MODELING AND EMPIRICAL RESEARCH ON ENERGY PARTITIONING OF REGIONAL SEISMIC PHASES USED FOR EXPLOSION MONITORING

• Main Authors: Mark D. Fisk, Thorne Lay, Steven Taylor
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Brune; Mueller; Novaya Zemlya
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.525.1694; http://www.ldeo.columbia.edu/res/pi/Monitoring/Doc/Srr_2005/PAPERS/03-06.pdf

We are investigating energy partitioning of local and regional seismic phases, focusing on geophysical causes of their frequency dependence and variances, mechanisms of P-to-S conversion, different scattering effects for P and S phases that affect their complexity, and implications for reliable and defensible use of P/S discriminants. For empirical studies, we are using large data sets consisting of Pn, Pg, Sn and Lg spectra and time-domain measurements at frequencies from 0.1 to 10 Hz, and correcting for geometrical spreading, attenuation, and magnitude, so that the variability and frequency dependence of individual phases may be assessed. Objectives are to quantify these aspects for explosions and earthquakes near the Lop Nor, Semipalatinsk, Novaya Zemlya, and Nevada test sites, and assess whether consistent patterns emerge. We plan to interpret empirical observations in terms of geophysical mechanisms by using complex elastic-screen simulations, spanning relevant spectral content (0.1 to 10 Hz) for distances of at least 0 to 600 km, using realistic models with multi-scale heterogeneity, rough Moho, topography, and other boundaries. Preliminary efforts have focused on examining spectral scaling as a function of source size and frequency-dependent P/S discrimination performance for nuclear explosions and selected earthquakes near the Lop Nor test site in China. Network-averaged relative spectra for given phases (using nearby events of various sizes) are compared to theoretical relative spectra using a modified Brune (1970) model for earthquakes and a Mueller and Murphy (1971) model