The “Long Beach Earthquake” occurred on March 10, 1933, at 5:54:08 p.m., P.S.T., very nearly. Its origin was very near to 33° 34′.5 north latitude, 117° 59′ west longitude, at a depth of about ten kilometers (6 miles).
Previous shocks, emanating from sources not far distant, were not definitely recognizable as “fore-shocks” in advance, notwithstanding discovery in recent years of small changes in level in the neighboring region.
Many aftershocks followed. The sources of some were very near the chief epicenter; others originated at some distance. The distribution, and its significance, must await thorough study.
Hard shaking probably continued for ten to fifteen seconds. The duration of perceptible vibration varied from place to place, and with local conditions.
Doubtfully, on account of ground conditions, “apparent” intensity of grade IX, 1931 scale, may have been developed in a few small places. Grade VIII was manifested in numerous places, and is the characteristic maximum intensity of this shock. Serious damage to bad construction resulted in many places inside an area of about 1,200 square kilometers (say 450 square miles), with the greatest concentration in and near Compton, and in and near Long Beach.
No fault displacement was found at the surface anywhere.
To a small extent minor disturbances to ground water, secondary cracks in the ground, and similar minor geological effects were observed in the meizoseismal area.
As usual miscellaneous effects—sounds, movement of liquids, visible surface waves (?), luminous phenomena (?), etc.—were reported from the area of vigorous shaking.
All the evidence indicates a fairly strong, moderately large shock in the local earthquake class, manifesting about the same intensity over an area of about the same size as the shock in Santa Barbara in 1925.
The disastrous consequences of the shock were due chiefly to poor construction on bad natural ground in a rather densely populated district.