USGS ShakeMap
Ground motion map published by the U.S. Geological Survey within minutes of an earthquake, and used as the reference index in parametric contracts.
ShakeMap is the ground motion map that the U.S. Geological Survey (USGS) publishes after a significant earthquake, and that parametric contracts use as their reference index. It comes out a few minutes after the shaking. It is a grid giving, point by point, peak ground acceleration (PGA), peak ground velocity (PGV), spectral accelerations at several periods and Modified Mercalli intensity (MMI). The product was born in Southern California in the late 1990s, after Northridge, to show emergency responders where the ground moved most, and it now covers the whole world. The map blends station recordings, public reports collected through Did You Feel It?, and, where instruments are sparse, ground motion models that estimate shaking from distance to the fault and site conditions. It feeds PAGER (Prompt Assessment of Global Earthquakes for Response), the rapid estimate of fatalities and economic losses that the USGS issues with a color-coded alert level. For an underwriter, ShakeMap is the bridge between the event and the book. You overlay the insured sites, read the intensity at each one, and move from a cat-in-a-box trigger, which knows only magnitude and epicenter, to a trigger that knows whether the plant actually shook. The catch is one word: versions. The first map rests on few stations and a rough fault geometry; it is revised as data come in, sometimes for weeks, and a site can move up or down a full intensity unit. A well-drafted contract names the variable read (PGA in g, or MMI) and the interpolation rule between grid points. It also names the governing version (the first one, or whatever is posted on a fixed date after the event) and the fallback source if the USGS changes its format or stops publishing. The USGS is party to none of these contracts and takes no responsibility for how its maps are used.
Textbook case, made-up numbers: a parametric policy pays 50% of limit if the ShakeMap peak ground acceleration (PGA) at the plant exceeds 0.25 g, and 100% above 0.40 g. The first version, posted twenty minutes after the quake, shows 0.38 g. A week later, two more stations and a finite fault model push the value to 0.43 g. The contract uses the version available on day ten, so the insured collects the full limit, where a first-version clause would have paid half.
ShakeMap, USGS ShakeMap, shake map, USGS ground motion map
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