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Volume 32 Issue 1 January 2019

ISSN 1674-4519 CN 11-5695/P

Adminidrated by: 
China Association of Science and Technology

Sponsored by: 
The Seismological Society of China and Institute of Geophysics, China Earthquake Administration

Editor-in-Chief: Yun-tai Chen

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Source parameter and rupture process of the MW6.3 early strong aftershock immediately following the 2016 MW7.8 Kaikoura earthquake (New Zealand)
Qingjun Meng, Aizhi Guo, Xiangteng Wang, Shuofan Wang
2019, 32(1): 1 -11   doi: 10.29382/eqs-2019-0001-1
[Abstract](462) [FullText HTML](4) [PDF 1681KB](14)
Abstract:
The 2016 MW7.8 Kaikoura (New Zealand) earthquake was the most complex event ever instrumentally recorded and geologically investigated, as it ruptured on more than 12 fault segments of various geometries. To study the mainshock rupture characteristics, geodetic methods like InSAR and GPS play an essential role in providing satisfactory spatial resolution. However, early strong aftershocks may cause extra ground deformation which bias the mainshock rupture inversion result. In this paper, we will focus on studying the MW 6.3 aftershock, which is the only M6+ thrust slip aftershock that occurred only 30 minutes after the Kaikoura mainshock. We will relocate the hypocenter of this event using the hypo2000 method, make the finite fault model (FFM) inversion for the detailed rupture processes and calculate the synthetic surface displacement to compare with the observed GPS data and figure out its influence on the mainshock study. Although we are not able to resolve the real ruptured fault of this event because of limited observation data, we infer that it is a west-ward dipping event of oblique slip mechanism, consistent with the subfault geometries of the Kaikoura mainshock. According to the inverted FFM, this event can generate 10–20 cm ground surface displacement and affect the ground displacement observation at nearby GPS stations.
Double-difference tomography of P- and S-wave velocity structure beneath the western part of Java, Indonesia
Shindy Rosalia, Sri Widiyantoro, Andri Dian Nugraha, Pepen Supendi
2019, 32(1): 12 -25   doi: 10.29382/eqs-2019-0012-2
[Abstract](0) [FullText HTML](0) [PDF 2624KB](0)
Abstract:
West Java in the western part of the Sunda Arc has a relatively high seismicity due to subduction activity and faults. In this study, double-difference tomography was used to obtain the 3D velocity tomograms of P and S waves beneath the western part of Java. To infer the geometry of the structure beneath the study area, precise earthquake hypocenter determination was first performed before tomographic imaging. For this, earthquake waveform data were extracted from the regional Meteorological, Climatological, Geophysical Agency (BMKG) network of Indonesia from South Sumatra to Central Java. The P and S arrival times for about 1,000 events in the period April 2009 to July 2016 were selected, the key features being events of magnitude > 3, azimuthal gap < 210° and number of phases > 8. A nonlinear method using the oct-tree sampling algorithm from the NonLinLoc program was employed to determine the earthquake hypocenters. The hypocenter locations were then relocated using double-difference tomography (tomoDD). A significant reduction of travel-time (root mean square basis) and a better clustering of earthquakes were achieved which correlated well with the geological structure in West Java. Double-difference tomography was found to give a clear velocity structure, especially beneath the volcanic arc area, i.e., under Mt Anak Krakatau, Mt Salak and the mountains complex in the southern part of West Java. Low velocity anomalies for the P and S waves as well as the vP/vS ratio below the volcanoes indicated possible partial melting of the upper mantle which ascended from the subducted slab beneath the volcanic arc.
A possible mechanism of stimulation of seismic activity by ionizing radiation of solar flares
Valery M. Sorokin, Alexey K. Yashchenko, Victor A. Novikov
2019, 32(1): 26 -34   doi: 10.29382/eqs-2019-0026-3
[Abstract](0) [FullText HTML](0) [PDF 723KB](0)
Abstract:
