Earthquakes and Richmond
Along the coast of British Columbia, earthquakes are a reality. Richmond's unique characteristics often raise questions about the potential effects of an earthquake on our community. Although we have no control over this natural phenomenon, we all have a role to play in preparing for our own safety.
Whether you are a response agency, a municipality, a resident or a business, a little knowledge can go a long way to help minimize the damaging effects of an earthquake. These sections provide factual information on earthquakes and the best available assessment on how Richmond will respond:
- Richmond & Earthquakes
- Richmond's Unique Situation
- Earthquake & Preparedness
- The Richter Scale
- Some Significant Earthquakes in our Region
To learn how to protect yourself during an earthquake visit During an Emergency.
Richmond and Earthquakes
Richmond’s Buildings are Expected to Perform Well
All new buildings in Richmond are required to meet the BC Building Code. As early as the 1955 edition, the code has included structural design criteria to mitigate forces from earthquakes. The objective of the code is to ensure an acceptable level of public safety, which is achieved by designing buildings to prevent major failure and loss of life. Buildings designed in conformance with these provisions should be able to resist major earthquakes without collapse.
Although this standard is periodically updated as new science and best practices become available, the fact that much of Richmond is of newer construction means buildings are expected to perform well. If concerned about how a building you own might be affected by an earthquake you will need to contact a Professional Structural Engineer to assess it against the latest BC Building Code.
Some Liquefaction May Occur, but Richmond Won't Slide into the Ocean
During an earthquake, shaking can cause loosely packed, water-saturated sediments such as sand or silt to turn into a fluid mass. This is known as liquefaction. When this happens the sediments lose their strength and can no longer fully support structures, which may lean or settle.
Some degree of liquefaction can occur during an earthquake depending on the location, size and duration of an earthquake. Some homes and buildings could settle and crack and roads and other surfaces could become uneven due to soil failure. The best geotechnical information available to date indicates that there are only limited areas that are at risk of liquefaction. All new structures in Richmond are built on densified or otherwise improved ground and use foundation systems such as piles or raft slabs that are specifically designed to eliminate or mitigate the risk of liquefaction.
We're Working to Ensure our Dikes Remain Stable
The City regularly inspects and upgrades its dikes to ensure their structural integrity. Studies have been completed at key locations to assess dike performance during an earthquake and to plan improvements. Additionally, dike raising programs make allowances for acceptable settlement during an earthquake.
Richmond is Not at Significant Risk of Tsunamis
Tsunamis are long, high ocean waves commonly generated by underwater earthquakes. The most recognized source of an underwater earthquake that may cause a tsunami capable of reaching the city of Richmond is from the Cascadia Subduction Zone located in the Pacific Ocean to the west of Vancouver Island. Vancouver Island lies as a kind of breakwater between the Pacific Ocean and Richmond, if a Pacific tsunami was generated it is estimated that waves would dissipate to around 0.5 metres in height as they reach the western shore of the Fraser delta. The City's dikes would adequately mitigate the effects of this type of event.
To learn more about Tsunamis and how they may impact the city of Richmond visit Tsunamis and Richmond.
Richmond’s Unique Situation
Richmond has unique characteristics. Richmond is renowned for its rich soil and stunning location between the arms of the Fraser River. These characteristics enhance Richmond's local economy and livability. They also present some unique challenges for earthquake emergency planning.
Richmond's soil is made of silt and sand. This is what makes Richmond a strong agricultural community. Our soil is ideal for growing cranberries, blueberries and the like; however, the energy caused by an earthquake could take longer to dissipate and the shaking more amplified in these softer soils than it would be on firmer soil and bedrock. The good news is that these softer soils tend to absorb the damaging high frequency shaking better than areas located on rock.
Richmond is an island. Being surrounded by water enhances Richmond's livability. It also means that Richmond is connected to other communities through a network of bridges. Seismic upgrades to a number of older bridges have been undertaken in recent years and continue as necessary to enhance their structural integrity. This will help to alleviate transportation impacts in the event of an earthquake.
Richmond has plans for coping with emergencies. The City of Richmond puts significant resources toward developing, refining and implementing emergency procedures. Community safety is of paramount importance. In the event of an earthquake, the City will activate its Emergency Operations Centre to coordinate response efforts.
No Surprise, Earthquakes are Inevitable in Our Region
The entire Lower Mainland is located in one of the most seismically active regions of Canada. Small earthquakes occur almost daily in this area. More than 100 earthquakes with a magnitude of 5 or greater have occurred in southwestern BC (most offshore) in the past 70 years. We must be prepared for more earthquakes.
