Public Release: 

Earthquakes, landslides, and tsunamis, plus other new Geology Online postings

Geology articles posted online ahead of print Dec. 19, 2014 and Jan. 5, 2015

Geological Society of America

Boulder, Colo., USA - Two papers in the latest online postings for Geology cover the 12 May 2008 Wenchuan, China, earthquake. One, an open access article, reports the work of the Wenchuan Earthquake Fault Scientific Drilling Project. The second discusses earthquake-triggered landslides and the impact of the Mw 7.9 earthquake on river catchments in the Longmen Shan. This study concludes that the "earthquake memory" of rivers is longest where landsliding is highest and where rainfall is the least intense.

FEATURED ARTICLES

Controls on fluvial evacuation of sediment from earthquake-triggered landslides

Jin Wang et al., Chinese Academy of Sciences, Beijing, China. Published online ahead of print on 5 Jan. 2015; http://dx.doi.org/10.1130/G36157.1.

Earthquakes can cause huge devastation in mountains by triggering landslides. But what happens when the shaking stops? In the months to years following large earthquakes, rocks and sediment moved by earthquake-triggered landslides still cause serious issues, filling rivers and causing flooding during rainfall. The sediment can also affect water resources and hydro-electric power generation. Loose sediment can also cause more damage if new landslides occur. Despite this, the lifespan over which landslide-produced sediment stays in mountain river catchments following large earthquakes is poorly understood. Here we examine the impact of the 2008 Wenchuan earthquake (Mw 7.9) on the river catchments of the Longmen Shan mountains. We find that the concentrations of mud and sand in rivers of the landslide-impacted areas were three to seven times higher than before the earthquake. Our calculations show that it would take decades to centuries for rivers to remove all of this fine sediment. Our results demonstrate for the first time that the memory of rivers to the earthquake is longest where the area of landsliding is high, and where the climate results in lower-intensity rainfall and river flows that are less efficient at removing the excess sediment.

Long-term temperature records following the Mw 7.9 Wenchuan (China) earthquake are consistent with low friction

Haibing Li et al., Chinese Academy of Geological Sciences, Beijing, China. Posted online ahead of print on 5 Jan. 2015; http://dx.doi.org/G35515.1. OPEN ACCESS.

The magnitude of the shear stress along a fault during an earthquake is unknown and is central to understanding the dynamics of faulting. Laboratory experiments measure friction between sliding rocks, but extrapolating to earthquakes is extremely challenging. One of the only ways to determine the shear stress in nature is to drill rapidly into a fault after a major earthquake and record the residual heat from energy dissipated during slip. Previous observations of fault temperature in Taiwan and Japan each lasted less than a year and showed that the shear stress was lower than expected. Here we report four years of borehole temperature measurements made by the Wenchuan Earthquake Fault Scientific Drilling project within the fault zone that ruptured during the catastrophic 12 May 2008 Mw 7.9 Sichuan, China, earthquake. We find that all of the recorded temperature anomalies in this fault zone failed to decay as expected for frictional transients. We conclude that the total heat generated at this location during the earthquake was much less than 29 MJ/m2. The mounting evidence from rapid response drilling after earthquakes is that faults have little shear resistance when they are slipping quickly.

Other recently posted GEOLOGY articles (see below) cover such topics as

1. The impact on Stone Age humans of the giant Storegga tsunami that occurred about 8,150 years ago and flooded margins of the North Sea and the Norwegian Sea;

2. The effect of mineralogic composition and the formation of a very large slip on the shallow portion of the subduction interface during the 2011 Tohoku-oki earthquake (Mw 9.0), which caused a huge tsunami along the northeast coast of Honshu, Japan; and

3. A new contribution to the continued, sometimes controversial, discussion of what happens to a coastline during a hurricane.

GEOLOGY articles published online ahead of print can be accessed online at http://geology.gsapubs.org/content/early/recent. All abstracts are open-access at http://geology.gsapubs.org/; representatives of the media may obtain complimentary articles by contacting Kea Giles at the address above.

Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Contact Kea Giles for additional information or assistance.

Non-media requests for articles may be directed to GSA Sales and Service, gsaservice@geosociety.org.

Moss growth patterns and timing of human exposure to a Mesolithic tsunami in the North Atlantic

Knut Rydgren and Stein Bondevik, Sogn og Fjordane University College, Sogndal, Norway. Published online ahead of print on 19 Dec. 2014; http://dx.doi.org/10.1130/G36278.1.

