Report on Post Disaster Need Assessment

Report on Post Disaster Need Assessment

(Halde Kalika Village Development Committee Nuwakot District, Nepal)

1)Prithvi Lal Shrestha (Senior Divisional Geologist/ Department of                                                 Mines & Geology)

2)Narayan Prasad Dahal (Account Officer / City Development 

                                                     Office)

 3)Khem Raj Bhatta  (Amin / Survey Office)

1. BACK GROUND

After the great earthquake of 7.6 Ml (NSC/DMG) which rocked central Nepal with casualties more than eight thousand on 25 April 2015, our team of three members was appointed in my leadership for Post Disaster Need Assessment in Halde Kalika Village Development Committee of Nuwakot District. The team was appointed for one month from Government side. Final report is submitted to the District Disaster Relief Committee, Bidur.

2. OBJECTIVES

i) Take or help to take immediate relief action after gathering information on earthquake victims.

ii) Help to make Integrated Resettlement Plan for earthquake victims if needed.

iii) Help to reuse or reconstruct public structures after collecting data of damage from an earthquake.

iv) Help to reuse or reconstruct all physical structures after accomplishing Post Disaster Need Assessment.

3. METHODOLOGY

Our team members filled up data of damage in two formatted forms; one is “Basic Information on Damage of Individual Households” with direct interaction (face to face) with the house owner individually from about 1000 houses of all nine wards. And second, public structures like, schools/hospitals/Government offices/industries and college etc., was filled up in “Damage of Government/Public Structures” form with direct interaction with the local Government officials and local people.

Instruction was given to the people that whether they can stay or not in particular house/structure after inspecting damage condition.

4. FINDINGS ON THE SITE

The pictures of the villages are horrible and heart touching. Almost all houses are made of adobe type with mud and stone having weak holding capacity, which are totally damage. Even with some houses, seem to be fine from outside is damage from inside, where people can’t live. 25 people were dead and more than 100 injured found in this VDC.

5. PROBLEMS

Major problem with people in the site is totally damage houses and improper shelters to live. Some people have not received tents yet. They build temporary but poor shelters by using the materials from their damage houses. The cash money 7000 Nepalese rupees from the Government side is not completely distributed yet. Relief materials and food didn’t go to all people up to now. News of loot and vandalize is coming from some places. Cunning and clever people got relief materials many times, which indicates lack of monitoring and security from the Government side. Almost all schools are damage so students have problem to get education timely. In some places water sources dried up so people are facing with water problem. There will be major problem of landslides in the area where fractures are made due to earthquake, in near future since monsoon (rainy season) is ahead. This may cause more disaster.

Beside these, strong psychological effects have been seen mostly in children, women and old people.

6. POSSIBLE SOLUTION

Immediate solution for villagers is to manage temporary shelters or houses before monsoon starts. Relief distribution should be equal and as early as possible under Government supervision. Psychologists and doctors should be appointed to take care of the people affected from mental problem. To start classes in school, temporary shelter should be built, students should be taught with enjoyment environment and recreational way like, singing/dancing/playing for few weeks so that the negative effects due to an earthquake would be gone. The experts should be appointed in villages to interact and teach people that an earthquake is a natural phenomenon, which is neither stoppable nor predictable, but we can lessen the aftermath of it. This can bring people down of trauma from earthquake and live normal lives. Yes, people now are aware of making earthquake resistance houses but local government should also be strict in implementing building code and monitor regularly.

7. RESETTLEMENT PLAN

Resettlement or united habitat is not possible in this VDC due to geological inhomogeneity of this area. Almost all villages in this VDC are situated in hilly land and it has lack of open land. Cultivation practices are in hilly terrain. Every individual has their own house and land for cultivation so they are not interested to move to other place. Government or public land is forest, which is also situated in hilly land. These are the reasons why resettlement of the village is impossible in this VDC.

8. SUMMARY

This Halde Kalika VDC which is about 15 Km east from Bidur, a district headquarter of Nuwakot, is facilitate with transportation, electricity and communication but remote due to its geological condition. Rich in hilly and inhomogeneity terrain, this VDC has the houses mostly made up of mud and stone, which are vulnerable to earthquake, the result we already saw after the great earthquake. Main cultivation of this area is paddy, wheat, corn and ginger.

While collecting a data we didn’t face any problems. We achieved a goal in time due to help of local people and social workers. And, the guidance and viability of official materials from center time to time made our work easier. Our team wants to thank all the concerned people for this national task for their help and support.

