Abstract
We developed the high-resolution three-dimensional seismic survey system for shallow water and carried out the survey of the active fault in the nearshore waters of the northern Suruga Bay using the system. The system is designed based on the following concepts, 1) usable system in nearshore waters using a small boat, and 2) acquirable seismic data in small bin size (2 m × 2 m) to image sub-seafloor geological structures in high-resolution. The system consists of onboard data acquisition instruments and towing equipment such as one boomer sound source and four receiver cables. Each receiver cable has 8 channel hydrophone arrays arranged at 2.5 m interval, and is towed behind the survey boat arranged at 8 m interval in the rectangular direction to the survey line.
The boomer was shot at intervals of 1.25 m under ship speeds between 3 and 4 knots.
The three-dimensional seismic survey area is 1,400 m long in the east-west and 300 m wide in the northsouth. The seismic stratigraphy is mainly divided into three units, Unit A, Unit B and Unit C in descending order. A prominent fault called the Kanbara Fault, which splits the survey area in two parts, is a reverse type extending from northeast to southwest. The deformation in Unit A seems to be extended near the seafloor. The amount of vertical displacement is 22 to 26 m based on the upper surface of Unit B. As the upper surface is interpreted to be approximately 11,000 years old, the average vertical slip rates on the fault is 2.0 to 2.4 m/kｙ calculated by the above-mentioned interpretations.
We obtained some remarkable stripe-like patterns on the time-slice sections related to the uplifting western part of the survey area. If a strike-slip fault crosses above-mentioned stripe-like patterns, it is expected that the amount of lateral displacement caused by the strike-slip movement will be estimated on the time-slice sections.
