USGS Earthquake Ground Motion Tool

[brquigle]

I've been using Google Earth to obtain latitude/longitude coordinates and entered them into the USGS software to determine Ss and S1.

Does anyone have a guideline as to the number of significant figures to use? For example, I've looked at the following coordinates: 37.70N, 122.14W.

If I enter 37.7/-122.1, then Ss=2.035 and S1=0.796.
If I enter 37.70/-122.14, then Ss=1.800 and S1=0.671.

That seems quite a difference just for rounding. What would you all suggest?

 

[JedClampett]

You're apparently in an area where the spectra values change in pretty close proximity and a small difference in location makes a large difference in your spectra value. Your two values are about three miles from each other and that is a lot in that area.
You have two approaches you can take. One is to get the exact address to the foot and use the latitude and longitude for that location. You probably need three or four digits after the decimal to get that accurate. As an alternative, you can just use the zip code and use the maximum value for that whole zip code. I think the second method is a little better and not so sensitve to somewhat arbitrary measurements.

 

[msquared48]

The second method is what I commonly use, unless it is a very large project where the cost implications could be profound.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[JStephen]

I use online maps to get latitude and longitude, then enter all the digits that are available. I use the zipcode thing if I don't have an exact location.