Field trip in Bangladesh at the end of Ramadan and Eid al-Fitr

Later this morning, I was celebrating Eid al-Fitr at the Bangladesh Open University (BOU) campus in Bangladesh. Last night Ramadan ended when Muslims fasted during the day. Our group was on the way back from the fields at sunset when Ramadan ended and Eid al-Fitr began. We stopped at a restaurant in Gadspur and had a big plate of biryani. Those in our group who are fasting have not eaten since 3:30 this morning.

Alman quickly breaks his Ramadan with mutton biryani to start Eid al-Fitr.

I am back in Bangladesh again. I’m collecting more electromagnetic data in northeastern Bangladesh using the magnetotelluric (MT) instrument I brought here on my last trip before sending it back to the United States. In addition to the 4 Broadband (BB) instruments we used March, Samer Naif from Georgia Institute of Technology brought 4 Long Term (LP) that can see deeper. This time, we deployed the instruments 3 (BB) to 6 (LP) days at a time. Longer deployments allow for better identification of low-frequency signals that can penetrate deep into Earth. With BB, we expect to see the entire 15-25 km of sediment here. Using LP, we will see 30-40 km from the Moho at the bottom of the crust.

Arman and Biplab used a hole digger to dig a hole for a vertical magnetometer in a recently harvested rice field.

We are conducting this experiment in a tectonically active region of Bangladesh. The same fault that ruptured in the 2004 Sumatra earthquake continued into Bangladesh, but was buried here by thick sediments. We wanted to image faults in sediments, subducting giant thrust faults, and the bending of the crust as the Indian plate subducted beneath the Indo-Myanmar subduction zone. Both are lesser known but influence our assessment of earthquake hazards here.

A local farmer uses kodal to help dig ditches for north-south magnetometers.

Field trips in May, the hottest and wettest month before the onset of the monsoon rains in June, were less than ideal. Neither struggled to make it through the end of Ramadan and the biggest holiday of the year. However, we are limited by the need to return BB MT instruments and the planting season. Since our instruments have to be buried in fields over 100 meters by 100 meters, we are struggling between harvesting the spring rice crops and planting the summer crops.

Masud helps Samer push his two trolleys full of equipment at Dhaka airport.

Our plans in Bangladesh have always had to be flexible, this time from the start. Samer missed his flight from the US as he tried to process travel paperwork and 7 pieces of luggage with LP MT instruments. My student Oliver and I arrived on time on the morning of April 29 to meet three Dhaka University students at the airport, Masud, Arman and Biplab, who were with me on my last trip and are therefore familiar with installing MT instruments . However, instead of a boat, we were in a van driven by our long-term driver and Sumon. We both continued north from the airport to the main BOU campus, where my long-time collaborator Humayun Akhter is now the Vice-Chancellor. BB MT is stored here. We spent our first afternoon retrieving our instruments and settling down at the BOU hotel where we would be staying.

Arman, Biplab, Samer and Oliver are standing next to the folding carts we brought to transport the equipment.

We will deploy these instruments in a 200-kilometer transect from here to the eastern edge of Bangladesh, traversing the subduction zone and the many folds and faults that deform the sediments. We’ll also make a shorter north-south sample strip to capture the deformation sloping north. After installing the instruments, we plan to replace 1-2 instruments per day for most of the month. Since the LP MTs are at each stop longer and have to return to the US when Samer leaves, we will have fewer stops. Our plan to start installing the LP MT immediately was thwarted by Samer’s missed flight.

Samer set up an LP MT instrument to record the data.

The electrodes included in the MT instrument must be placed in each principal direction approximately 50 m from the recorder to measure the electric field. The BB MT has 3 magnetometers which must be buried facing north, east and vertically. Burying the 1 m long coil is the most difficult part of deployment at high temperatures. The LP instrument has a smaller magnetometer that measures all 3 components, but must be carefully oriented in its bore. They are both powered by large car batteries – 1 for LP and 3 for BB.

Two farmers are cutting a ripe paddy field.

In order to install the MT without affecting the crop, we need a place to harvest the rice, at least for the central recorder and magnetometer. With a rough spatial arrangement for my array, we selected promising sites from Google Earth’s field imagery and Chris Small’s processing of satellite data to show vegetation, water, and soil. Unfortunately, during the first part of our deployment, clouds obscured the nearest image, so we kept flying blind.

Group photo of the 6 of us with local farmers and children.

To avoid the heat and adapt to Ramadan, we work early. Observers ate breakfast at 3:30 a.m. before morning prayers and naps. The rest of us had breakfast at 5:30am. Then, we all gathered at 6am, packed our bags, and headed to the field. The morning after arriving, we set off for the target area and scanned the fields along the way. We were lucky on our first try. We spied a promising area from the main road and took the local roads as close as possible. We hiked into the fields and found some recently harvested fields. A local farmer took us to the owners and we are deploying some. We hired another farmer to protect the instruments.

A marketplace that sells familiar and unfamiliar local products.

We finished our first stop just in time for Masood and I to pick up Summer at the airport. We were able to install an LP MT in the afternoon as he went through customs quickly. For that site, we tried a field we discovered on our way to the previous site with similar success. The first afternoon, the temperature was 94°, but the humidity made it feel like 110°. Despite the problems and the heat, it was the first day of the field trip.

Samer measures the distance with a laser rangefinder, while Oliver locates one of the electrodes by looking at the direction with a hand-held compass.

The next day also went well. One was because there were wires nearby, the first try wasn’t great, but the second time we found a good spot. In the middle of a large field is a harvested field. We can put the recorder, battery, and magnetometer there, while the electrodes extend into the still-ripening rice around it. For the second stop, we followed local roads and tried a barely passable road as much as possible. We walked far enough into open fields. Finally, we successfully added two LP sites.

After completing another MT site, Masud distributed sweets to local children.

Our third day, the last day of Ramadan, started off well. In our target area, we drove along the only local road big enough for our van. It didn’t go where I hoped, but it did take us to a nice place after about a 2km drive. Then our luck ran out. For the second site, we found a possible field, but the farmer did not give permission. Summer and Allman go to fix a cable that has been bitten by an animal, while the rest of us keep searching. After four more tries, we gave up. The area is so densely populated that a few potential locations have high-voltage power lines. We decided to build an additional location further east and scout there. Samer and Arman solved the problem, and they found another site. We met and drove back, quickly breaking Ramadan along the way. Scouting means we should be able to install both sites tomorrow, not the holiday we expected.