Shear wave reflection seismics yields subsurface dissolution and subrosion patterns: application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan

Abstract. Near-surface geophysical imaging of alluvial fan settings is a challenging task, but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline of the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development. For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 km and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m in high-resolution, and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area. The most surprising result of the survey is the absence of evidence for a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0–200 m depth. Furthermore, the underground of areas affected by sinkholes is characterized by highly-scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulphate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines, and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.

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Shear wave reflection seismic yields subsurface dissolution and subrosion patterns: application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan

Solid Earth ◽

10.5194/se-9-1079-2018 ◽

2018 ◽

Vol 9 (5) ◽

pp. 1079-1098 ◽

Cited By ~ 8

Author(s):

Ulrich Polom ◽

Hussam Alrshdan ◽

Djamil Al-Halbouni ◽

Eoghan P. Holohan ◽

Torsten Dahm ◽

...

Keyword(s):

Sea Level ◽

Shear Wave ◽

Seismic Reflection ◽

Wave Reflection ◽

Dead Sea ◽

Alluvial Fan ◽

Surprising Result ◽

Near Surface ◽

Sedimentary Architecture ◽

The Dead

Abstract. Near-surface geophysical imaging of alluvial fan settings is a challenging task but crucial for understating geological processes in such settings. The alluvial fan of Ghor Al-Haditha at the southeast shore of the Dead Sea is strongly affected by localized subsidence and destructive sinkhole collapses, with a significantly increasing sinkhole formation rate since ca. 1983. A similar increase is observed also on the western shore of the Dead Sea, in correlation with an ongoing decline in the Dead Sea level. Since different structural models of the upper 50 m of the alluvial fan and varying hypothetical sinkhole processes have been suggested for the Ghor Al-Haditha area in the past, this study aimed to clarify the subsurface characteristics responsible for sinkhole development.For this purpose, high-frequency shear wave reflection vibratory seismic surveys were carried out in the Ghor Al-Haditha area along several crossing and parallel profiles with a total length of 1.8 and 2.1 km in 2013 and 2014, respectively. The sedimentary architecture of the alluvial fan at Ghor Al-Haditha is resolved down to a depth of nearly 200 m at a high resolution and is calibrated with the stratigraphic profiles of two boreholes located inside the survey area.The most surprising result of the survey is the absence of evidence of a thick (> 2–10 m) compacted salt layer formerly suggested to lie at ca. 35–40 m depth. Instead, seismic reflection amplitudes and velocities image with good continuity a complex interlocking of alluvial fan deposits and lacustrine sediments of the Dead Sea between 0 and 200 m depth. Furthermore, the underground section of areas affected by sinkholes is characterized by highly scattering wave fields and reduced seismic interval velocities. We propose that the Dead Sea mud layers, which comprise distributed inclusions or lenses of evaporitic chloride, sulfate, and carbonate minerals as well as clay silicates, become increasingly exposed to unsaturated water as the sea level declines and are consequently destabilized and mobilized by both dissolution and physical erosion in the subsurface. This new interpretation of the underlying cause of sinkhole development is supported by surface observations in nearby channel systems. Overall, this study shows that shear wave seismic reflection technique is a promising method for enhanced near-surface imaging in such challenging alluvial fan settings.

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Calibrating a new attenuation curve for the Dead Sea region using surface wave dispersion surveys in sites damaged by the 1927 Jericho earthquake

Solid Earth ◽

10.5194/se-10-379-2019 ◽

2019 ◽

Vol 10 (2) ◽

pp. 379-390 ◽

Cited By ~ 2

Author(s):

