Document Type
Article
Publication Date
8-2011
Keywords
Nazko cone, Anahim volcanic belt, Volcanic-tectonic earthquakes
Abstract
On 9 October 2007, an unusual sequence of earthquakes began in central British Columbia about 20 km west of the Nazko cone, the most recent (circa 7200 yr) volcanic center in the Anahim volcanic belt. Within 25 hr, eight earthquakes of magnitude 2.3–2.9 occurred in a region where no earthquakes had previously been recorded. During the next three weeks, more than 800 microearthquakes were located (and many more detected), most at a depth of 25–31 km and within a radius of about 5 km. After about two months, almost all activity ceased. The clear P- and S-wave arrivals indicated that these were high-frequency (volcanic-tectonic) earthquakes and the b value of 1.9 that we calculated is anomalous for crustal earthquakes but consistent with volcanic-related events. Analysis of receiver functions at a station immediately above the seismicity indicated a Moho near 30 km depth. Precise relocation of the seismicity using a double-difference method suggested a horizontal migration at the rate of about 0:5 km=d, with almost all events within the lowermost crust. Neither harmonic tremor nor long-period events were observed; however, some spasmodic bursts were recorded and determined to be colocated with the earthquake hypocenters. These observations are all very similar to a deep earthquake sequence recorded beneath Lake Tahoe, California, in 2003–2004. Based on these remarkable similarities, we interpret the Nazko sequence as an indication of an injection of magma into the lower crust beneath the Anahim volcanic belt. This magma injection fractures rock, producing high-frequency, volcanic-tectonic earthquakes and spasmodic bursts.
Publication Title
Bulletin of the Seismological Society of America,
Volume
101
Issue
4
First Page
1732
Last Page
1741
Required Publisher's Statement
© Seismological Society of America
doi: 10.1785/0120100013
Recommended Citation
Cassidy, J. F.; Balfour, N.; Hickson, C.; Kao, H.; White, R.; Caplan-Auerbach, Jacqueline; Mazzotti, S.; Rogers, G. C.; Al-Khoubbi, I.; Bird, A. L.; Esteban, L.; Kelman, M.; Hutchinson, J.; and McCormack, D., "The 2007 Nazko, British Columbia, Earthquake Sequence: Injection of Magma Deep in the Crust beneath the Anahim Volcanic Belt" (2011). Geology Faculty Publications. 41.
https://cedar.wwu.edu/geology_facpubs/41
Subjects - Topical (LCSH)
Earthquake swarms--British Columbia; Earthquake swarms--Tahoe, Lake, Watershed (Calif. and Nev.)
Geographic Coverage
British Columbia; South Lake Tahoe (Calif.)
Genre/Form
articles
Type
Text
Language
English
Format
application/pdf
