Regional Lg attenuation for the continental United States

Measurements of the Fourier amplitude spectra of Lg phases recorded at high frequency (0.5 to 14.0 Hz) by broadband seismic stations are used to determine regional attenuation relationships for southern California, the Basin and Range Province, the central United States, and the northeastern United States and southeastern Canada. Fourier spectral amplitudes were measured every quarter octave from Lg phases windowed between 3.0 and 3.7 km sec−1 and recorded in the distance range of 150 to 1000 km. Attenuation at each frequency is determined by assuming a geometrical spreading exponent of 0.5 and inverting for Q and source and receiver terms. Both southern California and the Basin and Range Province are well described by low Lg Q and frequency-dependent attenuation. Lg spectral amplitudes in southern California are fit at low frequencies (0.625 to 0.875 Hz) by a constant Lg Q of 224 and by a frequency-dependent Lg Q function Q = 187−7+7f0.55(±0.03) in the frequency band 1.0 to 7.0 Hz. The Basin and Range Province is characterized by a constant Lg Q of 192 for frequencies of 0.5 to 0.875 Hz and by the frequency-dependent Lg Q function Q = 235−11+11f0.56(±0.04) in the frequency band 1.0 to 5.0 Hz. A change in frequency dependence above 5.0 Hz is possible due to contamination of the Lg window by Pn and Sn phases. Lg spectral amplitudes in the central United States are fit by a mean frequency-independent Lg Q of 1291 for frequencies of 1.5 to 7.0 Hz, while a frequency-dependent Lg Q of Q = 1052−83+91(f/1.5)0.22(±0.06) fits the Lg spectral amplitudes for the northeastern United States and southeastern Canada over the passband 1.5 to 14.0 Hz. Attenuation measurements for these areas were restricted to frequencies >1.5 Hz due to larger microseismic noise levels at the lower frequencies.

[1]  K. Aki.  Scattering and attenuation of shear waves in the lithosphere , 1980 .

[2]  K. Priestley,et al.  Measurement of frequency dependent Lg attenuation in the Great Basin , 1986 .

[3]  H. Hasegawa.  Attenuation of Lg waves in the Canadian Shield , 1985 .

[4]  Gail M. Atkinson,et al.  The shape of ground motion attenuation curves in southeastern Canada , 1992, Bulletin of the Seismological Society of America.

[5]  I. Gupta,et al.  Attenuation of ground motion in the Eastern United States , 1987 .

[6]  Robert B. Herrmann,et al.  Regionalization of crustal coda Q in the continental United States , 1983 .

[7]  B. Mitchell,et al.  Attenuation of multiphase surface waves in the Basin and Range province, part I: Lg and Lg coda , 1990 .

[8]  Raúl R. Castro,et al.  Site response, attenuation and source spectra of S waves along the Guerrero, Mexico, subduction zone , 1990 .

[9]  O. Nuttli,et al.  Seismic wave attenuation and magnitude relations for eastern North America , 1973 .

[10]  J. Ebel.  The MLg(F) Magnitude Scale: A Proposal for its use for Northeastern North America , 1994 .

[11]  M. Campillo.  Propagation and attenuation characteristics of the crustal phaseLg , 1990 .

[12]  Robert B. Herrmann,et al.  Lg attenuation and source studies using 1982 Miramichi data , 1987 .

[13]  G. Bollinger,et al.  Q estimates along the wasatch front in Utah derived from Sg and Lg wave amplitudes , 1992 .

[14]  Gordon F. West,et al.  A novel technique for measuring Lg attenuation—results from Eastern Canada between 1 to 10 hz , 1987 .

[15]  G. A. Bollinger,et al.  On the relation between modified Mercalli intensity and body-wave magnitude , 1979, Bulletin of the Seismological Society of America.

[16]  L. Knopoff,et al.  Interpretation of Lg , 1973 .

[17]  B. Kennett,et al.  Propagation of Lg waves in the North Australian Craton: Influence of crustal velocity gradients , 1991 .

[18]  T. J. Owens,et al.  Propagation characteristics of Lg across the Tibetan Plateau , 1996, Bulletin of the Seismological Society of America.

[19]  Robert B. Herrmann,et al.  Modeling some empirical vertical component Lg relations , 1983 .

[20]  P. Richards,et al.  Variability of crustal attenuation in the northeastern United States from Lg waves , 1996 .

[21]  O. Nuttli,et al.  Yield estimates of nevada test site explosions obtained from seismic Lg waves , 1986 .

[22]  Arthur Frankel,et al.  Energy-flux model of seismic coda: Separation of scattering and intrinsic attenuation , 1987 .

[23]  H. Sato.  Unified approach to amplitude attenuation and coda excitation in the randomly inhomogeneous lithosphere , 1990 .

[24]  S. Gregersen.  Lg-wave propagation and crustal structure differences near Denmark and the North Sea , 1984 .

[25]  A. Frankel.  Mechanisms of seismic attenuation in the crust: Scattering and anelasticity in New York State, South Africa, and southern California , 1991 .