Sources of Error Model and Progress Metrics for Acoustic/Infrasonic Analysis: Location Estimation STEPHEN ARROWSMITH, 1 DAVID NORRIS, 2 ROD WHITAKER, 1 and DALE ANDERSON 1 Abstract—How well can we locate events using infrasound? This question has obvious implications for the use of infrasound within the context of nuclear explosion monitoring, and can be used to inform decision makers on the capability and limitations of infrasound as a sensing modality. This paper attempts to answer this question in the context of regional networks by quantifying current capability and estimating future capability using an example regional network in Utah. This example is contrasted with a sparse network over a large geographical region (representative of the IMS network). As a metric, we utilize the location precision, a measure of the total geographic area in which an event may occur at a 95 % confidence level. Our results highlight the relative importance of backazimuth and arrival time constraints under dif- ferent scenarios (dense vs. sparse networks), and quantify the precision capability of the Utah network under different scenarios. The final section of this paper outlines the research and develop- ment required to achieve the estimated future location precision capability. Key words: Infrasound, event location, nuclear explosion monitoring. 1. Introduction Infrasound has been used for decades as a sensor modality to monitor atmospheric nuclear tests. Within the last ten years, the deployment of the international monitoring system (IMS) infrasound network under the comprehensive nuclear-test-ban treaty (CTBT), in addition to successes from proto- type regional networks, is highlighting the additional value of infrasound as a supplemental tool for mon- itoring underground tests. With the drive towards monitoring low yield tests at regional distances, infrasound has the potential to play a key role in identifying mining blasts and other manmade events that become prevalent at these low seismic magni- tudes. In addition, infrasound can provide constraints on source depth, which can be critical for reliably estimating the yield from seismic data and for source identification purposes. Within the context of treaty monitoring, it is important to communicate to decision makers the capability of different technologies. Recent papers (LE PICHON et al. 2009;GREEN and BOWERS, 2010) have quantified the detection capability of the IMS infra- sound network in terms of yield thresholds. However, there has not yet been any attempt to quantify what is achievable with regional networks of infrasound arrays, or to formally quantify localization uncer- tainty. With the recent deployment of a prototype infrasound network in Utah, it is possible to provide a preliminary assessment of the capability. While the capability will depend on the network configuration (e.g., number and density of stations), which will differ from network to network, there is value in providing an assessment of the Utah network for decision makers as an example scenario. The results will both quantify the current state-of-art capabilities in localization, as well as project what might be achievable in the future by leveraging research advances. The purpose of this paper is to outline a formal approach for assessing network location precision for decision makers. Previous studies at IMS scales have assessed location accuracy using some measure of the azimuthal gap. However, in treaty monitoring appli- cations the question of more relevance is how large a geographic area a given test is constrained within. For onsite inspection activities, areas of up to 1,000 km 2 are permitted. We discuss a methodology for esti- mating location precision for a regional infrasound 1 Los Alamos National Laboratory, Los Alamos, USA. E-mail: sarrowsmith@gmail.com 2 Applied Physical Sciences, Arlington, VA 22203, USA. Pure Appl. Geophys. Ó 2012 Springer Basel AG DOI 10.1007/s00024-012-0576-3 Pure and Applied Geophysics Author's personal copy