Yaniv Darvasi ◽

Amotz Agnon

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Dead Sea ◽

Attenuation Curve ◽

Surface Wave Dispersion ◽

Near Surface ◽

Moderate Seismicity ◽

Local Point ◽

The Dead

Abstract. Instrumental strong motion data are not common around the Dead Sea region. Therefore, calibrating a new attenuation equation is a considerable challenge. However, the Holy Land has a remarkable historical archive, attesting to numerous regional and local earthquakes. Combining the historical record with new seismic measurements will improve the regional equation. On 11 July 1927, a rupture, in the crust in proximity to the northern Dead Sea, generated a moderate 6.2 ML earthquake. Up to 500 people were killed, and extensive destruction was recorded, even as far as 150 km from the focus. We consider local near-surface properties, in particular, the shear-wave velocity, as an amplification factor. Where the shear-wave velocity is low, the seismic intensity far from the focus would likely be greater than expected from a standard attenuation curve. In this work, we used the multichannel analysis of surface waves (MASW) method to estimate seismic wave velocity at anomalous sites in Israel in order to calibrate a new attenuation equation for the Dead Sea region. Our new attenuation equation contains a term which quantifies only lithological effects, while factors such as building quality, foundation depth, topography, earthquake directivity, type of fault, etc. remain out of our scope. Nonetheless, about 60 % of the measured anomalous sites fit expectations; therefore, this new ground-motion prediction equation (GMPE) is statistically better than the old ones. From our local point of view, this is the first time that integration of the 1927 historical data and modern shear-wave velocity profile measurements improved the attenuation equation (sometimes referred to as the attenuation relation) for the Dead Sea region. In the wider context, regions of low-to-moderate seismicity should use macroseismic earthquake data, together with modern measurements, in order to better estimate the peak ground acceleration or the seismic intensities to be caused by future earthquakes. This integration will conceivably lead to a better mitigation of damage from future earthquakes and should improve maps of seismic hazard.

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Comment on Shear wave reflection seismic yields subsurface dissolution and subrosion patterns: application to the Ghor Al-Haditha sinkhole site, Dead Sea, Jordan by Polom et al. (2018)

10.5194/se-2019-132 ◽

2019 ◽

Author(s):

Michael Ezersky ◽

Anatoly Legchenko ◽

Lev Eppelbaum ◽

Abdallah Al-Zoubi ◽

Abdelrahman Abueladas

Keyword(s):

Shear Wave ◽

Seismic Data ◽

Seismic Reflection ◽

Wave Reflection ◽

Dead Sea ◽

S Wave ◽

Reflection Seismic ◽

Salt Layer ◽

Wave Technique

Abstract. Seismic reflection S-wave technique is very effective and has demonstrated nice results in previous investigations of various authors. However, the salt layer was not detected in the Ghor Al-Haditha area (Jordan) because of some reasons. The main reason is that about ~ 80 % of reflection lines were carried outside the salt area delineated by Ezersky et al. (2013b) based on results of El-Isa et al. (1995). Other possible factor is too strong filtering of seismic data obtained from the upper part of the section (up to 50 m deep). Our and Polom (2018) assessment of the work of other authors diverges. We affirm that the salt layer of 7–10 m thickness is located at ~ 40 m depth in the Ghor Al-Haditha area.

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Calibrating a New Attenuation Curve for the Dead Sea Region Using Surface Wave Dispersion Surveys in Sites Damaged by the 1927 Jericho Earthquake

10.5194/se-2018-52 ◽

2018 ◽

Author(s):

Yaniv Darvasi ◽

Amotz Agnon

Keyword(s):

Shear Wave ◽

Wave Velocity ◽

Shear Wave Velocity ◽

Dead Sea ◽

Macroseismic Data ◽

Attenuation Curve ◽

Surface Wave Dispersion ◽

Near Surface ◽

Local Point ◽

The Dead

Abstract. Strong motion data is not common around the Dead Sea region. Therefore, calibrating a new attenuation equation is a considerable challenge. However, the Holy Land has a remarkable historical archive, attesting to numerous regional and local earthquakes. Combining the historical record with modern measurements will enhance the regional equation. On 11 July 1927, a crustal rupture generated a moderate 6.25ML earthquake around the northern part of the Dead Sea. Up to five hundred people were killed and extensive destruction was recorded, even at places as far as 150 kilometers from the focus. We consider local near-surface properties, in particular, the shear-wave velocity, as an amplification factor. Where the shear-wave velocity is low, the seismic intensity at places far from the focus would likely be greater than expected from a standard attenuation curve. In this work, we used the Multi Analysis of Surface Waves (MASW) method to estimate seismic wave velocity at anomalous sites in Israel in order to calibrate a new attenuation equation for the Dead Sea region, based on 1927 macroseismic data integrated with modern measurements. Our new attenuation equation contains a term which quantifies solely lithological effects, whilst factors such as building quality, foundation depth, topography, earthquake directivity, type of fault, etc., remained out of the equation. Nonetheless, about 60 % of the measured anomalous sites fit expectations and better fitting is achieved compared to other relevant attenuation equations. From a local point of view, this is the first time that an integration between historical data and modern seismic measurements improves the attenuation relation for the Dead Sea region. In the wider context, regions of low-to-moderate seismicity should use historical earthquake data together with modern measurements in order to better estimate the peak ground acceleration or the seismic intensities caused by future earthquakes. This integration will conceivably lead to a better understanding of future earthquakes and improve maps of seismic risk.

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