Nature is complex and we need simplifications to grasp it. But just as "clouds are not spheres [and] mountains are not cones" similarly, earthquake hypocenters are not always single points with normal errors. Often they are complex distributions that can be adequately represented only by a mixture of several anisotropic Gaussian kernels (see Viddy 3D).

The need for absolute hypocenter locations with uniformly consistent uncertainty estimations has motivated us to relocate the last 30 years of Southern California seismicity using the probabilistic non-linear software NonLinLoc and a so-called minimum 1D velocity model with station delays.

We aim to provide an alternative to Double-Difference catalogs. We maintain that it is problematic to use DD catalogs for the development and testing of earthquake forecasting models. Because all the earthquakes, which in classical catalogs can be regarded as independent data points, are interconnected by the cross-correlation procedure. Thus, it is unreliable to test any model, be it physical or statistical, on such catalogs because it is impossible to obtain an independent validation set of earthquakes.

Read the full paper
KaKiOS-16: a probabilistic, non-linear, absolute location catalog of the 1981-2011 Southern California seismicity Y. Kamer, E. Kissling, G. Ouillon & D. Sornette, BSSA (2017)

For more inquisitive readers here are the Frequently Asked Questions

Chickens come out of eggs and eggs come out of chickens. Locating earthquakes is a similarly coupled problem that requires a robust and well resolved velocity model.

The KaKiOS catalog is located using the min1D P-wave velocity model YKEK05 and station corrections obtained by solving the coupled hypocenter-velocity inverse problem with VELEST. We used the best locatable ~10,000 events to constrain this model. The correspondance between the station corrections and the surface geology is a testament to the geophysical relevance of the min1D model.

Download the min1D model
YKEK05_min1D_staCor_NLL.zip (200 KB)

The catalog contains the probability density functions (PDFs) of 479,056 events located with NonLinLoc. Each event's PDF is expressed by a mixture of optimal number of Gaussians. Events are stored on multiple of lines, each representing an individual mixture component (i.e mixing weight and elements of the multivariate Gaussian covariance matrix).

Download the KaKiOS-16 Catalog
kakios_16_20160504.zip (48 MB)

The catalog spans the time range [1981/01/01, 2011/06/30], latitudes [30.0, 37.5] and longitudes [-122, -113]. Magnitudes are not re-estimated and are taken from the SCEC. All events in KaKiOS have been located with at least 4 P picks within a 100 km radius. Due to this minimum locatability requirement some events have not been located. Also, since SCEC updates catalogs retrospectively there are new events found in neither KaKiOS nor HYS-2012.

To facilitate comparisons between different catalogs we provide additional lists of these events seperately. We remind the user that these events are located by SCEC with their routine method and velocity model. The lists are created based on the SCEC catalog downloaded on 2016/04/27 including both regional and local events.

[1] Poorly locatable events present in HYS but not in KaKiOS
poorLocEvents_HYS_2012.txt (1.5 MB)
[2] Invalid events in HYS (replicated IDs, quary blasts...)
invalidEvents_HYS_2012.txt (24 KB)
[3] Newly detected events in SCEC (as of 2016/04/27)
newEvents_SCEC_2012.txt (1 MB)