The hills of Uttarakhand are hit frequently by mild earthquakes -- as many as 51 since January 1, 2015 -- which are often dismissed as "usual occurrences". But are these tremors indicative of a big earthquake in future?"Yes," says the head of state's Disaster Mitigation and Management Centre (DMMC)."Frequent mild earthquakes in the hills of Uttarakhand should not be dismissed as common occurrences but treated as pointers to a major earthquake which is long overdue in the central seismic gap of the Himalayan front spanning Himachal Pradesh Nepal and Uttarakhand," DMMC Executive Director Piyush Rautela told PTI.The DMMC is an autonomous body working under the Uttarakhand government for protection of people and environment against any kind of disaster. Its tasks among other include running training programme for people and communities for disaster mitigation.Rautela said the Garhwal region of Uttarakhand was hit by a catastrophic earthquake way back in 1803, and 200 years on there is a lot of "un-released energy in the Himalayan region"."This pent-up energy accumulated over more than 200 years has led to an apprehension among scientists that it could find an outlet in the form of a big earthquake in the Himalayan region, of which Uttarakhand is a part, in the near future," he said.Another factor which has led to the apprehension is that the 700-km long seismic gap on the Himalayan front, which spans Uttarakhand, neighbouring Himachal Pradesh and Nepal, has not been ruptured in any major earthquake in the last 200-500 years, he said."Hence, it is only a matter of time before this pent-up, cumulative energy releases in the form of a major shake-up," Rautela said.Asked as to what scientists mean by major earthquake, he said the earthquakes measuring more than eight on the Richter Scale are categorised as such.According to data available on the Uttarakhand MeT department's website, there have been as many as 51 mild earthquakes in different parts of the state, especially the hill districts of Chamoli, Uttarkashi, Pithoragarh, Almora and Rudraprayag, since January 1, 2015.On an average mild intensity earthquakes occur in the hills twice a month with the latest hitting Pithoragarh on April 1 this year. The magnitude of the quake was 3.5 and it was not felt by many.The Pithoragarh earthquake was preceded by another of 2.9 magnitude in Uttarkashi on February 28, which had already been hit by another with a magnitude of 3.2 on February 12.Chamoli and Rudraprayag districts were hit by an earthquake measuring 4.7 on the Richter Scale on December 28 last year, followed by a 2.9-magnitude earthquake in Chamoli just two days later."The mild earthquakes which hit the hills of Uttarakhand almost every month and are often dismissed as usual occurrences should better be treated as warning bells so that we could equip ourselves better to deal with a bigger disaster," the DMMC ED said."These earthquakes often measuring about 2.5-4.5 on the Richter Scale are reminder from the nature that we live in an area vulnerable to earthquakes and cannot afford to lower our guard." .When asked what would be the extent of damage if an earthquake of 8+ magnitude hits the state, Rautela said it was difficult to quantify. "But definitely the damage will be more in the thickly populated urban areas where there has been rapid and unplanned growth of population and infrastructure."The devastating earthquake of April-May 2015 in Nepal, which left nearly 9,000 dead, amply highlighted the seismic threat in the region as also the vulnerability of the building stock there, he said."Hence, it is important to assess the vulnerability of built environment before undertaking any seismic-risk reduction exercise."Rautela emphasised the importance of effective planning, preparedness and mitigation, underlining the "constraints in earthquake prediction".He said assessment of seismic vulnerability is a necessary precondition for realistic planning and effective mitigation. Citing a DMMC study conducted some time back to assess the seismic vulnerability of Nainital and Mussoorie, he said out of a total of 6,206 buildings surveyed in popular tourist cities, 14 per cent in Nainital and 18 per cent in Mussoorie show high probability of Category-5 damage (very significant damage) in the event of a seismic activity reaching intensity VII (earthquake measuring 7 on Ritcher Scale).Most of these buildings were reportedly constructed before 1951, he said.On infrastructure, the DMMC ED said, hospitals constitute the most critical facility required in the aftermath of any disaster and therefore it is important to assess the seismic performance of the buildings housing these facilities.Disruption of hospital services has the potential of magnifying the trauma and misery of the affected population manifold, he added. Safety of school buildings is also critical, he said. "The collapse of school buildings would disrupt relief work as they are often used as shelters, makeshift dispensaries and stores for relief supplies in the aftermath of any disaster."Tourism being the main economic activity in several cities of Uttarakhand, safety of hotel buildings must also be ensured. Seismic vulnerability assessment of such buildings is therefore highly recommended, according to the officer.In November last year, scientists had gathered for a two-day national workshop here. They were unanimous in their view about the high possibility of a devastating earthquake in Uttarakhand and asked the state government to work towards building tremor-resilient infrastructure.Professor ML Sharma from IIT-Roorkee recommended expansion of the earthquake early warning system network which has already been deployed in Uttarakhand.Scientists also spoke about the extra care that needs to be taken in designing the structures on hill slopes and the implications of wrong design or construction practices.