GEOSCAN Search Results: Fastlink


TitleAutomatically processed aftershock sequence for the 2012 Oct 27 Haida Gwaii Earthquake
AuthorMulder, T L; Vernon, F L; Rosenberger, A; Kilb, D; White, M C; Rogers, G C; Brillon, C; Bentkowski, W
SourceSSA 2014 Annual Meeting announcements, Seismological Society of America, technical sessions; Bulletin of the Seismological Society of America vol. 85, no. 2, 2014 p. 495,
Alt SeriesEarth Sciences Sector, Contribution Series 20150026
PublisherSeismological Society of America
MeetingSSA 2014 - Seismological Society of America Annual Meeting; Anchorage; US; April 30-May 2, 2014
Mediapaper; on-line; digital
File formatpdf (Adobe® Reader®)
ProvinceBritish Columbia
AreaHaida Gwaii
Subjects2012 Oct 27th Haida Gwaii Earthquake
ProgramCanadian Hazard Information Service
Released2014 03 01
AbstractThe 2012 Oct 27th Haida Gwaii earthquake occurred on the Pacific and North America plate boundary, producing a rich and continuing aftershock sequence. This was an unusual earthquake to occur on a predominately strike-slip fault margin as it showed significant thrust motion and produced a tsunami with a maximum recorded height of 0.76 meters in Maui, Hawaii. The plate vector sits at an approximately 15 degree angle to the plate margin resulting in an oblique convergence partitioned into margin parallel strike-slip on the Queen Charlotte fault and near vertical thrust faulting within the Queen Charlotte Terrace accretionary prism. The first few months of this aftershock sequence have been processed with traditional short-term average/long-term average (sta/lta) based detectors. Those results were used for automatic event locations. The same set of waveform data was also processed with Rosenberger's (2010) singular value decomposition (SVD) incorporated with an S-phase detector. The detections on the rotated traces were assigned as either P or S phases and the events were located using the same location program as was used for the traditional sta/lta detection dataset. The results show a four-fold increase in the returned number of automatically determined origins. These two datasets, and the smaller analyst located dataset, all outline an aftershock region approximately 50 km in width and 100 km in length. Three dimensional visualization of the aftershocks illustrate the structure of the seismicity. A variety of first motion focal mechanisms from the aftershock dataset were determined and compared to the processed datasets. Magnitude estimates are now available for the SVD dataset and Omori plots are compared for all 3 datasets.
Summary(Plain Language Summary, not published)
The 28 October 2012 Haida Gwaii earthquake had a very large aftershock sequence. A new procedure of automatically processing earthquakes was developed, using the singular value decomposition technique, and compared to previously existing standard automatic techniques and earthquakes located by human seismic analysts. The new technique showed a significant improvement in the number of high quality located earthquakes. Three dimensional, interactive visualization of the data was used to explore the spatial distribution of the aftershock earthquakes. Two faults to the west of Haida Gwaii were imaged, unquestionably confirming the existence of the previously unknown blind fault dipping to the east below Graham Island (Haida Gwaii). Results from this study have implications for early earthquake warning and seismic hazard studies.

Date modified: