\nThe Northeast Ohio seismic zone has had moderately frequent earthquakes at least since \nthe first one was reported in 1823. The largest earthquake (magnitude 4.8) caused \ndamage in 1986 in northeasternmost Ohio, and the most recent damaging shock \n(magnitude 4.5) occurred in 1998 at the seismic zone's eastern edge in northwestern \nPennsylvania. Earthquakes too small to cause damage are felt two or three times per decade.\n
\n\nEarthquakes in the central and eastern U.S., although less frequent than in the western \nU.S., are typically felt over a much broader region. East of the Rockies, an earthquake \ncan be felt over an area as much as ten times larger than a similar magnitude earthquake \non the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many \nplaces as far as 100 km (60 mi) from where it occurred, and it infrequently causes \ndamage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as \nfar as 500 km (300 mi) from where it occurred, and sometimes causes damage as far \naway as 40 km (25 mi).\n
\n\n\nEarthquakes everywhere occur on faults within bedrock, usually miles deep. Most of the \nseismic zone's bedrock was formed as several generations of mountains rose and were \neroded down again over the last billion or more years.\n
\n\nAt well-studied plate boundaries like the San Andreas fault system in California, often \nscientists can determine the name of the specific fault that is responsible for an \nearthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Northeast \nOhio seismic zone is far from the nearest plate boundaries, which are in the center of the \nAtlantic Ocean and in the Caribbean Sea. The seismic zone is laced with known faults but \nnumerous smaller or deeply buried faults remain undetected. Even the known faults are \npoorly located at earthquake depths. Accordingly, few, if any, earthquakes in the seismic \nzone can be linked to named faults. It is difficult to determine if a known fault is still \nactive and could slip and cause an earthquake. As in most other areas east of the Rockies, \nthe best guide to earthquake hazards in the Northeast Ohio seismic zone is the \nearthquakes themselves.\n
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