Premium
Power‐law decay characteristic of coda envelopes revealed from the analysis of regional earthquakes
Author(s) -
Lee Won Sang,
Sato Haruo
Publication year - 2006
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl025840
Subject(s) - coda , seismogram , seismology , amplitude , geology , envelope (radar) , attenuation , power law , geophysics , physics , mathematics , statistics , optics , telecommunications , radar , computer science
Seismic envelope of coda waves is an efficient measure to estimate physical parameters of the Earth heterogeneity. For NS component seismograms of regional earthquakes recorded by 11 IRIS stations, applying the Hilbert transform to make seismic envelopes in period bands from 0.25–0.5s to 16–32s with lapse time as long as 4000s, we discovered that coda envelopes decay according to some power of lapse time measured from the origin time. It is new and different from the present knowledge about coda envelopes which have been described by several bending curves with different decay rates. The ‘power‐law’ decay characteristic of seismic envelopes indicates that the spectra amplitude of seismic coda could be simply expressed as of the form A ( t , T C ) ∝ where t is lapse time and T C is central period in second. Applying regression analysis, we found that the exponent α value has period dependence and ranges α 1 = 1.3∼6.5 (0.25–0.5s∼16–32s), α 2 = 0.6∼6.1 (0.5–1s∼16–32s) for before and after ScS arrival, respectively. Moreover, it shows no significant difference between shallow and deep focus events for periods shorter than 8s. The simple and distinct characteristics of seismic coda envelopes could provide reliable information to determine physical characteristics such as attenuation and scattering to identify the regional difference of medium heterogeneity in the Earth.