Activity in the Long Valley caldera region this last week was dominated by a sequence of small earthquakes centered beneath the southern margin of the caldera 2 miles east of the airport. To date, the sequence has included 58 earthquakes with magnitudes M=1.0 or greater and ten with magnitudes M=2.0 or greater. The two largest earthquakes with magnitudes M=3.4 and M=3.8 at 11:16 PM on the 17th and 4:40 AM on the 22nd, respectively, produced perceptible shaking in the Mammoth Lakes area. The initial earthquake in this sequence was the M 2.0 earthquake at 9:54 PM on the 15th noted in last week's update. Data from tilt and strain meters in the area show no evidence for significant ground deformation associated with this sequence, and we see no other evidence indicating that this earthquake sequence is associated with the movement of magma beneath the caldera. Long Valley caldera has produced eight M 3 earthquakes since 2000 including the two during this sequence. This level of activity is considered normal for the area.
