How is the moment magnitude of an earthquake generally measured?

The moment magnitude of an earthquake is a more precise and standardized measure of an earthquake's size than older scales like the Richter scale, and it is primarily determined through analysis of seismic wave characteristics. This method assesses several key factors, including the area of the fault that slipped, the average amount of slip (displacement) on the fault, and the rigidity of the rocks involved.

The moment magnitude scale is designed to provide a consistent measure across different earthquake sizes and distances. It uses data from seismographs that capture the amplitude of seismic waves, which are generated by the accident of the fault slip. By analyzing these waveforms, geologists can infer important details about the event and ultimately calculate the moment magnitude more accurately than relying on other approaches.

In contrast, while analyzing damage reports can provide information about the impact of an earthquake, it does not directly calculate its magnitude. Ground acceleration data, while relevant for understanding the shaking intensity experienced at a specific location, is also not the primary method for determining moment magnitude. Historical earthquake records can help place an event in context or assess long-term seismic trends, but they don't measure the magnitude of a new earthquake directly. Therefore, the primary and most reliable method for calculating moment magnitude involves seismic wave characteristics.