3:30 PM - 5:00 PM
[STT41-P04] An Experimental Study for Application of SITES method to Subsurface Structure Survey
The SITES (Seismic Interferometry Tomography for the Estimation of tectonic Structure) method is a three-dimensional subsurface structure estimation method, which extends a seismic interferometry method from only vertical to three-dimensional components data on single station (Okubo, 2009). SITES method has advantages to evaluate spatial distribution of seismic reflectors (ex. faults, aquifers) and their connectivity. We applied the method to microtremor records obtained near the northern Atera fault system (Okubo, 2009) and the Aceh and the Seulimeum segments of the Sumatran fault (Yamashina et al., 2019, 2020, 2021), and reported that peaks of autocorrelation function (ACF) contrast with the reflected wave from the fault plane. Based on the characteristics of the SITES method and its past applications, the method is effective for preliminary surveys and surveys where a wide observation area (many receiving and/or source points) cannot be deployed. To examine applicability of the SITES method and be accepted as a valid exploration method, it is necessary to clarify conditions for observation and analysis, such as required recording time, sampling frequency, type of seismometer, the frequency band of the filter, etc.
In this presentation, we present the results of applying the SITES method under various analysis conditions to microtremor records recorded near the Okamura fault, Hatano fault and Ishizuchi fault in the Median Tectonic Line (MTL) active fault zone. For these faults, previous studies show the location of seismic reflectors and the subsurface structure. We use continuous microtremor records recorded at the Doi Earthquake Observatory (KC.DOI) operated by Kochi University. KC.DOI is located about 500 m, 2 km, and 2.5 km from the eastern end of the Okamura fault, the western end of the Hatano fault, and the Ishizuchi fault, respectively. Seismometers are VSE-11 (horizontal) and VSE-12 (vertical) manufactured by Tokyo Sokushin Co. Ltd, and sampling frequency is 200 Hz. VSE-11 and VSE-12 can output velocity and acceleration simultaneously, we use both type records. About 10 km west of KC.DOI, Tsutsumi et al. (2007) conducted seismic reflection survey across the Okamura and Ishizuchi faults. In this presentation, we compare the results of the SITES method under various analysis conditions (different data lengths (15 minutes, 30 minutes, 1 hour, 1 day, etc.) and filter bandwidths) with the results of Tsutsumi et al. (2007). In the initial analysis, peaks in ACF suggesting reflected waves from one of the above three faults were obtained (Figures (c) and (d)). The results of trials with various analysis conditions provide effective support for the interpretation and reanalysis of our previous studies for the Sumatran fault.
In the future, we plan to apply the SITES method to other observational records to evaluate the effect of distance between a reflector and an observation point and plan to re-examine our previously reported results for the Sumatran fault.
Figure:
(a): Map of the Median Tectonic Line (MTL) active fault zone around the Doi Earthquake Observatory (KC.DOI) and the seismic reflection survey line “2022 Niihama Line” from Tsutsumi et al. (2007). Modified to Fig. 1B of Tsutsumi et al. (2007).
(b): Stacked time section for the 2022 Niihama Line from Tsutsumi et al. (2007). Modified to Fig. 7a of Tsutsumi et al. (2007).
(c): Topographic image of autocorrelation functions (ACFs) for microtremor records at KC.DOI using by SITES method. Vertical distribution in the N160°E cross section, which is perpendicular to the 3 faults (OF, HF and IzF) of MTL.
(d): Same as (c). Horizontal distribution of ACFs in the case of the dip angle 30°.
References:
Okubo, M., 2009, Seismic Interferometric Tomography for the Estimation of tectonic Strucures (SITES), JpGU 2009, S157-015
Tsutsumi, H. et al., 2007, Seismic Reflection Surveys Across the Median Tectonic Line Active Fault Zone in Niihama City, Ehime Prefecture and Awa City, Tokushima Prefecture, Bull. Earthq. Res. Inst., 82, 105-117, doi:10.15083/0000032491
Yamashina, T. et al., 2019, Exploration of the fault extension using SITES method; Aceh and Seulimeum segments of the Sumatran fault, Indonesia, AGU Fall 2019, S11D-0373
Yamashina, T. et al., 2020, Estimation of the Sumatran fault segments using SITES method, SSJ Fall 2020, S10P-12
Yamashina, T. et al., 2021, Estimation of the Sumatran fault segments using SITES method (2), SSJ Fall 2021, S16P-11
In this presentation, we present the results of applying the SITES method under various analysis conditions to microtremor records recorded near the Okamura fault, Hatano fault and Ishizuchi fault in the Median Tectonic Line (MTL) active fault zone. For these faults, previous studies show the location of seismic reflectors and the subsurface structure. We use continuous microtremor records recorded at the Doi Earthquake Observatory (KC.DOI) operated by Kochi University. KC.DOI is located about 500 m, 2 km, and 2.5 km from the eastern end of the Okamura fault, the western end of the Hatano fault, and the Ishizuchi fault, respectively. Seismometers are VSE-11 (horizontal) and VSE-12 (vertical) manufactured by Tokyo Sokushin Co. Ltd, and sampling frequency is 200 Hz. VSE-11 and VSE-12 can output velocity and acceleration simultaneously, we use both type records. About 10 km west of KC.DOI, Tsutsumi et al. (2007) conducted seismic reflection survey across the Okamura and Ishizuchi faults. In this presentation, we compare the results of the SITES method under various analysis conditions (different data lengths (15 minutes, 30 minutes, 1 hour, 1 day, etc.) and filter bandwidths) with the results of Tsutsumi et al. (2007). In the initial analysis, peaks in ACF suggesting reflected waves from one of the above three faults were obtained (Figures (c) and (d)). The results of trials with various analysis conditions provide effective support for the interpretation and reanalysis of our previous studies for the Sumatran fault.
In the future, we plan to apply the SITES method to other observational records to evaluate the effect of distance between a reflector and an observation point and plan to re-examine our previously reported results for the Sumatran fault.
Figure:
(a): Map of the Median Tectonic Line (MTL) active fault zone around the Doi Earthquake Observatory (KC.DOI) and the seismic reflection survey line “2022 Niihama Line” from Tsutsumi et al. (2007). Modified to Fig. 1B of Tsutsumi et al. (2007).
(b): Stacked time section for the 2022 Niihama Line from Tsutsumi et al. (2007). Modified to Fig. 7a of Tsutsumi et al. (2007).
(c): Topographic image of autocorrelation functions (ACFs) for microtremor records at KC.DOI using by SITES method. Vertical distribution in the N160°E cross section, which is perpendicular to the 3 faults (OF, HF and IzF) of MTL.
(d): Same as (c). Horizontal distribution of ACFs in the case of the dip angle 30°.
References:
Okubo, M., 2009, Seismic Interferometric Tomography for the Estimation of tectonic Strucures (SITES), JpGU 2009, S157-015
Tsutsumi, H. et al., 2007, Seismic Reflection Surveys Across the Median Tectonic Line Active Fault Zone in Niihama City, Ehime Prefecture and Awa City, Tokushima Prefecture, Bull. Earthq. Res. Inst., 82, 105-117, doi:10.15083/0000032491
Yamashina, T. et al., 2019, Exploration of the fault extension using SITES method; Aceh and Seulimeum segments of the Sumatran fault, Indonesia, AGU Fall 2019, S11D-0373
Yamashina, T. et al., 2020, Estimation of the Sumatran fault segments using SITES method, SSJ Fall 2020, S10P-12
Yamashina, T. et al., 2021, Estimation of the Sumatran fault segments using SITES method (2), SSJ Fall 2021, S16P-11