What does NSTS stand for?

In other words, both of the data are non-stationary time series, respectively.

Topics include using volcanic processes as sources of statistical data, creating models for assessment, determining the probability of explosive eruption, using extreme value methods for historical modeling and spatial distribution, applying the Gutenberg-Richter Law, calculating stationary and non-stationary time series and finding new approaches, employing wavelet-based hidden Markov models, reading a coupled conduit and eruption column model, evaluating transient models of conduit flows, using multiple parameters in studies of processes, inverting tephra fallout and using probabilistic models for tephra dispersion.

Reichlin, "Segmented Trends and Non-Stationary Time Series.