For over thirty years, scientific minds have been endeavoring to unravel the enigma behind a specific category of submarine geological fractures that exhibit a remarkably consistent propensity for generating seismic events, outperforming other fault types in predictability.
These seismic occurrences transpire with near clockwork regularity, and their magnitude is consistently uniform.
A recent investigation proposes a potential explanation for this phenomenon.
It has been demonstrated by a collaborative team of researchers from institutions across the United States and Canada that these underwater strike-slip faults, commonly referred to as oceanic transform faults, are enveloped by zones designated as barriers. These areas function as natural decelerators, effectively dampening seismic activity.
The researchers assert that a mechanism termed dilatancy strengthening, which is activated as oceanic water penetrates deeply into the surrounding rock, acts as a stabilizing agent, shielding these fault segments from the destructive forces of major seismic shocks.
By illuminating the intricate workings of these uncharacteristically predictable fault systems, the aspiration is to enhance the accuracy and robustness of seismic hazard models on a broader scale.
“The existence of these barriers has been acknowledged for a considerable duration. However, the persistent question has revolved around their composition and the underlying reasons for their unwavering efficacy in arresting seismic events, cycle after cycle,” explains Jianhua Gong, a seismologist affiliated with Indiana University Bloomington in the United States.
The research team meticulously analyzed data pertaining to two segments of the Gofar transform fault. This extensive subterranean fissure delineates the boundary between the Pacific and Nazca tectonic plates, situated west of Ecuador and deep within the Pacific Ocean.
These tectonic plates are undergoing lateral movement relative to each other at an approximate rate of 140 millimeters (5.5 inches) per annum. Since the commencement of comprehensive record-keeping in 1995, this particular fault has consistently produced a magnitude six earthquake at intervals of approximately five to six years.
In two distinct experimental phases, conducted in 2008 and from 2019 to 2022, ocean-bottom seismometer (OBS) instruments were strategically deployed directly onto the seabed to monitor subterranean movements. These advanced instruments meticulously documented the seismic signatures of tens of thousands of minor tremors in proximity to two major seismic events.
The comprehensive analysis of the gathered data revealed a striking similarity in the seismic behavior of the two segments of the Gofar fault, each characterized by the presence of a barrier zone. Measurements indicated that these barrier zones are, in reality, intricate networks of smaller faults, functioning to absorb the numerous minor seismic disturbances that typically precede larger earthquakes.
During the occurrence of major seismic events, the fluid-saturated rock surrounding these buffer zones undergoes displacement and expansion, leading to an influx of additional water into newly formed voids. This process engenders alterations in pressure, causing the rock to ‘lock’ and impede further slippage, thereby effectively curtailing the escalation of the earthquake’s magnitude.
“These barriers are far from being inert geological features within the landscape,” states Gong.
“They represent active, dynamic components of the fault system, and comprehending their modus operandi fundamentally reshapes our perception of the inherent limitations on seismic activity along these faults.”
Seismologists have observed analogous patterns in oceanic transform faults across the globe. In these instances, earthquakes tend to be less severe than would be anticipated given the prevailing geological stresses and structural configurations.
While the current investigation has focused on a single specific fault, it is plausible that barrier zones akin to those identified along the Gofar fault may be present and exerting influence on other fault systems.
Such a scenario would necessitate the presence of the same type of intricate fracturing and subterranean seawater permeation observed in this study. Future research endeavors could explore this possibility, potentially by employing methodologies such as seafloor drilling, the researchers suggest.
Considering the geographical location of the Gofar fault, there is minimal apprehension regarding the potential for earthquakes originating from this region to inflict damage on populated areas or result in loss of life. Nevertheless, these findings may furnish valuable new perspectives on seismic zones that potentially pose greater risks.
Seismic events originating from most fault types, excluding oceanic transform faults, whether situated underwater or on land, are notoriously unpredictable. However, each advancement in scientific comprehension brings us incrementally closer to discerning the timing and locus of future seismic occurrences.
“The predictable seismic recurrence intervals and localized rupture zones documented through the 2008 and 2020 OBS experiments underscore the critical importance of targeted, multi-year observational campaigns for capturing the intricate details of seismicity associated with major oceanic transform fault earthquakes and for elucidating their underlying mechanisms,” articulate the researchers in their published findings.
“Such empirical observations yield novel insights into the physics of earthquakes and establish robust constraints for the development of numerical models.”
