Infrasonic Sound

The term "infrasonic" applied to sound refers to sound waves below the frequencies of audible sound, and nominally includes anything under 20 Hz.

“次声”一词用于描述低于可听声频率的声波，通常指低于20赫兹的声波。

Sources of infrasound in nature include volcanoes, avalanches, earthquakes and meteorites. The eruption of the Fuego volcano in Guatamala produced infrasonic sound in excess of 120 decibels in the range below 10Hz. Measurements on Mt Erebus, an active volcano in Antarctica, found very strong ultrasonic sounds while the audible sounds were unremarkable. Sound monitors on the Sakurajima volcano of Japan measured sharp signals just before an eruption. Ocean storms and waves generate a lot of infrasound. Early studies of infrasound of hurricanes offer some hope of deciphering the infrasound signature of an approaching hurricane.

自然界中的次声源包括火山、雪崩、地震和陨石。危地马拉的Fuego火山爆发产生了超过120分贝的次声波，频率低于10Hz。对南极洲的活跃火山埃雷布斯山的测量发现，当可听声不显著时，次声波非常强烈。日本的 Sakurajima 火山声监测器在喷发前测到了尖锐的信号。海洋风暴和波浪会产生大量次声波。早期对飓风次声波的研究提供了一些希望，或许能解读即将来临的飓风的次声波特征。

Monitoring of infrasound seems to be one of the best ways for detecting atmospheric nuclear tests. As of 2004 there were 24 such monitoring stations out of a projected total of 60. While no nuclear tests have been detected, in 2003 10 stations in the U.S. and Canada monitored the explosion of the space shuttle Columbia. A station in Fairbanks, Alaska detected the explosion of dynamite five miles from the detector.

对次声波的监测似乎是对大气核试验进行探测的最佳方法之一。截至2004年，已有24个这样的监测站，预计总共有60个。虽然尚未检测到任何核试验，但2003年，美国和加拿大有10个监测站监测到了航天飞机“哥伦比亚号”的爆炸。阿拉斯加州费尔班克斯的一个监测站检测到了距离探测器五英里处的炸药爆炸。

Infrasound detectors are used in Teton Pass, Wyoming to detect the frequent avalanches and send warning signals.

在怀俄明州的Teton Pass，使用次声波探测器来监测频繁的雪崩并发送警报信号。

A number of animals produce and use sounds in the infrasonic range. The rumbling vocalizations of elephants were measured to have frequencies as low as 14 Hz which were detectable at a range of 10 km. Observations of elephant behavior suggests that they responded to the waves through the ground before they heard them in the air - plausible since the waves would travel faster in the solid material. Whales and rhinos produce some very low frequency sounds. The flightless cassowary birds of Papua New Guinea and Australia emit low frequency calls around 23 Hz.

Auroral phenomena generate infrasound by the expansion of air accompanying the electrical discharges.

极光现象通过空气膨胀伴随的电 discharge 产生次声波。

许多动物会产生并利用次声波范围内的声音。大象的低鸣叫声被测量出频率可低至14 Hz，这种声音在10公里范围内是可以被检测到的。观察到大象的行为表明，它们通过地面传播的波先作出反应，而不是先听到空气中的声音——这在逻辑上是合理的，因为波在固体中传播得更快。鲸鱼和犀牛也会发出一些非常低频的声音。在巴布亚新几内亚和澳大利亚的不会飞的 cassowary 鸟类会发出约23 Hz的低频叫声。