1/2 hour seems safe....I lived 1/2 mile from the shoreline just south of Point Gorda for many years. I remember on year the sheriff came by to evacuate us for a possible tsunami. We went into town for some milkshakes until it was over...the actual rise was barely noticable....but if one of the quakes had happened late at night when Mendo Sheriffs on the coast number about 1 for thw whole coast......we could have slept right through our demise!