Calibration of the M(sub s):m(sub b) Discriminant at the International Monitoring System Array NVAR (PS-47)
Abstract
Surface wave magnitude [M(sub s)] estimation for small events recorded at near-regional distances will often require a magnitude scale designed for Rayleigh waves with periods between 5 and 25 seconds. We have completed several studies aimed at examining the usefulness of existing and new formulas at estimating surface wave magnitudes at periods not restricted to approximately 20 seconds. In Chapter 1, we show that 7-second surface waves can be used to estimate magnitudes for Nevada Test Site explosions and earthquakes using a modified version of the Marshall and Easham (1971) formula. Body wave magnitudes for recent earthquakes were estimated by calibrating the new NVAR array to the Denny et al. (1987) m(sub b) as shown in Chapter 2. New methods of measuring local and near-regional amplitudes for body wave magnitude estimation are also discussed in Chapter 3. Additionally, the Russell surface-wave magnitude formula (2005) and the M(sub s)(VMAX) measurement technique provide a new method for estimating surface-wave magnitudes as described in Chapter 4. There are several benefits to the new method. First, the technique allows for time domain measurements of surface wave amplitudes, giving an analyst the ability to visually confirm that the pick is correct and is an actual surface wave. Also, it allows for surface wave magnitudes to be measured at local and regional distances where traditional 20-second magnitudes cannot be used. And these magnitudes are not biased with respect to teleseismic estimates using the same M(sub s)(VMAX) measurement technique. Additionally, the application of narrow-band Butterworth filtering techniques appropriately handles Airy phase phenomena that prior to this study, had to be accounted for using Marshall and Basham's (1972) empirical corrections. Finally, because the method is variable period and not restricted to near 20-seconds period, the analyst is allowed to measure M(sub s), where the signal is largest.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2005
- Accession Number
- ADA455321
Entities
People
- David G. Harkrider
- David Russell
- Delaine T. Reiter
- Eugene Herrin
- Ileana M. Tibuleac
- Jessie L. Bonner
- Robert H. Shumway
- Robert Herrmann
- Sara A. Russell