 

9. PHOTOS

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Everest and the Toenail

One Day The Earth Will Drop Kathmandu – Earthquake Risk in Nepal

Nepal: Japan-size earthquakes, Haiti-like infrastructure.

Notes on a talk given by John Galetzka (Tectonics Observatory, CALTECH).

Presented by the Cultural Studies Group of Nepal

Last year I experienced a 6.6 earthquake here in Kathmandu, a few weeks earlier a 5.6 magnitude earthquake in Northern Virginia. Some years ago sitting outside in Malawi I watched the surface of the pleasant grass covered earth move towards me like an approaching wave. Those are my limited experiences of earthquakes. What follows is my interpretation of an absorbing talk given by John Galetzka. Any errors are mine and not his!

At this point the wonderful, hard continuous surface of planet earth feels more like a series of blocks of jelly, wobbling in constant motion. The two tectonic plates that concern us here in the Kathmandu valley are the Indian Plate — an Oceanic plate sliding on rock that is more dense than the Eurasian Plate above it. The Indian plate has an interesting history John illustrated in a rapid motion animation. About 100 million years ago it was cast adrift from the Antarctic Plate and began it’s voyage across what is now the Pacific Ocean. Essentially all alone on a long, very slow ocean voyage. Then it met and collided with the Eurasian Plate and is still subluxing (moving beneath) it. If I were sitting watching you in Northern India I could see you moving towards me at about 18mm – 22mm a year – hence the name of my blog for those that don’t know. That movement is faster than a toenail grows. This rate of movement is measured from a number of GPS stations that record not just horizontal but vertical movement of the earth’s surface. On one island in the Pacific the locals, having experienced a quake moved their village and rebuilt it around the GPS station so as to be safe. On another island John found all the cables had been cut and carried away because the local people thought George W. Bush was pushing a button in Washington and through the GPS device causing the ground to shake.

Kathmandu sits in the middle of the crush zone (which stretches to Russia) between the two plates. The city is built on top of the Main Himalayan Thrust plane – the direction the plate is moving in. Deep in the earth the rock moves smoothly, unnoticed, closer to the surface friction slows the rock, bending the Eurasian Plate (with the Himalaya Mountain Arc on top of it) causing the leading edge of the plate to bend backwards against the flow, rather like a ratchet on a clock against a cog. Closer to the surface the plates are locked and not moving. The plate flexes, creeping forward in the lock zone. Tension builds, the fault pops and cracks and then from time to time the fault line unzips and there is incomprehensible and unimaginable explosive release of energy. In geological time a minute advances on the clock. Tick, tock, bang.

There are millions of quakes every year throughout the world as plates jostle and move. Most of these nobody feels. In KTM I can feel minor vibrations from time to time and don’t notice them anymore — was that a truck going past? Ever so slightly the building is shaking, almost unnoticed. Fortunately the higher the intensity, the less frequent a major event.

Each step in the measurement of the magnitude of an earthquake represents a 33-fold increase in the release of energy. A magnitude 7 (close to that we experienced here last year – epicenter about 160 kms away and 20 kms down beneath the surface) releases the equivalent of 25 nuclear bombs – about half a million tons of TNT. A magnitude 9 quake in comparison (that which hit Japan) released the equivalent of 25,000 nuclear bombs – some 500 billions of tons TNT. The largest recorded earthquake occurred in Chile and registered 9.5. on Dr. Charles Richter’s Scale.

Some remarkable changes occur to the rock hard surface of the earth when there is an earthquake. In western Nepal there is evidence of a 15 meter (almost 50 foot) vertical displacement in the earth’s surface caused by an earthquake. John showed us a picture of a new 8 meter tall waterfall caused by a 7 magnitude quake. An 8.5 earthquake in the Pacific raised an entire an island up 3 meters. Where the ships used to dock there is now dry land.

When there is a massive earthquake the more developed the infrastructure the lower the loss of life. Maybe an obvious statement, but the facts are telling. The 7.0 quake that devastated Haiti recently killed 222,750 people, whereas the 9.0 quake that struck Japan killed 15,703 people — mostly as a result of the Tsunami. Japan is nearly back on it’s feet. In Haiti people are still living in tents and extremely vulnerable. Why? Because building codes are not only set but enforced in Japan. In the recording of the Japanese quake below had that been in a building in Kathmandu (where at best — and who knows how well built the houses are built — a house should withstand a magnitude 7) it would have been reduced to rubble. In Tokyo some hundreds of miles south of the main quake the building retained its structural integrity.

