|Region: 15 km North of Ottawa, Illinois|
|Time (gmt): 06:10:51.6|
|Magnitude: mb(Lg) 4.5 (NEIC), Mw=4.2 (LDEO)|
|Depth: 9 km|
Seismograms recorded by LCSN Station PAL (Palisades, NY)
Broadband, vertical-component seismic record at PAL (distance=1,260 km)
in Rockland County, NY (about 15 miles North of Manhattan).
Pn wave from the quake should arrives at around 06:13:30 (UTC), but it is very
weak. Broadband record was filtered between 0.6 -- 5 Hz to make it similar to short-period seismogram.
Notice that the large signals starting at 09:57 is from a magnitude 6.8 earthquake that occurred in Southeastern Alaska at 09:49:47.
Source Mechanism and Focal Deth
Source mechanism of the June 28, 2004, Illinois, earthquake determined by
using seismic signals recorded at regional distances (from 200 km to 885 km).
This is a preliminary result. Source mechanism indicates predominantly strike-slip
motion along steeply dipping fault planes striking 17 or 287 degree (measured clockwise from the North).
Source depth of about 9 km fits the observed records best.
Data source: broadband stations of the regional seismographic networks
in the Central United States.
Cooperative New Madrid (BLO, SLM, USIN, FVM, SIUC)
USNSN (JFWS, ACSO, MCWV, PLAL).
USNSN/Kansas Seismic Network (KSU1; http://earth.geol.ksu.edu/kanseis/),
Recent Earthquakes in the Central U.S.
Recent earthquakes in the Central U.S. with known source mechanism.
A red star indicates the epicneter of the June 28, 2004 Illinois earthquake.
Notice that June 28, 2004 earthquake occurred at northern end of the
Illinois basin where seismicity is relatively lower than Wabash Valley seismic zone
in southeastern Illinois and southerwestern Indiana, as well as the
New Madrid seismic zone in the Central Mississippi Valley.