Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archa... more Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archaeological excavations allude to a sea flood that crippled the ancient port at Kaveripattinam, a trading hub for Southeast Asia, and probably affected the entire South Indian coast, analogous to the 2004 Indian Ocean tsunami impact. We present sedimentary evidence from an archaeological site to validate the textual references to this early medieval event. A sandy layer showing bed forms representing high-energy conditions, possibly generated by a seaborne wave, was identified at the Kaveripattinam coast of Tamil Nadu, South India. Its sedimentary characteristics include hummocky cross-stratification, convolute lamination with heavy minerals, rip-up clasts, an erosional contact with the underlying mud bed, and a landward thinning geometry. Admixed with 1000-year-old Chola period artifacts, it provided an optically stimulated luminescence age of 1091 ± 66 yr and a thermoluminescence age of ...
The 1993 Killari earthquake occurred in the central part of the Indian shield, an area generally ... more The 1993 Killari earthquake occurred in the central part of the Indian shield, an area generally believed to be of low seismogenic potential. This rare event provided an opportunity to understand the seismogenesis within the shield regions. Trench excavations in the rupture zone as well as other natural exposures in the vicinity of the epicentral region of the Killari earthquake indicate episodic activity separated by long periods. Deep drilling in the epicentral area recorded a maximum of ∼6 m of slip in the deeper strata (Gupta et al., 1998a). Assuming an average of about 1 m slip for a moderate earthquake, as revealed by the 1993 event, accumulated slip indicates at least six moderate earthquakes at Killari. While the timing of the penultimate event may work out to be hundreds of thousands of years or more, evidence for at least one moderate earthquake ∼1500 yr ago was obtained from Ter, about 40 km northwest of Killari. Observations at Killari and Ter indicate the localization o...
Given the lack of proper constraints in understanding earthquake mechanisms in the cratonic inter... more Given the lack of proper constraints in understanding earthquake mechanisms in the cratonic interiors and the general absence of good quality database, here we reassess the seismic hazard in the province of Kerala, a part of the •stable continental interior•, based on an improved historical and instrumental database. The temporal pattern of the current seismicity suggests that >60% of the microtremors in Kerala occurs with a time lag after the peak rainfall, indicating that hydroseismicity may be a plausible model to explain the low-level seismicity in this region. Further, an increment in overall seismicity rate in the region in the recent years is explained as due to increased anthropogenic activities, which includes changes in hydrological pathways as a consequence of rapid landscape changes. Our analyses of the historical database eliminate a few events that are ascribed to this region; this exercise has also led to identification of a few events, not previously noted. The im...
The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala,... more The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala, earthquake (M 4.3) indicate subtle, but clearly recognizable expressions of geologically recent fault zone, consisting of fracture sets showing brittle displacement and a gouge zone. The fracture zone confines to the crystalline basement, and is spatially coincident with the elongation of the isoseismals of the 1994 mainshock and a 10-km-long WNW-ESE trending topographic lineament. The preliminary results from the electron spin resonance (ESR) dating on the quartz grains from the fault gouge indicate that the last major faulting in this site occurred 430 ± 43 ka ago. The experiments on different grain sizes of quartz from the gouge showed consistent decrease in age to a plateau of low values, indicating that ESR signals in finer grains were completely zeroed at the time of faulting due to frictional heat. The results show a relatively young age for displacement on the fault that occurs ...
The great 1934 Himalayan earthquake (Mw 8.1) generated a large zone of ground failure and liquefa... more The great 1934 Himalayan earthquake (Mw 8.1) generated a large zone of ground failure and liquefaction in north Bihar, India, in addition to the earthquakes of 1833 (Mw ~7.7) and 1988 (Mw 6.7) that have also impacted this region. Here we present the results of paleo-liquefaction investigations from four sites in the plains of north Bihar and one in eastern Uttar Pradesh. The liquefaction features generated by successive earthquakes were dated at AD 829-971, 886-1090, 907-1181, 1130-1376, 1112-1572, 1492-1672, 1733-1839 and 1814-1854. One of the liquefaction events dated at AD 829-971, 886-1090 and 907-1181 may correlate with the great earthquake of AD ~1100, recognized in an earlier study from the sections across the frontal thrust in central eastern Nepal. Two late medieval liquefaction episodes of AD 1130-1376 and 1492-1672 were also exposed in our sites. The sedimentary sections also revealed sandblows that can be attributed to the 1833 earthquake, a lesser magnitude event compared to the 1934. Liquefactions triggered by the 1934 and 1988 earthquakes were also evident within the topmost level in some sections. The available data lead us to conjecture that a series of temporally close spaced earthquakes of both strong and large types, not including the infrequent great earthquakes like the 1934, have affected the Bihar Plains during the last 1500 years with a combined recurrence interval of 124±63 years.
