Seismic Location Services using iLoc

iLoc, a single-event earthquake location algorithm was originally developed under an US Air Force Research Laboratory grant (Bondár et al., 2008) to address the issue that traditional, linearized event location algorithms systematically underestimate location uncertainties, that is, the error ellipse do not cover the true location. These algorithms assume that the observations are independent, but that assumption is often violated when 3D velocity heterogeneities are not captured by the velocity model. Similar ray paths traversing these heterogeneities will generate correlated travel-time prediction errors causing not only underestimated location uncertainties but also location bias. The location algorithm developed by Bondár and McLaughlin (2009a) takes into account correlated travel-time prediction errors. This algorithm has become the official locator at the International Seismological Centre (Bondár and Storchak, 2011).

Upon leaving the ISC, István Bondár continued to further develop the algorithm as the project iLoc (Bondár et al., 2015, 2018) by adding new features, such as the use of backazimuth and slowness measurements together with arrival times in the location, and obtaining travel-time predictions from the Regional Seismic Travel Times global 3D model of the crust and upper mantle (Myers et al., 2010, Begnaud et al., 2021a, 2021b).

iLoc has been implemented as a plugin into the SeisComp (Weber et al, 2019) seismic data collection and processing software. iLoc also forms the core of the European-Mediterranean Seismological Centre crowd-source location algorithm, CsLoc (Steed et al., 2019, Bondár et al., 2020).

iLoc is regularly used in CTBTO and LLNL capacity building workshops and training.

iLoc has been used several studies to relocate the seismicity of an entire region, such as the Caucasus (Bondár et al, 2023; Onur et al, 2020), the Pannonian Basin (Bondár et al, 2018), the Anatolian region (Kartal et al, 2022), Brazil (Carvalho et al., 2020), and to produce the ISC-GEM catalog (Bondár et al., 2015), as well as creating seismo-acoustic event bulletins (Bondár et al, 2022).