In Kathmandu where a 9.0 quake on a level with Japan is a distinct and enduring possibility given it’s location, the infrastructure is that of Haiti, the effect of a 9.0 quake on Kathmandu is hard to exaggerate. Sitting where we are, moving towards China, is one thing. Sediment amplifies seismic waves. Rock doesn’t vibrate as much. Kathmandu is built on sediment, surrounded by 2000 meter hills, in effect a wonderful way for nature to amplify the S waves that will shake and drop the majority of the buildings in this beautiful city to the trembling ground in a few short minutes, killing countless thousands, maybe a million people — hard to quantify. The process is called liquefaction where particles become suspended in liquid. The very ground will turn fluid. Most massive quakes occur under the ocean. In Nepal they occur beneath our feet, so a quake map like the one shown below of the last earthquake would be entirely deep red and over Kathmandu.

There is no sensible or known way to predict when an earthquake will happen. There are, however, ways of predicating in what region a quake will happen and the possible severity. In the movie below the P wave arrives first and gives tens of seconds notice for the arrival of the S wave. The P wave is fast and not that destructive, it is what comes next that inflicts the damage. If the fault unzips beneath Kathmandu there will be no advanced warning, the P and S waves arriving almost simultaneously. If it happens some 100 of kms away to the west or east there will be some warning.

So why are people building high rise apartment blocks in Kathmandu and tall office blocks with walls of glass? There is no manpower to enforce the building codes, even if they are adequate. Cultural problems exist in that less senior government officials will not pass up information that is problematic to their superiors. Preparation, advance warning, as seen in the Japanese video, is non existent here. Such preparation and education can allow the population to ride out an earthquake. If it is a mother of a quake it will devastate northern India too, so no aid will come from there. With no airport, no roads, a shattered infrastructure, Kathmandu feels remote.

When will it happen? All that is known is that it will. How big? Magnitude 8 or 9. A sure thing. Today, tomorrow, next week, next month, next year? The tension beneath Nepal builds as I type, incrementally it builds and builds. Irresistible forces propel us towards the sacred Himalayas. One day the plates will simply slip and unzip one or more devastating shifts in the structure of the ground beneath our feet and where shall Nepal be? What is the government doing about educating and preparing it’s people? It could prove to be too late to act. The Americans, however, following Haiti, beat a path to John’s door and have exhibited a level of preparedness that is at once pragmatic and admirable as was his excellent and riveting talk. John always travels with a ‘go bag’ of emergency supplies. Never stays above the first floor in a hotel (now he has a daughter) and from his lips today came words of wisdom presented not to create panic but to lay out the facts. It is for embassies and the government to begin serious and concerted preparations for what is occurring not in front of our eyes but beneath our feet.

Education, preparedness and early warning are the way forward. Make sure you have go bags in your house, car and office, keep walking boots (and socks) by the bed and a trunk full of equipment (ropes, sleeping bags, tents, pick axes, dry food, etc.) handy outside the house along with supplies of water and medications. Have photocopies of all your key documents. Know who your warden is and make sure that your embassy has the GPS location of your house.
The Last Ten Seconds: https://www.youtube.com/watch?v=n-FMpNBfna8

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Intensity of Nepal-Sikkim 6.8 Earthquake

Intensity Mapping in Eastern towns of Nepal

Prithvi Shrestha and Chintan Timsina

This is a report of field trip for the Intensity Mapping of some major towns in Northeast part of Nepal due to recent Taplejung-Sikkim earthquake of magnitude 6.8 occurred in Sept. 2011 in the evening. The location of the quake was latitude 27.71N and longitude 88.30E with shallow depth about 20 km. Strong shaking was felt in the capital city Kathmandu too 300 km far from the epicentre. This earthquake is intraplate earthquake and occurred in the higher mountain range. Observation was done in the following towns along with questionnaire and photographs, which are included.

1) Phungling Bazaar: - It is a centre town of Taplejung district about 70 km southwest from epicentre.  Few damage found in the centre although strong shaking felt by the people. Three houses are found to be damage outside of the town among them two are heavily damage. Many houses damage and landslides are reported in the remote side near to the epicentre. Talking to the local people it is expected that the intensity should be between V to VII in MMI scale.

2) Phidim Bazaar: - Also 70 km far from epicentre, Phidim Bazaar too felt the strong shaking. In the town three houses are fully damaged and several houses are cracked. Landslides on the way in some places are also observed. Here also many houses damage and landslides are reported in the remote village areas. By interaction with the people and questionnaire they filled suggest that intensity should be between V to VII. 

