A geology game

How much did Heber shake?

Every earthquake of magnitude 3 or more in northern Utah since 1900, from the USGS, with new ones added as they happen. I grew up in Midway, just west of Heber.

    IDAHOWYOMINGNEVADAGreat Salt LakeUtah LakeUinta MountainsWasatch Fault50 km
    • I
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    • IV
    • V
    • VI
    • VII+

      Every quake

        How the numbers work
        • The quakes come from the USGS earthquake catalog: magnitude 3 and up, latitude 39.5 to 42 inside Utah, since 1900. The page asks again every five minutes. Old records with no depth are put at 10 km.
        • Shaking is the Modified Mercalli Intensity from the intensity equation of Atkinson, Worden and Wald (2014), fit to millions of "Did You Feel It?" reports across North America. It uses the magnitude and the straight-line distance from the town to the quake's focus. It doesn't know about the soil under a town, so a basin full of soft sediment can shake harder than it says.
        • Ground motion turns that intensity into peak acceleration and velocity with Worden and others (2012).
        • Wave times use typical upper-crust speeds: 6.0 km/s for P waves and 3.5 km/s for S waves. The rings on the map are where each wave reaches the surface.
        • Energy is the Gutenberg and Richter relation, log10E = 1.5M + 4.8 in joules, at 4.184 billion joules per ton of TNT.
        • The fault patch is the rupture area from Wells and Coppersmith (1994) and the slip that fits the seismic moment (Hanks and Kanamori), with rock stiffness of 30 GPa. Their fits are for bigger quakes, so for a magnitude 3 it's a rough size.
        • What people said is the USGS "Did You Feel It?" survey, averaged over the town's ZIP codes.
        • The intensity words follow the USGS Modified Mercalli scale. The map is a sketch: the lakes and the Wasatch Fault are drawn by hand.