An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program
Abstract The Mw 7.0 mainshock of the 2016 Kumamoto earthquake sequence was triggered by dextral rupture of the Futagawa fault within the Aso volcanic region, Southwestern Japan. To reproduce its faulting patterns and to reveal the geological and geophysical characteristics of the fault and surroundi...
| Main Authors: | , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Wiley
2022-01-01
|
| Series: | Geochemistry, Geophysics, Geosystems |
| Subjects: | |
| Online Access: | https://doi.org/10.1029/2021GC009966 |
| _version_ | 1797637920222347264 |
|---|---|
| author | Susumu Shibutani Weiren Lin Koichiro Sado Akihiro Aizawa Katsuaki Koike |
| author_facet | Susumu Shibutani Weiren Lin Koichiro Sado Akihiro Aizawa Katsuaki Koike |
| author_sort | Susumu Shibutani |
| collection | DOAJ |
| description | Abstract The Mw 7.0 mainshock of the 2016 Kumamoto earthquake sequence was triggered by dextral rupture of the Futagawa fault within the Aso volcanic region, Southwestern Japan. To reproduce its faulting patterns and to reveal the geological and geophysical characteristics of the fault and surrounding lithological units, we report the results of a multiple‐borehole drilling program penetrating the Futagawa fault zone. By combining core descriptions with geophysical logs, we identified >200 m of normal faulting displacement along the currently dextral strike‐slip Futagawa fault. Considering previous kinematic and chronological studies of the fault, we interpret that the Futagawa fault dominantly slipped as a normal fault in a short period (∼300–87 ka) before switching to its current transtensional (dominant strike‐slip) regime ∼87 ka caused by a local change in the stress field associated with the termination of the Aso caldera‐forming eruptions. In the main borehole, three damage/slip zones were penetrated at depths of ∼354, 461, and 576 m. The 461 damage zone was identified as ∼45 m in vertical thickness and thicker than the other damage zones (∼3–6 m vertically) and was characterized by high fracture density and the presence of strike‐slip slickenlines. Depth profiles of physical properties revealed different patterns near the three damage zones; both the resistivity and the P‐wave velocity showed stronger deterioration at the 461 damage zone than the others. Based on these geological and geophysical observations, we suggest that the 461 damage zone is the primary candidate for seismogenic faulting during the 2016 Kumamoto earthquake mainshock. |
| first_indexed | 2024-03-11T12:55:10Z |
| format | Article |
| id | doaj.art-086dafea218e4b7daa3f968fe9281b44 |
| institution | Directory Open Access Journal |
| issn | 1525-2027 |
| language | English |
| last_indexed | 2024-03-11T12:55:10Z |
| publishDate | 2022-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Geochemistry, Geophysics, Geosystems |
| spelling | doaj.art-086dafea218e4b7daa3f968fe9281b442023-11-03T17:01:12ZengWileyGeochemistry, Geophysics, Geosystems1525-20272022-01-01231n/an/a10.1029/2021GC009966An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling ProgramSusumu Shibutani0Weiren Lin1Koichiro Sado2Akihiro Aizawa3Katsuaki Koike4Graduate School of Engineering Kyoto University Kyoto JapanGraduate School of Engineering Kyoto University Kyoto JapanChi‐ken Sogo Consultants Co., Ltd. (Headquarters) Tokyo JapanChi‐ken Sogo Consultants Co., Ltd. (Headquarters) Tokyo JapanGraduate School of Engineering Kyoto University Kyoto JapanAbstract The Mw 7.0 mainshock of the 2016 Kumamoto earthquake sequence was triggered by dextral rupture of the Futagawa fault within the Aso volcanic region, Southwestern Japan. To reproduce its faulting patterns and to reveal the geological and geophysical characteristics of the fault and surrounding lithological units, we report the results of a multiple‐borehole drilling program penetrating the Futagawa fault zone. By combining core descriptions with geophysical logs, we identified >200 m of normal faulting displacement along the currently dextral strike‐slip Futagawa fault. Considering previous kinematic and chronological studies of the fault, we interpret that the Futagawa fault dominantly slipped as a normal fault in a short period (∼300–87 ka) before switching to its current transtensional (dominant strike‐slip) regime ∼87 ka caused by a local change in the stress field associated with the termination of the Aso caldera‐forming eruptions. In the main borehole, three damage/slip zones were penetrated at depths of ∼354, 461, and 576 m. The 461 damage zone was identified as ∼45 m in vertical thickness and thicker than the other damage zones (∼3–6 m vertically) and was characterized by high fracture density and the presence of strike‐slip slickenlines. Depth profiles of physical properties revealed different patterns near the three damage zones; both the resistivity and the P‐wave velocity showed stronger deterioration at the 461 damage zone than the others. Based on these geological and geophysical observations, we suggest that the 461 damage zone is the primary candidate for seismogenic faulting during the 2016 Kumamoto earthquake mainshock.https://doi.org/10.1029/2021GC0099662016 Kumamoto earthquakeFutagawa faultanciently normal faultingcurrently strike‐slip faultingfaulting mechanism and volcanismactive fault drilling |
| spellingShingle | Susumu Shibutani Weiren Lin Koichiro Sado Akihiro Aizawa Katsuaki Koike An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program Geochemistry, Geophysics, Geosystems 2016 Kumamoto earthquake Futagawa fault anciently normal faulting currently strike‐slip faulting faulting mechanism and volcanism active fault drilling |
| title | An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program |
| title_full | An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program |
| title_fullStr | An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program |
| title_full_unstemmed | An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program |
| title_short | An Ancient >200 m Cumulative Normal Faulting Displacement Along the Futagawa Fault Dextrally Ruptured During the 2016 Kumamoto, Japan, Earthquake Identified by a Multiborehole Drilling Program |
| title_sort | ancient 200 m cumulative normal faulting displacement along the futagawa fault dextrally ruptured during the 2016 kumamoto japan earthquake identified by a multiborehole drilling program |
| topic | 2016 Kumamoto earthquake Futagawa fault anciently normal faulting currently strike‐slip faulting faulting mechanism and volcanism active fault drilling |
| url | https://doi.org/10.1029/2021GC009966 |
| work_keys_str_mv | AT susumushibutani anancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT weirenlin anancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT koichirosado anancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT akihiroaizawa anancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT katsuakikoike anancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT susumushibutani ancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT weirenlin ancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT koichirosado ancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT akihiroaizawa ancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram AT katsuakikoike ancient200mcumulativenormalfaultingdisplacementalongthefutagawafaultdextrallyrupturedduringthe2016kumamotojapanearthquakeidentifiedbyamultiboreholedrillingprogram |