1. Clustering and Scattering of Intraplate Earthquakes in the NMSZ and Other Regions: Preliminary Results From Geodynamic Modeling Qingsong Li Lunar and Planetary Institute, USRA

2. NMSZ Seismicity Is the NMSZ the permanent site of concentrated seismicity in the central US? or Is seismicity in the NMSZ transient and may migrate to elsewhere?

3. Spatiotemporal Patterns of Intraplate Seismicity CEUS seismicity is clustered around several active seismic zones. Australia seismicity seems be randomly scattered, lacking large earthquakes. In North China, earthquakes migrate eastward from the Shanxi Graben to the North China Plain in the past 200 years. CEUS North China Australia

4. Geodynamic Model (1) and Mechanisms (Horizontally homogeneous rheology) Strength Mechanisms incorporated include: 1.Far field boundary loading. 2.Each element fails when stress reaches strength (an earthquake). 3.Coseismic and postseismic stress evolution (butterfly patterns) 1 mm/yr (1) (3) (2)

5. Stress Evolution Cartoon

6. Seismicity in successive time periods (5000 years)

7. Seismicity in a longer time period (30000 years)

8. Geodynamic Model (2) (Strength anomaly in the upper crust) 1 mm/yr A weak zone, with lower strength in the upper crust, is added at the center of the model region.

9. Seismicity in successive time periods (5000 years)

10. Seismicity in a longer time period (30000 years)

11. Seismicity in much shorter time periods (500 years) abc fed

12. Seismicity in the CEUS, including the NMSZ or Transient activity of earthquakes along a much longer seismic belt. The NMSZ seismicity reflects either a temporary feature of spatially scattered seismicity in the CEUS over long-terms

13. Seismicity in the CEUS, including the NMSZ or transient activity of earthquakes along a much longer seismic belt. The NMSZ seismicity reflects either a temporary feature of spatially scattered seismicity in the CEUS over long-terms

14. Summary In a “homogeneous” intraplate region, seismicity may appear spatially clustered in “seismic zones” during a short period, but over long time they will become randomly scattered. Conversely, a weak zone in the upper crust can cause persistent clustering of earthquakes that tend to migrate back and forth along a belt that extends from the weak zone. Recent clustering of seismicity in the NMSZ may reflect a short-term feature of scattered seismicity over long-terms, or transient activity of earthquakes along a much longer seismic belt. In either case, future earthquakes may not be limited to the presently active NMSZ.