Washington ( CNN ) -- A seismic study found that the Washington Monument can withstand a worst-case earthquake scenario , officials said Thursday in describing needed repairs to the iconic landmark damaged in the 5.8-magnitude quake a year ago . The 555-foot monument will be under full scaffolding for repairs to damaged marble plates , stonework and other problems near its top , said Bob Vogel , superintendent of the National Mall and Memorial Parks . At a news conference with other U.S. officials , Vogel offered no time frame for the repairs . Officials previously said the monument could be closed through 2013 and possibly into 2014 . The monument has been closed since an earthquake struck the mid-Atlantic region near Richmond , Virginia , on August 23 , 2011 . Quake-damaged monument may stay closed until 2014 . `` This is the most significant earthquake to ever strike the U.S. east of the Rocky Mountains , '' U.S. Geological Survey Director Marcia McNutt said at the news conference . `` More people felt this earthquake than any earthquake in U.S . history . '' A comprehensive seismic study determined the monument faced no risk of collapse , even in the event of a `` maximum considered earthquake , '' the estimated worst possible quake over a 2,475-year period , Vogel said . Such a scenario `` did not present a concern for structural collapse , '' he said , adding that `` supporting soils are indeed adequate to withstand '' a maximum considered earthquake . At least nine marble panels on the outside of the monument near the top are cracked , according to a post-earthquake assessment . Others are chipped but not in danger of falling , the report said . Indoor repairs are also required . Some interior tie beams and some cracked panels will be fixed . About 700,000 visitors go to the top of the monument in a typical year . The Washington Monument was built between 1848 and 1884 and has been repaired three times previously , with the most recent work done from 1997 to 2000 . The signature obelisk was n't the only landmark in the U.S. capital city affected by last year 's quake . Three towers of the National Cathedral and carved pinnacles and embellishments that decorate them suffered severe damage . The church 's interim dean , the Rev . Francis H. Wade , said Thursday that the cost for repairs , restoration and historic preservation should exceed $ 50 million . It is expected this effort will take 10 years . Repairs done since last summer 's quake have focused on stabilizing stone . On Thursday , cathedral officials announced they had received a $ 5 million gift from the Indianapolis-based Lilly Endowment that will be used for architectural restoration . `` After a year 's time , we have a long way to go toward full restoration , '' Wade said . `` But we also have countless individuals , organizations and houses of worship to thank that have shared in their belief in the work of this sacred place -- and I have no doubt that they would join me in gratitude for this major restoration grant . '' The August 2011 tremor rattled buildings around the nation 's capital , as well as stoked concerns about whether residents , workers and visitors were prepared . During Thursday 's news conference outside the Washington Monument , officials described an upcoming drill designed to prepare people to react quickly if another big earthquake hits the region . Called the Great Southeast Shakeout , the drill is scheduled for 10:18 a.m on Oct. 18 . Its aim is to encourage people to drop to the floor or ground , take cover under a desk or table , and hold on until the shaking stops . Last year , they said , many people in the Washington business district fled their buildings like in a fire drill , putting them at potential risk from falling debris . The website for the drill is www.shakeout.org/southeast . Where to find exceptional America . CNN 's Greg Seaby , Tom Cohen , Eric Fiegel and Lindy Royce contributed to this report .
NEW : The damaged National Cathedral gets a $ 5 million gift for restoration efforts . The Washington Monument can withstand a worst-case earthquake , a study shows . Score: 6 Officials are planning an earthquake preparedness drill for the region .