The central part of the Himalaya (Kumaun and Garhwal Provinces of India) is noted for its prolong... more The central part of the Himalaya (Kumaun and Garhwal Provinces of India) is noted for its prolonged seismic quiescence and therefore, developing a longer-term time series of past earthquakes to understand their recurrence pattern in this segment assumes importance. In addition to direct observations of offsets in stratigraphic exposures or other proxies like paleoliquefaction, deformation preserved within stalagmites (speleothems) in karst system can be analysed to obtain continuous millennial scale time series of earthquakes. The Central Indian Himalaya hosts natural caves between major active thrusts forming potential storehouses for paleoseismological records. Here we present results from the limestone caves in the Kumaun Himalaya, and discuss the implications of growth perturbations identified in the stalagmites as possible earthquake recorders. This article focuses on three stalagmites from the Dharamjali Cave located in the eastern Kumaun Himalaya, although two other caves, one of them located in the foothills, were also examined for their suitability. The growth anomalies in stalagmites include abrupt tilting or rotation of growth axes, growth termination, and breakage followed by regrowth. The U-Th age data from three specimens allow us to constrain the intervals of growth anomalies, and these were dated at 4273±410 yr BP (2673-1853 BC), 2782±79 yr BP (851-693 BC), 2498±117 yr BP (605-371 BC), 1503±245 yr BP (262-752 AD), 1346±101 yr BP (563-765 AD), and 687±147 yr BP (1176-1470 AD). The dates may correspond to the timings of major/great earthquakes in the region and the youngest event (1176-1470 AD) shows chronological correspondence with either one of the great medieval earthquakes (1050-1250 and 1259-–1433 AD) evident from trench excavations across the Himalayan Frontal Thrust.
We report here on the campaign GPS data from the Andaman Islands just previous to the great 2004 ... more We report here on the campaign GPS data from the Andaman Islands just previous to the great 2004 Sumatra-Andaman earthquake. The campaign mode acquisitions at Port Blair showed that the site started to subside between 2003 and 2004. In addition, during this period, the horizontal displacement of Port Blair with respect to India, deduced from 1996-2000 GPS data, changed its orientation from to that obtained during the 26th Dec 2004 co-seismic. This short-term subsidence can be modeled as slip in the up-dip portion of the fault, a slip that is equivalent to an earthquake with moment magnitude of 6.3. Previously, slow slip was thought to appear at intermediate depths roughly 35–55 km but simple models of the deformation at this single site suggest slow slip at much shallower depth than this. This observation of subsidence obtained by GPS methods is in rough agreement with subsidence observed from tide gauge data. Campaign mode GPS data between 1996 and 2000 suggest uplift for Port Blair during the inter-seismic period and so does the reported field observations of interseismic micro-atoll emergence. Lack of exposed land with GPS stations along the southern part of the thrust fault deprive of arriving at any indication of this preseismic subsidence in those areas
Eos, Transactions American Geophysical Union, 2014
Ten years later, the Indian Ocean tsunami
of 26 December 2004 still looms large in
efforts to r... more Ten years later, the Indian Ocean tsunami
of 26 December 2004 still looms large in
efforts to reduce tsunami risk. The disaster
has spurred worldwide advances in tsunami
detection and warning, risk assessment, and
awareness [Satake, 2014].
Nearly a lifetime has passed since the
northwestern Indian Ocean last produced
a devastating tsunami. Documentation of
this tsunami, which was in November 1945,
was hindered by international instability
in the wake of World War II and, in British
India, by the approach of independence and
partition.
The parent earthquake (magnitude 8.1)
was centered west of Karachi along the
Makran subduction zone (Figure 1). The tsunami
registered on tide gauges, but intelligence
reports and newspaper articles say
little about inundation limits, and the consequences
in terms of lives lost differ by an
order of magnitude among the estimates in
today’s geophysical catalogs. What has been
established about the 1945 tsunami falls
short of what is needed today for ground-truthing
inundation models, estimating risk
to enlarged populations, and anchoring
awareness campaigns in local facts.
