up next on a second look, why is san francisco sinking? the problem, the cause, and the danger lurking under ground in the city by the bay. that's straight ahead tonight on a second look. good evening i'm julie haener and this is a second look. san francisco is sinking. at least parts of it are and

the extend of those areas might surprise people who live or work there. much of san francisco is built on landfill or sand. earlier this month ktvu's tara moriarty looked at how bad the problem is and how a big earthquake could make it worse. >> reporter: if you know where to look in san francisco you can see it, streets slowly sinking. at this house the first floor has sunk so much that the front bay window is only inches from the sidewalk. that's because that area was built on land created a century ago by filling marshes, creeks with sand and debris. it presents a major problem for engineers. >> you dig up a lot of places south of market where the pavement section on the street is 2 feet thick and so it's 2 feet thick because the ground continued to settle and they kept putting new asphalt. >> reporter: at b.a.r.t.'s station trains cross the now

submerged hayes river. bart comes out 2-1/2 million gallons of water every week. while a pump protects b .a.r.t., there's nothing that can help parts of old san francisco that sit on old bay mud. as the land is settle. >> most people don't want to see their building settle slowly toward china. >> reporter: frank wolo has been designing buildings to compensate for that. parts of selma along the embarcadero are still slowly sinking and sections of the former mission bay have settled 9 feet. some high rises along the former shoreline sunk over the years including the former pg & e headquarters and the standard oil building. the new transbay terminal project at third and fremont is also on bay mud. before crews can everyone begin building they must shore up tons of mud and pump up bay

water. engineers keep a close eye. >> if there's slight movement occurring but we know why it's happening, is that movement going to be detriplet -- detrimental to the building. >> and? >> it's not. >> we swayed, it felt like two or three inches back and forth. >> you could also kind of hear the iron, the metal kind of moving. >> reporter: frank willow says those high rises are safe and will support it but one place you would not be standing in the middle of an earthquake is here. after the 1906 quake this entire area was one giant sink hole. >> we know that area all

liquified in 1906 and it was all lateral building. huge chunks of the district and south of the market are former marsh land. this animation shows a victorian home. during the earthquake when the ground shakes it becomes filled with water. experts say liquid faction will happen again. >> and we know that in 1906 we saw up to 13 feet of movement. >> reporter: the usgs says areas of san francisco that will liquify in a quake are also those that will continue to settle. engineers tell us buildings with shallow foundations continue to sag and sink. while most high rises have finished settling or have less than a foot to go. the lack of solid ground under many san francisco buildings is of course not a new problem. as tara reported it was clear after the 1906 quake that some buildings were not just on shaky ground but on sinking

ground. in 1995, diane wire reported on a new map that showed which areas were the most in danger. >> reporter: there's nothing quite like a beautiful sunny day in san francisco. these are views famous around the world. but today, geologists introduced us to a new color code of san francisco. the red represents the bay mud or landfill areas which are the least stable and therefor the most dangerous. the yellow represent sand, the green sheet rock and the blue represents bedrock the most stable. just to give you an idea of this map. this two story home is built on bedrock. directly across the street, the high rise apartment building is

built on sand. much of the finings are expected. russian hill is bedrock. but there are some surprises despite what many believe much of pacific heights is sand along with most of the city. we show the map to people in the area, many said they thought -- >> pacific heights was all rock. so that's surprising to see that it's not true. >> reporter: but even more surprising is this area at van nuys and vallejo. stan lives along this lot. >> we're on rock, solid rock. >> reporter: not according to the map. this area is actually color coded red or landfill. the same type of soil that's in the marina. some other unexpected findings, seismologists say that a two story building will have the same kind of damage whether it's on sand or landfill. >> that means that for those homeowners who live on sand which is most of the city, i would say get rid of the false security. >> reporter: city planners say

the new detailed plan could ultimately change building codes throughout san francisco. >> it's a useful tool for the engineers so they know what they're about to face when they start the building. >> still to come on a second look. the connection between one of san francisco's greatest events and one of its greatest disasters. and later, what brought down this part of the city?

in 1989 the loma prieta devastated parts of the san francisco district. why was that area hit so hard. the answer lies underground. ktvu's craig heap first brought us this report 10 years ago.

