Earthquakes are natural disasters that can cause significant damage and loss of life. Scientists have made great strides in understanding and predicting earthquakes, but there are still many aspects that remain a mystery. One such mystery is the distinction between slow and fast earthquakes and how their magnitudes change over time. In this article, we will delve into the research conducted by the University of Tokyo and Stanford University, which sheds light on this topic and provides new insights into these phenomena.
Traditionally, earthquakes are known to last only a few minutes and generate strong seismic waves. However, around 23 years ago, scientists stumbled upon a unique type of earthquake called slow earthquakes. These earthquakes have an extended duration, lasting days or even months, and involve significant tectonic movement. Interestingly, slow earthquakes are often not felt by humans, making their detection and study challenging.
While slow earthquakes may seem less impactful, they could serve as indicators of future fast earthquakes. Monitoring and understanding slow earthquakes can provide crucial insights into the likelihood and severity of potential devastating earthquakes and tsunamis. Therefore, studying these phenomena becomes essential for accurate earthquake forecasting.
To understand slow and fast earthquakes, researchers rely on scaling laws, which establish relationships between different quantities over a wide interval. In 2007, a controversial scaling law relating the magnitude and duration of earthquakes was proposed. According to this law, for slow earthquakes, as the magnitude increases, the duration of the earthquake also increases proportionately. On the other hand, for fast earthquakes, the relationship is cubically proportionate, resulting in rapid increases in seismic moment within a short time.
The 2007 scaling law faced criticism from other researchers, casting doubts on its validity. Concerns were raised about the likelihood of events that do not fall within the law, indicating a gap between slow and fast earthquakes. Seismologists Satoshi Ide and Gregory Beroza conducted extensive research to address these criticisms and strengthen the scaling law.
Ide and Beroza found that previous challenges to the law had improper data calculations and were inconsistent given their data constraints. With new seismic detection technology and 16 years’ worth of data, they reinterpreted the scaling relation and provided evidence to support the law. Furthermore, they proposed the presence of a speed limit for slow earthquakes and revealed physical processes that differentiate slow and fast earthquakes.
Slow earthquakes exhibit a more diverse range of phenomena compared to fast earthquakes. They are known by various names such as low-frequency earthquakes, tectonic tremors, very low-frequency earthquakes, and slow slip events. In the past, researchers observing one type of slow earthquake often disregarded other types as irrelevant. However, Ide and Beroza’s study confirmed that all these phenomena are interconnected and should be regarded as a single phenomenon that manifests itself through various signals.
Detecting and monitoring slow earthquakes pose significant challenges due to their subtle nature and limited accessibility. The detection bias often leads to the observation of only large enough slow earthquakes, while smaller or more elusive events go unnoticed. To address this issue, Ide and Beroza proposed an upper limit to the speed of slow earthquakes, aiding in their accurate detection. This establishment of an upper limit contributed to the redefinition of the scaling law and resolved the debate surrounding it.
Previously, researchers were uncertain about the factors that distinguished slow and fast earthquakes. With the accumulation of more data and the development of theoretical models, Ide and Beroza were able to determine that the scaling differences between the two earthquake types are linked to the physical movement processes governing these events. Slow earthquakes are governed by diffusion processes, while fast earthquakes are dictated by seismic wave propagation. This distinction explains why the magnitude of slow earthquakes cannot reach the same levels as fast earthquakes, especially when the event lasts longer.
Despite the advancements made in understanding slow earthquakes, experts are still uncertain about the forecast information that can be derived from monitoring these events. However, the research conducted by Ide and Beroza serves as a foundation for building appropriate numerical models, making predictions, and implementing effective countermeasures. The insights gained from this study will undoubtedly contribute to improving our understanding of earthquakes and enhancing our ability to mitigate their devastating consequences.
The research conducted by the University of Tokyo and Stanford University provides valuable insights into the distinct characteristics of slow and fast earthquakes and how their magnitudes vary over time. By bolstering the scaling law and addressing previous criticisms, the study contributes to our understanding of these phenomena and their implications for earthquake forecasting. With ongoing research and technological advancements, we are gradually unraveling the mysteries of earthquakes and inching closer to a safer future.