Recent efforts to reduce tsunami risk
around the Arabian Sea include a project
in which eyewitnesses to the 1945 tsunami
were found and interviewed (Figure 1) and
related archives were gathered. Results are
being made available through the Indian
Ocean Tsunami Information Center (IOTIC)
of the United Nations Educational, Scientific
and Cultural Organization (UNESCO) in
hopes of increasing scientific understanding
and public awareness of the region’s tsunami
hazards.
The ~700-km-long “central seismic gap” is the most prominent segment of the Himalayan front not t... more The ~700-km-long “central seismic gap” is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200–500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue for a great earthquake. Despite the region’s recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly understood. Here, we place new constraints on the spatial distribution of rock uplift within the western ~400 km of the central seismic gap using topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic 10Be. The data sets show a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.
The Himalaya has experienced three great earthquakes during the last century- 1934 Nepal-Bihar, 1... more The Himalaya has experienced three great earthquakes during the last century- 1934 Nepal-Bihar, 1950 Upper Assam, and arguably the 1905 Kangra. Focus here is on the central Himalayan segment between the 1905 and the 1934 ruptures, where previous studies have identified a great earthquake between 13th and 16th centuries. Historical data suggest damaging earthquakes in AD 1255, 1344, 1505 1803 and 1833, although their sources and magnitudes remain debated. We present new evidence for a great earthquake from a trench across the base of a 13-m-high scarp near Ramnagar at the Himalayan Frontal Thrust. The section exposed four south verging fault strands and a backthrust offsetting a broad spectrum of litho-units, including colluvial deposits. Age data suggest that the last great earthquake in the central Himalaya most likely occurred between AD 1259 and 1433. While evidence for this rupture is unmistakable, the stratigraphic clues imply an earlier event, which can most tentatively be placed between AD 1050 and 1250. The postulated existence of this earlier event, however, requires further validation. If the two-earthquake-scenario is realistic, then the successive ruptures may have occurred in close intervals and were sourced on adjacent segments that overlapped at the trench site. Rupture/s identified in the trench closely correlate with two damaging earthquakes of 1255 and 1344 reported from Nepal. The present study suggests that the frontal thrust in central Himalaya may have remained seismically inactive during the last ~700 years. Considering this long elapsed time, a great earthquake may be due in the region.
Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archa... more Literature of the ancient Chola Dynasty (A.D. 9th–11th centuries) of South India and recent archaeological excavations allude to a sea flood that crippled the ancient port at Kaveripattinam, a trading hub for Southeast Asia, and probably affected the entire South Indian coast, analogous to the 2004 Indian Ocean tsunami impact. We present sedimentary evidence from an archaeological site to validate the textual references to this early medieval event. A sandy layer showing bed forms representing high-energy conditions, possibly generated by a seaborne wave, was identified at the Kaveripattinam coast of Tamil Nadu, South India. Its sedimentary characteristics include hummocky cross-stratification, convolute lamination with heavy minerals, rip-up clasts, an erosional contact with the underlying mud bed, and a landward thinning geometry. Admixed with 1000-year-old Chola period artifacts, it provided an optically stimulated luminescence age of 1091 ± 66 yr and a thermoluminescence age of ...
The 1993 Killari earthquake occurred in the central part of the Indian shield, an area generally ... more The 1993 Killari earthquake occurred in the central part of the Indian shield, an area generally believed to be of low seismogenic potential. This rare event provided an opportunity to understand the seismogenesis within the shield regions. Trench excavations in the rupture zone as well as other natural exposures in the vicinity of the epicentral region of the Killari earthquake indicate episodic activity separated by long periods. Deep drilling in the epicentral area recorded a maximum of ∼6 m of slip in the deeper strata (Gupta et al., 1998a). Assuming an average of about 1 m slip for a moderate earthquake, as revealed by the 1993 event, accumulated slip indicates at least six moderate earthquakes at Killari. While the timing of the penultimate event may work out to be hundreds of thousands of years or more, evidence for at least one moderate earthquake ∼1500 yr ago was obtained from Ter, about 40 km northwest of Killari. Observations at Killari and Ter indicate the localization o...
Given the lack of proper constraints in understanding earthquake mechanisms in the cratonic inter... more Given the lack of proper constraints in understanding earthquake mechanisms in the cratonic interiors and the general absence of good quality database, here we reassess the seismic hazard in the province of Kerala, a part of the •stable continental interior•, based on an improved historical and instrumental database. The temporal pattern of the current seismicity suggests that >60% of the microtremors in Kerala occurs with a time lag after the peak rainfall, indicating that hydroseismicity may be a plausible model to explain the low-level seismicity in this region. Further, an increment in overall seismicity rate in the region in the recent years is explained as due to increased anthropogenic activities, which includes changes in hydrological pathways as a consequence of rapid landscape changes. Our analyses of the historical database eliminate a few events that are ascribed to this region; this exercise has also led to identification of a few events, not previously noted. The im...
