STUDY ON THE TRIGGERING FACTOR OF THE LOESS LIQUE-FACTION INDUCED BY THE JISHISHAN EARTHQUAKE

doi:10.3969/j.issn.0253-4967.20240141

Abstract

Abstract:

An Extremely severe liquefaction and mudflow disaster was triggered by the Jishishan M6.2 earthquake that occurred on December 18, 2023, resulting in 20 fatalities. Many subsequent studies have been conducted on the liquefaction and mud-flow disaster triggered by this earthquake. However, those studies mainly focus on the issues of geological conditions, water content, dynamics of the mudflow, and the disaster chains triggered by this earthquake, and few studies are focusing on the issues related to earthquake triggering factors.

The EEW(Earthquake Early Warning) Networks in China was completed just before this earthquake, and as a result, the densely distributed early warning stations in the epicenter area recorded the strong motion vibration process, providing a large number of actual observations for loess liquefaction studies using strong motion data. Therefore, factors potentially affecting liquefaction are analyzed using the strong motion data obtained under different site conditions in the vicinity of the epicenter of the Jishishan Earthquake.

Two groups of collocated strong motion data, obtained from adjacent station pairs located in the loess covering regions, one group consisting of acceleration observations from on-ground soil site and rock site and the other consisting of acceleration observations from on-ground soil site and underground soil site, are used to carry out the analysis from the perspective of amplitude, duration, and frequency characteristics. Some important understandings are obtained as follows.

The surficial loess layer shows a significant amplification effect on the strong motion amplitude, and the PGA amplification factor can even exceed 2. Due to this amplification effect, the seismic energy released in the surficial layer is several times greater than that of bedrock or underground soil layers.

Due to the amplification effect of the surficial loess layer, the bracketed duration of strong motion vibration is prolonged for the on-ground site observations, with an average duration being 1.3-1.4 times longer than that of the bedrock site or underground soil site.

The results of spectral ratios show a significant amplification effect for seismic waves under 5Hz, with the most significant amplification effect being 1-3Hz. This frequency is consistent with the average predominant frequency of 2Hz obtained in previous studies in the liquefaction and mudflow covering area, suggesting that the amplification effect should be due to the resonance of the seismic wave with the surficial loess layer.

The vertical component of strong motion must play an important role in the liquefaction process near the epicenter as it can reduce a structure’s shear stress. The maximum PGA of this earthquake reaches 949Gal, obtained from the station closest to the liquefaction site.

The surficial loess layer near the liquefaction point is under saturated status due to continuous irrigation just before this earthquake, which liquefied rapidly and evolved into a mudflow disaster under the joint dramatic action of both the horizontal and vertical strong motion vibration amplified by the surficial loess layer.

Fewer liquefaction case studies use actual observations, especially for loess liquefaction. The results obtained in this paper help understand the earthquake triggering factor of loess liquefaction, and also have reference significance for using strong motion data to study geological hazards induced by earthquakes.

Key words: The Jishishan earthquake, loess liquefaction, ground motion, triggering factor, amplification effect, resonance effect

摘要：

2023年12月18日甘肃省积石山M6.2地震触发了严重的黄土液化及泥流灾害。为分析这次液化的地震动触发因素, 文中利用地震预警网获得的地震动数据展开了数据分析工作, 得到如下认识: 1)黄土区浅表地层对地震动时程振幅(包括PGA)普遍存在显著放大作用, 导致浅表地层释放能量数倍增加; 2)浅表地层的强震动作用时间延长; 3)浅表地层对频率<5Hz, 特别是1~3Hz的地震波有明显放大作用。黄土区浅表地层对低频地震波的放大作用源于共振效应, 加之震中附近剧烈的垂向与水平向强震动的长时间往复作用, 使得饱水黄土、砂土层快速液化并形成泥流灾害。文中结果有助于认识黄土液化的地震动触发因素, 对利用地震动数据研究地震触发地质灾害具有参考意义。

关键词: 积石山地震, 黄土液化, 地震动, 触发因素, 放大作用, 共振效应

WANG Xiu-ying, ZHAO Guo-cun, FAN Xi-wei, GAO Peng, ZHANG Guo-hong, MA Zhi-xia, CHEN Xu-geng. STUDY ON THE TRIGGERING FACTOR OF THE LOESS LIQUE-FACTION INDUCED BY THE JISHISHAN EARTHQUAKE[J]. SEISMOLOGY AND GEOLOGY, 2026, 48(3): 797-813.

王秀英, 赵国存, 范熙伟, 高鹏, 张国宏, 马志霞, 陈旭庚. 积石山地震黄土液化的地震动触发因素分析[J]. 地震地质, 2026, 48(3): 797-813.

Figures/Tables 9

Fig. 1 Distribution of the epicenter, liquefaction point and earthquake early warning stations.

Fig. 2 Attenuation of PGAs obtained by intensity meters from the Jishishan Earthquake within 100km epicenter distance.

Table1 Basic information of matching strong motion accelerometers and intensity meters

台站代码	台站类型	震中距离/km	台站代码	台站类型	震中距离/km	观测点间距/km
BX045	土层强震仪	15.67	B0087	烈度计	19.27	7.90
JSNGJ	基岩强震仪	17.86	N0029	烈度计	15.23	2.73

Table2 PGA, Ia and Db parameters for the matching strong motion accelerometers and intensity meters

台站代码	PGA/Gal			I_a/m·s^-1			D_b/s
台站代码	N	E	Z	N	E	Z	N	E	Z
BX045	347	302	217	1.1980	0.8562	0.3250	31.77	36.28	26.07
B0087	593	791	583	4.5862	4.4164	3.5265	41.49	42.76	38.63
JSNGJ	340	394	212	0.6945	0.9742	0.4091	31.04	31.27	29.01
N0029	388	458	277	1.6763	2.5332	0.8862	43.38	43.95	40.22

Fig. 3 Comparison of the matching PGA, Ia and Db parameters.

Table3 Ratios of the three parameters for the matching stations

匹配点	PGA比值			I_a比值			D_b比值
匹配点	N	E	Z	N	E	Z	N	E	Z
B0087/BX045	1.71	2.62	2.69	3.83	3.69	10.85	1.31	1.18	1.52
N0029/JSNGJ	1.14	1.16	1.31	2.41	2.60	2.17	1.40	1.41	1.39

Fig. 4 Spectrum curves of the four groups of data.

Fig. 5 Spectral ratios of horizontal components for the matching stations.

Fig. 6 Acceleration time history of the three components obtained by B0087 and BX045.

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