Fig. 7. LSH database and similarity search example.

(A) Database generated using LSH, with b = 3 hash tables (red boxes); each hash table has many hash buckets (ovals). LSH groups similar fingerprints into the same hash bucket with high probability; earthquake signals (colors) are likely to enter the same bucket, whereas noise (black) is grouped into different buckets. (B) Search for waveforms in database similar to query waveform (blue). First, LSH determines which bucket in each hash table has a waveform that matches the query. Next, we take all other waveforms in the same bucket in each hash table and calculate the FAST similarity between each (query, database) waveform pair: the fraction of hash tables containing the pair in the same bucket. The red waveform is in the same bucket as the blue query waveform in all three hash tables, so their similarity is 1; the green waveform is in the same bucket in two of three hash tables; and so on. This figure displays waveforms for easy visualization, but the database stores references to fingerprints in the hash buckets, and a search query requires converting the waveform to its fingerprint.