3) Ilam Bazaar:- Although shaking was strong but less damage are found here. This town is 95 km far from epicentre. We observed few houses with hair crack. On the way near Puwa river 5 meters rupture was seen. Little far from the town we observed weak plaster fallen in some adobe type houses. But still many houses and landslides are reported from remote areas. On the basis of filled questionnaire by the people here, the intensity should vary from IV to VI.

By interaction and questionnaire with the local people, we came to know that heavy damage was occurred in the villages where very old houses made of adobe and wood-mortar are likely to find. Landslides were also observed in some places on the way. Due to difficulty in accessing the road, heavy rain and less time our team was unable to reach to the earthquake affected remote areas, so less information from those areas.

The aim of the mission was not only to map intensity but also to install new GPS, Accelerometer and Broadband Seismic Stations and download GPS data. GPS stations are deployed in Tumlingtar, Ilam and Jhapa whereas Broadband seismic stations are deployed in Dhankuta, Jhapa, Ilam and Taplejung. In Taplejung, Tumlingtar and Ilam an Accelerometer are installed. Due to lack of time, inconvenient road access and remoteness of the affected area we lack the information of damage parameters. Although the intensity distribution seem to be between IV to VII in MMI but it is not justifiable to estimate intensity only on the basis of observation in the towns. It is reported that this earthquake heavily affected Sikkim side too. So it is better to wait for more information from both, Sikkim and our remote side to estimate the final intensity map.

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VALIDATION OF SPATIAL AUTOCORRELATION (SPAC) METHOD WITH L-SHAPE ARRAY IN JYOSO CITY,JAPAN
Prithvi Lal SHRESTHA*


ABSTRACT
This study is aimed to validate the efficiency of an L-shape array for SPAC method using microtremor in estimating the shear wave velocity (Vs) structure. The experiment for validation was conducted in the Toyota Community Baseball Ground, Jyoso City, Ibaraki Prefecture, Japan in March 2009 with an equilateral triangle array with side length of 40m and in June 2010 with an equilateral triangle array with side length of 50m, together with an L-shape array of the similar size. Multichannel Analysis of Surface Waves (MASW) was also performed simultaneously in June 2010. In the same lot PS-logging data are available from nearby IBRH10 station of the KIK-NET (NIED, Japan) that shows soft sediment of about 20m thick with Vs of 110 m/s in the geological column of the site. The comparison of the determined phase velocity and that calculated from PS logging data shows close matching of two sets of curves separately. One is between PS logging and the triangle array (40m) and the other is between the triangle array (50m) and the L-shape array (50m). Former two are of the almost same place whereas other two arrays are deployed about 200m away from the other set. Some discrepancy between two sets is shown. This seems due to lateral variation of underground velocity structure which is consistent with the result of MASW.
Based on the results of analysis we can say that an L-shape array can be applied to estimate shear wave velocity for shallow depth so it can be layout in urban areas to determine phase velocity information from microtremor. Therefore it may be feasible to apply it in the Kathmandu valley, Nepal that is based upon the soft soil with high possibility of liquefaction or earthquake hazard. Keywords: SPAC, PS logging data, Equilateral Triangle array, L-shape array. *National Seismological Centre, Department of Mines & Geology, Kathmandu, Nepal.

1. INTRODUCTION

Nepal Himalaya lies in the active seismic belt. Seismicity in the Himalaya is the consequence of under-thrusting of the Indian plate towards the north lying Tibetan plate. Nepal has suffered earthquake disasters through its history due to its high seismicity and highly vulnerable construction practices, therefore one of the most earthquake disaster prone countries in the world.

1.1. Purpose of my study:
Since we are expecting a great earthquake disaster in near future in our country Nepal, seismic hazard assessment is required. Estimation of the amplification factor of the ground, i.e., microzonation on the basis of the shallow Vs structure is a basic step of seismic hazard assessment. The microtremor array measurement will be applied in Nepal in future, because this SPAC method seems to be reliable, easy to,comparatively affordable and do not cause any environmental problems, thus suitable as a tool for seismic microzonation and earthquake disaster mitigation. Conventional circular or equilateral triangle arrays, however, are sometimes difficult to deploy in crowded urban areas where only L-shape or linear arrays layout can suit to road pattern. The purpose of this study is to understand the effectiveness, limitations and advantages of L-shape array for the SPAC method by applying and verifying the applicability and accuracy by comparison with standard equilateral triangle array in Jyoso city, Ibaraki, Japan.


