In the mid-ninth century, an earthquake triggered a landslide that blocked the narrow gorge of th... more In the mid-ninth century, an earthquake triggered a landslide that blocked the narrow gorge of the Jhelum River where it exits the Kashmir Valley. The landslide impounded a lake that extended ≈100 km along the floor of the valley, implying an impounded volume of ≤21 km 3 , flooding the capital, Srinagar, and much agricultural land. An engineered breach of the landslide was contrived by a Medieval engineer resulting in the catastrophic release of flood waters. Using reasonable assumptions we calculate the probable minimum drainage time of this Medieval flood (<4 days) and maximum downstream surge velocities (≈12 m/s). These would have been sufficient to transport boulders in the bed of the Jhelum with dimensions of ≈6 m, consistent with those currently present in some reaches of the river. Given the morphology of the Jhelum gorge we consider that landslide outburst floods may have been common in Kashmir's history. Ancient shorelines indicate that paleo-lake volumes in the Kashmir Valley may have exceeded 400 km 3 which, were they released in catastrophic floods, would have been associated with potential downstream outburst velocities >32 m/s, able to transport boulders with dimensions ≈40 m, far in excess of any found in the course of the Jhelum or in the Punjab plains. Their absence suggests that Kashmir's ancient lakes were not lowered by outburst mechanisms much exceeding those associated with Suyya's flood. Present-day floods have been many tens of meters shallower than those impounded by landslides in the Jhelum in the past several thousands of years. A challenge for future study will be to date Kashmir's ancient shorelines to learn how often landslides and major impoundment events may have occurred in the valley.
This article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in... more This article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in the Himalaya using geodetic, historical and seismological data, and identifies segments of the Himalaya that remain unruptured. The width of the Main Himalayan Thrust is quantified along the arc, together with estimates for the bounding coordinates of historical rupture zones, convergence rates, rupture propagation directions as constrained by felt intensities. The 2018 slip potential for fifteen segments of the Himalaya are evaluated and potential magnitudes assessed for future earthquakes should these segments fail in isolation or as contiguous ruptures. Ten of these fifteen segments are sufficiently mature currently to host a great earthquake (Mw ≥ 8). Fatal Himalayan earthquakes have in the past occurred mostly in the daylight hours. The death toll from a future nocturnal earthquake in the Himalaya could possibly exceed 100 000 due to increased populations and the vulnerability of p...
ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates... more ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates clockwise relative to India about a point a few hundred km west of the Shillong plateau The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89-93°E rotating clockwise at 1.15 deg/My, and the Assam block from 93.5°E-97°E rotating at ≈ 1.13 deg/My. These two blocks are more than 120 km wide in a north–south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastwards from 18 to ≈ 12 mm/yr, and convergence between the Shillong plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to &gt;8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 AD, is now ~5.4 m, similar to slip reported from alluvial terraces offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates... more ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates clockwise relative to India about a point a few hundred km west of the Shillong plateau The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89-93°E rotating clockwise at 1.15 deg/My, and the Assam block from 93.5°E-97°E rotating at ≈ 1.13 deg/My. These two blocks are more than 120 km wide in a north–south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastwards from 18 to ≈ 12 mm/yr, and convergence between the Shillong plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to &gt;8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 AD, is now ~5.4 m, similar to slip reported from alluvial terraces offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
Between January 17 and March 11, 1991, 0.15 km 3 of lava erupted initially from several radial fi... more Between January 17 and March 11, 1991, 0.15 km 3 of lava erupted initially from several radial fissures and subsequently from a single fissure on the SE flank of Hekla volcano, Iceland. Hekla is surrounded by an array of control points measured in 1989 using GPS geodesy and re-measured after the eruption. These measurements indicate that the eruption was associated with a surface deflation volume of +0 08 o +4 o +1 5 0.! o'o4 centered on Hekla (63.995 N 3 km, 19.69 W '2 lcm)'i 'The depth to the magma reservoir is 9.+• km, pooriy constrained due to the absence of GPS control points close to the volcano.
