Application of the Newmark Analysis Method in Stability Evaluation of Submarine Slope

The Newmark seismic time-history analysis method can take into account the effects of natural seismic peak ground acceleration (PGA), duration, and seismic frequency; seismic wave can be input into the method for simulation. This study calculates the dynamic response of the typical seabed slope of Caofeidian in the event of a similar Tangshan earthquake, and the displacement value can be used to quantitatively reflect the influence of the earthquake on the slope of the site. The allowable displacement value of the top of buildings or submarine slope can be used as a marker of security and stability analysis, which can further provide important reference for similar slope stability evaluation and offshore engineering construction.

Revisiting the Predictability of the Haicheng and Tangshan Earthquakes

We analyze a set of precursory data measured before but compiled in retrospect of the MS7.5 Haicheng earthquake in February 1975 and the MS7.6–7.8 Tangshan earthquake in July 1976. We propose a robust and simple coarse-graining method that aggregates and counts how all the anomalies together (levelling, geomagnetism, soil resistivity, earth currents, gravity, earth stress, well water radon, well water level) develop as a function of time. We demonstrate strong evidence for the existence of an acceleration of the number of anomalies leading up to the major Haicheng and Tangshan earthquakes. In particular for the Tangshan earthquake, the frequency of occurrence of anomalies is found to be well described by the log-periodic power law singularity (LPPLS) model, previously proposed for the prediction of engineering failures and later adapted to the prediction of financial crashes. Using a mock real-time prediction experiment and simulation study, based on this methodology of monitoring accelerated rates of physical anomalies measured at the surface, we show the potential for an early warning system with a lead time of a few days.

Inter-episodes earthquake migration in the Bohai-Zhangjiakou Fault Zone, North China: Insights from numerical modeling

In this paper, we focus on why intraplate seismic initiation and migration occurs, which has widely been considered to be caused by static stress triggering caused by earthquakes, as well as post-seismic slips. To illustrate the mechanism underlying large earthquakes, in particular the migration caused by two key episodes that occurred after 1500 in the Bohai-Zhangjiakou Fault Zone (BZFZ) of North China, we developed a high-resolution three-dimensional viscoelastic finite element model that includes the active faults with vertical segmentation, their periodical locking, and the lithosphere heterogeneity. We used the birth and death of element groups to simulate stress intensity changes during the two episodes (named Episode I and II), with our results showing that the Tangshan earthquake was primarily triggered by the Sanhe-Pinggu M8.0 earthquake in 1679, whereas the Zhangbei M6.2 earthquake in 1998 was not triggered by earthquakes in Episode I. According to our work, the calculated stress changes in the different segments of the fault zone correspond to the magnitude of the triggered earthquakes. Further, the largest stress decrease was near the Sanhe-Pinggu fault and occurred the largest earthquake in Episode I, whereas the largest stress increase was near the Tangshan fault and occurred during the largest earthquake in Episode II. Given the above, we propose a model for seismic migration to describe the dynamic mechanisms of earthquake migration within the BZFZ and North China, in which the factors affecting both the seismic migration path and intensity primarily include the distance between the triggered active fault and the original fault, the coupling of the active faults, the location and scale of the low-velocity anomaly, its distance from the active fault, and the location and scale of the crustal thinning.

Attenuation and Basin Amplification Revealed by the Dense Ground Motions of the 12 July 2020 Ms 5.1 Tangshan, China, Earthquake

