**8.1. Search for correlations between** *q***-factor alerts from adjacent HF radars**

A real tsunami would be seen at two coastal locations say 30 km apart, for example, within a definable time window (say 15 min). Tsunami waves refract as they move into the ever‐ shallower water of the continental shelf near the coast. This means they tend to arrive perpen‐ dicular to the shore. This forces similar arrival times at neighboring locations along a nearly straight coastline.

Hence, if a high *q*‐factor peak at Radar M arrives at a given range within 15 min of a high *q*‐ factor peak at Radar N, the presence of both raises the probability that a real tsunami is being seen by orders of magnitude. Likewise, if a high *q*‐factor at Radar M has no counterpart at Radar N, this raises greatly the probability that the "alert" was in fact a false alarm. Thus, the solitary alert can be either eliminated as a false alarm or attached a flag to give it a much lower credibility.
