Le Royaume du Bhoutan est situé dans l’Himalaya oriental. Ce pays souligne son éloignement géographique par un isolement volontairement choisi: seul un nombre réduit d’étrangers est autorisé à visiter le pays sous la direction d’agences de voyages locales. Ces restrictions visent à préserver les traditions et l’originalité culturelle. Elles génèrent un effet secondaire: au Bhoutan, la nature du sous-sol géologique est peu connue, comparativement aux régions voisines.
Le Bhoutan constitue l’une des rares régions inexplorées au sujet desquelles on ne sait pratiquement rien en matière de menace sismique, malgré sa position dans les montagnes de l’Himalaya qui grandissent chaque année de deux à quatre centimètres, en raison de la rencontre de deux plaques continentales. En règle générale, un risque sismique accru pèse sur de telles régions. Un nombre élevé de fortes secousses telluriques ayant ravagé d’importantes régions de l’Himalaya en témoigne. La partie occidentale du Népal ainsi que le Bhoutan ont été épargnés les 120 dernières années, ce qui soulève deux questions: le risque sismique est-il réellement plus faible dans ces régions? La période concernée a-t-elle été exceptionnellement calme?
C’est pour fournir des réponses à ces questions que le Service Sismologique Suisse (SED), en collaboration avec le groupe Sismologie & Géodynamique à l’EPF de Zurich, installera et assurera le suivi d’un réseau sismique temporaire au Bhoutan en 2013. Les données ainsi obtenues aideront à mieux comprendre la nature des tremblements de terre dans cette région. Elles serviront également à en apprendre davantage sur les structures lithosphérques des montagnes de l’Himalaya. Le soutien du Fonds national suisse (FNS) permettra aux sismologues de l’EPF de Zurich de renouer avec une longue tradition de la recherche suisse au Bhoutan. En effet, Augusto Gansser, décédé en 2012, acheva la première cartographie géologique du pays, il y a presque 30 ans de cela.
Le 7 janvier 2013, une équipe de sismologues et de techniciens se rendra au Bhoutan pour y installer 38 sismomètres. Au cours de l’année, d’autres expéditions garantiront que les stations seront entretenues et que le flux de données circulera. Une thèse de doctorat fournira à deux personnes le cadre adéquat qui leur permettra d’exploiter les données ainsi saisies. Par ailleurs, le contact amical établi avec le service géologique du Bhoutan garantira que les connaissances recueillies profiteront directement à ce pays.
Depuis le 7 janvier 2013, une équipe du SED se trouve au Bhoutan afin de d'installer un réseau sismologique temporaire en collaboration avec le groupe Sismologie et Géodynamique de l'EPF de Zürich. Le projet de recherche financé par le Fond National Suisse (FNS) sera mené avec le soutien actif et l'accompagnement de nos collègues bhoutanais, qui pourrons également utiliser les données acquises pour des projets futurs (p. ex. la production d'une carte d'aléa sismique). Nous publions ici chaque jour de courts textes que nous obtenons de nos collègues par SMS ou E-mail à propos de leur travail et de la vie au Bhoutan.
Vous trouverez de plus amples informations sur le projet GANSSER ci-dessous et sur le site web du projet.
After we installed the last station at a newly improvised site near Thimphu, and after repairing the last cables to bring current at another station near Thimphu, all field participants are more relieved. Today, on the last day in Bhutan, they packed away the remaining material in the storage room and spent a few hours free time in the capital before transferring to Paro, a town close to the airport. All of them will depart back to their home tomorrow morning, with a well-done and complete station network installation that, we hope, will run smoothly and safely. Our first maintenance visit is planned for April.
Our expedition will end very soon. In the remaining two days we have to install three more stations. Without the help of our Bhutanese colleagues it would be very difficult. They have their contacts and organize for example in no time an electrician to install an electrical socket. Beside work they find it quite amusing that we still can't handle the amount of chili they add to the food. Only yesterday we both had to cry because of a very spicy chili salad.
After a night in Thimpu we are driving towards South to install stations bhw04, bhw05 and bhw06. Yesterday we installed bhw08 in an outreach center of a hospital. The building is most of the time empty (good for our measurement). It is only used for special events like vaccination programs, health lessons or elections. We had beautiful conditions to install the station including a sunset on snowy mountains.
