Ohio-Penn EQ of Sept 25, 1998: Hypocenter

NEIC

• NEIC map with their quick hypocentral determination

Canadian National Seismographic Network

• The CNSN preliminary epicentral location is to the northwest of the NEIC location, but their stations are all to the north of the event
• Go to "other web sites" to see the CNSN report on this event

MichSeis

• Relocation of the epicenter based on local stations:
  
• Relocation result #1 (Oct. 3, by LJR):
  • Use close stations, all less than 500 km epicentral distance
  • Stations are a mixture of USNSN, Canadian (Univ. Western Ontario) & regional stations in Ohio & Michigan.
  • Relocation is with respect to the NEIC prelim. location: 41.471 N, 80.483 W, OT: 19:52:52.5
  • But, instead of the USGS travel times, the regional P travel time curves from the western Ohio Anna network are used (fully documented in final report for U.S. Nuclear Reg. Comm., report "NUREG/CR-3145, Vol. 10, 1992").
    In short, a Pg velocity of 6.21 km/s, a Pn velocity of 8.12 km/s, with Pn tau of 8.0 sec, for the "regional reference focal depth" of 5 km.
  • Overall, the NEIC location & OT are excellent, but in detail, dependent on stations included or not:
  • The best-fit epicenter ranges from:
    (i) 2. km to the northeast of NEIC epicenter (but error ellipse includes NEIC location), OT is +0.7 second; to
    (ii) 11. km to the west of NEIC epicenter (error ellipse major axis is 6 km), OT is within 0.1 second.
  • We need to resolve some of the apparent discrepancies between nearby stations to eliminate result (ii) above, which has a larger RMS.
  • Also, while the western Ohio veloicty model may be the best we have right now, it probably is not correct for the paths that go directly through the Appalachians.