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Is there any seismic risk in Montana or in the Flathead Valley?

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Presentation on theme: "Is there any seismic risk in Montana or in the Flathead Valley?"— Presentation transcript:

1 Is there any seismic risk in Montana or in the Flathead Valley?

2 We are part of the Intermountain Seismic Belt. Figure 3.3.1-1 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.

3 Personalizing the Earthquake Risk

4 Flathead Rating Changed After Fault in Mission determined active.

5 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, 7.5-7.9 Earthquake is possible

6 “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, 1964. Cause of our earthquake activity is the collision of the North American Plate and the Pacific Plate, causes extension of N. America

7 Significant Intermountain Seismic Belt Earthquakes 1. 1945 Flathead Lake, MT M 5.511. 1944 Central Idaho M 6.1 2. 1952 Big Fork, MT M 5.5 12. 1983 Borah Peak, ID (series) M 7.3 3. 1935 Helena, MT (series) M 6¼ 13. 1905 Shoshone, ID M 5½ 4. 1928 Helena, MT M 5½ 14. 1994 Draney Peak, ID M5.9 5. 1929 Lombard, MT M 5.6 15. 1930 Grover, WY M5.8 6. 1925 Clarkston Valley, MT M 6¾ 16. 1975 Pocatello Valley, ID M 6.0 7. 1947 Virginia City, MT M 6¼ 17. 1962 Cache Valley, UT M 5.7 8. 1959 Hebgen Lake, MT (series) M 7.5 18. 1884 Bear River, ID M 6.3 9. 1975 Yellowstone Park, WY M 6.1 19. 1909 Hansel Valley, UT M 6± 10. 1945 Central Idaho M 6.0 20. 1934 Hansel Valley, UT(series) M 6.6

8 Technical Paper of Southwest Montana Earthquake Hazards s/gsac2p8.pdf

9 The State of Montana Multi-Hazard Mitigation Plan and Statewide Hazard Assessment with photos Final%20Draft/Earthquake%20Hazard%20Profi le.pdf

10 Earthquake Hazard Areas

11 New Madrid

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