2004 Wave Amplitudes & Magnitudes

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The June 30, 2003 & June 30, 2004 NE Ohio EQs

These two events occurred a year apart along the Lake Erie shore in the general vicinity of Painesville. The 2003 EQ had a magnitude of 3.5, the 2004 event was smaller. a magntidue of around 3.2 or so. Together -- with the large 2001 Ashtabula EQ -- we begin to get a consistent picture of LLG characteristics in NE Ohio.

First, we do a direct comparison of seismograms from the two EQs recorded at LCCO:

Also, we do a direct comparison of seismograms from the two EQs recorded at CLEO

All four seismograms show the now "typical" large LLg phase seen at OhioSeis stations that are closer than 200 km to the epicenter.
In addition, the OhioSeis stations at ditances greater than 200 km also mimic the above-described behavior where S wave amplitudes are greater than LLg amplitude at these greater distances.

Lets plot the LLg amplitudes for these two EQs.

 

This graph shows amplitudes for LLg waves recorded by OhioSeis stations for the 2003.06.30 & 2004.06.30. Amplitudes are plotted in "digital units". The microseism noise amplitudes for these day are around 20 du, hence we have good signal-to-noise ratio.

Since the 2003 EQ is larger, the two EQs are plotted with different y-axis scales so that we can better compare the distance decay. The best-fit lines for a power law between distance and LLg amplitude are also plotted. Notice that the overall log slope decay isabout -1.5, a similar value was found for the large 2001 EQ.

This consistent behavior, and the fact that the assumed spatial decay for the MN formula is a log slope of -.90, argues that we should develop a modified formula for the NE Ohio LLg magntiude.

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