INSTRUCTIONS FOR PROPOSING REVISIONS TO PRELIMINARY

DRAFT MAP OF 100-STATION NATIONAL "BACKBONE"

(Excerpts from e-mail sent by Kaye Shedlock, USGS,

to ANSS Regional Coordinators, May 30, 2001)

[The following addresses] a PRELIMINARY DRAFT [MAP] of a 100 station backbone for the contiguous 48. Hawaii already has two likely 'backbone' stations (KIP and POHA), Puerto Rico has 1 (SJPR), and Alaska has 7 and that working group has agreed to propose another 7-8 more.

I capitalized the words [PRELIMINARY DRAFT], because your input/suggestions are not only most welcome, they are necessary. So please do not be hesitant to supply them. But first, some background.

This draft backbone was developed in the following fashion:

• Aim for a station spacing of approximately 278 km (based on the land area), give or take 50 km.
• Start with all existing USNSN and GSN stations as possible/probable backbone stations
• Choose 'new' locations based on the lat/lon of a mapped 'populated place'
• No attempt has been made to indicate which will be USNSN-type (80% of backbone) and which will be GSN-type (20% of backbone) stations. That will be determined with all of your input along with recommendations from the GSN Standing Committee and the National Networks Working Group.

Practical considerations that came into play:

• When two USNSN or GSN stations are closer together than the desired spacing, choose the most favorably located station as the backbone. This is why you will discover some 'missing' USNSN stations.
• When maintaining the desired spacing gets difficult, leave larger gaps in areas that we are certain will be well-covered with regional BB stations, or have little-to-no seismicity.

In a few instances, cooperating or contributed stations (by name) are included as possible backbone stations. You would need to concur or disagree about these in your regional plan recommendations. Several other (many, we hope) possible backbone stations locations may coincide with current station locations, but are not marked with current station names. When that occurs, and you concur, please just include that information in your regional plan. Any current USNSN station (including cooperatives and contributed) that do not appear as backbones on this draft are open game: you may 'adopt' them into your regional recommendations or suggest an altered backbone grouping that preserves the desired spacing and includes the 'missing' station.

[Regarding the "Preliminary Draft "Backbone" Map,] GSN, USNSN, and some other existing stations are plotted with colored symbols and listed with their call letters, lat, and lon. Possible 'new' backbone stations are plotted with black symbols and listed with fake station codes (the State they are in is denoted by the last two letters), lat, lon, and 'populated place'.

So, please consider these suggestions as input to your draft regional plan. Do not forget the assumed 50 km (or so) of 'play' in any direction when you comment on them (for example, if a possible station on this map is about 50 km or less from a good location you are familiar with, or an existing station that could be upgraded, by all means strongly suggest the 'better' location).

Kaye M. Shedlock shedlock@usgs.gov

USGS - MS 966 Ph: (303) 273-8571

Box 25046 Fax: (303) 273-8600

Denver, CO 80225