Cascading Rupture Research Articles

Historical seismicity and dynamic rupture process of the 2011 Tohoku-Oki earthquake

A number of studies have documented the complex rupture process of the M w 9.0 March 11, 2011 Tohoku-Oki earthquake, which is characterized by different stages of rupture, including a large delayed slip near the trench and multiple high-frequency ruptures along the down-dip edge of the seismogenic zone. In this study, a multiscale circular patch model was used to represent the spatial heterogeneity of fracture energy inferred on the plate interface, with spontaneous dynamic rupture simulated by solving the elasto-dynamic equation with a slip-weakening friction law. Historical seismicity, recorded over the past 100 years, was used to determine the spatial heterogeneity of seismic events, with an additional large patch used to model large slip movements near the trench. Dynamic rupture processes qualitatively consistent with observations were successfully modeled during this study, although slight adjustments, including the introduction of foreshock-related stress concentrations, were needed to accomplish this. The delayed failure of the shallow largest patch, representing the main rupture stage, was only achieved by a dynamic nucleation process comprising cascading ruptures within small and moderately sized patches near the down-dip edge of the seismogenic zone; this failure was followed by successive ruptures along the down-dip edge of the zone. This study confirms that a free surface significantly increases fault slip and released seismic moment during an earthquake. In addition, we found that the largest patch occupies the area where the b-value of the Gutenberg–Richter magnitude–frequency relationship is much smaller than 1, while the hypocenter corresponds to a local maximum b-value of about 1.5. This research also suggests that seismicity catalogs can be used to constrain the spatial segmentation of plate boundaries and to propose possible scenarios for the dynamic rupture processes of future earthquakes. ► Historical seismicity data are used to model plate interface heterogeneity. ► Simple model explains complex rupture processes during the Tohoku-Oki earthquake. ► Cascading ruptures of smaller patches work as a dynamic nucleation process.

Paleoseismic analysis of the San Vicente segment of the El Salvador Fault Zone, El Salvador, Central America

The El Salvador earthquake of February 13th 2001 (Mw 6.6) was associated with the tectonic rupture of the El Salvador Fault Zone. Paleoseismic studies of the El Salvador Fault Zone undertaken after this earthquake provide a basis for examining the longer history of surface rupturing earthquakes on the fault. Trenching at five sites along the San Vicente segment, a 21km-long and up to 2km-wide central section of the El Salvador Fault Zone, shows that surface fault rupture has occurred at least seven times during the past 8ka. Single-event displacements identified at each trench vary from several decimetres to at least 3.7m. Fault trace mapping, geomorphic analysis, and paleoseismic studies indicate a maximum magnitude for the El Salvador Fault Zone is c. Mw 7.6, with a recurrence interval of around 800yr. Earthquakes of Mw 6.6 or smaller, such as the February 2001 event are unlikely to be identified in the paleoseismic trenches, so our observations represent the minimum number of moderate to large earthquakes that have occurred on this part of the El Salvador Fault Zone. We observe significant variability in single-event displacement in the trenches, which we interpret as possible cascade rupture of several segments of the El Salvador Fault Zone. Combining displacements of river courses and the timing of events revealed in the trenches, we calculate a slip rate of c. 4mm/yr for El Salvador Fault Zone, identifying the fault zone as a major tectonic feature of the region, and a major source of seismic hazard and risk in El Salvador.

Conceptual multi-scale dynamic rupture model for the 2011 off the Pacific coast of Tohoku Earthquake

We present conceptual dynamic rupture models for the 2011 Tohoku Earthquake based on multi-scale heterogeneity in fracture energy. Regardless of frequently-occurring M 7.5 events in this area, it is significant that a large-scale fault heterogeneity corresponding to a M 9 event had not been clearly recognized until this earthquake. We show that the largest heterogeneity having a high fracture energy is consistent with the relatively slow rupture propagation of the Tohoku Earthquake. The large gap in fracture energy explains the separation of two groups of waves clearly visible in observed ground motions. Our simulations favour a cascading rupture that begins from a medium heterogeneity and then progresses over larger scale heterogeneity.

Surface Rupture of the 2008 Wenchuan, China, Earthquake in the Qingping Stepover Determined from Geomorphologic Surveying and Excavation, and Its Tectonic Implications

The Wenchuan Mw 7.9 earthquake of 12 May 2008 caused the rupture of the Longmen Shan thrust belt, which bounds the eastern margin of the Tibetan plateau, and generated a very complex surface rupture. The Beichuan-Yingxiu fault (BYF )w as themainseismogenicfaultandformedtwodistinctivelydifferentsurfacerupturezones separated by the Qingping and Gaochuan stepovers. Real-time kinematic (RTK) sur- veying of alluvial terrace sequences indicates that terraces T1-T3 and river floodplain T0 have the same vertical displacement associated with the Wenchuan earthquake. Trench excavation and optical stimulated luminescence (OSL) dating of alluvial depos- its indicate that only the deformation of the Wenchuan earthquake was recorded in the Qingping stepover since at least ∼20 ka. Other deformations since ∼20 ka probably occurred in other places or did not reach the surface. This can be meaningful to analyze the completeness of paleoearthquakes in trench excavation on thrust faults. The width of the Qingping stepover is ∼1 km and it is not strong enough to form a barrier to arrest the propagation of rupture in the 2008 Wenchuan earthquake. The Gaochuan stepover is ∼7 km wide and it is a barrier to separate the two surface rupture zones associated with the Wenchuan earthquake along the BYF. The empirical rela- tionship of rupture displacement and stepover dimensions on strike-slip faults is prob- ably suitable for the large thrust fault zone with a strike-slip component. This may be beneficial to the study of cascade rupture sections and seismic hazard assessment on large thrust faults.

