| Title | Accurate determination of local magnitude for earthquakes in the Western Canada Sedimentary Basin |
| |
| Author | Babaie Mahani, A; Kao, H |
| Source | Seismological Research Letters vol. 90, no. 1, 2018 p. 203-211, https://doi.org/10.1785/0220180264 |
| Year | 2018 |
| Alt Series | Natural Resources Canada, Contribution Series 20180221 |
| Publisher | Seismological Society of America (SSA) |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®); html; csv |
| Province | Alberta; British Columbia; Yukon; Northwest Territories |
| NTS | 82I; 82J; 82K; 82L; 82M; 82N; 82O; 82P; 83; 84; 85B; 85C; 85D; 85E; 85F; 85L; 92I; 92J; 92K; 92L; 92M; 92N; 92O; 92P; 93; 94; 95; 103A; 103H; 103I; 103J; 103O; 103P; 104A; 104B; 104G; 104H; 104I; 104J; 104O;
104P; 105A; 105B; 105G; 105H; 105I; 105J; 105O; 105P |
| Lat/Long WENS | -132.0000 -112.0000 64.0000 50.0000 |
| Subjects | geophysics; fossil fuels; seismology; earthquakes; earthquake magnitudes; earthquake risk; seismicity; seismic waves; attenuation; amplitude spectra; petroleum industry; hydrocarbon recovery;
seismological network; seismographs; earthquake catalogues; models; Western Canada Sedimentary Basin; monitoring |
| Illustrations | location maps; plots; tables |
| Program | Environmental Geoscience Shale Gas - induced seismicity |
| Released | 2018 11 07 |
| Abstract | In this study, we take a close look at the constituents of the Richter (1935) relation for calculation of local magnitude (ML), which is the basis for magnitude determination by Natural Resources Canada
(NRCan) in the western Canada sedimentary basin (WCSB). Using a comprehensive catalog of Wood-Anderson amplitudes from earthquakes in northeast British Columbia and western Alberta, we first compare the distance correction terms -log(A0) for the
Richter magnitude scale previously obtained forWCSB and several other regions. We also formulate a new correction term specifically for NRCan's routine ML calculation that better accounts for the attenuation of direct and refracted waves from events
within WCSB. Based on a bilinear model for ground-motion attenuation, our -log(A0) is
{
0.7974 × log(Rhypo)/100) + 0.0016 × (Rhypo - 100) + 3.0 Rhypo less than or equal to 85 km
-0.1385 × log(Rhypo/100) + 0.0016 × (Rhypo - 100) + 3.0
Rhypo >85 km
in which Rhypo is the hypocentral distance. Our -log(A0) results in lower ML by an average of 0.29, 0.27, 0.12, and 0.34 units, respectively, compared with those obtained by Richter (1958; California), Hutton and Boore (1987;
California), Brazier et al. (2008; Ethiopian plateau), and Bona (2016; Italy) over all distances, but gives higher ML values than those obtained by Yenier (2017; WCSB), with an average of 0.12 unit over all distances. The difference between our ML
calculation and Yenier (2017) is more significant for Rhypo less than or equal to 50 km (0.27 unit) and varies slightly for larger Rhypo: 0.08 unit for 50 km < Rhypo less than or equal to 100 km, 0.12 for 100 km < Rhypo less than or equal to 200 km,
and 0.10 for Rhypo > 200 km. |
| Summary | (Plain Language Summary, not published)
Precise determination of earthquake magnitude is especially important for events in the Western Canada Sedimentary Basin. In case of an event with local
magnitude (ML) 4.0 or larger, regulators in both British Columbia and Alberta issue suspension orders to temporarily stop injection operations. Besides the economic impact of ML overestimation for the oil and gas industry, underestimation of ML can
also have significant impact with regard to public safety. A recent study reported that the distance correction term used by NRCan in the calculation of ML is not suitable for WCSB. In this study, we investigate this issue using more than 4000
relocated events that occurred in WCSB. We propose a new formula for the distance correction term that can better account for the attenuation effect of seismic wave propagation and deliver more consistent ML values. |
| GEOSCAN ID | 311299 |
|
|