ABSTRACT Between the tenth and early 16th centuries three megaquakes allowed most of the northern... more ABSTRACT Between the tenth and early 16th centuries three megaquakes allowed most of the northern edge of the Indian plate to slip 20-24 m northward relative to the overlying Himalaya. Although the renewal time for earthquakes with this large amount of slip is less than 1300 years given a geodetic convergence rate of 16-20 mm/yr, recently developed scaling laws for the Himalaya suggest that the past 200 years of great earthquakes may be associated with slip of less than 10 m and renewal times of approximately 500 years. These same theoretical models show that the rupture lengths of the Himalaya&#39;s Medieval earthquakes (300-600 km) are too short to permit 24 m of slip given the relationships demonstrated by recent events. There is thus reason to suppose that recent earthquakes may have responded to different elastic driving forces from those that drove the megaquakes of Medieval times. An alternative source of energy to drive Himalayan earthquakes exists in the form of the elastic and gravitational energy stored in flexure of the Indian plate. The flexure is manifest in the form of a 200-450 m high bulge in central India, which is sustained by the forces of collision and by the end-loading of the plate by the Himalaya and southern Tibet. These flexural stresses are responsible for earthquakes in the sub-continent. The abrupt release of stress associated with the northward translation of the northern edge of the Indian plate by 24 m, were the process entirely elastic, would result in a deflation of the crest of the bulge by roughly 0.8 m. Geometrical changes, however, would be moderated by viscous rheologies in the plate and by viscous flow in the mantle in the following centuries. The hypothesized relaxation of flexural geometry following the Himalayan megaquake sequence would have the effect of backing-off stresses throughout central India resulting in quiescence both in the Himalaya and the Indian plate. The historical record shows an absence of great Himalayan earthquakes in the late 16th to early 19th centuries, and colonial records for this period contain few records of earthquakes in central India. Although this may be an artifact caused by a poor recorded history, it is unlikely that Mw&gt;8.2 earthquakes have escaped notice in the Mughal or early colonial histories. Recent mid-plate earthquakes in India may thus represent a redevelopment of flexural stressing of the Indian plate. Their return also signifies the development of stresses in the Himalaya that will eventually be released in great Himalayan earthquakes.
We quantify changes in gravity that have occurred over the past 15 years between latitudes 42.5°S... more We quantify changes in gravity that have occurred over the past 15 years between latitudes 42.5°S and 44°S in the South Island of New Zealand. Twelve of the points cross the southern Alps and four lie in the epicentral region of the 2011 Canterbury earthquakes. At each location gravity was measured using a free-fall absolute gravimeter (FG5-111) with a nominal accuracy of 1 µGal. Observed changes in gravity varied from -53 to +43 µGal in the presence of surface elevation changes in the range -12 cm to +22 cm. At all locations unmodeled local changes in surface or subsurface water contributed to the observed changes in gravity. Despite the difficulty in quantifying these local uncertainties, we identify an increase in mass relative to February 2000 in both the southern Alps and the Christchurch region, equivalent to a uniform water layer 12.1 cm and 42 cm thick respectively.
The Himalayan Nepal Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadb... more The Himalayan Nepal Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadband seismometers throughout eastern Nepal and southern Tibet in 2001-2002. The main goals of the project were to better understand the mountain building processes of this region through studies of seismicity and Earth structure determined from local and teleseismic earthquakes. The seismic deployment was in collaboration with the National Seismological Centre, Department of Mines and Geology, Nepal, and the Institute of Geology and Geophysics of the Chinese Academy of Sciences. Our new subsurface images from HIMNT teleseismic receiver functions and local earthquake tomography show evidence of the basal decollement of the Himalaya (Main Himalayan Thrust, MHT) and an increase in Moho depth from ~45 km beneath Nepal to ~75 km beneath Tibet. We find strong seismic anisotropy above the decollement, likely developed in response to shear on the MHT. The shear may be taken up as slip in great ea...
