5:15 PM - 7:15 PM
[SSS14-P08] Reconstructing Active Tectonic Structures Based on Uplifted Coastal Landforms: A Case Study from the Western Margin of the Tsugaru Plain
Keywords:Tephra analysis, Byoubusan Sand dune, Coastal area, Active tectonics
The 2024 Noto Peninsula Earthquake underscored the persistent challenges in understanding active tectonic structures concealed within coastal regions and the seismic characteristics they generate. The primary difficulty lies in the logistical challenges of conducting geological investigations in coastal environments. To effectively apply the lessons from this earthquake to future disaster mitigation and preparedness, it is essential to analyze pre- and post-earthquake coastal conditions to identify key geological indicators of active faulting and extend these findings to other regions. During the Noto Peninsula Earthquake, significant coseismic emergence landforms were documented. However, prior to the earthquake, well-developed uplifted marine benches, intertidal reef platforms, and marine terraces had already been recognized, suggesting sustained long-term tectonic uplift.
Objective and Study Area
This study focuses on identifying coastal geomorphic features indicative of uplift and aims to clarify the underlying active structures responsible for these topographic anomalies. The study area is the western margin of the Tsugaru Plain in northeastern Japan, where the Byobuyama Sand Dunes—a longitudinal dune system with elevations ranging from 50 to 70 meters—are situated. Beneath these dunes, a stratigraphic sequence has been documented, consisting of:
• The Yamatano Formation (MIS 5e), representing marine deposits from the last interglacial period,
• The Tateoka Formation, composed of lacustrine and palustrine deposits from the Last Glacial period, and
• The Dekijima Formation, consisting of Holocene inner bay to palustrine sediments.
These formations exhibit a general northward tilting trend. However, specific data on the rate, extent, and mechanisms of this deformation remain lacking, and the characteristics of the active structures responsible for this tilting are not yet well understood.
Approach and Findings
This study emphasizes the importance of reconstructing paleoenvironmental changes from Pleistocene deposits to decipher the spatiotemporal evolution of fault activity. Based on literature review and field investigations, we compiled the lithostratigraphy and spatial distribution of Pleistocene to Holocene deposits in the study area. Additionally, we conducted volcanic ash analysis on the Yamadano Formation, which is considered critical for understanding the region’s active structures. The results of these analyses and their implications for identifying active faults in the region will be discussed.
Objective and Study Area
This study focuses on identifying coastal geomorphic features indicative of uplift and aims to clarify the underlying active structures responsible for these topographic anomalies. The study area is the western margin of the Tsugaru Plain in northeastern Japan, where the Byobuyama Sand Dunes—a longitudinal dune system with elevations ranging from 50 to 70 meters—are situated. Beneath these dunes, a stratigraphic sequence has been documented, consisting of:
• The Yamatano Formation (MIS 5e), representing marine deposits from the last interglacial period,
• The Tateoka Formation, composed of lacustrine and palustrine deposits from the Last Glacial period, and
• The Dekijima Formation, consisting of Holocene inner bay to palustrine sediments.
These formations exhibit a general northward tilting trend. However, specific data on the rate, extent, and mechanisms of this deformation remain lacking, and the characteristics of the active structures responsible for this tilting are not yet well understood.
Approach and Findings
This study emphasizes the importance of reconstructing paleoenvironmental changes from Pleistocene deposits to decipher the spatiotemporal evolution of fault activity. Based on literature review and field investigations, we compiled the lithostratigraphy and spatial distribution of Pleistocene to Holocene deposits in the study area. Additionally, we conducted volcanic ash analysis on the Yamadano Formation, which is considered critical for understanding the region’s active structures. The results of these analyses and their implications for identifying active faults in the region will be discussed.