2. METHODOLOGY

2.1. SPAC method:
This is a successful method to determine the phase velocity information from surface waves contained in microtremor (e.g., Aki 1957; Okada 2003). The SPAC coefficient for distance r between two stations at the angular frequency ω provides the information about the phase velocity of the propagating waves in the array. This is obtained by the azimuthal average of coherency between microtremor records observed at two stations.

2.2. Procedure of analysis:
Triangle and L-shape arrays are set up to get the microtremor data. First SPAC coefficient is obtained after filtering and resampling and then screening is done. Second, the dispersion curve
of Rayleigh wave is determined and finally velocity structure model is estimated by the heuristic search method using the very fast simulated annealing method (VFSA) combined with the downhill simplex method (DHSM)(VFSA-DHSM, Yokoi 2005).

3. DATA ACQUISITION

3.1. Observation site:
The experiment was conducted in the Toyota Community Baseball Ground, Jyoso City, Ibaraki Prefecture, Japan in March 2009 and June 2010. IBRH10 of KIK-NET (NIED, Japan) is located at the south-east corner of the same lot where PS-logging data are available. MASW (Hayashi and Suzuki 2004) was also conducted this year. Soft sediment as thick as about 20 m with velocity of S-wave (Vs) 110 m/s is observed in the geological column at IBRH10. There are a national road R294 about 300 m west and a prefectural road 24 about 100 m south and both of them have heavy traffic all day long.
The baseball ground itself, however, was almost quiet during the measurement (Yokoi and Hayashi 2009).

3.2. Array deployment and instruments:
Equilateral triangle array with side length of 40m with 7 sensors was deployed in March 2009 nearby IBRH10 whereas 50 m of equilateral triangle with 10 sensors and L-shape array with 11 sensors were deployed in June 2010 about 200m away from IBRH10. All sensors are vertical component. MASW with total length of 105m was conducted in the same place.


4. ANALYSIS AND RESULTS

4.1. Preprocessing:
Multiplexing and re-sampling are done applying digital anti-aliasing filter (Saito 1978). The screening is conducted next with two steps. The data are divided into time blocks with 512 samples. The consecutive time blocks are overlapped each other by 50% of their duration.
First step: If peak is greater than “ajudge” times of RMS amplitude then this time block is not used in analysis. This is a countermeasure against impulsive noise due to traffic, i.e. vehicles passing near by sensors.
Second step: If RMS amplitude in a time block deviates more than another given constant “a_sgm” times the standard deviation from the average, this time block is not used in analysis, where the average and the standard deviation are calculated over the all time blocks that survived in the above mentioned screening step 1. This is a countermeasure against outliers. In this study ajudge=4 and a_sgm=2 are used for the screening of the obtained data.

4.2. SPAC coefficient calculation:
Re-sampled and screened time block files are used to calculate SPAC coefficient that is an azimuthal average of the coherency between microtremor records at two stations. The initial frequency range of analysis is set from 0.1Hz to 10Hz. Band width of Parzen window for smoothing power and cross spectra is set at 0.5Hz.

4.3. Determination of dispersion curve:
The dispersion curve of Rayleigh wave i.e., the phase velocity depending upon the frequency is determined from SPAC coefficient. First, SPAC coefficient ρ(ωr) is converted to the value of kr by applying the following fifth order polynomial equation that approximates the inverse function of J0(kr). The first maximum of c(ω) from the low frequency side is recognized as a lower limit of the available frequency range for the respective inter-station distance. The maximum from this lower limit to the highest one is recognized as the high frequency limit of the available frequency range. Then these values again are averaged and converted to c(ω) = rω/(kr). The weight coefficient used at averaging is the reciprocal of the variance of SPAC coefficients at the respective inter-station distance and the frequency.

4.4. Estimation of velocity structure by Heuristic search:
A heuristic search method is conducted to obtain the optimum underground structure by fitting the theoretical phase velocity of Rayleigh wave to the observed dispersion curve. Five layer models are introduced with its search range. The used method is the downhill simplex method (DHSM, e.g., Press et al. 2002) combined with the very fast simulated annealing (VFSA, Ingber 1989). Hereafter, the combined methods is called the DHSM-VFSA. The optimum, namely, the fastest schedule for the inversion of underground velocity structure from the dispersion curve of Rayleigh waves is used with the parameters t0=1.0, a=0.6, and c=1.3 as given by Yokoi (2005).


