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CHAPTER 10. EARTHQUAKE <br />10-7 <br />Date Latitude Longitude Depth (km) Magnitude <br />06/30/1995 47.1065 -120.5275 11.23 3.00 <br />12/17/1995 47.5950 -120.2192 12.42 3.10 <br />01/01/1997 46.7768 120.4545 19.03 3.70 <br />12/25/1999 47.6333 -120.2015 6.91 3.00 <br />07/25/2006 47.638 -120.2070 6.71 3.10 <br />03/29/2010 47.0033 -120.9583 1.3 3.7 <br />02/18/2015 47.2492 -120.7527 3.6 4.0 <br />10/10/2016 46.9172 -120.4357 7.8 3.1 <br />02/26/2017 47.0757 -120.9967 4.0 3.2 <br />04/29/2018 47.2467 -120.7440 -0.9 3.3 <br /> <br />10.2.2 Location <br />Identifying the extent and location of an earthquake is not as simple as it is for other hazards such as flood, <br />landslide or wild fire. The impact of an earthquake is largely a function of the following components: <br />• Ground shaking (ground motion accelerations) <br />• Liquefaction (soil instability) <br />• Distance from the source (both horizontally and vertically) <br />Mapping that shows the impacts of these components was used to assess the risk of earthquakes within the <br />planning area. While the impacts from each of these components can build upon each other during an <br />earthquake event, the mapping looks at each component individually. The mapping used in this assessment <br />is described below. <br />Shake Maps <br />A shake map is a representation of ground shaking produced by an earthquake. The information it presents <br />is different from the earthquake magnitude and epicenter that are released after an earthquake because shake <br />maps focus on the ground shaking resulting from the earthquake, rather than the parameters describing the <br />earthquake source. An earthquake has only one magnitude and one epicenter, but it produces a range of <br />ground shaking at sites throughout the region, depending on the distance from the earthquake, the rock and <br />soil conditions at sites, and variations in the propagation of seismic waves from the earthquake due to <br />complexities in the structure of the earth’s crust. A shake map shows the extent and variation of ground <br />shaking in a region immediately following significant earthquakes. <br />Ground motion and intensity maps are derived from peak ground motion amplitudes recorded on seismic <br />sensors (accelerometers), with interpolation based on estimated amplitudes where data are lacking, and site