investigated the size distribution of shallow tremor events observed along the Nankai trough The observed size distribution is well explained by a power law with b value about 1 with an exponential taper for the largest events This result implies that tectonic tremor follows a tapered Gutenberg‐Richter distribution