Our project aims at the understanding of the mountain building processes through earthquake sourc... more Our project aims at the understanding of the mountain building processes through earthquake source and crust and mantle structure imaging. It involves the deployment of 28 broadband seismometers throughout Eastern Nepal and Southern Tibet, using broadband instrumentation from the IRIS PASSCAL facility. The stations were in place for one year from Fall 2001 to Fall 2002. The current studies with
The Earth is a dynamic system-it has a fluid, mobile atmosphere and oceans, a continually changin... more The Earth is a dynamic system-it has a fluid, mobile atmosphere and oceans, a continually changing distribution of ice, snow, and groundwater, a fluid core undergoing hydromagnetic motion, a mantle under~oing both thermal convection and rebound from glacial loading of the last ice age, and mobile tectonic plates. These processes affect the distribution of mass in the Earth and produce variations in the Earth's gravitational field on a variety of spatial and temporal scales . Highly accurate measurements of the Earth's gravity field made with appropriate spatial and temporal sampling can thus be used to better understand the processes that move mass within the Earth, and on and above its surface.
The Kirthar Range in western Pakistan is the result of east-west compression caused by the indent... more The Kirthar Range in western Pakistan is the result of east-west compression caused by the indentation of the Indian Plate into the Eurasian Plate. The 1931 MW 7.3 Mach earthquake resulted in 65 cm of local uplift on a leveling line through the Bolan Pass in the northern Kirthar Range. Previous studies model the fault as an east-dipping blind thrust
... Shebalin (1997), earthquakes in eastern Iran are described in Ambraseys and Melville (1982) a... more ... Shebalin (1997), earthquakes in eastern Iran are described in Ambraseys and Melville (1982) and Moinfar et al ... 1881, [1569] Abu 'l-Fida Ismail b. Ali, Al-mukhtasir fi akhbar al-bashar, vol.2 ... al-muluk wa 'l-uman, ed. Hyderabad, 1938-41 [1181] Ibn al-shihna, Muhammad, Raudat al ...
In the mid-ninth century, an earthquake triggered a landslide that blocked the narrow gorge of th... more In the mid-ninth century, an earthquake triggered a landslide that blocked the narrow gorge of the Jhelum River where it exits the Kashmir Valley. The landslide impounded a lake that extended ≈100 km along the floor of the valley, implying an impounded volume of ≤21 km 3 , flooding the capital, Srinagar, and much agricultural land. An engineered breach of the landslide was contrived by a Medieval engineer resulting in the catastrophic release of flood waters. Using reasonable assumptions we calculate the probable minimum drainage time of this Medieval flood (<4 days) and maximum downstream surge velocities (≈12 m/s). These would have been sufficient to transport boulders in the bed of the Jhelum with dimensions of ≈6 m, consistent with those currently present in some reaches of the river. Given the morphology of the Jhelum gorge we consider that landslide outburst floods may have been common in Kashmir's history. Ancient shorelines indicate that paleo-lake volumes in the Kashmir Valley may have exceeded 400 km 3 which, were they released in catastrophic floods, would have been associated with potential downstream outburst velocities >32 m/s, able to transport boulders with dimensions ≈40 m, far in excess of any found in the course of the Jhelum or in the Punjab plains. Their absence suggests that Kashmir's ancient lakes were not lowered by outburst mechanisms much exceeding those associated with Suyya's flood. Present-day floods have been many tens of meters shallower than those impounded by landslides in the Jhelum in the past several thousands of years. A challenge for future study will be to date Kashmir's ancient shorelines to learn how often landslides and major impoundment events may have occurred in the valley.
This article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in... more This article summarizes recent advances in our knowledge of the past 1000 years of earthquakes in the Himalaya using geodetic, historical and seismological data, and identifies segments of the Himalaya that remain unruptured. The width of the Main Himalayan Thrust is quantified along the arc, together with estimates for the bounding coordinates of historical rupture zones, convergence rates, rupture propagation directions as constrained by felt intensities. The 2018 slip potential for fifteen segments of the Himalaya are evaluated and potential magnitudes assessed for future earthquakes should these segments fail in isolation or as contiguous ruptures. Ten of these fifteen segments are sufficiently mature currently to host a great earthquake (Mw ≥ 8). Fatal Himalayan earthquakes have in the past occurred mostly in the daylight hours. The death toll from a future nocturnal earthquake in the Himalaya could possibly exceed 100 000 due to increased populations and the vulnerability of p...
ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates... more ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates clockwise relative to India about a point a few hundred km west of the Shillong plateau The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89-93°E rotating clockwise at 1.15 deg/My, and the Assam block from 93.5°E-97°E rotating at ≈ 1.13 deg/My. These two blocks are more than 120 km wide in a north–south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastwards from 18 to ≈ 12 mm/yr, and convergence between the Shillong plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to &gt;8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 AD, is now ~5.4 m, similar to slip reported from alluvial terraces offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates... more ABSTRACT GPS data reveal that the Brahmaputra Valley has broken from the Indian plate and rotates clockwise relative to India about a point a few hundred km west of the Shillong plateau The GPS velocity vectors define two distinct blocks separated by the Kopili fault upon which 2–3 mm/yr of dextral slip is observed: the Shillong block between longitudes 89-93°E rotating clockwise at 1.15 deg/My, and the Assam block from 93.5°E-97°E rotating at ≈ 1.13 deg/My. These two blocks are more than 120 km wide in a north–south sense, but they extend locally a similar distance beneath the Himalaya and Tibet. A result of these rotations is that convergence across the Himalaya east of Sikkim decreases in velocity eastwards from 18 to ≈ 12 mm/yr, and convergence between the Shillong plateau and Bangladesh across the Dauki fault increases from 3 mm/yr in the west to &gt;8 mm/yr in the east. This fast convergence rate is inconsistent with inferred geological uplift rates on the plateau (if a 45°N dip is assumed for the Dauki fault) unless clockwise rotation of the Shillong block has increased substantially in the past 4–8 Myr. Such acceleration is consistent with reported recent slowing in the convergence rate across the Bhutan Himalaya. The current slip potential near Bhutan, based on present-day convergence rates and assuming no great earthquake since 1713 AD, is now ~5.4 m, similar to slip reported from alluvial terraces offsets across the Main Himalayan Thrust and sufficient to sustain a Mw ≥ 8.0 earthquake in this area.
Between January 17 and March 11, 1991, 0.15 km 3 of lava erupted initially from several radial fi... more Between January 17 and March 11, 1991, 0.15 km 3 of lava erupted initially from several radial fissures and subsequently from a single fissure on the SE flank of Hekla volcano, Iceland. Hekla is surrounded by an array of control points measured in 1989 using GPS geodesy and re-measured after the eruption. These measurements indicate that the eruption was associated with a surface deflation volume of +0 08 o +4 o +1 5 0.! o'o4 centered on Hekla (63.995 N 3 km, 19.69 W '2 lcm)'i 'The depth to the magma reservoir is 9.+• km, pooriy constrained due to the absence of GPS control points close to the volcano.
ABSTRACT Between the tenth and early 16th centuries three megaquakes allowed most of the northern... more ABSTRACT Between the tenth and early 16th centuries three megaquakes allowed most of the northern edge of the Indian plate to slip 20-24 m northward relative to the overlying Himalaya. Although the renewal time for earthquakes with this large amount of slip is less than 1300 years given a geodetic convergence rate of 16-20 mm/yr, recently developed scaling laws for the Himalaya suggest that the past 200 years of great earthquakes may be associated with slip of less than 10 m and renewal times of approximately 500 years. These same theoretical models show that the rupture lengths of the Himalaya&#39;s Medieval earthquakes (300-600 km) are too short to permit 24 m of slip given the relationships demonstrated by recent events. There is thus reason to suppose that recent earthquakes may have responded to different elastic driving forces from those that drove the megaquakes of Medieval times. An alternative source of energy to drive Himalayan earthquakes exists in the form of the elastic and gravitational energy stored in flexure of the Indian plate. The flexure is manifest in the form of a 200-450 m high bulge in central India, which is sustained by the forces of collision and by the end-loading of the plate by the Himalaya and southern Tibet. These flexural stresses are responsible for earthquakes in the sub-continent. The abrupt release of stress associated with the northward translation of the northern edge of the Indian plate by 24 m, were the process entirely elastic, would result in a deflation of the crest of the bulge by roughly 0.8 m. Geometrical changes, however, would be moderated by viscous rheologies in the plate and by viscous flow in the mantle in the following centuries. The hypothesized relaxation of flexural geometry following the Himalayan megaquake sequence would have the effect of backing-off stresses throughout central India resulting in quiescence both in the Himalaya and the Indian plate. The historical record shows an absence of great Himalayan earthquakes in the late 16th to early 19th centuries, and colonial records for this period contain few records of earthquakes in central India. Although this may be an artifact caused by a poor recorded history, it is unlikely that Mw&gt;8.2 earthquakes have escaped notice in the Mughal or early colonial histories. Recent mid-plate earthquakes in India may thus represent a redevelopment of flexural stressing of the Indian plate. Their return also signifies the development of stresses in the Himalaya that will eventually be released in great Himalayan earthquakes.
