भुकम्प, यसको असर र जोखीम

(भाद्र २६,२०७० को नागरिकमा प्रकाशित)

यहि भाद्र १४ गते रातको लगभग ११:३५ को आसपासमा नेपालको मध्यभाग ६ रिक्टर स्केल(स्थानिय मापन)को भुईचालोको कारण हल्लिन पुग्यो, सामाजिक संजालहरु एकै पटक भुकम्पमय बने, सबैजना यस प्रति चनाखो बनेको देखियो। UNDP को बिपद् ब्यबस्थापन संबन्धि संस्थाले २००४ मा निकालेको रिपोर्टको आधारमा बिश्वमा भुकम्पिय जोखिमको ११औं स्थानमा पर्ने देशमा हाम्रो तयारी कस्तो छ त? के हाम्रो समाजमा यस्ता भुकम्प आउदा के गर्नुपर्छ, कसरि सुरक्षित रहनुपर्छ भन्ने जनचेतना राम्रो छ त? हिजोकै केहि प्रतिक्रिया हरु हेर्दा र बुझ्दा यसको कमि देखिन्छ। पछिल्ला बर्षहरुमा भुकम्प आउने क्रम बढ्न थालेको देखिन्छ र यसले केहि बर्ष भित्रैमा ठुलै भुइचालो जान सक्छ भन्ने पनि बुझ्न सकिन्छ। भाग्यबस अहिले ठुलो भुईचालो आएको छैन, हामीले सानासाना भुइचालोहरु महसुस गरेका छौं, त्यसैले राजधानीमा ठुलो क्षति हुन पाएको छैन।

नेपालमा भुईचालोको ईतिहास करिब ई. सं. १२५५ देखिको रहेको पाईन्छ जुन समयमा काठमाण्डौंका एक तिहाई देखि एक चौथाई हाराहारी मानिसले ज्यान गुमाएको बताईन्छ। त्यस भन्दा पहिले पनि भुईचालो नगएका होईनन तर कुनै पनि यकिन समयका तथ्यहरु फेला नपरेका मात्र हुन।  यस्तै सन १४०८, १८१० मा पनि ठुला भुईचालो गएका थिए तर यसको यकिन तथ्यांक भेटिएको छैन। सन १८३३ देखि कुनै रुपमा तथ्यांकहरु पाउन सकिन्छ जुन समयमा ७.८ रिक्टरको भुइचालोका कारण काठमाण्डौंका करिब ५०० मानिसले ज्यान गुमाएका थिए। पछिल्लो सन १९३५ (बि. सं. १९९० माघ २) को भुईचालोलाई सबैभन्दा ठुलो भुइचालोको रुपमा लिईन्छ जसको कारण करिब १६००० मानिसको ज्यान गएको थियो। यसै महाभुकम्पको सम्झना र समाजमा भुकम्प संबन्धि जनचेतना फैलाउनको लागी त्यस दिनलाई प्रत्येक बर्ष भुकम्प दिबसको रुपमा मनाउन थालियो। यस बिचमा नेपाल वा भारतका बिभिन्न स्थानमा केन्द्रबिन्दु भएर गएका बिभिन्न भुकम्पको कारण पनि कयौं नेपालीले ज्यान गुमाइसकेका छन।

एक अनुसन्धानले हाम्रो देशको डिजाईन कोड (मापदण्ड) र प्रचलित निर्माण प्रबिधिले निर्मित संरचनाहरु अन्य मापदण्ड (ATC-40 र FEMA-356) बाट निर्मित संरचना भन्दा बढि जोखिममा रहेको जनाएको छ। पछिल्लो समयमा बिभिन्न नगरपालिकाहरुले भुकम्पिय प्रतिरोधि भवनसंहिता लागु गरेकाले नक्सा बनाउदा अनिबार्य पर्ने ठाउँमा मात्र आम मानिसले घर बनाउदा नक्सा बनाउने गर्दछन तर यि मध्ये करिब ८५% (अनुमान) घर हरु नक्सामा रहेको संरचनागत डिजाईन नअपनाई, सामान्य निर्माण ठेकेदारको भरमा बन्ने गरेका छन। निकै कम मानिसले मात्र ईन्जिनियरको रेखदेखमा आफ्नो घर बनाउने गरेका छन। यस किसिमले निर्माण गरिएका संरचना कति बलियो होलान त? हामी सहजै अनुमान लगाउन सक्छौं।

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car crushed by landslide on 31st August 2013, Taiwan

You can see this video how landslide can crush the car... be safe.... be aware, every where...
This video is taken on Keelung-Badouzi, Taiwan
   

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How to find out epicentre of earthquake?

