Quick seismo-tectonic interpretation of high-precision relocations of the Mw5.5 2023-05-11 Lake Almanor, CA earthquake sequence and background seismicity since 2000: Normal-faulting 2023 mainshock rupture towards the NW; oblique, normal + strike-slip splay and 2013 faulting to the SE.
The NCSS 2013 Mw5.7 fault plane matches the tabular spread of most 2013 aftershocks (violet). The Mw5.7 event has oblique, right-lateral + extensional faulting.
The relocated seismicity and fault planes show non-coplanar but adjoining 2013 and 2023 faulting.
Map views of the relocated seismicity 2000-present with NCSS 2013 Mw5.7 fault plane (violet) from https://earthquake.usgs.gov/earthquakes/eventpage/nc71996906/moment-tensor
NCSS 2023 Mw5.5 fault plane (yellow) from https://earthquake.usgs.gov/earthquakes/eventpage/nc73886731/moment-tensor
NLL-SSST-coherence (https://doi.org/10.1029/2021JB023190) is an enhanced, absolute-timing earthquake location procedure which uses 1) spatially-varying station time corrections to improve multi-scale precision and 2) waveform similarity to improve fine-scale precision.
Earthquake arrival time data from NCEDC https://ncedc.org
Velocity model (KS) from https://doi.org/10.1785/0220140121, https://eartharxiv.org/repository/view/1904
Faults from https://sciencebase.gov/catalog/item/589097b1e4b072a7ac0cae23
Only hypocenters with location error ≤ 5km are plotted.