Seismic Attribute and Logging Data Correlation at IODP NanTroSEIZE Sites C0001, C0002, and C0004

As a part of a Core-Log-Seismic integration study for the NanTroSEIZE project, we compare seismic attributes to logging data at three drill sites in the Nankai trough. Seismic attributes are calculated from seismic traces and often expose new information relative to the conventional seismic section. We calculate several seismic attributes from the high quality 3D seismic volume and correlate them with the logging data. Site C0001 The envelope attribute section shows high amplitude in the slope sediments of Log Unit I. Conversely, Log Unit II is characterized by very low envelope amplitude. The characteristics of gamma ray and ring resistivity log data within Log Units I and II do not exhibit significant difference between these Log Units except for some spikes in the log data in Log Unit II. However the seismic envelope attribute shows a clear difference between these intervals. The dominant frequency attribute also shows remarkable difference between Log Units I and Site C0002 A zone of low envelope amplitude is detected in the 3D attribute map just below the Bottom Simulating Reflector (BSR) near Site C0002. In this zone, gamma ray and ring resistivity log data indicate relatively less perturbed values compared to the depths above and below. On the other hand, a zone of high envelope amplitude exists just below the low envelope amplitude zone mentioned above. In this zone, gamma ray and ring resistivity log data are both characterized by increased high frequency content. This zone corresponds to Zone B, where log data suggested the existence of free gas. Dominant Frequency attribute data are correlated with ring resistivity log data. Above the depth of the BSR, we observe two intervals of high dominant frequency (~60Hz) at the depth ranges of 2150-2220 m LSS and 2280-2330 m LSS. At these depths, ring resistivity data frequently show spiky high values. Between these intervals, at the depths of 2220-2280 m LSS, the dominant frequency is lower (~35Hz) and ring resistivity is less spiky. The spiky resistivity signals are correlated with the existence of hydrate at this depth range at site C0002. High dominant frequency may suggest concentration of gas hydrate around this site. Site C0004 The upper part of Site C0004 (Log Units I and II) is a low envelope amplitude zone. This zone includes slope sediments and a wedge shaped thrust package. The gamma ray and resistivity log data indicate remarkable variation within this zone, however the envelope amplitude attribute does not reflect this variation. Log Unit III is characterized by a high envelope amplitude and high dominant frequency (50-60 Hz).