New Madrid and Central U.S. Region Earthquake Hazard

Transcription

1 New Madrid and Central U.S. Region Earthquake Hazard Rob Williams U.S. Geological Survey, Golden, CO March 16, 2017 Reelfoot Lake, TN U.S. Department of the Interior U.S. Geological Survey New Madrid sand blows

2 Talk Outline USGS Earthquake Hazards Program Earthquake hazard affecting the St. Louis region New Madrdid earthquake sequence Evidence for earlier big earthquakes USGS earthquake situational awareness tools

3 USGS Earthquake Hazards Program To improve the Nation s understanding of earthquake hazards and to mitigate their effects National Seismic Hazard Model USGS monitors the Nation s and World s earthquakes 24/7 Studies why they occur and how they shake the ground Provides earthquake-hazard assessments that affect building codes Helps promote loss-reduction measures using these results Global Seismograph Network US National Network Provides crucial scientific information to assist emergency responders when earthquakes occur.

4 USGS Earthquake Hazards Program To improve the Nation s understanding of earthquake hazards and to mitigate their effects National Seismic Hazard Model National Earthquake Information Center Earthquake research National Seismic Hazard Model National Earthquake Information Center (NEIC) Provides earthquake situational awareness through ShakeMap, Did you feel it?, and PAGER

5 For St. Louis region: 3 main areas of earthquakes: New Madrid Wabash Valley earthquake activity south and east of the city (but, can t rule out a damaging earthquake outside of these areas) Notable Wabash Valley SZ earthquakes all felt strongly in St. Louis: 1968 M5.5 (minor damage) 1987 M M5.4 (minor damage) Map shows earthquakes (red circles) greater than magnitude 2.5 occurring since 1973 (USGS PDE catalog). Green circles show notable earthquakes that occurred before

6 St. Louis has experienced minor earthquake damage at least 12 times in the last 205 years.

7 Seismic Networks in the St. Louis Region Collaborative Earthquake Monitoring with Saint Louis University, Center for Earthquake Research and Information (CERI) - University of Memphis, Incorporated Research Institutions for Seismology (IRIS), Kentucky Geological Survey

8 Liquefaction and sand blow formation Crucial features providing evidence of pre-historic earthquakes During earthquake, water-saturated sand is shaken. If shaking is strong and lasts long enough, porewater pressure builds up, sand loses its strength and acts like a liquid. A pressurized slurry of water and sand erupts to the surface, forming sand blows.

9 Geologic Evidence for Large Earthquakes Sand blow trenching in the New Madrid seismic zone E. Schweig et al.

10 The New Madrid Sequence 3 Main shocks ~M : 4 aftershocks ~M ~M7.5 ~M7.3 ~M7.5 ~6.8 ~6.1 ~6.0 ~5.0 ~6.0 dozens of smaller shocks ~4.2 ~5.2 ~5.2 ~4.2 ~5.2~ Weeks After Fuller, 1912; Nuttli, 1973; Hough et al. 2001; Hough and Martin, 2001; Hough 2009

11 Large New Madrid Earthquakes M6.0 to M7.5 - Before ? ~M ? ~M ~M ~M7.0 7 ~M7.5 ~M ~550 years ago ~1100 years ago? ~1700 years ago ~M6.2 ~M ?? ??? 1 2 ~4300 years ago ~3630 years ago After Holbrook et al., 2006; Nuttli, 1973; Hough et al. 2001; Hough and Martin, 2001; Tuttle et al., 2002; Hough 2009

12 In the central & eastern U.S., earthquakes affect much larger areas than in the west Did You Feel It? Comparison Napa vs. Oklahoma vs. Central Virginia M6.0 Napa earthquake August 24, :20 am local time M5.8 Pawnee, Ok earthquake Sept. 3, :02 am local M5.8 earthquake Central Virginia August 23, :51 pm local time Dots represent areas where people reported at least weak shaking Pawnee

13 April 2008 M5.2 Illinois earthquake 42,000 USGS Did You Feel It? reports STL

14 Earthquake Energy Release ~M7.5 Dec New Madrid ~350X stronger ~M7.5 Feb New Madrid M Virginia ~M7.3 Jan New Madrid ~177X stronger after Michael Germeraad

15 From New Madrid geologic studies we know: New Madrid Seismic Zone produced large quakes in , ~1450 AD, ~900 AD, and ~2350 BC The average time between these events is about 500 years at least during past 1200 years The prehistoric earthquakes were similar in size to the earthquakes Each New Madrid event was a sequence of earthquakes, including multiple very large mainshocks, much like the sequence

16 Wabash Valley Seismic Zone Earthquake History Less active than the New Madrid seismic zone but three Mag5-5.5 s in the last 44 years. Prehistoric earthquake history determined from sand blows. Age dating at widespread sites show up to 8 large earthquakes (M6.7 to M7.5) in the last 2 million years.

17 Situational Awareness tools (Advanced National Seismic System)

18 Thanks. Any questions? Get more information at: earthquake.usgs.gov St. Louis Area Earthquake Hazards Mapping Project: Google: USGS New Madrid earthquakes New Madrid earthquake simulation: