1. Geography

The Mid-America Region of the Advanced National Seismic System (ANSS) includes 26 states in the mid-west, south and southeast and the District of Columbia thus making it the largest ANSS region in the conterminous United States. The region is outlined by the red boundaries in Figure 1.



2. Seismology

The region has had significant historical earthquakes: the sequence of large earthquakes near New Madrid, Missouri during 1811-1812 and the 1886 Charleston, South Carolina earthquake. Other areas within this region affected by earthquakes large enough to cause structural damage are Anna, Ohio in 1937, Manhattan, Kansas in 1867, Tecumseh, Nebraska in 1935, southeastern Illinois in 1968, Maysville, Kentucky in 1986, to name a few.. The most continuously active area is that part of the central Mississippi valley n surrounding New Madrid. Figure 2 shows the location of known earthquakes with magnitudes greater than 4.5 in the region. Since this magnitude is the threshold of significant damage, this figure highlights the expected earthquake threat in the region.

Figure 2. Locations of known earthquakes with M > 4.5. The borders of the ANSS-MA region are indicated by the solid lines. Note that damaging or potentially damaging earthquakes have occurred with most states of the region.

Several significant observations can be made from Figure 2. First, significant earthquakes occur over a very broad region. Although the figure indicates a preponderance of significant events near New Madrid and South Carolina, an expanded view would indicate a broad geographical distribution even within these smaller regions.

The New Madrid region in the Central United States can be defined as the area bounded by lines connecting the major cities of Little Rock, St. Louis, Evansville and Memphis. The South Carolina region appears to cover the entire state and not just Charleston. A rough guide is that these two active regions have dimensions on the order of 250 miles x 250 miles. These large dimensions, the relatively small number of instruments to be deployed under the ANSS, the relative infrequency of events, and the history of significant damaging earthquakes in the remainder of the Mid-America region argue for a slightly different monitoring strategy compared to seismically active regions within the U.S.

3. ANSS working group(s) and advisory committee(s)

The ANSS-MA region has established an advisory committee. The committee membership was designed to represent all groups with an interest in the goals of the ANSS for Mid-America. The current members are listed in Appendix A and B of this plan. These committees have met and discussed the regional monitoring needs. Meeting minutes are documented at the ANSS-MA website:

http://www.ma-org/

The earthquake distribution and unique seismic wave propagation characteristics influence all aspects of the regional implementation. While the national backbone plan will provide uniform coverage of the entire region, other locations require denser monitoring to be accomplished by augmentation and enhancement of current monitoring.

Although national backbone will be able to define the earthquake size, source mechanism and depth for M > 4.5 earthquakes, precise locations require a denser deployment of instruments, which are also absolutely required to obtain the source parameters (hypocenter coordinates and magnitude) for smaller earthquakes (M > 3).

The deployment plan for broadband sensors and free-field strong motion sensors may be easier to define than that for the instrumentation of structures. The fraction of strong motion instruments deployed in the free-field versus within structures may be and perhaps should be different for ANSS-MA because of the large size of the region and the distribution of relatively infrequent, but historically significant seismic activity. In addition, the diversity of site conditions with currently poorly understood ground motion modification characteristics will weigh the deployment toward more free-field sites.

In May, 2001 the USGS provided a preliminary draft for a 100 station backbone for the contiguous 48 states. Currently it is projected that the national backbone will support 3-component broad band and 3-component strong motion data streams. To develop this draft, certain design assumptions were made:

1. An inter-station spacing of 278 km ± 50 km to ensure uniform coverage.
2. Incorporation of many of the existing USNSN, GSN and cooperating stations that contribute to the goal of uniform coverage
3. Choice of new locations based on a nearby community

No effort was made to define the specific type of instrumentation to be installed, e.g., USNSN or GSN type. Figure 3 presents the draft backbone. The proposed stations list for the Mid-America region is given in Appendix A.

The task before the ANSS-Central Region is to comment on this national level backbone and to use it as a guide for implementing the specific regional plan.

1. Comments/recommendations with respect to suggested sites

• The proposed national backbone will accomplish its task of uniform national monitoring. The ANSS Mid-America Region will assist in siting and requests guidance on the desired site characteristics for these stations, since bedrock, low noise sites may not be available at many of the proposed locations on the map. The ANSS Mid-America region will work with state and local governments to assist in selecting optimal sites.
• The Mid-America Region will propose minor station realignments to incorporate existing stations and yet meet the proposed national monitoring density. This will be addressed further in section B.
• The Mid-America Region acknowledges that existing broadband stations that are not incorporated into the national backbone may be incorporated into the regional monitoring system.
• To assist in regional planning, the detection and location capabilities of the proposed backbone must be quantified.

• The Mid-America Region will propose a prioritized implementation plan for the national backbone stations within the region.

1. Recommendations for the number and locations of regional broadband stations

The U. S. Geological Survey Circular 1188, Requirement for an Advanced National Seismic System, suggested a major upgrade of regional monitoring and the installation of strong ground motion monitoring in the free-field and in structures in urban areas of the nation. Approximately 10% of the strong ground motion monitoring suggested in the document was suggested for the Mid-America region. At full implementation this could cover about 100 sites for regional monitoring, and 300 sensors each for free-field and structural monitoring.

Because of the current rate of implementation, it is better to propose a regional monitoring philosophy that sets priorities for an incremental deployment of the ANSS and which can be drawn upon to design the implementation plan with an expedited deployment of the entire system:

• All earthquakes with magnitudes > 4.0 or intensities > V must be monitored with nearby instruments so that ground motion, source properties and alert functions can be accomplished.
• All earthquakes with M > 3.0-3.5 must be located.
• A regional monitoring strategy is essential. The combination of a large geographic area and infrequent but significant earthquakes argues for a broad regional monitoring strategy with a modified definition of urban monitoring. Selected communities may have a large number of strong motion instruments installed, but most others will have just a few instruments to sample different site conditions.

• The existing monitoring infrastructure will be the basis for regional implementation. Much of the current earthquake monitoring is in the proper place, but lacks the necessary sensor, data acquisition and communication infrastructure to contribute fully to the goals of the ANSS. Upgrading these sites builds upon local interest and supports prior investment required in developing new sites.

1. Interface with national system

The national backbone provides a uniform national monitoring that addresses national reporting requirements. It is de facto an integral part of regional monitoring. The national backbone implementation should be prioritized to assist regional monitoring needs by focusing on sites closest to those large historical earthquakes that are not well monitored at present. For example, the CLKS and TINE sites to monitor the Nemaha Uplift in Oklahoma, Kansas and Nebraska are required.

The SRIN site in central Indiana is near an existing quality site at Bloomington. Moving the SRIN site farther north in Indiana would permit better monitoring of earthquakes near Chicago. Departure from the initial 278 km station spacing goal is ameliorated by the data from the BLO station.

In the southeast, the southeastern

2. Suggested deployment sequence

FY2001

The initial deployment of urban ground motion monitoring during FY2001 is accomplished. Stations were installed in the Memphis, TN, urban region (7), Dyersburg, TN (3), Jonesboro, AR (1) and Covington, TN (1). Site selection was based on a prioritized list established by the regional Advisory Committee in late 2000.

FY2002

Upgrade some existing broadband recording sites with strong motion recording capability. Specifically

• BLO, Bloomington, IN, seismograph pier (1)
• SLM, St. Louis, MO, seismograph pier (1)
• SIUC, Carbondale, IL, seismograph pier (1)
• UALR, Little Rock, AR, free field (1)
• UTMT, University of Tennessee, Martin (1)

Establish new urban monitoring sites in

• Metropolitan Washington, DC, perhaps USGS Reston, U.S. Capitol, or Executive Office Building (1)
• Evansville, IN, in conjunction with proposed broadband site at University of Southern Indiana (rock) and Science Museum (river alluvium) (2)
• Charleston, SC (2)
• Columbia, SC (1)
• Giles County, VA (1)
• Anna, Ohio (1)

Establish new broadband sites at

• Lexington, KY at Kentucky Geological Survey Core Facility
• Tulsa, OK (get this facility into the system)

FY2003

Upgrade and incorporate stations of the PEPP, MichiSeis, OhioSeis and IndiSeis stations to be part of the ANSS system. These educational projects have found sites and communication links that can be used as part of the new system. The upgrade will not preempt the educational function but will serve to provide new data streams and build on local interest.

Expand free-field monitoring to Richmond, VA, Raleigh, NC, Knoxville and Chattanooga, TN, Augusta and Atlanta, GA, Birmingham, AL, Fayetteville, AR, Lawrence, KA, Omaha, NB, and Cleveland,OH.

Augment free-field monitoring in Charleston, and the broad central Mississippi Valley region.

Provide additional monitoring for the southern Appalachians.

Upgrade existing sites to broadband

• Tuckaleechee Caverns, TN (TKL) – a low noise site

Incorporate emerging ANSS stations into educational efforts

• Develop regional deployment philosophy
• Recommend sites for reference and free-field stations
• Recommend deployment sequence
• Recommend structures/types of structures

1. Description of number/type of instrumentation per structure
2. Rationale for chosen structure/location

• Define the relationship to existing strong motion instrumentation in the region.

This working outline for ANSS deployment in Mid-America establishes topics for this advisory committee to address. It is clear from the tabulations in the appendices that interested individuals in certain areas are not represented. To that purpose this document will be forwarded to seismologists in Texas, Oklahoma, Kansas and Iowa who must be included in the implementation process.

The following tabulation is the subset of station sites plotted in Figure 1. The stations are listed by state. A name given in the last column indicates that this stations does not currently exist, and that the location is approximate within the guidance noted above.

The members of the ANSS-MA Advisory Committee are give below. The function of this group is to provide guidance on the use of resources and monitoring goals in the ANSS-MA.