Neighborhoods west of Reno, Nev., are being jolted by a swarm of quakes that are fascinating seismologists but frustrating residents.

So far experts can't say what's causing the swarm, how long it will last or what's coming next. One consolation, though, is that a quake much bigger than 5.5 or 6 on the Richter scale seems pretty unlikely. The swarm, which began Feb. 28, hasn't produced any quakes with a bigger initial measurement than Friday's 4.7 event. It has produced hundreds of smaller quakes, though, many so shallow that people notice the shaking even at magnitudes of 1.5 or 2.The quakes have been cracking pavement and breaking glass.

Later this week seismologists from University of Nevada, Reno, Seismological Laboratory hope to place more monitoring equipment just west of Reno, near the communities of Mogul and Somersett. Seismologists say the quakes are originating from a buried fault zone that previously showed no surface signs of its existence.

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