Regional Amplitude-Distance Relations, Discrimination and Detection

Abstract

Amplitude-distance curves are different in the EUS and WUS; P decays-2.5-3.0 max as r and r in EUS and WUS, while for the maximum after 3.6 km/sec on-2-3 the vertical component (termed Lg) the decay rates are r and r. The EUS results are in general agreement with the literature and with the data presented by Nersesov and Rautian (1964) for events on the northern margin of tectonic regions in the Soviet Union suggesting that discrimination results in the EUS are relevant to NSS stations within the Soviet Union. Using these distance amplitude relations, network mean amplitudes at 1000 km were computed for L and P for earthquakes and explosions in the g max EUS and WUS and a separation of 0.6 magnitude units was observed thus forming a regional discriminant. The L is larger for earthquakes than for explosions. g This conclusion is somewhat uncertain in the WUS because of the large scatter in the explosion population. However, a reasonable explanation for this large scatter is that the small events at NTS are at such shallow depths in dry alluvium that the medium is weak, resulting in a low corner frequency. This decreases the ratio P /L since P contains comparatively more high frequency than L. The scatter probably would not be a problem in a true test ban situg ation since shots will be well buried to avoid surface collapse.

Study of Low and Lg from Explosions and Its Application to Seismic Monitoring of the CTBT

“…In the 1992 Report on the DARPA Seismic Identification Workshop, Blandford et al (1992) recommended that the current research on the Lg/P discriminants be followed up with further empirical, experimental, and theoretical development of discriminants based on high-frequency S/P ratios. Earlier, by using the relatively high-frequency (3 Hz peak) Long Range Seismic Measurements (LRSM) instrument, Blandford et al (1981) concluded that the S/P ratio would work well as a regional discriminant throughout the United States if averaged over several stations. More recently, higher frequencies have provided more reliable and robust discriminants than the more conventional discriminants based on the use of frequencies lower than about 5 Hz.…”

Magnitude: Yield for Nuclear Explosions in Granite at the Nevada Test Site and Algeria: Joint Determination with Station Effects and with Data Containing Clipped and Low-Amplitude Signals

“…For certain kinds of regional data (see Blandford et al (1981), Nuttli (1973), Bollinger (1973), Jones et al (1977 Note that unless a is fixed, it is updated using (A16) at the end of each iteration. The initial estimator in each case was taken to be the least squares estimated using only the observed data since this is what corresponds to the usual approach in the seismological literature.…”

“…The general amplitude-distance models that we will use here are special cases of that used by von Seggern (1973) Although we will analyze several more general versions of equation The second application focuses on estimating B for a more regional amplitude-distance study (see Blandford et al (1981)) without estimating the station effects.…”