Lg and Other Regional Phases in South America
Abstract
For South American epicenters south of 4/deg S, no Lg is recorded at LPB. Brazilian earthquakes have a ratio of amplitudes Lg/P 5.2 t 0.3. Rg is larger: Lg/Rg 0.7 t 0.3. For the measurement of magnitudes mbLg, the southernmost South America is excluded. The following formulas are adopted: mbLg = 3.80 + 2.00 log + log(A/T) for cordilleran epicenters and mbLg = 4.40 + 1.15 log + log(A/T) for shield epicenters (Appendix 1). Rg waves are very small from off the western coast, fair from the coast, clear from continental Peru and largest from southern Peru. Li are shear waves emerging among scattered waves. Preliminary values of Q across Peru and beneath LPB were obtained for P waves and short period guided waves. The intensity attenuation of the nine Bolivian seismogenic zones can be reduced to four values (Appendix 2). Positive P residuals average 2.6 s for oceanic earthquakes and 2.5 for continental ones. Particle motion, spectral analysis and wave recording envelope have been analyzed, but no solid conclusions have been reached for a region so large and diversified. Several hypotheses are presented. In the P-coda, besides pP, other phases originate by scattering, reflection, channelling, caused by subducted Nazca plate and by crustal thickening of the Andes roots. Appendices 3 and 4 expand the analysis of P type phases....South America, Lg, Earthquake, Mg Lg, Rg, P, Li, Velocity anomalies, pP, Q, Attenuation.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 01, 1992
- Accession Number
- ADA260117
Entities
People
- Estela R. Minaya
- Ramon R. Cabre