10:45 〜 12:15
[MIS19-P03] Single-channel seismic structure of mud volcanoes on the landward slope of Ryukyu Trench off Tanegashima island
キーワード：泥火山、反射法地震探査、琉球海溝
Mud volcanoes are topographic high formed by the eruption of sediments and fluids from the deep subsurface, a phenomenon widely observed on continental margins and on land. However, the mechanisms of their activities in individual fields are not fully understood. More than 30 mud volcanoes and mud diapir-like features were reported in previous studies off the east coast of Tanegashima Island (e.g., Ujiié, 2000), and at least 15 mud volcanoes have been numbered (MV#1~#15). Geophysical surveys conducted by JAMSTEC since 2012 have obtained multibeam bathymetry, single-channel reflection seismic (SCS) profiles, AUV side-scan sonar, and sub-bottom profiler data in this area (e.g., Kitada et al., 2018JpGU). Here we report the results of detailed observations and descriptions of SCS cross-sections obtained during the YK12-17, YK13-07, and YK14-15 cruises.
We individually observed 13 mud volcanoes of the 15 named mud volcanoes on the SCS cross-sections in addition to the newly identified mud volcanoes from the SCS images. Acoustically transparent shadows are distributed below the mud volcanoes, and no clear stratigraphic structures can be identified. Christmas tree structures were observed in most of the mud volcanoes and were incredibly well developed in MV#4, #7, and NewMV#1 and #3. In the case of MV#6, a buried structure of a mud volcano was observed adjacent to the present-day mud volcano, which is possibly abandoned conduits. In the other cases (MV#1, #12), a present-day mud volcano has developed directly above a completely buried mud volcano cone. In several locations with no topographic elevation in the cross-section, we observed buried structures with characteristics of well-developed mud volcanoes. In some cases, topographic elevations were observed near buried mud volcano structures. These may represent abandoned and buried mud volcanoes, similar to the MV#6 or buried base of mud volcanoes.
These stacked cones or Christmas tree structures imply the continuous activity of mud volcanoes in geologic time in the same region. The various patterns of mud volcanoes identified in the field may indicate variations in mud volcanoes' developmental stages or formation mechanisms. The integration of geochronological investigations is expected to furnish valuable insights into the progression of mud volcano evolution models.
We individually observed 13 mud volcanoes of the 15 named mud volcanoes on the SCS cross-sections in addition to the newly identified mud volcanoes from the SCS images. Acoustically transparent shadows are distributed below the mud volcanoes, and no clear stratigraphic structures can be identified. Christmas tree structures were observed in most of the mud volcanoes and were incredibly well developed in MV#4, #7, and NewMV#1 and #3. In the case of MV#6, a buried structure of a mud volcano was observed adjacent to the present-day mud volcano, which is possibly abandoned conduits. In the other cases (MV#1, #12), a present-day mud volcano has developed directly above a completely buried mud volcano cone. In several locations with no topographic elevation in the cross-section, we observed buried structures with characteristics of well-developed mud volcanoes. In some cases, topographic elevations were observed near buried mud volcano structures. These may represent abandoned and buried mud volcanoes, similar to the MV#6 or buried base of mud volcanoes.
These stacked cones or Christmas tree structures imply the continuous activity of mud volcanoes in geologic time in the same region. The various patterns of mud volcanoes identified in the field may indicate variations in mud volcanoes' developmental stages or formation mechanisms. The integration of geochronological investigations is expected to furnish valuable insights into the progression of mud volcano evolution models.