After driving on hilly roads for three weeks we found ourself on a flat road again. Now we are in Samdrup Jongkan, a town at the Indian border. Here in the Southeast of the East array we plan to build two more stations. The sites we haven investigated back home are a prison and a crematorium. We prefer to install the stations at schools and will first ask there.
At the moment we are having breakfast in Wamrong. With this new energy we will install two more stations today. John and Gayley have to drive back to station bhe05. The station hole was made too big. Nevertheless we are on time and sure to finalize everything in the time being.
Today we fixed some problems at the station near Trashigang, the one we have installed yesterday on a hill. Again the local community was very supportive. Additionally we installed station bhe06 further South. Tomorrow we will head towards the Indian boarder and from there on we will drive northwards.
To day we are very pleased to stay over night in the royal guest house above Damphu. It is located in a remote forest on the top of a hill. We will sleep in the staff guest house with simple rooms apart from beautiful painted wooden walls. We enjoy the quietness and exotic birds flying around. These attitudes make the place to a perfect site for station bhn03. We installed it in an abandoned store house nearby.
To reach the site of station bhe09 we had to drive through estimated 100 switchbacks. As we finally arrived on the top of a small hill we discovered an idyllic town. The farmer families living there were happy to be involved in a scientific project. They assisted in building the station and offered us tea and some snacks. We owed their generous help with a small contribution to the so called "community budget".
Half of the group went back to Trashigang to load instruments and material. The other half installed a new station (bhe14) in Trashiyangtse close to the Chinese boarder. They have to stay over night as the way back would take too long.
After waiting for a long time for keys and an electrician we finally installed two stations in school buildings. One of the directors offered us a really good tea with coffee taste. Now we are heading back to Wangdue.
After preparation and shipping of our instruments during Autumn 2012, project GANSSER finally started its field operations early this year. From their arrival to Bhutan on January 9th, eight seismologists (six from ETH Zürich, one from France and one from the US) work on the installation of 38 broadband seismic sensors across the country until the end of the month. Below György Hetényi gives a half-time summary of the events:
We spent the first few days on acclimatizing to the new time-zone and buying further equipment in town. One of the challenges was to get sand, of which the river bank had not enough but the minimum quantity to purchase was “one truck”, about 20 times more than we needed. At the end, we negotiated at the construction site of the new Supreme Court to get a couple of bags, which we bargained against a few empty but good quality sand bags! The other challenge was to wait the late delivery of 40 car batteries and 30 large plastic barrels from India patiently – at the end the delay was only slight. By the weekend (12-13th), everything was set to start working in the field.
We split into two groups with two vehicles each. The East Team had to install 18 stations. The West Team (20 stations to install) started installations near Thimphu, and then left to the next valley to install the northernmost stations of the array on the next three days (14-16th). Everything went easily and smoothly, people were open to have stations in their house, office or school storage. Our Bhutanese colleagues were very efficient in negotiating the sites, and our drivers did an excellent job and also helped us to construct the sites. We did not encounter problems bigger than no water in a hotel on one morning, or some rough roads late in the evening. The installation is at very good stage, and we look forward to the coming days to see the development of the network.
Instead of the predicted snowy weather we enjoyed a beautiful day continuing our work. The team in charge of the installation of the station in the furthest East of the array (bhe14) were stuck in a muddy road and had to turn. We will try it again tomorrow!
Yesterday on the way back from our stations "bhw08" and "bhw09" our driver suddenly stopped and bowed in the middle of a mountain road. The only thing we saw was a cyclist in sportive cloths passing by. It turned out that this man was the former king. The king and its achievements are highly regarded in Bhutan.
Arrived today in Trashiyangtse in the Northeast of Bhutan. We already installed four stations in Central Bhutan and today two of the total 14 stations in the East. Country and people are very impressive even though life is pretty simple but important things seem be available. Many things work here that one can't find at other places. For example free access to education and public health services and they really care about their environment.
Snow in Thimhu. People of all ages engage in snow ball fights. First snow of the year always is a public holiday. Happens not every year. Luckily shops are open and we can buy cables and wood to install another station today.