On 12 July 2020, an Ms 5.1 moderate earthquake occurred on the north segment of the Tangshan fault in North China, which was the seismogenic fault of the 1976 Ms 7.8 Tangshan earthquake and numerous small-to-moderate earthquakes in recent decades in the Tangshan seismic zone. The Ms 5.1 event was well-recorded by dense ground-motion observation stations, including the national strong-motion stations and seismic intensity stations. This many ground-motion recordings, obtained for such a moderate event in North China for the first time, provided a rare opportunity to investigate the attenuation and site effects on ground motion. The distance decay in the Tangshan seismic zone was first explored using the spectral amplitudes from the vertical component. The strong anelastic attenuation and weak geometrical spreading effects were clearly found. The hinged trilinear form may be more effective at describing the geometrical spreading. No geometrical spreading decay was visible at medium distances (60–100 km). Anomalous areas with extraordinary high amplitudes occurred in the spatial distribution of peak ground accelerations and peak ground velocities that we attribute to significant basin amplification effects, which was confirmed by the wideband and high amplifications on the standard spectral ratio and the later-arriving, long-period surface waves observed in waveforms in the Ninghe–Baodi area and south of Beijing. The basin-induced surface waves in the 2–5 s period were most prominent in the Ninghe–Baodi area. We further inferred that basin effects may be responsible for the high-intensity anomaly areas observed in the 1976 Ms 7.8 Tangshan earthquake.

Background Seismicity before and after the 1976 Ms 7.8 Tangshan Earthquake: Is Its Aftershock Sequence Still Continuing?

The aftershock zone of the 1976 Ms 7.8 Tangshan, China, earthquake remains seismically active, experiencing moderate events such as the 5 December 2019 Ms 4.5 Fengnan event. It is still debated whether aftershock sequences following large earthquakes in low-seismicity continental regions can persist for several centuries. To understand the current stage of the Tangshan aftershock sequence, we analyze the sequence record and separate background seismicity from the triggering effect using a finite-source epidemic-type aftershock sequence model. Our results show that the background rate notably decreases after the mainshock. The estimated probability that the most recent 5 December 2019 Ms 4.5 Fengnan District, Tangshan, earthquake is a background event is 50.6%. This indicates that the contemporary seismicity in the Tangshan aftershock zone can be characterized as a transition from aftershock activity to background seismicity. Although the aftershock sequence is still active in the Tangshan region, it is overridden by background seismicity.

Experiencing earthquake in the first trimester of the fetal life increases subsequent diabetes risk in the adulthood: a cross-sectional study

Objective To investigate the long-term effect of prenatal exposure to earthquake stress on diabetes risk in the adulthood. Methods This study included employees of Tangshan Kailuan Mining Group between July 29, 1976 and April 28, 1977. The exposure group included subjects who experienced the Tangshan Earthquake during their prenatal period and who had lived in Tangshan since birth. The non-exposure group included subjects who were born 1–1.9 years after the earthquake and who had lived in Tangshan since birth. A questionnaire was designed that included sociodemographic information, conditions during pregnancy, and earthquake experience. Anthropometric measurements including height and weight, body mass index (BMI), waist circumference were made. Fasting plasma glucose (FPG) and lipid profiles were also determined. Results Totally 947 subjects were included with 397 subjects in the exposed group and 550 subjects in the non-exposed group. The diabetes rate is significant different in these four groups(χ2 =8.045, P = 0.045). Moreover, 11.8, 7.5 and 8.0% of the subjects who were exposed to earthquake in the 1st, 2nd, and 3rd trimester of pregnancy had diabetes. 5.1% of the subjects had diabetes in non-exposure group. Our multivariate analysis showed that 1st trimester (OR 2.481, 95%CI 1.02, 6.034; P = 0.045) and loss of family members during earthquake (OR 2.452, 95%CI 1.293, 4.653; P = 0.006) were associated with significantly increased risk of diabetes. Conclusions Exposure to earthquake during the first trimester of pregnancy and experience of family member loss in the earthquake significantly increased the subsequent risk of diabetes in the middle age (36–39 years of age). Our data suggest that earthquake experience in the early pregnancy has a longer-term effect on diabetes risk during adulthood.

Earthquakes: Slope coefficient, potential energy coefficient or latitude coefficient?

Tangshan earthquake in China occurred with a periodicity of 297 years with focal depth of 11 km. An average of 0.10147 meter of earth crust is uplifted every day. The 9.0 magnitude earthquake was said to occur once every other 1100 years off the northeastern pacific coast of Japan with a focal depth of 20 km. An average of 0.04981 meter of earth’s crust is uplifted daily. These results can be viewed as slope coefficient or potential energy coefficient. Other coefficient such as latitude needs to be incorporated for theoretical calculations.