Questions about earthquakes

[Asimovian]

OP here. To clarify, I live in Southern California and have ABSOLUTELY heard earthquakes coming, but I’m talking about hearing it fractions of a second before feeling it. Not enough time for any kind of warning system.

But I (and my wife) have always assumed that what we’re hearing is the shaking of structures ahead of us in the impact area, and not the rumbling of the earth’s movements itself. That’s why I asked if you would hear the same noises standing in the middle of open land with no structures around.

[Chefguy]

@Asimovian

OP here. To clarify, I live in Southern California and have ABSOLUTELY heard earthquakes coming, but I’m talking about hearing it fractions of a second before feeling it. Not enough time for any kind of warning system.

But I (and my wife) have always assumed that what we’re hearing is the shaking of structures ahead of us in the impact area, and not the rumbling of the earth’s movements itself. That’s why I asked if you would hear the same noises standing in the middle of open land with no structures around.

Well, that booming noise I heard was certainly not buildings shaking. It was like a boom and an echo: BOOM…boom. The first time I heard it, I thought it was an explosion. After the building stopped shaking, I went outside to see if there was smoke rising from perhaps a gas explosion.

[Snnipe_70E]

The ranch where I grew up on was in the country about 3 miles from the fault. More than once I have heard an earthquake comming. Sounded like a freight train headed straight at me. And then the earth quake hit. In the 89 Loma Prieta quake I heard it first and then the building I ws in began to shake and kept moving after the roar passed.

[jovan]

@Chefguy

While I hate to disagree with you folks, I can tell you that in some circumstances one can hear it coming. It’s not enough time to take any precautions, however, unless you recognize what you are hearing.

I don’t think there’s any contradiction between what I wrote and your experience. The point is that an earthquake isn’t a single wave event but goes through a number of stages. When you hear a sound before you feel the shaking, you’re not hearing the earthquake coming to you, you’re hearing the effects of early waves that have already gone past you, imperceptibly. There’s no going around the fact that waves travel much, much more slowly in air than in solids like rock and earth.

This article has it nicely covered.

A test of this perception was recently performed in southern California by a team of U.S. Geological Survey personnel headed by David Hill. In a very active segment of the Imperial fault system near the Mexican border, they suspended a microphone several feet in the air and recorded its signals on a tape recorder simultaneously with those from a seismometer buried in the ground.

At night, when it was very still, they recorded three small earthquakes between magnitudes 2.0 and 3.0. An operator at the site reported that he did, indeed, hear the earthquakes before he felt them.

On playing back the data, it was found that the noise recorded by the microphone did coincide with the arrival of the P-wave recorded by the seismometer. (In fact, it actually followed it by a few hundredths of a second, but this was because the sound still had to travel upward from the ground to the microphone.) Strangely, there was no sound recorded when the stronger S-wave arrived a couple of seconds later, but this was probably because the S-wave vibrates more slowly, and its frequency was out of the audio range.

This test was significant because it was the first recording of earthquake sounds that came solely from the earth. Prior to this, existing sound recordings of earthquakes had all been made by happenstance inside buildings, which are the main source of noise during earthquakes. To my knowledge, this is the only documented case to explain the “heard-before- felt” phenomenon which demonstrates something that seismologists have been saying all along, but few people who have been through earthquakes are willing to accept.

[Chefguy]

@jovan

I don’t think there’s any contradiction between what I wrote and your experience. The point is that an earthquake isn’t a single wave event but goes through a number of stages. When you hear a sound before you feel the shaking, you’re not hearing the earthquake coming to you, you’re hearing the effects of early waves that have already gone past you, imperceptibly. There’s no going around the fact that waves travel much, much more slowly in air than in solids like rock and earth.

This article has it nicely covered.

I can get behind that. Still, that booming noise was very odd.

[jovan]

@Chefguy

I can get behind that. Still, that booming noise was very odd.

Before coming to Japan, I used to live in one of the least earthquake-prone areas of the world, on the edge of the Canadian Shield. We were resting on granite, going very very deep. Several of the infrequent earthquakes, I only heard. It sounded a lot like a car or truck crash actually, and twice I actually rushed outside to see what had happened. Since coming here, I’ve felt many earthquakes but I’ve yet to hear one.

I found an article that talks about these earthquake booms.

[Zoe]

In 1968 there was an earthquake that was centered in Illinois, but still felt here in Nashville. I was in college at the time, standing in the hallway in a dorm on the ground floor. I felt nothing. I heard some women scream down the hall, but had no idea why they were screaming. Across the campus in one of the taller dorms, some of the women were knocked out of bed. It’s strange that people felt it in such different ways.

I grew up in part of the New Madrid hot zone in West Tennessee. I can remember some tremors from my childhood. They were frequent enough that the kids took them for granted. The adults didn’t tell us about the big earthquakes from around 1812. They were estimated to have been around 8.9 and caused the Mississippi River to flow backward. That’s how Reelfoot Lake was formed. The Mississippi may be a mile wide at that point. These earthquakes make for some interesting reading.

I saw footage that was being shot when the earthquake in Alaska began. A little girl was playing with a ball on a street or sidewalk. Then suddenly everything was jumbled for quite some time. When the jumbling and shaking stopped, the little girl had disappeared. That was some of the saddest footage I’ve ever seen.

[Chefguy]

@jovan

Before coming to Japan, I used to live in one of the least earthquake-prone areas of the world, on the edge of the Canadian Shield. We were resting on granite, going very very deep. Several of the infrequent earthquakes, I only heard. It sounded a lot like a car or truck crash actually, and twice I actually rushed outside to see what had happened. Since coming here, I’ve felt many earthquakes but I’ve yet to hear one.

I found an article that talks about these earthquake booms.

Interesting reading. We are in close proximity to many active volcanoes here (compared to most of the US, Hawaii excluded), but I don’t believe these booms were associated with them, as there was a definite S-wave rolling afterward.