Ground Motion Signal Processing // Implements short-time Fourier transform (STFT) based processing of strong-motion time series: time-grid regularisation, STFT-window and anti-alias-resampling strategy selection, edge tapering, and frequency-domain integration and differentiation, mapping a single input (acceleration, velocity, or displacement) to a consistent triplet under a chosen analysis bandwidth. Also provides intrinsic-mode-function decomposition via empirical mode decomposition (EMD), ensemble EMD (EEMD), and variational mode decomposition (VMD) with optional band-rule filtering; elastic single-degree-of-freedom (SDOF) domain-normalised acceleration, velocity, and displacement response spectra from their corresponding time-series domains by exact state-space integration; intensity measures including peak, root-mean- square (RMS), Arias intensity, significant-duration, cumulative absolute velocity, mean period, and the derived indices earthquake destructiveness potential (EPI) and power-of-input (PDI); and D50 and D100 horizontal response spectra. Methods: Huang et al. (1998) doi:10.1098/rspa.1998.0193, Wu and Huang (2009) doi:10.1142/S1793536909000047, Dragomiretskiy and Zosso (2014) doi:10.1109/TSP.2013.2288675, Boore (2010) doi:10.1785/0120090179. An optional indexing layer parses provider files in formats including 'PEER' 'NGA-West2' 'AT2', 'CESMD' 'V2'/'V2c', 'NWZ' 'V2A', Geological Survey of Canada 'TR', 'IGP'/'UCR' 'AC' variants, and generic two-column ASCII text, normalises components, writes per-record CSV (comma- separated values) and JSON (JavaScript Object Notation) pairs, and computes per-record intensity tables.