At a certain point, something has to give. In a sudden, violent jerk, the two plates grate against each other, sending shock waves through the earth. This is an earthquake. Yes, there is a very good chance that within 50 years there will be another one. However, the energy continues to build in other areas.
Energy keeps building up until eventually there is another earthquake elsewhere along the fault.
Scientists monitor the energy with instruments they sink into the ground. A. Scientists predict there is a 30 to 50 percent chance of another big earthquake north of Los Angeles in the next 15 to 30 years. The earthquake sends out the strongest shock waves. The aftershocks are what occur later and in the same place along the fault line. As time passes, the aftershocks become less strong.