Presentation on theme: "Is there any seismic risk in Montana or in the Flathead Valley?"— Presentation transcript:
Is there any seismic risk in Montana or in the Flathead Valley?
We are part of the Intermountain Seismic Belt. Figure A belt of seismicity known as the Intermountain Seismic Belt extends through western Montana, from the Flathead Lake region in the northwest corner of the state to the Yellowstone National Park region. Source: MBMG,2004.
Personalizing the Earthquake Risk
Flathead Rating Changed After Fault in Mission determined active.
Do We Need to Worry about Earthquakes in Montana or the Flathead? A.We are part of the Inter mountain Seismic Belt 1. Many quakes, most small, but the potential for larger quakes based upon fault data. a. Flathead L. 5.5 ML 1945 b. Hebgen L. 7.5 ML1959 c. Helena 6.5 ML1935 B. Yikes Article 1. Rezoning of Flathead based on Seismic Risk of a “3”: Probable Major Damage 2. Due to an active fault in Finley Pt. area of Flathead Lake, Earthquake is possible
“Local Articles” Yikes: Active fault “built” the Mission Mountains Tsunami in Japan determined time of large earthquake on west coast in Cascadian: 9M. Hebgen Lake Earthquake in 1959, Largest in MT. Seiche at Birch Lake Good Friday Earthquake, Anchorage Alaska, Cause of our earthquake activity is the collision of the North American Plate and the Pacific Plate, causes extension of N. America
Significant Intermountain Seismic Belt Earthquakes Flathead Lake, MT M Central Idaho M Big Fork, MT M Borah Peak, ID (series) M Helena, MT (series) M 6¼ Shoshone, ID M 5½ Helena, MT M 5½ Draney Peak, ID M Lombard, MT M Grover, WY M Clarkston Valley, MT M 6¾ Pocatello Valley, ID M Virginia City, MT M 6¼ Cache Valley, UT M Hebgen Lake, MT (series) M Bear River, ID M Yellowstone Park, WY M Hansel Valley, UT M 6± Central Idaho M Hansel Valley, UT(series) M 6.6
Technical Paper of Southwest Montana Earthquake Hazards s/gsac2p8.pdf
The State of Montana Multi-Hazard Mitigation Plan and Statewide Hazard Assessment with photos Final%20Draft/Earthquake%20Hazard%20Profi le.pdf