Introduction

Approximately half of the Himalayan arc has ruptured in four great earthquakes in the past 100 years
(Figure 1). The largest region between the rupture zones of these recent events is a 500-800 km segment of
the Himalaya between the 1905 Kangra and the 1934 Bihar earthquakes, approximately between the
longitudes of Kathmandu and Delhi. Of importance in estimating the present slip potential of this segment,
termed the Central Gap by Khattri and Tyagi (1983), is the existence and severity of great historic
earthquakes that may have ruptured all or part of the gap. A severe earthquake occurred in Nepal in 1255
when "innumerable towns were utterly destroyed and thousands of their inhabitants killed" (Campbell,
December 1833) but the regional extent of this event is unknown. Other large pre-XX century earthquakes
in Nepal (1408, 1681, 1810, 1833, and 1866) are mentioned by Chitrakar and Pandey (1986) but none
appear to have been as damaging as the 13th century event, causing concern that considerable elastic strain
may be available presently to drive one or several M>8 earthquakes in the Central Gap.
An alternative mechanism to absorb slip between Tibet and India is to invoke the possibility of
aseismic slip (slow earthquakes or creep) over at least part of the region. Leveling data and recent GPS
measurements between India and central Nepal (Jackson and Bilham, 1994; Bürgmann et al., 1994) suggest
that creep processes that might otherwise release Indo-Asian convergence aseismically have been
insignificant in the past few years. If similar creep rates (2.5±2.5 mm/year) exist elsewhere along the arc
throughout the seismic cycle they are evidently inadequate to accommodate completely the slip budget
between India and southern Tibet, although they may delay rupture (Bilham et al., 1995). The possibility
that some Himalayan earthquakes may be slow events, with large slip but little radiated high-frequency
seismic energy, cannot be excluded (Sacks and Linde, 1981; Beroza and Jordan, 1990). Such events would
2 1833 earthquake Nepal
not appear in the historical record as great earthquakes although they could, in principal, release the elastic
strain associated with one.
Earthquakes in 1803, 1833 and 1866 appear to have occurred at least partly within the central gap
(Khattri, 1987) and the largest of these in terms of felt area is believed to be the 1833 event. Reports of the
1833 earthquake are found in newspapers starting the day after the earthquake, and these and other data are
collated in three issues of the Journal of the Asiatic Society of Bengal in the months following the
earthquake by Prinsep (1833) and Campbell (1833), and by Baird Smith in two articles a decade later
(1843,1844). Summaries of these summaries are found subsequently in various catalogs and comparative
studies: Mallet 1852, 1855; T. Oldham 1883; R. D. Oldham, 1897; Dunn et al. 1939; Bapat et al, 1983
and Dunbar et al. 1990. The compilation by Dunbar et al. 1990, lists the event as severe and records its
location as 25.1 N and 85.3 E , near Patna south of the River Ganges, at the southern limit of intense
shaking described in 1833 reports. A location west of Kathmandu is favored by some authors (Seeber and
Armbruster, 1981) who suggest tentatively that it may have occurred in the Central Himalayan Gap.
Khattri and Tyagi (1983) place the earthquake approximately 130 km west of the Bihar 1934 epicenter on
the edges of the Central Gap and assign the event M=7.6, a location and magnitude consistent with the
findings of the present study. One purpose of this article is to estimate more precisely the location and
magnitude of the 1833 Nepal earthquake using authentic accounts found in newspapers and scientific articles
published soon after its occurrence.