The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala,... more The field investigations in the epicentral area of the 1994 Wadakkancheri (Desamangalam), Kerala, earthquake (M 4.3) indicate subtle, but clearly recognizable expressions of geologically recent fault zone, consisting of fracture sets showing brittle displacement and a gouge zone. The fracture zone confines to the crystalline basement, and is spatially coincident with the elongation of the isoseismals of the 1994 mainshock and a 10-km-long WNW-ESE trending topographic lineament. The preliminary results from the electron spin resonance (ESR) dating on the quartz grains from the fault gouge indicate that the last major faulting in this site occurred 430 ± 43 ka ago. The experiments on different grain sizes of quartz from the gouge showed consistent decrease in age to a plateau of low values, indicating that ESR signals in finer grains were completely zeroed at the time of faulting due to frictional heat. The results show a relatively young age for displacement on the fault that occurs ...
The great 1934 Himalayan earthquake (Mw 8.1) generated a large zone of ground failure and liquefa... more The great 1934 Himalayan earthquake (Mw 8.1) generated a large zone of ground failure and liquefaction in north Bihar, India, in addition to the earthquakes of 1833 (Mw ~7.7) and 1988 (Mw 6.7) that have also impacted this region. Here we present the results of paleo-liquefaction investigations from four sites in the plains of north Bihar and one in eastern Uttar Pradesh. The liquefaction features generated by successive earthquakes were dated at AD 829-971, 886-1090, 907-1181, 1130-1376, 1112-1572, 1492-1672, 1733-1839 and 1814-1854. One of the liquefaction events dated at AD 829-971, 886-1090 and 907-1181 may correlate with the great earthquake of AD ~1100, recognized in an earlier study from the sections across the frontal thrust in central eastern Nepal. Two late medieval liquefaction episodes of AD 1130-1376 and 1492-1672 were also exposed in our sites. The sedimentary sections also revealed sandblows that can be attributed to the 1833 earthquake, a lesser magnitude event compared to the 1934. Liquefactions triggered by the 1934 and 1988 earthquakes were also evident within the topmost level in some sections. The available data lead us to conjecture that a series of temporally close spaced earthquakes of both strong and large types, not including the infrequent great earthquakes like the 1934, have affected the Bihar Plains during the last 1500 years with a combined recurrence interval of 124±63 years.
The central part of the Himalaya (Kumaun and Garhwal Provinces of India) is noted for its prolong... more The central part of the Himalaya (Kumaun and Garhwal Provinces of India) is noted for its prolonged seismic quiescence and therefore, developing a longer-term time series of past earthquakes to understand their recurrence pattern in this segment assumes importance. In addition to direct observations of offsets in stratigraphic exposures or other proxies like paleoliquefaction, deformation preserved within stalagmites (speleothems) in karst system can be analysed to obtain continuous millennial scale time series of earthquakes. The Central Indian Himalaya hosts natural caves between major active thrusts forming potential storehouses for paleoseismological records. Here we present results from the limestone caves in the Kumaun Himalaya, and discuss the implications of growth perturbations identified in the stalagmites as possible earthquake recorders. This article focuses on three stalagmites from the Dharamjali Cave located in the eastern Kumaun Himalaya, although two other caves, one of them located in the foothills, were also examined for their suitability. The growth anomalies in stalagmites include abrupt tilting or rotation of growth axes, growth termination, and breakage followed by regrowth. The U-Th age data from three specimens allow us to constrain the intervals of growth anomalies, and these were dated at 4273±410 yr BP (2673-1853 BC), 2782±79 yr BP (851-693 BC), 2498±117 yr BP (605-371 BC), 1503±245 yr BP (262-752 AD), 1346±101 yr BP (563-765 AD), and 687±147 yr BP (1176-1470 AD). The dates may correspond to the timings of major/great earthquakes in the region and the youngest event (1176-1470 AD) shows chronological correspondence with either one of the great medieval earthquakes (1050-1250 and 1259-–1433 AD) evident from trench excavations across the Himalayan Frontal Thrust.
