A magnitude 8.0 earthquake struck off the Santa Cruz Islands in the Pacific Wednesday morning local time, kicking up a thee-foot tsunami that killed six people. There are two small lessons for temblor-prone Charleston here. First, the tsunami was relatively small but still lethal. Tsunamis are rare here, but large fault zones in the Atlantic are capable of kicking one up, and tide gauges in Charleston Harbor have recorded several very small tsunamis, according to the Lowcountry Hazards Center at College of Charleston. Second, the Pacific quake was preceded by what seismologists call a “swarm” of magnitude 6 quakes. Seismologists at the college had been monitoring the Santa Cruz Islands since the swarm began in late January. Whether or when swarms indicate a major quake is on its way remains a keen interest among scientists hoping to predict the big ones. But swarms routinely occur without major quakes occurring, and major quakes occur without foreshocks. All researchers can say so far is that the probability of a quake increases when a swarm occurs. Worth pointing out that the devastating Great Charleston Earthquake of 1886 was preceded by a five-day swarm of 10, much smaller magnitude 2-3 range shocks. That earthquake has been estimated at magnitude of 7 or greater.