Attach two lengths of string to the at89s52.
At the ends of each string tie a tin can.
Fix the at89s52 to a raised object so the cans hand in free space.
When the earthquake strikes, the cans will bang together and sound the alarm.
It is so efficient, it doesn't even need a power supply.
hmm...maybe using accelerometer interface with microcontroller. when the ground shaking, the accelerometer is shaking too, and give the signal to microcontroller to sound an alarm for example...
thank you for replies. But if high noise appears when there are objects that fall around the sensor.
From data sheets "Static acceleration due to gravity can be used to determine tilt and inclination provided that the sensor is responsive to static acceleration"