Earthquake cycle

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A diagram illustrating the interseismic, preseismic, and postseismic periods for a subduction zone earthquake cycle. The over-riding plate bends to accumulate stress during the interseismic period and rebounds back to its previous position to release stress. Earthquake cycle for megathrust earthquake.svg
A diagram illustrating the interseismic, preseismic, and postseismic periods for a subduction zone earthquake cycle. The over-riding plate bends to accumulate stress during the interseismic period and rebounds back to its previous position to release stress.

The earthquake cycle refers to the phenomenon that earthquakes repeatedly occur on the same fault as the result of continual stress accumulation and periodic stress release. [1] [2] Earthquake cycles can occur on a variety of faults including subduction zones and continental faults. [3] [4] Depending on the size of the earthquake, an earthquake cycle can last decades, centuries, or longer. [1] [5] The Parkfield portion of the San Andreas fault is a well-known example where similarly located M6.0 earthquakes have been instrumentally recorded every 30–40 years. [6]

Contents

Theory

After Harry F. Reid proposed the elastic-rebound theory in 1910 based on the surface rupture record from the 1906 San Francisco earthquake, and accumulated geodetic data demonstrated continual stress loading from the plate motion, a theory of the "cyclic" earthquake re-occurrence began to form in the late twentieth century. [1]

Stress accumulation and elastic rebound

Earthquake-cycle theory combines the stress-accumulation hypothesis and elastic-rebound theory. [1] A complete earthquake cycle can be divided into interseismic, preseismic, coseismic and postseismic periods. [1] During the interseismic period, stress accumulates on a locked fault due to plate motion. [2] In the preseismic period, this stress is approaching the rupture limit, and some earthquake precursors may occur. [1] When this stress finally exceeds the rupture limit, the fault will start to move and both sides rebound to their previous positions, releasing their accumulated stress via an earthquake. During the postseismic period, the relaxation of the other parts of the fault caused by redistributed stresses may cause afterslip. [1] Because Earth's plate movement constantly stresses faults, this cycle will likely repeat. [2]

A diagram of the spring-slider model. A block on a rough surface is connected to a spring that is pulled at a constant velocity u. Mass-spring-slider.svg
A diagram of the spring-slider model. A block on a rough surface is connected to a spring that is pulled at a constant velocity u.

Spring-slider model

The simple spring-slider coupling model helps explain the recurrence of earthquake cycles. [1] The premise is that a stationary block in contact with a rough surface is dragged by a spring that is pulled at a constant velocity. This process causes stress to continuously accumulate on the spring. Once the drag force exceeds the static friction limit f(0), the block will slide along the ground surface. [1] [2] Assuming that the kinematic friction is smaller than the static friction, [7] the block's initial movement is unstable, which is equivalent to a fault rupture. Once the block comes to rest at a new location, stress begins to accumulate again. Coupled systems of spring-slider models have successfully reproduced the Gutenberg–Richter law. [7]

Rupture variety

Although simple models of earthquake recurrence are fully predictable, many real-world factors can significantly alter cycle length, including uneven stress accumulation, time-varying crustal strengths, and fluid migration. [2] [8] Under different conditions, stress can be released via rapid ruptures, aseismic slow slips, or earthquake swarms. Understanding the irregularity of these different slip types is crucial to comprehending earthquakes cycles. [8] [9] [10]

Observations

So far, complete earthquake cycles have barely been recorded, and geodetic and geology data become key sources for the analysis of different stages in an earthquake cycle. [1]

Geodetic measurement

Geodetic measurements are important tools to verify the interseismic stage stress accumulation and postseismic stage stress redistribution in earthquake cycles. For example, the GPS data collected in the past few decades has shown steady strain accumulations for the San Andreas fault system [11] and continuous surface uplift of the Nankai subduction zone's overriding plate caused by the stress accumulation. [1] Analysis of the slip rate on the southern San Andreas fault system with the interferometric radar (InSAR) technology also suggests that this fault may be approaching the end of its interseismic stage. [12] A significant amount of aseismic slow slip and creep during the interseismic period has also been discovered on both subduction zones and continental faults through GPS and InSAR measurements. [8]

The Wallace Creek offset across the San Andreas Fault. The present channel offset represents a recent fault rupture. There are multiple abandoned channels on the left of the current channel representing multiple ancient fault ruptures. Wallace Creek offset across the San Andreas Fault.png
The Wallace Creek offset across the San Andreas Fault. The present channel offset represents a recent fault rupture. There are multiple abandoned channels on the left of the current channel representing multiple ancient fault ruptures.

Geologic evidence

Geological surveys are another method used to uncover ancient earthquake reoccurrences. The multiple offsets of the stream channels across the San Andreas fault at Wallace creek on Carrizo Plain is the classic evidence of fault rupture recurrence. [1] [4] Once an earthquake happened, the stream across the fault was cut off, leaving the offset channel abandoned, and a new channel forms. A set of abandoned channels has been discovered and is believed to be the remains of multiple ancient earthquake cycles. [1] The sediment record is another key clue to finding ancient earthquakes. Examples are the coastal-uplift records of Muroto point near the Nankai subduction zone, caused by repeated megathrust earthquakes over many centuries; coastal uplift and tsunami records near the Hikurangi subduction margin, caused by 10 potential subduction earthquakes in the past 7000 years; [3] and sediment accumulation recorded by 24 successive earthquakes on the strike-slip Alpine fault in the past 8000 years. [13] Three repeated continental earthquakes in the Mongolia within the past 50,000 years have also been discovered from sediment-layer offset and growth records. [14]

Dynamic fault modeling

More complicated than the spring-slider model, dynamic modeling of fault ruptures based on the constitutive framework (such as the rate-and-state friction law and elastic equations) is widely used in earthquake-cycle analysis. [10] Dynamic fault modeling allows us to examine the role of different fault parameters in rupture-cycle behavior [10] and reproduces many seismic observations. [8]

Rate-and-state friction law

The rate-and-state friction law is widely applied in dynamic fault models [8] [10] [15] and critically influences a fault's possible slip features. [10] [16] The rate-and-state friction law assumes that the friction coefficient is a function of both the sliding velocity (the rate) and the system conditions (the state). [16] [17] [18] [19] In the rate-and-state friction law, the friction coefficient increases when the slip velocity abruptly increases and then gradually decreases to reach a new steady value. [16] The rate-and-state friction relation is influenced by a set of factors including thermal activation, the real area of contact (at the atomic scale), and molecular bonding effects. [16] [19] [20]

Recent developments

Dynamic fault modeling helps explain the mechanisms driving earthquake cycles. Based on the rate-and-state friction law, the transfer from slow-slip events to rapid rupture earthquakes related to geometric and elastic parameters of the fault zone has been discovered. [10] A computationally faster quasi-dynamic model that simplifies stress transfers allows new models taking plastic effects into consideration. [15] However, comparison of quasi-dynamic models with fully dynamic models of the same systems shows that the modeling approach has significant impacts on the proposed earthquake-cycle slip features. [21]

Earthquake prediction applications

Although many scientists still view earthquake predictions as challenging or impossible, [22] earthquake-cycle theories and modeling have long been consulted to produce hazard forecast values. For example, empirical models have been applied to forecast the likelihood of large earthquakes hitting the San Francisco Bay area in the near future. [23] In addition, scientists have established a fully dynamic model for the Parkfield portion of the San Andreas Fault. This model successfully reproduces complete earthquake cycles that match the last half century's seismic records and shows promise for future earthquake predictions. [5]

Related Research Articles

In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in the same area of the main shock, caused as the displaced crust adjusts to the effects of the main shock. Large earthquakes can have hundreds to thousands of instrumentally detectable aftershocks, which steadily decrease in magnitude and frequency according to a consistent pattern. In some earthquakes the main rupture happens in two or more steps, resulting in multiple main shocks. These are known as doublet earthquakes, and in general can be distinguished from aftershocks in having similar magnitudes and nearly identical seismic waveforms.

<span class="mw-page-title-main">Japan Trench</span> Oceanic trench part of the Pacific Ring of Fire off northeast Japan

The Japan Trench is an oceanic trench part of the Pacific Ring of Fire off northeast Japan. It extends from the Kuril Islands to the northern end of the Izu Islands, and is 8,046 metres (26,398 ft) at its deepest. It links the Kuril–Kamchatka Trench to the north and the Izu–Ogasawara Trench to its south with a length of 800 kilometres (497 mi). This trench is created as the oceanic Pacific plate subducts beneath the continental Okhotsk Plate. The subduction process causes bending of the down going plate, creating a deep trench. Continuing movement on the subduction zone associated with the Japan Trench is one of the main causes of tsunamis and earthquakes in northern Japan, including the megathrust Tōhoku earthquake and resulting tsunami that occurred on 11 March 2011. The rate of subduction associated with the Japan Trench has been recorded at about 7.9–9.2 centimetres (3.1–3.6 in)/yr.

<span class="mw-page-title-main">Cascadia subduction zone</span> Convergent plate boundary that stretches from northern Vancouver Island to Northern California

The Cascadia subduction zone is a 960 km (600 mi) fault at a convergent plate boundary, about 110–160 km (70–100 mi) off the Pacific coast, that stretches from northern Vancouver Island in Canada to Northern California in the United States. It is capable of producing 9.0+ magnitude earthquakes and tsunamis that could reach 30 m (98 ft). The Oregon Department of Emergency Management estimates shaking would last 5–7 minutes along the coast, with strength and intensity decreasing further from the epicenter. It is a very long, sloping subduction zone where the Explorer, Juan de Fuca, and Gorda plates move to the east and slide below the much larger mostly continental North American Plate. The zone varies in width and lies offshore beginning near Cape Mendocino, Northern California, passing through Oregon and Washington, and terminating at about Vancouver Island in British Columbia.

Coulomb stress transfer is a seismic-related geological process of stress changes to surrounding material caused by local discrete deformation events. Using mapped displacements of the Earth's surface during earthquakes, the computed Coulomb stress changes suggest that the stress relieved during an earthquake not only dissipates but can also move up and down fault segments, concentrating and promoting subsequent tremors. Importantly, Coulomb stress changes have been applied to earthquake-forecasting models that have been used to assess potential hazards related to earthquake activity.

<span class="mw-page-title-main">Aseismic creep</span> Surface displacement along a geological fault without earthquakes occurring

In geology, aseismic creep or fault creep is measurable surface displacement along a fault in the absence of notable earthquakes. Aseismic creep may also occur as "after-slip" days to years after an earthquake. Notable examples of aseismic slip include faults in California.

<span class="mw-page-title-main">Calaveras Fault</span> Geological fault in northern California

The Calaveras Fault is a major branch of the San Andreas Fault System that is located in northern California in the San Francisco Bay Area. Activity on the different segments of the fault includes moderate and large earthquakes as well as aseismic creep. The last large event was the magnitude 6.2 1984 Morgan Hill event. The most recent moderate earthquakes were the magnitude 5.1 event on 25 October 2022, and the magnitude 5.6 2007 Alum Rock event.

A slow earthquake is a discontinuous, earthquake-like event that releases energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. First detected using long term strain measurements, most slow earthquakes now appear to be accompanied by fluid flow and related tremor, which can be detected and approximately located using seismometer data filtered appropriately. That is, they are quiet compared to a regular earthquake, but not "silent" as described in the past.

<span class="mw-page-title-main">Queen Charlotte Fault</span> Active transform fault in Canada and Alaska

The Queen Charlotte Fault is an active transform fault that marks the boundary of the North American plate and the Pacific plate. It is Canada's right-lateral strike-slip equivalent to the San Andreas Fault to the south in California. The Queen Charlotte Fault forms a triple junction south with the Cascadia subduction zone and the Explorer Ridge. The Queen Charlotte Fault (QCF) forms a transpressional plate boundary, and is as active as other major transform fault systems in terms of slip rates and seismogenic potential. It sustains the highest known deformation rates among continental or continent-ocean transform systems globally, accommodating greater than 50mm/yr dextral offset. The entire approximately 900 km offshore length has ruptured in seven greater than magnitude 7 events during the last century, making the cumulative historical seismic moment release higher than any other modern transform plate boundary system.

Episodic tremor and slip (ETS) is a seismological phenomenon observed in some subduction zones that is characterized by non-earthquake seismic rumbling, or tremor, and slow slip along the plate interface. Slow slip events are distinguished from earthquakes by their propagation speed and focus. In slow slip events, there is an apparent reversal of crustal motion, although the fault motion remains consistent with the direction of subduction. ETS events themselves are imperceptible to human beings and do not cause damage.

In seismology, a supershear earthquake is an earthquake in which the propagation of the rupture along the fault surface occurs at speeds in excess of the seismic shear wave (S-wave) velocity. This causes an effect analogous to a sonic boom.

<span class="mw-page-title-main">Sunda megathrust</span> Geological feature

The Sunda megathrust is a fault that extends approximately 5,500 km (3300 mi) from Myanmar (Burma) in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia. It is a megathrust, located at a convergent plate boundary where it forms the interface between the overriding Eurasian plate and the subducting Indo-Australian plate. It is one of the most seismogenic structures on Earth, being responsible for many great and giant earthquakes, including the 2004 Indian Ocean earthquake and tsunami that killed over 227,000 people. The Sunda megathrust can be divided into the Andaman Megathrust, Sumatra(n) Megathrust and Java(n) Megathrust. The Bali-Sumbawa segment is much less active and therefore does not have the "megathrust" term associated with it.

The 1935 Sumatra earthquake occurred at 09:35 local time on 28 December. It had a magnitude of Mw 7.7 and a maximum felt intensity of VII (Damaging) on the European macroseismic scale. It triggered a minor tsunami.

Susan Y. Schwartz is a scientist at the University of California, Santa Cruz known for her research on earthquakes, through field projects conducted in locations in Costa Rica and the San Andreas Fault.

<span class="mw-page-title-main">UCERF2</span>

The 2008 Uniform California Earthquake Rupture Forecast, Version 2, or UCERF2, is one of a series of earthquake forecasts prepared for the state California by the Working Group on California Earthquake Probabilities (WGCEP), collaboration of the U.S. Geological Survey, the California Geological Survey, and the Southern California Earthquake Center, with funding from the California Earthquake Authority. UCERF2 was superseded by UCERF3 in 2015.

<span class="mw-page-title-main">Xianshuihe fault system</span> Geological feature in Asia

The Xianshuihe fault system is a major active sinistral (left-lateral) strike-slip fault zone in southwestern China, at the eastern edge of the Tibetan Plateau. It has been responsible for many major earthquakes, and is one of the most seismically active fault zones in this part of China.

An earthquake occurred in southern Mongolia on December 4, 1957, measuring Mw 7.8–8.1 and assigned XII (Extreme) on the Modified Mercalli intensity scale. Surface faulting was observed in the aftermath with peak vertical and horizontal scarp reaching 9 m (30 ft). Because of the extremely sparse population in the area, this event, despite its magnitude, was not catastrophic. However, 30 people died and the towns of Dzun Bogd, Bayan-leg and Baruin Bogd were completely destroyed.

Nadia Lapusta is a Professor of Mechanical Engineering and Geophysics at the California Institute of Technology. She designed the first computational model that could accurately and efficiently simulate sequence of earthquakes and interseismic slow deformation on a planar fault in a single consistent physical framework.

Ruth Harris is a scientist at the United States Geological Survey known for her research on large earthquakes, especially on how they begin, end, and cause the ground to shake. In 2019, Harris was elected a fellow of the American Geophysical Union who cited her "for outstanding contributions to earthquake rupture dynamics, stress transfer, and triggering".

<span class="mw-page-title-main">Oblique subduction</span> Tectonic process

Oblique subduction is a form of subduction for which the convergence direction differs from 90° to the plate boundary. Most convergent boundaries involve oblique subduction, particularly in the Ring of Fire including the Ryukyu, Aleutian, Central America and Chile subduction zones. In general, the obliquity angle is between 15° and 30°. Subduction zones with high obliquity angles include Sunda trench and Ryukyu arc.

The 1843 Nias earthquake off the northern coast of Sumatra, Indonesia caused severe damage when it triggered a tsunami along the coastline. The earthquake with a moment magnitude (Mw ) of 7.8 lasted nine minutes, collapsing many homes in Sumatra and Nias. It was assigned a maximum modified Mercalli intensity of XI (Extreme).

References

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