17:15 〜 18:45
[U16-P01] Landscape changes caused by the 2024 Noto peninsula earthquake and its relation to the long-term landscape evolution
キーワード：Noto peninsula earthquake、Coastal uplift、Hillslope slump
On 1st January 2024, a Mw7.5 earthquake struck the Noto Peninsula in Central Japan. The earthquake occurred on active reverse faults located offshore, a few km north of the peninsula. It caused extensive coastal uplift and numerous slope failures and landslides. To reveal the landscape changes due to the earthquake, we estimated the three-dimensional displacement field of the earthquake based on the pixel offset analysis of the SAR images acquired by the Japanese ALOS-2 satellite (Fukushima et al., 2024, JPGU, STT35-P02) and measured surface displacement in the field. The pixel offset analysis revealed that the maximum uplift of 4.4 m occurred in the northwestern part of the peninsula and the westward displacement up to ~2 m in the northern part of the peninsula. The vertical displacement field derived from the pixel offset analysis is consistent with the result of field measurement. The vertical displacement of the earthquake generally decreased to the south of the peninsula. This spatial pattern of coseismic uplift is similar to the long-term uplift pattern inferred from the elevation of Pleistocene marine terraces (Ota & Hirakawa, 1979).
To characterize the surface displacement associated with non-tectonic processes such as landslides, we subtracted the displacement due to the fault slip estimated from a joint kinematic inversion of GNSS and pixel offsets of ALOS-2 (Tang et al., 2024, JpGU, SGD02-P10) from the one derived from the pixel offset analysis. The residual displacement field showed hillslope slumps concentrating in the northwestern and northeastern parts of the peninsula. Around the Wakayama River, we observed extensional and compressional deformation along ridges and valleys, respectively, which are associated with downslope movement on hillslopes at both sides of the ridges and valleys. Aerial photos taken after the earthquake by Geospatial Information Authority in Japan revealed extensional cracks along a ridge north of the Wakayama River. The extensional cracks appeared along a double ridgeline, suggesting the repetition of similar extensional events. In contrast, vectors of the residual horizontal displacements revealed localized convergence at the valley bottom of the Wakayama River, which we interpret as the result of hillslope slumping that occurred at both valley flanks. In the field, we confirmed that the surface ruptures appeared parallel to the thalweg and were accompanied by vertical displacement up to two meters and contraction. Based on the facts that some of the scarps appeared along existing scarps and there is a secondary anticlinal structure beneath the river, we infer the current topography along the river resulted from the localized compression caused by the convergence of both slumps.
We revealed that the landscape changes due to the 2024 Noto Peninsula earthquake were consistent with existing geomorphic features, indicating that the landscape of the peninsula primarily resulted from the repetition of earthquakes similar to the one in 2024. However, it is also true that there is an apparent discrepancy between the coseismic deformation and the existing landforms. For instance, while bedrock platforms emerged extensively along the northern coast of the peninsula on January 1, 2024, the distribution of Holocene marine terraces is much more discontinuous than the distribution of the newly emerged platform. This difference in spatial continuity indicates that the platforms in some areas are more likely to be preserved than those in other areas due to the difference in wave power and rock strength. The 2024 Noto Peninsula earthquake provides a rare opportunity to understand the impacts of large earthquakes on landscape evolution and the combined roles of tectonic and erosive forces in the preservation of landforms.
To characterize the surface displacement associated with non-tectonic processes such as landslides, we subtracted the displacement due to the fault slip estimated from a joint kinematic inversion of GNSS and pixel offsets of ALOS-2 (Tang et al., 2024, JpGU, SGD02-P10) from the one derived from the pixel offset analysis. The residual displacement field showed hillslope slumps concentrating in the northwestern and northeastern parts of the peninsula. Around the Wakayama River, we observed extensional and compressional deformation along ridges and valleys, respectively, which are associated with downslope movement on hillslopes at both sides of the ridges and valleys. Aerial photos taken after the earthquake by Geospatial Information Authority in Japan revealed extensional cracks along a ridge north of the Wakayama River. The extensional cracks appeared along a double ridgeline, suggesting the repetition of similar extensional events. In contrast, vectors of the residual horizontal displacements revealed localized convergence at the valley bottom of the Wakayama River, which we interpret as the result of hillslope slumping that occurred at both valley flanks. In the field, we confirmed that the surface ruptures appeared parallel to the thalweg and were accompanied by vertical displacement up to two meters and contraction. Based on the facts that some of the scarps appeared along existing scarps and there is a secondary anticlinal structure beneath the river, we infer the current topography along the river resulted from the localized compression caused by the convergence of both slumps.
We revealed that the landscape changes due to the 2024 Noto Peninsula earthquake were consistent with existing geomorphic features, indicating that the landscape of the peninsula primarily resulted from the repetition of earthquakes similar to the one in 2024. However, it is also true that there is an apparent discrepancy between the coseismic deformation and the existing landforms. For instance, while bedrock platforms emerged extensively along the northern coast of the peninsula on January 1, 2024, the distribution of Holocene marine terraces is much more discontinuous than the distribution of the newly emerged platform. This difference in spatial continuity indicates that the platforms in some areas are more likely to be preserved than those in other areas due to the difference in wave power and rock strength. The 2024 Noto Peninsula earthquake provides a rare opportunity to understand the impacts of large earthquakes on landscape evolution and the combined roles of tectonic and erosive forces in the preservation of landforms.