Magnitudes and moments of duration

1984 ◽  
Vol 74 (6) ◽  
pp. 2335-2356
Author(s):  
William H. Bakun
Keyword(s):  
Epicentral Distance ◽  
Local Magnitude ◽  
Empirical Formulas ◽  
Central California ◽  
Station Corrections ◽  
Source Regions ◽  
San Andreas ◽  
Accuracy And Precision ◽  
Unbiased Estimates ◽  
Better Than

Abstract Coda-duration τ at 42 of the stations in the U.S. Geological Survey's central California seismic network (CALNET) for earthquakes in five source regions of central California—the Parkfield and San Juan Bautista sections of the San Andreas fault, the Sargent fault, the Coyote Lake section of the Calaveras fault, and the Livermore area—are used to obtain empirical formulas relating local magnitude ML and seismic moment M0 to τ and epicentral distance Δ. Models with log2 τ fit the data better than those assuming a log τ dependence. For 55 earthquakes with 1.1. ≦ ML ≦ 5.3, ML = 0.92 + 0.607 (±0.005)log2 τ + 0.00268(± 0.00012)Δ. These ML assume a Wood-Anderson seismograph magnification of 2800; 0.15 should be subtracted from these ML for continuity with magnitudes obtained from or calibrated against typical (magnification ∼ 2000) Wood-Anderson seismographs. For 53 earthquakes with 18.4 ≦ log M0 ≦ 22.3, log M0 = 17.97 + 0.719(± 0.0007)log2 τ + 0.00319(±0.00013)Δ. These relations provide unbiased estimates of ML for 1.5 ≲ ML ≲ 5.3 and 19 ≲ log M0 ≲ 22.3. Station corrections can significantly improve the accuracy and precision of ML and log M0 estimates, particularly if τ from a small number of stations are used. Regional variations in station corrections reflect an increase in coda duration toward the south within the CALNET.

Simplified estimation of seismic moment from seismograms

1983 ◽  
Vol 73 (3) ◽  
pp. 735-748
Author(s):  
Bruce A. Bolt ◽  
Miguel Herraiz
Keyword(s):  
Spectral Analysis ◽  
Least Squares ◽  
Empirical Result ◽  
Seismic Moment ◽  
Epicentral Distance ◽  
Moment Magnitude ◽  
Local Magnitude ◽  
Logarithmic Term ◽  
Central California ◽  
Maximum Peak

abstract This study proposes a method to estimate the seismic moment of regional and local earthquakes based on simple measurements made directly on Wood-Anderson seismograms. The method parallels the routine estimation of local magnitude in observatory work. The relation used is log M o = a + b log ( C × D × Δ p ) where C is the maximum peak-to-peak amplitude read on a Wood-Anderson seismogram, D is the duration between the S arrival and the onset with amplitude C/d, Δ is epicentral distance, and a, b, p, and d are constants. The form of the logarithmic term is suggested by the analytical expression for moment (Keilis-Borok, 1960). Least-squares fits were made to data from 73 Wood-Anderson records of 16 central California earthquakes with seismic moments already evaluated independently from spectral analysis or broadband displacement records. The values p = 1, d, = 3 proved appropriate and subsequent regression yielded log M o = ( 16.74 ± 0.20 ) + ( 1.22 ± 0.14 ) log ( C × D × Δ ) where Mo is dyne-cm, C in millimeters, D in seconds, and Δ in kilometers. The corresponding moment-magnitude relation is log M o = ( 17.92 ± 1.02 ) + ( 1.11 ± 0.15 ) M L , for 3 ≦ ML ≦ 6.2. The latter fit is close to an earlier empirical result (Johnson and McEvilly, 1974) for central California based on fewer cases and a different range of magnitude (2.4 ≦ ML ≦ 5.1).

Seismic moments, local magnitudes, and coda-duration magnitudes for earthquakes in central California

1984 ◽  
Vol 74 (2) ◽  
pp. 439-458 ◽  
Author(s):  
William H. Bakun
Keyword(s):  
Seismic Moment ◽  
San Andreas Fault ◽  
Seismic Network ◽  
San Juan ◽  
Local Magnitude ◽  
Central California ◽  
San Andreas ◽  
Duration Magnitude ◽  
San Juan Bautista ◽  
The U.S

Abstract Onscale seismograms recorded at stations in the U.S. Geological Survey's (USGS) central California seismic network (CALNET) have been used to estimate the seismic moment M0 and local magnitude ML for earthquakes of 1 ≦ ML ≦ 4 located on the San Juan Bautista and Parkfield sections of the San Andreas fault, the Coyote Lake section of the Calaveras fault, the Sargent fault, and near Livermore. These data, together with M0 and ML estimates for 4 ≦ ML ≦ 6 earthquakes in these areas, cannot be fit with a single linear log M0-versus-ML relation. Rather, the data are consistent with log M0 = 1.5 ML + 16 for 3 ≲ ML ≲ 6, with log M0 = 1.2 ML + 17 for 1 1/2 ≲ ML ≲ 3 1/2 and with a slope of ⅔ to 1 fro 1/2 ≲ ML ≲ 1 1/2. Whereas USGS coda duration magnitude MD is consistent with ML for 1 1/2 ≲ ML ≲ 3¼, MD is larger than ML at ML ≲ 1 1/2 and smaller than ML at ML ≳ 3¼. Log M0 can be estimated to a precision of 0.2 for 1 ≦ MD ≦ 3 1/2 earthquakes in central California by applying log M0 = 1.2 MD + 17 to the MD that have been routinely published by the USGS.

The closed-subpopulation method and estimation of population size from mark-recapture and ancillary data

2000 ◽  
Vol 78 (2) ◽  
pp. 320-326 ◽  
Author(s):  
Frank AM Tuyttens
Keyword(s):  
Population Size ◽  
Ancillary Data ◽  
Mark Recapture ◽  
Animal Populations ◽  
Accuracy And Precision ◽  
Population Size Estimates ◽  
Minimum Number ◽  
Flexible Framework ◽  
And Performance ◽  
Better Than

The algebraic relationships, underlying assumptions, and performance of the recently proposed closed-subpopulation method are compared with those of other commonly used methods for estimating the size of animal populations from mark-recapture records. In its basic format the closed-subpopulation method is similar to the Manly-Parr method and less restrictive than the Jolly-Seber method. Computer simulations indicate that the accuracy and precision of the population estimators generated by the basic closed-subpopulation method are almost comparable to those generated by the Jolly-Seber method, and generally better than those of the minimum-number-alive method. The performance of all these methods depends on the capture probability, the number of previous and subsequent trapping occasions, and whether the population is demographically closed or open. Violation of the assumption of equal catchability causes a negative bias that is more pronounced for the closed-subpopulation and Jolly-Seber estimators than for the minimum-number-alive. The closed-subpopulation method provides a simple and flexible framework for illustrating that the precision and accuracy of population-size estimates can be improved by incorporating evidence, other than mark-recapture data, of the presence of recognisable individuals in the population (from radiotelemetry, mortality records, or sightings, for example) and by exploiting specific characteristics of the population concerned.

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