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Prof Chan Lung SangDepartment of Earth Sciences

Some diagrams and information presented in this seminar were obtained from the following sources:

US Geological Survey, Seismological Bureau of China, IRIS, Taiwan National 

Sichuan Earthquake & Earthquake Prediction

Department of Earth Sciences The University of Hong Kong

HKU is a member of Incorporated Research Institution  for Seismology

, ,Space Organisation, Xinhua News Agency

Magnitude: 8.0Focal Depth: 10 kmGround shaking > 80sec

Wenchuan Earthquake (12.5.2008), Sichuan

Epicentral intensity: MMI = XFelt over 1500 kmQuake lakes formed = 34Deaths: >69,000 people

Major Seismic Zones of China

Source: State Seismological Bureau

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Animation showing motions of tectonic blocks 

GPS data show a convergence between Tibet and South China along Longmenshan at 4.0 mm± 2.0 mm (Zhang et al., 2004)

Credit: Clarice Chan

小江

斷斷裂

怒江

斷裂

Major Faults in Longmenshan Fault Zone

Modified from http://www.solotv.cn/ng/post/512dadizhen8.html

Longmenshan Fault ZoneLongmenshan Fault Zone Guanxian Fault灌縣斷裂

Beichuan Fault北川斷裂

Wenchuan Fault

MINYANG

Wenchuan Fault汶川斷裂

Longchuanshan Fault龍泉山斷裂

CHENGDU

DIJIANGYAN

Magnitude 震级

Magnitude measures the size of the earthquake.

Richter Scale (ML) Moment Magnitude Scale (Mw)

Charles Richter

g ( )

Each order of increase in magnitude corresponds to a 32 times increase in seismic energy.

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Earthquake Size vs Frequency

Description Mag (M) Frequency/year*Description Mag (M) Frequency/yearGreat Earthquake > 8.0 1Major Earthquake 7.0 - 7.9 18Strong Earthquake 6.0 - 6.9 ~200

Moderate Earthquake 5.0 - 5.9 ~2000

Light Earthquake 4 0 4 9Light Earthquake 4.0 - 4.9Increase

exponentiallyMinor Earthquake 3.0 - 3.9Microearthquake < 3.0

*For entire world

Moment Magnitude EstimatesDetermination of moment magnitude requires long-range seismogram data

Initial report (May 12):  7.6Revised (May 12):  7.8US Geological Survey:  7.9Seismological Bureau of China (May 18):  8.0Latest (pending confirmation): 8 3Latest (pending confirmation):  8.3

Seismic moment depends on force and displacement of the fault  = 4.4 x 1021 Nm for Sichuan Earthquake

Intensity 烈度Intensity measures the degree of damage (ground motion) at a place caused by an earthquake.

Modified Mercalli Intensity Scale (MMI) 12 divisions: I-XII

Intensity depends on earthquake magnitude, epicentral distance focal depth, geology and construction structures

MMI IntensityMMI Intensity100 km

Intensity X. Most masonry and frame structures destroyed with foundation. Ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Force = 0.6 g.

Intensity X. Most masonry and frame structures destroyed with foundation. Ground badly cracked. Rails bent. Landslides considerable from river banks and steep slopes. Force = 0.6 g.

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Beichuan Fault: Mainly a reverse fault with a lateral‐motion component

Main shock

Aftershocks

Rupture propagation: towards NE for 300 km Propagation speed: 3.1 km/sDuration of rupture: 80 sec

Aftershock map from USGS

Wenchuan 汶川Guangyuen 廣元

Fault plane dimension: 600 km x 50 km Orientation: 230o, inclining at 39o towards NW

Maximum ground displacement~10 m in Wenchuan

Fault displacement data from Seismological Bureau of China

Geology of LongmenshanAreabased on Bureau of G l d Mi lGeology and Mineral Resources of Sichuan Province

Mesozoic sedimentary

Precambrian basement rocks

Triassic sandstone 

Mesozoic sedimentary rocks

Igneous  rocks  

Diexi Quake‐dammed Lake 叠溪堰塞湖1933 M=7.5

160m‐tall dam burst 45 days after earthquake and drowned 2500 people downstream.A water wall over 60m high was reported.

Diexi Lake 叠溪海子

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Nature of Natural Processes

• Deterministic  e.g. object falling d itunder gravity

• Random e.g. radioactive disintegration

• Chaotic e.g. turbulenceDeterministic but unpredictableDeterministic but unpredictable

Not randomStrongly controlled by initial conditions

Scientific Earthquake Prediction

• The occurrence of earthquake is a chaotic process

• Scientific earthquake predictions should state where, when, how big, and how probable the predicted event is, and why the prediction is made

Types of earthquake prediction

• Earthquake forecast: statement on long‐term t ti ti l b bilit f th k istatistical probability of earthquake in a certain area

• Long‐term and medium‐term prediction• Short‐term prediction: a few weeks• Earthquake warning actionable declaration• Earthquake warning: actionable declaration, up to a few days

Possible earthquake precursors

Seismological precursorsseismicityseismic gaps, b-valueseismic wave velocity, velocity ratio

L, M, SLM

L: long‐term , yearsM: a few months ‐ a few yearsS: short term – days/weeks

Crustal strain and stress ground tilt, uplift rate, liquefactionfocal mechanismM, SM, S

Gravity anomalies absolute gravity valuetrend in gravity changeM,S

Electrical and geomagnetic anomalies

electrical potential, resistivity, magnetic field intensity, magnetic declination

S

Groundwater water level, flow rate, temperature, clarity, M, S

Groundwater odor

Hydrochemical radon emanation rate S

Animal behavior various S

Electromagnetic phenomena

ground noise, light emission, earthquake cloud

S

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Premonitory earthquake parameters

