Could a Large LIGO Detect Smaller Gravitational Events Like Earthquakes or Tiny Explosions?

The Laser Interferometer Gravitational-Wave Observatory (LIGO) is an incredible instrument designed to detect gravitational waves from events like merging black holes. But can it pick up smaller events such as earthquakes or even tiny explosions? Let's explore this fascinating question.

What Would Be the Point?

At first glance, it seems unlikely that LIGO would be able to detect smaller gravitational events like earthquakes or tiny explosions. LIGO is specifically designed to measure the incredibly subtle perturbations caused by large, cataclysmic events such as the merger of black holes. However, it has been used to detect large earthquakes, even those occurring many kilometers away from the detectors, due to the overwhelming ground movement.

There is speculation that LIGO might detect particles that only emerge from supernovae or their gravitationally frozen relics. These particles might correspond to ultra-soft X-rays that interact with matter only through gravitational forces. However, this is a topic of much theoretical exploration and is not proven technology.

LIGO and Earthquakes

One of the ways LIGO monitors seismic activity is by getting knocked out of its optical lock due to the disruption caused by large, slow movements of the ground. Even distant earthquakes can interfere with the delicate space-time measurements LIGO aims to make. The observatory is equipped with numerous seismometers to help filter out spurious signals from smaller seismic events that don't overwhelm the system's defenses. However, LIGO is many orders of magnitude less sensitive to the actual gravity signal from terrestrial disturbances compared to seismic vibrations.

Energy Release and Gravitational Waves

The energy released by a 9 Richter earthquake is on the order of (8 times 10^{17} text{ Joules}). The most powerful earthquake ever recorded, the 1960 Great Chilean earthquake, released an estimated (10^{19} text{ Joules}) of energy. In contrast, the energy released by the merging of two black holes, which resulted in 3 solar masses of gravitational radiation, is approximately (5 times 10^{47} text{ Joules}).

This is a staggering difference of about 28 orders of magnitude. While the gravitational waves from the merging black holes traveled for 1.3 billion years and weakened over distance, the energy from earthquakes is localized within a few kilometers of the detectors.

Gravitational Radiation from Seismic Sources

Research has been conducted to study the gravitational radiation from seismic sources, such as the 1964 Alaska earthquake, which was a 9.2 Richter-scale event. The results from this study, based on the weak-field approximation of general relativity, showed that earthquakes cannot be considered as a source of gravitational radiation. The magnitude of gravitational radiation from seismic events is 12 orders of magnitude below the smallest observable.

The study also noted that detectors like VIRGO have higher sensitivities at lower frequencies, making them more likely candidates for detecting the aforementioned effects. The mass redistribution from an earthquake may have an effect, but it was inconclusive in the research.

While LIGO is not designed to detect small gravitational events like earthquakes, the study of gravitational waves continues to expand our understanding of the universe. The potential to detect subtle radiation from supernova remnants or other astrophysical events remains a subject of theoretical and experimental interest.

In conclusion, despite its capability to detect large-scale gravitational events, LIGO is not sensitive enough to detect the gravitational waves from smaller events such as earthquakes or tiny explosions. However, ongoing research and technological advancements may open new possibilities in the future.