Density of Sediment in Kyoto Basin Inferred from 2D Gravity Analysis along Horikawa-Oguraike and Kuzebashi Seismic Survey Lines

Abstract

The Horikawa-Oguraike and Kuzebashi seismic reflection and refraction profiles were obtained in the Kyoto Basin from 1998 to 1999. The gravity measurements were conducted at 50-300m station intervals along the seismic profiles in order to estimate the density of sediments in the basin. The N-S and E-W gravity profiles correspond to the Horikawa-Oguraike and the Kuzebashi seismic profiles, respectively. The Kyoto Basin was composed of basement rocks covered by unconsolidated sedimentary layers. The top surface of the basement of 2D two-layers models were constructed with the constraints of seismic profiles. The inferred density contrast between the basement and the overlaying sediments in the N-S two-layer model was 0.3g/cm³ and the difference between observed and calculated gravity anomalies was within 1.5m gal. The results of the density loggings and the distribution of the seismic velocities along the Horikawa-Oguraike seismic section indicate the density variation. The multi-layered N-S model was constructed based on the seismic profile and the borehole data. On the other hand, the density contrast between the sedimentary cover and the basement in the E-W two-layer model was 0.7g/cm³ and the difference between observed and calculated gravity anomalies was within 1mgal. The regional gravity trend inferred from this study tilts toward the northeast in the Kyoto Basin.