>> reporter: in 1915 the area of san francisco now known as the marina district looked like this. a glorious display. in 1989 it looked like this, a glaring disaster. so what's the connection between this and this? one word, sand. it all has to do with an idea that germinated and grew in the rubble of the 1906 earthquake. the quake and fire destroyed 4/5 of the city. but remarkably by 1909 most had been rebuilt. it was time to tell the world san francisco was once again opened for business. and what better way than to celebrate another world class construction project the panama canal. >> the excuse was the panama canal had been a proposition before congress for some time to have something to celebrate like the panama canal. of course the people of san

francisco wanted it to show that they rebuilt their city and you know, one of the slogans was the city that knows how. >> reporter: so was born the concept for the panama pacific international exposition. the world's fair of 1915. raising as much as $16 million and beats cities such as san diego, washington, d.c. and new orleans. san francisco won the federal government's designation to hold the official fair to honor the opening of the panama canal. and with dry land as a premium, fair organizers decided to make land. and build the fair in a marshy area on the north shore of san francisco, edged with creeks and coves. work began in 1911. and that's where the sand came in. this is filmore street in the marina district. today the bay lies about a block and half that way. but the shoreline used to be

across the street. that was solid ground but this was water. a cove where people used to tie up their boats. that is until the builders of the pan pacific expo filled it with sand. sand made up about 70% of the material dredged from the bottom of the bay and used as fill. that part of the project took more than three months, and then on top of the fill workers constructed the exhibition halls and ornate courtyards that would cover the exhibition grounds. when the fair closed 10 months and 18 million visitors later the city simply tore it down. >> it was not made to last and the city didn't own most of the land on which it was built. they had to lease it. in fact, very few parcels actually belonged to the city. and so it was always meant to be temporary. >> unfortunately because all of the building were built of lath and covered with a plastic

called jute it was basically burlap that was inpregnated with plaster, the buildings had to be rebuilt. >> reporter: it was a seismic time bomb that would not go off until 1989. when the loma prieta earthquake hit, many of the buildings ended up crumbled, collapsed or nearly cockeyed. >> we're looking at buildings that were built in the 20s and 30s and our cities really didn't have building codes back then that addressed the earthquake hazard. >> reporter: and especially not

to survive the effects of something called liquid faction. the phenomenon on which soils turns to jelly and magnified the force of an earthquake. these pictures show the effects of liquid faction. piles of sand that bubbled up as the earthquake shook the deep base and under the marina district like a bowl of jello. even sew the usgs tom holder says the process to fill the marina district was state of the art at the time they did it. >> the engineers were concerned of the sand settling. they engineered the fill to be very clean and that's what is good for liquid faction. which is what we see during áet quake. >> reporter: as strong as the force of the earthquake was the mushy soil made it everyone stronger. >> the sand rests on younger and older bay mud. and what we've learned over the

years is that this kind of soil can amplify ground shaking. that was another reason why the marina district suffered as badly as it did. >> what about the seismic future of the marina district. most of the buildings have been retrofitted. but the soil is still the same. frank eves for a second look. bob mckinzie asks the question is landfill good or bad? a bit later the decision in the past century that's still bearing consequences on san francisco's telegraph hill.

a month after the loma prieta earthquake, bob mackenzie set out to answer the question is landfill a good or bad thing. the answer he found is its depend. >> reporter: when san francisco decided to stage a great exposition in 1915 a piece of shoreline was filled and leveled and the glorious but temporary buildings of the

world's fair erected. that piece of filled land became the neighborhood we now call the marina. last night's earthquake struck the marina suffered greater damage by far than other parts of the city. partly because the marina's landfill is largely sand and subject to a phenomenon called liquid faction. the sand supports the brick just fine until it's shaken. the water rises, the t fragile adhesion is broken and the soil becomes a kind of quick sand. much of san francisco's financial district is also built on landfill. but the damage there was much less. high rise buildings in the area are set in pilings that go down to bedrock or hard soil beneath the fill. the tragedy in the marina has given landfill a bad name. bay areans are wondering if it's a bad thing to own a home

on landfill. this development suffered almost no damage during the quake. like foster city across the bay harbor bay isles landfill meets specification. it doesn't liquify. >> as long as engineers know what the characteristics of what the fill is and they can accommodate it. >> reporter: herb is an engineer, with a crew he's taking a sample. when we arrived, the crew had drilled to 50 feet without finding bed rom. finally they found something at 58 feet. >> what is it? >> we're at bedrock.