The Earth Moves in not-so Mysterious Ways
Earthquakes occur when the tectonic plates that makes up the earth's outer shell slip past or under one another and release stress. Imagine the earth's outer crust as resembling cracked eggshells that are in subtle, constant motion. Earthquakes occur mainly along faults at the edges of the plates as well as along cracks within the plates. There are no known active faults under Richmond. All known active faults in our area are located offshore.
All Earthquakes are not Created Equal
There are three different types of earthquakes that can occur in our area: crustal, subcrustal and subduction.
Crustal earthquakes originate in the North American plate (see Fig.1) to depths of approximately 30 kilometers. These shallow earthquakes account for about 75% of small earthquakes in this region. In fact, between 200 and 300 of these shallow earthquakes occur in the continental crust of the North American Plate each year. Of the three major crustal earthquakes that have affected our area in the last 150 years, two occurred on Vancouver Island (in 1918 and 1946, with magnitudes of 7 and 7.3 respectively) and one in Northern Washington State (in 1872, with a magnitude of approximately 7).
Subcrustal earthquakes are earthquakes that extend to depths of approximately 100 kilometers. In this area, they take place within the Juan de Fuca Plate that slides beneath the North American Plate. This is the type of earthquake that occurred just south of Seattle, Washington in February 2001 (magnitude 6.8). The maximum magnitude for a subcrustal earthquake in our region is 7, primarily because the Juan de Fuca Plate is very thin and only relatively small rupture lengths are created.
Subcrustal earthquakes rarely have aftershocks and are concentrated in two areas within our region: 30 to 40 kilometers below the west coast of Vancouver Island and 50 to 60 kilometers below the Straight of Georgia. Significant earthquakes of this type occurred in 1949, 1965 and 2001 (as mentioned above) at the south end of Puget Sound. In addition, a subcrustal earthquake with a magnitude of 5.5 struck beneath Pender Island in 1976.
Subduction earthquakes are the rarest and most damaging types of earthquakes, with magnitudes of 8 or larger. The threat for our area lies just off the west coast of Vancouver Island where the Juan de Fuca and North American Plates interact. Pressure may be building at the contact points of these plates. When this pressure becomes excessive, enormous stress will be released, causing a huge subduction earthquake. The last such earthquake in this area occurred over three hundred years ago in January of 1700. Subduction earthquakes occur every few centuries.
The Richter Scale
The Richter Scale is a logarithmic measurement of the magnitude of, or the amount of energy released by, an earthquake. The following table describes the effects of earthquakes of various magnitudes (M):
|1-3||Recorded on local seismographs, but not generally felt|
|3-4||Often felt, no damage|
|5||Felt widely, slight damage near epicentre|
|6||Damage to poorly constructed buildings & other structures within 10's km|
|7||"Major" earthquake, serious damage up to approximately 100 km (recent Taiwan, Turkey, Kobe & California earthquakes)|
|8||"Great" earthquake, great destruction & loss of life over several 100 km (San Francisco 1906, Queen Charlotte Island 1949)|
|9||Rare great earthquake, major damage over a large region over 1000 km (Chile 1960, Alaska 1964, and the west coast of BC, Washington, & Oregon 1700)|
Some Significant Earthquakes in our Region
|1909||6.0||Gulf Island Region|
|1997||4.6||Strait of Georgia|
More information can be found at Earthquakes in BC on the Government of BC's website.
Reference materials used to prepare this brochure include: "The Tsunami Threat on the West Coast of Canada", John J. Clague, SFU, 1999, "Earthquake: Economic Impact Study", Munich Reinsurance Company of Canada, 1992, "Earthquakes in the Vancouver Area", Garry C. Rogers, 1994, "Variation in Earthquake Ground Motion on the Fraser Delta from Strong Motion Seismograph Records", G.C. Rogers, J.F. Cassidy, and D.H. Weichert, 1998, "Earthquakes in British Columbia", B.C., Ministry of Energy, Mines and Petroleum Resources.
The City of Richmond gratefully acknowledges the assistance of the staff of the Sidney office of Natural Resources Canada, Geological Survey of Canada, Pat Monahan, P. Geo., Monahan Petroleum Consulting and Dr. Graham Taylor, P. Eng., TBG Seismic Consultants Ltd. in the preparation of this brochure.