We quantify changes in gravity that have occurred over the past 15 years between latitudes 42.5°S... more We quantify changes in gravity that have occurred over the past 15 years between latitudes 42.5°S and 44°S in the South Island of New Zealand. Twelve of the points cross the southern Alps and four lie in the epicentral region of the 2011 Canterbury earthquakes. At each location gravity was measured using a free-fall absolute gravimeter (FG5-111) with a nominal accuracy of 1 µGal. Observed changes in gravity varied from -53 to +43 µGal in the presence of surface elevation changes in the range -12 cm to +22 cm. At all locations unmodeled local changes in surface or subsurface water contributed to the observed changes in gravity. Despite the difficulty in quantifying these local uncertainties, we identify an increase in mass relative to February 2000 in both the southern Alps and the Christchurch region, equivalent to a uniform water layer 12.1 cm and 42 cm thick respectively.
The Himalayan Nepal Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadb... more The Himalayan Nepal Tibet PASSCAL Seismic Experiment (HIMNT) included the deployment of 28 broadband seismometers throughout eastern Nepal and southern Tibet in 2001-2002. The main goals of the project were to better understand the mountain building processes of this region through studies of seismicity and Earth structure determined from local and teleseismic earthquakes. The seismic deployment was in collaboration with the National Seismological Centre, Department of Mines and Geology, Nepal, and the Institute of Geology and Geophysics of the Chinese Academy of Sciences. Our new subsurface images from HIMNT teleseismic receiver functions and local earthquake tomography show evidence of the basal decollement of the Himalaya (Main Himalayan Thrust, MHT) and an increase in Moho depth from ~45 km beneath Nepal to ~75 km beneath Tibet. We find strong seismic anisotropy above the decollement, likely developed in response to shear on the MHT. The shear may be taken up as slip in great ea...
Our project aims at the understanding of the mountain building processes through earthquake sourc... more Our project aims at the understanding of the mountain building processes through earthquake source and crust and mantle structure imaging. It involves the deployment of 28 broadband seismometers throughout Eastern Nepal and Southern Tibet, using broadband instrumentation from the IRIS PASSCAL facility. The stations were in place for one year from Fall 2001 to Fall 2002. The current studies with
The Earth is a dynamic system-it has a fluid, mobile atmosphere and oceans, a continually changin... more The Earth is a dynamic system-it has a fluid, mobile atmosphere and oceans, a continually changing distribution of ice, snow, and groundwater, a fluid core undergoing hydromagnetic motion, a mantle under~oing both thermal convection and rebound from glacial loading of the last ice age, and mobile tectonic plates. These processes affect the distribution of mass in the Earth and produce variations in the Earth's gravitational field on a variety of spatial and temporal scales . Highly accurate measurements of the Earth's gravity field made with appropriate spatial and temporal sampling can thus be used to better understand the processes that move mass within the Earth, and on and above its surface.
The Kirthar Range in western Pakistan is the result of east-west compression caused by the indent... more The Kirthar Range in western Pakistan is the result of east-west compression caused by the indentation of the Indian Plate into the Eurasian Plate. The 1931 MW 7.3 Mach earthquake resulted in 65 cm of local uplift on a leveling line through the Bolan Pass in the northern Kirthar Range. Previous studies model the fault as an east-dipping blind thrust
... Shebalin (1997), earthquakes in eastern Iran are described in Ambraseys and Melville (1982) a... more ... Shebalin (1997), earthquakes in eastern Iran are described in Ambraseys and Melville (1982) and Moinfar et al ... 1881, [1569] Abu 'l-Fida Ismail b. Ali, Al-mukhtasir fi akhbar al-bashar, vol.2 ... al-muluk wa 'l-uman, ed. Hyderabad, 1938-41 [1181] Ibn al-shihna, Muhammad, Raudat al ...
Uploads
Papers by Roger Bilham