The giant Storegga tsunami, about 8,150 years ago, flooded margins of the North Sea and the Norwegian Sea that were occupied by Stone Age humans. The impact on the population might have been devastating, but least in summer and early autumn when people went to the mountains to hunt reindeer. Here we use the growth pattern of moss stems that were buried alive in the tsunami deposits to show that the tsunami happened in autumn, probably in late October. In late October, people along the North Sea-Norwegian Sea coastline would have been near their seashore settlements. The huge waves that suddenly appeared and swept away people and their belongings must have been terrifying. The loss of stores, infrastructure and tools must have caused serious problems for the Stone Age humans, and many survivors may have succumbed during the first winter.

Pelagic smectite as an important factor in tsunamigenic slip along the Japan Trench

Jun Kameda et al., Hokkaido University, Sapporo, Japan. Published online ahead of print on 5 Jan. 2015; http://dx.doi.org/G35948.1.

The very large slip on the shallow portion of the subduction interface during the 2011 Tohoku-oki earthquake (Mw 9.0) caused a huge tsunami along the northeast coast of Honshu, Japan. In order to elucidate the mechanics of such tsunamigenic slip, the Integrated Ocean Drilling Program Expedition 343 (Japan Trench Fast Drilling Project, JFAST), was carried out one year after the earthquake and succeeded in recovering rocks constituting the active plate boundary fault. Our mineralogical analyses reveal that the shallow portion of the fault zone that caused the earthquake is significantly enriched in smectite, one of the frictionally weakest minerals known on Earth, and this mineralogical feature might have facilitated the tsunamigenic faulting during the earthquake. For comparison, we also analyzed cover sediments on the Pacific Plate just prior to subduction and found a characteristic 5-m-thick smectite-rich strata deposited widely in the deep central oceanic area. This occurrence of low-friction smectite may be important for increasing the potential of large slip during shallow megathrust earthquakes, and thus increase the possibility of large tsunamis at this region.

Tracking hurricane-generated storm surge with washover fan stratigraphy

John Shaw et al., University of Arkansas, Fayetteville, Arkansas; Jackson School of Geosciences, University of Texas at Austin, Texas, USA; and University of Wyoming, Laramie, Wyoming, USA. Published online ahead of print on 19 Dec. 2014; http://dx.doi.org/10.1130/G36247.1.

What happens to a coastline during a hurricane? This question is difficult to answer because a hurricane's severity prevents detailed measurements of sediment transport or coastal change during the storm. In this study, the stratigraphic record of a storm found in overwash deposits is used to constrain the conditions and timing of overwash deposition in records. The authors dug a trench through an overwash fan built on the Matagorda Peninsula, Texas during Hurricane Ike, in 2008. The detailed fan stratigraphy observed in the trench reveals a topset-foreset break that formed where water flowing over the fan entered the standing water behind the fan. The elevation of the topset-foreset break increased through the deposit, indicating that water levels behind the fan were rising due to storm surge. This stratigraphic signature was compared with storm surge measurements to estimate that the deposit took 0.52 to 0.90 days to build, or just 15% to 25% of the time when the hurricane was impacting the coast. The estimates gathered from this study are valuable for validating models of hurricane-induced coastal change, and for estimating the environmental conditions during historical and ancient storms.

Long-runout landslides and the long-lasting effects of early water activity on Mars

Jessica A. Watkins et al., iPLEX, University of California, Los Angeles, USA. Published online ahead of print on 5 Jan. 2015; http://dx.doi.org/10.1130/G36215.1.

Long-runout landsliding is rare on Earth, but it is one of the most prominent geomorphic processes shaping Valles Marineris in equatorial Mars, occurring widely within the canyon over the past 3.5 billion years. However, how these landslides form remains uncertain, and the involvement of water in their transport over exceptionally long-distances (>50 km) has been debated for four decades. This study decisively identifies hydrated silicates in the exposed sliding zone of a long-runout landslide in Valles Marineris. This composition suggests that hydrated clay minerals lubricated the basal sliding layer to facilitate landslide transport. These findings indicate that the water activity that generated clay minerals 3 to 4 billion years ago has an enduring impact on fundamental processes that shape the Martian surface.

A stable Ediacaran Earth recorded by single silicate crystals of the ca. 565 Ma Sept-Iles intrusion

Richard K. Bono and John A. Tarduno, University of Rochester, Rochester, New York, USA. Published online ahead of print on 19 Dec. 2014; http://dx.doi.org/10.1130/G36247.1.

