Agenda Index City of Vancouver

ADMINISTRATIVE REPORT

TO: Vancouver City Council

FROM: City Building Inspector in consultation with the General Manager of Community Services & the Director of Risk and Emergency Management.

SUBJECT: Seismic Hazard Abatement for Privately Owned Buildings


RECOMMENDATIONS

GENERAL MANAGER'S COMMENTS

COUNCIL POLICY

Through the adoption of seismic requirements in the Vancouver Building Code and through proactive programs to monitor and assess seismic design in new and existing buildings, Council has consistently promoted seismically safe building standards in Vancouver.

SUMMARY

Council has consistently promoted seismically safe building standards in Vancouver. These standards, reflected in Vancouver Building Code requirements, have continued to evolve over time as our collective knowledge of earthquakes and their effects grows. Currently there is sufficient research, understanding, and experience to support a more proactive approach to seismic upgrade. Many jurisdictions, in earthquake prone areas, have developed long term seismic hazard abatement programs to substantially reduce the life safety and financial risks associated with vulnerable structures. This report recommends that work commence to develop such a program in Vancouver.

The report identifies the need to create a permanent staff resource, funded from existing permit revenues. This senior seismic specialist will analyse the City's risk and develop recommended options for a comprehensive hazard abatement program and report back to Council in 18 months. In conjunction with that work the position would also support and improve the current structural review program for new buildings, which the report recommends be continued. To enhance the effectiveness of the structural review program, the report recommends that the building permit fee schedule be revised to permit recovery of the cost of third party reviews in instances of significant or repeated non-compliance.

PURPOSE

The purpose of this report is to:

BACKGROUND

1. Seismic Risk

2. Vancouver Initiatives

3. Federal and Provincial Initiatives

4. Other Jurisdictions

5. The Delcan Study

6. Structural Review Program

DISCUSSION

1. Buildings at Risk

2. A Seismic Mitigation Program for Existing Buildings

3. Structural/Seismic Review for New Buildings

It is also recommended that to discourage inadequate or deficient design the City charge back the costs of the third party review where major design deficiencies are found. The engineer in charge would be responsible for the cost of any independent design reviews commissioned by the City where such a review indicates significant levels of non-compliance. Safeguards to ensure that these charges are not imposed unfairly, include:

4. Senior Seismic Engineer

FINANCIAL IMPLICATIONS

It is recommended that funding of $92,000 per annum plus a one time cost of $11,000 for the new position of Senior Seismic Engineer and $75,000 for the continuation of the Structural Review Program be funded from existing permit revenues currently allocated to the structural review program.

CONCLUSION

The development of a comprehensive seismic hazard abatement program, in conjunction with the current Building By-Law review and Structural Review Program will provide the City with a long-term strategy for minimizing seismic risks associated with buildings. To the extent that this program addresses this risk over time, it will substantially reduce the life-safety, economic and recovery impacts of a major earthquake.

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APPENDIX A. SEISMIC HAZARDS IN VANCOUVER.
SEISMIC HAZARDS IN VANCOUVER.

Vancouver lies in a seismically active area of the Pacific Northwest which contains active seismic faults and is adjacent to the offshore subduction zone between the Pacific and the North American tectonic plates. Although Vancouver has not experienced a major earthquake in recent years, the BC coastal region area has been subjected to significant seismic activity. The following diagram, prepared by the Pacific Geoscience Centre in Victoria, illustrates the location and intensity of the major seismic events that have been felt in the Vancouver and Victoria areas. A listing of known historic and recent earthquakes in the Pacific North-West is contained in Table 1.

Table 1 - Known Historic and Recent Earthquakes in the Pacific North-West

Date

Location

Magnitude

Comments

~900

47.6N 122.5W

7+

Crustal Earthquake in Puget Sound near the present city of Seattle. Surface rupture and tsunami deposits in Puget Sound.

1700/01/26

Offshore

~9

Subduction earthquake off the west coast of Vancouver Island. Coastal native village destroyed and native houses on Vancouver Island may have been damaged.

1864/10/29

48.0N 123.0W

~5.5

Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and the Victoria area.

1872/12/15

48.5N 121.0W

~7.4

Washington State, south of Hope. Crustal earthquake, followed by many aftershocks. Location uncertain, based on felt reports. Felt strongly in the Lower Mainland and the Victoria area.

1909/01/11

48.7N 122.8W

~6.0

Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and on southern Vancouver Island.

1918/12/06

49.4N 126.2W

~7.0

West coast of Vancouver Island. Crustal earthquake, many aftershocks. Felt by most in the Lower Mainland and on Vancouver Island. Damage on the west coast of Vancouver Island.

1920/01/24

48.6N 123.0W

~5.5

Gulf Island region. Probably deep, no reported aftershocks. Felt strongly in the Lower Mainland and on southern Vancouver Island.

