135 



GEOLOGICAL STRUCTURE OF SANTA MONICA BAY 



Seismology 



The seisraological data used in the preparation of Figure 

 34 have been taken from the California Institute of Technology, 

 Seismological Laboratory, Bulletin on Local Shocks » The four 

 types of "Quality" shown in the legend of the diagram refer to 

 the accuracy in location of the epicenter, "Magnitude" ("M" on 

 the chart) refers to the relative movement of the ground using 

 Richter's scale (Gutenberg and Richter, 1942 )» The magnitudes 

 range from to about 8^, the latter being the largest shocks 

 recorded anywhere in the world, A brief comparison of magni- 

 tudes and their approximate extent in damage are listed below. 

 Magnitude Effects 



Slight shock - probably imperceptible to humans. 



1 Slight shock = possibly felt near epicenter. 



2 Very small shock - felt slightly over a small 

 area of a few miles in radius, 



3 Small shock - felt sharply over a small area, 

 but incapable of causing any but insignificant 

 damage, 



4 Moderate shock - may cause considerable minor 

 damage near the epicenter; felt to a distance 

 of about 45 miles, 



5 Minor shock - may be destructive near the epi- 

 center, with damage over a larger area; felt to 

 a distance of about 125 miles. 



6 Major shock - a strong destructive earthquake. 



7 & 8 Progressively stronger destructive earthquakes. 



The Long Beach earthquake of March 10, 1933, had a magni- 

 tude of about 6.3, The last series of major earthquakes in 

 southern California of comparable magnitude were the Kern County 

 shocks of July and August 1952, which had magnitudes of 7.6 to 

 7.7, 