The suggestion that the entire solid Earth rotated catastrophically by 90 degrees during Ediacaran to early Cambrian (ca. 635 to 530 Ma) times, and that this sparked the early Cambrian explosion of life, is highly contentious. Evidence for this "inertial interchange true polar wander" (IITPW) is the apparent occurrence of both steep and shallow magnetizations, of nearly the same age, in igneous rocks of north Quebec (Canada). This enigma has been examined using single silicate crystal paleomagnetic analysis, a method that allows the isolation of single domain magnetic grains having the highest recording fidelity. The new analyses reveal that only one direction can be considered primary (that is, 565 million years old), indicating that IITPW did not occur. Thus, the new data suggest the Ediacaran to early Cambrian diversification and explosion of life occurred on a rotationally stable Earth, driven by biotic and longer-term abiotic forcing. Because the purported early Cambrian IITPW event is the canonical example of a 90 degree rotation of Earth due to changes in its internal mass, the question of whether this type of rotation ever occurred in the past remains open. The ultimate answer has important implications for the history of Earth's mantle.

Saline Indian Ocean waters invaded the South Atlantic thermocline during glacial termination II

Paolo Scussolini et al., Vrije Universiteit, Amsterdam, Netherlands. Posted online ahead of print on 5 Jan. 2015; http://dx.doi.org/G36238.1.

When climate shifted from a glaciation to a warmer state, the circulation of the Atlantic Ocean slowed down. As a consequence, the distribution of heat from the tropics to the North Atlantic and the adjacent continents also diminished. Once the climatic transition was complete, Atlantic circulation was vigorous again. What caused this restart? A suspect is the Agulhas leakage: the flow of more salty water from the Indian Ocean into the Atlantic that occurs south of Africa. Ocean models show that this extra salt has the potential to alter the density of surface waters up to the North Atlantic, and strengthen the circulation. To verify this hypothesis, in our study we aim to check whether salt from the Agulhas leakage actually penetrated the Atlantic circulation. Our strategy is to collect microfossils of plankton from the sea floor sediment and, by analyzing them, reconstruct water properties of the water where they lived. We report that salt from the Agulhas leakage indeed travelled into the South Atlantic waters during the second-to-last deglaciation; we also suggest that that climatic transition followed a train of events similar to the last deglaciation, more than previously thought.

Aragonite-calcite seas -- Quantifying the gray area

Uwe Balthasar and Maggie Cusack, University of Glasgow, Glasgow, UK; Balthasar now at Plymouth University, Plymouth, UK. Published online ahead of print on 19 Dec. 2014; http://dx.doi.org/10.1130/G36293.1.

Aragonite and calcite, the main mineral forms of CaCO3, are the most abundant minerals used by marine organisms to secrete their shells and also commonly precipitated inorganically as marine cements and ooids. From changes in the mineral composition of CaCO3 cements and ooids through time we know that the dominance of aragonite or calcite fluctuated throughout the Phanerozoic. It has been a long-standing question whether calcifying organisms were affected by changes between the resulting aragonite-seas and calcite-seas. Here we present evidence from inorganic CaCO3 precipitation experiments that the intensity of the shifts between aragonite-seas and calcite-seas was temperature-driven and thus dependent on latitude. We show that inorganic precipitation of aragonite dominated in waters warmer than 25-30 degrees C, whereas exclusive calcite precipitation was constrained to cooler conditions. The most significant impact of changes between aragonite-calcite sea conditions should have therefore occurred in intermediate to high latitudes, whereas low latitudinal warm-water settings remained relatively stable throughout the Phanerozoic. This revised aragonite-calcite sea hypothesis provides a more realistic environmental framework in which to assess the evolution of skeletal composition of calcifying marine organisms. It explains, for example, the observation of an increasing occurrence of aragonite skeletal composition throughout the Phanerozoic.

Lake Tutira paleoseismic record confirms random, moderate to major and/or great Hawke's Bay (New Zealand) earthquakes

Basil Gomez et al., University of Hawai'i at Manoa, Hawaii, USA. Published online ahead of print on 19 Dec. 2014; http://dx.doi.org/10.1130/G36006.1.

The time intervals between recent, large earthquakes in Hawke's Bay, one of the most seismically active regions in New Zealand, can be assessed using historical and instrumental records kept for the past century. However, the calculations that help to protect society from earthquakes are dependent on the sparse histories of earthquake ground motions that span thousands of years. In geologic environments where sediment accumulates continuously, such as ocean basins and lakes, deposits created by ground shaking are natural repositories of this information. A 7,000-year record from Lake Tutira contains evidence of the past history of major and much larger earthquakes that can cause considerable or catastrophic destruction to buildings and infrastructure. Analysis of this long and extraordinarily detailed record shows that potentially damaging earthquakes occur on the average of every 57 years, which is broadly consistent with the estimate (39 years) derived from the methodology that currently is used to predict the seismic hazard in this area of New Zealand.

