OhioSeis Network must determine basic earthquake parameters:
Then, we can study enhanced characteristics such as Focal Mechanisms and Quarry Blast discrimination, and so on.
- Hypocenter parameters: Epicenter, depth, & origin time (Depends on regional velocity structure).
- Magnitude: requires reliable wave amplitudes & correction factors
Focus on Magnitude
Basic definition of magnitude
In the central & eastern North America, Lg becomes the dominant phase
What is Lg?
Lg is a complex surface waves that grows from the Sg phase
What does Lg look like?
A distinct high-amplitude phase with U=3.5 km/sec, easily seen at distances of hundreds of km from EQs with M>5
What do Ohio Earthquakes look like at regional distances?
We see an unusual regionally coherent "local Lg" wave with U<2.0 km/sec that is a distinct large wave at even small distances
So what should we do to calculate the Ohio EQs magnitude?
We must find a consistent wave arrival & procedure (see below).
Meanwhile, we are using the "LLg" wave & Hermann & Kijko (1983) formula.