a common occurrence

abnormal occurrence

Accident (Crash) Occurrence

air pollution occurrence

Analysis of reason of occurrence

annual earthquake occurrence rate

Anomalous occurrence

anticipated operational occurrence

area of grasshopper occurrence

area of probably occurrence

atmospheric pressure indexes of earthquake occurrence

average disaster occurrence

beginning occurrence stage

calculation of occurrence

Cause of occurrence

Causes for occurrence

character of occurrence

characteristics of occurrence

Characteristics of occurrence and damage

coalbed methane occurrence condition