I accompanied Lucinda Leonard and two students from UVIc  Megan Caston and Yijie Zhu – they are both working towards Masters degrees in Geophysics, working on earthquakes and faults to Race Rocks along with 6 students from Pearson College for the installation of two GPS stations. Many years ago , perhaps as early as 1991, this plug had been installed a meter in front of the Camera 5 location , and it had not been rechecked since.  Laas was able to get this picture of it to verify that it was still there .

The following is the research proposal by Lucinda Leonard, Assistant Professor (Geophysics) School of Earth and Ocean Sciences, University of Victoria PO Box 1700 STN CSC, Victoria, British Columbia, Canada V8W 2Y2

GPS Survey for Earthquake Hazard Assessment on Southern Vancouver Island

Participants: Lucinda Leonard, Assistant Professor, School of Earth and Ocean Sciences, University of Victoria
Julie Elliott, Assistant Professor, Purdue University
Yan Jiang, Research Scientist, Natural Resources Canada, and Adjunct Professor, University of Victoria 2-3 students will also take part in the fieldwork.

Objectives:

(1) To quantify seismic hazard of crustal faults on southern Vancouver Island. (2) To improve understanding of crustal deformation in subduction zone forearcs.

Scope of fieldwork:

The research project will establish and survey a relatively dense network of high-precision Global Positioning System (GPS) sites across fault zones on southeastern Vancouver Island that may host significant earthquakes. The 2018 survey will involve temporary instrument deployments at a number of pre-existing survey markers as well as new markers emplaced in bedrock. We anticipate future deployments every 1-2 years over the next 5-10 years.

Rationale:

Southeastern Vancouver Island is a region of high seismic hazard due to its location above the Cascadia subduction zone – the region is susceptible to damage from: earthquakes on the Cascadia megathrust fault offshore (magnitude ~9; similar to the devastating 2011 tsunamigenic Japan earthquake), deep earthquakes beneath the Salish Sea and Puget Sound (up to magnitude ~7; e.g., 2001 earthquake in Nisqually, Washington, that caused minor damage in Victoria), and earthquakes on poorly-understood shallow crustal faults (up to magnitude ~7.5; similar to the 2011 damaging earthquake in Christchurch, New Zealand). Crustal earthquakes, although smaller in magnitude than megathrust events, may produce strong shaking in urban areas due to their shallow source and possible close proximity. Modelling of a scenario crustal earthquake beneath the City of Victoria estimates extensive damage to 64% of building stock, 75% of the water pipeline system, and 90% of the sewer pipeline system in the city (VC Structural Dynamics Ltd., 2016).

Crustal faults remain poorly understood in the region, although recent progress includes the identification of surface-rupturing Holocene earthquakes on the Leech River fault (Morell et al., 2017) and its likely offshore equivalent, the Devil’s Mountain fault (Barrie and Greene, 2018). Fault mapping and trenching are important to determine the maximum magnitude of past and future earthquakes on individual fault strands, but these methods cannot provide accurate estimates of slip rates on fault zones, as required for input into seismic hazard assessments. GPS surveying can be used to track the relative motion of survey markers over time; a sufficiently dense GPS network can be further used to identify the location of active faults and to quantify their slip rates (e.g., Marechal et al., 2015). The existing network of continuous GPS stations on southeastern Vancouver Island is inadequate for this purpose, e.g., there are only three stations within 20 km of the active Leech River fault zone. Campaign-style deployments, repeated every 1-2 years over a time-span of 5-10 years, will provide the greater density of survey locations needed to assess strain build-up on fault zones. Several sites were established in 1991 and re-surveyed in 1996 (Henton, 2000; Mazzotti et al. 2003) – we propose to re-occupy these sites, where possible, and to establish a denser network of campaign GPS sites for temporary deployments (2-4 days at each site).

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Methodology
Site locations:
Site requirements: accurate GPS positioning (to within 1 mm) requires the GPS antenna to have a good view of the sky in order to maximize the satellite signals received. It also requires a marker to be emplaced in a stable substrate, ideally bedrock. Thus bedrock hilltops provide optimum site locations. In this region, many optimal locations are located within parks.

Proposed deployments include 5 pre-existing sites, in addition to ~16 new sites, at an average of ~3 km spacing perpendicular to the Leech River fault zone and adjacent faults offshore (Figure 1; Table 1). The greater number of sites to the north of the fault zone reflects greater accessibility over a larger land area in this region.

Figure 1. Proposed locations of campaign GPS sites. Also shown are the locations of continuous GPS sites, pre-existing campaign GPS sites, and mapped faults.