1 SURVEY OF GLOBAL SEISMICITY

A total of 8 strong earthquakes with MS≥7.0 occurred in 2017 （from January 1 to December 31， 2017） throughout the world， according to the China Seismic Network， including one with MS≥8.0， i.e.， the great earthquake with MS8.2 which occurred on September 8， 2017 in Chiapas， Mexico （Fig.1）.The 2017 MS8.2 Chiapas， Mexico earthquake was located in the east of the Circum-Pacific Seismic Belt.The mainshock was normal type and the rupture was unilateral along the NW direction，with maximum intensityⅨ.Features of global seismicity of MS≥7.0 in 2017 are as follows.

式(7)中：μt,m为混合物湍流黏度；Gk,m为湍动能的生成项。在k-ε混合物湍流模型中，各湍流常数的取值分别为：C1ε=1.44,C2ε=1.92,Cμ=0.09,σk=1.0,σε=1.3。

1.1 Global Seismicity Significantly Weak

One great earthquake with MS≥8.0 occurred in 2017.The global seismic strength nearly stayed the same compared with one great earthquake of MS≥8.0 in 2016 （Fig.2（a））.There were 8 earthquakes with MS≥7.0 occurring in the world in 2017.The seismic frequency was significantly decreased compared with the seismicity of 17 strong earthquakes with MS≥7.0 in 2016， and was significantly lower than the annual average of 19 strong earthquakes（Fig.2（b））.

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1.2 Seismicity Concentrated on the Circum-Pacific Seismic Belt and Eurasian Seismic Zone

Global earthquakes with MS≥7.0 were mainly distributed on the Circum-Pacific Seismic Belt and Eurasian Seismic Zone.There were 6 earthquakes with MS≥7.0 located in the Circum-Pacific Seismic Belt，3 in the East Belt and 3 in the West Belt.The epicenters of the 3 earthquakes in the East Belt were very close to one another.There were 2 earthquakes with MS≥7.0 occurring in the Eurasian Seismic Zone， including the MS7.0 earthquake on 8 August 2017 in Jiuzhaigou， Sichuan， China.

1.3 Temporal Distribution of Seismicity Was Uneven

During the period of January 1-December 31， 2017， there were 19 earthquakes with MS≥5.0 occurring in China （Fig.3）.Among those earthquakes， 13 occurred in the Chinese mainland， including 3 earthquakes with MS≥6.0， i.e.， the MS7.0 earthquake on August 8，2017 in Jiuzhaigou， Sichuan， the MS6.6 earthquake on August 9， 2017 in Jinghe， Xinjiang， and the MS6.9 earthquake on 18 November 2017 in Mainling， Tibet.6 earthquakes with MS≥5.0 occurred in Taiwan， of which the largest two were the February 11，2017 earthquake with MS5.6 in Kaohsiung， Taiwan and the May 16， 2017 earthquake with MS5.6 in Taitung.The 2017 MS7.0 Jiuzhaigou earthquake was located on the northeast boundary of Bayan Har block.Its mechanism was left-lateral strike-slip type.The mainshock occurred at the intersection of Tazang，Minjiang and Huya faults.Features of the seismicity in China in 2017 are as follows.

目前，我国大多数的乡村旅游建设是由政府主导，尤其是在各种扶持政策文件下，得到当地乡镇政府的极大重视，为乡村旅游发展提供了基础保证，但仅靠政府力量并不足够，需要整合行业协会、企业、志愿者、村民等共同形成管理机构，统一规范管理。如借鉴“法兰西最美丽村庄”协会的经营模式，建立严谨的组织结构和管理机制，让本村的干部、提供资助的社团或企业以及部分有经验的并有一定学历的服务行业从业者组成执行代表团，共同参与建设，更多地赋权给对本地区概况极其了解且有一定学历背景的本地村民及有权威性的协会部门或企业，共同参与标准的制订与考核，平衡各相关者的利益，达到利益均衡才是可持续发展的根本动力。

Fig.1 The epicenter distribution of global earthquakes with MS≥7.0 during 2016-2017

Fig.2 The M-t plot（a） and frequency diagram （b） for global earthquakes with MS≥7.0 during 2000-2017

2 SURVEY OF SEISMICITY IN CHINA

Global seismicity with MS≥7.0 was quiet for 97 days from January to April of 2017.It was the longest quiescence in the whole year.Because of this quiescence，only 3 earthquakes occurred in the first half of 2017.Compared to this weak seismicity，5 earthquakes occurred in the second half of the year， including the only MS≥8.0 earthquake， i.e.， the MS8.2 Chiapas，Mexico earthquake on September 8，2017.As the seismic frequency and strength of the second half of 2017 were significantly higher than that of the first half，the global seismicity in 2017 was inhomogeneous in time.

