Assessing precursory signals with kinematic GNSS: Insights from the 2023 Mw 7.8 Kahramanmaraş earthquake

Identifying precursors of large earthquakes is critical for minimizing the losses of life and property. Recently, Bletery and Nocquet (2023)captured a ∼2-hour-long exponential acceleration of slip using the high-rate (5-min) Global Navigation Satellite System (GNSS) time series from the 48 hours before the 2011 Mw 9.0 Tohoku-oki earthquake, which was obtained by simply concatenating daily kinematic results together. Here, we apply their method to sum the horizontal displacements of 24 high-rate GNSS stations in the direction predicted by fault slip at the hypocenter of the 2023 Mw 7.8 Kahramanmaraş earthquake to characterize its precursory phase. Results demonstrate a several-hour accelerating exponential slip before the mainshock. However, considering that single-day processing would lead to discontinuities at the day boundary, we process the multi-day GNSS data in continuous mode, repeat the experiment, and find that the observed acceleration-like signals vanish. Our work shows that inadequate data processing may lead to the detection of false precursory signals, highlighting the need to develop robust processing techniques in order to identify reliable precursory signals before large earthquakes.