TY - JOUR
T1 - Sensitivity of Seismic Velocity Changes to the Tidal Strain at Different Lapse Times
T2 - Data Analyses of a Small Seismic Array at Izu-Oshima Volcano
AU - Takano, Tomoya
AU - Nishimura, Takeshi
AU - Nakahara, Hisashi
AU - Ueda, Hideki
AU - Fujita, Eisuke
N1 - Funding Information:
We thank the Japan Meteorological Agency for providing us with continuous seismic data which were from the Data Management Center of National Research Institute for Earth Science and Disaster Resilience (http://www.hinet.bosai.go.jp) and volumetric strain data (http://www.data.jma.go.jp). All figures were made using the Generic Mapping Tool (Wessel & Smith,). Careful and constructive comments from reviewer Anne Obermann and an anonymous reviewer significantly improved this manuscript. We thank the Editor Martha Savage and the Associate Editor Gregory Waite for editorial efforts and comments. Tomoya Takano is grateful for support from the Japan Society for the Promotion of Science (JSPS) and a partial support from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program.
Funding Information:
We thank the Japan Meteorological Agency for providing us with continuous seismic data which were from the Data Management Center of National Research Institute for Earth Science and Disaster Resilience (http://www.hinet.bosai.go.jp) and volumetric strain data (http://www.data.jma.go.jp). All figures were made using the Generic Mapping Tool (Wessel & Smith, 1998). Careful and constructive comments from reviewer Anne Obermann and an anonymous reviewer significantly improved this manuscript. We thank the Editor Martha Savage and the Associate Editor Gregory Waite for editorial efforts and comments. Tomoya Takano is grateful for support from the Japan Society for the Promotion of Science (JSPS) and a partial support from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its Earthquake and Volcano Hazards Observation and Research Program.
Publisher Copyright:
©2019. American Geophysical Union. All Rights Reserved.
PY - 2019/3
Y1 - 2019/3
N2 - We investigate seismic velocity changes in response to the tidal strain at Izu-Oshima volcano, Japan, by analyzing the data of permanent seismic stations and a small seismic array to evaluate the characteristics of strain sensitivity of velocity changes. We estimate the seismic velocity changes by phase differences between cross-correlations functions of ambient noises at the frequency of 2–4 Hz stacked for time periods with different tidal strain amplitudes. The seismic velocity changes decrease and increase during dilatation and contraction periods, respectively, when analyzing the cross-correlations functions at early lapse times ranging from 2 to 7 s. The strain sensitivity of seismic velocity changes is estimated to be (−2.1 ± 0.2) × 104 at the early lapse times. However, we find that strain sensitivity of the seismic velocity changes decreases when analyzing the cross-correlation functions at later lapse times from 7 s to 35 s. Applying an array analysis to the cross-correlation functions, we observe apparent velocities of about 1 km/s at the early lapse times and those of higher than 1 km/s at the late lapse times. Since the group velocity of Rayleigh waves is 1.1 km/s at Izu-Oshima volcano, the apparent velocities at the late lapse times may indicate the scattered or reflected body waves incident from a deeper region. Decrease of strain sensitivity with the lapse times therefore results from the emergence of body waves on the late lapse times. These results highlight the need to pay attention to wave types of cross-correlation functions and their paths to interpret seismic velocity changes.
AB - We investigate seismic velocity changes in response to the tidal strain at Izu-Oshima volcano, Japan, by analyzing the data of permanent seismic stations and a small seismic array to evaluate the characteristics of strain sensitivity of velocity changes. We estimate the seismic velocity changes by phase differences between cross-correlations functions of ambient noises at the frequency of 2–4 Hz stacked for time periods with different tidal strain amplitudes. The seismic velocity changes decrease and increase during dilatation and contraction periods, respectively, when analyzing the cross-correlations functions at early lapse times ranging from 2 to 7 s. The strain sensitivity of seismic velocity changes is estimated to be (−2.1 ± 0.2) × 104 at the early lapse times. However, we find that strain sensitivity of the seismic velocity changes decreases when analyzing the cross-correlation functions at later lapse times from 7 s to 35 s. Applying an array analysis to the cross-correlation functions, we observe apparent velocities of about 1 km/s at the early lapse times and those of higher than 1 km/s at the late lapse times. Since the group velocity of Rayleigh waves is 1.1 km/s at Izu-Oshima volcano, the apparent velocities at the late lapse times may indicate the scattered or reflected body waves incident from a deeper region. Decrease of strain sensitivity with the lapse times therefore results from the emergence of body waves on the late lapse times. These results highlight the need to pay attention to wave types of cross-correlation functions and their paths to interpret seismic velocity changes.
KW - Earth tide
KW - active volcano
KW - ambient noise
KW - array analysis
KW - seismic interferometry
KW - seismic velocity changes
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U2 - 10.1029/2018JB016235
DO - 10.1029/2018JB016235
M3 - Article
AN - SCOPUS:85063517758
VL - 124
SP - 3011
EP - 3023
JO - Journal of Geophysical Research: Solid Earth
JF - Journal of Geophysical Research: Solid Earth
SN - 2169-9313
IS - 3
ER -