I think your calculation assumes that the waves are traveling parallel to the line connecting Livingston&#x2F;Hanford. In the diagram below, &#x27;s&#x27; is the source of the waves.<p><pre><code>    H-----L-------s
</code></pre>
If instead the waves are traveling perpendicularly to the line between those two cities, they should be detected at the same time.<p><pre><code>       s
      &#x2F;|\
     &#x2F; | \
    L-----H
</code></pre>
Since the measured time difference is between 0ms and 10ms, the reality is probably somewhere in between these two extremes.