We found that repeated slow slip events observed on the deeper interface of northern Cascadia subduction zone, which were at first thought to be silent, have unique nonearthquake seismic signatures. Tremorlike signals correlate temporally and spatially with identified from crustal motion data spanning past 6 years. During period between slips, tremor activity is minor or nonexistent. call this associated phenomenon episodic (ETS) propose ETS can used as a real-time indicator stress loading...

A fundamental problem in plate tectonics is the shear strength of major boundary faults. This translates to question whether generally observed small earthquake stress drops 3–10 MPa on faults release most accumulated or only a fraction it. There strong evidence that San Andreas fault, transform boundary, weak (<20 resistance). It not yet clear subduction thrust are also weak. We present two types from northern Cascadia zone indicate very low coupling interface and hence comparable...

Slip events with an average duration of about 10 days and effective total slip displacements severalc entimetres have been detected on the deeper (25 to 45 km) part northern Cascadia subduction zone interface by observing transient surface deformation a network continuously recording Global Positioning System (GPS) sites. The occur down-dip from currently locked, seismogenic portion zone, and, for geographic region around Victoria, British Columbia, repeat at 13 16 month intervals. These...

Evidence has been obtained for the accumulation of elastic strain across northern Cascadia subduction zone that may be released in a future very large thrust earthquake. Vertical and horizontal rates southern Vancouver Island region have determined through (1) long‐term trends tide gauge data, (2) changes repeated accurate leveling surveys, (3) high‐accuracy gravity profiles, (4) shortening observed precise positioning surveys. The outer coast is uplifting at rate few millimeters per year...

We explore the physical conditions that enable triggering of nonvolcanic tremor and earthquakes by considering local seismic activity on Vancouver Island, British Columbia during immediately after arrival large‐amplitude waves from 30 teleseismic 17 regional or earthquakes. identify triggered four The close temporal spatial proximity to ambient aseismic slip indicates when a fault is undergoing failure, it particularly susceptible further events. amplitude also influences likelihood both...

We analyze continuous seismic and GPS records collected in the last decade (1997–2007) to establish most comprehensive observational basis for northern Cascadia episodic tremor slip (ETS) events. A simple “ETS scale” system, using a combination of letter digit, is proposed quantitatively characterize spatial temporal dimensions ETS Clear correlation between signals observed all A/B class episodes, but signature less obvious minor ones. Regular recurrence can be established only episodes...

At the Cascadia margin Juan de Fuca plate is subducting beneath North America plate, causing active seismicity within both plates. Earthquakes occur down to a maximum depth of 80 km descending oceanic and about 30 in overriding continental plate. We use method seismic tomography invert 28,230 P wave arrival times from 2666 local earthquakes that occurred around Vancouver Island 1970 1990. The model uses horizontal 12–19 vertical grid spacing assumes velocity perturbations vary continuously...

We study in detail the two consecutive episodic tremor‐and‐slip (ETS) events that occurred northern Cascadia subduction zone during 2003 and 2004. For both sequences, newly developed Source‐Scanning Algorithm (SSA) is applied to seismic waveform data from a dense regional seismograph array determine precise locations origin times of tremors. In map view, majority tremors limited band bounded approximately by surface projections 30‐km 50‐km depth contours plate interface. The horizontal...

The seismicity of western Canada has been studied for the period 1899–1975. quality data collected improved through this as number recording stations increased and location analysis methods developed, but significant uncertainties biases remain. Although these restrictions limit detailed correlation seismic events with specific tectonic features, in general most active earthquake areas correspond to boundaries between major lithospheric plates. These are Queen Charlotte – Fairweather fault...

[1] Probabilistic seismic hazard analyses (PSHA) are commonly based on frequency - magnitude statistics from 50–100 yearlong earthquake catalogs, assuming that these representative of the longer-term large earthquakes. We test an alternative PSHA approach in continental western Canada, including adjacent areas northwestern U.S.A., using regional strain rates derived 179 Global Positioning System (GPS) horizontal velocities. GPS converted to statistics, moment rates, and ground shaking...

The active tectonic setting of the southwest coast Canada and Pacific northwest United states is dominated by Cascadia subduction zone. zone can be divided into four segments where oceanic lithosphere converging independently with North American plate: Winona Explorer in north, larger Juan de Fuca segment that extends both States, Gorda south. entering all extremely young, less than 10 Ma. Of other six zones around young (< 20 Ma) being subducted, five have had major thrust earthquakes...

More than 180 regional moment tensor (RMT) solutions for moderate-sized earthquakes (M ≥ 4) are used to examine the contemporary stress regime of western Canada and provide valuable information relating earthquake hazard analysis. The overall pattern shows mainly NE–SW-oriented P axes most with local variations. In northern cordillera, maximum compressive direction (σ1) varies from east–west north–south NE–SW south north. σ1 is consistent axis largest earthquakes, except in central Mackenzie...

We analyze hourly data from five tremor episodes in the northern Cascadia subduction zone over period 2003–2005 provided by Tremor Activity Monitoring System (TAMS). All correspond to slow slip events observed GPS. Fourier decomposition is used separate counts for each episode into “long‐period” (0 < f 0.8 cpd), “tidal” (0.8 2.2 and “short‐period” (f > cpd) components. The tidal component of observations compared with theoretical stress variations at depths 20, 30, 40 km, km being...

abstract Available near- and far-field data have been used to reassess reevaluate the focal parameters of June 23, 1946 British Columbia earthquake. The preferred epicenter (49.76°N, 125.34°W) is located on Vancouver Island, inland from population centers along east coast. This location consistent with observed intensities, water disturbances, calculated ground deformation. hypocentral depth near 30 km, making surface rupture a distinct possibility. A revised fault-plane solution indicating...

We develop a method to estimate the seismic moments of deep non‐volcanic tremor bursts observed in northern Cascadia. For each burst, maximum amplitudes at individual stations within time window ±5 s around predicted arrivals S phase are measured and compared from synthetic seismograms. The proposed is thoroughly calibrated using 464 local earthquakes results show excellent consistency between reported M L estimated w . apply Cascadia tremors infer that most have ∼1.0–1.7. corresponding b...

Operational earthquake forecasting (OEF) is the practice of continual updating and dissemination physics‐based short‐term (days) probabilities for occurrence damaging earthquakes. Although fully appreciating noble intention OEF scientific merits seismicity analyses it employs, we are concerned that its wide promotion may lead public to believe preparedness can fluctuate at timescales days or weeks. Scientists who support do recognize importance long‐term (decades centuries) forecast. Jordan...

Raising earthquake awareness is an important goal of seismological research. In this respect, the effect past local earthquakes excellent means to raise population's awareness. For reason, Natural Resources Canada has put numerous photographic examples impacts on its Web sites (see, for example, http://www.earthquakescanada.ca). The information site contains used in production various publications and pages source public. Another much-used public tool Atlas Canada, formerly paper but now...

Research Article| May 01, 2012 Regional Centroid-Moment-Tensor Analysis for Earthquakes in Canada and Adjacent Regions: An Update Honn Kao; Kao Geological Survey of Pacific Geoscience Centre 9860 West Saanich Road Sidney, BC V8L 4B2, Canadahonn.kao@nrcan-rncan.gc.ca (H. K.) 1Geological Canada, Centre, British Columbia, Search other works by this author on: GSW Google Scholar Shao-Ju Shan; Shan Allison Bent; Bent 2Geological Ottawa, Ontario, Catherine Woodgold; Woodgold Garry Rogers; Rogers...