We report here on the campaign GPS data from the Andaman Islands just previous to the great 2004 ... more We report here on the campaign GPS data from the Andaman Islands just previous to the great 2004 Sumatra-Andaman earthquake. The campaign mode acquisitions at Port Blair showed that the site started to subside between 2003 and 2004. In addition, during this period, the horizontal displacement of Port Blair with respect to India, deduced from 1996-2000 GPS data, changed its orientation from to that obtained during the 26th Dec 2004 co-seismic. This short-term subsidence can be modeled as slip in the up-dip portion of the fault, a slip that is equivalent to an earthquake with moment magnitude of 6.3. Previously, slow slip was thought to appear at intermediate depths roughly 35–55 km but simple models of the deformation at this single site suggest slow slip at much shallower depth than this. This observation of subsidence obtained by GPS methods is in rough agreement with subsidence observed from tide gauge data. Campaign mode GPS data between 1996 and 2000 suggest uplift for Port Blair during the inter-seismic period and so does the reported field observations of interseismic micro-atoll emergence. Lack of exposed land with GPS stations along the southern part of the thrust fault deprive of arriving at any indication of this preseismic subsidence in those areas
Eos, Transactions American Geophysical Union, 2014
Ten years later, the Indian Ocean tsunami
of 26 December 2004 still looms large in
efforts to r... more Ten years later, the Indian Ocean tsunami
of 26 December 2004 still looms large in
efforts to reduce tsunami risk. The disaster
has spurred worldwide advances in tsunami
detection and warning, risk assessment, and
awareness [Satake, 2014].
Nearly a lifetime has passed since the
northwestern Indian Ocean last produced
a devastating tsunami. Documentation of
this tsunami, which was in November 1945,
was hindered by international instability
in the wake of World War II and, in British
India, by the approach of independence and
partition.
The parent earthquake (magnitude 8.1)
was centered west of Karachi along the
Makran subduction zone (Figure 1). The tsunami
registered on tide gauges, but intelligence
reports and newspaper articles say
little about inundation limits, and the consequences
in terms of lives lost differ by an
order of magnitude among the estimates in
today’s geophysical catalogs. What has been
established about the 1945 tsunami falls
short of what is needed today for ground-truthing
inundation models, estimating risk
to enlarged populations, and anchoring
awareness campaigns in local facts.
Recent efforts to reduce tsunami risk
around the Arabian Sea include a project
in which eyewitnesses to the 1945 tsunami
were found and interviewed (Figure 1) and
related archives were gathered. Results are
being made available through the Indian
Ocean Tsunami Information Center (IOTIC)
of the United Nations Educational, Scientific
and Cultural Organization (UNESCO) in
hopes of increasing scientific understanding
and public awareness of the region’s tsunami
hazards.
The ~700-km-long “central seismic gap” is the most prominent segment of the Himalayan front not t... more The ~700-km-long “central seismic gap” is the most prominent segment of the Himalayan front not to have ruptured in a major earthquake during the last 200–500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue for a great earthquake. Despite the region’s recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly understood. Here, we place new constraints on the spatial distribution of rock uplift within the western ~400 km of the central seismic gap using topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic 10Be. The data sets show a distinctive physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.
The Himalaya has experienced three great earthquakes during the last century- 1934 Nepal-Bihar, 1... more The Himalaya has experienced three great earthquakes during the last century- 1934 Nepal-Bihar, 1950 Upper Assam, and arguably the 1905 Kangra. Focus here is on the central Himalayan segment between the 1905 and the 1934 ruptures, where previous studies have identified a great earthquake between 13th and 16th centuries. Historical data suggest damaging earthquakes in AD 1255, 1344, 1505 1803 and 1833, although their sources and magnitudes remain debated. We present new evidence for a great earthquake from a trench across the base of a 13-m-high scarp near Ramnagar at the Himalayan Frontal Thrust. The section exposed four south verging fault strands and a backthrust offsetting a broad spectrum of litho-units, including colluvial deposits. Age data suggest that the last great earthquake in the central Himalaya most likely occurred between AD 1259 and 1433. While evidence for this rupture is unmistakable, the stratigraphic clues imply an earlier event, which can most tentatively be placed between AD 1050 and 1250. The postulated existence of this earlier event, however, requires further validation. If the two-earthquake-scenario is realistic, then the successive ruptures may have occurred in close intervals and were sourced on adjacent segments that overlapped at the trench site. Rupture/s identified in the trench closely correlate with two damaging earthquakes of 1255 and 1344 reported from Nepal. The present study suggests that the frontal thrust in central Himalaya may have remained seismically inactive during the last ~700 years. Considering this long elapsed time, a great earthquake may be due in the region.