Fig.3 The epicenter distribution of earthquakes with MS≥5.0 in China from 2016-2017

2.1 Seismic Frequency with MS≥5.0 Was Significantly Low in the Chinese Mainland

一部分教师单一使用传统讲授，过分注重知识教育，缺少精神熏陶和情感培养，课堂教学虽然紧扣书本主题，却陷入照本宣科的泥潭。比如教师在讲解创新与社会实践的关系时，可以将诺贝尔文学奖获得者独特的生活经历与他们在文学中的创新做法联系在一起，从而让学生在增长见识的同时，记住社会实践的知识点。通过这种方式影响学生在课堂之外对文化问题和现象的看法与观点，形成一种良性循环。

2.2 Seismic Strength Increased Significantly

Strong earthquakes with MS≥7.0 have been active in the North-South Seismic Belt since the MS8.0 Wenchuan earthquake on May 5， 2008.After the Wenchuan earthquake， there occurred in succession the MS7.1 Yushu earthquake on April 14，2010，the MS7.0 Lushan earthquake on April 20，2013 and the MS7.0 Jiuzhaigou earthquake on August 8，2017.Currently， the North-South Seismic Belt is still in the seismically active stage of MS≥7.0 earthquakes（Fig.6）.

Fig.4 The annual frequency of earthquakes with MS≥5.0 in the Chinese mainland during 1950-2017

Table 1 Catalog of earthquakes with MS≥6.0 in the Chinese mainland during 2016-2017

Occurrence time Epicentral location a-m-d h：m：s Lat.／°N Lon.／°E Mag. Location 2016-01-02 12：22：19 44.80 129.90 6.4 Linkou， Heilongjiang 2016-01-21 01：13：13 37.70 101.60 6.4 Menyuan， Qinghai 2016-10-17 15：14：49 32.81 94.93 6.2 Zadoi， Qinghai 2016-11-25 22：24：30 39.27 74.04 6.7 Akto， Xinjiang 2016-12-08 13：15：03 43.83 86.35 6.2 Hutubi， Xinjiang 2017-08-08 21：19：46 33.20 103.82 7.0 Jiuzhaigou， Sichuan 2017-08-09 07：27：00 44.27 82.89 6.6 Jinghe， Xinjiang 2017-11-18 06：34：19 29.75 95.02 6.9 Mainling， Tibet

2.3 The Major Active Area of Earthquake with MS≥7.0 in Chinese Mainland Remained Unchanged

After the MS7.2 offshore Hengchun earthquake on December 26，2006， earthquake activity of MS≥7.0 was quiet in Taiwan for 11 years.It is the longest quiescence of MS≥7.0 earthquakes since 1900 （Fig.11）.In this context， the quiescence of MS≥6.0 earthquakes also lasted for nearly 1.6 years， and only 6 earthquakes with MS≥5.0 occurred in 2017， much less than the annual average of 13 earthquakes（Table 2）.

2.4 Strong Earthquake Activity Continued on the North-South Seismic Belt and Tianshan Seismic Belt

There were 3 earthquakes with MS≥6.5 occurring in the Chinese mainland in 2017，including a MS≥7.0 earthquake.The seismic strength increased significantly compared with the seismicity of only 1 strong earthquake with MS≥6.5 （the MS6.7 Akto， Xinjiang earthquake on November 25，2016） in 2016 （Table 1）.

The MS7.0 Jiuzhaigou， Sichuan earthquake on August 8，2017 indicated that the weak seismicity of MS≥5.0 earthquakes had ended （Fig.7）.

