Mapping the inside of Mt St. Helens
A new array of seismometers, combined with a series of planned explosions, will be used to map the interior of the Mt. St. Helens volcano to a depth of eighty kilometers or fifty miles.
To get the job done, starting next week roughly 65 people will fan out across the mountain to deploy 3,500 small seismometers along roads and back-country trails. They will drill 24 holes some 25 metres deep, drop in industrial explosives used for quarrying, and refill the holes (see ‘Under the dome’). The plan is to detonate the explosives in separate shots over four nights. Each blast will shake the ground as much as a magnitude-2 earthquake.
Results from the active blasts will be combined with the passive seismic part of the experiment, which is already under way: 70 larger seismometers around the mountain are measuring how long waves from natural earthquakes take to travel through the ground. Their data can be used to probe as far as 80 kilometres down, says Vidale.
A new array of seismometers, combined with a series of planned explosions, will be used to map the interior of the Mt. St. Helens volcano to a depth of eighty kilometers or fifty miles.
To get the job done, starting next week roughly 65 people will fan out across the mountain to deploy 3,500 small seismometers along roads and back-country trails. They will drill 24 holes some 25 metres deep, drop in industrial explosives used for quarrying, and refill the holes (see ‘Under the dome’). The plan is to detonate the explosives in separate shots over four nights. Each blast will shake the ground as much as a magnitude-2 earthquake.
Results from the active blasts will be combined with the passive seismic part of the experiment, which is already under way: 70 larger seismometers around the mountain are measuring how long waves from natural earthquakes take to travel through the ground. Their data can be used to probe as far as 80 kilometres down, says Vidale.