you can see the fabric of the rock there. >> that would provide excellent support for a building if one wanted to drive piles that deeply. >> reporter: instead, he's going to recommend that the ground be compacted and the building built on a slab. >> if the building moves in one piece. >> the whole idea is to make the building move as a unit rather than in different pieces in different directions that's what we don't want to happen. >> the marina district has another problem from what's in the ground. it's not landfill but two pg & e gas producing plants that were taken offline after the 1906 earthquake and buried. last month ktvu's health and science editor john fowler outlined the problem and what pg & e is doing about it. >> no one ever smelled gas or complained but who knows. >> reporter: this view from chopper 2 today you might never guess the marina district was once a swamp, washer woman's

lagoon. two smelly gas manufacturing plants operated here from the 1880. two areas totalling 10 blocks are known to be contaminated. pg & e is taking responsibility. it was not thought to be a problem until now. >> doing thorough investigations to identify any impacts, environmental impacts that need to be cleaned or remediated. >> we've learned that familys have agreed to move to allow crews to drill on east street. >> i think they've been honest about their disclosure. i think that's a good start. >> the contamination is like this asphalt and was about 5 feet below ground level. so far there's been no reports of serious effects. the work here will continue through the summer. when we come back on a second look, you saw it live

right here on channel 2. what caused the earth to give way under this house in san francisco's sea cliff district.

tonight on a second look, we've been looking at sinking san francisco. but sometimes it's not the ground but what's in the ground that's the problem. in 1995 a leaking sewer line created a sink hole that was disastrous to a house. >> reporter: about 2:30 a.m. san francisco firefighters saw storm water gushing out of a broken sewer pipe in the sea cliff neighborhood. then in the dark they saw that the street in front of this million dollars home had begun

sinking about 10 feet every 15 minutes. throughout the early morning the gushing water undermined the soil under the home. the house began to crumble, and crumble. and crumble while water continued to gush. then just after 7:30 this morning the ground gave way and within second the three story tudor home was gone. here it is again in slow motion. some neighbors were asking how the sewer pipes could rupture. some say because it was more

than 100 years old. >> i don't know what caused it and i don't know if we will ever know given that it's all gone. >> there was a lot of road work, they've been digging this tunnel and it seems the house to go down. you start wondering about all the different things going on in the past year. >> i know it wasn't. we tunneled under it. we had a 10-foot tunnel that was under it has been in place for over a year. so there was no contact made. >> reporter: construction crews were working in manholes to divert the storm water to other areas. by late today they said they had been able to reduce the flow of water at the sink hole but for this home that effort came too late. >> as we look tonight at sinking san francisco we've outlined a number of areas where people are living with the actions people took more than a century ago to fill the earth and build on it. in one area it's not the dirt they put in but the dirt they took out that's causing

problems. that's telegraph hill. ktvu's bob mackenzie brought us this report in 2007. >> reporter: people who have bought or built buildings in the precarious slopes of telegraph hill could have saved themselves a lot of heart ache by reading up on san francisco history. disastrous slides on telegraph hill are nothing new. in fact, the hill has been crumbling for about the last 130 years. in the mid-19th century only the poor lived on the hill because the only way to get to their homes was to back up. no one in power cared much when the grave brothers put 90 kegs of die dynamite into the side of the hill and started blasting it apart. the brother's business is quarrying. and to build a sea wall around the embarcadero they blasted out this section of the hill which became the street we call

broad way. retired city historian gladys hanson says they started thety -- -- this handsome art deco art building lost part of its footing. it was saved then by in 1982 the building really started losing its underpinning. with not much left underneath it the building had to be demolished. >> maybe the people that were

born and raised here might be a little more aware because stories like these are passed on through generations. but no people coming into the city, they look for the high places. they want to live higher and with a wonderful view. but they don't ask, how stable. they assume that everything is right. >> city engineers are talking about ways to stabilize the hill. but if history is any guide it will keep on sliding until some day there's nothing left to slide. >> and that's it for this week's second look. i'm julie haener, thank you for watching.