Fig.5 The epicenter distribution of shallow focus earthquakes with MS≥7.0 in China from 1997-2017

Fig.6 The earthquakes with MS≥7.0 since May 2008 （solid circle）and the earthquakes with MS≥6.0 since October 2015 （hollow circle）

2.5 The Weak Seismicity of MS≥5.0 Earthquakes Ended in Southwest China Area

After the MS5.5 Cangyuan earthquake on March 1， 2015， seismic quiescence of MS≥5.0 earthquakes with durations of 243， 200， 128， 185 and 134 days appeared in succession in the Southwest China area.Seismicity of MS≥5.0 earthquakes in the Southwest China area was weak.

After the MS7.8 Hindu Kush earthquake on October 26，2015 （intermediate-focus shock），the MS7.4 Tajikistan earthquake on December 7， 2015， the MS7.1 Afghanistan earthquake on April 10，2016 （intermediate-focus shock） and the MS6.7 Kyrghyzstan earthquake on June 26，2016，strong earthquakes were continuously active in the Tianshan Seismic Belt.There occurred in succession the MS6.7 Akto earthquake on November 25，2016，the MS6.2 Hutubi earthquake on December 8，2016， and the MS6.6 Jinghe earthquake on August 9，2017 （Fig.6）.

Fig.7 The M-t diagram of earthquakes with MS≥5.0 in the Southwest China area

2.6 Seismicity Increased Significantly in the Northwest China Area

After the 2013 Minxian-Zhangxian MS6.6 earthquake， only 5 earthquakes with MS≥5.0 occurred in the Northwest China area up to December 2015.Two strong earthquakes with MS≥6.0 occurred subsequently in 2016.In 2017， the Jiuzhaigou MS7.0 earthquake occurred on the branch of the Eastern Kunlun fault，indicating that the seismicity had increased continuously in the Northwest China area （Fig.8）.

Fig.8 Earthquakes with MS≥5.0 during 2013-2015 （solid circle） and earthquakes with MS≥6.0 during 2016-2017 （hollow circle） in the Northwest China Area and its adjacent area

2.7 Moderate Earthquakes and Strong Earthquakes Were Active in Xinjiang

Moderate earthquakes and strong earthquakes were active in Xinjiang since November，2016.A total of 9 earthquakes with MS≥5.0 occurred in that period， including 3 earthquakes with MS≥6.0， i.e.the MS6.7 Akto earthquake on November 25， 2016， the MS6.2 Hutubi earthquake on December 8， 2016， and the MS6.6 Jinghe earthquake on August 9， 2017（Fig.9）.

Fig.9 The epicenter distribution of earthquakes with MS≥5.0 in Xinjiang from November 2016 to December 2017

2.8 The Seismicity of MS≥6.0 Earthquakes Was Quiet Significantly in the Eastern Chinese Mainland

The longest quiescence of shallow focus earthquakes with MS≥6.0 was 14.9 years（excluding the MS6.1 Xinfengjiang reservoir-induced earthquake in 1962） in the eastern Chinese mainland since 1820 （the fourth seismic active period）.Currently， quiescence of earthquakes with MS≥6.0 in the eastern Chinese mainland has remained for 20 years after the 1998 Zhangbei MS6.2 earthquake.It is the longest quiescence since 1820 （Fig.10）.

蒋大伟吹着口哨，驱车行驶在街道上。姑娘叫郑馨，她的眼睛盯着窗外，额前的头发被风吹得乱飞。蒋大伟从后视镜里看看郑馨，没话找话地：喂，美女，去兰江大桥做啥？郑馨瞥了他一眼，继续看着窗外。蒋大伟猜测地：是来旅游吧？郑馨伸手整理了一下头发，还是一言未发。蒋大伟热情不减地：兰江大桥是咱这地界的标志性建筑！旅游不去兰江大桥等于没来。蒋大伟瞥了一眼后视镜，郑馨瞪大眼睛在看着他，继续说道：你坐我的车就对了！我保证不出一个钟头给你送到大桥顶上！郑馨从耳朵上取下耳机，皱紧眉头：你说什么？蒋大伟泄气地：得，白说了。

Fig.1 0 The M-t diagram of shallow focus earthquakes with MS≥6.0 in the eastern Chinese mainland

2.9 Significant Quiescence of MS≥7.0 Earthquakes and Weak Seismicity of MS≥5.0 Earthquakes in the Taiwan Area

The MS7.0 Jiuzhaigou， Sichuan earthquake on August 8， 2017 broke the 3.5-year-long quiescence of MS≥7.0 earthquakes in the Chinese mainland.The Chinese mainland is still in a relatively active stage of earthquakes with MS≥7.0.Since the 1997 MS7.5 Mani， Xizang earthquake， 8 earthquakes with MS≥7.0 occurring in the Chinese mainland were all located on the boundary of Bayan Har block.The 2017 Jiuzhaigou MS7.0 occurred on the boundary too，showing that the major active area of earthquakes with MS≥7.0 in the Chinese mainland was unchanged （Fig.5）.

