Magnitudes from Local and Regional Seismic Signals: Test Case Iran
Karl F. Veith
To properly utilize local, regional, and teleseismic phases for magnitude estimation, one needs to understand the relationships between these phases. In particular one needs to understand the division of energy among these phases. The relative amount of energy available for the different phases depends strongly upon the velocity at the source. The use of a single set of phase amplitude correction curves for phases from the mantle and core will give relatively consistent magnitudes, but they will need a source site correction factor to generate the correct magnitude/yield values from site to site. The biggest adjustment needed is for crustal phases since there can be very significant differences in the amount of source energy that is trapped in the crust and these differentials are directly opposite to those observed for the mantle and core phases.
A test set of more than 3280 local and regional amplitude measurements from fifty earthquakes that occurred in Iran was selected and analyzed. Magnitude correction curves for Pg, Pn, Sn, and Sg/Lg phases were developed along with station correction factors. Results are compared and evidence for differences between source locations within Iran is discussed.
Dr. Veith received a BS and MS in Geophysics from the University of Minnesota. He worked with the U.S. Bureau of Mines in Minneapolis while finishing his Masters. He moved to Texas where he received his PhD in Geophysics from Southern Methodist University. Dr. Veith spent 15 years doing applied research work for the Air Force Technical Applications Center. After a five year hiatus in SOHIO’s research lab, he moved to the Washington area where he has been providing technical advice and consulting services to the government for the last thirty years. While his main expertise lies in the seismic verification of nuclear testing, Dr. Veith has also worked in the detection and characterization of underground facilities, unexploded ordnance, and in the utilization of radar, thermal and electro-optical imagery for a variety of verification purposes.