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So what should we do to calculate the Ohio earthquakes magnitude?
The classic mN and mbLg formulations say that Sg/Lg will be the largest amplitude arrivals, but we observe "LLg" as the largest wave at distances closer than 100 km. What to do?
Again, here are the seismograms from the Ashtabula earthquake at LCCO and CLEO:
Considerations:
- As seen above, LLg iS the largest arrival.
- Is it always the largest arrival at distances less than 100 km? We will test that notion in the following section, but here let us suppose that it is true.
- Then should we follow the classic mbLg prescription, or develop our own new prescription that uses LLg amplitudes? (as we have been doing!)
- I argue that we must use LLg, because:
- Felt earthquakes in Ohio produce seismograms where we can just barely see LLg at the closest stations.
- To assign magnitudes to these small events, we must use LLg.
- Disadvantages of using LLg:
- Is it a regionally coherent phase? (Addressed in the next section)
- If it is, then we must do the research to develop this phase and connect its amplitude to the "classic" mN or mbLg. (Not a problem, we should use OhioSeis data to do this!)
The next step is to analyze OhioSeis/MichSeis seismograms from various earthquakes to determine amplitudes of S, Lg, and LLg waves — specifically how these amplitudes depend on distance.
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