5. DISCUSSION

5.1. Comparison of dispersion curves:
Fig shows a comparison of phase velocity over frequency between 40m triangle, 50m triangle and 50m L-shape arrays with the curve of PS logging data.This shows close matching of two sets of curves separately, one is between PS logging and 40m triangle and the other is 50m triangle and L-shape. PS logging and 40m triangle array are from the same place where other two arrays are also from the same place but about 200m away from the other set. A discrepancy is seen between these two sets. This seems to be due to lateral variation of underground structure as MASW result implies.

5.2. Comparison of velocity structure:
Figure shows the comparison of Vs
structure models determined by the data of the three arrays with the PS logging data. Vp is fixed to 1500m/s for the 1st to 4th layer and 1956m/s for the underlying half space.
Density is calculated from Vp then fixed to 1.9g/cm3 and 2.13g/cm3 respectively(Ludwig et al. 1970). As seismometer’s natural frequency is 2.0Hz, the lower limit of the frequency range for analysis is set at
2.0Hz and the upper one at 5.0Hz by considering on the S/N of microtremor. The value of misfit is as small as 3.0, 4.0 and 4.2 m/s for the triangular array (40m), triangular array (50m) and L-shape array respectively. From Figure it is clear that for the 20m depth Vs of all arrays are similar to the logging datai.e., around 110m/s to 150m/s that implies soft soil. Vs structures of the triangular array (50m) and L-shape array coincide to each other whereas 40m triangle shows a clear deviation from them and lower Vs than PS logging data. This shows that the lateral variation of underground velocity structure implied by MASW is detected also using SPAC method.


6. CONCLUSION

In this study I have conducted the analysis of the data of microtremor array observation held in the Toyota Community Baseball Ground, Jyoso city, Ibaraki prefecture, Japan for shallow depth using L-shape and equilateral triangle array with the SPAC method for Rayleigh wave in comparison with PS logging data and MASW. The dispersion curve and Vs Structures determined by the data of L-shape array coincide well to those of equilateral triangular array (50m). These deviate together from Vs structure of PS logging data and the dispersion curve calculated from PS logging data respectively. This discrepancy, however, is due to lateral variation of Vs structure as the result of the triangular array (40m) shows and that of MASW implies. Based on the results of analysis I conclude that L-shape array can be applied to estimate Vs structure for shallow depth so it can be layout in urban areas to determine phase velocity information from surface wave in microtremor.


ACKNOWLEDGEMENT

I would like to express my sincere gratitude to Dr. Koichi Hayashi, OYO Corporation for his help during the field work.

REFERENCES
Aki, K., 1957, Bulletin of Earthquake Research Institute, 35, 415-457.
Hayashi, K., and Suzuki, H., 2004, Exploration Geophysics, 35, 7-13.
Ingber, L., 1989, Mathematical and Computer Modeling, 12, 967-973.
Ludwig, W. J. et al., 1972, The Sea, Vol. 4, Wiley-Interscience, New York, 53-84
Okada, H., 2003, The Microtremor Survey Method. Society of exploration geophysicists.
Press, W. H., et al., 2002, Numerical recipes. Cambridge University Press.
Saito, M., 1978, BUTURI- TANSA, 31, 112-135 (in Japanese with English abstract).
Shiraishi, H., et al., 2006, Geophys. Res Let, Vol. 33, L18307.
Yamanaka, H., 2004, Proc. of 13th World Conference on Earthquake Engineering, Paper 1161.
Yokoi, T., 2005, Programme and Abstract, Seismological Society of Japan Fall Meeting, B049.
Yokoi, T., and Hayashi, K., 2009, Proc. of 9th Int. WS on Seismic Microzoning and Risk Reduction, Cuernavaca, Mexico.

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Report on Observation Visit for Earthquake Disaster Mitigation

Date: 16 Oct. 2009 (1st half day)
We observed two phases in this visit which are described below,

1. (i) Visit to Yokoami-Cho Koen Park area: This park is about ten minutes walk from Ryogoku station, Tokyo. We visited Tokyo Reconstruction Memorial Museum and Memorial Hall of the Great Kanto Earthquake[1]. We also visited the nearby Yasuda Park.

(ii) Aim of visit: To observe the aftermath memories of the Great Kanto Earthquake and Air Raid by US during 1923 and World War II respectively, and to learn some thing for preparing to cope with the affects caused by disaster in the future.

