Magnetotelluric evidence for thick-skinned tectonics in central Taiwan

Nat. Hazards Earth Syst. Sci.

Hsu

Wen

et al. 2013

The Parkinson vectors derived from 3-component geomagnetic data via the magnetic transfer function are discussed with respect to epicentre locations and hypocentre depths of 16 earthquakes (M ≥ 5.5) in Taiwan during a period of 2002–2005. To find out whether electric conductivity changes would happen particularly in the seismoactive depth ranges, i.e. in the vicinity of the earthquake foci, the frequency dependent penetration depth of the electromagnetic waves (skin effect) is taken into account. The background distributions involving the general conductivity structure and the coast effect at 20 particular depths are constructed using the Parkinson vectors during the entire study period. The background distributions are subtracted from the time-varying monitor distributions, which are computed using the Parkinson vectors within the 15-day moving window, to remove responses of the coast effect and underlying conductivity structure. Anomalous depth sections are identified by deviating distributions and agree with the hypocentre depths of 15 thrust and/or strike-slip earthquakes with only one exception of a normal fault event

Section: Methodsmentioning

confidence: 99%

Evaluation of seismo-electric anomalies using magnetic data in Taiwan

Nat. Hazards Earth Syst. Sci.

Hsu

Wen

et al. 2013

Terr. Atmos. Ocean. Sci.

“…Line charts of averages of best parameters versus training windows of the original and modified models for (a) the average Rad, (b) the average Dep, (c) the average N thr , (d) the average t thr , (e) the average t obs , (f) the average t pred , and (g) the average t lag . (Color online only) mountain region suggests the presence of abundant ground water Chen 1998, 2000;Bertrand et al 2009Bertrand et al , 2012. In the initial stage, small-scale irreversible deformations and fractures occur that generate electromagnetic radiation.…”

Section: Discussionmentioning

confidence: 99%

Using geoelectric field skewness and kurtosis to forecast the 2016/2/6, ML 6.6 Meinong, Taiwan Earthquake

Chen¹,

Chen²,

Ouillon³

et al. 2017

The earthquake-alarm model developed by Chen and Chen (Nat. Hazards 2016) is investigated to validate its forecasting performance for the 2016/2/6, M L 6.6 Meinong, Taiwan earthquake. This alarm model is based on geoelectric field skewness and kurtosis anomalies. The model parameters, such as the detection range and predicted time window, allow us to estimate the empirical relationships between geoelectric anomalies and large earthquakes. As a result, the skewness and kurtosis anomalies are shown to appear before the Meinong earthquake on the four neighboring stations (LIOQ, WANL, KAOH, and CHCH). According to the model analysis a time lag exists between anomaly clusters and earthquakes, depending on local geological features, as well as the durations over which anomalies are continuously observed, which might also display time dependence. In conclusion, this alarm model is able to correlate earthquakes and geoelectrical anomalies, with promising usefulness in forecasting large earthquakes.

“…The variations in the geomagnetic field caused by solar activity are most likely the same within a small region generally considered to be global effects (Chapman and Bartels 1940). Other sources such as induced geomagnetic fields caused by differences in electrical structure (Lilley and Arora 1982;Lilley 1984;Horng et al 1992;Hsu et al 1998;Lilley et al 1999;Yen et al 2009), pre-earthquake magnetic anomalies resulting from stressed rocks (Yanagihara and Nagano 1976;Rikitake 1979;Shiraki 1980;Chen and Fung 1985;Gong 1985;Chen et al 2006), and the magnetic coast effect due to the distinct conductivity between continental rocks and sea water (Parkinson 1959(Parkinson , 1962(Parkinson , 1983Bennett and Lilley 1971;Lilley and Bennett 1972;Parkinson and Jones 1979;Delaurier et al 1983;Yukutake et al 1983;Ogawa et al 1986;EMSLAB Group 1988;White et al 1990;Kellett et al 1991;Hitchman et al 2000;Armadillo et al 2001;Lee et al 2007;Bertrand et al 2009Bertrand et al , 2012Chiang et al 2010) affect the geomagnetic field within a local area. The GZH, HC, and PHU stations have similar geomagnetic latitudes from 10.92 -13.27°N.…”

Section: Discussionmentioning

confidence: 99%

Preliminary Studies on Unusual Magnetic Diurnal Variation on Hengchun Peninsula

Yen²,

Terr. Atmos. Ocean. Sci.

et al. 2016

The geomagnetic total intensity data recorded by a geomagnetic network in Taiwan comprised of 11 permanent proton magnetometers was used to compute diurnal variation ranges to examine if any discrepancies were present. Diurnal variations with similar ranges were obtained from all stations except for the HC station. The ranges at the HC station are often two times greater than those recorded at the other stations. This is an interesting phenomenon that requires considerable attention. Eight temporary stations were set up between the Taitung (TT) and Hengchun (HC) stations, distributed evenly over the Hengchum peninsula during 13 September 2012 to 25 January 2013 to clarify the phenomenon. The local stations in Taiwan are compared with 2 international stations to explain the diurnal ranges resulting from the interaction between solar activities and the Earth's main geomagnetic field and/or local effects. Analytical results show that the unusually large diurnal ranges were observed mainly on the Hengchun peninsula. The surrounding the sea water produces the magnetic coast effect.