Global perturbation of the carbon cycle at the onset of the Miocene Climatic Optimum

Ann Holbourn et al., Christian-Albrechts University, Kiel, Germany. Published online ahead of print on 5 Jan. 2015; http://dx.doi.org/10.1130/G36317.1.

The Miocene Climatic Optimum (ca. 17 to 14.7 million years ago) represents a major interruption in the long-term cooling trend of the past 50 million years. To date, the processes driving high-amplitude climate variability and sustaining global warmth during this remarkable interval remain highly enigmatic. We present high-resolution climate records from the eastern equatorial Pacific Ocean, which offer a new view of climate evolution over the onset of the Climatic Optimum. Our results show that abrupt climate warming ca. 16.9 million years ago was coupled to an intense perturbation of the carbon cycle. Our records additionally reveal that the Carbonate Compensation Depth behaved in a highly dynamic manner during the Climatic Optimum, supporting a crucial role for the marine carbon cycle as climate regulator. Comparison with a high-resolution record spanning the onset of Oceanic Anoxic Event 1a (ca. 120 million years ago) highlights the tight coupling between climate and carbon cycle feedbacks during the Cretaceous "super greenhouse" and the Miocene "icehouse" with dominant Southern Hemisphere ice cover and climatic conditions more akin to today's. Despite obvious differences with the modern ocean-climate system, these results provide a useful perspective to evaluate climate impacts in response to CO2 rise during widely differing states of Earth's climate.

Age and provenance of Grenville supergroup rocks, Trans-Adirondack Basin, constrained by detrital zircons

Jeff Chiarenzelli et al., St. Lawrence University, Canton, New York, USA. Posted online ahead of print on 5 Jan. 2015; http://dx.doi.org/10.1130/G36372.1.

Detrital zircons are used to record the changes in sediment sources during deposition of the Grenville supergroup in the Adirondack Lowlands. Despite high-grade metamorphism and deformation, quartzites from various stratigraphic levels in the sequence provide evidence of rifting, drift, and eventual closure of a back-arc basin that fringed the southeastern margin of ancestral North America. The Trans-Adirondack Basin was one of several that developed during extension of the leading edge of the continent and contains thick carbonate (now marble) sequences which host sedimentary exhalative zinc deposits.

Thermal and chemical evolution of the subarc mantle revealed by spinel-hosted melt inclusions in boninite from the Ogasawara (Bonin) Archipelago, Japan

Susumu Umino et al., Kanazawa University, Kanazawa, Ishikawa, Japan. Posted online ahead of print on 5 Jan. 2015; http://dx.doi.org/G36191.1.

Melt inclusions hosted in chrome spinel deliver unprecedented information on the enigmatic boninite magma genesis and the origin of their source mantle. Boninite is a peculiar magma type that requires melting of the mantle rocks at contradictory conditions of very high temperatures and under sufficient water. Boninite typically occurs at an early stage of beginning of plate subduction such as in the Izu-Ogasawara (Bonin)-Mariana region about 52 million years ago. Hence, elucidating how boninite magma was generated leads to understanding of the mantle dynamics during the initiation of plate subduction. Chrome spinel crystals from the Ogasawara Archipelago, the type locality of boninite, preserve pristine boninitic melts captured during crystallization of the host spinel from boninite magma and now quenched to natural glasses upon eruption. These glass (former melt) inclusions articulated the major and trace elements geochemistry of primary boninite magmas and were used to estimate the temperatures and pressures of the source mantle. The high temperatures for boninite magma generation >1400 degrees C at depths of 27-34 km can be reconciled by its refractory source material due to loss of a significant amount of melt component about 1 thousand million years ago, long before the Pacific Plate started subduction.

Iron oxides, divalent cations, silica, and the early earth phosphorus crisis

C. Jones et al. (corresponding author: S.A. Crowe), University of Southern Denmark, Odense, Denmark; and University of British Columbia, Vancouver, BC, Canada. Posted online ahead of print on 5 Jan. 2015; http://dx.doi.org/G36044.1.

From the abstract: As a nutrient required for growth, phosphorus regulates the activity of life in the oceans. Iron oxides sorb phosphorus from seawater, and through the Archean and early Proterozoic Eons, massive quantities of iron oxides precipitated from the oceans, producing a record of seawater chemistry that is preserved as banded iron formations (BIFs) today. Here we show that Ca2+, Mg2+, and silica in seawater control phosphorus sorption onto iron oxides, influencing the record of seawater phosphorus preserved in BIFs...

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