There were 13 earthquakes with MS≥5.0 occurring in the Chinese mainland in 2017.The seismic frequency was much lower than the annual average of 20 earthquakes.Currently，the seismic frequency has been lower than the average value for 3 years in succession.The seismic frequency was significantly low （Fig.4）.

Fig.1 1 The M-t diagram of earthquakes with MS≥7.0 in the Taiwan area

Table 2 Catalog of earthquakes with MS≥5.0 in Taiwan area during 2016-2017

Occurrence time Epicenter location a-m-d h：m：s Lat.／°N Lon.／°E Mag. Location 2016-01-19 10：13：26 22.80 121.40 5.4 Waters off Taitung， Taiwan 2016-02-02 22：19：22 25.40 123.40 6.2 Waters off northeastern Taiwan 2016-02-06 03：57：26 22.94 120.54 6.7 Kaohsiung， Taiwan 2016-02-09 08：47：00 23.90 121.80 5.3 Waters off Hualien， Taiwan 2016-02-18 09：09：40 23.00 120.90 5.0 Taitung， Taiwan 2016-04-27 23：17：00 24.22 121.71 5.6 Waters off Hualien， Taiwan 2016-04-28 02：19：00 23.26 121.30 5.2 Hualien， Taiwan 2016-05-12 11：17：13 24.70 122.00 6.2 Waters off Ilan， Taiwan 2016-05-12 12：29：56 24.80 122.00 5.8 Waters off Ilan， Taiwan 2016-05-13 16：24：12 24.80 122.00 5.0 Waters off Ilan， Taiwan 2016-05-31 13：23：49 25.43 122.41 6.2 Waters off New Taipei， Taiwan 2016-10-06 23：51：59 22.60 121.38 5.9 Waters off Taitung， Taiwan 2016-11-25 05：55：54 24.14 122.38 5.2 Waters off Hualien， Taiwan 2016-11-30 20：04：33 22.78 121.39 5.0 Waters off Taitung， Taiwan 2016-12-15 22：14：30 22.86 121.26 5.1 Waters off Taitung， Taiwan 2017-02-11 01：12：51 22.85 120.20 5.6 Kaohsiung， Taiwan 2017-04-30 09：57：22 21.43 121.80 5.0 Waters off Taitung， Taiwan 2017-05-16 07：12：53 23.31 121.49 5.6 Taitung， Taiwan 2017-09-20 22：29：55 23.35 121.85 5.5 Waters off Hualien， Taiwan 2017-11-11 20：22：53 23.68 120.69 5.0 Nantou， Taiwan 2017-11-22 22：20：10 23.71 120.60 5.2 Yunlin， Taiwan

3 SUMMARY

（1） Global seismicity was significantly weak， and the spatio-temporal distribution of seismicity was uneven.Strong earthquakes were concentrated on the Circum-Pacific Seismic Belt and Eurasian Seismic Zone.

（2） The 2017 Jiuzhaigou MS7.0 broke the approximately 3.5-year-long quiescence of MS≥7.0 earthquakes in the Chinese mainland.The seismic strength increased significantly in the mainland.The seismic frequency of MS≥5.0 earthquakes was significantly low in the mainland.

（3） The weak seismicity of MS≥5.0 earthquakes ended in Southwest China area.The seismicity increased significantly in the Northwest China and its adjacent area.Moderate earthquakes and strong earthquakes were active in Xinjiang since November 2016.The seismicity of MS≥6.0 earthquakes was remarkably quiet in the eastern Chinese mainland.The seismicity of MS≥7.0 earthquakes was remarkably quiet in the Taiwan area.

REFERENCES