1946/06/23

49.8N 125.3W

7.3

Central Vancouver Island. Crustal earthquake, very few aftershocks. Much damage in central Vancouver Island, and slight damage in the Lower Mainland. Felt strongly all over Vancouver Island, throughout the lower mainland.

1949/04/13

47.1N 123.0W

~7.0

Puget Sound area - at a depth of 54 km. Much damage in Seattle/Tacoma. Felt by most in Lower Mainland and southern Vancouver Island.

1965/04/29

47.4N 122.3W

6.5

Beneath downtown Seattle - at a depth of 63 km. Much damage in Seattle. Felt by most in the Lower Mainland and southern Vancouver Island.

1975/11/30

49.2N 123.6W

4.9

Beneath the Strait of Georgia. Shallow, many aftershocks. Felt by many in the Lower Mainland and on Vancouver Island.

1976/05/16

48.8N 123.4W

5.3

Beneath Pender Island at a depth of 60 km, no aftershocks. Felt by most, and some damage (broken windows) in the Lower Mainland and southern Vancouver Island.

1990/04/14

48.8N 122.2W

4.9

Northern Washington. Shallow, many aftershocks. Felt by many in the Lower Mainland.

1996/05/03

47.8N 121.9W

5.0

East of Seattle. Shallow, many aftershocks. Felt by many in the Lower Mainland and on southern Vancouver Island.

1997/06/24

48.4N 119.9W

4.6

Beneath the Strait of Georgia. Shallow, many aftershocks. Felt by many in the Lower Mainland and on Vancouver Island.

Vancouver is classified under the National Building Code of Canada (NBC) as Zone 4 with a design level firm ground acceleration of 0.21g. This classification corresponds roughly with Seattle and is less than Los Angeles and San Francisco. This acceleration is associatedwith an earthquake with a mean recurrence (return) interval of 475 years, or a 10% probability of occurrence over a fifty year period.

Awareness of the magnitude of the seismic risk in Western BC has increased significantly over the last 30 years. Seismic design provisions for new buildings were first included in the NBC in 1953 and adopted in Vancouver in 1967. Recent advances in seismic engineering have resulted in major improvements in North American seismic codes which are considered among the most comprehensive in the world. The recent earthquakes in San Francisco, (1989) Northridge (1994) Kobe (1995), Mexico (1995), Turkey (1999), Greece (1999) and Taiwan (1999) have further highlighted common design problems and served as a "wake up call" to other active seismic regions in the world.

Recent research has further highlighted the potential for a major earthquake occurring in the Cascadian subduction zone located approximately 125 km off Vancouver Island. The zone appears to experience a major earthquake on average every 600 years, but the interval between earthquakes has varied from 180 to 1800 years. The last recorded earthquake in this area occurred approximately 300 hundred years ago. The National Research Council of Canada (NRC) is currently preparing seismic zonation maps for BC and Canada which will more accurately reflect the seismic risk from this source. NRC are also considering utilizing a 1,000 year return period for seismic forces in lieu of the 475 year period currently employed. If adopted, this could result in a significant increase in the level of seismic design forces specified in our codes.

While the Cascadian Subduction Zone presents a major seismic hazard to Vancouver, a near field crustal earthquake may also have devastating results in an area close to its epicentre. In Kobe, the near field crustal earthquake of January 1995 of magnitude 7.2 on the Richter scale caused in excess of 5,000 deaths and $250 Billion in direct damages. This earthquake exposed significant vulnerability in local building practices and emergency planning which had been largely predicated on a major earthquake occurring in an offshore subduction zone approximately 150 km away. In Turkey, a similar near field earthquake of magnitude 7.4 occurred on the north Anatolian fault and caused 15,135 fatalities and 23,984 serious injuries. Damage is provisionally estimated in the range of $10 Billion to $40 Billion. This earthquake dramatically exposed the consequences of a lack of vigilance in the provision of Building Control services and has had a major impact on the assessment of earthquake hazards in seismically vulnerable areas of the world.

APPENDIX B - THE DELCAN STUDY

THE DELCAN STUDY

1. PHASE 1PDF

Figure 1 - Summary of Seismic Hazard Ratings - The Delcan Report.

PHASE 2

APPENDIX C - REFERENCES

1. The Threat of a Great Earthquake in Southwestern BC. Clague, Bobrowsky and Hyndman. The BC Professional Engineer, November 1995.

2. Regulatory Issues in the Proposed Changes to the New Zealand Building Act. Cashin and Brunsdon. Twelfth World Conference on Earthquake Engineering, Auckland, New Zealand 1999.

3. Why were over 5,500 lives lost in Kobe? How to Protect in Future. Yamada. Twelfth World Conference on Earthquake Engineering, Auckland, New Zealand 1999.

4. Plans, Code Enforcement, and Damage Reduction: Evidence from the Northridge Earthquake. Burby, French and Nelson. Earthquake Spectra February 1998.

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