Subduction. Todd Shimoda
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ridge, they cool and thicken [give specifics here].
The denser plate edge [explain why denser or obvious?] begins to slowly sink, pulling the rest of the plate along with it. When the thickened plate edge collides against the edge of another plate—either a continental plate or an oceanic plate—the subducted plate dives toward the mantle.
[give specific examples near m-j]
Regardless of the causative force, the island of Marui-jima was born of subduction and will ultimately die because of it. This article chronicles the life and death of the island as a case study in subduction. Marui-jima is not the only island one could study, indeed, there are many. Each case is unique, as no two snowflakes are exact copies [better word?], yet by studying this one island, the mysteries of the process of subduction, in particular, the forces that cause earthquakes, may be illuminated.
And when those mysteries have been solved, the matter of earthquake prediction would be at least one step closer to a precise science.
[further explain the difficulties of prediction]
I thought I grasped Aki’s key point: because every site of seismic activity is unique and the change to those sites is constant, the movement of plates is difficult to predict. Many variables contributed to plate movement, measuring them accurately and in real time was the key to prediction. The problem was determining which variables were the most important because they varied from site to site, from time to time. As Aki had noted before, it was a lot like diagnosing an illness, there are many variables to consider, some are relevant, some are not.
makes sense
until I think
Aki was talking again, showing me a program that he opened on his computer. “This is my earthquake warning system I’m also working on.” From what I grasped, the system was based on observations that the energy from an earthquake came in two wave forms: primary waves and secondary waves. The primary waves were faster but not as damaging as the secondary waves, which did the most damage. The secondary waves followed the primary waves by a few seconds.
The ground acceleration monitors he was installing around the island detected the primary waves and sent out a warning before the secondary waves hit. “Those seconds could make a difference between life and death. The warning system could be a public siren and also individual devices like one of these.” He handed me a vibrating pager, then clicked a button on the screen labeled “test.” The pager vibrated almost painfully in my hand.
“Interesting,” I said. “Is your system up and running?”
“Not yet. I have to install a few more accelerometers. I’m trying to see if there is a direction and location effect. I also need to calibrate the system to filter out background noise. If you can wait a few minutes I can show you one of the monitors.”
While I waited, I looked at photos tacked to the wall of locations around the island. I assume they were locations of his monitors. Amid the photos was a poster of the Japanese Omori seismic scale.
Aki and I walked up a narrow path lined with volcanic rock between two houses. A clearing emerged behind the homes, higher in elevation than the roofs of the homes. In the clearing, Aki brushed away leaves covering a metal box attached to a table-sized rock.
He opened latches and took off the top. Inside was a slender, weighted disk attached to a metal bar between two metal plates. “This is an accelerometer,” Aki told me. “When the ground moves, it creates an electrical signal and sends it back to the computer in the workshop.” At one end of the mechanism was a tiny computer that turned any motion of the weight into electric signals. At the other end of the mechanism was a data relay. Wires ran from it to an antenna.
Aki checked the connections, and ran a test to make sure it was working and the batteries were charged. “This one is set to go,” he said.
“How many others are there?”
“I’m putting in eight around the island. I know it’s probably overkill, but we always want more data, don’t we?”
“Absolutely.” Like a simple white blood cell count from a knee-surgery patient.
As we climbed down the path, I saw a slab of volcanic rock the size of a compact car had rolled into one of the homes and collapsed most of the back wall. Peering inside the ruined home, I could see that the floor and walls were blackened mush from water damage and rot.
A scrawny cat stared at us from the shadows. The scene reminded me of last night with Mari. After I ran out of the house chasing the voyeur, or whoever it was, I came back and she looked at me like I was mentally defective. I couldn’t blame her. “Must have been a ghost,” I said to her. “Must have,” she said. We sat in that old big house, not saying much of anything, until the candles burned out and ended our evening.
As if he could read my mind, Aki asked, “How are you getting along with Mari?”
“We’ve talked a couple of times,” I said. “That’s about it. We seem to get along fine.”
Aki didn’t say anything except for a terse, “Good.”
I didn’t tell him I spent the evening in the house with Mari, nor did I tell him about the person I saw in the darkness. Of course, it had to be Aki—I couldn’t imagine any of the islanders creeping out at night, moving nimbly around the house, and disappearing quickly into the darkness. So if it was Aki, then what was he up to? Maybe he didn’t know I was going to be there and was trying to snuggle up to Mari for the night. Or maybe he did just want a friendly peeping session.
I didn’t tell Aki I hadn’t see any of her demons. But I was beginning to think Aki Ishikawa had some.
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