Post-Mazama (7 KA) faulting beneath Upper Klamath Lake, Oregon

High-resolution seismic-reflection profiles (3.5 kHz) show that a distincti ve, widespread reflection occurs in the sediments beneath Upper Klamath Lak e, Oregon. Goring reveals that this reflection is formed by Mazama tephra ( MT), about 7 ka in age. The MT horizon is faulted in many places and locall y displaced by as much as 3.1 m. Differential displacement of multiple hori zons indicates recurrent fault movement, perhaps three episodes since depos ition of the Mazama, The pattern of faulting indicates northeast-southwest extension beneath the lake basin.