Magnetic and thermal constraint on the spatial distribution of
continental seismicity
Abstract
Recent fast developments of satellite magnetic observations facilitate
global Lithospheric Magnetic Field (LMF) modelling and their
applications to subsurface tectonics. Here, the vertical component (Bz)
of LMF at an altitude of 200km in Mainland China and surroundings is
calculated from two global LMF models NGDC-720 and EMM2017. Next, Bz is
used to invert the Curie Point Depth (CPD) by Equivalent Source Dipole
(ESD) forward and Nonlinear Conjugate Gradient Method (NCGM) inversion
scheme. Then, the surficial Heat Flux (HF) is derived by a simple
one-dimensional steady heat conduction equation from the CPD
distribution. At last, the continental seismicity is compared
statistically to Bz, CPD and HF. Our essential conclusions are as
follow: 1) Histograms and boxplots show that most (81.8%) earthquakes
(EQs, Ms≥5.0) occurred in negative Bz areas, and more than a half
(53.2%) number of EQs (corresponding to an energy percent of 94.6%)
occurred inside areas with Bz between -5 and -3nT, in a period between
2004 and 2007, which is the same with the satellite data collection.
When the time span is extended (most to 110 years), these phenomena
maintain while weaken; 2) Most (88%) EQs occurred in areas with CPD
between 10 and 30km, while only a few (7% and 5%) occurred in shallow
(<10km) and deep (>30km) CPD areas, in a period
between 2000 and 2010; 3) EQs seldom occurred inside cold areas
(HF<50mW/m2), and are prone to occur in warm areas
(HF>120mW/m2). EQs are also prone to occur along the
boundaries of warm or cold areas. The mechanism of the correlations
between EQs and Bz, CPD and HF maybe the lithospheric strength jumps
caused by the temperature variations at boundaries between blocks with
different CPDs.