Rupture mechanism and seismotectonics of the M_s6.5 Ludian earthquake inferred from three‐dimensional magnetotelluric imaging

Abstract

A three‐dimensional (3‐D) resistivity model around the 2014 Ms6.5 Ludian earthquake was obtained. The model shows that the aftershocks were mainly distributed in a shallow inverse L‐shaped conductive angular region surrounded by resistive structures. The presences of this shallow conductive zone may be the key factor leading to the severe damage and surface rupture of the Ludian earthquake. A northwest trending local resistive belt along the Baogunao‐Xiaohe fault interrupts the northeast trending conductive zone at the Zhaotong‐Lianfeng fault zone in the middle crust, which may be the seismogenic structure of the main shock. Based on the 3‐D electrical model, combining with GPS, thermal structure, and seismic survey results, a geodynamic model is proposed to interpret the seismotectonics, deep seismogenic background, and deformation characterized by a sinistral strike slip with a tensile component of the Ludian earthquake.

Locations of Injection‐Induced Earthquakes in Oklahoma Controlled by Crustal Structures

“…The aftershocks of the M 5.8 Pawnee earthquake show two directions: one is near along NE direction (Figure a) and the other is along conjugated SEE direction (Grandin et al, ; Pollitz et al, ). Although this conjugated earthquake shows complex fracture like 2014 M w 6.1 Ludian earthquake in Yunan, China (Cai et al, ; Zhang et al, ), the rupture directions of the above three earthquakes show some consistency with our anisotropy models. Our results show predominant NW‐SE anisotropy in Regions A and C, and predominant NE‐SW anisotropy in Regions B and D. Hence, we suggest that the inverted fast anisotropic direction, nodal planes of focal mechanism, and aftershock activities of three M 5 earthquakes are consistent and correspond to two background tectonic directions, NE orientation of the MCR and NW strike of the Southern Oklahoma Aulacogen (Figure ).…”

Magma Chamber and Crustal Channel Flow Structures in the Tengchong Volcano Area From 3‐D MT Inversion at the Intracontinental Block Boundary Southeast of the Tibetan Plateau

“…The MT method utilizes a broad spectrum of naturally occurring geomagnetic variations as signals to investigate electromagnetic induction effects in the Earth (Bahr & Simpson, 2005;Chave & Jones, 2012). Due to its sensitivity to interconnected conductive fluids and temperature, the MT method has been extensively used in geophysical surveys of various tectonic regions (Cai et al, 2017;Chave & Jones, 2012;Unsworth et al, 2000;Zhao et al, 2012;Zhang et al, 2016), including the probing of magma chambers (e.g., Heise et al, 2010;Hata et al, 2016). A 3-D model obtained from array broadband MT soundings covering the region of the Taupo volcano was carried out by Heise et al (2010).…”

Electrical Conductive Fluidized Zones and Their Influence on the Earthquake Nucleation, Growth, and Arrest Processes of the 2016 Kumamoto Earthquake Sequence, Kyushu Island, Japan

“…This may indicate that the lateral expansion of C1 in the lower crust was stimulated by the rupture of a large crustal earthquake. Deep low-resistivity zones, similar to C1, have been found beneath active faults (e.g., Ogawa et al, 2001;Yoshimura et al, 2009;Becken et al, 2011;Cai et al, 2017). These results suggest that there may be a positive feedback whereby deep uidized zones generate large crustal earthquakes and induce the evolution of high-temperature uidized zones in the mid-to-lower crust.…”

“…Figure 5a shows the schematic relationship between the low-resistivity zones and earthquake magnitude. A localized stress accumulation around the mechanically weak low-resistivity zones, and/or uid supply from the low-resistivity zone have been proposed as potential crustal earthquake nucleation mechanisms around low-resistivity zones (e.g., Ogawa et al, 2001;Ichihara et al, 2014;Aizawa et al, 2017;Cai et al, 2017). However, these proposed mechanisms might not account for the relationship between the lowresistivity zones and the nal earthquake magnitudes.…”

“…Electrically conductive uidized zones have been detected in the mid-crust of several island arc settings using broadband magnetotelluric (MT) observations, with numerous studies suggesting that the spatial relationship between these 10-30-km-wide low-resistivity zones and vigorous crustal seismicity highlights the importance of crustal uid migration and accumulation on the onset of earthquake rupture (e.g., Ogawa et al, 2001;Tank et al, 2005;Wannamaker et al, 2009;Yoshimura et al, 2009;Becken et al, 2011;Ichihara et al, 2014;Ogawa et al, 2014;Cai et al, 2017;Bedrosian et al, 2018). However, it is relatively unknown whether localized uids also play a role in the growth and/or arrest of earthquake rupture, largely because the nal earthquake magnitudes and their locations have not been analyzed to determine whether they are related to the subsurface uids, or if the observed earthquake/magnitude distribution is due to a purely random process.…”