What Controls Variations in Aftershock Productivity?

Abstract

The number of aftershocks increases with mainshock size following a well‐defined scaling law. However, excursions from the average behavior are common. This variability is particularly concerning for large earthquakes where the number of aftershocks varies by factors of 100 for mainshocks of comparable magnitude. Do observable factors lead to differences in aftershock behavior? We examine aftershock productivity relative to the global average for all mainshocks ( MW>6.5) from 1990 to 2019. A global map of earthquake productivity highlights the influence of tectonic regimes. Earthquake depth, lithosphere age, and plate boundary type correspond well with earthquake productivity. We investigate the role of mainshock attributes by compiling source dimensions, radiated seismic energy, stress drop, and a measure of slip heterogeneity based on finite‐fault source inversions for the largest earthquakes from 1990 to 2017. On an individual basis, stress drop, normalized rupture width, and aspect ratio most strongly correlate with aftershock productivity. A multivariate analysis shows that a particular set of parameters (dip, lithospheric age, and normalized rupture area) combines well to improve predictions of aftershock productivity on a cross‐validated data set. Our overall analysis is consistent with a model in which the volumetric abundance of nearby stressed faults controls the aftershock productivity rather than variations in source stress. Thus, we suggest a complementary approach to aftershock forecasts based on geological and rupture properties rather than local calibration alone.

Rapid response to the M w 4.9 earthquake of November 11, 2019 in Le Teil, Lower Rhône Valley, France

“…tern of the aftershocks (Figure 8a) indicates a clustering of events within 1-fault length distance from the co-seismic faulting, as expected from worldwide patterns [e.g. Dascher-Cousineau et al, 2020, De Arcangelis et al, 2016, Parsons and Velasco, 2009, Tahir and Grasso, 2015, Tahir et al, 2012. Most of these events are in the hanging wall as common in thrust faulting sequences.…”

“…The relative deficit of Le Teil aftershock rate is controlled by the weak productivity early on. Nevertheless, at a global scale the aftershock productivity for a given mainshock magnitude is known to have large variability; a 3fold aftershock productivity variation is not rare [Dascher-Cousineau et al, 2020].…”

Rupture Process of the 7 January 2020, MW 6.4 Puerto Rico Earthquake

“…The mainshock slip is localized in the eastern section of the quasi-cruciform seismicity distribution of the sequence, with the foreshock activity concentrated westward of the slip and relatively few aftershocks in the high-slip region ( Figure 5). The sequence has very high earthquake productivity relative to comparable size mainshocks (e.g., Dascher-Cousineau et al, 2020); an M W 6.4 mainshock is on average accompanied by only three aftershocks with magnitude ≥ 4.5 within 60 days. For the 2020 Puerto Rico mainshock, there were 25 such events January 2020 mainshock epicenter.…”

Northern Chile intermediate-depth earthquakes controlled by plate hydration

“…Since the six earthquakes have similar characteristics such as magnitude, focal mechanism, hypocenter and station coverage, we use the same spatial and temporal scale for all of them in order to preserve a homogeneous criterion that allows their comparison. After some tests with different windows size and considering some previous works (e.g., Persh and Houston, 2004;Dascher-Cousineau et al, 2020) we define the spatial limit using a 3D radius of 25 km from each hypocenter, and 25 days of data after each mainshock, as this is the maximum number of days for which the five stations closest to each event were operating continuously. Both continuous data and template waveforms were bandpass filtered from 5 to 10 Hz because this frequency range exhibits better signal to noise ratios, and decimated to 25 Hz.…”

“…A main issue is to understand if this general decrease in the number of aftershocks is real, or it is due to the lack of near-field data (Li et al, 2018). It is thus fundamental to tackle this issue, to better assess the aftershock activity (Dascher-Cousineau et al, 2020) and get new insights about the mechanism(s) and physical conditions controlling the occurrence of IDEs.…”