11:00 AM - 11:15 AM
[SSS08-06] Long-term seismic quiescence at the margin of co-seismic large slip area
Keywords:seismic quiescence, Maule earthquake, Iquique earthquake, Illapel earthquake
1. Introduction
In this study, we compare the slip distribution of great earthquakes and the seismic quiescence area that preceded the main shock. For example, Katsumata and Zhuang (2020, PAGEOPH) compared the slip distribution of the 2006 Kurile earthquake (Mw8.3) with the seismic quiescence area and pointed out that the seismic quiescence area is located at the edge of the large slip area. From a different perspective, the seismic quiescence area can be thought of as acting as a barrier to prevent the fault rupture. These characteristics are important when discussing the mechanism by which seismic quiescence occurs. Therefore, in this study, we investigated the seismic quiescence areas of three recent great earthquakes in South America: the 2010 Maule earthquake (Mw 8.8), the 2014 Iquique earthquake (Mw 8.2), and the 2015 Illapel earthquake (Mw 8.3). We will compare the slip distribution of the main shock and discuss the positional relationship between large slip areas and seismic quiescence areas.
2. Data and Analysis
The study area is the Pacific coast of South America from 45°S-10°N, 65°W-85°W. Earthquakes with a body wave magnitude of 5.0 or larger and a depth of less than 60 km that occurred in the study area from January 1, 1965 to December 31, 2020 were selected from the ISC Bulletin. We created 161 subcatalogs with a period length of 40 years by shifting the starting year by 0.1 year. The first and the second subcatalogs include earthquakes occurring between 1965.0 and 2005.0 and between 1965.1 and 2005.1. While the starting year increases by 0.1 year, the 161st subcatalog includes earthquakes occurring between 1981.0 and 2021.0. After declustering each subcatalog, we used the PMAP method (Katsumata and Zhuang, 2020) to search for long-term seismic quiescence.
3. Results
In the PMAP method, the smaller the P value, the stronger the seismic quiescence. The table shows long-term seismic quiescence with a P value of about 0.001 or less and events that may correspond to it. No. 7 in the table is considered to be the seismic quiescence that preceded the 2010 Maule earthquake (Mw8.8). The seismic quiescence area was found to be at two locations, the northern and southern edges of the large slip area where the co-seismic slip was more than 10 m. In addition, No. 4 is considered to be the seismic quiescence that preceded the 2014 Iquique earthquake (Mw8.2). It was found that this seismic quiescence area is located at the southern edge of the large slip area. No seismic quiescence was observed at the northern edge of the large slip area. Furthermore, No. 6 is considered to be the seismic quiescence that preceded the 2015 Illapel earthquake (Mw8.3). In two places, the northern and southern edges of the co-seismic large slip area, the seismic quiescence preceded the main shock.
4. Conclusion
Based on the above, the following three points were revealed in this study. (1) the long-term seismic quiescence was found to precede three great earthquakes in South America, (2) the areas of seismic quiescence were all located at the margins of the co-seismic large slip area, and (3) because of the fault rupture being blocked in the seismic quiescence area, the rupture appears to have stopped spreading in the direction of fault strike.
In this study, we compare the slip distribution of great earthquakes and the seismic quiescence area that preceded the main shock. For example, Katsumata and Zhuang (2020, PAGEOPH) compared the slip distribution of the 2006 Kurile earthquake (Mw8.3) with the seismic quiescence area and pointed out that the seismic quiescence area is located at the edge of the large slip area. From a different perspective, the seismic quiescence area can be thought of as acting as a barrier to prevent the fault rupture. These characteristics are important when discussing the mechanism by which seismic quiescence occurs. Therefore, in this study, we investigated the seismic quiescence areas of three recent great earthquakes in South America: the 2010 Maule earthquake (Mw 8.8), the 2014 Iquique earthquake (Mw 8.2), and the 2015 Illapel earthquake (Mw 8.3). We will compare the slip distribution of the main shock and discuss the positional relationship between large slip areas and seismic quiescence areas.
2. Data and Analysis
The study area is the Pacific coast of South America from 45°S-10°N, 65°W-85°W. Earthquakes with a body wave magnitude of 5.0 or larger and a depth of less than 60 km that occurred in the study area from January 1, 1965 to December 31, 2020 were selected from the ISC Bulletin. We created 161 subcatalogs with a period length of 40 years by shifting the starting year by 0.1 year. The first and the second subcatalogs include earthquakes occurring between 1965.0 and 2005.0 and between 1965.1 and 2005.1. While the starting year increases by 0.1 year, the 161st subcatalog includes earthquakes occurring between 1981.0 and 2021.0. After declustering each subcatalog, we used the PMAP method (Katsumata and Zhuang, 2020) to search for long-term seismic quiescence.
3. Results
In the PMAP method, the smaller the P value, the stronger the seismic quiescence. The table shows long-term seismic quiescence with a P value of about 0.001 or less and events that may correspond to it. No. 7 in the table is considered to be the seismic quiescence that preceded the 2010 Maule earthquake (Mw8.8). The seismic quiescence area was found to be at two locations, the northern and southern edges of the large slip area where the co-seismic slip was more than 10 m. In addition, No. 4 is considered to be the seismic quiescence that preceded the 2014 Iquique earthquake (Mw8.2). It was found that this seismic quiescence area is located at the southern edge of the large slip area. No seismic quiescence was observed at the northern edge of the large slip area. Furthermore, No. 6 is considered to be the seismic quiescence that preceded the 2015 Illapel earthquake (Mw8.3). In two places, the northern and southern edges of the co-seismic large slip area, the seismic quiescence preceded the main shock.
4. Conclusion
Based on the above, the following three points were revealed in this study. (1) the long-term seismic quiescence was found to precede three great earthquakes in South America, (2) the areas of seismic quiescence were all located at the margins of the co-seismic large slip area, and (3) because of the fault rupture being blocked in the seismic quiescence area, the rupture appears to have stopped spreading in the direction of fault strike.