(iii) Targets: It was touching moment to see the tragic effects of the Great Kanto Earthquake and Air Raid during WWII (Fig. 1 & 2). As a picture speaks out, the result was so horrible that anyone could get speechless. We observe the design of planned town to lessen the disaster affects (Fig.3). We observed Memorial Hall (praying place) designed by a famous architect Dr. Chuta ITO (received the Order of Culture in 1943) and constructed by the Metropolitan Government of Tokyo in the memories of those victims. This design is a sort of mixture of Buddhist temple, church and Castle. We, also observed the near by Yasuda park where we felt little ease by the Nature.

(iv) Name of the lecturers: Dr. YOKOI Toshiaki, Ms. OMUKA Hiromi

(v) Description: Observing these memories, I think people should be given education in awareness and preparedness for the disaster calamities. Planning, design and construction are other vital things. Of course you can’t do anything with Air strikes. The design of planned city was the good model. In my country’s case earthquake awareness and preparedness program and conducting building code would be the best solution to reduce Human casualties.

2.(i) Survival Walk Practice (2nd half day): From Yokoami-Cho Park to Asakusa temple along the National Route # 6 after crossing Kuramae Ryogoku-Bashi bridge over Shumida-Gawa river. It is about six km long.

(ii) Aim of visit: To observe and be familiar with the various supporting symbolic stickers of different symbols like danger objects, water available, supporting station, signal etc., along the supporting road[2].

(iii) Targets: After crossing the Ryogoku-Bashi bridge I saw a big ware house for disaster prevention on the right hand side (Fig. 4). I also saw stickers corresponding to the danger (Fig. 5) and supporting label (Fig. 6) a shop with fire cracker and chemicals, gas station, vending machine without anchor and an advertisement boards (Fig. 8). Some old houses and tilted house were also seen.

(v) Description: It is amazing to see the idea of Supporting Road toward the reduction of Natural Calamities with various information. It is very useful for safe evacuation when the big one hit. As my country being high risk in Earthquake Hazard I can try to communicate and implement this method to some extent. Other thing I like is the gaps between two buildings and pipelines going through it (Fig. 7). May be it is to reduce fire risk from one house to another.

Finally, I would like to thank Yokoi-San and Omuka-San for their valuable guidance about this trip and of course Saito-San for being as a guardian in the whole trip.

Fig.1 aftermath photo inside museum
Fig.2 remaining outside museum
Fig.3 design of planned city
Fig.4 symbol for danger
Fig.5 supporting label

Fig.6 gap and pipelines
Fig.7 advertisement boards

[1] It occurred in 1923 with magnitude 7.9 and depth 20-30 km.
[2] There are 16 main roads as a supporting road.

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GPS Stations in Nepal

Situated in Jomsom, mid-north part of Nepal at the altitude of 3,300 meters.

 Situated in Simikot, west-north part of Nepal at the altitude of 3,180 meters.

 Situated in Koldada, Palpa central part of Nepal.

Situated in Jomsom, Mt. Nilgiri on the back ground.

Situated in Darchula, west part of Nepal at the altitude of 1,988 meters.

Situated in Ghanteswor, west part of Nepal at the altitude of 2,416 meters.

Situated in Bayana, west-north part of Nepal at the altitude of 3,015 meters.

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Earthquake Season in the Himalayan Front

