October 25, 2012—The Ohio Geological Survey during the past year has taken steps to update its earthquake and seismic monitoring capabilities for the state. These improvements include partnering with the U.S. Geological Survey (USGS) and Lamont-Doherty Earth Observatory (LDEO) at Columbia University, New York; adding permanent stations to the Ohio Seismic Network (OhioSeis); and purchasing and deploying portable seismometers. Such steps will allow the Survey to gather and provide to the public information to help mitigate seismic risk in Ohio.

Though not tectonically active, Ohio has historically experienced persistent earthquake activity, and in 1999 the Ohio Seismic Network was established to better understand and assess the risks associated with these earthquakes and to educate the public and policy makers about these issues. Headquartered at the Survey’s H. R. Collins Laboratory in Delaware, Ohio, the network consists of 29 broadband seismic stations located primarily at colleges and universities throughout the state and operated by volunteers. Last year, the Survey began making improvements to the network, including upgraded software and digital helicorders, which allow users to log on to the OhioSeis Web site and see seismic activity recorded at any OhioSeis station, and purchase of new highly sensitive, portable seismometers and data recorders.

A number of earthquakes in Youngstown and Marietta during 2011–12 highlighted the need to better find, locate, and characterize some seismic events. Beginning in 2011, the Survey partnered with LDEO to deploy four high-precision, mobile seismometers in the Youngstown area. The USGS also deployed one NetQuake seismometer in the Youngstown area as well as two NetQuake seismometers and one high-end Trillium seismometer in the Marietta area.

The NetQuake sensors are connected via the Internet to the USGS in Menlo Park, California, which sends data to Ohio when a shake is detected, allowing OhioSeis to quickly determine if an earthquake has occurred. These instruments and the new OhioSeis seismometers are placed close to areas of interest to precisely determine the location and depth of an event and to find “microseismic” events that are too small to be felt but which still yield valuable information on any fault(s) that may be present. In addition to instrumentation, these partnerships have lent much expertise that has enabled the Survey to greatly expand the capabilities of OhioSeis.

As part of the expansion of OhioSeis, the Survey earlier this year added three new permanent stations and purchased and deployed very sensitive portable seismometers. The new stations were added at Marietta College (Washington County), Kent State University – Tuscarawas (Tuscarawas County), and Belmont College (Belmont County). These new stations not only will generate much-needed seismic data for these areas but also will provide educational opportunities for students.

Diagram of a portable seismometer station currently deployed by the Ohio Geological Survey. Click to enlarge.

The Survey thus far has procured four portable seismometers of its own and is purchasing several more in the near future. Two of the new seismometers have been deployed to the Marietta area and two to Youngstown. At least three stations are needed to adequately characterize a seismic event. Combined with portable seismometers on loan from the U.S. Geological Survey and with the permanent OhioSeis stations at Marietta College and Youngstown State University, the Survey has enough instruments to closely monitor and analyze events in these regions.

Small, portable, highly-sensitive seismic stations, such as those used in Youngstown last December, can be used to help characterize buried faults. Although the central and eastern United States are not located on a plate boundary, Ohio and other eastern areas of the country have some ancient and deeply buried structures and faults that still can be the focus of earthquakes. Portable devices, when located close to an event, provide high-resolution information in three components (N-S, E-W, and vertical) that is needed to determine precisely the locations, hypocenter depths and focal mechanisms. Determining an earthquake’s depth and focal mechanism generally is not possible using seismic stations that are often a great distance from the epicenter. However, such information is critical to accurately map geologic faults that lie deep beneath the Ohio landscape. The portable seismometers can be quickly deployed after a significant earthquake in order to monitor small aftershocks.

To illustrate the improvement, a single-component seismogram from our new OhioSeis station at Marietta College (MACO) can be compared to one from a new portable seismometer.

Two seismograms produced by Ohio Geological Survey seismometers. Click for more information and to enlarge.

In addition to the vertical component of ground movement captured by permanent OhioSeis stations, the portable instruments provide the horizontal accelerations and produce highly detailed seismograms for even very small earthquakes that are not felt. Whereas OhioSeis stations are usually set to record data at ten counts per second (cps), the portable sensors can be set all the way to 1000 cps. The sensitivity of the three-component data loggers allow for hypocentral locations and focal mechanism solutions. A catalogue of these small events, when combined with well logs, core observations from deep wells, and magnetic and gravity observations, offer a much clearer picture of the nature of a seismic event.

The Survey’s activities also dovetail nicely with the EarthScope/USArray program that will provide unprecedented seismic coverage for Ohio beginning this year. The EarthScope scientific community conducts multidisciplinary research across the Earth sciences utilizing freely available data from instruments that measure motions of Earth’s surface, record seismic waves, and recover rock samples from depths at which earthquakes originate. The USArray deployment coincides with the 200th anniversary of the devastating New Madrid earthquakes of 1811–1812, which also was marked last year by the Ohio Emergency Management Agency earthquake simulation drill called “The Great Central U.S. Shakeout.” The USArray is now leapfrogging across the nation and is scheduled to deploy 24 high-end seismometers in Ohio in 2012 whose data will become freely available.

Representing a variety of stakeholder organizations with regional diversification, OhioSeis coordinator Mike Hansen and geologist Tim Leftwich have been part of a working group of earth science professionals that prioritize selection of EarthScope USArray stations for long-term operations. The group’s efforts seek to improve earthquake monitoring and reporting, seismic hazard assessments, and solid earth research in the central and eastern United States.

With these tremendous new partnerships, equipment, and capabilities, Survey geologists can gather data from around the state, perform complex modeling of the subsurface, and provide the new knowledge gained to the public so that Ohioans may be better prepared for earthquakes.

For more information about the Survey's portable seismometers, contact geologist Tim Leftwich at (614) 265-6459 or tim.leftwich@dnr.state.oh.us.