Energy release patterns and shaking effects of earthquakes in the Japan
Trench: A Hilbert-Huang Transform approach
Abstract
Subduction zones showcase the multiplicity of earthquakes—interplate,
intraplate and intraslab—with shallow, intermediate, or deep focus,
associated with different energy release patterns and frequency
contents. An understanding of the duration and frequencies associated
with various pulses of energy is useful for damage assessment. Empirical
Mode Decomposition (EMD) of strong-motion records and the application of
Hilbert transform have been suggested to overcome the limitations of the
Fourier spectral analysis in dealing with highly non-linear
strong-motion records (Huang et al., 1998, Zhang et al., 2003).
Following the same approach, we have been trying various methods of
analysis using the KiK-net strong-motion records to explore the efficacy
of these techniques in representing the source of the rupture, in terms
of energy release and frequency distribution. Our previous studies used
EMD and time-frequency analysis tools such as spectrogram, scalogram,
and Hilbert spectrum, using Intrinsic Mode Functions (IMFs) of the
original signals as inputs. Nishant (2019) made random picks of IMFs to
represent sources by correlating the sum of the selected IMFs with the
original signal but found that the results were station dependent. We
selected IMFs based on their frequency content (0.1 to 3 Hz) and used
their linear combinations to develop the Energy Release Functions (ERF)
for individual earthquakes (Mache et al., 2019). They reported that the
ability to capture the signature of the original signal using the IMFs
varied between earthquakes and stations. Next, we selected stations
based on the direction of rupture inferred from teleseismic waveform
models. The use of appropriate combinations of individual IMFs, chosen
based on the direction of slip, resulted in ERFs whose shapes compared
better with the Moment Rate Functions (MRFs) obtained from the
teleseismic models. To further explore the station dependence on the
resolution of ERFs viz-a-viz the MRFs, we used the instrumental seismic
intensity distribution maps (JMA 1996, Shabestari and Yamazaki 2001) to
select the stations. We analyzed five earthquakes; two interplate (Mw
7.2 2005 Miyagi, and Mw 6.9 2008/07/19), two intraplate (Mw 7.0 2003
Sendai, and Mw 7.2 2012 Kamaishi) and one intraslab (Mw 7.1 2011
Miyagi), following the above methodologies. This abstract presents the
initial results of our study, which to our knowledge, is the first of
its kind and holds significant potential in understanding the spatial
and temporal patterns of energy release and their associated
frequencies. [cont.]