Earthquake Season in the Himalayan Front
SAN FRANCISCO, Calif.--Scientists have long searched for what triggers earthquakes, even suggesting that tides or weather play a role. Recent research spearheaded by Jean-Philippe Avouac, professor of geology and director of the Tectonics Observatory at the California Institute of Technology, shows that in the Himalayan mountains, at least, there is indeed an earthquake season. It's winter.
For decades, geologists studying earthquakes in the Himalayan range of Nepal had noted that there were far more quakes in the winter than in the summer, but it was difficult to assign a cause. "The seasonal variation in seismicity had been noticed years ago," says Avouac. Now, over a decade of data from GPS receivers and satellite measurements of land-water storage make it possible to connect the monsoon season with the frequency of earthquakes along the Himalaya front. The analysis also provides key insight into the timescale of earthquake nucleation in the region.
Avouac will present the results of the study on December 12 at the annual meeting of the American Geophysical Union (AGU) in San Francisco. They are also available online through the journal Earth and Planetary Science Letters, and will appear in print early next year.
The world's tallest mountain range, the Himalaya continues to rise as plate tectonic activity drives India into Eurasia. The compression from this collision results in intense seismic activity along the front of the range. Stress builds continually along faults in the region, until it is released through earthquakes.
Avouac and two collaborators from France and Nepal--Laurent Bollinger and Sudhir Rajaure--began their earthquake seasonality investigation by analyzing a catalog of around 10,000 earthquakes in the Himalaya. They saw that, at all magnitudes above this detection limit, there were twice as many earthquakes during the winter months--December through February--as during the summer. That is, in winter there are up to 150 earthquakes of magnitude three per month, and in summer, around 75. For magnitude four, the winter average is 16 per month, while in summer the rate falls to eight per month. They ran the numbers through a statistical calculation and ruled out the possibility that the seasonal signal was due merely to chance.
"The signal in the seismicity is real; there is no discussion," Avouac says. "We see this seasonal cycle," he adds. "We didn't know where it came from but it is really strong. We're looking at something that is changing on a yearly basis-the timescale over which stress changes in this region is one year."
Earlier studies suggested that seasonal variations in atmospheric pressure set off earthquakes, and this had been proposed for seasonal seismicity following the 1992 Landers, California, quake.
The scientists turned to satellite measurements of water levels in the region. Using altimetry data from TOPEX/Poseidon, a satellite launched in 1992 by NASA and the French space agency CNES (Centre National d'Etudes Spatiales), they evaluated the water level in major rivers of the Ganges basin to within a few tens of centimeters. They found that the water level over the whole basin begins its four-meter rise at the onset of the monsoon season in mid-May, reaching a maximum in September, followed by a slow decrease until the next monsoon season.
They combined river level measurements with data from NASA's GRACE--Gravity Recovery and Climate Experiment--mission, which studies, among other things, groundwater storage on landmasses. The data revealed a strong signal of seasonal variation of water in the basin. Paired with the altimetry data, these measurements paint a complete picture of the hydrologic cycle in the region.
In the Himalaya, monsoon rains swell the rivers of the Ganges basin, increasing the pressure bearing down on the region. As the rains stop, the river water soaks through the ground and the built-up load eases outward, toward the front of the range. This outward redistribution of stress after the rains end leads to horizontal compression in the mountain range later in the year, triggering the wintertime earthquakes.
The final piece connecting winter earthquake frequency to season, and lending insight into the process by which earthquakes nucleate, lay in GPS data. Installation of GPS instruments across the Himalayan front began in 1994, and now they provide a decade's worth of measurements showing land movement across the region. Instead of looking at vertical motions, which are widely believed to be sensitive to weather and the same forces that cause tides on Earth, the scientists concentrated on horizontal displacements. The lengthy records, analyzed by Pierre Bettinelli during his graduate work at Caltech, show that horizontal motion is continuous in the range front. Stress constantly builds in the region. But just as water levels near their lowest in the adjacent Ganges basin and earthquakes begin their doubletime, horizontal motion reaches its maximum speed.
"We had been staring at [the seasonal signal] for years, and then the satellite data came in and we deployed the GPS network and suddenly it became crystal clear," says Avouac. "It's like something you dream of."
While many scientists have suggested that changing water levels can influence the earthquake cycle, a definitive mechanism had yet to be pinpointed. "There are two main avenues by which people have tried to understand the physics of earthquakes: Earth tides and aftershocks," says Avouac. With the water level data, he could show that the rate at which stress builds along the rangefront, rather than the absolute level of stress, triggers earthquakes.
Although Earth tides induce stress levels similar to what builds up during seasonal water storage, they only vary over a 12-hour period. The Himalayan signal shows that it is more likely that earthquakes are triggered after stress builds for weeks to months, which matches the timescale of seasonal stress variation in that region.
About other earthquake-prone regions Avouac says, "seasonal variation has been reported in other places, but I don't know any other place where it is so strong or where the cause of the signal is so obvious."
Other authors on the paper are Pierre Bettinelli, Mireille Flouzat, and Laurent Bollinger of the Commissariat a l'Énergie Atomique, France; Guillaume Ramillien of the Laboratoire d'Etudes en Géophysique et Océanographie Spatiales, France; and Sudhir Rajaure and Som Sapkota of the National Seismological Centre in Nepal.
Avouac will present details of the group's findings at AGU on Wednesday, December 12, at 2 p.m., Moscone West room 3018, in session T33F: Earthquake geology, active tectonics, and mountain building in south and east Asia.
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Contact: Elisabeth Nadin (626) 395-3631 enadin@caltech.edu
Visit the Caltech Media Relations website at http://pr.caltech.edu/media.

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