The 5 Stages based on dilatancy model   

seismic eventsseismic velocity ratioelectrical resistivitygroundwater flow radon emanation ratecrustal movementcrustal movementelectromagneticsgravity

Precursory changes before 

1978 Izuearthquakeq

Earthquakes with reported anomalous animal behaviour

• 中国地震資料年表: 1261966邢台地震以來 41 (M 5)• 1966 邢台地震以來: >41 (M>5)

利用動物預報地震

• 60年代在河北建立多個生物預報觀察站• 根据鴿子和貓的異常行為“成功”預測多次地震地震

• 所謂預測，多是根据地震后憶敍• 太多民間性報導、缺乏科學性描述• 對成因缺乏系統性、歸納性研究• 沒有失敗個案數字

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全世界最可愛的動物有預報地震能力嗎？

日期 震例 震級 異常行為

1937.8.1 山東荷澤 7 上床嚎叫1969.7.26 陽江 6.4 母貓幾次將小貓叼上床1970.1.5 云南通海 5.5 惊惶、嚎叫、不捉老鼠1970.5.25 河北豐南 5.2 貓不回家1971.8.16 四川馬邊 5.9 貓跑掉1974 5 11 云南昭通 7 1 貓搬家1974.5.11 云南昭通 7.1 貓搬家1976.7.28 唐山 7.8 惊慌不安、抓門抓人、逃跑

结论与建议

龙小霞, 延军平, 孙虎, 王祖正基于可公度方法的川滇地区地震趋势研究 (2006)

结论与建议

从以上所进行的推算与预测结果看, 在2008 年左右, 川滇地区有可能发生≥6级强烈地震发生≥6级强烈地震。

龙小霞, 延军平, 孙虎, 王祖正基于可公度方法的川滇地区地震趋势研究(2006)

图2 20 世纪以来川滇地区发生≥617 级地震的部分年份关系图

EQ. YEAR

19 years

21 years

18 years

10 years

7 years

EQ.YEAR

19 years

21 years

18 years

10 years

7 years

1913 √ √ √ √ √ 1967 √ √ √ √

1917 √ √ √ √ √ 1970 √ √

Earthquake prediction accuracy using method by 龙小霞 et al. (2006)

1923 √ √ √ √ √ 1971 √ √ √

1925 √ √ 1973 √ √

1933 √ √ √ √ 1974 √ √

1936 √ √ √ √ 1976 √ √ √ √

1941 √ √ √ 1979 √ √ √

1942 √ √ 1981 √

1948 √ √ 1988 √ √ √

1950 √ √ 1989 √ √ √

1952 √ √ √ √ 1995 √ √

1955 √ √ √ 1996 √ √ √

1960 √ √ √ √ 2008 √ √ √ √ √

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Most prediction studies are by means of reverse tracing of precursors.

To study earthquake premonitory phenomena, scientists need to ‘trap an earthquake’.

Previous earthquakesin Parkfield

The Parkfield Experiment

in Parkfield1857 (+24)1881 (+20) 1901 (+21) 1922 (+12) 1934 (+32) 1966 average return period: 22 years

1988?

Monitoring equipment

• Creepmeters• Strainmeter• 2‐color laser: ranging device with thickness of 1 mm over 10 km range1 mm over 10 km range

Alert scheme

Status Level for ParkfieldE normalE:  normalD:  minor anomalyC:  moderate anomaly; alert major life‐support 

servicesB:  ~10% of major earthquake in a few days; state 

d id timay decide on actionA:  >30% of major earthquake in a few days; state 

have to issue warning

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1991: A‐level alert, public warning issued

waited 3 earthquakes, no major earthquake

1993: Another A‐level alert

Vladimir Keilis‐BorokProfessor of GeophysicsUCLA

…The prediction is for a magnitude 6.4 or greater earthquake to occur between January 5 and September 5, 2004 within a 12 440 sq miles2004, within a 12,440 sq. miles area of southern California…

ParkfieldEarthquake2004.9.28M=6.0

Storm/Flood EarthquakeAdvance warning Sudden

Magnitude, time and spaceifi

Nospecific

Frequent in one’s life‐time Infrequent in one’s lifetime

Incremental warning Incremental warning difficult

Premonitory phenomena visible Premonitory phenomena  in form of geophysical fields 

If event did not occur, it wouldnot occur

Predicted event still may occurnot occur

Visible reasons for non‐occurrence

Public has no visible evidence to confirm that an earthquake could have occurred

All of these considerations can affect public policy on issuing earthquake warning

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State Governor of California

California Office ofIndividual California Office of Emergency Services

California Earthquake Prediction Evaluation Council 

Individual Prediction Claim

(CEPEC)/National Earthquake Prediction Evaluation Council (NEPEC) (a seismologist group)

中國地震局科技司

處理

建議

國務院

各省分析預報部门

中國地震局分析預報中心

中國地震局

直屬研究單位

各級地震辦測分

析核實

`專業台站及流動觀測隊

各級地震辦公室及群測

台站

前綫

觀測

Counter‐productive consequences

Cost of failed prediction = Total  loss ‐

Cost if prediction was made + adjustmentprediction made + adjustment measures

• Economic disruption• Legal liability• Capital outflow• Emigration• Falling land value

l• unemploymentPolicy makers must continuously weigh the relative merits of making and not making a warning.  The tendency is tilted towards  non‐issuing of warnings as the nation progresses towards prosperity

Prediction vs. Warning

• A prediction is a neutral statement made b d l t d b tibased on accumulated observations

• A warning is a declaration that normal life routines should be altered to deal with the impending hazard

• Prediction: based on sciencePrediction: based on science• Warning: Interpretations of prediction that take public policy into account