A possible mechanism of earthquake triggering by ionizing radiation of solar flares is considered. A theoretical model and results of numerical calculations of disturbance of electric field, electric current, and heat release in lithosphere associated with variation of ionosphere conductivity caused by absorption of ionizing radiation of solar flares are presented. A generation of geomagnetic field disturbances in a range of seconds/tens of seconds is possible as a result of large-scale perturbation of a conductivity of the bottom part of ionosphere in horizontal direction in the presence of external electric field. Amplitude-time characteristics of the geomagnetic disturbance depend upon a perturbation of integral conductivity of ionosphere. Depending on relation between integral Hall and Pedersen conductivities of disturbed ionosphere the oscillating and aperiodic modes of magnetic disturbances may be observed. For strong perturbations of the ionosphere conductivities amplitude of pulsations may obtain ~102 nT. In this case the amplitude of horizontal component of electric field on the Earth surface obtains 0.01 mV/m, electric current density in lithosphere –10–6 A/m2, and the power density of heat release produced by the generated current is 10–7 W/m3. It is shown that the absorption of ionizing radiation of solar flares can result in variations of a density of telluric currents in seismogenic faults comparable with a current density generated in the Earth crust by artificial pulsed power systems (geophysical MHD generator " Pamir-2” and electric pulsed facility " ERGU-600”), which provide regional earthquake triggering and spatiotemporal variation of seismic activity. Therefore, triggering of seismic events is possible not only by man-made pulsed power sources but also by the solar flares. The obtained results may be a physical basis for a novel approach to solve the problem of short-term earthquake prediction based on electromagnetic triggering phenomena.
Earth's rotation-triggered earthquakes before the 2018 MS5.7 Xingwen earthquake
Xue-Zhong Chen, Yan-e Li, Yong-gang Wei
2019, 32(1): 35 -39   doi: 10.29382/eqs-2019-0035-4
[Abstract](0) [FullText HTML](0) [PDF 662KB](0)
Abstract:
For earthquakes (ML≥2.0) that occurred from January 2006 to October 2018 around the MS5.7 Xingwen earthquake occurred on 16 December 2018 in Xingwen, Sichuan province, China, we statistically investigated the correlation between the phase of Earth's rotation and the occurrence of earthquakes via Schuster's test to determine the signals that triggered earthquakes before the MS5.7 Xingwen event. The results were evaluated based on the P-value where a smaller P-value corresponded to a higher correlation between the occurrence of an earthquake and Earth's rotation. We investigated the spatial distribution of P-values in the region around the epicenter of the MS5.7 Xingwen event, and obtained a result exhibiting a extremely low-P-value region. The MS5.7 event occurred inside near the northern boundary of this region. Furthermore, we analyzed the temporal evolution of P-values for earthquakes that occurred within the extremely low-P-value region and found that some extremely low P-values (less that 0.1%), i.e., significant correlation, were calculated for earthquakes that occurred before the MS5.7 Xingwen earthquake. Among sixty-one earthquakes with the lowest P-value, occurred from May 2014 to April 2018, a vast majority of them occurred during the acceleration of Earth's rotation. The lower P-value obtained in this study reveals that the Xingwen source body probably was extremely unstable prior to the occurrence of the MS5.7 Xingwen earthquake.
Earthquake vulnerability disaster in the Lembang district of West Bandung Regency, Indonesia
Fahmi Arif Kurnianto, Fahrudi Ahwan Ikhsan, Bejo Apriyanto, Elan Artono Nurdin
2019, 32(1): 40 -46   doi: 10.29382/eqs-2019-0040-5
[Abstract](0) [FullText HTML](0) [PDF 310KB](0)
Abstract:
This research is concerned with an analysis of the level of vulnerability for an earthquake disaster in Lembang district, an area in West Java that includes the Bandung basin and has a high potential for earthquake disaster. The Lembang district is close to the active Lembang fault whose movement can cause earthquakes of magnitude 7 on the Richter scale (Tempo Interaktif, May 11, 2010). The research method used to assess the level of vulnerability is essentially a descriptive approach. The data analysis is based on calculating an earthquake disaster risk index (EDRI), which is in turn based on assessment of the region's social, physical and economic vulnerabilities. The vulnerability level for earthquake disaster in the Lembang is ranked as medium category. The social vulnerability of the population is the major contributing factor given the high population density and growth rate for the region. The physical characteristics of the district, which includes mild temperatures and attractive scenery, make many people want to stay in and visit Lembang. The construction quality of buildings is so bad that they are not designed to withstand earthquakes, so improvement of building infrastructure is an alternative to reducing the various physical vulnerabilities.
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