Uploads
Papers by Rajendran CP
of 26 December 2004 still looms large in
efforts to reduce tsunami risk. The disaster
has spurred worldwide advances in tsunami
detection and warning, risk assessment, and
awareness [Satake, 2014].
Nearly a lifetime has passed since the
northwestern Indian Ocean last produced
a devastating tsunami. Documentation of
this tsunami, which was in November 1945,
was hindered by international instability
in the wake of World War II and, in British
India, by the approach of independence and
partition.
The parent earthquake (magnitude 8.1)
was centered west of Karachi along the
Makran subduction zone (Figure 1). The tsunami
registered on tide gauges, but intelligence
reports and newspaper articles say
little about inundation limits, and the consequences
in terms of lives lost differ by an
order of magnitude among the estimates in
today’s geophysical catalogs. What has been
established about the 1945 tsunami falls
short of what is needed today for ground-truthing
inundation models, estimating risk
to enlarged populations, and anchoring
awareness campaigns in local facts.
Recent efforts to reduce tsunami risk
around the Arabian Sea include a project
in which eyewitnesses to the 1945 tsunami
were found and interviewed (Figure 1) and
related archives were gathered. Results are
being made available through the Indian
Ocean Tsunami Information Center (IOTIC)
of the United Nations Educational, Scientific
and Cultural Organization (UNESCO) in
hopes of increasing scientific understanding
and public awareness of the region’s tsunami
hazards.
during the last 200–500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue
for a great earthquake. Despite the region’s recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly
understood. Here, we place new constraints on the spatial distribution of rock uplift within the western ~400 km of the central seismic gap using
topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic 10Be. The data sets show a distinctive
physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases
in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity
data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially
variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the
kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the
décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.
of 26 December 2004 still looms large in
efforts to reduce tsunami risk. The disaster
has spurred worldwide advances in tsunami
detection and warning, risk assessment, and
awareness [Satake, 2014].
Nearly a lifetime has passed since the
northwestern Indian Ocean last produced
a devastating tsunami. Documentation of
this tsunami, which was in November 1945,
was hindered by international instability
in the wake of World War II and, in British
India, by the approach of independence and
partition.
The parent earthquake (magnitude 8.1)
was centered west of Karachi along the
Makran subduction zone (Figure 1). The tsunami
registered on tide gauges, but intelligence
reports and newspaper articles say
little about inundation limits, and the consequences
in terms of lives lost differ by an
order of magnitude among the estimates in
today’s geophysical catalogs. What has been
established about the 1945 tsunami falls
short of what is needed today for ground-truthing
inundation models, estimating risk
to enlarged populations, and anchoring
awareness campaigns in local facts.
Recent efforts to reduce tsunami risk
around the Arabian Sea include a project
in which eyewitnesses to the 1945 tsunami
were found and interviewed (Figure 1) and
related archives were gathered. Results are
being made available through the Indian
Ocean Tsunami Information Center (IOTIC)
of the United Nations Educational, Scientific
and Cultural Organization (UNESCO) in
hopes of increasing scientific understanding
and public awareness of the region’s tsunami
hazards.
during the last 200–500 yr. This prolonged seismic quiescence has led to the proposition that this region, with a population >10 million, is overdue
for a great earthquake. Despite the region’s recognized seismic risk, the geometry of faults likely to host large earthquakes remains poorly
understood. Here, we place new constraints on the spatial distribution of rock uplift within the western ~400 km of the central seismic gap using
topographic and river profile analyses together with basinwide erosion rate estimates from cosmogenic 10Be. The data sets show a distinctive
physiographic transition at the base of the high Himalaya in the state of Uttarakhand, India, characterized by abrupt strike-normal increases
in channel steepness and a tenfold increase in erosion rates. When combined with previously published geophysical imaging and seismicity
data sets, we interpret the observed spatial distribution of erosion rates and channel steepness to reflect the landscape response to spatially
variable rock uplift due to a structurally coherent ramp-flat system of the Main Himalayan Thrust. Although it remains unresolved whether the
kinematics of the Main Himalayan Thrust ramp involve an emergent fault or duplex, the landscape and erosion rate patterns suggest that the
décollement beneath the state of Uttarakhand provides a sufficiently large and coherent fault segment capable of hosting a great earthquake.