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Sichuantalk(long) · (CEPEC)/National Earthquake Prediction Evaluation Council (NEPEC) (a...
Transcript of Sichuantalk(long) · (CEPEC)/National Earthquake Prediction Evaluation Council (NEPEC) (a...
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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