Spatiotemporal distribution of seismic energy radiation from low‐frequency tremor in western Shikoku, Japan

Abstract

[1] The spatiotemporal patterns of the radiated seismic energy from low-frequency tremor associated with slow slip events in western Shikoku, Japan, have been estimated. A spatially decaying mean square amplitude and differential traveltime measurement from envelope correlations observed at Hi-net stations were used to locate tremors and to estimate their seismic energies. Tremor amplitude was corrected for the site amplification factors estimated using the coda normalization method. The location of the tremor is estimated as the position where both the decay of the observed energy and the differential travel times are well explained. The temporal pattern of the total energy released agrees very well with the observed tilt records. Although the spatial patterns of the energy radiation vary strongly among the six slow slip events (SSEs) in western Shikoku, the region where they overlap always radiates relatively high levels of energy. The estimated band-limited energy rate of the tremor for a 2 to 10 Hz bandwidth was typically between 10 5 and 10 6 J/min, though there is temporal variation of the radiation energy. The released total energy associated with the SSEs whose magnitude is 5.9-6.1 is on the order of 10 8 J within the duration of SSEs of 8-13 days. This is quite small energy radiation compared to the moment release of accompanying SSE. The scaled energy, which is the ratio of the seismic moment and the seismic energy, for the slow slip and a very low frequency earthquake was estimated to be 5 orders of magnitude smaller than that of a regular earthquake.Citation: Maeda, T., and K. Obara (2009), Spatiotemporal distribution of seismic energy radiation from low-frequency tremor in western Shikoku, Japan,

Discontinuous boundaries of slow slip events beneath the Bungo Channel, southwest Japan

“…(ii) The deep boundary between the major L-SSE area and the minor L-SSE area corresponds to the up-dip limit of the tremor area.

Figure 3Red polygon with the solid and dashed lines shows the 2010 L-SSE with more than 0.2 m and 0.1 m slip areas estimated in this study. Yellow and grey circles indicate deep tremors detected during the 2010 L-SSE data period (2009.5 to 2011.2) using the modified envelope correlation method considering tremor amplitude 34 and the hybrid-clustering method 35 of the National Research Institute for Earth Science and Disaster Prevention (NIED) of Japan. Open ellipses with dashed lines indicate approximate source areas of the 1946 Nankai and 1968 Hyuga-nada earthquakes.

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Characteristics and interactions between non-volcanic tremor and related slow earthquakes in the Nankai subduction zone, southwest Japan

“…Maeda and Obara (2009) modified the ECM by combining the spatial distributions of amplitude data and pinning tremor locations at the plate interface (Shiomi et al, 2008). Output from the method was processed by cluster analysis to eliminate nontremor source inputs , as shown in Fig a single station to obtain data for the entire Cascadia subduction zone.…”

“…Ito et al (2009) estimated the rate of seismic moment release by VLF earthquakes as 0.1% of the moment rate of release by short-term SSEs. Maeda and Obara (2009) evaluated the scaled energy, which is the ratio of the total seismic energy derived from tremor activity to the seismic moment, and found tremor and deep VLF earthquake energy release to be five orders of magnitude smaller than that of a regular earthquake. These results suggest that sources of tremor and VLF earthquakes occupy only a fractional portion of the short-term SSE fault plane.…”

Prediction of maximum P- and S-wave amplitude distributions incorporating frequency- and distance-dependent characteristics of the observed apparent radiation patterns

“…The frequency-dependent characteristics of the observed apparent radiation patterns have been incorporated into various applications such as the predictions of strong ground motions (e.g., Pitarka et al 2000;Pulido and Kubo 2004), the estimation of high-frequency seismic energy radiation during large earthquakes (e.g., Nakahara 2013), nonvolcanic/volcanic tremors (e.g., Maeda and Obara 2009;Kumagai et al 2010;Cannata et al 2013;, and landslides (e.g., Ogiso and Yomogida 2015), and the earthquake early warning systems (e.g., Okamoto and Tsuno 2015). Although the frequency-distance change model for S-wave radiation pattern proposed by Satoh (2002b) has been used in some applications, to achieve more accurate estimation and prediction of high-frequency seismic radiation, a precise frequency-and distance-dependent model for the apparent radiation pattern for both P and S waves is required.…”