Development of multiscale slip inversion method and its application to the 2004 mid‐Niigata Prefecture earthquake

We present a multiscale slip inversion method for earthquakes as a first attempt to analyze an initial rupture process on a small scale and a whole one on a large scale. A multiscale source model is constructed by renormalizing slip rate distributions on different scales. A multiscale observation equation includes a renormalized kernel matrix. Using the new method and employing theoretical and empirical Green's functions with two small events (Mw 2.3 and 3.3), we analyze the 2004 mid‐Niigata Prefecture earthquake (Mw 6.6). Following a preliminary deconvolution analysis suggesting a complexity of the initial phase, the multiscale analysis reveals details of the initial stage of the rupture process (the first 1 s) successfully. In the multiscale model, the estimated source process is consistent for all scales, while independent slip inversion analyses on three scales (monoscale analysis) result in inconsistent slip distributions with large errors. The maximum slip rate is about 1.0 m/s and the rupture velocity is 2.5–3.0 km/s in the initial rupture process. Four stages of rupture growth with different rupture directivities are found: the first 0.4 s with northeastward directivity; from 0.6 s to 1.0 s with southward directivity; until 2.0 s with northeastward directivity again; and after 2.0 s with southwestward directivity. These stages may represent cascading ruptures, evolving into a large earthquake. The image of the whole rupture process implies self‐similarity of the dynamic rupture process and is a breakthrough in the complete realization of earthquake source scaling.

Paleoearthquake rupture behavior and recurrence of great earthquakes along the Haiyuan fault, northwestern China

The Haiyuan fault is a major seismogenic fault in north-central China where the 1920 Haiyuan earthquake of magnitude 8.5 occurred, resulting in more than 220000 deaths. The fault zone can be divided into three segments based on their geometric patterns and associated geomorphology. To study paleoseismology and recurrent history of devastating earthquakes along the fault, we dug 17 trenches along different segments of the fault zone. Although only 10 of them allow the paleoearthquake event to be dated, together with the 8 trenches dug previously they still provide adequate information that enables us to capture major paleoearthquakes occurring along the fault during the past geological time. We discovered 3 events along the eastern segment during the past 14000 a, 7 events along the middle segment during the past 9000 a, and 6 events along the western segment during the past 10000 a. These events clearly depict two temporal clusters. The first cluster occurs from 4600 to 6400 a, and the second occurs from 1000 to 2800 a, approximately. Each cluster lasts about 2000 a. Time period between these two clusters is also about 2000 a. Based on fault geometry, segmentation pattern, and paleoearthquake events along the Haiyuan fault we can identify three scales of earthquake rupture: rupture of one segment, cascade rupture of two segments, and cascade rupture of entire fault (three segments). Interactions of slip patches on the surface of the fault may cause rupture on one patch or ruptures of more than two to three patchs to form the complex patterns of cascade rupture events.

Fault interactions and large complex earthquakes in the Los Angeles area.

Faults in complex tectonic environments interact in various ways, including triggered rupture of one fault by another, that may increase seismic hazard in the surrounding region. We model static and dynamic fault interactions between the strike-slip and thrust fault systems in southern California. We find that rupture of the Sierra Madre-Cucamonga thrust fault system is unlikely to trigger rupture of the San Andreas or San Jacinto strike-slip faults. However, a large northern San Jacinto fault earthquake could trigger a cascading rupture of the Sierra Madre-Cucamonga system, potentially causing a moment magnitude 7.5 to 7.8 earthquake on the edge of the Los Angeles metropolitan region.

Earthquake behavior of variable rupture-scale on active faults and application of the cascade-rupturing model

This study reveals preliminarily the earthquake behavior of variable rupture-scale on active faults of the Chinese mainland, that is that on an individual fault portion earthquake’s rupture-scale varies cycle to cycle, and hence earthquake’s strength changes with time. The tendency of this variation has no necessity. On defining relative size of rupture scales, a statistical result shows that it is of the lowest probability that ruptures with the same scale occur in two successive cycles. While the rupture’s scale in the preceding cycle is “small”, the probability of the following rupture’s scale being "large" is as many as 0.48. While the rupture’s scale in the preceding cycle is "middle", the probability of the succeeding rupture being "small" or "large" scale is 0.69 or 0.25. While the rupture’s scale in the preceding cycle is "large", the probability must be zero for the following rupture with "large" scale, and is 0.36 or 0.64 for the following rupture with "small" or "middle" scale. The author introduces and improves the cascade-rupturing model, and uses it to describe the variability and complexity of rupture scale on individual fault portions. Basic features of some active strike-slip faults on which cascade ruptures have occurred are summarized. Basing on these features the author proposes principles of cascade-rupture segmentation for this type of faults. As an example to application, the author segments one portion of the Anninghe fault zone, western Sichuan, for its future cascade rupture, and further assesses the probable strength and its corresponding probability of the coming earthquake.