The beginning of a mini field school

The beginning of a mini field school

This time I am in Bangladesh collecting magnetotelluric (MT) data. This electromagnetic method can go deep into the ground to help image sediments and faults beneath the surface. It will help us assess earthquake hazard in this densely populated country. Deploying the MT station consists of arranging electrodes in the north-south and east-west directions, 50-100 m apart, and burying magnetometers pointing north, east, and perpendicular. Battling cable-biting rats and foxes, and the ubiquitous interference of power lines, we learned the hard way that buried cable tea gardens are the most successful way to gather quality data.

Now, we are entering a new phase of this trip. We have added more students and professors to our team and will be building a small field school with the deployment. COVID disrupted our plans to build a full field school, but we managed a smaller number of students and used the savings to support the MT deployment. We have 4 American students from 3 universities and 7 Bangladeshi students from 3 different universities. Teaching, we have 3 American professors and 2 Bangladeshi professors from different places. We will be travelling around in 4 vans and currently store our equipment in a small truck.

Samer explains to new students how to deploy an MT site.

On the first day, we took everyone out to deploy the MT site, except for the American students who missed their flights. Half of us are now very experienced in deploying MT, and whole newbies are following us and learning how to do it. Finished by 1pm, we decided to head to Hum-Hum Falls on a nearby anticline hill. After some preparation, we started trekking with a guide. The forest is beautiful and noisy. After crossing a few streams on the bamboo bridge, the trail started to become more vertical as the weather warmed up.

Our group headed to the forest trail to Hum-Hum Falls.

Some of us decided to turn back after realizing it would take another 1.5 hours to reach the falls. We went back and watched late students eat a late lunch. A few others turned around near the top of the anticline when the thunderstorm could be seen approaching. The few remaining people went all the way to the waterfall. All but my first group were caught in a downpour and needed to be cautiously headed back down the mountain. Many people are also infected with leeches.

We met in the conference center of the first hotel for the initial lecture.

The next day, the lecture started. In the morning, I gave an overview of the history and structure of the area and why we are doing MT. Samer then outlines what MT is and what it can do. After lunch, we changed the hotel from the tea paradise to the tea house on the hill and the tea garden. The Tea Museum has bungalows with multiple rooms, nicely promoting the mixing of participants. The pool is also a great place to socialize. There are broader reasons. We ate in tents that were temporarily sheltered, it was almost like eating outside. There is a monkey who wants to know about this land. I share a bungalow with Paul and students Alex and Martin. Since our bungalow has the largest living room, this is where we do the demo. In the late afternoon, one group went out to retrieve an MT station while the rest of us settled down.

My bungalow also doubles as our lecture hall.

Samer explains the MT method to an attentive audience in our living room.

The next day we spent the morning learning more about Samer’s MT method and Paul’s regional geology. After lunch, we divided into 3 groups. Summer led a team to scout and visit geological outcrops far east of us. Oliver leads a team to search for nearby MT sites. I took half the people to one of my GPS sites. After arranging access to the school ladder, we went up to the roof, where the equipment is. I explained the setup and downloaded all the data since Sanju and I were last here. Data telemetry for this site is not working. Next month, Mie will be here to fix it with the parts I brought. In the meantime I can use the site for demos. When we were done, the MT group was done, but we still went to the site simply because it was the prettiest of our deployments, a 1km walk through tea tree covered hills to get to.

Anna, Tomolika, Alex, Liza, Fayima, Mohibul and Shofique are on the roof while the GPS data is downloaded to my laptop.

Lisa climbed down the ladder from the roof, and Tomolica, Alex, and Ana waited for their turn.

After we got back, Shofique, Oliver and I did some scouting around the area. We need a site to deploy with Field School in case other teams can’t find the site. We returned in time for me to cool off in the pool after the hot roof. Another scouting team didn’t return with jackfruit and pineapple until about 9pm. They found a potential location.

Our group walked through the beautiful tea plantation to the MT station.

The site is located on an anticline about 2 hours east. We left early and had breakfast on the way. Paul led the students through the geology with Rashid’s help while they all measured the strike and dip of the formations. As we traverse the anticline, we can see changes in the geometry of the bed, including very steeply sloping beds and deformed bands of gravel. They do a great job and really engage students. After the lunch break, we were ready to deploy in a tea garden in the middle of the anticline until it started to rain.

Tomolika measures strike and dip of formations along the cut.

Deploying electrical equipment in a potential thunderstorm is never a good idea, and we went back instead. In the evening, Paul was able to continue with his next set of lectures. It also rained in the morning, so it became a school day. We start with Samer completing his lecture on the MT method and how it works. Then, using measurements made by pairs of students, Paul walked them through the first steps of the analysis, and I relied on my computer to help some teams. After lunch, Samer, Paul and Oliver leave for the United States. With the long-term (LP) instruments gone, we no longer need a truck to carry around. After they left, Paul’s student, Alex, continued to teach. A full analysis proved too ambitious as we continued, but the students still grasped the gist of structural analysis.

Paul explains how measurements are made and how they can be used to determine the structure of the anticline.

That night we received a call that one of our MT receivers had been stolen. Our group immediately went to the police station to report the case. Then, after sleeping for less than 5 hours, we went back to the police station and went to the scene with them. Whoever did it, he unscrewed the magnetometer cable but snapped the cord holding the lid, so at least we didn’t have any more cables to cut. We found one of the two batteries about 100m south of the line of sight, and further on we found the other battery under the tea tree. They must be too heavy to carry. Still, there is no trace of the expensive receiver. We were suspicious of teens, as adult burglars were sure to take these precious batteries and carry them with ease, saw a teen there the day before. We learned that there were only 3 guards in rotation instead of 4, so there was a gap of hours between day and night guards.

Tea pickers working in a nearby field are doing a cross section of our structure.

After packing up the remaining equipment, we met with local officials and citizens who will mobilize to find our equipment. The guards refused to pay for their time until the consignee was found. After a while, Shofique and I went back to the Tea Museum, and since there was no Bengali language, I could only show some pictures of the receiver. Rashid and the others stayed behind to continue the search. Local police began house-to-house searches. It’s very exciting that everyone out there is motivated to find our stuff. We hope it will appear.

A beautiful and unusual multicolored flower on the side of the road.

In the morning, we were driving to the police station to complete the report, only to learn that the recipient’s nickname, Chinstrap, had been recovered. After picking up the police, we went to the scene. The recipient was left anonymously by the hospital in the early morning. However, when I checked it, the SD card with all the data was missing. The village will continue to look for a recovery SD card. We went back half satisfied.

Masud and Biplab, who were staring at the scene, used to be our recipients.

We lost 1.5 days of field school due to lost receivers. We ended our time in Sremongal where I taught my GPS work and then we went to the Monipuri market for 7-layer tea, a local specialty that layers different densities of tea in a glass , then shop. Tomorrow we drive north to the Sylhet anticline near the city of Sylhet for more geology, lectures and hopefully some final MT stops.

Local Chairman Shofique, Police Rashed, myself and Masud and the recovered MT receiver.