The question of maximum earthquake ground acceleration has intrigued seismologists and engineers for decades. Igor Beresnev, a prominent researcher, dedicated years to analyzing historical and modern earthquake records to determine an upper limit for ground acceleration. His findings have significant implications for earthquake-resistant design.
1. Historical Perspective
- Pre-1971:
- Scientists believed that ground acceleration during earthquakes could not exceed 0.5g (where g is the acceleration due to gravity, approximately 9.81 m/s²).
- For context, a car accelerating from 0 to 100 km/h in 10 seconds has an acceleration of 0.28g.
- 1971 San Fernando Earthquake (California):
- Recorded ground acceleration approached 1g, shattering previous assumptions.
- This is equivalent to a car accelerating from 0 to 100 km/h in 3 seconds (e.g., Ford GT or Mercedes AMG GT S).
- 1994 Northridge Earthquake (Los Angeles):
- Instruments recorded ground accelerations of up to 2g.
- This is comparable to a car accelerating from 0 to 100 km/h in 1.5 seconds (no commercial car achieves this).
- 2011 Tohoku Earthquake (Japan):
- Ground acceleration reached nearly 3g, setting a new record.
- For perspective, this is similar to the acceleration of a space shuttle during liftoff or a roller coaster, which humans can endure for only about 25 seconds.
- 2011 Christchurch Earthquake (New Zealand):
- Despite being a magnitude 6.3 earthquake, it produced ground accelerations of 2.2g, highlighting that high accelerations can occur even in smaller-magnitude quakes.
2. Beresnev’s Research
- Objective: To determine an upper limit for earthquake ground acceleration.
- Methodology:
- Analyzed data from modern seismographs (available since the 1960s).
- Studied fundamental forces in earthquakes, such as slip amount and velocity.
- Findings:
- Ground motion faster than 2 m/s is impossible and has never been observed.
- Using seismic wave propagation equations, Beresnev concluded that the maximum ground acceleration on bedrock is 3g.
3. Testing the Theory
- 1992 Landers Earthquake (California):
- Beresnev tested his calculations using data from the Lucerne Valley station of the Southern California Seismic Network.
- The station was nearly on top of the fault rupture, providing unique and accurate measurements.
- His calculations confirmed the relationship between earthquake magnitude and ground acceleration.
4. Key Insights
- Magnitude vs. Acceleration:
- High ground accelerations do not require magnitude 9 earthquakes.
- Even magnitude 5 or 6 earthquakes can produce high accelerations and significant damage, especially in smaller areas.
- Implications for Engineering:
- Earthquake-resistant structures must be designed to withstand extreme accelerations, even from moderate-magnitude quakes.
- The 3g limit provides a benchmark for designing safer structures.
Conclusion:
Igor Beresnev’s research has established 3g as the theoretical upper limit for earthquake ground acceleration. This finding underscores the importance of designing structures to withstand extreme forces, even from smaller-magnitude earthquakes. As seismic data continues to evolve, engineers must remain vigilant and adapt their designs to ensure safety and resilience in the face of nature’s unpredictability.
