![]() ![]() Between 20, induced seismic activity in the Fox Creek area (northwestern Alberta) posed the highest seismic hazard in Alberta. ![]() Other occurrences of induced seismicity happened before 2011 however, seismic activity dropped off after the peak in the early 1980s (Rocky Mountain House, west-central Alberta) and the late 1990s and early 2000s (Cordel oil field, west-central Alberta). The first known recorded case of induced seismicity related to hydraulic fracturing (i.e., injecting fluids to fracture rock) in Alberta occurred in 2011, the Cardston swarm in southwestern Alberta. ![]() To generate these maps, we used our earthquake catalogue, which includes induced and natural seismic activity and excludes mining blasts. These maps characterize the changing earthquake patterns in Alberta. To show the evolution of the seismic hazard in Alberta, we generated seismic hazard maps for each year from 2011 to 2020. Most masonry and frame structures are destroyed. Properly designed structures can collapse. Extreme - Objects are thrown upward into the air.Considerable damage in properly built structures. Slight damage in properly designed structures. Negligible damage in buildings of good design and construction. Shaking is like a heavy truck passing near a building. Weak - Felt only by a few people, especially indoors.The level of perceived shaking uses the following general terms identifying how people or structures in the area could feel the ground movement (based on the Modified Mercalli Intensity Scale): We then associate these values with levels of perceived shaking in the area and display these areas on seismic hazard maps. The PGA values are given as a percentage of g, where g is the standard acceleration due to the Earth’s gravity (9.81 metres per second squared). We express the ground motion values as peak ground accelerations (PGA), which is the maximum acceleration the ground reaches during an earthquake. Our seismic hazard maps show the 1% chance that an area could have experienced a certain level of perceived shaking from ground motion due to earthquakes in a specific year. Evaluating the seismic hazard at a regional scale is particularly important considering the amount of induced seismicity cases related to the energy sector in Alberta. Short-term retrospective seismic hazard maps provide a mechanism to quantify and report changes in the seismic hazard at a regional scale. We generate short-term (i.e., 1 year) seismic hazard maps that include the hazard from induced seismicity sources in Alberta. However, if we incorporate induced seismicity, these long-term time frames are no longer helpful as induced seismicity is unlikely to remain constant, and relevant industrial activity inducing the seismicity likely lasts less than the long-term time frames. Commonly, seismologists design seismic hazard maps for long-term time frames (e.g., 50 years) since they assume the rate of naturally occurring earthquakes remains constant for long periods. There are long-term and short-term seismic hazard maps. This analysis evaluates the magnitude and location of potential earthquakes, their frequency, and the properties of the rocks and sediments that earthquake waves travel through. We generate our seismic hazard maps retroactively on an annual basis using the Probabilistic Seismic Hazard Analysis. Seismic hazard maps illustrate the likelihood of an area to reach or exceed a certain level of ground motion caused by earthquakes over a set time period. ![]()
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