You may confuse that many agencies locate different points for the epicentre of same earthquake, it may happens because of recording stations around the possible location.

Here is one example of one method to find out epicentre.

To figure out just where that earthquake happened, you need to look at your seismogram and you need to know what at least two other seismographs recorded for the same earthquake. You will also need a map of the world, a ruler, a pencil, and a compass for drawing circles on the map.

Here's an example of a seismogram:

FIGURE 1 - OUR TYPICAL SEISMOGRAM FROM BEFORE,

 THIS TIME MARKED FOR THIS EXERCISE (FROM BOLT, 1978).

One minute intervals are marked by the small lines printed just above the squiggles made by the seismic waves (the time may be marked differently on some seismographs). The distance between the begining of the first P wave and First S wave tell you how many seconds the waves are apart. This number will be used to tell you how far your seismograph is from the epicenter of the earthquake.

Finding the Distance to the Epicenter and the Earthquake's Magnitude 1.     Measure the distance between the first P wave and the first S wave. In this case, the first P and S waves are 24 seconds apart. 2.     Find the point for 24 seconds on the left side of the chart below and mark that point. According to the chart, this earthquake's epicenter was 215 kilometers away. 3.     Measure the amplitude of the strongest wave. The amplitude is the height (on paper) of the strongest wave. On this seismogram, the amplitude is 23 millimeters. Find 23 millimeters on the right side of the chart and mark that point. 4.     Place a ruler (or straight edge) on the chart between the points you marked for the distance to the epicenter and the amplitude. The point where your ruler crosses the middle line on the chart marks the magnitude (strength) of the earthquake. This earthquake had a magnitude of 5.0. FIGURE 2 - USE THE AMPLITUDE TO DERIVE THE MAGNITUDE OF THE EARTHQUAKE,  AND THE DISTANCE FROM THE EARTHQUAKE TO THE STATION. (FROM BOLT, 1978)

Finding the Epicenter

You have just figured out how far your seismograph is from the epicenter and how strong the earthquake was, but you still don't know exactly where the earthquake occurred. This is where the compass, the map, and the other seismograph records come in.

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Moderately strong earthquake M6.2 rocked Mexico 21st August 2013

 A moderately strong earthquake shook Mexico's capital Wednesday, but there were no immediate reports of injuries or damages. The U.S. Geological Survey said the quake had a magnitude of 6.2 and was centered on the Pacific coast, near the resort of Acapulco. There was also another after shock of M5.3 lagging of about 32 minute with main shock.

Buildings swayed in the capital and some people evacuated buildings as an earthquake alarm sounded. The alarm also went off for a second, smaller quake a few minutes later. Mexico City is vulnerable even to distant earthquakes because much of it sits atop the muddy sediments of drained lake beds that quiver as quake waves hit.

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Series of earthquakes rocked New Zealand

Strong quakes of foreshock and aftershock for main tremor of M6.5 (initially reported M6.9 but later down to 6.5) at 2:31 PM NZ time rocked newzealand south island. Epicenter was in the north east tip of south island, which is near to the capital city wellington. On the same area about three weeks ago there was tremor of M6.5 caused several damages. Yesterday there was no any report of even serious injury, many people came down to the ground and evacuated to safe places. several people who trapped in elevators were successfully rescued. There were several structural and non structural damages.

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How bullets are loading on earthquake gun in developing countries??

When earthquake of level around M6.5 occur in Japan hardly claim life but if the same level will be in Indonesia, Philippines, India, Myanmar, Nepal, Pakistan, Afghanistan etc. countries will have to loss in several thousands? Bryan Walsh wrote in TIME as earthquakes are gun and structures are bullet that load on gun and fire to people. He specially focus on south central Asia about earthquake and disaster in his last article How Shoddily Constructed Buildings Become Weapons of Mass Destruction . I totally agree with his article that main problem developing countries are not focused on implementation of seismic design and building codes to public during their private building constructions, hardly they follow for just civic buildings.

Most of the structures in rural areas are still stone masonry in mud mortar, during rainy season even they are more vulnerable to collapse with wetting of mud mortar, even they are as like the stack of stones so they cant hold more tremor intensity and fall down as blow on head. Rural area people must have to aware about seismic risk and its mitigation during construction of their house, with just a small additional amount (about 10%) investment on their house they can get more safer (about double ) building. Rural settlements are also catering more population in developing countries even up to now.

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